Chilled water at 6 oC, produced by the Li Br based absorption refrigeration system operating on “Lo heat” – derived from low pressure steam, flue gases or even hot water – can be used to cool down gas at suction end of compressors. Reducing temperature of gas at suction end of compressor results in reduction in power required and saves corresponding steam in service boilers.
This system can be installed for suction cooling for following machines:
Ammonia synthesis gas compressor
Process air compressor for secondary reformer
Combustion air compressor for gas turbine
Carbon di-oxide gas compressor ( In urea plant)
Although this system has been in operation in Industry for a long time, recently it has gained importance due to the need to conserve energy and consciousness to utilize low grade heat like steam at 1-2 bar, hot water, hot vapors and other low heat streams.
This system is sensitive to variations in heat input, which may result into crystallization of Li-Br solution. It is also sensitive to vacuum fluctuations. Advanced instrumentation is required to fully automize the operation. Electricity requirement is low, since low heat is utilized.
In India this system has been installed in about 10 plants and suction end cooling is mostly provided to synthesis and process air compressors. The savings depend on the type of machine and source of low heat but benefits are highly encouraging (FAI, 2013).