Study On Milling Characteristics Of Fly Ash

Fly ash is the main solid waste discharged from coal-fired power plants with large emission but low comprehensive utilization rate.The application of fly ash in building materials mainly depends on its pozzolanic activity.However,the activity of raw ash of fly ash is generally low,which seriously limits the comprehensive utilization rate of fly ash.The pulverizing and refining treatment of fly ash makes the active composition easier to participate in hydration reaction and improve its activity.In addition,the refining treatment of fly ash also improves its particle morphology to a certain extent and enhances its micro-aggregate effect in material utilization,thus improving material performance.At present,ball mill is generally used in fly ash grinding,which has large noise,low energy utilization rate and serious wear.It is worth studying to achieve the maximum grinding efficiency with lower cost.Steam kinetic energy mill,also known as supersonic steam crusher,has the advantages of high crushing efficiency,small equipment wear,high product purity,low energy consumption and so on.Supersonic steam pulverizer is a more efficient way of pulverizing coal ash,but there are few researches on pulverizing coal ash with supersonic steam pulverizer at present.The main research of this paper is as follows:（1）Using pulverized coal ash as the raw material,the ball milling process was used to investigate the influence of fly ash ball milling time,ball milling media gradation,and material filling rate on the particle size distribution,specific surface area,energy consumption and other indicators.The microscopic characteristics are compared and analyzed,and the microscopic morphology（SEM）,phase composition（XRD）,gelling activity index and other change rules are systematically investigated,and the grinding efficiency is preliminary calculated.The results showed that the particle size of fly ash decreased with the increase of grinding time,the decrease of filling rate and the increase of the proportion of small balls in the ball milling medium;the gelling activity of fly ash increased with the decrease of median diameter D₅₀,and the ratio The surface area increases and increases;prolong the ball milling time,the energy consumption increases,and the grinding cost increases.The results show that the optimal grinding time of fly ash by ball mill is 1h,the filling rate is 60%,the steel ball grade is 10 mm:20 mm:30 mm:50 mm=3:1:1:1,the power consumption is 60 k W·h/t,the median diameter of fine powder D₅₀is 14.0μm,the specific surface area is 387.8 m²/kg,and the activity of fly ash specimens is 90.5%.The particle size of fly ash decreases with the increase of grinding time,the smaller filling rate and the increase of the proportion of small balls in the medium.The activity of fly ash is inversely proportional to the particle size and is proportional to the specific surface area.However,with the increase of grinding time,the grinding efficiency decreases and the energy consumption increases.The phase composition of fly ash does not change after grinding,but the crystallinity of mullite decreases,the number of amorphous components increases and the crystal composition of quartz decreases.The grinding can destroy the vitreous structure of the spherical fly ash particles,cause cracks and distortion of the crystals,and improve their activity.（2）Using pulverized coal furnace coal fly ash as raw materials,using the kinetic energy of the steam mill grinding process,particle size,specific surface area and activity as the main index,investigate steam mill crushing effect under different fractional frequency,and from the aspects of microstructure,mineral composition and so on to explore the crushing mechanism,provide a reference for the shattering of the fly ash and other mineral processing and using for reference.The pulverization of supersonic steam crusher is high and the energy consumption is low.The median diameter D₅₀ of fly ash powder obtained by supersonic steam crusher is up to 2.25μm,and the specific surface area is up to 1140.3 m²/kg.The activity of fly ash can reach up to 107.7%after being ground by supersonic steam pulverizer,and the median diameter D₅₀ of fine powder is 2.7μm.Using supersonic steam pulverizer to grind fly ash can effectively break fly ash microbeads,release internal Ca,Si,Al and other components,improve the dissolution rate of Si and Al,optimize the chemical composition of fly ash micropowder,strengthen hydration reaction,improve activity;The supersonic steam crusher will not change the phase composition of fly ash,but will reduce the crystallinity of the phase in fly ash.With the increase of grinding intensity,the particle size of fly ash decreases,and the crystallinity decreases.（3）Using CFB boiler ash as raw material,ball milling and steam flow ultrafine grinding processes were adopted respectively,and particle size and specific surface area were taken as main indexes to investigate the grinding effects of different ball milling time and different steam milling classification frequency.The grinding efficiency of steam kinetic energy mill is not significantly different from that of ball mill,and the D₅₀ and SSA of fly ash are4.78μm and 968.9 m²/kg for 6 h,while the D₅₀ and SSA of fly ash can reach4.27μm and 1156.2 m²/kg at the grading frequency of 134 Hz.（4）The above two kinds of the crushing process of circulating fluidized bed boiler ash superfine powder used as concrete admixture,and according to the actual production of solid waste production amount,to the national standard in the application of fly ash in concrete,the main indicators for testing,as a concrete admixture,recycling use of the power plant ash.The particle size of slag can be obviously reduced by ball milling and steam milling.The ball milling time of 2 h can reach the standard ofⅠgrade ash,and the fine powder obtained by steam kinetic energy grinding can reach the standard of lead grade ash.The water requirement of ash increases with the increase of milling time and grading frequency.When the ball-milling time is 0.5 h,the water demand ratio of ash powder is 105%,which meets the standard ofⅡash.When the ball-milling time is over 0.5 h and below 134 Hz,the water demand ratio of ash powder is within the range of lead ash.When the ball milling time reaches 6 h and the grading frequency reaches 134 Hz,the water requirement ratio of ash is not as good as the standard ofⅢgrade ash.The combustion loss of raw ash and fine powder of fly ash meet the requirements of gradeⅡ.Compared with the raw ash,the combustion loss of pulverized ash is slightly increased.The ball mill and steam kinetic mill have no obvious influence on the combustion loss of ash.The activity of ball-milling for 1h was higher（92.1%）,and the increase of activity was not obvious with the extension of milling time.The slag activity was the highest（94.9%）at the grading frequency of 120 Hz.（5）According to the above research results,a circulating fluidized bed boiler coal-fired power plant in Jiangsu Province was selected to carry out the design of engineering application project for preparing CFB ash slag ultrafine powder by steam flow ultrafine grinding technology,including:raw material scale,process design,equipment selection,product application,etc.