The Effect Of Mineral Properties On The Grinding Process Of E Type Vertical Spindle Pulverizer

Coal is the most important component in the energy structure of China.In 2016,the total energy consumption of China is 4.36 billion tons of standard coal,and the consumption of coal accounted for 62%,about half of which was used for power generation.Coal-fired power plant is faced with huge challenges to achieve the goal of energy-saving and emission reduction as high energy consumption,emission of pollution gases and other harmful issues happen in the process of coal-fired power generation.In the pulverizing process,the grindability of minerals with high density or high hardness is so poor that they will be gathered in the recirculating loads of power plant pulverizer and being repeatedly ground.The grinding material of the mill is composed of coal and large amount of recirculating loads,and effects of different minerals on the grinding characteristics of coal are different.In this paper,the E-type medium-speed pulverizer,which is widely used in coal-fired power plants,is used as the research object.The influence of mineral properties on the grinding process of coal is studied by means of laboratory grinding test and numerical simulation.First of all,modern analytical instruments were used for the mineralogical analysis of the recirculating loads.Results declare that the recirculating loads are mainly composed of aluminosilicate minerals,quartz and pyrite.And the content,embedded grain size and hardness of the three minerals are different with each other obviously.Thus,kaolinite,quartz and pyrite were mixed with coal samples in the size fraction of-1.25+0.71 mm respectively to be prepared as the mixed materials.The effect of mineral properties on the grinding process of coal is simulated by changing the content,size and species of minerals in the mixed materials.The abrasive behavior of coal and the law of energy consumption were studied by using the Husky grinders with the power measuring device.The results show that coal grinding would be promoted by high hardness minerals(pyrite and quartz in this study)while be hindered by fine grain(-0.09 mm),and the impact would be exacerbated by the enrichment of mineral.When the mineral content is less than 33.33%,the effect of mineral hardness on coal grinding is relatively greater,while higher than 33.33%,the effect of mineral particle size is larger.Besides,the grinding rule of coal in the mixed material is not in accordance with the original level grinding model.Then,first-order grinding dynamic model was modified by introducing a new parameter m,related to the material properties and replacing the time parameter t to tm.The parameters of the energy-particle size reduction model were optimized based on the modified first-order grinding dynamic model,including the parameter of mineral content obtained by the data fitting.The energy-particle size reduction model was used to study the energy distribution in the mixed grinding.When the mineral particle size was below 0.09 mm,the energy ratio of coal is small,and decreases with the mineral content and hardness increasing.when the mineral in the mixed grinding is quartz with particles in the size fraction of-1.25+ 0.71 mm and-0.30+0.20 mm,the energy ratio of coal increases firstly and then reduces with the mineral content increasing.When the mineral content reaches 50%,the energy ratio of coal gradually reduces,and the grinding efficiency also decreases.Based on the laboratory grinding test,the EDEM simulation model was established.The grinding process was simulated by the particle replacement model and the particle cohesive force model.The simulation of the constant pressure grinding process of the Hastelloy grinding instrument was realized by using the C ++ program.Through the experiment of laboratory stacking angle test and EDEM simulation,combined with GEMM database information,the material parameters of the simulation were determined,and the operating conditions and basic parameters of simulation were also set.Through the analysis of the numerical simulation results,conditions of the bond fracture,the movement and force of the particles,the energy consumption,the collision between particles and the collision energy were obtained.The influence of grinding time,mineral content and hardness on the grinding process of coal in mixed materials could be revealed by the motion,collision,stress and energy of coal particles.The results showed that under the influence of minerals with high hardness,the average force of coal,the number of collisions,and the energy loss are large,which results in a high grinding degree.However,the force of coal particles decreases with the increase of mineral content in the mixed material,and the number of collisions,the energy and the grinding degree also reduces.The simulation results of EDEM are consistent with those obtained from laboratory grinding tests,which proves the high reliability of simulation results.And the mechanism of the mineral properties on the coal grinding process is revealed from the microscopic particle dynamic research.