Direct reduction system and related processes

Abstract

The present invention provides a reduction system and method that can be operated with any ratio of gaseous hydrogen containing gas and gaseous hydrocarbon containing gas, with the possibility of continuing its operation when the gaseous hydrogen containing gas is not available for any reason and in the case of minor adjustments in the operation of the plant, allowing the substitution of the gaseous hydrogen containing gas with the gaseous hydrocarbon containing gas, ensuring high process availability and negligible production losses. The reduction system of the present invention is designed to be implemented in new and already established direct reduction plants, to operate efficiently and with lower capital and operating costs.

Description

Invention Field

[0001] This invention relates to a direct reduction system and related processes, particularly suitable for producing metallic iron by directly reducing iron oxide using a reducing gas. background

[0002] A system for producing known types of reduced iron ore (DRI - Direct Reduced Iron) includes a reactor and a line for handling and supplying reducing gases, including hydrogen and carbon monoxide, adapted to reduce the iron oxide in the reactor, where the iron oxide is loaded in pellets and / or lumps. The reducing gas is injected into the reaction chamber or reactor at high temperature. The reactor can be a static bed type, a moving bed type, a fluidized bed type, a rotary type, or a kiln type. In a moving bed reactor, the reducing gas is typically introduced into the central section of the reactor, flowing countercurrently upwards through the iron oxide, and is then extracted, reprocessed, and recycled in the reduction loop. The exhaust gas leaving the reactor is dusted, reaction products (H₂O and CO₂) are removed, and it is compressed; it is then mixed with make-up gases (natural gas, COG, gases obtained in the reformer, Corex gas, syngas, etc.). A gas stream defined by a mixture of fresh replenishment gas and exhaust gas that has been properly treated and recirculated is sent to a heating unit, which brings the gas stream to the temperature required for the reduction process, typically above 850°C.

[0003] A heated reducing gas stream, into which oxygen may be injected to further increase its temperature, is fed into the reactor. The iron oxide to be reduced is introduced into the reactor from above in the form of pellets and / or blocks and flows downward therein. The DRI (reduction product) is extracted at the opposite end of the reactor and is conveyed by pneumatic transfer system or by gravity or by belt to a blast furnace or electric arc furnace, or to an oxygen converter, or to any device capable of melting the produced DRI.

[0004] More specifically, in the direct reduction of iron oxide (DRI) process, oxygen is removed from iron ore through a chemical reaction with hydrogen and carbon monoxide to obtain a DRI with a high metallization level (the ratio of metallic iron to total iron in the DRI). The overall reduction reactions involved in this process are well known and are illustrated below:

[0005] Fe₂O₃ + 3H₂ -> 2Fe + 3H₂O (1)

[0006] Fe2O3 + 3CO -> 2Fe + 3CO2 (2).

[0007] According to reactions (1) and (2), hydrogen and carbon monoxide react with the oxygen in iron oxide and are converted into water and carbon dioxide. In addition to H2O and CO2, unreacted H2 and CO are also present in the exhaust gas leaving the reactor. The exhaust gas is treated as described above to recover these reducing agents.

[0008] Using feed gas (gases containing gaseous hydrocarbons such as natural gas, coke oven gas, Corex gas, syngas, etc.) into a reduction circuit containing a large amount of carbon has two main disadvantages:

[0009] Greenhouse gas emissions (CO2);

[0010] The relatively high content of carbon monoxide (CO) in the reducing gas stream entering the reactor can lead to a relatively high yield of fine powder during the reduction reaction, and the increase in temperature due to the exothermic reduction of carbon monoxide can increase the risk of agglomeration, hindering the movement of solid matter.

[0011] In the currently used process scheme, CO2 emissions are reduced by selectively removing CO2 from the exhaust gas recycled to the reactor (which can be stored and used in the food industry or for other industrial applications), and such emissions consist mainly of carbon dioxide released through the chimney of the hydrocarbon gas reformer (if present) or the heating unit of the reducing gas.

[0012] Regarding other known direct reduction processes, the process described above, which is supplied with natural gas to promote the methane reforming reaction inside the reduction reactor, or is supplied with reformed gas produced by an offline reformer, still ensures a good H2 / CO ratio in the composition of the reducing gas introduced into the reactor.

[0013] At present, further reductions in CO2 emissions are extremely difficult.

[0014] Therefore, it is believed that a direct reduction system and related processes that can overcome the above-mentioned shortcomings need to be developed. Invention Overview

[0015] The object of this invention is to develop a direct reduction system and related processes to allow for further reductions in carbon dioxide emissions, advantageously below 40 Nm³ in some embodiments. 3 / t DRI。

[0016] Another objective of this invention is to develop a direct reduction system that is flexible in terms of supplementary gas, meaning that different types of supplementary gas or even mixtures thereof can be fed without disrupting the equipment in the reduction loop and / or with short downtime periods, and these variations in supplementary gas feed are selected based on market availability or cost.

[0017] This invention achieves these and other objectives through a direct reduction system for the direct reduction of iron oxide, as will become apparent from this specification. The direct reduction system includes a circuit configured to:

[0018] A reactor having a reduction zone suitable for being loaded with the iron oxide;

[0019] A first external source of supplemental gas containing gaseous hydrogen, having a gaseous hydrogen content equal to at least 80% by volume;

[0020] The gas is supplemented with gaseous hydrocarbons, preferably a second external source of gaseous hydrocarbons having a gaseous hydrocarbon content of at least 25% by volume;

[0021] A recovery and treatment pipeline, located downstream of the reactor, is used to recover and treat exhaust gases leaving the reactor.

[0022] The processing and feed line, which is located upstream of the reactor, is used to process the process gas obtained by mixing supplemental gas containing gaseous hydrogen from a first external source and / or supplemental gas containing gaseous hydrocarbons from a second external source with the exhaust gas processed in the recovery and processing line, and to feed the process gas into the reduction zone of the reactor.

[0023] The recycling and processing pipeline is connected downstream to the processing and feed pipeline;

[0024] The recovery and treatment pipeline includes at least one first heat exchange device in which heat is transferred from the exhaust gas to the heat transfer fluid.

[0025] The processing and feeding pipeline includes at least one second heat exchange device;

[0026] The pipes capable of carrying heat transfer fluid connect at least one first heat exchange device to at least one second heat exchange device, whereby the heat of the heat transfer fluid can be transferred to the process gas through the at least one second heat exchange device.

[0027] The recovery and treatment pipeline also includes at least one carbon dioxide removal device for removing carbon dioxide from the exhaust gas;

[0028] The pipe has branches that connect the pipe to at least one carbon dioxide removal device, whereby the heat of the heat transfer fluid can be transferred wholly or partially to the at least one carbon dioxide removal device.

[0029] And wherein the first external source and the second external source are connected to the processing and feed line or the recycling and processing line.

[0030] Preferably, at least one second heat exchange device is placed between the humidifier and the heating unit, which are located in the processing and feeding pipeline.

[0031] Optionally, at least one first heat exchange device is placed between the reactor and at least one washing and cooling unit for removing water from the exhaust gas to obtain dehydrated gas, said at least one washing and cooling unit being located in the recovery and treatment pipeline.

[0032] Preferably, an additional conduit is provided to connect the discharge line of at least one washing and cooling unit to the humidifier for carrying hot water to the humidifier.

[0033] In this specification, the term "process gas" means a mixture of gases obtained by mixing a supplemental gas containing gaseous hydrogen from a first external source and / or a supplemental gas containing gaseous hydrocarbons from a second external source with exhaust gas processed in a recovery and treatment pipeline.

[0034] According to another aspect of the invention, a direct reduction process is provided, which can be carried out by the aforementioned system, and which, when fully operational, includes the following steps:

[0035] a) Recover and treat exhaust gases leaving the reactor through recovery and treatment pipelines;

[0036] b) Process gas is fed into the reduction zone of the reactor via a processing and feed line, the process gas being obtained by mixing supplemental gas containing gaseous hydrogen from a first external source and / or supplemental gas containing gaseous hydrocarbons from a second external source with exhaust gas processed in a recovery and processing line.

