Experimental Study On Boiling Heat Transfer In Clustered Phase-changing Heat Exchanger

Industrial furnace are the important equipment of energy conversion which is widely used in many kinds of industrial application. The heat has been taken away by flue gas that accounts for 80% of the total heat loss to 90%.So the flue gas is the main reason of heat loss. The recycling problem of waste heat of low-temperature flue gas has been the focus of energy conservation and emissions reduction work. Exhaust temperature and low-temperature corrosion, because of their contradiction and constraint to each other, have become the main problems in the recovery system of low-temperature flue gas waste heat. In order to solve this problem,this paper adopts the technology of clustered phase-changing heat exchanger.Clustered phase-changing heat exchanger is a device of transferring heats by using the latent heat of vaporization phase change substance in the parallel airtight tube bundle components. The water in the evaporation section absorbs heat and becomes saturation steam, and the steam rises to the condensation section under certain differential pressure and condenses into liquid with putting out heat. The saturation water turns back to evaporation section by gas-liquid separator, and evaporates again. Such as cycle, heat transfer from one section to the other.This paper mainly studies the heat transfer performance of "evaporation section" which is the core of the Clustered phase-changing heat exchanger. The low-temperature flue gas of the experimental system is produced by gas turbine, and the waste heat of low-temperature flue gas is recycled by Clustered phase-changing heat exchanger system. Under the condition of one bar pressure, the working medium evaporation temperature is about 100℃and tube wall temperature is about 105℃, Because of the tube wall temperature changes along with the change of working condition and the wall temperature is the acid dew point above, so there is no low temperature corrosion happened in this system. Experiment shows that when the range of super-heat is 4~10 ℃, boiling heat transfer coefficient increases with the increase of heat flux. So the experiment fits out a formula of tube flow boiling heat transfer coefficient is h=0.39×q0.89×p0.15(15000<q<35000). At the same experimental condition,Compared with the experiment of single-phase convection heat transfer in tube, the total heat transfer coefficient increases 10%~20%.After the waste heat recovery unit is applied at a cigarette factory in Yunnan, the exhaust temperature reduced from 170℃ to 140℃,the plant can recycle heat of 1075 MJ and reduce the steam consumption of 15 t each year,and save Standard coal of 222 t,which amounts to ￥362000. The payback period is 22 months. At the same time, the 499.7t CO2 emission and 26.6t SO2 emissions were reduced every year. As can be seen, the application of Clustered phase-changing heat exchanger in waste heat recovery system is worthy of promoting energy-saving measure, and more economic benefits and environmental benefits can be produced by the application. The effective measures are both the response of the national energy policy and reduce the emissions of pollutants.