NO reduction by potassium-containing coal briquettes. Effect of mineral matter content and coal rank

This paper reports the NO reduction activity of several potassium-containing coal briquettes obtained from different coal precursors (ranging from anthracite to lignite) with the purpose of understanding the effect of coal rank. Also, two fractions of a bituminous coal, with two very distinct ash contents, were selected to determine the influence of the mineral matter content of coals in NO reduction. The catalytic effect of potassium in this reaction was evaluated in a fixed-bed flow reactor at atmospheric pressure using two types of experiments: (i) temperature programmed reaction in a NO/He mixture; and (ii) isothermal reaction at 300-600 degrees C. The reaction products were monitored in both cases, thus allowing detailed oxygen and nitrogen balances to be determined. The effect of coal rank is manifested in two ways: larger amounts of potassium incorporated in coal briquettes and higher NO reduction activity as the coal rank precursor decreases, for all of the reaction temperatures tested. Ash contents of the coals (quartz, silicates) seem to have a negative effect in the NO-carbon reaction, acting as a sink that sinters and deactivates the potassium, forming potassium carbonate and silicates, both of them inactive for the process.