Abstract
To use high-temperature waste heat generated by diesel engines for onboard refrigeration of fishing vessels, an ammonia-based double-effect vapor absorption refrigeration cycle is proposed. Non-volatile ionic liquids are applied as absorbents in the double-effect absorption system. In comparison to systems using ammonia/water fluid, the complexity of the system can be reduced by preventing the use of rectification sections. In this study, a multi-scale method is implemented to study the proposed system, including molecular simulations (the Monte Carlo method) for computing vapor-liquid equilibrium properties at high temperatures and pressures, thermodynamic modeling of the double-effect absorption cycles, and system evaluations by considering practical integration. The Monte Carlo simulations provide reasonable vapor-liquid equilibrium predictions. 1-butyl-3-methylimidazolium tetrafluoroborate is found to be the best performing candidate among the investigated commercialized ionic liquids. In the proposed cycle, the best working fluid achieves a coefficient of performance of 1.1 at a cooling temperature of −5 °C, which is slightly higher than that obtained with generator-absorber cycles. Integrated with the exhaust gas from diesel engines, the cooling capacity of the system is sufficient to operate two refrigeration seawater plants for most of the engine operating modes in high-latitude areas. Thereby, the carbon emission of onboard refrigeration of the considered fishing vessel could be reduced by 1633.5 tons per year compared to the current practice. Diagrams of vapor pressures and enthalpies of the studied working fluids are provided as appendices.
Highlights
Global warming is one of the critical issues of the society in this age
To use high-temperature waste heat generated by diesel engines for onboard refrigeration of fishing vessels, an ammonia-based double-effect vapor absorption refrigeration cycle is proposed
Two sub-streams are heated in two generators (GENs) to generate refrigerant vapor: One of the sub-streams is heated in the high pressure generator (HG) by the external heat source at a high temperature
Summary
Global warming is one of the critical issues of the society in this age. According to the International Maritime Organization [1], maritime transport emits around 1000 million tons of carbon dioxide (CO2) annually and is responsible for about 2.5% of global greenhouse gas emissions along with 15% and 13% of global NOx and SOx emissions. 150 °C, double-effect vapor absorption refrigeration (DE-VAR) cycles, in which the refrigerant is generated twice, are able to achieve higher thermal efficiencies by taking advantage of the higher temperature of the heat sources [8] These cycles usually utilize the working fluid H2O/LiBr, which cannot meet the demand of below-freezing-point cooling. To use higher temperature exhaust gases for below-freezing-point cooling onboard, NH3 with ionic liquids (ILs) working fluids is proposed to be used in DE-VAR systems. Becker et al [19] showed that molecular simulation is able to predict relevant thermophysical properties for temperatures and pressures applied in SE-VAR cycles These authors pointed out that improved force fields are needed for an accurate prediction of the cycle performance. A case study based on a real vessel operating in high-latitude conditions is carried out to check the technoeconomic feasibility of the integrated system in practice
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
