Abstract:
A method for producing a sponge metal from metal ore or iron ore which comprises reacting said metal ore or iron ore in a reduction zone with a CO— and H 2 -containing, reducing feed gas source which has been compressed, and after said reaction, withdrawing the remaining feed gas as an export gas from the reduction zone, wherein the CO— and H 2 -containing feed gas is introduced into the reduction zone form at least to gas sources, whereby upon a breakdown of one of the feed gas sources, at least a portion of the export gas recovered from the reduction zone is compressed, subjected to CO 2  elimination recycled to the reduction zone together with the reducing feed gas.

Description:
This application is the national phase under 35 U.S.C. §371 of prior PCT International Application No. PCT/AT97/00044 which has an International filing date of Dec. 15, 1997 which designated the United States of America, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a method for producing sponge metal, in particular sponge iron, from charging materials consisting of metal ore or iron ore respectively, preferably in lumps and/or pellets, and optionally fluxes, wherein a CO— and H 2 -containing feedgas from a gas source which is compressed and optionally subjected to CO 2  elimination and heating is supplied to a reduction zone to serve as a reducing gas and after reaction with the metal ore is withdrawn from the reduction zone as an export gas for further use by a consumer. The present invention is also directed to a plant for carrying out the method. 
     A method of this type is known from AT-B-396.255 and from DE-C-40 37 977. With these known methods, the gas source is formed by a first reduction zone, in which iron ore is directly reduced to sponge iron, wherein the sponge iron is melted in a meltdown gasifying zone under the supply of carbon carriers and oxygen-containing gas and a CO— and H 2 containing reducing gas is produced which is fed to the first reduction zone, is reacted there and withdrawn as a feedgas for the further reduction zone. According to AT-B-396.255, the feedgas prior to being fed to the further reduction zone is subjected to CO 2  elimination by a reformer and at the same time is heated; in accordance with DE-C-40 37 977, CO 2  elimination is effected by a CO 2  scrubber. 
     With these known methods, export gas withdrawn from the further reduction zone is subjected to scrubbing and is subsequently mixed with the export gas from the first reduction zone, and the mixed gas thus formed is subjected to CO 2  elimination and heating. This gas mixture is then supplied to the further reduction process to serve as a reducing gas. It thereby becomes feasible to exploit a portion of the reductants still present in the export gas from the further reduction zone, as the export gas is supplied to the further reduction process as a recycle reducing gas. 
     Often, there is a requirement for the export gas from the further reduction zone to be available for an external consumer, f.i. as a fuel gas. The export gas from the further reduction zone will then not be recycled. In this case, provisions must therefore be made to ensure that a sufficient amount of reducing gas will be available at any time to enable steady operation of the reduction process. In particular, the supply to the further reduction zone of a sufficient amount of reducing gas is to be ensured even with different operating states of the entire plant, f.i. even in the event of a failure. 
     SUMMARY OF THE INVENTION 
     With a method of the initially described kind this object is achieved in that into the reduction zone a CO— and H 2 -containing feedgas is fed from at least two gas sources to serve as a reducing gas and that a breakdown of one of the gas sources is compensated for by recycling at least a portion of the export gas from the reduction zone, wherein said export gas is subjected to compression, to CO 2  elimination and optionally to heating and is supplied to the reduction zone along with the feedgas from the other intact gas source(s). 
     The special feature of this method is that if at least two gas sources are provided, the direct reduction process in the further reduction zone can be continued even in case of a breakdown of one of the gas sources. Actually the breakdown of one of the gas sources would normally cause too small an amount of reducing gas to be fed to the further reduction zone, which leads to difficulties and may possibly cause the disruption of the continuously progressing direct reduction process in this further reduction zone. In accordance with the invention this is avoided by recycling at least a portion of the export gas from the further reduction zone. 
