Effects of Flue Gas Internal Recirculation on NOx and SOx Emissions in a Co-Firing Boiler

Jun Li, Xiaolei Zhang, Weihong Yang, Wlodzimierz Blasiak

Division of Energy and Furnace Technology, KTH Royal Institute of Technology, Stockholm, Sweden.

DOI: 10.4236/ijcce.2013.22002                

Abstract

Volumetric combustion has been developed to realize a high substitution ratio of biomass in co-firing boilers, which features an intensive flue gas internal recirculation inside furnace. However, the characteristics of NOx and SOx emissions in large-scale boilers with volumetric combustion were not fully clear. In this paper, an Aspen Plus model of volumetric combustion system was built up based on a co-firing boiler. In order to characterize the reductions of NOx and SOx, three biomass substitution ratios were involved, namely, 100% biomass, 45% biomass with 55% coal, and 100% coal. The effects of flue gas recirculation ratio, air preheating temperature, oxygen concentration, and fuel types on pollutants emission in the volumetric combustion system were investigated. According to the results, it was concluded the higher substitution ratio of biomass in a co-firing boiler, the lower emissions of NOx and SOx. Moreover, flue gas internal recirculation is an effective pathway for NOx reduction and an increased recirculation ratio resulted in a significant decreasing of NOx emission; however, the SOx increased slightly. The influences of air preheating temperature and O₂ concentration on NOx emission were getting weak with increasing of recirculation ratio. When 10% or even higher of flue gas was recycled, it was observed that almost no NOx formed thermodynamically under all studied conditions. Finally, to reach a low emission level of NOx, less energy would be consumed during biomass combustion than coal combustion process for internal recirculation of flue gas.

