MXPA98003292A - Method and apparatus for the production of direct reduction iron with a better utilization of reduced gas - Google Patents

Abstract

A method and apparatus for the production of iron by direct reduction, pre-reduced materials, or similar products, used in the manufacture of steel, with a better use of the reducing gas, which increases the productivity of the reduction plant. CO2 is separated from the gas stream that is normally purged from the system and used as a fuel. The resulting gas stream after CO2 removal is recirculated to the reduction zone, to chemically utilize the reducing potential of the recirculated reducing gas instead of using it as a fuel.

Description

METHOD AND APPARATUS FOR THE PRODUCTION OF DIRECT REDUCTION IRON WITH A BETTER UTILIZATION OF REDUCING GAS BACKGROUND OF THE INVENTION The direct reduction plants used to produce direct reduction iron, known as HRD or sponge iron, hot briquetted iron, or similar products, (in general pre-reduced material, usable as raw material to produce steel), currently produce it by contact of a reducing gas, composed mainly of hydrogen and carbon monoxide, at temperatures in the range of 750 ° C to 1050 ° C, with a bed of a material containing iron in the form of pellets, pieces or mixtures of both. The bed of the.-... -'- 'XX • material containing iron can remain static or can descend by gravity into the reduction reactor. Examples of such processes are described in U.S. Patent Nos. 3,749,386; 3,764,123; 3,816,101; 4,336,063; 4,428,072; 4,556,417; 5,078,787; 4,046,557; 4,002,422 and 4,375,983. From the past, it is known that in reducing systems the reduction gas and the oxides that are reduced reach an equilibrium, which does not allow to achieve the complete use of the reducing gas in the reduction reactor. Consequently, the plants currently in operation are equipped with means to recirculate and regenerate the reducing gas in order to minimize the requirements of spare reducing gas, but the need to purge a large portion of the available reducing gas is always maintained, in order to avoid accumulation. of carbon dioxide, and other inert elements within the system. The portion of gas that is. Purge is normally used as fuel in the reformer or in the gas heater of the system. This use as fuel recovers only the heat of! reducing gas but not the i chemical potential of hydrogen and carbon monoxide. If the chemical potential is used for the reduction of iron oxides, then the amount of spare gas needed for a given level of production, or from another point of view, decreases to increase production for the same reforming capacity. The regeneration of the reducing gas effluent from the reduction reactor includes the elimination of the products of the reduction reactions, for example carbon dioxide and water, which leave the reduction reactor in quantities dictated by the chemical equilibrium of those products with the residual hydrogen , carbon monoxide and methane or heavier hydrocarbons present in smaller amounts in the reducing gas. According to several prior art references, for example, U.S. Patent Nos. 2,547,685 to Brassert et al .; No. 4,584,016 to Becerra-Novoa et al .; No. 4,001, 010 to Kanbara et al .; No.4,129,281 to Ono et al. and No. 3,853,538 to Nemeth et al .; It is known to separate water and carbon dioxide from the gas stream to be recirculated to the reduction reactor.

All of these patents, however, teach the use of a CO2 separating unit, usually of the type in which the gas containing the CO2 is contacted with a liquid solution which reacts with said CO2, to treat the total amount of carbon dioxide. gas that will be recirculated. These chemical absorption systems must be provided with a heating source, usually supplied in the form of steam, to regenerate the solution, which in some applications is not available. The energy required for the regeneration of the CO2-absorbing solution, and the capital investment costs for high-capacity CO2 separator units are high compared to the physical adsorption CO2 separator units called PSA and VPSA for short. 3n English (Pressure Swing Adsorption and Vacuum Pressure Swing Adsorption).

