Horizontal roller mill (Horomill) application versus hybrid HPGR/ball milling in finish grinding of cement

Industrial scale Horomill^® and hybrid HPGR/two-compartment ball mill applications at puzzolanic portland cement production were presented with emphasis on the general operational characteristics of the circuit configurations, size reduction and energy efficiencies of the Horomill^® and two-compartment ball mill grinding conditions. Horomill^® circuit configuration indicated to have advantages in terms of production of high strength cement as compared to Hybrid HPGR/two-compartment ball milling, depending on the classification performance of the separators influencing the circuit performance.     

Optimization of a fully air-swept dry grinding cement raw meal ball mill closed circuit capacity with the aid of simulation

Production capacity of a fully air-swept industrial scale two-compartment KHD Humboldt Wedag® cement ball mill was optimized with the aid of simulation. It was proposed to operate the mill as a single compartment by eliminating the pre-drying compartment. In this respect, grinding performance of the air-swept ball mill was evaluated and modelled as a perfectly mixed single tank using the perfect mixing ball mill modelling approach (Whiten, 1974). Static separator was modelled by efficiency curve model (Whiten, 1966). The empirical breakage function required in the estimation of average specific breakage rates was measured by drop-weight technique. The full scale model parameters were used to simulate the raw meal mill grinding circuit with the aid of JKSimMet Steady State Mineral Processing Simulator. Simulation results indicated 23% production capacity increase in cement throughput in case the pre-drying compartment was used in grinding.     

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.     

Investigation of the breakage of hard and soft components under high compression: HPGR application

In the cement industry, high pressure grinding rolls (HPGR) has been used since 1985. At the first applications, this equipment has been installed in the existing cement grinding circuits as an open circuit precrusher in order to crush clinker especially. The cement factories produce different type of cement by using basically clinker, gypsum and additives like limestone and trass. The additives generally are not precrushed before ball mill circuits.In this study, three different mixed feeds were prepared with clinker, gypsum, limestone and trass to evaluate the performance of an industrial scale open circuit HPGR. The results of the tests show that due to the stress concentrates on soft and fractured material, the performance of HPGR becomes worse when the relatively hard material (clinker) is fed together with soft and weak materials (i.e. gypsum, limestone, trass). In addition to the industrial tests, the piston die tests have been also performed with narrow size fractions of the mixed and unmixed materials.     

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.     

Analysis of specific discharge rate functions in industrial scale cement grinding multi-compartment ball mills to assist ball mill modeling

Specific discharge rates in industrial scale multi-compartment cement grinding ball mills were determined using industrial scale data to assist modeling of multi-compartment ball mills. Multi-compartment ball mill model structures were proposed to estimate normalized specific discharge rate functions. Multi-compartment mills were divided into perfectly mixed mill segments to describe material transport mechanism in the mill. Specific discharge rate functions were determined by using the estimated mill hold-up for perfectly mixed mill segments at the steady state condition of the cement grinding circuits. Estimated normalized discharge rate functions were found to be different than the basic pattern observed in semi-autogenous mills due to the differences in design and operational conditions of the mills. Coarse particle accumulation was found to have a significant effect on discharge rate function pattern. Estimated normalized discharge rate functions could be used in modeling of multi-compartment ball mills.     

Closed circuit ball mill – Basics revisited

Since the early days, there has been a general consensus within the industry and amongst grinding professionals that classification efficiency and circulating load both have a major effect on the efficiency of closed circuit ball mills. However, the effect of each is difficult to quantify in practice as these two parameters are usually interrelated. Based on experience acquired over the years and the investigative work conducted by F.C. Bond, it was established that the optimum circulating load for a closed ball mill – cyclone circuit is around 250%. This value is used as guideline for the design of new circuits as well as to assess the performance of existing circuits.The role of classification in milling appears to have been neglected in the current efforts to reduce the energy consumption of grinding. Two past approaches, experimental and modelling, for quantifying the effects of classification efficiency and circulating load on the capacity of closed ball mill circuits, are revisited and discussed in this paper. Application to the optimisation of existing circuits and design of new circuits is also discussed, with special attention to the development of more energy efficient circuits.     

