Method and system for producing direct reduced metal

Abstract

A method for manufacturing a direct reduction metal material (142) is disclosed. The method includes the following steps: a) charging the material into a closed furnace space (120); b) filling the furnace space with a heated inert gas and heating the material; c) supplying a reducing gas; d) supplying heat, whereby metal oxides present in the material are reduced and water vapor is formed in sequence; e) condensing and recovering the water vapor in a condenser (160); and f) discharging the remaining reducing gas from the furnace space. The method is characterized in that the reducing gas has a lower density than the inert gas at the same pressure, and in step c), the reducing gas is supplied while the inert gas is still present in the furnace space, so that the supplied reducing gas pushes the inert gas downward 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). In particular, the present invention relates to the direct reduction of metal oxides or metal ores in a controlled hydrogen atmosphere for producing such direct reduced metals.

Background Art

[0002] The production of direct reduced metals using hydrogen as a reducing agent is known per se. For example, SE7406174-8 and SE7406175-5 describe a method in which a charge of metal oxide or metal ore is exposed to a hydrogen atmosphere flowing through a charge of metal material, resulting in reduction to form a direct reduced pure metal.

[0003] Furthermore, Swedish published applications SE1950403-4, SE1951070-0 and SE2050771-1 disclose a process for directly reducing a metal material in a sealed hydrogen atmosphere and further a process for carburizing such a directly reduced metal material.

[0004] The present invention is particularly applicable when the metal material to be reduced is charged and processed batchwise.

Disclosure of the Invention

Problems to be Solved by the Invention

[0005] The prior art has several problems, including efficiency regarding heat loss and the amount of hydrogen gas used.

[0006] Also, it is desirable to enhance simplicity and procedure / time efficiency compared to the prior art solutions.

[0007] Therefore, it is desirable to realize a method for directly reducing a metal material that is thermally and energetically efficient and does not emit carbon monoxide or carbon dioxide into the atmosphere. The solution means must be expandable to a large throughput and be able to handle metal materials of different compositions.

[0008] The present invention solves the above problems.

Means for Solving the Problems

[0009] Therefore, the present invention relates to a method for producing a directly reduced metal material, the method comprising the following steps: a) charging 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 charged metal material to a first temperature; c) supplying a reducing gas to the furnace space; d) supplying heat to the furnace space so as to maintain the second temperature in the charged metal material sufficiently high, whereby metal oxides present in the charged metal material are reduced and water vapor is formed in sequence; e) condensing and recovering the water vapor formed in step d) in a condenser; and f) discharging the remaining reducing gas from the furnace space after the charged metal material has been reduced. The method is characterized in that the reducing gas has a lower density than the inert gas at the same pressure, and in step c), the reducing gas is supplied while the inert gas is still present in the furnace space, so that the supplied reducing gas pushes the inert gas downward until the charged metal material is completely surrounded by the reducing gas.

[0010] The present invention also relates to a system for producing a direct reduced metallic material, the system comprising: a furnace space arranged to receive and contain the metallic material to be reduced; heat and gas supply means arranged to supply heat, an inert gas, and a reducing gas to the furnace space; a control device arranged to control the heat and gas supply means to supply heat and the inert gas to the furnace space, whereby the heated inert gas fills the furnace space and heats the charged metallic material to a first temperature; to supply a reducing gas to the furnace space; to supply heat to the furnace space so as to maintain a second temperature of the charged metallic material sufficiently high, whereby metal oxides present in the charged metallic material are reduced and water vapor is formed in turn; and, after the charged metallic material has been reduced, to discharge residual reducing gas from the furnace space, the system comprising a condenser arranged to condense and recover the formed water vapor, the system being characterized in that the reducing gas has a lower density than the inert gas at the same pressure, and the control device controls the heat and gas supply means to supply the reducing gas while the inert gas is still present in the furnace space, such that the supplied reducing gas pushes the inert gas downward until the charged metallic material is completely surrounded by the reducing gas.

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

Brief Description of the Drawings

[0012]

Figure 1a

Figure 1b

Figure 1c

Figure 1d

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

DETAILED DESCRIPTION OF THE INVENTION

[0013] In Figures 1a to 1d, the same reference numerals are assigned to the same components.

[0014] Thus, Figures 1a to 1d show a furnace 100 for producing a directly reduced and carburized metallic material. In Figure 2, two such furnaces 210, 220 are illustrated. The furnaces 210, 220 may be identical to the furnace 100 or may differ in details. However, it is understood that everything described herein with respect to the furnace 100 is equally applicable to the furnaces 210 and / or 220, and vice versa.

[0015] Furthermore, it should be understood that everything described herein with respect to the method is equally applicable to the present system 200 and / or the furnaces 100; 210, 220, and vice versa.

[0016] The furnace 100 itself has many similarities with the furnaces disclosed in SE7406174-8, SE7406175-5, SE1950403-4, SE1951070-0 and SE2050771-1. For details of possible designs, please refer to these documents. However, an important difference between some of these furnaces and the furnace 100 of the present disclosure is that the furnace 100 of the present disclosure is not configured to operate in such a way that the reducing gas recirculates within the furnace 100 and returns to a recovery container arranged outside the furnace 100. In particular, the difference is that the reducing gas is not configured to operate in such a way that it recirculates from the furnace 100 (or the heating furnace space 120) and returns to the furnace 100 (or the heating furnace space 120) during a single and identical batch process of the charge material to be reduced.

[0017] Instead, as will be apparent from the following description, the furnace 100 is configured for the operation of batch-reducing, and optionally carburizing, one enclosure of material at a time, in the sense that a reducing gas is supplied to the furnace 100 but not removed therefrom during the batch-reducing and carburizing process; and, in the sense that a carbon-containing gas may be supplied to the furnace 100 but not removed therefrom during the batch-reducing and carburizing process described below, the furnace 100 is configured to operate as a closed system during such individual batch processes.

[0018] This means that the amount of reducing gas present within the furnace 100 is always maintained or increased during the reduction process. After the reduction is completed, the reducing gas is of course discharged from within the furnace 100, but there is no recirculation of the reducing gas during the reduction step. In some embodiments, as will become apparent below, the same applies to the carbon-containing gas.

[0019] Therefore, the furnace 100 is part of a closed system comprising a heating furnace space 120 configured to be pressurized to a pressure of 1 bar or more, for example 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 of the pressurization steps (with respect to inert gas, reducing gas and / or carbon-containing gas) can be configured such that the total pressure within the furnace space 120 remains within any one of the pressure intervals described in this paragraph and, in some cases, is maintained in that state. In particular, it applies to the first and second operating pressures described below.

[0020] In any case, the furnace space 120 is constructed to withstand the operating pressures described herein. The upper part 110 of the furnace 100 has a bell shape. The upper part 110 of the furnace 100 can be opened for loading the material 142 to be processed and can be hermetically closed using fastening means 111. The furnace space 120 is covered with a refractory material such as a brick material 130.

[0021] Unless otherwise stated, the term "pressure" in this specification specifically refers to the total gas pressure within the furnace space 120, as opposed to "partial pressure" which refers to the partial pressure of a specific gas.

[0022] Furthermore, since atmospheric pressure is approximately 1 bar, the expressions "pressure of 1 bar or more" and "pressure above atmospheric pressure" are intended to have the same meaning. Correspondingly, the expressions "pressure less than 1 bar" and "pressure below atmospheric pressure" are also intended to have the same meaning.

