Research On Boiler Flue Gas Heat Recovery And Low Temperature Corrosion Prevention

At present, the flue gas temperature of large coal-fired boiler ranges from 120 to 140℃, the waste heat loss takes more than half of the whole thermal loss in the boiler. Recovering the waste energy by heating the condensed water is the way which is the most widely used. Put waste heat back to the thermodynamic system can improve the economy of power plant, reduce coal consumption and pollution. As China′s thermal power installed capacity reached 86 million kilowatts in 2013, flue gas waste heat recovery and utilization has an important strategic significance for energy conservation and emission reduction.In this paper, taking a 1000 MW unit for the study, the impact of the low-pressure economizer with different installation methods in waste heat utilization system is calculated and analyzed. Using annual net profit as the project objective function to obtain a relatively reasonable solution while the investment, operation and maintenance costs are considered. It provides a theoretical basis for the design and optimization of waste heat utilization system.Low-temperature corrosion can seriously affect the security of the waste heat utilization system. And flue gas acid dew point is an important parameter to assess low temperature corrosion. In this paper, the flue gas acid dew point is studied in both theoretical and experimental. A flue gas acid dew point measurement instrument were designed and tested in several power plants. Different acid dew point empirical formulas were calculated and compared in a simplified model. The result shows that there is a large error between different formulas. And compared with the experimental result, the theoretical result is more conservative with 30℃ higher.It can effectively reduce low temperature corrosion by improving low-pressure economizer wall temperature. In this paper a scheme of laying low thermal conductivity coating on the inner wall of the low temperature duct of the low pressure economizer was presented. The influence of different coating thickness on the wall temperature and heat transfer coefficient was calculated and analyzed; the influence was further contrasted taking an 1000 MW unit installed with new low pressure economizer for example. The results show that, compared with the bare-tube heat exchangers which raise the wall temperature by increasing the feed water temperature under the same heat absorption, the new low pressure economizer’s overall heat transfer coefficient decreased by 9.1%, but the temperature difference increased by 19.1%, thus saving steel weight by 13.0%, reducing the flue gas resistance by 70 Pa and making it possible less or not to using expensive corrosion resistant steel.