Method and system for producing directly reduced metals

Abstract

A method is disclosed for producing directly reduced metallic materials (106) in a continuous process, in which hydrogen gas and inert gas are circulated in respective closed loop first and second gas circuits through different respective gas connection stations (130, 140, 120-122, 150-151) configured for individual mobile furnaces (101), comprising the steps of: a) charging metallic materials (106) into the furnace; b) moving the furnace and connecting it to the inert gas connection station; c) supplying heated inert gas to the furnace; d) disconnecting the furnace; e) moving the furnace and connecting it to the hydrogen gas connection station; f) supplying heated hydrogen gas to the furnace; g) disconnecting the furnace; h) moving the furnace and connecting it to the inert gas connection station; i) supplying cooled inert gas to the furnace; j) disconnecting the furnace; k) discharging the metallic materials. The invention also relates to a system.

Description

[Technical Field]

[0001] The present invention relates to a method and system for producing directly reduced metals, particularly directly reduced iron (also known as sponge iron) having a very low carbon content. In particular, the present invention relates to the direct reduction of metal ores and metal oxides under a controlled hydrogen atmosphere to produce such directly reduced metals. The present invention can further be used to produce such carburized directly reduced metals by supplying a carbon-containing gas as part of the same process to carburize the reduced metal material. [Background technology]

[0002] The production of directly reduced metals using hydrogen as a reducing agent is known per se, for example, in SE7406174-8 and SE7406175-5, which describe a process in which a hydrogen atmosphere is passed through a charge of metal ore, which is then reduced to form a directly reduced pure metal.

[0003] Furthermore, Swedish published application SE1950403-4, as well as Swedish applications SE1951070-0 and SE2050771-1, which were not published at the priority date of the present application, disclose processes for the direct reduction of metallic materials in a closed hydrogen atmosphere, and also for carburizing such directly reduced metallic materials. DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0004] The present invention provides a method for carrying out such reduction and possible carburization on a larger scale.

[0005] Specifically, these prior art processes are useful for batch production of directly reduced metals. To increase production, multiple small furnaces can be used in parallel. Also, as described in the aforementioned Swedish patent application, production can be largely automated.

[0006] However, with increasing production scale in mind, there is a need for a more scalable, flexible, and robust method for achieving the direct reduction of such metallic materials. Such a process should be fully automatable and arranged to accommodate temporary or permanent changes in output requirements at low cost.

[0007] The present invention solves the above-mentioned problems. [Means for solving the problem]

[0008] Accordingly, the present invention relates to a method for producing directly reduced metallic materials in a continuous process, the method comprising circulating hydrogen gas in a closed-loop first gas circuit by selectively circulating hydrogen gas through one or more of a set of a plurality of hydrogen gas connection stations using a first valve system, and the method further comprises circulating inert gas in a closed-loop second gas circuit by selectively circulating inert gas through one or more of a set of a plurality of inert gas connection stations using a second valve system. The method further includes the following steps, performed for each of a plurality of individual mobile furnaces: a) loading a quantity of metallic material to be reduced into the mobile furnace; b) moving and connecting the mobile furnace to a first one of the inert gas connection stations; c) supplying heated inert gas to the mobile furnace such that the metallic material is heated by the heated inert gas circulating past the metallic material in the mobile furnace; d) disconnecting the mobile furnace from the first inert gas connection station; e) moving and connecting the mobile furnace to a first one of the hydrogen gas connection stations; f) supplying heated hydrogen gas to the mobile furnace such that the metallic material is reduced by the heated hydrogen gas circulating past the metallic material in the mobile furnace; g) disconnecting the mobile furnace from the first hydrogen gas connection station; h) moving and connecting the mobile furnace to a second one of the inert gas connection stations; i) supplying a cooled inert gas to the moving furnace and cooling the metal material with the cooled inert gas circulating past the metal material in the moving furnace; j) disconnecting the moving furnace from the second inert gas connection station; and k) discharging the reduced and cooled metal material from the moving furnace.

[0009] The present invention also relates to a system for producing directly reduced metallic materials in a continuous process, the system comprising a circulation means for circulating hydrogen gas in a closed-loop first gas circuit, the system comprising a first valve system arranged to selectively circulate hydrogen gas through one or more of a set of a plurality of hydrogen gas connection stations configured in the system, the system further comprising a circulation means arranged to circulate inert gas in a closed-loop second gas circuit, the system comprising a second valve system arranged to selectively circulate inert gas through one or more of a set of a plurality of inert gas connection stations configured in the system, and the system further comprising a plurality of individual moving furnaces. The system is configured to: a) load an amount of metal material to be reduced into a moving furnace; b) move the moving furnace to and connect it to a first one of the inert gas connection stations; c) supply heated inert gas to the moving furnace, causing the metal material to be heated by the heated inert gas circulating past the metal material in the moving furnace; d) disconnect the moving furnace from the first inert gas connection station; e) move the moving furnace to and connect it to a first one of the hydrogen gas connection stations; f) supply heated hydrogen gas to the moving furnace, causing the metal material to be reduced by the heated hydrogen gas circulating past the metal material in the moving furnace; g) disconnect the moving furnace from the first hydrogen gas connection station; h) The mobile furnace is moved to and connected to a second one of the inert gas connection stations; i) a cooled inert gas is supplied to the mobile furnace and the metal material is cooled by the cooled inert gas circulating past the metal material in the mobile furnace; j) the mobile furnace is disconnected from the second inert gas connection station; and k) the reduced and cooled metal material is discharged from the mobile furnace.

[0010] The present invention will now be described in detail with reference to exemplary embodiments thereof and the accompanying drawings. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 shows a schematic diagram of a system according to the invention arranged to carry out the method according to the invention, in particular the inert gas flow for heating and cooling of the metallic charge in a moving furnace. [Figure 2] FIG. 2 is a schematic diagram corresponding to FIG. 1, but showing in particular the cooling flow of the charged metallic material. [Figure 3] FIG. 3 is a schematic diagram corresponding to FIG. 1, but showing in particular the heating flow of the charged metallic material. [Figure 4] FIG. 4 is a schematic diagram corresponding to FIG. 1, but specifically showing the flow of hydrogen gas for reducing the charged metallic material. [Figure 5] FIG. 5 is a schematic diagram corresponding to FIG. 1, but showing in particular the flow of hydrogen gas for sintering the metallic charge. [Figure 6] FIG. 6 shows a simplified diagram of the connection between the mobile furnace and the connection station. [Figure 7] Figure 7 is a simplified diagram of a moving furnace. [Figure 8] FIG. 8 is a flow chart illustrating a method in accordance with the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Figures 1-7 share the same reference numerals for the same or corresponding parts. It should be noted that Figures 1-5 show the system 100 according to the present invention from different perspectives, and the figures may differ in detail in each figure for purposes of clarity.

[0013] With reference to the aforementioned Swedish patent application, all prior solutions focus on carrying out the complete process, including preheating, reduction, and cooling, in the same stationary furnace. Process efficiency has been achieved by using an overpressure in the furnace, direct connection of a gas-to-gas heat exchanger to the furnace, particularly to the furnace bottom, and heating elements within the heated furnace space. Furthermore, such previously known solutions have achieved production flexibility by using several such furnaces in parallel and by utilizing thermal efficiency improvement mechanisms between such stationary furnaces.

[0014] Such a solution works well for small scale installations, but not necessarily for high throughput installations.

[0015] In large-scale installations such as those described here, it is advantageous to avoid using furnace spaces operating at atmospheric pressure or slight overpressure (such as at most 50% or even at most 10% overpressure relative to atmospheric pressure). Although a high overpressure favors the hydrogen-steam relationship and allows rapid reduction with little gas recirculation, it has proven possible to use lower pressures, which are also less costly.

[0016] At a reduction temperature of about 550°C, a superheat of about 100°C is required. The actual amount of hydrogen required is as follows (taking into account the relationship between hydrogen gas and water vapor at each temperature):

[0017] Reduction temperature (℃): 550 600 650 Hydrogen gas (%): 80 75 72.5 Water vapor (%): 20 25 27.5

[0018] Taking hematite (Fe2O3) as an example, with an average temperature of 600°C, the theoretical yield is 421 Nm per ton. 3 of hydrogen gas is required at equilibrium, with 25% water vapor produced, for a total of 1684 Nm per tonne for complete reduction. 3 This means that 387 Nm3 of hydrogen gas is required per ton of magnetite (Fe3O4).3 of hydrogen gas is used to reduce one ton of magnetite, and 1548 Nm 3 This means that you need 10 ...

