Improved plasma-induced fuming furnace

Abstract

A single-chamber furnace for fuming a vaporizable metal or metal compound from a metallurgical charge is disclosed, the single-chamber furnace comprising a bath furnace for accommodating a molten charge up to a determined level, the furnace being equipped with a non-transferred plasma torch for generating plasma and a first submerged injector for injecting the plasma below the determined level, the furnace also comprising an afterburning zone for forming an oxidized form of at least one vaporizable metal or metal compound, and a recovery zone for recovering the oxidized form from gases formed in the afterburning zone, wherein the furnace is further equipped with a second submerged injector for injecting additional gas into the furnace below the determined level. Further disclosed are uses of the furnace and a method for fuming a vaporizable metal or metal compound from a metallurgical charge.

Description

Technical Field

[0001] The present invention relates to the field of pyrometallurgical recovery of non-ferrous metals (e.g. copper, lead, tin and zinc) from primary and / or secondary raw materials (also known as recyclable materials) or from combinations thereof. More specifically, the present invention relates to the recovery of volatile metals, such as zinc and lead, from molten slag and / or metal baths by a process step generally known as fuming. Background Art

[0002] The production of non-ferrous metals, such as copper, nickel, lead, tin, and zinc, typically involves at least one, and often multiple, pyrometallurgical process steps in which both the metal and metal oxides are present in a liquid, molten state, and the metal oxides are separated by gravity as a separate, lower-density liquid slag phase from the higher-density molten metal phase. If the slag phase contains dilute valuable metals, the slag phase is typically removed from the process as a separate stream. This separation may result in the production of slag as a by-product of metal production, which may also be referred to as "final slag" or "last slag."

[0003] WO 2013 / 133748 A1 and US 2015 / 0040722 A1 disclose a two-stage smelting reduction process for producing molten iron from iron oxide-containing raw materials. The raw materials are first processed through a melting reactor and then through a smelting reduction reactor. The atmospheres in the two reactors are kept strictly separate, so that strong reducing conditions can be maintained in the smelting reduction reactor to improve the yield of liquid iron, while more neutral conditions can be maintained in the melting reactor to better utilize the combustion energy from the combustion of carbonaceous materials. The smelting reduction reactor is heated by an immersed plasma generator, and the reducing atmosphere is obtained by adding a reducing agent such as coal or petroleum coke. The reaction produces a combustible gas mixture containing CO and / or H2, and typically also contains low levels of CO2 and H2O. After impurities are removed, the gas mixture mainly consists of CO and / or H2, and a portion of it is recycled to the plasma generator to heat the smelting reduction reactor. The remainder of the gas mixture is used to heat the melting reactor by further combustion with the aid of another submerged plasma generator and / or by injecting a mixture of oxygen-containing gas and combustible gas into tuyeres below the surface of the melting furnace contents. Any sulfur in the iron-containing raw material will typically be removed in the melting reactor, either into the reactor gases or as part of the matte phase. Copper present in the raw material will typically be removed at the bottom of the melting reactor in the form of metallic copper and / or matte. The process may have much lower CO2 emissions than conventional blast furnace processes. WO 2013 / 133748 A1 and US 2015 / 0040722 A1 do not mention any stripping or fuming of the vaporizable metal or metal compound, and the described apparatus is not provided for recovering it as a separate product. Therefore, the described furnace is not suitable for fuming vaporizable metals or metal compounds from metallurgical charges.

[0004] US Pat. No. 4,601,752 discloses a relatively uncomplicated process for producing metal and / or slag, exemplified by the production of ferrochrome from chromite ore. Finely ground oxide ore, possibly together with a slag-forming agent, is treated in a single-chamber reactor comprising three zones: an upper oxidation zone, in which the material is preheated and possibly melted by combustion of carbon monoxide and hydrogen with an oxygen-containing gas rising from a lower intermediate zone; an intermediate zone consisting of a slag bath, in which the preheated and possibly melted oxide material is at least partially reduced by the simultaneous injection of carbonaceous and / or hydrocarbon-containing material and thermal energy provided primarily by a plasma generator; and a lower zone at the bottom of the reactor, into which metal formed during the reduction process sinks, and from which metal product and slag by-products can be discharged. The oxygen-containing gas introduced into the intermediate zone is 99.5 wt% pure oxygen. The addition of oxygen is controlled to generate sufficient energy to preheat and melt the ore and additives charged to the chamber, which occurs in a more oxidizing atmosphere controlled in the middle and upper zones of the chamber reactor. The energy provided by the plasma generator is controlled to drive the endothermic reaction between the slag and carbon, which occurs in a reducing atmosphere controlled in the lower portion of the chamber reactor. Most of the exhaust gas from the furnace is treated to remove H₂O and CO₂ and returned to the furnace as feed gas for the plasma generator. The remaining exhaust gas is removed from the process and used as fuel. US Pat. No. 4,601,752 mentions any stripping or fuming of the vaporizable metal or metal compound, and the apparatus described does not provide for its recovery as a separate product. The material balance in Figure 2 shows that no other gases are introduced into the furnace besides the plasma gas and oxygen. Therefore, this furnace is not suitable for fuming vaporizable metals or metal compounds from metallurgical charges.

[0005] WO 2016 / 078959 A1 describes a single-bath furnace for melting metallurgical charges and separating metals under flexible redox conditions. The furnace is equipped with a 3 MW plasma torch or burner and a 1.5 MW conventional "oxygen" burner. This equipment allows oxidation and reduction steps to be performed in the same furnace. The document proposes using oxygen mode in the furnace for melting and / or operating mildly reducing or any oxidizing conditions, and plasma mode for highly reducing conditions. If high energy input is required, both heating technologies can be operated simultaneously.

[0006] The final slag extracted from pyrometallurgical processes for the production of non-ferrous metals is typically cooled, granulated and crushed / screened and can be used in concrete production as a rock and gravel replacement or as aggregate for road construction. When ground, the slag can also be used for sandblasting or gravel blasting.

[0007] Certain substances that may be found in slag products known in the art are considered to be potentially harmful to the environment. Primarily lead, but also to some extent zinc, are prime examples of such undesirable substances. Both zinc and lead are metals that may be present at least in part in a form that can be leached from the slag, and their presence in large quantities prevents many uses of the slag product, particularly in more economically attractive applications, and may make the disposal of such slag in landfills more complicated and difficult, often forcing it to be considered a "hazardous waste". Acceptable use in certain applications is often determined by testing the leaching properties of the slag. Generally, elements such as Pb and Zn are more susceptible to leaching and may cause a particular slag to fail such acceptance tests.

[0008] Furthermore, the applicants have found that zinc levels of 5 wt% and above in the slag significantly slow the hardening of concrete and other building compositions, such as cement, when used in such compositions. This effect on the hardening rate discourages the use of slags containing significant amounts of zinc as cementitious materials and / or as aggregates in concrete or cement.

[0009] For at least some of the reasons stated above, non-ferrous metal producers attempt to reduce the zinc content, and also the lead content (if present), in their slag by-products, typically through a so-called "fuming" step.

[0010] Michael Borell in Sweden in 2005 In the paper "Slag - a resource in the sustainable society" (Proceedings, pp. 130-138), presented during the "Securing the Future" international conference on mining and environmental metal and energy recovery, it was described that since the 1960s, liquid slag from electric smelting furnaces producing copper matte can be treated with reducing gas in a slag fuming furnace (also known as a "box fuming furnace"). This is a batch process step in which the zinc content of the copper smelting slag and additional zinc recycling material is reduced to 1.2 wt%. The fumed slag is further cleaned in a settling furnace, where the remaining copper alloy and copper sulfide droplets are allowed to settle for a period of time to separate into a heavier liquid phase. The slag is then granulated, dewatered, and can be sold for use in road construction and blasting. The reducing gas for the fuming furnace is obtained by carefully mixing pulverized coal into the primary air injected into the furnace. The problem with this type of fuming is that the reaction of the coal with air must be limited to producing primarily carbon monoxide to maintain reducing conditions. Consequently, most of the heat of reaction, that generated by the continuous oxidation of carbon monoxide to carbon dioxide, is unavailable in the furnace core to drive endothermic reactions, such as the reduction of metal oxides, such as zinc oxide, to elemental metals that can be stripped from the bath. Another disadvantage of the box-type fumer is the production of large quantities of furnace exhaust gases, which must be cooled, filtered, and treated to recover the fumed metals and cleaned before discharge to the atmosphere.

[0011] US Pat. No. 4,588,436 discloses a method for recovering metals from batches of liquid slag in metallic or sulfided form by reduction with a carbonaceous reducing agent. The heat required to maintain temperature and perform the reduction and sulfidation is provided by blowing gas preheated in a plasma generator below the slag bath surface. The volatile metal vapors are condensed in a condenser and recovered as liquid metal. The non-volatile metals and sulfides formed are collected as molten droplets, which are allowed to settle out of the slag. Reducing conditions must be maintained throughout the process, downstream after the condenser, to allow the volatile metals to condense into a liquid metal product in the condenser. Furnace flue gases containing volatile metals also present a significant safety risk. They are highly reactive and hot. Any ingress of air, no matter how small, can cause the flue gases to spontaneously ignite and potentially explode.

[0012] In "ScanArc's Development of Plasma Based Processes for Recovery of Metals and Heat Energy from Waste and Hazardous Waste Materials," presented at the International Workshop on Plasma Technology for Hazardous Waste Destruction, held in Como, Italy, September 12-15, 1992, ScanArc Plasma Technology AB presented a non-transferred submerged plasma generator for slag reduction in the metallurgical industry by fuming, thereby reducing the heavy metal content, recovering metals, and producing vitrified, non-leaching slag. The plasma generator is capable of operating with most gases at any selected oxygen potential, generating very high available enthalpy while maintaining relatively low gas flows and having a dilute gas mixture, thus offering a major flexibility advantage. A very similar story was presented by SOSantén at the 21st McMaster Symposium on Steel and Steelmaking, “Pretreatment and Reclamation of Dusts, Sludges and Scales”, McMaster University, Hamilton, Ontario, Canada, May 11-13, 1993. Among others, the technology was developed in Norway by Energy Recycing AS (ERAS) in Sink Gjenvinning AS is operating commercially at the site, as evidenced by an environmental permit application, "Recovering of Metal Values ​​from EAF Dust by the Arcflashfuming Process," filed on October 10, 2002, which was publicly available approximately two weeks prior to a public hearing on the subject on October 31, 2002. The application also describes in considerable detail the process itself, the composition of the feedstocks and products (including the fluxing agent, also known as the slag former), the operating parameters, and the equipment design.

[0013] WO 2005 / 031014 A1 also describes such a fuming reactor for treating zinc-containing residues, which uses a submerged plasma combustion tuyeres attached to a plasma torch as its heat and gas source. WO 2008 / 052661 A1 describes a Zn fuming method using a submerged plasma torch to generate an oxidizing gas mixture, wherein a solid reducing agent is fed into the melt.

[0014] WO 2016 / 046593 A1 describes the smelting and fuming of metallurgical charges using a hot gas jet from an immersed plasma torch, the resulting hot gas (more precisely, "plasma") having an enthalpy of at least 200 MJ / kmol. WO 2016 / 156394 A1 describes a process for fuming zinc from metallurgical slag using an immersed plasma torch. The resulting slag has a zinc content of up to 1.00 wt%, and when finely ground and mixed with sodium silicate in a 50 / 50 ratio as an active binder for use in ceramic tile manufacturing, the purified slag has the advantage of rapid hardening.

[0015] The plasma fuming furnace described in the above document uses only a plasma generator, ie a burner that generates very high temperature heat by consuming electricity, as a heat source, which is a relatively high cost heat source in many countries.

[0016] However, the applicant has discovered that, in order to keep the arc running and stable, and to keep the enthalpy content of the hot gases from the plasma generator high enough to form the desired plasma, the gas flow that can be generated by an industrial-scale plasma generator is still limited. This will be explained in more detail later in this article. Consequently, the amount of stripping gas that a plasma generator can provide for stripping the vaporizable material from the liquid bath in the furnace is limited. This also limits the agitation that the gas injected from the plasma generator can cause in the liquid bath contained in the furnace.

[0017] Strong reducing conditions are advantageous in slag fuming because oxides of zinc and other vaporizable metals may need to be reduced to their respective metallic forms before the metals become vaporizable. Strong reducing conditions can be achieved by adding at least one reducing agent, which can be gaseous, liquid, solid, or a combination thereof, preferably a solid reducing agent, preferably carbon, to the hot plasma gas injected into the furnace. This method of introducing additional reducing agent is still limited due to the low amount of plasma gas available per plasma generator. Additional reducing agent can then be added to the furnace by dripping the solid reducing agent through the furnace filling opening, preferably onto the surface of the bath.

[0018] However, this alternative approach of introducing an additional reducing agent still leaves some room for improvement.

[0019] Gaseous reducing agents, such as natural gas, cannot be introduced through the furnace fill opening using this addition method because they would not reach the liquid bath in which they would exert their reducing activity, as this would require the gaseous reducing agent to travel against the flow of the furnace exhaust. Injecting liquid reducing agents, such as fuel oil, is also less preferred because its evaporation causes a high volume expansion, resulting in foaming and splashing within the furnace, and some of the reducing agent may be carried away with the exhaust gas before it can perform its intended function. Therefore, the choice of suitable reducing agents is quite limited.

[0020] The additional reducing agent, typically added through the fill and outlet openings in the furnace roof, must travel downward through the furnace roof's gas space before reaching the liquid surface. Just before the furnace gases enter the exhaust duct, additional air is often introduced to oxidize the evaporated elemental metal or metal compound into the corresponding metal oxide. The boiling and melting points of the oxides are much higher than those of the corresponding metals. The resulting oxides readily manifest as entrained flue gas dust and can themselves be recovered further downstream in the furnace exhaust system. During its passage through the furnace roof, the additional reducing agent comes into contact with air, and at the high temperatures in the furnace, at least a portion of the reducing agent is readily oxidized before the remainder can reach the liquid bath surface. The heat generated by this oxidation also does not reach the liquid bath, but remains in the exhaust gas. Far from providing any benefit, this heat becomes an additional burden on the exhaust gas treatment system.

