Production of carburized sponge iron by direct reduction of iron ore-containing feedstock and corresponding direct reduction plant

Abstract

The invention relates to a process for the climate-friendly, in particular CO2-neutral, production of carburized sponge iron by direct reduction of starting material containing iron ore by means of a hot reaction gas in a reduction zone of a reactor (12), wherein at least one gas is introduced into the reduction zone. It is planned that several gases will be introduced into the reduction zone, one of which is CO2, in order to achieve carburization of the sponge iron formed by the direct reduction with a temporal overlap with the direct reduction of the starting material in the reduction zone. The invention further relates to a corresponding direct reduction plant (10).

Description

The invention is based on a process for the climate-friendly, in particular CO 2- neutral, production of carbonized sponge iron by direct reduction of starting material comprising iron ore by means of a hot reaction gas in a reduction zone of a reactor, in which at least one gas is introduced into the reduction zone.The invention furthermore relates to a corresponding direct reduction plant for the climate-friendly, in particular CO 2- neutral, production of carbonized sponge iron by direct reduction of starting material comprising iron ore by means of a hot reaction gas in a reduction zone in the interior of a reactor of this direct reduction plant, having a line system via which at least one gas can be introduced into the reduction zone.An activity-here of the production of sponge iron-is referred to as climate-friendly if a significantly reduced discharge of greenhouse gases into the atmosphere takes place with this activity, which reduces the extent of the greenhouse effect. The term greenhouse gas neutrality is accordingly used for activities in which either no greenhouse gases are emitted into the atmosphere or in which the emissions are completely compensated for by "negative emissions" of these gases, that is to say that there is no overall increase in the concentration of these gases in the atmosphere. One of these greenhouse gases is CO 2( carbon dioxide), which is formed above all by the combustion of fossil fuels and accumulates in the atmosphere. The term CO 2- Neutral accordingly describes activities in which no CO 2 at all is emitted or in which existing CO 2- emissions are completely compensated.For the production of sponge iron by direct reduction, which is neutral or at least low in CO 2- by direct reduction, the use of hydrogen (H 2) as reducing gas is frequently stimulated, which in turn is generated by means of renewable energies. As an example, the document US2009 / 0249922 A1 is mentioned here, where hydrogen is generated for the direct reduction by means of electrolysis, which in turn is operated by means of regenerative energy.However, a sponge iron produced in this way has no carbon content or only an extremely low carbon content, which is disadvantageous both for the storage of the sponge iron and for further processing to steel of most types of steel. Therefore, several possibilities for carburizing the sponge iron are known, in which the carburizing takes place in the direct reduction plant and / or in the downstream process in the (electric) furnace.The production of sponge iron in the reactor comprises two basic steps: in a first step, the reduction of the iron ore to sponge iron is carried out in one or more reduction zone(s) with a suitable hot reducing gas. In a downstream second step, the sponge iron produced is cooled down to significantly lower temperatures in a cooling zone by means of a cooling gas.The reducing gas in the reduction zone is essentially composed of hydrogen (H 2) and carbon monoxide (CO) in conventional operation, and is exposed to temperatures in the range from 850° C. to 1100° C. The process gas methane (CH 4) in combination with oxygen (O 2) is often used as the basis for forming the reducing gas, which methane reacts with hydrogen and carbon monoxide and also to carbon dioxide (CO 2) and water (H 2 O) by a catalytic process in the reduction zone or as an upstream process to form the reducing gas. The carbon monoxide already carbonizes the sponge iron slightly. The carbon content in the sponge iron in this way reaches about 1 to 1.5% by weight. By using methane as cooling gas in the cooling zone, the sponge iron can then be further carbonized, so that it can have a carbon content of up to 6% by weight on leaving the cooling zone. Such a process may be more climate friendly than the corresponding blast furnace process using coke coal. However, no mention may be made of a climate-friendly or even CO 2- neutral production of carbonized sponge iron in such a direct reduction process using methane, since relatively large amounts of CO 2. are formed.The document DE 10 2019 217 631 A1 describes a process for the climate-friendly production of carbonized sponge iron by direct reduction of starting material comprising iron ore by means of a reaction gas which is introduced into a reduction zone of a reactor and has a high hydrogen content (H 2- content), wherein the carbonization, after the reduction, takes place in the cooling zone with a cooling gas mixture which in turn has hydrogen and carbon dioxide with a molar ratio of hydrogen to carbon dioxide of greater than 1.8:1 and in which the molar ratio of carbon dioxide is greater than 20 mol %. The temperature of the sponge iron on entry into the cooling zone is used here from 850° C. to 1000° C. in order to use the sponge iron as catalyst for the Bosch reaction, in which carbon deposits from the carbon dioxide on the sponge iron and then forms Fe 3 C there. The size of the region in which the carburizing can / takes place depends strongly on the degree of the cooling set.It is an object of the invention to specify a method and a direct reduction plant for the climate-friendly production of carbonized sponge iron by direct reduction, which, under the conditions of climate-friendly production, make possible effective carbonization with a wide range for the carbon content to be adjusted in the sponge iron.The object is achieved according to the invention by the features of the independent claims. Preferred embodiments of the invention are specified in the dependent claims, which can each represent an aspect of the invention individually or in combination.In the method according to the invention for the climate-friendly, in particular CO 2 neutral, production of carbonized sponge