Methanation method and power plant comprising CO2 methanation of power plant flue gas

Abstract

One embodiment relates to a methanation method comprising the conversion into methane (CH.sub.4) of CO.sub.2, in particular CO.sub.2 gas, originating from, in particular diverted or obtained from, power plant flue gas from a power plant fired with carbon-containing fuel, in particular carbon-containing gas, and having a connected water/steam circuit, said method being performed in a methanation plant. Some embodiments provide a solution that makes it possible to couple a power plant and a methanation plant to one another in an energetically favorable manner.

Claims

1. A methanation process comprising the conversion of CO.sub.2 into methane in a methanation plant, the CO.sub.2 originating from a power station which is an integral and/or integrated constituent of a smelting works or chemical works, the power station fired with a carbonaceous fuel with attached water/steam circuit and from a coproduct power station flue gas of gas of the smelting works or chemical works, and wherein the power station is supplied with the coproduct gas in the form of a gas mixture, the gas mixture containing one or more gaseous byproducts of the smelting works or chemical works as carbonaceous materials stream and fuel, said process comprising coupling out a heat energy arising as waste heat in the conversion of CO.sub.2 to methane in the methanation plant at least partly into at least one materials stream and/or heat energy stream wherein this stream is supplied at least partly to at least one medium flowing into a combustion chamber of a steam generator of the power station on the burner side and/or to the water/steam circuit of the power station and/or to a CO.sub.2 exhaust gas treatment or CO.sub.2 workup, which is connected upstream, in terms of process engineering, of the methanation plant, and/or to one or more operating stages of the smelting works or chemical works, and hydrogen obtained from the coproduct gas and generated by means of an electrolysis is supplied to the methanation plant, wherein the hydrogen required in the methanation plant for the methanation of the CO2 is obtained in the region of the smelting works or chemical works at least partly or temporarily from the one or more coproduct gases.

2. The methanation process as claimed in claim 1 wherein coupling out a heat energy arising as waste heat in the conversion of CO.sub.2 to methane in the methanation plat at least partly comprises coupling out a heat energy to the CO.sub.2 exhaust gas treatment or CO.sub.2 workup, and wherein at least a part of the power station flue gas arising in combustion of the carbonaceous fuel in the combustion chamber of the steam generator of the power station, or of the CO.sub.2 gas present in the power station flue gas, is supplied to the methanation plant, after the CO.sub.2 exhaust gas treatment or CO.sub.2 workup of the power station flue gas.

3. The methanation process as claimed in claim 1 wherein the CO.sub.2 gas, is obtained from the power station flue gas at least partly in the CO.sub.2 exhaust gas treatment or the CO.sub.2 workup by utilizing a Post-Combustion (Carbon) Capture operation (PCC or PCCC operation).

4. The methanation process as claimed in claim 1 wherein the methanation plant and/or the CO.sub.2 exhaust gas treatment or CO.sub.2 workup is operated, in times of excess power in the public power grid, at least partly or temporarily with the excess power and/or the methanation plant and/or the CO.sub.2 exhaust gas treatment or CO.sub.2 workup is supplied with power generated by a generator attached to the water/steam circuit of the power station.

5. The methanation process as claimed in claim 1 wherein the hydrogen supplied to the methanation plant is generated at least partly or temporarily by electrolysis integrated into the smelting works or chemical works.

6. The methanation process as claimed in claim 5, wherein the electrolysis, in times of excess power in the public power grid, is operated at least partly or temporarily with the excess power and/or the electrolysis is supplied with power generated by a generator attached to the water/steam circuit of the power station.

7. The methanation process as claimed in claim 1 wherein the hydrogen required in the methanation plant for the methanation of the CO.sub.2 is obtained in a region of the smelting works or chemical works at least partly or temporarily from the one or more coproduct gases by pressure swing absorption or membrane separation.

8. The methanation process as claimed in claim 1 wherein oxygen arising as a coproduct in the electrolysis is supplied as materials stream and/or energy stream to one or more operating stages of the smelting works or chemical works and/or to the power station as process gas.