[0021] Additional reducing agent that may reach the bath surface cannot function properly unless it is thoroughly mixed into the bath. However, the gas flow obtained from the plasma generator does not cause very strong agitation of the bath.

[0022] The additional reductant must also be able to travel downward through the furnace gas space, against the rising flow of the stripping gas, to reach the surface of the liquid bath. Therefore, the particle or droplet size of the solid or liquid reductant must be large enough to avoid excessive entrainment of particles and / or droplets with the stripping gas into the exhaust treatment system. However, large particles offer limited surface area per unit mass and are therefore less reactive when mixed into the liquid bath. Most reductants, such as solid carbon, have a much lower density than the liquid bath within the furnace. Larger particles exhibit higher buoyancy and therefore have a higher tendency to float to the top of the liquid bath, further reducing the contact surface between the solid reductant and the liquid bath.

[0023] Therefore, this alternative approach of adding additional reducing agent is significantly less efficient and effective.

[0024] Thus, there is room for improvement in the plasma-generated fuming processes and fuming furnaces known in the art. There remains a need for improved plasma-driven fuming processes and apparatus that provide increased fuming rates, particularly through more bath agitation and / or more fuming gas, and the possibility of introducing additional reducing agents in a more efficient and effective manner.

[0025] The present invention aims to obviate or at least alleviate the above-mentioned problems and / or provide general improvements. Summary of the Invention

[0026] According to the present invention, there is provided an apparatus and a method for fuming at least one vaporizable metal or metal compound from a metallurgical charge.

[0027] In an embodiment, the present invention provides a single-chamber furnace or apparatus for fuming at least one vaporizable metal or metal compound from a metallurgical charge, the single-chamber furnace or apparatus comprising a bath furnace adapted to accommodate a molten charge up to a determined level, wherein the furnace is equipped with at least one non-transferred plasma torch for generating a first hot gas of plasma-quality, and at least one first submerged injector for injecting the first hot gas from the plasma torch below the determined level, wherein the furnace further comprises an afterburning zone for oxidizing the at least one vaporizable metal or metal compound in the fuming gas to form an oxidized form of the at least one vaporizable metal or metal compound, and a recovery zone for recovering the oxidized form of the at least one vaporizable metal or metal compound from the gas formed in the afterburning zone, characterised in that the furnace is further equipped with at least one second submerged injector, different from the first submerged injector, for injecting additional gas into the furnace below the determined level.

[0028] In another embodiment, the present invention provides a method for fuming at least one vaporizable metal or metal compound from a metallurgical charge using a furnace or apparatus according to the present invention, the method comprising the steps of:

[0029] introducing a metallurgical charge comprising at least one vaporizable metal or metal compound into the furnace and forming a molten charge bath up to a determined level;

[0030] • fume a quantity of at least one vaporizable metal or metal compound from a bath using at least one reducing agent and plasma-quality hot gas from at least one plasma torch, thereby producing a fume gas comprising the vaporizable metal or metal compound;

[0031] post-combustion of said fuming gas in said post-combustion zone to oxidize said at least one vaporizable metal or metal compound into an oxidized form of said at least one vaporizable metal or metal compound,

[0032] extracting from the furnace the gases formed in the furnace and recovering from the gases formed in the post-firing step the oxidized form of the at least one vaporizable metal or metal compound;

[0033] Characterized in that during at least a portion of the fuming step, additional gas is injected into the bath by at least one second injector and below a determined level, thereby increasing the amount of fumes comprising the vaporizable metal or metal compound.

[0034] In the context of the present invention the term metallurgical charge denotes a broad class of compositions which may be present as furnace contents or furnace charge or as part thereof at any time during a pyrometallurgical process step, preferably a step which is part of a non-ferrous metal production process.

[0035] Preferably, the metallurgical charge is a first slag and the product obtained from the method according to the invention is a second slag having a reduced content of at least one vaporizable metal or metal compound compared to the content of the same vaporizable metal or metal compound in the first slag.

[0036] In another embodiment, the present invention provides the use of a furnace according to the invention for fuming at least one vaporizable metal or metal compound from a metallurgical charge.

[0037] The Applicant has found that the fuming of vaporizable metals or metal compounds from a metallurgical charge can be significantly improved by injecting additional gas into the molten bath through at least one second submerged injector, wherein the fuming step uses a first hot gas of plasma quality from a plasma torch injected into the molten bath by a first submerged injector.

[0038] Applicants have discovered that the introduction of additional gas through additional submerged injectors provides additional injection points and additional gas volume for stripping vaporizable metals or metal compounds from the molten metallurgical charge. Applicants have discovered that, using only the volume of plasma or hot gas from the plasma torches to strip zinc from copper smelter slag, the zinc concentration in the bubbles rising through the molten slag bath can reach values ​​as high as 40% by mole. Because the zinc fuming reaction (I) can at best reach equilibrium,

[0039] ZnO+C→Zn(g)+CO(g)(I)

[0040] Although the process enjoys a favorable equilibrium constant at the very high temperatures of the plasma-quality hot gases from the plasma torch, the high zinc content in the gas bubbles results in a significant amount of zinc oxide remaining in the bath. The applicant has found that this concentration in the gas phase can be significantly reduced by the present invention, both because additional gas is made available for stripping by means of an additional injector and because it enables an increased presence of reducing agent throughout the bath. Since the amount of hot gas that can be generated by the plasma torch is limited, the applicant has found that injecting additional gas into the molten bath is advantageous, and is particularly advantageous due to injection via at least one second submerged injector, distinct from the first submerged injector.

[0041] Therefore, another advantage of the present invention is that it provides at least one additional submerged gas injection point into the molten bath. This provides the advantage of additional agitation of the molten bath within the furnace, which improves mixing within the bath, resulting in a more uniform distribution of temperature and any reducing agent that may be introduced into the furnace, thereby also promoting the ongoing chemical reactions and achieving a more uniform distribution of the reduced metal or metal compound formed by reaction with the reducing agent. Thus, the additional submerged gas injection point also improves the fuming operation through these mechanisms.

[0042] Yet another advantage of the present invention is that it provides at least one additional means for introducing further reducing agents into the molten bath within the furnace. Because the at least one second injector is also a submerged injector, this additional means also provides a wider selection of suitable reducing agents compared to adding large particles of solid and / or liquid reducing agents through the fill and outlet openings at the top of the furnace. Where conventional methods are employed, any coke particles that fall into the furnace through the fill opening should preferably have an average particle size of at least 6 mm, so that most particles fall into the furnace and are limited in their entrainment by exhaust gases exiting the furnace through the same openings. The second submerged injector provides a wider selection of suitable reducing agents. The reducing agent introduced via the second submerged injector can be a gas, liquid, solid, or a combination thereof, and when solid, the reducing agent can have a finer particle size, which provides the additional advantages of a high surface-to-volume ratio and a larger contact surface, resulting in a higher reactivity when the reagent comes into contact with the molten bath within the furnace. Submerged introduction of the reducing agent also offers the advantage of closer contact between the reducing agent and the bath. This advantage applies to all physical states of the reducing agent, but is particularly prominent when the reducing agent is a solid, especially a finely divided solid.

[0043] Thus, the present invention achieves more than just providing more stripping gas for stripping vaporizable metals or metal compounds from the metallurgical charge. An additional effect is additional bath agitation, resulting in a more uniform bath within the furnace. Another added benefit is the ability to more efficiently inject more, and optionally different and more effective, reducing agents. These additional effects contribute to further improved fuming, as the improved conditions favor the desired chemical reactions. DETAILED DESCRIPTION

[0044] The present invention will be described below in the context of specific embodiments and, where appropriate, with reference to specific drawings, but the invention is not limited thereto but solely by the claims. Any drawings described are for illustrative purposes only and are non-limiting. In the drawings, the size of some elements may be exaggerated and not drawn to scale for illustrative purposes. The dimensions and relative sizes in the drawings do not necessarily correspond to actual reductions in practice of the invention.

[0045] Furthermore, in the description and claims, the terms first, second, third, etc. are used to distinguish similar elements and not necessarily to describe a sequential or chronological order. These terms are interchangeable under appropriate circumstances, and the embodiments of the invention can operate in other sequences than those described and / or illustrated herein.

[0046] Furthermore, in the description and claims, the terms top, bottom, over, under, etc. are used for descriptive purposes and not necessarily for describing relative positions. The terms so used are interchangeable under appropriate circumstances, and the embodiments of the invention described herein can operate in other orientations than described or illustrated herein.

[0047] The term "comprising" used in the claims should not be construed as being limited to the elements listed in the context. The term does not exclude that there are additional elements or steps. The term should be construed as providing for the presence of these features, integers, steps or components as required, but does not exclude the presence or addition of one or more other features, integers, steps or components or groups thereof. Thus, the volume of an "article comprising means A and B" may not be limited to an object consisting only of agents A and B. It means that A and B are only elements of interest in relation to the subject matter of the present invention. In accordance with this, the terms "comprising" or "including" also include the stricter terms "essentially consisting of" and "consisting of". By replacing "comprising" or "including" with "consisting of", these terms therefore represent the basis for preferred but narrower embodiments, which are also provided as part of the content of this document relating to the present invention.

[0048] Unless otherwise specified, all ranges provided herein are inclusive up to and including the stated endpoints, and values ​​for ingredients or components of the compositions are expressed as weight percent or wt % of each ingredient in the composition.

[0049] Unless otherwise specified, as used herein, "weight percent," "wt-%," "percent by weight," "% by weight," "ppm wt," "ppm by weight," "ppm by weight," or "ppm" and variations thereof refer to the concentration of a substance, i.e., the weight of the substance divided by the total weight of the composition and multiplied by 100 or 1,000,000, as appropriate. It will be understood that "percent," "%," as used herein, is intended to be synonymous with "weight percent," "wt-%," and the like.

[0050] It should be noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a composition containing "a compound" includes compositions having two or more compounds. It should also be noted that the term "or" is generally used in its sense to include "and / or" unless the context clearly dictates otherwise.

[0051] Furthermore, each compound used herein may be discussed interchangeably with respect to its chemical formula, chemical name, abbreviation, etc.

[0052] Plasma is considered the fourth state of matter, completing the series formed by solids, liquids, and gases with an additional category at higher energies. When the temperature of a gas is increased, at least some of its atoms separate into ions and electrons, forming an ionized gas. This is called "plasma," but it may also be called hot plasma gas or, by other sources, simply "hot gas." The ionization of atoms can be partial or complete, making the transition from gas to plasma quite slow. A defining characteristic of plasma is that ionization requires sustained action, which implies high temperatures.

[0053] In a non-transferred plasma arc torch, a plasma arc is generated between two electrodes within the torch body. Gas flows through the torch body, and the energy dissipated by the arc is converted into plasma. This contrasts sharply with a transferred plasma torch, in which the material to be processed is placed in an electrically grounded metal container, which acts as the anode. Therefore, the reactive material must be electrically conductive. In a transferred plasma torch, the anode can also be made of carbon. However, carbon electrodes have the disadvantage of fixed reducing conditions, which significantly reduces the versatility of the device for fume reduction processes.

[0054] In order to obtain plasma, the enthalpy content of the plasma gas generated by the plasma generator needs to be at least 1 kWh / Nm 3 Therefore, the plasma mass hot gas has a mass of at least 1 kWh / Nm 3 enthalpy content. Plasma torches known in the prior art can have a power of up to 5, or even 7 MW. A more typical plasma torch provides about 3 MW, which means that it is impossible to generate more than 3000 Nm 3 The plasma mass is hot gas. More typical operating systems provide plasma enthalpy contents in the range of 3.5-5.5 kWh / Nm 3 range, which means that a 3MW plasma torch is typically between 600-800Nm 3 Therefore, a plasma torch with a specific electrical power cannot produce more than the corresponding volume of plasma mass hot gas.

[0055] In the context of a plasma torch, the gas volumes specified only consider the volume of gas supplied to the plasma torch and under standard / normal conditions. The volumes specified for the volume of plasma-mass hot gas produced by a plasma generator (PG) in the context of this invention include only the gas that passes through the PG itself, the so-called "primary gas" or "primary volume of gas." Therefore, they do not take into account any additional gas that may be supplied directly to the downstream tuyere, referred to in the context of this invention as "secondary volume of gas," and which is typically mixed with the plasma-mass hot gas from the plasma generator and injected into the bath along with it. After such mixing, it is likely that the mixed gas no longer meets the qualifier "plasma mass" because the enthalpy content per unit volume may no longer meet the lower limits specified elsewhere in this document for such gases. All of these gas volume numbers are expressed under "normal" conditions. Therefore, they also do not take into account any volume changes that may occur due to temperature changes, pressure changes, chemical reactions, or phase changes that may occur in the plasma generator or its downstream tuyere.

[0056] A submerged injector is a connection pipe or tuyere between the gas source and the injection point, which is located below the level of the bath or a defined liquid level in the furnace and is therefore submerged or intended to be submerged during operation. This ensures a more direct and intimate contact between the gas and the molten material.

[0057] The tuyere or injector should preferably be short to minimize wear and tear. This also ensures low heat loss. Under severe temperature conditions, the tuyere can be cooled to reduce wear and tear. The tuyere can be mounted horizontally, penetrating the furnace wall below the level of the bath. The torch or burner, whether plasma-fired or oxygen-fired, that can supply the tuyere is then located in a submersible (also known as "immersed") position outside the furnace. Preferably, when a liquid bath of metallurgical charge is present in the furnace, the torch or burner is continuously supplied with gas to prevent molten material from flowing back into the tuyere, which would otherwise cause the tuyere to flood, potentially causing serious damage to the tuyere and any torch or burner that may be supplying the tuyere. Alternatively, the tuyere can be mounted at an angle that still blows into the bath but allows the burner or torch to reside above the bath level and outside the furnace. This arrangement makes the tuyere slightly longer, but it can be arranged so that it also ensures that no molten material will be able to flow back into the burner or torch. Although this may not be recommended in large furnaces, tuyeres can also be placed vertically. Tuyeres for injecting additional gas can be similarly arranged, i.e., perpendicular to the furnace wall or immersed and piercing the furnace wall at different angles to the furnace wall.