iron by direct reduction of raw material containing iron ore by means of a hot reaction gas in a reduction zone of a reactor, in which at least one gas is introduced into the reduction zone, it is provided that a plurality of gases are introduced into the reduction zone, one of which is 2 in order to achieve carbonization of the sponge iron formed by the direct reduction with temporal overlap for the direct reduction of the raw material in the reduction zone. The reactor for the direct reduction is preferably of the shaft furnace type, which is filled from above with the starting material containing iron ore. A plurality of gases are introduced into the reduction zone of this reactor, namely, on the one hand, at least one reaction gas itself or alternatively a gas for providing reaction gas(s) within the reduction zone by in situ reforming in the reactor, and, on the other hand, carbon dioxide (CO 2) for carburizing the sponge iron produced by direct reduction. This carbon dioxide is deliberately supplied to the corresponding direct reduction plant from the outside. The reducing gas or at least one of the reducing gases is hydrogen (H 2). This hydrogen is in turn preferably generated by means of renewable energies. By introducing CO 2 into the reduction zone, carbon monoxide (CO) and water vapor (H 2 O) are produced at the temperatures present there of more than 850° C. by partial reduction of the CO 2 by means of the hydrogen (H 2). This carbon monoxide (CO) then ensures the carbonizing of the sponge iron formed. This can be present both as DRI (DRI: Direct Reduced Iron) and as HBI (HBI: Hot Suppressed Iron).In a direct reduction plant in which in situ reforming is provided in the reactor, the hydrogen is formed only in the reactor itself. However, it is generally advantageously provided that one of the gases introduced into the reduction zone is hydrogen (H 2). The H 2- proportion of the gases introduced into the reduction zone is in particular more than 60 mol %. Furthermore, in particular, at least two of the gases are introduced together as a gas mixture into the reduction zone. These are preferably hydrogen (H 2) and carbon dioxide (CO 2). In this way, the formation of carbon monoxide for carburizing can be prepared in a targeted manner.According to a further preferred embodiment of the invention, the carbon of the carbon dioxide (CO 2) introduced into the reduction zone is of biogenic origin. If the CO 2 is not of fossil origin (i.e. from biogenic raw / residual materials), a negative CO 2- emission is caused by the carburizing of the starting material ("Fe carrier" for short). This makes it possible for a corresponding huttenwork, if only biogenic C-carriers are likewise used at other sites, to have an overall negative CO 2- balance and thus become the CO 2- sink.According to a further preferred embodiment of the invention, the carbon of the carbon dioxide (CO 2) introduced into the reduction zone is of fossil origin. Here too, a CO 2- sink results-this time by the binding of the carbon of fossil origin from the CO 2 in / on the sponge iron.Preferably, a portion of the carbon monoxide (COs) produced in the reduction zone is discharged from the reactor. This part of the carbon monoxide can then be used for other purposes, for example in the chemical industry. The carbon monoxide is generally discharged via a line system connected to the reduction zone, via which the carbon dioxide (CO 2) is also introduced into the reduction zone.According to yet another preferred embodiment of the invention, the carbonized sponge iron has a carbon content which is in the range from 0.5% by weight to 4.5% by weight on leaving the reactor. Such a carbon content is particularly advantageous for further processing to steel.Furthermore, it is preferably provided that the sponge iron is cooled in a cooling zone adjoining the reduction zone by means of a cooling gas or cooling gas mixture introduced there. If the cooling gas or one of the cooling gases is carbon-containing (for example a hydrocarbon of biogenic origin), the sponge iron can be selectively further carbonized during cooling.When cooling the sponge iron, it is provided in particular that at least a portion of the carbon monoxide discharged from the reactor as an exhaust gas stream is used as a portion of the cooling gas or cooling gas mixture. For this purpose, the carbon monoxide previously discharged as the exhaust gas stream is introduced into the cooling zone of the reactor via a cooling circuit.In the direct reduction plant according to the invention for the climate-friendly, in particular CO 2- neutral, production of carbonized sponge iron by direct reduction of raw material containing iron ore by means of a hot reaction gas in a reduction zone in the interior of a reactor of this direct reduction plant, which has a line system via which at least one gas can be introduced into the reduction zone, it is provided that a plurality of gases can be introduced into the reduction zone via this line system, wherein one of these gases is CO 2 in order to achieve carbonization of the sponge iron formed by the direct reduction with temporal overlap for the direct reduction of the raw material in the reduction zone. The direct reduction plant has in particular a source for the CO 2 in this case.Advantageous possible embodiments and advantages resulting therefrom, which were mentioned in connection with the previously described method according to the invention for the climate-friendly production of carbonized sponge iron, apply analogously also to the direct reduction plant according to the invention.According to a preferred embodiment of the direct reduction plant according to the invention, it is provided that the interior of the reactor also comprises a cooling zone downstream of the reduction zone, into which a cooling gas or cooling gas mixture is introduced.The invention is explained below by way of example with reference to the attached drawing on the basis of a preferred exemplary embodiment, wherein the features illustrated below can represent an aspect of the invention both individually and in combination. It shows: FIG. 1 shows a plant for the climate-friendly production of carbonized sponge iron by direct reduction of starting material comprising iron ore according to a preferred embodiment of the invention.FIG. 1 shows a direct reduction plant 10 for the climate-friendly production of carbonized sponge iron (DRI: Direct Reduced Iron or HBI: Hot Cooled Iron) in an exemplary schematic illustration. The direct reduction plant 10 comprises