CZ297878B6 - Method of treating metalline waste containing zinc in revolving furnace - Google Patents

Abstract

The present invention relates to a method of treating metalline waste containing zinc, lead and cadmium with total amount of these element greater than 5 percent, such as sludge and powder waste from steel manufacture, in a revolving tube furnace or an array of revolving tube furnaces in a batch or continuous process using fossil fuels in reduction and optional melting of metalline waste. Treatment of metalline waste containing zinc, lead and cadmium is carried out by reduction with carbon and namely: either by reduction in solid state with melt ratio in the reduced mixture of oxides less than 20 percent and maximum temperature of the reduction less than 1200 degC; or by reduction in semi-liquid state with melt ratio in the reduced mixture of oxides less than 60 percent and at a temperature of the reduction higher than 115O degC but less than 1350 degC; wherein metal reduced during reduction is carburized with excess of carbon in the reduced charge; or by reduction in liquid state with melt ratio in the reduced mixture of oxides higher than 60 percent but less than 96 percent and at a temperature of the reduction higher than 1250 degC but less than 1650 degC wherein the reduction is carried out on the level of iron melt with higher content of carbon. A device for making the above-described method comprises one or several revolving tube furnaces arranged in an array. The furnaces differ according to waste treatment process by the L/D proportion, wherein L represents length of the furnace and D denotes inside diameter of the furnace, whereby the furnaces for continuous treatment process are longer and have the L/D proportion of at least 10, and for the batch treatment furnaces the L/D proportion is not greater than 8 and wherein the interior of the furnace, filled with waste up to 40 percent of the furnace total inside volume, forms two distinctly separated zones, and namely a first zone with reducing environment and a second zone with oxidizing environment.

Description

Technology of processing of metal-bearing wastes containing zinc in rotary kiln

Technical field

BACKGROUND OF THE INVENTION The present invention relates to a method and apparatus for the treatment of metal-bearing wastes containing zinc, cadmium lead having a total content of these elements of greater than 5%, for example sludge and dust from steel production. The basis of the solution is that the wastes are treated in a rotary kiln or in a battery of rotary kilns in which the carbon reduction is carried out either in a liquid, semi-liquid or solid state. The rotary kiln is filled with treated waste up to a maximum of 40% of the total internal volume of the furnace, allowing free flow of gases over the charge and easy removal of zinc, lead and cadmium-rich dust components from the furnace. This process is carried out while maintaining the increased overall thermal efficiency of melting of metal-bearing raw materials, while reducing the investment intensity of the process and reducing the environmental burden on the environment. The product of the process is directly reduced iron, dusts rich in zinc, lead and cadmium and inert slag.

BACKGROUND OF THE INVENTION

A number of waste treatment processes are being developed worldwide. This indicates growing problems with the processing of metal-bearing wastes and increasing pressure on the ecology of metallurgical processes. However, there is still no clear winner in waste treatment technology. There are the following solutions:

• Direct reduction in rotary carousel furnace in Japan mastered for wastes with higher iron content for industrial realization, development in this direction is stopped in Europe • Melting processes in electric arc furnace especially in Europe, which is the current trend • Reduction and melting in rotary furnace is in the development stage

Based on current knowledge it is possible to state that nowadays the following various technologies are being finished or industrially tested for processing of ores and metal-bearing wastes. These processes are mostly focused on processing rich ores. The production of these devices makes them suitable for the commercial production of directly reduced products.

The ZERO WASTE process is a steel slag processing technology with the aim of reducing easily reducible oxides (iron and manganese and, in the case of stainless steel wastes, chromium, nickel and molybdenum) and adjusting the slag composition to make it suitable as a hydraulic binder. The process produces some savings in CO ₂ production. Everything takes place in a furnace similar to a ladle furnace. This technology was investigated in a pilot project in VÍTKOVICE - Engineering. Technical problems are the durability of the injection tubes, the control of slag flowability and the shape and design of the furnace.

In 2000 the PRIMUS process was put into trial operation. This technology is currently used for processing dust from EOP and rolling mill scale. The process uses a rumble multi-story oven, often called Herreshoff-Wedgen; this type of furnace was often used in the past for roasting ores. The material is continuously fed to the center of the platform on the top floor of the furnace and the scraper gradually rakes it and transports it to the perimeter where it falls to the lower floor. The furnace is divided in height into several sections in which the respective chemical reactions take place according to the temperature. Drying takes place in the upper part of the furnace. In the middle part there is preheating, evaporation of oils and calcination. In the lower part of the furnace with the highest temperature, zinc and lead are reduced and evaporated. These metals are then grown and leave the process in the form of dust. After a year of operation, the design capacity of the equipment was not achieved. This is due to the recalcination of iron oxides in the region where the distillation of oils and volatile constituents of coal is complete. In this recalcination, ferrous carbonate is adhered to the rake, thereby disrupting the flow of material in the furnace.

-1 CZ 297878 B6

NIPPON STEEL has developed a melting and reduction process in a shaft furnace - the NSC process. The source of heat is municipal waste. In the shaft furnace, waste is melted and vitrified. The process is connected to the use of outgoing gases with a high content of chemical heat. The equipment is widely used and is used for municipal waste treatment. Feeding at different levels of the shaft should be considered important.

In the Comet production method, the basic device is a rotary hearth fumace (RHF). The hearth moves in the center of the circular furnace tunnel and is continuously covered with a thin layer of dried material, alternately crushed coal and fine iron ore. For desulphurisation, coal is mixed with a small amount of limestone or slaked lime. During the solution of the project to expand the production capacity of the pilot plant to a 750 kt / year production plant, a number of hard-to-overcome problems arose. The temperatures in the hearth of the rotary carousel have reached 1425 to 1520 ° C. The dust generated in the process at such high temperatures reacts with the lining and leads to its rapid degradation. Also, sufficient process stability was not achieved before the planned increase in equipment, which was supposed to be about 50 times.

