基于POS-BP的磨矿过程磨机负荷智能分析方法研究

主要针对有色金属行业选矿厂的磨矿过程半自磨机、球磨机等磨矿设备的负荷进行分析,利用OPC技术,通过计算机实现对磨矿过程的实时工艺数据的采集、处理、分析存储,利用POS-BP算法构建磨机功率软测量模型,从而实现对磨机功率的在线预测分析,之后结合案例分析技术,实现对磨机负荷的智能在线分析,能够有效地减少磨机涨肚次数,提高磨机处理量以及磨矿粒度合格率,降低衬板和钢球损耗,并且预测值可以为磨矿过程的优化控制、专家控制等先进控制提供有效的参数依据,从多方面提高磨矿过程乃至整个选矿过程的运行效率,从根本上提高矿山企业经济效益。     

Spreadsheet-based modeling of liner wear impact on charge motion in tumbling mills

Grinding remains the major constituent of the total cost of processing minerals in most applications. Charge motion is one of the key parameters affecting grinding efficiency and mill power draw. Although there have been numerous investigations on the effect of liner design on charge motion, the effect of charge profile due to liner wear during mill operation along the mill length has not received much attention. In this research, Powell’s analytical approach to calculate the charge trajectory with respect to the liner profile was used to develop a software based on Microsoft Excel© . As a case study, the liner wear profile of the Sarcheshmeh copper complex SAG mill was used to model the liner wear rate and calculate the changes of lifter face angle and lifter height during mill operation. Results were then used to determine charge motion in the SAG mill at any given operation time. The results indicated that after 4000 h of operation the lifters face angle increased from 14° to 47.1° and the height of lifters decreased from 15.2 to 5.8 cm. Modeling charge motion in the mill after 3000 h of operation showed 34° difference between the maximum and minimum of angles of impact along the mill length due to the nonuniform wear profile. It was also found that the variation in the pattern of the charge motion depends on the mill working hours and the distance of the desired point from the feed end. It was determined that the ratio of spacing to the height of lifters (S/H) plays an important role in the grinding efficiency and throughput. After 4000 h of operation, S/H ratio of the Sarcheshmeh SAG mill increased from 1.7 to 4.6.     

应用专家PID实现某矿山半自磨机的控制

为了解决国内某矿山[?]8.8 m×4.8 m型半自磨机的自动控制问题，采用专家PID控制系统进行了系统控制设计研究。结果表明：①影响半自磨机工作状况的因素较多，主要包括矿石性质、磨矿介质、给矿速率、磨矿浓度、衬板和格子板的状态等；物料充填状态可通过半自磨机的功率、轴压和磨音来判断，而料位状态控制可通过调节给矿量、给水量、加球量实现。②专家PID算法与传统PID的算法有明显的优势，其本质上是采用非线性设计手段，将专家经验引入控制策略的制定中，更适合复杂对象控制策略的实施，较好地克服常规PID对非线性系统适应性差、难以克服异常扰动以及对滞后时间常数难以确定等缺点。③在充分考虑了半自磨机工作特点的基础上，设计的专家PID控制系统可将半自磨机的轴压、功率稳定在设定值范围内，同时能根据半自磨机给矿量、给水量、顽石量、磨音等参数的综合分析，判断出半自磨机处于较为稳定的工作状态。     

Comparison of open and closed circuit HPGR application on dry grinding circuit performance

A conventional cement grinding circuit is composed of a two compartment tube mill, a mill filter which collects the fine material inside the mill and a dynamic air separator where final product with required fineness is collected. In general the material fed to the circuit has a top size of 50 mm which is very coarse for the ball mill. For this purpose, later in 1980s, high pressure grinding rolls (HPGR) has found applications as a pregrinder which increased throughput of the grinding circuit at the same fineness.In early applications, HPGR was operated in open circuit. But later as the operating principle of the equipment based on the compression, some portion of the HPGR discharge recycled back to improve efficiency of the mill or operated closed circuit with classifiers. Within this study effect of open and closed circuit HPGR applications on dry grinding circuit performance was examined. For this purpose sampling studies around three different cement grinding circuit were completed. In the first study, a circuit including open circuit HPGR, ball mill and air separator was sampled and chosen as the basic condition. As the final product size distribution is important for grinding circuit, model structure of each equipment was developed. The second and third surveys were carried out around closed circuit HPGR operation with V and VSK separator to develop models for the separators. Finally the separator models were used in basic condition to simulate closed circuit HPGR application.It was understood from the studies that closed circuit HPGR operation improved the overall circuit efficiency at the same final product fineness by reducing the specific energy consumption.     

