Method for producing purified biogas and system for producing purified biogas

Abstract

A method for producing purified biogas, wherein biogas obtained through anaerobic fermentation of organic waste raw material is conveyed from the space above the liquid fraction of the fermenter (1) to the inlet of a photocatalytic carbon dioxide reduction absorber (3), which is supplied with thermal energy, electrical energy, and water. Biomethane and methanol are discharged from the photocatalytic carbon dioxide reduction absorber (3) via outlets. In the photocatalytic carbon dioxide reduction absorber (3), the process of absorbing waste CO2 from the biogas stream delivered from the liquid fraction of the fermenter (1) is carried out. For the production of biomethanol, water purified from digestate and waste CO2 from biogas, originating from the liquid fraction of the fermenter (1), is supplied to the photocatalytic carbon dioxide reduction absorber (3) via a water line (6). The heat required to evaporate the methanol obtained in the photocatalytic carbon dioxide reduction absorber (3) is supplied via a heat system (4) from a cogeneration unit (7), which is powered by biogas conveyed via a first biogas line (8) from the liquid fraction of the fermenter (1). The photocatalytic carbon dioxide reduction absorber (3) has an oxygen outlet (9) connected via a pipe (9a) to the fermenter, where the oxygen is used to biologically reduce the concentration of H2S.

Description

[0001] METHOD FOR PRODUCING PURIFIED BIOGAS AND SYSTEM FOR PRODUCING PURIFIED BIOGAS

[0002] The subject of the invention is a method for producing purified biogas and a system for producing purified biogas.

[0003] Full-scale anaerobic digestion (AD) is carried out in large tanks or vessels, where, in the absence of oxygen, biological conversion of organic carbon into mineral carbon (biogas) occurs. Biogas may undergo various forms of valorization, the dominant one being utilization in a combined heat and power unit (CHP). An increasing share of biogas is converted into biomethane using various technologies, including solid-state adsorption, chemical or physical absorption (water or amine scrubbing), membrane separation, or cryogenic separation. Stricter greenhouse gas emission regulations require the reduction of methane emissions from biogas through its upgrading or purification to a quality comparable to natural gas (max. 0.2%). State-of-the-art membrane processes can achieve such targets only through high recycling rates or an additional stage of methane removal from carbon dioxide-enriched streams before release into the atmosphere. Both measures increase costs and decrease process efficiency compared to the state of the art. Therefore, there remains a strong need for an effective process of methane and carbon dioxide separation from a biogas stream that would meet stringent greenhouse gas emission regulations while requiring minimal additional equipment and energy consumption.

[0004] Carbon dioxide, hydrogen sulfide, etc. contained in biogas are removed using methods such as absorption, adsorption, and membrane separation, while methane is separated in high concentration and used as an energy or heat source. In the case of carbon dioxide separated from biogas, it is degassed, desorbed, and released back into the atmosphere. Scrubbing is commonly used to remove CO2 and H2S from biogas, as these gases have higher solubility in certain liquids, such as water or polyethylene glycol, than methane. The absorption process in such scrubbers is purely physical. An exemplary system involves compressing and feeding biogas to the bottom of a scrubber column, while the scrubbing liquid is supplied to the top of the scrubber column, enabling counter-current absorption. Then the scrubbing liquid exits the bottom of the scrubber column carrying absorbed CO2 or H2S. The contaminated scrubbing liquid can then be regenerated (i.e., CO2 or H2S is removed from the scrubbing liquid) and reintroduced into circulation into the absorption column. Regeneration of the scrubbing liquid is typically carried out by removing the absorbed CO2 or H2S with air in a second column (sometimes called a stripping column), operating similarly to the scrubbing column.

[0005] In the description of the invention disclosed in international patent application PCT No. WO 2012 / 000727, a membrane process comprising three membrane units is disclosed, which can separate biogas into a biomethane stream containing more than 98% by volume of methane and a carbon dioxide-enriched stream containing approximately 0.5% methane, at a low recycling ratio below 60%.

[0006] From the description of the invention in U.S. Patent Application No. US2014134710 (Al), solutions are known for biogas purification that eliminate air flow from the scrubbing system.

