The effect of the calcium in lignite on its effectiveness as a reburn fuel

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 °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 3COO) 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 °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.