It known that membrane unit is flexible and easy-to-install; therefore, retrofit designs developed in this study is not limited to the assumed feedstock. Keeping the operating conditions unchanged, OSMAHRD and TSMAHRD can be modified by adding/reducing membrane module (thus changing membrane area) and installing parallel compressors (for TSMAHRD) so as to process feed with different CO2mole fraction. In this section, two scenarios are considered. In the first scenario, mole fraction of CO2is only 0.15 (instead of 0.2 considered in the retrofit design) while mole fraction of CH4increases from 0.648 to 0.698, and concentrations of other components remain the same. In the second scenario,CO2mole fraction rises from 0.2 to 0.35 while mole fraction ofCH4decreases from 0.648 to 0.498, and concentrations of other components remain the same.