Abstract
The method and system for removing CO.sub.2 from the atmosphere or the ocean having the steps of, feeding a solid oxide fuel cell (SOFC) system with a gaseous hydrocarbon feed, converting the gaseous hydrocarbon feed in the SOFC system into an anode exhaust stream having carbon dioxide CO.sub.2, the SOFC system thereby producing electricity; injecting the anode exhaust stream as an injection gas into an underground coal bed; in the underground coal bed the injection gas causing coal bed methane (CBM) to desorb from the coal and CO.sub.2 to adsorb onto the coal; extracting the coal bed methane (CBM) from the underground coal bed; and discharging a production gas having the coal bed methane (CBM) from the underground coal bed.
Claims
1.-21. (canceled)
22. A method for removing CO.sub.2 from the atmosphere or the ocean comprising the steps of, sequestering of carbon dioxide CO.sub.2 by a biomass, converting the biomass to biogas, collecting the biogas and purifying the biogas from polluting gases, and feeding the purified biogas as gaseous hydrocarbon feed to a solid oxide fuel cell SOFC system, converting the gaseous hydrocarbon feed in the SOFC system into an anode exhaust stream comprising carbon dioxide CO.sub.2, the SOFC system thereby producing electricity (6); injecting the anode exhaust stream as an injection gas into an underground coal bed; in the underground coal bed the injection gas causing coal bed methane (CBM) to desorb from the coal and CO.sub.2 to adsorb onto the coal; extracting the coal bed methane (CBM) from the underground coal bed; and discharging a production gas (108) comprising the coal bed methane (CBM) from the underground coal bed, wherein the biogas mainly contains methane with a proportion in the range of about 50-75% and CO.sub.2 with a proportion in the range of about 25%-45%, and contains proportions of other gaseous substances such as water vapor, oxygen, nitrogen, ammonia and hydrogen.
23. The method of claim 22, wherein the purified biogas comprises 50% to 60% methane and 40% to 50% CO.sub.2, along with other minor gas impurities.
24. The method of claim 22, wherein the carbon dioxide is sequestered from the air by a plant biomass.
25. The method of claim 22, wherein the carbon dioxide is sequestered from the ocean by a phytoplankton biomass.
26. The method of claim 22, comprising the step of adding the production gas as gaseous hydrocarbon feed to the SOFC system.
27. The method of claim 26, comprising the step of providing an amount of production gas to the SOFC system sufficient for producing CO.sub.2-neutral or CO.sub.2-negative electricity.
28. The method of claim 22, comprising the step of feeding at least part of the production gas in a public gas grid.
29. The method of claim 28, comprising the step of providing an amount of biogas or an amount of biogas and an amount of the production gas to the SOFC system sufficient for producing CO.sub.2-neutral or CO.sub.2-negative fuel gas, in particular methane, from the coal bed methane (CBM).
30. The method of claim 22, comprising the steps of, converting the anode exhaust stream with a controlled amount of air to thereby control the amount of CO.sub.2 and nitrogen N.sub.2 in a carbon dioxide rich gas stream, and injecting the carbon dioxide rich gas stream as the injection gas into the underground coal bed.
31. The method of claim 22, comprising the steps of converting the anode exhaust stream with a controlled amount of a cathode off gas of the SOFC system, to thereby control the amount of CO.sub.2 and nitrogen N.sub.2 in a carbon dioxide rich gas stream, and injecting the carbon dioxide rich gas stream as the injection gas into the underground coal bed.
32. The method of claim 22, comprising the steps of feeding the anode exhaust stream of the SOFC system into a second SOFC system, converting the anode exhaust stream in the second SOFC system into a CO.sub.2 enriched anode exhaust stream, and injecting the carbon dioxide enriched anode exhaust stream as the injection gas into the underground coal bed.
33. The method of claim 30, comprising the step of adapting the ratio of N.sub.2 to CO.sub.2 in the anode exhaust stream depending on a coal quality of the underground coal bed.
34. The method of claim 33, comprising the step of adapting the ratio of N.sub.2 to CO.sub.2 in the injection gas in the range of between 20% N.sub.2, 80% CO.sub.2 and 45% N.sub.2, 55% CO.sub.2.
