The
landfill gas is taken directly from the collection system, compressed and
dehydrated prior to further low temperature removal of most contaminants
found in LFG. A liquid CO2 wash
system effectively reduces contaminants and VOCs to < 1ppm. The refined
and purified LFG is then fed to the membrane system, which efficiently
separates the CO2 from the LFG,
resulting in pressurized methane with small amounts of CO2
to meet pipeline gas requirements.
For
clients interested in CO2 recovery,
a CO2 rich permeate stream from the
membrane is recovered and recycled to the landfill compressor for
additional processing. Overall CO2
yield from the landfill gas is about 88%. Methane is produced at
approximately 150 psig for direct use, pipeline distribution, or
compression to higher pressures, if required. The diagram above assumed no
nitrogen in the LFG, but any N2 concentration in the LFG will be
effectively doubled in the product gas produced by the membrane, which
will affect the heating value of the natural gas.
With
further CO2 and H20 removal to less than 1 ppm, the highly enriched
methane can be liquefied in a cryogenic liquefaction cycle. The LNG can
then be readily stored or transported sizeable distances as a cryogen by
conventional cryogenic equipment. Typical LNG production is 10,000 to
20,000 gallons of LNG per day from an average producing landfill.
