Theoretical and experimental investigation of an absorption refrigeration and pre-desalination system for marine engine exhaust gas heat recovery

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Absorption-refrigeration-cycle-based exhaust gas heat recovery technology is effective in improving the thermal efficiency and fuel economy of marine diesel engines. However, the absorption refrigeration system is inflexible in the start–stop operation, and this cannot fulfil the fluctuating demand of refrigeration. This paper presents both the theoretical and experimental investigations of an absorption refrigeration and freezing pre-desalination-based marine engine exhaust gas heat recovery system. The energy storage subcycle is introduced to overcome the energy underutilisation and balance the excessive refrigerating output of the absorption refrigeration cycle. Seawater is utilised as the phase-change material and it is pre-desalinated in the energy storage subcycle. A mathematical model of the system is established and experimental investigation is conducted. Furthermore, the theoretical and experimental performances are compared, and an economic analysis of seawater desalination is performed to evaluate its economy. The results show that the total refrigeration output of the system ranges from 6.1 kW to 9.9 kW, and the system COP (Coefficient of Performance) can reach 16% under the experimental operating conditions. Additionally, the salinity of pre-desalinated seawater can be reduced to below 10 ppt. Moreover, the cost of RO (Reverse Osmosis) seawater desalination can be reduced by 26% through the pre-desalination process of seawater.