Analysis of ammonia/water and ammonia/salt mixture absorption cycles for refrigeration purposes in fishing ships

• Ammonia absorption systems can provide refrigeration necessities for fishing ships.
• Absorption refrigeration systems reduce the energy consumption of fishing ships.
• The NH3/(LiNO3 + H2O) mixture is recommended for absorption refrigeration cycles.

In this work, the use of waste heat energy of jacket water in diesel engines of fishing ships was analysed for use as a heat source for absorption refrigeration systems. The thermodynamic simulation of an absorption refrigeration cycle with three different working fluid mixtures that use ammonia as a refrigerant was carried out. This analysis was assessed in terms of the cooling demand and cycle performance as a function of the evaporator, condenser and generator temperatures. Moreover, the need for rectifying the vapour stream leaving the generator was analysed together with the drag of the fraction of non-evaporated liquid to the absorber.The results show that the NH3/(LiNO3 + H2O) and NH3/LiNO3 fluid mixtures have higher values of COP as compared to NH3/H2O fluid mixture, the differences being more pronounced at low generation temperatures. If the activation temperature is set to 85 °C, the minimum evaporation temperatures that can be achieved are −18.8 °C for the cycle with NH3/LiNO3, −17.5 °C for the cycle with NH3/(LiNO3 + H2O) cycle and −13.7 °C for the NH3/H2O cycle at a condensing temperature of 25 °C. Also, for the NH3/(LiNO3 + H2O) fluid mixture, it has been demonstrated that the absorption refrigeration cycle can be operated without a distillation column and in this case the water content in the refrigerant stream entering the evaporator is less than 1.5% in weight at the operating conditions selected.