We have waste heat available at 30ºC-40°C in the form of hot water that is thrown to atmosphere via a cooling tower. We want to pump this heat above 100°C. We are also having steam available at 10 kg/cm2. A part of the steam is used at 1-5 kg/cm2. Can we evaporate the water at 30ºC-40°C and use it above 100°C by means of a thermal vapor recompressor (evaporating water under vacuum and carry away heat by steam ejector)? Can we pump a part of the heat available above 100°C by using the rest of the heat available at 30ºC-40°C?
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Jim Grant Forum Moderator 119 Posts
Re: Recycle waste heat16 January 2007 at 1:29pmThe water can be evaporated at 30ºC-40°C as you suggest, however, the efficiency of doing this must be calculated based on the energy required to bring this vapor to 5 kg/cm2. There will be a certain minimum flow of 10 kg/cm2 steam required to pump the vapor and bring it to the saturation temperature of 5 kg/cm2. This involves the basic thermodynamic calculation for enthalpy change from saturated vapor at 30ºC-40°C to saturated vapor at 5 kg/cm2 and the hydraulic calculation for pumping the recovered vapor from vacuum to 5 kg/cm2. This type of energy recovery can also be done with a standard compressor. The same efficiency calculations must be done in order to fully understand the economics of this type of energy recovery.