9. The methanation process as claimed in claim 1 wherein the methane (CH.sub.4) arising in the methanation plant is wholly or partly supplied as materials stream and/or energy stream to a production operation, which is a conversion operation, of the smelting works or chemical works and/or is fed into a natural gas grid and/or is stored in a container.

10. The methanation process as claimed in claim 1 further comprising storing excess electrical energy generated by said power station fired with a carbonaceous fuel, and/or present in a public grid, in the form of methane (CH.sub.4) generated in the methanation plant, utilizing the heat energy arising in the methanation plant.

11. The methanation process claimed in claim 10, wherein said process is performed in the smelting works or chemical works that comprises the power station, which has an attached CO.sub.2-separating power station flue gas treatment plant for the power station flue gas and which has, connected downstream thereof, a methanation plant or methanator wholly or partly processing the CO.sub.2 stream separated in the power station flue gas treatment plant, the methanation plant or the methanator being supplied with the hydrogen originating from the coproduct gas and/or obtained by the electrolysis, and wherein the process is utilized for the reaction of the CO.sub.2 supplied from the power station flue gas treatment plant, under methane (CH.sub.4)-generating conditions, and wherein power generated by a generator, which is driven by a turbo set or turbine set disposed in the water/steam circuit of the power station and/or power originating as excess power from the public grid and supplied to the methanation plant and/or to the flue gas treatment plant and/or to the electrolysis is stored in the methane (CH.sub.4) of the methanation plant or the methanator.

12. The methanation process claimed in claim 11, wherein the power station is a coproduct gas power station and/or the attached CO.sub.2-separating power station flue gas treatment plant, is in the form of a CO.sub.2 gas scrubber by utilizing an absorbent.

13. The methanation process as claimed in claim 1, wherein the CO.sub.2 exhaust gas treatment or CO.sub.2 workup is a power station flue gas treatment plant.

14. The methanation process as claimed in claim 1, wherein the combustion chamber of the steam generator, is supplied with the coproduct gas in the form of a gas mixture, containing one or more gaseous byproducts of the smelting works or chemical works as carbonaceous materials stream and fuel.

15. The methanation process as claimed in claim 1, wherein the CO.sub.2 is obtained, from the power station flue gas at least partly in the CO.sub.2 exhaust gas treatment or the CO.sub.2 workup, by utilizing a CO.sub.2 gas scrubber with an absorbent.

16. A power station or combustion plant with attached water/steam circuit that comprises a combustion chamber of a steam generator, said chamber being fired with a carbonaceous fuel and said station or plant being designed as an integral constituent of a smelting works or chemical works where the flue gas line of the combustion chamber of the steam generator of the power station or of the combustion plant stands in a line connection, said line connection carrying power station flue gas and/or CO.sub.2 obtained therefrom and/or from coproduct gas of the smelting works or chemical works, with a methanation plant or a methanator that reacts said gas to form methane (CH.sub.4), wherein the power station or the combustion plant has a line which stands in media-carrying line connection with one or more production-engineering or process-engineering units of the smelting works or chemical works and which supplies a carbonaceous fuel to the combustion chamber of the steam generator of the power station, and via which the combustion chamber of the steam generator can be supplied with a carbonaceous material or materials stream, which comprises one or more byproducts or waste products of the production-engineering or process-engineering units of the smelting works or chemical works, wherein the methanation plant or the methanator stands in at least one heat energy-carrying line connection, said connection at least partly coupling out waste heat arising in the methanation of the flue gas or power station flue gas or CO.sub.2 gas, with at least one medium flowing into the combustion chamber of the steam generator of the power station on the burner side, and/or with the water/steam circuit of the power station and/or with a CO.sub.2 exhaust gas treatment or CO.sub.2 workup connected, in terms of process engineering, upstream of the methanation plant, and/or to one or more production-engineering or process-engineering units of the smelting works or chemical works and hydrogen obtained from the coproduct gas and/or generated utilizing an electrolysis is supplyable to the methanation plant.

