METHOD FOR OPERATING A COKE OVEN PLANT

Abstract

A method for operating a coke oven plant, comprising providing a blast furnace gas stream and a coke oven gas stream treating a part of the blast furnace gas stream in a CO converter unit to obtain a treated blast furnace gas stream, subjecting the treated blast furnace gas stream in a CO.sub.2-depletion unit to obtain a primary CO.sub.2-depleted blast furnace gas stream, mixing the primary CO.sub.2-depleted blast furnace gas stream with a proportion of the blast furnace gas stream in a first mixing unit to obtain a secondary CO.sub.2-depleted blast furnace gas stream, mixing the secondary CO.sub.2-depleted blast furnace gas stream with a proportion of the coke oven gas stream in a second mixing unit to obtain a tertiary CO.sub.2-depleted gas stream, feeding said tertiary CO.sub.2-depleted gas stream to an underfiring system of a coke oven from the coke oven plant to convert coal to coke thereby producing a coke oven gas and an exhaust gas, where properties of the secondary CO.sub.2-depleted blast furnace gas stream are determined by a first analyzer downstream the first mixing unit are determined by properties of the tertiary CO.sub.2-depleted gas stream in a second analyzer downstream the second mixing unit, wherein the proportion of the blast furnace gas stream and the proportion of the coke oven gas stream are controlled based on said properties determined by said first and second analyzers to adjust at least one of CO.sub.2 content, CO content, H.sub.2 content, Wobbe Index, stoichiometric combustion air demand and Lower Heating Value in said tertiary CO.sub.2-depleted gas stream thereby controlling operation of the underfiring system.

Claims

1. A method for operating a coke oven plant, the method comprising the steps of: a) providing a blast furnace gas stream comprising carbon monoxide CO, carbon dioxide CO.sub.2 and hydrogen H.sub.2, and a coke oven gas stream comprising hydrogen H.sub.2, carbon monoxide CO and methane CH.sub.4; b) treating a part of the blast furnace gas stream by converting carbon monoxide to carbon dioxide in a CO converter unit to obtain a treated blast furnace gas stream; c) subjecting the treated blast furnace gas stream from step b) to a removal of carbon dioxide in a CO.sub.2-depletion unit to obtain a primary CO.sub.2-depleted blast furnace gas stream; d) mixing the primary CO.sub.2-depleted blast furnace gas stream from step c) with a proportion of the blast furnace gas stream in a first mixing unit to obtain a secondary CO.sub.2-depleted blast furnace gas stream; e) mixing the secondary CO.sub.2-depleted blast furnace gas stream from step d) with a proportion of the coke oven gas stream in a second mixing unit to obtain a tertiary CO.sub.2-depleted gas stream; f) feeding said tertiary CO.sub.2-depleted gas stream to an underfiring system of a coke oven from the coke oven plant to convert coal to coke thereby producing a coke oven gas and an exhaust gas; wherein properties of the secondary CO.sub.2-depleted blast furnace gas stream are determined by a first analyzer downstream the first mixing unit and properties of the tertiary CO.sub.2-depleted gas stream are determined by a second analyzer downstream the second mixing unit; wherein the proportion of the blast furnace gas stream and the proportion of the coke oven gas stream are controlled based on said properties determined by said first and second analyzers to adjust at least one of CO.sub.2 content, CO content, H.sub.2 content, Wobbe Index, stoichiometric combustion air demand and Lower Heating Value in said tertiary CO.sub.2-depleted gas stream thereby controlling operation of the underfiring system.

2. The method as claimed in claim 1, wherein the proportion of the blast furnace gas stream and the proportion of the coke oven gas stream are controlled based on said properties determined by said first and second analyzers to adjust at least one of Wobbe Index and Lower Heating Value in said tertiary CO.sub.2-depleted gas stream.

3. The method as claimed in claim 1, wherein the proportion of the blast furnace gas stream and the proportion of the coke oven gas stream are controlled to reduce fluctuations in the operation of the underfiring system.

