METHOD FOR OPERATING AN IRON- OR STEELMAKING- PLANT

Abstract

A method of operating an ironmaking or steelmaking plant with low CO.sub.2-emissions is provided. Hydrogen and oxygen are generated by water decomposition and at least part of the generated hydrogen is injected as a reducing gas into one or more ironmaking furnaces with off-gas decarbonation and reinjection into the furnaces of at least a significant part of the decarbonated off-gas and at least part of the generated oxygen is injected as an oxidizing gas in the one or more ironmaking.

Claims

1.-15. (canceled)

16. A method of operating an ironmaking or steelmaking plant comprising an ironmaking furnace set comprising one or more furnaces in which iron ore is transformed into liquid hot metal by means of a process which includes iron ore reduction, melting and off-gas generation, the ironmaking or steelmaking plant, the method comprising the steps of: a. charging the ironmaking furnace set with iron ore and coke, b. injecting oxidizing gas into the ironmaking furnace set, c. producing an off-gas and decarbonating the off-gas downstream of the ironmaking furnace set thereby obtaining a CO.sub.2-enriched tail gas stream and a decarbonated off-gas stream containing not more than 10% vol CO.sub.2, d. injecting at least 50% of the decarbonated off-gas stream back into the ironmaking furnace set as a reducing gas recycle stream, e. generating hydrogen and oxygen by means of water decomposition, f. injecting at least part of the hydrogen generated in step into the ironmaking furnace set, and g. injecting at least part of the generated oxygen into the ironmaking furnace set and/or the converter as oxidizing gas.

17. The method according to claim 16, whereby at least part of the hydrogen generated in step (e) which is injected into the ironmaking furnace set is mixed with the reducing gas recycle stream before the gas mixture so obtained is injected into the ironmaking furnace set.

18. The method according to claim 16, wherein: h. the gas recycle stream or the mixture of hydrogen generated in step (e) with the gas recycle stream is heated upstream of the ironmaking furnace set to a temperature between 700 C. and 1300 C.

19. The method according to claim 18, wherein: i. a low-heating-value gaseous fuel having a heating value of from 2.8 to 7.0 MJ/Nm.sup.3 is produced containing (i) at least a portion of the tail gas stream and (ii) a second part of the hydrogen generated in step (e), said low-heating-value gaseous fuel being used to heat the hot stoves used for heating the gas recycle stream.

20. The method according to claim 16, whereby the ratio between: (i) the hydrogen generated in step (e) and injected into the ironmaking furnace set and (ii) the oxygen generated in step (e) and injected into the ironmaking furnace set and/or the converter in step (g) is between 1.50 and 2.50.

21. The method according to claim 16, whereby the ratio between: (i) the hydrogen generated in step (e) and injected into the ironmaking furnace set and (ii) the oxygen generated in step (e) and injected into the ironmaking furnace set in step (g) is between 1.75 and 2.25.

22. The method according to claim 16, wherein pulverized coal and/or another organic combustible substance is injected into the blast furnace by means of tuyeres.

23. The method according to claim 16, wherein all or part of the generated hydrogen which is injected into the ironmaking furnace set is injected into the ironmaking furnace set via tuyeres.

24. The method according to claim 16, wherein all or part of the oxygen generated in step (e) is mixed with oxygen-containing gas not generated in step (e) so as to obtain a mixture which is injected as oxidizing gas into the ironmaking furnace set.

25. The method according to claim 16, wherein the oxidizing gas which is injected into the ironmaking furnace set in step (b) consists of oxygen generated in step (e).

26. The method according to claim 16, wherein in step (e), hydrogen and oxygen are generated by biological and/or electrolytic water decomposition.

27. The method of claim 26, wherein in step (e), hydrogen and oxygen are generated by electrolytic water decomposition at a pressure above atmospheric pressure and/or at a temperature above ambient temperature.