[0058] A non-transferred plasma torch is a hot gas generator that uses an arc maintained between electrodes within the torch unit. Gas enters a flow chamber through an input port, where the arc is maintained. The gas is heated to extreme temperatures and exits through an output port as plasma-mass hot gas that is at least partially plasma.

[0059] Between the plasma torch and the injection point into the furnace, additional substances, such as shielding or dilution gases, may be added to the flow from the torch to the injection point. In the context of the present invention, the amount of hot gas produced by the plasma torch includes only the primary gas passing through the plasma generator and does not include the addition of secondary gases, such as any additional gases or other substances that may be added between the plasma torch itself and the injection point or tuyere through which the plasma-quality primary hot gas from the plasma torch is injected into the furnace.

[0060] An oxyfuel burner is a hot gas generator that mixes and burns a carbon-containing fuel and an oxygen-containing gas. To easily achieve the high temperatures required for proper operation of an oxyfuel burner, the oxygen-containing gas is preferably enriched with oxygen, more preferably substantially pure oxygen with low levels of inert components. This not only allows for higher flame temperatures but also reduces the amount of inert gas that is carried by and needs to be handled by the furnace exhaust system. The mixing zone of an oxyfuel burner is internal to the burner unit, while the combustion zone can be internal or external to the burner unit.

[0061] A metallurgical charge in the context of the present invention can be any composition that can be present in a liquid, molten state during a pyrometallurgical process step for producing non-ferrous metals. Thus, the metallurgical charge can be, for example, a molten metal composition comprising at least one non-ferrous metal, but can also be a molten slag phase that occurs during such a process step. The metallurgical charge can be in the form of a molten liquid, but can also have any kind of solid form; for example, the charge can be in the form of an aggregate that can be obtained by cooling or granulating a liquid, molten phase from a furnace in which the pyrometallurgical process step was carried out.

[0062] Metallurgical slag is usually not a pure substance, but a mixture of many different components. Therefore, metallurgical slag does not have a clear melting point. In the field, the term "liquidus temperature" is commonly used, which is the temperature at which the slag is completely liquid.

[0063] As mentioned in the background section, "fuming" is a process that has been commercially used in the field of pyrometallurgy since the 1960s. It is well known to those skilled in the art that certain metals or metal compounds can be evaporated from metallurgical charges by gas stripping, also known as "fuming," which is performed at pressures close to atmospheric pressure and therefore does not require a deep vacuum, as is done for distilling lead from tin. This ability is due to the fact that the vapor pressure of the vaporizable metal or metal compound is much higher than the vapor pressure of most of the other compounds remaining in the charge. Therefore, such compounds are considered and referred to in the art as "evaporable" from metallurgical charges.

[0064] A well-known example is the fuming of zinc from other pyrometallurgical components. This fuming of zinc can even be performed as part of another pyrometallurgical step, such as removing (usually a portion of) the zinc from the exhaust fumes generated during a copper smelting or refining step. Less frequently, fuming can be performed as a separate process step, for example, as described by Michael Borell in the "box fumer" or by the authors of ScanArc, as discussed above. As mentioned above, when the metallurgical charge is slag, zinc may be present in the charge primarily as its non-volatile oxide, ZnO, and fuming may therefore be achieved by first reducing the oxide to the elemental metal, a compound that can be stripped by fuming. Another example is the recovery of lead and tin as their oxides by volatilization during copper recovery from copper-containing scrap, as described in the background section of US Pat. No. 3,682,623. Furthermore, elements such as bismuth, indium, and / or germanium are also known to be vaporizable metals or have vaporizable metal compounds in the context of the present invention. The vaporizable metal compound may be the corresponding oxide, chloride and / or sulfide.

[0065] Throughout this document, unless otherwise specified, the amounts of metals and oxides are expressed in accordance with typical pyrometallurgical practice. The presence of each metal is generally expressed in terms of its total presence, whether in its elemental form (oxidation state = 0) or in any chemically combined form, usually in its oxidized form (oxidation state > 0). Metals that are relatively easily reduced to their elemental form and typically occur as molten metal during pyrometallurgical processes are quite commonly expressed in terms of their elemental metal form, even when slag compositions are given, where most of these metals may actually be present in oxidized form. Thus, the composition of slags, such as those according to the present invention, specifies the contents of Fe, Zn, Pb, Cu, Sb, and Bi as elemental metals. Less noble metals are more difficult to reduce under nonferrous pyrometallurgical conditions and are mostly present in oxidized form. These metals are generally expressed in their most common oxide form. Thus, slag compositions typically give the contents of Si, Ca, Al, and Na as SiO2, CaO, Al2O3, and Na2O, respectively.

[0066] The total slag composition reported according to this method will not usually approach 100 wt% because oxygen bound to more noble metals in the slag is not reflected in the composition which provides only the elemental metal content.

[0067] In an embodiment of the apparatus or furnace according to the invention, the apparatus is equipped to inject, via the at least one second injector, additional gas in a total amount of at least 10%, preferably at least 15%, more preferably at least 20%, 25%, 30%, 35%, 40%, 45%, 50% or 55%, more preferably at least 60%, preferably at least 70%, more preferably at least 75%, 80%, 90%, 100%, 110%, 120%, 125%, 130%, 140%, 150%, 175%, 200%, 225% and even more preferably at least 230% of the amount of hot gas by mass of the plasma, said amount of hot gas having an enthalpy content expressed in units of volume under normal conditions of at least 3.5 kWh / Nm 3%, 70%, 60%, 50%, 40%, 30% and even more preferably at most 20% of the amount of plasma when the at least one plasma torch delivers an enthalpy content expressed in units of volume under normal conditions of at least 3.5 kWh / Nm 3 The plasma can be generated by the single element of the torch having the highest rated power when the amount of additional gas is increased. The applicant has found that the main advantages of the invention can be achieved by injecting an additional gas flow rate closer to the lower limit indicated by the second injector, in particular when the additional gas flow is used as a carrier for the additional reducing agent, in particular when a fine powder such as coal powder or petroleum coke powder is used as the additional reducing agent. The applicant has found that the advantages of the invention described in detail in the above summary of the invention can be further enhanced when the amount of additional gas is further increased. However, the applicant also prefers to observe the upper limit indicated in order to reduce the risk of splashing and foaming of the liquid bath, thereby reducing vibrations and other types of dynamic stresses on the tuyere and the rest of the furnace structure, as well as reducing the volume of gas that needs to be treated downstream of the furnace roof, for example through the afterburning zone and the recovery zone.

[0068] In the afterburning zone of the furnace or apparatus according to the present invention, at least one vaporizable metal or metal compound in the fuming gas is oxidized to form an oxidized form of the at least one vaporizable metal or metal compound. This step is intended to reduce safety hazards posed by the fuming gas and to facilitate metal recovery from the fuming gas.

[0069] The fuming gases that form at the top of the furnace present a safety hazard. The gases are very hot. The evaporated metals or metal compounds contained in the gases typically represent reduced forms of the metals and are therefore also highly reactive when exposed to oxidizing conditions, such as contact with oxygen. Consequently, the fuming gases that form at the top of the furnace present a significant safety hazard. Any oxygen that enters the plant in an uncontrolled manner and comes into contact with the fuming gases from the furnace, for example as part of the ambient air that may be drawn into the furnace top or downstream in the exhaust gas treatment section of the plant, will readily react and oxidize the evaporated metals or metal compounds, a highly exothermic reaction. Under inadequately controlled conditions, for example where mixing is low and / or particularly in relatively stagnant areas, the combination of such hot gases with oxygen will almost inevitably lead to uncontrolled combustion and may even result in an explosion of the gas cloud.

[0070] In a stable and relatively fast-flowing gas stream, and with good mixing, the combination of this gas with known incoming air or another source of oxygen can produce a flame front that can be maintained stable and well controlled. Therefore, as part of the present invention, the applicant provides an afterburning zone in which the hot gases from the top of the fuming furnace are drawn away in a controlled manner, put into a stable and relatively fast-flowing motion, and mixed intensively with oxygen so that the conditions in the gas mixture change from reducing to oxidizing. The result of the good mixing and high temperature is that a flame front develops and establishes in the gas stream drawn from the top of the furnace, and this flame front can be easily maintained in a stable state. The applicant prefers to provide this flame front in the space above the fuming furnace, which has the advantage that radiation from the stable flame front can still reach the liquid bath in the furnace and some heat from the flame front can be returned to the liquid bath.

[0071] Another consequence of the afterburning step or afterburning zone is that the safety hazard presented by the hot and highly reactive gases at the top of the furnace remains confined to the volume of gas upstream of the flame front.

[0072] The oxidized form of the at least one vaporizable metal or metal compound is most typically a metal oxide. The oxide form of the metal or metal compound is generally non-volatile and generally forms a fine particle dust that is entrained in the gas stream, which makes the oxide form easier to recover therefrom.

[0073] The furnace according to the invention further comprises a recovery zone for recovering an oxidized form of at least one vaporizable metal or metal compound from the gases formed in the post-combustion zone. The method according to the invention further comprises a corresponding step of recovering an oxidized form of at least one vaporizable metal or metal compound from the gases formed in the furnace and which have undergone the post-combustion step.

[0074] In an embodiment of the apparatus or furnace according to the invention, the apparatus comprises a plurality of second injectors, each injector being equipped to inject, through each second injector, an amount of additional gas of at least 10%, preferably at least 15%, more preferably at least 20%, 25%, 30%, 35%, 40%, 45% or 50%, more preferably at least 55%, more preferably at least 60%, more preferably at least 65%, even more preferably at least 70%, yet more preferably at least 75%, more preferably at least 80% of the amount of first hot gas by mass of the plasma, the amount of first hot gas by mass of the plasma being such that the at least one plasma torch delivers an enthalpy content expressed in units of volume under normal conditions of at least 3.5 kWh / Nm 3%. Optionally, each second injector is equipped to inject, through the second injector, an additional gas in an amount of at most 200%, preferably at most 190%, more preferably at most 180%, 170%, 160%, 150%, 140%, 130%, 125%, 120%, 115%, 110%, 105%, 100%, 95%, even more preferably at most 90% of the amount of plasma mass hot gas when at least one plasma torch delivers an enthalpy content expressed in volume units under normal conditions of at least 3.5 kWh / Nm 3 The plasma generated by the torch can be generated by the single element with the highest power rating.

[0075] In an embodiment of the furnace or apparatus according to the invention, the apparatus is connected to at least one compressed gas supply source and / or is equipped with a compressor for supplying compressed gas to at least one second injector. The applicant has found that this provides a very convenient method of supplying additional gas to the furnace. The term "compressor" can be interpreted in a very broad sense and may, for example, include a gas turbine from which combustion gas can be obtained at a pressure above atmospheric pressure.

[0076] In an embodiment of the furnace or apparatus according to the present invention, the supply source for supplying the additional gas to the apparatus comprises a gas source selected from the group consisting of hydrogen, nitrogen, air, carbon dioxide, argon, neon, helium, methane, ethane, propane, butane, and combinations thereof, preferably nitrogen or air, more preferably air, even more preferably compressed air. Applicants have found that nitrogen and air, preferably compressed air, are very convenient gases as a basis for the additional gas to be injected into the furnace.

[0077] In an embodiment of the furnace or apparatus according to the invention, the apparatus comprises, upstream of the at least one second injector, means for thermally treating the additional gas in order to modify its enthalpy content. Preferably, the means for thermally treating the additional gas comprises at least one heat exchanger. If, during operation, the temperature of the gas supplied to the furnace is lower than the temperature of the liquid bath within the furnace, the applicant preferably heats the gas before it is injected through the at least one second injector. This reduces the cooling effect that the injection of the additional gas may have on the furnace and makes it easier to maintain the thermal balance in the furnace. Preferably, this heating utilizes, at least in part, the heat available in the system for treating the exhaust gases from the furnace.

[0078] In an embodiment of the furnace or apparatus according to the present invention, the apparatus is further equipped with means for introducing a reducing agent into the additional gas upstream of the at least one second injector. As explained above in the Summary of the Invention, injecting the additional gas into the furnace via the at least one second injector represents an additional entry point for the reducing agent into the furnace. Furthermore, since the at least one second injector is submerged, the choice of suitable reducing agents is very broad.

[0079] In embodiments of the furnace or apparatus according to the present invention, the reductant to be introduced can be selected from gases, liquids, solids, and combinations thereof. Applicants have discovered that the injection of additional gas according to the present invention is suitable for a wide range of reductants, both when the reductant is gaseous or liquid, and also when the reductant is solid, in terms of the volume or weight of the reductant that can be conveniently introduced. Furthermore, solid reductants can have very fine particle sizes, thereby providing a high surface-to-weight ratio and, therefore, high reactivity for participating in the target chemical reaction.

[0080] In an embodiment of the furnace or apparatus according to the present invention, the apparatus includes means for controlling the lambda of the additional gas to be injected into the bath by the second injector. Lambda ("λ") is a very convenient parameter commonly used in burners and combustible fuels, particularly internal combustion engines, representing the difference between the actual air-fuel ratio in the numerator and the stoichiometric air-fuel ratio of the same fuel in the denominator. If the air / fuel mixture is in a stoichiometric ratio for complete combustion, its lambda is 1.0. Applicants apply this lambda parameter to all gaseous mixtures containing oxygen and another substance that can readily react with oxygen, such as a combustible substance, where the other substance can be a gas, liquid, solid, or a combination thereof. Applicants have discovered that controlling the lambda of the additional gas injected by at least one second injector is a very convenient means of controlling the atmosphere within the furnace, thereby setting whether the atmosphere is neutral, oxidizing, or reducing, and the degree of oxidizing or reducing. Applicants have discovered that the additional addition point of the reducing agent in the apparatus according to the present invention is highly versatile, and controlling the lambda of the additional gas to be injected provides a very convenient method for controlling the redox conditions within the furnace and, therefore, regulating the chemical reactions occurring within the furnace. The applicant has found that the combination of injection of additional gas and injection of hot gas from the plasma generator enables a wide range of redox conditions to be obtained whereby, unlike more conventional heating arrangements such as those using natural gas burners, the redox conditions can be set substantially independently of the heat input to the furnace.

