Method and apparatus for producing direct reduction metals

Abstract

The invention relates to a method for producing a directly reduced metallic material (142), said method comprising the following steps: a) loading the material into a closed furnace space (120); b) filling the furnace space with a heated inert gas to heat the material; c) providing a reducing gas; d) providing heat such that the metal oxide present in the material is reduced, resulting in the formation of water vapor; e) condensing and collecting the water vapor in a condenser (160); and f) discharging the remaining reducing gas from the furnace space. The method is characterized in that, at the same pressure, the reducing gas has a lower density than the inert gas, and in step c), when the inert gas is still present in the furnace space, the reducing gas is provided, whereby the provided reducing gas thus pushes the inert gas downwards until the material is completely contained in the reducing gas. The invention also relates to a system.

Description

Technical Field

[0001] The present invention relates to a method and apparatus for producing direct reduced metals, such as direct reduced iron (also known as sponge iron). The present invention particularly relates to the direct reduction of metal oxides or metal ores in a controlled hydrogen atmosphere to produce such direct reduced metals. Background Art

[0002] The production of direct reduced metals using hydrogen as a reducing agent is well known per se. For example, processes are described in SE7406174-8 and SE7406175-5, in which a charge of metal oxides or metal ores is subjected to a hydrogen atmosphere flowing through a charge of metallic material, resulting in it being reduced to form directly reduced pure metal.

[0003] Furthermore, in Swedish applications SE1950403-4, SE1951070-0 and SE2050771-1, processes are disclosed for directly reducing a metal material in a closed hydrogen atmosphere and further carburizing the directly reduced metal material. Summary of the invention

[0004] The present invention is particularly suitable for batch loading and processing of the material to be reduced.

[0005] There are several issues with existing technologies, including those regarding heat losses and efficiency of hydrogen usage.

[0006] It is also desirable to improve simplicity and procedural / time efficiency relative to prior art solutions.

[0007] It is therefore desirable to have a thermally and energy efficient process for the direct reduction of metallic materials which does not result in the release of carbon monoxide or carbon dioxide into the atmosphere. The technical solution should be scalable to large production volumes and be able to process metallic materials of different structures.

[0008] The present invention solves the above-mentioned problems.

[0009] Therefore, the present invention relates to a method for producing a direct reduced metal material, comprising the following steps: a) loading the metal material to be reduced into a closed furnace space; b) supplying heat and an inert gas to the furnace space, whereby the heated inert gas fills the furnace space and heats the loaded metal material to a first temperature; c) supplying a reducing gas to the furnace space; d) supplying heat to the furnace space to keep a second temperature in the loaded metal material sufficiently high so that the metal oxides present in the loaded metal material are reduced, thereby causing water vapor to form; e) condensing and collecting the water vapor formed in step d in a condenser; and f) discharging the remaining reducing gas from the furnace space after the loaded metal material is reduced, the method being characterized in that, at the same pressure, the reducing gas has a lower density than the inert gas, and in step c), the reducing gas is supplied while the inert gas is still present in the furnace space, whereby the supplied reducing gas thereby pushes the inert gas downwards until the loaded metal material is completely contained in the reducing gas.

[0010] The present invention also relates to a system for producing a directly reduced metal material, the system comprising: a furnace space arranged to receive and accommodate the metal material to be reduced; a heating and gas supply device arranged to provide heat, an inert gas and a reducing gas to the furnace space; a control device arranged to control the heating and gas supply device to provide heat and an inert gas to the furnace space so that the heated inert gas fills the furnace space and heats the loaded metal material to a first temperature; supplying the reducing gas to the furnace space; supplying heat to the furnace space to keep a second temperature in the loaded metal material sufficiently high , so that metal oxides in the loaded metal material are reduced, thereby causing water vapor to be formed; and after the loaded metal material has been reduced, the remaining reducing gas is discharged from the furnace space, wherein the system includes a condenser, which is arranged to condense and collect water vapor, and the system is characterized in that at the same pressure, the reducing gas has a lower density than the inert gas, and the control device is arranged to control the heating and gas supply device to provide reducing gas while the inert gas is still present in the furnace space, whereby the reducing gas provided thereby pushes the inert gas downwards until the loaded metal material is completely contained in the reducing gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Hereinafter, the present invention will be described in detail with reference to exemplary embodiments thereof and the accompanying drawings, in which:

[0012] Figure 1a-1d a simplified furnace cross section for a system according to the invention in the first, second and third operating stages, respectively;

[0013] Figure 2 is a schematic diagram of a system according to the present invention;

[0014] Figure 3 is a flow chart of a method according to the present invention;

[0015] Figure 4 is a diagram showing the various steps of a method according to the present invention;

[0016] Figure 5 is a graph showing the functional relationship between temperature and the reducibility of H2 relative to the Fe3O4 to be reduced (removal of oxygen in % on the Y axis); and

[0017] Figure 6 is the equilibrium diagram for the reduction of iron oxides with hydrogen and carbon monoxide. DETAILED DESCRIPTION

[0018] Figure 1a-1d Reference numerals share corresponding parts.

[0019] therefore, Figure 1a-1d A furnace 100 is shown for producing direct reduced and carburized metallic materials. Figure 2 , two such furnaces 210, 220 are shown. The furnaces 210, 220 may be identical to the furnace 100, or may differ in detail. However, it should be understood that everything described herein with respect to the furnace 100 is also applicable to the furnaces 210 and / or 220, and vice versa.

[0020] Furthermore, it should be understood that everything described herein with respect to the present method is also applicable to the present system 200 and / or furnaces 100; 210, 220, and vice versa.

[0021] Such a furnace 100 has many similarities with the furnaces described in SE7406174-8, SE7406175-5, SE1950403-4, SE1951070-0 and SE2050771-1, and reference may be made to these documents for possible design details. However, an important difference between some of these furnaces and the furnace 100 of the present invention is that the furnace 100 of the present invention is not arranged to operate in such a way that the reducing gas is recirculated through the furnace 100 and returned to a collecting container arranged outside the furnace 100, in particular in such a way that the reducing gas is recirculated out of the furnace 100 (or the heated furnace space 120) and then returned to the furnace 100 (or the heated furnace space 120) during the same batch treatment of the charge material to be reduced.

[0022] Rather, as will be apparent from the following description, the furnace 100 is arranged for batch reduction and possible carburizing operations of one batch of material at a time, and operates as a closed system during such individual batch processes, in the sense that reducing gas is supplied to the furnace 100 but is not removed from the furnace 100 during the batch reduction and carburizing processes; and that carbon-containing gas may be supplied to the furnace 100 but is not removed from the furnace 100 during the batch reduction and carburizing processes described below.

[0023] This means that during the reduction process, the amount of reducing gas present in the furnace 100 is always maintained or increased. After the reduction is completed, the reducing gas is of course exhausted from the furnace 100, but there is no recirculation of reducing gas during the reduction step. In some embodiments, as will become clear below, the same is true for the carbon-containing gas.

[0024] Thus, the furnace 100 is part of a closed system comprising a heated furnace space 120 which is arranged to be pressurized, such as to a pressure greater than 1 bar, such as to a pressure of at least 1.5 bar, or at least 2 bar, or at least 2.3 bar, or at least 2.5 bar, or at least 3 bar, or at least 4 bar, or at least 5 bar, or even at least 6 bar. Any pressurized treatment steps (with respect to the inert gas, reducing gas and / or carbon-containing gas) may be arranged to be performed until and possibly maintain the total pressure within the furnace space 120 within any one of the pressure intervals mentioned earlier in this paragraph. In particular, this applies to the first and second operating pressures discussed below.

