Biofuel are gaining increased public and scientific attention, driven by shortage of fossil fuels and greenhouse gas emissions. Biofuel have different physical and chemical characteristics in comparison with fuel oil used in general industrial applications. In order to maintain the same heating and emission characteristics, it is not recommended to burn biofuel directly in the industrial boilers or furnaces, but to burn them as a emulsion of biofuel and fuel oil instead. This research aims to examine the combustion characteristics and pollutant emissions of burning an emulsion of biofuel and fuel oils. This thesis was carried out with three main studies: (1) mixing stability between biofuel and diesel/heavy oil; (2) experimental study of single suspended droplet evaporation; (3) biofuel and heavy-oil emulsion co-firing tests in furnace. Based on these experimental studies, the feasibility of co-firing biofuel with fuel oils can be evaluated to conclude with some strategies for burning biofuel. The experiments results are as described below.
We found that the biofuel was difficult to be mixed with diesel. The emulsion maintained well-mixed no longer than 5 minutes even after adding surfactant. And for the emulsion of biofuel and heavy-oil it was difficult to determine the mixing stability, due to indistinguishable color between each other even though we observed via the optical microscope. In single suspended droplet experiment, the increasing of the heating temperature would accelerate the evaporation rate. In the case of pure biofuel and heavy oil, there were several additional phenomena not found in the experiments using pure diesel. Micro-explosion and random behavior occurred during the experiment. The increasing of temperature caused the random behavior and micro-explosion to occur frequently, due to large amount of water content and impurities in the biofuel. And also ignition occurs at 500 OC in the cases of biofuel/diesel oil emulsion and also biofuel C3/heavy oil at higher biofuel content in the emulsion.
The results of furnace tests indicated the 2.5% biofuel co-firing ran smoothly in the long-term test, with the similar temperature distribution and emission compared to pure heavy oil test. However, the 5% and 10% biofuel co-firing tests were extremely unstable under fuel-preheated condition. Each case of the experiment was tuned to meet the minimum excess oxygen requirement for complete consumption of fuel therefore CO emission level was kept near-zero. NO emission level decreased with biofuel addition, which can be attributed to large amount of water content lowering the combustion temperature. SO2 concentration in the flue gas was directly associated to sulfur content in the fuel we had supplied, which was coincided with the test results for the cases of 2.5% biofuel co-firing and burning pure heavy oil alone. In order to prevent unstable co-firing characteristics, it is suggested to use the separate burners for realistic commercial application of co-firing biofuel.

1. Fenger, J., "Air Pollution in the Last 50 Years – From Local to Global," Atmospheric Environment, Vol. 43(1), pp. 13-22, 2009.
2. Saidur, R., et al., "A Review on Biomass as a Fuel for Boilers," Renewable and Sustainable Energy Reviews, Vol. 15(5), pp. 2262-2289, 2011.
3. Arent, D.J., Wise A., and Gelman R., "The Status and Prospects of Renewable Energy for Combating Global Warming," Energy Economics, Vol. 33(4), pp. 584-593, 2011
4. Hoel, M. and Kverndokk S., "Depletion of Fossil Fuels and the Impacts of Global Warming," Resource and Energy Economics, Vol. 18, pp. 115-136, 1996.
5. Ramanathan, V. and Feng Y., "Air Pollution, Greenhouse Gases and Climate Change: Global and Regional Perspectives," Atmospheric Environment, Vol. 43(1), pp. 37-50, 2009.
6. Zevenhoven, R. and Beyene A., "The Relative Contribution of Waste Heat from Power Plants to Global Warming," Energy, Vol. 36(6), pp. 3754-3762, 2011.
7. Demirbas, A., "Combustion Characteristics of Different Biomass Fuels," Progress in Energy and Combustion Science, Vol. 30(2), pp. 219-230, 2004.
8. Demirbas, A., "Potential Applications of Renewable Energy Sources, Biomass Combustion Problems in Boiler Power Systems and Combustion Related Environmental Issues," Progress in Energy and Combustion Science, Vol. 31(2), pp. 171-192, 2005.
9. Tewfik, S.R., "Biomass Utilization Facilities and Biomass Processing Technologies," Energy Education Science and Technology, Vol. 14, pp. 1-19, 2004.
10. Demirbas, A., "Biomass Resources for Energy and Chemical Industry," Energy Education Science and Technology, Vol. 5, pp. 21-45, 2000.