4. The method as claimed in claim 1, wherein the proportion of the blast furnace gas stream and the proportion of the coke oven gas stream are controlled to reduce CO.sub.2 content in the exhaust gas and/or CO.sub.2 footprint of the exhaust gas.

5. The method as claimed in claim 1, wherein the proportion of the blast furnace gas stream and the proportion of the coke oven gas stream are controlled to achieve a target value of Wobbe Index and/or to raise the Lower Heating Value of the tertiary CO.sub.2-depleted gas stream.

6. The method as claimed in claim 5, wherein the Wobbe Index of the tertiary CO.sub.2-depleted stream is controlled to be within a range of +/20% of a preset target value of Wobbe Index.

7. The method as claimed in claim 5, wherein the Wobbe Index of the tertiary CO.sub.2-depleted stream, regulated to be within a range of 3.5 to 7 MJ/Nm.sup.3.

8. The method as claimed in claim 5, wherein the Lower Heating Value of the tertiary CO.sub.2-depleted stream is raised by at least 10% compared to the Lower Heating Value of the blast furnace gas from the blast furnace gas source.

9. The method as claimed in claim 5, wherein the Lower Heating Value of the tertiary CO.sub.2-depleted stream is controlled to be within a range of 3700 to 5300 kJ/Nm.sup.3.

10. The method as claimed in claim 1, wherein, in step b), the treating of the part of the blast furnace gas stream in the CO converter unit comprises a water gas shift reaction.

11. The method as claimed in claim 1, wherein, in step c), the removal of carbon dioxide in the CO.sub.2-depletion unit comprises one or more of physical adsorption and/or chemical absorption.

12. The method as claimed in claim 1, wherein both steps b) and c) are effected in a sorption enhanced water gas shift reactor.

13. The method as claimed in claim 1, wherein, in step c), the removal of carbon dioxide in the CO.sub.2-depletion unit is such that the CO.sub.2 content of the primary CO.sub.2-depleted blast furnace gas stream is at most 7.5 vol.-%.

14. A coke oven plant comprising a) a source of blast furnace gas, in particular a blast furnace gas network, configured for providing a blast furnace gas stream comprising carbon monoxide CO, carbon dioxide CO.sub.2 and hydrogen H.sub.2, and a source of coke oven gas, in particular a coke oven gas network, configured for providing a coke oven gas stream comprising hydrogen H.sub.2, carbon monoxide CO and methane CH.sub.4; b) a CO converter unit connected to said source of blast furnace gas and configured for treating a part of the blast furnace gas stream by converting carbon monoxide to carbon dioxide to obtain a treated blast furnace gas stream; c) a CO.sub.2-depletion unit connected to said CO converter unit and configured for removing carbon dioxide from said treated blast furnace gas stream to obtain a primary CO.sub.2-depleted blast furnace gas stream; d) a first mixing unit connected to said CO.sub.2-depletion unit and controllably connected to said source of blast furnace gas, said first mixing unit being configured for mixing the primary CO.sub.2-depleted blast furnace gas stream from the CO.sub.2-depletion unit with a proportion of the blast furnace gas stream to obtain a secondary CO.sub.2-depleted blast furnace gas stream, said controllable connection to said source of blast furnace gas comprising a controllable blast furnace bypass stream regulator; e) a second mixing unit connected to said first mixing unit and controllably connected to said source of coke oven gas, said second mixing unit being configured for mixing the secondary CO.sub.2-depleted blast furnace gas stream from the first mixing unit with a proportion of the coke oven gas stream to obtain a tertiary CO.sub.2-depleted gas stream, said controllable connection to said source of coke oven gas comprising a controllable coke oven gas stream regulator; f) a coke oven from the coke oven plant comprising an underfiring system connected to said second mixing unit and configured for burning said tertiary CO.sub.2-depleted gas stream to convert coal to coke thereby producing a coke oven gas and an exhaust gas; wherein the coke oven plant further comprises a first analyzer downstream the first mixing unit configured for determining properties of the secondary CO.sub.2-depleted blast furnace gas stream and a second analyzer downstream the second mixing unit configured for determining properties of the tertiary CO.sub.2-depleted gas stream; a control unit configured for controlling operation of the underfiring system by determining the proportion of the blast furnace gas stream and the proportion of the coke oven gas stream based on said properties provided by said first and second analyzers and by controlling the controllable blast furnace bypass stream regulator and the controllable coke oven gas stream regulator so as to adjust at least one of CO.sub.2 content, CO content, H.sub.2 content, Wobbe Index, stoichiometric combustion air demand and Lower Heating Value in said tertiary CO.sub.2-depleted gas stream.

