what is VAPOUR ABSORPTION MACHINES (VAM)



VAPOUR ABSORPTION MACHINES (VAM):

        The vapour absorption machines are becoming popular. The vapour compression machines use secondary energy in the form of electricity which is normally costly and these machines use CFC based refrigerant which may cause environmental pollutions like warming up or ozone depletion. On account of power shortage, and with increasing availability of natural gas the vapour absorption machines are becoming popular and attractive. The absorption system uses lithium bromide as absorbent and water as refrigerant. The machines are available with dual fired boilers so that they can be operated by using high speed diesel in emergencies when there is a disruption in the gas supply. These machines have no moving parts and are thus noiseless and vibration less. The maintenance costs are negligible as compared to vapour compression machines. Various options are available with single stage, two stage , parallel flow and series flow machines . A typical vapour absorption machine operates on the following principle

(i) Evaporator:
The refrigerant pump sprays the water over the evaporator tube bundle. the water, to be chilled, circulating in the evaporator tubes get cooled, as the refrigerant water evaporates because of extremely low pressure in the evaporator. 


(ii) Absorber:
The refrigerant water vapour goes to the absorber through the mist eliminator. Concentrated LiBR-water solution is sprayed over the absorber tube bundle. The refrigerant vapour is absorbed by the strong solution being sprayed and the heat of absorption is removed by cooling water passing through the absorber tube. Weak solutions from the absorber is sent by the Solution to the high temperature and low temperature generators to recover the refrigerant water vapour.

(iii) High Temperature Generator:
The weak solution is heated by direct firing of fuel in furnace of H.T generator. Due to the heat supplied in the high temperature generator, the weak solution of lithium bromide and water gets concentrated and refrigerant water is separated by evaporation.

(iv) Low Temperature Generator:
The hot evaporated water vapour from a high temperature generator is used to heat the weak solution that has been pumped into the low temperature generator to concentrate it even further.

(v) Condenser:
The water vapour evaporated in the generator at a higher temperature and pressure is condensed to liquid form in the condenser, where the heat of condensation is picked up by the cooling water from an absorber outlet circulating in the condenser tubes. The condensed refrigerant water is returned to the evaporator through an expansion device.

(vi) Heat Exchangers:
To recover the heat energy from the strong solution returning to the absorber, heat exchangers are used. The cold weak solution being pumped from the absorber pick up excess heat from the strong solution in the heat exchangers. This improves cycle efficiency.

The vapour absorption machines work on the reverse cycle and  thus are capable of providing winter heating. Thus, the conventional heating methods by electrical or hot water generators can be eliminated  resulting into substantial energy savings

WORKING CYCLE OF VAM





Comments

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