Oxygen-Enriched Side-Blown Furnace

— Oxygen-Enriched Bottom-Blowing Furnace for Matte and Bullion

An oxygen-enriched side-blown furnace is a bath-smelting reactor whose tuyeres or multi-channel lances are set in copper water jackets on the two long side walls of a stationary furnace, so that oxygen-enriched air is blown horizontally into the slag layer rather than down onto the bath or up through its floor, violently stirring the upper bath into a jetting layer in which the charge melts, desulphurises and slags within seconds of landing on it, while the products of that reaction sink into the quiet lower bath and separate by gravity into a slag layer and a metal layer that are drawn off separately. YuSai Machinery engineers the stationary shell and its copper water jackets, the tuyere or lance set with its spacing and its water-cooling circuit, the oxygen supply and the fuel and reductant injection, the sealed top charging arrangement, the slag and metal tapholes with their launders, the enclosed off-gas train with its waste-heat boiler and its electrostatic precipitator.

Product Overview

An oxygen-enriched side-blown furnace is a stationary, refractory-lined, water-jacketed reactor that smelts a solid charge by blowing oxygen-enriched gas horizontally into a molten bath rather than by burning fuel against a pile of material. The distinction that matters is not that it is hot and not that it is large: it is that the charge lands in a bath rather than on a hearth, so the reaction it undergoes is a bath reaction between a molten slag, a molten metal or matte phase, a gas jet and a solid particle, and the furnace’s job is to keep that reaction going at a rate that justifies the oxygen it consumes. Everything on this page is downstream of that single statement.

The vessel is fixed, with straight or elliptical walls and no trunnion, drive or articulated hot-gas joint; the oxygen-enriched blast enters through nozzles set in water jackets on the two long side walls, charge, flux and fuel are fed through the top, and gas leaves by an uptake at one end. The horizontal jets stir the upper bath into a jetting layer in which the charge melts, desulphurises and slags within seconds, while below that zone the stirring dies away and slag and metal separate by gravity and are tapped from separate openings, continuously rather than in batches. A bottom-blown furnace delivers the same oxygen through the floor into the matte layer and a top-blown furnace drops a lance onto the bath surface; what separates the side-blown arrangement is the delivery position, and that position decides the nozzle’s survival, the slag it can tolerate and the intensity it can be pushed to.

Running 60–90 per cent oxygen is a piece of mechanical engineering rather than a piece of chemistry. A nozzle set in the wall above the melt line is not immersed, its tip is not consumed by liquid slag and its body carries its own water-cooling pipe, so it needs neither an inert-gas shroud nor demineralised-water protection; nothing in that arrangement holds the concentration down, and published practice runs 60–90 per cent oxygen, with 70–85 per cent as the ordinary band and up to 90 per cent in the oxidation stage, against the roughly 28 per cent a blast-furnace tuyere is limited to. The jacket is the other half: copper is used in the melting zone because its thermal conductivity is far higher than steel’s, so slag freezes against the jacket face quickly and stays hung there, and that coating — not the jacket and not the brick behind it — is what the bath touches, which is why the melting temperature is set by slag chemistry rather than by refractory grade and why published furnace-body life for this family reaches five years. Because a copper block is heavy, each one is carried on steel columns rising around the shell rather than on the furnace foundation, which moves the foundation, the steelwork and the maintenance route.

Almost any solid charge will do if its chemistry suits the slag and its price suits the metal: lead and copper concentrates, battery paste, copper oxide and sulfide ore, black copper, electronic waste, and leaching residue that is a hazardous waste until it is detoxified. Moisture up to about 8 per cent is charged directly, particle size is not tightly controlled, and the published workable grades run down to about 30 per cent lead and about 10 per cent copper, a tolerance that exists because there is no charge column to keep permeable and which deletes the dryer, the briquetting press and the sinter strand from the flowsheet. What the operator controls is the flux and the fuel: the burden is blended against its assay, flux is dosed to bring the slag into its working composition, and the coal is split between the heat it must supply and the carbon the reduction needs. Where the multi-channel lance is used, the pulverised coal and the enriched air enter the middle of the bath together, so the pool is even and the slag runs below 1,300 °C; where a single-channel tuyere is used, the lump coal is charged from the top and burns unevenly, so the upper bath reaches 1,400 °C or more and the nitrogen oxides run several times higher. Published consumption is 270–290 kg of standard coal and 270–300 Nm³ of oxygen per tonne of residue in the first arrangement, against 300–340 kg and 350–380 Nm³/t in the second.

The gas side decides the flowsheet, because the gas has to go somewhere and this furnace produces a concentrated one: the continuous oxidation stage delivers a stable 12–18 per cent sulphur dioxide stream that feeds a two-stage contact acid plant directly, while the reduction and fuming stages produce a weaker stream that is desulphurised by absorption. In the published lead project the waste-heat-boiler outlet carried 32,000–38,000 Nm³/h at 350–380 °C with 120–160 g/Nm³ of dust, and the route chosen was dry — settling followed by a high-temperature electrostatic precipitator — so the metals came out as dust rather than into a wastewater; the precipitator was preferred to a bag filter because the gas burns bags and its dew point blinds them. On lead-zinc material the furnace is normally built as a chain rather than a single vessel: published practice runs oxidation, reduction and fuming continuously in three side-blown furnaces joined by chutes, with hot slag launder-fed from one to the next in a fully insulated circuit without ladle transfer, and reports about 60 t/(m²·d), 90 per cent oxygen in the oxidation furnace, a 99.5 per cent desulphurisation rate, an 8.6 per cent coal rate in reduction, five-year furnace life and lead and zinc recoveries above 97 and 92 per cent. The station smelts and separates rather than refines: it does not raise the grade of the metal it taps, and the antimony, bismuth and silver that arrive in the charge are reported by assay against the refining step that is built to remove them.

Key Facts

The blowing position is the whole machine. A side-blown furnace injects oxygen horizontally through the side wall into the slag layer; a bottom-blown furnace injects through the floor into the matte layer; a top-blown furnace drops a lance onto the bath. The side wall is chosen because a nozzle set in the wall is not immersed, and because a horizontal jet entering the slag layer is what creates the jetting layer that gives this furnace its reaction rate.
The tuyere does not touch the melt, so it needs no protective gas and no softened water, and it can take high-purity oxygen. A water-cooled nozzle body tolerates above 65 per cent oxygen, and published practice runs the blast at 60 to 90 per cent, with 70–85 per cent as the common industrial band and up to 90 per cent in the oxidation stage; it needs neither an inert-gas shroud nor demineralised-water protection. A blast-furnace tuyere tolerates no more than about 28 per cent enrichment, because its nozzle carries no internal water cooling and its steel jacket hangs a protective slag coating less effectively.
The copper water jacket protects itself by hanging slag on its own inner face, and its weight changes the structure. Copper is used in the melting zone because its thermal conductivity is far higher than steel’s, so a frozen slag coating forms quickly and stays there; the melting temperature in the bath zone is therefore not limited by the refractories, and published furnace-body life for this family reaches five years of campaign. Because a jacket block is heavy, published practice supports it from steel columns rising around the furnace shell rather than from the foundation, which sets the steelwork, the civil design and the maintenance access.
The jetting layer is where the smelting happens, and it is why the furnace is fast. The enriched blast enters the slag layer through primary tuyeres in the copper water jackets on both side walls, the upper bath is stirred violently into a jetting layer, and the charge, flux and fuel are fed through the furnace top into that layer, where smelting and slag-forming complete almost immediately; the products fall into the lower bath and settle under gravity into a slag layer and a crude-metal layer tapped separately. Published specific smelting capacity is 40–50 t/(m²·d) on residue and lead duty, around 60 t/(m²·d) in published lead-zinc oxidation practice, and above 120 t/(m²·d) on copper duty.
Nothing is dried, granulated or finely ground before it goes in, and there is no coke column to support. The furnace takes moisture up to about 8 per cent and a lead grade as low as about 30 per cent or a copper grade as low as about 10 per cent, because there is no packed bed to keep permeable; that removes the dryer, the briquetting press and the sinter strand from the flowsheet, and it means the furnace runs on cheap anthracite or bituminous coal granules instead of metallurgical coke.
The nozzle family decides the nitrogen oxides. A single-channel tuyere passes enriched air only, takes its heat from lump coal at the top, runs an upper bath at 1,400 °C or more and produces 2,000–8,000 mg/Nm³ of nitrogen oxides, with manual punching every shift and only about half the tuyeres in service. A multi-channel lance injects pulverised coal with the enriched air into the middle of the bath, holds the slag below 1,300 °C and produces 500–1,500 mg/Nm³, with more than 70 per cent of lances in service and no routine manual work. Their published pitches are 1.5–2 m and 2–2.5 m.
Sulphur leaves as a gas strong enough to make acid, and it leaves continuously. The oxidation stage produces a stable 12–18 per cent sulphur dioxide stream by volume, against the 3–4 per cent band quoted for the fuming stage of the same flowsheet, so it goes straight to a two-stage contact acid plant rather than to a scrubber.
The dust from that gas is captured dry, and the choice was made on resistivity. In a published lead project the boiler outlet ran 32,000–38,000 Nm³/h at 350–380 °C carrying 120–160 g/Nm³ of dust. Dry collection is used so the metals come out as dust rather than into a wastewater; a precipitator is preferred to a bag filter because the gas is hot enough to burn bags and its dew point high enough to blind them; and the dust’s own high lead-oxide resistivity, which would otherwise disqualify a precipitator, is brought back into the 10⁴–10¹⁰ Ω·cm window by the sulphur dioxide, sulphur trioxide and water vapour in the same gas.
Oxidation, reduction and fuming are three furnaces in a line, not one furnace doing three jobs. A lead-rich slag flows from the oxidation furnace to a reduction furnace and then to a fuming furnace, all three side-blown and operated continuously, with the hot slag launder-fed from one to the next in a fully insulated circuit without ladle transfer. Reported results on 22–40 per cent lead and about 10 per cent zinc feed are a 99.5 per cent desulphurisation rate, an 8.6 per cent coal rate in reduction, a lead recovery above 97 per cent and a zinc recovery above 92 per cent.
Smelting a wet residue costs 270–340 kg of standard coal per tonne. Across four published industrial cases treating zinc leaching residue, standard-coal consumption ran 270–290 kg/t in the multi-channel-lance configuration against 300–340 kg/t in the single-channel-tuyere one, with oxygen at 270–300 Nm³/t against 350–380 Nm³/t. The published conclusion is that this route uses more than 30 per cent less standard coal than the other pyrometallurgical processes it is compared with, and that zinc, lead, silver and germanium volatilise at 90–98 per cent.
Low-temperature smelting is a slag-system decision, and it is on the table. A published route replaces the classical 1,200–1,250 °C lead bath with a sodium carbonate molten-salt medium and a quaternary iron-silicon-calcium-sodium slag, working below 1,100 °C, and burns pyrite in the bath for make-up heat (4FeS₂ + 7O₂ = 2Fe₂O₃ + 8SO₂, 1,654.64 kJ per mole at 1,000 °C). It buys fuel and refractory life at the cost of a tighter slag-chemistry window.
The vessel taps crude metal, and the grade work belongs to the next stage. The furnace smelts and separates; it does not remove silver, bismuth or antimony from crude lead or take a matte to cathode grade, and the bullion it taps is released against assay rather than against a refined specification. Taking it to a specification is the duty on the lead refining machine page, and melting metal that is already metal in a crucible is the duty on the precious metal smelting machine page.
Capacity, power, footprint and utility loads are engineered, not listed. Hearth area, smelting rate, jacket count and size, oxygen plant, nozzle count and pitch, boiler duty, precipitator area, ducting, floor loading and the station footprint are calculated from your feed assay, your tonnage, the metal you are collecting and your building’s oxygen, fuel, power and draught capacity, and issued as figures in the process design package rather than quoted from a fixed model list.

