Proposal and investigation of a novel small-scale natural gas liquefaction process using diffusion absorption refrigeration technology

Conventional vapor compression refrigeration systems need a considerable amount of power, especially when they are used in the cryogenic processes. Therefore, alternative cooling technologies driven by thermal energy have been considered for introducing new refrigeration systems in the natural gas liquefaction processes. This study proposes and analyzes a novel process configuration for liquefied natural gas production at a small scale. A conventional single mixed refrigerant (SMR) LNG process is upgraded using a diffusion absorption refrigeration (DAR) system in this configuration. The DAR cycle is a refrigeration system that can be driven purely by heat load without the need for power or mechanical inputs. Therefore, integrating the DAR cycle with a conventional SMR system can supply a portion of the cooling load in the LNG production process, and the power consumption of compressors and pumps in the SMR cycle is reduced. The amount of thermal energy required of the DAR system is provided through the PTC with an aperture area of 130,000 m(2) based on the weather information of Yazd city during a year. The heater is employed as auxiliary equipment to provide this energy required in special situations. The DAR system uses an inert gas such as hydrogen that helps the evaporation of the refrigerant by decreasing its partial pressure in the evaporator. The results illustrate that the COP of the DAR system is about 0.157, and the ratio of power consumption to LNG production can reach 0.225 kW/kg(LNG), which is lower than the base case SMR process. Therefore, it can be claimed that energy and coal consumption is reduced in the LNG production process by 19.36%, and CO2 emissions reduce by 17.85% through the integration of the DAR cycle with the SMR cycle. The solar fraction and efficiency of the solar system are 0.5 and 62%, respectively. Next, the energy and exergy aspects of the process are analyzed. Also, the consequences of the variation in effective parameters such as the ratio of the hydrogen to the mixture of water and ammonia, ammonia percentage, and the DAR operating pressure are investigated. [GRAPHICS] .