[0025] In any case, the furnace space 120 is constructed to withstand the operating pressures described herein. The upper part 110 of the furnace 100 can be bell-shaped. It is openable for loading the material 142 to be processed and can then be closed in an airtight manner using fastening means 111. The furnace space 120 can be enclosed with refractory material, such as brick material 130.

[0026] If not otherwise indicated, the term "pressure" herein refers to the total gas pressure, particularly the total gas pressure within the furnace space 120, as opposed to "partial pressure," which refers to the partial pressure of a particular gas.

[0027] Furthermore, since atmospheric pressure is approximately 1 bar, the expressions "pressure greater than 1 bar" and "pressure above atmospheric pressure" are intended to have the same meaning. Accordingly, the expressions "pressure less than 1 bar" and "pressure below atmospheric pressure" are intended to have the same meaning.

[0028] The furnace space 120 is arranged to be heated using one or several heating elements 121. Preferably, the heating elements 121 are electric heating elements. However, radiator burner tubes or similar fuel heating elements may also be used. However, the heating elements 121 do not generate any combustion gases that interact chemically directly with the furnace space 120, which must remain chemically controlled for the purposes of the present invention. Preferably, during the main heating process described below, the only gaseous substances provided to the furnace space are reducing gases, and any carbon-containing gases used as carbon source for carburizing the metal material.

[0029] from Figure 1a-1d It can be clearly seen that the heating element 121 can be arranged inside the furnace space 120 and / or outside the furnace space 120. In the latter case, the heating element 121 can be provided so that the gas entering the furnace space 120 via the supply duct 171 passes the heating element 121 before entering the furnace space 120.

[0030] Preferably, the heating element 121 may be made of a heat-resistant metal material, such as a molybdenum alloy.

[0031] Additional heating elements may also be arranged in the furnace space 120. For example, heating elements similar to element 121 may be provided at the side walls of the furnace space 120, such as at a height corresponding to the loaded material or at least to the container 140. Such heating elements contribute not only to heating the gas but also to heating the loaded material by heat radiation.

[0032] As will be described below, the heat exchanger 160 is arranged to transfer thermal energy from the exhaust gases of the furnace space 120 to the incoming gases of the furnace space 120 .

[0033] At least during the reduction step, additional thermal energy is required to heat the charge material 142, as will be understood from the following. Preferably, a majority, such as substantially all or all, of this additional thermal energy provided to the furnace space 120 during the reduction step is provided by a heating element 121 arranged outside the furnace space 120 and arranged to heat the gases entering the furnace space 120 before the gases enter the furnace space 120.

[0034] The oven 100 may also comprise a lower part 150 which forms a sealed container together with the upper part 110 either permanently or when the oven is sealingly closed using the fastening means 111 as described above.

[0035] A container 140 for material 142 to be treated (reduced or carburized) is present in the lower portion 150 of the furnace 100. The container 140 may be supported on the refractory floor of the furnace space 120 in a manner that allows gas to pass beneath the container 140, such as along open channels 172 formed in the floor.

[0036] Preferably, the container 140 is an open structure, which means that the gas can freely pass through at least the bottom / bottom surface of the container 140. This can be achieved, for example, by forming holes in the bottom of the container 140.

[0037] The material to be treated includes metal oxides, preferably iron oxides, such as Fe2O3 and / or Fe3O4. The material may include scales or various types of waste. The material may be granular, such as in the form of pellets or balls, or may be made into such forms in a suitable pre-treatment step. A suitable loading material for batch reduction is rolled iron ore balls, such as ground waste rolled into balls, which have been rolled into balls with a diameter of about 1-1.5 cm in water. If this material additionally contains oxides, in the present method, the reduced metal evaporates at a temperature lower than the final temperature of the loading material, and this metal can be condensed in condenser 160 and easily collected in powder form. This oxide may include metal oxides, such as oxides of Zn and Pb.

[0038] Advantageously, the furnace space 120 is not loaded with very large amounts of material to be reduced 142. Each furnace 100 is preferably loaded with at most 50 tons, such as at most 25 tons, such as 5 tons to 10 tons in each batch. This load can be kept in a separate container 150 in the furnace space 120. Depending on the production volume requirements, several furnaces 100 can be used in parallel, and then the waste heat from one furnace 220 can be used to preheat another furnace 210 (see Figure 2 and below), or in a continuous system, a cooling gas, preferably an inert gas, may be used to preheat the incoming material.

[0039] A system 200 is provided that is suitable for installation and use directly at a mining or other material production site, without the need for expensive transportation of ore (or other materials) prior to reduction. Instead, directly reduced and carburized metallic materials can be produced on site, packaged under a protective atmosphere, and transported to a different site for further processing.

[0040] Thus, in the case of rolling iron ore pellets or balls, it is envisioned that the furnace 100 may be mounted in connection with the iron ore pellet or ball production system so that the metal material in the container 140 may be loaded into the furnace 100 in a fully automated manner, wherein the container 140 is automatically cycled from the metal pellet or ball production system to the system 100 and back, filled with metal pellets or balls to be reduced and carburized; inserted into the furnace space 120; subjected to the reducing and possibly carburizing reducing gas / heat / carbon-containing gas treatment described herein; removed from the furnace space 120 and emptied; brought back to the metal pellet or ball production system; refilled; and so on. A greater number of containers 140 may be used than furnaces 100, so that at each batch changeover, the reduced and possibly carburized load in a particular container is immediately replaced in the furnace 100 by a different container containing material that has not yet been reduced or carburized. Using several smaller furnaces 100 rather than one very large furnace, such a larger system, for example at a mining site or where other types of raw materials (such as scale) are produced, can be fully automated and very flexible in terms of output.

[0041] Below the container 140, the furnace 100 comprises a gas-gas type heat exchanger 160 (or the system comprises both the furnace 100 and the heat exchanger 160), which can advantageously be a tubular heat exchanger such as known per se. The heat exchanger 160 is preferably a counter-current type heat exchanger. Below the heat exchanger 160, a closed tank 161 is connected to the heat exchanger 160 for collecting and containing condensed water from the heat exchanger 160. The tank 161 can also be configured to withstand the working pressure of the furnace space 120 in an airtight manner.

[0042] The heat exchanger 160 is connected to the furnace space 120, preferably such that the cold / cooled gases reaching the furnace space 120 via the supply duct 171 pass through the heat exchanger 160 along externally / peripherally provided heat exchanger tubes and further to the top 125 of the furnace space 120, where they are released into the furnace space 120. Along this supply duct 171, the gases thus supplied can therefore be heated by the heat exchanger and / or using the heating element 121.

[0043] In a manner to be described in detail below, the heated gas flows downwardly from the furnace space 120, passes through the heat exchanger 160 through the internally / centrally disposed heat exchange tubes, thereby heating the incoming cold / cooled gas. In this process, the downwardly flowing gas is cooled and the water vapor contained condenses into liquid water. Therefore, the exhaust gas heats the incoming gas through the heat transfer caused by the temperature difference between the two and the condensation heat of the condensed water vapor contained in the exhaust gas, thereby effectively heating the incoming gas.

[0044] Condensed water formed from the exhaust gas is collected in the tank 161 .