Product Core Selling Points

The tuyere geometry is published, because that is what the buyer is actually choosing. Two side-blowing arrangements are in industrial service and they behave differently: a single-channel tuyere that passes only oxygen-enriched air, with a close tuyere pitch of 1.5–2 metres, a large number of small tuyeres, only about half of them in normal service, and manual tuyere punching every shift to clear them and read the slag; and a multi-channel lance that injects pulverised coal together with the enriched air, with a wider pitch of about 2–2.5 metres, fewer injection points, more than 70 per cent of them in service, and a fully automatic circuit in which the gas flow, the gas pressure and the coal injection rate of every lance are monitored online. We state which arrangement suits your feed and why, instead of quoting a furnace with a fixed nozzle count.
The oxygen concentration is stated with the reason it can be that high. The side nozzle is set in the wall and does not contact the high-temperature melt, so it needs no inert-gas shroud and no demineralised-water protection, and a water-cooled nozzle body tolerates an oxygen concentration above 65 per cent. That is the mechanical basis for running 60–90 per cent oxygen, and it is also the cleanest single comparison against a blast furnace, whose ordinary nozzle tolerates no more than about 28 per cent enrichment.
The water jacket is described as the protection, not as a cooling accessory. The melting zone is copper-jacketed and the jacket is protected by the slag that freezes and hangs on its inner face. Because that frozen layer is what the bath actually touches, the smelting temperature in the bath zone is not limited by refractory material, and the jacket campaign is long — published furnace life for this family reaches five years. A page that sells jackets as cooling equipment has missed the mechanism.
The support structure is in the scope, because copper changes the civil design. A copper jacket block is heavy, and published practice supports each block from steel columns rising around the furnace shell rather than carrying it on the foundation. That decision moves into the foundation drawing, the steelwork drawing, the crane and maintenance access, and it is stated at the proposal stage rather than discovered on site.
The jetting layer is treated as the process, and the bath beneath it is treated as a settler. The furnace does two different jobs in two different places: a violently stirred surface zone where melting, desulphurisation and slagging complete in seconds, and a quiet lower bath where slag and metal separate under gravity. The oxygen flow, the lance pitch and the bath depth are set so that the first zone is properly stirred and the second is not, because a lower bath that is being stirred is a lower bath that entrains metal into the slag.
The slag system is chosen on melting behaviour and on what happens to the residue afterwards. The bath temperature, the fuel rate, the off-gas volume, the jacket campaign and the metal carried out with the slag all follow from the slag’s melting point and its fluidity at the working temperature, so the slag is designed with a stated composition and a stated working temperature rather than treated as an additive that is thrown in until the melt looks right. Where a low-temperature molten-salt slag is used, the working temperature comes down below 1,100 °C against the classical 1,200–1,250 °C lead bath, and that is quoted with its tighter chemistry control attached.
Feed preparation is removed from the line wherever the feed allows it. Moisture up to about 8 per cent is charged directly, a lead grade down to about 30 per cent and a copper grade down to about 10 per cent are workable, and there is no requirement for deep grinding or drying. Fewer unit operations means less fuel, less maintenance, less dust in the preparation bay and a shorter line to permit.
The reductant bill is not a coke bill. Because there is no packed column to hold open, the furnace does not need metallurgical coke, and published practice runs on anthracite or bituminous coal granules as fuel and reductant, with natural gas as an alternative heat source and the coal-to-gas ratio adjusted against the feed. That is the difference between a fuel whose price is set by the steel industry and one whose price is set by the coal market.
The sulphur route is designed before the furnace is sized. The oxidation stage produces a 12–18 per cent sulphur dioxide gas that goes to a two-stage contact acid plant; the reduction and fuming stages produce a weaker gas that is desulphurised by absorption. Both are part of the flowsheet the furnace is quoted into, because they decide the off-gas volume, the boiler duty, the gas cleaning and the reagent consumption — and because a plant that has not decided where its sulphur goes has not decided whether it needs an acid plant.
Dust is returned to the charge rather than stored. The waste-heat boiler and the precipitator catch the metal-bearing dust, and published practice conveys it back to the batching system so it re-enters the furnace. That converts the site’s finest and most dispersible material into a controlled input and removes the accumulation that otherwise grows in a corner of the yard.
Continuous tapping is offered as a flowsheet property, not as an operating convenience. Because the furnace is a stationary vessel with no rotating or moving joints, it has a low air-inleakage rate and it can smelt and tap slag continuously — which is what allows oxidation, reduction and fuming to run as three connected vessels and what keeps the off-gas composition steady enough for the acid plant and the waste-heat boiler behind it.
The three-furnace arrangement is offered as three duties, not as one vessel doing three regimes badly. For lead-zinc material the oxidation furnace runs at one temperature with one slag type, the reduction furnace runs at a reducing potential with a different slag, and the fuming furnace runs for zinc volatilisation. Each vessel is then designed around a single duty, and the transfer between them is a launder carrying hot slag rather than a ladle carrying cooled slag.
Emissions are engineered as an enclosed circuit rather than argued at the permit stage. The furnace is fitted out as a sealed process with a controlled draught, its charging, tapping and launder points are enclosed, the gas is cooled and cleaned before it is released or sent to acid making, and the dust is returned rather than discharged. No zero-emission claim is made on this page; the claim made is that the gas volume is small and concentrated, that its sulphur is captured as a product, and that its particulate is captured dry.
The metal that leaves is handed over with its numbers. Charge weight and assay, flux and reductant additions, bath temperature and hold, metal weight and assay, slag weight and assay, dust weight and assay and the off-gas sulphur balance are recorded per shift, and the metal balance is closed on measurements. The bullion or matte is released against assay with its crude grade stated, and the grade work is described on the refining pages rather than promised here.
The honest boundaries are on the page. This furnace does not refine, it does not separate silver or bismuth from lead or take a matte to cathode grade, it cannot run at high enrichment without a sealed and instrumented gas circuit, and below a certain tonnage it cannot carry its jackets, its boiler, its precipitator, its oxygen supply and its operator. Where the tonnage is short, where the metal is present as a dilute solution rather than as a solid, or where the value is in a metal that needs a different chemistry, this page says so and names the route that fits.
Everything that decides the plant is available before the order. The feed survey basis, the burden and flux recipe, the slag chemistry and working temperature, the tuyere or lance arrangement, the oxygen balance, the off-gas volume, the boiler and precipitator duty, the site service schedule and the performance test method are issued as documents, so the buyer can cost the whole project and not only the vessel.

Application Scenarios

Secondary lead smelters running spent lead-acid batteries. Batteries broken and separated into grid metal and paste, with the paste smelted on a side-blown line to crude lead bullion for the refining kettles and the sulphur leaving as a gas strong enough to make acid rather than being fixed in a disposable slag.
Primary lead smelters treating sulfide concentrate directly. Galena and mixed lead-zinc sulfide concentrates charged without a sinter strand, oxidised and desulphurised in the first furnace and reduced in the second, which is the arrangement the published three-furnace lead-zinc flowsheet was developed around.
Lead-zinc combined smelters that have to move leaching residue. Zinc plant leach residues defined as hazardous waste and required to be detoxified, smelted for their zinc, lead, silver, indium and germanium and fumed to a zinc oxide dust, with the tailings leaving as general solid waste rather than as a stored liability.
Zinc smelters replacing a Waelz kiln or a box fuming furnace. Plants whose existing residue line burns 40–60 per cent coke or coal, produces a large weak gas and recovers silver poorly, and which want the same duty on a concentrated gas and a lower coal rate.
Copper smelters treating low-grade and complex copper feed. Copper oxide ore, copper sulfide ore, copper-nickel sulfide concentrate, black copper and copper scrap smelted and converted in one continuous circuit, with a copper grade as low as about 10 per cent charged directly and the smelting slag low enough in copper to be granulated and sold without a flotation step.
Copper refineries that want their smelting slag finished in one pass. Plants whose slag copper content has to be carried by a separate slag-cleaning circuit, and which want a smelting vessel whose slag leaves close enough to the discard band to be quenched and sold.
Nickel and cobalt producers handling lateritic and sulfide feed. Nickel ore and nickel-bearing residues smelted to a matte that collects the nickel, cobalt and precious metals into one phase for the downstream separation step.
Electronic and electrical waste processors with a metal concentrate. Printed circuit board concentrates, component scrap and mixed non-ferrous fractions smelted to a copper matte or a lead bullion that collects the gold, silver and platinum group metals into one dense phase.
Precious metal refineries needing a collector step. Residues, slags, dusts and low-grade materials in which the values are too dilute for a wet route, smelted so that the gold and silver are collected into a bullion or a matte that a refinery can part — with the parting duty itself described on the precious metal recovery and refining system page.
Smelters and refineries treating their own internal residues. Baghouse dusts, launder skulls, slag scraps, grinding sludges and floor sweepings returned to the bath as part of the burden rather than consigned to a landfill.
Slag and dross recovery operations. Old lead and copper slags, drosses and skimmings that still carry metal and that have to be reduced or fumed to release it.
Steel and foundry plants with zinc-bearing dust. Electric arc furnace dust and similar streams in which the zinc is worth recovering and the lead has to be separated, treated on a reducing bath to a zinc oxide dust and a lead-bearing residue.
Antimony, tin and bismuth processors. Sulfide and oxide feeds for those metals smelted on a reducing side-blown bath, and the by-product slags of their circuits recovered in the same vessel type.
Metal recyclers with mixed low-grade non-ferrous scrap. Cable residues, shredded non-ferrous fractions, swarf and dross smelted to a crude metal or an alloy rather than sorted by hand to a specification.
Plants whose constraint is the permit rather than the tonnage. Operations in a jurisdiction with a strict particulate, sulphur dioxide or heavy-metal limit, where the vessel and its gas train are sized by the allowable emission and the concentrated gas volume is a compliance advantage rather than a cost.
Sites that already own an oxygen plant or a captive power demand. Because the furnace consumes oxygen at 270–380 Nm³ per tonne of residue and produces steam from its waste-heat boiler, a site with an oxygen supply and a steam demand gets more out of the same investment than one that has to buy both.
Operations where the feed changes often. Feed-flexible plants that buy residues, dusts and secondary concentrates on the market and cannot commit to one mineralogy, because the vessel tolerates a different moisture, a different particle size and a different grade from charge to charge without a change of preparation line.
Brownfield expansions inside an existing smelter. A side-blown stage added ahead of an existing converter, fuming furnace or refining kettle line, taking the load off a blast furnace or a short rotary furnace that has become the bottleneck.
Pilot and demonstration installations. Small side-blown units used to establish how a particular residue, dust or concentrate behaves on a few hundred kilograms before a production line is committed, and to train operators on bath control, tuyere practice and slag reading before the full-scale unit demands it.

Applicable Raw Materials

A side-blown furnace is fed solid material, and what decides whether a lot is admitted is its chemistry, its physical form and its identifiable origin rather than its commercial name. Each feed below enters the furnace at the point its condition allows: material that is dry enough, coarse enough, identified and inside the sulphur, halogen and grade window is blended into the burden and charged directly; material that is wet, fine, coated, halogen-bearing or outside the metal window is dried, blended, agglomerated, separated or routed to a different step first. The output of each feed is stated, because what a furnace does to a material is what the buyer is paying for.