a reactor 12 for the actual reaction, i.e. the direct reduction, and a feed device 14 arranged above the reactor 12 for feeding material comprising iron ore (arrow 16) into the reactor 12, wherein this material is present in the form of bulk material. This bulk material is generally composed of lump ore, pellets, sintered material or a mixture thereof. For this purpose, the feed device 14 is arranged above the reactor 12 and has a lock device 18, via which the bulk material is introduced into the reactor 12. The reactor 12 extends in the vertical direction from an upper side 20 along its central longitudinal axis 22 as far as a lower end 24, and it has a reactor container 26, in the interior of which-i.e. the interior of the reactor 12-the corresponding reactions take place. For this purpose, a reduction zone is located in an upper part 28 of the reactor 12 in which the Fe from the iron ore is reduced, and a cooling zone is located in a lower part 30 of the reactor 12 in which the sponge iron formed can be / is cooled. The lower part 30 of the reactor 12 is conically shaped and converges at the lower end 24 in an outlet 32 for the optionally still hot or cold sponge iron, which can be removed there from the reactor 12 (arrow 34).The direct reduction device 10 has the following function: The material containing iron ore (arrow 16) is fed to the reactor 12 via the lock device 18. The individual particles of the material thus supplied descend through the reduction zone of the reactor 12 and react at high temperature (850° C. to 1100° C.) in countercurrent contact with a reducing gas containing hydrogen (H 2) which is supplied to the reactor 12 together with carbon dioxide (CO 2) via a line system 36. For this purpose, the corresponding gases, i.e. in particular also the carbon dioxide (CO 2), are introduced into the line system 36 from the outside via at least one access 45. The resulting gas mixture is introduced at an inlet via a line 38 of the line system 36 into the reactor 12 which opens into the lower part of the reduction zone. In the example shown, the gas mixture introduced into the reduction zone contains more than 75 mol % of H 2. Due to the high temperatures in the reduction zone of the reactor 12, the carbon dioxide reacts with the hydrogen to form carbon monoxide and water vapor. The carbon monoxide then subsequently ensures the carburizing of the sponge iron formed / formed in that carbon deposits from the carbon dioxide on the sponge iron and Fe 3 C (cementite) then forms there. As stated, the reducing gas in the reduction zone contains a high hydrogen content, so that the reduction of the iron ore to sponge iron is essentially based on the reaction Fe 2 O 3+ 3 H 2 ->2 Fe+3 H 2 O.In the upper part of the reduction zone, gas is then taken from the reactor 12 at an outlet via a further line 40 of the line system 36. However, a major portion of this re-drawn gas continues to have its reducing potential and is then recycled to the reactor 12 at the inlet via line 38 in a circuit of line system 36. "Excess" carbon monoxide (CO) is discharged from line system 36 via a purification / treatment device 42 as a CO exhaust stream 44. In this way, a portion of the carbon monoxide generated in the reduction zone is discharged from the direct reduction plant 10.The cooling zone is located in the lower part 30 of the reactor 12. This part 30 is preferably conically shaped converged to the outlet 32, through which the already reduced ore, i.e. the sponge iron or the DRI, is discharged hot or cold. In the cooling zone in the lower part 30 of the reactor 12, a cooling gas stream (with a comparatively cool, non-oxidizing, inert or reducing gas, for example hydrogen) is normally circulated in countercurrent in order to extract heat from the hot sponge iron / DRI, among other things. This cooling gas is introduced through a cooling gas conduit 46 into a lower portion of the conically shaped lower part 30 of the reactor 12 and is removed from an upper portion of the lower part 30 of the reactor 12 heated by another cooling gas conduit 48 and then returned in a closed circuit back to the conduit 46. In this resulting cooling circuit 50 of the direct reduction plant 10, the hot gas is purified and cooled before being reintroduced into the reactor 12. For this purpose, the cooling circuit 50 comprises a cooler 52 and a compressor 54. In addition, in the example shown, it is provided that at least a portion of the carbon monoxide discharged from the reactor 12 as exhaust gas stream 44 is used as part of the cooling gas or cooling gas mixture. For this purpose, the carbon monoxide previously discharged as exhaust gas stream 44 is introduced into the cooling zone of the reactor 12 via a feed line 56 to the cooling circuit 50 and its cooling gas line 46.When it is desired to discharge the sponge iron / DRI at high temperature, the cooling circuit 50 is shut down and the DRI does not experience some form of active cooling before being discharged from the reactor 12 via the outlet 32, for example for hot coupling to an electric arc furnace (EAF).The inventive carburizing of the sponge iron by means of CO 2 already in the reduction zone of the reactor 12, i.e. with temporal overlap for the direct reduction of the starting material, results in a simple and effective possibility for realizing a reduction process based on 100% hydrogen, in which the sponge iron produced is provided with an adjustable carbon content with a simultaneous reduction of the CO 2- emissions.By using biogenic CO 2 a CO 2- sink can be established in a corresponding huttenwork which can even ensure negative CO 2- emissions in otherwise CO 2- neutral operation. By using CO 2 for carburizing the sponge iron (DRI / HBI) in the direct reduction plant, it is also possible to reduce the use of injection coal in the electric arc furnace (EAF), since the carbon from the carbonized DRI / HBI is likewise used for foaming the slag in the furnace.Reference numerals denote reference numerals10 Direct reduction plant 12 Reactor 14 Feed device 16 Arrow (starting material) 18 Lock device 20 Upper side 22 Longitudinal axis (reactor) 24 Lower end 26 Reactor container 28 Upper part (reduction zone) 30 Lower part (cooling zone) 32 Outlet 34 Arrow (sponge iron) 36 Line system 38 Line (reducing gas) 40 Further line 42 Cleaning / conditioning device 44 CO exhaust gas stream 45 Access 46 Cooling gas line 48 Further cooling gas line 50 Cooling circuit 52 Cooler 54 Compressor 56 Feed lineReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedUS 2009 / 0249922 A1

