(25d) Removal of Heavy Hydrocarbons from Lean Natural Gas

Removal of heavy hydrocarbons, such as C₆+ from natural gas is essential prior to cryogenic liquefaction in order to prevent freeze-out of these components in the liquefier.  Traditionally, cryogenic methods such as passing feed gas through a scrub column or a front-end NGL extraction unit have been employed for this purpose.  However, these conventional approaches may not be feasible for certain feed gas streams such as lean natural gas containing low amounts of C₂-C₄, yet significant amounts of C₆+.  Lately, several sources of natural gas, such as domestic pipelines, shale gas, coal-bed methane, etc., report lean feed gas of this nature.  Adsorption-based separation processes are an alternative method to strip trace heavy hydrocarbons from natural gas.  In this paper, we discuss important considerations for evaluating such adsorption systems as well as possible integration with conventional cryogenic methods for the effective removal of heavy hydrocarbons from natural gas.