Computational prediction of performance for a full scale Isamill: Part 2 – Wet models of charge and slurry transport

The Isamill is a horizontal stirred media mill used for fine and ultrafine grinding of slurry transported rock particles. The charge motion is analysed using two different approaches, (1) a fluid only model, and (2) a 1-way coupled DEM + SPH model. The flow pattern when the classifier is closed is regular with a pair of oppositely oriented vortices between each pair of grinding discs. A strong radial outflow from the middle of the classifier is generated by the high centrifugal force which creates a pair of toroidal vortices at the discharge end of the mill. The classifier, when open, acts as a pump drawing slurry axially along the mill. It enters the classifier through the holes in its end plate and is then forced radially outward by rotational acceleration of the classifier cage. The enhanced outflow significantly strengthens the large toroidal vortices on the outside of the classifier. This produces a strong retrograde annular flow along the mill shell that penetrates a significant distance back into the grinding chamber. The effect of the classifier is significant and strongly influences the flow over much of the mill and controls slurry (feed and product) transport and discharge. The predictions of the different models are qualitatively similar but with important differences including the fluid only model predicting higher flow speeds because it cannot capture the strong slip between the media and the grinding discs. The strength of the axial transport is strongly dependent on the slurry viscosity. A critical viscosity can be identified above which there is insufficient axial transport to enable mill operation.     

Analysis of grinding media effect on specific breakage rate function of particles in a full-scale open circuit three-compartment cement ball mill

A full-scale three-compartment FLSmidth® cement grinding ball mill with dimensions of Ø3.5 × L10 operating in open circuit was sampled to analyse the grinding media effect on specific breakage rate function of particles. Size reduction performance of the ball mill was evaluated with respect to the applied grinding media size. Samples from the circuit and inside the mill were collected. Mass balance of the circuit was done using JKSimMet Steady State Mineral Processing Simulator. Specific discharge and breakage rate functions of particles were estimated using perfect mixing modeling approach (Whiten, 1972) on the basis of the proposed open circuit three-compartment ball mill model structure (Genç and Benzer, 2015). Maximum specific breakage rate was related to maximum grinding media size in the grinding compartments. An exponential correlation was found to exist between maximum grinding media size and maximum specific breakage rate. Relationship between maximum grinding media size and maximum particle size was also fitted to an exponential function. Findings indicated that, grinding performance of cylpebs applied in the third compartment did not improved the size reduction performance as compared to the grinding performance of the first and second compartment.     

Modeling breakage rates in mills with impact energy spectra and ultra fast load cell data

A new era in modeling particle size distribution in grinding mills started at the beginning of 2000s. A direct estimation of breakage parameters became possible via computation of collision energy by discrete element method (DEM) and material breakage data.The material breakage data can be obtained for primary modes of breakage. In this study, impact and abrasion are assumed to be the primary modes of particle breakage, which are readily studied in the laboratory. The impact breakage mode is studied in a drop-weight apparatus and in a specialized device known as the ultra fast load cell. The abrasion mode of breakage is studied in a laboratory scale ball mill. Next, the particle breakage versus energy data is converted into breakage rates via impact energy spectra of the grinding mill computed by a DEM code. The fundamental material breakage information is converted into energy based breakage distribution function.The verification of the modeling concepts is shown for a 90 cm laboratory scale ball mill. In the batch mill, approximately a 10 kg mass of limestone in the 30 mm size is ground with around 100 kg of 50 mm steel ball charge. The breakage rate and the breakage distribution functions constitute the parameters of the energy based batch population balance model. It is shown that accurate particle size distribution predictions are possible with this modeling approach for different grinding regimes.     