[0019] Charge weight (tons): 1 2 5 Container diameter (m): 0.98 1.38 2.19 Material Bed height (m): 0.5 0.5 0.5 Gas space (Nm 3 ): 0.18 0.36 0.90

[0020] Using these values, it is possible to calculate the required flow rate given the desired reduction rate and similar inputs. By varying the gas flow rate and measuring the amount of water produced, the temperature of the exhaust gas, and other parameters, it is possible to control the process for optimum efficiency.

[0021] Preventing air from entering the system 100 requires one or more fans or pumps to seal the system 100 and circulate gases within the system 100. A vacuum pump can be used to pump any air out of the system 100 in connection with starting the process and also for gas exchange during processing between processing steps.

[0022] According to the above-mentioned conventional solutions, the gas / gas heat exchanger is connected to the underside of the furnace so as to be in close contact with the charge material. However, the inventors have discovered that such a gas / gas heat exchanger can be located away from the furnace space. This is advantageous when metals such as lead or zinc condense in the gas / gas heat exchanger and require cleaning. Locating a used gas / gas heat exchanger in a central location rather than directly connected to the furnace is also advantageous because it facilitates duplication. One such gas / gas heat exchanger can be shut down for cleaning while a parallel-mounted gas / gas heat exchanger is operated to perform heat exchange. The use of multiple parallel heat exchangers that can be operated independently allows for the use of one, two, or more such gas / gas heat exchangers at any one time, increasing production flexibility and reducing the risk of production downtime. This is particularly true when two or more sets of such parallel-mounted gas / gas heat exchangers are interconnected to simultaneously supply gas flows from multiple individual furnaces.

[0023] The inventors also propose using a separate gas heater located externally to the furnace space. That is, a heating element within the furnace space heats the furnace walls and the exterior of the basket filled with charge material before the charge material itself is heated. A separate external heating unit can be used to heat the gas before it enters the furnace space, and this externally heated gas can be supplied to the furnace space from below the charge material and upward through the charge material. In this way, the charge material is heated before it reaches the furnace and basket walls. Heating the charge material in this manner also reduces the insulation thickness requirements within the furnace space, thereby reducing the weight and cost of the furnace.

[0024] Correspondingly, during cooling of the charge, the cooling gas is preferably introduced into the furnace space from below through the charge.

[0025] As with the gas / gas heat exchangers described above, the gas heaters and / or coolers used may be located externally to the furnace space, for example centrally located, or may consist of two, three or more parallel heater / coolers, operating one or more at a time with each parallel flow providing flexibility and resilience.

[0026] Providing furnaces, heat exchangers and other equipment as interchangeable components, allowing one or more to be used in parallel, greatly increases the flexibility of the overall system in terms of total throughput, production and maintenance.

[0027] Similar to the above conventional solutions, the present invention further uses the basic concept of using one and the same furnace space for both heating, reduction and cooling, simplifying the process and reducing the requirements for transporting material between and through the furnace spaces.

[0028] However, instead of connecting different gas streams to a stationary furnace, the present invention proposes physically moving the furnace to different stationary stations to supply different gas streams to accomplish the heating, reduction, cooling, and other required processing steps. These stations can be interconnected to handle the heat transfer between different parts of the system, overall resulting in a very flexible and efficient system for carrying out the direct reduction of metallic materials.

[0029] As shown in FIG. 7 , such a mobile furnace 101 according to the present invention may comprise a furnace body consisting of a lower section 105 and an upper section 104. The upper section 104 may be openable using a hinge 104a or a similar mechanism to expose the interior 101a of the heated furnace space for loading and unloading a metal material 106 into and from the furnace 101. The upper section 104 may be constructed of sheet metal insulated with a ceramic material. A connector 103 for the flow of cooling water or various gases may be arranged at the connection 102 between the upper section 104 and the lower section 105. Cooling water may be arranged to circulate within the furnace 101 to cool the furnace 101 and the connection between the upper section 104 and the lower section 105, which may optionally be arranged as a peripheral connecting ring that is water-cooled along the entire length of the connection running circumferentially between the connection sections 104, 105.

[0030] The furnace 101 further includes a pedestal 108, which provides a secure and stable table on which the furnace 101 can be mounted. Each such pedestal 108 can be arranged for a single furnace 101, but can also be arranged to support two furnaces 101, both of which are interconnected so that one furnace uses the waste heat from the other furnace by means of a suitably arranged gas / gas heat exchanger in a manner corresponding to that described in the Swedish patent application.

[0031] The platform 108 can also be used in smaller installations with a fixed furnace 101. In that case, the platform 108 can be placed directly on the floor of the production facility. However, according to the present invention, the platform 108 is provided with a means of movement, such as wheels. In a preferred embodiment shown in FIG. 7, the platform 108 is mounted on a movable platform 109, such as a trolley, having wheels 109a. The furnace 101, particularly its lower part 105, can be placed directly on the movable platform 109, and the rest of the platform 109 can be omitted, with wheels provided directly on the platform 101 or the lower part 105. The configuration shown in FIG. 7 is preferred because it offers the greatest overall flexibility.

[0032] A mobile furnace 101 including a base 108 and / or a movable platform 109, and in particular including a means of movement such as wheels 109a, is referred to herein as a "mobile furnace."

[0033] The wheels 109a may be arranged to roll freely directly on the floor surface, or may be arranged to roll while being guided on rails or the like. In either case, the system may comprise mobile furnace movement control devices, such as furnace control devices 109b, arranged on each mobile furnace 101 and arranged to control the propulsion and / or direction of the wheels 109a, and / or a central furnace control device 20 arranged to control the movement of each mobile furnace 101 by rail control or remote control. It should be understood that the control devices 109b, 20 may cooperate in any suitable manner, conventional per se, to achieve a desired movement pattern of the mobile furnace 101 used in the system 100. In particular, the control devices 109b, 20 may be arranged to communicate using any suitable wired or wireless communication protocol. The furnace control device 109b may also comprise a battery or an electrical energy receiving device for powering the propulsion of the wheels 109b and the control electronics mounted on the mobile furnace 101. The controller 109b may also comprise a control mechanism for enabling the mobile furnace 101 to automatically dock the connector 103 to the connection 11 (see FIG. 6 and below). Such docking may be achieved in any suitable manner known per se, such as using guide rails, computer vision guidance, laser guidance, etc.

[0034] Controller 20 is configured with logic and communication interfaces to automatically perform all of the method steps described herein by mechanically controlling various portions of system 100, unless otherwise specified, using control mechanisms conventional per se, such as using digital, electronic communication protocols arranged to provide control to physical control elements located locally on the various interacting components of system 100. Controller 20 may also be configured or connected to communicate with a suitable user interface for control and monitoring of system 100.

[0035] The connections 102 are shown in more detail in Figure 6, along with the corresponding connections 11 of an exemplary connection station. Gases and cooling water are supplied from the connection station via conduits 14 connected to the rest of the system 100 to a centrally controlled valve system 13. The valve system 13 is arranged to control the supply of the desired fluids as a function of the current processing step of the mobile furnace 101 connected to the connection station.

[0036] The fluids are supplied from the connection station to the mobile furnace 101 via interacting gas / water connectors 12, 103 and returned in a closed loop circulation that constitutes the mobile furnace 101, as shown in FIG.

[0037] Alignment means 15 may be used when docking connecting portion 102 to connecting portion 11 .

[0038] Connection 11 may also include the necessary measuring devices to measure the pressure, temperature, and / or other desired parameters of the incoming and / or outgoing gas and / or cooling water and report such recorded measurements to controller 20 for use in controlling the operation of system 100.

[0039] The electric heating elements are not located within the mobile furnace 101, but rather are located at fixed, preferably central, locations associated with the gas supplied to the connections 11 of each connection station. Such heating elements may be electric molybdenum heating elements and may be located within an enclosed space, such as a box, for the express purpose of providing heating to the gas flowing through that space. As mentioned above, two or more separate such heating devices may be arranged in parallel to increase flexibility and resilience.

