(1) Chemical absorption. One chemical absorption mechanism is to use amine, alkali, alcohol and other composite solution absorbers to absorb CO2, H2S and other acidic substances in biogas by acid-base neutralization reaction. At the same time, it can also absorb NH3 and other gases easily soluble in water and alcohol. The other chemical absorption mechanism is to use dry chemical substances (such as Fe2O3) absorbs impurity gas as absorbent. The chemically absorbed absorbent can release various impurities and gases through the self purification system and regeneration system of the device for regeneration and recycling.
(2) Physical purification. Pressure swing adsorption is the main method to purify biogas through this mechanism. Different components in biogas are separated by using the principle that adsorbents have different adsorption capacity for different gases under different pressure conditions. Strong adsorption components with large adsorption capacity such as H2O, CO2 and H2S in biogas are adsorbed by adsorbents under certain pressure and stay in the bed, while weak adsorption with small adsorption capacity The components N2 and CH4 are output from the bed outlet, so as to realize the purification of biogas.
(3) Biological removal. Under certain conditions, the use of microbial growth and reproduction requires some impurity gases in biogas as as nutrients, so as to realize the purification of biogas.
At present, physicochemical methods have been widely used and accumulated rich experience. However, this method has some disadvantages, such as high operation cost, large investment, difficult regeneration, secondary pollution and so on. Biological method has the advantages of no catalyst and oxidant, no treatment of chemical sludge, less pollution, low energy consumption, high efficiency and recyclable elemental sulfur. It is becoming the development trend in the field of biogas desulfurization.