Process for purifying biogas from biogas

Abstract

The invention discloses a process for purifying biogas from biogas. The process comprises the following steps: S1, carrying out buffer flow stabilization, desulfurization and impurity removal and liquid water separation on the biogas generated by an anaerobic fermentation system; s2, carrying out pre-pressurization, cooling and high-efficiency separation of gaseous water on the desulfurized biogas; s3, mixing and compressing the dehydrated biogas and the recovered flash steam, and absorbing carbon dioxide through countercurrent flow of process water under the condition of specific pressure and temperature; s4, performing reduced-pressure flash evaporation on the decarburized process water to recover methane, performing air regeneration to desorb carbon dioxide, and performing split-flow treatment on regenerated process water; s5, performing multi-component online analysis and detection on the biological natural gas after decarburization and dehydration; s6, performing pressure regulation, metering and odorization treatment on the qualified biological natural gas; and S7, collecting sewage-containing liquid of the system and carrying out gas-liquid separation to prevent methane gas from entering a sewer. By optimizing each process link, high methane recovery rate, low energy consumption and stable operation are realized, and high-quality output of the biogas is ensured.

Description

Technical Field

[0001] The present invention belongs to the field of biogas extraction, and more specifically, relates to a process for purifying biogas from biogas. Background Art

[0002] Biogas is a renewable, clean energy source primarily derived from anaerobic fermentation systems. However, biogas often contains impurities such as sulfide, carbon dioxide, and water, limiting its direct application. Traditional biogas purification processes suffer from low methane recovery, poor equipment operational stability, and high energy consumption. Therefore, developing an efficient, stable, and energy-efficient biogas purification process is of great practical significance. Based on this, we propose a biogas purification process. Summary of the Invention

[0003] The purpose of the present invention is to solve the shortcomings of the existing technology and propose a biogas purification biogas process. By optimizing each process link, a high methane recovery rate, low energy consumption, stable operation and high-quality output of biogas are achieved.

[0004] To achieve the above object, the present invention provides the following technical solutions: A biogas purification process comprises the following steps: S1, pretreatment stage, the biogas produced by the anaerobic fermentation system is buffered and stabilized, desulfurized and impurities removed, and liquid water separated; S2, compression and dehydration stage, pre-pressurization, cooling and high-efficiency separation of gaseous water are carried out on the desulfurized biogas; S3, deep decarbonization stage, dehydrated biogas and recovered flash gas are mixed and compressed, and carbon dioxide is absorbed through process water countercurrent under specific pressure and temperature conditions; S4, flash regeneration stage, the decarbonization process water is subjected to reduced pressure flash evaporation to recover methane, air regeneration to desorb carbon dioxide, and the regenerated process water is diverted for treatment; S5, quality control stage, conduct multi-component online analysis and detection on the biogas after decarbonization and dehydration; S6, during the grid-connected output phase, the qualified biogas is subjected to pressure regulation, metering and odorization treatment; S7, during the sewage treatment stage, the polluted liquid in the system is collected and gas-liquid separation is performed to prevent methane gas from entering the sewer.

[0005] Preferably, the pretreatment stage adopts a three-stage continuous operation: the biogas storage tank smoothes the gas pressure fluctuation, the high-efficiency desulfurization device deeply removes sulfides through chemical adsorption or catalytic conversion, and the mechanical interception structure is installed in the water separator tank to realize the gravity separation of liquid water.

[0006] Preferably, the compression and dehydration stage adopts a step-by-step temperature and pressure control strategy: after the Roots blower compresses a small volume of biogas, the temperature is regulated to a low temperature range by a dedicated cooler. After cooling, the gas flows through a high-efficiency demisting and defoaming device to achieve physical dehydration, thereby simultaneously reducing water vapor saturation and the risk of compressor failure.

[0007] Preferably, the deep decarbonization stage is operated under the protection of a double buffer tank: the mixed gas flow is pressurized by a compressor and enters a transition buffer container to stabilize the flow rate and pressure, the process water in the decarbonization tower selectively absorbs carbon dioxide in a continuous reverse contact manner, and a high-efficiency water separation component is set on the top of the tower to block tiny droplets.

