DE1270581B - Process for reducing iron oxide - Google Patents

Description

Process for reducing iron oxide The present invention relates to on the reduction of iron oxide and in particular on a process in which the iron oxide is first partially reduced with hydrogen and then the reduction is continued using carbon monoxide.

The present invention is an improvement on that disclosed in the UK Patent 751105 described process in which iron oxide is reduced, by putting very pure hydrogen through one at such a rate upwards Bed of finely divided iron oxide is performed that this bed moves or whirled is, with this moving bed at a reaction temperature of 370 to 540 ° C and a pressure of 14 to 42 kg / cm2 is maintained. The maximum water vapor content of the highly purified hydrogen is related to the reaction temperature and at a reaction temperature of 370 ° C is not more than 0.5 percent by volume and a reaction temperature of 540 ° C not more than 3 percent by volume, based in each case on the hydrogen content of the highly purified hydrogen. A similar process is described in U.S. Patent 2,805,144, one being richer in hydrogen reducing gas stream is preheated to a temperature that is at least about 28 ° C, preferably at least about 55 ° C, higher than the temperature at which the reduced iron particles tend to agglomerate. This hydrogen stream is then in indirect heat exchange with a fluidized bed of iron oxide particles brought into contact until the temperature of the preheated stream dropped so much is that the current is then brought into direct contact with the swirled particles without causing agglomeration.

These recently developed reduction processes suffer like all previous ones Processes in which iron oxide is reduced by hydrogen have the disadvantage that with increasing content of reduced or free iron in the reaction mass the permissible moisture content of the hydrogen decreases. So is for a typical Hematite ore at the beginning of the reduction a hydrogen with 5 volume percent water vapor readily permissible, while after an 80 percent reduction of the oxide the The moisture content of the hydrogen should be less than 2 percent by volume continue the reduction effectively. When 95% of that hematite ore has been reduced the permissible maximum moisture content of the hydrogen drops to 0.2 Percentage by volume, as otherwise the reduction practically comes to a standstill. This appearance explains the absolute need to remove the water of reaction from the recycled Hydrogen must be removed before reintroducing it into the reduction vessel. As the reduction progresses and the free iron content in As the reaction mass in the reaction vessel grows, the need for hydrogen increases attributed, more and more. With this return of the hydrogen, the will not Used hydrogen is first cooled, then water is removed from it, the remainder Hydrogen is heated and compressed for the desired return into the reaction vessel. These steps in the hydrogen recycle add to the cost of the reduction.

An essential aim of the present invention is to provide technical and to lessen economic disadvantages associated with continuing the reduction of iron oxide with hydrogen occur if a substantial reduction has already been achieved has been.

The inventive method for reducing iron oxide, in which Iron oxide partially reduced, the partially reduced iron oxide with carbon monoxide brought into contact and thereby on the surface of the partially reduced iron oxide Carbon is deposited, after which the carbon-coated iron oxide particles for their further complete reduction into metallic iron to one temperature are heated by more than 700 ° C, is now characterized in that the partial Reduction of the iron oxide with hydrogen at a pressure of at least 14 kg / cm2 and a temperature of 370 to 540 ° C up to 40 to 95 percent Reduction is carried out.

It is already known from German patent specification 678326 that iron oxide at temperatures above 800 ° C to 20 to 30% with a gas mixture, such as z. B. carbonic acid and water vapor, can partially reduce. This procedure is due to the higher temperature to be used, the other reducing temperature to be used Gases and the lower reduction of iron oxide in the first stage different from the claimed method. The technical progress compared to the known process is that, according to the invention, the reduction only takes place in two stages is carried out and that powdered ore is also used by means of fluidized bed processes due to the low temperatures an agglomeration of the particles is avoided. Compared to the reductions in which only hydrogen is used as the reducing agent is used, there is the advantage that the last percent of iron oxide is in the present two-stage process can be reduced faster than with one one-step process in which only hydrogen is used as a reducing agent.