[0037] The following steps are also provided:

[0038] Heat from the exhaust gas leaving the reactor is transferred to the heat transfer fluid through at least one first heat exchange device in the recovery and treatment pipeline.

[0039] and

[0040] If the supplemental gas containing gaseous hydrogen from the first external source, when mixed with the exhaust gas processed in the recovery and treatment pipeline, is sufficient for the direct reduction process, then the heat from the heat transfer fluid is completely transferred to the process gas through the pipes of at least one second heat exchanger carried by the heat transfer fluid to the treatment and feed pipelines.

[0041] If the supplemental gas containing gaseous hydrogen from the first external source is unusable or insufficient for the direct reduction process when mixed with the exhaust gas processed in the recovery and treatment pipeline, then the supplemental gas containing gaseous hydrocarbons from the second external source is mixed with the exhaust gas or with both the exhaust gas and the supplemental gas containing gaseous hydrogen, and the heat of the heat transfer fluid is completely or partially transferred to the at least one carbon dioxide removal device, respectively.

[0042] The first external source of the supplemental gas can be a source of commercially pure gaseous hydrogen or a source of reducing gas rich in gaseous hydrogen, wherein the gaseous hydrogen content is equal to at least 80% by volume. The supplemental gas containing gaseous hydrogen can come from any external source, which uses, for example, partial combustion or reforming of natural gas, electrolysis, or any other process capable of producing such a gas.

[0043] The second external source of the supplemental gas can be a source of gas containing gaseous hydrocarbons, preferably having a gaseous hydrocarbon content of at least 25% by volume, such as natural gas, coke oven gas, Corex gas, syngas, etc.

[0044] The system and method of the present invention allow for the production of DRI by supplementing the loop feed with only gaseous hydrogen, or only gaseous hydrocarbon, or a mixture of gaseous hydrogen and gaseous hydrocarbon in any proportion, depending on any particular availability and convenience.

[0045] Preferably, the system and method of the present invention thus allow 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 gas rich in gaseous hydrogen) without requiring related equipment modifications, but only by adjusting some operating process parameters.

[0046] Rather, in particular, existing technologies cannot be directly converted to the use of a high proportion of gaseous hydrogen without prior equipment redesign and related modifications.

[0047] As an example, the operating process parameters can be system pressure or the amount of nitrogen injected.

[0048] When the system operates using only supplemental gas containing gaseous hydrocarbons, the system pressure measured at the reactor outlet (e.g., between 5 barg and 7 barg) will be higher than the system pressure when the system operates using only supplemental gas containing gaseous hydrogen (where, for example, the pressure can be adjusted between 3 barg and 5 barg). When operating using a mixture of supplemental gas containing gaseous hydrocarbons and supplemental gas containing gaseous hydrogen, the system pressure will be at an intermediate pressure.

[0049] In this example, regulating the operating pressure of the system allows for partial or complete compensation for the different characteristics of the gases circulating in the system, which are due to the varying percentages of supplementary gas containing gaseous hydrogen and supplementary gas containing gaseous hydrocarbons. In this way, the fluid dynamic response of the machinery arranged in the system loop will be substantially equal whether operating with high-pressure hydrocarbon gases (high molecular weight gases) or low-pressure hydrocarbon gases (low molecular weight gases).

[0050] Specifically, to partially or completely compensate for the different characteristics of the gases circulating in the system, nitrogen injection is provided. This serves both to increase the molecular weight of the circulating process gases without altering their reducing properties and to utilize the nitrogen present in the circulating gases as a carrier of thermal energy within the reduction reactor. More specifically, pressure decompensation occurs in the channels from supplementing with gaseous hydrocarbon-containing gas to supplementing with gaseous hydrogen-containing gas, particularly at the pumping devices 42 and 42' respectively located on pipes 40 and 54. One possible solution is to inject nitrogen into the loop when supplementing with gaseous hydrogen-containing gas. In this way, the reducing gas mixture is heavier, and the pumping devices operate optimally.

[0051] Preferably, the injection of nitrogen or other suitable gas (e.g., CO2) is carried out at the pumping device.

[0052] In some preferred embodiments of the invention, the heat transfer fluid is water, thereby generating steam in the first heat exchange device and carrying it through a pipe connecting the first heat exchange device and the second heat exchange device.

[0053] Steam or other heat transfer fluids from the first heat exchanger can be used in the second heat exchanger to increase the temperature of the process reduction gas entering the heating unit, thereby reducing energy consumption.

[0054] If a gas containing gaseous hydrogen is unavailable and the system requires operation with a gas containing gaseous hydrocarbons, such as natural gas, coke oven gas, syngas, or other types of reducing gases, then steam or other heat transfer fluids from the first heat exchange unit can be readily transferred to a carbon dioxide removal unit for the removal of carbon dioxide, for example, by absorbing carbon dioxide, in order to regenerate the amine solution.

[0055] Steam or other heat transfer fluids can be flexibly used to preheat process reduction gases in the second heat exchange unit and / or in the operation of the removal unit for removing carbon dioxide. The amount of steam or other heat transfer fluid specified for each use can be flexibly set according to the ratio of the amount of gaseous hydrogen-containing gas to the amount of gaseous hydrocarbon-containing gas fed into the reduction system loop.

[0056] In short, the direct reduction system of the present invention is adaptable to operation using a wide variety of gaseous hydrocarbon-containing gas sources and / or gaseous hydrogen-containing gas sources or other reducing gas sources that have emerged over the years as supplementary gases, without disrupting the equipment and allowing for dynamic changes from one source to another.

[0057] Another advantage of this invention is that operation can continue even when the gas containing gaseous hydrogen is unavailable for any reason, ensuring high process availability and negligible production losses.

[0058] In fact, the system configuration allows the use of gaseous hydrocarbons instead of gaseous hydrogens with simple adjustments to the system operation.

[0059] Optionally, the additional gaseous hydrocarbon gas, such as natural gas, can be supplied in the lower region of the reactor, preferably in a conical region, below the reduction zone, via at least one device for injecting additional gaseous hydrocarbon gas.

[0060] The following are some additional advantages of the solution of the present invention compared to the prior art:

[0061] Depending on the percentage of supplemental gaseous hydrocarbons present in the feed mixture, devices for removing carbon dioxide, such as carbon dioxide absorbers, can be partially or completely bypassed.

[0062] When only gas containing gaseous hydrogen is fed into the loop, the humidifier required to increase the water content in the process gas to prevent carbon deposition in the process gas heating unit can be completely bypassed by a simple additional bypass pipe.

[0063] Typically, by increasing the gaseous hydrogen content in the gas fed into the loop, carbon deposition within the heating unit is extremely limited (if any), and system shutdown for chemical cleaning is not required, thus increasing system reliability and availability.

[0064] When the reducing gas stream is pure or nearly pure gaseous hydrogen, no additional energy is required to promote the reforming reaction in the reactor, so the oxygen injection downstream of the heating unit can be shut off.

[0065] Since the obtained process gas preferably has a fairly low CO and CO2 content, the acidification of the process water in contact with the process gas is extremely limited, and there is no need for increased consumption of expensive materials or chemical reagents in the water return line to control the water quality.

[0066] The reduction of iron ore using gaseous hydrogen, which determines the temperature drop inside the reactor, allows for more conventional operation with virtually no risk of agglomeration (typical of the reduction with CO and its exothermic reaction, as well as expansion).

[0067] Introducing commercially pure gaseous hydrogen or gas containing gaseous hydrogen with an increased gaseous hydrogen content directly into the loop improves the efficiency of current direct reduction systems based on gaseous hydrocarbon gases (such as natural gas or coke oven gas), such as the ZR process or processes with online reformers.

[0068] To minimize the phenomenon of pellet expansion during reactor startup, a characteristic of using CO as a reducing agent, which can lead to the cessation of solid flow and reactor blockage.

