The first Nitrogen Reduction Membrane
Unit (NRMU) to pretreat natural gas supplying a fuel cell
power generation system has been commissioned by Enerfex
Inc., USA. Each of the NRMU’s 18 membrane modules
contains about 15 miles of 250-micron hollow fibre coated
with a 0.5-micron plasma-deposited semipermeable gas-separation
barrier. The membrane is selective for hydrocarbons and
carbon dioxide over nitrogen, with greater selectivity
for higher hydrocarbons. Permeation flux is on the order
of 80 times greater than for a typical air-separation
membrane. The product stream is the permeate, which goes
to the fuel cells, while the residual nonpermeate is either
consumed onsite in another process or recycled back to
the gas distribution system.
Normally available gas pressure in
the range of 15 to 45 psig is the driving force. Most
natural gas contains some nitrogen. Above certain levels,
it can substantially degrade fuel cell electrolyte and
life cycle. Reducing nitrogen content by only 30% can
increase cell stack life by as much as four times, the
company claims.