[0023] The furnace space 120 is configured to be heated using one or more heating elements 121. Preferably, the heating element 121 is an electric heating element. However, a radiator combustion tube or a similar fuel heating element can also be used. However, the heating element 121 does not generate combustion gases that chemically interact directly with the furnace space 120, which must continue to be chemically controlled for this purpose. The gaseous substances supplied to the furnace space during the main heating process described later are preferably only reducing gases and carbon-containing gases used as a carbon source for carburizing the metal material.

[0024] As is apparent from FIGS. 1a to 1d, the heating element 121 may be disposed inside and / or outside the furnace space 120. In the latter case, the heating element 121 may be provided such that the gas entering the furnace space 120 via the supply conduit 171 passes through the heating element 121 before entering the furnace space 120.

[0025] The heating element 121 is preferably made of a heat-resistant metal material such as a molybdenum alloy.

[0026] Additional heating elements can also be arranged in the heating furnace space 120. For example, heating elements similar to the element 121 may be provided on the side walls of the furnace space 120, for example, at a height corresponding to the charged material or at least at a height corresponding to the container 140. Such heating elements can assist in heating the charged material not only by gas but also by heat radiation.

[0027] As will be described later, the heat exchanger 160 is arranged to transfer thermal energy from the outflow gas from the furnace space 120 to the inflow gas into the furnace space 120.

[0028] As can be understood from the following, additional thermal energy is required to heat the charge material 142, at least during the reduction step. Most, for example substantially all or all, of this additional thermal energy supplied to the furnace space 120 during the reduction step is preferably supplied by a heating element 121 arranged outside the furnace space 120 and configured to heat the gas flowing into the furnace space 120 before such gas flows into the furnace space 120.

[0029] The furnace 100 also comprises a lower part 150 which, together with the upper part 110, forms a sealed container when the furnace is closed using fastening means 111.

[0030] In the lower part 150 of the furnace 100 there is a container 140 for the material 142 to be treated (reduced carburized). The container 140 may be supported on the refractory floor of the furnace space 120, for example along an opening channel 172 formed in the floor, such that gas can pass beneath the container 140.

[0031] The container 140 is preferably of an open type, which means that gas can freely pass through at least the bottom / floor of the container 140. This can be achieved, for example, by forming holes in the bottom of the container 140.

[0032] The material to be treated is a metal oxide, preferably Fe 2 O 3 and / or Fe 3 O 4It consists of iron oxide such as []. The material is composed of scale or various types of scrap materials. The material may be granular, such as in the form of pellets or balls, or may be made into such a form in an appropriate pretreatment process. One suitable material charged for batch reduction is rolled iron ore balls, for example, ground scraps rolled into a ball shape, rolled in water so that the ball diameter is about 1 - 1.5 cm. If such a material further contains oxides in which the reduced metal evaporates at a temperature lower than the final temperature of the charged material in this method, such a metal can condense in the condenser 160 and can be easily recovered in the form of powder. Such oxides may consist of metal oxides such as zinc oxide and lead oxide.

[0033] Advantageously, a very large amount of the material to be reduced 142 is not charged into the furnace space 120. Each furnace 100 is preferably charged between a maximum of 50 tons, for example a maximum of 25 tons, for example between 5 tons and 10 tons, in each batch. This charge may be accommodated in a single container 150 within the furnace space 120. Depending on the processing capacity requirements, multiple furnaces 100 can also be used in parallel, and the waste heat from a batch of one furnace 220 can be used for preheating another furnace 210 (see below Figure 2), or in a continuous system, preferably an inert gas, the cooling gas can be used for preheating the incoming material.

[0034] Thereby, a system 200 suitable for direct installation and use at a mining or other material production site is provided, without the need for expensive transportation of the ore (or other materials) before reduction. Instead, a directly reduced and carburized metal material can be manufactured on-site, packaged in a protective atmosphere, and further transported to another site for further processing.

[0035] Accordingly, it is foreseen that the furnace 100 can be installed in relation to an iron ore ball or pellet production system so that the charging of the metal material into the furnace 100 within the container 140 can be carried out in a fully automated manner. Here, the container 140 is automatically circulated from the metal ball or pellet production system to the system 100, filled with metal balls or pellets to be reduced and carburized, and returned; inserted into the furnace space 120; subjected to the reduction gas / heat / carbon-containing gas treatment for reduction and optionally carburization disclosed herein; removed from the furnace space 120 and emptied; returned to the metal ball or pellet manufacturing system; refilled, and so on. A larger number of containers 140 than the furnace 100 may be used so that, at each batch switch, the reduced and carburized charge within a particular container is immediately exchanged in the furnace 100 with another container transporting material that has not yet been reduced and carburized. Such a large-scale system can be fully automated at a mining site or at a site producing other types of raw materials such as in terms of scale, and can be implemented using a plurality of small-scale furnaces 100 instead of one very large-scale furnace, being very flexible in terms of throughput.

[0036] Below the container 140, the furnace 100 is provided with a gas-gas type heat exchanger 160 (or the system comprises both the furnace 100 and the heat exchanger 160), and this heat exchanger may advantageously be a tubular heat exchanger known per se. The heat exchanger 160 is preferably a countercurrent heat exchanger. Below the heat exchanger 160, a sealed trough 161 for collecting and containing the condensed water from the heat exchanger 160 is connected to the heat exchanger 160. The trough 161 is also configured to be airtight and withstand the operating pressure of the furnace space 120.

[0037] The heat exchanger 160 is connected to the furnace space 120. Preferably, the cooling / cooled gas that reaches the furnace space 120 via the supply conduit 171 passes through the heat exchanger 160 along the heat exchanger tubes provided externally / peripherally, and further reaches the top 125 of the furnace space 120 and is discharged into the furnace space 120. Along this supply conduit 171, such supply gas is heated by the heat exchanger and / or using the heating element 121.

[0038] Details will be described later. The heated gas flows out downward from the furnace space 120, passes through the heat exchange tubes provided internally / centrally and through the heat exchanger 160, thereby heating the incoming cooling / cooled gas. In that process, the gas passing downward is cooled, and the contained water vapor condenses into liquid water. Therefore, the outflow gas heats the inflow gas and effectively heats the inflow gas by both heat transfer due to the temperature difference between the two and the latent heat of condensation of the condensed water vapor contained in the outflow gas.

[0039] The condensed water generated from the outflow gas is collected in the trough 161.

[0040] The furnace 100 may be provided with a set of temperature, flow rate and / or pressure sensors at the trough 161 (122), at the bottom of the furnace space 120 such as below 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 possible carburizing processes as described below.

[0041] 173a and 173b indicate different outlet conduits for the gas from the furnace space 120, such as the used inert gas or cooling gas. 173a is arranged to receive such gas from within the furnace space 120 below the charged material 142 in the container 140, while 173b is arranged to receive such gas from downstream (such as below) of the heat exchanger 160.

[0042] The condensed water may be led from the condenser / heat exchanger 160 into the trough via a spout 164 or the like and flow out at the bottom of the trough 161, such as a local low point 165 of the trough 161. Here, preferably, as shown in FIGS. 1a to 1d, the orifice of the spout 164 is arranged completely below the main bottom 166 of the trough 161. This reduces the turbulent flow of the liquid water in the trough 161 and provides more controllable operating conditions.

