Evaluation of slagging and fouling characteristics during Zhundong coal co-firing with a Si/Al dominated low rank coal

Blending is a promising method to improve ash related problems to meet combustion requirements. To evaluate the slagging and fouling characteristics of Zhundong coal (ZD) co-firing with a Si/Al dominated low rank coal (WD), the influence factors of slagging and fouling propensity based on ash composition and fusion temperatures was discussed. Release, thermal change and transformation behaviors of minerals in the mixed ashes were investigated by Thermogravimetric analysis and FactSage software. Morphology and chemical characteristics of ash deposits along heating surfaces of a practical boiler co-firing these two coals were also analyzed. The results show that when alkali/acid ratio (R-B/A) is higher than 0.400 and difference value between ST and DT (ST-DT) lower than 20 degrees C, blending presents a severe slagging and fouling tendency. Under high temperature, ZD ash underwent a major weight loss which, is characterized by intense endothermic reactions and leads to the low ST-DT value. Feldspar, tridymite and anhydrite are the dominated minerals for blending ashes, and transformation of them contributes to the low fusion temperatures. Deposits along heating surfaces of boiler for burning ZD coal blending could be divided into two groups: condensed deposits and molten deposits. The former is due to the volatilization of mineral elements and have higher AFTs and the latter mainly due to the formation of low fusion temperature eutectics.