This paper presents numerical simulation of the flow and combustion process in the furnace of a pulverized coal fired utility boiler of 350 MWe with 24 swirl burners installed at the furnace front wall. Five different cases with 100, 95, 85, 70 and 50% boiler full load are simulated. The comparison between the simulation and the plant data is stressed in this study. The heat flux to furnace walls between the measured values and the calculation results is compared. It is found that increasing the load leads to consistent variations in the properties presented and the exception is observed for the full load case where the predicted exit gas temperature is lower than the 95% one and the total heat to the boiler walls is smaller. This might be due to the fact of considering a linear scaling of the input parameters between the 70% and 100% load. The increase of the air flow rate led as expected to a reduction of the furnace outlet temperature and to a small decrease in NOx emissions. It shows that the NOx model used shows a higher sensitivity to temperature than to oxygen level in the furnace. The model used considered the De Soete mechanism for the nitrogen from volatiles and the contribution of char was considered in a similar way. The agreement for all cases except the one of 50% boiler load between the calculation results with the plant data validates the models and algorithm employed in the computation. The furnace performance under different boiler loads is predicted and compared in order to meet the requirements of NOx abatement and avoiding some negative side effects on the furnace. q2000 Elsevier Science Ltd. All rights reserved.

The mechanism of detailed chemical reactions in combustion is very complicated, especially when the formation of a pollutant such as NOx is considered. Based on regression analysis, a simplified fuel-NOx model is developed for premixed flame. The new model iS available for a wider range of temeperature and fuel-air ratios compared with De Soete's (1975) fuel NO model. The reduction CHi species on NO iS considered so that the model can be used in both fuel-lean and fuel-rich combustion systems. After a great simulation of a one-dimensional premixed flame system using Miller and Bowman'S (1989, Prog. Energy Combust. Sci., 15, 287) detailed elementary reaction model, the calculation of all the reaction rates is presented based on regression analysis.Copyright

The mechanism of detailed chemical reactions in combustion is very complicated, especially when the formation of pollutant such as NOx is considered. Based on Glarborg's and Bilger's full model (Glarborg P. et al., Combustion and Flame, 65, 177; (1986), Bilger R. W., Starner S.H., Kee, R.J., Combustion and Flame, 80, 135 (1990)), a simplified model of the mechanism of NOx formation in a CH4/Air system is presented. Sensitivity calculation and eigenvalue-eigenvector analysis fprincipal component analysis (Vajda S., Valko P., Turanyi T., Int. J. Chemicaf Kinetics, 17: 55 (1985)) are used in the model. Compared with the conventional methods of simplification of chemical reaction mechanisms such as quasi. steady-state approximation, the eigenvalue-eigenvector analysis can indicate the important reactions efficiently without providing any balance hypothesis. The new model consists of only 15 elementary reactions, which is simpler than the full model composing 39 reactions. The deviations in NOx concentration and other major species between the simplified and the full model are rather small over a wide range of fuel-air ratio．Meanwhile, the calculated NOx concentrations by the simplified model are in quite good agreement with Bartok's experimental data (Bartok W. et al., AICHE Symp. Ser. 126 (1972)), especially in the fuel-lean region.

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