水射流粉碎技术在制备超精细煤浆中的应用.doc

作者姓名：崔龙连论文题目：水射流粉碎技术在制备超精细煤浆中的应用研究作者简介：崔龙连，男，1980年09月出生，2004年09月师从于中国矿业大学（北京）安里千教授，于2007年6月取得博士学位。中 文 摘 要能源是国民经济的基础产业，对国民经济的持续快速发展和人民生活的改善发挥着十分重要的促进与保证作用。我国拥有极其丰富的煤炭资源，煤炭在我国化石能源资源中所占比例高达95.5%。因此，在今后相当长的一段时间内，煤炭在我国一次能源结构中仍将处于主导地位。煤炭资源在为社会做出巨大贡献的同时，在其开采、加工、储运和使用的过程中，也产生了一系列环境污染问题，危害生态平衡和人类生存。为保证国民经济的可持续发展，必须提高煤炭的利用率，减少燃煤污染，发展洁净煤技术。洁净煤技术分为四个方面： 煤炭加工、 煤炭转化、 煤炭燃烧及后处理。水煤浆技术、煤炭液化和煤炭气化又是煤炭转化中最主要的途径。水射流粉碎技术始于二十世纪八十年代初，该技术最突出优点是粉碎能耗低。水射流粉碎技术的颗粒破碎机理不同于传统机械粉碎工艺。在水射流粉碎颗粒的过程中，高压水通过表面裂纹渗进颗粒内部的裂纹顶端，高压水的存在减小了裂纹扩展所需要的力，提高了颗粒的破碎效率。颗粒宏观上的破碎实际是颗粒内部微裂纹的生成、发育、扩展的最终结果。颗粒受其内部高压水穿渗过程中产生的张应力和冲击力共同作用导致颗粒破碎，其粉碎能耗要远低于传统的研磨工艺。高压水射流粉碎的另一个优点是：水射流粉碎技术具有良好的选择解离破碎性，即可使物料中的不同矿物组份在赋存粒度下有效解离。射流沿颗粒的裂隙和不同矿物组份界面的穿渗效应，使得水射流粉碎过程变成了一种高效的矿物分选过程。特别是颗粒有较大尺寸时，这种粉碎过程中分离不同组份的方法是传统粉碎工艺所无法比拟的。高压水射流粉碎煤的过程中，射流粉碎的分选和选择性解离破碎作用，可使粉碎后的细煤颗粒很容易实现煤中矿物质像黄铁矿、硅石及其它杂质的有效分离。上世纪70年代的石油危机给以石油为主要能源的西方各国带来很大冲击，人们纷纷研究以煤代油的策略。常规水煤浆是由70%左右的煤颗粒，30%左右的水及少量的化学添加剂组成，近似流体，可像油一样泵送、雾化、储存和稳定燃烧。为实现全面代油的目标，20世纪80年代，世界各国开展了可用于内燃机、燃气轮机燃烧的精细煤浆的研究。精细水煤浆也被称为第二代水煤浆，其含固体煤颗粒的平均粒径小于10m，黏度为300400 mPas，浓度约为50%，灰分低于1%，基本属于牛顿流体的煤水混合物。尽管代油煤浆在柴油机上燃烧具有低氮氧化物排放和经济性高等优势，但限制大规模工业应用的主要障碍有以下两方面：煤颗粒粉碎能耗过高、粉碎后细煤颗粒的分选效率低。煤的超细粉碎是制备精细水煤浆工艺中最为关键的一步。精细煤浆制备的全部工艺中（煤初级破碎、粉碎、细煤颗粒的分选以及制浆过程中的搅拌），煤颗粒的超细粉碎所消耗能量占制备工艺消耗总能量的85%以上。因此，降低超细粉碎的能耗对降低煤浆制备工艺的总能量消耗、提高精细煤浆的经济性具有极其重要的意义。结合水射流粉碎技术特点和目前超精细煤浆制备的工艺中存在的问题，提出了水射流粉碎技术制备超精细煤浆的新工艺。为证明水射流粉碎技术制备超精细煤浆的可行性、展示该新型制备工艺的优势，通过实验方法将新型制备工艺与传统球磨制备工艺进行了对比。研究了两种工艺制备细煤颗粒的性质，对比了两种细煤颗粒的浮选结果，比较了两种细煤颗粒所制备精细煤浆的性质，计算了两种工艺的粉碎能耗。设计了用于制备超精细煤浆的新型超细粉碎喷嘴，制备了平均粒径仅为3m，稳定性极高、表观黏度低、热值高且具有“剪切变稀”效应的超精细煤浆。这种超精细煤浆非常适合用于高速柴油机燃烧。从射流流场的基本理论出发，将红外测试技术用于射流流场的测试，结合数值模拟，得到了射流温度场与速度场的对应关系和射流的有效靶距，将研究结果用于优化射流粉碎机的靶距。通过单因素实验，优化后混合射流粉碎机的其它工艺参数。通过数值模研究了准直管内的流动状态，特别是其内部颗粒的运动规律。这些研究对提高射流粉碎机的粉碎效率、降低粉碎能耗以及新型超细粉碎喷嘴的设计都有着重要意义。水射流粉碎工艺与球磨粉碎工艺的比较。制备精细煤浆要求颗粒粒径小，平均粒径约为10m。在这种粒度下，颗粒的粒径对细煤颗粒的浮选是一个重要的影响因素。因此要比较两种工艺制备细煤颗粒的浮选效果，就必须确保两种粉碎工艺所制备细煤颗粒具有相同的粒度分布。为保证两种粉碎工艺得到的煤颗粒的粒度一致，采用的措施是先调节水力旋流器的给料压力、底流口直径等工艺参数，使溢流口收集到的颗粒的粒度分布满足制浆要求，然后再根据溢流颗粒的粒度确定球磨机的磨矿时间。以多个粒径作为参考尺寸，分别计算两种粉碎工艺的粉碎能耗。计算结果表明：煤的不同导致粉碎能耗存在一定差别，总体上水射流粉碎能耗要低于球磨工艺，水射流粉碎能耗仅为球磨工艺的35%55%。细煤颗粒有关性质的研究。这些性质都是对絮凝浮选和制备煤浆有着重要的影响，包括：矿物解离度、颗粒表面氧化程度和颗粒表面电动电位等。矿物解离度通过显微镜光度计测定。显微镜光度计的工作原理是根据不同矿物组分在显微镜下的颜色不同进行区分。通过对多个随机视域下的点分别统计单体与结合体的数目，最终计算出两种不同的粉碎工艺在相同粉碎粒度分布下的矿物解离度。实验结果表明在平均粒径为10m时，水射流粉碎后细煤颗粒的解离度为97，而球磨机的解离度为90。在计算解离度的同时结合SEM，研究了两种粉碎工艺制备细煤颗粒的形状。实验结果也反映出了水射流解离破碎的特点。通过红外光谱分析研究了两种粉碎工艺下细煤颗粒表面被氧化程度。通过原子吸收光谱分析了细煤颗粒中铁元素含量。实验结果表明：水射流粉碎后细煤颗粒中铁含量与原煤相比没有明显增加，而球磨粉碎后细煤颗粒中的铁含量比原煤中铁含量增大了4倍；这表明在球磨粉碎过程中有大量铁元素进入细煤中，也反映了球磨设备磨损严重。煤中因粉碎设备磨损造成的铁含量大幅下降，对减少大气污染中因燃煤产生的固体颗粒物有重要的意义。细煤颗粒的分选和制浆。细煤颗粒首先采用重力分选方法比较两种工艺制备细煤颗粒的可选性。由于本研究中所用细煤的粒径过细，故采用四氯化碳、苯及三溴甲烷根据密度要求配比制备成重液。小浮沉实验结果表明：水射流制备工艺的细煤颗粒可选性优于球磨工艺。这也表明水射流粉碎后细煤颗粒的解离效果好，更容易在高产率的情况下得到灰分更低的精煤。采用絮凝浮选的方法对细煤颗粒进行分选。絮凝实验中采用两组试剂：柴油、仲辛醇，正十二烷、仲辛醇。通过大同原煤的实验结果表明：水射流粉碎后细煤颗粒的分选效率提高了15%左右，能耗降低了约45%65%。造成差异的主要原因是由于水射流粉碎工艺与球磨工艺的粉碎机理不同。将粉碎后的两种细煤颗粒制备成精细水煤浆，比较两种精细水煤浆的性质。在相同的浓度下，水射流粉碎后制备的精细水煤浆与球磨工艺制备煤浆相比，其稳定性高、黏度低，同时煤浆具有“剪切变稀”效应。将两种工艺用于唐山赵各庄煤泥的粉碎、分选和制浆实验结果与大同煤的实验结果一致，即水射流制备工艺优于球磨工艺。这说明与传统的球磨制备工艺相比，水射流粉碎制备工艺具有明显的优势，利用该新工艺制备精细煤浆是可行的。超精细煤浆制备。根据红外测试结果和射流粉碎机理，设计了新型射流超细粉碎喷嘴，并将喷嘴用于超精细油煤浆的制备。经新型喷嘴粉碎后，细煤颗粒的平均粒径由10m降至3m。制备的超精细油煤浆具有极高的稳定性，70天沉淀后清澈层体积与煤浆总体积比小于1.6%；剪切速率小于200s-1时，表观黏度低于150 mPas。此外超精细煤浆还具有热值高和“剪切变稀”的效应，非常适合用于高速柴油上代油燃烧。