Study of Liquefied Natural Gas Production Cycles for Novel Low-temperature Natural Gas Purification Processes

Abstract

The primary energy mix forecasted for the future shows that growth rates will be the highest for renewable energy sources but, in absolute terms, fossil fuels will remain dominant. Among them, natural gas is the most attractive due to the advantages it offers in terms of environmental impact. This has recently contributed to the increased demand for natural gas and to the interest in developing those reserves that were left undeveloped in the past because of their high acid gas (particularly CO2) content. This has driven the recent research towards novel technologies that are suitable for the production of these gas fields. These novel technologies are based on low-temperature/cryogenic separation methods, which produce a purified natural gas stream at a temperature much lower than that reached when conventional technologies are used for acid gas removal. In addition to the key role played by natural gas, it is important to also take into account the one played by liquefied natural gas, which represents a valuable alternative to the common method for natural gas transportation via pipelines to reach the utilization zones. Currently, all the natural gas liquefaction technologies are developed for a natural gas stream coming from a conventional purification process that produces a purified stream at about ambient temperature. Considering the recent development of low-temperature/cryogenic natural gas purification technologies, it is important to study liquefaction cycles so that they can be applied to a purified natural gas stream at low/cryogenic temperatures. This work deals with this study and aims at adapting the Single Mixed Refrigerant (SMR) liquefaction process currently used to liquefy a natural gas stream at ambient temperature, so that it can be applied to a purified natural gas stream at low/cryogenic temperatures. Simulations have been carried out in Aspen Hysys® V9.0 in order to adjust the composition and flowrate of the mixed refrigerant depending on the conditions of the purified natural gas stream that undergoes the liquefaction process.