Abstract
A method of producing pig iron in a shaft furnace is provided. The shaft furnace is charged in an upper region with raw materials which fall within the shaft furnace under the influence of gravity. A portion of the raw materials is melted and/or partly reduced under the action of the atmosphere that exists within the shaft furnace. A hot gas stream which is introduced in a lower region of the shaft furnace flows through and influences the atmosphere that exists within the shaft furnace in terms of chemical composition and temperature. A cold gas stream is fed to a heat exchanger in which the cold gas stream is heated to a temperature higher than 700 C. to give a hot gas stream. The cold gas stream comprises a CO.sub.2 component of at least 5% by volume. The cold gas stream may contain, air and/or pure oxygen as residual component.
Claims
1-10 (canceled)
11. A method of producing pig iron in a shaft furnace which is charged in an upper region of the shaft furnace with raw materials which fall within the shaft furnace under the influence of gravity, wherein a portion of the raw materials is at least one of melted and at least partly reduced under the action of the atmosphere that exists within the shaft furnace, and a hot gas stream which is introduced in a lower region of the shaft furnace flows through and influences the atmosphere that exists within the shaft furnace in terms of chemical composition and temperature, wherein a cold gas stream is fed to at least one heat exchanger in which the cold gas stream is heated to a temperature higher than 700 C. to give a hot gas stream, wherein the cold gas stream, before being introduced into the at least one heat exchanger, comprises a CO.sub.2 component of at least 5% by volume, wherein the cold gas stream contains, aside from impurities, at least one of air and pure oxygen as residual component.
12. The method as claimed in claim 11, wherein the cold gas stream contains CO.sub.2, air and pure oxygen in addition to impurities, where the proportion of air is limited to not more than 50% by volume.
13. The method as claimed in claim 11, wherein the cold gas stream contains CO.sub.2 and pure oxygen in addition to impurities, wherein the proportion of CO.sub.2 is at least 70% by volume.
14. The method as claimed in claim 12, wherein the CO.sub.2 is provided from a CO.sub.2 separation.
15. The method as claimed in claim 14, wherein hydrogen is additionally introduced in the lower region of the shaft furnace.
16. The method as claimed in claim 15, wherein pure oxygen is additionally introduced in the lower region of the shaft furnace.
17. The method as claimed in claim 16, wherein carbon is additionally introduced in the lower region of the shaft furnace.
18. The method as claimed in claim 17, wherein the hydrogen is produced and provided from electrolysis, and the pure oxygen from an air fractionation plant.
19. The method as claimed in claim 12, wherein at least the air component of the cold gas stream, before being combined with the other components, is compressed to a pressure above the ambient pressure before being combined with the other components and before the cold gas stream is introduced into the at least one heat exchanger.
20. The method as claimed in claim 12, wherein the cold gas stream is compressed to a pressure above the ambient pressure before the cold gas stream is introduced into the at least one heat exchanger.
Description
[0026] There follows a detailed elucidation of specific configurations of the invention with reference to the drawing. The drawing and accompanying description of the resulting features should not be read as being restricted to the respective configurations, but instead serve for illustration of exemplary configuration. In addition, the respective features may be utilized together with one another or else together with features of the above description for further possible developments and improvements of the invention, specifically in the case of additional configurations that are not shown. Identical parts are always given the same reference numerals.
[0027] The drawing shows:
[0028] FIG. 1) a schematic of a blast furnace with an upstream blast heater and corresponding streams of matter in a conventional mode of operation and
[0029] FIG. 2) a schematic of a blast furnace with an upstream blast heater and corresponding streams of matter in an inventive mode of operation.
