There are four methods for biogas purification, namely absorption method, pressure swing adsorption method, low-temperature condensation method and membrane separation method.
The absorption and purification method is realized by using the physicochemical absorption characteristics of organic amine solution (primary amine, secondary amine, tertiary amine, steric amine, etc.) and carbon dioxide, that is, it reacts with carbon dioxide in biogas under pressure and normal temperature in the absorption tower to decarbonize and purify methane, and absorb the decompression and purification of rich liquid in the regeneration tower The reverse analytical reaction occurs under heating conditions to release high-purity carbon dioxide gas. At the same time, the rich liquid is regenerated and has the ability to re absorb carbon dioxide, so as to realize the continuous decarburization and purification of methane in the absorption tower, and make the decarburized liquid carry out continuous absorption and regeneration cycle.
PSA purification method uses the selective adsorption characteristics of adsorbents (such as molecular sieves) for carbon dioxide, that is, carbon dioxide has a higher separation coefficient than other gaseous components on the adsorbent to achieve the purpose of removing carbon dioxide from biogas.
During the adsorption process, the carbon dioxide in the feed gas is adsorbed in the adsorption tower under pressurized conditions, and other weakly adsorbed gases such as methane are discharged as purified gas. When the adsorption is saturated, the adsorption column is depressurized or even vacuumized to release the adsorbed carbon dioxide. In order to ensure the continuous treatment of gas, PSA requires at least two adsorption towers, or three towers, four towers or more.
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