[0081] In an embodiment of the furnace or apparatus according to the present invention, the apparatus is equipped to inject oxygen and a gaseous or liquid fuel as part of the additional gas, such that the velocity of the additional gas in at least one second injector or at another location upstream of the second injector is greater than the flame propagation velocity of the fuel as part of the additional gas. Applicants have discovered that injecting gaseous or liquid fuel as part of the additional gas, preferably when the additional gas further comprises oxygen, can provide additional heat input to the furnace, even when the additional gas is not heated or ignited before reaching the liquid bath, and thus the fuel and oxygen do not react. Typically, the temperature of the liquid bath within the furnace is significantly higher than the temperature at which the fuel and oxygen in the additional gas begin to react, and even without an ignition source, once injected into the bath, they can readily react. Applicants prefer this embodiment because they have discovered that otherwise, such reactions could propagate upstream against the flow direction of the additional gas in the conduit upstream of the at least one second injector and in the second injector itself. This "flashback" phenomenon can lead to heat release in the conduit or injector, resulting in elevated temperatures and, consequently, wear and tear, or even explosion of the additional gas upstream of and / or within the injector. The applicant has found that the risk of damage to the equipment due to such heating inside or upstream of the injector can be reduced if the equipment is equipped so that the velocity of the additional gas in the second injector or at another location upstream thereof is higher than the flame propagation velocity in the additional gas. A further advantage is that the additional gas is injected at a lower temperature, which further reduces wear and tear on the second injector.

[0082] In an embodiment of the furnace or apparatus according to the invention, the apparatus is equipped to limit the amount of injected fuel so that the combustion of the injected fuel under the predetermined operating conditions of the furnace increases the enthalpy of the additional gas so that the temperature of the additional gas at the injection point into the bath is at most the temperature of the molten charge in the furnace during operation. This also helps to reduce wear and tear on the second injector.

[0083] In an embodiment of the furnace or apparatus according to the invention, the at least one second injector directs its additional gas toward a second volume, which second volume is a portion of the interior space of the furnace below a predetermined level, the second volume being different from the first volume toward which the at least one first injector directs its first hot gas. Applicants have found that this feature enhances the advantages associated with the present invention described in the Summary of the Invention section above, including improved bath agitation, more uniform liquid bath composition, improved chemical reactions, and most certainly improved stripping of vaporizable metals or metal compounds from the liquid bath.

[0084] In an embodiment of the furnace or apparatus according to the invention, the at least one first injector is located in a side wall of the furnace, wherein the at least one second injector is preferably located in the furnace wall opposite to the at least one first injector along the horizontal perimeter of the furnace, extending at substantially the same height as the at least one first injector. The applicant has found that this arrangement is very convenient and effective for obtaining the desired effects of the invention as explained in the Summary of the Invention section above. The at least one first injector can inject its additional gas in a direction approximately perpendicular to the side wall of the furnace. However, the applicant prefers to inject the additional gas downwardly or upwardly at an angle to the horizontal plane, because the additional gas provides additional drive to the vertical flow in the liquid bath, which improves the agitation of the liquid bath and also draws more reducing agent that may float on the top of the liquid bath into the main body of the liquid bath. The applicant prefers an upward direction because this can better create a torus-shaped flow path in the liquid bath.

[0085] In an embodiment of the furnace or apparatus according to the invention, the apparatus comprises at least two and preferably at least three first injectors distributed along the horizontal perimeter of the furnace side wall, whereby at least one second submerged injector directs its additional gas towards a volume that is part of the interior space of the furnace and is below a predetermined level approximately close to the vertical axis of the furnace, and / or at least one second submerged injector is located at approximately equal distances along the furnace side wall between the positions of the two nearest first injectors of the at least two first injectors. In an embodiment in which at least one second submerged injector is along the furnace side wall, at least one second injector preferably directs its injected additional gas towards a volume that is part of the interior space of the furnace and is below the predetermined level and is different from the volume towards which the first injectors direct their first hot gases. The applicant has found that this enhances the advantageous effects obtained by the invention as detailed in the Summary of the Invention section above.

[0086] In an embodiment of the furnace or apparatus according to the present invention, the apparatus is further equipped to introduce a reducing agent into the first hot gas upstream of the at least one first injector. This offers the advantage that even more reducing agent can be introduced into the furnace than could otherwise be introduced, such as with additional gas and / or through a feed port. The amount of additional reducing agent that can be introduced via the at least one first injector is independent of the enthalpy input to the furnace. Therefore, this method of introducing the reducing agent is highly convenient for controlling the redox properties of the furnace atmosphere. An additional advantage is that the reducing agent introduced via the first injector is introduced at the same time as the highest temperature enthalpy input to the furnace. At higher temperatures, the equilibrium constant of the desired zinc fuming reaction (I) favors the formation of zinc metal, a vaporizable species. Therefore, the effectiveness of the reducing agent introduced with the first hot gas is greater. Furthermore, since this injection is also performed via a submerged injector, it is also highly efficient because the first hot gas is in very close contact with the liquid in the bath, meaning that little of the reducing agent reaches the bath surface without coming into contact with liquid from the bath.

[0087] In an embodiment of the furnace or the apparatus according to the invention, the reducing agent to be introduced upstream of the at least one first injector may be selected from the group consisting of gases, liquids, solids and combinations thereof. The Applicant has found that the introduction of the first hot gas from the plasma torch via the first injector provides a very versatile option for introducing the additional reducing agent, as it offers a high degree of flexibility in the choice of reducing agent, in particular in its physical state, but also in the amount that can be introduced.

[0088] In an embodiment of the furnace or apparatus according to the present invention, the apparatus is further equipped with at least one oxygen burner for generating an additional first hot gas in an amount exceeding the plasma mass of the first hot gas from the at least one plasma torch. This has the advantage that an additional enthalpy input can be provided to the furnace that is higher than the enthalpy input provided by the plasma generator. This can contribute to maintaining a favorable thermal balance in the furnace, the apparatus, and / or the entire process.

[0089] In an embodiment of the furnace or apparatus according to the invention, the apparatus is equipped with at least one submerged third injector for injecting the additional first hot gas below the determined level. This offers the advantage of highly intimate contact between the additional first hot gas and the liquid bath, which facilitates heat transfer from the additional first hot gas to the liquid bath in the furnace. This results in a very efficient heat transfer.

[0090] In an embodiment of the furnace or the plant according to the invention comprising at least one oxygen burner, the at least one oxygen burner is located below the determined level.

[0091] In an embodiment of the device according to the invention, the plasma torch is located below the determined level.

[0092] The feature of positioning the hot gas and / or plasma generator below the defined level allows for very short connecting pipes, and the hot gas or plasma generator can be located outside the furnace at the injection point. However, measures must be taken to prevent the generator from being flooded by the molten material within the furnace. Therefore, a continuous shielding gas flow through the injector can be used.

[0093] In an embodiment of the furnace or apparatus according to the present invention, the afterburning zone is provided as part of a single-chamber furnace above the determined level. Preferably, the afterburning zone is provided above the liquid bath, as radiant heat can be returned from the afterburning zone to the liquid bath in the furnace. As explained elsewhere in this document, oxidizing conditions are established in the afterburning zone to oxidize the vaporizable metal or metal compound into the corresponding oxidized form. A primary effect achieved by the complete conversion of the oxidized reduced form produced in the fuming step is that the gas containing the oxidized form is no longer highly flammable, thereby curbing the safety hazards presented by the gas from the fuming step and removing it downstream in the afterburning zone or step. A secondary purpose of the afterburning step is also to oxidize most of the carbon monoxide, which may have been generated in the fuming step by the reaction of carbon in the reducing agent with oxygen present as metal oxides, for example, in the slag, into carbon dioxide and / or to oxidize hydrogen into water. This further reduces safety hazards and also makes further processing of the furnace exhaust, including any eventual release to the atmosphere, easier, safer, and more environmentally friendly.

[0094] Preferably, the applicant performs post-combustion by introducing an oxidant into the fuming gas, preferably the oxidant is oxygen.

[0095] In an embodiment of the furnace or apparatus according to the invention, the afterburning zone comprises a connection to a supply source of oxygen-containing gas, preferably selected from the group consisting of air, oxygen-enriched air and purified oxygen. Applicants prefer to use air because it is readily available. Applicants preferably introduce oxygen by injecting oxygen-containing gas into the flue gas stream leaving the furnace top. Typically, the flue gas leaving the furnace top is at a pressure below atmospheric pressure because of the air flow generated by the downstream exhaust treatment, which typically includes at least a furnace chimney and, optionally, an induced draft fan upstream of the chimney. Therefore, the oxygen-containing gas can be provided at atmospheric pressure. Applicants prefer to provide the oxygen-containing gas at a pressure above atmospheric pressure because this provides a higher pressure difference between the source of the oxygen-containing gas and the flue gas that is drawn into the furnace exhaust treatment apparatus by the natural or induced air flow generated as described. The advantage of the higher pressure difference is that it is easier and more accurate to control the flow of oxygen-containing gas entering the flue gas.

[0096] In a simpler embodiment, applicants provide at least one opening to the atmosphere in the conduit connecting the furnace to the downstream exhaust gas treatment equipment, through which ambient air can be drawn in. Preferably, the size of the opening in the conduit is controllable. Multiple openings can be provided, thereby providing the advantage of faster and more intimate mixing of the oxygen-containing gas with the fuming gas.

[0097] Applicants have found that a stable flame front can be formed in the afterburning zone in which oxidation reactions occur. Applicants have found that as the fuming gas is moved faster and as the mixing with the oxygen-containing gas is faster and / or more intense, the flame front is more stable.

[0098] The applicant preferably provides a large excess of oxidant to the post-combustion zone or step so that the oxidation reaction in the post-combustion zone is substantially complete. This ensures that safety hazards in the post-combustion zone or step and upstream thereof are completely contained. It also ensures that the final exhaust gas is substantially free of carbon monoxide, a toxic gas, and hydrogen.

[0099] In an embodiment of the furnace or the apparatus according to the invention, the apparatus further comprises a cooling zone upstream of the recovery zone for cooling the gases being or having been formed in the post-firing zone.The cooling can be performed in various suitable ways.

[0100] One suitable approach is to provide a so-called waste heat boiler—a heat exchanger in which the heat from the post-firing gas is used to generate steam. This has the advantage that the heat is used to generate steam, and the steam can be used elsewhere to transport power or heat, where it can be utilized. Thus, the higher investment cost of a waste heat boiler compared to other alternatives is offset by the value of the steam generated. However, suitably sized steam consumers are not always available near the furnace according to the invention.

[0101] Another suitable cooling method is to use a radiant water cooler, in which the water on the coolant side circulates quickly enough to avoid steam generation, thereby producing only hot water. Preferably, once the water has removed most of its heat, it is recirculated to the radiant water cooler. This hot water can also be used economically in heating services, such as for heating multiple residential buildings, and more preferably, the water is recirculated after being used in heating services. In addition and / or as an alternative, the hot water can be cooled in a conventional cooling tower. Before the remaining water is returned to the radiant water cooler, the amount of water evaporated in the cooling tower needs to be replenished. Because salts accumulate in such a water cycle, the cycle usually also requires a discharge flow, which also needs to be replenished. The radiant water cooler also has the advantage of not changing the amount of gas that needs to be processed downstream on the gas side of the cooling step. Another advantage of the radiant water cooler is that the cooling step can be combined with the afterburning zone, which means that the afterburning step can be performed within the radiant water cooler. This embodiment further simplifies the equipment, thereby reducing investment costs.

[0102] Another cooling method is spray cooling, or "evaporative cooling." This involves injecting water into the hot gas stream, which extracts its heat of evaporation from the gas stream. This method is efficient and rapid, requiring minimal equipment and therefore low investment costs. However, a disadvantage is that this method increases the volume of gas that needs to be handled downstream of the cooling step.

[0103] Another suitable method is to use a gas / gas heat exchanger, where the gas from the post-firing step is on one side of the heat exchanger and, for example, ambient air is on the other side. This has the advantages of being compact and not increasing the flow rate of gas that needs to be handled downstream of the cooling step.

[0104] The preferred cooling step may comprise a number of similar or different cooling methods selected from the cooling methods listed above. A suitable combination may be, for example, first providing a radiant water cooler on the hot inlet side to reduce the temperature of the gas from the supplemental firing step from, for example, about 1500° C. to, for example, about 1000° C., and then providing a spray cooler to further reduce the gas temperature to about 200° C., which may be sufficiently low for the equipment used in the subsequent recovery zone.

[0105] In an embodiment of the furnace or apparatus according to the invention, the recovery zone comprises a gas filtration zone, preferably comprising at least one gas filter cloth. Applicants prefer to use filter sleeves made of polytetrafluoroethylene (PTFE) cloth because they can withstand process temperatures up to 260°C.

[0106] Typically, the last piece of equipment in the gas handling sequence is a blower or ventilator, which is used to push the gas from the recovery zone into the exhaust stack and also to enhance upstream draft by drawing gas through the afterburning zone, optional cooling zone, and recovery zone in sequence. The use of a blower or ventilator has the advantage of reducing the natural draft requirement of the exhaust stack, allowing the stack to be built less tall.

[0107] In an embodiment of the furnace or apparatus according to the present invention, the furnace has a generally cylindrical shape, preferably further comprising a tapered lower section that tapers toward a smaller, circular bottom, wherein the cylindrical shape of the furnace has a maximum inner diameter d and the furnace has a total inner height h from bottom to top, the ratio of h to d being at least 0.75, preferably at least 0.80, more preferably at least 0.85, more preferably at least 0.90, even more preferably at least 0.95, more preferably at least 1.00, more preferably at least 1.05, more preferably at least 1.10, even more preferably at least 1.15, more preferably at least 1.20, more preferably at least 1.25, and even more preferably at least 1.30. In the context of the present invention, the inner diameter of the furnace is the distance between two opposing surfaces of the furnace wall, or, in the case of a refractory lining, the distance between the surfaces of the refractory lining in the furnace during construction. The inner diameter is considered to preclude any possible accumulation of frozen slag (i.e., a layer that can be referred to as a "frozen lining") on the surface. Applicants have found that this feature results in less splashing of molten material in the furnace bath during operation. This splashed molten material can solidify against any solid and cooler surfaces, such as the furnace feed throat and / or furnace exhaust duct, where it can cause problems due to its high temperature and where such material growth can cause other operational problems, such as impairing airflow and / or feed introduction capabilities.