[0040] In large installations, such electric heating devices may be located only at the connection stations for reduction, sintering, and / or carburizing, while in smaller installations, all connection stations may be equipped with heating devices. That is, in larger installations, each connection station may be specialized for use with a specific purpose, while in smaller installations, one connection station may be used for different purposes depending on the current processing status of the system 100. The same applies to the gas / gas heat exchangers described above.

[0041] The gas supplied to the connection stations is propelled using suitable fans or pumps to provide an appropriate flow of the gas and thus an optimized result in terms of processing time and flow rate / throughput of the material to be reduced throughout the process line used. It should be noted that the gas flow, and possibly one or more of the associated parameters such as gas volume flow rate, temperature and humidity, are preferably always controlled individually for each individual connection station by the control device 20 using the fans or pumps and / or other devices described herein.

[0042] In larger installations, there may be separate gas circulation systems for heating the charge material and for cooling the charge material. Such separate gas circulation systems may be inert gas circulation systems and may include gas dryers to control the humidity of the circulation gases, especially the cooling gas. Heat exchangers may be used in such systems according to the invention to transfer heat from the cooling gas to the heating gas. In other embodiments, such as those shown in Figures 1-5, heating and cooling may share one and the same inert gas circuit.

[0043] System 100 may also include fans or pumps for circulating gas within the cooling / heating system, and may be arranged to control the gas flow rate from cooling the hot charge material to heating the cold charge material. In small-scale installations, one and the same fan or pump may accomplish some or all of these gas circulation tasks, while in larger installations, there may be one or more dedicated fans and / or pumps for each of the gas circulation tasks. For example, in large-scale installations, heating and cooling of the charge material may be performed using the same fan or pump, and possibly the same gas dryer, while gas circulation for reduction, sintering, and / or carburizing may be performed using separate, dedicated fans and / or pumps, and possibly separate, dedicated gas dryers.

[0044] FIG. 8 illustrates a method according to the present invention, which is carried out using the system 100 shown in FIGS.

[0045] The present method generally is a method for producing directly reduced metallic material 106 in a continuous process. As used herein, the term "continuous process" refers to a process that is not carried out batchwise. Such a continuous process thus involves the charging of new material at an entry point in the process and the discharge of reduced material at an exit point, with one or more intermediate processing steps occurring between the entry and exit points, and the charging of a new material before the discharge of the immediately preceding entry. While the charging and discharging themselves may, of course, be discontinuous, the intermittent but continuous charging of material at one point and similarly discharging at another point forms a continuous process over time.

[0046] In the present invention, this process continuity is achieved by using the presently described moving furnace 101, which moves between connecting stations. Specifically, the metallic material 106 to be reduced is charged into one of the moving furnaces 101 at the entry point, then moves within that same moving furnace 101, without being discharged or recharged, through multiple different processing connecting stations, and finally to the exit point where it is discharged from the moving furnace 101. Thus, while each such charge of metallic material 106 can be considered a "batch," multiple such "batches" are processed simultaneously along the production line, moving simultaneously from one to the other, making the overall process continuous in the above sense.

[0047] The method includes circulating hydrogen gas in a closed-loop first gas circuit by selectively circulating the hydrogen gas through one or more of a set of multiple hydrogen gas connection stations 130, 140 (see FIG. 1 ) using a first valve system.

[0048] Here, the phrase "through" the connection station means that the gas is introduced to the connection station in a leading conduit and then circulated further away from the connection station in a separate conduit in a closed-loop conduit circuit. As mentioned above, the connection station is provided with a connector 12 for supplying gas from the leading conduit via conduit 103 to the mobile furnace 101 connected to the connection station, whereupon the gas is circulated to the mobile furnace 101 and then returned to the connection station for further transport via the separate conduit. Typically, the gas circulates through the furnace space 101a of the connected furnace 101. In other words, the connection station and the connected furnace 101 form part of the closed-loop circuit. It is understood that cooling water is also circulated in a corresponding manner, but not through the furnace space 101a (see FIG. 7, where the two lower conduits indicate the gas connections and the two upper conduits shown in bold indicate the cooling water connections). Preferably, each mobile furnace 101 has two gas connections 103 (one lead conduit and one return conduit) that are used for all gas circulation, such as inert gas, hydrogen gas, carburizing gas, etc., depending on the process step currently being performed for that mobile furnace.

[0049] The method also includes circulating an inert gas, such as nitrogen or argon, in a closed-loop second gas circuit by using a second valve system to selectively circulate the inert gas through one or more of the set of multiple inert gas connection stations 120-122, 150-151, 160. The circulation of the inert gas is a closed-loop circulation similar to, but at least partially different from, the circulation of hydrogen gas.

[0050] At each connection station, the flow of hydrogen gas, inert gas, and other circulating gases, as well as access to the connected mobile furnace 101, is controlled by a valve system 13 under the control of a control device 20. These gas circuits are preferably configured so that the inert gas is not mixed with the hydrogen gas for circulation, separate from the residual gas remaining in the mobile furnace 101, for example after gas evacuation.

[0051] As will be described in more detail below, system 100 also includes heaters and heat exchangers for controlling the temperature of such gases circulated to each mobile furnace 101 at any particular time.

[0052] The method may further include multiple processing steps performed on each of a plurality of individual mobile furnaces 101 of this type.

[0053] Generally, each mobile furnace 101 moves between the above-mentioned connection stations and undergoes a number of different processing steps, including heating, reducing, sintering, carburizing, and / or cooling, in addition to charging and unloading, with each such processing step being handled by one or more separate connection stations, each arranged in series or parallel.

[0054] Thus, in the first step, the method begins.

[0055] In a subsequent step, the amount of metal material 160 to be reduced is charged into the mobile furnace 101, for example by opening the top 104 and charging the metal material 106 into the furnace space 101a via a suitable automatic charging system, after which the top 104 is closed again.

[0056] In a subsequent step, the mobile furnace 101 is moved to and connected to a first one of the inert gas connection stations 120-122, 150-151, 160. In FIG. 1, this first one is illustrated as one of the heating connection stations 120, 121, 122.

[0057] In the subsequent heating step, heated inert gas is supplied to the moving furnace 101 in the manner described above, whereby the metal material 106 in the moving furnace 101 is heated in the heating furnace space 101a by the heated inert gas circulating through the metal material 106 in the moving furnace 101.

[0058] Therefore, the inert gas is preferably heated outside the furnace space 101a, and even outside the moving furnace 101, and circulated past the metal material 106, so that the metal material 106 is heated thereby.

[0059] In a subsequent step, the mobile furnace 101 is disconnected from the first inert gas connection stations 120-122.

[0060] In a subsequent step, the mobile reactor 101 is physically moved to and connected to a first one of the hydrogen gas connection stations 130, 140. It is understood that the hydrogen station 130, 140 is a physically different connection station from the first inert gas connection stations 120, 121, 122.

[0061] In the subsequent reduction step, heated hydrogen gas is supplied to the moving furnace 101 in the manner described above, and the metal material 106 is reduced by the heated hydrogen gas circulating through the metal material 106 in the moving furnace 101 .

[0062] Thus, hydrogen gas is circulated through the heated metallic material 106, which is thereby reduced.

[0063] In a subsequent step, the mobile furnace 101 is disconnected from the first hydrogen gas connection station 130, 140.

[0064] In a subsequent step, the mobile furnace 101 is physically moved to and connected to a second one of the inert gas connection stations 120-122, 150-151, 160. In FIG. 1, this second one is illustrated as either of the cooling connection stations 150, 151.

[0065] In the subsequent cooling step, cooled inert gas is supplied to the moving furnace 101 in the manner described above, whereby the cooled inert gas circulating through the metal material 106 in the moving furnace 101 cools the metal material 106 contained therein, thus performing the cooling in a manner corresponding to the heating step described above.

[0066] In the next step, the mobile furnace 101 is disconnected from the second active gas connection station 150-151.

[0067] In the next step, the reduction-cooled metal material 106 is discharged from the transfer furnace 101 .

[0068] In a subsequent step, the method may end. However, it will be understood that the method is typically carried out using multiple mobile furnaces 101 moving one after the other along a chain of connected stations, as exemplified below, and thus may continue for any length of time in a continuous flow without interruption. Once the two mobile furnaces 101 have discharged their material, they can return to the charging station 110 to be refilled and start over.

[0069] In some embodiments, hydrogen gas circulates in the closed loop first gas circuit at atmospheric pressure, or at a pressure up to 1.5 bar, or even at a pressure up to 1.1 bar.

