Direct Reduction Systems and Related Processes

Abstract

The present invention provides a reduction system and method that can operate with any ratio of gaseous hydrogen-containing gas to gaseous hydrocarbon-containing gas, which may continue operation if gaseous hydrogen-containing gas is unavailable for any reason, allowing the gaseous hydrogen-containing gas to be replaced with gaseous hydrocarbon-containing gas with minor adjustments in plant operation, ensuring high process availability and negligible production losses. The reduction system of the present invention is designed to be implemented in new and already constructed direct reduction plants in order to operate efficiently and have low capital and operating costs.

Description

[Technical Field]

[0001] More particularly, the present invention relates to a direct reduction system and related processes for producing metallic iron by directly reducing iron oxide with a reducing gas. [Background technology]

[0002] A known type of direct reduced iron (DRI) production system includes a reactor filled with pelletized and / or lumped iron oxide and a line for processing and supplying a reducing gas containing hydrogen and carbon monoxide to reduce the iron oxide in the reactor. The reducing gas is injected at high temperature into the reaction chamber or reactor. The reactor may be of a static-bed type, a moving-bed type, a fluidized-bed type, a rotary or kiln type. In a moving-bed reactor, the reducing gas is typically introduced into the center of the reactor, where it flows countercurrently upward through the iron oxide, is extracted, reprocessed, and recycled to the reduction circuit. The exhaust gas from the reactor is de-dusted, freed of reaction products (HO, CO), and compressed before being mixed with makeup gas (natural gas, COG, reformer gas, Corex gas, syngas, etc.). The mixed gas stream of fresh make-up gas and appropriately treated recycled exhaust gas is sent to a heating unit, which brings it to the temperature required for the reduction process, typically above 850°C.

[0003] The heated reducing gas stream, which may be further heated by injecting oxygen, is sent to a reactor in which the iron oxide to be reduced is introduced from above in pellet and / or lump form and flows downward, and the DRI (reduction product) is extracted at the other end of the reactor and sent by a pneumatic conveying system, gravity, or belt to a blast furnace or electric arc furnace, or to an oxygen converter, or to any device capable of melting the DRI produced.

[0004] Specifically, in the iron oxide direct reduction process, oxygen is removed from iron ore by chemical reaction with hydrogen and carbon monoxide to obtain DRI with a high metallization level (ratio of metallic iron to total iron in the DRI). The overall reduction reaction involved in this process is well known and is shown below: Fe2O3+3H2->2Fe+3H2O(1) Fe2O3+3CO->2Fe+3CO2(2).

[0005] Hydrogen and carbon monoxide react with the oxygen in the iron oxide and are converted to water and carbon dioxide by reactions (1) and (2) above. In addition to H2O and CO2, unreacted H2 and CO are also present in the exhaust gas leaving the reactor. In order to recover these reducing agents, the exhaust gas is treated as described above.

[0006] The use of make-up gas fed to the reduction circuit containing a significant amount of carbon (gaseous hydrocarbon-containing gases such as natural gas, coke oven gas, Corex gas, Syngas, etc.) has two main drawbacks: -Greenhouse gas emissions (CO2), - If the carbon monoxide (CO) content in the reduction gas flowing into the reactor is relatively high, a relatively large amount of fine particles will be generated during the reduction reaction, and the temperature rise caused by the exothermic reduction of CO increases the risk of forming clusters, which may hinder the movement of solids.

[0007] Currently used process methods reduce CO2 emissions by selectively removing CO2 from the exhaust gas recycled to the reactor (which can also be stored and used in the food industry or other industrial applications), but these CO2 emissions consist mainly of carbon dioxide released via the chimney of the hydrocarbon gas reformer (if present) or the heating unit of the reducing gas. In other known direct reduction processes, the processes mentioned above, which feed natural gas or reformed gas produced in an offline reformer to promote the methane reforming reaction in the reduction reactor, ensure a good H2 / CO ratio in the composition of the reducing gas introduced into the reactor.

[0008] Currently, it is extremely difficult to further reduce CO2 emissions.

[0009] Therefore, there is a need to develop a direct reduction system and related processes that can overcome the aforementioned drawbacks. Summary of the Invention

[0010] The objective of the present invention is to provide a 40 Nm 3 / t DRI It would be advantageous to develop direct reduction systems and related processes that allow for further reductions in carbon dioxide emissions.

[0011] A further object of the present invention is to develop a direct reduction system that is flexible in terms of make-up gas, capable of supplying various types of make-up gas or mixtures thereof without upsetting the reduction circuit equipment and / or without long shutdown periods, and the change in supplied make-up gas is selected based on market availability or cost.

[0012] The present invention achieves these and other objects that will become apparent herein by a direct reduction system for the direct reduction of iron oxide as set forth in claim 1, comprising a circuit comprising: a reactor having a reduction zone in which said iron oxide is charged; a first external source of make-up gaseous hydrogen-containing gas having a gaseous hydrogen content of 80% by volume or more; a second external source of make-up gaseous hydrocarbon-containing gas, preferably having a gaseous hydrocarbon content of 25% by volume or more; - a recovery and treatment line disposed downstream of the reactor for recovering and treating the exhaust gas emitted from the reactor; a treatment and feeding line disposed upstream of the reactor, for treating a process gas obtained by mixing a make-up gaseous hydrogen-containing gas from a first external supply source and / or a make-up gaseous hydrocarbon-containing gas from a second external supply source with the exhaust gas treated in the recovery treatment line, and for supplying the process gas to the reduction zone of the reactor; a recovery processing line communicating downstream of the processing supply line; the recovery process line includes at least one first heat exchange device that transfers heat from the exhaust gas to a heat transfer fluid; the process supply line includes at least one second heat exchange device; a duct capable of conveying a heat transfer fluid connects the at least one first heat exchange device to the at least one second heat exchange device, such that heat from the heat transfer fluid can be transferred to the process gas by the at least one second heat exchange device; the recovery process line also includes at least one carbon dioxide removal unit that removes carbon dioxide from the exhaust gas; the duct has a branch connecting the duct to at least one carbon dioxide removal device, thereby allowing heat of the heat transfer fluid to be transferred completely or partially to the at least one carbon dioxide removal device; The first external source and the second external source are connected to the process supply line or the return process line.