破碎方式对邦铺钼铜矿石可磨性及钼浮选的影响

分别采用高压辊磨工艺和传统破碎工艺将西藏墨竹工卡县邦铺钼铜矿石破碎到-3.2 mm,分析了两种破碎产品的粒度特性,测定了两种破碎方式下矿石的 Bond球磨功指数,考察了两种破碎方式对后续球磨-钼浮选的影响。结果表明：高压辊磨产品比传统破碎产品细粒级含量多且粒度分布更均匀;高压辊磨产品在不同目标粒度下的Bond 球磨功指数比传统破碎产品至少降低9.05%;高压辊磨产品和传统破碎产品浮选钼的最佳磨矿细度分别为-0.074 mm占65%和75%,相应地,前者的Bond球磨功指数比后者降低10.87%,但浮钼回收率减少2.32个百分点。     

Optimisation of the secondary ball mill using an on-line ball and pulp load sensor – The Sensomag

The ball load and pulp load have a significant influence on the ball mill product size and production capacity. To improve the circuit performance at industrial scale these variables must be tweaked to levels where the plant can get grind and capacity benefits. In most grinding circuits the influence of these variables are not quantified because it is difficult to obtain precise measurements of the pulp load for an industrial scale mill and the conventional method of obtaining ball load measurements that involves crash stops is not attractive. A comprehensive investigation was performed on an industrial scale mill to quantify the effects of both ball and pulp load. A wide range of ball and pulp loads were tested and the findings are reported in this paper. The Sensomag, a sensor developed by Magotteaux, was used to obtain ball and pulp load measurements during the experimental work.     

Ball motion,axial segregation and power consumption in a full scale two chamber cement mill

Grinding of clinker for cement production is often performed in a two chamber ball mill. In the first shorter chamber, raw feed is ground using media consisting of large balls. The ground product of the first chamber exits through a discharge grate and enters the second longer chamber. Here smaller balls are used to grind the product material even finer. In this paper we analyse the charge motion, short term ball segregation processes and energy utilisation in a 4 m diameter cement ball mill using DEM. The power draw predicted is consistent with the rated power of the mill. The energy dissipation in the mill is dominated by shear interaction. The gentle liner profiles ensure that few balls move on cataracting trajectories. The distribution of energy utilisation between the different size media fractions is explored as are differences in the collisional environment between the two mill chambers.     

Investigating multicomponent breakage in cement grinding

The production of blended cements involves grinding raw materials such as cement clinker, pozzolan, blast furnace slag, limestone and gypsum, within the same mill. This is known as intergrinding. However, it is not possible to control the product fineness of each component separately in the multicomponent system and this results in overgrinding of relatively softer components. Since each component exhibits different breakage characteristics, the fineness of the components around the closed grinding circuit will vary depending on relative grindabilities and the overall fineness of the cement will then depend on the ratio of the components in the blend with different grindabilities. This paper aims to examine the size by mass distribution of each component around a closed circuit ball mill during cement production by intergrinding. For this purpose, a ball mill with an air classifier in a cement plant was sampled and size by assay analyses of the samples was carried out to calculate the particle size distribution of each component around the circuit. The results indicated that the size distributions of the components in each stream vary depending on their grindabilities and the final product comprises components with different fineness. The breakage rates of the components were calculated and it was seen that the breakage rates of the relatively softer components are higher than that of harder ones.     

