Radiative heat transfer in flyash cloud: effect of unburnt carbon in ash

✍ Scribed by S.P. Bhattacharya; R.P. Gupta; T.F. Wall

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 342 KB
• Volume: 72
• Category: Article
• ISSN: 0016-2361
• DOI: 10.1016/0016-2361(93)90633-d

✦ Synopsis

Catalysis by CaO, CaCO, and CaSO, of the oxidation of a well-defined, high purity synthetic char, Spherocarb, was investigated at low reaction temperatures using thermal gravimetric analysis (TGA). Oxidation rates were likewise measured for fresh, demineralized, and Ca-impregnated samples of a high temperature char prepared in a flat-flame burner at z 1600K from Beulah Zap coal. Spherocarb and demineralized Zap char were impregnated with Ca using aqueous impregnation and ion-exchange techniques.

The resulting kinetic parameters for Spherocarb indicate significant catalytic effects ~ at least a lo-to lOO-fold increase in the oxidation rate of Spherocarb for CaCO,, at least a 200-to 300-fold increase in the oxidation rate of Spherocarb containing CaSO, and a 500-to 3000-fold increase in the case of CaO. The oxidation rates of CaO-catalysed Spherocarb and Beulah Zap char are the same within experimental error, suggesting that the high reactivity of the Zap char is due in larg part to catalysis by CaO. The reactivity of demineralized Beulah Zap char is significantly higher than for pure Spherocarb;

this result suggests significant differences in the reactivity if the carbon matrices for these two chars.

Experiments involving temperature-programmed surface reaction (TPSR) of oxygen with adsorbed CO and adsorbed carbon produced by decomposition of ethylene on an unsupported high surface area CaO as well as TPO experiments on demineralized and CaO-catalysed char provide evidence that the CaO-catalysed reaction produces mainly CO,, while the reaction of oxygen with uncatalysed char produces mainly CO. These results have important implications for the mechanism of CaO-catalysed combustion of char.