MEMBRANE PROCESSES FOR THE REMOVAL OF ACID GASES FROM NATURAL-GAS .1. PROCESS CONFIGURATIONS AND OPTIMIZATION OF OPERATING-CONDITIONS

The objective of this study is to assess the economics of some membrane separation processes for the removal of CO2 from crude ('sour') natural gas so as to obtain pipeline quality gas. Seven different membrane process configurations have been examined by computer simulations. The 'base-case' studies considered a 35 MMSCFD (million standard cubic feet per day) feed stream of natural gas at 800 psia with CO2 concentrations in the range of 5 to 40 mole%. The operating variables for each of the process configurations were optimized on the basis of new process variables in order to determine the lowest cost of CO2 removal from natural gas. It was concluded that, for the base-case operating conditions, the separation cost for the removal of CO2 from natural gas is lowest for a three-stage configuration. This configuration consists of a single permeation stage (a 'premembrane' stage) in series with a two-stage permeation cascade with recycle, as indicated also by other investigators. A following study will compare the separation cost for membrane processes with that for diethanolamine (DEA) gas absorption processes. The effects of variations in a number of economic and operating parameters and in membrane properties on the relative economics of membrane and DEA gas absorption processes will also be discussed in that study.