Disturbance rejection of dead-time processes using disturbance observer and model predictive control

This article mainly focuses on disturbance rejection of dead-time processes by integrating a modified disturbance observer (MDOB) with a model predictive controller (MPC). The effect caused by model mismatches is regarded as a part of the lumped disturbances. This means that the disturbances considered here include not only external disturbances, but also internal disturbances caused by model mismatches. Control structure of the proposed method includes two parts which can be designed separately. The MPC which acts as a prefilter, is employed to generate appropriate control actions such that a desired setpoint tracking response is achieved. The MDOB is employed to estimate the disturbances of the closed-loop system, and the estimation is used for feedforward compensation design to reject disturbances. Rigorous analysis of setpoint tracking and disturbance rejection properties of the closed-loop system are given in the presence of both model mismatches and external disturbances. The proposed scheme is applied to control the temperature of a simplified jacketed stirred tank heater (JSTH). Simulation results demonstrate that the proposed method possesses a better disturbance rejection performance than those of the MDOB-PI, MPC and PI methods in controlling such dead-time processes.     

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.     

立磨终粉磨与辊压机联合粉磨的工艺比较

选取两个设计产量相同、主机装机功率相近、水泥性能稳定且均已稳定生产的立磨终粉磨和辊压机联合粉磨车间,对其工艺配置和主要经济技术指标以及水泥产品的粒度分布和物理性能进行了对比和分析。结果表明,立磨终粉磨相比辊压机联合粉磨,工艺流程更简单、占地面积更小,单位粉磨电耗和金属磨耗更低,更能发挥节能、低耗、高产的特点。     

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.     

Open and closed circuit dry grinding of cement mill rejects in a pilot scale vertical stirred mill

In this study, separator rejects of a closed circuit cement tube milling were dry ground in a 10-l pilot scale vertical stirred mill. Tests were done as open and closed circuit. The results were evaluated by size distributions, Blaine surface area of the products and the specific energy consumed during the tests. Mill capacity and the stirring speeds were the investigated parameters for the open circuit tests, whereas closed circuit tests were carried out at a constant stirring speed but variable discharge rate. Five speed levels used in the open circuit grinding tests are 200, 400, 600, 800 and 1000 rpm. The capacities were determined to obtain product Blaine surface areas in the limits between 2000 and 5000 cm²/g. Closed circuit tests have resulted in 87%, 182% and 452% circulating loads.     

生产水煤浆用新型超细搅拌球磨机的研究

介绍一种新型超细搅拌球磨机,用于磨制生产水煤浆用超细煤粉;分析了该机的结构特点、工作原理、性能特点以及磨矿介质粒径的选取等;论述了磨机各组成部分的技术特点。     

广义磨在硫磺粉磨中的应用

对硫磺的性质及广义磨结构和原理进行了分析，探讨了广义磨在硫磺粉磨中的应用。     

An optimal filter based MPC for systems with arbitrary disturbances

In this study, a linear model predictive control (MPC) approach with optimal filters is proposed for handling unmeasured disturbances with arbitrary statistics. Two types of optimal filters are introduced into the framework of MPC to relax the assumption of integrated white noise model in existing approaches. The introduced filters are globally optimal for linear systems with unmeasured disturbances that have unknown statistics. This enables the proposed MPC to better handle disturbances without access to disturbance statistics. As a result, the effort required for disturbance modeling can be alleviated. The proposed MPC can achieve offset-free control in the presence of asymptotically constant unmeasured disturbances. Simulation results demonstrate that the proposed approach can provide an improved disturbance õrejection performance over conventional approaches when applied to the control of systems with unmeasured disturbances that have arbitrary statistics.     

Steady state inferential modeling of temperature and pressure in an air-swept coal pulverizing ball mill

Mill discharge temperature and differential pressure have a strong effect on efficiency and safety of a coal fired power plant. Therefore, it is imperative that they are closely monitored and controlled during mill operation to keep their levels within a predetermined safe and efficient operating range regardless of the rate at which the raw coal is fed to the mill. One way to achieve this is through a control schedule that compares the value obtained from the process to the stored set-point value to determine if there is any deviation that requires correction. This paper describes a steady state model that could be used alongside conventional controllers as an on-line shadow that provides inferential estimates of desired temperatures and pressure drops in the mill circuit which can be continuously compared with the actual values for adjustment. This would not only help to avoid the difficulties associated with direct measurement but also provide a means for early detection of drifts and failing sensors and serve as a temporal back-up for the out-of-order sensors. The model was tested using industrial data collected from four ball mills at a coal fired power plant in South Africa and the results show a reasonable agreement between the measured data and model predictions both qualitatively and quantitatively within a 5% error margin. The model outputs were found to be highly sensitive to the variation in mill loading, the primary air (PA) flow and the mill channel dimensions. Therefore, for validity of this model, accurate determination of all significant parameters is essential. For now, the model is only valid for the ball mills involved in the current study, but with availability of data it can be reproduced elsewhere.     

