Performance analysis of a novel mode using solar energy to recycle and reuse water vapor from flue gas of coal-fired power station

Abstract

Coal-fired power stations need to use massive quantities of coal and discharge substantial amounts of pollutants every year. Coupling solar energy with traditional coal-fired power stations can solve these problems. Most studies focus on using solar energy to heat boiler inlets, feedwater and high-temperature steam. However, areas with more solar energy are often water-deficient areas and saving water resources is particularly important. In this study, a 600 MWe coal-fired power station and solar energy are combined into a solar-aided coal-fired power generation (SACPG) system. Five SACPG systems are studied. There are parallel steam heating, reheating, double reheating, heating feedwater before pump and recycle and reuse water vapor from flue gas. For the first time propose using solar energy to recycle and reuse water vapor from the flue gas of coal-fired power stations in power-boosting (PB) and fuel-saving (FS) modes to analyze its thermal characteristics, exergy characteristics and energy savings. The research shows that feedwater recycle mode has the largest total thermal efficiency, which is 42.47 % and boiler thermal efficiency of 95.02 %. Three operation modes of saving water scheme including feedwater recovery, reheat steam recovery and FS mode are considered in this paper. Among three modes, FS has the smallest exergy loss of all parts, except fans. The FS mode coal saving rate is 10.79 g/kWh and the water saving rate is 3.87 × 105 t per year. The PB mode water saving rate is 4.04 × 105 t per year. Feedwater recycling output is larger than that of reheated steam recycling. The mode with the highest total thermal efficiency, largest solar field exergy efficiency and coal saving rate is using solar energy to heat feedwater parts and parallel steam generation employing thermal solar energy, which are 42.76 %, 27.70 % and 15.53 g/kWh, respectively. Using thermal solar energy to heat feedwater prior to the feedwater pump offers the highest boiler thermal efficiency (94.44 %) and the lowest exergy loss of all parts except fans. Using solar energy to heat high-temperature parts, the reheated steam mode has the largest boiler thermal efficiency, total thermal efficiency and solar field exergy efficiency, which are 94.16 %, 43.68 % and 33.61 % respectively and the smallest exergy loss of all parts, except fans. Meanwhile, the double reheated steam mode has the largest coal saving rate, which is 9.60 g/kWh.