Lead sulfide concentrate. Galena and galena-sphalerite concentrates from flotation, charged without sintering or pelletising into the oxidation furnace where the sulfide is oxidised and the sulphur driven into the gas. Output: a lead-rich slag for the reduction furnace and a 12–18 per cent sulphur dioxide gas for the acid plant.
Lead oxide and mixed lead-zinc ore. Oxide, carbonate and mixed oxide-sulfide lead ores, and the oxide fractions of complex polymetallic deposits, which need no desulphurisation but do need their zinc routed. Output: crude lead bullion and a zinc-bearing slag for the fuming stage.
Spent lead-acid battery paste. Partially or fully desulphurised paste carrying lead sulfate, lead dioxide, lead monoxide and lead carbonate, blended into the burden with the sulphur it still holds routed either to the gas or to the slag, depending on whether the plant desulphurises upstream. Output: crude lead bullion from the largest single lead fraction in a battery.
Battery grid metal and lead scrap. Cast and wrought lead-calcium and lead-antimony grids, straps, posts and terminals, cable sheathing, sheet, pipe and shielding, and the metallic fraction of a battery-breaking plant. Output: crude lead bullion at a grade set by the alloy that was charged, from a batch that needs little flux and no reduction.
Lead-bearing flue dust and baghouse residue. Collected dust from lead furnaces, sintering machines, dryers and agglomerating units, and filter cakes bought in from other smelters. Output: recovered lead and a dust that is itself recycled to the batching system rather than discarded.
Zinc leaching residue. The hazardous leach residue of a zinc electrowinning plant, carrying zinc as oxide, ferrite, silicate and sulfate together with lead sulfate, silver, indium and germanium. Output: a fumed zinc oxide dust above 50 per cent zinc, and a tailing reduced to the 1–2 per cent zinc and 0.02–0.2 per cent lead band of published practice.
Jarosite, goethite and other iron residues. Iron-bearing residues from zinc circuits which hold zinc, lead and silver in a refractory form, charged as a smelting feed rather than stored. Output: a zinc oxide dust and a discardable slag, with the iron taken into the slag.
Electric arc furnace and steel-plant dust. Zinc and lead-bearing baghouse dusts from steelmaking, charged to a reducing bath. Output: a zinc oxide dust for the zinc circuit and a lead-bearing residue for the lead circuit.
Copper sulfide concentrate. Chalcopyrite and complex copper concentrates, smelted and converted in the same vessel family, with the iron taken into the slag by silica flux. Output: a copper matte for the converter and a smelting slag low enough in copper to granulate and sell.
Copper oxide ore and copper oxide concentrate. Oxide copper feed that cannot be concentrated by flotation economically, charged directly where the grade clears about 10 per cent. Output: copper matte or black copper, with the acid-consuming gangue taken into the slag.
Copper-nickel sulfide concentrate. Nickel-bearing copper concentrates in which the nickel, cobalt and precious metals have to be collected together. Output: a copper-nickel matte that carries the nickel and the precious metals into one phase for the downstream separation.
Black copper, copper scrap and brass. Smelting-grade copper scrap, refinery black copper, brass and bronze residues and mixed non-ferrous shredder fractions. Output: black copper or a matte, with the zinc and the lead reporting to the slag and the gas rather than to the copper.
Printed circuit board concentrate and electronic scrap fractions. Separated metallic concentrates and component fractions from electronic waste processing, in which the copper is the collector and the gold, silver and palladium are the values. Output: a copper matte or a lead bullion that concentrates the precious metals into one dense phase.
Anode slime, slime residues and refinery intermediates. Copper and lead anode slimes, slime treatment residues and the lead-bearing intermediates of an electrolytic refinery. Output: a bullion or matte that concentrates the precious metals and takes the tellurium, selenium and bismuth into a phase a refinery will buy.
Lead-bearing slag from older operations. The high-lead slag of a reverberatory, short rotary or older blast-furnace line, charged as a reducing feed rather than stored. Output: the lead recovered from the slag into bullion, with the slag declining to the discard band of the vessel being used.
Copper smelting slag. Converter and smelting slags carrying copper in the tenths of a per cent, treated as a reducing or cleaning feed. Output: recovered copper and a slag clean enough to granulate, with the published performance for the copper version of this vessel leaving under 0.3 per cent metal in the settler slag.
Drosses, skimmings and kettle residues. Copper dross, antimonial dross, softening litharge, dezincing residues and the skims of a kettle refining line. Output: recovered lead or copper returned to the refining circuit, and a slag that carries the antimony and arsenic out of the metal.
Antimony, tin and bismuth feed. Antimony sulfide concentrate, tin-bearing residues and bismuth-bearing intermediates smelted on a reducing bath. Output: crude antimony, tin or bismuth metal, or a matte or speiss that concentrates them for a separate refinery.
Nickel laterite and nickel residue feed. Oxide nickel ore, nickel-bearing slags and nickel plating and battery residues smelted to a matte. Output: a nickel matte that carries the cobalt and the precious metals with the nickel.
Spent catalysts and catalyst residues. Hydroprocessing and chemical catalysts in which the metals of value are held in a refractory oxide matrix. Output: a collector matte or bullion that takes the molybdenum, vanadium, nickel and precious metals into a phase a hydrometallurgical plant can treat — with the wet route itself on the precious metal hydrometallurgical refining plant page.
Ferrous and non-ferrous shredder residues. The heavy and mixed fractions of a shredding plant that are too contaminated or too mixed for mechanical sorting. Output: a crude metal or matte with the copper, lead and precious metals collected, and a slag for discard.
Fluxes, reductants and fuels as part of the burden. Silica sand or quartz, limestone, and where the slag chemistry asks for it fluorspar, charged with the feed as designed additions rather than as corrective additions after the bath has gone wrong; anthracite or bituminous coal granules, natural gas or a coal-and-gas combination as fuel and reductant; and oxygen from a captive plant or a delivered supply. Output: a slag at its designed composition, a bath at its designed temperature, and a metal at its designed grade.
Dust returned from the plant’s own gas train. Boiler and precipitator dust, launder skulls and the fine screenings of the feed preparation area, returned to the batching system. Output: a burden in which the plant’s own fine material is an input rather than an accumulation.
Feeds admitted only after preparation. Wet material dried or blended down to the moisture window; fines agglomerated or briquetted where the draught would carry them into the duct; oversized scrap cut; high-halogen plastic, cable insulation and separator material separated before the feed; high-antimony or high-zinc material blended to the metal specification being sold; oily or painted material degreased or burnt off in a controlled step. Output: a charge the furnace can accept without losing metal to the duct, without attacking its jackets and without missing the metal specification.
Feeds routed to a different step before smelting. Material whose metal is present as a dilute solution, leachate or rinse water, which belongs in a hydrometallurgical circuit; material whose mercury, cadmium or beryllium content makes it a different class of problem; and material whose value lies in a single metal that a wet route will recover at a higher yield and a lower tonnage. Output: a smelting feed that is inside specification, and by-products recovered on the route built for them instead of being diluted into a slag.
Charges that are not admitted — unidentified or unassayable. Sealed drums, closed containers, unlabelled sacks and any lot that cannot be opened, inspected and sampled before charging. The furnace is the last place on a site to discover what a material contains, and the discovery is paid for in the jackets, the gas train and the metal balance. Output: not admitted; opened, identified, sampled and approved first.
Charges that are not admitted — free water, ice or free acid. Free-draining or dripping charge, ice-bearing material and material carrying free acid. Water entering a molten bath flashes to steam at a volume ratio that turns a vessel into a mortar, and free acid attacks the ducting and loads the gas cleaning with sulphate. Output: not admitted; drained, dried to the moisture window and neutralised first.
Charges that are not admitted — halogen-rich plastics and salt-bearing material. Polyvinyl chloride battery separators and cable insulation, chlorinated plastics and salt-bearing residues above the window the jackets and the gas train were designed for. Halide attacks the lining, shortens the campaign and loads the abatement system. Output: not admitted in bulk; the plastic separated before feed and the remainder leached or blended down.
Charges that are not admitted — mercury, cadmium or beryllium bearing. Mercury-contaminated material, amalgam, mercury-cell residues, cadmium-bearing plating and battery material and beryllium alloys. Those metals fume below or around the smelting temperature, so the furnace would volatilise them into a gas train that was never sized or permitted for them. Output: not admitted; routed to a dedicated treatment step with its own abatement and monitoring.
Charges that are not admitted — reactive, explosive or oxidiser-bearing. Live or depleted ammunition and primers, sealed gas-cylinder fragments, nitrate, chlorate and peroxide residues, and any material that reacts with a molten bath rather than dissolving in it. Output: not admitted; made safe under a competent authority’s procedure before any thermal treatment is considered.
Charges that are not admitted — radioactive or naturally occurring radioactive material. Scale, filter cake and dust carrying naturally occurring radioactive material above the clearance level, and any material found to carry a radioactive source. Output: not admitted; the site’s radiation screening gate decides the route before the material is accepted for storage, let alone for charge.

Finished Products

The station is configured around the products the plant sells or feeds forward, from crude metal for the refining kettles through to the slag, the matte, the dust and the acid gas that each have their own market or their own return route. Where the plant already runs a refining kettle line, an assay bench and a slag storage area, the smelting station is delivered as the vessel, its jackets and water circuit, the tuyere or lance set, the oxygen and fuel train, the sealed charging arrangement, the slag and metal launders and the gas train; where it does not, those interfaces are inside the scope.

Crude lead bullion. The primary output on lead duty: charge melted, oxidised, reduced, fluxed and separated, with the antimony, copper, tin, bismuth and silver content set by the charge and reported by assay. Output: crude or hard lead bullion tapped from the low point into trays or a holding furnace, for transfer to the refining kettles.
Black copper or blister copper. The primary output on copper duty, produced where the bath is run oxidising and the iron and sulphur are driven into the slag and the gas. Output: black copper or blister copper for the converter or the anode furnace, with the published consumption for the copper version of this vessel at about 140 kg of standard coal per tonne of blister copper.
Copper or copper-nickel matte. The intermediate product where the bath is run to a matte rather than to metal, collecting the copper, nickel, cobalt and precious metals into one dense sulfide phase. Output: a matte tapped separately from the slag and transferred hot to the converting or separation step.
Zinc oxide dust. The product of the fuming stage on zinc-bearing feed, produced by reducing and volatilising the zinc and re-oxidising it in the gas phase. Output: a zinc oxide dust above 50 per cent zinc in published practice, collected in the boiler and the precipitator and sent to the zinc circuit.
Lead-bearing dust and its recycle fraction. The dust caught by the waste-heat boiler and the precipitator on the lead line, which carries lead and a share of the silver and which is returned to the burden. Output: a weighed and assayed dust conveyed back to the batching system, so it re-enters the furnace rather than accumulating on site.
High-lead oxidation slag. The hot intermediate slag that flows by launder from the oxidation furnace into the reduction furnace, carrying the lead that the first stage did not take to metal. Output: a hot slag transferred without a ladle, as an internal stream rather than a sold product.
Reduction slag for fuming. The slag that leaves the reduction furnace still carrying zinc, germanium and a residue of lead, flowing on to the fuming furnace. Output: an internal stream that becomes a zinc oxide dust at the next stage.
Discard slag. Slag reduced to the target metal band for the vessel and the duty being run, quenched into granules or cast into blocks so that entrained metal can settle. Output: granulated slag within the design band, assayed before it is declared spent, sold as aggregate or used as cement raw material — the published reuse route for water-quenched side-blowing slag.
Sulphuric acid. The product of the acid plant behind the oxidation furnace, made from the 12–18 per cent sulphur dioxide stream. Output: saleable contact-plant sulphuric acid, which converts the furnace’s largest by-product problem into a revenue line.
Waste-heat steam. The heat recovered from the gas in the waste-heat boiler, available as process steam or for power generation. Output: steam at the boiler’s designed pressure and flow, metered and recorded against the burden.
Antimony, tin, bismuth or speiss by-product streams. The phases that form when antimonial, tinny or bismuth-bearing feed is smelted, and the speiss that carries arsenic and antimony to the top of the bath. Output: by-product streams tapped separately, assayed and sold or toll-treated for their own metals.
Metal released against assay and ready for refining. Bullion or matte weighed, sampled and released with its assay and its shift number, in a form the next stage can accept directly. Output: a documented handover to the refining or converting stage, on the terms set out on the lead refining machine page.
Shift record and closed metal balance. Charge weight and assay, flux, coal and oxygen additions, bath temperature and working condition, metal weight and assay, slag weight and assay, dust weight and assay, and the sulphur balance between gas, slag and dust. Output: a shift whose metal balance can be reconstructed and defended, and a slag metal figure that can be compared against the design target.

Oxygen-Enriched Side-Blown Furnace Process Flow

The nine stages below are one working sequence, from the reception that decides whether a lot is admitted through to a surveyed vessel put back into service. Stages 4 and 5 are where the furnace is actually decided: the side-blown injection at Stage 4 is what creates the jetting layer that gives the vessel its reaction rate and its tolerance of coarse and moist feed, and the oxidation smelting at Stage 5 is where the sulphur leaves the metal and enters the gas that the acid plant depends on. Whatever the crude metal still contains — antimony, copper, tin, bismuth, silver — is not this vessel’s business to remove; the grade is set downstream, and that duty is described on the lead refining machine page. Engineering setpoints are fixed during process design against your own feed assay and confirmed on the first production campaign.

Oxygen-enriched side-blown furnace flow — one working sequence from a surveyed feed to a tapped crude-metal lot and a measured slag metal figure, with the sulphur leaving as acid-plant gas, the dust returned to the burden and the waste heat recovered as steam.

Steps 1 — Feed Reception, Assay and Burden Batching. Nothing is charged before the lot has been surveyed, because every figure downstream — the flux the slag needs, the coal the reduction needs, the oxygen the oxidation needs, the metal grade the vessel will reach, the gas volume the acid plant will see — is calculated from that survey. The lot is weighed, its form recorded, and its lead or copper, zinc, sulphur, iron, carbon, silica, halide and moisture content established by sampling, by XRF on a prepared and milled surface, and by a reference determination where the lot is heterogeneous or where the result sits near a commercial or a permit boundary. The acceptance screen is then applied and the reason is written against each excluded fraction: halide above the lining’s window, moisture above the charge window, a metal content too low to clear the vessel’s own consumption, a mercury or cadmium load the gas train is not permitted for, an unidentified container, or a value that a wet route would recover at a higher yield. Where a fraction is diverted, the route sheet names the step it goes to — drying, blending, agglomeration, plastic separation, a hydrometallurgical circuit or refusal — rather than leaving it on the pad. Reagent and utility input: weighing, milling and sample preparation, XRF and reference analysis, moisture determination, route sheet and shift record, acceptance checklist. Output: a surveyed and accepted charge with its burden recipe basis, its oxygen and coal demand and its expected metal grade confirmed, or a documented diversion with the reason stated.