Even if all known processes for the reduction of iron oxide with Hydrogen can be used to carry out the first stage of this process, so it is very advantageous to carry out the reduction as in the above mentioned British and United States patent specification is described, since such a obtained, partially reduced iron oxide shows unusual reactivity with carbon monoxide shows. It is believed that the reduced or free iron in such partially reduced particles even the deposition of carbon from carbon monoxide catalyzed. The term "carbon deposition" as used herein in general The sense used does not only include free carbon that is physically adheres to the treated particles, but also carbon that interacts with the Iron in these particles chemically combines to form an iron carbide. There is the Assumption that the reduction during the third or final stage of the invention The more carbon is deposited than iron carbide, the faster the process takes place is present instead of free carbon. Instead of the well-known reduction of iron oxide with hydrogen at temperatures between about 650 to 760 ° C, that too can recently developed process for reduction at temperatures not exceeding approximately 540 ° C be used to obtain a partially reduced iron oxide, which the carbide formation during the subsequent treatment with carbon monoxide is severe favored.

The first step in reducing iron oxide with hydrogen, preferably at temperatures in the range from 400 to 540 ° C, is carried out so that an essential and preferably the major part of the reduction of the iron oxide takes place, d. that is, at least 40%, and preferably greater than 50%, of that for manufacture of the finished iron to be removed is removed. In no case will by the first partial reduction with hydrogen more than 95% of the to be removed, chemically bound oxygen in iron oxide removed. In general, the preferred range of reduction in this first stage from 60 to 90% of the total oxygen to be removed.

Albeit different methods of reducing the iron oxide particles can be used with hydrogen, but the fluidized bed technology that used in the process of the aforementioned British patent is preferred. The reducing gas used in the first stage of the process is not only rich in hydrogen but should also have a small amount of carbon oxides contain, d. i.e. not more than 2 to 3 percent by volume and usually less than 1 percent by volume, based on the hydrogen content of the reducing gas. The precise control the moisture content of the reducing gas (see also the British patent specification) has already been mentioned. The hydrogen-rich reducing gas is used in most Cases contain at least 70 percent by volume of hydrogen. Usually the Hydrogen content 80 to 95 percent by volume. The bulk of the diluting gases in this reducing gas, which is rich in hydrogen, generally consists of nitrogen, Argon and methane.

In the second stage of this process, the partially reduced Iron oxide treated with a gas containing substantial amounts of carbon monoxide, usually at least 10 percent by volume, preferably at least 20 percent by volume, to to cause such a carbon deposition that this in the third and last Stage is sufficient to achieve the desired final degree of reduction, usually at least 95% and often 98% and more. The carbon deposition on the partial reduced iron oxide particles should be at least the stoichiometric amounts for correspond to the desired final reduction. To do this, 1 mole of carbon is deposited required for every 0.5 moles of residual oxygen in the partially reduced iron oxide. Often, an excess of carbon deposition is favorable, which of the final Use of discounted products depends. Is z. B. the finished reduced product a charge for an electric furnace for manufacture. of steel so are about 5 kg of coal per ton of feed is desirable. Even when that's done Reduced product to be melted for any other purpose is made easier an excess of carbon deposition causes the melting, since the carbon has the melting point of iron lowers.

The carbon deposition is generally carried out at temperatures between performed around 230 and 675 ° C, although the best results are at temperatures between about 425 and 540 ° C. At this second stage are atmospheric or near atmospheric pressures favorable. Increased pressures can also be used be, since in the carbon deposition essentially the conversion of 2 mol Carbon monoxide is made to 1 mole of carbon and 1 mole of carbon dioxide. Contains the used Carbon monoxide, but also hydrogen, is about atmospheric pressure advisable, since the partially reduced iron oxide easily acts as a catalyst at elevated pressures acts to synthesize hydrocarbons from hydrogen and carbon monoxide. That ordinary synthesis gas, which is mainly a mixture of hydrogen and Is carbon monoxide in a ratio of about 2 moles of hydrogen per mole of carbon monoxide, is thus usable for this second process stage; However, it is expedient, the consumption of carbon monoxide in such a gas by the formation of Hydrocarbons, like methane, diminish by keeping this at near atmospheric Press, d. i.e., below about 2 kg / cm2. As already mentioned, with carbon dioxide occurs as a reaction product of the carbon deposition, it is advisable to limit the carbon dioxide content of the gas used for carbon capture. If such a gas contains carbon dioxide, the carbon monoxide content should be at least four times as large, preferably at least ten times as large as the carbon dioxide content be.

