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Show 4.0 Summary This exploratory study examined the impact of cofiring switch grass with coal on N O x emissions and unburned carbon in the pilot/laboratory scale pulverized fuel combustors. Model predictions were compared to measurements of unburned carbon, and C 0 2 and 0 2 concentration profiles made while cofiring biomass and coal in the Multifuel Combustor (MFC) at Sandia National Laboratories. There is relatively good agreement between the measurements and the model predictions. Interestingly, despite the larger biomass (switch grass) particle size relative to coal, blending biomass reduces the unburned carbon. W e attribute this phenomenon to the high volatile content of the switch grass. The model predicts this trend, however if the biomass particle size is too big to devolatilize inside the combustor or has a short residence time for the particle to go any significant char oxidation after the devolatilization then the trend may reverse. It is also predicted that the injection of 1 5 % of biomass (by weight) in the main heat release zone with an optimum fuel/air stoichiometry reduces N O x by 4 6 % when compared with the pulverized coal combustion. Also, the low turn around time to converge the solutions with the multiple species, and complicated devolatilization and char oxidation models makes the current C F D code an attractive option for the industrial scale boiler problems. 5.0 REFERENCES Baxter, L. L., and Mitchell, R. E. (1992). 'The Release of Iron During the Combustion of Illinois #6 Coal. Combustion and Flame," Vol. 88 pp. 1-14. Brewster, B.S., Smoot, L.D., and Barthelson, S.H., (1995), "Model Comparison with Drop Tube Combustion Data for Various Devolatilization Submodels," Energy and Fuels, Vol. 9, pp. 870-79 Field, M.A., (1969), "Rate of Combustion of Size-Graded Fractions of Char From a Low-Rank Coal Between 1200K and 2000K," Combustion and Flame, Vol. 13, pp.237-52 Fiveland, W.A., (1984), "Discrete-Ordinates Solutions of the Radiative Transport Equation for Rectangular Enclosures,'1 J. eat Transfer, Transactions of the A S M E , Vol. 106, pp. 699-06 F L U E N T USERS GUIDE, (1999), Fluent Incorporated, 10 Cavendish Court, Centerra Resource Park, Lebanon, N H 03766 Freeman, M.C., P.M. Goldberg, and S.I. Plasynski, (1998), "Biomass Cofiring R & D and Utility Experiences: What's Happened, What's Next," BioEnergy*98, Madison, Wisconsin, October 4-8, 1998. Freeman, M.C., Chitester, D.C., James, R.A., Ekmann, J.M., Walbert, G.A., (1999), "Results of Pilot-Scale Biomass Co-firing for P C Combustors Proceedings of the Advanced Coal-Based and Environmental Systems 97 Conference, DOE/FETC. Pittsburgh, Pennsylvania, July 22-24, 1997 Grow, D.T., (1990), "Mass and Heat Transfer to an Ellipsoidal Particle," Combustion and Flame, Vol. 80, pp.209-13 Jones, J.M., Patterson, P.M., Pourkasanian, M., Williams, A., Arenillas, A., Rubiera, F., and Pis, J.J., (1999), "Modeling N O x Formation in Coal Particle Combustion at High Temperature: An Investigation of the Devolatilization Kinetic Factors," Fuel, Vol. 78, pp. 1171-79 Kobayashi, H., Howard, J.B., and Sarofim, A.F., (1976), "Coal Devolatilization at High Temperatures," 16th Symposium (Int'l) on combustion, The Combustion Institute, Pittsburgh, pp.411-25 Mitchell, R.E., Hurt, B., Baxter, L.L., and Hardesty, D.R., (1992), "Compilation of Sandia Coal Char Combustion Data and Kinetic Analyses," Milestone Report, Office of Fossil Energy, Pittsburgh Energy Technology Center Morsi, S.A., and Alexander, A.J., (1972), "An Investigation of Particle Trajectories in Two-Phase Flow Systems," J. Fluid Mechanics, Vol. 55(2), pp. 193-208 Robinson, A.L., L.L. Baxter, G. Sclippa, H. Junker, K.E. Widell, D.C. Dayton, M . Freeman, G. Walbert, and P. Goldberg, (1997), "Fireside Considerations When Cofiring Biomass With Coal in P C Boilers," Engineering Foundation Conference on the Impact of Mineral Impurities in Solid Fuel Combustion, Kona, Hawaii, November 2- 7, 1997. Smoot, L.D., Hill, S.C., and Xu, H., (1998), "NOx Control Through Reburning," Progress in Energy Combustion Science, Vol. 24, pp. 385-408 Zamansky, V.M., P.M. Maly, V.V.Lissianski, and M.C. Freeman, (1998), "Development of Biomass Reburning Technologies," BioEnergy 98, Madison, Wisconsin, October 4-8, 1998. |