[0069] Further features and advantages of the invention will become more apparent from the detailed description of the illustrative but non-exclusive embodiments.

[0070] The dependent claims describe specific embodiments of the invention. Brief description of the attached diagram

[0071] Reference is made to the accompanying drawings in the description of the invention, which are given by way of non-limiting examples, wherein:

[0072] Figure 1 The figure illustrates a first embodiment of the direct reduction system according to the present invention;

[0073] Figure 2 The figure illustrates a second embodiment of the direct reduction system according to the present invention.

[0074] Description of illustrative embodiments of the present invention

[0075] refer to Figure 1 and Figure 2 The figures illustrate some examples of direct reduction systems that constitute the subject matter of the present invention, the direct reduction system including a loop provided with:

[0076] Reactor 1, which has a reduction zone 12 suitable for being loaded with iron oxide through inlet pipe 2;

[0077] A first external source 200 having a supplemental gas containing gaseous hydrogen with a gaseous hydrogen content or hydrogen content equal to at least 80% by volume;

[0078] A second external source 210 for supplementing gaseous hydrocarbons, preferably having a gaseous hydrocarbon content of at least 25% by volume;

[0079] Recovery and treatment pipeline 10, which is located downstream of reactor 1, is used to recover and treat exhaust gas leaving reactor 1;

[0080] The processing and feed line 11, which is located upstream of the reactor 1, is used to process a gas mixture that defines the process gas by mixing supplemental gas containing gaseous hydrogen from a first external source 200 and / or supplemental gas containing gaseous hydrocarbons from a second external source 210 with the exhaust gas processed in the recovery and processing line 10, and to feed the process gas into the reduction zone 12 of the reactor 1.

[0081] The recycling and processing line 10 is connected downstream to the processing and feed line 11.

[0082] The recovery and treatment pipeline 10 includes at least one first heat exchange device 22, such as only one first heat exchange device, wherein heat is transferred from the exhaust gas to the heat transfer fluid 70.

[0083] Advantageously, the processing and feed line 11 includes at least one second heat exchange device 72, for example, only one second heat exchange device, and is provided with a pipe 75, preferably only one pipe 75, which is capable of carrying the heat transfer fluid and connecting the first heat exchange device 22 to the second heat exchange device 72, so that the heat of the heat transfer fluid can be transferred to the process gas through the second heat exchange device 72.

[0084] In addition, the recycling and treatment pipeline 10 also includes at least one carbon dioxide removal device 50, for example, only one removal device, for removing carbon dioxide from the exhaust gas, for example, absorbing carbon dioxide.

[0085] Advantageously, the conduit 75 has a branch 76 connecting the conduit 75 to the carbon dioxide removal device 50, whereby if the supplemental gas containing gaseous hydrogen is unavailable or only partially available, the heat of the heat transfer fluid can be transferred completely or partially to the removal device 50, respectively.

[0086] Preferably, in order to better adjust the operation of the direct reduction system based on input data, the input data includes availability data of supplemental gas containing gaseous hydrogen or consists of availability data of supplemental gas containing gaseous hydrogen. The system of the present invention includes:

[0087] A bypass pipe 52 in the recovery and treatment pipeline 10 is used to bypass the removal device 50;

[0088] A first flow regulating device 62, placed along branch 76, is used to regulate the flow rate of the heat transfer fluid toward the removal device 50;

[0089] A second flow regulating device 65 along pipe 75 is used to regulate the flow rate of heat transfer fluid toward the second heat exchange device 72;

[0090] The third flow regulating device 63 is used to close or at least partially open the bypass pipe 52;

[0091] The fourth flow regulating device 32 is used to regulate the flow rate of the supplementary gas containing gaseous hydrocarbons to be fed into the gas circulation loop;

[0092] The fifth flow regulating device 31 is used to regulate the flow rate of the supplementary gas containing gaseous hydrogen to be fed into the gas circulation loop.

[0093] Optionally, for example, Figure 2 As shown, the control unit 64 is configured to send control signals 110 to the first flow regulator 62, 111 to the second flow regulator 65, 112 to the third flow regulator 63, 114 to the fourth flow regulator 32, and 116 to the fifth flow regulator 31, respectively, based on input data including a signal 118 indicating the availability of supplemental gas containing gaseous hydrogen. The control unit 64 may also be configured to... Figure 1 The implementation plan.

[0094] Advantageously, in all embodiments of the invention, the first external source 200 for supplementing the reducing gas is a commercially pure source of gaseous hydrogen (at least 99% by volume) or a gas source having a gaseous hydrogen content equal to at least 80% by volume, preferably equal to at least one value equal to 85% to 98% by volume.

[0095] In the case of a supplemental gas containing gaseous hydrogen having a gaseous hydrogen content of at least 80% by volume, the remainder of the composition may contain carbon monoxide, water, carbon dioxide, methane, and nitrogen.

[0096] Purely through examples, the composition of a gas containing gaseous hydrogen can be supplemented as a volume percentage as follows:

[0097] Gaseous hydrogen in the range of 92%-96%;

[0098] Carbon monoxide in the range of 1.5%-2.5%;

[0099] Water 0.2%-0.6%;

[0100] Carbon dioxide 0.0-0.4%;

[0101] Methane 0.3%-0.9%;

[0102] Nitrogen gas 2.0%-4.0%.

[0103] The second external source 210 for supplementing the reducing gas is a gas source containing gaseous hydrocarbons, such as natural gas, coke oven gas, Corex gas, syngas, etc., having a gaseous hydrocarbon content of at least 25% by volume.

[0104] The gas containing gaseous hydrocarbons can also be a gas derived from biomass, biogas, or biomethane.

[0105] The second external source 210 is normally off, but may be turned on to use the gaseous hydrocarbon gas in the loop in the event of poor or no availability of the supplemental gas containing gaseous hydrogen.

[0106] Preferably, at least one first heat exchange device 22 is located near the reactor 1, while the at least one removal device 50 is located away from the reactor 1 and near the processing and feed line 11.

[0107] Advantageously, in all embodiments, the processing and feeding line 11 may include or may consist of the following:

[0108] The first conduit is used to obtain process gas by mixing treated exhaust gas from reactor 1 with supplemental reducing gas from first external source 200 and / or second external source 210.

[0109] At least one humidifier 60, for example only one humidifier, is used to adjust the water content of the process gas in the case of high CH4 and heavy gaseous hydrocarbon content in the process gas;

[0110] A second heat exchange device 72, such as a condenser, is used to recover the heat energy from the heat transfer fluid of the first heat exchange device 22.

[0111] At least one heating unit 180, for example only one heating unit, is used to heat the process gas at a temperature suitable for introduction into reactor 1.

[0112] When only gas containing gaseous hydrogen is fed into the circuit, the humidifier 60 can be completely bypassed by a simple additional bypass pipe 80.

[0113] Downstream of the heating unit 180, an oxygen injection device 300 may be provided for injecting oxygen into the process gas stream.

[0114] Another advantage of the system of the present invention is indicated by the fact that the recycling and treatment pipeline 10 may include or be composed of the following:

[0115] The second pipe is suitable for the exhaust gas leaving reactor 1 to pass through;

[0116] A first heat exchange device 22, for example, only one first heat exchange device, is used to cool the exhaust gas leaving the reactor 1;

[0117] At least one washing and cooling unit 36, for example only one washing and cooling unit, is arranged downstream of the first heat exchange device 22 for removing water from the exhaust gas to obtain dehydrated gas;

[0118] Preferably, at least one pumping device 42, for example only one pumping device, is used to pump the dehydrated gas toward the processing and feed line 11;

[0119] A carbon dioxide removal device 50, such as an absorption device, is arranged downstream of the at least one washing and cooling unit 36, preferably downstream of the pumping device 42; and

[0120] Bypass pipe 52 is used to bypass removal device 50 when the supplemental reducing gas fed into the loop is only a supplemental gas containing gaseous hydrogen.

