Nitrogen Reduction From Fuel Cell Feed

Description and Advantage

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.

Source

Chemical Engineering Progress, 1, 2001.