关键词：红外测试；射流粉碎技术；浮选；制备；精细煤浆Study on the Application of Waterjet Comminution Technology to the Preparation of Ultra-clean Superfine Coal SlurryCui LonglianABSTRACTEnergy is the foundation of the national economy industries, which play a very important promotion and guarantee role in the national economys sustained and rapid development and improving peoples lives. China has extremely rich in coal resources, coal in Chinas fossil energy resources in the proportion as high as 95.5 percent. Therefore, in the future for a long period of time, coal in Chinas primary energy structure will remain the leading position. Coal resource makes a great contribution to society development; on the other hand, series pollutions are generated during their mining, processing, transportation and utilization, which influence on ecological balance and endanger the survival of mankind. To guarantee the sustainable development of the national economy, we must improve the utilization of coal, reduce coal-fired pollution, and develop clean coal technology. Clean Coal Technology is divided into four areas: coal processing, coal conversion, coal combustion and disposing after combustion. The most important approaches on coal conversion are coal water slurry technology, coal liquefaction and coal gasification.High pressure water jet comminution technology was developed in 1980s. The most prominent advantage of this comminution technology is low in energy consumption. The comminution mechanism of the water jet comminution technology is different from that of the traditional ball mill. In the process of water jet comminution, high-pressure water penetrates to the crack top through surface cracks, the presence of high-pressure water reduces the need to expand the cracks, and improve the efficiency of the particles broken. Particle fragmentation in macro is the final result of the internal micro-crack formation, development and expansion. Tensile stress generated from the penetration of high pressure water and the impact stress cause particle comminuting, and the energy consumption is much lower than the traditional abrasive process.Another advantage of water jet comminution technology is that water jet has a good selective dissociation broken. Hence, the different mineral components can be effective separated in their occurrence sizes. The water will extend the microcracks by hydraulic fracturing and differential compression due to the change in modulus, and thereby establish a separation of the two minerals. Because of the fluid penetration along the grain boundaries, a much better separation of the different components of the material was achieved, at a much larger particle size than has historically been the case. Such a beneficiation which can easily be translated into an efficient separation of pyrite, silica and other dirt from coal is brought about by the water jet ability to penetrate along preexisting microcracks on the individual particle boundaries.In 1970s, many counties began to find coal replacing oil products to deal with international oil crises resulted in oil price sharp increase. Traditional coal oil slurry composes with 70(wt.)