Comminution Energy Consumption Research Articles

A crushing index for granular soils based on comminution energy consumption theory

Particle crushing is a common phenomenon in granular soils, which can affect the physical and mechanical properties of soils. The index which used to quantify the amount of particle crushing is crucial for the relevant research. Based on Kick's comminution energy consumption theory, size potential regarding as a property of soil and representing the energy of particles in a certain state was defined in this study, and a crushing index was proposed based on it. This index was determined according to a density distribution of particle size that voids the problem of sieving error propagation when using a cumulative grain size distribution curve. The validation of the proposed crushing index showed that it could quantitatively describe the amount of particle breakage, regardless of material, gradation, test type and particle size scale. In addition, the proposed crushing index was considered as a soil property index and could be divided into two categories: the ultimate crushing index and the mobilized crushing index, where the mobilized crushing index is obtained from the ultimate crushing index by replacing the ultimate breakage state with the final breakage state. The test results showed that the mobilized crushing index was equivalent to the input energy ratio between current and final breakage states. This relationship contributes to the understanding of the evolution of the grading curve caused by particle breakage.

Optimization of Fluidization State of a Circulating Fluidized Bed Boiler for Economical Operation

To reduce the auxiliary power consumption and improve the reliability of large-scale circulating fluidized bed (CFB) boilers, we developed energy-saving CFB combustion technology based on the fluidization state re-specification. A calculation model of coal comminution energy consumption was used to analyze the change in comminution energy consumption, and a 1D CFB combustion model was modified to predict the operation parameters under the fluidization state optimization conditions. With a CFB boiler of 480 t/h, the effect of fluidization state optimization on the economical operation was analyzed using the above two models. We found that combustion efficiency presents a nonmonotonic trend with the change in the bed pressure drop and feeding coal size. There are an optimal bed pressure drop and a corresponding feeding coal size distribution, under which the net coal consumption is the lowest. Low bed pressure drop operation achieved by reducing the coal particle size is not beneficial to SO2 and NOx emission control, and the pollutant control cost increases. The effect of fluidization state optimization on the gross cost of power supply can be calculated, and the optimal bed pressure drop can be obtained.

Use of drilling performance to improve rock-breakage efficiencies: A part of mine-to-mill optimization studies in a hard-rock mine

In a hard-rock mine, blasting is an important rock-breakage process that impacts energy consumption both in downstream comminution processes and mine productivity. Optimizing the blast fragmentation to improve rock-breakage efficiencies during crushing and grinding is key to mine-to-mill (MTM) optimization. This study explores the use of monitoring while drilling (MWD) data to achieve this goal. Representative penetration rates (PRs) were extracted from blastholes to estimate intact rock properties and predict the breakage efficiencies that directly affect comminution energy consumption. Two intact rock properties, tensile strength (TS) and Bond work index (BWI), were correlated with the PR data to predict these efficiencies in crushing and grinding, respectively. Because of the complexity of the raw MWD data and effects of various disturbances, the MWD data was preprocessed and normalized to achieve a representative PR value at each blasthole. This preprocessing entailed defining valid PR ranges from the MWD data that could eliminate the noise related to discontinuity features in the rock mass structure as well as errors in operator behaviors. The PR data was also normalized using the adjusted penetration rate (APR) to minimize the effects of mechanical factors such as drill feed force, torque, and rotational speed. To correlate the representative APR value with intact rock properties, TS and BWI, various laboratory experiments were conducted: drilling tests using a high-precision coring machine, Brazilian disc tests, and Bond grindability tests. Based on the results of these experiments, models were developed to predict rock-breakage efficiencies during crushing and grinding based on APR. The result of this study can be used to obtain blast energy designs that consider comminution energy consumption and efficiency in the downstream rock-breakage processes.

Improving milling operation using uncertainty and global sensitivity analyses

In general, semi-autogenous grinding (SAG) mills are difficult to operate due to several factors, including the uncertainty of the process. The uncertainty can be epistemic or stochastic, the first is related to the geological factors and the second with operating factors. Changes in these factors could generate an increase in the power consumption, which must be avoided because the energy consumption in comminution represents between 56% and 70% of the costs in the mining industry. Usually, the simulation is used to help adjust the operating conditions of the SAG mill, however, in the literature, there are few publications that propose how to consider these uncertainties in milling operations. This work shows that the uncertainty analysis (UA) and the global sensitivity analysis (GSA) can provide useful tools for the identification of operational conditions for mill systems under uncertainties, considering a SAG as case study UA allows the study of the effect of the distribution and the magnitude of the uncertainties of the input variables in the responses of the grinding process. The GSA method of Sobol'-Jansen (Jansen, 1999; Saltelli et al., 2010) is utilized to identify influential input variables. Then, the regionalization of the input variables is applied to identify the operational regions. It is shown that the control of the uncertainty of the significant input variables allows the control of the uncertainty in the output variables. Therefore, the systematic method proposed in this work allows to evaluate the uncertainties in the processes as a valuable tool for any practitioner in the field of mineral processing. The novelty of this method is that allows to quantify results that have been exposed in the literature only from an experimental approach.

