Study On The Heterogeneous Melting Behaviors Of Pulverized Shanxi Three-high Coal Ashes

Coal resources are abundant in Shanxi province,however those with characterizations of high ash?22%-30%?,high sulfur?2.4%-3.0%?and high ash melting temperature?softening temparature higher than 1500 ^oC?are also included.These features have impeded the spread and application.It turns out that ash agglomerating fluidized bed is an effective way to make use of these special coals,but discrepancy has been found between theoretical prediction and practical production.The concept of heterogeneous melting was then put forward,and two typical Shanxi coals?Datong and Jincheng?were chosen as raw materials.Ash melting behaviors under high temperature were studied,which might help to solve the problem of these special coals.Firstly,the influence of raw coal particle size on the melting of coal ash was studied.The results show that the melting temperatures of coal ash of different particle sizes are almost constant with the change of coal size.The raw coals were subsequently ground into powder and separated by sieving actoion and float-sink tests.It's found that there are differences between high-rank Jincheng anthracite and relatively low-rank Datong bituminite in both partticle sizes distribution and density fraction distribution.Also,differentiations on different degrees were found in both chemical composition and mineral composition.Ash melting temperatures and sintering characteristic of raw coal and all classified samples particle sizes and density were studied by AFT and PDT,respectively.It's found that the difference value of softening temperature?ST?among DT samples with different particle sizes is nearly 200 ^oC,while that of JC samples with different densities reaches up to 300 ^oC.Mechanism research indicates that the different existence forms of minerals lead to the difference in the fusibility of coal ash between DT and JC samples.However,the change trend of sintering temperature,which is acutely affected by particle size,is different from that of melting temperature.Moreover,SEM-EDX research states that there exist significant differences between macroscopic and microcosmic melting states under high temperature.FactSage software was used for thermodynamic calculation and ternary phase diagram.The simulation results have a good correlation with the experimental results.It's considered that the heterogeneous melting behaviors of both two coals are caused by the formation of eutectic minerals,such as cordierite and anorthite.While the higher anorthite content in JC resultes in its intenser inhomogeneity.In actual production of ash agglomerating fluidized bed,the initial deposition layer is formed by the interaction of metal cations(Ca²⁺,Na⁺and others)with amorphous ferric silicates.Apparently,the probability of impacting the sticky deposition layer for particles with large density and large particle size would significantly increased.Meanwhile,these particles themselves are characteristiced by higher minerals and lower melting temperatures.Thus,they begin to melt and form sticky aggregation at the temperature lower than ST,and eventually lead to the wholly molten state.