[0045] The furnace 100 may include a set of temperature and / or pressure sensors in the tank 161 (122), at the bottom of the furnace space 120 (such as in the container 140 (123) and / or at the top (124) of the furnace space 120. These sensors can be used by the control unit 201 to control the reduction and / or possible carburization process, as will be described below.

[0046] 173a and 173b represent different outlet conduits for gases, such as spent inert gas or cooling gas, from the furnace space 120. 173a is arranged to receive such gases from inside the furnace space 120 below the charge material 142 in the container 140; while 173b is arranged to receive such gases from downstream (such as below) of the heat exchanger 160.

[0047] Condensate may be introduced from the condenser / heat exchanger 160 downwardly into the trough via a nozzle 164 or the like, and out at the bottom of the trough 161, such as at a local low point 165 of the trough 161, preferably with the orifice of the nozzle 164 disposed completely below the main bottom 166 of the trough 161, such as Figure 1a-1d This will reduce the turbulence of the liquid water in tank 161, providing more controllable operating conditions.

[0048] The size of the tank 161 can be designed to receive and contain all the water formed during the reduction of the loaded material. Therefore, the size of the tank 161 can be adapted to the type and volume of a batch of reduced materials. For example, when 1000 kg of Fe3O4 is fully reduced, 310 liters of water are formed, and when 1000 kg of Fe2O3 is fully reduced, 338 liters of water are formed. In other embodiments, depending on the degree of contamination, the collected water is transferred for waste treatment. In any case, it is preferred to measure the volume of the collected water, such as using a flow meter or liquid level meter that is conventional per se.

[0049] exist Figure 2 , a system 200 is shown in which a Figure 1a-1d In particular, one or both of the furnaces 210 and 220 may be Figure 1a-1d The type shown, or at least the type according to claim 1.

[0050] 230 denotes a gas-gas type heat exchanger. 240 denotes a gas-liquid type heat exchanger. 250 denotes a fan or a pump. 260 denotes a vacuum pump. 270 denotes a compressor. 280 denotes a container for used reducing gas. 290 denotes a container for fresh / unused reducing gas. 310 denotes a container for fresh / unused carbon-containing gas. 320 denotes a container for used carbon-containing gas, such as a mixture of the type of gas stored in the container 310 and reducing gas. 330 denotes a container for used inert gas, and 340 denotes a container for fresh inert gas. V1-V24 denote valves.

[0051] 201 represents a control device, which is connected to the sensors 122, 123, 124 and valves V1-V24 and is generally arranged to control the process described herein. The control device 201 can also be connected to a user control device, such as a graphical user interface presented to a user of the system 200 by a computer (not shown) for supervision and further control.

[0052] Figure 3 The method according to the invention is shown, which uses Figure 2 A system 100 of the type shown, in particular Figure 1a-1d A furnace 100 of the type shown. In particular, the method uses a reducing gas as a reducing agent and a possible carbon-containing gas as a carburizing carbon source to produce a directly reduced and possibly carburized metallic material.

[0053] After this direct reduction and possible carburization, the metal material 142 can form a carburized or non-carburized sponge metal. In particular, the metal material can be an iron oxide material, and the product obtained after the direct reduction can be a carburized sponge iron. The reduced, possibly carburized metal material obtained can then be used in subsequent method steps to produce cast iron, steel, etc.

[0054] In a first step, the method starts.

[0055] In the subsequent step, the metal material 142 to be reduced is loaded into the furnace space 120. This loading can be carried out by placing the loaded container 140 in a Figure 1a-1d The orientation shown is carried out by inserting it into the furnace space 120 , which can then be closed and sealed in a gas-tight manner using the fastening device 111 .

[0056] In a subsequent step, the existing atmosphere can be exhausted from the furnace space 120, thereby achieving a gas pressure of less than 1 bar in the furnace space 120. It should be noted that this lower gas pressure is below atmospheric pressure. This can be achieved by closing valves 1-8, 11 and 13-24 and opening valves 9-10 and 12, and the vacuum pump 260 sucks out and thus exhausts the air contained in the furnace space 120 through the conduits 240 and 250. Then, in the case where the furnace space 120 is filled with air, valve 9 can be opened to allow these exhausted gases to flow out into the surrounding atmosphere. If the furnace space 120 is filled with used reducing gas and / or carbonaceous gas, these gases are exhausted into the container 280 or 320, as the case may be. Accordingly, in the case where the furnace space 120 is filled with inert gas, the inert gas is exhausted into the container 330.

[0057] In this embodiment, furnace air is exhausted through conduit 173a or 173b, although it is appreciated that any other suitable outlet conduit disposed in furnace 100 may be used.

[0058] In this exhaust step, as well as in other steps described below, the control device 201 can be used to control the pressure in the furnace space 120, for example based on readings from pressure sensors 122, 123 and / or 124. The same is true with respect to the other exhaust and filling steps of the various gases exhausting and entering the furnace space 120 described below.

[0059] The evacuation can be continued until a pressure of at most 0.5 bar, preferably at most 0.3 bar, is reached in the furnace space 120 .

[0060] In a subsequent initial heating step, heat and an inert gas are provided to the furnace space 120 , whereby the heated inert gas fills the furnace space 120 and heats the charged metal material 142 to a first temperature.

[0061] Inert gas can be supplied from container 330 and / or 340. Since furnace 100 is closed, as described above, in the process, substantially no gas is provided, including reducing gas and any carbon-containing gas, and there may also be no inert gas that will escape. In other words, gas loss (except reducing gas and any carbon-containing gas consumed in reduction and carburizing reactions) will be very low or even non-existent. On the contrary, only reducing gas that is chemically consumed in the reduction reaction during the reduction process will be used, and correspondingly for any carbon-containing gas. In addition, the only reducing gas required in the reduction process is the amount required to maintain the necessary pressure and the chemical balance between hydrogen and water vapor during the reduction process. This will be described in detail below.

[0062] As described above, container 340 contains fresh (unused) inert gas, while container 330 contains inert gas that has been used in one or more reduction steps and has been collected in system 200. The first time the process is performed, only fresh inert gas is used that is provided from container 340. During subsequent process runs, the reused inert gas from container 340 is used, supplemented with fresh inert gas from container 340 as needed.

[0063] The same is true for the reducing gas supplied from vessel 290 or 280, as the case may be; and any carbon-containing gas supplied from vessel 310 or 320, respectively.

[0064] During the optional initial phase of the initial heating step, which is one of the inert gas introduction phases, which is carried out without providing any heat, until the pressure in the furnace space 120 reaches about 1 bar, or even about 2 bar, valves 1-9, 11 and 13-24 are closed, while valves 10 and 12 are opened. Depending on whether fresh or recycled inert gas is used, valve V21 or V23 is also opened, and, depending on the pressure, if a compressor is required, valves V6, V22 or V24 are opened, while V21 or V23 is closed.

[0065] When the pressure in the furnace space 120 reaches or approaches the desired pressure, such as atmospheric pressure (approximately 1 bar), the heating elements 121 inside or outside the furnace 120 are switched on (if this has not occurred before). Preferably, the heating elements 121 provide said heat to the furnace space 120 by heating said supplied (inert / reducing / carbon-containing) gas, which in turn heats the material 142 in the container 140. As already mentioned above, the heating elements 121 may be arranged at a position through which the inert / reducing / carbon-containing gas supplied to the furnace space 120 flows, so that the heating elements 121 will be substantially immersed in (completely or substantially completely surrounded by) the newly supplied inert / reducing / carbon-containing gas during the initial heating, reduction and carburizing steps, respectively. In other words, heat may advantageously be provided directly to the inert gas and / or directly to the reducing gas and / or directly to the carbon-containing gas, whichever gas is simultaneously provided to the furnace space 120 (in said initial or subsequent steps).