35. System for removing CO.sub.2 from the atmosphere or the ocean, comprising a gaseous hydrocarbon source, a first well, a second well, and an SOFC system comprising a solid oxide fuel cell with an anode side, a cathode side and an electrical output, wherein the first well fluidly connecting an inlet with a coal bed, wherein the second well fluidly connecting the coal bed with an outlet, wherein the output of the anode side of the Solid oxide fuel cell is fluidly connected with the inlet, to provide the coal bed with CO.sub.2, and wherein the input of the anode side is fluidly connected with the gaseous hydrocarbon source, wherein a biogas reactor forms the gaseous hydrocarbon source, wherein the system further comprises means for collecting biogas, a pre-treatment unit for purifying the collected biogas from polluting gases, and means for feeding the purified biogas as the gaseous hydrocarbon geed to the SOFC system, wherein the pre-treatment unit is adapted such that the biogas mainly contains methane with a proportion in the range of 50-75% and CO.sub.2 with a proportion in the range of 25%-45%, and contains proportions of other gaseous substances such as water vapor, oxygen, nitrogen, ammonia and hydrogen.
36. The system of claim 35, wherein the pre-treatment unit is adapted such that the purified biogas comprises 50% to 60% methane and 40% to 50% CO.sub.2, along with other minor gas impurities.
37. The system of claim 35, wherein the outlet is fluidly connected with a public gas grid.
38. The system of claim 35, wherein the outlet is fluidly connected with the input of the anode side for fluidly connecting the coal beds with the anode side, wherein coal bed methane (CBM) of the coal bed forms part of the gaseous hydrocarbon source.
Description
BRIEF DESCRIPTION OF THE FIGURES
[0053] Preferred embodiments of the invention will be described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various figures.
[0054] FIG. 1 is a schematic view of a first embodiment of a system for removing CO.sub.2 and for producing CBM;
[0055] FIG. 2 is a flow diagram of a first process for removing CO.sub.2 and for producing CBM;
[0056] FIG. 3 is a schematic view of a second embodiment of a system for removing CO.sub.2 and for producing CBM;
[0057] FIG. 4 is a flow diagram of a second process for removing CO.sub.2 and for producing CBM;
[0058] FIG. 5 is a schematic view of a further system for removing CO.sub.2 and for producing CBM;
[0059] FIG. 6 is a schematic view of a further system for removing CO.sub.2 and for producing CBM;
[0060] FIG. 7 is a schematic top view of a system for removing CO.sub.2 and for producing CBM;
[0061] FIG. 8 is a process flow diagram of an SOFC system;
[0062] FIG. 9 is a process flow diagram of a further SOFC system.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0063] FIG. 1 shows a first embodiment of a system 1 and method for removing CO.sub.2 and for producing coal bed methane (CBM). The system 1 comprises an SOFC system 2 comprising a solid oxide fuel cell 2a. Exemplary embodiments of suitable SOFC systems 2 are disclosed in FIGS. 8 and 9 in detail. A biogas reactor 5 produces a biogas 5a from for example biological waste, plant biomass collected from the earth's surface or phytoplankton biomass collected from the ocean. The biogas 5a is preferably purified in a pre-treatment unit 110 and leaves the pre-treatment unit as a gaseous hydrocarbon feed 100. The gaseous hydrocarbon feed 100 is fed to the anode side of the solid oxide fuel cell 2a. The gaseous hydrocarbon feed 100 is at least partially oxidized in the solid oxide fuel cell 2a, and leaves the solid oxide fuel cell 2a as an anode exhaust stream 101, the solid oxide fuel cell 2a thereby producing electricity 6, 61. The anode exhaust stream 101 serves as an injection gas 105 which through a wellhead 102 and an inlet 103a is injected into a first well 103. The first well 103 may convey the injection gas 105 from the earth's surface 71 to a coal bed 74. As the coal bed 74 may be a narrow geological layer, for example, having a thickness of only a few meters to a few tens of meters, the first well 103 may have a section 104 that is directionally drilled through the coal bed 74, for example, a horizontal section 104 if the coal bed 74 is relatively horizontal. The horizontal section 104 may be perforated to allow the injection gas 105 to enter the coal bed 74.
[0064] The CO.sub.2 of the injection gas 105 is used for the production of CBM. CO.sub.2 has a stronger chemical bond with coal than CBM. CO.sub.2 molecules thus displace CH.sub.4 molecules on the coal surface and the CO.sub.2 molecules adsorbs on the coal surface permanently in its place. The displaced CH.sub.4 (methane), which means CBM, can thus be recovered as a free-flowing production gas 108, so that the production gas 108 becomes a gaseous hydrocarbon source 99. The CO.sub.2 molecules are permanently bound in its place in the coal bed, thus sequestering at least a portion of the CO.sub.2 of the injection gas 105. The method and system according to the invention thus allow permanent removal of CO.sub.2 contained in the injection gas stream 105 from above the earth's surface 71 atmosphere.