[0043] The trough 161 is advantageously dimensioned to receive and accommodate all the water formed during the reduction of the charged material. The size of the trough 161 can thus be adapted to the type and amount of the reduction material in one batch. For example, when completely reducing 1000 kg of Fe 3 O 4 310 liters of water are formed as a result, and when completely reducing 1000 kg of Fe 2 O 3 338 liters of water are formed as a result. In other embodiments, depending on the degree of contamination, the recovered water is diverted for waste treatment. In any case, it is preferable to measure the amount of the recovered water, such as by using a conventional flow meter or level meter.

[0044] FIG. 2 shows a system 200 in which a furnace of the type shown in FIGS. 1a to 1d can be used. In particular, one or both of the furnaces 210 and 220 may be of the type shown in FIGS. 1a to 1d and may be at least in accordance with claim 1 herein.

[0045] 230 represents a gas-gas heat exchanger. 240 represents a gas-water heat exchanger. 250 represents a fan or a pump. 260 represents a vacuum pump. 270 represents a compressor. 280 represents a container for used reducing gas. 290 represents a container for fresh / unused reducing gas. 310 represents a container for fresh / unused carbon-containing gas. 320 represents a container for used carbon-containing gas, such as a mixed gas of the type of gas stored in container 310 and reducing gas. 330 represents a container for used inert gas, and 340 represents a container for fresh inert gas. V1 to V24 represent valves.

[0046] 201 represents a control device connected to sensors 122, 123, 124 and valves V1 to V24 and configured to generally control the processes described herein. The control device 201 may also be connected to a user control device, such as a graphical user interface presented to the user of the system 200 by a computer (not shown), for monitoring and further control.

[0047] Figure 3 is a diagram showing the method according to the present invention, which method uses a system 100 of the type generally shown in Figure 2, in particular a furnace 100 of the type generally shown in Figures 1a - 1d. In particular, this method is for manufacturing a directly reduced and optionally carburized metal material using a reducing gas as a reducing agent and optionally a carbon-containing gas as a carburizing carbon source.

[0048] After such direct reduction and optionally carburization, the metal material 142 can form a carburized or non-carburized sponge metal. In particular, the metal material is an iron oxide material, and the product after direct reduction may be carburized sponge iron. As a result, the reduced and optionally carburized metal material can be used in subsequent method steps for manufacturing, such as steel.

[0049] In the first step, the method starts.

[0050] In a subsequent step, the metal material 142 to be reduced is charged into the furnace space 120. This charging is done by placing the charged container 140 in the furnace space 120 in the orientation shown in FIGS. 1a - 1d, and the furnace space 120 is then hermetically closed and sealed using the fastening means 111.

[0051] In a subsequent step, the existing atmosphere can be evacuated from the furnace space 120 to achieve a gas pressure of less than 1 bar within the furnace space 120. Note that this low gas pressure is lower than atmospheric pressure. This can be done by closing valves 1 - 8, 11, and 13 - 24, opening valves 9 - 10 and 12, and the vacuum pump 260 sucking and exhausting the contained atmosphere within the furnace space 120 via conduits passing through 240 and 250. Valve 9 can be opened such that the exhausted gas flows out into the surrounding atmosphere when the furnace space 120 is filled with air. If the furnace space 120 is filled with used reducing gas and / or carbon - containing gas, instead it is exhausted into container 280 or 320. Correspondingly, if the furnace space 120 is filled with inert gas, this is instead exhausted into container 330.

[0052] In this example, the furnace atmosphere is exhausted via conduit 173a or 173b, but other suitable outlet conduits arranged within the furnace 100 may be used.

[0053] In this evacuation step, as well as in other steps as described below, the control device 201 can be used to control the pressure within the furnace space 120 based on readings from pressure sensors 122, 123, and / or 124, etc. This also applies to the other discharge and filling steps of various gases to and from the furnace space 120 as described later.

[0054] The evacuation is continued until a pressure of up to 0.5 bar, preferably up to 0.3 bar, is obtained within the furnace space 120.

[0055] In a subsequent initial heating step, heat and an inert gas are supplied to the furnace space 120, whereby the heated inert gas fills the furnace space 120 and heats the charged metallic material 142 to a first temperature.

[0056] The inert gas can be supplied from the containers 330 and / or 340. Since the furnace 100 is closed as described above, there is substantially no leakage of supply gases including reducing gases and carbon-containing gases during the process, and in some cases, there is no leakage of the inert gas either. In other words, (apart from the reducing gas and carbon-containing gas consumed in the reduction reaction and carburization reaction) the gas loss is very small or even non-existent. Instead, only the reducing gas chemically consumed in the reduction reaction during the reduction process is used, and correspondingly, a carbon-containing gas is also used. Furthermore, the reducing gas required during the reduction process is only the amount necessary to maintain the pressure required during the reduction process and the chemical equilibrium between the reducing gas and steam. This will be described in detail below.

[0057] As described above, the container 340 holds fresh (unused) inert gas, and the container 330 holds the inert gas that has already been used in one or more reduction steps and then recovered into the system 200. At the first execution of the process, only the fresh inert gas supplied from the container 340 is used. At subsequent executions of the process, the recycled inert gas from the container 340 is used, and if necessary, fresh inert gas from the container 340 is replenished.

[0058] The same applies to the reducing gas that may be supplied from the containers 290 or 280 and the carbon-containing gas supplied from the containers 310 or 320, respectively.

[0059] During any initial stage of the initial heating step (this initial stage is one of the inert gas introductions and is carried out without heat supply until the pressure in the furnace space 120 reaches about 1 bar or about 2 bar), valves 1 - 9, 11, 13 - 24 are closed and valves 10 and 12 are open. Depending on whether fresh inert gas or recycled inert gas is used, valve V21 or V23 is also opened, and depending on the pressure required by the compressor, valves V6, V22 or V24 are opened and V21 or V23 is closed.

[0060] When the pressure in the furnace space 120 reaches or approaches a desired pressure such as atmospheric pressure (about 1 bar), the switch of the heating element 121 inside or outside the furnace 120 is turned on (if this has not been done previously). Preferably, heat is supplied to the furnace space 120 by heating the supplied (inert / reducing / carbon-containing) gas by the heating element 121, whereby the material 142 in the container 140 is heated. As already described above, the heating element 121 can be arranged at a position through which the inert / reducing / carbon-containing gas supplied to the furnace space 120 passes, whereby the heating element 121 is substantially immersed (completely or substantially completely surrounded) in the newly supplied inert / reducing / carbon-containing gas during each step of initial heating, reduction and carburizing. In other words, heat is preferably supplied directly to the inert gas and / or directly to the reducing gas and / or directly to the carbon-containing gas, and any gas may be supplied to the furnace space 120 simultaneously (in the said initial step or subsequent steps).

[0061] During the remainder of the initial heating step, valves V1 - V5 and V7 - V20 are closed, and valves V21 - V24 and V6 are controlled by a control device together with the compressor 270 to achieve a controlled supply of recycled and / or fresh inert gas as described below.

[0062] Therefore, during this initial heating step, the control device 201 is configured to control the heat and inert gas supply means 121, 330, 340 to supply heat and inert gas to the furnace space 120. This can be done such that the heated inert gas heats the charged metallic material 142 to a temperature above the boiling temperature of the water contained in the metallic material. As a result, the contained water evaporates.

