BIOGAS PLANT AND BIOGAS TREATMENT

Abstract

A biogas plant includes a fermenter, a biogas processing unit and a thermal engine. The biogas processing unit includes a gas separation unit and a compression unit for the separation of raw biogas from the fermenter into two gas streams, whereby the first gas stream includes a product gas that is enriched in biomethane with respect to the composition of the raw biogas and the second gas stream includes a residual gas that is enriched with carbon dioxide with respect to the composition of the raw biogas and has a biomethane concentration of less than 20%. The thermal engine produces energy that is used for operation of the compression unit.

Claims

1. Biogas plant including a fermenter for the production of raw biogas from biomass, a thermal engine, which is provided with a combustion gas for combustion for the production of mechanical and/or thermal energy, a biogas treatment plant including a compression unit and a gas separation unit for the separation of the raw biogas into a first and second gas stream, wherein the first gas stream consists of a product gas that is enriched in biomethane with respect to the composition of the raw biogas, and the second gas stream consists of a residual gas that comprises less than 20% biomethane and is enriched in carbon dioxide with respect to the composition of the raw biogas, and an exhaust gas treatment unit, which is provided with an exhaust gas for treatment, wherein at least part of the energy produced by combustion of the combustion gas in the thermal engine is used for operating the compression unit.

2. Biogas plant according to claim 1, wherein at least one of the combustion gas and the exhaust gas comprises at least a fraction of the residual gas.

3. Biogas plant according to claim 1, wherein the residual gas has a biomethane concentration of less than 15%.

4. Biogas plant according to claim 1, wherein the combustion gas includes a variable amount of natural gas and/or raw biogas of the fermenter and/or product gas.

5. Biogas plant according to claim 1, wherein the exhaust gas includes exhaust gases from the thermal engine.

6. Biogas plant according to claim 1, wherein at least one of the combustion gas and the exhaust gas consists of gases from the biogas plant.

7. Biogas plant according to claim 1, wherein the exhaust gas treatment unit is a catalytic gas processing unit.

8. Biogas plant according to claim 1, wherein the thermal engine and the compression unit are mechanically connected via a rigid coupling.

9. Biogas plant according to claim 1, wherein the gas separation unit includes a simplified membrane separation plant.

10. Biogas plant according to claim 1, wherein the gas separation unit has a methane slip of within the range of 0.1% to 5%.

11. Biogas plant according to claim 1, wherein the combustion gas includes a biomethane concentration of at least 10%.

12. Biogas plant according to claim 1, wherein all residual gas from the gas separation unit is delivered directly or indirectly to the thermal engine and/or the exhaust gas treatment unit.

13. Biogas plant according to claim 1, characterised by a first gas pipeline for the delivery of raw biogas from the fermenter to the biogas treatment plant and a second gas pipeline for the delivery of raw biogas from the fermenter to the thermal engine.

14. Biogas plant according to claim 1, wherein thermal energy produced during the compression of the raw biogas and/or by the thermal engine is used for operating the fermenter.

15. Method for obtaining biomethane from raw biogas according to claim 1, the method comprising at least the following steps: a) raw biogas from a fermenter is compressed with the aid of a compression unit; b) the compressed raw biogas is separated with the aid of a gas separation unit into a product gas that is enriched in biomethane in relation to the raw biogas and into a residual gas that has a biomethane concentration of less than 20% and is enriched in carbon dioxide in relation to the raw biogas; and c) combustion of the combustion gas in a thermal engine produces energy that is at least partly used for operating the compression unit.

16. Method according to claim 15, wherein at least a fraction of the residual gas is delivered as part of a combustion gas to the thermal engine and/or as part of an exhaust gas to an exhaust gas treatment unit.

17. Method according to claim 15, wherein at least part of the energy produced within the thermal engine and/or the compression unit is used for operating the fermenter.

Description

[0052] In the following the present invention will be further explained with reference to the embodiment presented in FIG. 1, which shows

[0053] FIG. 1 a schematic representation of a biogas plant of the present invention.

[0054] An embodiment of a biogas plant 10 in accordance with the present invention as shown in FIG. 1 includes a fermenter 12, a thermal engine 19 and a biogas treatment plant 16 for the production of biomethane 17. The thermal engine 19 is provided with a combustion gas. The biogas plant 10 further includes an exhaust gas treatment unit 18 that is provided with an exhaust gas. The thermal engine 19 and the exhaust gas treatment unit 18 are preferably connected, such that exhaust gases from the thermal engine 19 can be delivered to the exhaust gas treatment unit 18.