Midrex, together with Kobe Steel, has developed its own ITMK3 metal waste reduction process in a rotary carousel kiln. The pilot plant is built in Kakogawa Works and has a hearth diameter of 4 m. However, this process is in its inception. This corresponds to a relatively small pilot equipment. The idea of separating the slag and metal phases in the semi-liquid state is very interesting. From a technical point of view, it is particularly demanding for the preparation of pellets and stabilization of their chemical but also phase composition. Another problem, however, is the possibility of the interaction of the slag phase with the hearth of the furnace hearth.

The OXYFINE process is used for sintering and drying of dusty materials. The process makes it possible to process conveyable sludge both pneumatically and by a sludge pump. The principle is based on the injection of waste into the center of the oxy-gas burner flame. The material melts and the flammable components burn. The oxidation rate is low. In this way, for example, subnets from the production of FeSi are processed. During the treatment of the waste, the solid particles are melted and a slag accumulates at the bottom of the reactor. Dry and wet wastes up to 65% moisture can be melted on the burner. The decisive factor for proper functioning is the perfect dispersal (atomisation) of the treated waste.

The CONTOP process is basically a melt cyclone - that is, it is a device for melting at very high temperatures (around 1800 to 2000 ° C). It is designed for melting metals and oxides. It does not allow reduction directly in the aggregate. It is planned to extend the cyclone with a fixed hearth where possible reduction would be possible. The equipment is designed for working hazardous wastes whose liquidity causes considerable problems. These are mainly paint residues and other organic waste. These wastes also serve as a heat source.

The low-shaft furnace TECNORED has been developed in cooperation with DANIELI-CORUS as an alternative way of producing pig iron without the use of coke. This method is also declared to be suitable for waste treatment. This technology takes advantage of long-term experience in the development of low-shaft furnaces in the GDR and, at the same time, in Belgium in the Uiège at the age of 50. Research in this field is still ongoing. Application of self-reducing pellets and shaft branching can be considered as the main advantage. The preparation of hot wind during waste processing with higher zinc content can be considered problematic. The treatment of zinc wastes leads to very high dust contents and will worsen heat transfer conditions in recuperators. Also, data on the interaction of dust with the charge and on reducing the throughput of the furnace are not published.

The OXYCUP process was invented by Kuttner in cooperation with Thyssen and is based on a modified cupola furnace. This device is very suitable for remelting bars, but processing of sludges with higher Zn content is very complicated. In cupola furnaces, the removal of Zn from metal-bearing wastes is difficult due to the low boiling point of the metal and the high boiling point of the oxides. Zinc metal vapors easily condense and oxides are always in the solid state at metallurgical temperatures. Oxidation of Zn vapors leads to another very unpleasant solid oxide property because of the oxidized zinc vapor

-2GB 297878 B6 forms a very fine dust that adheres to virtually all surfaces. The intrinsic mechanisms of Zn and Pb behavior are very complex. These elements are not only present in the sludge in the form of oxides or metals. Their forms are much more complex interactions arise between zinc and iron oxides and the whole situation is further complicated by the presence of chlorides and fluorides.

A known process for ore processing in a rotary kiln is the technology used to reduce iron and ore. There are various designs of the inner furnace cylinder, whereby iron reduction can occur in both solid and liquid state. The best known method, however, is the reduction in the dough state, the so-called clumping. Here the furnace is longer and thus the temperature at the outlet end of the furnace is higher. Under suitable conditions, larger particles of reduced iron, which are called lumps, will be formed. The whole process is called clumping, and the furnace zone in which it runs is called clumping zone. The lump requires a higher temperature of 1250 to 1300 ° C and assumes a choice of retention ring at the end of the furnace in order to achieve a balanced reduction and oxidation environment so that the lumps can form. Some slag viscosity is required to form the lumps so that the lumps do not drop to the lining and stick to it. Some acidity of the slag must also be guaranteed - so lumping is particularly suitable for processing more acidic ores. A characteristic feature of all lumps is that 60 m long furnaces are operated with an external diameter of 3.6 m. It rotates approximately once per minute. However, there are also larger furnaces in the world. The size of the lumps then depends on the viscosity of the slag and the length of the lump zone, with a maximum of 2 to 8 mm under optimal conditions. The biggest problems here are the productivity of the march and the lower durability of the linings. Possibilities of further processing are given by their composition. They are usually higher in phosphorus and sulfur and are especially suitable as an additive to blast furnaces. They can be used for adding to electric furnaces, but at the expense of increasing the time for de-phosphorizing and desulphurisation. Melting of the lumps was also tested in a drum furnace, with desulfurization being treated with solid lime.

The advantages of rotary kilns have led to a number of technologies and patents in the iron and steel industry. The following patent documents are known in the steel industry:

EP 0134336 discloses the use of a rotary kiln in conjunction with secondary metallurgy and continuous steel casting.

EP 0933436 describes the use of a rotary kiln for melting, preheating directly reduced iron and its desulphurization.

WO 94/11536 discloses a continuous rotary kiln divided into two sections. The first section serves for preheating and melting, and the second section for heating the melt to the desired temperature. The apparatus is equipped with carbon injection into the melt in the second section.

WO 95/29137 discloses an apparatus for removing slag from metallurgical aggregates, for example rotary kilns.

WO 99/60172 discloses a continuous rotary kiln divided into two sections. The first section serves for preheating and melting, and the second section for heating the melt to the desired temperature. The apparatus is equipped with carbon injection into the melt in the second section. At the end of the second section a vacuum device is connected with which molten steel can be pumped from the rotary kiln.

