The catalytic gasification of carbon in incinerator fly ash

Abstract

Four fly ashes collected from electrostatic precipitators—three from municipal solid waste incinerators and one from a coal-fired power plant—were studied for their potential to catalyze carbon gasification reactions. A fixed-bed tubular reactor employing mixtures of oxygen and nitrogen was used to measure CO and CO 2 evolved from native carbon in fly ash in the temperature range 275–350°C. Experiments using pure carbon were also run for comparison. MSWI fly ash was discovered to accelerate carbon gasification rates by at least an order of magnitude. At 300°C, gasification rates of native carbon in the different MSWI fly ash ranged from 1–8 mg-C/g-min, compared to pure carbon gasification rates of 0.03–0.2 mg-C/g-min. Activated carbon, having a high internal surface area, mixed to MSWI fly ash also showed an accelerated gasification rate, suggesting that the catalytic action was long-range. No catalytic activity was observed with coal fly ash. Apparent activation energies for gasification of native carbon in MSWI fly ash ranged from 25–34 kcal/mole, while those for pure carbon ranged from 10–20 kcal/mole. The apparent activation energy of gasification in coal fly ash was 14 kcal/mole. The oxygen concentration dependence on gasification rate in fly ash was determined to be 0.54; that for pure carbon was 0.71.