Single stage ammonia absorption refrigeration cycle
An ammonia absorption refrigeration plant consists of two circuits, the ammonia circuit described with the red lines and the water-ammonia solution circuit with the blue ones.
Ammonia changes state from liquid to gas in the evaporator (1) producing the refrigeration capacity at a temperature from a few degrees down to – 60 deg C. The natural tendency of water to absorb ammonia permits it to collect the ammonia vapor by the weak solution in the absorber (2). This absorption of ammonia vapor in water is exothermic. The generated heat has to be dissipated to grant a continuous and high absorption capacity of the solution. The enriched solution coming from the absorber is pumped (8) to the desorber (3). In the desorber the solution boils and due to its higher volatility mainly ammonia evaporates. To maintain a high efficiency ammonia must be as pure as possible, therefore it’s distillated in the rectification column (5). This almost pure ammonia vapor liquefies in the condenser (4) and is ready to evaporate again (1).
For efficiency consideration, two heat exchangers are added to the system. The solution heat exchanger (6) is used to recuperate the heat from the weak solution and to pre-heat the strong solution. In the subcooler (7) the cold ammonia vapor leaving the evaporator (1) is used to pre-cool the liquid ammonia before it enters the evaporator.