Method for operating a top gas recycling blast furnace installation

Abstract

Method of operating a blast furnace installation comprising a top gas recycle blast furnace and hot stones, whereby a hydrocarbon containing fuel is transformed into a transformed gas stream consisting mainly of CO and H.sub.2 and substantially devoid of hydrocarbon, whereby a low-heating-value gaseous fuel is generated comprising a mixture of the transformed gas with a portion of the CO.sub.2-rich tail gas obtained by decarbonatation of the blast furnace gas, and whereby the low-heating-value fuel is used to heat the hot furnace gas is heated before being injected into the blast-furnace.

Claims

1. A method of operating a blast furnace installation comprising a top gas recycle blast furnace generating blast furnace gas, comprising the steps of: decarbonating the blast furnace gas so as to obtain a CO.sub.2-enriched rich tail gas stream and a decarbonated blast furnace gas stream containing not more than 3% vol CO.sub.2; transforming a hydrocarbon-containing gaseous fuel not generated by the blast furnace to generate a transformed gas stream containing at least 70% vol of CO and H.sub.2 in total and at most 7% vol of hydrocarbon; producing a low-heating-value gaseous fuel having a heating value of from 2.8 to 7.0 MJ/Nm.sup.3 and containing (i) a portion of the tail gas stream and (ii) at least a first portion of the transformed gas stream and using said low-heating-value gaseous fuel for heating hot stoves; heating at least 70% vol of the decarbonated blast furnace gas stream in the hot stoves to a temperature between 700 C. and 1300 C. to generate heated decarbonated blast furnace gas; and injecting the heated decarbonated blast furnace gas into the blast furnace.

2. The method of claim 1, wherein the hydrocarbon-containing gaseous fuel contains natural gas and/or coke oven gas.

3. The method of claim 1, wherein partial combustion of the hydrocarbon-containing gaseous fuel is used to generate the transformed gas stream.

4. The method of claim 1, wherein a fuel reforming process is used to generate the transformed gas stream.

5. The method of claim 4, wherein the hydrocarbon-containing fuel is reformed using CO.sub.2 as a reforming agent.

6. The method of claim 5, wherein a part of the tail gas is used as a reforming agent.

7. The method of claim 1, wherein at least a portion of the transformed gas stream is mixed with the decarbonated blast furnace gas so as to obtain a fortified decarbonated blast furnace gas stream upstream of the hot stoves.

8. The method of claim 7, wherein the low-heating-value gaseous fuel contains a first portion of the fortified decarbonated blast furnace gas stream.

9. The method of claim 7, wherein partial combustion of the hydrocarbon-containing gaseous fuel in a partial combustion reactor is used to generate the transformed gas stream and a second portion of the fortified decarbonated blast furnace gas stream is used to heat the partial combustion reactor.

10. The method of claim 7, wherein a fuel reforming process is conducted in a reformer to generate the transformed gas stream and whereby a third portion of the fortified decarbonated blast furnace gas stream is used to heat the reformer.

11. The method of claim 10, wherein combustion of said third portion with air is used to heat the reformer.

12. The method of claim 1, whereby 80 to 90% vol of the decarbonated blast furnace gas stream is heated in the hot stoves and injected into the blast furnace.

13. The method of claim 1, whereby the heated decarbonated blast furnace gas is injected into the blast furnace via hearth tuyeres.

14. The method of claim 13, wherein the heated decarbonated blast furnace gas is injected into the blast furnace also via shaft tuyeres.

15. The method of claim 1, whereby a vacuum pressure swing adsorption, a pressure swing adsorption or a chemical absorption unit is used to decarbonate the blast furnace gas.

16. The method of claim 1 whereby the hot stoves are heated by burning the low-heating-value gaseous fuel with air.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a schematic of a first embodiment of the invention.