     If export gas from the further reduction zone is to be recycled, preferably said gas will first of all be pre-compressed in order to level out differences of pressure and pre-compressed and in the pre-compressed state will be admixed to the reducing gas from the intact gas source and subjected to further compression along with the same. In that case, compression of the recycled export gas to the pressure level required for the further direct reduction process takes place in stages, thus allowing it to get by with not too expensively designed compressors (in terms of capacity). 
     Other possible gas sources apart from a plant with a first reduction zone where iron ore is directly reduced to sponge iron and the sponge iron melted in a meltdown gasifying zone under the supply of carbon carriers and oxygen-containing gas would be coal gasification processes and blast furnace processes, so that at least one gas source could also be a coal gasification means or a blast furnace. 
     A plant for carrying out the method according to the invention, with a reduction reactor for producing sponge metal, in particular sponge iron, from charging materials consisting of metal ore or iron ore respectively, preferably in lumps and/or pellets, and optionally fluxes, with a reducing-gas feed duct and an ore feed duct leading to said reduction reactor, an export-gas discharge duct departing from this reduction reactor and a discharging means for the reduction product formed in said reduction reactor, wherein from a gas source dispensing a CO— and H 2 -containing feedgas a feedgas duct conducting the feedgas dispensed by the gas source runs into the reducing-gas feed duct via a compressor and optionally a CO 2  elimination plant and optionally a gas heater, characterized in that at least a second gas source dispensing a CO— and H 2 -containing gas likewise runs into the reducing-gas feed duct via a feedgas duct equipped with a compressor and optionally via a CO 2  elimination plant as well as optionally a gas heating plant and that a conveying duct for at least a portion of the export gas formed in the reduction reactor is adapted to be flow-connectable with the reducing-gas feed duct of the reduction reactor via the compressors, which are connectable in series via a connection duct, and via a CO 2  elimination plant and optionally a heating means. 
     The compressors that are anyway provided for the two gas sources being optionally switchable from a parallel to a serial connection, there is no need for a separate compressor for the recycled gas if recycling the export gas, so that enormous savings in terms of capital expenditures will result. 
     Herein suitably the two feedgas ducts departing from the gas sources can be cut off individually by means of valves prior to running into one each of the compressors and are connectable via a connection duct. 
     A preferred embodiment is characterized in that at least one gas source is formed by a first reduction reactor for iron ore, preferably in lumps and/or pellets, a melter gasifier, a feed duct for a reducing gas connecting the melter gasifier with the first reduction reactor, a conveying duct for the reduction product formed in the first reduction reactor connecting the first reduction reactor with the melter gasifier, an export-gas discharge duct departing from the first reduction reactor, feed ducts for oxygen-containing gases and carbon carriers opening into the melter gasifier and a tap for pig iron and slag provided at the melter gasifier, wherein the export-gas discharge duct departing from the first reduction reactor serves as a feedgas duct. 
     Preferably, two gas sources are formed in the same way by first reduction reactors having one melter gasifier each and through feedgas ducts are flow-connected with the reducing-gas feed duct of the further reduction reactor via one compressor each. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, the invention is explained in more detail with reference to an exemplary embodiment represented in the drawings, wherein; 
     FIG. 1 is a block diagram illustrating a plant in accordance with the invention; 
     FIGS. 2 and 3 each explain the gas paths in the event of a breakdown of one of the gas sources; 
     FIG. 4 illustrates a possible embodiment of a gas source. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The two gas sources A and B represented in FIG. 1, which supply a feedgas, are preferably constructed as described below: 
     To a shaft furnace forming a first reduction reactor  1 , lumpy iron ore and/or pelletized iron ore is top-charged via a conveying means  2  through a sluice system not illustrated in the drawing, optionally along with fluxing materials under the formation of a moving bed. The shaft furnace  1  communicates with a melter gasifier  3 , in which from coal and oxygen-containing gas a reducing gas is formed which is fed to the shaft furnace  1  via a feed duct  4 , a gas purification means  4 ′ for dry dedustification being optionally provided inside the feed duct  4 . 
