粉煤变径脉动气流分选过程的分离机制及参数优化

发布时间：2018-05-22 13:45

本文选题：粉煤 + 干法　；参考：《中国矿业大学(北京)》2017年博士论文

【摘要】：随着我国煤炭工业西进战略的逐步实施,开展针对西部、北部地区煤炭资源储备特点的新型煤炭分选技术势在必行。新疆、内蒙地区煤炭资源储量丰富,以褐煤、次烟煤等低阶煤为主。现行的湿法选煤方法在分选低阶煤时,面临煤泥水处理困难、产品水分过高等诸多难题,应用受限。论文以-6mm粉煤为研究对象,采用自主研发的变径脉动气流分选方法,综合运用矿物加工学、流体力学、数值分析和数值模拟等理论,对粉煤气流分选进行了系统的实验、过程计算与数值模拟研究,揭示了粉煤变径脉动气流分选过程的强化分离机理、协同优化了分选机的结构与操作参数、阐明了物性对分选特性的影响规律。主要研究内容包括五部分:(1)粉煤变径脉动气流分选机脉动流场特性及强化分离机理;(2)粉煤变径脉动气流分选过程中结构参数和操作参数的协同优化;(3)物性差异对粉煤气流分选过程的影响规律;(4)基于气固两相耦合的分选过程数值模拟;(5)粉煤变径脉动气流连续分选试验。主要研究内容和重要结论如下:(1)采用波动理论,建立了线性阻尼条件下脉动气流波动传递方程,研究了脉动气流的波动传递机制:分选机中各处脉动速度由沿流动方向的行波和逆流动方向的行波合成,脉动速度振幅的大小主要取决于阻尼系数和变径段速度缩放系数。(2)基于网格模型理论,数值模拟了颗粒在脉动气流场中的阻力特性,建立了脉动气流场颗粒绕流阻力系数经验公式,结果表明:脉动气流场中,阻力系数较恒定流增大;随着脉动流速度振幅的增大,阻力系数近似线性增加;脉动频率对阻力系数影响不大。(3)通过颗粒运动动力学分析,建立了颗粒在脉动气流场中运动的动力学方程,采用提出的脉动气流场颗粒绕流阻力系数经验公式,数值计算了脉动气流对不同密度、粒度颗粒的加速、减速效应,揭示了变径脉动气流分选机强化分离机理:脉动气流的周期性累积振荡作用可强化不同密度颗粒相互分离,借助变径结构的减速作用可进一步提高颗粒按密度分离的趋势。(4)实验研究了气体分布器结构、给料位置、直筒段高度和变径段结构等参数对粉煤气流分选效果的影响:气体分布器排料口直径越大,分选密度越低,排料口面积占分选柱底部横截面积16%时,可能偏差最低;给料位置距底部排料口距离越近,分选密度越低,给料位置在变径段时分选效果优于直筒段;直筒段高度越高,分选密度越高,可能偏差越小,直筒段高度超过0.75m后,分选密度和可能偏差变化不明显;变径段锥比越大,分选密度越小,可能偏差随锥比变化的规律不明显。(5)实验研究了主风量、脉冲风量和脉冲周期等参数对粉煤气流分选效果的影响:随着主风量增大,分选密度和可能偏差均逐渐增大;脉冲风量增大,分选密度和可能偏差略有升高;脉冲周期延长,分选密度略有升高,可能偏差逐渐增大。(6)采用响应曲面方法,研究了主风量、脉冲风量、脉冲周期、锥比对分选密度和可能偏差的影响,建立了分选密度、可能偏差与各因素间的定量关联式,结果表明:主风量对分选密度影响极其显著,脉冲周期和锥比影响显著,脉冲风量影响不显著;主风量、脉冲周期、主风量×锥比、主风量×主风量对可能偏差影响极其显著,脉冲风量影响显著,锥比影响不显著。(7)基于分选密度、可能偏差与各因素间的定量关联式,研究了分选机结构参数与操作参数的协同匹配关系,结果表明:给定分选密度较低时,小锥比结构的分选机,分选精度更高;给定分选密度较高时,大锥比结构的分选机,分选精度更高。(8)实验研究了密度组成、粒度组成对6~3mm粉煤气流分选过程的影响,结果表明:煤样的密度组成对粉煤气流分选效果影响较小、对分级效应影响较大,粒度组成对分选效果影响较大、对分级效应影响较小;粗粒级含量越多、分选密度越低,高密度级含量越多,分级粒度越低;某密度级分配率应等于各粒级相应密度级分配率的加权之和,某粒级分配率应等于各密度级相应粒级分配率的加权之和。(9)综合考察了粉煤变径脉动气流分选过程中分选效果与分级效应的关系:随着主风量的变化,分选密度、分级粒度均与主风量呈正相关性;分选可能偏差与主风量呈正相关性,分级可能偏差与主风量呈负相关性。(10)采用DDPM与DEM模型相耦合的方法,考虑固相体积分数与颗粒间碰撞作用,数值模拟了粉煤变径脉动气流分选过程。DDPM+DEM模型适用于不同处理量和风量条件下的分选过程模拟,DPM模型仅适用于低处理量条件下的分选过程模拟。(11)DDPM+DEM模型数值模拟结果表明:加入颗粒前,分选机内压降值随脉动气流作周期性变化,此时的压降主要为沿程压力损失;加入颗粒后,流场均匀性降低,压降值急剧增加,且分选机处理量越高,压降增加越明显,此时的压降主要为离散相颗粒加入导致风阻增大而造成的压力损失。(12)采用数值模拟方法研究了操作制度对粉煤气流分选效果的影响规律,建立了分选密度与分选机风量和处理量的数学模型。(13)对6~3mm、3~1mm和1~0mm粒级粉煤进行了连续分选实验研究,相同风量条件下,处理量增大,分选密度升高,可能偏差增大;主风量为270 m3/h、处理量为200kg/h时,6~1mm粉煤气流分选数量效率高达91.02%。
[Abstract]:With the gradual implementation of the western strategy of the coal industry in China, it is imperative to carry out the new coal separation technology for the characteristics of coal resources reserve in the western and northern regions. Xinjiang, Inner Mongolia area has rich coal reserves, mainly with lignite, secondary coal and other low rank coal. The current wet method of coal preparation is faced with the treatment of coal mud water in the separation of low rank coal. In this paper, the paper takes -6mm powder coal as the research object, uses the self developed variable diameter pulsating air separation method, and comprehensively uses the theory of mineral processing, fluid mechanics, numerical analysis and numerical simulation to carry out systematic experiment, process calculation and Numerical Simulation Research on the separation of powder gas flow. The strengthening separation mechanism of the pulverized coal pulsating pulsating flow separation process is revealed, the structure and operating parameters of the separator are optimized, and the effect of the physical property on the separation characteristics is clarified. The main research contents include five parts: (1) the characteristics of pulsation flow field and the strengthening separation mechanism of the pulverized coal pulsating pulsating pulsating machine; (2) the pulverized coal flow pulsating flow Synergetic optimization of structural parameters and operating parameters in the process of separation; (3) the influence of physical difference on the separation process of powder gas flow; (4) numerical simulation based on the separation process of gas-solid coupling; (5) continuous separation test of pulverized coal with variable