| This paper is based on the influence of Slagging and fouling on wall temperature of high temperature surface.The calculation formula of wall temperature about convection and semi-radiation with or without slagging and fouling is derived The heat flux and convection heat transfer coefficient in tube are the most important factors.Flue gas temperature will mostly affect heat flux and radiation will have a stronger influence on heat flux than convection.Also,the order of magnitude of heat flux in high temperature flue gas zone is bigger than that in the low temperature flue gas zone.The steam velocity will affect convection heat transfer coefficient in tube.The larger tube heat transfer coefficient and lower heat flux cause wall temperature close to medium temperature.60KW experimental system was setup to simulate the real boiler running state.Also,the temperature of flue gas containing the dust is measured accurately.The distribution of wall temperature along the axial direction is analyzed.The curve of wall temperature and heat flux density presents a single hump in the state of non-contamination and double humps for contamination,whose distribution curves of non-uniform coefficient of heat flux density is different.According to the wall temperature iteration calculation model and calculation program,the inter-relationship of heat flux 、 the thickness of the contaminated slagging layer and its surface wall temperature and wall temperature of tube under the different condition of slagging and fouling state is analyzed in the 700℃ ultra super-critical boiler.At the same time,the influence of the limited service temperature of material on the high-temperature heating surface is analyzed.Combined with thermal calculation of 660 MW unit,the wall temperature of reheater about changing its position is calculated and checked,which shows that the radiative heat transfer generated by high-temperature has an lager influence on wall temperature of high-temperature heating surface. |
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