Steps 2 — Blending, Moisture Control and Sealed Charging. The burden is built here, and it is arithmetic rather than judgement. Grade and sulfur are balanced across the lots so that the bath sees a steady feed instead of a series of shocks; silica and limestone are weighed against the gangue so the slag lands in its designed composition instead of being corrected after the bath has gone wrong; the coal is split between the heat it has to supply and the carbon the reduction needs; and the recycle dust from the plant’s own gas train is blended back in at a controlled rate so the plant’s finest material is an input rather than an accumulation. Moisture is measured rather than trusted: the vessel tolerates up to about eight per cent directly, so most material can be charged as received, but a wetter lot is blended down or dried rather than charged, because water meeting a molten bath flashes at a volume ratio that turns the vessel into a mortar. Charging is through a sealed top opening into a controlled draught, so the gas volume leaving the furnace stays inside the duty the boiler and the precipitator were sized for, and the feed rate is held against the oxygen rate rather than run open loop. Reagent and utility input: calibrated weighing and blending, silica and limestone flux, coal and natural gas, recycle dust, moisture determination and drying where needed, sealed top charging with draught control, batch and rate records. Output: a weighed and recorded burden with its flux, coal and oxygen demand set against the assay, delivered to the bath at a controlled rate under seal.

Steps 3 — Furnace Preheat and Molten Bath Establishment. The vessel is brought to temperature and the bath is established before the line is put into continuous service, and the two side-blowing families do this very differently. Where the furnace uses pulverised-coal multi-channel lances, the start-up method is simple: a small quantity of wood and crushed coke is burnt in the hearth and the bath is then built up under automatic heating from the lances, with the gas flow, pressure and coal rate of every lance visible online. Where the furnace uses single-channel tuyeres, published practice is the traditional method — the furnace is opened by hand, with workers charging large quantities of wood, lump coke, lump slag and lead plates to create the molten pool, a figure of 60–70 tonnes of material being added by hand per pool on a 13 square metre unit. That difference is not a matter of taste: it decides the start-up cost, the start-up time, the exposure of the crew and how quickly a furnace can be brought back after a stop. The jackets, the water circuit, the refractory dry-out curve, the draught and the gas train are all verified before the bath is built. Reagent and utility input: controlled refractory dry-out curve, jacket water flow and temperature verified, draught and gas train running, wood and coke for hearth establishment, burner or lance heating, bath level and temperature measurement. Output: a lined and dried vessel with a molten bath at its design level and temperature, and a gas train proven against its design duty.

Steps 4 — Side-Blown Oxygen Injection and Bath Jetting. This is the stage the furnace is named for. Oxygen-enriched air at 60–90 per cent oxygen is blown horizontally through nozzles set in the copper water jackets on both side walls into the slag layer, and the horizontal jets stir the upper bath so violently that it becomes a jetting layer — a violently agitated surface zone in which the charge, the flux and the fuel meet hot slag with a very large contact area. Because the nozzle body is water-cooled internally and sits in the wall rather than in the melt, it needs no inert-gas shroud and no demineralised-water protection, and it can be run at an oxygen concentration above 65 per cent without consuming itself. The oxygen rate, the number of nozzles in service and the bath level are held together, because the jetting layer exists only while the bath is above the nozzle and the jets are actually penetrating the slag; a bath run too shallow gives a short-circuit towards the uptake, and a bath run too deep gives a still surface. Where the multi-channel lance arrangement is used, the coal and the enriched air are injected together into the middle of the bath, which is what keeps the pool temperature even and the slag below 1,300 °C in the published comparison; where single-channel tuyeres are used, the heat comes from lump coal charged at the top and the upper bath runs hotter, which is why those furnaces need their tuyeres punched by hand each shift and produce several times the nitrogen oxides. Reagent and utility input: oxygen plant or delivered oxygen, oxygen-enriched blast at its design concentration, water-cooled nozzles or multi-channel lances with pulverised coal, nozzle-in-service selection, bath level and temperature control, jacket water flow and temperature, gas analysis. Output: a bath stirred into a stable jetting layer at its design oxygen potential, with the charges meeting hot slag on arrival instead of melting slowly against a cooler surface.

Steps 5 — Oxidation Smelting and High-Lead Slag Formation. In the jetting layer the charge is melted, desulphurised and slagged almost immediately, and this is the stage where the sulphur leaves the metal and enters the gas. On sulfide feed the oxygen attacks the metal sulfide and the iron sulfide, the sulphur goes off as sulphur dioxide and the iron joins the slag under the silica flux; on oxidic and sulfated feed such as battery paste it is the sulfate that decomposes, releasing its sulphur to the gas as the bath oxidises. The published performance of the oxidation stage on lead-zinc feed is a desulphurisation rate of 99.5 per cent, with an oxygen concentration of 90 per cent in the oxidation furnace, and the sulphur dioxide that leaves it sits at 12–18 per cent by volume — high enough and stable enough to feed a two-stage contact acid plant directly. What is produced in the bath is a lead-rich slag and a partly metallic lead phase, and both sink into the quiet lower bath where the slag rises and the metal settles. The stage is controlled on the gas analysis and the bath temperature together, because an oxidising potential that is driven too hard takes metal into the slag as oxide, and one that is too weak leaves sulphur in the bath and starves the acid plant. Reagent and utility input: continuous oxygen-enriched injection, silica and limestone flux, bath temperature control at the working band, off-gas analysis for sulphur dioxide and oxygen, bath sampling, jacket and uptake temperature trending. Output: a desulphurised bath producing a high-lead slag and a metal phase, and a stable sulphur dioxide gas stream for the acid plant.

Steps 6 — Reduction Smelting and Crude Lead Tapping. The hot high-lead slag flows by launder from the oxidation furnace into the reduction furnace, which is the reason the circuit is designed as a fully insulated process without ladle transfer: the slag arrives hot, so the fuel that would otherwise be burnt to re-melt it is not burnt at all, and the plant does not pay for the heat twice. In the reduction furnace the bath is run on a reducing potential, the lead oxide in the slag is reduced to metal, and a reduction slag forms that still carries the zinc. The published coal rate for the reduction stage on lead-zinc feed is 8.6 per cent, and the published metal recovery across the line is above 97 per cent for lead and above 92 per cent for zinc. Crude lead is tapped from the low point of the bath, skimmed of entrained slag at the spout rather than letting it freeze into the ingot, and transferred hot to the refining kettles where the plant has them, so the heat in the metal is not thrown away and paid for again. The vessel does not raise the grade: the antimony, copper, tin, bismuth and silver in the charge report to the metal along with the lead, and they are reported in the assay rather than removed here. Reagent and utility input: hot slag transfer by launder, coal or gas reductant at its designed rate, bath temperature and reducing-potential control, crude lead tapping and skimming, weighing and sampling of the metal, hot transfer to refining. Output: a weighed and sampled crude lead bullion lot transferred for refining, and a reduction slag carrying the zinc to the fuming stage.

Steps 7 — Slag Fuming and Zinc Oxide Dust Recovery. The reduction slag, still hot and still carrying zinc together with germanium, indium and a residue of lead, flows on to the fuming stage, where the bath is held strongly reducing and the zinc is reduced and volatilised out of the slag. The zinc vapour is re-oxidised in the gas phase as it meets oxygen on its way out, forming fine zinc oxide particles that are carried into the boiler and the dust collector and captured as a product rather than a waste. Published figures for the side-blowing plus fuming arrangement are volatilisation of 90–98 per cent of the zinc, the lead, the silver and the germanium in the feed, a dust above 50 per cent zinc, and a tailing in the 1–2 per cent zinc and 0.02–0.2 per cent lead band, which takes a hazardous leaching residue to a general solid waste that can be stored or sold. The fuming stage runs on air or lightly enriched air rather than on the high-enrichment blast of the oxidation furnace, and its own off-gas is weaker in sulphur dioxide and is desulphurised by absorption rather than sent to the acid plant. Reagent and utility input: fuming-stage reductant, bath temperature at the fuming band, off-gas cooling and dust collection, dust weighing and assay, tailing sampling and assay. Output: a zinc oxide dust above 50 per cent zinc for the zinc circuit, and a tailing reduced to the discard band of published practice.

Steps 8 — Waste Heat Recovery, Dedusting and Acid Making. The gas leaves the furnace at a temperature and a dust load that make the route behind it an engineering decision rather than a formality. In the published lead project the oxidation furnace’s waste-heat-boiler outlet carried 32,000–38,000 Nm³/h at 350–380 °C with 120–160 g/Nm³ of dust against a furnace chamber temperature of 1,100–1,300 °C, so the gas is first cooled in a waste-heat boiler that recovers the heat as steam and brings the temperature below 400 °C, then given a gravity pre-cleaning pass, then cleaned in a high-temperature electrostatic precipitator, and finally handed to the acid plant by a fan. The dust route was chosen dry so the metals are recovered as dust rather than dissolved into a wastewater, and the precipitator was chosen ahead of a bag filter for two recorded reasons: the gas temperature is high enough to burn bags, and its high sulphur content gives a high dew point, so sticky condensation blinds them. The electrical side of that choice rests on the dust’s own physics — a dust high in lead oxide has a high resistivity, which alone would rule a precipitator out, but the sulphur dioxide, sulphur trioxide and water vapour in the same gas bring the resistivity back into the 10⁴–10¹⁰ Ω·cm window a precipitator needs. Captured dust is conveyed back to the batching system. On the fuming and reduction lines, whose gas is too weak in sulphur dioxide for acid making, absorption desulphurisation is used instead, and the whole circuit is held under controlled draught with its charging, tapping and launder points enclosed. Reagent and utility input: waste-heat boiler with feedwater treatment and steam export, gravity settling chamber with wall vibrators, high-temperature electrostatic precipitator with its high-voltage supply, induced-draught fan, acid plant feed or absorption desulphurisation, dust conveying and return, gas monitoring. Output: steam, a weighed and assayed dust returned to the burden, and either saleable sulphuric acid or a desulphurised gas released to atmosphere.

Steps 9 — Campaign Inspection and Water-Jacket Survey. The campaign closes with the vessel surveyed rather than assumed. The furnace is cooled on a controlled curve, the bath is drained and the jackets are inspected for wear, for slag coating integrity and for water-side scaling, because the copper jacket’s whole working principle is that a frozen slag layer protects it — and a jacket whose coating has been lost or which has been overheated is a jacket whose remaining campaign cannot be judged from the outside. The refractory behind the jackets is measured against its wear curve, the nozzles or lances are checked for burn-back, blockage and alignment and are replaced or repositioned to their design reference, the uptake and the boiler are inspected for accretion, the precipitator electrodes and rappers are checked, the launders and the tapholes are gauged, the jacket support columns and their load paths are examined, and the control and interlock schedule is proven, including the trips for loss of oxygen pressure, loss of jacket water flow, high bath temperature, high gas temperature at the boiler inlet and loss of feed. The metal balance is then closed over the campaign — feed in against metal, slag, dust and gas out, with the drained bath and the metal attached to spent refractories accounted for — and the result drives the next campaign’s burden recipe rather than being filed. Reagent and utility input: controlled cool-down, bath draining, refractory and jacket survey, nozzle or lance change-out set, boiler and precipitator inspection, launder and taphole gauging, interlock proving, campaign metal balance closure. Output: a surveyed vessel with its wear documented, a replaced wear part set, and a closed campaign metal balance that the next campaign is planned from.

Product Structure (Main Equipment)

The station is assembled from the three module groups below. Materials are selected for the two environments the vessel actually lives in — a molten bath of slag and metal on one side, and an oxygen-enriched gas circuit on the other: the copper water jackets in forged or rolled copper plate with a machined cooling channel and a replaceable nozzle boss, the refractory behind them in magnesia-chrome or chrome-magnesite brick with a castable working lining, the uptake and the hot ducting in heat-resistant alloy or water-cooled panels, the nozzle or lance bodies in water-cooled copper or heat-resistant alloy, the gas train in carbon steel with refractory-lined hot sections and stainless steel at the change-over points, the ducts and the precipitator casings in corrosion-resistant steel sized for a sulphur-bearing gas, and the launder, tapping and handling equipment in mild steel with replaceable refractory linings.

Furnace body, copper water jackets and refractory

The vessel is a stationary furnace with straight or elliptical side walls, and it has no rotating parts, no trunnion and no moving joints — a structural choice whose value is that the shell has a low air-inleakage rate and the off-gas volume therefore stays where the furnace design put it. The melting zone is built from copper water jackets, and the reason is thermal rather than mechanical: copper’s conductivity is far higher than steel’s, so slag freezes against the jacket face quickly and hangs there, and that frozen coating is the barrier the bath actually touches. Because the coating, and not the refractory, is what faces the reacting bath, the smelting temperature in the melting zone is not limited by refractory material; the published consequence is a long jacket campaign and a high operating rate, with furnace-body life for this family reaching five years.

The jackets are heavy, and they are not carried on the furnace foundation. Each jacket block is supported from steel columns rising around the furnace shell, whereas a steel-jacketed blast furnace is comparatively light and is carried on a whole-body support bearing on its foundation. This is a real design decision and it is taken at the proposal stage, because it sets the foundation layout, the structural steelwork, the crane, the maintenance access around the vessel and the floor loading the building has to take. The refractory behind the jackets is a magnesia-chrome or chrome-magnesite brick against the slag zone with a castable working lining where the geometry demands it, and hot spots are trended on shell thermocouples so that wear is visible on a curve rather than discovered as a leak.