Even if different in the first stage of the process according to the invention Methods can be used to keep the solid particles in contact with the gas a whirling process is preferable in most cases, especially because the carbon deposition is a highly exothermic reaction is. The whirling process not only ensures the maintenance of a practical uniform temperature through the entire mass of the treated particles, rather also facilitates the dissipation of heat from this mass. It is known that vortex process the circulation of a stream of swirled particles from the inside the reaction vessel contained mass to an externally mounted heat exchanger and return to Allow appropriate cooling in the reaction vessel. Another known method for temperature control within the swirled mass consists in the attachment of heat exchange tubes in the reaction vessel that are in contact with the swirled Stand mass. There is a considerable overlap in the temperature ranges of the first and the second stage of the process according to the invention is present, a fluidized bed reaction vessel can be used to perform both stages in sequence.

When carrying out the second stage of the process according to the invention samples of the solid particles to be treated are periodically removed from the reaction vessel subtracted and chemically examined to compare the amount of carbon deposition to determine the amount of residual oxygen contained in these particles. Once the chemical analysis shows that the carbon deposition is desired for final reduction is sufficient or the finished reduced product then the desired excess carbon is contained, the solid particles are for the third Stage of the process according to the invention ready.

The third stage essentially consists of heating the partial reduced iron oxide particles containing the carbon deposit to react of the carbon (in iron carbide or as free carbon) with the rest oxygen contained in the particles so as to effect a further reduction. In general, temperatures from 700 to 980 ° C are suitable for these purposes; preferred temperatures of 870 ° C.

Even if a fluidized bed technique is used for this third stage of the procedure can be used, there is only a minor technical advantage in this, as this stage is easily performed in a rotary kiln or in other known devices for heating particles to temperatures in the above range can be. During the heating, the carbon deposit reacts with the rest Oxygen in the partially reduced iron oxide particles, and carbon monoxide is formed. This gaseous reaction product is advantageously used in the second stage of the process according to the invention or by known processes for production of hydrogen used, which is then applied in the first stage. If in If a fluidized bed process is used in this third stage, part of the developed carbon monoxide is returned to the reaction vessel for the third stage be to the mass of particles contained therein during the entire stage in to maintain a vortex-shaped state. By those treated in this way in the third stage Particles can be passed through an inert gas such as nitrogen; however, diluted such an inert gas produces carbon monoxide, and the addition should therefore be regulated in order to .an excessive dilution of the developed carbon monoxide prevent, as this would impair its subsequent use.

The completion of the third stage of the process according to the invention The reaction taking place is indicated by the end of the evolution of carbon monoxide. In other words, to perform the third stage alone it is not necessary to to be heated longer than carbon monoxide is evolved. Because the third stage is the reaction includes solid reactants that provide carbon monoxide an increased pressure the reaction. On the other hand, the third stage is advantageous to be carried out at a high pressure if the resulting carbon monoxide is subsequently added should be used at a high pressure because of the cost of compressing of carbon monoxide can be saved.

Depending on the use of the finished reduced product, it can be useful be the heating of the finished product over those selected for the third stage Continue temperatures to sinter the particles together into tablets or spheres, etc. or even to melt these particles, e.g. B. for the production of blocks.

For a better understanding of the present invention, reference is made to the drawing referenced, which diagrammatically depicts a preferred embodiment.

The first stage of the process is carried out in reaction vessel 10 to which finely divided Swedish magnetite containing 3 percent by weight gangue is fed through line 11. A reducing gas containing 85 percent by volume of hydrogen, 0.3 percent by volume of carbon oxides and 0.3 percent by volume of water vapor is fed to the reaction vessel 10 through line 12; this goes up through the vortex-shaped mass of Swedish magnetite, maintaining a reaction temperature of about 480 ° C and a reaction pressure of 28 kg / cm2. The majority of the exhaust gases which leave the reaction vessel 10 through line 13 are returned to line 12 through line 14 and through a water removal system 15. Without a significant decrease in pressure, the recirculated exhaust gas is washed in system 15 with water at a temperature of about 32 ° C. in order to remove the water of reaction from the recirculated portion of the exhaust gases. Since the reducing gas entering the reaction vessel 10 through the line 12 contains methane, nitrogen and argon, a smaller part of the exhaust gases exiting through the line 13 is discharged through the line 16.

