Study On The Influence Of Particle Sizes And Alkali Metal Oxides On Dielectric Property Of Fly Ash

The carbon content in fly ash is one of the important technical andeconomic indicators in the operation of coal-fired power plant boilers，so it is ofa very important significance to monitor the carbon content in fly ash accuratelyin real-time for improving the combustion efficiency of the boiler．Currently inorder to acquire the carbon content in fly ash，the microwave measurementtechnologies are generally used by coal-fired power plants to measure complexdielectric constant of fly ash．However，this technology does not consider theinfluence of particle sizes and alkali metal oxides on dielectric property of flyash，which decreases microwave measurement technology accuracy．Thereforeit is impossible to adjust combustion accurately and promptly．The thesis uses the fly ash from four different power plants as theresearch objects．The resistivity of fly ash is measured by the power resistancetester，and the complex dielectric constant of fly ash is measured by the vectornetwork analyzer in the frequency range of30MHz~3.2GHz．The influence ofparticle sizes and alkali metal oxides on the resistance and dielectric loss of flyash is researched through lots of experiments and profound analyses in themechanism of pulverized coal combustion and fly ash formation． The fly ash samples are collected and sieved into different particle sizeranges．The author studied the impact of particle sizes on the resistance anddielectric loss of the fly ash with carbon and the fly ash without carbon has beenstudied respectively．The results show that the impact of particle size and thecarbon content on resistance has no obvious rule for the fly ash with carbon，while the resistance of fly ash is the comprehensive effect of the both．Theresistance decreases when the particle size decreases for the fly ash withoutcarbon，while the original fly ash sample has the smallest resistance．Thedielectric loss also has nothing to do with particle size for the fly ash withcarbon，but the dielectric loss increases when the carbon content of fly ashincreases．The larger the carbon content is，the more obviously the dielectricloss increases．There is a peak phenomenon at the particle size with themaximum carbon content．The dielectric loss increases when the particle sizedecreases for the fly ash without carbon．The smaller the particle size is，themore obviously the dielectric loss increases．In order to study the influence of alkali metal oxides Li2O，Na2O，K2O onthe dielectric property of fly ash，the fly ash samples with different contents ofLi2O，Na2O，K2O are prepared in the laboratory．The results of the resistanceand dielectric loss show that the resistance decreases with the increase of thecontents of alkali metal oxides Li2O，Na2O，K2O．In the case of the samecontents of alkali metal oxides，the resistance of the fly ash with Li2O ismaximum and the resistance of the fly ash with K2O is minimum．The dielectric loss of fly ash decreases when the contents of Li2O increase in the frequencyrange of30MHz～1500MHz，while the dielectric loss of the fly ash increaseswith the increase of the contents of Li2O when the frequency range is more than1500MHz．The dielectric loss of the fly ash increases when the contents ofNa2O and K2O increase．If the contents of Na2O in the fly ash is more than10%，the dielectric loss increase greatly．So the scholars should fully considerthe influence of particle size and alkali metal oxides in fly ash when the carboncontent of fly ash is measured by microwave online carbon meters．...