[0121] Optionally, the humidifier 60 of the processing and feed line 11 receives hot water from the discharge line of the washing and cooling unit 36 ​​via pipe 54 and discharges water via pipe 81.

[0122] Preferably, the second conduit of the recycling and treatment line 10, downstream of the washing and cooling unit 36, includes:

[0123] Branch pipe 34 connects the recovery and treatment line 10 to the burner of the heating unit 180, and a first stream of dehydrated exhaust gas in the branch pipe 34 can be transported as a combustible gas for the burner.

[0124] And a branch pipe 40, which connects the recovery and treatment line 10 to the treatment and feed line 11, and possibly a pumping device 42 and a carbon dioxide removal device 50 are arranged along the branch pipe 40, and a second stream of dehydrated exhaust gas is recirculated in the branch pipe 40.

[0125] Preferably, an additional regulating device 30, such as a pressure control valve, is provided along the branch pipe 34.

[0126] Heating unit 180 is supplied by the combustion of a suitable combustible material from source 182. The combustible material may be dehydrated exhaust gas from branch pipe 34, or pure gaseous hydrogen or natural gas or other hydrocarbon-containing gases or mixtures thereof.

[0127] exist Figure 1In a first embodiment of the system of the present invention shown, an external source 200 of gaseous hydrogen containing gas with a gaseous hydrogen content of at least 80% by volume and an external source 210 of gaseous hydrocarbon containing gaseous hydrocarbon containing gaseous hydrocarbons with a gaseous hydrocarbon content of at least 25% by volume are connected to the processing and feed line 11, for example, directly connected to the processing and feed line 11.

[0128] Specifically, both the first external source 200 and the second external source 210 are connected to the stretch of the loop, which includes the pumping device 42 of the recovery and processing line 10 and the heating unit 180 of the processing and feed line 11, preferably in the stretch between the carbon dioxide removal device 50 or bypass pipe 52 of the recovery and processing line 10 and the humidifier 60 of the processing and feed line 11.

[0129] A flow regulating device 31, such as a pressure control valve, is preferably disposed along a conduit 61 that connects an external source 200 to the processing and feed line 11. Similarly, a flow regulating device 32, such as another pressure control valve, is preferably disposed along a conduit 71 that connects an external source 210 to the processing and feed line 11.

[0130] exist Figure 2 In a second embodiment of the system of the present invention shown, an external source 200 containing gaseous hydrogen and an external source 210 containing gaseous hydrocarbons are connected to a recovery and treatment line 10, for example, directly connected to the recovery and treatment line 10.

[0131] Specifically, both the first external source 200 and the second external source 210 are connected to the section of the loop including between the washing and cooling unit 36 ​​and the pumping device 42, for example, along branch pipe 40. In this way, supplemental reducing gas can also be distributed from external sources 200 and 210 at low pressure and subsequently compressed by the subsequent pumping device 42.

[0132] A flow regulating device 31, such as a pressure control valve, is preferably provided along a conduit 61 that connects an external source 200 to a recovery and treatment line 10.

[0133] A flow regulating device 32, such as an additional pressure control valve, is preferably provided along a conduit 71 that connects an external source 210 to a recovery and treatment line 10.

[0134] In both the first and second embodiments of the system of the present invention, at least one gas injection device 191 containing gaseous hydrocarbons may be included to inject gas containing gaseous hydrocarbons (such as natural gas or coke oven gas or gas from biomass or biogas or biomethane) into the lower zone 14, preferably conical zone, of the reactor 1 located below the reduction zone 12, or directly into the transition zone of the reactor 1 between the reduction zone 12 and the emission zone. In both cases, this injection allows for adjustment of the DRI carbon content.

[0135] The following describes an example of a process for the direct reduction of iron oxide performed using the system described in this invention when fully operational. The process, when fully operational, includes the following steps:

[0136] a) The exhaust gas leaving reactor 1 is recovered and treated through recovery and treatment pipeline 10;

[0137] b) Process gas is fed into the reduction zone 2 of reactor 1 via processing and feed line 11, the process gas being obtained by mixing supplemental gas containing gaseous hydrogen from a first external source 200 and / or supplemental gas containing gaseous hydrocarbons from a second external source 210 with exhaust gas processed in recovery and processing line 10.

[0138] The following steps are also provided:

[0139] The heat from the exhaust gas leaving the reactor 1 is transferred to the heat transfer fluid by the first heat exchange device 22 of the recovery and treatment pipeline 10.

[0140] and

[0141] If the supplemental gas containing gaseous hydrogen from the first external source 200, mixed with the exhaust gas processed in the recovery and treatment line 10, is sufficient for the direct reduction process, the heat of the heat transfer fluid is completely transferred to the process gas via the pipe 75 of the second heat exchanger 72 carried by the heat transfer fluid to the treatment and feed line 11, through the second heat exchanger 72, and thus the entire heat transfer fluid reaches the second heat exchanger 72. However, if the supplemental gas containing gaseous hydrogen from the first external source 200 is unusable or insufficient for the direct reduction process when mixed with the exhaust gas processed in the recovery and treatment line 10, then the supplemental gas containing gaseous hydrocarbons from the second external source 210 is mixed with the exhaust gas or with both the exhaust gas and the supplemental gaseous hydrogen, and the heat of the heat transfer fluid is completely or partially transferred to the carbon dioxide removal unit 50, respectively. Therefore, if the supplemental gas containing gaseous hydrogen is unavailable, all the heat transfer fluid reaches the removal unit 50. Conversely, if a supplemental gas containing gaseous hydrogen is available but insufficient, the heat transfer fluid partially reaches both the removal device 50 and the second heat exchange device 72.

[0142] Preferably, in order to better adjust the operation of the direct restore system, the following steps are provided:

[0143] Input data including a signal (118) indicating the availability of supplemental gas containing gaseous hydrogen;

[0144] The input data is processed, and preferably by the control unit 64.

[0145] Send a first control signal 110 to the first flow regulating device 62 to regulate the flow rate of the heat transfer fluid toward the carbon dioxide removal device 50;

[0146] Send a second control signal 111 to the second flow regulating device 65 to regulate the flow rate of the heat transfer fluid toward the second heat exchange device 72;

[0147] Send a third control signal 112 to the third flow regulating device 63 for at least partially closing or opening the bypass pipe 52;

[0148] Send a fourth control signal 114 to the fourth flow regulating device 32 to regulate the flow rate of the supplementary gas containing gaseous hydrocarbons to be fed into the loop;

[0149] And send a fifth control signal 116 to the fifth flow regulating device 31 to regulate the flow rate of the supplementary gas containing gaseous hydrogen to be fed into the loop.

[0150] Therefore, if the supplemental gas containing gaseous hydrogen from the first external source 200, mixed with the exhaust gas treated in the recovery and treatment line 10, is available and sufficient for the entire direct reduction process, the second external source 210 is typically shut off. Control unit 64 sends corresponding control signals 110, 111 to the first flow regulator 62 and the second flow regulator 65, and control signal 114 to the fourth flow regulator 32, causing the line 76 and the second external source 210 to shut off, and the line 75 to open. Control unit 64 also sends control signal 112 to the third flow regulator 63 and control signal 116 to the fifth flow regulator 31, causing the bypass line 52 and the first external source 200 to open, respectively. In this case, the removal device 50 is completely bypassed.

[0151] When the supplemental gas containing gaseous hydrogen from the first external source 200 is mixed with the exhaust gas processed in the recovery and treatment line 10 and is available but insufficient for the entire direct reduction process, the control unit 64, based on the control signal 118 from the gas source 200 containing gaseous hydrogen:

[0152] A control signal 114 is sent to the fourth flow regulating device 32 to partially open the second external source 210, and thus to regulate the flow rate of the supplementary gas containing gaseous hydrocarbons to be fed into the loop.

[0153] A control signal 116 is sent to the fifth flow regulating device 31 to regulate the flow rate of the supplementary gas containing gaseous hydrogen to be fed into the loop.

