φ2200mm×4400mm风扫球磨机的使用

由于过磷酸钙装置生产能力由50 kt/a提高到200kt/a,φ22 2mm×4 400mm风扫球磨机磨粉负荷增大,磨机出现筒体变形和烧电机等问题.采取若干技改措施筒体厚增加4 mm;更换额定功率280 kW的电机;入磨矿块度从60 mm降为30 mm,入磨前矿石进行预干燥,使单台磨机磨粉能力满足了200kt/a过磷酸钙生产的需要.     

Constrained model predictive control in ball mill grinding process

Stable control of grinding process is of great importance for improvements of operation efficiency, the recovery of the valuable minerals, and significant reductions of production costs in concentration plants. Decoupled multi-loop PID controllers are usually carried out to manage to eliminate the effects of interactions among the control loops, but they generally become sluggish due to imperfect process models and a close control of the process is usually impossible in real practice. Based on its inherent decoupling scheme, model predictive control (MPC) is employed to handle such highly interacting system. For high quality requirements, a three-input three-output model of the grinding process is constructed. Constrained dynamic matrix control (DMC) is applied in an iron ore concentration plant, and operation of the process close to their optimum operating conditions is achieved. Some practical problems about the application of MPC in grinding process are presented and discussed in detail.     

Modeling and simulation of a fully air swept ball mill in a raw material grinding circuit

A raw material grinding circuit was modeled using plant data. Samples were collected from around the circuit and, following a crash stop, from inside the mill. The size distributions of the samples were determined down to a few microns. Using the data from inside the mill a modeling approach, based on perfect mixing, was developed. The modelling approach implicitly assumes that the mixture of feed materials broken is homogenous from the breakage point of view. The air classification around the circuit was modeled using the efficiency curve approach. In order to measure the success of the method the circuit performance was predicted by simulation studies while it was operating at different conditions. The results were then compared with the measured data. It is concluded that modeling gives a useful quantitative indication of what may occur in fully air swept mills.     

Effect of ball size and powder loading on the milling efficiency of a laboratory-scale wet ball mill

Alumina powder was wet-milled by zirconia balls with varying diameter at varying rotation speed, and the resultant particle size of the milled powder was analyzed. At a given rotation speed, there exists an optimum ball size to yield minimum particle size of alumina. The optimum ball diameter decreases as the rotation speed increases. This result has been interpreted in light of the competition between the reduced kinetic energy of the smaller balls (a negative source for milling efficiency) and the increased number of contact points of the smaller balls (a positive source), which yields the optimum ball diameter at an intermediate size. As the rotation speed increases, kinetic energy of the balls increases, which, in turn, shifts the optimum ball size toward a smaller value. As the powder loading increases from 1 to 35 g at a given rotation speed and ball size, the milling efficiency decreases monotonically.     

Disturbance rejection of ball mill grinding circuits using DOB and MPC

Ball mill grinding circuit is essentially a multivariable system with couplings, time delays and strong disturbances. Many advanced control schemes, including model predictive control (MPC), adaptive control, neuro-control, robust control, optimal control, etc., have been reported in the field of grinding process. However, these control schemes including the MPC scheme usually cannot achieve satisfying effects in the presence of strong disturbances. In this paper, disturbance observer (DOB), which is widely used in motion control applications, is introduced to estimate the disturbances in grinding circuit. A compound control scheme, consisting of a feedforward compensation part based on DOB and a feedback regulation part based on MPC (DOB-MPC), is thus developed. A rigorous analysis of disturbance rejection performance is given with the considerations of both model mismatches and external disturbances. Simulation results demonstrate that when controlling the ball mill grinding circuit, the DOB-MPC method possesses a better performance in disturbance rejection than that of the MPC method.     