[0070] Correspondingly, in some embodiments, the inert gas circulates in the closed-loop second gas circuit at atmospheric pressure, or at a pressure of up to 1.5 bar, or even at a pressure of up to 1.1 bar.

[0071] As mentioned above, the cooling inert gas, i.e., the inert gas used to cool the metallic material 106 in the cooling step, can also be used to preheat the inert gas used to heat the metallic material 106 in the heating step c. Such heat transfer can be performed using a gas-to-gas heat exchanger. Alternatively, as shown in Figures 1-3, the inert gas used to cool the metallic material can be used as the inert gas used to heat the metallic material 106 to be reduced after such cooling, possibly after additional heating by a gas heater 173.

[0072] The method may include using multiple gas / gas heat exchangers in parallel to exchange heat between the flows of inert gas, as described above, where multiple parallel flows of hot gas and / or multiple parallel flows of cold gas may be configured as parallel heat transfer flows in heat exchange with each other.

[0073] In addition to (or instead of) such heat exchange, the method may further include preheating the inert gas used to heat the metal material 106 in the heating step and / or preheating the hydrogen gas used in the reduction step using a gas heater 173, 191, such as an electric heater, located upstream of the inert gas or hydrogen gas connection stations 120-122, 130, 140.

[0074] As mentioned above, the mobile furnace 101 is preferably passive with respect to heat supply, in the sense that it does not have an internal thermal energy source. Instead, all thermal energy supplied to the metallic material 106 during processing, particularly during heating and / or reduction and / or sintering and / or carburizing, is supplied externally via heated gas flowing into the furnace volume 101a. However, thermal energy may also be supplied by exothermic reactions in the metallic material 106 itself. Importantly, no additional thermal energy is supplied to the furnace volume 101a apart from the heat input resulting from such exothermic reactions. Instead, by supplying all thermal energy externally, the mobile furnace can be simple, without any internal heaters or electrical connections, and can be robust and fault-resistant while being movable between different connection stations as described herein.

[0075] As described above, the inert gas and / or hydrogen gas may be supplied to flow into the moving furnace 101 and pass through the metal material 106 from below to above the metal material 106 in the heating, reducing, and / or cooling steps, as well as in the sintering and / or carburizing steps.

[0076] Each mobile furnace 101 may comprise two furnace sections 104, 105 of the type described above, adapted to engage with each other to form a closed furnace space 101a. At least one of the two furnace sections 104, 105, or the connection between the two furnace sections 104, 105, may be water-cooled using cooling water supplied from a cooling water circulation system 180. In this case, the method may further comprise circulating the cooling water in the separate cooling water circuit. Furthermore, the hydrogen connection stations 130, 140 and / or the inert gas connection stations 120-122, 150-151 may comprise connections for the cooling water so that the circulating cooling water is supplied when the mobile furnace 101 is connected to the connection station 120-122, 130, 140, 150-151. This provides a method for efficiently cooling all of the circulating mobile furnaces 101 in the system 100, and also provides a method for effectively utilizing the heat that is cooled by the mobile furnaces 101 and carried away by the cooling water from the mobile furnaces 101. For example, the heated cooling water can be used to supply heated water in a district heating system.

[0077] The circulation rate (or volumetric flow rate per time unit) of the gas circulating in the first and / or second gas circuits can be controlled by the controller 20 using speed-controllable fans or pumps (172, 194) to control the heating power, reduction rate, sintering rate, carburization rate and / or cooling power of the metallic material 106 to desired set points, which may of course vary over time. Measurements of temperature from each of the mobile furnaces 101, as well as measurements of temperature, moisture content, chemical composition, moisture content, etc. from other parts of the system 100, can also be used as input data to the controller 20 as a basis for controlling the operation of the system 100.

[0078] Additionally, in some embodiments, the reduction step may further include continuing to supply heated hydrogen gas after the metallic material 106 has been reduced to further sinter the metallic material 106. In Figures 1 and 5, this is illustrated by a separate sintering connection station 140, which supplies gas to the connected transfer furnace 101 in the general manner described above.

[0079] Additionally, in some embodiments, a carbon-containing gas, such as CH4, can be used to carburize the metallic material. The carbon-containing gas can be supplied via a dedicated connection station (not shown), a reduction connection station 130, and / or a sinter connection station 140. In the example shown in Figures 1 and 5, the sinter station 140 is configured to supply CH4 gas via the valve system 13 to perform the carburization.

[0080] Thus, the method may further include circulating the carbon-containing gas in a closed-loop third gas circuit by using a third valve system to selectively circulate such carbon-containing gas through two or more of the set of multiple hydrogen gas connection stations 130, 140. Specifically, the reduction step (or subsequent sintering step or dedicated carburization step) may further include supplying the carbon-containing gas to the moving furnace 101 such that the metal material 106 is carburized by the carbon-containing gas circulated through the metal material 106 in the moving furnace 101.

[0081] The third closed loop gas circuit may be partially or entirely the same as the second closed loop gas circuit, or may be a separate gas circuit.

[0082] If carburization is not performed at the reduction connection station 130, the system 100 may include a set of one or more carbon-containing gas connection stations. In that case, the method may further include the following steps, which are performed after the transfer furnace is disconnected from the reduction connection station 130 and before the cooling step:

[0083] First, the mobile furnace 101 may be moved to and connected to a first one of the carbon-containing gas connection stations.

[0084] Second, a carbon-containing gas may be supplied to the moving furnace 101 such that the metal material 106 is carburized by the carbon-containing gas circulating through the metal material 106 in the moving furnace 101 .

[0085] Third, the mobile furnace 101 may be disconnected from the first carbon-containing gas connection station.

[0086] 1 shows sintering stations 140 used to sinter the metallic material 106 at a higher temperature than the reduction step uses. A carbon-containing gas may be supplied through one or more of such sintering stations 140, such as a controlled mixture of hydrogen gas and a carbon-containing gas.

[0087] In the case of two or more heating stations 120-122, two or more reducing stations 130, two or more sintering stations 140, two or more carburizing stations, and / or two or more cooling stations 150-151, the method may further include disconnecting the mobile furnace 101 from a first connection station of that type, moving the mobile furnace 101 to a second connection station of that type, and connecting it thereto, so that the mobile furnace 101 can be connected to two or more connection stations of the same type in series and processed therein, as exemplified below. Additionally or alternatively, multiple parallel flows of mobile furnaces 101 using different connection stations of the same type can be provided, depending on the size of the facility and the desired total throughput.

[0088] As noted above, the method uses separate joining stations for processing the metallic material 106 in each moving furnace 101 in multiple successive processing steps, including all or part of heating, reducing, sintering, carburizing, and cooling. As noted above, carburizing may occur in a separate joining station or may occur as part of the sintering joining station 140, for example.

[0089] Of these steps, the reduction step is typically the least time-consuming, especially if the material 106 is heated to the appropriate reduction temperature during the heating step. It is the heating and cooling steps that typically take the most time. This is important when designing large, highly automated facilities where many moving furnaces 101 are used.

[0090] Typically, a large installation will have at least 10 mobile furnaces 101 in use at the same time, for example, at least 20 mobile furnaces 101 in use at the same time. However, due to the modular design of the mobile furnace 101, it is also possible to use the mobile furnace 101 itself in smaller installations. To scale up or down, simply add or remove connecting stations, and use the appropriate number of mobile furnaces 101 of the same type.

[0091] Preferably, each moving furnace 101 is designed to hold at least 1000 kg of metal material, and each moving furnace 101 is designed to hold a maximum of 10000 kg of metal material.

[0092] Generally, the system 100 may consist of the following parts: a grinding device configured to produce a metal-containing powder material suitable for producing balls of such material; a ball-making apparatus configured to produce directly reduced balls of metal-containing material using the method, e.g., 1-5 cm in diameter; a charging device configured to charge manufactured balls (or similar or other metallic materials produced locally or received from a remote production facility) into said mobile furnace 101; a heating device consisting of one or preferably several heating connection stations 120-122 for heating the charged metallic material to a process temperature of, for example, 550-600°C, preferably using preheated gas received from the downstream cooling step; a reduction device consisting of one or preferably several reduction connection stations 130; a sintering / carburizing step comprising one or preferably several sintering / carburizing stations 140; a cooling step comprising one or preferably several cooling connection stations 150-151 configured to cool the metallic charge 106 to a temperature of at most 100°C, for example at most 50°C; and / or A discharge / packaging step 160 in which the reduced / sintered / carburized material 106 is discharged from the transfer furnace 106 and suitably packaged for further processing and / or transportation.