US 4 105 438 discloses a rotary kiln apparatus and method for evacuating molten metal by vacuum.

US 3 991 987 describes the connection of a rotary kiln to an electric arc furnace. In the rotary furnace, the melt itself is heated to the desired temperature.

-3GB 297878 B6

US 3,514,280 discloses an apparatus for the continuous production of steel by melting in a rotary kiln. This rotary kiln is equipped with a pair of burners located on opposite sides of the kiln. The metal flows from the furnace continuously through a siphon device.

US 4,062,674 describes the use of a high speed rotary kiln for the production of iron and steel. The speed of rotation of this furnace is such that the centrifugal force holds the charge on the inside of the shell.

US 3,689,251 discloses a rotary kiln system for direct reduction and subsequent melting and processing of a steel melt.

US 5 163 997 discloses an apparatus for the continuous production of steel by melting in a rotary kiln. This rotary kiln is divided into two zones and is equipped with a pair of burners located on opposite sides of the rotary kiln. The burner on the planting side is used to set up and preheat the solid charge. WO 91/07127 discloses a rotary kiln for the incineration of hazardous waste followed by melting the resulting slag.

EP 0442040 discloses a pellet reduction device.

EP 0982407 discloses an apparatus for melting inorganic substances under their flame injection.

The following patent documents are known for use in the foundry industry:

US 5,141,208 discloses joining two furnaces in series, one serving as a melting aggregate and the other for preheating.

EU 067387 describes furnaces which are commonly used in foundry industry.

After 2000, interest in rotary kilns in the USA continues.

US 2001/6012 discloses an apparatus for continuously melting metal in a rotary kiln. The machine is equipped with a series of nozzles, burners and a batch conveyor that allows continuous production. The device utilizes the flue gas heat from the melting zone in the charge preheating zone.

US 2002/130448 discloses a very complicated device associated with a single rotary kiln for the direct production of pig iron or steel from ore. The equipment consists of a reduction reactor in which the reduction of oxides in the gas phase takes place. The reduction reactor may be, for example, a shaft furnace, the author admitting all known methods of direct reduction in the gas phase. The partially reduced product is in the hot state transferred to a long rotary kiln in which the reduction and melting are completed. Decarburization is also possible in this apparatus. It is therefore a universal device of the continuous type, in which the individual phases of the process are clearly separated in individual zones.

EP 0441052 and US 5,188,658 disclose an apparatus for treating zinc-containing waste materials in an electric arc furnace. In addition to the waste treatment unit, this patent differs in the furnace atmosphere. Rather, a reducing atmosphere is maintained in the furnace and the CO ₂ to CO ratio is kept below 0.3. Evaporated zinc and other volatile metals are trapped in metallic form.

CZ 295780 is engaged in the production of steel in a rotary furnace, including the processing of metallurgical wastes on iron melt with higher carbon content. This technology is limited to batch processing with a maximum waste content of 50%. The product of the process of this patent patentes liquid metal for post-processing on technologies common in existing steel mills. The treatment of a batch with a lower waste content reduces the zinc content of the dust collectors.

-4GB 297878 B6

SUMMARY OF THE INVENTION

SUMMARY OF THE INVENTION The present invention relates to a process for the treatment of metal-bearing wastes from the production of zinc-containing steel by means of fossil fuels and oxygen or oxygen-enriched preheated air in a rotary oven. The proposed method consists in reducing metal-bearing wastes from the production of steel containing zinc, lead and cadmium with a total content of these elements greater than 5% in a rotary kiln or battery of rotary kilns in a batch or continuous manner under intensified heat transfer conditions. Such conditions can be created in a rotary kiln in which the heat source is fossil fuels and oxygen or oxygen-enriched air. The production of the device is ensured by the size or number of rotary oven furnaces by a battery arrangement. Good heat transfer is ensured by mixing the charge.

Waste treatment produces three products:

• directly reduced iron in the form of an iron sponge, lumps or in a liquid state;

• dusts rich in lead and cadmium zinc oxides with a total content of more than 30%; and • inert slag suitable for further use in construction.

Process for processing metal-bearing wastes from steel production using fossil fuels and oxygen or oxygen-enriched preheated air in a rotary oven. Metal waste processing is carried out in a rotary kiln or rotary kiln battery, with the rotary kiln being filled with treated waste up to a maximum of 40% of the total internal furnace volume, allowing free gas flow over the charge and easy removal of zinc, lead and cadmium rich dusts. from the furnace. In this way, distinct zones are formed, namely a zone with a reducing environment, which is the part of the furnace in which the charge is present in the condensed phase, in the presence of carbon and carbon monoxide; and a zone with an oxidizing medium, which is the portion of the furnace above the charge, in which the gaseous products of the reduction occur, the combustion of fossil fuels with oxygen and the oxidation of the vaporized metals leaving the furnace in the form of dusts. The free oxygen content in the exhaust from this zone is at least 2%.

The actual reduction process in the rotary kiln ensures the separation of slag, iron and dust-rich dusts for zinc, lead and cadmium suitable for further processing, the ZnO content of dust-dusts being higher than 30%. The required temperature is ensured by means of an oxygen burner for which hydrocarbons or pulverized coal are used as fuel. The high efficiency of the process is ensured by the intensive heat transfer, which leads to an increase in the overall thermal efficiency of heating, reducing and eventually melting the metal-bearing wastes.

The treatment of metal-bearing wastes is carried out by reducing the metal-containing wastes containing zinc, lead and cadmium by carbon, either by solid state reduction or by semi-liquid state reduction or by liquid state reduction.