[0013] Preferably, at least one second heat exchange device is arranged between a humidifier and a heating unit in the process supply line.

[0014] Optionally, at least one first heat exchange device is disposed between the reactor and at least one scrubbing / cooling unit in the recovery process line for removing water from the exhaust gas to obtain a dehydrated gas.

[0015] Preferably, the system further comprises a duct connecting the discharge line of the at least one cleaning and cooling unit to the humidifier for conveying heated water to the humidifier.

[0016] As used herein, "process gas" refers to a mixture of gases obtained by mixing a make-up gaseous hydrogen-containing gas from a first external source and / or a make-up gaseous hydrocarbon-containing gas from a second external source with the treated exhaust gas in the recovery process line.

[0017] A direct reduction process that can be carried out by the aforementioned system according to claim 9 according to a further aspect of the present invention, when fully operational, comprises: a) recovering and treating the exhaust gas discharged from the reactor through a recovery and treatment line; b) supplying the process gas obtained by mixing a make-up gaseous hydrogen-containing gas from a first external supply source and / or a make-up gaseous hydrocarbon-containing gas from a second external supply source with the exhaust gas treated in the recovery treatment line to a reduction zone of the reactor through a treatment supply line; - transferring heat from the exhaust gas leaving the reactor to a heat transfer fluid by at least one first heat exchange device in the recovery process line; If the make-up gaseous hydrogen-containing gas from the first external source mixed with the treated exhaust gas in the recovery treatment line is sufficient for the direct reduction process, the heat of the heat transfer fluid is completely transferred to the process gas by the duct that conveys the heat transfer fluid to at least one second heat exchange device in the treatment supply line, whereas When the makeup gaseous hydrogen-containing gas from the first external source mixed with the treated flue gas in the recovery processing line is unavailable or insufficient for the direct reduction process, makeup gaseous hydrocarbon-containing gas from a second external source is mixed with the flue gas, or with the flue gas and the makeup gaseous hydrogen-containing gas, and the heat of the heat transfer fluid is transferred fully or partially to the at least one carbon dioxide removal device, respectively.

[0018] The first external source of make-up gas can be a commercially available source of pure gaseous hydrogen or a source of reducing gas enriched with gaseous hydrogen, having a gaseous hydrogen content of 80% or more by volume. The make-up gaseous hydrogen-containing gas can be gas from an external source, for example, using partial combustion or reforming of natural gas, electrolysis, or any other process capable of producing such types of gas.

[0019] The second external source of make-up gas may preferably be a source of gaseous hydrocarbon-containing gas, such as natural gas, coke oven gas, Corex gas, synthesis gas, etc., having a gaseous hydrocarbon content of 25% or more by volume.

[0020] The systems and methods of the present invention allow for the production of DRI by supplying to the circuit only makeup gaseous hydrogen-containing gas, only makeup gaseous hydrocarbon-containing gas, or a mixture of makeup gaseous hydrogen-containing gas and makeup gaseous hydrocarbon-containing gas in any proportions, depending on any particular availability and convenience.

[0021] Therefore, preferably, the system and method of the present invention allows for continuous switching from conventionally available reducing gas sources (natural gas, coke oven gas, reformed gas, Corex gas, etc.) to newly available environmentally friendly reducing gas sources (gaseous hydrogen or gaseous hydrogen-rich gas) through only adjustment of a few operating process parameters, without requiring any modification of the associated plant.

[0022] Instead, in particular, the prior art does not allow for a direct switch to using high proportions of gaseous hydrogen without first incurring the redesign and associated modification steps of the plant.

[0023] As an example, the operating process parameter can be the system pressure or the amount of nitrogen injected.

[0024] When the system is operated using only makeup gaseous hydrocarbon-containing gas, the system pressure measured at the reactor outlet (e.g., between 5 and 7 barg) will be higher than when the system is operated using only makeup gaseous hydrogen-containing gas (e.g., the pressure can be adjusted to between 3 and 5 barg). When operating using a mixture of makeup gaseous hydrocarbon-containing gas and makeup gaseous hydrogen-containing gas, the system pressure will be intermediate.

[0025] In one example, adjusting the operating pressure of the system can partially or completely compensate for the different characteristics of the gas circulating within the system resulting from different usage ratios of the makeup gaseous hydrogen-containing gas and the makeup gaseous hydrocarbon-containing gas. In this way, the hydrodynamic response of equipment located within the system circuit is substantially equivalent both when operating with a high-pressure hydrocarbon-containing gas (high molecular weight gas) and when operating with a low-pressure hydrocarbon-containing gas (low molecular weight gas).

[0026] In particular, this involves the injection of nitrogen both to partially or completely compensate for the different characteristics of the gases circulating in the system, to increase the molecular weight without changing the reducing properties of the circulating process gas, and to utilize the nitrogen present in the circulating gas as a thermal energy vector in the reduction reactor. Specifically, the transition from using a make-up gaseous hydrocarbon-containing gas to a make-up gaseous hydrogen-containing gas creates pressure decompensation, particularly in the pumping devices 42 and 42' located in ducts 40 and 54, respectively. A possible solution is to inject nitrogen into the circuit when using a make-up gaseous hydrogen-containing gas. In this way, the reducing gas mixture becomes heavier, allowing the pumping device to operate optimally.