[0008] Preferably, the flash regeneration stage integrates gas recovery and resource circulation: the flash tower releases dissolved methane under low pressure conditions and refluxes it to the main process; the regeneration tower uses air aeration to release residual carbon dioxide; and the process water branch system simultaneously supports decarbonization water circulation and refrigeration system cooling supply.

[0009] Preferably, the process water diversion system is provided with an independent control valve group: the decarbonization tower reflux branch maintains a stable liquid supply pressure through a high-pressure pump; the refrigeration cycle branch controls the operating temperature of the decarbonization tower through cold capacity distribution, forming a closed-loop energy recycling mode.

[0010] Preferably, an interlocking protection mechanism is set up in the quality control stage: the online analyzer monitors the content of key components in real time, and the pressure regulating and metering skid can only receive gas when the methane purity, sulfide concentration, carbon dioxide residual amount, oxygen ratio and dew point temperature all meet the urban gas standards.

[0011] Preferably, the grid-connected output stage is achieved through two-stage pressure regulation: the high-pressure gas first passes through a filter device to remove solid particles, then is reduced in pressure to the pipeline pressure range by a pressure reducing valve group, and finally is distributed into the pipeline network through a metering instrument and an odorizing device.

[0012] Preferably, the sewage treatment stage adopts a negative pressure sealing collection system: the sewage tank is equipped with an airtight tank body and a dedicated exhaust pipe, the separated methane gas is recycled through a safe channel, and the waste liquid is discharged in a targeted manner after meeting the standards.

[0013] The technical effects and advantages of the present invention: Compared with traditional technologies, the present invention provides a biogas purification biogas process. Through buffering treatment, high-efficiency desulfurization, water separation, cooling and dehydration, compressor compression, decarbonization, flash evaporation, regeneration and other processes, the present invention ensures the stable operation of the entire system, reduces equipment failures and downtime, and improves production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a diagram of the process architecture for purifying biogas from methane in the present invention; Figure 2This is a process flow chart for purifying biogas from methane in the present invention. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0016] The present invention provides Figure 1 A biogas purification process for biogas shown includes a pre-treatment device, a purification device and a post-treatment device connected in sequence; The pretreatment device includes a biogas storage tank for buffering and stabilizing the biogas pressure and flow, a desulfurization device for efficiently removing sulfides to below the safe content, and a first-stage water separator tank equipped with a high-efficiency demister and demister for removing liquid water by physical separation; the purification device includes a pre-boosting module containing a Roots blower to boost the biogas pressure to 40-55 kPa, a cooling module containing a biogas cooler to cool the biogas to 15-20°C, a second-stage water separator equipped with a high-efficiency demister and demister for preliminary dehydration, a flash gas recovery tank, a biogas compressor for two-stage compression of the biogas mixed with flash gas to 0.9MPa, a buffer tank after the compressor, a buffer tank before the decarbonization tower, a decarbonization tower that absorbs CO2 through countercurrent contact with process water at 0.6-0.9MPa and 8-15°C, and a high-efficiency water separator at the top of the tower; The post-processing device includes a dehydration device, an online detection module for real-time analysis of methane, hydrogen sulfide, carbon dioxide, oxygen content and dew point, a pressure regulating and metering skid for filtration, pressure reduction to 0.3-0.4 MPa, metering and odorization.

