Method and Device for Upgrading of Biogas and Hydrogen Production From Anaerobic Fermentation of Biological Material

Abstract

Method and device for biogas upgrading and hydrogen production from anaerobic fermentation of biological material under production of energy rich gases selected among methane and hydrogen or a combination thereof. The method comprises addition of hydrogen gas to a fermentation step to enhance the methane: CO.sub.2 ratio in the raw biogas produced. At least part of the raw biogas is subjected to a step of sorption enhanced reforming without prior separation of CO.sub.2, using CaO as an absorbent to capture CO.sub.2 from the raw biogas as well as CO.sub.2 released in the reforming reaction. CaO is regenerated in an endothermic reaction using heat at least partially provided, directly or indirectly, by the bio-gas to be upgraded, thereby producing substantially pure hydrogen and substantially pure CO.sub.2.

Claims

1-15. (canceled)

16. A method for upgrading biogas from anaerobic fermentation of biological material under production of energy rich gases selected from one or more of methane (24) and hydrogen (16, 26), comprising in a fermentation step (50) that produces raw biogas (12), adding hydrogen gas to increase a ratio of methane:CO.sub.2 in the raw biogas (12) produced; desulfurizing the raw biogas; subjecting at least a portion of the desulfurized raw biogas to sorption enhanced reforming (70) without prior separation of CO.sub.2, capturing CO.sub.2 from the raw biogas and CO.sub.2 released in the reforming reaction using CaO as an absorbent, regenerating CaO in an endothermic reaction (80) using heat at least partially provided, directly or indirectly, by the bio-gas to be upgraded, thereby producing substantially pure hydrogen (15) and substantially pure CO.sub.2 (23).

17. The method as claimed in claim 16, comprising a step of desulfurization (60) upstream of the step of sorption enhanced reforming (70).

18. The method as claimed in claim 16, comprising treating a partial flow of desulfurized raw biogas (13) in a CO.sub.2 separation unit (110), thereby providing one discharge flow of vehicle grade biomethane (24) and one discharge flow (25) containing CO.sub.2.

19. The method as claimed in claim 18, wherein the CO.sub.2 separation unit (110) uses a principle for separation selected from the group consisting of water scrubbing, physical or chemical absorption using organic solvents, pressure swing adsorption, and permeation using membranes.

20. The method as claimed in claim 16, comprising further purifying (100) the substantially pure H.sub.2 (15) to produce vehicle grade H.sub.2 (16).

21. The method as claimed in claim 16, wherein heat for regenerating CaO is provided by burning a gas containing a partial flow of desulfurized raw biogas (13c).

22. The method as claimed in claim 18, wherein heat for regenerating CaO is provided by burning a gas containing a partial flow of desulfurized raw biogas (13c).

23. The method as claimed in claim 16, wherein heat for regeneration of CaO is provided in part from one or more of the group consisting of a solid oxide fuel cell (120) charged by hydrogen (15a) from the sorption enhanced reforming step (70) and by desulfurized raw biogas 13c.

24. The method of claim 18, wherein heat for regeneration of CaO is provided in part from one or more of the group consisting of a solid oxide fuel cell (120) charged by hydrogen (15a) from the sorption enhanced reforming step (70) and by desulfurized raw biogas 13c.

25. The method as claimed in claim 23, wherein additional heat for regeneration of CaO is provided by a heater (95) charged with hydrogen (15c) discharged from the sorption enhanced reforming step (70).

26. The method as claimed in claim 23, wherein a heat medium (21, 22) is circulated in a closed loop between at least the solid oxide fuel cell (120), the heater (95) and the regenerator (80).

27. The method as claimed in claim 25, wherein a heat medium (21, 22) is circulated in a closed loop between at least the solid oxide fuel cell (120), the heater (95) and the regenerator (80).

28. The method as claimed in claim 16, wherein the raw biogas to be upgraded is produced in a digestion process (50) based on digestion of a raw material selected from one or more of the group consisting of sewage, sludge, municipal waste, domestic waste, animal waste, and agricultural waste.

29. The method as claimed in claim 18, wherein the raw biogas to be upgraded is produced in a digestion process (50) based on digestion of a raw material selected from one or more of the group consisting of sewage, sludge, municipal waste, domestic waste, animal waste, and agricultural waste.

30. The method as claimed in claim 21, wherein the raw biogas to be upgraded is produced in a digestion process (50) based on digestion of a raw material selected from one or more of the group consisting of sewage, sludge, municipal waste, domestic waste, animal waste, and agricultural waste.

31. The method as claimed in claim 26, wherein the addition of hydrogen to the digestion process is arranged at least in part as a recycle hydrogen flow (15b) from the reforming step (70).