[0093] Preferably, loading and unloading is done automatically, such as by using a suitable robotic arm.

[0094] In small scale installations, heating, reducing, sintering and / or cooling may be performed using only one connected station per such processing step, whereas in larger scale installations, one or more of the above processing steps may be performed using two or more connected stations arranged in parallel and / or series.

[0095] In smaller installations, transportation of the mobile furnace between the above-described docking stations can be accomplished using overhead cranes or trucks, thereby eliminating the need for wheels 109a on the mobile furnace and, in some cases, even the trolley 109. On the other hand, in larger installations, transportation can be performed using rails as described above or a free-floating, computer-controlled trolley 109. It will be appreciated that the above-described structure with the pedestal 108 and platform 109 provides a convenient way to scale up or down between such small and large production units, using the same components and simply changing the number of mobile furnaces 101 and docking stations, and, if necessary, the transport mechanisms.

[0096] Apart from the desired total throughput, the number of different types of connection stations is primarily determined by the combination of the processing time (total time consumed) of the mobile furnace 101 for any one processing step and the number of connection stations operating in parallel for that processing step. Because different processing steps are typically associated with different processing times, a processing step with a relatively short processing time determines how preceding and subsequent processing steps are arranged. For example, if a preceding processing step has a long processing time, the subsequent processing step will need to have more parallel connection stations than the previous processing step to ensure a smooth and uniform flow of the mobile furnace 101 between processing steps. The same is true if the subsequent processing step is slower (longer in time) compared to the preceding processing step.

[0097] For example, the reduction process is typically a relatively fast process (requiring the shortest processing time). The reduction process is typically followed by a sintering / carburizing process, which also involves heating the material 106. For example, if the sintering / carburizing process takes twice as long as the reduction process, the number of sintering / carburizing connection stations 140 that receive the transfer furnaces 101 from the reduction connection stations 130 must be twice the number of reduction connection stations 130. Correspondingly, at the interface between the heating connection stations 120-122 and the reduction connection stations 130, more heating connection stations 120-122 than reduction connection stations 130 are typically required, since the reduction process typically takes less time than the time it takes to heat the metal material 106 to the reduction temperature.

[0098] As mentioned above, another difference between the different processing steps is that the heating and cooling steps use an inert gas, such as nitrogen gas, to transport thermal energy to and from the moving furnace 101, while the reduction and sintering uses, for example, hydrogen gas. Additionally, the carburization process uses a carbon-containing gas, such as a hydrocarbon, for example, CH4, which can be used together with hydrogen gas in the same closed loop circuit.

[0099] FIG. 1 shows a schematic diagram of an example of a large scale installation system 100 according to the present invention.

[0100] As shown in this Figure 1, the heating and cooling treatment sections are interconnected and together form a closed gas system in which nitrogen gas (or other inert gas) is pumped or circulated to transfer thermal energy from the metal material 106 at the cooling end to heat the cooled metal material 106 arriving from the charge before being passed on to reduction. As mentioned above, the transportation of the metal material 106 is carried out by the metal material 106 being transported in this type of moving furnace 101 and moving for an appropriate / predetermined time between different connection stations to which different gas flows are sequentially supplied.

[0101] As mentioned above, the time required to heat and cool the metallic material 106 is typically longer than the time required to reduce and sinter / carburize the metallic material 106, and therefore, at any given time, there will typically be more bonding stations and transfer furnaces operating in these heating / cooling processing steps than there are time required for reduction and sintering / carburization.

[0102] As a result, the method may include using a greater number of inert gas connection stations 120-122, 150-151 used in parallel and / or series than the number of hydrogen gas connection stations 130, 140 used in parallel and / or series.

[0103] In this embodiment, reduction and sintering are carried out in the manner described below, however, both the inert gas circulation system and the hydrogen / carbon-containing gas circulation system are each closed systems and are configured so as not to substantially discharge such gases into the environment or interfere with each other.

[0104] Therefore, all process steps according to the present invention can preferably be carried out in a closed system 100 in which the mobile furnace 101 is moved between different steps in the system 100. Within the framework of each process step, the mobile furnace 101 is connected to a respective connection station at some point within that process step.

[0105] A set of several mobile furnaces 101 transporting the metal material through the various processing steps forms part of this same closed system 100, whereby all processes are carried out in said mobile furnaces 101 which move and connect between the connecting stations of the various processing steps in the closed system 100. For this purpose, the opening mechanism 104a of the mobile furnaces 101 is preferably configured so that the closed furnace space 101a is gas-tight and can withstand a constant overpressure (and corresponding underpressure) of at least 1.5 bar without gas leakage. For example, the upper part 104 can be held closed relative to the lower part 107 by means of a hydraulic or screw-type pressing mechanism that is automatically activated in connection with the charging at station 110.

[0106] All, or at least some, of the mobile furnaces 101 may be identical or may have at least the same interface to the connections 11, while each connection station is arranged to supply the desired gas with the desired properties to the mobile furnace 101 at the respective connection station, preferably together with a parallel flow of cooling water as described above. In this way, the mobile furnaces 101 are interchangeable, allowing the system 100 to be expanded or contracted simply by adding or removing mobile furnaces 101.

[0107] From a thermal standpoint, most of the heat transfer occurs to the charge metal material 106 during pre-reduction heating (which occurs at 550-580°C) and sintering / carburizing (which occurs at 900-1000°C). Thermal energy then transfers from the charge material 106 during cooling, which may reach approximately 20-50°C, for discharge and packaging.

[0108] In order to match the shortest processing time (typically the reduction time), the heating and cooling steps may each advantageously be arranged as a series of one or more serially connected connection stations 120-122; 150-151, the processing time associated with each such connection station 120-122; 150-151 being at most, or exactly, or at least approximately, the same as the processing time of the shortest processing step (in this case, the processing time at a single reduction connection station 130). Thus, if the reduction step takes 30 minutes, another mobile furnace 101 will arrive at the first cooling connection station 150 every 30 minutes, still maintaining a temperature of, for example, 900°C.

[0109] Because the first cooling connection station 150 after the sintering / carburizing connection station 140 must be available when a new transfer furnace 101 arrives from station 140 (not currently connected to an in-service transfer furnace 101), the preceding transfer furnace 101 must have already moved along the next connection station by that time. Thus, the transfer furnace 101 moves sequentially along the series of cooling connection stations 150-151 until the temperature of the metal material 106 within the transfer furnace reaches a desired temperature for discharge, e.g., 50°C, at the end of the series. Thus, the series of cooling connection stations 150-151 may consist of a number of such stations 150-151 (greater than the two such stations shown in FIG. 1 ) such that the metal material 106 reaches approximately 50°C at the end of the series after spending approximately 30 minutes connected to each of the series-connected connection stations 150-151. For finer adjustment, the control device 20 can individually control the pressure or cooling gas flow rate circulated to each of the cooling connection stations 150-151 at each time by controlling valves V12, V14, V15, V17, or by controlling the fan or pump 172 to control the total flow rate through all of the cooling connection stations 150-151 at a higher level.

[0110] The same applies to the heating connection stations 120-122 operating in series.

[0111] Furthermore, such a series of heating / cooling connection stations 120 - 122 ; 150 - 151 can also be arranged in two or more parallel flows, one for each flow of the mobile furnace 101 .

[0112] When the mobile furnace 101 is disconnected from a particular connection station, the gas connection to the mobile furnace 101 is cut off and the valves of the valve system 13 switch off the gas supply to the connector 12. When the mobile furnace 101 is connected to a particular connection station, the gas connection to the mobile furnace 101 is opened and the valves of the valve system 13 switch on the gas supply to the connector 12.

[0113] At the packaging station 160, the temperature of the reduced material 106 is preferably below 50°C to avoid re-oxidation of the reduced material. In the charging step, charging at the charging station 110 may be performed by charging the material 106 into baskets 106a (FIG. 7), which are filled with the metal material 106 to be reduced in the furnace space 101a of the mobile furnace 101. Next, the discharging step consists of discharging the baskets 106a from the furnace space 101a. Thus, the metal material 106 is transported around the system 100 in a number of such baskets 106a, with each basket 106a being charged into and discharged from the mobile furnace 101 in turn.