[0065] A second well 106, for example a production well, may be drilled into the coal bed 74 to harvest the production gas 108, in particular the CBM produced from the coal. As for the first well 103, the second well 106 may be perforated to collect the CBM released from the coal bed 74, and the second well 106 may comprise a horizontal section to follow a narrow coal bed 74, or may have a vertical section 107 only, as indicated in FIG. 1. The present technology is not limited to horizontal wells, as other embodiments may have different well geometries to follow coal beds at different angles, or may have vertical wells if a coal bed is thick. The wells 103 and 106 may for example be displaced laterally by tens or hundreds of meters. The production gas 108 collected is transported to the earth's surface 71 through the second well 106 with outlet 106a, and through a second wellhead 109.
[0066] In a preferred embodiment the production gas 108 may be fed into a public gas grid 113, and the CBM, which is methane, can be burned in the usual way by consumers of the public gas grid 113. One advantage of the embodiment according to FIG. 1 is that such burning of methane received from the public gas grid 113 is CO.sub.2-neutral, because CO.sub.2 is sequestered in the coal bed 74 before releasing CBM.
[0067] In might be advantageous to use a pre-treatment unit 112 to purify the production gas 108 and/or to pressurize the production gas 108 before feeding it into the public gas grid 113. It might be advantageous in the pre-treatment unit 112 to for example reduce the water content by a dehydration device, remove particulates, remove heavy-end hydrocarbons or other contaminants. An analysis unit, such as an automatic gas chromatography analyzer, may be used after the second well head 109 to test the composition of the production gas 108. The results may be used to control the injection rate of the injection gas 105 or the composition of the injection gas 105 through the first well 103, for example, to balance the concentration of N.sub.2 and CBM in the production gas 108, to lower the amount of CO.sub.2 in the production gas 108, or to control CBM recovery based on an advantageous mixture of the injection gas 105, in particular the concentration of CO.sub.2 and N.sub.2.
[0068] Preferably such an amount of biogas or such an amount of biogas and production gas 108 is provided to the SOFC system 2 that is sufficient for producing CO.sub.2-neutral or CO.sub.2-negative fuel gas in the public gas grid 113, in particular methane, from the coal bed methane CBM.
[0069] FIG. 2 shows a flow diagram of the basic method used in FIG. 1. Biogas is for example produced from biological waste, the biological waste containing CO.sub.2 extracted from the atmosphere. The biogas is fed as a gaseous hydrocarbon feed 100 into an SOFC system, the fuel cell thereby producing an anode exhaust stream 101 comprising CO.sub.2 and producing electricity 6. The electricity 6 is delivered to a user, and the anode exhaust stream 101 is most advantageously compressed and is injected as an injection gas 105 into a coal bed 74 to desorbing CBM from coal and thereby producing a production gas 108 comprising CBM, so that CBM is delivered. In an advantageous method step, at least part of the production gas 108 comprising CBM may be used as the gaseous hydrocarbon feed 100 and may be fed to the solid oxide fuel cell 2a, in particular to continue the process of CBM recovery running in case of temporary lack of biogas.
[0070] FIG. 3 shows a second embodiment of a system 1 and method for removing CO.sub.2 and for producing CBM. In contrast to the embodiment disclosed in FIG. 1, in the system and method disclosed in FIG. 3, at least part of the production gas 108 is fed back to the SOFC system 2 and used as the gaseous hydrocarbon feed 100, which is fed to the solid oxide fuel cell 2a. The production gas 108 may directly be fed to the solid oxide fuel cell 2a. In an advantageous embodiment the production gas 108 is purified in a pre-treatment unit 110 before feeding the pretreated production gas 108 as the gaseous hydrocarbon feed 100 into the anode side of the solid oxide fuel cell 2a. The solid oxide fuel cell 2a thereby producing electricity 6 and the anode exhaust stream 101. A compressor 111 may be used to compress the anode exhaust stream 101 before feeding it into the first well head 102. The method for feeding the anode exhaust stream 101 into the first well head 102 and for collecting the production gas 108 at the second well head 109 disclosed in FIG. 3 is the same as already describe with FIG. 1.
[0071] FIG. 4 shows a flow diagram of the method used in FIG. 3. A gaseous hydrocarbon feed 100 is fed into an SOFC system, the fuel cell thereby producing an anode exhaust stream 101 comprising CO.sub.2 and producing electricity 6. The electricity 6 is delivered to a user, and the anode exhaust stream 101 is injected as an injection gas 105 into a coal bed 74 to desorb CBM form coal and thereby producing a production gas 108 comprising CBM, whereby the production gas 108 becomes the gaseous hydrocarbon source that causes the gaseous hydrocarbon feed 100.