[0066] During the remainder of the initial heating step, valves V1 - V5 and V7 - V20 are closed, whereas valves V21 - V24 and V6 together with compressor 270 are controlled by the control means to achieve a controlled recycle and / or supply of fresh inert gas as described below.

[0067] Therefore, during this initial heating step, the control device 201 is arranged to control the heat and inert gas providing device 121, 330, 340 to provide heat and inert gas to the furnace space 120. This can take place in such a way that the heated inert gas heats the charged metal material 142 to a temperature above the boiling point of water contained in the metal material 142. As a result, said contained water evaporates.

[0068] During the initial heating step, the charge material 142 is heated to a first temperature, which may be a predetermined temperature, such as a temperature above the boiling point of water at the current pressure within the furnace space 120. Preferably, however, the first temperature to which the charge material is heated is the desired processing temperature in the subsequent reduction step, or at least within 100°C of the desired processing temperature. This desired processing temperature is hereinafter referred to as the "second" temperature. It should be noted that the second temperature will typically be significantly above the boiling temperature of water. In embodiments of reduced iron oxide materials, the desired reduction processing temperature (second temperature) is in the range of about 350°C or more, such as about 400-700°C.

[0069] The inert gas may be nitrogen, but may also be any other suitable inert gas, such as a noble gas, or any mixture of several such inert gases. The inert gas preferably has a lower density than water vapor at the same pressure.

[0070] In some embodiments, during the initial heating step, the inert gas is circulated in a closed loop through the loaded metal material 142. For example, a fan or pump 250 may be used to push the inert gas through 230, 240 in a closed loop, the furnace space 120 forming part of such a closed loop, and the inert gas flows through and through the furnace space 120 on the way around the closed loop. Such circulation may occur during the filling of the furnace space 120 with the inert gas to a desired pressure (a "first" operating pressure) and / or after such desired pressure has been reached. During the circulation process, the inert gas may be heated to ultimately assume the first temperature.

[0071] In some embodiments, during the initial heating step, the inert gas is provided at or up to a predetermined overpressure (again, the first operating pressure), which may be at least 2 bar, such as at least 3 bar. Then, before the subsequent reduction step, the inert gas is exhausted again, such as into the container 330, to a pressure lower than the overpressure. This lower pressure may be approximately 1 bar, such as 0.5-2 bar, such as 0.8-1.5 bar.

[0072] Figure 1a The state of the furnace 100 during the heating step is shown, wherein the furnace space 120 is completely filled with an inert gas.

[0073] Figure 4 A timeline of an exemplary process according to the present method is shown. Figure 4 In the figure, the solid line shows the partial pressure of nitrogen (inert gas) as a function of time (horizontal axis) (measured on the left vertical axis); the dashed line shows the partial pressure of hydrogen (reducing gas) as a function of the same time (measured on the left vertical axis); the dotted line shows the partial pressure of air as a function of the same time (measured on the left vertical axis); the sparse dashed line shows the partial pressure of methane (carbon-containing gas) as a function of the same time (measured on the left vertical axis); the dense dashed line shows the temperature of the furnace 120 as a function of the same time (measured on the right vertical axis).

[0074] It is worth noting that Figure 4 It is provided merely to illustrate the concepts presently described and is simplified for the sake of clarity.

[0075] from Figure 4 As can be clearly seen in FIG. 1 , the partial pressure of the inert gas increases with increasing temperature until a first temperature (in this example, about 650° C.) is reached, which in the illustrated case is the same as the second temperature and is the desired reduction step treatment temperature. The pressure and temperature are maintained for a period of time while the inert gas can circulate in the closed loop, at least until the charge material 142 has reached the first temperature and all or substantially all of the contained water has evaporated to form water vapor. Figure 4 As can be seen in Figure 1, the air is first exhausted to about 0.5 bar, but since the air consists mainly of nitrogen and oxygen, the amount of air will be reduced to about zero (note that Figure 4 is a simplified view).

[0076] In the subsequent reduction step, reducing gas is supplied to the furnace space 120 .

[0077] Prior to supplying the reducing gas, the current pressure of the inert gas may first be reduced, such as by evacuating a portion of the inert gas to the vessel 330 via outlets 173a or 173b in the general manner discussed above, to a desired predetermined total pressure within the furnace space 120 used at the start of the reduction step. The predetermined pressure may be, for example, at least 0.8 bar. The predetermined pressure may also be at most 2 bar, such as at most 1.5 bar. Most preferably, the predetermined pressure is about 1 bar. However, in Figure 4 In the simple example provided, substantially the same total pressure of about 6 bar is maintained throughout the process, so that nitrogen is exhausted while hydrogen is filled at a corresponding rate.

[0078] In other embodiments, an inert gas partial pressure, such as 1-2 bar, may be maintained from the initial heating to the reduction stage and during the reduction stage.

[0079] like Figure 1a-1dAs shown, the reducing gas is preferably provided to the top 125 of the furnace space 120, above the loaded metal material 142. Preferably, the top 125 is positioned so that the reducing gas is released into the furnace space 120 at a point less than 0.5 m from the highest position of the furnace space 120. Preferably, the reducing gas is released into the furnace space 120 at least 0.3 m, such as at least 0.5 m, above the highest point of the loaded material 142.

[0080] Furthermore, in some embodiments, the reducing gas is provided in a flow that is at least predominantly laminar at the point of release of the reducing gas into the furnace space 120. In other words, at least 50% by volume of the released reducing gas is laminar at the point of release.

[0081] The reducing gas may be hydrogen or any other suitable reducing gas, such as carbon monoxide. In any case, preferably, at the current pressure in the furnace space 120, the density of the reducing gas is less than, preferably significantly less than, the inert gas, and also less than, preferably significantly less than, water vapor. Preferably, the inert gas is at least 5 times lighter than the inert gas and water vapor. In the preferred case of using hydrogen as the reducing gas, at the same pressure, the density of hydrogen is only about 10% of the density of nitrogen and water vapor, respectively.

[0082] The laminar release flow is intended to minimize the mixing of inert gas and reducing gas. Due to the density difference, the reducing gas will move upwards, while the inert gas moves downwards, evaporating and forming (through the reduction process) water vapor. Depending on the detailed embodiment, for example in terms of time and detailed furnace space 120 design, it is preferred to use a laminar reducing gas release in the top 125 of the furnace space 120 to minimize the mixing of reducing gas and inert gas.

[0083] For example, the reducing gas may be released into the furnace space 120 through a porous block of ceramic material, or through a metal or refractory plate comprising a plurality of through holes, so as to spread the released reducing gas over a large surface. Such a release surface for the reducing gas may be at least 0.1 m 2 , such as at least 0.2m 2 Alternatively or in addition, the opening of the duct 171 into the furnace space 120 may have a large cross section perpendicular to the main reducing gas flow direction, such as at least 0.02 m 2 Or even at least 0.02m 2 .