Plant concepts for ultrafine dry grinding with the agitated media mill MaxxMill®

The agitated media mill MaxxMill^® has successfully been used for several years by a number of customers worldwide in mono-product and multi-product production plants for the fine and ultrafine dry grinding of mineral raw materials. The special construction principle of the MaxxMill^® featuring a rotating grinding chamber and one or several eccentrically positioned agitators in combination with a static hollow flow deflector, allows, apart from effective grinding, also unproblematic material supply and material removal from the mill, without requiring additional equipment for handling the grinding media. The mill is usually operated in connection with dynamic air classifiers from different manufacturers, so that the desired maximum particle size can be accurately adjusted down to 97% < 3 μm. Depending on the grinding task, different air classifiers are selected, which are used with different plant concepts, i.e. in open and closed grinding circuits and with or without pre-classification of pre-ground raw materials. Thus the MaxxMill^® concept allows energy-efficient and cost effective production of fine and ultrafine products, yielding a throughput rate of up to several tons per hour.     

An analysis of the energy split for grinding coal/calcite mixture in a ball-and-race mill

Interactions among components in the heterogeneous grinding would change energy consumed characteristics of components if compared with those in the single-component breakage. In this paper, energy split phenomenon for the coarse grinding of super clean anthracite coal (SCAC)/calcite mixture of 2.8–2 mm in the ball-and-race mill is investigated. Before the analysis of experimental results, accuracy of energy split function in terms of time-dependent breakage rate is first discussed. Energy consumed characteristics of grinding in the ball mill and ball-and-race mill are also compared. Breakage model of product t₁₀ (yield of progenies in −0.237 mm) vs specific energy is used to describe the energy-size reduction of the single-component and multi-component grinding. Interaction between components is reflected by the comparison of specific energy of components in mixture and single breakage to yield the same product t₁₀. Based on the energy balance, energy split factors of components in different time and mixed conditions are first determined. This parameter shows no change with time. Calcite increases the grinding efficiency of SCAC significantly, with the energy split factor for SCAC ranging from 0.68 to 0.73, which means less specific energy is consumed by SCAC to yield the same t₁₀ if compared with the single breakage. As the volumetric ratio of calcite increases in mixture, grinding energy efficiency decreases and energy split factor of calcite increases from 1.70 to 1.83. Soft material reduces the grinding energy efficiency of hard one in the multi-component breakage.     

The effect of ball size on breakage rate parameter in a pilot scale ball mill

The objective of this study is to investigate the effect of ball size on grinding kinetics in a pilot scale ball mill. Six different ball media gradings were tested. Comparative tests were conducted in batch ball mill having 1.2 m diameter and 0.6 m length at constant operating condition of mill such as media mass, mill speed and input specific energy. Feed samples were ground batchwise and representative sample was taken from inside the mill for each determined grinding period. Grinding process in ball mill was modeled and the specific rate of breakage was calculated for the each test. The results indicated that the relationship between different breakage rate and particle size has a maximum for each ball size distribution. Consequently, a new equation to correlate maximum ball size and particle size at maximum breakage occurs is proposed.     

Effects of grinding on the preg-robbing potential of quartz in an acidic chloride medium

The effect of high-energy milling on the surface properties of quartz is examined with regard to its preg-robbing behavior towards gold. A standard ring mill is used to process dry quartz samples, and the changes in the morphology of the particles, structural deformations and surface chemistry are investigated to explain the increased preg-robbing ability of quartz in acidic chloride solutions. The transition from fine grinding to mechanochemical activation of quartz can be observed from changes in the morphology of the particles, as well as the types of structural deformations. The transition occurs between 1 and 5 min of grinding in the mill used, corresponding to particle sizes around 0.55 μm. Structural studies differentiate two stages of fine grinding: particle breakage with limited structural disruption, and structural disturbance by mechanochemical alteration, which occurs after particles reach their grinding limits. Quartz keeps its structural order to some degree even after 30 min of aggressive grinding. The surface chemistry of ground quartz demonstrates generation of point defects including low valence silicon and non-bridging oxygen centers. These defect sites play an important role in the surface reactivity of the quartz, and influence the extent of gold loss during preg-robbing.     