17. The power station or combustion plant as claimed in claim 16, wherein the line connection carrying power station flue gas or CO.sub.2 gas obtained therefrom comprises a CO.sub.2 exhaust gas treatment or CO.sub.2 workup, which is connected, in process engineering terms, upstream of the methanation plant or the methanator, and which stands, in the direction of gas flow, on the input side in power station flue gas, supplying line connection with the combustion chamber of the steam generator and, on the output side, in CO.sub.2 gas-discharging line connection with the methanation plant or the methanator, and which stands in a heat energy-carrying line connection, said line connection coupling out the waste heat arising in the CO.sub.2 exhaust gas treatment or CO.sub.2 workup with at least one medium flowing on the burner side to the combustion chamber of the steam generator, and/or with the water/steam circuit of the power station and/or of the methanation plant connected downstream in terms of process engineering, and/or with one or more production-engineering or process-engineering units of the smelting works or chemical works.

18. The power station or combustion plant as claimed in claim 16, wherein the CO.sub.2-separating CO.sub.2 exhaust gas treatment plant (6) or CO.sub.2 workup is designed as a CO.sub.2 gas scrubber utilizing an absorbent (PC(C)C =Post-Combustion (Carbon) Capture).

19. The power station or combustion plant as claimed in claim 16 wherein the power station or the combustion plant comprises a generator, which is attached to its water/steam circuit and is driven by a turbo set disposed in the water/steam circuit, said generator standing in power-conducting line connection with the methanation plant or the methanator and/or with the CO.sub.2 exhaust gas treatment or the CO.sub.2 workup and/or with the electrolysis stands or stand in an excess power-supplying, power-conducting line connection with an attached public power grid.

20. The power station or combustion plant as claimed in claim 16 wherein the carbonaceous material or materials stream with which the power station or the combustion plant can be supplied comprises the one or more byproducts or waste products of the production-engineering or process-engineering units of the smelting works or chemical works in the form of a gas mixture, as carbonaceous fuel in the form of a coproduct gas.

21. The power station or combustion plant as claimed in claim 16 wherein the power station is a coproduct gas power station, which is integrated into a smelting works or chemical works, and the line connection which carries the power station flue gas or CO.sub.2 gas obtained therefrom supplies the methanation plant and/or the CO.sub.2 exhaust gas treatment or CO.sub.2workup with at least a part of the power station flue gas arising in the combustion of the carbonaceous fuel in the combustion chamber of the steam generator.

22. The power station or combustion plant as claimed in claim 16 wherein said power station or combustion plant is configured to perform a methanation process comprising the conversion of CO.sub.2, said methanation process comprising coupling out the heat energy arising as waste heat in the conversion of CO.sub.2to methane in the methanation plant at least partly into the materials stream and/or heat energy stream wherein this stream is supplied at least partly to at least one medium flowing into the combustion chamber of the steam generator of the power station on the burner side and/or to the water/steam circuit of the power station and/or to a CO.sub.2 exhaust gas treatment or CO.sub.2 workup, which is connected upstream, in terms of process engineering, of the methanation plant, and/or to one or more operating stages of an attached smelting works or chemical works.

23. The power station or combustion plant as claimed in claim 22, wherein the CO.sub.2 exhaust gas treatment or CO.sub.2 workup is a power station flue gas treatment plant.

24. The power station or combustion plant as claimed in claim 16, wherein the CO.sub.2 exhaust gas treatment or CO.sub.2 workup is a power station flue gas treatment plant.

25. The power station or combustion plant as claimed in claim 16, wherein the power station is a blast furnace gas power station or a coking plant gas power station.

Description

(1) The invention is elucidated in more detail below by way of example with reference to a drawing. In said drawing,

(2) FIG. 1 shows in schematic representation a power station of the invention,

(3) FIG. 2 shows in schematic representation a further exemplary embodiment of a power station of the invention,

(4) FIG. 3 shows in schematic representation a coproduct gas power station of the invention, integrated into a smelting works,

(5) FIG. 4 shows in schematic representation a comparison between a prior-art process and the process of the invention,

(6) FIG. 5 shows a schematic representation of a smelting works with a coproduct gas power station without attached methanation plant,

(7) FIG. 6 shows a schematic representation of a smelting works with a coproduct gas power station with methanation plant attached in accordance with the invention,

(8) FIG. 7 shows a schematic representation of the catalyst,

(9) FIG. 8 shows a schematic representation of a first exemplary embodiment of a water/steam circuit of a coproduct gas power station of the invention, and

(10) FIG. 9 shows a schematic representation of a second exemplary embodiment of a water/steam circuit of a coproduct gas power station of the invention.