[0084] As can be understood from the above, when the reducing gas begins to be released, the furnace space 120 may already be completely filled with the inert gas. Then, when the reducing gas is released at the top 125 of the furnace space 120, due to the density difference, the reducing gas will occupy the topmost part of the furnace space 120. A horizontal gas surface will be defined between the reducing gas and the bulk of the inert gas, and as the amount of reducing gas increases, the reducing gas pushes the surface and the inert gas downward due to its lower density.

[0085] Preferably, when reducing gas is provided, it is provided to the furnace space 120 without any recirculation of reducing gas. Preferably, there is also no recirculation of inert gas. In this article, "no recirculation" means that no reducing / inert gas is discharged from the furnace space 120. In other words, all reducing / inert gases released into the furnace space 120 are retained in the space defined by the furnace space 120 in combination with any peripheral space (such as heat exchanger 160 and groove 161), which together with the furnace space 120 form a closed space for gas. Preferably, this closed space also does not include any closed-loop circulation loop of the type discussed above, through which a fan, pump or the like is used to actively force gas to pass. Therefore, with regard to the inert gas during the heating step, this is different from the circulation situation discussed above.

[0086] In contrast, when reducing gas is supplied to the furnace space 120 , the pressure within the furnace space 120 increases accordingly as the surface moves downward through the furnace space 120 , unless an inert gas simultaneously flows out from the bottom of the furnace space 120 .

[0087] From 25 minutes onwards, this downward movement of the surface Figure 4 As shown in the figure. Figure 1b , where the surface boundary 126 between the upper reducing gas 126a and the lower inert gas 126b is still located above the material 142. Figure 1c , the surface boundary 126 is completely located below the loading material 142, in other words, the material 142 is completely surrounded by the reducing gas.

[0088] Throughout the initial heating step, the reduction step and any carburizing step (see below), the gas flow supplied to (or exhausted from) the furnace space 120 is controlled by the control device 201. As a result, in the particular case of the reduction step, there will be a continuous, relatively slow but steady flow of reducing gas, increasing the total pressure in the furnace space 120 and forcing the boundary surface 126 downward. When the boundary surface 126 has reached Figure 1c When the pressure reaches the position shown, the set pressure should have been reached and additional reducing gas should only be added to compensate for the reducing gas converted to water vapor.

[0089] It should also be understood that during the reduction step, heat is provided to the furnace space 120 (via the heating element 121 and heat exchanger 160 as described above) in order to reach (if not already prevail) and maintain a second temperature of the loaded metal material 142. The second temperature is high enough that the metal oxides present in the loaded metal material 142 are reduced, thereby causing water vapor to form. As described above, the formed water vapor is condensed and collected in the condenser 160.

[0090] However, reduction of the material 142 will not begin until the reducing gas contacts the material 142. Therefore, during the reduction step, as discussed above, while the inert gas is still present in the furnace space 120, the reducing gas is provided, and the control unit 201 is arranged to provide a flow of reducing gas such that the reducing gas is provided and thereby pushes the boundary surface 126 downward, the inert gas being pushed downward until the loaded metallic material 142 is completely contained in the reducing gas. Due to the heat provided, the reducing gas surrounding the material 142 will maintain a predetermined temperature despite the endothermic nature of the reduction process.

[0091] The loaded material 142 will remain completely surrounded by this hot reducing gas until the material 142 is completely reduced. The length of the holding time varies depending on the type of material, but it is expected that about 5-15 minutes will be sufficient in typical cases. During this period, the second operating pressure is maintained by the control device 201.

[0092] In general, the control device 201 is arranged to continuously add reducing gas during the reduction step, e.g. at a determined reduction temperature, in order to maintain at least a desired stable or increasing (e.g. monotonically increasing) reducing gas partial pressure curve (and total pressure curve) in the furnace space 120 and in particular to counteract the pressure drop in the lower part of the furnace space 120 (and in the lower part of the heat exchanger 160) due to the continuous condensation of water vapor in the heat exchanger 160 (see below). The total energy consumption depends on the efficiency of the heat exchanger 160, in particular its ability to transfer thermal energy from the hot gases entering the heat exchanger 160 and the condensation heat of the condensed water vapor to the incoming reducing gas. In the exemplary case of Fe2O3, when hydrogen is used as the reducing gas, the theoretical energy required for heating the oxide, heat compensating the endothermic reaction and reducing the oxide is about 250 kWh per 1000 kg of Fe2O3. For Fe3O4, the corresponding figure is about 260 kWh per 1000 kg.

[0093] Once the loading material 142 is surrounded by the reducing gas, the reducing gas contacting the loading material 142 will form a gas mixture with the water vapor from the reduced loading material. Since the water vapor is heavier than the reducing gas, the water vapor will flow downward into the inert gas below the reducing gas and further downward to the condenser 160.

[0094] In the heat exchanger 160, heat will be exchanged from the hot gases coming from the furnace space 120 to the newly supplied cold reducing gas arriving at the duct 171, whereby the latter will be preheated by the former.

[0095] Due to the cooling of the hot gas flow in the heat exchanger 160, water vapor contained in the cooling gas will condense. This condensation produces liquid water, which is collected in the tank 161, but also produces condensation heat. Preferably, the heat exchanger 160 is also arranged to transfer this condensation heat energy from the condensed water to the inert / reducing / carbon-containing gas to be provided into the furnace space 120.

[0096] The condensation of the contained water vapor will also reduce the pressure of the hot gases flowing downward from the furnace space 120 , providing space for more hot gases to pass downward through the heat exchanger 160 .

[0097] The condensation of water vapor in the heat exchanger 160 will reduce the partial pressure of the water vapor at the lower end of the structure, further causing the water vapor generated in the loading material 142 to flow downward.

[0098] Preferably, the reducing gas supplied to the heat exchanger 160 and any carbon-containing gas supplied are at room temperature or have a temperature slightly below room temperature. Figure 1a-Figure 1c The heating element 121 shown as being arranged upstream of the heat exchanger in FIG. 1 may, if used, be arranged after (downstream) the heat exchanger 160 along the conduit 171, after the heat exchanger 160 and before the discharge point at the top 125 of the furnace space 120. The latter case is as shown in FIG. Figure 1d shown.

[0099] like Figure 4 As shown, the downward pressure of the surface boundary 126 can be achieved by increasing the total pressure in the furnace space 120 while maintaining a constant partial pressure of the inert gas. However, in some embodiments, the inert gas can be discharged to a certain extent from a point below the charge material 142, such as via a conduit 173a above the condenser 160, but preferably via a conduit 173b below the condenser 160. Such a discharge point is preferably located in the lower part of the furnace space 120 or completely below the furnace space 120.

[0100] A combination of an increase in the partial pressure of the reducing gas and a decrease in the partial pressure of the inert gas may also be used. This is then controlled by the control device 201. However, preferably, during the reduction step, no inert gas is discharged from the enclosed space to which the furnace space 120 belongs. It should be understood that the control device 201 needs to adjust the flow rate of the reducing gas (and any discharge of the inert gas) to take into account the gas pressure increased due to the water vapor formed and the gas pressure reduced due to the condensation of the water vapor formed. This adjustment can be based on pressure measurements and / or experience. It is important to control the vertical position of the boundary surface 126 so that all the material 142 is in contact with the reducing gas.

[0101] Of course, during the reduction step, the control device 201 is also arranged to control the supplied heat (in 160, 201) accordingly so that the loaded metal material 142 is again maintained at the second temperature at which the reduction chemical reaction is maintained until completion.