The solid state reduction is carried out with a melt content in the reduced oxide mixture of less than 20% and a maximum reduction temperature of less than 1200 ° C. The basicity of the ballast oxides, such as CaO, SiO ₂ , MgO and Al ₂ O ₃ , is adjusted so that the CaO to SiO ₂ ratio is greater than 1.5, allowing desulfurization. The whole process is very sensitive to slag composition. In the waste treatment process, carbon in powder form is added to the solid state reduction mixture so as to ensure contact between oxides and carbon upon mixing, and where the reduction can take place continuously or batchwise. The productivity of the plant depends on the reduction temperature and the fineness of the added wastes, reducing substances and slag-forming additives; in this case, the productivity is less than 0.08 t per 1 m ^{3 of} internal furnace volume per hour. The reduced metal is subsequently separated by magnetic separation and, after magnetic separation, is briquetted or used directly in the steel mill as a scrap replacement or for enrichment of the charge in a blast furnace.

The semi-liquid reduction with a melt content in the reduced oxide mixture of less than 60% is carried out at a temperature of more than 1150 ° C and less than 1350 ° C. The reduced metal is carburised through

This leads to a reduction in the melting point of the reduced metal below the reduction temperature, and the carburized metal droplets in the highly viscous slag gradually merge into nuggets larger than 2 mm in size. allows slag with a CaO to SiO ₂ ratio in the range of 0.05 to 0.7 and with a MgO and Al ₂ O ₃ content not exceeding 30% of the total ballast content. These ballast substances are dough-like and have a high viscosity. The slags do not allow substantial desulphurisation and the sulfur partition coefficient between the slag and the metal is less than 10. The dust mixture is added to the reduction mixture so as to ensure contact between the metal oxides and the carbon when mixed with the waste and where the reduction can take place continuously; in a batch manner. The productivity of the plant depends on the reduction temperature and the fineness of the added wastes, reducing substances and slag-forming additives; in this case, the productivity is less than 0.15 t / m ^{3 of} internal furnace volume per hour. The reduced metal is separated by magnetic separation, and after magnetic separation it is briquetted or used directly in the steel mill as a replacement for scrap or for enrichment of the charge in a blast furnace.

The liquid reduction with a melt content in the reduced oxide mixture of greater than 60% and less than 95% and a reduction temperature of greater than 1250 ° C and less than 1650 ° C is carried out at the iron melt level with higher carbon content, with the mixture of oxides is selected such that the CaO to SiO ₂ ratio is in the range of 0.5 to 1.5, optimally around 1.2, and the MgO content does not exceed 20%, and the Al ₂ O ₃ content does not exceed 40% of the total ballast content such that the melt permits the escape of gaseous reduction products in the form of bubbles. Carbon is added to the iron melt below the metal level by means of an injection nozzle which is also used as a mixing device. After reduction, the slag is stripped off and part of the melt is decanted. The treated melt is again added to the remaining melt. The reduced metal is separated from the slag by gravity separation of the slag and the molten metal, and the liquid metal is then treated by conventional methods, for example by casting or directly as a liquid feed for the steel aggregate. When reduced in the liquid state, the productivity is less than 0.3 t per 1 m ^{3 of} internal furnace volume per hour.

The apparatus for carrying out a method of treating metal waste containing zinc, lead and cadmium with a total content of these elements greater than 5% according to the invention consists of one or more rotary oven furnaces arranged in a battery to achieve suitable capacity for the treatment of The batch is added either continuously, which means that the metal-bearing waste containing zinc, lead and cadmium is added to the rotary kiln for at least 60% of the reduction time, or the rotary kilns operate in batch mode. Furnaces differ according to the waste treatment process by the ratio of L / D, where L is the length of the furnace, and D is the inside diameter of the furnace, with continuous furnaces having a L / D ratio of at least 10. / D value 8. Furnace interior filled with waste not more than 40% of the total furnace volume creates two distinctly separated zones, where the first zone with reducing environment is the part of the furnace in which the condensed phase feedstock contains carbon and carbon monoxide wherein the second zone with the oxidizing medium is the portion of the furnace above the charge in which the gaseous products of the reduction are grown, fossil fuels are oxygenated, and the vaporized metals are leaving the furnace in the form of dusts; at least 2%.

The main advantage of the process according to the invention is the direct exploitation of the chemical potential of fossil fuels for heating the charge, reducing it and possibly melting it. Technical solution with separate space with oxidizing and reducing atmosphere allows full utilization of chemical heat of fuel. Furthermore, the rotary oven makes it possible to increase the overall thermal efficiency since this arrangement ensures a very good heat transfer. The main difference from conventional methods of direct reduction in a rotary kiln is the harmonization of the technological process with feed materials rich in volatile components such as zinc and lead and optimization of the slag regime according to the temperature and type of reduction carried out and further production of three products directly reduced iron, zinc concentrate and inert. slags. In particular, the possibility of directly producing zinc concentrate distinguishes this process from other ore processing processes in rotary kilns. From a constructional point of view, the advantage is to create a relatively small compact waste treatment unit while reducing the investment costs

-6E 297878 B6 process simplification compared to other known waste treatment processes. In the case of a battery arrangement of melting units, the advantage is the optimum utilization of the capacity of the waste gas treatment plant, typesetting equipment and the like. The multi-unit concept allows a tandem arrangement suitable for preheating. From a technological point of view, the advantage of the proposed process is the direct exploitation of the chemical potential of fossil fuels for the processing of metal-bearing wastes and that the process allows to control the degree of contact of the solid charge with the flue gas.

Overview of the figure in the drawing

Figure 1 shows an example of a solid state reduction process.