[0027] Preferably, the injection of nitrogen or other suitable gas (e.g., CO2) is carried out with a pumping device.

[0028] In some preferred embodiments of the invention, the heat transfer fluid is water, and steam is generated in the first heat exchange device and transported through a duct connecting the first heat exchange device and the second heat exchange device.

[0029] Steam or other heat transfer fluid from the first heat exchange device can be utilized in a second heat exchange device to increase the temperature of the process reducing gas going to the heating unit, thereby reducing energy consumption.

[0030] If gaseous hydrogen-containing gas is not available and the system needs to operate on gaseous hydrocarbon-containing gas, such as natural gas, coke oven gas, syngas, or other types of reducing gases, the steam or other heat transfer fluid from the first heat exchange device can easily be routed to a carbon dioxide removal device that removes, e.g., absorbs, carbon dioxide to regenerate an amine solution.

[0031] Steam or other heat transfer fluid can be flexibly used to preheat the process reduction gas in the second heat exchanger and / or to operate the carbon dioxide removal device. The amount of steam or heat transfer fluid corresponding to each application can be flexibly set according to the ratio of the amount of gaseous hydrogen-containing gas to the amount of gaseous hydrocarbon-containing gas supplied to the circuit of the reduction system.

[0032] In short, the direct reduction system of the present invention can be operated using as make-up gas a wide variety of gaseous hydrocarbon-containing and / or gaseous hydrogen-containing gas sources, or other reducing gas sources emerging over the years, without upsetting equipment and making a live change from one source to the other.

[0033] Another advantage of the present invention is that if for any reason gaseous hydrogen-containing gas is not available, it has the potential to continue operation, ensuring high process availability and negligible production losses.

[0034] In fact, the configuration of the system allows for the use of gaseous hydrocarbon-containing gas to replace gaseous hydrogen-containing gas with simple adjustments to system operation.

[0035] If desired, injection of other gaseous hydrocarbon-containing gases, such as natural gas, can be provided in the lower part of the reactor, preferably in the conical region, located below the reduction zone, by means of at least one device for injecting said other gaseous hydrocarbons.

[0036] Below we list some further advantages of the inventive solution over the state of the art: - depending on the proportion of make-up gaseous hydrocarbon-containing gas present in the feed mixture, the carbon dioxide removal, e.g., absorption, device can be partially or completely bypassed, - if only make-up gaseous hydrogen-containing gas is supplied to the circuit, a simple other bypass duct allows completely bypassing a possible humidifier required to increase the moisture content of the process gas and prevent carbon buildup in the process gas heating unit, In general, by increasing the gaseous hydrogen content in the gas supplied to the circuit, carbon buildup in the heating unit is significantly limited and, if present, does not require shutdown and chemical cleaning, thereby improving the reliability and availability of the system; when the reducing gas stream is pure or almost pure gaseous hydrogen, the injection of oxygen downstream of the heating unit can be switched off, since no additional energy is required to promote the reforming reaction in the reactor; The resulting process gas preferably has a relatively low content of CO and CO2, so that acidification of the process water in contact with the process gas is very limited and does not require increased consumption of expensive materials or chemicals in the water return line to control the quality of the water; - The high degree of iron ore reduction by gaseous hydrogen, which determines the temperature drop in the reactor, allows for a more steady operation with almost no cluster risk (typical of CO reduction and its exothermic reactions, such as swelling); - The efficiency of current gaseous hydrocarbon-containing gas (natural gas, coke oven gas, etc.) based direct reduction systems (ZR process, process with line reformer, etc.) can be increased by direct introduction into the circuit of commercially available pure gaseous hydrogen or gaseous hydrogen-containing gas with an increased gaseous hydrogen content, The phenomenon of pellet swelling during reactor start-up, which is characteristic when CO is used as a reducing agent and which can lead to a cessation of solids flow and blockage of the reactor, is minimized.

[0037] Further features and advantages of the present invention will become more apparent in light of the detailed description of illustrative, but non-exclusive, embodiments.

[0038] The dependent claims describe particular embodiments of the invention. [Brief explanation of the drawings]

[0039] In describing the present invention, reference is made to the accompanying drawings, given as non-limiting examples.

[0040] [Figure 1] 1 is a diagram showing a first embodiment of a direct reduction system according to the present invention. FIG. [Figure 2] FIG. 2 is a diagram showing a second embodiment of the direct reduction system according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0041] 1 and 2, there are shown some examples of direct reduction systems that are the subject of the present invention. a reactor 1 having a reduction zone 12 which is charged with iron oxide via an inlet duct 2; a first external source 200 of a gaseous hydrogen content or make-up gaseous hydrogen-containing gas having a hydrogen gas content of 80% or more by volume; a second external source 210 of make-up gaseous hydrocarbon-containing gas, preferably having a gaseous hydrocarbon content of 25% or more by volume; a recovery and treatment line 10 arranged downstream of the reactor 1, for recovering and treating the exhaust gas discharged from the reactor 1; a circuit disposed upstream of the reactor 1, for treating the mixed gas to define a process gas obtained by mixing a make-up gaseous hydrogen-containing gas from a first external supply source 200 and / or a make-up gaseous hydrocarbon-containing gas from a second external supply source 210 with the exhaust gas treated in the recovery treatment line 10, and a treatment supply line 11 for supplying the process gas to a reduction zone 12 of the reactor 1.

[0042] The recovery treatment line 10 communicates with the treatment supply line 11 downstream.

[0043] The recovery process line 10 includes at least one first heat exchange device 22, for example only one first heat exchange device, that transfers heat from the exhaust gas to the heat transfer fluid 70.

