Design and simulation of an ammonia absorption chiller for the precooling of natural gas in a small-scale liquefaction plant

This paper describes an ammonia absorption chiller used to precool a natural gas stream to be liquefied. This application is referred to a novel small-scale LNG (Liquefied Natural Gas) plant, whose purpose is the liquefaction of small amounts of natural gas directly on site for the final user. In order to have the economic feasibility of a LNG small scale production, it is necessary to achieve the highest energy efficiency of the liquefaction process. For this purpose an ammonia refrigeration machine is used, powered by waste heat from exhaust gases of the I.C. engine that drives the LNG plant compressor. The absorption chiller uses water-ammonia as working pair and cools the compressed natural gas stream down to –30°C.
In the paper a simulation of the ammonia absorption chiller is performed for the abovementioned application, describing its operating conditions, energy efficiency and influence on the energy balance of the whole plant.