Tuyeres, multi-channel lances and the oxygen circuit

The nozzle set is where the two side-blowing arrangements differ, and choosing between them is the first process decision on this vessel. A single-channel tuyere passes only oxygen-enriched air into the slag layer; published practice sets those tuyeres 1.5–2 metres apart, uses a relatively large number of them, and keeps only about half in normal service, with manual punching carried out every shift to clear blockages and to read the slag. A multi-channel lance injects pulverised coal together with oxygen-enriched air, which puts the primary fuel into the middle of the bath; published practice sets those lances about 2–2.5 metres apart, uses fewer of them, keeps more than 70 per cent in service, and runs them automatically, with the gas flow, the gas pressure and the coal injection rate of every lance monitored online, so there is no routine manual tuyere work at all.

Both arrangements share the property that makes high enrichment possible: the nozzle is set in the wall and does not contact the high-temperature melt, so it requires neither an inert-gas shroud nor demineralised-water protection, and a water-cooled nozzle body tolerates an oxygen concentration above 65 per cent. That is the mechanical basis for running the blast at 60–90 per cent oxygen. The oxygen circuit around them is a designed system rather than a pipe: an oxygen plant or a delivered supply with its storage and vaporisation, metering and pressure control on the main, a per-tuyere or per-lance flow and pressure indication, a fast-acting isolation and purge arrangement, a nitrogen or instrument-air supply for purging and for the shroud where one is used, and an interlock set that trips on loss of oxygen pressure, on loss of jacket water flow and on high bath or gas temperature. Coal for a multi-channel arrangement is dried, milled, metered and conveyed to the lance manifolds with its own inerting provisions.

Feed, gas train, dust and control

Feed arrives at a sealed top charging opening and falls into the jetting layer, and the charging arrangement is designed around the two things that make a top opening a problem: the gas that escapes when it is open, and the air that leaks in when it is not sealed properly. Charges are proportioned by weigh feeders, the recycle dust from the plant’s own gas train is blended into the burden, and the feed rate is interlocked against the oxygen rate so the bath cannot be starved or overcharged. The gas train begins at the uptake and runs through a waste-heat boiler that recovers the heat as steam and cools the gas below the temperature the precipitator will take — in the published lead project from a chamber temperature of 1,100–1,300 °C down below 400 °C at the boiler outlet — then through a gravity settling chamber that takes out the coarse fraction, then through a high-temperature electrostatic precipitator selected on the dust’s resistivity once the sulphur dioxide, sulphur trioxide and water vapour in the gas have brought it into the 10⁴–10¹⁰ Ω·cm window, then through the induced-draught fan to the acid plant, or through an absorption desulphurisation train where the gas is too weak in sulphur dioxide for acid making.

Dust from the boiler, the settling chamber and the precipitator is collected, weighed, assayed and conveyed back to the batching system so it re-enters the furnace. The control system runs the furnace as a continuous circuit: charging rate, oxygen flow and concentration, coal rate, bath and jacket temperatures, uptake temperature, boiler outlet temperature, precipitator electrical parameters, fan duty and gas analysis are all trended, the slag and metal temperatures are measured on the bath rather than on the flame or the shell, and the alarm and interlock schedule is built around the states that actually damage the vessel — loss of jacket water, loss of oxygen pressure, high bath temperature, high gas temperature at the boiler inlet, draught failure and loss of feed. Steam export, acid plant feed and the dust return rate are metered so that the shift balance closes on measurements, and the whole gas circuit is held under controlled draught with the charging, tapping and launder points enclosed.

Product Features

A stationary vessel with no rotating or moving joints. The furnace is a fixed, straight-walled or elliptical vessel with no trunnion, no drive and no articulated connection carrying hot gas. The features that follow are the ones that matter in service: a low air-inleakage rate, so the off-gas volume the boiler and the precipitator were sized for is the volume they actually see; a low thermal loss, so less fuel is burnt to cover loss that never reached the bath; fewer mechanical faults, because there is very little to fail; and a stable gas composition, which is the condition the acid plant behind it needs.
Copper water jackets protected by their own hung slag coating. The melting zone is copper-jacketed, and the jacket’s working protection is the slag that freezes and hangs on its inner face. That design gives a bath zone whose working temperature is set by slag chemistry rather than by refractory grade, a long jacket campaign with a high operating rate, and — because the jacket blocks carry real weight — a support arrangement in which each block is carried by steel columns around the shell rather than on the furnace foundation.
Side nozzles that do not touch the melt. The tuyere or lance sits in the side wall and is isolated from the liquid bath, with its own internal water cooling. It therefore needs no inert-gas shroud and no demineralised-water protection, it can be run at an oxygen concentration above 65 per cent, and the whole furnace can be driven at 60–90 per cent enrichment where a blast-furnace nozzle is limited to about 28 per cent.
A jetting layer that does the smelting in seconds. The horizontal side blast stirs the upper bath into a violently agitated jetting layer, the charge and the flux land in it, and melting, desulphurisation and slagging complete almost immediately rather than over the minutes a static bath takes. Published specific smelting capacity is 40–50 t/(m²·d) on residue and lead duty, around 60 t/(m²·d) in published lead-zinc oxidation practice and above 120 t/(m²·d) on copper duty, which is what makes a vessel this size carry that tonnage.
A quiet lower bath that separates rather than mixes. Because the stirring is concentrated in the upper zone, the lower bath is relatively still, and slag and metal separate by gravity instead of being held in emulsion. That is why the vessel tolerates a metal content in its discard slag that published copper practice puts below 0.3 per cent, low enough to granulate and sell without a flotation step.
Continuous smelting and continuous slag tapping. The furnace smelts and taps continuously, which is what allows oxidation, reduction and fuming to be arranged as three vessels in a chain connected by launders and operated simultaneously. Continuous operation is also what keeps the sulphur dioxide band stable enough for an acid plant to make a saleable product instead of a variable weak stream.
No sinter strand, no pelletiser, no deep drying. Moisture up to about eight per cent is charged directly, particle size and moisture are not tightly controlled, and there is no packed column whose permeability has to be maintained. The published consequence is a shorter flowsheet with fewer unit operations, less fuel, less maintenance and less dust in the feed preparation area — and a lead grade as low as about 30 per cent, or about 10 per cent copper, that is still worth charging.
Coal granule or natural gas instead of metallurgical coke. With no column to support, the vessel does not need coke, and published practice runs anthracite or bituminous coal granules as fuel and reductant, with natural gas as an alternative and the coal-to-gas ratio adjusted against the feed. The published consumption on residue duty is 270–290 kg of standard coal per tonne in the multi-channel-lance configuration and 300–340 kg in the single-channel-tuyere configuration, against the 40–60 per cent coke or coal rate of the kiln and box-fuming processes it replaces.
A nozzle choice that can be read off the nitrogen oxides. The multi-channel lance injects pulverised coal into the middle of the bath, so the pool temperature is even, the slag runs below 1,300 °C and the nitrogen oxides sit at 500–1,500 mg/Nm³. The single-channel tuyere takes its heat from lump coal at the top, so the upper bath reaches 1,400 °C or more and the nitrogen oxides run 2,000–8,000 mg/Nm³. The same choice decides the lance pitch, the fraction in service and whether anyone has to punch tuyeres by hand every shift.
A concentrated sulphur dioxide stream that goes to acid rather than to a scrubber. The oxidation stage produces 12–18 per cent sulphur dioxide by volume in a stable band, high enough to feed a two-stage contact acid plant directly. The reduction and fuming stages produce a weaker gas and are desulphurised by absorption. Sulfur is therefore accounted for as a product on the flowsheet, and the acid plant’s feed condition is a design output of the furnace rather than an assumption made after it.
Dry dust collection chosen on solid-resistivity reasoning. The gas leaves the boiler at 350–380 °C in published practice with 120–160 g/Nm³ of dust, and the collection route is dry — gravity settling then a high-temperature electrostatic precipitator — so the metals come out as a dust rather than into a wastewater. The precipitator is selected ahead of a bag filter because the gas is hot enough to burn bags and high in sulphur enough to condense and blind them, and the dust’s own high lead-oxide resistivity is brought back into the 10⁴–10¹⁰ Ω·cm working window by the sulphur dioxide, sulphur trioxide and water vapour in the same gas.
Dust and slag as internal streams and saleable products. Precipitator and boiler dust is conveyed back to the batching system and re-enters the furnace rather than accumulating on site; water-quenched slag is granulated, assayed and sold as aggregate or used as a cement raw material; and the fuming stage’s zinc oxide dust is a product for the zinc circuit. Published side-blowing practice also returns dust collected from the side-blown furnaces to the feed preparation system as a matter of course.
A fully insulated circuit with no ladle transfer between the stages. The three-furnace line is arranged so the hot slag runs from one vessel to the next down a launder. Published characteristics for the side-blown lead arrangement state it directly — a fully insulated process without ladle transfer, which minimises fugitive emission and environmental pollution — and the operational effect is that the heat in the slag is not thrown away and then paid for again as fuel in the next vessel.
An enclosed gas circuit rather than a claimed zero-emission plant. Charging, tapping, launder and slag handling points are enclosed and held under controlled draught, the gas is cooled, dedusted and either acidified or desulphurised before release, and dust is returned rather than discharged. No zero-emission claim is made; the claim made is that the gas volume is small and concentrated, that its sulphur is captured as a product and its particulate is captured dry, which is a compliance position that can be measured rather than asserted.
Feed flexibility that survives a market change. The vessel accepts a changing mixture of sulfide concentrate, oxide ore, battery paste, leaching residue, dust, dross and scrap without a change of preparation line, which is what lets a plant buy residues opportunistically instead of being tied to one mineralogy. Blending is designed into the module rather than improvised at the charging door.
A control basis written as setpoints, not as experience. Charging rate, oxygen flow and concentration, coal rate, bath temperature, jacket water flow and uptake temperature are held as figures in a recipe, with the interlock set built around the failure modes that actually damage the vessel. That is what lets an operator move the metal grade or the slag condition deliberately instead of changing the oxygen flow and waiting to see what happens.

Technical Parameters And Specifications

The figures below are the standard design basis and are confirmed or adjusted during process design once the feed survey is complete. Capacity, hearth area, jacket count and jacket size, nozzle count and pitch, oxygen plant size, boiler duty, precipitator area, ducting diameter, fan duty, refractory quantity, floor loading and the station footprint are engineered to your feed assay, your tonnage, the metal you are collecting and your building’s oxygen, fuel, power and draught capacity rather than taken from a catalogue of fixed models. Process figures — oxygen concentration, working temperature, coal and oxygen consumption, slag band, recovery and gas composition — are retained as published values because they are what the vessel is bought on, and each is quoted with the duty it applies to.

Oxygen-enriched side-blown furnace — technical parameters and specifications.