In the initial heating phase, the waste is slightly oxidized and the Fe ₂ O ₃ content increases. After reaching the temperature of 900 ° C the reduction process is relatively fast and after a time slightly exceeding 2 hours approximately 90% metallization is achieved.

DETAILED DESCRIPTION OF THE INVENTION

EXAMPLE 1 Treatment of Metal Waste by Solid State Reduction in a Rotary Furnace Batch Process

The equipment and technology is designed so that the process achieves optimum thermal efficiency and limits the oxidation of the charge and the already reduced material to the minimum necessary. For this solution it is necessary to ensure a high flame temperature, intensive heat transfer and strong reducing conditions in the furnace. Both of these requirements are achieved in the proposed plant. The high flame temperature is achieved by burning the fuel with oxygen or with preheated oxygen enriched air. The reducing environment is achieved by the addition of pulverized coal, anthracite, coke or semi-coke, or substances with a high carbon content. The reducing agent is added to the charge with excess. The reduction temperature in this case does not exceed 1200 ° C.

Intense heat transfer is achieved by a combination of several heat transfer mechanisms. These include:

• direct heating of the charge by flame at its low surface temperature;

• flame radiation on the charge and lining after reaching the surface temperature of the charge 900 ° C;

• other heat transfer mechanisms caused by the rotating furnace:

o agitating the charge to ensure the transfer of the relatively cold charge to the surface and the heated charge from the surface to the charge volume;

o the heated charge is brought into the volume by stirring, where it transfers heat to the surrounding cooler charge;

o transfer of heat from the heated lining to the charge upon contact of the lining with the charge.

The proposed process therefore consists in reducing the solid charge of metal-bearing wastes containing zinc, lead and cadmium with a total content of more than 5% by means of fossil fuels in conditions of intensified heat transfer. Such conditions are created in a rotary oven. The heat transfer is ensured by mixing the charge and the large heat transfer-charge area is heated not only from above but also from below.

The treatment of metal-bearing wastes is similar to the processing of ores in rotary kilns. The process differs from the ore processing by the high zinc content in the feed and the high amount of dusts exceeding 10% of the wastes charged, as well as the design furnace, which in this case has an L / D (furnace length / furnace diameter) ratio of less than 8. Processing time of metal-bearing wastes

Depending on how the batch is mixed with the carbon-based reducing agents, it varies from 0.5 hours to 20 hours. An example of the metallization process is shown in Figure 1. After the initial heating stage, rapid reduction occurs. The heating and reduction time is given by the utilized volume of the furnace and with decreasing utilization the time decreases. The degree of reduction achieved is greater than 60%. The degree of reduction is given by economic optimization. A higher degree of reduction leads to higher energy costs, but does not substantially affect the degree of removal of zinc, lead and cadmium. The reduced material is discharged from the furnace to a cooler where the reduction product is cooled under conditions of limited oxygen access. Subsequently, the reduction product is mechanically treated for subsequent magnetic separation.

Example 2 Treatment of Metal Waste by Solid State Reduction in a Rotary Furnace Continuously

The equipment and technology is designed so that the process achieves optimum thermal efficiency and limits the oxidation of the charge and the already reduced material to the minimum necessary. For this solution it is necessary to ensure a high flame temperature and intensive heat transfer and strong reducing conditions in the furnace. Both of these requirements are achieved in the proposed plant. The high flame temperature is achieved by burning the fuel with oxygen or with preheated oxygen enriched air. The reducing environment is achieved by the addition of pulverized coal, anthracite, coke or semi-coke or high carbon substances directly to the charge. The reducing agent is added to the charge in excess, and the mixing of the feedstocks can also occur in the furnace during the process. The reduction temperature does not exceed 1200 ° C at the end of the furnace. In this case, the charge is treated by pelletizing, briquetting or planted untreated and the charge need not be pre-dried. The bet is placed continuously.

Intense heat transfer is achieved by a combination of several heat transfer mechanisms. These include:

• direct heating of the charge by flame at its low surface temperature;

• flame radiation on the charge and lining after reaching the surface temperature of the charge 900 ° C;

• other heat transfer mechanisms caused by the rotating furnace:

o agitating the charge to ensure the transfer of the relatively cold charge to the surface and the heated charge from the surface to the charge volume;

o the heated charge is brought into the volume by stirring, where it transfers heat to the surrounding cooler charge;

o transfer of heat from the heated lining to the charge upon contact of the lining with the charge.

Thus, the proposed process consists in reducing the solid charge of metal-bearing wastes containing zinc, lead and cadmium with a total content greater than 5% by means of fossil fuels in conditions of intensified heat transfer. Such conditions are also created in a continuous rotary oven. Good heat transfer is ensured by mixing the charge and a large heat transfer area - the charge is heated not only from above but also from below.

The treatment of metal-bearing wastes is similar to the processing of ores in rotary kilns. The process differs from ore processing by the high zinc content in the feed and the high amount of dust that exceeds 10% of the wastes charged. The furnace design in this case is extended with an L / D ratio (length of the furnace / inside diameter of the furnace) of greater than 10. The processing time depends on the manner of mixing the charge with the carbon-based reducing agents and varies from 0.5 hours to 20 hours. After the initial heating phase, rapid reduction occurs. The heating and reduction time is given by the utilized volume of the furnace and with decreasing utilization the time decreases. The degree of reduction achieved is greater than 60%. The degree of reduction is given by economic optimization. A higher degree of reduction leads to higher energy costs, but does not substantially affect the degree of removal of zinc, lead and cadmium. The reduced material is discharged from the furnace into a continuous cooler where the reduction product is cooled under conditions

-8EN 297878 B6 Oxygen Restricted. Subsequently, the reduction product is mechanically treated for subsequent magnetic separation.