[0102] In the case of hydrogen reduction of iron oxide material, the hydrogen will begin to reduce the charge material 142 at approximately 350-400°C to form metallic iron, forming pyrophytic iron and water vapor according to the following formula:

[0103] Fe2O3+3H2=2Fe+3H2O

[0104] Fe3O4+4H2=3Fe+4H2O

[0105] As described above, the reaction is endothermic and is driven by thermal energy provided by hot hydrogen flowing downward from above in the furnace space 120 .

[0106] Therefore, during the reduction step, water vapor is generated in the loaded material. The formed water vapor is continuously condensed and collected in a condenser arranged below the loaded metal material. Figure 1a-1d In the example shown, the condenser is in the form of a heat exchanger 160 .

[0107] As mentioned above, in some embodiments of the invention, the reduction step and possibly any carburizing step, including the condensation of water vapor, is performed so that a pressure greater than 1 bar relative to atmospheric pressure (second operating pressure) is established in the furnace space 120. In particular, the reducing gas is provided so that the pressure greater than 1 bar is reached and maintained. It should be noted that this pressure greater than 1 bar is a pressure higher than atmospheric pressure.

[0108] Specifically, in the reduction step, additional reducing gas may be supplied to the furnace space 120 in order to achieve and / or maintain a predetermined overpressure (corresponding to the second operating pressure) therein.

[0109] In a subsequent reduction gas discharge step performed after the metal material 142 has been reduced (preferably completely reduced or at least substantially completely reduced), the remaining reduction gas is discharged from the furnace space 120. This discharge of the reduction gas is preferably performed from a discharge point at the top of the furnace space 120 (the same top from which the reduction gas is released in the reduction step). For example, the reduction gas can be discharged via the same conduit 171 as the conduit 171 used to release the reduction gas, but then discharged in the opposite flow direction. Under the control of the control unit 201 as described above, the used reduction gas can be directed to the container 280 to be reused in a subsequent processing cycle with the new material to be reduced.

[0110] It will be appreciated that during the discharge process, as the pressure of the reducing gas decreases, the inert gas will push the reducing gas upward, whereby almost all of the reducing gas can be collected for reuse. This may involve the amount of inert gas in the closed system (including the furnace space 120) remaining constant throughout the discharge process, or supplying additional inert gas from below, such as by supply 173a or 173b, so as to increase the pressure in the furnace space 120. The evacuation may return to atmospheric pressure in the furnace space 120, and the furnace space 120 may then be completely filled with inert gas. This may require discharging any excess inert gas, preferably from a discharge point below the material 142 as described above (from a lower portion of the furnace space 120 or a point below the entire furnace space 120).

[0111] The method may further include a carbonization step, i.e., a step of supplying a carbon-containing gas to the furnace space 120, so that the metal material 142, which has been heated by the supplied heat and reduced by reacting with the reducing gas, is carbonized by the carbon-containing gas. This supply of the carbon-containing gas may then be performed by mixing the carbon-containing gas with the reducing gas before the reducing gas is discharged from the furnace space 120 back to the atmospheric pressure in the furnace space 120 (and thereafter discharged to the container 280).

[0112] The carbon-containing gas can be any carbon-containing gas that can react chemically with the reduced metal material to carburize the latter. Examples of suitable carbon-containing gases include various gaseous (at the temperature and current pressure in the furnace space 120 during the implementation of the present method) hydrocarbons, such as methane, ethane, propane, propylene and the like. Preferably, the carbon-containing gas does not contain more than trace amounts of carbon monoxide, because this will effectively prevent carbon monoxide and carbon dioxide from forming residual products after the current carburizing process is completed. In particular, it is preferred that no carbon monoxide is supplied to the furnace space 120 in the carbon supply step. The density of the carbon-containing gas should be less than that of an inert gas, such as methane and nitrogen (for example).

[0113] As mentioned above, during the reduction of iron, free iron (Fe) is formed, which then opens to accept carbon (C) to form Fe3C.

[0114] Figure 5 This shows the relationship between the ability of H2 to reduce Fe2O3 and the increase in temperature. Figure 5 As shown, reduction using hydrogen is particularly active in the temperature range of about 400°C to 700°C.

[0115] Correspondingly, carburization of the same Fe2O3 using a gaseous carbon source is most active in the interval of approximately 650°C-900°C.

[0116] For example, Fe3O4 exhibits similar properties with respect to reduction / carburization and temperature.

[0117] This means that a process in which the bulk of the reduction of the metallic material is first carried out at a relatively low temperature and then the bulk of the carburization of the metallic material is carried out after additional heating will be efficient.

[0118] like Figure 4 As shown, the subsequent carburizing step is performed at a third operating temperature higher than the second operating temperature, such as between 650°C and 900°C ( Figure 4 The operating temperature can be controlled by the control unit 201 through corresponding control of the heating element 201.

[0119] Likewise Figure 4 As shown, the supply of carbon-containing gas also takes place together with a corresponding exhaust of inert gas, so that substantially the same total pressure is maintained within the furnace space 120 .

[0120] The subsequent carburizing step may also be performed at a third operating pressure, which may be the same as or different from the second operating pressure.

[0121] There are also cases where the presence of water vapor assists the carburizing process, which is one reason for carrying out the carburizing step and the reducing step simultaneously using a mixed reducing gas and carbon-containing gas.

[0122] In the specific case of methane as carbon-containing gas and hematite / magnetite as metallic material, the following carburizing chemical reaction takes place in the furnace space 120:

[0123] Fe3O4+4H2=3Fe+4H2O

[0124] 3Fe+CH4=Fe3C+2H2

[0125] The reaction between CH4 and Fe includes a sub-reaction in which methane reacts with water vapor formed from the reducing hydrogen:

[0126] CH4+H2O=2CO+3H2

[0127] The carburization itself then takes place primarily via the well-known hydrogen-water reaction, in which carbon monoxide and hydrogen react with the iron surface formed and form water vapor, while the released carbon atoms can be taken up in place of the previously released oxygen atoms.

[0128] Because the surface of the reduced iron is porous due to reduction, the total iron surface area will generally be very large, which results in an efficient carburizing process, especially when the metallic material 142 is provided as a particulate material.

[0129] From the above formula it can be seen that a certain amount of hydrogen is formed during carburizing, which is why less hydrogen is required compared to other cases.

[0130] Preferably, after the carbon supplying step is completed, the final carburized metal material has a carbon content of 1 wt% to 4 wt%.

[0131] In some embodiments, the reduction step, including any carbonization step performed simultaneously with the reduction step, is performed for at least 10 minutes, such as at least 20 minutes, such as at least 30 minutes. In particular, preferably, during this time, the loaded metal material 142 is completely surrounded by the reducing gas.

[0132] Accordingly, this period of time may be at most 30 minutes, such as at most 15 minutes, such as at most 10 minutes.

[0133] Furthermore, the reduction step may be performed until no additional reducing gas is needed to maintain a predetermined overpressure in the furnace space 120, and / or until a predetermined amount of liquid water has been collected in said condenser 160, and / or until no additional heat is needed to maintain a second operating temperature in the furnace space 120. Such current pressures, amounts and temperatures as well as the additional pressure or heat provided may be measured as described above and checked by the control device 201.

[0134] For these purposes, the aforementioned third predetermined temperature may be at least 600°C, such as between 640-750°C, preferably about 660°C.

[0135] The temperature of the charge material 142 may be measured directly, for example by measuring thermal radiation from the charge material 142 using a suitable sensor, or indirectly via the temperature sensor 123 .