Effects of operating parameters on the efficiency of dry stirred milling

Stirred media milling is an industrially accepted efficient grinding method for fine and coarse particles. The stirred mills can be operated both in vertical and horizontal configurations and the selection depending on the process variables. Successful operation of horizontal stirred milling (i.e. IsaMill) in wet applications encouraged the studies in dry applications. In this study, series of dry grinding tests were performed in a prototype horizontal stirred mill (42 L) to investigate the effects of operating parameters such as stirrer speed, feed rate, media filling and ball size on grinding considering the degree of size reduction and the energy consumption. The test results have shown that the stirrer speed, the media size and the media filling are directly proportional and the feed rate is inversely proportional with the specific energy consumption. Besides, energy savings up to 27% were achieved by adjusting the milling conditions properly (suitable media size) and the size reduction values (F₅₀/P₅₀) were between 1.05 and 2.42.     

Modeling the contribution of specific grinding pressure for the calculation of HPGR product size distribution

Vale, one of the largest mining companies in the world, has prioritized the development of HPGR technology for practical application in its current projects. An existing model for the HPGR, capable of predicting product size distributions, has been evaluated under distinct grinding conditions for one feed material. The effect of grinding pressure and feed size distribution were investigated. The model response showed a clear dependency of product size distribution with specific grinding pressure. As a result, specific grinding pressure was incorporated into the model, allowing for predicting product size distribution at practical values of this important process parameter. Based on this result, a characterization procedure was envisaged so as to produce parameters for the model. The procedure does not require complex experimental procedures, and all of the testing can be carried out in an expedited form in an instrumented bench-scale HPGR, using small samples of about 10 kg. The only analyses required are size distributions. The model was implemented in the Modsim? plant-wide simulator, with facilities to predict product size distribution for any roll diameter, length and speed of an HPGR machine.     

基于PLC的半自磨机介质取运自动控制系统设计

摘要:针对某选矿厂半自磨机的人工作业加球的问题,提出采用工业机器人对介质钢球进行自动取运的方案并设计了一套基于西门子S7-200 SMART CPUSR30 PLC的自动化取运钢球控制系统,完成对加球过程的自动化控制。整个控制系统以PLC控制模块为核心与各个模块进行相连,完成半自磨机自动加取钢球的过程,最后将运行结果信息显示在触摸屏上,实现对自动加球过程的实时监测。实验结果表明,该控制系统可以较好的完成半自磨机自动加球的作业过程,与人工操作电磁铁取球相比稳定性高,介质填充率保持相对稳定,磨矿质量得到提升。     

Value adding limestone to filler grade through an ultra-fine grinding process in jet mill for use in plastic industries

In this study, ultra-fine grinding of limestone was carried out in jet mill using four levels of classifier rotational speed and grinding pressure. The holdup amount was determined during the grinding process, while the feed rate was kept constant at 8 kg/h. The ground product was characterized for its particle size and shape. In addition, the mechanochemical effect on the ground product was characterized through XRD. The particles size of the ground product ranged from 2.21 μm to 7.29 μm, demonstrating various particle shapes such as cubical, angular, and elongated. The degree of crystallinity of the ground product ranged from 54.5% to 93.7%. Afterwards, the ground product was incorporated as filler in polypropylene (PP), and its performance was characterized for mechanical properties. After conducting the test work, we find that the PP filled with ground limestone exhibited excellent thermal and mechanical properties. The composite flexural modulus, impact strength, tensile strength, and elongation at break were 2.1 GPa, 42 kJ/m², 22.75 MPa, and 21%, respectively, when loaded up to 20%. It likewise exhibited CTE value of 57.2 ppm/°C.     

The effects of chamber diameter and stirrer design on dry horizontal stirred mill performance

This paper focussed on investigating the effects of chamber diameter and stirrer design on cement grinding performance of a horizontal type dry stirred mill. Within the scope, pilot scale test works were undertaken with two different chamber diameters (20.4 cm and 26.4 cm) having the same length and three different stirrer designs (wing, cross and disc) having the same diameter (16 cm). The chamber diameter tests were performed at the same stirrer design, media size and media filling. The studies concluded that, the use of larger chamber improved the grinding efficiency since 31.8% and 35.8% less energy was consumed than the smaller mill at the RR_d50 of 1.41 and 1.66 respectively. This behaviour of the larger mill can be attributed to the increased gap distance between the chamber wall and stirrer edge. With regards to stirrer design, the statistical evaluations, grinding results and temperature measurements all indicated that the disc design of stirrer ground the particles more effectively at high energy levels (>40 kW h/t). The use of the disc design reduced the energy consumption by 21% (at RR_d50 of 3.5). This was attributed to dissipation of energy as heat since the temperature measured for the wing and cross types were higher than the disc type.     