28. The method according to claim 16, wherein the reducing gas is injected into the ironmaking furnace set via tuyeres.

29. The method according to claim 16, wherein the ironmaking furnace set comprises one or more blast furnaces.

30. The method according to claim 16, wherein the hydrogen generated in step (e) consists for at least 70% vol of H.sub.2 molecules.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0085] For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

[0086] FIG. 1 schematically illustrates a prior art steelmaking plant, and

[0087] FIG. 2 schematically illustrates an embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0088] The present invention and its advantages are further clarified in the following example, reference being made to FIGS. 1 and 2, whereby FIG. 1 schematically illustrates a prior art steelmaking plant whereby the IFS consists of one or more non-TGRBFs (only one blast furnace is schematically represented and in the corresponding description reference is made to only one non-TGRBF) and FIG. 2 schematically illustrates an embodiment of the method according to the invention applied to a steelmaking plant whereby the IFS consists of one or more TGRBFs (only one TGRBF is represented and in the corresponding description reference is also made to only one TGRBF), whereby identical reference numbers are used to indicate identical or analogous features in the two figures.

[0089] FIG. 1 which shows a prior art conventional blast furnace 1 without top gas decarburization or recycling. Blast furnace 1 is charged from the top with coke and iron ore 2 which descend in the blast furnace 1.

[0090] Air 28 is preheated in hot stoves 20 before being injected into blast furnace 1 via hearth tuyeres 1b. Substantially pure oxygen 22 can be added to blast air 28 via the hearth tuyeres 1b or upstream of the hot stoves 20.

[0091] Pulverized coal (or another organic combustible substance) 23 is typically also injected into the blast furnace 1 by means of hearth tuyeres 1b.

[0092] The air 28, and, if added, the substantially pure oxygen 22 and the pulverized coal (or another organic fuel) 23 combine inside the blast furnace so as to produce heat by combustion and reducing gas 1d (in contact with the coke present in solid charge 2). Reducing gas 1d ascends the inside of blast furnace 1 and reduces the iron oxides contained in the ore to metallic iron. This metallic iron continues its descent to the bottom of the blast furnace 1 where it is removed (tapped) la along with a slag containing oxide impurities.

[0093] The off-gas, better known as blast furnace gas (BFG), 3 exits the blast furnace 1 and travels to an initial dust removal unit 4 where large particles of dust are removed. It continues to a second dust removal system 5 that removes the fine dust particles to produce a clean gas 6. The clean gas 6 is optionally dewatered before entering the BFG distribution system 7a where part of the clean gas 6 can be sent distributed to the hot stoves 20, where it is used as a fuel, and part 8 of the clean gas 6 can be sent to other locations 8a of the steel plant for various uses. The flow of BFG to the one or more other locations 8a is controlled by control valve system 8b.

[0094] Hydrogen, CO or a mixture of hydrogen and CO may be also be injected into the blast furnace 1 via hearth tuyere 1b as additional reducing gas. (A single tuyere is schematically represented in the figure, whereas in practice, a blast furnace comprises a multitude of tuyeres)

[0095] In order to limit the carbon footprint of the known blast furnace operation, the hydrogen, CO or the mixture of hydrogen and CO can be sourced from environmentally friendly sources, such as biofuel partial combustion or reforming.

[0096] As indicated earlier, in order to limit CO.sub.2 emissions by the blast furnace, hydrogen could appear to be the preferred additional reducing gas. Unfortunately, the cost of substantially pure hydrogen gas is usually inhibitive for this kind of industrial application.

[0097] A further technical problem related to hydrogen (and CO) injection into a blast furnace relates to the thermodynamics of the blast furnace process, namely the fact that the efficiency of hydrogen (and CO) usage in the blast furnace rarely exceeds 50%, 50% of the hydrogen injected in the blast furnace thus exits the top of the blast furnace without participating in the reactions. This limits the use of hydrogen in a conventional blast furnace.

[0098] Table 1 presents a theoretical comparison, based on process simulation, between operations of a conventional blast furnace injecting 130, 261 and 362 Nm.sup.3 hydrogen/tonne hot metal (thm) into a standard blast furnace with powdered coal injection (PCI) when that hydrogen is used to replace coal while keeping the coke rate constant. Also presented in Table 1 are the cases when 130 and 197 Nm3 of hydrogen are replacing coke while keeping the coal injection (PCI) rate constant.