[0030] FIG. 1 shows a schematic of a conventional blast furnace with an upstream blast heater. Although only one blast heater (heat exchanger) is shown in a symbolic manner, there are in principle at least two, especially at least three, blast heaters (heat exchangers) disposed in the periphery of the shaft furnace/blast furnace. The mode of operation of the heat exchanger(s) (blast heater(s)) is prior art. Conventionally, air is sucked in from the environment, guided through compressors (not shown) and compressed, and introduced as cold gas stream (cold blast) into at least one of the heat exchanger(s) (blast heater(s)) which is already at an appropriate temperature. The blast heater is flooded with cold blast, and the heat stored in the blast heater is transferred to the compressed cold blast and, on attainment of a predefined temperature, generally between 700 C. and 1400 C., fed as hot gas stream (hot blast) to the blast tuyeres (tuyeres, nozzles) of a shaft furnace or blast furnace in which pig iron has been produced. In the upper region of the shaft furnace, raw materials required for production of pig iron are charged via the furnace top. Under the influence of gravity, the raw materials drop down within the shaft furnace, with melting and/or at least partial reduction of a portion of the raw materials under the action of the atmosphere that exists within the shaft furnace. In the lower region of the shaft furnace, a hot gas stream (hot blast) is introduced, which flows through the atmosphere within the shaft furnace in countercurrent and affects the chemical composition and temperature thereof. In addition, and depending on the mode of operation, it is possible to introduce carbon (carbon-based additives) and/or oxygen in the lower region of the shaft furnace separately from the hot gas stream. The blast furnace process and the mode of operation thereof are also prior art. Conventionally, air with about 79% by volume of nitrogen and about 21% by volume is introduced into the shaft furnace as cold gas stream (cold blast) or hot gas stream (hot blast). Coke is used as fuel and carbon carrier for the reduction of the iron ore, the primary material from which pig iron is to be produced in the blast furnace, and this coke, which, like the iron ore, is introduced into the shaft furnace via the top as the burden in a layered or mixed manner in each case, and if required additionally coal dust, which is additionally injected especially via the blast tuyeres. Alternatively, and depending on the plant design, it is also possible to use heating oil, natural gas, coking furnace gas, plastic or hydrogen, for example, as replacement reducing agent, which are injected via specific devices. The top gas exits at the top at about 140 C. to 250 C., and between 1500-1850 standard cubic meters (m.sup.3 (STP)) of top gas may be obtained per tonne of pig iron in a normal mode of operation. Some of the top gas or all of the top gas serves as fuel for the blast heater, which is mixed with further gases, for example natural gas and air, and recombusted. A composition of the top gas measured in normal operation contains, in % by volume: CO at 21%, CO.sub.2 at 21%, H.sub.2 at 2% and N.sub.2 at 56%, of which there may be HCN at 0.0025% to 1.2% and NOx at 0.001% to 0.15%.
[0031] FIG. 2 shows a schematic of the same conventional shaft furnace (blast furnace) with an upstream heat exchanger (blast heater), but with the difference that, in accordance with the invention, CO.sub.2 is used wholly or partly as cold gas stream (cold blast). Pure oxygen is given an * in FIG. 2, which is supposed to mean that oxygen is introduced either into the cold gas stream and/or into the hot gas stream before the hot gas stream (hot blast) is introduced into the shaft furnace. Alternatively, it is also possible for only CO.sub.2 together with impurities to be used as cold/hot gas stream, or for CO.sub.2 in conjunction with air up to a maximum of 50% by volume and/or with pure oxygen up to 30% by volume (not shown here). The inventive example in FIG. 2 shows that, with virtually 100% by volume of CO.sub.2, firstly, the CO.sub.2 balance of the overall process is positive and, secondly, the level of nitrogen in the process can be reduced, or it is absent, such that also only reduced to zero NOx emissions and reduced to zero potassium cyanide compounds or hydrogen cyanide are obtained within the process by comparison with the conventional mode of operation. In one experiment, air was replaced completely by CO.sub.2 in the cold gas stream (cold blast), with separation of CO.sub.2 from a direct reduction process (alternatively oxyfuel process) and provision with a pressure of 6 bar, such that there was no longer any need to use the conventionally present (blast) compressor and it was thus possible to save power for this piece of equipment. In the heat exchanger (blast heater), the CO.sub.2 was heated to 1200 C. and injected into the blast furnace as hot gas stream (hot blast). In addition, hydrogen was injected at up to 1000 m.sup.3 (STP)/h, especially per blast tuyere (tuyere), where the blast furnace may have multiple (blast) tuyeres, in which case it is especially possible, in the case of reduction of hydrogen, additionally to separately inject carbon, for example as coal powder, and/or oxygen. Via the top, especially between 250 and 400 kg of coke per tonne of pig iron produced is fed in. Up to 12 000 m.sup.3 (STP) of top gas was obtained per tonne of pig iron, for which a composition was ascertained in % by volume: CO.sub.2 at 47%, CO at 38% and H.sub.2 at 15%. Contamination with nitrogen or harmful NOx, potassium cyanide compounds or hydrogen cyanide was not present in the top gas, and so it had an improved calorific value and better emission characteristics. It was possible to reduce the use of further gases for the post-combustion in the heat exchanger (blast heater), dispensing in this case with air and using pure oxygen for nitrogen-free combustion. The offgas/combustion gas led off from the blast heater after combustion was of excellent suitability for recycling since, because there are few troublesome components in the offgas, the CO.sub.2 can be fed back to the (blast furnace) process relatively easily and effectively as recycled CO.sub.2.
[0032] The invention is also implementable with proportions of air and/or pure oxygen in the cold gas stream (cold blast), since at least 5% by volume, especially at least 10% by volume, preferably at least 20% by volume, more preferably at least 30% by volume, especially preferably at least 40% by volume of CO.sub.2 in the cold gas stream (cold blast) and hence partial to complete replacement of the air can lead to a reduction in NOx emissions caused by nitrogen, and this can, for example, also increase/improve the efficiency of the (overall) process.
[0033] The invention is applicable to any type of shaft furnace, i.e. not just restricted to blast furnaces, but is also implementable in cupola furnaces, primary energy furnaces etc. that work by the principle of action described.