EXAMPLE 3 Treatment of Metal Waste by Semi-Liquid Reduction in a Batch Process

The equipment and technology is designed so that the process achieves optimum thermal efficiency and limits the oxidation of the charge and the already reduced material to the minimum necessary. For this solution it is necessary to ensure a high flame temperature and intensive heat transfer and strong reducing conditions in the furnace. Both of these requirements are achieved in the proposed plant. The high flame temperature is achieved by burning the fuel with oxygen or with preheated oxygen enriched air. The reducing environment is achieved by the addition of pulverized coal, anthracite, coke or semi-coke or high carbon substances to the excess charge. The reduction temperature in this case does not exceed 1350 ° C.

Intense heat transfer is achieved by a combination of several heat transfer mechanisms. These include:

• direct heating of the charge by flame at its low surface temperature;

• flame radiation on the charge and lining after reaching the surface temperature of the charge 900 ° C;

Mixing highly viscous slag;

• other heat transfer mechanisms caused by the rotating furnace:

o agitating the charge to ensure the transfer of the relatively cold charge to the surface and the heated charge from the surface to the charge volume;

o the heated charge is brought into the volume by stirring, where it transfers heat to the surrounding cooler charge;

o transfer of heat from the heated lining to the charge upon contact of the lining with the charge.

Thus, the proposed process consists in reducing the solid charge of metal-bearing wastes containing zinc, lead and cadmium with a total content of more than 5% in the slag in the batter state by means of fossil fuels in conditions of intensified heat transfer. Such conditions are created in a rotary oven. Good heat transfer is ensured by mixing the charge and a large heat transfer area - the charge is heated not only from above but also from below.

The treatment of metal-bearing wastes in this case is similar to the processing of ores into lumps in rotary kilns. The process differs from the ore processing by the high zinc content of the feed and the high amount of dust that exceeds 10% of the wastes charged and the furnace design, which in this case has an L / D ratio (furnace length / furnace diameter) of less than 8. is adjusted so that the CaO / SiO ₂ ratio is between 0.05 and 0.7 and that the SiO ₂ / Al ₂ O ₃ ratio is between 1.5 and 8. This is achieved by adding fine-grained SiO ₂ -based materials , such as power fly ash. The advantage of fly ash is its low cost, very fine granulometry and carbon content suitable for reduction. Further, Al ₂ O ₃ , or CaO and MgO or mixtures thereof can be added to the feed. The chemical composition of the slag is adjusted so that the viscosity of the slag is high and the slag is in a pasty state. Rolling the slag in a rotary kiln helps to improve mass transfer and ultimately to join droplets of reduced metal. The slag is saturated with the dominant lining material, which limits the interaction of the slag with the lining. The disadvantage of working with low basic slags is an increase in the sulfur content of the reduced material. The sulfur content can be influenced by a suitable choice of the input materials, especially the reducing additives. The processing time depends on how the batch is mixed with the carbon-based reducing agents and varies from 0.5 hours to 20 hours. After the initial heating stage, a rapid reduction occurs, followed by a gradual carburization of the iron and its melting. Small metal droplets join in larger slags. The heating and reduction time is given by the utilized volume of the furnace and with decreasing utilization the processing time is shortened. The degree of reduction achieved is greater than 60%. The degree of reduction is

-9EN 297878 B6 due to economic optimization. A higher degree of reduction leads to higher energy costs, but does not substantially affect the degree of removal of zinc, lead and cadmium. The reduced material is discharged from the furnace to a cooler where the reduction product together with the paste slag is cooled under conditions of limited oxygen access. Subsequently, the reduction product is mechanically treated for subsequent magnetic separation. The reduced metal is processed, for example, in a blast furnace as an iron source or, after compression, as a replacement for scrap for steel production.

Example 4 Treatment of metal-bearing wastes by reduction in a semi-liquid state in a continuous manner

The equipment and technology is designed so that the process achieves optimum thermal efficiency and limits the oxidation of the charge and the already reduced material to the minimum necessary. For this solution it is necessary to ensure a high flame temperature, intensive heat transfer and strong reducing conditions in the furnace. Both of these requirements are met in the proposed equipment. The high flame temperature is achieved by burning the fuel with oxygen or with preheated oxygen enriched air. The reducing environment is achieved by the addition of pulverized coal, anthracite, coke or semi-coke or high carbon substances to the charge. The reducing agents are in excess in the charge. The reduction temperature in this case does not exceed 1350 ° C.

Intense heat transfer is achieved by a combination of several heat transfer mechanisms. These include:

• direct heating of the charge by flame at its low surface temperature;

• flame radiation on the charge and lining after reaching the surface temperature of the charge 900 ° C;

Mixing highly viscous slag;

• other heat transfer mechanisms caused by the rotating furnace:

o agitating the charge to ensure the transfer of the relatively cold charge to the surface and the heated charge from the surface to the charge volume;

o the heated charge is brought into the volume by stirring, where it transfers heat to the surrounding cooler charge;

o transfer of heat from the heated lining to the charge upon contact of the lining with the charge.

Thus, the proposed process consists in reducing the solid charge of metal-bearing wastes containing zinc, lead and cadmium with a total content of more than 5% in the slag in the batter state by means of fossil fuels in conditions of intensified heat transfer. Such conditions are created in a rotary oven. Good heat transfer is ensured by mixing the charge and a large heat transfer area - the charge is heated not only from above but also from below.

