Study On Comparison Of Low-temperature Waste Heat Utilizations And New Type Of Combined System

The industry sectors, like architectural material industry, metallurgical industry, chemical industry, light industry, have a lot of low-temperature heat resource. To recovery these resource with correct techniques is very important for solving our country’s energy and environmental problem. These techniques are mature, large-scale application, and with good economic benefit, include aqua-ammonia absorption refrigerating unit, lithium-bromide absorption refrigerating machine, ORC system, low temperature multi-effect distillation and multi-stage flash desalination. In order to determine which one is the best scheme to recovery waste heat resource, we compared above-mentioned five systems with multiple parameters(Net Income, Emission reductions of Carbon dioxide, Exergy loss). At last, according to the results, a combined system is established and analyzed. Meanwhile we also compared the conditions between combined system and others individual systems.In the comparison of five individual systems, LT-MED has the maximum NI when the temperature of the heat source is under 110℃. Li Br-H2 O absorption refrigeration get the maximum NI as the temperature of the heat source is between 110℃and 220℃. However, when the temperature of the source is higher than 220℃, ORC has the maximum NI. CO2 emission reduction of LT-MED is the largest as heat source temperature is under 110℃. Otherwise, ORC has the largest CO2 emission reductions. When heat source temperature is higher than 180℃, ORC following with Li Br-H2 O absorption refrigeration gets the minimum exergy loss. Whereas, Li Br-H2 O absorption refrigeration following with ORC has the minimum exergy loss. Considering all three objective functions, it is found that, LT-MED is the best way in waste heat recovery when heat source temperature is under 110℃, Li Br-H2 O absorption refrigeration is the best choice as temperature is between 110℃ and 210℃. While heat source temperature is higher than 210℃, ORC is the optimum way.The combined system, based on lithium-bromide absorption refrigerating machine and ORC system, is not coupled at any conditon. Only when the temperature of heat resorce is under 200℃,it can couple with the condition that ΔT=5℃,TE2=5℃. But the temperature that the system can couple will rise while pinch point temperature difference is rose. At the same time, when ΔT is rose, the evaporation temperature, efficiency, and Net Income will reduce. However the flux of cooling water, the system required will increase. Net Income and the flux of the refrigerant water will increase when the evaporation temperature of refrigerant system is rose. But the temperature of heat resource that combined system can couple will be lower.Moreover, in the comparative analysis between combined system and others, the former one can get a better effect for energy recovery, when the system is coupled. Even in the case that system is not coupled, the effect of combined system is also more excellent than those individual systems.