TABLE-US-00001 TABLE 1 11.72 Kg H2 11.72 Kg H2 17.7 Kg H2 2 .44 Kg H2 .61 Kg H2 Period (Enter the name Reference Replacing Replacing Replacing Replacing Replacing of the period) Units Final Coal Coke Coke Coal Coal Reductant Consumption Coke rate (small + big) Kg/ 293 293 2 5 2 3 293 293 Fuel Injection Rate Kg/ 197 179 209 215 164 1 3 Coal Injection Rate Kg/ 197 167 197 197 141 120 Hydrogen Injection Rate Kg/ 0 11.72 11.72 17.70 23.44 32.61 Hydrogen Injection Rate N 0 130 130 197 281 62 Total Fuel Rate Kg/ 490 471 474 4 457 445 Tuyeres Blast Volume (Air Only) N 32 2 27 1 814 801 Blast Temperature C. 117 117 117 117 117 117 Oxygen Volume Calculated N 82.0 76. 79.7 0.4 75.7 75.1 Oxygen in the cold blast % 27. % 27.2% 27.4% 27. % 27.2% 27.2% Water Vapour added to Blast g/Nm 12.23 .00 5.00 5.00 5.00 .00 Raceway Gas Volume N 1 11 13 1413 147 149 16573 (Bosh Gas Volume) Bosh Reducing Gas N 33 723 739 03 8 920 (CO 2) Volume RAFT (Raceway Adiabatic C. 2251 2124 20 9 200 1992 1901 Flame Temp.) Top Gas Volume (dry) N 1441 1453 145 146 14 1477 Temperature C. 12 154 17 200 181 200 CO % 24.5 22. 6 22. 21.7 20.9 19.7 CO2 % 24.1 22.4 22.3 21.5 20.9 19.6 H2 % 4.3 8.5 8.9 11.4 13. 1 .5 N2 % 47.1 46.4 4 .2 45.4 45.2 44.2 CO2/(CO + CO2) 0.4 0.499 0.497 0.497 0.49 0.499 BF Operational Results Gas Utilization at FeO Level % 93.0 93.0 93.0 93.0 9 .0 9 .0 Calculated Heat Lo M 40 .7 40 .7 40 .7 40 .7 40 .7 40 .7 % of Heat Losses in the Lower BF % 0.7 0.7 0.7 0.7 0.7 0.7 Global Direct Reduction Rate % 30. % 26.1% 2 .4% 22.2% 20. % 1 .2% Direct Reduction Degree of % 2 .7% 24.9% 24.1% 20.9% 19.2% 14.8% Iron Oxides Reduction of CO2 Emission (per tonne HM) Carbon Consumption Kg/ 423 398 399 388 376 359 CO2 Emissions Kg/ 1590 14 9 1461 1421 1378 1315 CO2 Savings Kg/ 92 89 130 172 235 % CO2 Savings Kg/ 5.9% 5.7% 8.4% 11.1% 15.2% Relative Production Rate Kg/ 100% 100.0% 100.0% 100.0% 100.0% 100.0% CO2 for electricity @ 00 g CO2/kWh / 24.0 24.0 24.0 24.0 24.0 24.0 (not including oxygen) O2 for electricity @ 00 g CO2/kWh / 27.1 25. 26.3 2 .5 25.0 24.8 (oxygen) Total CO2 saved / 0 9 90 130 174 237 % CO2 saved % 5.8% 5. 8.1% 10.9% 14.8% Hydrogen to Oxygen Ratio 1.7 1.64 2.45 3.44 4.83 indicates data missing or illegible when filed