MLS4531立式辊磨机的开发与研制

大型MLS4531立式辊磨机的开发研制和首次成功应用于5000t/d级生产线，这是我国水泥工业装备技术的重大突破，文中详细介绍了其主要技术开发内容，结构，原理和主要技术特点。另外，对MLS4531立式辊磨机在首次使用中出现的问题和改进措施也作了简要介绍。     

从生产实践探讨挤压联合粉磨系统的设计优化

通过对ZD、DW公司2套4条水泥挤压联合粉磨生产线的技术经济指标进行对比,从系统的提产效率、运行稳定性和成品质量等多个角度分析了不同工艺线各自的优劣所在。生产实践表明,根据产品品种选择粉磨工艺路线能有效提高系统效率。同时还探讨了对系统进行其他设计优化的可能。     

对角CARIMA模型抗扰约束广义预测控制

针对存在输入和输入增量约束的多变量系统,提出了一种基于变权重的对角CARIMA模型抗扰动约束广义预测控制算法。根据对角CARIMA模型中的A和C矩阵为对角形式的特点,将多输入多输出系统分解为多个多输入单输出系统进行预测和控制,简化了控制器的设计,降低了变量之间的耦合性。根据模型预测值与参考轨迹之间的偏差实时调整目标函数中各输出跟踪误差的权重,达到抑制由耦合而造成回路之间扰动的目的。权重调整的基本原则是,每个输出的预测值跟踪参考轨迹的权重由其他输出在同时刻偏离其参考轨迹的误差平方加权和构成。当某个输出偏离其目标值时,其他输出的控制作用相对增强,避免输出之间的相互扰动,达到抑制扰动的目的。同时,分析了系统输入和输入增量约束的表达形式。利用多变量广义预测控制（MGPC）以及提出的扰动抑制方法,分别对Shell重油分馏问题进行了仿真实验,仿真结果验证了算法的有效性。     

立式磨在苏丹BERBER项目水泥粉磨系统的应用

在新型干法水泥生产线的设计中,国内水泥粉磨系统基本上采用单独球磨机或者球磨机加辊压机系统,球磨机虽然可靠,但能耗相对较大。苏丹BERBER项目水泥粉磨系统的设计采用了立式磨粉磨水泥的方案,重点介绍该系统的特点、工艺流程等,对今后辊磨的发展,认识及设计应用均有帮助。     

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.     

Analysis of ball movement for research of grinding mechanism of a stirred ball mill with 3D discrete element method

A simulation of the three-dimensional motion of grinding media in the stirred media mill for the research of grinding mechanism has been carried out by 3-dimensional discrete element method (DEM). The movement of ball assemblies was graphically displayed with some snapshots from start of the milling to 0.20 s. From these simulation results, the grinding zone in the mill was confirmed to be distributed into two regions, which is near the stirrer and the side wall of mill around the stirrer. The power changing the rotation speed of stirrer was examined based on the micro interactive forces at all the contact points between ball-to-ball and between ball-to-stirrer. DEM is a very powerful tool for the microanalysis of movement of balls, which could not have been solved by a conventional experimental method.     

利用立磨粉磨高湿原料的理论与实践

通常认为立磨对水分适中的原料有较强的适应性。安徽省皖维高新材料股份有限公司水泥分厂1000t/d预热预分解窑生产线,因采用该公司化工生产废渣——电石渣配料生产,其原料综合水分高达13%￣15%。在该线的高湿原料粉磨系统设计中,采用了MLS2619立磨方案。实践证明,采用立磨方案粉磨高湿原料是完全可行的。     

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.     

MLN型熟料立磨的技术特点及粉磨矿渣水泥的效果

在水泥生产过程中,立磨主要被用于粉磨水泥生料和矿渣,在水泥终粉磨方面的应用尚未普及。从熟料立磨的技术特点出发,结合实际生产中立磨代替传统球磨机进行水泥终粉磨时的产品特性和经济效益,论证了以立磨系统取代球磨系统进行水泥生产的可行性。     

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。