The treatment of metal-bearing wastes is similar to the processing of ores in rotary lump kilns. The process differs from ore processing by the high zinc content in the feed and the high amount of dust that exceeds 10% of the wastes charged and the furnace design, which in this case has an L / D ratio (furnace length / furnace diameter) greater than 10. is adjusted so that the CaO / SiO ₂ ratio is between 0.05 and 0.7 and that the SiO ₂ / Al ₂ O ₃ ratio is between 1.5 and 8. This is achieved by adding fine-grained SiO ₂ -based materials . Examples include fine quartz sand or various SiO _2- rich wastes, such as power fly ash. The advantage of fly ash is its low cost, very fine granulometry and carbon content suitable for reduction. Further, Al ₂ O ₃ , or CaO and MgO or mixtures thereof can be added to the feed. The chemical composition of the slag is adjusted so that the viscosity of the slag is high and the slag is in a pasty state. Rolling the slag in a rotary kiln helps to improve mass transfer and ultimately to join droplets of reduced metal. The slag is saturated with the dominant lining material, which limits the interaction of the slag with the lining. The disadvantage of working with low basic slags is an increase in the sulfur content of the reduced material. The sulfur content can be

-10GB 297878 B6 by suitable selection of the input materials, especially reducing additives. The processing time depends on how the batch is mixed with the carbon-based reducing agents and varies from 0.5 hours to 20 hours. After the initial heating stage, there is a rapid reduction, followed by gradual ironing and melting. Small drops in the slag join into larger ones. The heating and reduction time is given by the utilized volume of the furnace and with decreasing utilization the processing time is shortened. The degree of reduction achieved is greater than 60%. The degree of reduction is given by economic optimization. A higher degree of reduction leads to higher energy costs, but does not substantially affect the degree of removal of zinc, lead and cadmium. The reduced material is discharged from the furnace to a cooler where the reduction product together with the paste slag is cooled under conditions of limited oxygen access. Subsequently, the reduction product is mechanically treated for subsequent magnetic separation. The reduced metal is processed, for example, in a blast furnace as an iron source or, after compression, as a replacement for scrap for steel production.

Example 5 Treatment of metal-bearing wastes by liquid reduction by a batch process

Prior to the start of the process, a higher-carbon iron melt, for example liquid pig iron, is poured into the furnace, or a charge in the form of scrap, preferably solid pig iron or cast iron, is charged. This solid charge is first melted and the carbon content is adjusted. Carbon is supplied to the metal during betting and continuously through one of the three methods specified below or a combination thereof:

• adding carbon to the surface of the slag and metal; • injecting carbon below the metal level; • injecting a gaseous or liquid hydrocarbon below the metal level.

When injecting liquid or gaseous hydrocarbons, the injection device is subsequently inerted with an inert gas. The addition of carbon allows the control of the carbon content of the melt, i.e. keeping the carbon content within a selected range, thereby controlling the minimum melting point of the metal melt. The carbon content in the melt is maintained between 0.8 to 5%, the optimum carbon content is 4%. The higher the temperature, the reduction rate and the productivity of the equipment increase, while the higher the temperature has a negative influence on the lining life and the temperature of the exhaust gases and thus on the utilization of the heat of the combustion gases. The optimum temperature of the iron melt during the reduction is 1350 to 1550 ° C. The possibility of adding carbon to the iron melt allows the melt to be used as a heat and carbon source for reduction. The proposed technological process enables the processing of metal-bearing wastes containing zinc, lead and cadmium. The fraction of the volume of the non-foamed slag and the reaction area, i.e. the molten metal surface area, is less than 0.3 m. Repeated batches of less waste are optimized so that the ratio is less than 0.1 m to rapidly heat the charge. it also enables rapid reduction. Reduction products are:

• metal that gradually passes into the melt, • CO-rich gases, which must pass through the slag.

The interaction of the gaseous products of the reduction leads to foaming of the slag and to an increase in its volume. In order to reduce these negative consequences of reducing and improving the conditions for the exit of gaseous products from the slag, the chemical composition of the slag should be adjusted so that the viscosity of the slag is as low as possible and at the same time the slag is not aggressive to the lining. This is achieved by the addition of SiO ₂ , Al ₂ O ₃ , or CaO and MgO or mixtures thereof. The chemical composition of the slag is adjusted so that the slag is near the eutectic point and at the same time saturated with the dominant lining material. The low viscosity of the slag allows the bubbles to flow out quickly. As the amount of slag increases, a portion of the slag is retracted by tilting the furnace or by mechanical means. When the amount of metal is increased to an amount suitable for subsequent handling, a portion of the metal is poured from the furnace for further processing or cast into ingots to replace scrap. The process continues on the remaining iron melt by the further addition of zinc, lead and cadmium metal-containing wastes in the cycles described above.

Claims (9)