[0063] During the initial heating step, the charged material 142 is heated to a first temperature, which can be a predetermined temperature, for example, a temperature above the boiling point of water at the actual pressure within the furnace space 120. However, it is preferable that the first temperature to which the charged material is heated is the desired processing temperature during a subsequent reduction step or at least within 100 °C of such a desired processing temperature. Such a desired processing temperature is hereinafter referred to as the "second" temperature. Generally, it should be noted that the second temperature is considerably higher than the boiling temperature of water. In an example of the reduction treatment of an iron oxide material, the desired reduction treatment temperature (second temperature) is in the range of about 350 °C or higher, for example, 400 °C to 700 °C or around that.

[0064] The inert gas may be nitrogen, but may also be other suitable inert gases such as noble gases, or a mixed gas of several such inert gases. The inert gas preferably has a lower density than water vapor at the same pressure.

[0065] In some embodiments, during the initial heating step, the inert gas is circulated in a closed loop past the charged metallic material 142. For example, a fan or pump 250 may be used to propel the inert gas in a closed loop circuit past 230, 240, the furnace space 120 forms part of the closed loop circuit, and the inert gas flows through the furnace space 120 on its way around the closed loop circuit and past the furnace space 120. Such circulation may be carried out while filling the inert gas to a desired pressure (the "first" operating pressure) within the furnace space 120 and / or after reaching such a desired pressure. During circulation, the inert gas may be heated to eventually reach the first temperature described above.

[0066] In some embodiments, during the initial heating step, the inert gas is supplied at a predetermined overpressure (again, the first operating pressure) or to a predetermined overpressure, which may be at least 2 bar, for example at least 3 bar. Subsequently, before the subsequent reduction step, the inert gas is evacuated again to a pressure lower than the overpressure, for example to a container 330 or the like. This low pressure may be approximately 1 bar, for example 0.5 - 2 bar, for example 0.8 - 1.5 bar.

[0067] Figure 1a shows the state of the furnace 100 during the heating step, where the furnace space 120 is completely filled with an inert gas.

[0068] Figure 4 shows the time series of an exemplary process according to the present method. In Figure 4, the solid line illustrates the partial pressure of nitrogen (inert gas) (measured on the left vertical axis) as a function of time (horizontal axis), the dashed line illustrates the partial pressure of hydrogen (reducing gas) (measured on the left vertical axis) as a function of the same time; the dash-dotted line indicates the partial pressure of air (measured on the left vertical axis) as a function of the same time; the thick dotted line indicates the partial pressure of methane (carbon-containing gas) (measured on the left vertical axis) as a function of the same time; the dense dotted line indicates the temperature of the furnace space 120 (measured on the right vertical axis) as a function of the same time.

[0069] Note that Figure 4 is provided only to illustrate the concept currently being described and is simplified for clarity.

[0070] As is apparent from Figure 4, the partial pressure of the inert gas increases with the temperature up to a first temperature (in this example, approximately 650 °C). This temperature is the same as the second temperature in the illustrated case and is the desired reduction step treatment temperature. The pressure and temperature are maintained for some time while the inert gas is circulated within the closed loop circuit until at least the charge 142 reaches the first temperature and all or substantially all of the contained water has evaporated to form water vapor. As is apparent from Figure 4, the air is initially evacuated to approximately 0.5 bar, but since air mainly contains nitrogen and oxygen, the amount of air decreases to approximately zero (note that Figure 4 is a simplified diagram).

[0071] In the subsequent reduction step, a reducing gas is supplied to the furnace space 120.

[0072] Before the reducing gas is supplied, first, the actual pressure of the inert gas can be reduced to a desired predetermined total pressure in the furnace space 120 used at the start of the reduction step by exhausting a part of the inert gas from the container 330 in the general method described above via, for example, the outlet 173a or 173b. This predetermined pressure can be, for example, at least 0.8 bar. Also, the predetermined pressure may be up to 2 bar, for example up to 1.5 bar. Most preferably, the predetermined pressure is about 1 bar. However, in the simple example shown in FIG. 4, the same total pressure of about 6 bar is substantially maintained throughout the process, so that hydrogen gas is filled at the corresponding rate while nitrogen gas is withdrawn.

[0073] In other embodiments, an inert gas partial pressure, for example 1 - 2 bar, may be maintained from the initial heating to the reduction stage.

[0074] As shown in FIGS. 1a - 1d, the reducing gas is preferably supplied to the top 125 of the furnace space 120 above the charged metallic material 142. Preferably, the top 125 is arranged such that the reducing gas is discharged into the furnace space 120 at a position less than 0.5 m from the uppermost part of the furnace space 120. Preferably, the reducing gas is discharged into the furnace space 120 at least 0.3 meters, for example at least 0.5 meters, above the uppermost part of the charged material 142.

[0075] Furthermore, in some embodiments, the reducing gas is supplied in a laminar flow at least in a dominant part at the point of discharge of the reducing gas into the furnace space 120. In other words, at least 50% of the volume of the discharged reducing gas is in laminar flow at the discharge point.

[0076] The reducing gas may be hydrogen or other suitable reducing gases, such as carbon monoxide. In any case, the reducing gas preferably has a density smaller than that of the inert gas, preferably considerably smaller than that of the inert gas, and smaller than that of water vapor, preferably considerably smaller than that of water vapor, at the actual pressure in the furnace space 120. Preferably, the inert gas is at least five times lighter than both the inert gas and water vapor. In the preferred case of using hydrogen as the reducing gas, the hydrogen gas has a density of only about 10% of the densities of nitrogen gas and water vapor at the same pressure.

[0077] The layered discharge flow aims to minimize the mixing of the inert gas and the reducing gas. Due to the above density difference, the reducing gas moves upward, while the inert gas moves downward together with the evaporated (formed by the reduction process) water vapor. Depending on the detailed embodiment, such as the time and the detailed design of the furnace space 120, it is preferable to minimize the mixing of the reducing gas and the inert gas by using the layered reducing gas discharge in the upper part 125 of the furnace space 120.

[0078] For example, the reducing gas can be discharged into the furnace space 120 through a porous block of a ceramic material or through a metal plate or a refractory plate provided with a plurality of through holes, and the discharged reducing gas can be spread over the entire large surface. Such a discharge surface of the reducing gas can be at least 0.1 m 2 for example, at least 0.2 m 2 and so on. Alternatively or in addition, the opening of the conduit 171 into the furnace space 120 may have a large cross-section perpendicular to the main reducing gas flow direction, for example, at least 0.02 m 2 and even at least 0.02 m 2 in area.

[0079] As can be understood from the above, when the release of the reducing gas is started, the furnace interior space 120 may already be completely filled with the inert gas. Thereafter, as the reducing gas is released into the furnace space 120 from the top 125 of the furnace space, the reducing gas will occupy the uppermost part of the furnace space 120 due to the above density difference. A horizontal gas surface is defined between the reducing gas and the inert gas, and since the density of the reducing gas is low, as the amount of the reducing gas increases, the gas surface and the inert gas are pushed downward.

[0080] The reducing gas is preferably supplied to the furnace space 120 without recirculation of the reducing gas while being supplied. Preferably, there is also no recirculation of the inert gas. "Without recirculation" means, in this context, that the reducing / inert gas is not exhausted from the furnace space 120. In other words, all the reducing / inert gas released into the furnace space 120 remains in the space defined by the combination of the furnace space 120 and any peripheral space (such as the heat exchanger 160 and the trough 161) that forms a closed space for the gas together with the furnace space 120. Preferably, this closed space does not include a closed-loop circulation loop of the above-described type in which the gas is actively and forcibly circulated using a fan, a pump, or the like. Therefore, this is different from the case of the circulation described above with respect to the inert gas during the heating step.