TABLE-US-00002 TABLE 2 ULCOS ULCOS ULCOS Version 4, Version 4, Version 4, ULCOS 50% recycle 50% recycle 50% recycle Version 4, gas in belly gas in belly gas in belly Period (Enter the name Reference 10% recycle 130 Nm3 260 Nm3 350 Nm3 of the period) Units Final gas in belly H2/thm H2/thm H2/thm Reductant Consumption Coke rate (Small + big) Kg/thm 293 359 320 255 230 Fuel Injection Rate Kg/thm 197 23 0 0 0 Coal Injection Rate Kg/thm 197 23 0 0 0 Hydrogen Injection Rate Kg/thm 0 0.00 11.73 23.45 31.5 Hydrogen Injection Rate Nm3/thm 0 0 130 2 0 350 Total Fuel Rate Kg/thm 4 0 382 332 279 2 2 Tuyeres Blast Volume (Air Only) Nm3/thm 832 0 0 0 0 Blast Temperature C. 117 Oxygen Volume Calculated Nm3/thm 82.0 218.1 192.8 161.3 149.4 Oxygen in the cold blast % 27. % 100.0% 100.0% 100.0% 100.0% Water Vapour added to Blast g/Nm3 12.23 0.00 0.00 0.00 0.00 Raceway Gas Volume Nm3/thm 1311 1271 973 991 939 (Bosh Gas Volume) RAFT (Raceway Adiabatic C. 2251 1901 2078 1900 1900 Flame Temp.) Top Gas Volume (dry) Nm3/thm 1441 13 7 1401 1339 1188 Temperature C. 128 200 200 17 101 CO % 24.5 51.2 42.2 32.0 28.5 CO2 % 24.1 3 .3 2 .7 24.2 23.1 H2 % 4.3 2. 13.1 2 .1 3 .1 N2 % 47.1 11.0 14.9 17.8 12.3 CO2/(CO + CO2) 0.4 0.408 0.413 0.430 0.448 BF Operational Results Gas Utilization at FeO Level % 3.0 3.0 3.0 3.0 3.0 Calculated Heat Looses M /thm 108.7 408.7 408.7 40 .7 408.7 % of Heat Losses in the Lower BF % 80.7 80.7 80.7 0.7 80.7 Global Direct Reduction Rate % 30.8% 10.4% 5.8% 0.0% 0.0% Direct Reduction Degree of % 29.7% 8.8% 4.2% 0.0% 0.0% Iron Oxides Reduction of CO2 Emission (per tonne HM) Carbon Consumption Kg/thm 423 337 2 4 224 204 CO2 Emissions Kg/thm 1550 1236 1042 22 749 CO2 Savings Kg/thm 314 509 72 801 % CO2 Savings Kg/thm 20.3% 32.8% 47.0% 51.7% Relative Production Rate Kg/thm 100% 100.0% 101.9% 120.9% 145.3% CO2 for electricity @ 00 g CO2/kWh kg/thm 24.0 24.0 23. 19.9 1 .5 (not including oxygen) O2 for electricity @ 00 g CO2/kWh kg/thm 27.1 72.0 3. 53.2 49.3 (oxygen) Total CO2 saved kg/thm 0 269 473 70 787 % CO2 saved % 16.8% 29.5% 41.1% 49.1% Hydrogen to Oxygen Ratio 0.00 0.67 1.61 2.34 indicates data missing or illegible when filed