When the reduction in magnetite in the reaction vessel reaches 10-85% has, the partially reduced magnetite is through line 17 into the reaction vessel 18, where the second stage of the procedure is carried out. The gaseous one stream introduced into reaction vessel 18 through line 19, which is 62 percent by volume Hydrogen, 35 percent by volume carbon monoxide and small amounts of methane, carbon dioxide, Containing nitrogen, argon and water vapor is produced by partial combustion of Methane is obtained with very pure oxygen and is commonly referred to as synthesis gas. The gaseous stream then flows through the vortex-shaped mass of the partially reduced Magnetite upwards, with a reaction temperature of 510 ° C and a pressure of 0.7 kg / cm? is maintained in the reaction vessel 18. The reaction vessel 18 Exhaust gases leaving line 20 show carbon monoxide conversion in the Reaction vessel 18 from 35% on. The exhaust gases therefore still contain noticeable quantities of carbon monoxide and can through line 21, - the carbon dioxide removal system 22 and the line 19 are partially returned. In system 22, the The reaction vessel 18 gasses off the carbon dioxide by scrubbing with any known liquid absorbent for carbon dioxide, such as. B. Diethanolamine, removed. 10 percent by volume of the scrubbed gas leaving system 22 will be returned through line 19 into reaction vessel 18.

The remaining bulk of the scrubbed gas leaving system 22 goes through line 23 to system 24, where a water-gas reaction is carried out. In this, the hydrogen-rich gas is reacted in a known manner with steam in the presence of iron and chromium oxide catalysts in order to convert the remaining carbon monoxide in this gas into carbon dioxide and additional hydrogen. The gas thus treated is washed again with a liquid absorbent for carbon dioxide, and the remaining hydrogen-rich gas, which contains small amounts of carbon oxides, is passed through the line 12 into the reaction vessel 10 to be supplied with hydrogen for the partial reduction of magnetite supply. If necessary, additional hydrogen can be passed through line 25 into line 12.

The treatment of the partially reduced magnetite in the reaction vessel 18 continues until the carbon deposition on the magnetite is 3.8 percent by weight amounts to. Thereupon the ponds of the reduced, a carbon deposit carrying magnetite is transferred through the line 26 into a furnace 27 in which the shredded material by a multitude of parallel, externally heated by hot exhaust gases Tubes about 5 cm in diameter are allowed to fall through. During the descent of the particles through the heated tubes reach a temperature of 900 ° C, and most of the carbon deposit on the particles underreacts Development of carbon monoxide. The particles heated in this way leave the furnace 27 through the line 28 in the form of an iron powder which is 0.7 percent by weight excess Contains carbon. An analysis of these iron particles shows that the final Degree of reduction is 980/0. This occurs during the heating of the particles in the oven 27 Developed carbon monoxide contains a small amount of carbon dioxide. This gas will passed through line 29 to line 19 for use in reaction vessel 18.

The iron powder obtained according to the invention can be in tablet or Briquette form are pressed, which are then fed to an electric furnace. Man can also be the partially reduced iron oxide containing the carbon deposit process in tablet or briquette form and then according to the invention in the heat the third stage so that the final reduction is obtained. In such a In this case, the tablets or briquettes can be conveniently heated by a thin layer of it is passed through an oven with ceiling radiation.

Another preferred embodiment of the present invention includes a pretreatment of the synthesis gas that is fed through line 19, a. The pretreatment consists in the separation of a substantial part of the Carbon monoxide in the original synthesis gas by common methods, by scrubbing of the gas with a liquid absorbent for carbon monoxide, such as containing copper Liquids, or by partially liquefying the gas, to give a hydrogen rich fraction and a fraction rich in carbon monoxide having a molar ratio of Carbon monoxide to hydrogen of at least 10: 1. Instead of of the synthesis gas, the carbon monoxide thus separated from the synthesis gas is preferably at an elevated pressure of 7 to 35 kg / cm2, the reaction vessel 18 through the line 19 supplied. Since the gas supplied to the reaction vessel 18 is only very small Content of hydrogen, it is not necessary in this case to part of the gas discharged from the carbon dioxide removal system 22 through line 23 to the system 24 is performed to derive. The residue of the synthesis gas, from which an essential Part of the carbon monoxide removed becomes the water-gas reaction system 24 supplied to convert the remaining carbon monoxide in this gas into carbon dioxide and additional To transform hydrogen. After this water-gas reaction, the gas becomes with a liquid absorbent for carbon dioxide washed and the remaining, on Hydrogen rich gas is recycled through line 12 to the first stage. _ Albeit the use of synthesis gas to produce hydrogen and carbon monoxide for the present process because of the low cost to manufacture of the synthesis gas through partial combustion of hydrocarbons with very pure Oxygen is very favorable, it should be noted that these two are gaseous Reactants advantageously also from two independent sources can originate. So can be in areas where cheaper coke or anthracite is accessible is to put such a fuel in a Wellman-Galusha generator and with air blow to generate a generator gas with 35 percent by volume carbon monoxide, 3 volume percent carbon dioxide, 4 volume percent hydrogen and one mainly to obtain a remainder consisting of nitrogen. This generator gas is for use suitable in the second stage of the process according to the invention. Usually will this generator gas is used for carbon deposition without recirculation takes place, the washing of the to remove a large amount of carbon dioxide Would make exhaust gases from the reaction vessel of the second stage necessary. In one in such a case, it is preferred to pass the carbon monoxide flowing out of the furnace 27 through the line 29 to lead to line 23 instead of to line 19, so that this carbon monoxide with steam to produce hydrogen for the first stage of the invention Procedure can be implemented. If necessary, everything can be done in the first stage used hydrogen can be obtained by evolving in the third stage Carbon monoxide is reacted with water vapor, but should in such a case the reduction of iron oxide with hydrogen is less than 50% of that achieved by the invention Process to be removed, the oxygen chemically bound in the iron oxide. Even if the one needed for the first stage to partially reduce the iron oxide Hydrogen can come from any suitable source, so can if that Hydrogen was obtained by first producing synthesis gas and then this was subjected to a water-gas reaction to convert carbon monoxide into hydrogen and To convert carbon dioxide, the carbon dioxide usually separated from hydrogen are fed to the generator for the production of generator gas to reduce its carbon monoxide content to increase. At the same time, the generator can further increase the carbon monoxide content the gas can be blown with oxygen instead of air.