15. The coke oven plant as claimed in claim 14, wherein the CO converter unit comprises a water gas shift reactor.

16. The coke oven plant as claimed in claim 14, wherein the CO.sub.2-depletion unit comprises one or more of physical adsorption device and/or chemical absorption device.

17. The coke oven plant as claimed in claim 14, wherein both CO converter unit and CO.sub.2-depletion unit are formed by a sorption enhanced water gas shift reactor.

18. The coke oven plant as claimed in claim 14, wherein the CO.sub.2-depletion unit is operated such that the CO.sub.2 content of the primary CO.sub.2-depleted blast furnace gas stream is at most 7.5 vol.-%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0070] A preferred embodiment will now be described, by way of example, with reference to the accompanying drawing in which:

[0071] FIG. 1 is a schematic view of an embodiment of a (part of a) coke oven plant.

[0072] Further details and advantages of the present disclosure will be apparent from the following detailed description of several not limiting embodiments with reference to the attached drawing.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0073] An embodiment of the method of operating a coke oven plant, or of an embodiment of such a coke oven plant itself, is schematically represented in FIG. 1.

[0074] A coke oven or coke oven battery 80 is fed with a coke oven feeding stream which is a so-called tertiary CO.sub.2-depleted stream F, which is produced from mainly a(n initial) blast furnace gas (BFG) stream B from a BFG source, such as a BFG network 10, and a proportion of coke oven gas (COG) stream C from a COG source, such as a COG network or using the coke oven gas stream H directly from the coke oven.

[0075] As can be seen in FIG. 1, part B1, i.e. a first part, of the BFG stream B is first fed to a CO converter unit 30 to convert at least part, preferably essentially all, such as >90 mol.-%, preferably >95 mol.-%, more preferably >99 mol.-%, of the carbon monoxide CO contained in the BFG to carbon dioxide. Advantageously, the CO converter unit comprises a water gas shift reactor to convert CO in the presence of water vapor to CO.sub.2 and H.sub.2. The CO conversion not only reduces significantly the content of toxic CO and not only allows its removal together with the original CO.sub.2 in the following step, but it also allows for recovering the energy still contained in the CO by the generation of additional hydrogen.

[0076] The resulting treated BFG thereafter enters a CO.sub.2-depletion unit 40 to capture and remove most of the CO.sub.2 (original and produced by CO converter unit 30). The capture and removal may be made by any suitable technique, such as one or more of physical adsorption and/or chemical absorption processes, e.g. Pressure Swing Adsorption (PSA), Vacuum Pressure Swing Adsorption (VPSA) and capture with washing liquid(s). The overall reduction in CO.sub.2 depends on the initial contents of CO and CO.sub.2, on the processes used both in the CO converter unit and in the CO.sub.2-depletion unit. Generally however, reductions of more than 85%, more preferably more than 90%, or even above 95% in the CO.sub.2 footprint can be achieved within the primary CO.sub.2-depleted BFG stream leaving the CO.sub.2-depletion unit as compared to the initial BFG B (or B1 or B2).

[0077] The resulting primary CO.sub.2-depleted BFG stream D is thereafter fed to a first mixing unit 60, where it is or can be mixed with a proportion B2, i.e. a second part, of initial BFG if needed to adjust one or more of its properties, such as CO.sub.2 content, CO content, H.sub.2 content, Wobbe Index and Lower Heating Value. The adjustment of these one or more properties is controlled by a control unit (not shown) based on the measurement of these properties made by a first analyzer 65 located downstream the first mixing unit 60 and by controlling the amount of BFG B2 added to the first mixing unit 60 via the BFG bypass line by acting on the BFG bypass stream regulator 15, which may be e.g. a controllable valve. The BFG treatment stream, i.e. part B1, and the BFG bypass stream, i.e. proportion B2, add up to the total quantity of BFG stream B.

