The effect of the calcium present in lignite on the effectiveness of NO reduction in the reburning method has been studied in the 900-1100 degrees C temperature range. Lignites from three Polish mines were used. The experiments were carried out in a laboratory scale drop-tube furnace reactor. The demineralised lignites were loaded with Ca using: calcium acetate Ca(CH(3)COO)(2), calcium hydroxide Ca(OH)(2) and calcium carbonate CaCO(3). For the reburning process the catalytic effect of the presence of calcium in lignite was found to be rather modest (approx +/- 20%) in the temperature range studied. It was shown that up to 1000 degrees C the calcium added to the demineralised lignites improved their effectiveness as reburn fuels. The effect was almost reversed when the reburn temperature was raised to 1100 C. With the impregnated lignites the extent of NO reduction appeared to be practically independent of the calcium compound used. Mineral matter in raw lignite exerts a similar catalytic effect to calcium introduced by impregnation. (c) 2004 Elsevier Ltd. All rights reserved.