Shall be a gas that is both hydrogen and carbon dioxide in essence Contains quantities, separated into a hydrogen-rich and a carbon dioxide-rich fraction the separation can advantageously be carried out by an absorption process be carried out at a lower temperature. This process uses a liquid Absorbents, such as acetone, are used at a temperature below about -10 ° C. This method is very suitable to carry out the separation in cases where the carbon monoxide developed in the third stage was reacted with water vapor, to provide practically all of the hydrogen required for the first stage.

Claims (7)

Claims: 1. Process for the reduction of iron oxide, in which Iron oxide partially reduced, the partially reduced iron oxide with carbon monoxide brought into contact and thereby on the surface of the partially reduced iron oxide Carbon is deposited, after which the carbon-coated iron oxide particles for their further complete reduction into metallic iron to one temperature are heated by more than 700 ° C, thereby g e k e n n n -z e i c h n e t that the partial reduction of the iron oxide with hydrogen at a pressure of at least 14 kg / cm2 and a temperature of 370 to 540 ° C up to 40 to 95 percent Reduction is carried out. 2. The method according to claim 1, characterized in that that the iron oxide used has a size that it passes through a sieve with a clear mesh size of 0.84 mm passes through it, and the partial reduction and the Coal deposition can be carried out in zones in which the iron oxide upwardly guided rapid gas streams fluidized beds are generated. 3. Procedure according to claims 1 and 2, characterized in that for the deposition of the carbon then a gaseous mixture of carbon monoxide and hydrogen is used the remaining carbon monoxide and the carbon dioxide formed during this treatment be separated from the gaseous mixture, and the remaining, hydrogen rich gas is used to carry out the partial reduction in the first stage will. 4. The method according to claims 1 to 3, characterized in that the partial reduction of 40 to 5011 / o of the final reduction is carried out, the carbon deposition with a generator gas, the substantial amounts of carbon monoxide and contains a major amount of nitrogen, is carried out, and that during the Further reduction developed carbon monoxide as a reactant in a water-gas reaction to produce hydrogen, which is then used to carry out the partial reduction is used. 5. The method according to claims 1 to 3, characterized characterized in that the iron oxide is reduced by 60 to 90% in the partial reduction will. 6. The method according to claims 1 to 5, characterized in that the Treatment with carbon monoxide is carried out so that more carbon is deposited is than needed for further reduction and that after further reduction the ferrous product containing the excess carbon is melted will. 7. The method according to claims 1 to 6, characterized in that a Fresh gaseous forms containing a substantial amount of carbon monoxide and hydrogen Mix in a fraction rich in carbon monoxide, which has a molar ratio of carbon monoxide to hydrogen of at least 10 and at an increased pressure for deposition of carbon is used, and a hydrogen-rich fraction that is used for partial reduction is used, is separated. Considered publications: German Patent No. 678,326; British Patent No. 754182; “Iron and Coal Trades Review ', 1957, pp. 31 and 32.