(2) FIG. 2 is a schematic of a second embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(3) FIG. 1 describes a preferred embodiment of the invention. A blast furnace 1 is charged from the top with coke and iron ore 2 which descend in the blast furnace 1. Substantially pure oxygen 22, pulverized coal (or another organic combustible substance) 23 along with recycled decarbonated blast furnace gas (a.k.a. product gas) 21 are injected in the hearth tuyeres 1b. Optionally a portion of recycled product gas 29 is injected into the shaft tuyere 1c to combine inside the blast furnace with the gases produced at the hearth tuyeres to produce a reducing gas 1d that ascends the inside of blast furnace 1, contacts the iron ore and coke 2 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. The 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 CO.sub.2 removal system 7. The CO.sub.2 removal system 7 can be a vacuum pressure swing adsorption system (VPSA), a pressure swing adsorption system (PSA) or a chemical absorption system such as an amines-based absorption system or any other type of system that removes CO.sub.2 from the (clean) BFG. Substantially all of the CO.sub.2 is removed at 7 with the exception of that which is not practical to remove (<10% vol).

(4) The clean gas stream 6 is split into two streams during CO.sub.2 separation: a CO.sub.2-enriched tail gas 8 and a CO.sub.2-lean product gas or decarbonated BFG 9. The CO.sub.2 rich tail gas 8 is mixed with supplementary fuel gas 10 and if required, steam 10a to provide a gas composition 11 that can be reformed or partially combusted to create the desired CO+H.sub.2 containing mixture (low in hydrocarbons) suitable (a) for use in the low-heating-value fuel for heating the stoves and (b) for mixing with the decarbonated BFG 9 for recycling into the blast furnace (see below). The quantity of CO.sub.2 rich tail gas that is used in the reforming or partial combustion process will depend on the process used, the process for treating the mixture (reforming and/or partial oxidation) and the pressure in reactor 14. The quantity of tail gas 8 used in reactor 14, and in the low-heating value fuel (see below) will be regulated using valves 8b and 25a, which also determine the quantity of tail gas 8a leaving the system (purge).

(5) The CO.sub.2-lean product gas stream (decarbonated BFG) 9 exits the CO.sub.2 removal system 7 at elevated pressure (typically 4-8 Bar) and is fortified with synthetic gas (transformed gas) created from the reformation and/or partial oxidation of NG or COG 18, the synthetic or transformed gas consisting mainly of CO and H.sub.2 coming from the reactor 14. COG or NG 10 plus (optionally) steam 10a and CO.sub.2 rich tail gas 8 will normally need to be pressurized to improve the kinetics of the reforming and/or partial oxidation process taking place in 14. The pressurization of these gases will be done at compressor 12 to make a pressurized mixture of gases 13 that are reformed and/or partially combusted in reactor 14. After conversion of gases 13 to a mixture rich in CO and H.sub.2 (stream 15), the gases 15 may need to be depressurized to an appropriate pressure for injection in the blast furnace. This would be accomplished using gas expander 17. Depending on the pressure drop between the entrance and exit of the expander, energy from the expander 17 could be used to generate electricity.

(6) Fortified gas stream 19 is created from mixing stream 9 with stream 18. A portion 26 of stream 19 is diverted for making a mixed gas 27 that will be used as a low-heating-value fuel for heating the stoves. This portion 26 of stream 19 used in the mixed gas 27 is regulated using valve 26a. Mixed gas 27 has a heating value appropriate for heating stoves 20. Mixed gas 27 is created using a portion 25 of CO.sub.2-rich tail gas whose flow rate will be regulated by valve 25a to be mixed with a portion 26 of stream 19. The heating value of mixed gas 27 is typically low (5.5-6.0 MJ/Nm.sup.3) and the mixed gas has (a) a low content of hydrocarbons to prevent vibration in the stove combustion chamber and (b) a high content of CO and H.sub.2 for facilitating smooth combustion. Another portion of stream 19 (stream 16) is used as fuel to heat reactor 14. The flow rate of stream 16 will be regulated using valve 26b. Air stream 28 is used as an oxidant to combust stream 27 for heating the stoves and air stream 24 is used as an oxidant to combust stream 16 for heating reactor 14.

