FirmGreen's Modular Technology

Process Description

Figure 1 (at right) shows a biogas wash column, in which the biogas cleansing action takes place. 

Landfill gas (LFG) or other biogas feedstock is first dehydrated and compressed to high pressure, typically 400 to 700 psi.  Hydrogen sulfide, up to levels of 200 parts per million (ppm), is removed with a guard bed, which converts H₂S to inert iron sulfide, a non-hazardous solid waste that is landfilled. 

The dry, compressed biogas is introduced into a conventional packed column where contaminants are removed at ‑70°F.  Pure liquid CO₂ condenses from treated biogas at the top of the column.  A small portion of this liquid is sent down the column (descending blue drops) where, in intimate contact with rising biogas, it absorbs (or washes) contaminants.  The larger portion of this condensed liquid is available as clean liquid CO₂ product (blue stream at top of column). 

The clean biogas methane product stream (green stream at top of column), composed of 80% methane and 20% CO₂, exits from the top of the column.  It can be used as clean fuel gas (800 Btu/cubic foot), as feedstock to make methanol, or as a power source for fuel cells.

Alternatively, the stream can be further processed to remove any residual carbon dioxide from methane to produce pipeline-quality gas or transportation fuel (compressed or liquefied), and additional liquid carbon dioxide. A schematic of possible applications can be viewed here.

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