Sintering temperatures and the initial deformation temperatures of ashes from Turkish Elbistan lignite, and biomass species such as hazelnut shell and rice husk were investigated up to 1450 degrees C by Heating Microscope Technique. Sintering temperatures were found 1300, 1269, and 1320 degrees C for hazelnut shell, rice husk, and lignite, respectively, while the initial deformation temperatures were >1450, 1370, and >1450 degrees C. Lignite/biomass blends were prepared by adding of biomass into coal in the ratios of 5 or 10 wt.%, and then effects of biomass presence on sintering temperature and the initial deformation temperature were tested. It was determined that the addition of potassium-rich hazelnut shell reduced the sintering temperatures to 919 and 730 degrees C for the blends of 5 and 10 wt.%, respectively. Also, initial deformation temperature dropped to 788 degrees C in case of the blend of 10 wt.%. Such a big antagonistic influence of hazelnut shell on the thermal behaviour of ash is attributed to the interaction of potassium from biomass with silicon compounds found in mineral matter of lignite. In addition, concentration of CaO may be another reason for this. On the other hand, the presence of rice husk showed limited effect on the sintering temperature as well the initial deformation temperature. (c) 2010 Elsevier Ltd. All rights reserved.