[0007] From the description of the invention disclosed in international patent application No. WO2024074658 (Al), plant solutions are known. In this description, the installation consists of a biogas production system for the production of biogas by anaerobic fermentation of organic (waste) raw materials, and a biogas upgrading sysdtem for the production of biomethane from the biogas generated in the biogas production system. The biogas production installation comprises a production tank, in particular a fermentation chamber constituting a closed reactor where anaerobic digestion or methanation occurs. The production tank may operate at atmospheric pressure or approximately 3 mbar. The production tank consists of a lower volume configured for storing postfermentation product and an upper volume configured for storing the biogas generated during anaerobic fermentation of organic waste raw material. The production tank further comprises at least one feed inlet for organic waste to introduce a stream of organic raw material into the production tank. The biogas production installation is connected to the biogas upgrading installation via a supply conduit. The supply conduit directs the biogas produced by the biogas production system to the biogas upgrading system. The supply conduit has a first fluid communication end with the headspace of the production tank and a second fluid communication end with the biogas upgrading system. The raw biogas generated by the biogas production system is introduced into the biogas upgrading system via the supply conduit. The biogas upgrading installation comprises a biogas pressure-increasing device or pressure-boosting device, in particular a compressor, and a membrane separation unit located downstream of the pressureboosting device. The membrane separation unit comprises two membrane separation stages connected in series, each comprising one or more membranes.

[0008] From the description of the invention disclosed in U.S. Patent Application No. US2014134710 (Al), systems for biogas conditioning and purification are known, where the air flow from the scrubbing system is eliminated. In these solutions, the biogas purification installation comprises a gas processor for the reduction of CO2, volatile organic compounds and H2S in the biogas, the gas processor consisting of a scrubbing tank and a liquid scrubber; as well as a scrubbing washer in fluid connection with the gas processor in order to reduce the amount of gas absorbed by the liquid scrubber, a scrubber regenerator comprising: a stripping tank; an off-gas pump configured such that the contents of the stripping tank are subjected to vacuum, and the off-gases are removed from the stripping tank; and a mixing device placed in a scavenger tank. The mixing device is configured to mix the scrubbing liquid contained in the scavenger tank. In some embodiments, the mixing device consists of one or more mechanical mixing devices. One or more mechanical mixing devices are selected from the group consisting of a propeller, an impeller, and a turbine. In such a case, one or more mechanical mixing devices are in contact with the scrubbing liquid in the scavenger tank.

[0009] From the description of the invention in the patent application filed with the Korean Intellectual Property Office No. KR20240072406A, solutions are known for wastewater treatment plants equipped with systems for capturing and utilizing carbon dioxide in biogas. The device described in the document, for wastewater purification with a carbon dioxide capture and utilization system, comprises a biogas storage tank, a methane tank, a first absorption tower, a first circulation tank for absorbent liquid, an absorbent storage tank, a sodium bicarbonate storage tank, a desorption liquid storage tank, and a nitrification reaction tank. The biogas tank stores the biogas generated during anaerobic fermentation carried out in a fermentation tank, while the methane tank is intended for high-purity methane and serves as a gas storage element. Such methane is conveyed to a generator and used as a source of energy production or an additional source of heat. The first absorption tower contains methane and carbon dioxide, and the separated methane is directed to the methane tank. The first circulation tank for the absorbent liquid provides circulation of the mixed absorbent liquid containing sodium hydroxide and carbon dioxide separated from the first absorption tower to the first absorption tower and the sodium hydroxide supply. It is intended for conducting the carbon dioxide absorption process, in which sodium hydroxide (NaOH) reacts with carbon dioxide and converts it into sodium bicarbonate (NaHCOs). The absorbent liquid to be delivered to the first circulation tank is stored in the absorbent storage tank. In the first absorbent liquid circulation tank, carbon dioxide in aqueous solution separated from the first absorption tower and absorbent liquid flowing from the absorbent storage tank are mixed to form a mixed liquid, and the sodium hydroxide contained in the absorbent liquid is circulated repeatedly with the mixed liquid through the first absorption tower. The nitrification reaction tank introduces desorbed liquid obtained from the anaerobic fermentation process into the anaerobic fermentation tank, along with the sodium bicarbonate produced during carbon dioxide absorption, ammonium ions present in the desorbed liquid, and bicarbonate ions resulting from the CO2 absorption process, which serve to carry out the nitrogen oxidation process. For this purpose, in this embodiment, a desorbed liquid storage tank which stores desorbed liquid generated in the anaerobic fermentation process in the anaerobic fermentation tank and flowing into the nitrification reaction tank, and bicarbonate generated in the carbon dioxide absorption process and fed into the nitrification reaction tank.

