Experimental investigation of ash deposition behaviour modification of straws by lignite addition

The ash-deposition (AD) characteristics of straws (corn stalk [CS], wheat straw [WS], cotton stems [CCS], and soybean stalk [SS]), and the effects of lignite (Husheng [HS], Huolinhe [HLH]) on the characteristics were investigated. Under the same conditions, the AD mass ratio (Mad) decreases as WS > CS > CCS > SS, and the Mad of the four straws decreases more obviously with HS addition than that for HLH addition. The Mad of SS and CSS increases slowly before 1000 °C and then increases rapidly; whereas for CS and WS, the change occurs at 950 °C. The differences result mostly from the higher potassium-oxide contents in CS (26.34%) and WS (30.04%) over those in CCS (11.63%) and SS (10.25%). Ca2+ replaces K+ in semi-molten alumino-silicate (orthoclase and leucite) and results in the formation of a high melting-point anorthite. This, together with the generation of high melting-point mullite, leads to a decrease in Mad of the mixed ashes with an increase in lignite mass ratio. The position changes of the ash composition in the ternary phase diagrams and their variation in liquid-phase content with increasing temperature based on the FactSage software calculation may explain the variation in Mad.