Comparison of energy efficiency between ball mills and stirred mills in coarse grinding

Stirred mills are primarily used for fine and ultra-fine grinding. They dominate these grinding applications because greater stress intensity can be delivered in stirred mills and they can achieve better energy efficiency than ball mills in fine and ultra-fine grinding. Investigations were conducted on whether the greater performance of stirred mills over ball mills in fine grinding can be extended to coarse grinding applications. Four different laboratory ball mills and stirred mills have been tested to grind seven ore samples with feed sizes ranging from 3.35 mm to 150 μm. A case study on full scale operations of a 2.6 MW IsaMill replacing the existing 4 MW regrind ball mill at Kumtor Gold Mine in Kyrgyzstan is also included. This paper summarizes the major findings from these investigations.     

Effect of grinding parameters on the rheology of pyrite–heptane slurry in a laboratory stirred media mill

The influences of wet ultra-fine grinding parameters on the rheological behavior of pyrite–heptane slurry in a laboratory stirred media mill were investigated with solid concentration, dispersant dosage, grinding time and carbon numbers of organic acid as dispersant. The results reveal that when the solids concentration is increased from 64 wt% to 79 wt%, the rheological behavior of slurry with 1 wt% of stearic acid transforms from Bingham characteristic to the pseudoplastic one with a yield stress. The Casson model fits well for the experimental data. And the apparent viscosity of the pyrite–heptane slurry increases exponentially with increase solid concentration at a given shear rate. The increase of viscosity is propitious to reduce the particle size of pyrite. When the solid concentration is 64 wt%, stearic acid is superior to octadecanol for the reduction of the slurry viscosity, and the slurry with 1 wt% of stearic acid possesses the best flowability. The extrapolated Bingham yield stress with dispersant almost stays constant when the dosage is over 2 wt%. Besides, the rheological behavior and particle size are also related to the grinding time and carbon numbers of organic acids as dispersant.     

Effects of slurry filling and mill speed on the net power draw of a tumbling ball mill

The pool of slurry is known to lower the power drawn to the mill. An attempt to ascertain this observation by relating load orientation to mill power for a range of speeds and slurry fillings was undertaken.To this end, a Platinum ore (−850 μm) was used to prepare a slurry at 65% solids concentration by mass. The Wits pilot mill (552 × 400 mm), initially loaded with 10 mm balls at 20% volumetric filling, was run at 5 different speeds between 65% and 85% of critical. The net power draw and media charge position were measured. After this, the slurried ore was gradually added to the media charge for slurry filling U between 0 and 3. A proximity probe and a conductivity sensor mounted on the mill shell provided a means of measuring both the position of the media charge and that of slurry. The data collected for the load behaviour and net power draw was later analysed.It was found that Morrell’s model could not fully explain the effect of slurry volume on net power draw especially for an under-filled media charge (i.e., for U < 1). The size of lifters and grinding balls used could be the reason for this. That is why a piece-wise function was curve-fitted to the power data to help make sense of the inconsistencies observed.     

一种半自磨机智能控制技术

半自磨机具有多变量、非线性、强耦合、大滞后、时变性等特征,且很多过程参数难以检测,难以通过常规控制方法实现自动控制。为此,乌山选矿厂以人工经验为基础,找出半自磨机工作时给矿量、磨音、功率、轴压、磨矿浓度、给矿粒度比例之间的关系,并用计算机语言表述出来,得到一种定性的智能控制系统。实践表明：这种半自磨机智能控制系统可根据服务器设定的控制策略,实时采集半自磨机过程参数,自动调整至最优的半自磨机运行状态,在乌山选矿厂应用后较原人工控制可以提高处理量24.7 t/h、延长衬板使用寿命11.1 d、降低吨矿能耗0.49 kWh/t,具有显著的经济效益,在金属矿山领域具有重要推广应用前景。