Modeling of an open mill with scalped feed for the maximum production of a desired particle size range

ABSTRACTMilling circuits play an important role in achieving the desired product; tonnage, size distribution, and properties, since they are directly linked to the comminution energy consumption for the whole process. A grinding model with a mathematical simulation was developed for an open milling circuit with a scalped feed from a hydrocyclone. The circuit was optimized by determining the optimal conditions in terms of energy consumption which would produce a floatable product having a desired size range (i.e., −75 to +9 µm) for a platinum-bearing ore. The simulation results showed an operating region comprising the best combination of the ball filling and mill speed to achieve the highest production of a floatable size class, with the minimum energy consumption.

Kinetic energy and its applications in mining engineering

Reduction of energy consumption in comminution is of significant importance in mining industry. To reduce such energy consumption the energy efficiency in an individual operation such as blasting must be increased. By using both new investigations and previous experimental results, this paper demonstrates that (1) kinetic energy carried by moving fragments in rock fracture is notable and it increases with an increasing loading rate; (2) this kinetic energy can be well used in secondary fragmentation in crushing and blasting. Accordingly, part of the muck pile from previous blast should be left in front of new (bench) face in either open pit or underground blasting. If so, when new blast occurs, the fragments from the new blast will collide with the muck pile left from the previous blast, and the kinetic energy carried by the moving fragments will be partly used in their secondary fragmentation.

Assessing the specific energy consumption and physical properties of comminuted Douglas-fir chips for bioconversion

Size reduction homogenizes the bulk biomass and facilitates downstream feedstock handling, transportation, and storage. Effects of feeding rate, mill-type (hammer and knife mill), screen size, and moisture content on comminution energy consumption of commercial Douglas-fir (Pseudotsuga menziesii) pulp chips were quantified. The resulting particles were characterized by geometric mean diameter, size distribution, aspect ratio and bulk density. We also employed scanning electron microscopy (SEM) to visualize the dominant fracture surface features. A linear regression was used to describe the relationship between specific energy consumption (SEC) and comminution ratio, which can be used for estimating SEC of various particle sizes of feedstock. Results demonstrated that with a screen size of 3.18mm, the hammer mill consumed 141kJkg−1, while the knife mill consumed 345kJkg−1. Selecting the feeding rate, which allows the machine reach its rated power, can result in lowest total SEC. SEC also increased substantially with an increase in moisture content from 11% to 17% (fraction in total mass basis). Analysis of the particle morphology revealed that the dominant fracture mechanism was across lumen for hammer milling and along middle lamella for knife milling.

Calculation model of coal comminution energy consumption

Experiments on comminution energy of different coals under conditions for CFB (circulating fluidized bed) boilers were carried out in a jaw crusher and a parallel roller crusher. The R–R (Rosin–Rammler) distribution was used to describe the size distribution of the crushing product. The size distribution of the product has a significant influence on comminution energy. With lower values of xP=63.2% (size modulus) or α (distribution modulus), the comminution energy increases. With a fixed particle size distribution of the product, the comminution energy increases gradually with the increasing of feed coal size, while, when the feed coal size is larger than 15mm, the effect can be neglected. With a fixed outlet width of the crusher, the average product size tends to be finer when smaller sized particles or coal with higher HGI (Hardgrove grindability index) are fed into the crusher. Therefore, in coal preparation process, the adjustment of the crusher should be performed considering coal grindability or crushability and the feed coal size distribution. At last, an empirical model of comminution energy was proposed and validated by the measured values with ±25% of accuracy.

Benchmarking comminution energy consumption for the processing of copper and gold ores

A survey of the comminution energy requirements of gold and copper producing mines has been conducted to provide reliable benchmarking data which can be used to compare comminution energy consumption across different mine sites. The total gold and copper production of the mines included in the study equated to 15% and 24% respectively of global production and all of Australian production. The comminution energy per unit metal product has been presented in a graphical form similar to a cost curve. This simple technique allows individual mines to be ranked with respect to energy consumption and clearly displays the potential energy and cost benefits of moving down the graph into more efficient operating regimes. Assuming similar specific energy requirements for other sites, comminution of gold and copper ores can be expected to consume about 0.2% of global, and 1.3% of Australia’s electricity consumption. Efforts to reduce this figure should be aimed at the top third of consumers as they are responsible for 80% of the total consumption. Analysis of the contribution of circuit efficiency, ore competence, grind size and ore grade showed that ore grade was the greatest determinate of specific comminution energy. Therefore, concentrating the ore via gangue rejection or grade engineering prior to grinding is likely to achieve the largest positive effect on comminution energy efficiency.