[0017] The Roots blower in the pre-boosting module pressurizes the desulfurized and dehydrated biogas to 40-55 kPa. After cooling to 15-20°C in a biogas cooler, the gas enters the second-stage water separator, where it is physically dehydrated by a high-efficiency demister and demister. This pre-boosting and cooling process significantly reduces the processing load of the subsequent biogas compressor by reducing the biogas volume. The cooling and dehydration step also effectively lowers water saturation and reduces the risk of compressor failure. The decarbonization unit includes a pressure and temperature coordinated control structure: the buffered biogas enters the decarbonization tower under the operating conditions of 0.6-0.9MPa and 8-15℃. The process water and biogas in the tower flow in the opposite direction to perform gas-liquid exchange, selectively absorbing and removing CO2; the biogas generated after decarbonization is further separated from liquid water by a high-efficiency water separator at the top of the tower and then transported to the dehydration device; all buffer tanks ensure that the airflow state is stable before entering the decarbonization tower; It also includes: setting up a decarbonization wastewater treatment and flash recovery unit: it includes a flash tower connected in sequence with a pressure control of 0.3-0.5MPa, which is used to desorb dissolved gas in CO2-rich process water and release flash gas with a CH4 content of about 70%, a flash gas recovery tank to collect and reuse the flash gas to the front section of the compressor for mixing, a regeneration tower to use air to aerate and regenerate the flashed process water to release CO2 gas, and a process water pump to pressurize part of the regenerated solution to 0.7-1.2MPa and return it to the decarbonization tower; by recovering 3-6% of the flash gas intake, the overall methane recovery rate of the system is significantly improved, and the regeneration tower outlet process water diversion control system: a part of the regenerated process water is directly returned to the decarbonization tower for recycling after being pressurized by the process water pump; the other part is diverted to the chiller to form a refrigeration cycle, and the water temperature of the decarbonization tower is maintained in the range of 8-15℃ through load regulation; the refrigeration cycle provides a cold source for system cooling; The online detection module includes a multi-parameter analyzer that continuously and in real time detects the methane content, hydrogen sulfide concentration, carbon dioxide concentration, oxygen content, and dew point parameters of the dehydrated biogas. Only when all parameters meet the preset quality standards will the gas be allowed to enter the pressure regulating and metering skid and, after pressure reduction, filtration, metering, and odorization, be incorporated into the medium-pressure gas pipeline network. The system also has a sewage discharge and safety assurance structure: the polluted liquid generated in each link of the system is collected in the sewage tank for centralized treatment; the sewage tank has a gas-liquid separation function, and the separated methane-containing gas is separated from the CO2 at the top of the flash tower and the CO2 at the top of the regeneration tower for separate treatment or safe discharge to ensure that methane does not enter the sewer; the pressure regulating and metering skid has a built-in pressure reducing valve to accurately control the outlet pressure to 0.3-0.4MPa, and is equipped with an odorant injection device and flow metering instrument.

