Comprehensive Waste Heat Utilization And Energy-saving Analysis Of The Low-temperature Flue Gas In Large-scale Coal-fired Units

With the steady increase of coal price and stringent energy saving and emission reduction requirement, increasing the power generation efficiency, reducing the unit standard coal consumption and alleviating the pollutant emissions reduction have become the key elements for the development of coal-fired plants in China. At present, recycling the low-temperature flue gas which exhausts from the boiler is one of the most promising energy-saving measures.To begin with, with full consideration of the low-temperature corrosion issue, reasonable mathematical models for the major heat transfer units and processes involved in the low-temperature waste heat utilization system are built combining with the corresponding thermodynamic theory, this lays the firm foundation for further analyzing the optimization design in order to recycle the low energy grade of the flue gas.Based on the above knowledge, a typical 1000 MW coal-fired unit located in Shanghai is selected for case study, several feasible schemes are proposed by referring to the actual operation condition, including the connection mode on both the flue gas side and water side, material type and parameters, etc. The most appropriate scheme is finally determined, and it is determined to utilize the flue gas waste heat to heat the condensed water.Finally, comprehensive thermal analysis is undertaken for the reference case with the help of the proposed model, and in-depth analysis of the coal-saving and water-saving potentials as well as the effects of the added low-temperature economizer on the system is carried out. Besides, this paper also discuss the investment cost and off-design operation of the proposed low-temperature flue gas waste heat utilization system.This paper applies the thermal theory to solve the actual waste heat utilization issue in coal-fired power plants, and in-depth analysis of the retrofitting scheme is conducted. The research result of this paper provides an alternative for optimizing the waste heat utilization system, and to a certain extent, is beneficial to the energy-saving retrofitting of the coal-fired power plants in service.