Parameter	Specification
Station type	Side-blown bath-smelting station: stationary furnace with copper water jackets, side tuyere or multi-channel lance set, oxygen and fuel train, sealed top charging, slag and metal launders, enclosed off-gas train with waste-heat boiler and electrostatic precipitator, dust return and the shift record
Furnace family	Stationary straight-walled or elliptical side-blown furnace; single-channel-tuyere and multi-channel pulverised-coal-lance arrangements both available, quoted against the feed and the duty
Blowing position	Oxygen-enriched gas injected horizontally through nozzles set in the copper water jackets on both side walls into the slag layer, forming a jetting layer in the upper bath while the lower bath separates slag from metal by gravity
Applicable feed state	Solid lead, zinc, copper, nickel, tin, antimony and bismuth bearing feed: sulfide and oxide concentrates, battery paste and grid metal, zinc leaching residue, steel-plant dust, copper scrap, black copper, electronic scrap concentrate, anode slime, drosses, slags and residues
Capacity	Engineered to your feed tonnage, the metal you are collecting and the number of vessels in the line, with the hearth area, the smelting rate, the oxygen demand and the vessel count calculated and stated as figures in the process design package rather than selected from a model list
Specific smelting capacity	40–50 t/(m²·d) on residue and lead duty, about 60 t/(m²·d) in published lead-zinc oxidation practice, and above 120 t/(m²·d) on copper duty
Oxygen concentration in the blast	60–90 per cent oxygen, with 70–85 per cent as the ordinary industrial band and up to 90 per cent quoted for the oxidation stage of a published lead-zinc line
Oxygen nozzle limit and its basis	Water-cooled nozzles tolerate above 65 per cent oxygen enrichment because the nozzle body is internally water-cooled and does not contact the high-temperature melt, so it needs no inert-gas shroud and no demineralised-water protection; a blast-furnace nozzle is limited to about 28 per cent enrichment
Working temperature band	1,200–1,500 °C quoted for side-blown residue smelting; 1,150–1,250 °C in the published multi-channel-lance comparison and 1,350–1,450 °C in the single-channel-tuyere comparison; furnace chamber gas temperature 1,100–1,300 °C in the published lead project
Low-temperature option	A sodium carbonate molten-salt medium with an iron–silicon–calcium–sodium quaternary slag brings the working temperature below 1,100 °C against the classical 1,200–1,250 °C lead bath, with pyrite burnt in the bath as make-up heat
Fuel and reductant	Anthracite or bituminous coal granules as fuel and reductant, pulverised coal injected through multi-channel lances where that arrangement is used, natural gas as an alternative heat source, and a coal-to-gas ratio adjusted against the feed; no metallurgical coke is required because there is no packed column to support
Standard coal consumption	270–290 kg of standard coal per tonne of residue in the multi-channel-lance configuration and 300–340 kg per tonne in the single-channel-tuyere configuration, as published on four residue cases; about 140 kg of standard coal per tonne of blister copper on the published copper duty
Oxygen consumption	270–300 Nm³ per tonne of residue in the multi-channel-lance configuration and 350–380 Nm³ per tonne in the single-channel-tuyere configuration, as published on the same four residue cases
Tuyere or lance pitch	1.5–2.0 m between tuyeres for the single-channel arrangement and about 2.0–2.5 m between lances for the multi-channel arrangement, as published
Nozzles in service	About 50 per cent of the tuyeres in normal service in the published single-channel practice, with manual punching each shift; above 70 per cent of the lances in service in the published multi-channel practice, with no routine manual work
Nitrogen oxides in the furnace off-gas	500–1,500 mg/Nm³ with the multi-channel pulverised-coal lance arrangement and 2,000–8,000 mg/Nm³ with the single-channel tuyere arrangement, as published
Sulphur dioxide in the oxidation off-gas	12–18 per cent by volume in published side-blowing lead practice, stable because the stage runs continuously; 3–4 per cent quoted for the fuming stage of the same flowsheet and desulphurised by absorption rather than sent to acid
Desulphurisation performance	99.5 per cent desulphurisation rate in the oxidation furnace of a published lead-zinc line
Reduction performance	Coal rate of 8.6 per cent in the reduction stage of a published lead-zinc line
Metal recovery	Above 97 per cent for lead and above 92 per cent for zinc in the published lead-zinc line; 90–98 per cent volatilisation of zinc, lead, silver and germanium in the published side-blowing plus fuming residue cases; above 98 per cent lead recovery quoted in published side-blowing lead practice
Metal in the discard slag	Below 0.3 per cent metal in the settler slag on published copper duty, low enough to granulate and sell without flotation; 2–4 per cent lead as a design band on lead duty with the slag assayed per shift
Zinc oxide dust product	Above 50 per cent zinc in the published dust product of the fuming stage
Tailing after fuming	1–2 per cent zinc, 0.02–0.2 per cent lead and 0.001–0.002 per cent silver in the published residue cases, against 0.5–1.5 per cent zinc and lower lead after a converted line
Charge moisture	Up to about 8 per cent charged directly, on published lead, copper and residue duty; no drying, granulation or deep grinding required for material inside that window
Charge grade window	Lead grade as low as about 30 per cent and copper grade as low as about 10 per cent charged directly in published practice; 22–40 per cent lead with about 10 per cent zinc quoted for the published lead-zinc line
Furnace geometry	Stationary vessel with straight or elliptical walls, a shallow hearth, copper water jackets in the melting zone of the upper bath, and no rotating parts, trunnion or moving joints
Water-jacket construction	Copper jackets in the melting zone with an internal cooling channel and a replaceable nozzle boss, protected in service by a hung slag coating; the published service rationale is that copper’s thermal conductivity hangs and holds that coating far better than steel, so the melting temperature in the bath zone is not limited by refractory material
Jacket support	Each copper jacket block supported from steel columns rising around the furnace shell rather than carried on the furnace foundation, as published practice does for the copper-jacketed side-blown design; a steel-jacketed blast furnace is comparatively light and is carried on a whole-body support bearing on its foundation
Refractory	Magnesia-chrome or chrome-magnesite brick at the slag and melt zone behind the jackets, with a castable working lining where the geometry demands it, and hot spots trended on shell thermocouples against a warning threshold
Furnace campaign life	Up to five years of furnace-body life in published side-blowing lead-zinc practice, with the jacket and lining campaign tracked as a wear curve rather than a calendar interval
Charging	Sealed top charging opening into a controlled draught, with weigh feeders proportioning the burden, flux, coal and recycle dust, and the feed rate interlocked against the oxygen rate
Tapping	Crude metal tapped at the low point and slag tapped or laundered from the high point into the next vessel of the line, with the two streams separated by the quiescent lower bath rather than by cutting a single stream
Line configuration	Single vessel on one duty, or the published three-furnace line in which oxidation, reduction and fuming run continuously in three side-blown furnaces connected by chutes, or a side-blown furnace feeding an existing box fuming furnace
Inter-vessel transfer	Hot slag transferred from one vessel to the next by launder in a fully insulated circuit without ladle transfer, as published practice specifies
Off-gas handling	Uptake into a waste-heat boiler that recovers heat as steam and cools the gas below 400 °C, a gravity settling chamber with wall vibrators, a high-temperature electrostatic precipitator, an induced-draught fan, and then either a two-stage contact acid plant or an absorption desulphurisation train
Published gas basis	32,000–38,000 Nm³/h at the waste-heat-boiler outlet, 350–380 °C, 120–160 g/Nm³ dust, against a furnace chamber temperature of 1,100–1,300 °C in the published lead project
Dust-collection selection basis	Dry collection so the metals are recovered as dust rather than dissolved into a wastewater; electrostatic precipitator selected ahead of a bag filter because the gas is hot enough to burn bags and its sulphur content gives a dew point high enough to condense and blind them; the dust’s own lead-oxide resistivity would rule a precipitator out, but the sulphur dioxide, sulphur trioxide and water vapour in the gas bring it into the 10⁴–10¹⁰ Ω·cm working window
Dust return	Boiler, settling-chamber and precipitator dust collected, weighed, assayed and conveyed back to the batching system to re-enter the burden, as published practice returns dust from the side-blown furnaces to the feed preparation system
Slag handling	Slag quenched into granules or cast into blocks so entrained metal can settle, then cooled, sampled and assayed; granulated slag used as aggregate or as cement raw material on the published reuse route
Instrumentation and control	Continuous control of charging rate, oxygen flow and concentration, coal rate, bath and jacket temperatures, uptake and boiler-outlet temperature, precipitator electrical parameters, fan duty and gas analysis, with steam export and acid-plant feed metered so the shift balance closes on measurements
Alarm and interlock set	Loss of oxygen pressure, loss of jacket cooling-water flow, jacket water temperature high, bath temperature high, gas temperature high at the boiler inlet, draught failure, precipitator fault and loss of feed, each with a defined trip action
Enclosure and draught	Charging, tapping, launder and slag handling points enclosed and held under controlled draught, with the gas circuit sealed so the off-gas volume stays inside the duty the boiler and the precipitator were sized for
Site services	Oxygen supply and storage or a captive oxygen plant with its rating, fuel gas or coal supply with its pressure and flow, cooling water flow and inlet temperature, boiler feedwater with its treatment, compressed air and instrument air, electrical supply and rating, floor loading and headroom for the vessel and the jacket handling, containment and drainage, and the off-gas route to the acid plant or to atmosphere — each issued as a schedule with a value against the line
Materials of construction	Copper water jackets with machined cooling channels, magnesia-chrome and chrome-magnesite refractories with a castable working lining, water-cooled or heat-resistant alloy nozzle and lance bodies, heat-resistant alloy or water-cooled uptake and hot ducting, carbon steel with refractory-lined hot sections and stainless steel at the change-over points in the gas train, corrosion-resistant precipitator casings sized for a sulphur-bearing gas, and replaceable refractory linings in the launders and tapping arrangements
Mass balance per shift	Charge weight and assay, flux, coal and oxygen additions, bath temperature and working condition, metal weight and assay, slag weight and assay, dust weight and assay, and the sulphur balance between gas, slag and dust, with the difference closed as the measured loss for that shift
Duty and cycle	Engineered for continuous multi-shift operation, with the whole line run continuously on the three-vessel arrangement and the campaign set by the slag chemistry, the halide load and the jacket survey
Operating crew	Engineered to your shift structure; the standard crew runs the vessel and the bath, the charging and batching area, the nozzles or the lance and coal circuit, the boiler and precipitator, the dust return and the slag handling, with no routine manual tuyere work in the multi-channel-lance arrangement
Installed footprint	Engineered to the vessel size, the number of vessels in the line and the site’s available bay, headroom, service routes and off-gas run, and stated as a figure in the process design package
Compliance basis	Design basis aligned to the sulphur dioxide, particulate, nitrogen oxide and heavy-metal provisions applicable to the smelting operation, to the oxygen and fuel-gas handling requirements for the site, and to the requirements applying to the storage and consignment of the residues and by-products the line produces

Technical Advantages

The geometry is chosen on the nozzle’s survival, and the consequence is stated. A nozzle that sits in the wall and does not touch the melt does not have to be consumable, so it can carry its own water cooling and it needs no inert-gas shroud and no demineralised-water protection. That is why this vessel runs 60–90 per cent oxygen while a blast-furnace tuyere is held to about 28 per cent, and it is the single design fact that explains the whole difference in intensity between the two furnace families.
A horizontal jet into the slag layer is a better mixing device than a vertical one. The jetting layer it creates is a violently stirred surface zone with a very large slag-to-charge contact area, so melting, desulphurisation and slagging complete almost immediately instead of over the minutes a static bath needs. The published specific capacity that follows — 40–50 t/(m²·d) on residue and lead duty, around 60 t/(m²·d) on published lead-zinc duty and above 120 t/(m²·d) on copper duty — is what lets the vessel carry its tonnage on a small hearth.
The stirring is deliberately concentrated where the reaction is and absent where the separation is. A bath that is stirred everywhere entrains metal into its slag at every tap. This vessel stirs the upper bath hard and leaves the lower bath quiet, so slag and metal separate by gravity rather than by chance, and the published metal content of a settler slag on copper duty is below 0.3 per cent — low enough to granulate and sell without a flotation circuit behind it.
The jacket’s working protection is a slag coating, and saying so changes the refractory decision. Because frozen slag hangs on the copper face and the bath touches that coating rather than the brick, the working temperature in the melt zone is not set by refractory grade. Published furnace-body life for this family reaches five years, and the refractory behind the jacket can then be chosen for the zones where it actually faces the bath instead of being over-specified to survive the reaction zone.
The jacket’s weight is a structural fact and it is quoted as one. Copper jacket blocks are carried by steel columns rising around the shell rather than on the furnace foundation, and that moves into the foundation drawing, the steelwork, the crane and the maintenance route. A supplier who quotes copper jackets without quoting their support has quoted a different vessel from the one that will be built.
The nitrogen oxide figure is a choice, not a property. A multi-channel lance puts pulverised coal and enriched air into the middle of the bath, gives an even pool temperature and a slag below 1,300 °C, and produces 500–1,500 mg/Nm³ of nitrogen oxides; a single-channel tuyere takes its heat from lump coal at the top, runs an upper bath at 1,400 °C or more, and produces 2,000–8,000 mg/Nm³. The same decision sets the pitch, the number of injection points and whether a person punches tuyeres by hand every shift.
The published start-up comparison is a cost and an exposure figure, and it is stated. A single-channel-tuyere furnace in published practice is opened by hand, with workers charging large quantities of wood, lump coke, lump slag and lead plates to build the molten pool — a figure of 60–70 tonnes of material per pool on a 13 square metre unit. A multi-channel-lance furnace needs only a small quantity of wood and crushed coke before automatic pulverised-coal heating takes over. Start-up cost, start-up time and crew exposure all follow.
The reductant bill is a coal bill, and the comparison is published. With no column to support, the vessel runs on coal granules or natural gas rather than metallurgical coke: 270–290 kg of standard coal and 270–300 Nm³ of oxygen per tonne of residue in the multi-channel configuration, against 300–340 kg and 350–380 Nm³/t in the single-channel one. The published conclusion against the other pyrometallurgical residue routes is more than 30 per cent less standard coal.
The sulphur route is a product line rather than an abatement problem. A stable 12–18 per cent sulphur dioxide stream from a continuous oxidation stage is acid-plant feed, not a waste gas, and sulfur recovery is the difference between a disposal cost and a by-product revenue. The weaker gas from the reduction and fuming stages is handled by absorption, which is cheaper than trying to make acid from a stream that is too dilute for it.
The gas train was designed around the dust’s physics rather than around a template. Dry collection is used so metal-bearing dust is recovered as dust; the precipitator is preferred to a bag filter because the gas is hot enough to burn bags and high in sulphur enough to condense and blind them; and the dust’s high lead-oxide resistivity — which would normally disqualify a precipitator — is brought into the workable window by the sulphur dioxide, sulphur trioxide and water vapour in the same gas. That chain of reasoning is a published design record, and it is why the choice can be defended rather than asserted.
The waste heat is recovered as steam rather than rejected. The boiler takes the gas down from the chamber temperature to below 400 °C and puts that heat into steam, so a plant with its own steam or power demand gets part of its fuel back. The boiler is also what makes the downstream collection possible, because a bag filter or a precipitator cannot be handed gas at furnace chamber temperature.
The dust returns to the burden and the slag becomes a saleable aggregate. Published practice returns collected dust from the side-blown furnaces to the feed preparation system, and quenched granulated slag is used as aggregate or cement raw material. The two largest by-product streams on the site therefore stop being a storage problem and become an input and a product.
The three-vessel line turns one difficult duty into three easy ones. Oxidation, reduction and fuming each run at one temperature with one slag type and one gas composition in a vessel designed for that duty, instead of one vessel alternating between incompatible regimes. Published results for the line on 22–40 per cent lead and about 10 per cent zinc feed are a 99.5 per cent desulphurisation rate, an 8.6 per cent coal rate in reduction, lead recovery above 97 per cent, zinc recovery above 92 per cent and an oxidation-stage oxygen concentration of 90 per cent.
No ladle transfer between the stages, which is where the heat and the metal are usually lost. The published arrangement is a fully insulated process in which the hot slag runs by launder from vessel to vessel, which minimises fugitive emission and stops the plant paying twice for the same heat. Ladle transfer is where slag crusts, where fume escapes and where a plant’s thermal balance quietly deteriorates.
Feed preparation is removed rather than optimised. Moisture up to about eight per cent, particle size uncontrolled, lead grade down to about 30 per cent or copper down to about 10 per cent, and no deep grinding or drying — which deletes the dryer, the briquetting press and the sinter strand from the flowsheet along with their fuel, their maintenance and their dust. It is also what lets a plant buy its feed on the market instead of contracting to one mineralogy.
A stationary vessel keeps its gas volume where the design put it. With no trunnion, no drive and no articulated hot-gas joint, the shell’s air-inleakage rate is low: the boiler, the precipitator and the fan see close to the volume they were sized for, less fuel is burnt to cover losses that never reached the bath, and there is very little mechanical equipment to fail.
The metal leaves hot, and the grade work is handed over rather than promised. The vessel reports the crude grade it reaches and transfers liquid metal to the refining kettles where the plant has them, so the heat is not thrown away and re-bought as fuel. A supplier who quotes a refined specification from a smelting vessel is quoting somebody else’s process step, and the buyer discovers that at the assay bench.
The honest boundaries are part of the offer. The vessel smelts and separates; it does not refine, it does not remove silver, bismuth or antimony from crude lead, and it cannot run at high enrichment without a sealed and instrumented gas circuit or carry a full oxygen supply and gas train below a certain tonnage. Where the material’s value sits in a dilute solution, where the metal is present in a refractory form that a wet route handles better, or where the tonnage is short, the right answer is a different route and this page names it.
Everything that decides the plant is issued before the order. The feed survey basis, the burden and flux recipe, the slag chemistry and working temperature, the nozzle arrangement and oxygen balance, the vessel count, the boiler and precipitator duty, the site service schedule and the performance test method are documents. The buyer can cost the vessel, the oxygen supply, the gas train and the acid plant together — which is the only way the project’s economics are actually visible.

