Techno-economic comparison of boiler cold-end exhaust gas heat recovery processes for efficient brown-coal-fired power generation

Abstract

An important way to increase power plant thermal efficiency is to recover exhaust gas heat at the boiler cold-end with the stepwise integration of a steam turbine heat regenerative system. To this end, there are currently three typical heat recovery processes, i.e., a low-temperature economizer (LTE), segmented air heating (SAH) and bypass flue (BPF), for recovery. To provide useful guidance to thermal power plants for optimal and efficient processes, the thermal economy and techno-economic performance of the three aforementioned processes were calculated and compared using an in-service 600 MW brown-coal-fired supercritical power unit as a reference. The results demonstrate that with the use of these three processes, the net standard coal consumption rate of the unit can be reduced by 4.43, 5.84 and 6.48 g/(kW · h); meanwhile, 3.84, 3.52 and 3.39 million USD are the initial costs of the three heat recovery projects. If the 600 MW unit runs 5500 h per year at the rated load, the three processes can annually increase the earnings of the unit by 1.49, 2.03 and 2.27 million USD from coal savings, meaning that their dynamic payback periods are 3.12, 2.00 and 1.71 years, respectively. The results indicate that for a brown-coal-fired power unit, the coal savings achieved by exhaust heat recovery are significant. In comparison with the conventional LTE, SAH shows an improvement in thermal economy and techno-economic performance, but it currently faces difficulties in engineering applications. Among the three processes, the BPF shows the best thermal economy and techno-economic performance, as well as good engineering feasibility; therefore, it is recommended for application.