Design And Research On Flue Gas Waste Heat Utilization System Of Power Plant Boiler Based On Heating Condensate By Primary Air

In order to satisfy the safety and economic of the coal pulverizing system for boilers that burning low moisture and high volatile coal,it is necessary to reduce the primary air temperature of the entrance of the coal mill by mix cold air.However,this will result in a decrease in the heat flow and the decrease in the heat transfer capacity of air preheater and the increase of flue gas temperature.The high flue gas temperature will cause adverse effect on the economy and safe of the power plant.In order to make full use of the heat transfer capacity of air preheater,reduce the flue gas temperature and recover the waste heat,we proposed a kind of flue gas waste heat utilization system of power plant boiler based on heating condensation water by hot primary air.The system can recycle the surplus heat of primary air to the regenerative system through the primary air-condensate/feed water heat exchanger.The system can improve the energy utilization level of flue gas heat,so the energy saving effect is excellent.At same time,the heat exchanger has no abrasion and low-temperature corrosion.In this paper,we has designed a primary air waste heat utilization system for a supercritical 600 MW coal-fired unit.According to the method of equivalent enthalpy drop,the energy saving effect and technical economy of the system is analyzed,and compared with the traditional low pressure economizer.The results show that,Using the primary air waste utilization system can avoid mixing cold air to the coal pulverizing system,and the system can make flue gas temperature drop with more heat be exchanged by the preheater.Due to the high temperature,it can supplant more advanced extracted steam from turbine even before the reheater.The system can save 2.3 g/(kW·h)power supply standard coal consumption rate and it can save 7593 t standard coal every year which is 2.47 times as much as conventional waste heat utilization system.This paper also analyzed the fuel characteristics of the system and the primary air waste utilization system with the air preheat capacity increased.The results show that,the system is suitable for the unit that burns low moisture coal especially low moisture bitumite,but doesn't apply to the unit that burns high moisture lignite.By increasing the heat exchange area of the air preheater,more flue gas waste heat will be recycled to the hot air and the heat regenerative system.As the flue gas temperature decreases,it is necessary to consume more air preheater metal heat transfer area.When the flue gas temperature is 90?,the system achieves the optimum economic efficiency,however,the air preheater is too large now.For the new power plant,it can be considered in the design of the primary air waste heat utilization system.It is feasible for the existing power plant to be reworked and the air preheater is expanded by 20%.Reduce the flue gas temperature from 143.2 ?to 120 ?,the arrangement of the primary-condensate/water heat exchanger is optimized.In this paper,five kinds of arrangement are presented,and they are compared and analyzed.The results show that,the energy saving effect and economy are optimal when the primary-condensate/feed water heat exchanger is arranged in parallel with the 2# high pressure heater and the heat exchanger water inflow is 50 kg/s.At this time,the system can save 3.7 g/(kW·h)of power supply standard coal consumption rate?...