Service Process

Step 1 — Feed data and duty review. You provide the feed types and their proportions, an assay or typical analysis covering the metal of interest together with zinc, sulfur, iron, silica, carbon, halide and moisture, the physical form the feed arrives in, the tonnage per shift, the metal grade or the intermediate product you intend to sell, and the site constraints on oxygen, fuel, power, water, draught, floor loading and headroom. We state at this stage whether each feed is chargeable as surveyed or needs drying, blending, agglomeration, plastic separation or refusal, which of the two nozzle arrangements suits it, and whether the tonnage clears the economic floor for a bath-smelting line. Output: a preliminary route statement, the boundary conditions and a clear scope of supply.
Step 2 — Slag chemistry, nozzle arrangement and vessel configuration. The slag system and its working temperature, the silica and limestone additions, the coal and oxygen demand, the nozzle type, the tuyere or lance pitch and the number in service, the hearth area, the bath depth, the vessel count in the line, the off-gas volume, the waste-heat boiler duty, the precipitator area and the fan duty are calculated from your feed survey, with the metal grade expected, the slag metal band and the sulphur distribution written down beside them. Output: a configuration proposal with the design basis stated, plus a draft site interface schedule.
Step 3 — Laboratory and pilot smelting test on your material. A representative sample of your feed is smelted at bench and pilot scale to establish the melting and desulphurisation behaviour, the flux additions that bring the slag into its working window, the working temperature band, the metal or matte grade reached from that feed, the slag metal content it produces and the sulphur distribution between gas, slag and dust on real material rather than on assumption. Output: a test report with a metal sample and a slag sample returned for your own assay.
Step 4 — Module fabrication and factory function test. The shell and its jacket set, the refractory, the tuyere or lance assembly with its water and coal circuits, the oxygen and fuel train, the sealed charging arrangement, the launders and tapping arrangements, the waste-heat boiler, the electrostatic precipitator, the dust return and the control system are fabricated, assembled and function-tested before shipment, with material certificates and test records retained and issued. Output: a factory function test record and the shipping documentation set.
Step 5 — Site interface schedule and building preparation. The site services are confirmed against your building together with the foundation and the jacket support steelwork, the floor loading for the loaded vessel and the handling equipment, the containment and drainage under the tap and the slag area, the off-gas route to the acid plant or to atmosphere with its sampling provisions, the reagent and coal storage, and the dust and slag storage areas. Output: a signed interface schedule, equipment layout and utility connection drawings that your builder can work from.
Step 6 — Installation, jacket and gas circuit commissioning. Our engineers supervise setting the vessel, assembling the copper jackets and pressure-testing the water circuit, drying out and bringing up the refractory lining on a controlled heating curve, checking out the nozzles or lances with their flows and pressures balanced, proving the oxygen train and its interlocks, verifying the enclosure and the controlled draught, commissioning the waste-heat boiler with its feedwater treatment, commissioning the electrostatic precipitator and the dust return, and proving the fan duty against the calculated volume. Output: a mechanically complete station with a measured draught, a tested oxygen circuit and a boiler and precipitator proven against their design duty.
Step 7 — First production campaign on your own feed. The line is run on your feed with the burden and flux recipe, the coal and oxygen rates, the working temperature band and the nozzle arrangement written against that feed, and the metal grade reached, the slag metal content, the sulphur distribution and the closed metal balance measured against the process design basis. Output: a commissioned station with its setpoints recorded and measured slag, metal and gas figures for your material.
Step 8 — Operator training and production qualification. Training covers feed reception and the acceptance screen, blending and moisture control, preheat and bath establishment, nozzle or lance practice and the oxygen circuit, bath temperature and slag reading, tapping and stream separation, dust return and slag handling, boiler and precipitator operation, enclosure discipline and housekeeping, and the shift record, all taught on the actual vessel. The production trial then confirms the metal grade, the slag metal figure, the consumption figures and the closed metal balance, and the operators sign off the standard operating procedures. Output: trained operators, a signed SOP set and a performance certificate for the first production campaign.
Step 9 — Consumables, spares and continuing process support. Jacket spares and nozzle or lance bodies, refractory and patching stock, coal milling and injection wear parts, precipitator electrodes and rappers, boiler components, boiler feedwater chemicals, launder refractories and tapping tooling are handed over with the station, spare parts are supplied afterwards, and our engineers stay available for process troubleshooting and for re-specifying the burden recipe, the flux addition and the working temperature band as your feed mix or your product specification changes. Output: continuing production support with a stocked consumables position and revised procedures as the feed changes.

Warranty And After-Sales Service

Warranty period. Twelve months from successful commissioning or eighteen months from shipment, whichever falls earlier, covering design, manufacture and assembly defects of the supplied equipment. Excluded: consumables such as refractory brick and patching material, nozzle and lance bodies, coal milling and injection wear parts, precipitator electrodes, boiler tubes and gaskets, filter elements in any auxiliary circuit, reagents and boiler feedwater chemicals, together with damage from misuse or from a feed outside the agreed specification.
Performance commitment. Where the feed matches the tested sample, we stand behind the metal grade reached, the slag metal figure, the consumption figures and the closed metal balance established in the process design package, with the production trial as the reference point. Output: a documented performance acceptance attached to the station’s file.
Spare parts and jacket supply. Copper jacket blocks and their seals, nozzle and lance assemblies, refractory brick and castable material, oxygen train valves and instrumentation, coal mill and injection spares, boiler tubes and gaskets, precipitator electrodes, rappers and high-voltage sets, launder and tapping refractories and control hardware are quoted at the time of order and held available afterwards, with a recommended on-site stock list issued at handover. Output: an on-site consumables position agreed before the station enters production.
Remote support. Telephone, email and messaging support on operating questions, alarm interpretation, bath and slag behaviour, nozzle or lance condition, oxygen circuit faults, boiler and precipitator performance, gas analysis and the burden recipe, whenever the line is running. Output: same-day response on operating issues.
On-site service. Engineer attendance for warranty faults, process problems and periodical check-ups, with response and attendance times agreed in the contract according to your location. Output: on-site intervention and a service report.
Jacket, refractory and campaign assessment visits. Periodical survey of the copper jackets against their coating condition and their water-side scaling, and of the refractory against its wear curve and its campaign target, together with a written view on how much of the remaining campaign is being consumed by the feed’s halide load, the bath temperature and the slag chemistry. Output: a reline and jacket-replacement plan built from your own survey record.
Slag, metal and consumption review. A periodical review of the slag assays, the metal assays, the coal and oxygen consumption and the closed metal balance against the design targets, with the levers that are actually moving the slag metal figure identified and a revised burden and flux schedule issued where the feed has changed. Output: a revised recipe and an updated expectation of the plant’s recovery.
Gas train performance review. Review of the boiler outlet temperature, the precipitator electrical parameters and rapping cycle, the dust load and the gas analysis against the design basis, with recommendations on the boiler cleaning cycle, the precipitator settings and the dust return rate where the feed has changed the dust character. Output: a revised gas train operating schedule.
Operator retraining and refresher visits. Additional training, refresher sessions and process optimisation visits as the feed mix, the metal specification or the permit condition changes, including re-establishing the bath and slag parameters after a change of feed supplier. Output: updated training and revised procedure documents.
Feed-mix change support. Where a customer adds a feed type — a new residue, a different concentrate, a dust from another process — we assess it against the acceptance screen, establish the flux addition and the coal and oxygen demand it needs and the slag it will produce, run a bench smelt where the answer is not obvious, and update the route sheet and the burden recipe accordingly. Output: a documented admission decision and a revised recipe for the new feed.
Documentation set. Operation and maintenance manuals, the process design package with the feed survey basis, the slag recipe and the mass balance method, the site interface schedule, equipment layout, electrical, oxygen, fuel, water and ducting drawings, the alarm and interlock schedule, the shift record and metal balance templates, the spare parts catalogue, the safety and hazard assessment for oxygen, fuel gas, coal dust and molten metal, and the emergency response plan. Output: complete documentation handover at commissioning.
Compliance support. Assistance with the emission parameter declarations, the stack and ambient monitoring arrangements, the precipitator performance verification, the handling, storage and consignment requirements for the residues and by-products, and the technical data behind your air, effluent and waste permit applications and your periodic compliance reporting. Output: the technical data for your permit applications and compliance reporting.
Lifetime technical support. The process design remains yours, and our engineering team remains available for modification and expansion advice — a second vessel for a three-furnace line, an added fuming stage, a slag-cleaning pass, an acid plant interface — for the operating life of the station. Output: long-term engineering continuity.

Frequently Asked Questions

What is an oxygen-enriched side-blown furnace and where does the oxygen actually enter?

An oxygen-enriched side-blown furnace is a stationary bath-smelting vessel in which oxygen-enriched gas is blown horizontally through tuyeres or multi-channel lances set in water-cooled jackets on the two long side walls of the furnace. The gas enters the slag layer rather than the matte layer or the furnace floor, and rather than being blown down onto the bath from above. The horizontal jets stir the upper bath violently into a jetting layer, the charge, the flux and the fuel are fed in through the furnace top and react in that layer almost immediately, and the products fall into the quieter lower bath where slag and metal separate under gravity and are tapped from different openings. The vessel is a fixed straight-walled or elliptical shell with no trunnion, no drive and no rotating or articulated joints, so its air inleakage is low and its off-gas composition is stable.

Why can a side-blown furnace run on 60 to 90 per cent oxygen when a blast furnace cannot?

