Novel refrigeration cycle configurations for performance improvements in LNG processes at small scale

Abstract

Abstract The refrigeration cycles employed in the LNG industry are highly energy-intensive. The costs associated to the shaft work energy required for refrigerant compression usually dominates the overall operating costs of the LNG plant. In this work, four different single mixed refrigerant (SMR) cycle configurations, including the commercial PRICO cycle and the CryoMan cycle, are studied for energy-efficiency improvements in the production of LNG at small scale (i.e. up to 1 million tonnes per annum, MTPA). The cycle configurations are based on structural modifications applied to the PRICO cycle. The four configurations are first optimised to minimise shaft work demand, so analysis is carried out in the scenario in which each cycle fully exploits their corresponding configuration. Additionally, the complexity of the SMR cycles, in terms of number of compression stages is kept similar, so the energy savings can be associated to the structural modifications only. From the four SMR cycles, the CryoMan cycle is the most energy-efficient, achieving saving of around 8.5% compared to the commercial PRICO cycle. The exergy analysis applied to their multi-stream heat exchangers (MSHE) suggests that the structural modifications allow reducing the refrigeration duty at the lowest temperature level to bring energy savings.