[0072] FIGS. 3 and 4 show a closed loop application where the production gas 108 removed from underground becomes the gaseous hydrocarbon fee 100 which is fed to the SOFC system 2. One advantage of this method and system is that the CO.sub.2 produced in the SOFC system 2 is sequestered in a coal bed, which allows the production of electrical energy using coal, but without an emission of CO.sub.2 into the atmosphere.
[0073] In a preferred embodiment an additional source of a gaseous hydrocarbon feed 100a is provided for the system and method disclosed in FIGS. 3 and 4. As disclosed in FIG. 4, biogas 5a may be produced and may be fed as an additional gaseous hydrocarbon feed 100a to the SOFC system 2. FIG. 3 shows the biogas reactor 5, providing biogas 5a, which is an additional gaseous hydrocarbon feed 100a, that is fed to the SOFC system 2, and that may, if necessary, in addition be pre-treated in the pre-treatment unit 110. Such an additional source of a gaseous hydrocarbon feed 100a is in particularly desirable to start the process disclosed in FIG. 4, which means to start producing CO.sub.2, and then to start desorbing CBM from the coal bed, so that the production gas 108 is provided and the SOFC system 2 may produce the anode exhaust stream 101 and electricity 6. After starting the process disclosed in FIG. 4, the process may become self-sustaining. Most preferably the additional gaseous hydrocarbon feed 100a is fed to the closed loop application to make sure that sufficient CO.sub.2 is delivered to the coal bed 74 to desorbing CBM from coal, in particular in view that a minimum of two CO.sub.2 molecules displace one CH.sub.4 molecule and adsorb on the coal. Instead of biogas or in addition to, a further source for an additional gaseous hydrocarbon feed 100a such as natural gas may be used.
[0074] FIG. 5 shows a further embodiment of the invention, which, in contrast to the embodiment disclosed in FIG. 3, comprises two SOFC systems 2, 2b, where the anode exhaust stream 101 of the first SOFC system 2 is fed to the input of the second SOFC system 2b, and the anode exhaust stream 101 of the second SOFC system 2b forming the injection gas 105. One advantage of the two SOFC systems 2, 2b in series is that the CO.sub.2 content in the anode exhaust stream 101 of the second SOFC system 2b is increased which, beside steam consists mostly of CO.sub.2. Most advantageously steam is removed and the injection gas 105 consisting mostly of CO.sub.2 is injected into the coal bed 74. Most advantageously, both SOFC systems 2, 2b have an electrical output 61 and produce electricity 6.
[0075] FIG. 6 shows a further embodiment of the invention which, in contrast to the embodiment disclosed in FIG. 1, comprises a second SOFC system 2b that converts the production gas 108 into an anode exhaust stream 101 and electricity 6. The electricity 6 produced by the first and second SOFC system 2, 2b is CO.sub.2 neutral because the gaseous hydrocarbon feed 100 is produced from a biogas reactor 5, which means the gaseous hydrocarbon feed 100 is biogas. Taking into account that a minimum of two CO.sub.2 molecules are needed to displace one CH.sub.4 molecule and adsorb on the coal surface permanently in its place, the electricity produced with an embodiment according to FIG. 6 is CO.sub.2 negative, even though the anode exhaust stream 101 of the second SOFC system 2b is released into the atmosphere because the method allows to remove and sequester two CO.sub.2 molecules, but only one CO.sub.2 molecule is released to the atmosphere. In a preferred method such an amount of production gas 108 is provided to the SOFC system 2 that electricity 6 is produced CO2-neutral or CO2-negative.
[0076] FIG. 7 shows a top view of a system 1 for removing CO.sub.2 and for producing CBM. An anode exhaust stream 101 from preferably a single SOFC system 2 is fed as injection gas 105 through pipelines 114 into a plurality of first well heads 102a, 102b, 102c, 102d, the injection gas 105 is flowing through the coal bed 72 and is converted into production gas 108, and the production gas 108 is collected at a single second well head 109, and is then fed through a pipeline 115 to the single SOFC system 2. Such a system is in particular useful if a mobile SOFC system 2 is used that works autonomously and that can be located in any location. Most preferably the single SOFC system 2 is a system as disclosed in FIG. 1 comprising a biogas reactor 5, so that the biomass may preferably be harvested locally a the cite of the SOFC system 2. The electrical energy 6 produced by the system 2 is particularly useful if a mobile SOFC system 2 is us, whereby advantageously at least such an amount of electrical energy is produced by the SOFC system 2 that the entire system 1 for carbon dioxide sequestration can be operated self-sufficiently, without the need of additional electricity. This allows the system to be installed very flexibly at locations where at least one of biomass and coal beds and preferably biomass and coal beds are available. In another preferred embodiment, the single SOFC system 2 is a closed loop system as disclosed in FIG. 3, so that the electrical energy 6 may be harvested by the use of an electric line. The electric line is cheap to build, also over long distances and the single SOFC system 2 can be installed in any suitable location. The system 1 according to FIG. 7 may also comprise a plurality of SOFC systems 2 and/or a plurality of first well heads 102 and/or of second well heads 109 as well as a multitude of corresponding first wells 103 and second wells 106.