(7) Fortified gas stream 19 is heated in stoves 20 to create gas streams 21 and 29 having a temperature greater than 700 C. and as high as 1300 C. However, the preferred temperature of stream 21 is between 850 C. and 1000 C. and more preferably 880-920 C. in order to prevent possible reduction of the oxide refractory lining the pipeline to the blast furnace. Gas stream 29 may or not be used depending on the configuration of the particular TGRBF. The distribution of flow rates between streams 21 and 29 are governed by valve 30.

(8) FIG. 2 describes a second embodiment where a blast furnace 1 is charged from the top with coke and iron ore 2 which descend in the blast furnace. Substantially pure oxygen 22, pulverized coal (or another organic combustible) 23 along with recycled decarbonated blast furnace gas (product gas) 21 are injected in the hearth tuyeres 1b. Optionally a portion of recycled product gas 29 is injected into the shaft tuyere 1c to combine inside the blast furnace with the gases produced at the hearth tuyeres to produce a reducing gas 1d that ascends the inside blast furnace 1, contacts the iron ore and coke 2 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 where it is removed (tapped) la along with a slag containing oxide impurities. The 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 CO.sub.2 removal system 7. The CO.sub.2 removal system 7 can be a vacuum pressure swing adsorption system (VSPA), a pressure swing adsorption system (PSA), and a chemical absorption system such as amines or any other type of system that removes CO.sub.2 from the clean gas. Substantially all of the CO.sub.2 is removed at 7 with the exception of that which is not practical to remove (<10%).

(9) The clean gas stream 6 is split into two streams during CO.sub.2 separation: a CO.sub.2-rich tail gas 8 and a CO.sub.2-lean product gas (decarbonated BFG) 9. The CO.sub.2-rich tail gas 8 is mixed with supplementary fuel 10 and, if required, steam 10a to provide a gas composition 11 that can be reformed or partially combusted to create the desired CO+H.sub.2 mixture (low in hydrocarbons) for use in the low-heating-value fuel for heating the stoves. The quantity of CO.sub.2 rich tail gas that is used in the reforming or partial combustion process depends on the process used, the process for treating the mixture (reforming or partial oxidation) and the pressure in reactor 14. The quantity of tail gas 8 used thereto is regulated using valves 8b and 25a which also determines the quantity of tail gas 8a leaving the system.

(10) The CO.sub.2-lean product gas stream 9 exits the CO.sub.2 removal system 7 at elevated pressure (typically 4-8 Bar) and is split into a portion 19 that is recycled in the blast furnace and another portion 16 that is used to heat reactor 14. COG or NG 10 plus steam 10a and CO.sub.2-rich tail gas 8 normally need to be pressurized to improve the kinetics of the reforming or partial oxidation process taking place in reactor 14. The pressurization of these gases is done at compressor 12 to make a pressurized mixture of gases 13 that is reformed and/or partially combusted in reactor 14. After conversion of gases 13 to a mixture rich in CO and H.sub.2 (stream 15), the gas stream 15 may need to be depressurized to an appropriate pressure for injection in the blast furnace. This is accomplished using gas expander 17. Depending on the pressure drop between the entrance and exit of the expander 17, energy from the expander could be used to generate electricity. After CO and H.sub.2 rich stream 15 is expanded at 17 to become stream 18 which is now suitably rich in CO and H.sub.2 and sufficiently lean in hydrocarbons, it mixes with CO.sub.2-rich stream 25 in order to have a low enough heating value (5.5-6.0 MJ/Nm.sup.3) (stream 27) to be used in the stoves. Air stream 28 is used as an oxidant to combust stream 27 for heating the stoves and air stream 24 is used as an oxidant to combust stream 16 for heating reactor 14.

(11) Product gas stream 19 will be heated in stoves 20 to create gas streams 21 and 29 having a temperature greater than 700 C. and as high as 1300 C. However, the preferred temperature of stream 21 is between 850 C. and 1000 C. and more preferably 880-920 C. in order to prevent possible reduction of the oxide refractory lining the pipeline to the blast furnace. Gas stream 29 may or not be used depending on the configuration of the particular TGRBF. The distribution of flow rates between streams 21 and 29 are governed by valve 30.

