Study On Heat Transfer Characteristics Of High Temperature Convective Heating Surface Of Pressurized Oxygen Enriched Coal Fired Boiler

The technology of the oxygen enrich-ed combustion is a very promising new power generation technology for cleaning coal.The use of pressurized oxygen enriched combustion technology can not only improve the efficiency of boiler,combustion efficiency and power generation efficiency, but also can reduce the concentration of NOx in the flue gas, and recovery the CO2 and SO2 without installing desulfurization and denitrification equipment.Today the ultra clean emissions and environmental requirements are increasingly high, the oxygen enriched combustion technology with its unique advantages has attracted people's attention.This paper takes a 300 MW coal-fired boiler for study, calculates the properties of flue gas of the pulverized coal combustion under the air and oxygen and pressurized oxygen enriched(CO2/O2=70:30,0.1MPa/1MPa) conditions by using ASPEN PLUS software, and then uses FLUENT software platform combined with radiation model DO to simulate high temperature re-heater and Super-heater in three different conditions, then analyzes the change regulation,then simulates high temperature re-heater and Super-heater at the different fuel gas velocity, and exchanges heat optimization simulation for heat exchanger structure using iterative method in the different flue gas conditions, gets optimization model under the different flue gas conditions,analysis the variation of the parameters of the heat exchanger,and finally, uses economic methods to set up the optimal model,and determines the best design structure and best gas velocity in principle of minimum total investment cost of heat exchanger in unit time.The results show that flue gas generated is low in the oxygen-rich atmosphere,flue gas enthalpy is small; when the flue cross-sectional area isn't changed, the gas Reynolds number remains the same in the pressurized oxygen-rich atmosphere, the radiation heat transfer coefficient and convection heat transfer coefficient increases;when the flue cross-sectional area is changed, the gas Reynolds number increases gradually with the increase of flue gas velocity, radiation heat transfer coefficient change is small, the convective heat transfer coefficient is increased, the total heat transfer coefficient is about three times under air atmosphere;with the increase of flue gas velocity, flue size and heat exchange area of heat exchanger after optimization were decreased, cutting down the initial investment of the construction,but the rise of pressure drop caused increase of the operating costs, and therefore the appropriate retrofit scheme is needed to ensure economic benefit; The outlet flue gas temperature is lower than air condition, resulting in heat absorption of tail heat exchanger is not enough;It is determined in principle of minimum total investment cost of heat exchanger in unit time that the optimum gas velocity of high temperature reheat is 1m/s,and the optimum gas velocity of high temperature superheat to 3m/s.