[0154] A control signal 110 is sent to the first flow regulating device 62 and a control signal 111 is sent to the second flow regulating device 65 to regulate the flow rate of the heat transfer fluid toward the removal device 50 and the flow rate of the heat transfer fluid toward the second heat exchange device 72, respectively. The flow rate of the heat transfer fluid is flexibly set according to the ratio of the amount of gas containing gaseous hydrogen to the amount of gas containing gaseous hydrocarbon in the circuit fed into the reduction system.

[0155] A control signal 112 is sent to the third flow regulating device 63 for partially shutting off the bypass pipe 52 and partially feeding the removal device 50. The partial shut-off and partial feeding are flexibly set according to the ratio of the amount of gaseous hydrogen-containing gas to the amount of gaseous hydrocarbon-containing gas fed into the reduction system loop.

[0156] Finally, if there is no availability of supplemental gas containing gaseous hydrogen from the first external source 200, the first external source 200 is normally shut off. Control unit 64 sends control signal 110 to the first flow regulator 62, control signal 111 to the second flow regulator 65, and control signal 114 to the fourth flow regulator 32, causing pipe 76 and the second external source 210 to open, while the portion of pipe 75 closest to the second heat exchanger 72 is completely shut off. Control unit 64 also sends control signal 112 to the third flow regulator 63 and control signal 116 to the fifth flow regulator 31, causing bypass pipe 52 and the first external source 200 to close, respectively.

[0157] In an example of the process of the present invention, the exhaust gas leaving the reactor 1, preferably at a temperature in the range of about 250°C to about 550°C, is guided into a pipe 50 in the recovery and treatment line 10, which carries the exhaust gas to the first heat exchange device 22 for its cooling.

[0158] Optionally, if water is used in the first heat exchanger 22 to cool the exhaust gas leaving the reactor 1, the heat transfer fluid in the pipe 75 will be steam.

[0159] After cooling, the exhaust gas flows through pipe 24 to the washing and cooling unit 36 ​​to remove water and obtain dehydrated gas.

[0160] After cooling and dehydration, the dehydrated exhaust gas is divided into two branch pipes 34 and 40.

[0161] A smaller portion of the dehydrated exhaust gas flows through a branch pipe 34 equipped with a pressure control valve 30, which allows a portion of the dehydrated exhaust gas to be discharged from the circuit to eliminate the accumulation of unwanted inert gas. The larger portion of the dehydrated exhaust gas flows through branch pipe 40.

[0162] The feed of supplemental gas containing gaseous hydrogen from the first external source 200 and / or supplemental gas containing gaseous hydrocarbons from the second external source 210 is provided in the processing and feed line 11 or in the recovery and processing line 10.

[0163] When the first external source 200 and the second external source 210 are connected to the processing and feed line 11, the feeding occurs in a section of the loop including the pumping device 42 of the recovery and processing line 10 and the heating unit 180 of the processing and feed line 11, preferably in the section between the removal device 50 or bypass pipe 52 of the recovery and processing line 10 and the humidifier 60 of the processing and feed line 11.

[0164] Reference Figure 1 The dehydrated exhaust gas flowing in pipe 40 is propelled by pumping device 42, which may be a compressor or blower, to recirculate this portion of the dehydrated exhaust gas and bring it back to reactor 1. Downstream of pumping device 42, the dehydrated exhaust gas flows through pipe 44, through carbon dioxide removal device 50 and / or bypass pipe 52, and is then mixed in processing and feed line 11 with supplemental gas containing gaseous hydrogen from first external source 200 and / or supplemental gas containing gaseous hydrocarbons from second external source 210 to define process gas. If the feed of gaseous hydrocarbon gas is not required, carbon dioxide removal device 50 can be completely bypassed through bypass pipe 52.

[0165] Conversely, when the first external source 200 and the second external source 210 are connected to the recycling and processing line 10, the feeding occurs in the section of the loop between the washing and cooling unit 36 ​​and the pumping device 42 of the recycling and processing line 10.

[0166] Reference Figure 2 ,and Figure 1In a different implementation, the dehydrated exhaust gas flowing in pipe 40 is mixed here with supplemental gas containing gaseous hydrogen from a first external source 200 and / or supplemental gas containing gaseous hydrocarbons from a second external source 210. The resulting gas mixture defining the process gas is propelled by a pumping device 42, which may be a compressor or a blower, to carry the process gas to the processing and feed line 11. Specifically, downstream of the pumping device 42, the process gas flows through pipe 44, through the carbon dioxide removal unit 50 and / or bypass pipe 52, and then to the processing and feed line 11. If the feed of gaseous hydrocarbon-containing gas is not required, the carbon dioxide removal unit 50 can be completely bypassed via the bypass pipe 52.

[0167] In all embodiments, the process gas continues to flow sequentially through a possible humidifier 60, a second heat exchange device 72 that can raise the temperature of the process gas, and then through a pipe 15 to a heating unit 180, in which the process gas reaches a temperature of approximately 850°C-950°C.

[0168] When only gas containing gaseous hydrogen is fed into the circuit, the humidifier 60 can be completely bypassed by the bypass pipe 80.

[0169] Downstream of the heating unit 180, the process gas flows through the pipe 16 until it reaches the interior of the reactor 1.

[0170] Downstream of the heating unit 180 and upstream of the reactor 1, gaseous oxygen can be injected into the process gas stream via a gaseous oxygen injection device 300.

[0171] Preferably, additional gaseous hydrocarbons, such as natural gas or coke oven gas or gas from biomass or biogas or biomethane, are injected into the lower zone of reactor 1, preferably a conical zone 14, located below the reduction zone 12, or are directly supplied to the transition zone of reactor 1 between the reduction zone 12 and the discharge zone via at least one injection device 191.

[0172] Iron oxide material in the form of pellets or blocks is supplied from above into the reduction zone 12 of reactor 1 and reacts with hot reducing gas. The iron oxide material flows countercurrently relative to the hot reducing gas and is eventually discharged as hot DRI.

[0173] Optionally, the iron oxide material has a particle size of about 2.5 mm to 19 mm, preferably about 3.5 mm to 15 mm.

[0174] This invention also provides the following items:

[0175] 1. A direct reduction system for the direct reduction of iron oxide, comprising a gas circulation loop, said gas circulation loop comprising:

[0176] A reactor having a reduction zone suitable for being loaded with the iron oxide;

[0177] A first external source of supplemental gas containing gaseous hydrogen, having a gaseous hydrogen content equal to at least 80% by volume;

[0178] The gas is supplemented with gaseous hydrocarbons, preferably a second external source of gaseous hydrocarbons having a gaseous hydrocarbon content of at least 25% by volume;

[0179] A recovery and treatment pipeline, located downstream of the reactor, is used to recover and treat exhaust gases leaving the reactor.

[0180] A processing and feed line, located upstream of the reactor, is used to process the process gas obtained by mixing the supplementary gas containing gaseous hydrogen from the first external source and / or the supplementary gas containing gaseous hydrocarbons from the second external source with the exhaust gas processed in the recovery and processing line, and to feed the process gas into the reduction zone of the reactor.

[0181] The recycling and processing pipeline is connected downstream to the processing and feed pipeline;

[0182] The recovery and treatment pipeline includes at least one first heat exchange device in which heat is transferred from the exhaust gas to a heat transfer fluid.

[0183] The processing and feed line includes at least one second heat exchange device;

[0184] The pipes capable of carrying the heat transfer fluid connect the at least one first heat exchange device to the at least one second heat exchange device, thereby allowing the heat of the heat transfer fluid to be transferred to the process gas through the at least one second heat exchange device.

[0185] The recovery and treatment pipeline also includes at least one carbon dioxide removal device for removing carbon dioxide from the exhaust gas;

[0186] The pipe has branches that connect the pipe to the at least one carbon dioxide removal device, whereby the heat of the heat transfer fluid can be transferred wholly or partially to the at least one carbon dioxide removal device.