diameter pulsating flow. The main contents and important conclusions are as follows: (1) using the wave theory, the linear resistance is established. The wave transfer equation of pulsating airflow under the condition of Nei condition is used to study the wave propagation mechanism of pulsating airflow: the pulsating velocity in the separator is synthesized by travelling waves along the flow direction and the moving direction of the countercurrent in the direction of flow. The amplitude of the pulsating velocity is mainly dependent on the damping coefficient and the velocity scaling coefficient of the variable diameter section. (2) the numerical model is based on the grid model theory. The resistance characteristics of the particles in the pulsating flow field are proposed. The empirical formula of the flow resistance coefficient of the particles in the pulsating flow field is established. The results show that the drag coefficient increases with the constant flow in the pulsating flow field. With the increase of the amplitude of the pulsating flow velocity, the resistance coefficient increases approximately linearly; the pulsating frequency has little influence on the drag coefficient. (3) through the particle transport. Dynamic equation of particle movement in pulsating flow field is established. The empirical formula of flow resistance coefficient of particle flow in pulsating flow field is adopted. The acceleration and deceleration effect of pulsating airflow on different density, particle size particles are calculated, and the strengthening separation mechanism of variable pulse kinetic gas flow separator is revealed, and the cycle of fluctuating air flow is revealed. The accumulation of different density particles can be strengthened with each other. (4) the influence of the gas distributor structure, the feeding position, the height of the cylinder and the structure of the variable diameter section on the separation effect of the powder gas flow is studied experimentally: the gas distributor discharging The larger the diameter of the mouth, the lower the separation density and the lowest possible deviation when the discharge mouth area is 16% of the bottom cross section of the separation column; the closer the distance between the feed position and the bottom discharge port, the lower the separation density, the better the separation effect of the feeding position in the variable diameter section; the higher the height of the feeding section, the higher the separation density, the smaller the possible deviation and the height of the straight tube section. After more than 0.75m, the change of separation density and possible deviation is not obvious; the larger the cone ratio of the variable diameter section, the smaller the separation density, the possibility of the variation with the cone ratio is not obvious. (5) the effects of the parameters of the main air volume, the impulse volume and the pulse period on the separation effect of the powder gas flow are studied in the experiment: the separation density and the possible deviation are all with the increase of the main air volume. With the increase of the pulse air volume, the separation density and possible deviation increased slightly; the pulse period extended, the separation density increased slightly and the possible deviation increased gradually. (6) the influence of the main air volume, the pulse wind volume, the pulse cycle, the cone ratio, the conical ratio and the possible deviation were studied by the response surface method, and the separation density and possible deviation were established. The results show that the influence of the main air volume on the separation density is extremely significant, the pulse cycle and the cone ratio have significant influence, and the influence of the pulse wind volume is not significant; the main air volume, the pulse cycle, the main air volume