[0010] From the description of the invention in international patent application PCT No. WO2013131517 (Al), a process and system for separating carbon dioxide from biogas are known. Biogas is produced in a digester of a biogas plant. Afterward, it exits the digester through a conduit and is subsequently purified. Pressure washing with the scrubbing solution "Genosorb 1753" (dimethyl ether of polyethylene glycol; manufacturer Clariant GmbH) is carried out in the first scrubbing column KI. Scrubbing column KI contains a filled bed. Alternative suitable packing materials can also be used. The purified biogas enters scrubbing column KI via a conduit at a temperature of 20°C and comes into contact with a countercurrently supplied scrubbing solution, with CO2 and water contained in the biogas being physically bound to the scrubbing solution. Purification is carried out initially using fresh scrubbing solution, which after loading and regeneration circulates in a loop. The regenerated scrubbing solution obtained from the desorption column K4 reaches the scrubbing columns KI and K3 via conduits equipped with an integrated pump. The scrubbing solution obtained from the bottom of the column, containing CO2 and methane, is conveyed via a conduit to the first desorption column K2 (desorption step). Gaseous nitrogen is introduced via a conduit as the stripping gas, which contacts the scrubbing solution in a countercurrent to remove the methane contained in the scrubbing solution. The operating pressure of the desorption column K2 is approximately 5.6 bar. Under these conditions, the stripping gas escapes through a conduit from the top of the K2 stripping column. The scrubbing solution collected from the bottom of the first desorption column K2, containing carbon dioxide and methane, is discharged via conduits together with the solution coming from the second scrubbing column K3. The scrubbing solution is fed into the second desorption column K4. Stripping air is supplied to the second desorption column K4 through a conduit with an integrated second compressor V2, which removes the remaining CO 2 from the scrubbing solution. The regenerated scrubbing solution obtained from the bottom of this desorption column K4 now has the required capacity to be reused as a scrubbing solution. To remove CO2, it is now redirected back to scrubbing columns KI and K3. The resulting exhaust gases are discharged through a conduit at the top of the second desorption column K4. The stripping gas collected from the first desorption column K2 is passed to the second scrubbing column K3, where the carbon dioxide contained in the stripping gas is removed using regenerated scrubbing solution supplied via a conduit. The gas emerging from scrubbing column K3 is of biomethane quality. Biomethane is discharged via a conduit. The methane content in the biomethane can be increased up to approx. 99 vol.% by enhancing CO2 separation in the first scrubbing column KI.

[0011] Photocatalysis is known in the prior art and understood as a process in which light (typically sunlight) is used to activate a chemical catalyst, in the presence of which chemical reactions can proceed more easily. Photocatalysis has many applications and, for example, can be used for the reduction of carbon dioxide. In the description of the invention in international patent application PCT No. WO2014099843 (A2), solutions are presented for photocata lytic systems for carbon dioxide reduction using photocatalytic colloidal nanocrystals with shells, including first and second semiconductor nanocrystals.

[0012] In the description of the invention in patent application No. FR3095598 (Al) filed with the French Patent Office, solutions are presented for photocatalytic carbon dioxide reduction processes carried out in the presence of an external electric field. The invention describes a method for photocatalytic carbon dioxide reduction conducted in the liquid phase and / or gas phase, wherein the process comprises the following steps: a) contacting a load containing carbon dioxide and at least one protector compound with a photocatalyst, b) subjecting the photocatalyst to an external electric field, it being understood that the photocatalyst is not in electrical contact with the electrodes generating the field, c) irradiating the photocatalyst with at least one radiation source producing at least one wavelength absorbable by said photocatalyst, such that the carbon dioxide is reduced and the protector compound is oxidized in the presence of said photocatalyst activated by said radiation source, such that a discharge is generated containing at least partially carbon-containing molecules in Cl or higher, different from CO2.

[0013] The objective of the invention is to provide a wastewater treatment system that effectively suppresses the emission of carbon dioxide from biogas into the atmosphere and reduces the inflow load of the wastewater treatment plant. The objective of the invention is to provide a method for producing purified biogas with the highest possible percentage of biomethane content, while achieving the highest possible percentage of carbon dioxide reduction.

