Perspectives of Biogas Conversion into Bio-CNG for Automobile Fuel in Bangladesh

Table 4

Some commonly used biogas cleaning methods and their features.

Biogas cleaning methods	Diagram	Characteristics	Reference
Water scrubbing		(i) Eliminates CO2, NH3, dust, and so forth and provides up to 96.1% CH4 purity; (ii) Large quantity is required	[49]
Pressure swing adsorption		(i) Eliminates CO2, N2, and O2 and purifies biogas up to 95.8% of CH4(ii) Low emission and power demand, however, relatively more expensive; (iii) Additional steps are required for removing H2S prior to the process	[49]
Chemical absorption		(i) High efficiency, complete removal of H2S, and 94.6% CH4 containing biogas; (ii) Relatively high cost and additional chemical and energy input requirement	[49]
Membrane permeation		(i) Light in weight, simple in operation and maintenance; (ii) Comparatively low CH4 (90.3%) percentage in biogas; (iii) High cost of membrane	[49]
Physical absorption		(i) Requires less energy input, about 93% CH4 purity in biogas; (ii) Requires more absorbent to capture CO2	[50]
Cryogenic method		(i) Removes CO2, H2S, and all other impurities from biogas and contains 88% CH4(ii) Additional equipment like turbines, compressors, and heat exchangers causes high investment cost	[51]
Biological filtration		(i) Eliminates H2S, and purifies biogas up to 94% of CH4(ii) Low energy requirement; (iii) Additional nutrients requirement and biogas may contain small amount of O2 and N2	[51]
Dynamic temperature swing adsorption		(i) Low operating cost with the lowest CH4 (84%) percentage among the cleaning methods; (ii) Requirement of high energy input	[52]