x cone ratio, the main air volume and the main air volume have extremely significant influence on the possible deviation, the pulse air volume has significant influence and the cone ratio is not significant. (7) base The co matching relation between the structural parameters and the operating parameters of the separator is studied on the separation density, the possible deviation and the quantitative correlation between the various factors. The results show that the small cone is more accurate than the structure sorting machine when the given separation density is low. When the given separation density is high, the separation precision of the large cone ratio structure is higher. (8) the actual separation precision is higher. The effect of density composition and particle size composition on the separation process of 6~3mm powder gas flow is studied. The results show that the density composition of coal sample has little influence on the separation effect of the powder gas flow, which has great influence on the classification effect, the particle size composition has great influence on the separation effect, and has little influence on the classification effect; the more coarse grain level, the lower the separation density and the high density. The more grade content is, the lower the grading granularity is, the distribution rate of a density grade should equal to the weighted sum of the corresponding density level distribution rate of each grain level, and the distribution rate of a grain level should be equal to the weighted sum of the corresponding grain level distribution rate of each density grade. (9) the relationship between the separation effect and the classification effect in the process of pulverized coal pulsating pulsating flow separation is investigated comprehensively. There is a positive correlation between the separation density and the grading granularity, the possible deviation of the separation and the main air volume is positive correlation, the possibility deviation of the classification and the main air volume have a negative correlation. (10) the method of coupling the DDPM and the DEM model, considering the collision between the solid volume fraction and the particle, is used to simulate the separation of the pulverized coal pulsating pulsation. The process.DDPM+DEM model is suitable for the simulation of the separation process under the conditions of different treatment and air volume. The DPM model is only suitable for the simulation of the separation process under the low conditions. (11) the numerical simulation results of the DDPM+DEM model show that the pressure drop in the separator varies with the pulsating flow, and the pressure drop is mainly along the range pressure before adding the particles. After adding the particles, the uniformity of the flow field is reduced, the pressure drop value increases sharply, and the higher the volume of the separator is, the more obvious the pressure drop increases. The pressure drop is mainly the pressure loss caused by the increase of the wind resistance by the addition of the discrete phase particles. (12) the effect of the operation system on the separation effect of the powder gas flow is studied by the numerical simulation method. The mathematical model of the separation density, the air volume and the processing quantity of the separator was established. (13) the continuous separation experiments were carried out on the 6~3mm, 3~1mm and 1~0mm particle grade pulverized coal. Under the same air volume, the amount of treatment increased, the separation density increased and the deviation increased; when the main air volume was 270 m3/h and the treatment amount was 200kg/h, the 6~1mm powder gas flow separation was highly efficient. Up to 91.02%.
【学位授予单位】：中国矿业大学(北京)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TD94

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