[0077] FIG. 8 shows an exemplary embodiment of an SOFC system 2 comprising a solid oxide fuel cell 2a. The SOFC system 2 allows producing an anode exhaust stream 101 comprising CO.sub.2 as well as producing electricity 6 from a gaseous hydrocarbon feed 100, such as biogas, CBM or natural gas. The gaseous hydrocarbon feed 100 is preferably entering a fuel pre-treatment unit 110, and the pretreated gaseous hydrocarbon feed 100b is heated in heat exchanger 2d and fed into a reformer 2c. In addition, steam 200 is fed into a reformer 2c, the reformer 2c producing a reformed process gas feed 100c typically consisting of CO, CO.sub.2, H.sub.2O and H.sub.2, whereby the reformed process gas feed 100c is heated in heat exchanger 2e, and the heated reformed process gas feed is fed to the anode side 2f of the solid oxide fuel cell 2a, wherein the reaction takes place. The anode exhaust stream 101 may be used as the injection gas 105, as for example disclosed in FIGS. 1 and 3.
[0078] In a further advantageous embodiment, as disclosed in FIG. 8, the anode exhaust stream 101 may be cooled down in heat exchanger 2g, and may be fed into a high temperature water-gas-shift reactor 2h, and may then be cooled in heat exchanger 2i and fed into a low-temperature water-gas-shift membrane reactor 2k. The gas entering the low temperature water-gas-shift membrane reactor 2k is depleted of hydrogen 201 so that a carbon dioxide rich gas stream 101a results, which is cooled in heat exchanger 2l and is fed to a conditioning unit 2o, which at least separates water 202 from the carbon dioxide rich gas stream 101a, for example by condensation, so that a carbon dioxide rich gas stream 101b results, which may be used as injection gas 105.
[0079] The solid oxide fuel cell 2a also comprises a cathode side 2m and a membrane 2n, the membrane 2n being connected with an electrical output 61 for transferring electricity 6. Most preferably ambient air 120 is heated in heat exchanger 2o, and is then fed into the cathode side 2m of the solid oxide fuel cell 2a. An oxygen-depleted air stream 121, which is the cathode off gas, is cooled in heat exchanger 2p and is vented as depleted air stream 121. Document WO2015124700A1, which is herewith incorporated by reference, discloses further exemplary embodiments suitable for producing an anode exhaust stream 101 which may be used as injection gas 105 for CBM production.
[0080] In a preferred embodiment at least part of the depleted air stream 121, which contains a high amount of N.sub.2, may be mixed with the anode exhaust stream 101, to control the amount of CO.sub.2 and N.sub.2 in the injection gas 105, and for example in the carbon dioxide rich gas stream 101b.
[0081] FIG. 9 shows a further exemplary embodiment of an SOFC system 2. In contrast to the embodiment disclosed in FIG. 8, in the embodiments according to FIG. 9 an afterburner 2q is used to burn residual hydrogen contained in the anode exhaust stream 101, instead of using the water gas shift membrane reactor 2k. Oxygen depleted air stream 121 and/or ambient air 120 may be fed to the afterburner 2q. The amount of the oxygen depleted air stream 121 and/or the ambient air 120 fed to the afterburner 2q may be controlled to control the ratio of N.sub.2 and CO.sub.2 in the carbon dioxide rich gas stream 101a, 101b. A sensor may be provided to automatically sense the ration of N.sub.2 and CO.sub.2, and a control unit may be provided to feed such an amount of oxygen depleted air stream 121 and/or ambient air 120, that the carbon dioxide rich gas stream 101a, 101b contains a given ratio of N.sub.2 and CO.sub.2.
[0082] It is advantageous to use the system according to the invention for extracting coal bed methane (CBM) from coal beds.
[0083] It is advantageous to use the system according to the invention for extracting coal bed methane (CBM) from non-minable coal beds.
[0084] It is advantageous to use the system according to the invention for providing CO.sub.2-neutral or CO.sub.2-negative electricity 6 from coal beds.
[0085] It is advantageous to use the system according to the invention for providing CO.sub.2-neutral or CO.sub.2-negative fuel gas, in particular methane, from coal beds.
