Influence of Application of Hottels Zonal Model and Six-Flux Model of Thermal Radiation on Numerical Simulations Results of Pulverized Coal Fired Furnace

Difference of results of numerical simulation of pulverized coal fired furnace when mathematical models contain various radiation models has been described in the paper. Two sets of numerical simulations of pulverized coal fired furnace of 210 MWe power boiler have been performed. One numerical simulation has contained Hottels zonal model, whereas the other numerical simulation has contained six-flux model. Other details of numerical simulations have been identical. The influence of radiation models has been examined through comparison of selected variables (gas-phase temperature, oxygen concentration, and absorbed radiative heat rate of surface zones of rear and right furnace walls), selected global parameters of furnace operation (total absorbed heat rate by all furnace walls and furnace exit gas-phase temperature). Computation time has been compared as well. Spatially distributed variables have been compared through maximal local differences and mean differences. Maximal local difference of gas-phase temperature has been 8.44%. Maximal local difference of absorbed radiative heat rate of the surface zones has been almost 80.0%. Difference of global parameters of furnace operation has been expressed in percents of value obtained by mathematical model containing Hottels zonal model and has not been bigger than 7.0%. Computation time for calculation of 1000 iterations has been approximately the same. Comparison with other radiation models is necessary for assessment of differences

A computer code for the prediction of mill gases and hot air distribution between burners sections at the utility boiler

One of the main tasks during the design or simulation and analyses of the utility steam boiler operation is the prediction of a distribution of mill gases and hot air flow rates between burners sections. These are the boundary conditions for the combustion process in the boiler furnace, and they strongly influence the steam boiler economy and reliability of operation. A computer code for the prediction of mill gases and hot air distribution between boiler burners has been developed. The code is based on simultaneous calculations of material and heat balances for the fail mill and corresponding air tracts. This paper presents a methodology of performed calculations, the code structure, and results obtained for the steam boiler furnace of 350 MWe thermal power plant equipped with eight fall mills. (C) 2008 Elsevier Ltd. All rights reserved

Reconstruction of the aero-mixture channels of the pulverized coal plant of the 100MW power plant unit

After the last revitalization of thermal power block of 100 MW in TPP “Kostolac A”, made in the year 2004, during the operation of the plant, pulverized coal deposition often occurred in horizontal sections of the aero-mixture channels. Deposition phenomenon manifested itself in places ahead of spherical compensators in the direction of flow of pulverized coal to the burners, due to unfavorable configuration of these channels. Coal dust deposited in the channels dried and spontaneously combusted, causing numerous damage to channels and its isolation as well as the frequent stoppage of the operation for necessary interventions. The paper presents the original solution of reconstruction of aero-mixture channels which prevented deposition of coal dust and its eventual ignition. In this way the reliability of the mill plant is maximized and higher availability of boiler and block as a whole is achieved

Possibilities for reconstruction of existing steam boilers for the purpose of using exhaust gases from 14 MW or 17 MW gas turbine

Within the energy system in Methanol vinegar complex (MVC) in Kikinda, beside process boiler and auxiliary equipment, there are three equal steam boilers made by Minel Kotlogradnja, provided for combustion of natural gas, fuel oil and process gases. Aiming to increase the MVC Kikinda energy plant capacity, one gas turbine of 14 MW or 17 MW is going to be installed. In regard to relatively high gas temperature and a large amount of the unused oxygen from the air in the exhaust gas, it is specified to split exhaust gas into the two equal streams and import them into the two existing steam boilers, each having production of 16.67 kg/s (60 t/h). In order to use the exhaust gas heat, as well as oxygen contained within, it is necessary to replace the existing burners and to reconstruct the heat exchangers in the steam boiler vertical convective pass. Besides, it is necessary to verify if the existing flue gases fan can comply with the new operating regime, during which a half of the turbine exhaust gas is imported into the steam boiler. (c) 2013 Elsevier Ltd. All rights reserved

Numerical prediction of processes for clean and efficient combustion of pulverized coal in power plants

Coal-fired power plant technologies should provide higher efficiency of energy conversion, reduction of pollutants emission, operation of facilities in a wide range of loads and efficient utilization of variable quality fuels. In order to achieve these tasks, mathematical modeling is regularly used worldwide for optimization of boiler operation. Reduction of pollutants emission is the task of greatest concerns. Among the most important pollutants are oxides of nitrogen and sulfur. Combustion process modifications for NOx control and sorbent injection for SO2 control are cost-effective clean coal technologies, used either standalone or with other methods. An in-house developed computer code was applied for simulation of processes in the 350 MWe boiler furnace, tangentially fired by pulverized lignite. Predictions suggested optimal combustion organization providing the NOx emission reduction of up to 20 -30%, with the flame position improvement. Boiler thermal calculations showed that the facility was to be controlled within narrow limits of working parameters. SO2 reduction by injection of Ca-based sorbent particles into the furnace was simulated for different operation parameters. Such a complex approach enables effective evaluation of alternative solutions, considering emissions, flame position and efficiency of furnace processes and the boiler unit. (C) 2013 Elsevier Ltd. All rights reserved.6th International Conference on Clean Coal Technologies (CCT), May 12-16, 2013, Thessaloniki, Greec

Radiative heat exchange inside the pulverized lignite fired furnace for the gray radiative properties with thermal equilibrium between phases