(11) FIG. 1 shows in schematic representation an operationally integrated power to gas application of a methanation process of the invention and of a power station 2 of the invention. The power station 2 comprises a steam generator 18 with combustion chamber 17 and attached water/steam circuit 11, disposed in which is a turbo set or turbine set 12 with attached generator 5. On the flue gas side, a CO.sub.2 exhaust gas treatment in the form of a power station flue gas treatment plant 6a is attached to the power station 2 or the combustion plant. The combustion chamber 17 and the steam generator 18 are connected via a line 15a to the power station flue gas treatment plant 6a, and flue gas 15 is supplied to the power station flue gas treatment plant 6a by means of the flue gas line 15a. The flue gas 15 arises in the combustion chamber 17 of the steam generator 18 as a result of combustion of a carbonaceous materials stream 3a as fuel 3, with an oxygen-containing medium 4 being supplied as oxidant.

(12) In the power station flue gas treatment plant 6a, which is designed as a PCC (Post-Combustion Capture) plant, the flue gas is worked up into a CO.sub.2 gas stream 8, which has a high CO.sub.2 fraction, and is passed in a line connection 8a to a methanation plant 7. The power station flue gas treatment plant 6a is a customary CO.sub.2 gas scrubber with an absorbent, wherein the CO.sub.2 is removed from the flue gas 15 by means of the absorbent and subsequently separation from the CO.sub.2 takes place. Such processes are customary in the prior art, and so are not addressed in detail here.

(13) In the methanation plant 7, in a likewise customary process which is known from the prior art, the carbon dioxide (CO.sub.2) supplied in the CO.sub.2 stream 8 is reacted, by means of hydrogen (H.sub.2) obtained with an electrolysis 9 and supplied, 19a, to form methane (CH.sub.4), which is taken off from the methanation plant 7 as materials stream and energy stream 21. Similarly, water formed is guided off from the methanation plant 7 as materials stream and energy stream 26.

(14) The heat energy arising as waste heat in the CO.sub.2 conversion of the CO.sub.2 gas 8 into methane 21 in the methanation plant 7 is coupled out at one or more locations 33, 34 at least partly into a materials stream and/or heat energy stream 13, 14. The two energy streams 13 and 14 are supplied to the water/steam circuit 11 of the power station 2 and their heat energy content is coupled by means of suitable devices 35, 36 into the water/steam circuit 11. Examples of devices for this purpose are heat exchangers. Depending on the heat energy content of the materials streams and/or heat energy streams 13, 14, the coupling takes place into a high-energy or low-energy region of the water/steam circuit 11. For this purpose, the materials streams and/or heat energy streams 13 and 14 coupled out from the methanation plant stand in fluid-conducting connection, via line connections 13a and 14a, with the water/steam circuit 11 of the power station 2.

(15) FIG. 2 shows a further exemplary embodiment of an operationally integrated power to gas application, which relative to the embodiment according to FIG. 1 is represented with yet further schematicization, and which differs essentially in the supplying of electrical power 5a, 5b, 5c and/or of excess power 10a, 10b, 10c to the electrolysis 9, to the methanation plant 7 and/or to the power station flue gas treatment plant 6a and also in the supplying of a materials stream and/or heat energy stream 37 from the methanation plant 7 to the power station flue gas treatment plant 6a, and in a materials stream and/or heat energy stream 38 which is coupled out from the power station flue gas treatment plant 6a and is recycled for the purpose of heat reintegration into the power station 2, from the exemplary embodiment according to FIG. 1.