[0081] Rather, as the reducing gas is supplied to the furnace space 120, the pressure in the furnace space 120 correspondingly increases as the above surface moves downward through the furnace space 120, unless the inert gas is simultaneously withdrawn from the bottom of the furnace space 120.

[0082] The downward movement of this surface is shown after 25 minutes in FIG. 4. The situation after the passage of time is shown in FIG. 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. In FIG. 1c, the surface boundary 126 is located completely below the charged material 142, in other words, the material 142 is completely surrounded by the reducing gas.

[0083] Through the initial heating step, reduction step, and carburizing step (see below), the gas flow supplied to (or discharged from) the furnace space 120 is controlled by the control device 201. As a result, in certain cases of the reduction step, a relatively slow but stable flow of reducing gas continuously exists, the total pressure within the furnace space 120 increases, and the interface 126 is forced downward. When the interface 126 reaches the position in Figure 1c, the set pressure should have been reached, and additional reducing gas should only be added to supplement the reducing gas converted to steam.

[0084] Furthermore, in the reduction step, it is understood that heat is supplied to the furnace space 120 (through the heating element 121 and the heat exchanger 160 as described above) so as to reach and maintain the second temperature of the charged metallic material 142 (if not yet evenly distributed). The second temperature is high enough for the metal oxides present in the charged metallic material 142 to be reduced and, in turn, steam to be formed. This formed steam is condensed and recovered by the condenser 160 as described above.

[0085] However, the reduction of the material 142 does not start until the reducing gas comes into contact with the material 142. Thus, during the reduction step, the reducing gas is supplied while the inert gas is still present within the furnace space 120 as described above, and the control unit 201 is configured to supply the flow of the reducing gas. As a result, the interface 126 is pushed downward by the supply of the reducing gas, and the inert gas is pushed downward until the charged metallic material 142 is completely surrounded by the reducing gas. Due to the supplied heat, the reducing gas surrounding the material 142 maintains a predetermined temperature despite the endothermic nature of the reduction process.

[0086] The charged material 142 is kept completely surrounded by such a high-temperature reducing gas until the material 142 is completely reduced. The length of the holding time varies depending on the type of material, but in a typical case, it is expected that about 5 to 15 minutes is sufficient. During this time, the second operating pressure is maintained by the control device 201.

[0087] Generally, during the reduction step, the control device 201 continuously adds a reducing gas at a determined reduction temperature or the like, thereby maintaining at least a desired stability or increase (such as a monotonic increase) in the reducing gas partial pressure curve (and total pressure curve) within the furnace space 120. In particular, it is configured to counteract the pressure drop in the lower part of the furnace space 120 (and the lower part of the heat exchanger 160) caused by the continuous condensation of water vapor in the heat exchanger 160 (described later). The total energy consumption depends on the efficiency of the heat exchanger 160, particularly the ability to transfer thermal energy from the high-temperature gas flowing into the heat exchanger 160 and the latent heat of condensation of the condensing water vapor to the reducing gas flowing in. Fe 2 O 3 In the case of using hydrogen as the reducing gas, when heating the oxide and thermally compensating for the endothermic reaction, the theoretical energy required to reduce the oxide is approximately 250 kWh per 1000 kg of Fe 2 O 3 . For Fe 3 O 4 , the corresponding value is approximately 260 kWh per 1000 kg of Fe 3 O 4 .

[0088] When the charged material 142 is surrounded by the reducing gas, the reducing gas in contact with the charged material 142 forms a mixed gas with the water vapor from the reducing charged material. Since water vapor is heavier than the reducing gas, the water vapor flows downward, enters the inert gas below the reducing gas, and further flows into the condenser 160.

[0089] In the heat exchanger 160, heat exchange occurs from the high-temperature gas reaching from the furnace space 120 to the newly supplied low-temperature reducing gas reaching the conduit 171, whereby the latter is preheated by the former.

[0090] Due to the cooling of the high-temperature gas flow in the heat exchanger 160, the water vapor contained in the cooled gas condenses. This condensation produces liquid water, which is collected in the trough 161, but also produces latent heat of condensation. The heat exchanger 160 is preferably further configured to transfer such latent heat energy from the condensed water to the inert / reducing / carbon-containing gas supplied to the furnace space 120.

[0091] The condensation of the contained water vapor also reduces the pressure of the hot gas flowing downward from the furnace space 120, providing space for more hot gas to pass downward through the heat exchanger 160.

[0092] The condensation of water vapor in the heat exchanger 160 reduces the gas partial pressure of water vapor at the lower end of the structure, further inducing the downward flow of the water vapor generated in the charging material 142.

[0093] The reducing gas and the carbon-containing gas supplied to the heat exchanger 160 preferably have a room temperature or a temperature slightly lower than room temperature. Accordingly, the heating element 121, as shown disposed upstream of the heat exchanger in FIGS. 1a-1c, may, if used, instead be disposed along the conduit 171 at a position after (downstream of) the heat exchanger 160 and before reaching the discharge point at the top 125 of the furnace space 120. The latter case is shown in FIG. 1d.

[0094] It is understood that the depression of the surface boundary 126 can be achieved by increasing the total pressure within the furnace space 120, as shown in FIG. 4, while maintaining the partial pressure of the inert gas constant. However, in some embodiments, the inert gas may be exhausted to some extent from a point below the charging material 142, such as through the conduit 173a above the condenser 160, but preferably through the conduit 173b below the condenser 160. Such an exhaust location is preferably at the lower part of the furnace space 120 or completely below the furnace space 120.

[0095] In addition, a combination of an increase in the reducing gas partial pressure and a decrease in the inert gas partial pressure can also be used. This is controlled by the control device 201. However, during the reduction step, it is preferable that the inert gas is not exhausted from the closed space to which the furnace space 120 belongs. It is understood that the control device 201 needs to adjust the flow rate of the reducing gas (and the discharge of the inert gas) in consideration of the increase in gas pressure due to the formed water vapor and the decrease in gas pressure due to the condensation of the formed water vapor. Such adjustment can be based on pressure measurement and / or experience. What is important is to control the vertical position of the interface 126 so that all of the material 142 is in contact with the reducing gas.

[0096] Of course, during the reduction step, the control device 201 is configured to control the supplied heating (160, 201) so that the charged metal material 142 is maintained at the second temperature and until the reduction chemical reaction is completed.

[0097] When hydrogen gas reduces iron oxide, the hydrogen gas starts to reduce the charged material 142 at about 350 - 400 °C to form metallic iron, and forms wustite and water vapor according to the following equation: Fe 2 O 3 + 3H 2 = 2Fe + 3H 2 O Fe 3 O 4 + 4H 2 = 3Fe + 4H 2 O

[0098] As described above, this reaction is an endothermic reaction and is driven by the thermal energy supplied through the high-temperature hydrogen gas in the furnace space 120.

[0099] Therefore, during the reduction step, water vapor is generated in the charged material. This generated water vapor is continuously condensed and recovered by a condenser disposed below the charged metal material. In the examples of FIGS. 1a to 1d, the condenser is in the form of a heat exchanger 160.

[0100] As described above, in some embodiments of the present invention, the reduction step including the condensation of water vapor, and optionally the carburizing step, are carried out such that a pressure exceeding 1 bar (second operating pressure) with respect to atmospheric pressure is built up in the furnace space 120. In particular, the reducing gas is supplied such that a pressure exceeding 1 bar is achieved and maintained. It should be noted that such a pressure exceeding 1 bar is a pressure higher than atmospheric pressure.