32. A device for upgrading biogas from anaerobic fermentation of biological material under production of energy rich gases, selected from one or more of methane (24) and hydrogen (16), comprising: a digester (50), a device (60) for desulfurization, a reformer unit (70, 80), wherein the reforming unit (70, 80) is arranged downstream of the digester (50) and the device for desulfurization for reforming according to sorption enhanced reforming principle based on Ca-looping to provide a reforming which is inherently integrated with carbon capture and subsequent purification of the hydrogen (15) with a hydrogen purification unit (100, 100).

33. The device as claimed in claim 32, comprising a solid oxide fuel cell (120) arranged to receive at least a portion of a gas discharged from the reformer unit, is subjected to purification in a hydrogen purification unit (100).

34. The device as claimed in claim 32, comprising a solid oxide fuel cell (120) arranged to receive the at least part of the gas discharged from the reformer, is charged to a solid oxide fuel cell for production of electric energy and heat.

35. The device as claimed in claim 32, wherein part of a gas discharged from the device for desulfurization is charged to a CO.sub.2 separation unit to split the gas flow into a vehicle grade biomethane (24) and pure CO.sub.2 (25).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Different embodiments of the invention are illustrated below with reference to the enclosed drawings, where:

[0020] FIG. 1 is a schematic view of a first embodiment of the disclosure, in which vehicle grade hydrogen is produced from anaerobic fermentation of biological material in a cost-efficient and sustainable manner.

[0021] FIG. 2 is a schematic view of another embodiment of the disclosure, in which vehicle grade hydrogen and vehicle grade biomethane is produced from anaerobic fermentation of biological material in a cost-efficient and sustainable manner.

[0022] FIG. 3 is a schematic view of a third embodiment of the disclosure, in which vehicle grade hydrogen is produced from anaerobic fermentation of biological material in a cost-efficient and sustainable manner, while also producing electricity.

[0023] FIG. 4 is a schematic view of a fourth embodiment of the disclosure, in which vehicle grade hydrogen and vehicle grade biomethane is produced from anaerobic fermentation of biological material in a cost-efficient and sustainable manner, while also producing electricity.

DETAILED DESCRIPTION

[0024] Attention is drawn to FIG. 1. An anaerobic digester 50 for biogas production is charged with a charge material 11 based on sewage sludge, domestic organic waste, animal or agricultural waste. The produced raw biogas 12 is desulfurized 60, and the desulfurized, still raw biogas 13 (CH.sub.4+initial CO.sub.2) is charged to a reformer 70 together with water 14 in the form of steam for a sorption enhanced reforming (SER) process. A substantially pure hydrogen 15 gas leaves the reformer unit. In the reformer unit, one part 15b of which typically being returned to the digester 50 to enhance the methane yield while another and typically larger part 15a is subjected to purification in a hydrogen-purifier 100. The hydrogen purification may typically be performed as a pressure swing adsorption process. The purified hydrogen 16 leaving the purifier is of vehicle grade.

[0025] While the step of desulfurization 60 is a step commonly used in such processes and not inventive as such, it is a step which for practical chemical purposes will rarely or never be omitted.

[0026] The process of reforming and CO.sub.2 capture in the reformer 70 involves a reaction between fuel (CH.sub.4), water (steam), CO.sub.2 (both from the original biogas and from the SER process) and CaO as a CO.sub.2 absorber, a process in which CaO is converted to CaCO.sub.3 in an exothermic reaction known per se.

[0027] The off-gas 17 from the hydrogen purification unit 100 is mixed with raw biogas 13c, which may be a partial flow of biogas flow 13, and charged to a burner 90 for production of the necessary heat (850 to 900 C.) for regeneration of CaCO.sub.3 to CaO in a CaO regenerator 80, in an endothermic process. The CO.sub.2 (100%) flow 23 produced in the reformer 70 and released in regenerator 80, may be used or stored (sequestration). The burner 90 is also charged with an oxygen containing gas 18, typically air.

[0028] The CO.sub.2 in the exhaust from the burner 90 would have no climatic consequence since the fuel source is of biogenic origin. In addition, the CO.sub.2 flow captured as flow 23 has a negative CO.sub.2 climate impact, if this flow of CO.sub.2 is stored or used.

[0029] Flow 19 is a flow from the reformer 70 to the regenerator 80 of solid CaCO.sub.3, resulting from CaO having absorbed CO.sub.2, while flow 20 is a flow of solid CaO, converted back from CaCO.sub.3, from the regenerator 80 back to the reformer 70. This Ca-looping process is well known as such, but not in the context here presented.

