A cost-effective solution for upgrading low-pressure, low-BTU natural gas: an experiment with a micro-scale pressure-swing adsorption plant in central Kansas

Saibal Bhattacharya1,   Dave Newell2,   Lynn Watney3,   Jake Sigel4

¹Kansas Geological Survey ,  ²Kansas Geological Survey ,  ³Kansas Geological Survey ,   ⁴American Energies Corporation

Upper Pennsylvanian and Permian strata in central Kansas typically contain small reservoirs of low-BTU natural gas at relatively low pressure that have historically been disregarded by operators that drill for deeper oil or high-BTU gas. The low-BTU natural gas is principally diluted by nitrogen (N2) in this part of the Mid-Continent. Experimental hardware to reject this N2 and upgrade the low-BTU gas – a non-patented, skid-mounted, two-tower micro-scale pressure-swing adsorption (PSA) plant constructed with commonly available components – was tested at the Elmdale Field on the Nemaha Uplift in east-central Kansas. Inexpensive activated charcoal made from coconut husks was used as the adsorbent.

Low-BTU gas (~700 BTU/scf) at about 20 to 35 psi is fed into the plant. The charcoal adsorbs the hydrocarbons while the N2 remains free. The N2 is then vented and a vacuum subsequently draws off the now upgraded gas from the adsorption bed. A PSA plant such as this cannot perfectly upgrade low-BTU gas, for only about 75-80% of the hydrocarbons can be recovered, but its simplicity, low operative costs, mobility, and reusability are its main economic advantages. A plant built for $120,000 with feedstock of 150 mcf/day can pay for itself in about 10 months with $7/mcf gas, or commensurately longer at lower gas prices. Compressor engines can run on feed gas, so the plant can be away from the electrical grid. Being compact and portable, the plant can be used in other types of upgrading applications such as N2 removal from landfill and frac gases.

AAPG Search and Discover Article #90097 © 2009 Tulsa Geological Society, Tulsa, Oklahoma

 

 

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