[0136] Alternatively, the reduction and / or any carburizing steps may be performed for set times based on experience.

[0137] In some embodiments, the reduction and / or any carburizing steps may also be performed iteratively, with the control device 201 allowing a steady-state pressure to be reached inside the furnace space 120 in each iteration before an additional amount of hydrogen is supplied to the furnace space. The heat supply may also be iterative (pulsed), or on during the entire main reduction and possible carburizing steps.

[0138] The formation of water vapor in the charge material 142 locally increases the gas pressure, in effect creating a pressure change between the furnace space 120 and the tank 161. As a result, the water vapor that forms will sink through the charge material 142 and condense in the heat exchanger 160, thereby reducing the pressure on the far side (relative to the furnace space 120) of the heat exchanger 160. These processes thus create a net downward movement of gas through the charge 142, wherein the newly added hydrogen compensates for the pressure loss in the furnace space 120.

[0139] The heat content of the gas flowing out of the furnace space 120 , in particular the heat of condensation of the water vapor, is transferred to the incoming inert / hydrogen / carbon-containing gas in the heat exchanger 160 .

[0140] Thus, as long as there is metal material to be reduced and water vapor generated thereby, the process is maintained, resulting in the downward gas movement. Once water vapor ceases to be generated (this is because substantially all of the metal material 142 has been reduced), without the supply of additional reducing (or carbonaceous) gas, the pressure is balanced throughout the interior of the furnace 100, and the measured temperature is similar throughout the furnace space 120. For example, the measured pressure difference between a point in the gas-filled portion of the tank 161 and a point above the loaded material 142 will be less than a predetermined amount, which may be at most 0.1 bar. Additionally or alternatively, the measured temperature difference between a point above the loaded material 142 and a point below the loaded material but on the furnace space 120 side of the heat exchanger will be less than a predetermined amount, which may be at most 20°C. Thus, when such homogeneity of pressure and / or temperature is reached and measured, the reduction step may end.

[0141] Typically, the heating element 121 is not turned off until carburization (if used in the process) is complete, which typically occurs at a later point in time.

[0142] After complete reduction and carburization have occurred, the method according to the invention may comprise a cooling step and an emptying step, which will be described below.

[0143] Therefore, in a subsequent cooling step, the remaining inert gas atmosphere in the furnace space 120 is cooled to a temperature of at most 100° C., preferably approximately 50° C., and thereafter discharged from the furnace space 120 and collected, such as into a container 330 .

[0144] In the case where a single furnace 100 / 220 is not connected to one or several furnaces, the charge material 142 can be cooled using a fan 250 arranged downstream of an air-water type cooler 240, which fan 250 is in turn arranged to cool the inert gas (such as circulating in a closed loop through the fan 250, passing through valve V12, heat exchanger 240, fan 250 and valve V10, leaving the furnace space 120 via outlet duct 173a or 173b, and entering the furnace space 120 again via inlet duct 171).

[0145] Thus, the heat exchanger 240 transfers heat energy from the circulating hydrogen to water (or a different liquid) from which it can be put to use in a suitable manner, for example in a district heating system. A closed loop is achieved by closing all valves V1-V24 except valves V10 and V12.

[0146] Since the inert gas circulates through the charge material 142 in the vessel 140 in this case, the inert gas absorbs thermal energy from the charge material 142, thereby providing effective cooling of the charge material while the inert gas circulates in a closed loop.

[0147] In a different example, the heat energy obtained from the cooling of the furnace 100 / 220 is used to preheat the different furnace 210. This is then achieved by the control device 201, in contrast to the cooling closed loop described above, closing the valve V12 and opening the valves V13, V14. In this way, the hot inert gas coming from the furnace 220 is taken to a gas-gas type heat exchanger 230, preferably a countercurrent heat exchanger, in which the hydrogen supplied in the initial or main heating step performed relative to the other furnace 210 is preheated. Thereafter, the slightly cooled gas coming from the furnace 220 can be circulated through the heat exchanger 240 to be further cooled before being reintroduced into the furnace 220. Again, the inert gas coming from the furnace 220 is circulated in a closed loop using a fan 250.

[0148] Therefore, as described above, cooling of the inert gas in the cooling step may be performed via heat exchange with the reducing gas supplied to the different furnace 210 space 120 so as to perform the reducing step and condensation related to the different furnace 210 space 120 .

[0149] As soon as the inert gas is not hot enough to heat the reducing gas supplied to the furnace 210 , the control device 201 closes the valves V13 , V14 again and opens the valve V12 again so that the reducing gas from the furnace 220 is brought directly to the heat exchanger 240 .

[0150] Regardless of how its thermal energy is processed, the inert gas from the furnace 220 is cooled until it (or more importantly, the charge material 142) reaches a temperature below 100° C. to avoid reoxidation of the charge material 142 when subsequently exposed to air. The temperature of the charge material 142 may be measured directly using a suitable means (such as one of the means described above), or indirectly by measuring the temperature of the inert gas exiting via the outlet conduit 173 using a suitable means.

[0151] Cooling of the inert gas can be carried out while maintaining the pressure of the inert gas (which can be above atmospheric pressure after venting the reducing gas and any carbon-containing gas), or the pressure of the inert gas can be reduced because once valves V10 and V12 are opened, the hot inert gas is allowed to occupy a larger volume (the volume of the closed-loop conduit and the heat exchanger).

[0152] In a subsequent step, the inert gas is exhausted from the furnace 220 space 120, and collected in a container 330 for used inert gas, the exhaust being carried out by means of a vacuum pump 260, possibly in combination with a compressor 270. The exhaust of the furnace space 120 is preferably carried out before a pressure of at most 0.5 bar, or even at most 0.3 bar, is detected inside.

[0153] Since the furnace space 120 is closed, only the reducing / carbon-containing gas consumed in the chemical reduction reaction is removed from the system, while the remaining reducing gas is necessary to maintain the reducing gas / water vapor balance in the furnace space 120 during the reduction step. This exhausted reducing gas is fully available for running subsequent batches of newly loaded metal material to be reduced.

[0154] Thereafter, valves V7, V8 are closed, valve V9 is opened to allow air to enter the system to replace the charge material, and valve V11 is opened to drain condensed water, if applicable.

[0155] In a subsequent step, the furnace space 120 is opened, for example by loosening the fastening means 111 and opening the upper part 110. The container 140 is removed and replaced by a container containing a new batch of charged metallic material to be reduced.

[0156] In a subsequent step, the removed reduced material may be placed under an inert atmosphere, such as a nitrogen atmosphere, to avoid reoxidation during transportation and storage.

[0157] For example, the reduced metal material may be arranged in a flexible or rigid transport container filled with an inert gas. A plurality of such flexible or rigid containers may be arranged in the transport container, and then the space around the flexible or rigid containers may be filled with an inert gas. Thereafter, the reduced metal material may be safely transported without the risk of reoxidation.

[0158] In the following step, the method ends.

[0159] The following table shows the approximate balance between hydrogen H2 and water vapor H2O for different temperatures in the furnace space 120:

[0160]

[0161] Requires approximately 417Nm 3 of hydrogen H2 to reduce 1000kg of Fe2O3, and about 383m 3 of hydrogen H2 to reduce 1000kg of Fe3O4.