球磨机在煤样制备中的应用

介绍了球磨机在煤样制备中的工作特性,阐明球磨机的设计、建模及工作原理,验证了球罐转速控制和钢球介质装入量对研磨效果的影响,并提出球磨机在煤样制备中的应用技巧。     

Experimental analysis of wet mill load based on vibration signals of laboratory-scale ball mill shell

Real-time measurement of the mill load is the key to improve the production capacity and energy efficiency for the grinding process. In this paper, experimental analysis of the wet mill load based on the vibration signals of the laboratory-scale ball mill shell is presented. A series of experiments are conducted to investigate the vibration characteristics corresponding to different grinding conditions such as dry grinding, wet grinding and water grinding. The power spectral density of the vibration signals is systematically interpreted.Experimental results show that the rheological properties of the pulp affect the amplitude and frequency of the vibration signal. The most important conclusion is that the frequency range of the shell vibration of the laboratory wet mill can be divided into three parts, namely natural frequency band, main impact frequency band and secondary impact frequency band. Finally, soft-sensor models between vibration signal and mill operating parameters of mill load are established using genetic algorithm-partial least square (GA-PLS) technology. After more work on industry scale ball mill is done, the soft-sensor modeling based on the mill shell vibration for operating parameters of mill load will improve the performance of the ball mill in the grinding process.     

罗河铁矿复合铁矿石高压辊磨工艺应用研究

为了解高压辊磨破碎对罗河铁矿选矿厂细碎产品可磨性的影响,对现场细碎产品进行了开路辊压破碎、边料返回闭路辊压破碎试验,边料返回闭路辊压破碎产品与现场细碎产品相对可磨度测定试验,样品和高压辊磨机边料返回闭路破碎产品球磨功指数测定试验,以及增设高压辊磨工艺后一段球磨扩能效果分析。结果表明：①高压辊磨作业可大幅度提高产品中细粒级含量,边料返回闭路破碎试验产品-3 mm粒级含量由辊磨前的56.73%提高至85.30%,提高28.57个百分点;-5 mm粒级含量由辊磨前的67.79%提高至92.65%,提高24.86个百分点;单位处理量为252 ts/（hm3）。②高压辊磨作业可显著改善入磨矿石的磨矿性能,当磨矿细度为-0.075 mm占60%时,与样品相比,高压辊磨机边料返回闭路破碎产品的相对可磨度为1.294;样品经高压辊磨破碎后,其球磨邦德功指数由16.15 kWh/t降至13.75 kWh/t,降幅为14.86%。③选矿厂增设高压辊磨边料返回超细碎作业后,由于入磨矿石可磨性的改善,一段球磨的产能可提高35.41%。     

精确化装补球技术在黄金氰化细磨球磨机中的研究

Absrtact: Overflow ball mill is a common equipment in fine grinding of gold cyanide. There are problems of high energy consumption and ball consumption in fine grinding ball mill of Jinqiling gold mine cyanide plant in Shandong province. In order to solve this problem, the fine grinding ball mill is studied by precise ball filling technology. Firstly, the mechanical properties of the ore are tested by the rock mechanics experimental system, and the preliminary pellet scheme is calculated accurately by using the semi-theoretical formula of the diameter of the ball of Duan, and a precise supplementary pellet scheme is proposed on the basis of these. The results show that compared with the original steel ball system, the processing capacity of the mill is increased by 1,915 tons and 179 tons, and the grinding fineness is increased by 3.88% and 1.78%, respectively, by using steel ball and short cylindrical cast iron as grinding media. When cast iron is used as grinding medium, the grinding fineness index is better than that of steel ball, but the ball consumption is higher. Therefore, accurate ball filling technology can effectively reduce the energy consumption of overflow ball mill in large gold cyanide plant, and has a good promotion value.     