     The term “moving bed” is generally understood to refer to a continuously moving material stream, the movable particles of which come into contact with a reducing gas flowing in the opposite direction. Preferably, a material stream is utilized which moves continuously downward by gravity. 
     Instead of a shaft furnace  1 , it is also feasible to provide a reactor incorporating a Venturi-fluidized bed, a circulating fluidized bed, a fluidized bed or a reactor incorporating a traveling grate or a rotary tubular kiln as the reduction reactor. 
     The melter gasifier  3  has a feed duct  5  for solid carbon carriers, a feed duct  6  for oxygen-containing gases and optionally feed ducts  7  for carbon carriers that are liquid or gaseous at room temperature, such as hydrocarbons, and for calcined fluxes. Inside the melter gasifier  3 , molten pig iron  9  and molten slag  10  collect below the meltdown gasifying zone  8  and are run off through a tap  11 . 
     Along with the fluxes calcined in the direct reduction zone  12 , the iron ore which has been reduced to sponge iron in a direct reduction zone  12  inside the shaft furnace  1  is introduced through a conveying duct  13  connecting the shaft furnace  1  with the melter gasifier  3 , f.i. by means of delivery worms etc. To the upper portion of the shaft furnace  1 , a duct  14  is connected for the export gas which forms from reducing gas in the direct reduction zone  12  and which is to serve as a feedgas for a further reduction process. 
     From each of the gas sources A and B exhibiting the above-described construction, export gas is withdrawn through the feedgas duct  14  (for gas source A) and  14 ′ (for gas source B) and is first subjected to purification in a scrubber  15  to free it from dust particles as completely as possible and to reduce the water vapor content. By means of a gas compressor  16  (for gas source A) and  16 ′ (for gas source B) the export gas subsequently passes into a CO 2  elimination plant  17  (f.i. a CO 2  scrubber or a pressure-swing adsorption plant) where it is freed from CO 2  as completely as possible. 
     As can be seen from FIG. 1, the gas sources A and B are arranged parallel to each other, with their feedgas discharge ducts  14 ,  14 ′ uniting at a position after the compressors  16  and  16 ′, so that the two feedgases from the gas sources A and B are supplied to CO 2  elimination in a mixed state. As a consequence, only a single CO 2  elimination plant  17  is required, which is advantageous particularly if the feedgases from the gas sources A and B are similar or equal in chemical composition. 
     The offgas exiting the CO 2  elimination plant  17  optionally is supplied to a desulphurizing plant  18 . The feedgas thus purified from CO 2  is now available for a further reduction process. Through a reducing-gas feed duct  19  it is supplied to a second reduction reactor constructed as a shaft furnace  20 , which like the first shaft furnace  1  is also provided with a moving bed and is operated in accordance with the counter-current principle. In this second shaft furnace  20  metal ore, preferably lumpy and/or pelletized iron ore, is directly reduced to sponge iron in a reduction zone  21 . The ore feed duct is designated by the reference numeral  20 ′ and the sponge iron discharging means by the reference numeral  20 ″. 
     In the second shaft furnace  20  metal ores, such as manganese ore, lead ore and zinc ore, could also be subjected to partial or complete reduction. 
     Since the mixed feedgases of the gas sources A and B have experienced substantial cooling by CO 2  elimination, the reducing gas emerging from the CO 2  elimination plant is subjected to heating in a gas heater  22  prior to being fed to the second reduction shaft furnace  20 . The reducing gas hereby reaches the temperature necessary for reduction in the second reduction shaft furnace  20 , which lies in a temperature range of between 600 and 900° C. For reducing gases that are rich in H 2  even a temperature range of above 900° C. may be contemplated. 
     Depending on its intended use, the export gas withdrawn from the second reduction shaft furnace  20  through an export-gas duct  23  is also subjected to purification and cooling in an export gas scrubber (not illustrated) to clean it from dust particles and reduce the water vapor content, whereupon it is ready for feeding to a consumer. 