[0108] In an embodiment of the furnace or apparatus according to the present invention, the furnace includes a conical lower section, and wherein the determined level is approximately at the height of the cylindrical shape when converted into the conical lower section. Applicants have found that the conical lower section provides a very convenient arrangement in which a plurality of submerged injectors, and preferably also the corresponding feed providers for these submerged injectors, can be arranged to very efficiently inject into the liquid bath within the furnace with minimal connecting pipework, while also limiting the amount of floor space that the apparatus may occupy. This arrangement offers the advantage of placing the first injector closer to the central vertical axis of the furnace, which facilitates bath agitation. This arrangement also provides greater agitation in the bottom section, into which the first hot gas is injected, and in embodiments of the apparatus with tuyeres in the furnace wall of the smaller bottom section, into which additional gas is also injected, while in the top section, due to its larger diameter, there is less splashing. Another advantage is that a torus-like liquid flow can be formed in the top section, which facilitates the entrainment of any solid reducing agent particles that may be floating on top of the liquid surface within the bath.

[0109] In an embodiment of the furnace or apparatus according to the invention, the furnace is provided with an internal refractory lining, particularly where contact with molten metal and / or matte is possible. This offers the advantage of being able to process or treat metallurgical charges with high melting temperatures and / or high liquidus temperatures. The refractory lining is preferably provided in the bottom section, where free molten metal and / or matte phases are likely to occur, thereby offering the benefit of increased resistance to chemical and / or mechanical attack by these liquids.

[0110] In an embodiment of the furnace or apparatus according to the present invention, the peripheral walls of the furnace are water-cooled. Applicants have discovered that this contributes to a longer lifespan of the apparatus's resistance to the very high temperatures that may occur within the furnace during operation. An additional benefit is that a freeze lining can be formed within the furnace against the sidewalls. This freeze lining can provide additional insulation against the very high temperatures that may occur within the furnace during operation and offer additional protection for any refractory material that may already be provided on the furnace walls.

[0111] In an embodiment of the method according to the invention, the amount of additional gas injected by the at least one second injector is at least 10%, preferably at least 15%, more preferably at least 20%, 25%, 30%, 35%, 40%, 45%, 50% or 55%, more preferably at least 60%, more preferably at least 70%, more preferably at least 75%, 80%, 90%, 100%, 110%, 120%, 125%, 130%, 140%, 150%, 175%, 200%, 225% and even more preferably at least 230% of the first amount of hot gas by plasma mass, which first amount of hot gas can be delivered by the at least one plasma torch with an enthalpy content expressed in volume units under normal conditions of at least 3.5 kWh / Nm 3 %, 80%, 70%, 60%, 50%, 40%, 30% and even more preferably at most 20% of the amount of plasma when the at least one plasma torch delivers an enthalpy content expressed in volume units under normal conditions of at least 3.5 kWh / Nm 3The applicant has found that the main advantages of the invention can be achieved by injecting an additional gas flow rate closer to the lower limit indicated through the second injector, in particular when the additional gas flow is used as a carrier for an additional reducing agent, in particular when a fine powder such as coal powder or petroleum coke powder is used as the additional reducing agent.

[0112] In an embodiment of the method according to the invention, wherein the apparatus comprises a plurality of second injectors, the amount of additional gas injected by each second injector is at least 10%, preferably at least 15%, more preferably at least 20%, 25%, 30%, 35%, 40%, 45% or 50%, more preferably at least 55%, more preferably at least 60%, more preferably at least 65%, even more preferably at least 70%, still more preferably at least 75%, more preferably at least 80% of the amount of first hot gas by plasma mass, which first hot gas amount, when the at least one plasma torch delivers an enthalpy content expressed in volume units under normal conditions, of at least 3.5 kWh / Nm 3 When the first hot gas is generated by the single element with the highest rated power in the torch, the amount of additional gas injected by each second injector is at most 200%, preferably at most 190%, more preferably at most 180%, 170%, 160%, 150%, 140%, 130%, 125%, 120%, 115%, 110%, 105%, 100%, 95%, even more preferably at most 90% of the amount of the first hot gas by plasma mass when at least one plasma torch delivers an enthalpy content expressed in volume units under normal conditions of at least 3.5 kWh / Nm 3 The first hot gas may be generated by the single element in the torch having the highest power rating.

[0113] In an embodiment of the method according to the invention, the additional gas injected by the at least one second injector comprises at least one gas selected from the group consisting of hydrogen, nitrogen, air, carbon dioxide, argon, neon, helium, methane, ethane, propane, butane, and combinations thereof, preferably nitrogen or air, more preferably air, even more preferably compressed air. The applicant has found that nitrogen and air, preferably compressed air, are very convenient gases as a basis for the additional gas to be injected into the furnace.

[0114] In an embodiment of the method according to the invention, the additional gas injected via the at least one second injector is subjected to a heat treatment upstream of the at least one second injector in order to modify its enthalpy content. Preferably, the heat treatment of the additional gas is performed using at least one heat exchanger. If the gas is supplied to the furnace at a temperature lower than the temperature of the liquid bath in the furnace, the applicant preferably heats the gas before it is injected via the at least one second injector. This reduces the cooling effect that the injection of the additional gas may have on the furnace and makes it easier to maintain the thermal balance in the furnace. Preferably, this heating utilizes, at least in part, the heat available in the system for treating the exhaust gas from the furnace.

[0115] In an embodiment of the method according to the invention, the temperature of the additional gas entering the at least one second injector is at most equal to the temperature of the furnace bath, preferably at least 20 degrees Celsius below the bath temperature, more preferably at least 50 degrees Celsius below the bath temperature, even more preferably at least 100 degrees Celsius, and even more preferably at least 200 degrees Celsius below the bath temperature. This has the advantage of less wear and tear on the injection points or tuyere. Alternatively, the temperature of the additional gas entering the at least one second injector is at most 400 degrees Celsius below the bath temperature, preferably at most 350 degrees Celsius below the bath temperature, more preferably at most 300 degrees Celsius below the bath temperature, even more preferably at most 250 degrees Celsius below the bath temperature, preferably at most 200 degrees Celsius below the bath temperature, more preferably at most 150 degrees Celsius below the bath temperature, even more preferably at most 100 degrees Celsius below the bath temperature, preferably at most 75 degrees Celsius below the bath temperature, more preferably at most 50 degrees Celsius below the bath temperature, even more preferably at most 25 degrees Celsius below the bath temperature. This has the advantage of less risk of solidified slag accumulating at the injection points or tuyere mouths, which may be caused by the cooling effect of the additional gas passing through the injection points or tuyere and entering the furnace.

[0116] In an embodiment of the method according to the invention, the additional gas injected by the at least one second injector comprises at least one first reducing agent, preferably, the at least one reducing agent is selected from the group consisting of any substance containing an element other than oxygen and an inert gas and capable of reacting with oxygen under furnace conditions, preferably any substance containing carbon and / or hydrogen in readily oxidizable chemically bound form, more preferably, the reducing agent is selected from the group consisting of natural gas, gaseous and / or liquid hydrocarbons, fuel oil, rubber, plastic, preferably plastic made of at least one polyolefin, more preferably waste rubber and / or plastic, charcoal or coke and combinations thereof, even more preferably coke, still more preferably petroleum coke, which is a highly carbon-rich by-product of crude oil processing. As explained above in the Summary of the Invention section, the injection of additional gas into the furnace by the at least one second injector represents an additional entry point for the addition of reducing agent to the furnace. Moreover, since the at least one second injector is submerged, the choice of suitable reducing agents is very wide.

[0117] In an embodiment of the method according to the invention using a first reducing agent, the first reducing agent is a solid, preferably a solid in particulate form, more preferably having an average particle size of at most 6 mm, even more preferably at most 5, 4, 3, 2 or 1 mm, preferably at most 500 μm, more preferably at most 250, 200, 150, 100 or even 50 μm particles. Applicants have found that suitable solid reducing agents are available in various types and qualities and are available from various sources. In addition, some of these suitable solid reducing agents have almost no alternative disposal options that would require any significant economic value. Therefore, these solid reducing agents represent very interesting sources for use according to the invention. As explained elsewhere herein, smaller particle sizes provide the advantages of providing a higher surface-to-weight ratio and less buoyancy, and therefore enabling more efficient and effective use of the reducing agent.

[0118] In an embodiment of the method according to the present invention, the additional gas injected via the at least one second injector further comprises oxygen and an amount of fuel suitable, upon combustion under the operating conditions of the furnace, to provide an enthalpy input to the furnace that compensates for at least 50% of the cooling effect that the additional gas would otherwise provide to the furnace if the temperature of the additional gas at the injection point were lower than the temperature of the molten charge in the furnace. The applicants prefer to add an amount of fuel that compensates for at least 75%, and preferably at least 100%, of this cooling effect. The applicants have discovered that additional heat input to the furnace can be provided by injecting a gaseous or liquid fuel as part of the additional gas, preferably when the additional gas further comprises oxygen, more preferably at least sufficient oxygen to achieve the desired lambda of the additional gas. Typically, the temperature of the liquid bath within the furnace is above the temperature at which the fuel and oxygen in the additional gas begin to react, even in the absence of an ignition source. With sufficient oxygen present in the additional gas, the added fuel readily combusts upon contact between the additional gas and the molten furnace charge. The applicant has found that the gas flow can be easily set high enough so that the combustion reaction does not propagate upstream against the flow direction of the additional gas in the second injector and / or in the piping leading to at least one second injector. Consequently, the risk of such a "flashback" phenomenon is very low. The applicant has found that the risk of equipment damage due to such heating inside or upstream of the injector can be easily eliminated if the additional gas reaches a velocity in the second injector or at another location upstream of the second injector that is higher than the flame propagation velocity of the additional gas. The applicant has found that this condition is easily met.

[0119] In an embodiment of the method according to the present invention, the first lambda of the additional gas injected via the at least one second injector (considering only gaseous and liquid combustibles) is less than 1.0, preferably at most 0.9, more preferably at most 0.8, even more preferably at most 0.7, and even more preferably at most 0.6. Lambda ("λ") is a very convenient parameter commonly used in burners and combustible fuels, particularly internal combustion engines, which represents the ratio of the actual air / fuel ratio in the numerator to the stoichiometric air / fuel ratio of the same fuel in the denominator. If the air / fuel mixture is stoichiometric, its lambda is 1.0. Applicants apply this first lambda parameter to all gaseous mixtures containing oxygen and another substance, such as a combustible substance, that can readily react with oxygen, where the other substance is a gas or a liquid, or a combination thereof. Applicants have found that, if a solid reducing agent is not used in the method, controlling the first lambda of the additional gas injected via the at least one second injector is a very convenient means of controlling the furnace atmosphere, thereby setting whether the atmosphere is neutral, oxidizing, or reducing, and the degree of oxidation or reduction. The applicant has found that the additional addition point for the reducing agent in the apparatus according to the invention is highly versatile and that controlling the first lambda and / or second lambda of the additional gas to be injected (as further described below) provides a very convenient method for controlling the redox conditions within the furnace and, therefore, regulating the chemical reactions occurring within the furnace. The applicant has found that the combination of the injection of the additional gas with the injection of the first hot gas from the plasma generator enables a wide range of redox conditions to be obtained, whereby, unlike more conventional heating means such as the use of natural gas burners, the redox conditions can be set substantially independently of the heat input to the furnace.

[0120] Applicants also consider a second lambda, which takes into account all combustibles used in the process and added to the additional gas, i.e., including any solid combustibles, such as most reducing agents described above in this document. In an embodiment of the process according to the present invention, the second lambda of the additional gas injected via the at least one second injector is less than 0.6, preferably at most 0.5, more preferably at most 0.4, even more preferably at most 0.3, and even more preferably at most 0.2. Applicants have found that such low second lambda values ​​are highly advantageous for fuming metals, such as zinc, from metallurgical slag.

[0121] In an embodiment of the method according to the present invention, the additional gas injected through the at least one second injector is flammable, and the additional gas reaches a velocity in the at least one second injector that is greater than the flame propagation velocity of the additional gas. The applicant has discovered that additional heat input to the furnace can be provided by injecting a gaseous or liquid fuel as part of the additional gas, preferably when the additional gas further comprises oxygen. Typically, the temperature of the liquid bath in the furnace is higher than the temperature at which the fuel and oxygen in the additional gas begin to react, even in the absence of an ignition source. The applicant has discovered that this reaction can proceed upstream against the flow direction of the additional gas in the conduit leading to the at least one second injector and in the second injector itself. This "flashback" phenomenon can result in the release of heat in the injector conduit, resulting in an increase in the temperature of the additional gas upstream of and / or within the injector. The applicant has discovered that if the additional gas reaches a velocity in the injector or at another location upstream of the injector that is greater than the flame propagation velocity of the additional gas, the risk of equipment damage due to such heating within or upstream of the injector can be easily reduced or even eliminated.

[0122] In an embodiment of the method according to the invention, the at least one vaporizable metal or metal compound is a metal in elemental form or a vaporizable metal-containing compound. Preferably, the metal is selected from the group consisting of zinc, lead, tin, bismuth, cadmium, indium, germanium, and combinations thereof, wherein the vaporizable compound may be, for example, an oxide, a sulfide, a chloride, or a combination thereof. The applicant has found that the method according to the invention is well suited for removing, by evaporation, metals or metal-containing compounds selected from a specified list. The applicant has found that the method provides a highly competitive alternative for recovering one of the specified metals from metallurgical charges.

