Techno-Economic Analysis of LNG Production Using Cryogenic vs Conventional Techniques for Natural Gas Purification

LNG is a global commodity, i.e. a product that is usable and that can be delivered worldwide to meet the energy demand. Statistics reveal the complexity of commercial, political and technical drivers and how these drivers are conspiring to increase the future LNG demand. For LNG production the removal of CO2 is required down to concentrations of around 50 ppm against the 0.02-0.025 molar fraction of the gas net. On the other hand increasing world energy demand and pricing trends encourage oil and gas companies to look at exploiting acid natural gas fields previously uneconomic. Conventional technologies for natural gas purification may not be suitable for treating gas with high CO2 (and/or H2S) content. As a matter of fact, the traditional amine washing method is not competitive because the power required for solvent regeneration is proportional to the quantity of acid gas to be removed. At the same time environmental concerns are pushing to adopt practices for reducing CO2 emissions. The use of cryogenic methods can meet the requirement of energy saving in both the purification process and in the geo-sequestration since CO2 is captured in liquid form, easy to be pumped underground for storage or sent for enhanced oil recovery. Cryogenic techniques include cryogenic distillation methods, for instance the Ryan-Holmes process and other more recent ones, and the anti-sublimation methods. The present paper presents a techno-economic analysis where conventional methods are compared to cryogenic ones, not only in the CO2 removal process but for the overall LNG production where the low temperatures required in the purification step are synergic to the LNG production.