(12) Table 5 illustrates the differences between, on the one hand, a prior-art TGRBF as demonstrated at pilot scale in Europe and, on the other hand, a TGRBF according to the preferred embodiment of the invention as illustrated in FIG. 1, both when reformed natural gas and when reformed COG is used to fortify the recycled top gas.

(13) This example was calculated from actual blast furnace data using a blast furnace model which was initially used to calculate the performance of a TGRBF, taking into consideration the reduction efficiency and heat losses.

(14) The model simulated a TGRBF that injects 50% of the heated (900 C.) recycled gas through the hearth tuyeres and 50% through the shaft tuyeres.

(15) The operation of a TGRBF was then modeled to include the preferred embodiment with identical gas utilization at FeO level, identical total heat losses and identical percentages of the heat loss in the lower blast furnace, so as to illustrate the advantages of the invention for operating the stoves.

(16) Due to the hydrogen content of COG, the biggest reduction in coke rate is predicted for a TGRBF that is using reformed COG as taught in the preferred embodiment of the invention. A coke rate reduction of 25 kg/thm is expected using the invention with COG. Significant coke rate reduction can be achieved also when using reformed natural gas where a 21 kg/thm coke rate reduction can be anticipated using the invention.

(17) In all three cases shown in Table 5, the raceway adiabatic flame temperature (RAFT), and top temperature are within the limits generally accepted by blast furnace operators. However, the reference TGRBF in Table 5 is operating at its maximum limits of both RAFT (2300) and top gas temperature (200 C.). The predictions calculated for a TGRBF using the preferred embodiment show blast furnace operations that are more comfortable with RAFT well below the commonly agreed upon maximum. Less oxygen is needed to supply a TGRBF using the preferred embodiment of the invention.

(18) Table 5 also illustrates how the extra gas reformed from COG or NG and used to fortify the decarbonated blast furnace gas enabled the total recycle ratio (last row Table 5) to drop to 80.0-81.5%. This provided enough left over gas to: Heat the stoves, Heat the reformer; Improve the thermodynamics of reduction,

(19) This compares to the reference TGRBF where it would be necessary to recycle more than 90% to achieve a higher coke rate reduction. The recycled feed gas left over (10%) was not enough to heat the stoves and in this case it would have been necessary to use fuel (COG or NG) to heat the stoves.

(20) TABLE-US-00005 TABLE 5 Example Blast Furnace improvement using the Preferred Embodiment. Preferred Embodiment Preferred using Embodiment Reference Reformed using TGRBF NG Reformed COG Reductant Consumption Coke rate calculated Kg/thm 273 252 248 Coal Injection Rate Kg/thm 150 150 150 Tuyeres Oxygen Volume Calculated Nm3/thm 262 250 248 Raceway Gas Volume (Bosh Nm3/thm 1005 1009 1019 Gas Volume) RAFT (Raceway Adiabatic C. 2295 2205 2200 Flame Temp.) Top Gas Volume (dry) Nm3/thm 1426 1403 1410 Temperature C. 199 189 188 CO % 57.3 53.6 50.1 CO2 % 33.5 32.4 31.1 H2 % 6.6 12.3 14.5 N2 % 2.7 1.7 4.3 CO2/(CO + CO2) 0.369 0.376 0.383 BF Operational Results Global Direct Reduction Rate % 10.2% 7.8% 7.5% Direct Reduction Degree of Iron % 8.5% 6.0% 5.7% Oxides Type of Operation Total Gas Recycled into the BF Nm3/thm 816 869 897 Recycle Gas Temperature ( C.) C. 900 900 900 Percent Decarbonated Top Gas % 91.9 80.3 81.5 Recycled to Blast Furnace

(21) While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fail within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

(22) The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

(23) Comprising in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing i.e. anything else may be additionally included and remain within the scope of comprising. Comprising is defined herein as necessarily encompassing the more limited transitional terms consisting essentially of and consisting of; comprising may therefore be replaced by consisting essentially of or consisting of and remain within the expressly defined scope of comprising.

(24) Providing in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

(25) Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

(26) Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within the range.

(27) All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.