CFD modeling of MPS coal mill with moisture evaporation

Coal pulverizers play an important role in the functioning and performance of a PC-fired boiler. The main functions of a pulverizer are crushing, drying and separating the fine coal particles toward combustion in the furnace. It is a common experience that mill outlet pipes have unequal coal flow in each pipe and contain some coarse particles. Unequal coal flow translates into unequal air-to-fuel ratio in the burner, deviating from the design value and thus increasing unburned carbon in fly ash, NO_x and CO. Coarser particles at the mill outlet originate from poor separation and decrease the unit efficiency. In addition, coarser particles reduce burner stability at low load. Air flow distribution at the mill throat, as well as inside the mill, significantly influences the mill performance in terms of separation, drying, coal/air flow uniformity at the mill outlet, wear patterns and mill safety. In the present work, a three-dimensional computational fluid dynamics (CFD) model of the MPS Roll Wheel pulverizer at Alliant Energy's Edgewater Unit 5 has been developed. The Eulerian-Lagrangian simulation approach in conjunction with the coal drying model in Fluent, a commercial CFD software package, has been used to conduct the simulation. Coal drying not only changes the primary air temperature but it also increases the primary air flow rate due to mass transfer from coal. Results of the simulation showed that a non-uniform airflow distribution near the throat contributes significantly to non-uniform air-coal flow at the outlet. It was shown that uniform velocity at the throat improves the air and coal flow distribution at the outlet pipes. A newly developed coal mill model provides a valuable tool that can be used to improve the pulverizer design and optimize unit operation. For example, reject coal rate, which is controlled by the air flow near the mill throat, can be reduced. The model can also be used to further aid in identifying and reducing high temperature or coal-rich areas where mill fires are most likely to start.     

钢球磨煤机钢球级配和补球优化试验研究

为降低钢球磨煤机制粉单耗和研究较佳的补球规律,针对某600 MW机组双进双出钢球磨进行了煤粉等速取样、钢球筛分以及补球优化的运行试验。结果表明:根据煤粉细度和均匀性指数可以推测出钢球级配的变化;补球应将钢球平均球径控制在初始平均球径附近,且补球时应先稳住大球级配,逐步适当提高小球级配;合理的级配可以使得相同工况下煤粉均匀性指数提高至0.8以上、制粉单耗平均下降近3 k Wh/t;得到了钢球磨损量与合理补球的信号。     

Experimental investigations and modelling of the ball motion in planetary ball mills

Planetary ball mills feature attractive properties, like the possibility of dry or wet operation, straightforward handling, cleanability and moderate costs. Consequently they are very well suited for lab scale process development in diverse industries, including pharmaceuticals and new materials. A number of questions still remain unanswered regarding this mill type. These include the stress conditions as well as transfer of the grinding results to other types of mills with free moving balls, such as stirred media mills, which can be built in large scales and operated continuously.In order to measure the ball motion and, thus, the stress conditions, a planetary ball mill was equipped with a high speed video camera, so that the grinding ball motion during the comminution process can be recorded and analysed. The influence of important process parameters on the ball motion pattern was assessed in this study, namely speed ratio, ball filling ratio and friction conditions, the latter by applying different mill feeds. The experimental results show considerable influences of the ball filling ratio and friction conditions. The measured ball motion patterns differ significantly from ball trajectories which were calculated using kinetic equations proposed in older publications.In addition to the measurements the ball motion was simulated using a three dimensional Discrete Element Model (DEM). An attempt was made to account for mill feed via altered friction coefficients. Correlations of the DEM results and experimental findings at different operating conditions show a good agreement. Based on simulation data the frequency distribution of the stress energies in the mill could be calculated and compared for different operating conditions.     

Ultra-fine grinding mechanism of inorganic powders in a stirred ball mill

An experimental investigation on grinding mechanism for calcite used in a stirred ball mill was carried out. The slurry concentration and the amount of grinding aids were chosen as main experimental factors of the grinding process. The effect of grinding aids on particle size distribution and grinding efficiency, defined as the increases of specific surface area per the specific grinding energy, was investigated. It was demonstrated that the grinding rate for calcite could be improved by addition of grinding aids. The grinding energy efficiency by adding a specific grinding aids was improved approximately 45.2% in comparison with and without grinding aids (n=700rpm, J=0.7, d_B= 1.0 mm, C_s=60wt%). This paper was presented at the ‘First Asian Particle Technology Symposium’ held at Bangkok between December 13 and 15, 2000.     