11. Mark, J., "Wood Powder: an Upgraded Wood Fuel," Forest Products, Vol. 6, pp. 42-52, 1992.
12. Hughes, E., "Biomass Co-firing: Economics, Policy and Opportunities," Biomass Bioenergy, Vol. 19. pp. 457-465, 2000.
13. Demirbas, A., "Recent Advances in Biomass Conversion Technologies," Energy Edu. Sci. Technol., Vol. 6, pp. 19-41, 2000.
14. Sami, M., Annamalai, K. and Wooldridge, M., "Co-firing of Coal and Biomass Fuel Blends," Progress in Energy and Combustion Science, Vol. 27, pp. 171-214, 2001.
15. Demirbas, A., "Yields of Hydrogen-rich Gaseous Products Via Pyrolysis from Selected Biomass Samples," Fuel, Vol. 80, pp. 1885-1891, 2001.
16. Bridgwater, A.V., Meier, D., and Radlein, D., "An Overview of Fast Pyrolysis of biomass," Organic Geochemistry, Vol. 30, pp. 1479-1493, 1999.
17. Goyal, H.B., Seal, D., and Saxena, R.C., "Bio-fuels from Thermochemical Conversion of Renewable Resources: A review," Renewable and Sustainable Energy Reviews, Vol. 12(2), pp. 504-517, 2008.
18. Chiaramonti, D., Oasmaa, A., and Solantausta, Y., "Power Generation using Fast Pyrolysis Liquids from Biomass," Renewable and Sustainable Energy Reviews, Vol. 11(6), pp. 1056-1086, 2007.
19. Brammer, J.G., Lauer, M., and Bridgwater, A.V., "Opportunities for Biomass-derived “Bio-oil” in European Heat and Power Markets," Energy Policy, Vol. 34(17), pp. 2871-2880, 2006.
20. Asadullah, M., et al., "Jute Stick Pyrolysis for Bio-oil Production in Fluidized Bed Reactor," Bioresource Technology, Vol. 99(1), pp. 44-50, 2008.
21. Rizal, F.M., et al., "Vaporization Characteristics of a Single Drop of Diesel-Biofuel Mixtures," in Annual Conference on Liquid Atomization and Spray Systems, Taiwan, 2011.
22. Brown, T.R., Wright, M.M., and Brown, R.C., "Estimating Profitability of Two Biochar Production Scenarios: Slow Pyrolysis vs Fast Pyrolysis," Biofuels, Bioproducts and Biorefining, Vol. 5(1), pp. 54-68. 2011.
23. Erbil, H.Y., "Evaporation of Pure Liquid Sessile and Spherical Suspended Drops: a Review," Advances in Colloid and Interface Science, Vol. 170(1-2), pp. 67-86, 2012.
24. LAW, C.K., Combustion Physics, New York: Cambridge University Press, 2006.
25. Law, C.K., Chung, S.H., and Srinivasan, N., "Gas-phase Quasi-steadiness and Fuel Vapor Accumulation Effects in Droplet Burning," Combust. Flame, Vol. 38, pp. 173-198, 1980.
26. Calabria, R., Chiariello, F., and Massoli, P., "Combustion Fundamentals of Pyrolysis Oil Based Fuels," Experimental Thermal and Fluid Science, Vol. 31(5), pp. 413-420, 2007.
27. Pan, K.-L., et al., "On Droplet Combustion of Biodiesel Fuel Mixed with Diesel/alkanes in Microgravity Condition," Combustion and Flame, Vol. 156(10), pp. 1926-1936, 2009.
28. Stanley, C., “Physical Test and Microexplosion Analysis for Water-Oil Emulsions Prepared by Ultrasonic Method,” Master thesis Kun Shan University, Tawian, 2010.
29. Bradley, D., European Market Study for BioOil (Pyrolysis Oil). 2006.
30. Zheng, J.-L. and Kong, Y.-P., "Spray Combustion Properties of Fast Pyrolysis Bio-oil Produced from Rice Husk," Energy Conversion and Management, Vol. 51(1), pp. 182-188, 2010.
31. Sturzl, R., The Commercial Co-firing of RTP Bio-oil at the Manitowoc Public Utilities power generation station.
32. Wagenaar, B.M., et al., "Bio-oil as a Coal Substitute in a 600MWe Power Station," in 12th European Conference and Technology Exhibition on Biomass for Energy, Industry and Climate Protection, Amsterdam, 2002.
33. Wagenaar, B.M., et al., "Bio-oil as Natural Gas Substitute in a 350MWe Power Station," in Second World Conference on Biomass for Energy, Industry and Climate Protection, Rome, 2004.