[0018] In addition, this embodiment also proposes Figure 2 The biogas purification process shown in the figure is implemented using the above system and includes the following steps: S1. Pretreatment and desulfurization: Biogas from the anaerobic fermentation system passes through a biogas storage tank to buffer and stabilize pressure and flow, a desulfurization device to remove sulfides to a safe level, and a first-stage water separator tank (with a built-in high-efficiency demister and demister) to physically separate and remove liquid water. The first-stage water separator removes liquid water through gravity settling and mechanical defoaming. The desulfurization device efficiently removes sulfur to keep hydrogen sulfide concentration below the standard limit for urban gas pipelines. S2, pre-boosting and cooling dehydration: The pre-boosting unit uses a Roots blower to boost the biogas to 40-55 kPa. The boosted biogas is then cooled to 15-20°C in a biogas cooler. The cooled gas then enters the second-stage water separator (with a built-in high-efficiency demister and demister) for physical dehydration, removing approximately 70% of the gaseous moisture. The pre-boosting process uses a Roots blower to boost the biogas to 40-55 kPa, then cools it to 15-20°C in a dedicated biogas cooler. The high-efficiency demister and demister reduce the gaseous water saturation, reducing the compressor unit failure rate by 80%. S3, biogas compression and decarbonization, dehydrated biogas and recovered flash gas are mixed in the flash gas recovery tank - compressed to 0.9MPa in two stages by the biogas compressor - the air flow is stabilized by the buffer tank after the compressor and the buffer tank before the decarbonization tower - enters the decarbonization tower (control pressure 0.6-0.9MPa, temperature 8-15℃), process water and biogas are in countercurrent contact to absorb CO2 - the gas after decarbonization is separated from liquid water by the high-efficiency water separator at the top of the tower - and is sent to the dehydration device for deep dehydration; after the flash gas and dehydrated biogas are mixed in the flash gas recovery tank, they are compressed to 0.9MPa in two stages by the biogas compressor. The gas is stabilized and fed into the decarbonization tower after the flow rate and pressure are balanced by multiple buffer tanks. The decarbonization process operates under the conditions of 0.6-0.9MPa pressure and 8-15℃ temperature. The process water absorbs at least 90% of CO2 in reverse contact, and a high-efficiency water separator is set at the top of the tower to intercept residual liquid water; S4, decarbonization wastewater treatment: The CO2-rich process water discharged from the decarbonization tower is depressurized to 0.3-0.5MPa and enters the flash tower to desorb flash gas with a CH4 content of 70%, of which the recovered amount accounts for 3-6% of the intake air. The flash gas is collected in a recovery tank and returned to step S3 for mixing. The water discharged from the flash tower is then depressurized and enters the regeneration tower, where air aeration separates the CO2 from escaping. The operating pressure of the flash tower is 0.3-0.5MPa, and the flash gas recovery rate is controlled to 3-6% of the intake air volume. The flash gas is collected in the recovery tank and returned to the main process to achieve a comprehensive methane recovery rate of 99%; S5, recycled water recycling treatment, the process water discharged from the regeneration tower is divided into two routes: the first route is pressurized to 0.7-1.2MPa by the process water pump and returned to the decarbonization tower; the second route enters the chiller to maintain the refrigeration cycle, and the water temperature of the decarbonization tower is controlled at 8-15℃ by adjusting the refrigeration load; after the regeneration tower desorbs CO2, the process water diversion is dynamically adjusted according to the operating load: the process water returning to the decarbonization tower is pressurized to 0.7-1.2MPa by the pump; the process water entering the chiller controls the decarbonization tower temperature by adjusting the refrigeration load; S6. Product testing and grid connection: After dehydration, the biogas is tested for methane, hydrogen sulfide, carbon dioxide, oxygen content, and dew point using an online analyzer. Qualified gas enters the pressure regulating and metering skid for filtration, pressure reduction to 0.3-0.4 MPa, metering, odorization, and then is connected to the medium-pressure gas pipeline network. The online analyzer monitors in real time the methane purity, hydrogen sulfide concentration ≤ standard limit, carbon dioxide concentration ≤3%, oxygen content ≤1%, and dew point compliance. Only gas that meets all indicators is allowed to enter the pressure regulating and metering skid. S7. Sewage treatment: The system sewage is collected in the sewage tank for gas-liquid separation, and the methane gas is recovered and treated to avoid entering the sewer; the sewage tank performs sealed gas-liquid separation on the system sewage, and the separated methane gas is connected to the main process through the recovery pipeline, and the liquid is discharged after harmless treatment.

[0019] The above-mentioned desulfurization device is a non-limiting description of multi-stage adsorption filler based on high-efficiency desulfurization technology; the water separator is an extension of the high-efficiency demister and demister into a mechanical interception structure, corresponding to the working principle of physical separation; the process water diversion is based on the part entering the chiller to form a refrigeration cycle with refined control logic, avoiding the involvement of quantification of cooling capacity.

[0020] In addition, the buffer system constructs a multi-stage pressure stabilization chain based on a multi-stage buffer tank setting (gas storage cabinet / buffer tank after the compressor / buffer tank before the decarbonization tower); sewage discharge protection strictly follows the technical requirements of gas-liquid separation in the sewage tank and prevention of methane gas from being discharged into the sewer.

[0021] In summary, this application has the following effects: High methane recovery rate: By optimizing the decarbonization, regeneration and other process links, as well as the flash steam recovery process, the present invention can increase the methane recovery rate to 99%, thereby achieving efficient utilization of biogas resources and increasing the output of biogas.

[0022] Stable operation: Through processes such as buffering treatment, efficient desulfurization, water separation, cooling and dehydration, compressor compression, decarbonization, flash evaporation, and regeneration, the stable operation of the entire system is ensured, equipment failures and downtime are reduced, and production efficiency is improved.

[0023] High-quality biogas output: The biogas processed by the process of the present invention has a high content of methane (CH4), its main component, and undergoes strict quality testing to ensure the high quality of the biogas, which meets the requirements for integration into the medium-pressure gas pipeline network.