In the prior art of direct reduction processes, it is not shown or suggested to recover more hydrogen from the purged gas and in this invention preferably a CO2 separation unit of the PSA type is used. This concept has as advantages that the unit is smaller because it treats only a small amount of the gas and hence the capital costs are lower, besides that the regeneration of the adsorbing agent is carried out by changes in pressure and not by heat. This type of gas separation produces a gas stream rich in hydrogen that can be advantageously recycled to the reactor system. The present invention involves the recirculation of a first portion of the effluent gas from the reduction reactor to said reactor and simultaneously the separation of a hydrogen-rich stream from the second portion of the effluent gas, where said portion is smaller, than the said first portion. The present invention is based on the principle of hydrogen separation from the reducing gas portion which is normally purged from the reactor system and used as a fuel. The invention then differs from the prior art in that the hydrogen and carbon monoxide recycled to the reduction reactor is effected in two ways: one is directly recirculating a portion of the effluent gas and the other is recirculating a stream with a hydrogen content obtained of a CO2 separation unit. With the present invention, hydrogen is recovered and used as a chemical reductant instead of burning it as fuel.

DETAILED DESCRIPTION OF THE INVENTION The invention is described herein as applied to direct reduction systems having mobile bed reactors, but it will be understood that it can be adapted to plants with fixed bed or fluidized bed reactors. With reference to Figure 1, the number 10 designates in general form the reduction reactor having a reduction zone 12 and a discharge zone 14. The solid particles containing iron oxides 16, for example iron ore in the form of pellets or pieces, is fed to the upper part of the reduction zone 12 and flows down through said reactor where the iron oxides are at least partially reduced to metallic iron and are finally discharged from the reactor through the discharge 14 as indicated by arrow 18. A stream of hot reducing gas 20, composed of reducing agents such as hydrogen and carbon monoxide, as well as some oxidants such as water and carbon dioxide produced by the reduction reactions of said oxides of iron, is fed to the lower part of the reduction zone 12, and is flowed upwards in countercurrent to the descent of the solid particles. The reducing gas leaves the reduction zone at the top as the reduction effluent gas stream 22, which is cooled with water in a direct contact cooler 24. This cooling and cleaning cleans the gas 22, the which usually contains powders, and also condenses and separates the water produced by the reduction reactions. The gas stream 22, once cool and clean, as a stream 26, is divided into the gas stream 28 and the gas stream 30. The gas stream 28 is moved by the means of. pumping 32, which can be a blower or a compressor depending on the operating pressure of the reduction system, and it is taken to the gas heater134 before being recycled into the reduction zone 12. ¿? "; Natural gas (and / or other reformable hydrocarbon) 36 combined with steam 38 is fed to a conventional gas-steam reformer 40 where it is reformed to hydrogen and carbon monoxide in a manner known in the art, producing a stream of hot reducing gas 42 which it is cooled in a cooler 44 resulting in a reducing gas stream 46 of high reducing power.This replacement gas stream 46 is added as a replacement to stream 28, producing a reducing gas 48, suitable for the efficient reduction of iron oxides The other portion of gas stream 26, designated as stream 30, which in prior art systems is normally used as a fuel in the reformer and in the gas heater, it is moved by a second pumping means 50 and then treated in a CO2 separating unit of the PSA or VPSA type 52, (both hereinafter referred to as PSA). The PSA unit uses adsorbent surfaces to adsorb most of the carbon dioxide from the gas stream 30 which also contains hydrogen, m, or carbon oxide, carbon dioxide, methane, water and nitrogen, and produces a hydrogen-rich stream. 54 with a hydrogen content between 92% and 99% volume and a lean stream 56 with a hydrogen content between 10% and 20% volume. The stream 54 with high hydrogen content is combined with the gas stream 48 formed by the replacement gas and recycled reduct gas producing a reducing gas stream 58 with a content. of H2: from 52% to 70% and CO: % to 17% in% volume and dry basis. The power! reducer and the quality of the gas stream 58 is higher compared to the composition of the reducing gas used in the prior art systems. The temperature of the reducing gas stream 58 is increased in the gas heater 34 to levels between 750 ° C and 1050 ° C, preferably between 900 ° C and 950 ° C, suitable for an efficient reduction of the iron oxides. Additionally, oxygen can be added o air enriched with oxygen to the reducing gas csliente 20 to obtain higher temperatures within the reduction zone with a corresponding increase in productivity or a lower thermal load in the gas heater for the same production. This productivity is increased since at higher temperatures the reaction rates increase and also the transformation of hydrocarbons present in the reducing gas to H2 and CO by the partial combustion of the reducing gas with oxygen. Poor gas stream 56 still contains carbon monoxide and methane, as well as small amounts of other gaseous hydrocarbons which have calorific value and can be used as fuel in the gas heater 34. The energy in the gas stream 56 is usually insufficient to meet the heating needs of the heater. . way that it is necessary to feed natural gas or other fuel 62 as a complement to said current 56. The direct reduction iron (HRD) or the prereduced material 18 produced in the reduction zone 12 can be discharged at high temperature, in the order of 400 ° C to 700 ° C and can be hot-briquetted or pneumatically transported to steelmaking ovens, for example electric arc furnaces, thus reducing the energy needs in steelmaking. Optionally, the HRD is cooled in the discharge zone 14 by contacting the hot HRD with a stream of cooling gas 66 which must not oxidize the HRD and can be natural gas, a portion of the reducing gas stream 30 or the current 56. The current, gas 68 se. It is cooled and recirculated as the stream 66 in a manner known in the art.