[0044] Advantageously, the process supply line 11 comprises at least one second heat exchanger 72, for example only one second heat exchanger, and a duct 75 capable of conveying a heat transfer fluid, preferably only one duct 75, connects the first heat exchanger 22 to the second heat exchanger 72, thereby allowing the heat of the heat transfer fluid to be transferred to the process gas by the second heat exchanger 72.

[0045] Additionally, the recovery process line 10 also includes at least one carbon dioxide removal unit 50, eg, only one removal unit, that removes, eg, absorbs, carbon dioxide from the flue gas.

[0046] Advantageously, duct 75 has a branch 76 connecting said duct 75 to carbon dioxide removal device 50, thereby allowing the heat of the heat transfer fluid to be fully or partially transferred to said removal device 50 when make-up gaseous hydrogen-containing gas is unavailable or partially available. Preferably, to better regulate the operation of the direct reduction system based on input data including or consisting of make-up gaseous hydrogen-containing gas availability data, the system of the present invention comprises: a bypass duct 52 in the recovery and treatment line 10 that bypasses the removal device 50; a first flow regulator 62 arranged along the branch 76 and regulating the flow of heat transfer fluid to the removal device 50; a second flow regulator 65 for regulating the flow of heat transfer fluid along a duct 75 to the second heat exchanger 72; a third flow regulator 63 that closes or at least partially opens the bypass duct 52; a fourth flow rate adjusting device 32 that adjusts the flow rate of the makeup gaseous hydrocarbon-containing gas supplied to the gas circulation circuit; and a fifth flow rate adjusting device 31 that adjusts the flow rate of the makeup gaseous hydrogen-containing gas supplied to the gas circulation circuit.

[0047] 2, the control unit 64 sends a control signal 110 to the first flow regulator 62, a control signal 111 to the second flow regulator 65, a control signal 112 to the third flow regulator 63, a control signal 114 to the fourth flow regulator 32, and a control signal 116 to the fifth flow regulator 31, respectively, according to input data including a signal 118 indicating the availability of make-up gaseous hydrogen-containing gas. The control unit 64 can also be provided in the embodiment of FIG.

[0048] Advantageously, in all embodiments of the present invention, the first external source 200 of make-up reducing gas is a commercially available pure gaseous hydrogen source (99% by volume or more) or a gas source having a gaseous hydrogen content of 80% by volume or more, preferably 85-98% by volume or more.

[0049] For make-up gaseous hydrogen-containing gases having a gaseous hydrogen content of 80% or more by volume, the remaining composition can include carbon monoxide, water, carbon dioxide, methane, and nitrogen.

[0050] Purely by way of example, the make-up gaseous hydrogen-containing gas composition may comprise, in volume percentages: Gaseous hydrogen in the range of 92-96%; Carbon monoxide in the range of 1.5 to 2.5%; 0.2 to 0.6% water, 0.0-0.4% carbon dioxide, 0.3-0.9% methane, and 2.0 to 4.0% nitrogen.

[0051] The second external source 210 of make-up reducing gas is a source of gaseous hydrocarbon-containing gas, such as natural gas, coke oven gas, Corex gas, or synthesis gas, having a gaseous hydrocarbon content of 25% or more by volume.

[0052] The gaseous hydrocarbon-containing gas can also be a gas from biomass, biogas, biomethane.

[0053] The second external source 210 is normally closed, but can be opened to allow the gaseous hydrocarbon-containing gas to be used in the circuit if the make-up gaseous hydrogen-containing gas is insufficient or unavailable.

[0054] Preferably, the at least one first heat exchange device 22 is adjacent to the reactor 1 , while the at least one removal device 50 is remote from the reactor 1 and adjacent to the process feed line 11 .

[0055] Advantageously, in all embodiments, the process supply line 11 comprises: a first duct through which the process gas obtained by mixing the treated exhaust gas from the reactor 1 with the make-up reducing gas from the first external source 200 and / or the second external source 210 passes; at least one humidifier 60, for example only one humidifier, for adjusting the water content in the process gas in the case of a high CH4 and heavy gaseous hydrocarbon content in said process gas; a second heat exchange device 72, for example a condenser, for recovering the thermal energy of the heat transfer fluid from the first heat exchange device 22; It may comprise or consist of at least one heating unit 180, for example only one heating unit, for heating the process gas to a temperature suitable for introduction into the reactor 1.

[0056] If only make-up gaseous hydrogen-containing gas is fed to the circuit, a simple further bypass duct 80 allows the humidifier 60 to be bypassed entirely.

[0057] Downstream of the heating unit 180, an oxygen injector 300 may be provided for injecting oxygen into the process gas stream.

[0058] A further advantage of the system of the present invention is that the recovery and processing line 10: a second duct through which the exhaust gas leaving the reactor 1 passes; a first heat exchanger 22, for example only one first heat exchanger, for cooling the exhaust gases leaving the reactor 1; at least one scrubbing / cooling unit 36, for example only one scrubbing / cooling unit, arranged downstream of said first heat exchange device 22, for removing water from the exhaust gas to obtain a dehydrated gas; at least one pumping device 42, for example only one pumping device, which preferably pumps the dehydration gas into the treatment supply line 11; a carbon dioxide removal device 50, such as an absorber, arranged downstream of the at least one cleaning and cooling unit 36, preferably downstream of the pumping device 42; and a bypass duct 52 for bypassing the removal device 50 in the case where the make-up reducing gas supplied to the circuit is only make-up gaseous hydrogen-containing gas.

[0059] If necessary, the humidifier 60 in the treatment supply line 11 receives hot water by duct 54 from the discharge line of the cleaning and cooling unit 36 ​​and discharges the water by duct 81 .