[0101] Specifically, in the reduction step, additional reducing gas may be supplied to the furnace space 120 so as to achieve and / or maintain a predetermined overpressure (corresponding to the second operating pressure) therein.

[0102] In a subsequent reducing gas discharge step carried out after the metal material 142 has been reduced (preferably completely reduced, or at least substantially completely reduced), the remaining reducing gas is discharged from the furnace space 120. This discharge of the reducing gas is preferably carried out from a discharge point at the top of the furnace space 120 (the same top as the release of the reducing gas during the reduction step). For example, the reducing gas can be exhausted through the same conduit 171 that was used to release the reducing gas, in which case it is exhausted in the reverse flow direction. The used reducing gas can be led to the container 280 for reuse in a later processing cycle with a new material to be reduced under the control of the control unit 201 as described above.

[0103] During the exhaust, the inert gas pushes the reducing gas upwards as the pressure of the reducing gas decreases, whereby almost all of the reducing gas can be recovered for reuse. In this case, the amount of inert gas in the closed system including the furnace space 120 remains the same during the exhaust, or additional inert gas may be supplied from below, such as via the supply section 173a or 173b, so as to increase the pressure in the furnace space 120. The exhaust may be returned to the atmospheric pressure of the furnace space 120, and the furnace space is then completely filled with the inert gas. This may involve the discharge of excess inert gas, which is preferably discharged from a discharge point below the material 142 (from the lower part of the furnace space 120 or a point below the entire furnace space 120) as described above.

[0104] This method may further include a carbonization step, i.e., a step of supplying a carbon-containing gas to the furnace space 120 such that the metal material 142 heated by the supplied heat and reduced by reaction with the reducing gas is carburized by the carbon-containing gas. This supply of the carbon-containing gas may then be performed before the exhaust of the reducing gas from the furnace space 120 returns to atmospheric pressure within the furnace space 120 by the carbon-containing gas being mixed with the reducing gas (and then exhausted to the container 280).

[0105] The carbon-containing gas may be any carbon-containing gas capable of chemically reacting with the reduced metal material to carburize the reduced metal material. Examples of suitable carbon-containing gases include various gaseous hydrocarbons such as methane, ethane, propane, propene, etc. (at the temperature and pressure prevailing in the furnace space 120 during the implementation of this method). Preferably, the carbon-containing gas does not contain more than a trace amount of carbon monoxide. This is to efficiently prevent both carbon monoxide and carbon dioxide from forming residual products after the completion of the carburization process of the present invention. In particular, in the carbon supply step, it is preferred that no carbon monoxide is supplied to the furnace space 120. The carbon-containing gas is preferably less dense than an inert gas, as is the case with methane or nitrogen for example.

[0106] As described above, when iron is reduced, free iron (Fe) is produced, and the free iron accepts carbon (C) to form Fe 3 C.

[0107] FIG. 5 shows the reduction ability of H 2 with respect to Fe 2 O 3 as a function of the increase in temperature. As suggested by FIG. 5, reduction by hydrogen gas is particularly active in the temperature range of approximately 400° - 700°.

[0108] Correspondingly, carburization using the same gaseous carbon source of Fe 2 O 3 is most active at intervals of approximately 650° - 900°.

[0109] For example, Fe 3 O 4 exhibits similar characteristics with respect to reduction / carburization and temperature.

[0110] That is, a process in which most of the reduction of the metal material is first carried out at a relatively low temperature and then most of the carburization of the metal material is carried out after further heating is efficient.

[0111] As shown in FIG. 4, the subsequent carburization step is carried out at a third operating temperature higher than the second operating temperature, for example, 650°C to 900°C (about 750°C in FIG. 4). This operating temperature can be controlled by the control unit 201 by corresponding control of the heating element 201.

[0112] As also shown in FIG. 4, since the supply of the carbon-containing gas is carried out simultaneously with the extraction of the corresponding inert gas, the inside of the furnace space 120 is maintained at substantially the same total pressure.

[0113] The subsequent carburization step can also be carried out at a third operating pressure that may be the same as or different from the second operating pressure.

[0114] Also, the carburization process is promoted by the presence of water vapor. This is one of the reasons for mixing the reducing gas and the carbon-containing gas to carry out the carburization step and the reduction step simultaneously.

[0115] In a specific case where methane is used as the carbon-containing gas and hematite / magnetite is used as the metal material, the following carburization chemical reaction occurs in the furnace space 120: Fe 3 O 4 + 4H 2 = 3Fe + 4H 2 O 3Fe + CH 4 = Fe 3 C + 2H 2

[0116] CH 4The reaction with Fe consists of side reactions in which water vapor and methane formed by the reducing hydrogen gas react: CH 4 + H 2 O = 2CO + 3H 2

[0117] Carburization itself is mainly carried out by the well-known hydrogen-water reaction in which carbon monoxide and hydrogen formed react with the iron surface to form water vapor. On the other hand, the released carbon atoms are incorporated into the positions of the previously released oxygen atoms.

[0118] Since the surface of the reduced iron is porous due to reduction, the total surface area of the iron is usually very large, leading to an efficient carburization process, especially when the metal material 142 is provided as a granular material.

[0119] As can be understood from the above formula, a certain amount of hydrogen gas is generated by the carburization treatment, so that less hydrogen gas is required than in other cases.

[0120] Finally, the carburized metal material preferably has a carbon content of 1 wt% to 4 wt% after the carbon supply step.

[0121] In some embodiments, the reduction step is carried out for at least 10 minutes, for example at least 20 minutes, for example at least 30 minutes, including a carbonization step carried out simultaneously with the reduction step. In particular, it is preferable that the charged metal material 142 is completely surrounded by the reducing gas during this time.

[0122] Correspondingly, this period can be up to 30 minutes, for example up to 15 minutes, for example up to 10 minutes.

[0123] Furthermore, the reduction step may be carried out 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 is recovered in the condenser 160 and / or until no additional heat is required to maintain a second operating temperature in the furnace space 120. Such actual pressure, amount and temperature, as well as the additional pressure or heat provided, may be measured as described above and checked by the control device 201.

[0124] For these purposes, the above-mentioned third predetermined temperature may be at least 600 °C, for example 640 - 750 °C, preferably about 660 °C.

[0125] The temperature of the charge 142 may be measured directly, for example by measuring the thermal radiation from the charge 142 using a suitable sensor, or indirectly by means of the temperature sensor 123.

[0126] Alternatively, the reduction process and / or the carburizing process can also be carried out within a time set based on experience.

[0127] In some embodiments, the reduction step and / or the carburizing step may be carried out repeatedly, and in each iteration, the control device 201 enables the steady-state pressure to be reached in the furnace space 120 before supplying an additional amount of reducing / carbon-containing gas into the furnace space 120. The heat supply may also be iterative (pulsed), or may be in the switched-on state throughout the reduction step and / or the carburizing step.

[0128] When water vapor is formed in the charge 142, the gas pressure locally increases, and in fact, a pressure fluctuation occurs between the furnace space 120 and the trough 161. As a result, the formed water vapor sinks downward through the charge 142, condenses in the heat exchanger 160, and in turn reduces the pressure on the far side (with respect to the furnace space 120) of the heat exchanger 160. Thus, these processes result in a net downward movement of the gas through the charge 142, and the newly added hydrogen gas compensates for the pressure loss in the furnace space 120.