Referring now to Figure 2, where the same numbers are used to designate the same elements as in Figure 1, this embodiment illustrates the invention incorporated into a reduction system where the reducing gas is not generated in a natural gas reformer. steam but is generated by the reformation of natural gas by the partial combustion of the methane present in the reducing gas with oxygen and also by the "cracking" or decomposition and reformation of methane with the oxidants present in the reduction zone by the action catalytic activity of iron-containing particles in said reduction zone. In this embodiment, the steam reformer is not required and the natural gas replacement stream 36 is added directly to the recirculated gas stream 28, which is combined with the hydrogen-rich stream 54 to produce a combined gas stream 58. The water content in the gas stream 58 is adjusted by the addition of the water / steam stream 67 so that the amount of water present is between 3% and 10% by volume, to carry out said methane reformation within of the reduction zone.

This regulation of the water content can be performed for example as described in U.S. Patent 5,110,350 where the added water 66 is advantageously taken from the hot water effluent df I gas cooler 24. Figure 3 illustrates the invention applied to a system of reduction where the reducing gas is generated in a reformer of the type where the natural gas is combined with recirculated gas from the reduction reactor and reacts with oxidants as the CO2 and H2O present in said recirculated gas. Examples of these reduction systems are illustrated in the US Patents Nos. 3,748,120 and 3,749,386. In this type of reduction systems, the reformer 40 is fed with a combination of natural gas 36 and recirculated gas 28, and the reducing gas produced leaves the reformer at a temperature between 800 ° C and 950 ° C. In this embodiment the temperature of the reducing gas can be increased by the addition of an oxygen or air stream enriched with oxygen 60 for the purpose of increasing the productivity of the reduction reactor. For existing reduction systems, the reformer 40 will probably not have sufficient capacity to heat an additional amount of gas and consequently it is required to provide a gas heater 34 for this purpose. Referring now to Figure 4, the process diagram shown here illustrates a mode as shown in Figure 3 where the hydrogen-rich stream 54 is heated in the reformer 40 without the need for a separate heater, assuming the reformer has enough heating capacity to heat the additional amount of hydrogen-rich gas 54.

Although it is preferable to provide an additional heater as shown in Figure 3, because in this way the recirculated stream of hydrogen-rich gas 54 does not need to pass through the reformer catalyst bed 40, it is possible to design new reduction systems without said separate heater 34. An example of the process claimed herein calculated for a potential implementation in an existing reduction system of the type illustrated in Figure 3 is as follows: A reducing gas 46 produced in a 40 'reformer has the following composition in% volume and dry base: H2: 50% to 60%; CO: 30% a 37%; CO2: 2% to 3.5%; CH4: 1% a.3%; N2: 0% to 1.5% and the rest hydrocarbons and inert gases. This gas is fed, as a replacement, to the reduction system as the current 46. About 50% of the gas in the upper part of the reduction zone is divided as the current 30, with. A former on dry basis and a% volume as follows: H2: 35% to 45%; CO: 18% to 25%; CO2: 10% to 20%; CH4: 2% to 4%; N2: 0% to 3% compressed and passed to an adsorption system PSA. A gas stream 54 with a content of hydrogen in% volume and a dry base between 90% and 99% is then obtained. The recovery of hydrogen from the gas stream 30, which is now used as a chemical reducer instead of being used only as fuel, produces an increase in the production of the reduction reactor in the best conditions greater than 50%.