[0123] In an embodiment of the method according to the invention, a metal less noble than the metal in the vaporizable metal or metal compound, preferably iron and / or aluminum, is added to the furnace. Preferably, the less noble metal is added in the form of particles, more preferably particles having an average particle size of at most 5, 4, 3, 2, or 1 mm, preferably at most 500 μm, more preferably at most 250, 200, 150, 100, or even 50 μm. Under the process conditions, the concentration of the less noble metal in the slag is preferably maintained below its solubility limit in the slag. Applicants have found that this offers the advantage of improved fluidity of the slag phase, which may be present as part of the liquid bath within the furnace. However, Applicants have found that it is preferable to maintain the concentration of these compounds below their solubility limit in the liquid bath, as exceeding the solubility limit may result in certain compounds forming separate phases in the furnace. This separate phase risks impairing the contact between the other liquid phase in the liquid bath and the injected additional gas and / or the first hot gas generated by the plasma torch and / or the additional first hot gas generated by the oxygen burner (if present), and thus may impair the desired chemical reactions in the furnace, in particular leading to an impairment of the evaporation of the vaporizable metal or metal compound.

[0124] In an embodiment of the method according to the present invention, a second reducing agent is added to the plasma-quality first hot gas upstream of the at least one first injector. This has the advantage that even more reducing agent is introduced into the furnace than could be introduced with the additional gas. The amount of additional reducing agent that can be introduced via the at least one first injector is independent of the furnace's enthalpy input. Therefore, this method of introducing the reducing agent is very convenient for controlling the redox properties of the furnace atmosphere. An additional advantage is that the reducing agent introduced via the first injector is introduced with the furnace's highest temperature enthalpy input. At higher temperatures, the equilibrium constant of the desired zinc fuming reaction (I) favors the formation of zinc metal, which is a vaporizable metal or metal compound. Therefore, the reducing agent introduced with the first hot gas from the plasma torch is more effective. This is also because such injection is performed via a submerged injector. It is also highly efficient because the first hot gas is in very close contact with the liquid in the bath, meaning that little of the reducing agent reaches the bath surface without coming into contact with the liquid from the bath.

[0125] In embodiments of the method of the present invention using a second reducing agent, the second reducing agent is selected from the group consisting of gases, liquids and solids, and combinations thereof, preferably the second reducing agent is selected from the group consisting of natural gas, gaseous and / or liquid hydrocarbons, fuel oil, charcoal or coke, and combinations thereof, even more preferably coke, even more preferably petroleum coke, preferably in the form of solid particles, more preferably particles having an average particle size of at most 6 mm, even more preferably at most 5, 4, 3, 2 or 1 mm, even more preferably at most 500 μm, preferably at most 250, 200, 150, 100 or even 50 μm. Applicants have found that introducing the plasma via the first injector provides a very versatile option for introducing the additional reducing agent, as it offers great flexibility in the choice of reducing agent, in particular in its physical state, but also in the amount that can be introduced.

[0126] In an embodiment of the method according to the present invention, the oxygen potential in the slag is adjusted to 10 to 10 -9 Pa (i.e. 10 -4 to 10 -14 atm). Preferably, the oxygen potential in the slag is adjusted by adding the first and / or second reducing agent. Due to the use of plasma torches, almost any oxygen potential can be combined with any heat generation. In combination with the recovery of one or more vaporizable metals or metal compounds, other metals can also be extracted from the material introduced into the furnace. In one embodiment, the oxygen potential in the slag can be adapted to selectively reduce the metal compounds in the slag to a molten metal phase. Typical examples of metals that can be reduced from the slag are Cu, Ni, Sn, Pb, Ag, Au, Pt and Pd. The molten metal phase can then be collected at the bottom of the furnace. The molten metal phase can then be removed continuously or in batches through the outlet end. For this purpose, the furnace can be provided with a refractory lining at the bottom. In another embodiment, where the material introduced into the furnace and the slag produced thereby include sulfur or sulfur compounds, a matte phase can also be obtained. The oxygen potential in the slag can then be adapted to prevent the sulfur from being oxidized. The metal can then be recovered in the molten matte phase. Examples of metals that can be recovered from the slag in a matte phase are Fe, Cu, Ni, Sn, Pb, Ag, Au, Pt and Pd. The molten matte phase can then also be collected at the bottom of the furnace. The molten matte phase can be removed continuously or in batches via the outlet port. In yet another embodiment, a metallic phase and a matte phase can be obtained by appropriately adjusting the oxygen potential and the sulfur content. As non-limiting examples, Au, Pt and Pd can be reduced to a metallic phase, while Cu and Ni can be made to form a matte phase. The matte phase typically appears on top of the metallic phase because it typically has a lower density than the metallic phase and because the two phases remain more or less insoluble in each other. The matte phase and the metallic phase can be extracted from the furnace through separate outlets or a common outlet.

[0127] In an embodiment of the method according to the invention, the supplementary firing takes place inside the single-chamber furnace. This results in the advantage of a more compact plant design and thus reduced investment costs.

[0128] In an embodiment of the method according to the invention, the post-firing comprises introducing an oxygen-containing gas into the post-firing zone, the oxygen-containing gas preferably being selected from air, oxygen-enriched air and purified oxygen. The applicant has found that this option is a relatively simple and low-cost option for performing the function of the post-firing zone. As mentioned above, the applicant prefers to simply use air.

[0129] In an embodiment of the method according to the invention, an oxidized form of at least one vaporizable metal or metal compound is recovered from the gas as dust. The applicant has found that this option is much safer than the alternative of condensing the metal to form a liquid metal phase (for example, as explained in US Pat. No. 4,588,436), because the risk of spontaneous combustion and / or explosion of the exhaust gas from the furnace at the outlet of the afterburning zone is essentially eliminated. The applicant has also found that the investment costs of this option are relatively low, for example, compared to the alternative described in US Pat. No. 4,588,436.

[0130] In an embodiment of the method according to the invention, recovering the oxidized form of the at least one vaporizable metal or metal compound from the gas comprises filtering the gas containing the oxidized form of the at least one vaporizable metal or metal compound using a filter, preferably a filter cloth. As mentioned above, applicants prefer to use a filter sleeve made of polytetrafluoroethylene (PTFE) cloth. In such a gas filter, the local gas velocity can be very low. However, oxygen is expected to be present. Therefore, it is important for the method according to the invention that substantially all of the reduced form of the metal or metal compound has been oxidized to its oxidized form, so that the risk of spontaneous combustion and / or explosion is acceptably low.

[0131] In an embodiment of the method according to the invention, the method further comprises a cooling step upstream of recovering the oxidized form of the at least one vaporizable metal or metal compound from the gas.As mentioned above, a variety of suitable cooling methods can be applied.

[0132] Typically, the last step in the gas treatment sequence is a blower or ventilator that pushes the gas from the recovery zone into the exhaust stack and enhances upstream draft by drawing the gas through a sequence of afterburning, optional cooling, and recovery zones.

[0133] In an embodiment of the method according to the invention, the method comprises forming a molten metal phase, the method further comprising the step of removing the molten metal phase from the furnace. Applicants have found that the method according to the invention may result in the formation of a separate molten liquid phase, which is caused by the reduction of the less volatile metal to its elemental form. This may be a pure metal phase or a molten alloy. In this case, it is very convenient to remove the separate molten metal phase from the furnace as a separate by-product. In the case of an alloy, it may be preferred to further process the alloy so that at least one metal in the alloy is recovered separately from some other metals in the alloy. This further processing may include a pyrometallurgical step and / or an electrolytic step.

[0134] In an embodiment of the method according to the invention, wherein the metal charge comprises slag, wherein the slag comprises sulphur and / or sulphur compounds, the method further comprises the step of forming a molten matte phase and the further step of removing the molten matte phase from the furnace. This is optionally in addition to recovering the liquid molten metal or alloy from the process.

[0135] In an embodiment of the method according to the invention, the metallurgical charge is introduced into the furnace in liquid form. This has the advantage that the metallurgical charge does not need to be melted and / or smelted as part of the process running in the plant and / or furnace, which is beneficial to the thermal balance of the furnace and therefore to the productivity of the process and its plant (e.g. the furnace itself).

[0136] In an embodiment of the method according to the invention, the metallurgical charge is a metallurgical slag, preferably selected from copper smelting slag, copper refining slag, and combinations thereof, and wherein the method produces a secondary slag. The applicant has found that the method (and apparatus) according to the invention is well suited for processing the specified raw materials.

[0137] In an embodiment of the method according to the present invention, the average temperature of the molten slag is less than 50 degrees Celsius above the liquidus temperature of the slag. This has the advantage that the frozen lining of solid slag, which forms against the inner surface of the furnace wall and protects the refractory lining, is easily maintained at a sufficient thickness to provide adequate protection and insulation. This frozen lining is very beneficial in terms of the thermal balance of the furnace, as it acts as a barrier between the hot liquid slag in the furnace and the furnace wall, which is preferably cooled to protect its mechanical integrity. Thus, the frozen lining reduces heat losses from the furnace to the cooling walls.

[0138] In an embodiment of the method according to the invention, the oxide selected from the group consisting of CaO, Al2O3, and combinations thereof is preferably added to the slag in the fuming furnace at a temperature of at least 1000°C, preferably at least 1050°C, and more preferably at about 1150°C. This feature offers the further advantage that the final composition of the secondary slag after the fuming step can be further optimized and stabilized, and that the slag can be made more suitable for specific end uses by also possibly influencing the mineralogy. The applicant has found that the addition at high temperature (as specified) and in the molten state is more effective in achieving the desired effect.

[0139] In an embodiment of the method according to the invention, the temperature of the slag in the furnace is at least as specified in the previous paragraph, and more preferably even higher, for example at least 1200, 1250, or 1300° C., more preferably about 1350° C. This has the advantage of a more favorable equilibrium constant between the vaporizable metal or metal compound and its precursor in the liquid slag. Another advantage of the higher temperature is that it facilitates the removal of the fumed slag from the furnace, the so-called "tapping," whether this is done by overflow or by bottom tapping through bottom tapping holes appropriately located in the furnace wall.

[0140] In an embodiment of the method according to the present invention, the method further comprises a step of cooling the second slag to a solid state. Preferably, the second slag is first removed from the furnace in liquid form. This has the advantage that, while the second slag is cooling, the fuming furnace can be freed for further slag processing. The slag can be cooled and / or solidified by contacting it with a cooling medium, such as air and / or water, possibly ambient air.

[0141] In an embodiment of the method according to the invention, in which the second slag is cooled, the cooling is performed by contacting the liquid second slag with water. The applicant has found that cooling with water is very effective and can be applied in various ways to obtain a relatively well-controlled cooling rate.

[0142] In an embodiment of the method according to the invention in which the second slag is cooled, the second slag is cooled at a rate of at least 30 degrees Celsius per second, preferably at least 40 degrees Celsius per second, more preferably at least 50 or 60 degrees Celsius per second. The applicant has found that at higher cooling rates as specified, a higher amorphous content of the slag can be obtained, which is of interest for certain end uses, for example when the slag is intended to be used as a binder in the construction industry.

[0143] In an embodiment of the method according to the invention, wherein the second slag is cooled, the method further comprises the step of grinding the solid second slag, preferably grinding the second slag into a powder.

[0144] In an embodiment of the method according to the invention, in which the second slag is cooled, the second slag is cooled at a rate of less than 40 degrees Celsius per second, preferably at most 30 degrees Celsius per second, more preferably at most 20 degrees Celsius per second. The applicant has found that at a lower cooling rate as specified, a lower amorphous content of the slag and, therefore, a higher degree of crystallinity can be obtained, which is of interest for certain end uses, for example when the slag is intended to be used as aggregate or for decorative purposes.

[0145] In an embodiment of the method according to the invention, in which a secondary slag is formed by the method, the method further comprises the step of adding the secondary slag as a binder or aggregate during the manufacture of an object for use in the construction industry. The applicant has discovered that the secondary slag can be used as a binder for aggregates, preferably as an active binder, preferably as a binder having pozzolanic activity. The applicant has discovered that the slag can be used as a binder to replace cement, for example to partially replace cement, such as Portland cement, and can also be used as a binder in the production of geopolymer compositions.

[0146] In an embodiment of the method according to the invention, wherein the slag is used as a binder during the production of an object for the construction industry, the object further comprises aggregate, wherein the aggregate preferably comprises sand and / or a secondary slag.

[0147] In one embodiment of the method according to the present invention, in which the slag is used as a binder during the manufacture of an object for the construction industry, and the object further comprises aggregate, the method further comprises the step of adding an activator during the manufacture of the object. Applicants have discovered that the second slag can act as an active binder, capable of reacting with a suitable activator, thereby exhibiting strong binding properties to the aggregate. Thus, the second slag can be used to replace Portland cement or as the sole binder in the object, in which case it is considered a "geopolymer," which imparts fire- and heat-resistant properties to, for example, coatings, adhesives, composites, and the like.

[0148] In an embodiment of the method of the present invention using an activator, the activator is selected from the group consisting of sodium hydroxide NaOH, potassium hydroxide KOH, sodium silicate Na2SiO3, potassium silicate K2SiO3 and combinations thereof. Preferably, the activator is NaOH.

[0149] In an embodiment of the method according to the invention in which an object for the construction industry is formed, the object for the construction industry is a building element.

[0150] In an embodiment of the method according to the invention, wherein building elements are formed, the building elements are selected from the list consisting of tiles, pavers, blocks, concrete blocks and combinations thereof.

[0151] In an embodiment of the method according to the invention in which an object for the building industry is formed, the object for the building industry has a foamed structure.

[0152] In an embodiment of the use according to the present invention, the metallurgical charge is selected from the group consisting of copper smelting slag, copper refining slag and combinations thereof.

[0153] In an embodiment of the use according to the invention, the vaporizable metal or metal compound is selected from zinc, lead, tin, bismuth, cadmium, indium, germanium and combinations thereof.

[0154] In an embodiment of the method according to the present invention, at least part of the method is electronically monitored and / or controlled, preferably by a computer program. Applicants have discovered that electronically controlling the steps of the method according to the present invention, preferably by a computer program, provides the advantages of better processing and more predictable results that are closer to the method's objectives. For example, based on temperature measurements, and if necessary, pressure and / or level measurements, and / or in conjunction with chemical analysis results of samples extracted from the process stream and / or analytical results obtained online, the control program can control equipment related to the supply or removal of electrical energy, the supply of heat or cooling media, and flow and / or pressure control. Applicants have discovered that such monitoring or control is particularly advantageous for steps operating in a continuous mode, but can also be advantageous for steps operating in batch or semi-batch mode. Furthermore, and preferably, monitoring results obtained during or after the execution of a step in the method according to the present invention can also be used to monitor and / or control other steps that are part of the method according to the present invention, and / or processes applied upstream or downstream of the method according to the present invention as part of an overall process of which the method according to the present invention is only a part. Preferably, the entire process is fully electronically monitored, more preferably by at least one computer program. Preferably, the entire process is electronically controlled to the greatest extent possible.