[0114] To empty the furnace space 101a from the inert cooling gas, before opening the furnace space 101a at the packaging station 160, the mobile furnace 101 is connected to a fan or pump 174 via valves V10 and V11, and the inert gas is directed into the inert gas reservoir 171. Then, valves V10 and V11 are closed, the fan or pump 174 is switched off, and atmospheric air is introduced into the open furnace space 101a. The top 104 is lifted, and the basket 106a containing the reduced and cooled metal material 106 is lifted from the mobile furnace 101. The basket 106a is emptied and placed back into place in the mobile furnace 101. The mobile furnace 101 is then returned to the charging station 110, and the metal material 106 to be reduced is again charged. Alternatively, the baskets 106a can travel in a separate stream such that the mobile furnace 101 leaves the discharge station 160 empty and is provided with freshly filled baskets 106a at the loading station 110 for another run along the processing line.

[0115] The cooling and heating loop forms a closed unit and begins with filling with gas from gas reservoir 171, which enters via valve V6. When valve V5 is closed, the gas continues via valve V7 (valve V8 is closed), fan or pump 172, valve V9 to the final cooling connection station 151. If the mobile furnace 101 is not currently connected to this connection station 151, valves V12 and V14 are closed and valve V13 is opened, allowing the gas to bypass the disconnected connection station 151 and be sent to the next upstream cooling station 150. On the other hand, when the last cooling station 151 is connected to the moving furnace 101, valve V13 is closed, while valves V12 and V14 are open. Therefore, the inert cooling gas enters the cooling station 151 via V12, enters the connected moving furnace 101, cools the material 106 therein, and then enters the next upstream cooling connection station 150 via valve V14 and then enters the currently connected moving furnace 101 via valve V15. In this situation, valve V16 is closed, and the cooling gas already warmed somewhat by the material 106 at the connection station 151 is used to cool the material 106 in the moving furnace 101 connected to the connection station 150, which is warmer than the material already cooled at the connection station 151. There may be two or more cooling connection stations 150-151 corresponding to the flow of the moving furnace 101, with the cooling gas flowing in the opposite direction compared to the general direction of travel D of the moving furnace 101.

[0116] The flow of cooling gas is shown in Figure 2 using flow arrows for cooling gas and cooling water from the cooling water circulation system 180. The switch-off valve is shown in dashed lines.

[0117] In the most upstream arranged cooling connection station 150, the warmed cooling gas is discharged through the valve V17 at a temperature of about 800-900°C.

[0118] The hot inert gas is used to heat the metallic material 106 to be reduced at the heat connection stations 120 - 122 before the material 106 is conveyed to the reduction station 130 .

[0119] Heating with this inert heating gas (coming from the cooling connection stations 150-151, where the very same inert gas acts as cooling gas), as in the case of the cooling connection stations 150-151, may occur countercurrently (countercurrently) to the general direction of movement D of the mobile furnace 101 as it moves along the heating stations 120-122 forming the processing line, the flow of cooling gas being shown in Figure 3 by means of arrows as in Figure 2. Thus, in Figure 1, the inert gas flows to the left while the mobile furnace 101 moves to the right along the series of connection stations 120-122, 150-151.

[0120] Thus, the inert heating gas flows through valve V21 into the transfer furnace 101 located most downstream of the heating connection station 122. Valve V22 is closed, and the heating gas flows via valves V23 and V24 (valve V25 is closed) to the next upstream transfer furnace 101 of the connection station 121, via valves V26 and V27 (valve V28 is closed) to the most upstream transfer furnace 101 of the connection station 120, and out via valve V29.

[0121] Generally, in some cases, multiple inert gas connection stations 120-122, 150-151 can be used simultaneously to heat and / or cool multiple mobile furnaces 101 in parallel. In this case, the method may include circulating heated and / or cooled inert gas through the multiple mobile furnaces 101 in a direction opposite to a general process flow D of the mobile furnaces 101, passing the mobile furnaces 101 in series, and moving the mobile furnace 101 one by one between the inert gas connection stations 120-122, 150-151 in the process flow D by disconnecting the mobile furnace 101 from one of the inert gas connection stations 120-122, 150-151, moving the mobile furnace 101, and connecting the mobile furnace 101 to the next inert gas connection station 120-122, 150-151 in sequence.

[0122] Prior to reduction, the metallic material 106 may be heated to at least 350°C, e.g., at least 400°C, e.g., at least 500°C, and / or at most 650°C, e.g., at most 500°C. Because the heating gas is inert, the charge material 106 is not chemically affected by this heating. However, contained metals with relatively low smelting or vaporization points may change their agglomeration state at too high a temperature. Therefore, the metallic material 106 is preferably not heated to a temperature at which contained metals in the metallic material 106 begin to melt or vaporize prior to reduction; vaporization of such contained metals may instead occur in the reduction station 130, which has means for condensing such vaporized metals in the form of a gas-to-gas heat exchanger 195.

[0123] Generally, the reduction step may include heating the metallic material 106 above the melting and / or vaporization temperature of contaminants present in the metallic material 106 using heated hydrogen gas as the heat source for said heating.

[0124] If the inert heating gas requires additional heating before entering the most downstream heating connection station 122, valve V19 is closed and valves V18 and V20 are opened, allowing the inert gas to pass through gas heater 173 between station 150 and station 122. As noted above, this may depend on the desired maximum heating temperature of the metallic material 106 to be reduced, for example, based on the chemical composition of the metallic material 106. For example, if the metallic material 106 does not contain any easily smeltable / vaporizable metals, a heating temperature of approximately 700°C may be supplied to station 122, and then gas heater 173 may be selectively engaged to achieve this temperature for the inert heating gas. If no additional heating is required, valve V19 is opened and valves V18 and V20 are closed, allowing gas heater 173 to be disengaged.

[0125] If the most downstream heating connection station 122 is not occupied by a currently connected mobile furnace 101, valve V22 may be opened and valves V21 and V23 may be closed so that the inert heating gas bypasses station 122 and is supplied directly to the next upstream connection station 121.

[0126] Once the metal material 106 in the mobile furnace 101 connected to station 122 reaches the desired temperature, valve V22 is opened, valves V21 and V23 are closed, and inert gas is supplied directly to the next upstream station 121. At this point, the mobile furnace 101 in the last heating station 122 is filled with inert gas, so valve V31 is opened, connecting it to the fan or pump 174 and then to the gas reservoir 171 (open) via valve V10. In this way, the inert gas is exhausted from the mobile furnace 101 in station 122 to the gas reservoir 171. If the exhausted inert gas temperature is too high, it can be cooled using a cooler before storage. Once the inert gas has been exhausted from the mobile furnace 101, valves V31, V10, and V11 are closed, the fan or pump 174 is switched off, and the mobile furnace 101 is ready to move on to the reduction step 130.

[0127] The somewhat cooled inert gas continues upstream toward the first heating connection station 120 (which is the first station 120 after the loading station 110), as described, heating the metal material 106 in each successively connected moving furnace along the way.

[0128] The most upstream station 120 may be empty, in which case valves V27, V29 are closed and valve V28 is open to bypass this station 120.

[0129] The inert gas is sent via valve V2 to a gas / water heat exchanger 170, where it is cooled to about 20°C or another suitable temperature that achieves sufficient drying of the inert gas. A gas dryer (not shown) can also be used in connection with the gas / water heat exchanger 170. The water thus heated can be used, for example, in a district heating system.

[0130] If the inert heating gas loses temperature along its path along stations 120-122 so that it is no longer useful for heating the circulating metal material 106, valves V2, V24-V29, or correspondingly depending on where the flow of inert gas is interrupted in stations 120-122, can be operated so that the heating gas is conveyed directly to gas / water heat exchanger 170 instead of continuing to flow through metal material 106. The temperature of the heating gas leaving the most upstream heated moving furnace 101 is preferably at least 100°C, thereby conveying any contained water vapor to gas / water heat exchanger 170 and depositing such water in liquid form.

[0131] The inert gas is returned to the cooling step via a fan or pump 172, forming the second closed circulation loop described above. A gas reservoir 171 is used to control the inert gas pressure in this loop to a selected uniform pressure between 1.0 and 1.5 bar, for example between 1.0 and 1.1 bar.