[0060] Preferably, the second duct of the recovery and treatment line 10 is downstream of the washing and cooling unit 36 ​​and includes: a branch duct 34 connecting the recovery treatment line 10 to the burner of the heating unit 180 and capable of sending the first dehydrated exhaust gas stream as combustible gas for said burner; a branch duct 40 connecting the recovery treatment line 10 and the treatment feed line 11, in which a possible pumping device 42 and a carbon dioxide removal device 50 are arranged and in which the second dehydrated flue gas stream is recycled;

[0061] Other regulators 30, such as pressure control valves, are preferably provided along the branch ducts 34.

[0062] Heating unit 180 is powered by the combustion of a suitable combustible from source 182. The combustible may be dehydrated exhaust gas from branch duct 34, pure gaseous hydrogen, natural gas, other hydrocarbon-containing gases, or mixtures thereof.

[0063] In a first embodiment of the system of the present invention shown in FIG. 1, an external source 200 of gaseous hydrogen-containing gas having a gaseous hydrogen content of 80% by volume or more and an external source 210 of gaseous hydrocarbon-containing gas having a gaseous hydrocarbon content of 25% by volume or more are connected, e.g., directly connected, to the process supply line 11.

[0064] In particular, both the first external supply source 200 and the second external supply source 210 are connected in an extension of a circuit configured between the pumping device 42 of the recovery processing line 10 and the heating unit 180 of the processing supply line 11, preferably between the carbon dioxide removal device 50 or bypass duct 52 of the recovery processing line 10 and the humidifier 60 of the processing supply line 11.

[0065] A flow regulator 31, e.g., a pressure control valve, is preferably provided along duct 61 connecting external supply 200 and process supply line 11. Similarly, a flow regulator 32, e.g., another pressure control valve, is preferably provided along duct 71 connecting external supply 210 and process supply line 11.

[0066] In a second embodiment of the system of the present invention shown in FIG. 2, an external source of gaseous hydrogen-containing gas 200 and an external source of gaseous hydrocarbon-containing gas 210 are connected directly to the recovery process line 10, for example.

[0067] In particular, both the first external supply source 200 and the second external supply source 210 are connected to an extension of the circuit established between the cleaning and cooling unit 36 ​​and the pumping device 42, for example along the branch duct 40. In this way, make-up reducing gas can be delivered at low pressure from the external supplies 200, 210, which is then compressed by the pumping device 42.

[0068] A flow regulator 31 , such as a pressure control valve, is preferably provided along the duct 61 connecting the external supply 200 and the recovery process line 10 .

[0069] A flow regulator 32 , such as another pressure control valve, is preferably provided along the duct 71 connecting the external supply 210 and the recovery process line 10 .

[0070] In both the first and second embodiments of the system of the present invention, the at least one gaseous hydrocarbon-containing gas injector 191 can be configured to inject a gaseous hydrocarbon-containing gas, such as natural gas, coke oven gas, or gas from biomass, biogas, or biomethane, into a lower, preferably conical, region 14 of the reactor 1, located below the reduction region 12 or directly in the transition region of the reactor 1 between the reduction region 12 and the discharge region. In either case, this injection can adjust the DRI carbon content.

[0071] An example of a fully operational process for direct reduction of iron oxide using the system of the present invention described above will now be described. When fully operational, this process: a) recovering and treating the exhaust gas discharged from the reactor 1 through a recovery and treatment line 10; b) mixing a make-up gaseous hydrogen-containing gas from a first external supply source 200 and / or a make-up gaseous hydrocarbon-containing gas from a second external supply source 210 with the exhaust gas treated in the recovery treatment line 10 to obtain a process gas, and supplying the process gas to the reduction zone 2 of the reactor 1 via a treatment supply line 11; Furthermore, transferring heat from the exhaust gas leaving the reactor 1 to a heat transfer fluid by means of a first heat exchange device 22 in the recovery process line 10, If the make-up gaseous hydrogen-containing gas from the first external source 200 mixed with the treated exhaust gas in the recovery treatment line 10 is sufficient for the direct reduction process, the heat of the heat transfer fluid is completely transferred to the process gas by the duct 75 which conveys the heat transfer fluid to the second heat exchanger 72 of the treatment supply line 11 and traverses the second heat exchanger 72 so that the entire heat transfer fluid reaches the second heat exchanger 72, whereas If the makeup gaseous hydrogen-containing gas from the first external source 200 mixed with the treated flue gas in the recovery processing line 10 is not available or is insufficient for the direct reduction process, makeup gaseous hydrocarbon-containing gas from the second external source 210 is mixed with the flue gas, or with the flue gas and makeup gaseous hydrogen-containing gas, and the heat of the heat transfer fluid is transferred fully or partially to the carbon dioxide removal device 50, respectively.

[0072] Thus, when makeup gaseous hydrogen-containing gas is not available, the entire heat transfer fluid reaches the removal device 50. Alternatively, when makeup gaseous hydrogen-containing gas is available, but not enough, the heat transfer fluid reaches both the removal device 50 and the second heat exchange device 72 partially.

[0073] Preferably, to better regulate the operation of the direct reduction system, the process comprises: - providing input data including a signal 118 indicative of make-up gaseous hydrogen-containing gas availability data; - processing said input data, preferably by a control unit 64, a first control signal 110 to a first flow regulator 62 that regulates the flow of heat transfer fluid to the carbon dioxide removal device 50; a second control signal 111 to a second flow rate regulator 65 that regulates the flow rate of the heat transfer fluid to the second heat exchanger 72; a third control signal 112 to a third flow regulator 63 that at least partially closes or opens the bypass duct 52; a fourth control signal 114 to a fourth flow regulator 32 that regulates the flow rate of the make-up gaseous hydrocarbon-containing gas supplied to the circuit; and and sending a fifth control signal 116 to a fifth flow regulator 31 that regulates the flow rate of the make-up gaseous hydrogen-containing gas supplied to the circuit.

