CO₂ Absorption From Biogas And Production Of CO₂ Gas Fertilizer Applied In The Agricultural Greenhouse By Using The Amino Acid Salt As The Medium

As clean and renewable energy,biogas can be purified to produce bio-natural gas as an important supplement to conventional natural gas.At the same time,carbon-negative emissions can also be achieved by recycling the CO₂ separated in the purification process.One of the keys to biogas purification lies in the separation and utilization of CO₂ in biogas,but at present,the main concern is the separation of biogas CO₂,and less attention is paid to the utilization of CO₂ after separation.At the same time,for conventional biogas CO₂chemical absorption technology,due to the direct contact between gas and liquid,there are operational problems such as liquid bubbling,channeling,and entrainment during operation.Based on this,this paper adopts the membrane CO₂ absorption technology that integrates the advantages of membrane separation and chemical absorption technology for biogas CO₂ separation,and the CO₂-rich absorbent solution generated during the CO₂absorption process is purged and regenerated by air to supply CO₂ gas fertilizer for the greenhouse.possible.This paper focuses on the CO₂ absorption performance and air-purging regeneration characteristics of amino acid salt absorbents and builds a small test device.The research conclusions are as follows:（1）In the study of CO₂ membrane absorption characteristics,a polytetrafluoroethylene（PTFE）hollow fiber membrane contactor was first fabricated,and potassium glycinate,potassium sarcosine,potassium proline,and glutamate were explored in the membrane contactor.The biogas CO₂ absorption characteristics of five CO₂ absorbents,including potassium acid and ethanolamine（MEA）,were investigated.The effects of reaction temperature,gas flow velocity,liquid flow velocity,and absorbent concentration were investigated.The research shows that when the absorbent flows in the tube side of the membrane contactor and the biogas flows in the reverse direction on the membrane shell side,within the test parameters,the CO₂ removal rate of the absorbent in the biogas is ranked as follows:potassium proline>potassium glycinate>potassium sarcosine>MEA>Potassium Glutamate.When the absorption temperature increased,the CO₂ removal rate and mass transfer rate showed an overall upward trend,and the MEA achieved the maximum value(55.16%,1.26×10^-3 mol·m^-2·s^-1)at 50°C.When the liquid flow rate of the absorbent increases,the CO₂ removal rate,and mass transfer rate have been increasing.When the liquid flow rate reaches 143 m L/min,the potassium proline in the five absorbents reaches the maximum value(45.08%,9.92×10^-4 mol·m^-2·s^-1).When increasing the gas velocity,the CO₂ removal rate decreased,but the mass transfer rate increased.When the absorbent concentration varies between 1 and 3 mol/L,the CO₂ removal rate and mass transfer rate will increase with the increase of the absorbent concentration,but when the absorbent concentration is higher than 3 mol/L,the concentration will be further increased.This will have a negative impact on CO₂ absorption.（2）In the study of the influence of membrane parameters,the influence of membrane fiber diameter,membrane area,and membrane fiber arrangement on the absorption performance of biogas CO₂ membrane was investigated.The research shows that within the diameter range of the membrane fiber used in the experiment,the membrane fiber with a diameter of 1.0 mm can achieve the best CO₂ absorption and mass transfer performance,and when the gas phase velocity is 250 m L/min,the CO₂ removal rate reaches 91.61%（potassium glycinate）.situation).Increasing the membrane area can improve the CO₂removal rate and mass transfer rate.At the same time,in the scheme of expanding the membrane area,the method of increasing the length of the membrane fiber can have better CO₂ removal performance than increasing the number of membrane fibers.Under the premise of the same membrane area,the staggered woven membrane fibers have better CO₂removal performance than the traditional non-woven membrane,and the CO₂ removal rate can reach up to 99.11%（in the case of potassium glycinate absorption）.（3）In the research on the regeneration of CO₂-rich absorbent solution aiming at increasing CO₂ application,the CO₂ release rate was used as the evaluation index,and 5kinds of absorbents were preliminarily screened using the woven PTFE hollow fiber membrane contactor.The study found that at the same concentration,the saturated CO₂solubility of potassium glutamate was too low,which made it difficult to meet the needs of increased CO₂ gas fertilizer application.In the study of membrane regeneration performance of the other four absorbents,increasing the regeneration temperature and increasing the flow rate of the rich liquid in the membrane can both increase the CO₂ release rate.For example,when the temperature increased from 50°C to 80°C,the CO₂ release rate of potassium glycinate increased by 55.07%,and when the rich liquid flow rate increased from 56 m L/min to 143 m L/min,the CO₂ release rate of potassium glycinate increased by98.1%.However,when the gas phase velocity increases,it has little effect on the CO₂release rate.In the process of 0.5～2 L/min,the CO₂ release rate of potassium proline only increases by 18.7%.To further,obtain a more comprehensive parameter influence,the test results under all factors were simulated through the orthogonal test of four factors and three levels and the numerical software Design-Expert 13,to obtain the absorbent temperature（X₁）,gas-phase velocity（X₃）,liquid phase The fitting relationship formula of flow rate（X₂）,CO₂ loading（X₄）and CO₂ release rate（Y）:Y=243.88+2.83X₁+0.68X₂+96.30X₃-2168.66X₄-0.0059X₁ X ₂-0.15X₁ X₃+13.05X₁ X ₄+0.16X₂ X₃+0.086X₂ X₄-126X₃ X₄-0.053X₁²-0.00096X₂²-12.13X₃²+1752X₄²（4）Based on the experimental research,an Arduino-controlled greenhouse CO₂augmentation equipment was designed and fabricated,which releases CO₂ by membrane purging and regeneration of potassium glycinate-rich solution,and uses CO₂ concentration,light intensity,temperature,and humidity at the same time.The sensor module monitors the environmental data in the greenhouse and automatically adjusts the CO₂ release rate.In the actual test of the CO₂ augmentation equipment in the small greenhouse module with a volume of 0.4 m³ from 6:00 to 12:00 in the morning,the CO₂ concentration in the greenhouse can be maintained at 1000 ppm on a sunny day with sufficient light,and the CO₂ concentration in the greenhouse can be maintained at 800 ppm on a cloudy day with insufficient light,which proves that the equipment meets the expected requirements.