[0129] The amount of heat in the gas flowing out of the furnace space 120, particularly the latent heat of condensation of water vapor, is transferred to the inert / hydrogen / carbon-containing gas flowing into the heat exchanger 160.

[0130] Accordingly, the reduction process is maintained as long as there is metal material to be reduced and thus water vapor is generated, resulting in the downward movement of the water vapor gas described above. Once the generation of water vapor stops (because substantially all of the metal material 142 has been reduced), if no additional reducing (or carbon-containing) gas is supplied, the pressure equalizes throughout the interior of the furnace 100 and the measured temperature becomes the same throughout the furnace space 120. For example, the measured pressure difference between the gas-filled portion of the trough 161 and the point above the charged material 142 becomes less than a predetermined amount and at most 0.1 bar. Additionally or alternatively, the measured temperature difference between the point above the charged material 142 and the point below the charged material and on the furnace space 120 side of the heat exchanger is less than a predetermined amount, which is at most 20 °C. Accordingly, when such pressure and / or temperature uniformity is reached and measured, the reduction process can be stopped.

[0131] Normally, the heating element 121 is not switched off until the carburizing (when used in this method) is complete, which usually occurs at a later time.

[0132] After complete reduction and carburizing, the method according to the invention can include a cooling step and an exhaust step described below.

[0133] Accordingly, in the subsequent cooling step, the inert gas atmosphere remaining in the furnace space 120 is cooled to a temperature of at most 100 °C, preferably about 50 °C, and then exhausted from the furnace space 120 and recovered in a container 330 or the like.

[0134] In the case of a single furnace 100 / 220 not connected to one or more furnaces, the charge material 142 is arranged downstream of the gas-water cooler 240 and can be cooled using a fan 250 arranged to cool the inert gas in turn (e.g., through valves V12, heat exchanger 240, fan 250 and valve V10, exiting the furnace space 120 via outlet conduit 173a or 173b and entering the furnace space 120 again via inlet conduit 171, circulated in a closed loop by fan 250).

[0135] The heat exchanger 240 transfers thermal energy from the circulating inert gas to water (or another liquid), from which the thermal energy can be utilized in a suitable way, e.g., in a district heating system. The closed loop is achieved by closing all valves V1 - V24 except valves V10 and V12.

[0136] In this case, since the inert gas is circulated through the charge material 142 in the container 140, it absorbs thermal energy from the charge material 142 and provides efficient cooling of the charge material while the inert gas is circulating in the closed loop.

[0137] In another embodiment, the thermal energy obtained from the cooling of furnace 100 / 220 is used to preheat another furnace 210. In this case, compared to the cooling closed loop described above, it is realized by the control device 201 closing valve V12 and opening valves V13 and V14 instead. In this way, the hot inert gas arriving from furnace 220 is preferably conveyed to a gas-gas heat exchanger 230, which is a countercurrent heat exchanger, where the reducing gas supplied in the reduction step carried out in relation to another furnace 210 is preheated. Subsequently, the somewhat cooled gas from furnace 220 can be circulated through the heat exchanger 240 for further cooling before being reintroduced into furnace 220. Also in this case, the inert gas from furnace 220 is circulated in a closed loop using fan 250.

[0138] Therefore, as described above, the cooling of the inert gas in the cooling step may be performed in relation to the space 120 of the other furnace 210 through heat exchange with the reducing gas supplied to the space 120 of the other furnace 210 for performing the reduction step and condensation.

[0139] If the temperature is insufficient for the inert gas to heat the reducing gas supplied to the furnace 210, the control device 201 closes the valves V13 and V14 again and opens the valve V12 again, so that the reducing gas from the furnace 220 is directly sent to the heat exchanger 240.

[0140] Regardless of how the thermal energy is processed, the inert gas from the furnace 220 (more importantly, the charged material 142) may be cooled to a temperature below 100°C to avoid reoxidation of the charged material 142 when it is later exposed to air. The temperature of the charged material 142 can be measured directly by an appropriate method as described above, or indirectly by measuring the temperature of the inert gas exiting through the outlet conduit 173 by an appropriate method.

[0141] The cooling of the inert gas may be performed while maintaining the pressure of the inert gas (which may be above atmospheric pressure after the discharge of the reducing gas and the carbon-containing gas), or when the valves V10 and V12 are opened, the pressure of the inert gas may decrease as the hot inert gas occupies a larger volume (of the closed-loop conduit and the heat exchanger).

[0142] In a subsequent step, the inert gas is exhausted from the space 120 of the furnace 220 and recovered by the vacuum pump 260, optionally in combination with the compressor 270, into the container 330 for the used inert gas. The evacuation of the furnace space 120 is preferably performed until a pressure of at most 0.5 bar, or at most 0.3 bar, is detected within the furnace space 120.

[0143] Since the furnace space 120 is closed, only the reducing / carbon-containing gas consumed in the chemical reduction reaction is removed from the system, and the remaining reducing gas was necessary to maintain the reducing gas / water vapor balance within the furnace space 120 during the reduction step. This discharged reducing gas can be fully utilized in subsequent batch operations of a new charge of the metal material to be reduced.

[0144] Thereafter, valves V7 and V8 are closed, valve V9 is opened to introduce air into the system for the replacement of the charged material, and valve V11 is opened to empty the condensed water as required.

[0145] In a subsequent step, the furnace space 120 is opened, for example, by releasing the fastening means 111 and opening the upper part 110. The container 140 is removed and replaced with a container containing a new batch of the charged metal material to be reduced.

[0146] In a subsequent step, in order to avoid reoxidation during transportation or storage, the removed reduced material can be placed under an inert atmosphere such as a nitrogen atmosphere.

[0147] For example, the reduced metal material can be placed in a flexible or rigid transport container filled with an inert gas. A plurality of such flexible or rigid containers can be arranged within the transport container, and the space surrounding the flexible or rigid containers can be filled with an inert gas. Thereafter, the reduced metal material can be safely transported without taking the risk of reoxidation.

[0148] In a subsequent step, the method ends.

[0149] The following table shows the approximate equilibrium of hydrogen gas H 2 and water vapor H 2 O at different temperatures in the furnace space 120: Temperature (°C): 400 450 500 550 600 H 2 (vol%): 95 87 82 78 76 H 2O (vol%): 5 13 18 22 24

[0150] 1000 kg of Fe 2 O 3 To reduce requires approximately 417 Nm 3 of hydrogen gas H 2 is required, and for 1000 kg of Fe 3 O 4 to be reduced requires approximately 383 m 3 of hydrogen gas H 2 is required.

[0151] The following table shows the amount of hydrogen gas required to reduce 1000 kg of Fe 2 O 3 and Fe 3 O 4 at atmospheric pressure and in an open system (according to the prior art) at different temperatures: Temperature (°C): 400 450 500 550 600 Nm 3 H 2 / ton Fe 2 O 3 : 8340 3208 2317 1895 1738 Nm 3 H 2 / ton Fe 3 O 4 : 7660 2946 2128 1741 1596

[0152] The following table shows the amount of hydrogen gas required to reduce 1000 kg of Fe 2 O 3 and Fe 3 O 4 by changing the pressure and temperature: Temperature (°C): 400 450 500 550 600 Nm 3 H 2 / ton Fe 2 O 3 : 1 bar 8340 3208 2317 1895 1738 2 bar 4170 1604 1158 948 869 3 bar 2780 1069 772 632 579 Nm 3 H 2 / ton Fe 3 O 4 : 1 bar 7660 2946 2128 1741 1596 2 bar 3830 1473 1064 870 798 3 bar 2553 982 709 580 532

[0153] As described above, the reduction process according to the present invention is preferably carried out at a pressure exceeding 1 bar and a high temperature. In most of the reduction steps where partial reduction is progressing, it has been found advantageous to use a combination of a heating hydrogen gas temperature of at least 550 °C and a furnace space 120 pressure of at least 2.3 bar.