% solids, 30% water and a small amount of additives, which can be pumped, storied, atomized and burned as oil. In 1980s, to replace oil burnt in high speed diesel engine and gas turbine, ultra-clean fine coal water slurry was developed. Fine coal water slurry is regard as the second generation coal water slurry. The mean diameter of coal particles is about 10m, and the ash content is less than 1%. The solids concentration is about 50% in weight, and the viscosity of fine coal slurry ranges 300400 mPas, the fluidity likes Newton fluid. The exhaust pollutant emissions, most notably NOx is reduced by 50% with the coal slurries. Along with this remarkable performance, over higher comminution energy consumption and lower yield of fine coal separation remains a major obstacle to the development of a coal fueled engine. Fine grinding process is a key step of the process for preparation ultra-clean fine coal water slurry. The energy consumption for fine grinding process is above 85% of the total energy consumption for the preparation fine coal slurry (coal primary crush, grinding, fine coal separation and agitation in mixing coal and water). Therefore, the reduction of the energy consumption in fine comminution is very important for reducing the total energy consumption in preparation, increasing the fine coal water slurry economical. Combined the advantages of water jet comminution with the problems existing in the preparation of ultra-fine coal slurries, a novel process for preparation of ultra-clean fine coal water slurry is resented in this dissertation. To prove the novel process feasibility and demonstrate its advantages, the novel process is compared with the traditional process based experiments. The fine coal particles properties obtained from the two processes are investigated; the flotation results of these fine coal particles and the properties of ultra-clean fine coal slurries are compared. The energy consumptions of the two processes are calculated. A novel superfine comminution nozzle is developed for preparation of ultra-clean superfine coal slurry. Ultra-clean superfine coal slurry has a high heat value, a high level of stability, and low viscosity. The mean diameter of coal particles in the slurry is about 2.5m. The slurry can be used as fuel in a high-speed diesel engine.Based on basic theoretical research of water jet flow, using infrared thermal imager to test the temperature field of high speed free water jet, the relationship between the temperature field distributions and velocity distribution are obtained, and the standoff of the water jet mill is optimized with the aid of theoretical analysis and numerical simulation. Others process parameters are also optimized in the case of single parameter test. Numerical simulation is employed to reveal the flow state such as velocity distribution, pressure distribution and particle trajectory in the mixing tube of the abrasive water jet mill, in particular the movement of abrasive particles in the mixing tubing, which is significant to improve comminution efficiency, reduce comminution energy and design novel comminution nozzle.For ultra-clean fine coal water slurry, the fine coal particle sizes are fine, and the mean diameter is about 10m. For fine particle with that size, the size of fine particle is a main influence factor on separation results. In order to compare the results of the froth floatation and sink-float separation obtained from the two different preparation processes, we had to control the fine coals having the same size for these two mills. According to the size of the fine coal particle obtained from the hydrocyclone, the milling time can be determined for the traditional process. Several reference sizes are used for calculation the energy consumption. The calculation results shows that despite the coal difference lead to the comminution energy in some