International Scientific Journal


This paper presents the findings of research into cofiring two Bosnian cola types, brown coal and lignite, with woody biomass, in this case spruce sawdust. The aim of the research was to find the optimal blend of coal and sawdust that may be substituted for 100% coal in large coal-fired power stations in Bosnia and Herzegovina. Two groups of experimental tests were performed in this study: laboratory testing of co-firing and trial runs on a large-scale plant based on the laboratory research results. A laboratory experiment was carried out in an electrically heated and entrained pulverized-fuel flow furnace. Coal-sawdust blends of 93:7% by weight and 80:20% by weight were tested. Co-firing trials were conducted over a range of the following process variables: process temperature, excess air ratio and air distribution. Neither of the two coal-sawdust blends used produced any significant ash-related problems provided the blend volume was 7% by weight sawdust and the process temperature did not exceed 1250ºC. It was observed that in addition to the nitrogen content in the co-fired blend, the volatile content and particle size distribution of the mixture also influenced the level of NOx emissions. The brown coal-sawdust blend generated a further reduction of SO2 due to the higher sulphur capture rate than for coal alone. Based on and following the laboratory research findings, a trial run was carried out in a large-scale utility - the Kakanj power station, Unit 5 (110 MWe), using two mixtures; one in which 5%/wt and one in which 7%/wt of brown coal was replaced with sawdust. Compared to a reference firing process with 100% coal, these co-firing trials produced a more intensive redistribution of the alkaline components in the slag in the melting chamber, with a consequential beneficial effect on the deposition of ash on the superheater surfaces of the boiler. The outcome of the tests confirms the feasibility of using 7%wt of sawdust in combination with coal without risk to the efficiency of the unit, its combustion process and with the benefits of emissions reductions. Furthermore, they show that no modification to the existing coal transport system and boiler equipment is necessary to achieve this outcome.
PAPER REVISED: 2012-05-08
PAPER ACCEPTED: 2012-06-21
CITATION EXPORT: view in browser or download as text file
  1. European Commission, Energy for the Future: Renewable sources of energy, White paper for a community strategy and action plan. See also:
  2. Wischnewski R, Werther J, Heidenhof N. Synergy Effects of the Co-combustion of Biomass and Sewage Sludge with Coal in the CFB Combustor of Stadtwerke Duisburg AG, VGB PowerTech 2006;12:63-70.
  3. Baxter, L. L., Rumminger M., Lind T., Tillman D. And Hughes E. Cofiring Biomass in Coal Boilers: Pilot- and Utility-scale Experiences. Biomass for Energy and Industry: 1st World Conference and Technology Exhibition, Seville, Spain, 2000.
  4. Koppejan J., 2004: Overview of experiences with cofiring biomass in coal power plants, IEA Bioenergy Task 32: Biomass Combustion and Cofiring, 2004.
  5. KEMA, IEA Bioenergy Task 32, August, 2009.
  6. Kakaras E. Low emission co-combustion of different waste wood species and lignite derived products in industrial power plants. In: XXXII Krafwerkstechnisches colloquium 2000. Nutzung schwieriger brennstoffe in kraftwerken. Dresden 2000., p. 37-46.
  7. Kazagić A., Smajević I., Experimental investigation of ash behavior and emissions during combustion of Bosnian coal and biomass, Energy (Elsevier), Volume 32, Issue 10 (October 2007), p. 2006-2016., doi:10.1016/
  8. Kazagić A., Smajević I., Synergy Effects of Co-firing of Woody Biomass with Bosnian Coal, Energy (Elsevier), Volume 34 (May 2009), p. 699-707, doi: 10.1016/
  9. Kazagić A., Smajević I., Evaluation of Ash Deposits During Experimental Investigation of Co-firing of Bosnian Coal with Woody Biomass, Tagungsband, Kunftiges Brennstoff- und Technologieportfolio in der Kraftwerkstechnik, 40. Kraftwerkstechnisches Kolloquium, Dresden, 14-15. October 2008., Band 2, pg. 238-249.
  10. Kazagić A., Smajević I., Duić N., Selection of sustainable technologies for combustion of Bosnian coals, International scientific journal Thermal Science, Volume 14, No. 3 (Year 2010), pg. 715-727.
  11. Kupka T., Zajac K., Weber R., Influence of fuel type and deposition surface temperature on the growth and chemical and physical structure of ash deposit sampled during co-firing of coal with sewage sludge and saw dust, 8. International INFUB Conference, Vilamoura, Portugal, 25.-28. March 2008.
  12. Raask E., Mineral Impurities in Coal Combustion, Central Electricity Generating Board - Technical Planning and Research Division, Leatherhead, England, U.K., 1985.
  13. Rozendaal M. Impact of coal quality on NOx emissions from power plants. Delft: Delft University of Technology, 1999.
  14. Di Nola G, Protopapas G, De Jong W, Spliethoff H. In-flame measurement of HCN and NH3 in pulverized biomass co-firing: influence of primary stoichiometry on NOx emissions abatement, In: 14th European Biomass Conference, October 2005, Paris.

© 2017 Society of Thermal Engineers of Serbia. Published by the Vinča Institute of Nuclear Sciences, Belgrade, Serbia. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International licence