Pressure swing adsorption (PSA), water washing, chemical absorption, membrane separation and selective separation are the current purification processes of biogas. Pressure swing adsorption (PSA) and chemical absorption (amine purification) are the most mature and widely used methods in the world. The following biogas purification equipment manufacturers will give you a detailed introduction!
1. Pressure swing adsorption (PSA)
Pressure swing adsorption (PSA) is a method to separate gas components under pressure by using different adsorption capacities of CH4, CO2 and N2 in biogas on the surface of adsorbent. The adsorption capacity of components is affected by pressure and temperature. The adsorption capacity increases with the increase of pressure and decreases with the decrease of pressure. The adsorption capacity decreases with the increase of temperature and increases with the decrease of temperature. Pressure swing adsorption (PSA) requires very strict gas sources. The existence of H2S will lead to permanent poisoning of adsorbents. PSA requires gas drying. So H2S and H2 should be removed before PSA.
Adsorption materials play a key role in this technology. Generally, different types of activated carbon, zeolite, silica gel, alumina and molecular sieve are used as adsorption materials. Different adsorption materials have different purification effects on biogas. At present, carbon-based adsorbents, mainly activated carbon and molecular sieve, are often used in the study of biogas purification. In recent years, some new adsorption materials, such as ordered mesoporous materials, amine-modified adsorbents and metal frameworks (MOFs), have high adsorption selectivity for CO2, and have broad application prospects. MOFs are considered to have potential in CO2 separation.
2. Chemical Absorption Method
Chemical absorption is a method of separating CO2 from CH4 by using amine solution. In the process of separation, CO2 is absorbed and reacted with amine solution further. The regeneration of amine solution is completed by heating. Because of the strong selectivity of chemical reaction and the very low absorption of CH4 by amine solution, the loss rate of CH4 in this method is less than 0.1%. The operating pressure of this technology is generally 1 atm.
The commonly used amine solutions are ethanolamine (MEA), diethanolamine (DEA) and methyl diethanolamine (MDEA) . Because of the chemical reaction between CO2 and amine solution after absorption, the absorption process can be carried out under lower pressure. Generally, only slightly higher pressure is needed on the basis of the existing pressure of methane. The regeneration process of amine solution is very difficult and needs 160 C temperature. Therefore, the operation process needs to consume a lot of process heat, which has the disadvantage of high energy consumption. In addition, because of the evaporation loss, the ammonia solution needs to be replenished frequently during operation.
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