Co-combustion of pulverized coal and solid recovered fuel in an entrained flow reactor - General combustion and ash behaviour

Co-combustion of a bituminous coal and a solid recovered fuel (SRF) was carried out in an entrained flow reactor, and the influence of additives such as NaCl, PVC, ammonium sulphate, and kaolinite on co-combustion was investigated. The co-combustion experiments were carried out with SRF shares of 7.9 wt.%, 14.8 wt.% and 25 wt.%, respectively. The effect of additives was evaluated by maintaining the share of secondary fuel (mixture of SRF and additive) at 14.8 wt.%. The experimental results showed that the fuel burnout, NO and SO₂ emission in co-combustion of coal and SRF were decreased with increasing share of SRF. The majority of the additives inhibited the burnout, except for NaCl which seemed to have a promoting effect. The impact of additives on NO emission was mostly insignificant, except for ammonium sulphate which greatly reduced the NO emission. For SO₂ emission, it was found that all of the additives increased the S-retention in ash. Analysis of the bulk composition of fly ash from different experiments indicated that the majority of S and Cl in the fuels were released to gas phase during combustion, whereas the K and Na in the fuels were mainly retained in ash. When co-firing coal and SRF, approximately 99 wt.% of the K and Na in fly ash was present in water insoluble form such as aluminosilicates or silicates. The addition of NaCl, PVC, and ammonium sulphate generally promoted the vaporization of Na and K, resulting in an increased formation of water soluble alkalis such as alkali chlorides or sulphates. The vaporization degree of Na and K was found to be correlated during the experiments, suggesting an interaction between the vaporization of Na and K during pulverized fuel combustion. By collecting deposits on an air-cooled probe during the experiments, it was found that the ash deposition propensity in co-combustion was decreased with increasing share of SRF. The addition of NaCl and PVC significantly increased the ash deposition propensity, whereas the addition of ammonium sulphate or kaolinite showed a slight reducing effect. The chlorine content in the deposits generally implied a low corrosion potential during co-combustion of coal and SRF, except for the experiments with NaCl or PVC addition.     

立式煤磨系统燃爆原因分析及控制措施

立式煤磨系统的防燃爆直接关系到全线的安全稳定生产。在分析系统燃爆隐患(如细度小，大部分小于75μm；Vad高，一般都大于20％等)的基础上，提出了系列防燃爆措施：(1)控制入磨气体温度≤220～260℃，出磨气体温度≤65～75℃，袋除尘器气体温度高于露点；(2)控制系统内煤粉的沉降和粘附；(3)控制系统中产生火源或带明火；(4)进行系统工艺优化。     

球磨机研磨体级配设计与计算

球磨机研磨体合理的级配,对提高磨机产量和产品质量、降低粉磨电耗,具有重大的作用。在总结几百家水泥厂磨机工艺技术员工作经验的基础上,根据笔者长期从事物料粉磨研究和实践的心得体会,综合考虑研磨体总装载量、各仓填充率、平均球径、物料水分、物料流动性、物料粒度、隔仓板形式、隔仓板篦缝大小、各仓长度、粉磨流程等因素,详细介绍了球磨机研磨体级配计算的方法、原理和步骤,并编制成“球磨机研磨体级配及补球计算程序”软件。     

Empirical and scale-up modeling in stirred ball mills

Stirred ball mills are frequently used for ultrafine- and nanogrinding in food, pharmaceutical and chemical industry, but only few investigations have been published on empirical or scale-up modeling of stirred ball mills. Experiments have been carried out with a laboratory scale stirred ball mill. During the experiments the main technical parameters such as stirrer speed, grinding media, filling ratio, grinding time and the solid mass concentration have been systematically adjusted. The particle size distribution of mill products can be well estimated by empirical functions, so an empirical model has been prepared for the laboratory mill. The relation between the grinding fineness, grinding time and specific grinding work was represented for several materials such as pumice, andesite, limestone and tailings of ore mining industry. The power consumption of the stirred ball mill for scale-up was determined by a method based on the dimensional analysis. A new scale-up model has been presented as well by with industrial size stirred ball mills can be designed on the basis of the laboratory measurements.     