[0024] Energy saving and consumption reduction: The pre-pressurization and biogas cooling process reduces the processing capacity of the biogas compressor and reduces energy consumption, with the system power consumption reduced to 0.4kwh / m3 of biogas; the flash steam recovery process improves the methane recovery rate and reduces resource waste; the refrigeration cycle is used for the cooling needs of the system, further improving energy utilization efficiency and reducing production costs.

[0025] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A biogas purification process, characterized in that: The steps include: S1, pretreatment stage, the biogas produced by the anaerobic fermentation system is buffered and stabilized, desulfurized and impurities removed, and liquid water separated; S2, compression and dehydration stage, pre-pressurization, cooling and high-efficiency separation of gaseous water are carried out on the desulfurized biogas; S3, deep decarbonization stage, dehydrated biogas and recovered flash gas are mixed and compressed, and carbon dioxide is absorbed through process water countercurrent under specific pressure and temperature conditions; S4, flash regeneration stage, the decarbonization process water is subjected to reduced pressure flash evaporation to recover methane, air regeneration to desorb carbon dioxide, and the regenerated process water is diverted for treatment; S5, quality control stage, conduct multi-component online analysis and detection on the biogas after decarbonization and dehydration; S6, during the grid-connected output phase, the qualified biogas is subjected to pressure regulation, metering and odorization treatment; S7, during the sewage treatment stage, the polluted liquid in the system is collected and gas-liquid separation is performed to prevent methane gas from entering the sewer.

2. A biogas purification process according to claim 1, characterized in that: The pretreatment stage adopts a three-stage continuous operation: the biogas storage tank smoothes gas pressure fluctuations, the high-efficiency desulfurization device deeply removes sulfides through chemical adsorption or catalytic conversion, and the mechanical interception structure in the water separator tank realizes liquid water gravity separation.

3. The biogas purification process according to claim 1, characterized in that: The compression and dehydration stage adopts a step-by-step temperature and pressure control strategy: after the Roots blower compresses a small volume of biogas, the temperature is regulated to a low temperature range by a dedicated cooler. After cooling, the gas flows through a high-efficiency demisting and defoaming device to achieve physical water removal, thereby simultaneously reducing water vapor saturation and the risk of compressor failure.

4. The biogas purification process according to claim 1, characterized in that: The deep decarbonization stage operates under the protection of a double buffer tank: the mixed gas flow is pressurized by a compressor and then enters a transition buffer container to stabilize the flow rate and pressure; the process water in the decarbonization tower selectively absorbs carbon dioxide in a continuous reverse contact manner; and a high-efficiency water separation component is set on the top of the tower to block tiny droplets.

5. The biogas purification process according to claim 1, characterized in that: The flash regeneration stage integrates gas recovery and resource circulation: the flash tower releases dissolved methane under low pressure conditions and refluxes it to the main process; the regeneration tower uses air aeration to release residual carbon dioxide; and the process water branch system simultaneously supports decarbonization water circulation and refrigeration system cooling capacity supply.

6. The biogas purification process according to claim 1, characterized in that: The process water diversion system is provided with an independent control valve group: the decarbonization tower reflux branch maintains a stable liquid supply pressure through a high-pressure pump; the refrigeration cycle branch controls the operating temperature of the decarbonization tower through cold capacity distribution, forming a closed-loop energy recycling mode.

7. The biogas purification process according to claim 1, characterized in that: An interlocking protection mechanism is set up in the quality control stage: the online analyzer monitors the content of key components in real time, and the pressure regulating and metering skid can only receive gas when the methane purity, sulfide concentration, carbon dioxide residual amount, oxygen ratio and dew point temperature all meet the urban gas standards.

8. The biogas purification process according to claim 1, characterized in that: The grid-connected output stage is achieved through two-stage pressure regulation: the high-pressure gas is first filtered to remove solid particles, then reduced to the pipeline pressure range by a pressure reducing valve group, and finally distributed into the pipeline network through a metering instrument and an odorizing device.

9. The biogas purification process according to claim 1, characterized in that: The sewage treatment stage adopts a negative pressure sealed collection system: the sewage tank is equipped with an airtight tank body and a dedicated exhaust pipe, the separated methane gas is recycled through a safe channel, and the waste liquid is discharged in a targeted manner after meeting the standards.

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