Keywords

Flue Gas Internal Recirculation; Co-Firing; NOx; SOx

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	http://europa.eu/legislation_summaries/energy/european_energy_policy/l28012_en.htm
[2]	J. Werther, et al., “Combustion of Agricultural Residues,” Progress in Energy and Combustion Science, Vol. 26, No. 1, 2000, pp. 1-27. doi:10.1016/S0360-1285(99)00005-2
[3]	L. Zhang, C. Xu and P. Champagne, “Overview of Recent Advances in Thermo-Chemical Conversion of Biomass,” Energy Conversion and Management, Vol. 51, No. 5, 2010, pp. 969-982. doi:10.1016/j.enconman.2009.11.038
[4]	http://www.bipac.net/afpa/AFPACarbonNeutralityWhitePaper2_4_10.pdf
[5]	E. Biagini, F. Barontini and L. Tognotti, “Devolatilization of Biomass Fuels and Biomass Components Studied by TG/FTIR Technique,” Industrial & Engineering Chemistry Research, Vol. 45, No. 13, 2006, pp. 4486-4493. doi:10.1021/ie0514049
[6]	P. Basu, J. Butler and M. A. Leon, “Biomass Co-Firing Options on the Emission Reduction and Electricity Generation Costs in Coal-Fired Power Plants,” Renewable Energy, Vol. 36, No. 1, 2011, pp. 282-288. doi:10.1016/j.renene.2010.06.039
[7]	J. Li, et al., “Volumetric Combustion of Biomass for CO2 and NOx Reduction in Coal-Fired Boilers,” Fuel, Vol. 102, 2012, pp. 624-633. doi:10.1016/j.fuel.2012.06.083
[8]	H. Tsuji, A. K. Gupta, T. Hasegawa, M. Katsuki, K. Kishimoto and M. Morita, “High Temperature air Combustion: From Energy Conservation to Pollution Reduction,” CRC Press, Boca Raton, 2002. doi:10.1201/9781420041033
[9]	G. Cho, et al., “Effects of Internal Exhaust Gas Recirculation on Controlled Auto-Ignition in a Methane Engine Combustion,” Fuel, Vol. 88, No. 6, 2009, pp. 1042-1048. doi:10.1016/j.fuel.2008.10.042
[10]	S.-R. Wu, et al., “Combustion of Low-Calorific Waste Liquids in High Temperature Air,” Fuel, Vol. 90, No. 8, 2011, pp. 2639-2644. doi:10.1016/j.fuel.2011.04.001
[11]	V. K. Arghode and A. K. Gupta, “Development of High Intensity CDC Combustor for Gas Turbine Engines,” Applied Energy, Vol. 88, No. 3, 2011, pp. 963-973. doi:10.1016/j.apenergy.2010.07.038
[12]	J. A. Wünning and J. G. Wünning, “Flameless Oxidation to Reduce Thermal No-Formation,” Progress in Energy and Combustion Science, Vol. 23, No. 1, 1997, pp. 81-94. doi:10.1016/S0360-1285(97)00006-3
[13]	W. Blasiak, W. H. Yang and J. von Schéele, “Flameless Oxyfuel Combustion for Fuel Consumption and Nitrogen Oxides Emissions Reductions and Productivity Increase,” Journal of the Energy Institute, Vol. 80, No. 1, 2007, pp. 3-11. doi:10.1179/174602207X174379
[14]	F. Normann, et al., “High-Temperature Reduction of Nitrogen Oxides in Oxy-Fuel Combustion,” Fuel, Vol. 87, No. 17-18, 2008, pp. 3579-3585. doi:10.1016/j.fuel.2008.06.013
[15]	H. Zhang, et al., “Development of High Temperature air Combustion Technology in Pulverized Fossil Fuel Fired Boilers,” Proceedings of the Combustion Institute, Vol. 31, No. 2, 2007, pp. 2779-2785. doi:10.1016/j.proci.2006.07.135
[16]	N. Schaffel-Mancini, et al., “Novel Conceptual Design of a Supercritical Pulverized Coal Boiler Utilizing High Temperature Air Combustion (HTAC) Technology,” Energy, Vol. 35, No. 7, 2010, pp. 2752-2760. doi:10.1016/j.energy.2010.02.014
[17]	D. Popp, “Exploring Links between Innovation and Diffusion: Adoption of NOx Control Technologies at US Coal-Fired Power Plants,” Environmental and Resource Economics, Vol. 45, No. 3, 2010, pp. 319-352. doi:10.1007/s10640-009-9317-1
[18]	D. Popp, “International Innovation and Diffusion of Air Pollution Control Technologies: The Effects of NOX and SO2 Regulation in the US, Japan, and Germany,” Journal of Environmental Economics and Management, Vol. 51, 1, 2006, pp. 46-71. doi:10.1016/j.jeem.2005.04.006
[19]	L. Y. B. Higgins, H. Gadalla, J. Meier, T. Fareid, G. Liu, A. R. M. Milewicz, M. Ryding and W. Blasiak, “Biomass Co-Firing Retrofit with ROFA for NOx Reduction at Edf-Wroclaw Kogeneracjia,” 2009. www.nalcomobotec.com/files/Mobotec_Wroclaw_Biomass_Cofiring.pdf
[20]	S. Niksa and G. S. Liu, “Incorporating Detailed Reaction Mechanisms into Simulations of Coal-Nitrogen Conversion in p.f. Flames,” Fuel, Vol. 81, No. 18, 2002, pp. 2371- 2385. doi:10.1016/S0016-2361(02)00172-2
[21]	G. G. De Soete, “Overall Reaction Rates of NO and N2 Formation from Fuel Nitrogen,” Symposium (International) on Combustion, Vol. 15, No. 1, 1975, pp. 1093- 1102. doi:10.1016/S0082-0784(75)80374-2
[22]	H. Liu and B. M. Gibbs, “Modelling of NO and N2O Emissions from Biomass-Fired Circulating Fluidized Bed Combustors,” Fuel, Vol. 81, No. 3, 2002, pp. 271-280. doi:10.1016/S0016-2361(01)00170-3
[23]	F. Winter, et al., “The NO and N2O Formation Mechanism during Devolatilization and Char Combustion under Fluidized-Bed Conditions,” Symposium (International) on Combustion, Vol. 26, No. 2, 1996, pp. 3325-3334. doi:10.1016/S0082-0784(96)80180-9
[24]	M. A. Field, et al., “Combustion of Pulverized Coal,” Industrial & Engineering Chemistry, Vol. 61, No. 3, 1969, pp. 8-9.
[25]	P. B. Nielsen and O. L. Jepsen, “An Overview of the Formation of SOx and NOx in Various Pyroprocessing Systems,” IEEE Transactions on Industry Applications, Vol. 27, No. 3, 1991, pp. 431-439. doi:10.1109/28.81847
[26]	W. Doherty, A. Reynolds and D. Kennedy, “The Effect of Air Preheating in a Biomass CFB Gasifier Using ASPEN Plus Simulation,” Biomass and Bioenergy, Vol. 33, No. 9, 2009, pp. 1158-1167. doi:10.1016/j.biombioe.2009.05.004
[27]	J. Baltasar, et al., “Flue Gas Recirculation in a Gas-Fired Laboratory Furnace: Measurements and Modelling,” Fuel, Vol. 76, No. 10, 1997, pp. 919-929. doi:10.1016/S0016-2361(97)00093-8
[28]	ECN, “Clean Coal Technologies-Report,” in SENERES workshop, Warsaw, Poland, 2012.
[29]	L. Chen, S. Z. Yong and A. F. Ghoniem, “Oxy-Fuel Combustion of Pulverized Coal: Characterization, Fundamentals, Stabilization and CFD Modeling,” Progress in Energy and Combustion Science, Vol. 38, No. 2, 2012, pp. 156-214. doi:10.1016/j.pecs.2011.09.003
[30]	T. Mendiara and P. Glarborg, “Ammonia Chemistry in Oxy-Fuel Combustion of Methane,” Combustion and Flame, Vol. 156, No. 10, 2009, pp. 1937-1949. doi:10.1016/j.combustflame.2009.07.006
[31]	H. Stadler, et al., “Experimental Investigation of NOx Emissions in Oxycoal Combustion,” Fuel, Vol. 90, No. 4, 2011, pp. 1604-1611. doi:10.1016/j.fuel.2010.11.026
[32]	S. Munir, W. Nimmo and B. M. Gibbs, “The Effect of Air Staged, Co-Combustion of Pulverised Coal and Biomass Blends on NOx Emissions and Combustion Efficiency,” Fuel, Vol. 90, No. 1, 2011, pp. 126-135. doi:10.1016/j.fuel.2010.07.052