[0132] After valve V29, the inert gas passes through either valve V1 or valve V2, depending on which of these valves V1 and V2 is open. If the gas is already dry, it returns to gas reservoir 171 via valve V1 (valve V2 is closed) and passes through fan or pump 172. If the gas is wet, valve V1 is closed and valve V2 is opened, allowing the gas to pass through gas / water heat exchanger 170 for drying before returning to fan or pump 172 via valves V3 and V5. As long as the inert gas continues to circulate, valve V8 is closed and valves V7 and V9 are open.

[0133] At the loading station 110, the basket 106a is filled with the metal material to be reduced, and the basket 106a is placed in the mobile furnace 101. After the furnace interior space 101a is sealed, a vacuum pump 111 is used to evacuate the contained air through valve V30, bringing the furnace interior space 101a to a predetermined low pressure. The mobile furnace 101 is then moved from the loading station 110 to the first heating connection station 120, beginning its movement between the aforementioned connection stations in the general direction indicated by D in FIG. 1. At station 120, the mobile furnace 101 is connected to the inert gas circuit, from which point it becomes part of the closed inert gas circuit.

[0134] As noted above, the most quickly accomplished processing step in the method is typically reduction, possibly followed by sintering, if used. The slowest accomplished processing steps are cooling, followed by heating. Therefore, each reduction docking station 150 preferably has multiple moving furnaces 101 with newly loaded baskets 106a waiting to be heated.

[0135] The reduction step is shown in more detail in Figure 4. For reduction, hydrogen gas is used, as opposed to the inert gases mentioned above, and is heated by a separate hydrogen gas heater 191. This heater 191 is also used to maintain the desired hydrogen gas temperature, and it should be noted that the reduction of the metallic material 106 is an endothermic chemical reaction.

[0136] Preferably, pure or substantially pure hydrogen gas is used.

[0137] The reduction step also uses a gas / gas heat exchanger 195 for heat transfer from the hydrogen gas exiting the connected transfer furnace 101 to the hydrogen gas 190 entering the transfer furnace 101. The reduction reaction produces water in the form of steam, which is condensed in the gas / gas heat exchanger 195. To further reduce the water content in the hydrogen gas, further cooling can be performed in a connected gas / water heat exchanger 192, or a gas dryer 193 can be used. The hydrogen gas is circulated using a fan or pump 194 and heated by a gas heater 191 (which can be an electric heater of the type described above).

[0138] Generally, the reduction step may include heat exchanging hydrogen gas exiting the moving furnace 101 with hydrogen gas entering the moving furnace 101, cooling and drying the heat-exchanged hydrogen gas, and further recovering liquid water formed from the drying.

[0139] During reduction, hydrogen gas is consumed and replenished from controlled reservoirs 197, 198 for used / unused hydrogen gas to a desired pressure, which may be 1.0-1.5 bar, for example 1.0-1.1 bar.

[0140] The reduction rate can be controlled by the controller 20 controlling the amount of hydrogen gas per unit time passing through the material 106 in the connected moving furnace 101 and / or by the controller 20 controlling the selected overpressure of the hydrogen gas.

[0141] All condensed water is collected in a condensed water tank 196. The amount of water in the tank 196 can be measured by a suitable level sensor and used by the controller 20 to determine the total amount of reduced metallic material 106.

[0142] Once the reduction of the metallic material 106 is complete, the circulating pump or fan 194 is switched off, as is the heater 191. The cooling water and hydrogen gas supply valves are closed by the valve system 13 of the docking station 130. Other fixed (stationary) equipment of the docking station 130 may be temporarily switched off until the next mobile furnace 101 arrives at the station 130. The condensate tank 196 is emptied.

[0143] Preferably, to minimize re-oxidation of the metallic material 106, the transfer furnace 101 is transferred to the sintering / carburizing connection 140 station while maintaining hydrogen gas pressure within the furnace space 101a.

[0144] When connected to the sintering / carburizing connection station 140, the atmosphere circulated by the system 100 within the transfer furnace 101 is also hydrogen gas or at least contains hydrogen gas as a minor component. As shown in FIG. 5, the system 100 uses elements 180, 190, 191, 193, 194, 195, 197, and 198 in a corresponding manner as shown in FIG. 4. It will be understood that each of these components may be the same as or additional to those shown correspondingly in FIG. 4, depending on the mode of operation of the system 100. That is, the reduction 130 and sintering 140 stations may be arranged to operate simultaneously or may be configured to operate one at a time.

[0145] Generally, the hydrogen gas exiting the reduction bonding station 130 is typically held at 650-750°C and can be used for sintering after its temperature is raised to the desired sintering temperature, e.g., 850-950°C, using the gas heater 191.

[0146] In the preferred case where hydrogen gas is mixed with a carbon-containing gas such as CH supplied from CH virgin gas tank 200, it is desirable to use a separate circuit for the sintering gas compared to the reduction gas circuit. However, in some cases the circuits can be interconnected if energy from the reduction step is utilized by recycling the heated hydrogen gas used in the reduction step as input to the sintering step.

[0147] In some embodiments, sintering can be performed initially by circulating only hot hydrogen gas in a closed loop circuit as shown in Figure 5, and then a carbon-containing gas can also be circulated to perform carburizing. The next moving furnace 101 can then be connected to station 140, and a vacuum pump 202 to a spent gas reservoir 202 can be used to evacuate the gas 201 from the circuit and replace the hydrogen / carburizing gas with an inert gas such as nitrogen gas, before the hydrogen gas is circulated back into the circuit.

[0148] Upon leaving the docking station 140, the furnace space 101a of the transfer furnace 101 is also filled with an inert gas, preferably nitrogen gas, in preparation for the cooling treatment steps 150-151.

[0149] As noted above, the present invention further relates to such a system 100 itself, configured for producing directly reduced metallic materials 106 in a continuous process of the type generally described herein, as well as the method, comprising circulating means 194 for circulating hydrogen gas in a closed-loop first gas circuit; said first valve system; circulating means 172, 174 configured to circulate an inert gas in a closed-loop second gas circuit; said second valve system; and a plurality of individual moving furnaces 101 of the type described herein.

[0150] System 100 may then be configured to perform a series of automatically performed steps corresponding to the steps described herein in connection with the present method. Generally, these steps are performed using the automated processing equipment described and illustrated herein under the control of controller 20. In particular, system 100 is configured as follows: Charge the moving furnace 101 with an amount of metal material 106 to be reduced; The mobile furnace 101 is moved to and connected to a first one of the inert gas connection stations 120-122, 150-151; supplying a heated inert gas to the moving furnace 101, so that the metal material 106 is heated by the heated inert gas circulating through the metal material 106 in the moving furnace 101; disconnecting the mobile furnace 101 from the first inert gas connection station; moving and connecting the mobile furnace 101 to a first one of the hydrogen gas connection stations 130, 140; Heated hydrogen gas is supplied to the moving furnace 101, and the metal material 106 is reduced by the heated hydrogen gas circulating through the metal material 106 in the moving furnace 101; disconnecting the mobile furnace 101 from the first hydrogen gas connection station 130, 140; moving and connecting the mobile furnace 101 to a second one of the inert gas connection stations 120-122, 150-151; A cooling inert gas is supplied to the moving furnace 101, and the metal material 106 is cooled by the cooling inert gas circulating through the metal material 106 in the moving furnace 101; Decoupling the mobile furnace 101 from the second inert gas connection stations 120-122, 150-151; and The reduced and cooled metal material 106 is discharged from the moving furnace 101 .

[0151] Although the preferred embodiments have been described above, it will be apparent to those skilled in the art that many modifications can be made to the disclosed embodiments without departing from the essential concepts of the invention.

[0152] For example, system 100 may include additional process steps other than those described herein, and mobile furnace 101 may vary in design and functionality other than those described herein.

[0153] Everything said about the present method is equally applicable to the present system, and vice versa.

[0154] Therefore, the invention is not limited to the described embodiments, but can be modified within the scope of the appended claims.

