This paper first aims to evaluate the possibility of synthesizing organic calcium through the use of pyroligneous acid and raw limestone. The factors affecting this reaction were investigated including the particle size of limestone, the type of pyroligneous acid and reaction conditions as well. Secondly, two low-rank coals were mixed with the calcium-enriched pyroligneous acid to evaluate the possibility of desulfurization in the combustion furnace. The soluble calcium within pyroligneous acid is in the form of calcium acetate having a low decomposition temperature around 400 degreesC, far lower than that of raw limestone being about 700 degreesC. Due to its solubility, calcium within pyroligneous acid was loaded readily on the coals, forming the ultrafine particles in the impregnated coal matrix. During coal combustion, the loaded calcium underwent quick decomposition prior to char combustion and subsequently, the formed ultrafine calcium oxide captured the evolved sulfur oxide. Around 85% desulfurization efficiency was achieved for coal combustion. S/Ca molar ratio around 1.0 was formed for the particles less than 1.0 mum, whereas it decreased gradually with the increasing particle size. (C) 2004 Elsevier Ltd. All rights reserved.