Processing of Low BTU Gas

Abstract

Natural gas is the cleanest fossil fuel available yet geological sources of natural gas are not free of impurities which require extensive processing to be commercialized. Practical use of gas reserves with high impurities is imperative in the future as the reserves with better quality are being depleted hence there is a need for environment friendly and cost-effective gas purification methods. Pakistan is the 21st largest gas consumer with large and low-cost gas fields but the gas sector is facing shortages because of low quality gas fields and many fertilizer plants are being shut down. The revised 2011 LNG policy provides incentives to the private sector for LNG production. This paper provides an overview and comparison of conventional and emerging gas separation technologies for the removal of the most common natural gas contaminant i.e. CO2. The processes discussed and researched include Chemical and Physical Absorption, Adsorption, Membrane Technology and Cryogenics. For each technology and their subsets, the working principle, operating conditions and level of innovation are discussed and a comparison is made between all aforementioned technologies based on applicability, versatility, cost-effectiveness, eco-friendliness etc. A further screening between the best methods is done to select a final process of which the most versatile subset technology is selected and further expanded upon in detail. From available gas separation technologies, Controlled Freeze Zone TM (CFZ) integrated with Linde’s Nitrogen Rejection Unit (NRU) is found out to be the most applicable and innovative technology for low BTU gas processing. A Preliminary process design for a gas processing plant treating Uch (Pakistan) gas field is presented. The process is expected to yield an 887 BTU product gas stream boasting 98% removal of CO2 and N2 from the natural gas stream.