[0078] The control of BFG bypass stream regulator 15 may be made to predominantly use CO.sub.2-depleted BFG by favoring the use of the primary CO.sub.2-depleted BFG stream D, thereby significantly reducing the overall content of CO.sub.2 in the exhaust G at the stack 90 of the coke oven 80. Alternatively, the control of BFG bypass stream regulator 15 may be made to predominantly reduce the fluctuations of one or more of the above-mentioned properties by adjusting the flow through the bypass line to best straighten said property or properties, at least as long as this is possible within the rates of mixing streams B2 and D. The control of BFG bypass stream regulator 15 can of course also be made to best compromise between reducing the overall content of CO.sub.2 in the exhaust G and reducing the fluctuations.

[0079] Even with the reduction in the fluctuation of said one or more properties, which can be achieved by using at least some primary CO.sub.2-depleted BFG stream D instead of only initial BFG B2 stream, it will generally be necessary or desirable to further controllably add a proportion of coke oven gas for these same reasons, i.e. reducing fluctuation and/or raising the calorific value of the gas stream D.

[0080] Hence, the primary CO.sub.2-depleted BFG stream E leaving the first mixing unit 60 is fed to a second mixing unit 70 together with a proportion of coke oven gas GOG stream C, said proportion being controllable through COG stream regulator 25. Again, the control of said regulator is advantageously made based on one or more of the aforementioned properties determined by the second analyzer 75 downstream of the second mixing unit 70.

[0081] Likewise, the control of COG stream regulator 25 may be made to predominantly use secondary CO.sub.2-depleted BFG E, thereby keeping the reduction in the overall content of CO.sub.2 in the exhaust G at the stack 90 of the coke oven 80.

[0082] Alternatively, the control of COG stream regulator 25 may be made to predominantly reduce the fluctuations of one or more of the above-mentioned properties within the tertiary CO.sub.2-depleted stream by adjusting the flow from the COG stream C to best straighten said property or properties, at least as long as this is possible within the rates of mixing streams C and E. Again, the control of COG stream regulator 25 can of course also be made to best compromise between reducing the overall content of CO.sub.2 in the exhaust G and reducing said fluctuations.

[0083] If necessary or desirable, further analyzers may be provided, such as a third analyzer 10.5 determining the one or more properties of the initial BFG stream B and/or a fourth analyzer 20.5 determining the one or more properties of the COG stream C. The values of the determined properties can be fed to the control unit to further improve the control of the composition, and thus of the properties, of the tertiary CO.sub.2-depleted stream which will be fed to the underfiring system of the coke oven 80.

[0084] In the coke oven (battery), coal is converted to coke with the heat produced by the underfiring system burning the tertiary CO.sub.2-depleted stream F. The combustion produces an exhaust stream G and the coking operation produces a coke oven gas H, which as mentioned earlier, can be used as source of COG in COG stream C.

[0085] As an example of what can be achieved with the present disclosure, reference is made to the following table, which shows some ameliorations when operating according to the disclosure (Tertiary CO.sub.2-depleted gas) as compared to operating with mixed BFG and COG without CO.sub.2-depletion (conventional Mixed blast furnace gas and coke oven gas): while the LHV can be reasonably raised, the CO.sub.2 emissions at the stack can be significantly reduced.

TABLE-US-00001 TABLE Coke oven battery underfiring LHV of CO.sub.2 underfiring emissions gas at stack Case kJ/Nm.sup.3 kg CO.sub.2/t coke Mixed blast furnace gas and coke oven 3000-5000 675-1254 gas (not according to the disclosure) Normal: 4200 Tertiary CO.sub.2-depleted gas (according 3700-5000 80-300 to the disclosure) Normal: 4200