(16) FIG. 2 shows a power station 2 whose flue gas 15 is supplied to a power station flue gas treatment plant 6a, where it is worked up into a CO.sub.2 stream 8, which is supplied to the methanation plant 7. In the methanation plant 7, hydrogen 19a obtained by an electrolysis 9 is converted with the inflowing CO.sub.2 8 to form a materials stream and energy stream 21 composed of methane and a materials stream and energy stream 26 composed of water, which leave the methanation plant 7. Of the materials streams and/or heat energy streams 13, 14, and 37 leaving the methanation plant 7, at least a part, in this case the heat energy stream 37, is supplied to the power station flue gas treatment plant 6a. There, the heat energy contained in the materials stream and/or heat energy stream 37 is coupled out for the purpose of implementing the CO.sub.2 separation operation in the power station flue gas treatment plant 6a. The waste heat arising in the CO.sub.2 separation is coupled out in turn into a materials stream and/or heat energy stream 38, which is supplied to the power station 2 where it is coupled by reintegration into the water/steam circuit 11, for example.

(17) Furthermore, in the case of the embodiment according to FIG. 2, power is generated with the generator 5 attached to the water/steam circuit. This power is supplied as operating power 5a to the power station flue gas treatment plant 6a and as operating power 5b to the methanation plant 7. As a result of this power supply, an improvement in the efficiency of the power station of 0.5-5% points can be achieved. Another part of the power generated by means of the generator 5 can be supplied as operating power 5c to the electrolysis which, however, is preferably operated with excess power 10a when such power is in excess in the public grid. The methanation plant 7 can also be operated with excess power 10b, and the power station flue gas treatment plant 6a with excess power 10c.

(18) FIG. 3 shows, in a schematic overview representation, a power station 2 which is integrated into an industrial plant formed by a smelting works 1 and which is designed as a coproduct gas power station 2a. The combustion chamber 17 of the steam generator 18 is supplied with blast furnace gas 30, derived from a blast furnace 16, as carbonaceous fuel 3 via a line 3b. The coproduct gas 30 may be a gas mixture composed of a plurality of product gases of the smelting works 1. From the steam generator 18, the flue gas 15 arising in the combustion chamber 17 enters via a flue gas line 15a into a power station flue gas treatment plant 6a. A part of the power station flue gas 15 is returned to the combustion chamber 17 as recirculated flue gas 15c via a flue gas line connection 15b. In the power station flue gas treatment plant 6a, the flue gas 15 is freed from CO.sub.2. The CO.sub.2 gas stream 8 arising is supplied via a line connection 8a to the methanation plant 7 or the methanator 7a. Here, the CO.sub.2 gas 8 is converted into methane 21 and water 26. The waste heat arising in this process is coupled out and reintegrated as materials streams and/or heat energy streams 13, 14 into the water/steam circuit 11 of the power station 2, by coupling-out therein. Here, however, the materials stream and/or heat energy stream 37 can also be supplied to the power station flue gas treatment plant 6a. Any waste heat arising in the power station flue gas treatment plant 6a can be coupled out as materials stream and/or heat energy stream 38 and supplied likewise to the water/steam circuit 11. The materials streams and/or heat energy streams 13, 14, 37, and 38 are carried in respectively assigned line connections 13a, 14a, 37a, and 38a. The heat energy needed for the operation of the power station flue gas treatment plant 6a can be supplied to said plant by means of tapped steam 27 tapped from the water/steam circuit 11, via a line connection 29.

(19) The hydrogen 19a needed in the methanation plant 7 can be generated by means of an electrolysis 9 and supplied to the methanation plant 7 via a hydrogen-carrying line connection 19. Another possibility, however, is to supply hydrogen 19b obtained from the coproduct gas 30 to the methanation plant 7. The oxygen 20 arising in the electrolysis 9 or electrolysis unit can be supplied to the combustion chamber 17 as process gas 20a or as oxygen-containing medium 4, more particularly as pure oxygen 4a. The power required respectively for the electrolysis 9 and/or for the implementation of the methanation in the methanation plant 7 and/or the power required respectively for the CO.sub.2 separation in the CO.sub.2 exhaust gas treatment 6, more particularly the power station flue gas treatment plant 6a, is advantageously and usefully supplied to these plants in the form, in particular, of excess power 10a, 10b, 10c, if in the attached public grid there is an excess supply of electrical power, in other words an excess power. In order to ensure the operation of these plants, however, it is possible, moreover, for the respectively required operating power to be generated by means of the generator 5 attached to the water/steam circuit 11 of the power station 2 and for it to be supplied as operating power or power 5a, 5b, 5c to the plant in question, as shown in FIG. 3.

