The Experiment Research And Analysis Of Flue Gas Condensation Heat Transfer In Gas-fired Boilers

With the development of our country’s economy, China’s total energy consumption is growing quickly. But as we take coal as our country’s primary energy, the energy consumption structure of our country is unreasonable.Coal combustion produces contains a large number of pollutants, causing serious environment pollution. Compared with coal, natural gas is much more cleaning. There are less air pollutants and more water vapor in its flue. At present our country is trying to optimize the energy structure. As a kind of clean energy, natural gas is used more and more widely.This essay is about theoretical and experimental researches of gas-fired boiler flue condensation heat transfer. First this paper analyzes flue compositions, calculates latent and sensible heat contented in the flue gas. Analysis shows that the water vapor content in flue gas is changed from17.41% to 21.33%. The water vapor content is so huge that if we can recycle the latent heat of flue gas, the boiler efficiency will increase a lot. Also we analyze the way how flue gas dew point temperature changing with different excess air coefficient. It shows that the dew point temperature decreases with increasing of excess air coefficient. The dew point temperature also be affected by environmental temperature and air humidity ratio. In Chongqing area, air humidity ratio is high, so that air humidity ratio is the main reason for point temperature variation. Analysis shows that the mutative extent of dew point temperature can be 5℃.In addition this paper also calculates recovery quantity of residual heat when go through a heat exchanger, which the excess air coefficient is 1.2 and the inlet temperature is 150℃.Second, we also do some experiments to analyze influence factors of flue gas condensation heat transfer, mainly about excess air coefficient, inlet flue gas temperature, inlet temperature of cooling water and flue gas velocity. In the experiment, we use 30 k W gas turbine to generate flue gas and simulate gas boiler flue gas by adding water vapor and air to the gas turbine flue. The experiment show that the smaller excess air coefficient is, the more conducive to the latent heat of flue gas heat. And with inlet flue gas temperature increase, Flue gas side heat transfer coefficient will increase too, but latent heat transfer coefficient will decrease. So we can conclude that high inlet flue gas temperature is not good for flue gas latent heat recycling. Cooling water inlet temperature increasing leads to the increase of heat exchanger wall temperature, it is bad for condensation heat transfer. With the increase of flue gas velocity, both latent heat transfer coefficient and overall heat transfer coefficient will increase, but when the velocity reach a certain degree, the speed of latent heat transfer coefficient increasing will become slowly.Finally, by using dimensionless temperature Ln and experimental data, we can get a flue gas side convection-condensing heat transfer formula:8203.03/17167.0u =491.0Pr R2 e Ln N(6000<Re<15000, 0.6<Pr<0.8).