[0074] Therefore, when the make-up gaseous hydrogen-containing gas from the first external supply source 200 mixed with the treated exhaust gas in the recovery processing line 10 is available and sufficient for the entire direct reduction process, the second external supply source 210 is normally closed. The control unit 64 closes the duct 76 and the second external supply source 210 and opens the duct 75 by sending control signals 110 and 111 to the first and second flow regulators 62 and 65, respectively, and sends a control signal 114 to the fourth flow regulator 32. The control unit 64 also opens the bypass duct 52 and the first external supply source 200 by sending a control signal 112 to the third flow regulator 63 and a control signal 116 to the fifth flow regulator 31, respectively. In this case, the removal device 50 is completely bypassed.

[0075] When the make-up gaseous hydrogen-containing gas from the first external source 200 mixed with the treated flue gas in the recovery treatment line 10 is available for the entire direct reduction process but is not sufficient, the control unit 64, according to the control signal 118 from the gaseous hydrogen-containing gas source 200, a control signal 114 to a fourth flow regulator 32 that partially opens the second external supply 210 to regulate the flow rate of make-up gaseous hydrocarbon-containing gas supplied to the circuit; a control signal 116 to a fifth flow regulator 31 for adjusting the flow rate of the make-up gaseous hydrogen-containing gas supplied to the circuit; a control signal 110 to the first flow regulator 62 and a control signal 111 to the second flow regulator 65 for adjusting the flow rate of the heat transfer fluid to the removal device 50 and the flow rate of the heat transfer fluid to the second heat exchange device 72, respectively, which are flexibly set according to the ratio of the amount of gaseous hydrogen-containing gas and the amount of gaseous hydrocarbon-containing gas fed to the circuits of the reduction system; sending a control signal 112 to a third flow regulator 63, which is flexibly set according to the ratio between the amount of gaseous hydrogen-containing gas and the amount of gaseous hydrocarbon-containing gas supplied to the circuit of the reduction system, to partially close the bypass duct 52 and partially supply the removal device 50;

[0076] Finally, when make-up gaseous hydrogen-containing gas from the first external source 200 is unavailable, the first external source 200 is normally closed. The control unit 64 sends a control signal 110 to the first flow regulator 62, a control signal 111 to the second flow regulator 65, and a control signal 114 to the fourth flow regulator 32 to open the duct 76 and the second external source 210, while completely closing the portion of the duct 75 adjacent the second heat exchanger 72. The control unit 64 also sends a control signal 112 to the third flow regulator 63 and a control signal 116 to the fifth flow regulator 31 to close the bypass duct 52 and the first external source 200, respectively.

[0077] In one example of the process of the present invention, the exhaust gas leaving reactor 1, preferably at a temperature of about 250 to about 550°C, is introduced into duct 50 in recovery process line 10 and taken into first heat exchanger 22 for cooling.

[0078] Optionally, when water is used in the first heat exchange device 22 to cool the exhaust gases leaving the reactor 1, the heat transfer fluid in the duct 75 will be steam.

[0079] The cooled exhaust gas flows through duct 24 towards scrubbing and cooling unit 36 ​​where water is removed to form a dehydrated gas.

[0080] The dehydrated exhaust gas after cooling and dehydration is branched into two branch ducts 34 and 40.

[0081] A small portion of the dehydrated exhaust gas flows through a branch duct 34 having a pressure control valve 30 that can purge a portion of the dehydrated exhaust gas from the circuit to eliminate unwanted buildup of inert gases.

[0082] On the other hand, most of the dehydrated exhaust gas flows through the branch duct 40 .

[0083] A supply of make-up gaseous hydrogen-containing gas from a first external source 200 and / or a make-up gaseous hydrocarbon-containing gas from a second external source 210 is provided to the process feed line 11 or the recovery process line 10 .

[0084] In the case of the first external supply source 200 and the second external supply source 210 connected to the treatment supply line 11, the supply is made in the extension of the circuit configured between the pumping device 42 of the recovery treatment line 10 and the heating unit 180 of the treatment supply line 11, preferably between the removal device 50 or bypass duct 52 of the recovery treatment line 10 and the humidifier 60 of the treatment supply line 11.

[0085] 1 , in order to recycle a portion of the dehydrated exhaust gas and reintroduce it into reactor 1, the dehydrated exhaust gas flowing in duct 40 is compressed by a pumping device 42, which may be a compressor or a blower. Downstream of pumping device 42, the dehydrated exhaust gas flows through duct 44 and passes through carbon dioxide remover 50 and / or bypass duct 52 before being mixed with makeup gaseous hydrogen-containing gas from first external source 200 and / or makeup gaseous hydrocarbon-containing gas from second external source 210 in process feed line 11 to become process gas. Bypass duct 52 allows carbon dioxide remover 50 to be completely bypassed when the supply of gaseous hydrocarbon-containing gas is not required.

[0086] Alternatively, in the case of the first external supply source 200 and the second external supply source 210 connected to the recovery processing line 10, the supply is made in an extension of the circuit formed between the cleaning and cooling unit 36 ​​of the recovery processing line 10 and the pumping device 42.