[0155] Applicants prefer that computer control also provide for the transfer of data and instructions from one computer or computer program to at least one other computer or computer program or module of the same computer program to monitor and / or control other processes, including but not limited to the processes described herein.

[0156] Example 1

[0157] In this Example 1, a furnace equipped with three plasma generators was provided.

[0158] The total height of the furnace (also called "device", "reactor" or "fume-inducing device") from the bottom to the top feed opening is about 7.34 m. The furnace roof is formed by a dome including the top feed opening and the tail gas evacuation duct. Below the top dome with a height of 1.09 m, the furnace includes a top section, which is cylindrical around a vertical axis, with a height of about 3.00 m and an outer diameter of 5.50 m. Below this top section, the furnace gradually narrows downwards over a height distance of about 1.66 m, ending in a bottom cylindrical section with a diameter of about 3.19 m and a height of 1.00 m. The height of the bottom dome is 0.60 m. The height of the bottom cylindrical section is 1.00 m, and the height of the conical section is 1.66 m.

[0159] During operation, the furnace should contain a bath of molten liquid at least above the highest opening at which the plasma-quality first hot gas and the additional hot gas enter. To this end, applicants prefer to maintain a liquid level within the furnace at least as high as the bottom of the tapered section. More preferably, the liquid level is maintained slightly higher somewhere along the height of the tapered section. If desired, the level can be raised above the tapered section, but it should be maintained at a level at which the static head becomes too burdensome for the introduction of the first hot gas and / or the additional gas, so that bath agitation is affected.

[0160] The furnace shell, with the exception of sections well protected by a refractory lining, is a double-walled, water-cooled alloy steel structure. During operation, the space within the double walls is supplied with circulating cooling water as part of a pumped circuit. This cooling is provided to protect the structural integrity, particularly the mechanical strength, of the reactor walls. Cooling also causes a portion of the liquid slag within the furnace to solidify against the furnace walls below the liquid level, forming a so-called "frozen lining," and also, due to splashing, against the majority of the furnace walls above the liquid level. This solid, frozen lining protects the walls from many forms of chemical and mechanical wear. It also provides thermal insulation, reducing the amount of heat that could be lost from the furnace contents to the cooling water. Because some molten metal phases may also form during this process, the bottom cylindrical section and bottom dome are lined with a suitable refractory material—in this case, a combination of insulating bricks, wear-resistant lining, and refractory concrete. Most of these sections are not part of the water cooling system.

[0161] In the wall of the bottom cylindrical section, and therefore below the liquid level during operation, three plasma generators (PG) are arranged at the same height and approximately equidistantly along the circumference for injecting their hot gases into the furnace through tuyere in a direction perpendicular to the furnace wall.

[0162] A plasma generator is a device that produces very hot gas (at least partially converted into plasma). Typical gas temperatures range from 3500-5000°C. This gas is heated by electrical energy. A high voltage difference across two electrodes creates an arc between them. During operation, air is blown through the arc and heated by the energy of the arc. As the current increases, more air can be heated and more electricity can be transferred to the air. The power of a plasma generator (W - expressed in watts) is defined as voltage (V - volts) * current (A - amperes). In the operation of this type of plasma, there is a relationship between the nominal power of the plasma generator and the amount of air that can be blown through it.

[0163] In this embodiment, the nominal power of the three plasma generators of the reactor is 3 MW, and during the operation of the furnace, the amount of electricity supplied to each plasma generator is between 300 and 900 Nm 3 / h range of pressurized air. The reference enthalpy of the generated gas is 3.5kWh / Nm 3 Each plasma generator can generate 857Nm 3 This plasma mass of hot gas serves as the "primary gas".

[0164] The PGs are not mounted directly into the reactor wall. They blow their first hot (plasma generated and plasma quality) gases into the furnace through tuyeres. Tuyeres are nozzles forming openings in the reactor through which hot gases can be fed into the reactor. If desired, the tuyeres can further be used to mix a secondary volume of natural gas and / or additional air into the hot gases from the PGs. Preferably, when a hot liquid bath is present in the furnace, the applicant always keeps a large amount of secondary gas flowing through the tuyeres. The aim is that even if the PGs would need to be shut down and / or removed, there would still be enough gas flowing through the tuyeres to prevent hot liquid from entering the tuyeres and to avoid some liquid from flowing back up into the tuyeres where it would cool and solidify and which would represent a significant burden to remove before the tuyere is fully fit for its intended purpose again.

[0165] During operation, another 90-200Nm is passed through the holes in the corresponding tuyere. 3 / h of natural gas is added to the first hot gas from each PG. In addition, additional air is usually added through each of these tuyere at a rate of 100-250Nm 3 These volumes therefore qualify as secondary gas volumes.

[0166] The natural gas used in this example comprises 84.206% by volume of methane, 3.646% by volume of ethane, 0.572% by volume of propane, and 9.966% by volume of nitrogen. The remainder, less than 1% by volume, is composed of higher alkanes, primarily butane and pentane.

[0167] Opposite each plasma generator-tuyere combination, another tuyere is provided for injecting additional gas into the furnace, so that the entire furnace also has three such tuyeres. These additional tuyeres or injectors represent the second submerged injectors according to the present invention. They are also arranged to inject their additional gas in a direction perpendicular to the furnace wall, but it is planned to change the preferred option for injecting at a certain angle upward into the bath.

[0168] The second submerged injector is constructed using the same type of tuyeres as those used downstream of the plasma generator. These tuyeres, and therefore also the tuyeres downstream of the PG, are water-cooled, cylindrical, double-walled, and protrude through the furnace wall into the furnace space, which is expected to be below the level of the liquid bath within the furnace during operation. The tuyeres are provided for injecting secondary gas into their double walls. The inner barrel of the tuyeres is provided with a plurality of holes that allow the secondary gas to enter the central volume of the tuyeres, through which the primary gas, in the case of an upstream PG, passes. This central volume will be the plasma-quality hot gas generated in the PG itself. The holes are preferably provided as nozzles to impart additional velocity to the gas, thereby promoting mixing of the secondary gas with the primary gas passing through the tuyeres. In the case of the second submerged injector, the PG is replaced by a simple pipe that protrudes through the tuyeres in the direction of the liquid bath, preferably substantially to the point where the tuyeres extend into the furnace. Primary gas, such as compressed air, can be propelled through this pipe, optionally supplemented with a certain amount of natural gas. A quantity of an additional reducing agent, such as finely divided coal, may be mixed into the primary gas or one of its components.

[0169] During operation, a total of 300-600 Nm is supplied to each of the other three injectors. 3 / h of compressed air, primary and secondary gases, mixed with 30-60Nm 3 / h of natural gas and, where appropriate, approximately 150-200 kg / hr of pulverized coal as an additional reducing agent. The average particle size of the pulverized coal is 120 μm. The gas pressure upstream of the other tuyeres is 6 barg. During operation, the gas velocity in the other tuyeres is typically greater than 330 m / s.

[0170] To inject the pulverized coal, a dual pressure vessel system is used. The top vessel acts as a pressure lock: it is kept at atmospheric pressure while being filled from a hopper located at the top of the pressure vessel, usually through a discharge valve. The hopper is filled by mechanical transport, usually using a feed belt or screw, but optionally also by unloading from big bags. After filling, the vessel is pressurized to the injection pressure. Subsequently, the bottom vessel, which is kept at the injection pressure, can be filled by discharging the contents from the top vessel into the bottom vessel. From the bottom vessel, a weight-regulated feed system is provided to feed the pulverized coal into the injected air. The air and pulverized coal are then conveyed by pressure to further injectors and the liquid slag. The advantage of the dual vessel system is that the inflow of reducing agent into the reactor can be kept uninterrupted.

[0171] The tuyere, plasma generator and injector are all water-cooled.

[0172] A radiant water cooler is provided at the top of the furnace and is provided as a double walled metal cylinder wherein the exhaust gases from the furnace pass through the centre of the cylinder and push cooling water through the walls of the cylinder.

[0173] Between the furnace roof and the radiant water cooler, ambient air is allowed to enter and mix with the furnace exhaust. The evaporated zinc and the CO present in the gases come into contact with oxygen in the air. Due to the high temperature of the gases, these substances spontaneously ignite, forming an afterburning zone. Due to the extensive ventilation within the furnace and water cooler, the exhaust flows at high speed. Ambient air is allowed to enter through appropriately designed openings to allow rapid and intensive mixing of air and exhaust. This results in a stable flame front within the radiant water cooler, with some of its radiant heat radiating downward from the afterburning zone back into the liquid bath within the furnace. The furnace roof and radiant water cooler are also equipped with multiple injection points through which pressurized air can be injected into the furnace exhaust. This capability can be used in conjunction with allowing ambient air to enter through the openings. However, preferably, the openings for admitting ambient air are substantially closed, and substantially all the required oxygen is introduced through the injection points. This mode of operation is preferred because the oxygen intake is more stable and better controlled than the alternative of admitting ventilation air.

[0174] Inside the afterburning zone, the gas temperature reaches up to 1500℃.

[0175] The gas temperature leaving the afterburning zone is approximately 1200°C. Downstream of the radiant water cooler, approximately 6-7000 liters / hour of water are injected into the gas stream. This spray cooling step reduces the gas temperature to around 220°C.

[0176] The wet gas from the spray cooling step is directed to a gas filter in which a porous polytetrafluoroethylene sleeve is placed on a cylindrical stub, the sleeve retaining dust consisting of oxidized forms of the vaporizable metals or metal compounds formed in the afterburning zone.

[0177] Downstream of the gas filter, a ventilator provides suction from the furnace and blows the filtered gases into the exhaust stack.

[0178] The fuming process and furnace are operated in batch mode. The operational batches reported below consist of a sequence of clearly defined and distinguishable process steps. Depending on the desired effect, the reactor is fed with more or less electricity, pulverized coal, air, and natural gas in different process steps. The operation of the PG, tuyere, and additional injectors or tuyere varies depending on the process step. The different steps are now described in detail.

[0179] First process step: Liquid filling of the furnace:

[0180] At the start of the batch, 76,900 kg of liquid slag from an upstream copper smelter was fed into four slag pots on a bridge crane. Each slag pot had a net weight of approximately 19 tonnes, as measured by a weighing device. The bridge crane transferred the slag pots between different furnaces.

[0181] In the upstream copper smelter, the slag is thoroughly mixed before being poured from the smelting furnace. Therefore, the slag composition can be considered homogeneous. The bulk metal composition of the slag is measured using inductively coupled plasma atomic emission spectrometry (ICP-AES), also known as inductively coupled optical emission spectrometry (ICP-OES), sometimes simply referred to as ICP. SiO₂ is measured by X-ray diffraction (XRF). The XRD technique used is quantitative X-ray diffraction analysis using Topas Academic software V5, using Al₂O₃ as an internal standard.

[0182] Table 1: Feed slag composition

[0183] Elements (wt%) analyze Cu 0.6 Pb 0.46 Sn 0.11 Ni 0.04 Fe 30.63 Si 0.00 Al 0.00 Zn 11.48 Bi 0.00 As 0.00 Sb 0.00 CaO 3.09 <![CDATA[SiO2]]> 25.07 <![CDATA[Al2O3]]> 6.88

[0184] For this process step, the power level per PG is set to 1400kW, which is approximately 437Nm per PG. 3 The average air flow rate of / h is used as the primary gas. In addition, the following secondary gases are used. The natural gas flow rate through the tuyere is controlled at 125Nm 3 / h. The air flow through the air outlet is controlled at 100Nm 3 / h level.

[0185] The total flow rate of primary and secondary gases through the additional injector as a second submerged injector was set to 380 Nm per injector. 3 / h air, natural gas at 44Nm 3 In this process step, the pulverized coal injection has not yet started.

[0186] Second process step: fuming step

[0187] After the liquid slag is filled, the fuming step begins. In this step, the input of energy and reducing agent is increased to promote the volatilization of zinc into vapor.

[0188] The power level of each PG is 2500kW, and the average primary air flow rate is 714Nm per PG 3 / h. In addition, the following secondary gases were used. Natural gas was added to each tuyere downstream of the PG and 3 The additional air flow through the tuyere was set to 100 Nm 3 / h.

[0189] The total flow rate of primary and secondary gas through the other injectors is 380 Nm per injector. 3 Air is supplied at a rate of 44 Nm / h in each injector. 3 The pulverized coal injection rate for each injector was set at 180 kg / h.

[0190] The input of energy and reducing agents causes the volatile compounds in the liquid slag to fume. The most volatile element is zinc, which is present in the slag as zinc oxide (ZnO). The temperature in the reactor is maintained in the range of 1180-1250°C to ensure that the slag remains fluid. The input of various reducing agents, namely pulverized coal and various natural gases, reduces ZnO to metallic zinc (Zn). At atmospheric pressure, Zn can evaporate at temperatures above 906°C. Zn is thus evaporated from the slag bath and transported from the furnace as part of the process gas to the furnace exhaust treatment equipment.

[0191] In the reactor's exhaust duct, a large amount of air is mixed with the process gas, subjecting it to a complete afterburning. Any remaining CO, Zn, and H₂ are completely oxidized in this step. Zinc in vaporous form is oxidized to ZnO, forming solid particles. This ZnO therefore forms dust in the combustion process off-gas stream. This secondary combustion, or afterburning, step is followed by a cooling step. At the cooling step outlet, the process gas temperature is below 220°C. The process gas is then filtered using a polytetrafluoroethylene cloth in a bag filter. After filtration, the process gas is discharged to the atmosphere via a chimney. The ZnO dust particles are recovered in the filter, cooled, and stored in a dust silo. From the silo, the zinc-rich dust product can be unloaded onto a silo truck for sale.

[0192] Samples are taken during the fuming process and analyzed using the fast but slightly less accurate XRF method. When the zinc content in the slag in the furnace reaches the desired level, fuming is stopped and the fine-tuning step begins.