[0014] The objective of the invention is to provide a wastewater treatment system with high total energy efficiency.

[0015] The essence of the method for producing purified biogas, according to the invention, lies in that biogas obtained through anaerobic fermentation of organic waste raw material is conveyed from the space above the liquid fraction of a fermenter via a biogas line to the inlet of an absorber supplied with thermal energy via a heat system, with electrical energy via an electrical system, and additionally with water delivered via a water line, while biomethane and methanol are discharged from the absorber via outlet lines, characterized in that a photocatalytic carbon dioxide reduction absorber is used as the absorber, and a process is carried out for the absorption of waste CO2 from the biogas stream supplied from the space above the liquid fraction of the fermenter. According to a preferred embodiment of the invention, for the production of biomethanol, the photocatalytic carbon dioxide reduction absorber is supplied via a water line with water purified from digestate and with waste CO2 from biogas, originating from the liquid fraction of the fermenter. According to another preferred embodiment of the invention, the heat required for the evaporation of methanol obtained in the photocatalytic carbon dioxide reduction absorber is supplied via the heat system from a cogeneration unit, which is powered by biogas conveyed through a first biogas line from the space above the liquid fraction of the fermenter. According to a further preferred embodiment of the invention, the electrical energy used to generate the light necessary in the photocatalysis process carried out in the photocatalytic carbon dioxide reduction absorber system is supplied via the electrical system from the cogeneration unit. According to yet another preferred embodiment of the invention, oxygen from the oxygen outlet of the photocatalytic carbon dioxide reduction absorber is transported via a pipeline into the interior of the fermenter, thereby biologically intensifying the reduction of hydrogen sulfide contained in the biogas. According to another preferred embodiment of the invention, oxygen from the oxygen outlet of the photocatalytic carbon dioxide reduction absorber is transported via a pipeline to the cogeneration unit, and the carbon dioxide produced by the combustion of biogas and oxygen is returned via an auxiliary line to the photocatalytic carbon dioxide reduction absorber, resulting in the production of an additional amount of methanol.

[0016] The essence of the system for producing purified biogas, according to the invention, lies in that it comprises a fermenter, the gas fraction space of which is connected via a gas line to the cogeneration unit supply, and a carbon dioxide absorber with outlet lines for biomethane and methanol, and is characterized in that the carbon dioxide absorber is a photocatalytic carbon dioxide reduction absorber, one inlet of which is connected via a first biogas line to the gas fraction space of the fermenter, and the other inlet is connected via a water line to a tank of water purified from digestate originating from the liquid fraction of the fermenter, and furthermore, the photocatalytic carbon dioxide reduction absorber is connected to the cogeneration unit via a heat system and an electrical system. According to another preferred embodiment of the invention, the photocatalytic carbon dioxide reduction absorber has an oxygen outlet connected via a pipeline to the interior of the fermenter. According to a further preferred embodiment of the invention, the oxygen outlet of the photocatalytic carbon dioxide reduction absorber is connected via a pipeline to the cogeneration unit supply, and the exhaust outlet of the cogeneration unit is connected via an auxiliary line to the interior of the photocatalytic carbon dioxide reduction absorber. The beneficial effects of the invention include effective suppression of carbon dioxide emissions from biogas into the atmosphere and reduction of the influent load of the biogas plant, achieved through the use of the photocata lytic carbon dioxide reduction absorber technology for the production of purified biomethane from biogas by absorbing waste CO2 from the biogas stream.

[0017] Additional advantages, which enable high total energy efficiency of the process, include the use of water from digestate and waste CO2 from biogas to produce biomethanol in the photocata lytic carbon dioxide reduction absorber, the use of heat from the biogas plant's cogeneration unit for evaporating methanol obtained in the absorber system, and the use of electricity from the biogas plant's cogeneration unit to generate the light required for the photocatalysis process in the absorber system.

[0018] Unless otherwise stated, all terms (including technical and scientific terms) used in this description are intended to have the same meaning as commonly understood by a person skilled in the art to which this invention pertains. Furthermore, terms defined in commonly used dictionaries are to be interpreted as having a meaning consistent with their use in the relevant technical field and are not to be interpreted in an idealized or overly formal manner unless explicitly defined herein.

