PAPERS SELECTED FOR THE SYMPOSIUM

• MODELING OF RADIATIVE HEAT TRANSFER INSIDE THE PULVERIZED COAL FIRED FURNACE OF POWER PLANT

  Nenad Crnomarkovic - VINCA Institute of Nuclear Sciences, Miroslav Sijercic - VINCA Institute of Nuclear Sciences, Srdjan Belosevic - VINCA Institute of Nuclear Sciences

  Abstract Text

  Thermal radiation is dominant mode of heat transfer from hot combustion products to furnace walls and colder parts of furnace medium, inside the pulverized coal fired steam boiler furnaces. Therefore, accurate modeling of radiative heat transfer is very important for... show full text »
  Abstract Text

  Thermal radiation is dominant mode of heat transfer from hot combustion products to furnace walls and colder parts of furnace medium, inside the pulverized coal fired steam boiler furnaces. Therefore, accurate modeling of radiative heat transfer is very important for prediction of steam boiler behavior in various operating conditions. A number of methods for radiative heat transfer has been developed, among which the most important are: Monte Carlo, finite volume method (FVM), discrete ordinate method (SN), spherical harmonics method (PN), six flux method, and Hottel’s zonal method. In this work, Hottel’s zonal method has been applied, because it is characterized by the great accuracy of evaluation of absorbed radiative fluxes. Hottel’s zonal method is based on division of furnace volume and walls to volume and surface zones. For each pair of zones, direct exchange areas and total exchange areas that allow for multiple reflection of radiation from furnace wall are evaluated. Absorbed heat of one zone (volume or surface) is determined as sum of heat exchange of that zone with all the zones in the furnace. Heat exchange among zones depends on radiative properties of medium that emits, absorbs and scatter radiation. Furnace medium is two phase mixture, that contains products of complete coal combustion and particles of coal, char, fly ash and soot. Since coal particles exist only in the vicinity of burners, and char particles exist in the zone of intensive combustion, which is not extensive, furnace medium can be considered to consist of gaseous combustion products and particles of fly ash and soot. The most important radiative properties are absorption coefficient, scattering coefficient and scattering phase function. Absorption coefficient of furnace gases is determined from single gray gas model. Spectral absorption coefficient of the cloud of fly ash particles is determined from the value of efficiency factor for absorption evaluated by the Mie theory, and from particle size distribution. Total absorption coefficient of the cloud of fly ash particles is determined as Planck mean value. Absorption coefficient of the cloud of soot particles is found from assumed soot volume fraction. Particle size distribution of fly ash is obtained from particle size distribution of pulverized coal under assumption that that particle of coal turns into particle of fly ash after process of complete combustion. Scattering phase function is unity, because uniform scattering of radiation at every direction is adopted. Adopted model of radiative heat transfer has been applied for modeling the processes in the furnace of TENT A2 steam boiler rated at 240 MWe. Two phase flow has been modeled with exchange of momentum mass and heat among phases, with chemical reactions and radiative heat exchange. Temperature field, as well as flow field and concentration fields have been obtained from transport equations for momentum, heat and mass. Set of equations has been closed by the transport equations for kinetic turbulent energy and its decay. Results of modeling showed acceptable agreement with results of measurement and enabled determination of absorbed radiative fluxes along the furnace walls. « hide
  Symposium Session: Thermal, hydro, wind and other Power Plants | Eksploatacioni problemi termo, hidro, vetro i drugih elektrana