Study On The Fusion Behavior Of Fly Ash Particle And Single Particle In Different Size Ranges From The Entrained Flow Coal Gasifier

entrained flow coal gasification technology is an effective way to achieve clean and efficient utilization of coal,the gasifier radiation waste pot to recover the sensible heat of synthesis gas,energy saving effect is remarkable,but the high temperature synthesis gas entrapped with different particle size fly ash particles,there is a significant difference in the melting and deposition behavior on the heat exchange surface,when the deposition layer is too thick,the block ash slag off blocking the slag outlet,seriously affect the whole gasification system of high efficiency and This can seriously affect the efficient and safe operation of the entire gasification system.Therefore,it is of great theoretical and practical importance to study the melting behaviour of fly ash particles in different particle sizes to improve the heat transfer efficiency of the radiant waste pot and to ensure the safe operation of the gasifier.In addition,the classical ash melting point alone cannot reflect the difference between the sintering and melting processes,and the melting behaviour of single particle fly ash in air bed gasifier is not clear.In this paper,the fly ash of Shell gasifier was selected as the object of study and the fly ash particles were divided into eight different particle size ranges by sieving（<15μm,15-25μm,25-45μm,45-65μm,65-85μm,85-105μm,105-150μm and>150μm）,the physicochemical properties and melting behaviour of fly ash of different particle sizes and single particle fly ash were studied using thermogravimetric analyser,ash melting tester,thermomechanical analyser,thermodynamic calculations and high temperature thermal bench.The main findings and conclusions are as follows:（1）The physical and chemical properties of different particle sizes of fly ash were investigated by laser particle size measurement（PSD）,X-ray diffraction analyzer（XRD）,inductively coupled plasma spectrometer（ICP）and thermogravimetric analyzer（TG）,and the results showed that:the particle sizes of Lu’an fly ash showed a bimodal distribution;the fly ash particl es in different particle sizes contained high amorphous phases,and their main components were silica-aluminates;as the particle sizes increased,the residual carbon content of the fly ash follows a“W”pattern.At the same time,the contents of Si O₂,K₂O and Na₂O in the particles increased,but the contents of Al₂O₃,Fe₂O₃and Ca O decreased,and the Si O₂/Al₂O₃ increased.（2）The melting behaviour of fly ash of different particle sizes was analysed using an ash melting point tester（AFT）,the thermodynamic software Factsage and a thermomechanical analyser（TMA）.The results of the ash melting point tester showed that the melting temperature of fly ash of different particle sizes gradually decreased with increasing particle size,mainly because the silica-aluminium of fly ash with particle size<45μm was relatively low（Si O₂/Al₂O₃<2.5）,the reaction of hematite and calcium-containing minerals with silicate is more likely to produce high melting point minerals such as iron spinel,cordierite and calcium feldspar,resulting in a higher melting point of fly ash with particle size<45μm;the silica-aluminium of fly ash with particle size>45μm is higher（Si O₂/Al₂O₃>3）,and the reaction of alkali metals with silicate particles is more likely to produce low melting point minerals.react more readily to produce low melting point minerals such as iron olivine,pyroxene,potassium feldspar and sodium feldspar.The results of the TMA experiments show that the melting behaviour of fly ash particles of different particle sizes varies significantly and is divided into three zones according to their melting rates:a fast melting zone for small fly ash particles（maximum particle size<45μm）,a medium melting zone（45-150μm）and a slow melting zone for large fly ash particles（minimum particle size>150μm）.At the same time,the melting mechanism differs between particle sizes,with fly ash particles in the fast melting zone having a higher shrinkage rate（average shrinkage rate of0.80%/°C）and a narrower melting zone,belonging to the“melting-dissolving”mechanism.The shrinkage rate of fly ash between the medium and slow melting zones is small（average shrinkage rate of 0.38%/°C）and the melting zone is wide,which belongs to the“softening–melting”mechanism.（3）The particles were dispersed with 0.2%sodium carboxymethyl cellulose solution as a dispersant and the melt morphology of the whole particle population and single particles of different particle sizes of fly ash was further investigated using high temperature hot stage microscopy,the results show that there are significant differences in the melting behaviour of single particles of fly ash of different particle sizes,with a wide range of melting temperatures for single particles of fly ash<45μm（1000℃-1200℃）,the melting temperature is high,with traces of unfused minerals still present at the edges of the particles at1200°C,the melting starts at the centre of the particles and gradually spreads in all directions.While>45μm particle size single particle fly ash melting temperature range is narrower（900℃-1050℃）,melting temperature is lower,1050℃particle melting has been basically completed,melting process of unfused minerals exist in the centre of the particle area,melting behavior is first from the periphery,gradually spread to the centre.The melting temperatures of single particles and whole particle groups of fly ash of different particle sizes follow the same trend,both gradually decrease with the increase of particle size,while the melting process is significantly different,the liquid phase generation rate is faster during the warming process of single particles,and there is no obvious plateau and expansion phase,after the occurrence of sintering quickly into the melting phase,in addition,the initial liquid phase temperature and melting temperature of single particle fly ash is significantly lower than that of whole particle group fly ash.