[0162] The following table shows the amount of hydrogen required to reduce 1000 kg of Fe2O3 and Fe3O4 respectively at atmospheric pressure and in an open system (according to the prior art), but at different temperatures:

[0163]

[0164] The following table shows the amount of hydrogen required to reduce 1000kg Fe2O3 and Fe3O4 at different pressures and temperatures:

[0165]

[0166] As described above, the reduction step according to the invention is preferably carried out at high pressure and temperature exceeding 1 bar. In most reduction steps where partial reduction is carried out, it has been found to be advantageous to use a combination of a heated hydrogen temperature of at least 550°C and a pressure of at least 2.3 bar in the furnace space 120.

[0167] Preferred embodiments have been described above. However, it will be apparent to those skilled in the art that many modifications may be made to the disclosed embodiments without departing from the basic concept of the invention.

[0168] For example, depending on the detailed prerequisites, the geometry of the furnace 100 may be different.

[0169] The heat exchanger 160 is depicted as a tubular heat exchanger. While this has been found to be particularly advantageous, it will be appreciated that other types of gas-to-gas heat exchangers / condensers are possible. The heat exchanger 240 may have any suitable configuration.

[0170] The waste heat from the cooled inert gas can also be used in other processes requiring thermal energy.

[0171] The metallic material to be reduced is described as an iron oxide. However, the present method and system can also be used to reduce and carburize metallic materials, such as the above-mentioned metal oxides containing Zn and Pb, which evaporate at a temperature below about 600-700°C.

[0172] The combined direct reduction and possible carburization principle of the invention can also be used for metallic materials having a higher reduction temperature than iron ore, after appropriate adjustments to the structure of the furnace 100, such as to the structural materials used.

[0173] The invention is thus not limited to the described embodiments but may vary within the scope of the appended claims.

Claims

1. A method for producing a direct reduced metal material (142), the method comprising the following steps: a) loading a metal material (142) to be reduced into a closed furnace space (120); b) providing heat and an inert gas to the furnace space (120), whereby the heated inert gas fills the furnace space (120) and heats the loaded metal material (142) to a first temperature; c) providing reducing gas to the furnace space (120); d) providing heat to the furnace space (120) to maintain a second temperature in the loaded metal material (142) sufficiently high so that metal oxides present in the loaded metal material (142) are reduced, thereby causing water vapor to form; e) condensing and collecting the water vapor formed in step d) in a condenser (160); and f) exhausting the remaining reducing gas from the furnace space (120) after the loaded metal material (142) has been reduced, It is characterized in that, at the same pressure, the reducing gas has a lower density than the inert gas, and in step c), the reducing gas is provided while the inert gas still exists in the furnace space (120), whereby the provided reducing gas thereby pushes the inert gas downwards until the loaded metal material (142) is completely contained in the reducing gas.

2. The method according to claim 1, characterized in that: In step b), the inert gas is circulated in a closed loop through the loaded metallic material (142).

3. The method according to claim 1 or 2, characterized in that: In step b), the inert gas is provided at a predetermined overpressure and, prior to step c), the inert gas is evacuated to a pressure below the overpressure.

4. The method according to any one of the preceding claims, characterized in that In step c), the reducing gas is provided to the top (125) of the furnace space (120), above the charged metal material (142).

5. The method according to claim 4, characterized in that In step c), the reducing gas is provided in the form of a flow which is at least predominantly laminar.

6. The method according to any one of the preceding claims, characterized in that In steps c) to e), the reducing gas is provided to the furnace space (120) without any recirculation of the reducing gas or of the inert gas.

7. The method according to any one of the preceding claims, characterized in that In step d), additional reducing gas is supplied to the furnace space (120) in order to achieve and / or maintain a predetermined overpressure therein.

8. The method according to any one of the preceding claims, characterized in that The method includes exhausting the inert gas from the furnace space (120) from a lower portion of the furnace space (120) or a point below the furnace space (120), below the loaded metal material (142).

9. The method according to any one of the preceding claims, characterized in that In step (f), the remaining reducing gas is exhausted from the furnace space (120) from the top (125) of the furnace space (120) above the loaded metal material (142).

10. The method according to claim 9, characterized in that Step f) results in the furnace space (120) being filled with an inert gas, and the method further comprises a subsequent step in which the inert gas circulates in a closed loop in order to cool the reduced metallic material (142).

11. The method according to any one of the preceding claims, characterized in that The method further comprises an initial step of evacuating the existing atmosphere from the furnace space (120) so as to achieve a gas pressure of less than 1 bar, such as a gas pressure of at most 0.5 bar, within the furnace space (120).

12. The method according to any one of the preceding claims, characterized in that The method also includes providing a carbon-containing gas, such as a gaseous hydrocarbon, to the furnace space (120) such that the heated and reduced metal material (142) is carburized by the carbon-containing gas.

13. The method according to any one of the preceding claims, characterized in that The reducing gas is hydrogen and / or carbon monoxide.

14. The method according to any one of the preceding claims, characterized in that The inert gas is nitrogen.

15. The method according to any one of the preceding claims, characterized in that The reducing gas is preheated in a heat exchanger (160) arranged to transfer thermal energy of water evaporated from the loaded metal material (142) to the reducing gas.

16. The method according to any one of the preceding claims, characterized in that Step d) and step e) are performed until no additional reducing gas is required to maintain a predetermined overpressure in the furnace space (120), and / or until a predetermined amount of liquid water has been collected in the condenser (160), and / or until no additional heat is required to maintain a second temperature in the furnace space (120).

17. The method according to claim 3, 7 or 13, characterized in that The predetermined overpressure is an absolute pressure of at least 2.3 bar, such as at least 2.5 bar, such as at least 3 bar.

18. The method according to any one of the preceding claims, characterized in that For an amount of metal material (142) up to 5 tons, step d) and step e) are performed within at least 2 minutes, such as at least 3 minutes; and for an amount of metal material (142) up to 10 tons, step d) and step e) are performed within at least 5 minutes, such as at least 10 minutes.

19. The method according to any one of the preceding claims, characterized in that For an amount of metal material (142) up to 5 tons, step d) and step e) are performed within at most 30 minutes, such as at most 15 minutes, such as at most 10 minutes; and for an amount of metal material (142) up to 10 tons, step d) and step e) are performed within at most 60 minutes, such as at most 30 minutes, such as at most 15 minutes.

20. A system for producing a direct reduced metal material (142), the system comprising: a furnace space (120) arranged to receive and contain a metallic material (142) to be reduced; a heating and gas supply device (250) arranged to provide heat, inert gas and reducing gas to the furnace space (120); a control device (201), the control device (201) being arranged to control the heating and gas supply device (250) to provide heat and inert gas to the furnace space (120) so that the heated inert gas fills the furnace space (120) and heats the loaded metal material (142) to a first temperature; to provide reducing gas to the furnace space (120); to provide heat to the furnace space (120) to keep a second temperature in the loaded metal material (142) high enough so that metal oxides in the loaded metal material (142) are reduced, thereby causing water vapor to form; and to exhaust the remaining reducing gas from the furnace space (120) after the loaded metal material (142) has been reduced, The system comprises a condenser (160), wherein the condenser (160) is arranged to condense and collect water vapor, Characterized in that, at the same pressure, the reducing gas has a lower density than the inert gas, and the control device (201) is arranged to control the heating and gas supply device (250) to provide the reducing gas while the inert gas is still present in the furnace space (120), whereby the reducing gas provided thereby pushes the inert gas downwards until the loaded metal material (142) is completely contained in the reducing gas.

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