[0087] 2, unlike the embodiment of FIG. 1, here the dehydrated exhaust gas flowing in duct 40 is mixed with make-up gaseous hydrogen-containing gas from a first external source 200 and / or make-up gaseous hydrocarbon-containing gas from a second external source 210. A pumping device 42, which can be a compressor or a blower, pressurizes the resulting gas mixture, which becomes the process gas, to introduce the process gas into the process feed line 11. In particular, downstream of the pumping device 42, the process gas flows through duct 44 and passes through a carbon dioxide remover 50 and / or a bypass duct 52 before reaching the process feed line 11. The bypass duct 52 allows the carbon dioxide remover 50 to be completely bypassed when no supply of gaseous hydrocarbon-containing gas is required.

[0088] In all embodiments, the process gas passes through a duct 15, which in turn flows through a humidifier 60, a second heat exchanger 72 capable of increasing the temperature of the process gas, and then arrives at a heating unit 180 where the process gas reaches a temperature of approximately 850-950°C.

[0089] Bypass duct 80 allows humidifier 60 to be bypassed entirely when only make-up gaseous hydrogen-containing gas is supplied to the circuit.

[0090] Downstream of the heating unit 180 the process gas flows through a duct 16 until it reaches the inside of the reactor 1 .

[0091] Downstream of the heating unit 180 and upstream of the reactor 1, a gaseous oxygen injection system 300 can provide gaseous oxygen injection into the process gas stream.

[0092] Preferably, injection of natural gas, coke oven gas, or other gaseous hydrocarbon-containing gas, such as gas from biomass, biogas, or biomethane, is provided by at least one injection device 191 into a lower, preferably conical, region 14 of the reactor 1, located below said reduction region 12 or directly in the transition region of the reactor 1 between the reduction region 12 and the discharge region of the reactor.

[0093] Pellets or chunks of iron oxide material are fed from above into the reduction zone 12 of the reactor 1, where they react with hot reducing gas flowing countercurrently thereto, and are ultimately discharged as Hot DRI.

[0094] Optionally, the particle size of the iron oxide material is about 2.5 to 19 mm, preferably about 3.5 to 15 mm.

Claims

1. 1. A direct reduction system for the direct reduction of iron oxide to metallic iron, comprising a gas circulation circuit, the gas circulation circuit comprising: a direct reduction reactor (1) having a reduction zone (12) filled with the iron oxide, and configured to carry out the direct reduction in a single unit by being supplied with a process gas containing a make-up gaseous hydrogen-containing gas and / or a make-up gaseous hydrocarbon-containing gas through a single line; a first external source (200) of make-up gaseous hydrogen-containing gas, the gas content of which is 80% by volume or more of gaseous hydrogen; a second external source (210) of make-up gaseous hydrocarbon-containing gas; a recovery and treatment line (10) located downstream of the reactor (1) for recovering and treating the exhaust gases leaving the reactor (1); a treatment supply line (11) arranged upstream of the reactor (1) for treating a process gas obtained by mixing the make-up gaseous hydrogen-containing gas from the first external supply source (200) and / or the make-up gaseous hydrocarbon-containing gas from the second external supply source (210) with the exhaust gas treated in the recovery treatment line (10), and for supplying the process gas to the reduction zone (12) of the reactor (1); Including, The recovery processing line (10) communicates downstream with the processing supply line (11), The recovery process line (10) includes at least one first heat exchange device (22) for transferring heat from the exhaust gas to a heat transfer fluid, and at least one scrubbing and cooling unit (36) for removing water from the exhaust gas to obtain a dehydrated gas; the process supply line (11) includes at least one humidifier (60) for adjusting the moisture content of the process gas and at least one second heat exchange device (72); the system further includes a duct (54) connecting a discharge line of the at least one washing and cooling unit (36) to the humidifier (60) for conveying heated water to the humidifier (60); a duct (75) capable of conveying the heat transfer fluid connects the at least one first heat exchange device (22) to the at least one second heat exchange device (72) so that heat of the heat transfer fluid can be transferred to the process gas by the at least one second heat exchange device (72); The recovery process line (10) also includes at least one carbon dioxide removal unit (50) for removing carbon dioxide from the exhaust gas; the duct (75) has a branch (76) connecting the duct (75) to the at least one carbon dioxide removal device (50), thereby allowing the heat of the heat transfer fluid to be transferred completely or partially to the at least one carbon dioxide removal device (50); The first external supply source (200) and the second external supply source (210) are connected to the processing supply line (11) or the recovery processing line (10); The direct reduction system further comprises: a bypass duct (52) in the recovery process line (10) bypassing the at least one carbon dioxide removal unit (50); a first flow regulator (62) for regulating the flow of said heat transfer fluid to said at least one carbon dioxide removal device (50); a second flow regulation device (65) for regulating the flow of said heat transfer fluid to said at least one second heat exchange device (72); a third flow regulation device (63) for at least partially closing or opening said bypass duct (52); a fourth flow rate regulator (32) for regulating the flow rate of the make-up gaseous hydrocarbon-containing gas supplied to the gas circulation circuit; a fifth flow rate regulator (31) for regulating the flow rate of the make-up gaseous hydrogen-containing gas supplied to the gas circulation circuit; a control unit (64) configured to send a first control signal (110) to the first flow regulator (62), a second control signal (111) to the second flow regulator (65), a third control signal (112) to the third flow regulator (63), a fourth control signal (114) to the fourth flow regulator (32), and a fifth control signal (116) to the fifth flow regulator (31) according to input data including a signal (118) indicative of availability data of the make-up gaseous hydrogen-containing gas.

2. 2. The system of claim 1, wherein the at least one second heat exchange device (72) is disposed between the humidifier (60) and a heating unit (180) in the process supply line (11).

3. 3. The system of claim 2, wherein the at least one first heat exchange device (22) is disposed between the reactor (1) and the at least one scrubbing and cooling unit (36) provided in the recovery treatment line (10) for removing water from the exhaust gas to obtain a dehydrated gas.

