Performance analysis and evaluation of a commercial absorption-refrigeration water-ammonia (ARWA) system

The Robur absorption-refrigeration water-ammonia (ARWA) system is analyzed using Aspen Plus flowsheet simulator. The results are compared with experimental and some manufacturer data reported in the open literature. Among performance parameters analyzed are coefficient of performance (COP), heat duties of the evaporator, absorber, and the condenser, refrigerant concentration in the weak and strong solution, and flow rates of the weak solution and the flow rate of refrigerant passing through the evaporator. In general, a very good agreement between the simulator's results and the experimental measurements was found. Also, results obtained for the effect of separator (input) heat duty on the COP agree well with the reported experimental data with a maximum percentage deviation of 1.8%. Efficiency of the separator in splitting off the refrigerant at the column top is shown to be of crucial importance; COP increased by 15% in going from 1 to 5 theoretical equivalent mass transfer stages in the separator. Some innovative modifications to Robur cycle aimed at enhancing the separator operation have shown a promising improvement in the COP. In particular, introducing a throttling process directly before the separator can alleviate the separator heat load and enhance the COP by up to 20%. Use of stripping gas injected at the bottom of the boiler is another strategy that has been investigated in this work.