[0019] The method according to the invention will be further explained on the basis of exemplary embodiments illustrated in the drawings, in which Fig. 1 and Fig. 2 are simplified block diagrams of the installation for carrying out the method. The system according to the invention will be further explained based on its exemplary embodiments illustrated in the drawings, wherein Fig. 2 is a simplified block diagram of the installation according to Examples 2 and 3 of its embodiments, and Fig. 1 is a simplified block diagram of the installation according to Example 4 of its embodiment. Example 1

[0020] A method for producing purified biogas, according to an exemplary embodiment of the invention, consists in that from the liquid fraction area of a fermenter 1 the biogas obtained through anaerobic fermentation of organic waste feedstock is directed via a biogas line 2 to the inlet of a photocatalytic carbon dioxide reduction absorber 3, powered by thermal energy supplied through a heat system 4 and electrical energy supplied through an electrical system 5, and additionally supplied with water via a water line 6. Biomethane, methanol, and oxygen are discharged from the photocatalytic carbon dioxide reduction absorber 3 via outlet lines. In the photocatalytic carbon dioxide reduction absorber 3, the process of absorbing waste CO2 from the biogas stream delivered from the fermenter 1 is carried out. To produce biomethanol, the photocatalytic carbon dioxide reduction absorber 3 receives water purified from digestate and waste CO2 from the biogas, sourced from the liquid fraction of the fermenter 1 via the water line 6. Heat required to evaporate methanol obtained in the photocatalytic carbon dioxide reduction absorber 3 is provided by a heat system 4 from a cogeneration unit 7, which is powered by biogas delivered via a first biogas line 8 from the space above the liquid fraction of the fermenter 1. Oxygen from the oxygen outlet 9 of the photocatalytic carbon dioxide reduction absorber 3 is transported via a pipe 9a into the fermenter 1 to biologically intensify the reduction of hydrogen sulfide contained in the biogas. Oxygen from the oxygen outlet 9 of the photocatalytic carbon dioxide reduction absorber 3 is transported via another pipe 9b to supply the cogeneration unit 7, and the CO2 resulting from the combustion of biogas and oxygen is recirculated back to the photocatalytic carbon dioxide reduction absorber 3 through an auxiliary line 13, yielding additional methanol. Example 2

[0021] The system, according to an exemplary embodiment of the invention, comprises a fermenter 1, the gas fraction space of which is connected via a gas line to a cogeneration unit power supply 2, and a photocatalytic carbon dioxide reduction absorber 3 with an outlet for biomethane 10 and an outlet for methanol 11. One inlet to the photocatalytic carbon dioxide reduction absorber 3 is connected via a first biogas line 8 to the gas fraction space of the fermenter 1, and the second inlet is connected via a water line 6 to a digestate-purified water tank 12 sourced from the liquid fraction of the fermenter 1. The photocatalytic carbon dioxide reduction absorber 3 features an oxygen outlet 9 connected via a pipe 9a to the fermenter 1 and is linked to the cogeneration unit 7 via a heat system 4 and an electrical system 5. The applied fermenter 1 is used for biogas production through anaerobic fermentation of organic waste, based on the solution described in the Polish patent application P.436191. The cogeneration unit 7 is a commercially available unit produced by Bosch, series: "CHP CE..." The photocatalytic carbon dioxide reduction absorber 3 utilizes photocatalytic CO2 reduction systems disclosed in PCT application WO2014099843 (A2). The photocatalytic carbon dioxide reduction absorber 3 enables purified biomethane production from biogas by absorbing waste CO2 from the biogas stream. It also allows the use of digestate water and waste CO2 from biogas to produce biomethanol. Heat from the cogeneration unit 7 is used to evaporate the methanol formed in the photocatalytic carbon dioxide reduction absorber 3. Electrical energy from the cogeneration unit 7 is used to generate light for the photocatalysis process occurring in the photocatalytic carbon dioxide reduction absorber 3. The photocatalytic carbon dioxide reduction absorber 3 features an oxygen outlet connected via pipe 9b to the cogeneration unit 7, and the exhaust outlet of the cogeneration unit 7 is connected via an auxiliary line 13 with the inside of the photocatalytic carbon dioxide reduction absorber 3. Hydraulic fittings, including pumps, can be installed as needed depending on the spatial configuration of the system components.

