Abstract
It is difficult to recover the residual heat from flue gas when supercritical carbon dioxide (S-CO2) cycle is used for a coal fired power plant, due to the higher CO2 temperature in tail flue and the limited air temperature in air preheater. The combined cycle is helpful for residual heat recovery. Thus, it is important to build an efficient bottom cycle. In this paper, we proposed a novel exergy destruction control strategy during residual heat recovery to equal and minimize the exergy destruction for different bottom cycles. Five bottom cycles are analyzed to identify their differences in thermal efficiencies (ηth,b), and the CO2 temperature entering the bottom cycle heater (T4b) etc. We show that the exergy destruction can be minimized by a suitable pinch temperature between flue gas and CO2 in the heater via adjusting T4b. Among the five bottom cycles, either the recompression cycle (RC) or the partial cooling cycle (PACC) exhibits good performance. The power generation efficiency is 47.04% when the vapor parameters of CO2 are 620/30 MPa, with the double-reheating-recompression cycle as the top cycle, and RC as the bottom cycle. Such efficiency is higher than that of the supercritical water cycle power plant.
Highlights
Coal fired power generation accounts for nearly 32% of the world’s total electricity production [1].this application is a concern due to environmental pollution and carbon dioxide emissions [2,3]
In respect of flue gas energy distribution, the high temperature region is absorbed by top cycle, middle temperature region is absorbed by bottom cycle, low temperature region is absorbed by air preheater
The residual heat is caused by two effects: (1) The CO2 temperature is high in the tail flue: differences of heating surface layout between this paper and [28] is that in this paper the preheater in tail flue is eliminated
Summary
Coal fired power generation accounts for nearly 32% of the world’s total electricity production [1]. This application is a concern due to environmental pollution and carbon dioxide emissions [2,3]. Due to its high efficiency [13,14], simple system [10,15], and compact layout [16,17]. These advantages make it attractive to apply a S-CO2 cycle to coal fired power generation, but this system faces a residual heat problem.
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