differences, but the overall energy consumption of water jet process is lower than that of the ball mill by about 45%65%.Some properties which can effect on fine coal froth flotation and fine coal slurry preparation are investigated including degree of liberation, oxidation degree of fine coal surface and potential of coal particle surface. A MPV3 microscope photometer (LEITZ) with a VARIO-ORTHOMAT microscope photograph system was employed for analyzing the fine particle fracture characteristic and the degree of liberation under these two different grinding processes. The fine particles were deposited uniformly on a ceramic micro slide as a sample. Putting the sample on the stage of the microscope photometer, different components of coal and minerals show different colors. The numbers of the fine particles were counted with several random view field of the microscope photometer. The analysis of the results shows that the degree of liberation is higher for HPWJM than for the traditional ball mill at the same size distribution. At the same time, the shapes of two fine coal particles were studied with the help of SEM. The results demonstrate that the fracture easily occurs at the interface of coal and mineral phase in the case of HPWJM, and the fine coal particle natural shapes can be well kept with a higher degree of liberation, which are resulted from the high speed collision and the penetration capacity of the high speed water jet. Iron content tests were performed using a WFX-120 atomic absorption spectrophotometer (BRAIC) for the coal before and after comminuted by both mills. The analysis of the results shows that the iron content of the coal comminuted by the traditional ball mill is about 5 times more than the raw coal. For HPWJM, the iron content only increases marginally. It is obvious that the iron content is much higher for the coal samples comminuted by the ball mill than by HPWJM. The iron is mixed into the fine coal when the raw coal is ground by the ball mill due to the long-time repeated grinding. The lower iron content means lower equipment wears in the case of HPWJM. Iron content generated by the equipment wear is declined sharply, which has great significance in reducing solid particles caused by coal burning in air pollution.In this dissertation, two separation ways were used with froth flotation tests of the fine particles ground by both mills using 0# diesel oil and n-dodecane as collector, 2-octanol as frother, and sink-float separation tests using mixtures of carbon tetrachloride-benzene and carbon tetrachloride-bromoform as dense liquid. The separation efficiency of HPWJM is higher than that of the ball mill. It indicates that the liberation effect of the fine particles ground by HPWJM is better than the ball mill, and it is easy to recover clean coal from the fine coal particles with high yield and low ash content. The superior flotation performance of the fine coal comminuted by HPWJM is clearly seen with the substantial improvements about 15% in separation efficiency and combustible recovery. This phenomenon may attribute to the difference of the comminution mechanism of the processes. The ultra-clean fine coal slurries were prepared using the clean fine coal. Compared the two kind fine coal slurries, the results show that the viscosities of slurries containing fine coal obtained from water jet comminution process are lower than that of ball m