Because of where the nozzle sits, not because of what it is made of. A side-blown nozzle is set in the furnace wall and is not in contact with the high-temperature melt, so the nozzle body can be built with its own internal water-cooling pipe and needs neither an inert-gas shroud nor demineralised-water protection. There is nothing in that arrangement that caps the oxygen concentration at a low figure, and published side-blowing practice therefore runs 60 to 90 per cent oxygen, with 70 to 85 per cent as the ordinary industrial band and figures up to 90 per cent quoted for the oxidation stage. A blast-furnace tuyere is a different device: it is limited to roughly 28 per cent enrichment, and the published comparison attributes that to a steel jacket that does not hang a protective slag coating as effectively and a nozzle without internal water cooling.

What is the jetting layer, and why does it set the furnace’s capacity?

The jetting layer is the violently agitated upper zone of the bath that forms where the horizontal oxygen-enriched jets enter the slag. Because the jets are horizontal and enter at speed, they break the upper bath into a spray-like mixture of slag, gas and reacting particles with an enormous contact area, and material arriving from the furnace top meets hot slag rather than a cooler surface. Melting, desulphurisation and slag formation therefore complete almost immediately rather than over the minutes a static bath takes. That is the direct cause of the published specific smelting capacity for this furnace family, which is 40 to 50 tonnes per square metre of hearth per day on residue and lead duty, about 60 t/(m²·d) in published lead-zinc oxidation practice, and above 120 t/(m²·d) on copper duty. It also explains the feed tolerance: there is no packed column whose permeability has to be preserved.

Why are the side walls built from copper water jackets rather than steel ones?

Because a copper jacket protects itself, and the protection is what does the work. Copper’s thermal conductivity is far higher than steel’s, so a layer of slag freezes against the jacket face quickly and stays hung there, and that frozen coating is what the molten bath actually touches. Copper jackets hang and hold that coating much better than steel jackets do, which has two consequences that matter commercially. First, the working temperature in the melting zone is not limited by the refractory, because the refractory sits behind the jacket rather than in the reaction zone. Second, the campaign is long: published practice reports long jacket life and a high operating rate for copper-jacketed side-blown units, and published furnace-body life for this family reaches five years.

Why is a copper jacket carried on steel columns instead of on the furnace foundation?

Because of its weight. A copper jacket block is heavy, and published practice for the copper-jacketed side-blown design supports each block from steel columns rising around the furnace shell rather than carrying it on the furnace foundation. A steel-jacketed blast furnace is comparatively light, and for that reason it is carried on a whole-body support that bears on its foundation. The structural consequence is not cosmetic: it changes the foundation drawing, the amount and layout of structural steel, the crane and rigging arrangements, the maintenance access around the vessel and the floor loading the building has to take. We treat it as a proposal-stage decision and state it, because a supplier who quotes copper jackets without quoting their support has quoted a different vessel from the one that gets built.

What is the difference between a single-channel tuyere and a multi-channel lance?

They are two different ways of getting heat and oxygen into the same bath. A single-channel tuyere passes oxygen-enriched air only; the heat comes from lump coal charged at the furnace top. Published practice sets those tuyeres 1.5 to 2 metres apart, uses a fairly large number of them, keeps only about half in normal service, and requires manual punching of the tuyeres every shift to clear them and to read the slag. A multi-channel lance injects pulverised coal together with the oxygen-enriched air into the middle of the bath. Published practice sets those lances about 2 to 2.5 metres apart, uses fewer of them, keeps more than 70 per cent in service, and runs them fully automatically with gas flow, gas pressure and coal injection rate monitored online for every lance. Both arrangements share the wall-mounted, water-cooled, melt-free nozzle that allows high oxygen enrichment.

How do the two nozzle arrangements compare on nitrogen oxides and on operating labour?

The published figures put the multi-channel arrangement at 500 to 1,500 milligrams per normal cubic metre of nitrogen oxides in the furnace off-gas, against 2,000 to 8,000 mg/Nm³ for the single-channel arrangement. The difference is thermal rather than chemical: pulverised coal injected into the middle of the bath heats the pool evenly and holds the slag below 1,300 degrees Celsius in the published comparison, while lump coal burnt at the top leaves the slag temperature uneven with the upper bath reaching 1,400 degrees or more, and the higher local temperature is what makes the extra nitrogen oxides. The labour difference runs the same way, because the single-channel furnace needs its tuyeres cleared by hand every shift while the multi-channel furnace needs no routine manual tuyere work at all, and start-up follows suit: published single-channel practice builds the first molten pool by hand, with 60 to 70 tonnes of wood, lump coke, lump slag and lead plates charged per pool on a 13 square metre furnace, where the multi-channel furnace needs only a small amount of wood and crushed coke before automatic pulverised-coal heating takes over.

Can moist, coarse and low-grade feed be charged without preparation?

Within limits, yes, and the limits are published. Moisture up to about 8 per cent can be charged directly on lead, copper and residue duty, and material particle size and moisture are not tightly controlled because there is no packed column to keep permeable. The grade window is wider than a blast furnace will accept: published practice takes a lead grade as low as about 30 per cent and a copper grade as low as about 10 per cent straight into the vessel, and it accepts mixed lead-zinc material of 22 to 40 per cent lead with about 10 per cent zinc. What that removes from the flowsheet is the dryer, the briquetting press and the sinter strand, along with their fuel, their maintenance and their dust. What it does not remove is the acceptance screen: feed that is free-draining, ice-bearing, acid-bearing, halogen-rich, or unidentified is still refused or routed to a preparation step first.

What is the difference between a side-blown and a bottom-blown furnace?

The blowing position, and everything that follows from it. A side-blown furnace injects through the side wall into the slag layer, so the oxygen has to cross the slag before it reaches the metal or matte, which makes the slag’s fluidity and its chemistry central to the process and makes the jetting layer the mechanism that drives the reaction rate. A bottom-blown furnace injects through lances set in the furnace floor into the matte layer, so most of the oxygen reacts with the sulfide below the slag and very little of it crosses the slag layer, which changes the slag behaviour, the magnetite formation and the slag type that can be used. Both are bath-smelting reactors and both can run autothermal or semi-autothermal, and the two are chosen on the feed, on the product you are collecting and on the slag you have to discard rather than on one being generally better.

Why are oxidation, reduction and fuming built as three separate vessels?

Because they are three incompatible regimes, and running them in one vessel means being poor at all three. In published lead-zinc practice the charge enters the first side-blown furnace for oxidation smelting and desulphurisation, producing a lead-rich slag; that slag flows down a chute into the second furnace, which is run reducing to produce crude lead and a reduction slag; and the reduction slag flows on to the third furnace, which is run for zinc volatilisation. Because each vessel then holds one temperature, one slag type and one gas composition, the oxidation furnace can be run at 90 per cent oxygen and a 99.5 per cent desulphurisation rate, the reduction furnace at an 8.6 per cent coal rate, and the fuming furnace on air or lightly enriched air whose weaker gas is desulphurised by absorption rather than sent to acid. The published recoveries across that line are above 97 per cent for lead and above 92 per cent for zinc.

How much coal and oxygen does the furnace consume per tonne of feed?

The published figures for treating zinc leaching residue are 270 to 290 kilograms of standard coal and 270 to 300 normal cubic metres of oxygen per tonne of residue in the multi-channel-lance configuration, against 300 to 340 kg and 350 to 380 Nm³/t in the single-channel-tuyere configuration. The same published comparison concludes that the side-blowing route uses more than 30 per cent less standard coal than the other pyrometallurgical residue processes it is compared with. On copper duty, published consumption is about 140 kilograms of standard coal per tonne of blister copper. Those are figures for a duty and a configuration, not universal constants: your own coal and oxygen demand is calculated from your feed assay, its sulfur and its iron, and is confirmed on the first production campaign.

What concentration of sulphur dioxide leaves the furnace, and can it make acid?

Published side-blowing lead practice produces 12 to 18 per cent sulphur dioxide by volume in the oxidation stage off-gas, and because that stage runs continuously the band is stable rather than swinging with a batch cycle. That concentration and that stability are what allow the gas to go straight to a two-stage contact acid plant and produce saleable sulphuric acid, which turns the plant’s largest by-product problem into a revenue line. The reduction and fuming stages of the same flowsheet produce a much weaker gas, quoted at 3 to 4 per cent by volume in the same published comparison, and that stream is desulphurised by absorption instead. The two routes are designed together with the furnace, because they decide the off-gas volume, the boiler duty, the gas cleaning and the reagent consumption behind it.

Why is the dust collected in an electrostatic precipitator rather than a bag filter?

Because of temperature, dew point and dust resistivity, in that order, and the reasoning is a published design record rather than a preference. In the published lead project the oxidation furnace’s waste-heat-boiler outlet carried 32,000 to 38,000 Nm³/h at 350 to 380 degrees Celsius with 120 to 160 grams per normal cubic metre of dust, against a furnace chamber temperature of 1,100 to 1,300 degrees. Dry collection was chosen so that the metals are recovered as dust rather than dissolved into a wastewater; the gas temperature is high enough to burn filter bags; and its sulphur content gives it a high dew point, so condensation blinds them. A dust high in lead oxide has a high electrical resistivity, which would on its own rule a precipitator out, but the sulphur dioxide, sulphur trioxide and water vapour in the same gas bring the resistivity back into the 10⁴ to 10¹⁰ ohm-centimetre window a precipitator needs. The dust that is collected is conveyed back to the batching system and re-enters the furnace.

How is the metal kept out of the slag?

By three things that are held together rather than separately. First, the stirring is concentrated in the upper bath and the lower bath is deliberately left quiet, so slag and metal separate by gravity instead of being held in emulsion, and the molten layer that is tapped is not being re-mixed on its way out. Second, the slag chemistry and the working temperature are designed so the slag stays fluid enough at the bath temperature to release the droplets of metal it has taken up, because a slag that is not fluid at the working temperature traps metal rather than letting it settle. Third, the reduction is taken far enough on the reducing stage: on lead duty the lead locked in the oxidation slag has to be reduced out in the next vessel, and a reduction run short leaves that lead in the slag rather than in the metal. Published performance on the settler slag of the copper version of this vessel is under 0.3 per cent metal, low enough to granulate and sell without a flotation circuit behind it.

Can the furnace be run at a lower temperature than the classical lead bath?

Yes, and it is a slag-system decision rather than a burner setting. A published development route for this furnace family replaces the classical 1,200 to 1,250 degrees Celsius lead bath with a low-temperature molten-salt system that uses sodium carbonate as the reaction medium and a quaternary iron-silicon-calcium-sodium slag, exploiting the low melting point of sodium silicate to bring the working temperature below 1,100 degrees. The same route burns pyrite in the bath to make up heat, with 4FeS2 plus 7O2 giving 2Fe2O3 plus 8SO2 and releasing 1,654.64 kilojoules per mole at 1,000 degrees, so less fuel is burnt and less carbon is emitted. What the low-temperature route buys is fuel and refractory life; what it costs is a tighter control window on the slag chemistry, and it is therefore offered as a configuration rather than recommended as a default.

How long does the campaign last, and what ends it?

Published furnace-body life for this family reaches five years, and the campaign is ended by the wear that a survey actually finds rather than by a calendar interval. Three things decide it. The first is the slag chemistry and the working temperature, because a bath run hotter than the slag and the reduction need consumes the lining faster and volatilises more metal into the gas train. The second is the halide load in the feed, because chloride attacks the lining and shortens the campaign, which is why plastic and salt-bearing material is separated or refused at the gate. The third is the condition of the copper jackets, whose whole working principle is that a hung slag coating protects them, so a jacket that has lost its coating or has been overheated has to be judged from a survey and not from the outside. Shell thermocouples at the slag line and the jacket zone give the campaign a visible wear curve, so a reline and a jacket change are scheduled against production instead of being triggered by a leak.

What is tested at commissioning, and how is the metal balance closed?

Acceptance is run as a performance test on your own feed and it is measured as a metal balance, not as a duration. The line is operated at the designed charging rate to demonstrate the designed metal grade, the agreed slag metal content and the throughput, and during the test every stream is weighed and assayed: the feed with its flux and reductant, the crude metal or the matte, the slag, the dust and the gas. The balance is then closed on feed in against metal plus slag plus dust plus the metal carried in the gas, with the bath drained at shutdown and the metal attached to spent refractories also accounted for, and the difference is reported as the loss for the test rather than absorbed. The nozzle set is checked at its designed pitch with its per-nozzle flows balanced and recorded, the jacket water circuit is proven at its designed flow and temperature, and the control and interlock schedule is demonstrated, including the trips for loss of oxygen pressure, loss of jacket water flow, high bath temperature, high gas temperature at the boiler inlet and loss of feed. The performance test report, the balancing record and the closed metal balance are handed over with the plant, so that the recovery figure is one you can audit and reproduce.

Oxygen-Enriched Side-Blown Furnace

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Oxygen-Enriched Side-Blown Furnace Process Flow

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Furnace body, copper water jackets and refractory

Tuyeres, multi-channel lances and the oxygen circuit

Feed, gas train, dust and control

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