[0004] DE 10 2019,217 631 A1

[0008]

Claims

A process for the climate-friendly, in particular CO 2- neutral, production of carbonized sponge iron by direct reduction of raw material containing iron ore by means of a hot reaction gas in a reduction zone of a reactor (12), wherein at least one gas is introduced into the reduction zone, characterized in that a plurality of gases are introduced into the reduction zone, one of which is CO 2 in order to achieve carbonization of the sponge iron formed by the direct reduction with temporal overlap for the direct reduction of the raw material in the reduction zone.Process according to Claim 1, characterized in that a further one of the gases H introduced into the reduction zone is 2.Process according to Claim 2, characterized in that the H 2- fraction of the gases introduced into the reduction zone is more than 60 mol%.Process according to any one of Claims 1 to 3, characterized in that the carbon of the CO 2 introduced into the reduction zone is of biogenic origin.Process according to any one of Claims 1 to 3, characterized in that the carbon of the CO 2 introduced into the reduction zone is of fossil origin.Process according to one of Claims 1 to 5, characterized in that some of a carbon monoxide generated in the reduction zone is discharged from the reactor (12).Method according to one of Claims 1 to 6, characterized in that the carbonized sponge iron has a carbon content which is in the range from 0.5% by weight to 4.5% by weight on leaving the reactor (12).Method according to one of Claims 1 to 7, characterized in that the sponge iron is cooled in a cooling zone adjoining the reduction zone by means of a cooling gas or cooling gas mixture introduced there.Method according to Claim 8, characterized in that at least some of the carbon monoxide discharged from the reactor (12) as an exhaust gas stream (44) is used as part of the cooling gas or cooling gas mixture.Direct reduction plant (10) for the climate-friendly, in particular CO 2- neutral, production of carbonized sponge iron by direct reduction of raw material containing iron ore by means of a hot reaction gas in a reduction zone in the interior of a reactor (12) of this direct reduction plant (10), having a line system (36) via which at least one gas can be introduced into the reduction zone, characterized in that a plurality of gases can be introduced into the reduction zone via this line system (36), wherein one of these gases is CO 2 in order to achieve carbonization of the sponge iron formed by the direct reduction with temporal overlap for the direct reduction of the raw material in the reduction zone.

Images