[0030] Attention is now directed to FIG. 2. Most of the components and flows of FIG. 2 are the same as the ones in FIG. 1 and are numbered equally. The process according to FIG. 2, however, has the additional ability of producing vehicle grade biogas. A first part 13a of the desulfurized biogas 13 is charged to the reformer 70 like in FIG. 1 and treated accordingly. A second part of the biogas 13b from the desulfurization unit 60 is charged to a CO.sub.2 separation unit 110. The CO.sub.2-separation is normally carried out by water scrubbing, physical or chemical absorption using organic solvents, pressure swing adsorption, or by permeation using membranes, depending on the location and size of the system. The bio methane 24 discharged from CO.sub.2 separation unit 110 may be said to be of natural gas quality or of vehicle grade and hence used for such purposes.

[0031] The CO.sub.2 25 released from the CO.sub.2 separation unit 110 may be stored or used, if the method applied makes this economically feasible. This is however usually not the case. Regardless of the method used, the biogenic origin of the fuel source would result in no climatic consequence. The purity of the CO.sub.2 25 released from the CO.sub.2 separation unit 110 depends on the type and nature of this unit.

[0032] Attention is now directed to FIG. 3. Most of the components of FIG. 3 are the same as the ones in FIG. 1 and are equally numbered. The process according to FIG. 3, however, has the additional ability of producing electricity and high temperature heat due to the presence of a solid oxide fuel cell (SOFC) integrated in the process and equipment. Thus, the substantially pure hydrogen discharged from the reformer, is typically divided into three substreams, namely substream 15a which is charged to the SOFC, substream 15b which is recycled to the digester 50 (like in FIGS. 1 and 2) and substream 15c which, when present, is used as a fuel for a heater 95.

[0033] The hydrogen substream 15a is partially used to produce electricity in the SOFC while another part of the hydrogen flow 16 leaves the SOFC for further upgrading in a hydrogen purifier 100 which may or may not be similar to the unit 100 shown in FIGS. 1 and 2 to obtain vehicle grade hydrogen 26. The electricity may be used internally or externally or both.

[0034] The high temperature exhaust gas of the SOFC is used to heat the regenerator 80, but may typically need some assistance since the temperature needed in the regenerator 80 is 850 to 900 C. This temperature may be reached (without any assistance) if ceramic interconnects are used in the SOFC system.

[0035] In practice, however, the temperature of the exhaust gas (830 C., Megel et. al 2013) is too low to effectively provide a temperature in the regenerator at which the CaCO.sub.3 is converted to CaO for further use. A dedicated system, to elevate the temperature of the exhaust gas in a temperature increasing cell/heating device, would thus be necessary.

[0036] The heat integration between the SOFC 120 and the Regenerator 80, via the heater 95, is in FIG. 3 provided by a closed heat loop 21, 22, however other options are possible.

[0037] The heat transfers medium of the heat loop 21, 22 in FIG. 3, can be different gases, such as for example; Hydrogen, CO.sub.2, air, helium, water vapor, different gas mixtures or fluids such as; mineral oils, hydrocarbons and different types of molten salts. The heat of the heat loop in FIG. 3, leaving the SOFC system, is typically about 830 C. The heat of this heat loop is enhanced in the heater 95 to at least 850 C., more preferable at least 950 C. and most preferred at least 1000 C., in order to meet the temperature regeneration requirement in the regenerator 80 where CaCO.sub.3 is converted to CaO while releasing CO.sub.2. While the heater 95 may be heated in different ways, one convenient way is the use of a partial flow of hydrogen 15c from the reformer. Another option for fuel to 95 would be raw biogas 13c. Whether the fuel for the heater has the form of raw biogas 13c according to FIG. 1, 2, or 4 or hydrogen 15c according to FIG. 3, the heat delivered by the burner 90 or by the heater 95 is at least partially provided, directly or indirectly, by the desulfurized raw bio-gas to be upgraded. The SOFC exhaust air 27 provides the oxygen for the heating process in 95. The CO.sub.2 in the exhaust outlet 28 from the heating device would be climate neutral because of the biogenic origin of the fuel used. If required, additional air (not shown) may be supplied to the heater 95.

[0038] Attention is now directed to FIG. 4. Most of the components in FIG. 4 are the same as in FIG. 3. The process of FIG. 4, however, has the additional ability of allowing production of vehicle grade biogas, in a manner similar to the difference between FIG. 1 and FIG. 2.

[0039] Thus, according to FIG. 4, the flow of desulfurized biogas 13 is split into a first flow 13a which is charged to the reformer 70 while the other flow 13b is charged to a CO.sub.2 separation unit 110 to be separated into vehicle grade biomethane 24 and CO.sub.2 25. The treatment of the first flow 13a is as described above in relation to FIG. 1, while the other flow 13b is subjected to a treatment as generally described in relation to FIG. 2.

