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 (M-ad) decreases as WS > CS > CCS > SS, and the M-ad of the four straws decreases more obviously with HS addition than that for HLH addition. The M-ad of SS and CSS increases slowly before 1000 degrees C and then increases rapidly; whereas for CS and WS, the change occurs at 950 degrees 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 M-ad 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 M-ad. (C) 2017 Elsevier Ltd. All rights reserved.