From the above description it can be seen that the present invention provides a process capable of achieving the objects of the invention mentioned above.

This provides a new and exceptionally efficient method for increasing the production capacity of existing reduction systems by the advantageous use of hydrogen, which in the prior art was burned as fuel, instead of taking advantage of its chemical reducing potential. It should be understood that the foregoing description is intended to be illustrative only and that numerous changes may be made in the structure of the described system and in its operating conditions without departing from the spirit of the invention. how the claims are defined.

FIELD OF THE INVENTION The present invention relates to a method and apparatus for the production of prereduced iron ore, Iron Direct Reduction (HRD), Iron Sponge, or other similar product, in a reduction system comprising a reduction reactor, a source of natural gas, which is transformed in the operation of said system by a reformer, or by the catalytic action of metallic iron in said reducing reactor, to a reducing gas composed of carbon monoxide to hydrogen as its main components, and a heating device for heating said reducing gas before its introduction to said reduction reactor. More specifically, the invention relates to a method and apparatus that allows a better use of the reducing chemical potential of the reducing gas in the reduction system with a corresponding increase in the productivity of said reduction reactor or a decrease in the necessary amount of gas replacement for a certain level of production. This invention provides a way to increase the productivity of existing direct reduction systems with lower investment and operating costs when compared to the alternative of increasing the capacity of the reducing gas generator: or the known measure of installing a system for the removal of carbon dioxide in the. recycle stream of the reducing gas.

OBJECTIVES OF THE INVENTION It is therefore an objective of the present invention to provide a method and apparatus for producing direct reduction iron in a reduction system where the productivity of said system is increased - by the recirculation of a second reducing gas stream. from which the carbon dioxide has been separated. It is another object of the invention to provide a method and apparatus for increasing the productivity of a direct reduction system and at the same time lowering the investment and operation costs necessary for the aforementioned increase in productivity. Other objects and advantages of the invention will be apparent to those skilled in the art or will be described in this specification of the invention and the accompanying drawings. According to the present invention, the aforementioned objects are achieved by providing a method and apparatus as follows:, Jl;,.)? , A method for producing iron by direct reduction, comprising feeding a reducing gas composed mainly of hydrogen and carbon monoxide and also containing methane, carbon dioxide and water, heated at a temperature between 850 ° C and 1050 ° C, to a reduction reactor within which solid particles containing oxides are reduced by the reaction of said iron oxides with said reducing gas; extracting said reducing gas from said reactor after reacting with the iron oxides as a reducing effluent gas; cooling, cleaning and dehydrating said reducing effluent gas; recirculating a first portion of said reducing effluent gas to the reduction reactor; separating CO2, preferably in a PSA or VPSA adsorption unit, from a second portion of! said reducing effluent gas to form a gas stream rich in hydrogen and a gas stream poor in n hydrogen; and recirculating said hydrogen-rich gas stream to said reduction reactor. The objects of the invention are also achieved by providing an apparatus for producing direct reduction iron comprising a reduction reactor having a reduction zone with a gas inlet and a gas outlet; a gas cooler connected to the gas outlet of said reduction zone; a reducing gas heater communicated with the gas inlet to said reduction zone; first pumping means connected to said cooler and said heater to recirculate the reducing gas from said gas outlet to said gas inlet; driving means for diverting a portion of the reducing gas effluent from said gas outlet from the reduction zone to second pumping means; a CO2 separation unit preferably of the PSA or VPSA type; and driving means communicating said second pumping means to said CO2 separation unit; and means for driving to communicate said CO2 separating unit co? the gas inlet of said reduction zone.