(20) FIGS. 4 and 6 show, in a schematic representation, exemplary embodiments of the invention wherein an industrial plant is realized as a smelting works 1, represented schematically as a dashed line. A constituent of the smelting works 1 is a coproduct gas power station 2a in the form of a blast furnace gas power station, in which blast furnace gas 24 originating from a blast furnace 16 is burnt as coproduct gas 30 with supply of an oxygen-containing medium 4. In this case, power station flue gas 15c recycled from the exhaust gas space of the combustion chamber 17 of a steam generator 18 of the power station 2a, or a CO.sub.2-enriched gas stream, may also be passed into the coproduct gas power station 2a and may additionally find use in the combustion of the coproduct gas 30 or in the conversion of furnace gas constituents.

(21) The power station flue gas 15 arising during the combustion of the coproduct gas 30 and emerging from the coproduct gas power station 2a is intended in particular to have a CO.sub.2 fraction of at least about 30 wt % or vol %, and hence it is particularly advantageous to supply the coproduct gas power station 2a, for the purpose of combustion of the coproduct gas 30, with a pure oxygen stream 4a or with a highly oxygen-enriched gas stream which has a higher oxygen fraction than does air.

(22) As represented in FIGS. 3 and also 8 and 9, a steam generator 18 with a water/steam circuit 11 with integrated turbine set 12 is attached in a customary way to the fire compartment or the combustion chamber 17 of the coproduct gas power station 2a, into which the coproduct gas 30 and the oxygen-containing medium 4 are introduced for combustion. The turbo set 12 communicates in a customary way with a generator 5 for power generation. By means of the coproduct gas power station 2 with attached generator 5, power can be generated with an efficiency . This efficiency alters, i.e. improves, by an amount of 0.5-5% points if at least a part of the energy generated with the generator 5 in the form of electrical power 5a, 5b, 5c is utilized in order to provide electrical energy for a CO.sub.2 exhaust gas treatment 6 or power station flue gas treatment plant 6a and/or for a methanation 7 or a methanator 7a and/or for an electrolysis 9, which are shown in the operational schemes depicted in FIGS. 1 to 3, such provision of energy being as depicted schematically by means of the arrows 5a, 5b and 5c shown in jagged form in FIGS. 2 and 3.

(23) In a downstream CO.sub.2 exhaust gas treatment 6 or power station flue gas treatment plant 6a, the CO.sub.2-containing power station flue gas 15 originating from the coproduct gas power station 2a is freed from the CO.sub.2 by means of a CO.sub.2 separation operation or a scrubbing process, and is worked up to give a virtually pure, highly CO.sub.2-containing gas stream 8. The CO.sub.2 exhaust gas treatment 6 involves more particularly the implementation of a Post-Combustion (Carbon) Capture operation (PCC or PCCC operation). A CO.sub.2 gas scrubber or a CO.sub.2 gas scrub is preferably part of the PCC or PCCC operation and hence of the CO.sub.2 exhaust gas treatment 6, by means of which the power station flue gas is worked up with an absorbent, more particularly with an amine-containing absorbent, which is preferably regenerated again. The amines accumulate with the carbon dioxide and, with heat being supplied, the CO.sub.2 is subsequently released in a controlled way. Amine solutions used are preferably diethanolamine (DEA), methyldiethanolamine (MDEA), and monoethanolamine.