Comminution of forest biomass by modified beater wheel mill in a power plant

Today, renewable energy sources – e.g. forest biomass – are of great importance, not only domestic but also industrial – f.i. wood fired power station – utilization is wide spread as well. However, the comminution of such fibrous texture materials requires relatively high energy and special grinding stress. In the thermal power station of AES Co. Ltd., Berente mainly wood biomass is burned as fuel. The size reduction of biomass is achieved by beater wheel mills, which were designed originally for coal. The aim of the research carried out by the University of Miskolc was to increase the capacity of the fuel supplying system.Systematic industrial and laboratory experimental series were carried out under different conditions and results are presented in this study. During the on-site industrial tests four fuel supplying systems (beater wheel mill, air classifier, heat exchanger, pipes) were equipped with a complete data acquisition system containing different sensors. Three sampling points were built 1) from the feed, 2) from the rejected coarse material after the air classifier and 3) from the final product (isokinetic) from the pneumatic transport pipe. Biomass moisture significantly influenced comminution energy consumption, especially for finer size reduction.

Energy requirement for comminution of biomass in relation to particle physical properties

The energy requirement for biomass comminution and the resulting particle physical properties are important factors to study logistic components, select equipment, and assess the overall efficiency of feedstock supply–conversion chain. In this study, mechanical size reduction of Miscanthus (Miscanthus giganteus), switchgrass (Panicum virgatum), willow (Salix babylonica), and energy cane (Saccharum spp.) was carried out using a commercial-scale hammer mill, a bench-scale Retsch SM2000 knife mill and a Retsch SK100 hammer mill. The results showed that the specific energy consumption of biomass comminution and the aperture sizes of the milling screens were related in power-law forms. Biomass moisture significantly influenced comminution energy consumption, especially for finer size reduction. Given a specific milling screen, the Retsch SK100 hammer mill was found more energy efficient than the SM2000 knife mill. This was mainly attributed to the higher motor speed and axial feeding mechanism of the hammer mill. The particle sizes after comminution were found inversely proportional to the bulk densities of all four energy crops used in experiments. In addition, the comminution ratio, being the ratio of the final mean particle size and the original mean particle size, was proportional to energy consumption for all four energy crops. The bulk densities for 4-mm and smaller Miscanthus and switchgrass particles were higher than those of the original bale. Particle size and surface area estimates using commonly used ANSI/ASAE Standards S424.1 and 319.4 were highly sensitive to particle size distributions and shapes. Further studies on standardization of particle size and surface area estimates are needed.

Energy Consumption in Comminution of Mica with Cavitation Abrasive Water Jet

Abstract We have studied the efficiency of energy consumption in the comminution of mica powder with cavitation abrasive water jet technology. The energy required to create new surfaces in the comminution of mica powder with cavitation abrasive water jet was calculated, in order to estimate its efficiency of energy consumption. The particle size distribution and the specific surface area were measured by applying a JEM-200CX transmission electron microscope and an Autosorb-1 automatic surface area analyzer. The study results show that the efficiency of energy consumed in creating new surface areas is as high as 2.92%, or 4.94% with the aid of cavitation in the comminution of mica powder. This efficiency will decrease with an increase in the number of comminutions. After three comminutions, the efficiencies will become 1.91% and 2.29% for comminution without cavitation and with cavitation, respectively. The abrasive water jet technology is an effective way for comminution of mica powder.

The effect of ball size on the energy efficiency of hybrid high-pressure roll mill/ball mill grinding

To find ways to reduce energy consumption in comminution, dolomite was ground in a hybrid grinding system, involving the operation of a laboratory-scale high-pressure roll mill and ball mill in series. The work presented here has demonstrated the energy efficiency of the hybrid system can be increased by reducing ball size, provided the roll mill product contains sufficient internal damage to allow for the use of the smaller balls. There is an optimum range of energy partitioning between the high-pressure roll mill and the ball mill in the hybrid system. The increased efficiency of hybrid grinding is related to the particle damage imparted by the roll mill, as evidenced by the increased breakage rates of high-pressure roll mill product relative to particles that had not been roll milled.

Short-pulse microwave treatment of disseminated sulfide ores

Theoretical and experimental analyses are used to study the feasibility of using short-pulse microwave energy as a pretreatment step in comminution. Ores of interest contain microwave-absorbing mineral in a low-absorbing gangue. A finite element numerical model is used to predict the thermomechanical response of a single pyrite particle in a calcite host rock during microwave heating. The effects of power density and mineral particle size are presented. Using microwave power densities within those expected in currently available equipment, significant temperature differences are predicted between the pyrite particle and the calcite matrix. Resulting thermomechanical stress exceeds typical strengths of these minerals. Laboratory tests verify rapid, selective heating of crushed sulfide minerals. Tests with mixtures of pure minerals show heating rates directly proportional to the mass of high-loss mineral; thus, shielding of mineral grains by other grains does not appear to be significant. A cursory energy-use analysis suggests that short pulse microwave treatment can be accomplished with relatively small energy input compared with current energy consumption in comminution. Although improved comminution has yet to be experimentally demonstrated, initial results are promising from both a technical and an economic standpoint.

Capacities and performance characteristics of jaw crushers

By using the data of E.A. Hersam and F.C. Bond’s equation for energy consumption in comminution, a method was developed to analyze the performance of industrial jaw crushers. The study showed that industrial jaw crushers are generally operated below capacity. The study also showed that industrial jaw crushers generally have sufficient installed power to operate at full capacity. The method presented can be used to estimate the capacities and power requirements of jaw crushers.