Steady state modeling and simulation of an industrial sugar continuous crystallizer

The profile of supersaturation along a continuous crystallizer of sugar factories, is the decisive factor that determines the performance of this apparatus. In order to control this profile, a mathematical model was developed taking into account the main physicochemical phenomena involved in crystallization process. The model is based on flow pattern, which was assumed and validated against plant measurements using a tracer test. The steady state mathematical model developed describes the most important aspects of the crystallizer behavior in each compartment: supersaturation, crystal size distribution and flow rate of the product crystals. The model can also describe the undesirable behavior such as dissolution and nucleation. Validation of the developed model was performed using industrial data. A parametric sensitivity study confirmed that the syrup supply distribution is the main variable that should be manipulated to achieve good performance for the crystallizer.     

Analysis of energy-size reduction relationships in batch tumbling ball mills

A theoretical energy-size reduction relationship is derived for tumbling ball mills based on a solution of the integro-differential equation of comminution kinetics, in which the proportional relationship is applied between the grinding rate constant and the net mill power. The derived formula is similar to an empirical energy law, dW ∝ dx_r/x_rⁱ, where W is the specific energy input, x_r is the particle size of product and the exponent i is shown to be a variable depending upon the ground material, the type of mill and the method to measure energy. Derived results are confirmed with reported data in reasonable agreement. Also, the Bond's energy law is examined and a method for the correction of the Bond work index is discussed.     

Hexagonal boron nitride nanosheets exfoliated by sodium hypochlorite ball mill and their potential application in catalysis

The unique physicochemical properties of two-dimensional (2D) h-BN and its promising applications in future optoelectronics have motivated an extensive study of its properties. However, a major limiting factor is its high quality and scalable preparation of few-layer h-BN. Herein, a facile, low cost, and high yield process is developed by using a sodium hypochlorite aqueous solution-assisted ball milling exfoliation process. The facile process results in scalable production of few-layer (2–4 sheets) h-BN from commercial BN powders, with little damage of its in-plane structure and high yield amounting to 21%. Furthermore, few-layer h-BN has been demonstrated to be good carrier to support and disperse Ag nanoparticles with high catalytic activity for the reduction of p-nitrophenol to p-aminophenol with NaBH₄. The pseudo-first-order reaction rate constant of the pre-prepared catalyst was calculated to be 7.13×10⁻³ s⁻¹, larger than that of pristine BN supported Ag nanoparticles. The results indicate that stable exfoliation process could open the way to a range of important applications of h-BN based materials.     

磷矿细碎溢流式球磨机运行缺陷及改进

磷酸车间的溢流式珠磨机是磷矿细碎的主要设备,分析球磨机运行中的缺陷,阐述了相应的改进措施和效果。改进后设备运行和生产指标达到了较好状态。     

MP型中速磨煤机在水泥厂的应用

MP型中速磨煤机属于外加力型辊盘式磨煤机，是集碾磨、干燥、选粉三项功能为一身，具有对煤种适应性强，结构性能先进、节省能耗等特点的新型制粉设备。     

工业煤粉锅炉煤粉制备中磨煤机的选型及发展

磨煤机是工业煤粉锅炉煤粉制备系统中的核心设备。我国煤炭种类的多样性决定了磨煤机类型的多样化,磨煤机的正确选型在煤粉制备系统中至关重要。详细介绍了低速、中速和高速三大类别中各类型磨煤机各自的发展历程、工作原理、结构特点以及优缺点,分析了各类型磨煤机对煤种的适用性,说明中速磨煤机最适宜应用于目前工业煤粉锅炉煤粉制备系统,指出随着工业煤粉锅炉的快速发展,磨煤机不仅要适应性强,粉磨效果好、产量高、质量硬,还要在降耗及环境方面有所突破。