     Each of the feedgas ducts is provided with first valves  24 ,  24 ′ and second valves  25 ,  25 ′, all of which are arranged preceding the compressors  16 . Between the first and second valves  24 ,  25  or  24 ′,  25 ′ respectively, a connection duct  26  is provided which links the feedgas ducts  14  and  14 ′ of the two gas sources A and B and is fitted with a valve  27 . 
     From the feedgas duct  14  of the gas source A, a further connection duct  28  l inking the feedgas ducts  14 ,  14 ′ departs at a position after the compressor  16 , which duct is also fitted with a valve  29  and at a position before the compressor  16 ′ of the other gas source B opens into the feedgas duct  14 ′ of said gas source B, but at a position after the second valve  25 ′ of the same. At a position after the branching-off point the export-gas duct  14 , from which this further connection duct  28  branches off is fitted with an additional valve  30 . 
     From the export-gas duct  27  of the further shaft furnace  20  a conveying duct  32  fitted with a valve  31  branches off to join the feedgas duct  14  of the gas source A at a position preceding the compressor  16  allocated to said source. 
     In the following, the functioning of the plant will be described: 
     If both gas sources supply feedgas for the further reduction plant, i.e. the further shaft furnace  20 , on a roughly equal order (quantity , chemical composition), all valves of the feedgas ducts  14  and  14 ′ will be open and the valve  31  of the conveying duct  32  serving for recycling an export gas formed in the further shaft furnace  20  as well as the valves  27  and  29  of the connection ducts  26  and  28  between the feedgas ducts  14  and  14 ′ will be in a closed position. 
     In the event that the gas source A breaks down-this is illustrated in FIG. 2, a portion of the export gas formed in the further shaft furnace  20  will be fed to the feedgas duct  14  through the conveying duct  32  after opening the valve  31  of the latter. Here, the recycled export gas f.i. exhibits a pressure above atmospheric of roughly 0.3 bar. The recycled export gas via the compressor  16  and the connection duct  28  branching off from the feedgas duct  14  at a position after the compressor  16  is conducted to the compressor  16 ′ allocated to the other intact gas source B an d is mixed wit h the feedgas from the gas source B and compressed by means of the compressor  16 ′ allocated to said gas source B. The initial compression is effected f.i. to roughly 1.5 bar pressure above atmospheric and the second compression by means of the compressor  16 ′ will then be effected to the pressure above atmospheric of f.i. roughly 3 bar which is necessary for the shaft furnace  20 . Here, the valves  24 ,  30 ,  27  sketched in black in FIG. 2 are closed and the valves  31 ,  24 ′,  25 ′ and  29  are open. In FIG. 2 (and also in FIG.  3 ), the flow path of the gas has been illustrated in broken lines. 
     If there is a breakdown of gas source B, as illustrated in FIG. 3, then the export gas recycled from the further shaft furnace  20  will also be supplied to the gas source B via the further connection duct  28  of the feedgas duct  14 ′ and the feedgas from the gas source A will also be fed into the feedgas duct  14 ′ of the gas source B via the first connection duct  26 . During this time, the valves  25 ,  30 ,  24 ′ are in a closed position and the valves  31 ,  24 ,  27 ,  29  and  25 ′ are open. 
     Depending on the shaft capacity of the reduction reactor  20  and the actual dimensions of the compressors  16 ,  16 ′ up to 100% of the export gas available can be recycled, yet in doing so the inert gas portion must be taken into account. 
     The invention is not limited to the exemplary embodiment illustrated in the drawing but also encompasses further embodiments. The essential requirement here is that the two compressors  16 ,  16 ′ must be constructed so as to be connectable in parallel with respect to gas distribution whenever the two gas sources A and B are in operation at the same time and connectable in series in case of a breakdown of one of the two gas sources A and B. The foregoing also applies to the compressors allocated to each gas source if more than two gas sources are utilized.