(24) A result of the CO.sub.2 exhaust gas treatment 6 is a high-purity CO.sub.2 gas stream 8, which is supplied to the methanation plant 7. In the course of the methanation, the CO.sub.2 is converted by means of hydrogen (H.sub.2) into methane (CH.sub.4). This preferably occurs catalytically, in which case an RhMn/Al.sub.2O.sub.3 catalyst, identified in FIG. 7 as Hitachi Catalyst, has proven advantageous. The methanator 7a or the methanation plant 7 is also supplied with hydrogen (H.sub.2), in which case preferably hydrogen 19a originating from an electrolysis 9 is used. In the methanation plant 7 or the methanator 7a, methane (CH.sub.4) is generated by synthesis, and can then be stored in a conventional way. In order to generate the hydrogen 19a in the electrolysis 9, electrical power 10a is used, preferably so-called excess power, arising frequently as grid overcapacity in the generation of power from regenerative energy sources. Since this power cannot be consumed in a conventional way, the methanation of CO.sub.2 therefore opens up the possibility of energy storage. However, it is also possible for power 5c generated by means of the generator 5 to be used for implementing the electrolysis 9. This is especially so when the power station 2, more particularly coproduct gas power station 2a, is operated, in a resting phase, in a minimal load range, without delivering power to any attached public power grid with power production nevertheless taking place or having to take place for technical reasons.

(25) Also used is the heat arising in the methanation and/or in the CO.sub.2 exhaust gas treatment. The catalytic methanation proceeds at a temperature of about 300 C., and for this reason the waste heat of the methanation is utilized as coupled-out materials stream and/or heat energy stream 13, 14, 37 as an energy input into the CO.sub.2 exhaust gas treatment 6 (heat flow 37) and/or into the coproduct gas power station 2a and/or its water/steam circuit 11 (heat flows 13, 14) and/or into one or more operating stages of the industrial plant, in the present case the smelting works 1. Another possibility is to couple out the waste heat of the CO.sub.2 exhaust gas treatment 6, which is in the range between 300 C. and 120 C., as a materials stream and/or heat energy stream 38, and to utilize it in the coproduct gas power station 2a and/or its water/steam circuit 11 and/or in one or more operating stages of the industrial plant, in the present case the smelting works 1. By this means it is possible to achieve further improvement in the overall efficiency of the coproduct gas power station 2a and hence of the industrial plant, since the coproduct gas power station 2a, the CO.sub.2 exhaust gas treatment 6, and the methanation are integrated into the materials streams and/or energy streams of the industrial plant, in the present case the smelting works 1. A carbonaceous materials stream 3a, in the present case blast furnace gas 30, arising as a byproduct or waste product in the industrial plant is supplied as fuel 3 to the power station 2, in the present case the coproduct gas power station 2a. A part of the power generated by the generator 5 is supplied as electrical energy 5a, 5b to the CO.sub.2 exhaust gas treatment 6 downstream of the power station, and more particularly to the assigned methanation plant 7 downstream. The power station flue gas 15 of the power station 2, 2a is likewise supplied to the methanation plant 7 as a materials stream optionally worked up beforehand. From the methanation plant 7, in turn, heat energy in the form of waste heat is supplied as heat energy stream 13, 14, 37 to one or more of the operations taking place in the industrial plant and/or to the coproduct gas power station 2a, more particularly to at least one medium supplied thereto, more particularly the combustion oxygen, and/or to the CO.sub.2 exhaust gas treatment 6. Heat energy in the form of waste heat is also supplied, as heat energy stream 38 originating from the CO.sub.2 exhaust gas treatment 6 or power station flue gas treatment plant 6a, to the industrial plant and/or to the power station 2, 2a.

(26) Depicted in FIG. 4 in the top part A is the hitherto customary, prior-art procedure in relation to a smelting works 1 and a gas recovery. According to that procedure, iron ore and coal are smelted to form steel, with emission of CO.sub.2, and natural gas is conveyed in conveying fields and also transported by a pipeline system to the end consumer. As depicted in the lower part B of FIG. 4, in accordance with the present invention, the CO.sub.2 arising in a smelting works 1 is converted, in a power station 2 of the smelting works 1 that is designed as a coproduct gas power station 2a, into synthetic natural gas in the form of methane (CH.sub.4), which is transported on to consumers. The resulting methane gas can then be put to energetic use by other consumers and also processed further to form methanol.

