Numerical Analyses Of The Effect Of Arch On Combustion Characteristics Of Coal-fired Travelling Grate Boiler

In recent years, most of the coal-fired travelling grate boilers in China have already been the high energy-consumption facilities that our country intends to bring under control,because they are operated under low efficiency situation and release a great deal of pollutants. The boiler parameters such as structure and combustion are related to coal types. The different property coal causes some problems such as ignition and burnout. The problems cause low efficiency and serious emissions of pollutant of boilers. So research of arches and air distribution modes plays an important part in increasing the efficiency of coal-fired travelling grate boilers.First, in the dissertation, the burn characteristic of the coal and the process of combustion in the travelling grate stoker has been studied. A series of mathematic model such as flowing, transferring heat and burning process of SZL15-1.25-Aâ…¡double-drum steam boiler has been given. The dissertation carefully introduced the principle and formula of the turbulent flow model, radiation model, and standard wall function method and gas-phase combustion model. According to FLUENT and UDF, CFD software, the temperature, pressure and mole fraction of species without gas-phase combustion in the boiler are analyzed and simulated. The burn characteristic of the coal in the travelling grate stoker is better displayed. Based on the analyses, the rationality of the physical and mathematic model and the numerical method in this dissertation is validated. The calculation results indicate agreement with the fact and the studies both here and abroad.Second, the condition in common rear arch, herringbone rear arch, different rear arch heights, different rear arch lengths, different front arch heights, different front arch lengths and different air distribution mode are numerical simulated. The temperature, pressure, velocity and mole fraction of species in the boiler furnace and stokehole are analyzed and simulated. The results of the simulation indicate that:By comparing common rear arch and herringbone rear arch, the latter can accelerate the ignition and the burnout, conducive to the burning of combustible gas, reduce q2 and lower the temperature at the furnace exit. The rear arch has an important influence on the combustion. Compared with rear arch, the front arch has less influence on the combustion. The longer rear arch can accelerate the ignition and the burnout, reduce q2 and lower the temperature at the furnace exit. However, the issues that increasing the pressure of arch area needs to be attended. Compared with rear arch length, the rear arch height has less influence on the combustion. Compared with rear arch, the front arch has less influence on the combustion. The lower front arch will affect the rate of ignition, the burning of combustible gas and the temperature at the furnace exit. Compared with front arch height, the front arch length has less influence on the combustion. So the front arch can be slightly shorter. The arch can achieve a good effect with air distribution mode. They complement each other and promote each other.The study of this dissertation, offer an assistant means of boilers' design, they also provide a significant reference basis of boilers'reform.