Abstract:

Co-combustion of biomass and coal is one of the main directions of clean energy utilization. The melting temperature characteristics of Ningxia high ash （WWA），sunflower straw ash （SSA） and mixed ash of WWA and SSA with different mass ratios （W₃S₁， W₂S₁， W₁S₁， W₁S₂， W₁S₃） at high temperature were studied. The chemical composition of ash was analyzed by X-ray fluorescence diffraction （XRF）， the mineral evolution behavior was analyzed by X-ray diffraction （XRD）， the microscopic morphology of ash at high temperature was analyzed by scanning electron microscopy （SEM）， and the liquid phase content of ash at high temperature was calculated by Factsage thermodynamic software to clarify the influencing factors of ash melting process and explain the melting mechanism of ash. The results show that with the increase of SSA content， the four melting characteristic temperatures of mixed ash begin to decrease， and the melting temperature of W₂S₁ is the lowest， and its deformation temperature is reduced to 1228 ℃， which is about 50 ℃ lower than WWA. With the continuous increase of SSA content， the deformation temperature （DT） and softening temperature （ST） of mixed ash increased slightly， but the hemisphere temperature （HT） and flow temperature （FT） increased significantly. At high temperature， the formation of alkaline components such as leucite， diopside， potassium nepheline and magnesium feldspar in ash is the main reason for the decrease of ash melting temperature. With the increase of the proportion of SSA， some alkaline components exist in the form of oxides with high melting point or amorphous substances with high melting point， resulting in an increase in the flow temperature of ash. When a small amount of SSA is added to WWA， the initial liquid phase temperature of the mixed ash is reduced， and the melting process is similar to that of coal ash， with the main melting process （liquid phase content exceeding 80%） occurring before 1300 ℃. When the content of SSA exceeds 50%， the initial liquid phase temperature increases， and the main melting process occurs at 1400 ℃. The research results provide a theoretical reference for solving the problem of slagging during the co-combustion of sunflower straw and coal.

Key words: Coal ash, Sunflower straw ash, Ash melting characteristics, Mineral evolution, Slagging mechanism