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Show prompt NO, and fuel NO. Since prompt NO contributes negligibly to the total NO formed, it has not been included in the present model. Thermal NO is generally described by Zeldovich or the modified Zeldovich mechanism. The reactions involved in the thermal NO formation are very slow compared to the major combustion mechanisms. Therefore, equilibrium values are used for the major chemical species and the rate of thermal NO formation is obtained as described in [9]. After the recommendation of Smoot and Smith [6], the following assumptions are employed: (1) Nitrogen is released at a rate equal to the mean rate of coal weight loss. (2) Fuel nitrogen evolved during char oxidation follows the same reaction sequence as nitrogen that evolves during devolatilization. (3) Fuel nitrogen that evolves during devolatilization and char oxidation is rapidly converted to HCN in the gas phase. Fuel NO model is based on the global reaction mechanism proposed by DeSoete [10] for decay of HeN. The global time-mean reaction rates for the formation of NO and N2 from HCN are obtained by convoluting the instantaneous rates with an appropriate probabili ty density function (PDF). A two-parameter Gaussian distribution is assumed for the shape of the PDF. The heterogeneous reaction of NO with char is employed as the same manner as [9]. 3. SOLUTION TECHNIQUE A control-volume based approach is employed to solve the equations governing the conservation of mass, momentum and other scalars such as enthalpy, species concentration etc. The coupling between the continuity and momentum equation is handled via the SIMPLER [1] algorism. The nominally linear discretization equations are solved by a line-by-line tridiagonal matrix algorithm (TDMA) [1]. To enhance the convergence, the TDMA is supplemented by blockcorrection procedure [7]. The particle trajectories are obtained by integrating the equations of motion [Eqn.(2)] for the particle in the gas-flow field. At various points along these trajectories, the particle-gas mass and energy transfer rates are computed. The particle source term required in the gas-flow equations are obtained by calculating the differences in mass, momentum and energy of the particles as they enter and leave each computational cell. 4. APPLICATION TO POWER STATION UTILITY BOILER The mathematical model is applied to the 1000 MW coal fired e utility boiler furnace. The configuration of the furnace is shown in Fig. 1. Its width, depth, and height are 31.1 m, 15.5 m, and 59.5 m, respectively. It employs the opposed firing system and is equipped with 70 burners (BNR) and 20 NO ports (NOP). Since the fourth stage burners of the front wall and the rear wall are placed in a staggered position, the whole furnace is chosen as a 6 |