A potential auto-cascade absorption refrigeration system for pre-cooling of LNG liquefaction

•A potential pre-cooling system for LNG liquefaction is investigated experimentally.•Pre-cooling at −52.9 °C is achieved experimentally by 122.5 °C actuating heat.•It could provide −30 °C pre-cooling for LNG liquefaction by 90 °C waste heat.•Its energy saving could be equivalent to that of NH3/H2O systems.•It could show comprehensive advantages over NH3/H2O systems.

Low temperature cooling is required during production or recovery processes of the liquefied natural gas (LNG). An absorption refrigeration system for pre-cooling of LNG production or recovery, which can be powered by low-grade thermal energy and produce low temperature cooling, could provide great potential of energy saving by recovering waste heat. An auto-cascade absorption refrigeration (ACAR) system is investigated for potential pre-cooling of LNG liquefaction in this context. Under the actuating heat with a temperature of 122.5 °C, a minimum refrigeration temperature of −52.9 °C is obtained by the ACAR system. An experimental COPr value of the ACAR system reaches 0.011 with a refrigeration temperature of −52.9 °C. For an absorption refrigeration system, used for re-liquefaction of a LNG bulk gas carrier by utilizing exhaust engine heat with a temperature of 145 °C, the required minimum value of COPr is about 0.05 with a refrigeration temperature of −30 °C. However, under the actuating heat with a temperature of 120 °C, the minimum value becomes about 0.023 with a refrigeration temperature of −53 °C. Therefore, performance of the experimental ACAR prototype is approaching the basic requirements for re-liquefaction of a LNG bulk gas carrier, which could utilize exhaust engine heat. Based on the theoretical COPr values of the ACAR system, it is found that its energy saving could be equivalent to that of an ammonia/water absorption refrigeration system for pre-cooling of LNG liquefaction. Moreover, the ACAR system could show good performance in broader operational conditions. Besides, it overcomes some drawbacks on the manufactured materials and operational maintenance of an ammonia/water absorption refrigeration system. In summary, an ACAR system could provide pre-cooling at lower temperatures for LNG liquefaction by utilizing waste heat and show comprehensive advantages over an ammonia/water absorption refrigeration system. Hence, it shows good potential for pre-cooling of LNG liquefaction, especially for re-liquefaction of a LNG bulk gas carrier.

Graphical abstractA −52.9 °C refrigeration temperature of an auto-cascade absorption refrigeration (ACAR) system is provided for pre-cooling of LNG liquefaction. Under an actuating temperature of 122.5 °C, a minimum refrigeration temperature of −52.9 °C is obtained with a COPr value of 0.011 by the ACAR prototype, which uses R23 + R134a mixtures as a refrigerant and DMF as an absorbent. The performance of the experimental ACAR prototype is approaching the basic requirements for re-liquefaction of a LNG bulk gas carrier by utilizing exhaust engine heat, which COPr value is 0.023 with an actuating temperature of 120 °C and refrigeration temperature of −53 °C.Figure optionsDownload full-size imageDownload high-quality image (83 K)Download as PowerPoint slide