A method of treating metal-bearing wastes containing zinc, lead and cadmium with a total content of these elements exceeding 5%, such as sludge and dust from steelmaking, using fossil fuels and oxygen in conditions of intensified heat transfer with increased overall thermal efficiency of heating, optional melting of metal waste, characterized in that the waste is treated in a rotary kiln or in a battery of rotary kilns, wherein the rotary kiln is filled with processed waste up to a maximum of 40% of the total internal volume of the kiln, the removal of zinc, lead and cadmium-rich dust components from the furnace, thereby creating distinctly separated zones, namely the reducing environment zone, which is the portion of the furnace in which the condensed phase feed occurs in the presence of carbon and carbon monoxide; and a zone with an oxidizing environment, which is part of the furnace above the charge, in which the gaseous reduction products are grown to oxygen fossil fuel combustion and oxidation of the vaporized metals leaving the furnace in the form of dusts, with a free oxygen content of at least 2% and that the actual reduction process in the rotary kiln ensures the separation of slag, iron and dusts rich in zinc, lead and cadmium oxides suitable for further processing, the ZnO content of the dusters being greater than 30%, and the temperature required by the oxygen burner, for which hydrocarbons or pulverized coal are used as fuel, with the actual reduction of metal-bearing wastes containing zinc, lead and cadmium by carbon, either as a solid state reduction with a melt content in the reduced oxide mixture of less than 20% and a maximum a reduction temperature lower than 1200 ° C at which basicity was baled of oxides such as CaO, SiO ₂ , MgO and Al ₂ O ₃ , is adjusted so that the CaO to SiO ₂ ratio is greater than 1.5, allowing desulfurization, and the powdered carbon is added to the mixture so that when mixed provide contact between the oxides and the carbon, and wherein the reduction can take place both continuously and in a batch manner; the productivity of the equipment depends on the reduction temperature and the fineness of the added wastes, reducing substances and slag-forming additives; the reduced metal is separated by magnetic separation, and after magnetic separation it is briquetted or used directly in the steel plant as scrap replacement or for enrichment of the charge in a blast furnace; or as a semi-liquid reduction with a melt content in the reduced oxide mixture of less than 60% and a reduction temperature of more than 1150 ° C and less than 1350 ° C, in which the reduced metal is carbonized by excess carbon in the reduced charge, of the reduced metal below the reduction temperature, and the carburized metal droplets in the highly viscous slag gradually combine into nuggets of greater than 2 mm to form a slag with a CaO to SiO ₂ ratio ranging from 0.05 to 0 7 as MgO and A1 ₂ O ₃ exceeding 30% of the total content of ballast substances, which does not allow substantial desulfurization and partition coefficient síiy between slag and metal of less than 10, wherein the composition is formulated carbon in powder state so that when mixed ensures contact between metal oxides and carbon with the waste and where the reduction can take place both continuously and in a batch manner ; the productivity of the equipment depends on the reduction temperature and the fineness of the added wastes, reducing substances and slag-forming additives; the reduced metal is separated by magnetic separation and, after magnetic separation, is briquetted or used directly in the steel mill as a replacement for scrap or for enrichment in a blast furnace; or as a liquid reduction with a melt content in the reduced oxide mixture of greater than 60% and less than 95% and a reduction temperature of greater than 1250 ° C and less than 1650 ° C carried out at the iron melt level of higher carbon content, and wherein the mixture of oxides is selected such that the CaO to SiO ₂ ratio is in the range of 0.5 to 1.5, optimally around 1.2 and the MgO content does not exceed 20% and the Al ₂ O ₃ content does not exceed 40% of the total ballast content such that the melt permits the escape of gaseous reduction products in the form of bubbles; carbon is added to the iron melt below the level of the metal by means of an injection nozzle which is also used as a mixing device; after reduction, the slag is stripped off and part of the melt is decanted, and the remaining melt is again treated with waste; the reduced metal is separated from the slag by gravity separation of the slag and the molten metal, and the liquid metal is then treated by conventional methods, for example, by casting or directly as a liquid feed for the steel aggregate. - 12GB 297878 B6 Method for processing metal-bearing wastes according to claim 1, characterized in that, for reduction in solid or semi-liquid state, the waste-based feedstocks are premixed with higher-carbon substances, for example powdered coke, semi-coke, coal or anthracite, or crushed high carbon waste materials, such as crushed activated carbon, tires, and the mixture thus prepared is added directly to the furnace in the form of briquettes, pellets or pieces into the furnace. Method for processing metal-bearing wastes according to claim 1, characterized in that an iron melt with a carbon content in the range of 0.8 to 5%, preferably in the range of 2 to 4%, in this case For example, the iron melt carbon is used for the reduction, optionally in combination with the carbon dispersed in the molten slag. A method for treating metal-bearing wastes according to claim 1, characterized in that the wastes are charged into the rotary kiln either batchwise or continuously. The method of treating metal waste according to claim 1, characterized in that the reduction product is removed from the rotary kiln or battery of the rotary kiln in batches or continuously. Method for processing metal-bearing wastes according to claims 1 to 5, characterized in that in the reduction in solid or semi-liquid state, the waste is charged into the rotary kiln in a cold or preheated state and after reduction the reduction products are removed from the furnace and cooled. means that the slag / metal mixture is rapidly cooled in conditions of limited air access, preventing the re-oxidation of the reduced iron. 7. The method of treating metal-bearing wastes according to claim 1, characterized in that a batch process is preferably used in the molten state reduction and a continuous process is preferably used in the solid or semi-liquid state reduction. Device for carrying out the method according to claims 1 to 7, characterized in that it consists of one or more rotary oven furnaces arranged in a battery, allowing to achieve a suitable capacity for processing metal waste, to which the charge is added either continuously, that metal-bearing waste containing zinc, lead and cadmium is added to the rotary kiln for at least 60% of the reduction period, or rotary kilns operate in batch mode, and the kilns differ according to the waste treatment ratio L / D, where L is the length of the kiln, and D is the inside diameter of the furnace, wherein the continuous processing furnaces are longer and have an L / D ratio of at least 10, and for batch process furnaces the L / D ratio does not exceed 8; the furnace interior filled with waste to a maximum of 40% of the total furnace internal volume constitutes two distinct zones where the first zone with the reducing medium is the portion of the furnace in which the condensed phase feed is present and carbon and carbon monoxide are present; zone with oxidizing environment is the part of the furnace above the charge in which the gaseous products of the reduction, the combustion of fossil fuels with oxygen and the oxidation of the vaporized metals leaving the furnace in the form of dedusting occur, with at least 2% free oxygen . 9. The method of claim 8, wherein the rotary kiln or rotary kiln battery is further equipped with an injection nozzle for injecting carbon-containing material below the metal level, and the nozzle also serves and is also used as a mixing device for mixing the bath, and the device is further provided with a slag retractor or nozzle for blowing the slag from the furnace.