Small scale fully liquefied biogas plant

The biogas from the front-end enters the biogas purification system, which undergoes biogas desulfurization, cold dry dehydration, preliminary pressurizationPSAAfter pressure swing adsorption decarbonization, bio natural gas is obtained（CH₄≥97%TheCO₂≤3%）. Bionatural gas is sent to the refined purification system, which undergoes secondary pressurization and refined dehydration in sequenceCO₂After adsorption dehydration and mercury removal, it is sent to the cryogenic liquefaction system to obtainLNGProduct（-162℃). The decomposed gas generated by the biogas purification system is sequentially passed throughCO₂Drying system and low-temperature distillation separation system are used to obtainLCO₂Product（-25℃). The non condensable gas produced by the low-temperature distillation separation system is returned to the biogas purification system.

Purification and liquefaction of biogasLNGandLCO₂The system mainly includes:Biogas purification system, refined purification system, liquefaction cryogenic systemLNGLoading systemCO₂Drying systemCO₂Low temperature distillation systemLCO₂Storage and transportation system, coolingSystem, instrument air and nitrogen generation system, safety release system, thermal oil furnace systemPower distribution system and analysis and testing systemwait.Purification and liquefaction of biogasLNGandLCO₂Process route as shown in the diagram1As shown.

picture1 Purification and liquefaction of biogasLNGandLCO₂Process Route

product quality

（1）The quality of bio natural gas meets the requirements《GB/T41328-2022》Requirement in the middle;

（2）LNGThe product quality meets the requirements《GB/T38753-2020》Requirement in the middle.

（3）LCO₂The product quality meets the requirements《GB/T6052-2011According to the requirements of 'Liquid Carbon Dioxide'.

1Process route for crude purification of biogas

The biogas from the front-end first enters the biogas holder for temporary storage, and then enters the biogas desulfurization system for dry desulfurization（Or wet method first and then dry method)to≤4ppm, sent to the refrigerated dryer（I）After cold drying and dehydration (dehydration temperature)5~10(℃), sent to the biogas compressor for pressurization and cooling, and then passed through the refrigerated dryer（II）After dehydration, it is sent to the pressure swing adsorption system（PSA）, removeCO₂After obtaining bio natural gas（CH₄≥97%TheCO₂≤3%）And rich inCO₂The analytical gas is sent inCO₂Recycling system. The purification route of biogas is shown in the diagram2As shown.

picture2 Process route of biogas crude purification system

2Biological natural gas purification process route

Bionatural gas from the biogas crude purification system, after secondary pressurization, is sent to the activated amine system for decarbonization and then to the natural gas drying system for dehydration and mercury removal to obtain qualified natural gas that meets liquefaction requirements（CO₂≤50ppmTheH₂O≤1ppm,). absorbCO₂The activated amine solution is sent to the analysis tower for regeneration and cooling, and then pumped to the decarbonization tower for the next cycle. The purification route of biological natural gas is shown in the figure3As shown.

picture3 Purification process route of biological natural gas

3Qualified natural gas cryogenic liquefaction process route

Qualified natural gas, gas-liquid, and liquid-phase refrigerants (from the outlet of the refrigerant compressor) from the biological natural gas purification system enter the upper part of the liquefaction cold box through their respective flow channels,Heat exchange with the mixed refrigerant after throttling until-50℃The pre cooled bio natural gas continues to enter the cryogenic section of the cold box and exchange heat with the throttled gas-phase refrigerant until-162℃After being throttled and depressurized by the throttle valve, it is sent inLNGloadingsystem.

ButThe pre cooled liquid refrigerant is throttled by a throttle valve to0.13Mpa. GAfter entering the medium temperature refrigerant separator, it will flow back to the pre cooling section of the cold box together with the gas-phase refrigerant from the cryogenic section of the cold box (after throttling) to provide cold energy for the pre cooling section.

The pre cooled gas-phase refrigerant continues to enter the cryogenic section of the cold box and exchange heat with the throttled gas-phase refrigerant until-161.8℃Afterwards, the throttle valve is throttled to0.15Mpa. G（-165℃）Then it enters the low-temperature refrigerant separator and flows back to the deep cooling section of the cold box for reheating. It then flows back together with the throttled liquid-phase refrigerant to the pre cooling section of the cold box for reheating37℃（0.11Mpa. G）Afterwards, it flows back to the inlet of the refrigerant compressor. Pressurize by refrigerant compressor to3.1Mpa. GAfterwards, it is cooled by the compressor outlet cooler to40℃After being separated by the gas-liquid separator at the outlet, the gas-liquid two-phase mixture enters the pre cooling section of the cold box for the next cycle of operation.