[0187] And wherein the first external source and the second external source are connected to the processing and feed line or the recycling and processing line.

[0188] 2. The system described in Project 1, wherein the following are set up:

[0189] The bypass pipe in the recovery and treatment pipeline is used to bypass the at least one carbon dioxide removal device;

[0190] A first flow regulating device is used to regulate the flow rate of the heat transfer fluid toward the at least one carbon dioxide removal device;

[0191] A second flow regulating device is used to regulate the flow rate of the heat transfer fluid toward the at least one second heat exchange device;

[0192] A third flow regulating device is used to at least partially close or open the bypass pipe;

[0193] The fourth flow regulating device is used to regulate the flow rate of the supplementary gas containing gaseous hydrocarbons to be fed into the gas circulation loop;

[0194] The fifth flow regulating device is used to regulate the flow rate of the supplementary gas containing gaseous hydrogen to be fed into the gas circulation loop;

[0195] Preferably, a control unit is configured to send a first control signal to the first flow regulating device, a second control signal to the second flow regulating device, a third control signal to the third flow regulating device, a fourth control signal to the fourth flow regulating device, and a fifth control signal to the fifth flow regulating device based on input data including a signal indicating the availability of the supplemental gas containing gaseous hydrogen.

[0196] 3. The system according to item 1 or 2, wherein the at least one second heat exchange device is placed between the humidifier and the heating unit, the humidifier and the heating unit being disposed in the processing and feed line.

[0197] 4. The system according to Project 3, wherein the at least one first heat exchange device is placed between the reactor and at least one washing and cooling unit for removing water from the exhaust gas to obtain dehydrated gas, and the at least one washing and cooling unit is disposed in the recovery and treatment pipeline; preferably, an additional pipeline is provided to connect the exhaust pipeline of the at least one washing and cooling unit to the humidifier for carrying hot water to the humidifier.

[0198] 5. The system according to item 2 or 4, wherein the processing and feed lines, in addition to the first conduit through which the process gas is adapted, sequentially include

[0199] At least one humidifier for adjusting the water content of the process gas;

[0200] The at least one second heat exchange device;

[0201] At least one heating unit for heating the process gas;

[0202] And preferably, the recovery and treatment pipeline, in addition to the second pipe through which the exhaust gas is adapted, sequentially includes

[0203] The at least one first heat exchange device is used to cool the exhaust gas leaving the reactor;

[0204] At least one washing and cooling unit is provided for removing water from the discharged gas to obtain dehydrated gas;

[0205] Preferably, at least one pumping device is used to pump the dehydrated gas into the processing and feed line;

[0206] The at least one carbon dioxide removal device and the bypass pipeline.

[0207] 6. The system according to item 5, wherein, with the first external source and the second external source connected to the processing and feed line, both the first external source and the second external source are connected to a section of the gas circulation loop, the section being included between a possible pumping device of the recovery and processing line and the heating unit of the processing and feed line, preferably between the at least one carbon dioxide removal device of the recovery and processing line or the bypass line and the at least one humidifier of the processing and feed line.

[0208] 7. The system according to item 5, wherein, with the first external source and the second external source connected to the recovery and treatment pipeline, both the first external source and the second external source are connected to a section of the gas circulation loop, the section being included between the at least one washing and cooling unit and the at least one pumping device.

[0209] 8. The system according to any one of items 5 to 7, wherein the second conduit of the recovery and treatment pipeline comprises:

[0210] The first branch pipe connects the recovery and treatment line to the burner of the heating unit, and the first stream of dehydrated exhaust gas is delivered to the first branch pipe as the combustible gas of the burner.

[0211] And a second branch pipe that connects the recovery and treatment line to the treatment and feed line, and possibly at least one pumping device and the at least one carbon dioxide removal device are arranged along the second branch pipe, and a second stream of dehydrated exhaust gas is recirculated in the second branch pipe.

[0212] 9. A direct reduction process for the direct reduction of iron oxide, said process being carried out using a system according to any one of the preceding items, said process comprising the following steps when fully operational:

[0213] a) The exhaust gas leaving the reactor is recovered and treated through the recovery and treatment pipeline;

[0214] b) Process gas is fed into the reduction zone of the reactor through the processing and feed line, the process gas being obtained by mixing the supplemental gas containing gaseous hydrogen from the first external source and / or the supplemental gas containing gaseous hydrocarbons from the second external source with the exhaust gas processed in the recovery and processing line;

[0215] The following steps were also set.

[0216] Heat is transferred from the exhaust gas leaving the reactor to the heat transfer fluid through the at least one first heat exchange device in the recovery and treatment pipeline;

[0217] And among them

[0218] If the supplemental gas containing gaseous hydrogen from the first external source, mixed with the exhaust gas processed in the recovery and treatment pipeline, is sufficient for the direct reduction process, then the heat of the heat transfer fluid is completely transferred to the process gas through the pipes of the at least one second heat exchanger carried by the heat transfer fluid to the treatment and feed pipeline.

[0219] If the supplemental gas containing gaseous hydrogen from the first external source, when mixed with the exhaust gas processed in the recovery and treatment pipeline, is unusable or insufficient for the direct reduction process, then the supplemental gas containing gaseous hydrocarbons from the second external source is mixed with the exhaust gas or with both the exhaust gas and the supplemental gas containing gaseous hydrogen, and the heat of the heat transfer fluid is transferred completely or partially to the at least one carbon dioxide removal device, respectively.

[0220] 10. According to the process described in Project 9, the following steps are also included:

[0221] The flow rate of the heat transfer fluid toward the at least one carbon dioxide removal device is adjusted by a first flow regulating device;

[0222] The flow rate of the heat transfer fluid toward the at least one second heat exchange device is adjusted by a second flow regulating device;

[0223] By means of a third flow regulating device, at least partially close or open a bypass pipe provided in the recovery and treatment pipeline to bypass the at least one carbon dioxide removal device;

[0224] The flow rate of the supplementary gas containing gaseous hydrocarbons to be fed into the gas circulation loop is adjusted by the fourth flow regulating device.

[0225] The flow rate of the supplementary gas containing gaseous hydrogen to be fed into the gas circulation loop is adjusted by the fifth flow regulating device.

[0226] 11. According to the process described in Project 10, the following steps are also included:

[0227] Provide input data, which includes signals indicating the availability of the supplemental gas containing gaseous hydrogen;

[0228] Process the input data and control the control unit

[0229] Send a first control signal to the first flow regulating device to regulate the flow rate of the heat transfer fluid toward the at least one carbon dioxide removal device;

[0230] Send a second control signal to the second flow regulating device to regulate the flow rate of the heat transfer fluid toward the at least one second heat exchange device;

[0231] Send a third control signal to the third flow regulating device to at least partially close or open the bypass pipe for possible bypassing the at least one carbon dioxide removal device;

[0232] A fourth control signal is sent to the fourth flow regulating device to regulate the flow rate of the supplementary gas containing gaseous hydrocarbons to be fed into the gas circulation loop;

[0233] And send a fifth control signal to the fifth flow regulating device to regulate the flow rate of the supplementary gas containing gaseous hydrogen to be fed into the gas circulation loop.

[0234] 12. The process according to item 10 or 11, wherein if water is used to cool the exhaust gas leaving the reactor in the at least one first heat exchange device, the heat transfer fluid in the pipe is steam.

[0235] 13. The process according to any one of items 9 to 12, wherein the feed of supplemental gas containing gaseous hydrogen from the first external source and / or supplemental gas containing gaseous hydrocarbon from the second external source is provided in the processing and feed line or the recovery and processing line.

[0236] 14. The process according to item 13, wherein, with a first external source and a second external source connected to the processing and feed line, the feed occurs in a section of the gas circulation loop, the section being included between the pumping device of the recovery and processing line and at least one heating unit of the processing and feed line, preferably between the at least one carbon dioxide removal device of the recovery and processing line or the bypass line and at least one humidifier of the processing and feed line.

