Choosing Tower Internals for LNG, Shale Gas, and Tail Gas Treating

It is well known that for best performance, tail gas treating requires the utmost in selectivity.  Shale gas often contains a small amount of H₂S in a much larger concentration of CO₂.  Sometimes this too demands highly selective treating to meet transmission pipeline specifications. This paper shows that the inherent selectivity of trays in such applications can be greatly improved by simple changes in tray design parameters.

Treating gas in an LNG plant to reduce CO₂ to a level sufficient for liquefaction of the gas (typically 50 ppmv) is a completely non-selective process and one that often uses an absorber containing either random or structured packing.  This paper compares structured packings of various sizes with trays, and shows the profound effect of packing type and size on absorber performance.  There is an optimal packing size for each application.  Specifying too large a packing will result in failure to meet the treating goal.  Choosing a packing size that is unnecessarily small is not only costly because of higher packing cost; it invites plugging and reduces tower capacity, too.  This paper provides a quantitative way to determine just what the right size is.