(27) FIG. 5, in the left-hand image, shows the materials streams and energy streams which come about in the case of a coproduct gas power station 2a integrated into a smelting works 1. This system involves the introduction of coal 22, more particularly in the form of coke, and of iron ore and further materials for steel making. The product gases arising from the carbon sources in the course of the steel making in the smelting works 1, examples being coking plant gas 23, blast furnace gas 24, steelworks offgas 25, and sintering unit offgas 28, are combined as a gas mixture to form a coproduct gas 30, and passed on to the coproduct gas power station 2a. The power 31 generated by the combustion of the coproduct gases 30 in the coproduct gas power station 2a in the course of combustion in the combustion chamber 17 of a steam generator 18 with attached water/steam circuit 11 with integrated turbo set 12 and generator 5, and the heat 32 arising, are supplied again to the smelting works 1, and so as a result of this it is possible to achieve an efficiency of approximately 42% for the coproduct gas power station 2a. If, in accordance with the invention, a power station 2, more particularly a coproduct gas power station 2a, with attached CO.sub.2 exhaust gas treatment 6 and attached methanation plant 7 or attached methanator 7a is integrated into a smelting works 1 of this kind, as shown in FIG. 6, the efficiency , for otherwise the same power station 2 or the same combustion plant, can be increased to 60%.

(28) FIGS. 8 and 9 show different possibilities in accordance with the invention for integration of a power station 2, designed as a coproduct gas power station 2a, with attached water/steam circuit 11 and integrated turbine set 12, into a smelting works 1, the coproduct gas power station 2a being a coproduct gas power station 2a which combusts blast furnace gas 24. FIG. 8 shows a first possibility in accordance with the invention for integration of a power station 2, designed as coproduct gas power station 2a with attached water/steam circuit 11 and integrated turbine set 12, into a smelting works 1, the coproduct gas power station 2a being one which combusts blast furnace gas 24. A further integration possibility is shown in FIG. 9, and differs from that according to FIG. 8 with regard to the coupling-out of heat from the water/steam circuit 11.

(29) Although a number of exemplary embodiments relate to a coproduct gas power station 2a, the invention can nevertheless be applied very generally to power stations 2 fired with a carbonaceous fuel 3 and to the flue gas stream 15 which forms in each case. A power station 2 is understood, consequently, to be any kind of a carbon-fired, more particularly fossil-fuel-fired, power station, more particularly large power station, i.e., a power station fired with bituminous coal or lignite coal or gas. Biomass-fired and biogas-fired power stations as well can be subsumed under the power station rubric, and in the case of the latter may also be not only large power stations, but also small power stations or small plants, i.e., combustion plants. A power station flue gas or flue gas is then the gas or the gas stream which in the case of one of the aforementioned power stations forms the exhaust gas from the combustion chamber or steam generator, respectively. Accordingly, in place of the coproduct gas power station 2a shown in FIGS. 3 and 6, any of the aforementioned types of power station may form the power station 2, which is in the operative connection described earlier on above with the methanation plant 7 or with the methanator 7a and/or with the CO.sub.2 exhaust gas treatment 6, on the one hand by means of the flue gas stream 15, via the CO.sub.2 exhaust gas treatment 6 and the CO.sub.2-rich exhaust gas stream 8 formed therein, and also, on the other hand, by means of at least a part or one of the heat energy streams 13 and/or 14 and/or 37 and/or 38 waste heat reintegration taking place.

(30) The waste heat coming from the methanation, more particularly from the methanation plant 7, more particularly the materials streams and/or heat energy streams 13, 14, 37, and 38, can be supplied to the water/steam circuit 11 of the power station 2, 2a at least partly to boost performance.

(31) Likewise, the oxygen 20 arising as a coproduct in the electrolysis 9 can be used at least partly to boost the performance of the power station 2, 2a, more particularly of the power station operation or of an attached operating unit, more particularly a blast furnace 16 or a reactor. As a result of this, use is made not only of the hydrogen arising in the electrolysis, for the methanation, but also of the oxygen, thereby further increasing the overall energetic efficiency.