TABLE-US-00003 TABLE 3 Total CO2 Iron Oxygen Volume saved with Additional Production Coke Charge Coal Injection Required in CO2 respect to % CO2 Hydrogen Rate rate Rate Blast Furnace Produced conventional BF saved Injected Units tonne/d Kg/thm Kg/thm Nm3/thm kg/thm tonnes/year % Nm3/h Reference 5784 293 146 92.2 1510 Conventional w. PCI 5784 300 189 58.1 1550 Conventional w. NG 5784 303 0 173.4 1402 308971 9.8% Conventional 100 Nm3 H2/thm 5784 270 189 63.7 1467 242922 7.7% 24098 Conventional 200 Nm3 H2/thm 5784 240 189 69.8 1385 483163 15.4% 48197 Conventional 300 Nm3 H2/thm 5784 210 189 74.9 1259 814611 26.0% 72295 ULCCS Version 4 6383 209 190 239.6 1258 903884 26.1% ULCOS 100 Nm3/t H2 injection 7019 185 190 227.5 1180 1258836 33.1% 29246 ULCOS 100 Nm3/t H2 injection 6344 263 74 203.9 1082 1138784 33.1% 26432 74 Kg/thm PCI ULCOS 200 Nm3/t H2 injection 7506 169 190 219.3 1127 1539163 37.8% 62546 ULCOS 200 Nm3/t H2 injection 6812 291 1 177.4 947 1463335 39.6% 56764 No PCI ULCOS 300 Nm3/t H2 injection 7866 170 164 206.0 1053 1810700 42.4% 98319 ULCOS 300 Nm3/t H2 injection 7526 258 1 160.6 840 2006584 49.2% 94071 No PCI ULCOS 400 Nm3/t H2 injection 8197 167 151 197.2 1003 2041574 45.9% 136624 w 151 Kg PCI ULCOS 400 Nm3/t H2 injection 8188 195 94 180.0 920 2176259 49.0% 136472 w 94 Kg PCI Total Oxygen Requirements Total Oxygen Additional Additional (80% Hot Metal, requirement Oxygen Oxygen Additional Hydrogen 20% Scrap, 93% yield) for Blast Surplus/Deficit Surplus/Deficit produced/Additional Blast L-D Converter Furnace and () from Water () from Water Oxygen required Furnace (55 Nm3/thm) L-D Converter Decomposition Decomposition Units H2/O2 Ratio Nm3/h Nm3/h tonnes/day NmS/h tonnes/day Reference 22211 15408 1289 Conventional w. PCI 13996 15408 1008 Conventional w. NG 41791 15408 1960 Conventional 100 Nm3 H2/thm 1.57 15348 15408 1054 18707 641 Conventional 200 Nm3 H2/thm 2.87 16816 15408 1104 8125 278 Conventional 300 Nm3 H2/thm 4.01 18050 15408 1147 2690 92 ULCCS Version 4 63714 17004 2766 ULCOS 100 Nm3/t H2 injection 0.44 66532 18699 2921 70608 2420 ULCOS 100 Nm3/t H2 injection 0.49 53894 16900 2426 57578 1973 74 Kg/thm PCI ULCOS 200 Nm3/t H2 injection 0.91 68582 19995 3036 57304 1964 ULCOS 200 Nm3/t H2 injection 1.13 50347 18147 2347 40112 1375 No PCI ULCOS 300 Nm3/t H2 injection 1.46 67516 20954 3032 39310 1347 ULCOS 300 Nm3/t H2 injection 1.87 50347 20049 2412 23360 801 No PCI ULCOS 400 Nm3/t H2 injection 2.03 67352 21838 3057 20879 716 w 151 Kg PCI ULCOS 400 Nm3/t H2 injection 2.22 61406 21814 2852 14984 514 w 94 Kg PCI

[0099] Table 3 demonstrates the reduced requirement for external oxygen at the blast furnace and at the L-D Converter as illustrated in FIG. 2 when oxygen from the water decomposition process is used in the steelmaking plant.

[0100] As shown in Table 3, if oxygen from the water decomposition process is used for the blast furnace and the L-D converter, the need for external oxygen, typically from an air separation plant, to meet the oxygen requirement of the steel plant is greatly reduced or non-existent.

[0101] For most of the embodiments illustrated in Table 3, the use of water decomposition to meet the entire requirement of the blast furnace for additional hydrogen results in a generation of oxygen which is insufficient to meet the (additional) oxygen requirement of the blast furnace and the converter. Consequently, additional oxygen must be obtained from a further oxygen source, such as an ASU, in order to meet said requirement. However, the amount of oxygen to be obtained from said further oxygen source is drastically reduced.

[0102] However, when the use of water decomposition to meet the entire requirement of the blast furnace and/or for the converter (if present) results in the generation of oxygen in excess of the additional oxygen requirement of the blast furnace (and, if applicable, the converter), surplus generated oxygen may advantageously be used in other processes/installations of the iron- or steelmaking plant and/or be sold to generate revenue. The present invention thus provides a method for reducing CO.sub.2 emissions from an iron- or steelmaking plant comprising an iron furnace set (IFS) by means of the injection into the IFS of a non-carbon-based reducing agent and this at lower overall cost. It also greatly reduces the amount of external oxygen produced by ASU, VSA, VPSA or any other method to complete the oxygen requirement of the iron- or steelmaking plant. In doing this the amount of indirect CO.sub.2 emissions from oxygen production are also avoided or reduced. The carbon footprint of the iron- or steelmaking plant can be further reduced by using low-carbon-footprint electricity as described above.

[0103] It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.