[0022] Example 3

[0023] The system, in another exemplary embodiment, includes a fermenter 1 the gas fraction space of which is connected via a gas line to the power supply of a cogeneration unit 7, and a photocatalytic carbon dioxide reduction absorber 3 with an outlet for biomethane 10 and an outlet for methanol 11. One inlet to the photocatalytic carbon dioxide reduction absorber 3 is connected via a first biogas line 8 to the gas fraction space of the fermenter 1, and the second inlet is connected via a water line 6 to a digestate- purified water tank 12 sourced from the liquid fraction of the fermenter 1. The photocatalytic carbon dioxide reduction absorber 3 features an oxygen outlet 9 connected via a pipe 9a to the inside of the fermenter 1 and is linked to the cogeneration unit 7 via a heat system 4 and an electrical system 5. The applied fermenter 1 is used for biogas production through anaerobic fermentation of organic waste, based on the solution described in the Polish patent application P. 401726. The cogeneration unit 7 is a solution manufactured by Bergerat Monnoyeur Sp. z o.o. The photocatalytic carbon dioxide reduction absorber 3 uses a photocatalytic carbon dioxide (C02) reduction method in the presence of irradiation using a photocatalyst and a photocatalyst. During the photocatalytic reduction of carbon dioxide carried out in the liquid phase and / or in the gas phase, the following stages are carried out: a) contacting a load containing carbon dioxide and at least one protector compound with a photocatalyst, b) subjecting the photocatalyst to an external electric field, it being understood that the photocatalyst is not in electrical contact with the electrodes generating the field, c) irradiating the photocatalyst with at least one radiation source producing at least one wavelength absorbable by said photocatalyst, such that the carbon dioxide is reduced and the protector compound is oxidized in the presence of said photocatalyst activated by said radiation source, such that a discharge is generated containing at least partially carbon-containing molecules in Cl or higher, different from CO2.

[0024] The solutions used in the photocatalytic carbon dioxide reduction absorber 3 are disclosed in detail in the description of the invention to PCT application number W02020221600 (Al). The photocatalytic carbon dioxide reduction absorber 3 enables the production of purified biomethane from biogas consisting in the absorption of waste CO2from the biogas stream. In the photocatalytic carbon dioxide reduction absorber 3 it is possible to use water from the digestate and waste CO2 from biogas for the production of biomethanol. In the photocatalytic carbon dioxide reduction absorber 3 system, the heat from the cogeneration unit 7 is used to evaporate the methanol produced in the photocatalytic carbon dioxide reduction absorber 3. Electrical energy from the cogeneration unit 2 is used to produce the light necessary for the photocatalysis process carried out in the photocatalytic carbon dioxide reduction absorber 3. The photocatalytic carbon dioxide reduction absorber 3 features an oxygen outlet 9 connected by pipe 9b to the cogeneration unit 7, and its exhaust outlet from the cogeneration unit 7 is linked via auxiliary line 13 to the photocatalytic carbon dioxide reduction absorber 3. Individual pipes may be fitted with hydraulic fittings, including pumps, whose location is selected depending on the spatial configuration of the individual system elements.

[0025] Example 4

[0026] The system, according to another exemplary embodiment of the invention, includes a fermenter 1, the gas fraction space of which is connected via a gas line to a cogeneration unit 2, and a photocatalytic carbon dioxide reduction absorber 3 with an outlet for biomethane 10 and an outlet for methanol 11. One inlet of the photocatalytic carbon dioxide reduction absorber 3 is connected via a first biogas line 8 to the gas fraction space of the fermenter 1, and the other inlet is connected via a water line 6 to a digestate- purified water tank 12 from the space of the liquid fraction part of the fermenter 1. The photocatalytic carbon dioxide reduction absorber 3 features an oxygen outlet 9 connected to the interior of the fermenter 1 and is also connected to the cogeneration unit 7 via a heat system 4 and an electrical system 5. The applied fermenter 1 is used for the anaerobic fermentation of organic waste, and in this implementation is based on the solution described in the Polish patent application P.436191. The cogeneration unit 7 is manufactured by 2G POLSKA Sp. z o.o. The photocatalytic carbon dioxide reduction absorber 3 utilizes a photocatalytic CO2 reduction system disclosed in PCT application WO2014099843 (A2). The photocatalytic carbon dioxide reduction absorber 3 enables the production of purified biomethane from biogas by absorbing waste CO2 from the biogas stream. The photocatalytic carbon dioxide reduction absorber 3 also allows the use of digestate water and biogas-derived waste CO2 for the production of biomethanol. In the photocatalytic carbon dioxide reduction absorber 3 system, the heat from the cogeneration unit 7 is used to evaporate the methanol produced in the photocatalytic carbon dioxide reduction absorber 3 system. Electrical energy from the cogeneration unit 7 is used to generate light necessary for the photocatalysis process carried out in the photocatalytic carbon dioxide reduction absorber 3. Individual pipes may be fitted with hydraulic fittings, including pumps, whose location is selected depending on the spatial configuration of the individual system elements.