Measurement system of the mill charge in grinding ball mill circuits

Investigation of a dry fine grinding circuit has shown significant influence of the mill load (powder filling) on the production capacity. To improve the circuit performance at industrial scale, alternative ways of mill load measurement were investigated. Detection of strain changes in the mill shell during mill rotation, by using a piezoelectric strain transducer, provided very interesting results, allowing evaluation of the weight of the mill charge and control of the powder filling to obtain an optimal level. Power draw has thus been increased by about 5% compared to the old configuration where mill motor power input was used to control the mill charge. By measuring mechanical vibration with the transducer, additional useful information has been obtained about the behavior of the cataracting and cascading balls inside the mill shell. Finally an important factor was simplicity and low investment cost of the total installation, as many fine grinding mills operate in relatively small circuits that do not warrant large investment for alternative measurement methods.     

不同破碎方式对鞍山式赤铁矿石磨矿特性的影响

高压辊磨破碎是基于料层粉碎的一种新型破碎方式,不仅本作业破碎效率高、能耗低、粉矿量大,而且破碎产品颗粒内部丰富的微裂纹也有利于后续磨矿作业节能。为了定量评价高压辊磨破碎对后续磨矿的影响,以鞍山式某赤铁矿石为试样,进行了磨矿技术效率和Bond球磨功指数试验。结果表明：由于高压辊磨产品中小于指定粒度（-0.074 mm）的物料产率明显较高,因而在较粗磨矿细度下,高压辊磨产品的磨矿技术效率均略低于颚式破碎产品,但随着磨矿细度的提高,二者的差距越来越小,当-0.074 mm占85%时,二者的磨矿技术效率相当,超过该磨矿细度,则磨矿效率开始小幅反超;目标粒度为280、150、105、74 μm时,高压辊磨产品的Bond球磨功指数比颚式破碎产品分别低9.41%、7.70%、4.97%和4.28%,降低的幅度随目标粒度的降低而减小,表明高压辊磨破碎对一段磨矿有显著的节能效果。     

Flowsheet considerations for optimal use of high pressure grinding rolls

High pressure grinding roll (“HPGR”) technology is very rapidly gaining a wide acceptance within the mineral processing industry. Benefits, including a superior energy efficiency and a lower overall operating cost of an HPGR based circuit compared to alternative technologies have been demonstrated at a number of operations throughout the world. Increasing numbers of units are presently being installed in the minerals industry world-wide. This trend is an excellent reflection of the confidence now placed in the technology by new and existing users.This paper summarizes basic principles of the equipment and of various options how to include an HPRG in the grinding circuit for most efficient use. Case studies demonstrate the application of HPGR’s in different grinding circuit set-ups and for the comminution of different ore types. Benefits of the options of open circuit grinding, closed circuit grinding incorporating wet and dry screening as well as the option of achieving a finer grind by recirculating part of the HPGR product using a mechanical splitter are discussed.From a processing point of view the effects of partial product recycle are detailed and some guidance for selection of cut size between HPGR and ball mill is provided.     

基于知识的球磨机选型专家系统的研究

针对球磨机以往设计需要依赖专家经验进行的弊端,将专家系统原理和实例推理技术应用于粉磨系统的选型中,以提高选型设计的效率。文章介绍了球磨机选型系统的结构、知识库组成、推理技术及开发工具。     

Simulation assisted capacity improvement of cement grinding circuit: Case study cement plant

Extensive sampling campaign was performed around the cement grinding circuit of a cement plant in Turkey, for different production types of cement, as CEM I 42.5, CEM II 32.5/42.5/52.5, for the modelling and simulation purposes. During the sampling surveys; samples were collected from around the circuit for the steady state condition of the operation and, following a crash stop, from inside the mill. The size distributions of the samples were determined down to 2 μm by the combination of sieving and laser sizing methods. By using the size distributions around the circuit and control room data mass balance studies were performed. Then equipments in the circuit; ball mill, air-classifier and filter, were modelled individually by using the appropriate model structures. After modelling the circuit, simulation studies were performed for capacity improvement, mainly by the ball size optimization. By implementing the proposed optimization, the capacity of the circuit was increased up to 12.7–20.5% for different production types, hence; the overall specific energy consumption of the circuit was reduced, as predicted in simulation studies.