Systematic and efficient optimisation-based design of a process for CO2 removal from natural gas

Abstract

Natural gas is an important resource for bridging technology on the way to mostly renewable power. A significant number of natural gas sources with high CO2 contents have not been exploited yet due to high cost of CO2 separation. Growth in global natural gas demand, however, has lead to re-evaluation of unconventional natural gas reserves. In this contribution, different hybrid processes for CO2 removal from natural gas are optimised with regard to minimum process energy requirements. Considered separation operations are cryogenic distillation, membrane separation, and physical absorption with methanol. The influence of a wide range of CO2 contents in the natural gas feed (40mol-% to 80mol-%) on different process alternatives is investigated. This is combined with limits for CO2 contents in the natural gas product varying from pipeline transport (2–3 mol-%) to LNG specification (50ppm). As a result, we provide an overview over which process topology is optimal for which combination of natural gas feed and natural gas product specifications. Process optimisation is performed using a framework for systematic optimisation-based process design which includes robust and computationally efficient reduced models for unit operations and hence enables automated performance of a large number of optimisation calculations.