Claims

1. 1. A method for producing directly reduced metallic materials (106) in a continuous process, comprising: The method includes circulating hydrogen gas in a closed-loop first gas circuit by selectively circulating hydrogen gas through one or more of a set of a plurality of hydrogen gas connection stations (130, 140) using a first valve system; The method further includes circulating the inert gas in a closed-loop second gas circuit by selectively circulating the inert gas through one or more of a plurality of inert gas connection stations (120-122, 150-151) using a second valve system; The method further comprises the following steps, performed for each of the plurality of individual mobile furnaces (101): a) charging the amount of metal material (106) to be reduced into the moving furnace (101); b) moving and connecting the mobile furnace (101) to a first one of the inert gas connection stations (120-122, 150-151); c) supplying a heated inert gas to the moving furnace (101) so that the metal material (106) is heated by the heated inert gas circulating past the metal material (106) in the moving furnace (101); d) disconnecting the mobile furnace (101) from the first inert gas connection station; e) moving and connecting the mobile furnace (101) to a first one of the hydrogen gas connection stations (130, 140); f) supplying heated hydrogen gas to the moving furnace (101) so that the metal material (106) is reduced by the heated hydrogen gas circulating past the metal material (106) in the moving furnace (101); g) disconnecting said mobile furnace (101) from said first hydrogen gas connection station (130, 140); h) moving and connecting the mobile furnace (101) to a second one of the inert gas connection stations (120-122, 150-151); i) supplying a cooled inert gas to the moving furnace (101) and cooling the metal material (106) by the cooled inert gas circulating past the metal material (106) in the moving furnace (101); j) disconnecting the mobile furnace (101) from the second inert gas connection station (120-122, 150-151); and k) Discharging the reduced and cooled metal material (106) from the moving furnace (101); A method characterized by:

2. 10. The method of claim 1, The hydrogen gas and / or the inert gas are circulated in the first and / or second gas circuits of the closed loop at atmospheric pressure or at a maximum of 1.5 bar. A method characterized by:

3. 3. The method of claim 1 or 2, the inert gas used to cool the metallic material (106) in step i) is used to preheat or is used as the inert gas used to heat the metallic material (106) in step c); A method characterized by:

4. 4. The method according to any one of claims 1 to 3, The method further comprises preheating the inert gas used to heat the metal material (106) in step c) and / or the preheated hydrogen gas used in step f) using a heater (173, 191) provided upstream of the inert gas or hydrogen gas connection station (120-122, 130, 140). A method characterized by:

5. 5. The method of claim 4, the mobile furnace (101) is passive in terms of heat supply, in the sense that it does not constitute an integrated source of thermal energy; A method characterized by:

6. 6. The method according to any one of claims 1 to 5, The inert gas and / or the hydrogen gas is supplied in steps c), f) and / or i) so that the inert gas and / or the hydrogen gas flows into the moving furnace (101) and passes through the metal material (106) from below to above the metal material (106) in the moving furnace (101). A method characterized by:

7. 7. The method of any one of claims 1 to 6, The mobile furnace (101) is configured to have two furnace sections (104, 105) arranged to engage with each other to form a closed furnace space (101a), At least one of the two furnace sections (104, 105) is water-cooled; The method includes circulating cooling water in a cooling water circuit; the hydrogen gas (130, 140) and / or inert gas (120-122, 150-151) connection station further comprises a connection for the cooling water so that the circulating cooling water is supplied to the mobile furnace (101) when the mobile furnace (101) is connected to the connection station (120-122, 130, 140, 150-151); A method characterized by:

8. 8. The method according to any one of claims 1 to 7, The method further comprises controlling the circulation speed in the first and / or second gas circuits using a speed-controllable fan or pump (172, 194), thereby controlling the heating power, reduction rate and / or cooling power of the metallic material (106). A method characterized by:

9. 9. The method of any one of claims 1 to 8, Step f) further comprises continuing to supply heated hydrogen gas to further sinter the metallic material (106) after the metallic material (106) has been reduced. A method characterized by:

10. 10. The method of any one of claims 1 to 9, the method further includes circulating the carbon-containing gas in a closed-loop third gas circuit by selectively circulating the carbon-containing gas through one or more of the set of hydrogen gas connection stations (130, 140) using a third valve system; Step f) further comprises supplying the carbon-containing gas to the moving furnace (101) so that the carbon-containing gas circulating through the metal material (106) in the moving furnace (101) carburizes the metal material (106); A method characterized by:

11. 10. The method of any one of claims 1 to 9, the method further includes circulating the carbon-containing gas in a closed-loop third gas circuit by selectively circulating the carbon-containing gas through one or more of a set of a plurality of carbon-containing gas connection stations using a third valve system; The method further comprises the following steps, which are performed after step g) and before step h): moving and connecting the transfer furnace (101) to a first one of the carbon-containing gas connection stations; supplying a carbon-containing gas to the moving furnace (101) so that the carbon-containing gas circulates through the metal material (106) in the moving furnace (101) to carburize the metal material (106); and disconnecting the transfer furnace (101) from the first carbon-containing gas connection station; A method characterized by:

12. 12. The method of any one of claims 1 to 11, The method further includes using more inert gas connection stations (120-122, 150-151) in parallel and / or series than the number of hydrogen gas connection stations (130, 140) used in parallel and / or series. A method characterized by:

13. 13. The method of any one of claims 1 to 12, several of the inert gas connection stations (120-122, 150-151) are used simultaneously to heat and / or cool several parallel-arranged mobile furnaces (101); the method comprises circulating heated and / or cooled inert gas in a direction opposite to the process flow of the mobile furnaces (101), passing the mobile furnaces (101) in series, and then moving the mobile furnaces (101) one by one in the process flow between the inert gas connection stations (120-122, 150-151) by disconnecting the mobile furnace (101) from one of the inert gas connection stations (120-122, 150-151), moving the mobile furnace (101), and connecting it to a next one of the inert gas connection stations (120-122, 150-151), A method characterized by:

14. 14. The method of any one of claims 1 to 13, Step f) further comprises heating the metallic material (106) above the melting and / or vaporization temperature of contaminants present in the metallic material (106) using heated hydrogen gas as a heat source for heating. A method characterized by:

15. 15. The method of any one of claims 1 to 14, Step a) comprises charging a basket (106a) filled with the metal material (106) to be reduced into the furnace space (101a) of the mobile furnace (101), Step k) comprises ejecting the basket (106a) from the furnace space (101a), A method characterized by:

16. 16. The method of any one of claims 1 to 15, Step f) comprises exchanging heat between the hydrogen gas exiting the moving furnace (101) and the hydrogen gas entering the moving furnace (101), cooling and drying the heat-exchanged hydrogen gas, and recovering the liquid water formed from the drying. A method characterized by:

17. A system (100) for producing directly reduced metallic materials (106) in a continuous process, comprising: The system includes a circulation means for circulating hydrogen gas in a closed-loop first gas circuit, the system including a first valve system arranged to selectively circulate hydrogen gas through one or more of a set of a plurality of hydrogen gas connection stations (130, 140) configured in the system (100); The system further comprises circulation means (172, 174) arranged to circulate an inert gas in a closed-loop second gas circuit; the system includes a second valve system arranged to selectively circulate inert gas through one or more of a set of a plurality of inert gas connection stations (120-122, 150-151) configured within the system (100); The system further comprises a plurality of individual moving furnaces (101); The system is configured as follows: a) charging the amount of metal material (106) to be reduced into the moving furnace (101); b) moving and connecting the mobile furnace (101) to a first one of the inert gas connection stations (120-122, 150-151); c) supplying heated inert gas to the moving furnace (101) so that the metal material (106) is heated by the heated inert gas circulating through the metal material (106) in the moving furnace (101); d) disconnecting the mobile furnace (101) from the first inert gas connection station; e) moving and connecting the mobile furnace (101) to a first one of the hydrogen gas connection stations (130, 140); f) supplying heated hydrogen gas to the moving furnace (101) so that the metal material (106) is reduced by the heated hydrogen gas circulating through the metal material (106) in the moving furnace (101); g) disconnecting said mobile furnace (101) from said first hydrogen gas connection station (130, 140); h) moving and connecting the mobile furnace (101) to a second one of the inert gas connection stations (120-122, 150-151); i) supplying a cooling inert gas to the moving furnace (101) and cooling the metal material (106) by the cooling inert gas circulating past the metal material (106) in the moving furnace (101); j) disconnecting the mobile furnace (101) from the second inert gas connection station (120-122, 150-151); and k) Discharging the reduced and cooled metal material (106) from the moving furnace (101); A system characterized by:

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