[0237] 15. The process according to item 13, wherein, with a first external source and a second external source connected to the recovery and treatment pipeline, the feeding occurs in a section of the gas circulation loop, the section being between the washing and cooling unit and the pumping device of the recovery and treatment pipeline.

[0238] 16. The process according to any one of items 9 to 15, wherein the operating pressure of the system is adjusted to partially or completely compensate for the molecular weight difference caused by the different percentages of the supplementary gas containing gaseous hydrogen and the supplementary gas containing gaseous hydrocarbon.

[0239] 17. The process according to Project 16, wherein nitrogen is injected to both increase the molecular weight of the circulating process gas and to use the nitrogen present in the circulating process gas as a heat carrier inside the reactor.

Claims

1. A direct reduction system for direct reduction of iron oxides, comprising a gas circulation loop, said gas circulation loop comprising: - a reactor (1) having a reduction zone (12) adapted to be loaded with said iron oxides; - a first external source (200) of a supplementary gaseous-hydrogen-containing gas having a gaseous-hydrogen content equal to at least 80% by volume; - a second external source (210) of a supplementary gaseous-hydrocarbon-containing gas; - a recovery and treatment line (10) placed downstream of said reactor (1) for recovering and treating an exhaust gas exiting said reactor (1); - a treatment and feeding line (11) placed upstream of said reactor (1) for treating a process gas obtained by mixing said supplementary gaseous-hydrogen-containing gas from said first external source (200) and / or said supplementary gaseous-hydrocarbon-containing gas from said second external source (210) with said exhaust gas treated in said recovery and treatment line (10) and for feeding said process gas to said reduction zone (12) of said reactor (1); wherein said recovery and treatment line (10) communicates downstream with said treatment and feeding line (11); wherein said recovery and treatment line (10) comprises at least one first heat exchange device (22) in which heat is transferred from said exhaust gas to a heat transfer fluid; wherein said treatment and feeding line (11) comprises at least one second heat exchange device (72); wherein a duct (75) able to carry said heat transfer fluid connects said at least one first heat exchange device (22) to said at least one second heat exchange device (72), whereby heat of said heat transfer fluid can be transferred to said process gas through said at least one second heat exchange device (72); wherein said recovery and treatment line (10) further comprises at least one carbon dioxide removal device (50) for removing carbon dioxide from said exhaust gas; wherein said duct (75) has a branch (76) connecting said duct (75) to said at least one carbon dioxide removal device (50), whereby heat of said heat transfer fluid can be transferred, totally or partially, to said at least one carbon dioxide removal device (50); and wherein said first external source (200) and said second external source (210) are connected to said treatment and feeding line (11) or to said recovery and treatment line (10).

2. The system according to claim 1, wherein there are provided - a bypass duct (52) in said recovery and treatment line (10) for bypassing said at least one carbon dioxide removal device (50); - a first flow rate regulation device (62) for regulating the flow rate of said heat transfer fluid towards said at least one carbon dioxide removal device (50); - a second flow rate regulation device (65) for regulating the flow rate of said heat transfer fluid towards said at least one second heat exchange device (72); - a third flow rate regulation device (63) for at least partially closing or opening said bypass duct (52). - a fourth flow regulating device (32) for regulating the flow rate of the make-up gaseous hydrocarbon-containing gas to be fed to the gas circulation circuit; - a fifth flow regulating device (31) for regulating the flow rate of the make-up gaseous hydrogen-containing gas to be fed to the gas circulation circuit.

3. The system according to claim 2, wherein there are also provided: - a control unit (64) configured for sending first control signals (110) to the first flow regulating device (62), second control signals (111) to the second flow regulating device (65); third control signals (112) to the third flow regulating device (63); fourth control signals (114) to the fourth flow regulating device (32) and fifth control signals (116) to the fifth flow regulating device (31) as a function of input data comprising a signal (118) indicative of the availability of the make-up gaseous hydrogen-containing gas.

4. The system according to any one of claims 1-3, wherein the at least one second heat exchange device (72) is placed between a humidifier (60) and a heating unit (180), said humidifier (60) and said heating unit (180) being provided in the treatment and feed line (11).

5. The system according to claim 4, wherein the at least one first heat exchange device (22) is placed between the reactor (1) and at least one scrubbing and cooling unit (36) for removing water from the exhaust gas, obtaining a dehydrated gas, said at least one scrubbing and cooling unit (36) being provided in the recovery and treatment line (10).

6. The system according to claim 5, wherein there is provided a further duct (54) connecting a discharge line of the at least one scrubbing and cooling unit (36) to the humidifier (60) for carrying hot water to the humidifier (60).

7. The system according to claim 2 or 3, wherein the treatment and feed line (11) comprises, in sequence, in addition to a first duct through which the process gas is adapted to pass: - at least one humidifier (60) for regulating the water content of the process gas; - the at least one second heat exchange device (72); - at least one heating unit (180) for heating the process gas.

8. The system according to claim 7, wherein the recovery and treatment line (10) comprises, in sequence, in addition to a second duct through which the exhaust gas is adapted to pass: - the at least one first heat exchange device (22) for cooling the exhaust gas leaving the reactor (1); - at least one scrubbing and cooling unit (36) for removing water from the exhaust gas, obtaining a dehydrated gas; - the at least one carbon dioxide removal device (50) and the bypass duct (52).

9. The system according to claim 7, wherein the recovery and treatment line (10) comprises, in sequence, in addition to a second duct through which the exhaust gas is adapted to pass: at least one first heat exchange device (22) for cooling the exhaust gas leaving the reactor (1); at least one washing and cooling unit (36) for removing water from the exhaust gas, obtaining a dehydrated gas; at least one pumping device (42) for pumping the dehydrated gas into the treatment and feeding line (11); the at least one carbon dioxide removal device (50) and the bypass duct (52).

10. The system of claim 9, wherein, In the case where the first external source (200) and the second external source (210) are connected to the treatment and feeding line (11), both the first external source (200) and the second external source (210) are connected to a section of the gas circulation circuit comprised between the at least one pumping device (42) of the recovery and treatment line (10) and the heating unit (180) of the treatment and feeding line (11).

11. The system of claim 8, wherein, In the case where the first external source (200) and the second external source (210) are connected to the treatment and feeding line (11), both the first external source (200) and the second external source (210) are connected to a section of the gas circulation circuit comprised between the at least one carbon dioxide removal device (50) or the bypass duct (52) of the recovery and treatment line (10) and the at least one humidifier (60) of the treatment and feeding line (11).

12. The system of claim 9, wherein, In the case where the first external source (200) and the second external source (210) are connected to the treatment and feeding line (11), both the first external source (200) and the second external source (210) are connected to a section of the gas circulation circuit comprised between the at least one carbon dioxide removal device (50) or the bypass duct (52) of the recovery and treatment line (10) and the at least one humidifier (60) of the treatment and feeding line (11).

13. The system of claim 9, wherein, In the case where the first external source (200) and the second external source (210) are connected to the recovery and treatment line (10), both the first external source (200) and the second external source (210) are connected to a section of the gas circulation circuit comprised between the at least one washing and cooling unit (36) and the at least one pumping device (42).

14. The system according to any one of claims 8 and 11, wherein the second duct of the recovery and treatment line (10) comprises: a first branch duct (34) connecting the recovery and treatment line (10) to a burner of the heating unit (180), and a first flow of dehydrated exhaust gas being conveyed to the first branch duct (34) as combustible gas of the burner; a second branch duct (35) connecting the recovery and treatment line (10) to the at least one humidifier (60) of the treatment and feeding line (11), and a second flow of dehydrated exhaust gas being conveyed to the second branch duct (35) as humidification gas of the at least one humidifier (60). and a second branch duct (40) connecting the recovery and treatment line (10) to the treatment and feed line (11), and along which the at least one carbon dioxide removal device (50) is arranged, and a second stream of dehydrated exhaust gas is recirculated in the second branch duct (40).