DETAILED DESCRIPTION OF THE DRAWINGS In this specification and in the accompanying drawings, some embodiments of the invention are shown and described and various alternatives and modifications thereof are suggested; but it will be understood that these are not shown exhaustively and that many other changes and modifications may be made within the scope of the invention. The aforementioned suggestions have been selected and included for purposes of illustration so that other experts in the art better understand the invention and the principles thereof and then they are able to modify it in a variety of ways, each of which as best suits the conditions of a particular use. . Figure 1 shows schematically one of the preferred embodiments of the present invention, illustrated by a diagram of a moving bed process for the production of direct reduction iron, where the reducing gas source is a natural gas-steam reformer conventional. Figure 2 schematically shows another embodiment, of j and jyption where a reformer is not necessary and the natural gas is transformed into hydrogen and carbon monoxide within said system, particularly within said reduction reactor, by the catalytic action of the reduced iron present in said reactor. Figure 3 schematically shows another embodiment of the invention where the reducing gas is produced within the reduction system by a CO2-natural gas reformer of the combination of natural gas and recycled reducing gas. In this embodiment, the recovered hydrogen is heated in a separate heater and fed to the reduction reactor without passing through said reformer.

Figure 4 schematically shows the embodiment shown in Figure 3, with the difference that the hydrogen-rich stream is combined with the recycle reducing gas and heated in the reformer without the need for a separate gas heater.

Claims (8)

R E I V I N D I C A C I O N E S 'd •': Having sufficiently described my invention, I consider as a novelty and therefore claim as my exclusive property, what is contained in the following claims:

1. - A method to produce direct reduction iron, prereduced materials or similar products, with a better use of the reducing gas that comprises feeding a first stream of reducing gas, composed mainly of hydrogen and carbon monoxide and also containing methane, carbon dioxide and water, heated to a temperature between 850 ° C and 1050 ° C, to a reduction zone of a reduction reactor, inside which solid particles containing iron oxides are reduced by the reaction of said iron oxides with the reducing gas; extracting from said reduction zone a second stream of reducing gas effluent from the reactor after reacting with said iron oxides; cooling and cleaning said second stream of effluent gas from the reactor and separating water therefrom by a third stream of reducing gas; recirculating a first portion of said third reducing gas stream to said reduction zone; separating carbon dioxide from a second portion of said third effluent gas stream from the reactor to form a fourth stream of reducing gas; and recirculating said fourth reducing gas stream to the reduction zone of the reduction reactor to form said first reducing gas stream. You; í} / , Y.

2. A method for producing direct reduction iron according to claim 1, wherein the separation of carbon dioxide from said second portion of third current is done by means of an adsorption unit of the PSA type or a unit of Adsorption of the VPSA type.

3. A method for producing direct reduction iron according to claim 1, further comprising introducing oxygen or air enriched with oxygen to the first reducing gas stream before being fed to said reduction zone.

4. A method for producing direct reduction iron according to claim 1, further comprising producing a replacement reducing gas in a natural gas / steam reformer and combining a replacement reducing gas stream with said first portion of the third stream of reducing gas.

5. A method for producing direct reduction iron according to claim 1, further comprising producing a replacement reducing gas in a natural gas reformer / CQ2 ^, circulating said first portion of the third reducing gas stream to through said reformer. ..,. > .,.

6. A method for producing direct reduction iron according to claim 5, further comprising heating said fourth stream of reducing gas in a gas heater separated from said reformer.

7. A method for producing iron of direct reduction non-conformity with claim 1, further comprising combining a stream of natural gas with said third stream of reducing gas and heating them to form said first stream of gas. reducer, whereby the reducing reducing gas is formed in said reduction reactor taking advantage of the catalytic action of the iron present in said reactor.

8. An apparatus for producing direct reduction iron, pre-reduced materials or similar products, with a better use of the reducing gas, comprising a reduction reactor having a reduction zone with a gas inlet and a gas outlet; a gas heater connected to the gas outlet of said reduction zone; a connected with the entrance of! gas from said reduction zone; first pumping means connected to said cooler and said heater for recirculating the reducing gas from the gas outlet from the reduction zone to the gas inlet of the reduction zone; driving means for directing a portion of the reducing gas stream effluent from said reduction zone to second pumping means; a separating unit CO2; driving means communicating said second pumping means with said CO2 separating unit; and driving means for communicating said CO2 separation unit with the gas inlet to said reduction zone. An apparatus for producing direct reduction iron, pre-reduced materials or similar products according to claim 8, wherein said .COs separating unit is of the chemical absorption type. An apparatus for producing iron, direct reduction, pre-reduced materials or similar products in accordance! with claim 8, wherein said CO2 separating unit is of the PSA or VPSA physical adsorption type.