[0040] With regard to the SOFC and the processes involved therein, there is no difference between the embodiments of FIGS. 3 and 4. The same is to be said about the closed loop heat exchange 21, 22 including the use of the heater 95.

[0041] It is to be understood that the processes according to FIGS. 2 and 4 allows a split of the desulfurized raw biogas into a first flow 13a and a second flow 13b, covering a ratio between the two from 5:95 to 100:0. Thus, if demand is high for vehicle grade biomethane and low for vehicle grade hydrogen and electricity, the flow 13a would be reduced so as to basically just cover the need for hydrogen in the digester. On the other hand, if the demand for vehicle grade biomethane is low, the flow 13b could basically be cut off, rendering the embodiment of FIG. 2 temporarily identical to the embodiment of FIG. 1 and/or rendering the embodiment of FIG. 4 temporarily identical to the embodiment of FIG. 3.

[0042] The general concept disclosed herein is a method for the manufacture of vehicle grade fuels from biological materials in a cost-efficient and sustainable manner, involving a minimum of steps. There is a versatility in the method in the sense that vehicle grade biomethane and vehicle grade hydrogen may be produced at a flexible mutual ratio, as well as flexible amounts of electricity.

[0043] While not representing the core of the inventive concepts disclosed herein, a step of desulfurization 60 is typically conducted upstream of the step of sorption enhanced reforming 70.

[0044] As explained in relation to the drawings, a partial flow of desulfurized biogas 13 is according some embodiments subjected to treatment in a CO.sub.2 separation unit 110 thereby providing one discharge flow of vehicle grade biomethane 24 and one discharge flow 25 containing CO.sub.2.

[0045] The CO.sub.2 separation unit 110 is typically one using a principle for separation selected among water scrubbing, physical or chemical absorption using organic solvents, pressure swing adsorption, and permeation using membranes.

[0046] According to at least some embodiments the heat required for regenerating CaO is provided by burning a gas containing a partial flow of desulfurized biogas. In some embodiments heat for regeneration of CaO may also be provided in part from a solid oxide fuel cell 120 charged with hydrogen 15a from the sorption enhanced reforming step 70. Additional heat may in case be provided by a heater 95 charged with hydrogen 15c discharged from the sorption enhanced reforming step 70. In other embodiments the fuel cell 120 may be charged with raw biogas or a combination of hydrogen and raw biogas.

[0047] In some embodiments a heat medium 21, 22 is circulated in a closed loop between at least the solid oxide fuel cell 120, the heater 95 and the regenerator 80. The addition of hydrogen to the digestion process may be arranged at least in part as a recycle hydrogen flow 15b from the reforming step 70.

[0048] In a number of embodiments the raw biogas to be upgraded is produced in a digestion process based on digestion of a raw material selected among one or more of sewage, sludge, municipal waste, domestic waste, animal waste, and agricultural waste.

LIST OF REFERENCES

[0049] 11 feed to digester 50 [0050] 12 biogas from digester 50 [0051] 13 desulfurized biogas to reformer 70 [0052] 13a partial flow desulfurized biogas to reformer 70 [0053] 13b desulfurized biogas to CO.sub.2 separator 110 [0054] 13c raw, desulfurized biogas to heater 95/burner 90 [0055] 14 water to reformer 70 [0056] 15 substantially pure hydrogen from reformer 70 [0057] 15a partial flow hydrogen to reformer 70 [0058] 15b recycle partial flow of hydrogen to digester 50 [0059] 15c partial hydrogen flow to heater 95 [0060] 16 vehicle grade hydrogen from hydrogen purifier 100 [0061] 16 Subst pure hydrogen from SOFC 120 [0062] 17 off gas from hydrogen purifier 100 [0063] 18 air inlet to burner 90 [0064] 19 CaCO.sub.3 from reformer 70 to regenerator 80 [0065] 20 CaO from regenerator 80 to reformer 70 [0066] 21 hot gas from burner 90 to regenerator 80 [0067] 21 hot gas from heater 95 to regenerator 80 [0068] 22 off gas from regenerator 80 [0069] 22 off gas from regenerator to SOFC 120 in closed loop [0070] 23 CO.sub.2 from regenerator 80 [0071] 24 vehicle grade bio-gas from CO.sub.2 separator 110 [0072] 25 CO.sub.2 from CO.sub.2 separator 110 [0073] 26 Vehicle grade hydrogen from 100 [0074] 27 Exhaust from SOFC 120 [0075] 28 Exhaust from heater 95 [0076] 50 digester [0077] 60 desulfurizer [0078] 70 reformer [0079] 80 regenerator [0080] 90 burner [0081] 95 heater [0082] 100 hydrogen purifier [0083] 100 hydrogen purifier [0084] 110 CO.sub.2 separator [0085] 120 solid oxide fuel cell