4. The process supply line (11) comprises, in addition to a first duct for passing the process gas, said at least one humidifier (60); said at least one second heat exchange device (72); at least one heating unit (180) for heating said process gas, The recovery and treatment line (10) includes, in addition to a second duct through which the exhaust gas passes, - said at least one first heat exchange device (22) for cooling the exhaust gases leaving said reactor (1); said at least one washing and cooling unit (36); A system according to claim 1 or 3, comprising, in order, said at least one carbon dioxide remover (50) and said bypass duct (52).

5. 5. The system according to claim 4, wherein in the case of the first external supply source (200) and the second external supply source (210) connected to the processing supply line (11), both the first external supply source (200) and the second external supply source (210) are connected in an extension of the gas circulation circuit configured between a possible pumping device (42) of the recovery processing line (10) and the heating unit (180) of the processing supply line (11).

6. 6. The system of claim 5, wherein both the first external supply source (200) and the second external supply source (210) are connected to an extension of the gas circulation circuit configured between the at least one carbon dioxide removal device (50) or bypass duct (52) of the recovery processing line (10) and the at least one humidifier (60) of the processing supply line (11).

7. 5. The system of claim 4, wherein in the case where the first external supply source (200) and the second external supply source (210) are connected to the recovery processing line (10), both the first external supply source (200) and the second external supply source (210) are connected to an extension of the gas circulation circuit configured between the at least one cleaning and cooling unit (36) and the at least one pumping device (42).

8. The second duct of the recovery and processing line (10) a first branch duct (34) connecting said recovery treatment line (10) to the burner of said heating unit (180) and through which a first dehydrated exhaust gas stream is sent as combustible gas for said burner; - a second branch duct (40) connecting the recovery treatment line (10) to the treatment supply line (11) and arranged along the possible at least one pumping device (42) and the at least one carbon dioxide removal device (50), through which a second dehydrated exhaust gas stream is recirculated.

9. 9. A direct reduction process for the direct reduction of iron oxide to metallic iron carried out by the system of any one of claims 1 to 8, which, when fully operational, comprises: a) recovering and treating the exhaust gas discharged from the reactor (1) through the recovery and treatment line (10); b) supplying a process gas obtained by mixing the make-up gaseous hydrogen-containing gas from the first external supply source (200) and / or the make-up gaseous hydrocarbon-containing gas from the second external supply source (210) with the exhaust gas treated in the recovery treatment line (10) to the reduction zone (2) of the reactor (1) via the treatment supply line (11), - transferring heat from the exhaust gas leaving the reactor (1) to a heat transfer fluid by means of the at least one first heat exchange device (22) of the recovery process line (10), When the make-up gaseous hydrogen-containing gas from the first external source (200) mixed with the treated exhaust gas in the recovery treatment line (10) is sufficient for the direct reduction process, the heat of the heat transfer fluid is completely transferred to the process gas by the duct (75) that conveys the heat transfer fluid to at least one second heat exchange device (72) of the treatment supply line (11), whereas If the make-up gaseous hydrogen-containing gas from the first external source (200) mixed with the treated flue gas in the recovery processing line (10) is unavailable or insufficient for the direct reduction process, make-up gaseous hydrocarbon-containing gas from the second external source (210) is mixed with the flue gas, or the flue gas and the make-up gaseous hydrogen-containing gas, and heat of the heat transfer fluid is transferred fully or partially to the at least one carbon dioxide removal unit (50), respectively; - providing input data including a signal (118) indicative of availability data of said make-up gaseous hydrogen-containing gas; - processing said input data and by a control unit (64), a first control signal (110) to a first flow regulator (62) for regulating the flow of the heat transfer fluid to the at least one carbon dioxide removal device (50); a second control signal (111) to a second flow regulator (65) for regulating the flow rate of the heat transfer fluid to the at least one second heat exchanger (72); a third control signal (112) to a third flow regulator (63) for at least partially closing or opening a bypass duct (52) that optionally bypasses said at least one carbon dioxide removal device (50); a fourth control signal (114) to a fourth flow rate regulator (32) for regulating the flow rate of the make-up gaseous hydrocarbon-containing gas supplied to the gas circulation circuit; and sending a fifth control signal (116) to a fifth flow regulator (31) to regulate the flow rate of the makeup gaseous hydrogen-containing gas supplied to the gas circulation circuit.

10. 10. The process according to claim 9, wherein the heat transfer fluid in the duct (75) is steam when water is used in the at least one first heat exchange device (22) for cooling the exhaust gas leaving the reactor (1).

11. 11. The process of claim 9 or 10, wherein a supply of make-up gaseous hydrogen-containing gas from the first external source (200) and / or a make-up gaseous hydrocarbon-containing gas from the second external source (210) is provided to the process feed line (11) or the recovery process line (10).

12. 12. The process according to claim 11, wherein in the case of the first external supply source (200) and the second external supply source (210) connected to the process supply line (11), the supply is made in the extension of the gas circulation circuit arranged between at least one pumping device (42) of the recovery process line (10) and at least one heating unit (180) of the process supply line (11).

13. 12. The process of claim 11, wherein the first external supply source (200) and the second external supply source (210) connected to the recovery process line (10) are provided in the extension of the gas circulation circuit configured between at least one cleaning and cooling unit (36) and at least one pumping device (42) of the recovery process line (10).

14. 14. The process of claim 9, further comprising adjusting the operating pressure of the system to partially or completely compensate for differences in molecular weight resulting from different ratios of the make-up gaseous hydrogen-containing gas and the make-up gaseous hydrocarbon-containing gas used.

15. 15. The process of claim 14, including the injection of nitrogen to increase the molecular weight of the circulating process gas and to use the nitrogen present in the circulating process gas as a thermal energy vector within the reactor.

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