Optimal Resarch On Power Cycles For Waste Heat From Exhaust Gases Of Moderate Temperature

There are large amount of waste heat from the flue gas at temperature level about300-600℃during the industrial production processes. Carried out waste heat powerrecycling is of great significance to achieve energy conservation and sustainabledevelopment. Existing medium temperature waste heat power recovery technology ismainly based on water as the working fluid of the Rankine cycle (Water RankineCycle, WRC), and its system cost-effective is limited by two aspects, one is thethermo stability of working fluids, the other is temperature pinch point in the cycle.This research focus on improving cost-effective of power cycle for industrial flue gas.Three power cycles (WRC-ORC-OTC) have been compared. Another objective of thisdissertation is to study a new-presented combined cycle.The results of WRC-ORC-OTC comparison shows that,when the isentropicefficiency of steam turbine and medium pump were0.8and0.7respectively, the orderof network from largest to smallest of these three cycles aforementioned which are atoptimum cycle parameters respectively is OTC,ORC,WRC with flue gas temperaturelower than470℃. With the reduction of the efficiency of the system components orthe increase of the flue gas temperature, the comparative advantages of ORC, OTCsystem with WRC is decreased. One main reason is the thermo stability of workingfluids of ORC and OTC, and the other is the pump work of organic fluids faroutweigh than it in WRC. When flue gas inlet temperature higher than470℃thenetwork of the WRC system exceeds that of ORC, OTC system.Based on earlier research, we found that the locations of pinch in this cyclevariables with the temperature of heat resource and the kind of working fluid. In theORC system optimization study, a new optimization method were presented and usedin this thesis.Furthermore, a new kind of hybrid cycle was designed to achieve a good matchof the change of the working fluid and the heat source temperature endothermicprocess, and to avoid the constraints of the organic working fluid thermal stabilityceiling. The hybrid cycles significantly better than WRC, ORC, and OTC at all therange of medium temperature. When the flue gas inlet temperature were300℃,400℃,500, the network of combined cycle system are38.9%,8.1%,4.1%,41.2%,24.5%, 21.0%, and26.7%,32.3%,28.5%higher compared with the WRC, ORC, OTC system,respectivelyThere are few studies on heat exchanger performance of organic supercriticalworking fluid. These heat transfer correlations are not accuracy enough to the study ofOTC, combined cycle systems. Based on the analysis of heat transfer of supercriticalfluid law, a scheme of supercritical heat transfer performance of organic fluids testdevice was designed in this dissertation.