The objective of the research was to find if an agreement of the results of a numerical investigation with experimental data could be achieved considering the two-phase medium in thermal equilibrium. Influence of the gray radiative properties on the radiative heat exchange inside pulverized lignite fired furnaces was investigated using the computational fluid dynamics (CFD) code based on a comprehensive mathematical model of the process. Radiative heat exchange was calculated using Hottels zonal model. Heat transfer rates and wall fluxes increased for small values of the total extinction coefficient, K-t LT 0.2 m(-1); decreased for large values of K-t, K-t GT 2.0 m(-1); and were maximal for moderate values of K-t, 0.2 LT K-t LT 2.0 m(-1). Heat transfer rates and wall fluxes decreased with the increase of the scattering albedo, though the decrease was considerable only for omega GT 0.5. Agreement with the experimental data was obtained for the moderate values of the K-t and for scattering albedo 0.1 LT omega LT 0.5. (C) 2014 Elsevier Masson SAS. All rights reserved

Numerical investigation of processes in the lignite-fired furnace when simple gray gas and weighted sum of gray gases models are used

Comparison of the numerical investigation results was carried out when the simple gray gas (SGG) and weighted sum of gray gases (WSGG) models are used to model the radiative properties of the gas phase inside the lignite fired furnaces. Comprehensive mathematical model of the tangentially fired furnace by pulverized lignite was made. Gas radiative properties were modeled by the SGG and WSGG models. Radiative heat transfer was modeled by the zonal model. Gas-phase variables and absorbed wall fluxes were compared on the basis of the relative differences that were determined for all control volumes and surface zones. Average relative differences of the gas-phase temperatures were about 1.0%. Average relative differences of the absorbed wall fluxes were from 2.0% to 5.0%. Absorbed wall fluxes determined by the SGG model were bigger than those determined by the WSGG model. Differences of the heat transfer rates of the absorbed radiation through the furnace walls were expressed in percents of heat transfer rates determined by the SGG model and were similar to the average relative differences of absorbed wall fluxes. Results justify application of the SGG model in comprehensive mathematical models of lignite-fired furnaces. (C) 2012 Elsevier Ltd. All rights reserved

Influence of forward scattering on prediction of temperature and radiation fields inside the pulverized coal furnace

A possibility of simplification of the scattering phase function of a pulverized coal flame was analyzed in the paper. It was showed that the type of radiation scattering of a pulverized coal flame is between two limiting cases: isotropic and forward scattering. A comprehensive mathematical model of a tangentially fired furnace by pulverized coal was formed. Radiative heat transfer was modeled using the six-flux model. Grid independent results of the numerical simulations were obtained. The mathematical model was verified by comparison of the results of numerical simulations with results of measurements. The influence of the type of radiation scattering on results of numerical simulation was analyzed through the relative and average differences of the gas-phase temperatures, the total radiation fluxes, and the absorbed wall fluxes of the left furnace wall. The investigation showed that the total radiation fluxes were considerably influenced by the type of radiation scattering. On the other hand, the gas-phase temperatures and the absorbed wall fluxes were much less influenced by the type of radiation scattering. The results justify the use of the scattering phase function corresponding to isotropic scattering in radiation models of comprehensive mathematical models of pulverized coal fired furnaces. (C) 2012 Elsevier Ltd. All rights reserved

Influence of application of Hottel’s zonal model and six-flux model of thermal radiation on numerical simulations results of pulverized coal fired furnace

Difference of results of numerical simulation of pulverized coal fired furnace when mathematical models contain various radiation models has been described in paper. Two sets of numerical simulations of pulverized coal fired furnace of 210 MWe power boiler have been performed. One numerical simulation has contained Hottel’s zonal model, whereas the other numerical simulation has contained six-flux model. Other details of numerical simulations have been identical. The influence of radiation models has been examined through comparison of selected variables (gas-phase temperature, oxygen concentration, and absorbed radiative heat rate of surface zones of rear and right furnace walls), selected global parameters of furnace operation (total absorbed heat rate by all furnace walls and furnace exit gas-phase temperature). Computation time has been compared as well. Spatially distributed variables have been compared through maximal local differences and mean differences. Maximal local difference of gas-phase temperature has been 8.44%. Maximal local difference of absorbed radiative heat rate of the surface zones has been almost 80.0%. Difference of global parameters of furnace operation has been expressed in percents of value obtained by mathematical model containing Hottel’s zonal model and has not been bigger than 7.0%. Computation time for calculation of 1000 iterations has been approximately the same. Comparison with other radiation models is necessary for assessment of differences

Numerical Analysis of NOx Control by Combustion Modifications in Pulverized Coal Utility Boiler

Considerable research efforts focus on modeling NOx formation/destruction and predicting NOx emission so that it can be controlled. A motivation for this numerical study was to examine the efficiency of combustion modifications in the furnaces of Kostolac B 350 MWe boiler units, tangentially fired by pulverized lignite. Numerical analysis was done by an in-house developed NOx submodel, coupled with differential comprehensive combustion model, previously developed and validated. The NOx submodel focuses on homogeneous reactions of both the fuel and the thermal NO formation/destruction processes. The submodel was validated by comparison of predicted NOx emissions with available measurements at the boiler units. Selected predictions of the emission, the furnace exit gas temperature, NO concentration, gas temperature, and velocity field are given for the case-study furnace under different operating conditions. The individual or combined effects of coal and preheated air distribution over the individual burners and the burner tiers, the grinding fineness and quality of coal, and the cold air ingress were investigated. Reduced emissions of up to 20-30% can be achieved only by proper organization of the combustion process. Obtained results were verified by the boiler thermal calculations. An optimal range of the furnace exit gas temperatures was proposed, with respect to the safe operation of the steam superheater. Simulations by means of a computer code developed for the purpose, showed that the air staging using overfire air ports might provide the NOx emission reduction of up to 24% in the test-cases with relatively high emission and up to 7% of additional reduction in already optimized cases.Sino-Australian Symposium on Advanced Coal and Biomass Utilisation Technologies, Dec 09-11, 2011, Wuhan, Peoples R Chin