A thermoacoustic refrigerator with multiple-bypass expansion cooling configuration for natural gas liquefaction

Abstract

A small-scale, energy-efficient and reliable refrigeration system is required for on-site liquefaction of natural gas in distributed stations. The thermoacoustic refrigerator is regarded as one of the most promising options to meet this demand. However, existing work on thermoacoustic refrigerators to date has been limited to a single cooling temperature only at the liquefaction temperature, without consideration of the significant irreversible losses that arise from the large temperature difference between the natural gas being cooled and the working gas being heated in the heat exchanger. To overcome this limitation, this paper proposes a novel multi-stage thermoacoustic refrigerator with multiple-bypass expansion cooling configuration that is capable of cascade liquefaction of natural gas. The irreversible losses can be reduced greatly by organizing the decreasing temperatures of the natural gas to occur across heat exchangers with decreasingly lower temperatures to achieve smaller temperature drops. Theoretical analyses were performed on the working characteristics of both two-stage and three-stage systems and comparisons are made with the conventional single-stage system. The system performances are compared based on whether the system covers only the sensible heat or the combined sensible and the latent heat of natural gas. Results show that the proposed system improves the relative liquefaction efficiency if it is used to cover only sensible heat of natural gas (improved by 57.0%) or to cover the combined sensible and latent heat of natural gas (improved by 12.6%), when compared to conventional single-stage system. These findings demonstrate the system’s promise for use in natural gas liquefaction applications.