LOW QUALITY COALS AND BLENDING: OPPORTUNITIES FOR MITIGATION OF FOULING

Several out-of-spec coals have been studied with respect to their ash behaviour in relation to ash deposition problems in pulverized coal-fired boilers. The coals have been analysed in detail and show increased concentrations of Ca, Fe, Mg, Na or K. Experimental deposition tests with single coals and blends have been performed in a lab-scale facility and in a semi-industrial scale furnace. The results have been evaluated especially with respect to interactions between inorganic species from different coals. Observed mechanisms for the formation of sticky ash particles, responsible for the initiation of ash deposition, are used to derive blending guidelines for the coals.