[0055] The term “thermal engine” thereby generally refers to a combustion engine, e.g. a gas (piston) engine, a micro gas turbine or a pilot injection engine, which uses a combustion gas—e.g. natural gas, biogas, or hydrogen—instead of or in addition to a liquid fuel for the conversion of chemical energy into mechanical and/or thermal energy. The thermal engine generally also includes at least one heat exchanger (not shown).

[0056] In case of the biogas plant 10 of FIG. 1, a substrate preparation unit 20 provides the fermenter 12 with organic material (biomass) 21. The biomass 21 is fermented in the fermenter 12 and subsequently transported to a substrate postprocessing unit 22.

[0057] During the fermentation of the biomass 21 within the fermenter 12, raw biogas 26 is produced. In the shown embodiment, raw biogas 26 from the fermenter 12 is delivered to the biogas treatment plant 16 through a first gas pipeline 23. A second gas pipeline 24 is provided for the delivery of raw biogas 26 from the fermenter 12 to the thermal engine 19. The two pipelines 23, 24 may be entirely separated or have a common origin that later divides into two separate pipelines. The fraction of raw biogas 26 fed to the thermal engine 19 is generally smaller than the fraction that is fed to the biogas treatment plant 16.

[0058] Within the biogas treatment plant 16 the raw biogas 26 is separated into a product gas 28 and a residual gas 30. The separation is performed with the aid of a gas separation unit 32 and a compression unit 33 for compression of the raw biogas 26 to be separated. The gas separation unit 32 comprises a membrane separation plant 34.

[0059] The membrane separation plant 34 includes at least one membrane 37, by means of which the raw biogas 26 is separated into a first gas stream comprising the product gas 28 and a second gas stream comprising the residual gas 30. The separation occurs on grounds of different permeabilities of biomethane and carbon dioxide through the membrane. The product gas 28 comprises a higher biomethane concentration with respect to the composition of the raw biogas 26, whereas the residual gas 30 comprises more carbon dioxide than the composition of the raw biogas 26. The residual gas 30 contains less than 20% biomethane.

[0060] The gas separation unit 32 may be simplified in its construction, which means that it involves less separation steps and/or a reduced membrane area compared to gas separation units known in the art that are built for minimizing the amount of residual biomethane within the residual gas, i.e. the methane slip. Since the biogas plant 10 according to the present invention allows for using the residual biomethane within the residual gas 30 for energy production (see next paragraph), the gas separation unit 32 of the inventive biogas plant may be significantly simplified, if desired.

[0061] In the shown embodiment of the biogas plant 10, some of the residual gas 30 from the separation unit 32 is fed to the thermal engine 19 and/or the exhaust gas treatment unit 18. Thus, a fraction 30a between 0% and 100% of said residual gas 30 is fed to the thermal engine 19 and forms part of the combustion gas that is combusted within the thermal engine 19. In the shown embodiment presented in FIG. 1, a remaining fraction 30b of the residual gas 30 is fed to the exhaust gas treatment unit 18 and forms part of the exhaust gas to be treated (cleaned) in the exhaust gas treatment unit 18. The exhaust gas to be cleaned by means of the gas treatment unit 18 may further comprise exhaust gases 31 from the thermal engine 19. Thus, in the shown embodiment, the exhaust gas treatment unit 18, e.g. a catalytic gas processing unit, serves for cleaning i) the fraction 30b of residual gas 30 that is not fed to the thermal engine 19 and ii) exhaust gases 31 from the thermal engine 19, such that the latter can be cleaned, in particular from incompletely burnt carbon compounds (e.g. NMHC, carbon monoxides or methane) and/or nitrogen oxides, before releasing it into the atmosphere.

[0062] By combustion of the combustion gas within the thermal engine 19, mechanical and/or thermal energy 39 is produced. Said energy 39 is used for the operation of the biogas treatment plant 16, specifically the compression unit 33. It may additionally be used for other purposes, e.g. for operation of the fermenter 12, or it may be stored in a heat storage 40. If the content of combustible material (in particular biomethane) in the residual gas 30 is too low to allow adequate combustion and thus energy production within the thermal engine 19, additional other combustibles—e.g. raw biogas 26 from the fermenter 12 or natural gas 36 from an external source (e.g. from a public gas grid (not shown)) or product gas 28 from the biogas treatment plant 16 can be added to the combustion gas of the thermal engine 19. In addition, at least part of thermal energy 39 produced by the thermal engine 19 and/or the compression unit 33 can also be used for heating the fermenter 12.