[0193] The third process step: trimming

[0194] The purpose of this step is to oxidize the last remaining pulverized coal in the charge and heat the slag to a more suitable tapping temperature. The target temperature is 1220-1250°C.

[0195] Each PG is maintained at a power level of 2500kW, with an average primary air flow of 714Nm per PG. 3 / h. In addition, the following secondary gases are used. The natural gas flow rate through the tuyere is set to 102Nm 3 / h. The air flow through the air outlet is set to 100Nm 3 / h.

[0196] Each of these second submerged injectors was supplied with 380 Nm2 of gas as the total flow of primary and secondary gas through the additional injectors. 3 / h of air and 44Nm 3 / h of natural gas. During this fine-tuning step, pulverized coal injection was stopped.

[0197] After the fine-tuning step is completed, no slag sampling is taken. Slag tapping begins immediately.

[0198] The fourth process step: slagging and granulation

[0199] The purpose of this step is to extract the liquid slag from the reactor. A tap hole located on the side of the reactor is drilled to allow the liquid slag to flow from the reactor into a launder. From this launder, the slag product is granulated by a water granulation system, in which large amounts of water are sprayed into the falling slag stream, solidifying the liquid slag and breaking the resulting solid into particles of ±1 mm.

[0200] During the deslagging and granulation steps, the PGs continued to operate at a power level of 2000 kW each, with an average primary air flow of 606 Nm per PG. 3 / h. As the secondary gas, the natural gas flow rate to the tuyere is set to 128Nm 3 / h, and then set the air flow directly to the air outlet to 100Nm 3 / h.

[0201] Additional injectors also continue with a total of 380 Nm per injector for primary and secondary gas. 3 / h rate of air and 44Nm 3 / h of natural gas operation. Pulverized coal injection was stopped.

[0202] The final product after granulation was sampled and its composition was found to be close to that of the slag after the fuming step.

[0203] Further operating parameters of the PG in each process step are shown in Table 2, where "enthalpy" is calculated from the input power of the PG and the air flow rate fed to the PG.

[0204] Table 2: PG operating parameters

[0205]

[0206] The evolution of the slag composition during the batch is shown in Table 3, which shows the analysis results of the slag samples taken after each step:

[0207] Table 3: Evolution of slag composition

[0208] Elements (wt%) Feed After filling After smoke After granulation Cu 0.6 0.57 0.48 0.42 Pb 0.46 0.44 0.03 0.025 Sn 0.11 0.10 0.08 0.07 Ni 0.04 0.05 0.03 0.03 Fe 30.63 30.80 35.63 35.8 Zn 11.48 11.08 1.64 1.58 CaO 3.09 3.10 3.78 3.75 <![CDATA[SiO2]]> 25.07 25.15 29.64 29.82 <![CDATA[Al2O3]]> 6.88 6.95 7.58 7.74

[0209] Output material composition

[0210] This batch produced approximately 10,500 kg of filter dust, the composition of which is shown in Table 4, which is the result of ICP analysis of a representative sample:

[0211] Table 4: Composition of filtered dust products

[0212]

[0213]

[0214] For comparison, a second batch was run during which no additional tuyeres were installed. To provide a similar amount of reducing agent in the fuming step, the same amount of carbon was introduced by introducing crude petroleum coke having a particle size in the range of 6-10 mm through the feed port.

[0215] The amount and composition of the liquid slag feed are very similar to those of the first batch, as are the feeding time, fine-tuning time, and slag discharge time. The main difference is the fuming time.

[0216] The amount and composition of the granulated product and the filtered dust were similar.

[0217] In this comparative batch, the time required for the fuming step to achieve a very similar zinc content in the final slag was significantly higher than in the batch according to the present invention described above. This means that the comparative batch had a significantly lower zinc fuming rate compared to the working example, and therefore, the present invention significantly increased the zinc fuming rate during the fuming step.

[0218] Example 2

[0219] In this Example 2, the same furnace as in Example 1 was used, but with a different configuration with respect to the second submerged gas injection. The supply of natural gas and its quality were the same.

[0220] At the same level or height of the three plasma generator-tuyere combinations, only one additional injector-tuyere combination is provided this time as a single second submerged injector for injecting additional gas and fine coke into the furnace. The tuyere is water-cooled and the air is supplied at 350-400 Nm 3 The gas was passed through the tuyere at a constant rate of 1 / 2 hour and then injected through the holes in the inner wall of the tuyere. No natural gas supply was used in this embodiment.

[0221] The injectors located in the additional injector-tuyeres combination supply additional gas to the liquid slag bath in a direction perpendicular to the furnace wall. During operation, the feed rate to the additional injectors is 100-400 Nm 3 / h of compressed air as the primary gas, and where appropriate, about 100-700 kg / hr of pulverized coal as an additional reducing agent was mixed into this additional injector. The average particle size of the pulverized coal was 120 μm. The pressure of the compressed gas upstream of the second submerged injector assembly was 6 bar gauge.

[0222] The gas velocity in the other injector-tuyere combinations was typically higher than 150 m / s during operation.

[0223] First process step: Liquid filling of the furnace:

[0224] The same procedures, qualities and amounts as for this step as part of Example 1 were used with the following exceptions.

[0225] The flow rate of secondary gas through a single additional tuyeres as part of a single additional injector-tuyeres combination was set to 350 Nm 3 / h of air and no natural gas was added. The primary gas flow rate through the additional injector as part of a single additional injector-tuyeres combination was set to 200 Nm 3 / h of air. In this process step, fine coke injection has not yet started.

[0226] Second process step: fuming step

[0227] The same procedure as in Example 1 was applied.

[0228] Again, the power level of each PG is 2500kW, and the average primary air flow rate is 714Nm per PG. 3 / h. In addition, the following secondary gases were used. Natural gas was added to each tuyere downstream of the PG and 3 The air flow rate through the tuyere is set to 100 Nm 3 / h.

[0229] The secondary gas flow rate through the additional tuyere as part of a single additional injector-tuyere combination is 350 Nm 3 / h of air, to which no natural gas was added. As primary gas, the flow rate through the additional injector as part of the additional injector-tuyeres combination was set to 200 Nm 3 In this process step, the fine coke injection is set at 700 kg / h.

[0230] The temperature in the reactor is maintained in the range of 1180-1250°C, ensuring that the slag remains fluid. The input of various reducing agents, namely pulverized coal and various natural gases, reduces ZnO to metallic zinc (Zn). The Zn evaporates from the slag bath and is transported from the furnace to the furnace exhaust treatment equipment as part of the process gas.

[0231] Samples are taken during the fuming process and analyzed using the fast but slightly less accurate XRF method. When the zinc content in the slag in the furnace reaches the desired level, fuming is stopped and the fine-tuning step begins.

[0232] The third process step: fine-tuning

[0233] The target temperature is again 1220-1250°C.

[0234] The PGs are each maintained at a power level of 2500kW, with an average air flow of 714Nm per PG. 3 / h. In addition, the following secondary gases are used. The natural gas flow rate through the tuyere is set to 102Nm 3 / h. The air flow through the air outlet is set to 100Nm 3 / h.

[0235] The secondary gas flow rate through the additional tuyere as part of a single additional injector-tuyere combination was set to 350 Nm 3 / h of air and no natural gas was added. The primary gas flow rate through the additional injector as part of a single additional injector-tuyeres combination was set to 200 Nm 3 / h of air. Fine coke injection has not yet been started in this process step.

[0236] After the fine-tuning step is completed, no slag sampling is taken. Slag tapping begins immediately.

[0237] The fourth process step: slagging and granulation

[0238] The same procedure as in Example 1 was applied.

[0239] During this deslagging and granulation step, each PG again continued to operate at a power level of 2000kW, with an average primary air flow rate of 606Nm per PG. 3 / h. As a secondary gas, the natural gas flow rate is 128Nm 3 / h to the air outlet, the air flow is 100Nm 3 / h directly to the air outlet.

[0240] The secondary gas flow rate through the additional tuyere as part of a single additional injector-tuyere combination is 350 Nm 3 / h of air and no natural gas was added. The primary gas flow rate through the additional injector as part of a single additional injector-tuyeres combination was set to 200 Nm 3 / h of air. Fine coke injection has not yet been started in this process step.

[0241] The final product after granulation was sampled and its composition was found to be close to that of the slag after the fuming step.

[0242] The further operating parameters of PG in each process step are the same as those shown in Table 2 of Example 1.

[0243] The final results of this example are very similar to those of example 1, except that they were again obtained in a shorter time than the batch carried out for comparative reasons as part of example 1.

[0244] Applicants have found that by implementing the methods according to the present invention and also in Example 2, a significant increase in production rates can be established. Applicants believe that this effect is due to a combination of: (i) higher bath agitation, (ii) more stripping gas, (iii) more reducing agent, and perhaps most importantly (iv) the use of a solid reducing agent with a smaller particle size, whereby the reducing agent is more reactive. This effect allows the target fuming operating conditions to be reached more quickly than with crude petroleum coke. The combination of these beneficial effects allows the fuming step to be much faster when fully operational, as shown by the much faster increase in the amount of heat that needs to be removed from the afterburning zone, and also allows the fine-tuning step to be significantly reduced in time, almost an order of magnitude, since the time required can be reduced from about a quarter of an hour to as little as 2-3 minutes. Fuming furnaces employing a second submerged injector can be operated more stably, with greater throughput, and closer to the maximum value of their capabilities.

[0245] Having now fully described the present invention, those skilled in the art will appreciate that the present invention can be implemented within a wide range of parameters within the scope of the claims without departing from the scope of the invention defined by the claims.

Claims

1. A single-chamber furnace for fuming at least one vaporizable metal or metal compound from a metallurgical charge, the single-chamber furnace comprising a bath furnace adapted to accommodate a molten charge up to a determined level, wherein the furnace is equipped with at least one non-transferred plasma torch for generating a first hot gas of plasma quality, and at least one first submerged injector for injecting the first hot gas from at least one of the plasma torches below the determined level, wherein the furnace further comprises an afterburning zone, a cooling zone, and a recovery zone downstream of the cooling zone, the afterburning zone being downstream of the furnace roof for oxidizing the at least one vaporizable metal or metal compound in the fuming gas to form an oxidized form of the at least one vaporizable metal or metal compound, the cooling zone being for cooling the gas formed in the afterburning zone, the recovery zone being for recovering the oxidized form of the at least one vaporizable metal or metal compound from the gas formed in the afterburning zone and cooled in the cooling zone, characterized in that The furnace is further equipped with at least one second submerged injector, different from at least one of the first submerged injectors, for injecting additional gas into the furnace below the determined level, the additional gas being a gas in addition to the amount of plasma-quality first hot gas generated by at least one of the non-transferred plasma torches and injected by at least one of the first submerged injectors during operation.

2. The furnace according to claim 1, wherein At least one of the second submerged injectors directs additional gas of at least one of the second submerged injectors toward a second volume, the second volume being part of the interior space of the furnace below a predetermined level, the second volume being different from the first volume toward which at least one of the first submerged injectors directs the plasma-quality first hot gas.

3. The furnace of claim 1 , comprising at least two first submerged injectors distributed along the horizontal perimeter of the furnace side wall, wherein At least one of the second submerged injectors directs additional gas of at least one of the second submerged injectors toward a volume that is part of the interior space of the furnace, said volume being below a predetermined level, close to the vertical axis of the furnace, and / or at least one of the second submerged injectors being located at an equal distance along the side wall of the furnace between the positions of two nearest first submerged injectors of at least two of the first submerged injectors.

4. The furnace according to claim 1, wherein The cooling zone includes a radiant water cooler followed by a spray cooler.

5. The furnace according to claim 1, wherein The recovery zone includes a gas filtration zone.

6. A method for fuming at least one vaporizable metal or metal compound from a metallurgical charge using a furnace according to claim 1, comprising the steps of: introducing a metallurgical charge comprising said at least one vaporizable metal or metal compound into said furnace and forming a bath of molten charge up to a determined level; fume a quantity of said at least one vaporizable metal or metal compound from said bath using at least one reducing agent and a plasma-quality first hot gas from at least one plasma torch to produce a fume gas comprising said vaporizable metal or metal compound; post-combustion said fuming gas in said post-combustion zone to oxidize said at least one vaporizable metal or metal compound into an oxidized form of said at least one vaporizable metal or metal compound, extracting from said furnace the gases formed in said furnace and recovering, in said recovery zone, said at least one oxidized form of a vaporizable metal or metal compound from the gases formed in said post-firing step; Characterized in that during at least part of the fuming step, additional gas is injected into the bath by at least one second submerged injector and below a determined level, thereby increasing the amount of fumes comprising vaporizable metals or metal compounds.

7. The method according to claim 6, wherein: The furnace comprises a plurality of second submerged injectors, and wherein the amount of additional gas injected through each second submerged injector is at least 10% of the amount of first hot gas, the first hot gas amount having an enthalpy content expressed in volume units under normal conditions of at least 3.5 kWh / Nm 3 The first hot gas can be generated by a single element with the highest rated power in the at least one plasma torch.

8. The method according to any one of claims 6 to 7, wherein The additional gas injected through the at least one second submerged injector is subjected to a heat treatment upstream of the at least one second submerged injector to change the enthalpy content of the additional gas.

9. The method according to any one of claims 6 to 7, wherein: The additional gas injected through the at least one second submerged injector includes at least one first reducing agent.

10. The method according to any one of claims 6 to 7, wherein: The at least one vaporizable metal or metal compound is a metal or a vaporizable metal-containing compound in elemental form of the at least one vaporizable metal or metal compound.

11. The method according to any one of claims 6 to 7, wherein: The oxidized form of the at least one vaporizable metal or metal compound is recovered from the gas as dust.

12. The method according to any one of claims 6 to 7, wherein: The metallurgical charge is a metallurgical slag, and wherein the method produces a secondary slag.

13. The method according to claim 12, further comprising the step of cooling the second slag into a solid state.

14. The method according to claim 13, further comprising the step of adding said second slag as a component selected from the group consisting of a binder and an aggregate during the manufacture of an object for use in the construction industry.

15. Use of the furnace according to claim 1 for fuming at least one vaporizable metal or metal compound from a metallurgical charge.

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