Claims

Patent Claims1. A method for producing purified biogas, wherein biogas obtained through anaerobic fermentation of organic waste raw material is conveyed from the space above the liquid fraction of the fermenter via a biogas line to the inlet of an absorber supplied with thermal energy via a heat system and with electrical energy via an electrical system, and additionally with water delivered via a water line, while biomethane and methanol are discharged from the absorber via outlet lines, characterized in that the absorber used is a photocata lytic carbon dioxide reduction absorber (3), and a process is carried out for the absorption of waste CO2 from the biogas stream supplied from the space above the liquid fraction of the fermenter (1).

2. The method for producing purified biogas according to claim 1, characterized in that for the production of biomethanol, water purified from digestate and waste CO2 from biogas, originating from the liquid fraction of the fermenter (1), is supplied to the photocata lytic carbon dioxide reduction absorber (3) via the water line (6).

3. The method for producing purified biogas according to claim 1 or 2, characterized in that the heat necessary for the evaporation of methanol obtained in the photocatalytic carbon dioxide reduction absorber (3) is supplied via the heat system (4) from a cogeneration unit (7), which is powered by biogas conveyed through a first biogas line (8) from the space above the liquid fraction of the fermenter (1).

4. The method for producing purified biogas according to claim 2 or 3, characterized in that the electrical energy used to generate light necessary in the process of photocatalysis carried out in the photocatalytic carbon dioxide reduction absorber (3) is supplied via the electrical system (5) from a cogeneration unit (2).

5. The method for producing purified biogas according to claim 2, 3, or 4, characterized in that oxygen from the oxygen outlet (9) of the photocatalytic carbon dioxide reduction absorber (3) is conveyed via a pipe (9a) into the fermenter (1), thereby biologically intensifying the reduction of hydrogen sulfide contained in the biogas.

6. The method for producing purified biogas according to claim 2, 3, or 4, characterized in that oxygen from the oxygen outlet (9) of the photocatalytic carbon dioxide reduction absorber (3) is conveyed via a pipe (9b) to supply the cogeneration unit (7), and the CO2 generated from the combustion of biogas and oxygen is returned via an auxiliary line (13) to the photocatalytic carbon dioxide reduction absorber (3), resulting in the production of an additional amount of methanol.

7. A system for producing purified biogas, comprising a fermenter, the gas fraction space of which is connected via a gas line to the supply of a cogeneration unit, and a carbon dioxide absorber with outlets for biomethane and methanol, characterized in that the carbon dioxide absorber is a photocatalytic carbon dioxide reduction absorber (3), one inlet of which is connected via a first biogas line (6) to the gas fraction space of the fermenter (1), and the other inlet is connected via a water line (8) to a digestate- purified water tank (12) from the liquid fraction of the fermenter (1), and furthermore, the photocatalytic carbon dioxide reduction absorber (3) is connected to the cogeneration unit (7) via a heat system (4) and an electrical system (5).

8. The system for producing purified biogas according to claim 7, characterized in that the photocatalytic carbon dioxide reduction absorber (3) has an oxygen outlet (9) connected via a pipe (9a) to the interior of the fermenter (1).

9. The system for producing purified biogas according to claim 7, characterized in that the photocatalytic carbon dioxide reduction absorber (3) has an oxygenoutlet (9) connected via a pipe (9b) to the cogeneration unit (7), and the exhaust outlet of the cogeneration unit (7) is connected via an auxiliary line (13) to the interior of the photocatalytic carbon dioxide reduction absorber (3).

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