Improving waste incineration CHP plant efficiency by waste heat recovery for feedwater preheating process: energy, exergy, and economic (3E) analysis

In this work, waste heat recovery, as a passive technique with low cost, is used for increasing the efficiency of a waste incineration CHP plant via an innovative way. Here, the recovered thermal energy is suggested to be used for the feedwater preheating process instead of steam extractions of turbines or any other auxiliary heat input for this purpose. For investigating the effects of the proposal, three different scenarios are considered and compared to each other. The first scenario is an old design waste CHP plant with a fuel-burning preheating process; the second scenario is a CHP plant with steam extractions from turbines for feedwater preheating; and the last scenario is when both of the previous preheating tools are removed from the cycle and instead, the energy of the exhaust gas of the incinerator is recovered and utilized for feedwater preheating. The energy, exergy, and economic analyses of the three scenarios are carried out, and the main performance factors of these power plants are compared. The results show that the efficiency of the heat recovered case considering both heat and power outputs can reach about 94% while the plants with old-fashion design and with steam extraction lines could give only 77% and 82% efficiencies. The exergetic efficiency of the proposed solution reaches the top value of 81% among the three scenarios, and its unit product cost will be lowest among all with a value of below 11 $/GJ. In the end, the effects of several operating parameters on the efficiency of the proposed system are investigated and reported.