Method for recycling water and heat in flue gas discharged by coal-fired power plant and system thereof

Abstract

The invention discloses a method for recycling water and heat in flue gas discharged by a coal-fired power plant and a system thereof. The method is realized by two systems, namely a hollow fiber membrane water vapor trapping system and a heat pump system. The hollow fiber membrane water vapor trapping system comprises a membrane assembly, a condenser A, a vacuum pump, a condensate water pump andwater purification equipment; the heat pump system comprises an evaporator, a compressor, a condenser B and an expansion valve connected end to end by a heat exchange circulating pipeline A so as to form a circulation loop, and provides a cold source for the hollow fiber membrane water vapor trapping system by condensing the trapped water vapor into water so as to realize water recovery; the hollow fiber membrane water vapor trapping system provides a heat source for the heat pump system for heating boiler circulating water so as to realize heat recovery. According to the method disclosed by the invention, 20-40% of water and heat in the flue gas discharged by the coal-fired power plant can be recycled, and the aims of saving water and energy can be achieved; meanwhile, the parameters of the flue gas discharged by the power plant are improved, and the white smoke phenomenon and gypsum rain problem can be avoided.

Description

technical field [0001] The invention relates to the technical field of water and heat recovery and utilization, in particular to a method and system for water and heat recovery and utilization of flue gas discharged from a coal-fired power plant. Background technique [0002] For coal-fired power plants, due to the installation of wet desulfurization towers, the exhaust gas contains a large amount of saturated water vapor. For a 600MW coal-fired unit, the amount of flue gas discharged at about 50°C per hour is about 200×10 4 N m 3 / h, the saturated water vapor content in the flue gas is about 200t / h, and the latent heat carried by the water vapor is about 1.24×10 8 kcal / h, if the coal-fired unit operates for an average of 5,500 hours per year, the annual discharge of water is about 1.1 million tons, and the annual discharge of heat is equivalent to burning 97,000 tons of standard coal. [0003] Due to the low temperature of flue gas discharged from coal-fired power plants...

AI Technical Summary

Problems solved by technology

[0003] Due to the low temperature of flue gas discharged from coal-fired power plants, it is difficult to recover moisture and heat. At present, some research institutions at home and abroad have used hollow fiber membranes and ceramic membranes to conduct research on the recovery of moisture and heat in flue gas, such as Nanjing University of Technology has studied "a ceramic membrane condensation treatment and recovery method for flue gas waste heat and water in power plants" ZL201310685026.X, North China Electric Power University has studied "a device and method for capturing water vapor in flue gas based on hollow fiber membranes" "ZL201310410548.9, but there are still some problems in the existing research results of these two technologies, and they cannot be commercialized in power plants

Among them, the ceramic membrane recovery technology flows flue gas and cooling water in opposite directions on both sides of the ceramic membrane. Although water can be recovered, it is difficult to realize waste heat utilization due to the limited temperature rise of the cooling water, and the lift of the flue gas is insufficient due to the decrease in temperature. It has a bad impact on the environment around the chimney; the hollow fiber membrane water vapor capture and recovery technology first separates water vapor and then condenses and recovers it. Although it does not reduce the exhaust gas temperature of the power plant, there are fatal flaws in the condensing system whether it is air-cooled or water-cooled. , where the air-cooling method is greatly affected by the ambient temperature and consumes a lot of energy, while the water-cooling method requires a large amount of cooling water and is difficult to realize heat utilization

In the face of the abundant water and heat resources in the flue gas emitted by coal-fired power plants, although the existing flue gas moisture and heat recovery and utilization technologies have achieved good results in the laboratory, some key problems still need to be solved before commercial application

Images