The Numerical Simulation On The Process Of Coal Bias Air-stage Combustion

The number of power plants in China is big. The pollutant NOx emission which comes from coal combustion in power plants is a major source of air pollutant NOx. By the environment protection have been paid more and more attention in the world, to develope the technology of clean coal-fired electric power is a big task and need much time to study. Researchers have been study the NOx reduction efficiency and mechanism of air-stage, LNE (Low NOx Emission) burners and fuel reburn combustion technology. Air-stage and LNE burners have been already used in boilers reconstruction and production. Coal bias (use LNE burner to form coal bias condition) and air-stage combustion are measures of reduced NOx in the coal combustion in furnace. They reduce the NOx emission and generation by to form an environment which is far from the stoichiometric ratio. Up to now, the study of NOx reduction measure which uses the two technologies is few.In this paper, air-staged, coal bias and combine the two technologies combustion process in a 400(?)/h tangentially fired boiler are simulated. The influence of coal rich/lean ratio on emission of NOx and soot is studied. And some optimized parameters obtained for production and design. The prime task and conclusion are as follows:(1) Gas turbulent flow model, combustion model, two-phase flow model and radiative heat transfer model are analysis and appropriate form of model parameters and mesh are selected. It provides good experience for numerical simulation of boiler combustion.(2) The furnace is as research object. The NOx, soot, heat loss and combustion efficiency of equal distribution combustion results are compared with them of pagoda type second-air distribution, pagoda down second-air distribution, shrinked-middle second-air distribution and waist drum type second-air distribution.Results show that styles of the shrinked-middle second-air distribution and equal second-air distribution are recommended when OFA closed and equal second-air distribution and pagoda down second-air distribution are recommended when OFA open.(3) Based on the condition of equal second-air distribution, the coal bias combustion and coal bias air-stage combustion are proposed to study the effection of coal rich/lean ratio on NOx and soot emission, while the combustion efficiency and heat loss were considered,too. Then, the influent of coal particle size to combustion NOx and soot are studied. The combustion combined coal bias with air-stage technology can reduce both NOx and soot formation. The small size partical contributed greatly to the formation of NOx, and large size partical coal contributed greatly to the formation of soot. The best coal rich/lean ratio is 5. Coal bias air-staged combustion technique which can reduce the emission of NOx and soot may be used to boiler reconstruction to optimize the combustion process.(4) The lower NOx emission reason of coal bias air-stage combustion preocess is analyzed. Air-stage, coal bias combustion rcspectively allocate the process of coal mixed with air reasonably in the direction of vertical and horizontal. The oxygen in main combustion area is reducd by air-stage technology, local fuel-rich oxygen-poor conditions are formed by coal rich/lean technology, which delay the time of coal burnout, and reduce the maximum temperature in furnace. Though, the coal bias air-stage combustion process inhibits the formation of NOx and soot.The innovations of this paper are follows:(1) Combine the coal bias and air-stage two low-NOx combustion technology, study the reason of NOx reduction and have obtained some optimized parameters which are can be used for engineering.(2) Considering the pollutants NOx and soot, combustion efficiency and heat utilization comprehensively in the different combustion conditions. We obtain the optimizied program and optimize parameters which can both reduce NOx and soot emission, and the combustion efficiency and thermal efficiency stay on a high level, at the same time.