15. The system according to any one of claims 9-10 and 12-13, wherein the second duct of the recovery and treatment line (10) comprises: a first branch duct (34) connecting the recovery and treatment line (10) to a burner of the heating unit (180), and a first stream of dehydrated exhaust gas is conveyed to the first branch duct (34) as combustible gas of the burner; and a second branch duct (40) connecting the recovery and treatment line (10) to the treatment and feed line (11), and along which the at least one pumping device (42) and the at least one carbon dioxide removal device (50) are arranged, and a second stream of dehydrated exhaust gas is recirculated in the second branch duct (40).

16. The system according to any one of claims 1-3, 5-6 and 8-13, wherein the supplemental gaseous hydrocarbon-containing gas has a gaseous hydrocarbon content equal to at least 25% by volume.

17. The system according to claim 4, wherein the supplemental gaseous hydrocarbon-containing gas has a gaseous hydrocarbon content equal to at least 25% by volume.

18. The system according to claim 7, wherein the supplemental gaseous hydrocarbon-containing gas has a gaseous hydrocarbon content equal to at least 25% by volume.

19. The system according to claim 14, wherein the supplemental gaseous hydrocarbon-containing gas has a gaseous hydrocarbon content equal to at least 25% by volume.

20. The system according to claim 15, wherein the supplemental gaseous hydrocarbon-containing gas has a gaseous hydrocarbon content equal to at least 25% by volume.

21. A direct reduction process for direct reduction of iron oxides, said process being carried out by the system according to any one of the preceding claims, said process comprising the following steps when fully operating: a) recovering and treating the exhaust gas exiting the reactor (1) by means of the recovery and treatment line (10); b) feeding a process gas to the reduction zone (2) of the reactor (1) by means of the treatment and feed line (11), said process gas being obtained by mixing the supplemental gaseous hydrogen-containing gas from the first external source (200) and / or the supplemental gaseous hydrocarbon-containing gas from the second external source (210) with the exhaust gas treated in the recovery and treatment line (10); wherein the following steps are also provided transferring heat from the exhaust gas exiting the reactor (1) to a heat transfer fluid by means of the at least one first heat exchange device (22) of the recovery and treatment line (10); and wherein if the make-up gaseous-hydrogen-containing gas from the first external source (200) mixed with the exhaust gas treated in the recovery and 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 ducts (75) that carry the heat transfer fluid to the at least one second heat exchange device (72) of the treatment and feeding line (11), whereas if the make-up gaseous-hydrogen-containing gas from the first external source (200) mixed with the exhaust gas treated in the recovery and treatment line (10) is not available or insufficient for the direct reduction process, a make-up gaseous-hydrocarbon-containing gas from the second external source (210) is mixed with the exhaust gas or with the exhaust gas and the make-up gaseous-hydrogen-containing gas and the heat of the heat transfer fluid is completely or partially transferred to the at least one carbon dioxide removal device (50), respectively.

22. The process according to claim 21, wherein the following steps are also provided: adjusting the flow rate of the heat transfer fluid towards the at least one carbon dioxide removal device (50) by means of a first flow rate adjustment device (62); adjusting the flow rate of the heat transfer fluid towards the at least one second heat exchange device (72) by means of a second flow rate adjustment device (65); at least partially closing or opening a bypass duct (52) provided in the recovery and treatment line (10) for bypassing the at least one carbon dioxide removal device (50) by means of a third flow rate adjustment device (63); adjusting the flow rate of the make-up gaseous-hydrocarbon-containing gas to be fed to the gas circulation loop by means of a fourth flow rate adjustment device (32); adjusting the flow rate of the make-up gaseous-hydrogen-containing gas to be fed to the gas circulation loop by means of a fifth flow rate adjustment device (31).

23. The process according to claim 22, wherein the following steps are also provided: providing input data comprising a signal (118) indicative of availability data of the make-up gaseous-hydrogen-containing gas; processing the input data and sending, by means of a control unit (64) sending a first control signal (110) to the first flow rate adjustment device (62) for adjusting the flow rate of the heat transfer fluid towards the at least one carbon dioxide removal device (50); sending a second control signal (111) to the second flow rate adjustment device (65) for adjusting the flow rate of the heat transfer fluid towards the at least one second heat exchange device (72); sending a third control signal (112) to the third flow rate adjustment device (63) for at least partially closing or opening a bypass duct (52) for bypassing the at least one carbon dioxide removal device (50); sending a fourth control signal (114) to the fourth flow rate adjustment device (32) for adjusting the flow rate of the make-up gaseous-hydrocarbon-containing gas to be fed to the gas circulation loop; sending a fifth control signal (115) to the fifth flow rate adjustment device (31) for adjusting the flow rate of the make-up gaseous-hydrogen-containing gas to be fed to the gas circulation loop. and sending a fifth control signal (116) to said fifth flow regulating device (31) for regulating the flow rate of said make-up gaseous hydrogen-containing gas to be fed to said gas circulation loop.

24. Process according to claim 22, wherein if water is used to cool the effluent gas leaving the reactor (1) in said at least one first heat exchanger device (22), the heat transfer fluid in said conduit (75) is steam.

25. Process according to claim 23, wherein if water is used to cool the effluent gas leaving the reactor (1) in said at least one first heat exchanger device (22), the heat transfer fluid in said conduit (75) is steam.

26. Process according to claim 21, wherein the feeding of make-up gaseous hydrogen- containing gas from said first external source (200) and / or of make-up gaseous hydrocarbon- containing gas from said second external source (210) is provided in said treatment and feeding line (11) or in said recovery and treatment line (10).

27. The process of claim 26, wherein, In the case where the first external source (200) and the second external source (210) are connected to said treatment and feeding line (11), the feeding occurs in a section of the gas circulation loop comprising between a pumping device (42) of said recovery and treatment line (10) and at least one heating unit (180) of said treatment and feeding line (11).

28. Process according to any one of claims 22 to 25, wherein the feeding of make-up gaseous hydrogen-containing gas from said first external source (200) and / or of make-up gaseous hydrocarbon-containing gas from said second external source (210) is provided in said treatment and feeding line (11) or in said recovery and treatment line (10).

29. The process of claim 28, wherein, In the case where the first external source (200) and the second external source (210) are connected to said treatment and feeding line (11), the feeding occurs in a section of the gas circulation loop comprising between a pumping device (42) of said recovery and treatment line (10) and at least one heating unit (180) of said treatment and feeding line (11).

30. The process of claim 28, wherein, In the case where the first external source (200) and the second external source (210) are connected to said treatment and feeding line (11), the feeding occurs in a section of the gas circulation loop comprising between said at least one carbon dioxide removal device (50) or said bypass conduit (52) of said recovery and treatment line (10) and at least one humidifier (60) of said treatment and feeding line (11).

31. The process of claim 26, wherein, In the case where the first external source (200) and the second external source (210) are connected to said recovery and treatment line (10), the feeding occurs in a section of the gas circulation loop comprising between a washing and cooling unit (36) and a pumping device (42) of said recovery and treatment line (10).

32. The process of claim 28, wherein, In the case where a first external source (200) and a second external source (210) are connected to said recovery and treatment line (10), said feeding takes place in a section of said gas circulation circuit comprised between a scrubbing and cooling unit (36) and a pumping device (42) of said recovery and treatment line (10).

33. The process according to any one of claims 21 to 27 and 29 to 32, wherein an adjustment of the operating pressure of the system is provided to partially or totally compensate for the difference in molecular weight due to the different percentages of use of the make-up gaseous hydrogen-containing gas and of the make-up gaseous hydrocarbon-containing gas.

34. The process according to claim 28, wherein an adjustment of the operating pressure of the system is provided to partially or totally compensate for the difference in molecular weight due to the different percentages of use of the make-up gaseous hydrogen-containing gas and of the make-up gaseous hydrocarbon-containing gas.

35. The process according to claim 33, wherein an injection of nitrogen is provided both 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 carrier inside the reactor.

36. The process according to claim 34, wherein an injection of nitrogen is provided both 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 carrier inside the reactor.

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