Numerical Simulation Of Slagging Process In PC Boiler And Optimization Of Combustion

The slagging problem in Power Plant operation strongly influences the operationsecurity and economy. How to efficiently reduce slagging degree is a mainconsideration in engineering. We used numerical simulation to study the slaggingprocess on waterwall near the swirl burner outlet, and also researched the effect ofratio distribution of each air in burner, their swirling number and coal character on theslagging process.To get accurate simulation results of coal combustion, we conducted anexperiment of cold flow field in swirl burner to validate the accuracy of turbulencemodel which will be used in the coal combustion to simulate the swirling flow. Weused PDA to measure the velocity information near the swirl burner model outlet andcompute the flow field using Realizable κ-ε model in computational domain havingthe same size with swirl burner model. The comparison between computationalresults and experimental data shows there is very good agreement near the burnermodel outlet. Realizable κ-ε model can precisely predict the strong swirl flowcharacteristics in this domain.We used PDF combustion model to research the effect of distribution of each airin burner, their swirling number and coal character on the combustion character, andthen generalize some optimal work conditions. The computation results indicate thatthere is a high temperature, high carbon concentration and high oxygen consumptionnear the joint between primary air outlet and secondary air outlet. Larger secondaryair swirling number will result in earlier coal combustion, larger maximum oftemperature, larger reflow velocity and earlier central recirculation. Increment of ratioof each air strengthens rigidity of air, which will cause central recirculation occurlater and reduce the degree of early coal combustion. There is an optimal value ofprimary air has for improve combustion. Coal with high carbon content will resultearlier and much intensive combustion. Coal particle with small mean diameter willmake easier and complete combustion, so temperature increase rapidly.Based on the temperature field from combustion simulation result, we usedsticking model to compute the number of particle sticking to the waterwall. Wedeveloped a method to count sticking particle number to study the slagging degree.The computation results indicates that maximal sticking particle numbers occur atuppermost waterwall, while sticking particle number at nether waterwall near swirlburner outlet is very small. Swirling number has significant impact on the number ofsticking particle. Sticking particle number increases rapidly with the increment ofouter secondary air and primary air swirling number respectively because it canstrengthen flow entrainment ability to carry more particle to waterwall. Innersecondary air has complicated influence on slagging. When inner secondary airswirling number is about middle intensive degree, sticking particle number reachesmaximum. If inner secondary air swirling number continues increasing, coal particlewill combust complete and reduce the particle concentration, thus decrease thesticking particle number. Ratio of each air has slight influence on the sticking particlenumber relative to swirling number. Coal with high ash content will result in largesticking particle number. Coal particle with small mean diameter combustscompletely, and it will reduce sticking particle number.