[0154] The preferred embodiments have been described above. However, it will be apparent to those skilled in the art that many modifications can be made to the disclosed embodiments without departing from the basic idea of the present invention.

[0155] For example, the shape of the furnace 100 may vary depending on detailed preconditions.

[0156] The heat exchanger 160 has been described as a tubular heat exchanger. Even if this is found to be particularly advantageous, it is understood that other types of gas-gas heat exchangers / condensers are also possible. The heat exchanger 240 may have any suitable configuration.

[0157] The surplus heat from the cooled inert gas can also be used in other processes that require thermal energy.

[0158] The metal material to be reduced and carburized has been described as iron oxide. However, the method and system of the present invention can also be used for the reduction and carburization of metal materials such as the above metal oxides containing Zn and Pb that evaporate at temperatures below about 600 - 700 °C.

[0159] The present principle combining direct reduction and carburization can be used for metal materials having a reduction temperature higher than that of iron ore by appropriately adjusting the structure of the furnace 100 such as building materials to be used.

[0160] Therefore, the present invention is not limited to the described embodiments, and various modifications are possible within the scope of the appended claims.

Claims

1. A method for directly producing a metal material (142), The aforementioned method includes the following steps: a) The metal material to be reduced (142) is charged into the closed furnace space (120); b) Heat and inert gas are supplied to the furnace space (120), so that the heated inert gas fills the furnace space (120) and the charged metal material (142) is heated to a first temperature; c) Reducing gas is supplied to the furnace space (120); d) Heat is supplied to the furnace space (120) so as to maintain a sufficiently high second temperature in the charged metal material (142), thereby reducing the metal oxides present in the charged metal material (142) and sequentially forming steam; e) In the condenser (160), the water vapor formed in step d) is condensed and recovered; and f) After the charged metal material (142) has been reduced, the remaining reducing gas is discharged from the furnace space (120). The aforementioned method, The reducing gas has a lower density than the inert gas at the same pressure. In step c), the reducing gas is supplied while the inert gas is still present in the furnace space (120), and as a result, the supplied reducing gas pushes the inert gas downward until the charged metal material (142) is completely contained in the reducing gas. A method characterized by the following:

2. The method according to claim 1, In step b), the inert gas is circulated in a closed loop by passing through the charged metal material (142). A method characterized by the following:

3. The method according to claim 1, In step b), the inert gas is supplied at a predetermined overpressure, Before step c), the inert gas is evacuated to a pressure lower than the overpressure. A method characterized by the following:

4. The method according to claim 1, In step c), the reducing gas is supplied to the top (125) of the furnace space (120) above the charged metal material (142). A method characterized by the following:

5. The method according to claim 4, In step c), the reducing gas is supplied in a flow in which at least the dominant portion is laminar. A method characterized by the following:

6. The method according to claim 1, In steps c) to e), the reducing gas is supplied to the furnace space (120) without recirculating either the reducing gas or the inert gas. A method characterized by the following:

7. The method according to claim 1, In step d), additional reducing gas is supplied to the furnace space (120) so as to achieve and / or maintain a predetermined overpressure therein. A method characterized by the following:

8. The method according to claim 1, The method includes exhausting the inert gas from the furnace space (120) below the charged metal material (142) and from a point below the furnace space (120) or below the furnace space (120). A method characterized by the following:

9. The method according to claim 1, In step f), the remaining reducing gas is exhausted from the furnace space (120) above the charged metal material (142) and from the top (125) of the furnace space (120). A method characterized by the following:

10. The method according to claim 9, As a result of step f), the furnace space (120) is filled with inert gas. The method further includes a subsequent step of circulating the inert gas in a closed loop to cool the reduced metal material (142), A method characterized by the following:

11. The method according to claim 1, The method further includes an initial step of exhausting the atmosphere present in the furnace space (120) so that the gas pressure in the furnace space (120) is less than 1 bar, for example, a maximum of 0.5 bar. A method characterized by the following:

12. The method according to claim 1, The method further includes supplying a carbon-containing gas, such as a gaseous hydrocarbon, to the furnace space (120), thereby causing the heated and reduced metal material (142) to be carburized by the carbon-containing gas. A method characterized by the following:

13. The method according to claim 1, The reducing gas is hydrogen gas and / or carbon monoxide. A method characterized by the following:

14. The method according to claim 1, The inert gas is nitrogen. A method characterized by the following:

15. The method according to claim 1, The reducing gas is preheated in the heat exchanger (160), The heat exchanger (160) is arranged to transfer thermal energy from the water evaporated from the metal material (142) that has been placed inside to the reducing gas. A method characterized by the following:

16. The method according to claim 1, Steps d) and 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 is recovered in the condenser (160), and / or until no additional heat is required to maintain the second temperature in the furnace space (120). A method characterized by the following:

17. A method according to any one of claims 3, 7, or 13, The predetermined overpressure is an absolute pressure of at least 2.3 bar, for example, at least 2.5 bar, for example, at least 3 bar. A method characterized by the following:

18. The method according to claim 1, Steps d) and e) are performed for at least 2 minutes, for example, at least 3 minutes, for a maximum amount of 5 tons of the metal material (142). Steps d) and e) are performed for at least 5 minutes, for example, at least 10 minutes, for a maximum amount of 10 tons of the metal material (142). A method characterized by the following:

19. The method according to claim 1, Steps d) and e) are performed for a maximum of 30 minutes, for example, a maximum of 15 minutes, for example, a maximum of 10 minutes, for a maximum amount of the metal material (142) of up to 5 tons. Steps d) and e) are performed for a maximum of 60 minutes, for example, a maximum of 30 minutes, for example, a maximum of 15 minutes, for a maximum amount of the metal material (142) of up to 10 tons. A method characterized by the following:

20. A system for directly producing a metal material (142), A furnace space (120) arranged to receive and contain the metal material (142) to be reduced; Heat and gas supply means (250) arranged to supply heat, inert gas, and reducing gas to the furnace space (120); The control device (201) is configured to control the heat and gas supply means (250) to supply heat and inert gas to the furnace space (120), thereby heating the inert gas to fill the furnace space (120) and heating the charged metal material (142) to a first temperature; supply reducing gas to the furnace space (120); supply heat to the furnace space (120) to maintain a sufficiently high second temperature of the charged metal material (142), thereby reducing the metal oxides present in the charged metal material (142) and sequentially forming water vapor; and, after the charged metal material (142) has been reduced, to discharge the remaining reducing gas from the furnace space (120). The system includes a condenser (160) configured to condense and recover the formed water vapor. The aforementioned system, The reducing gas has a lower density than the inert gas at the same pressure. The control device (201) controls the heat and gas supply means (250) to supply the reducing gas while the inert gas is still present in the furnace space (120), so that the supplied reducing gas pushes the inert gas downward until the charged metal material (142) is completely contained in the reducing gas. A system characterized by the following features.

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