Closed-circuit Mill Research Articles

A process mineralogy approach to study the efficiency of milling of molybdenite circuit processing

This study is conducted with the aim of investigating the efficiency of open and closed-circuit molybdenite ore comminution processes (primary and secondary mill, respectively), through mineralogical study of mills feed and product. For this purpose, particle size distribution, minerals distribution, degree of liberation and interlocking of minerals in mills feed and product were studied. According to the results, chalcopyrite, molybdenite, pyrite and covellite constitute the major part of the mineral composition of open-circuit mill feed. Minerals at the mill product, in the order of abundance include liberated molybdenite particles, liberated chalcopyrite and interlocked chalcopyrite with pyrite, liberated and interlocked pyrite particles, and associated silicate gangues. The d50 values of the feed and product particles of the open-circuit mill are equal to 13.80 and 13.40 microns, respectively. Degree of liberation of molybdenite for the feed and product of this mill is almost the same and is equal to 98.0%. Closed-circuit mill feed includes, in order of is abundance, liberated molybdenite particles in the form of blades and irregular polygonal shapes, liberated and interlocked chalcopyrite, and liberated and interlocked pyrite particles with gangue minerals. Molybdenite particles in the mill product are almost completely liberated, and the degree of liberation values of chalcopyrite and pyrite are 84.40% and 91.40%, respectively. According to particles size distribution of the feed (d50 equal to 25.03 microns) and the product (d50 equal to 24.24 microns) of closed-circuit mill, it can be stated that comminution is not well-operated in closed-circuit mill due to the low solid percentage of closed-circuit mill feed and the inefficiency of hydrocyclone. Examination of Mo, Cu, and Fe grade variations for 10 days in both off and on modes of mill shows that closed-circuit mill does not have an impact on comminution process. It can even be concluded that the mill has a destructive effect the flotation process by producing slimes.

Analysis on Production Plan and Results of Ground Granulated Blast Furnace Slag Based on Circle Flow Mill

The change of the specific surface area, particle size and activity index of ground granulated blast furnace slag under different grinding conditions is researched based on closed-circuit mill in the paper. The research shows that the grinding effect is greatly different with the different grinding body, and proper pre-grinding time can help to improve the grinding effect. The optimum plan in this paper is as follow: pre-grinding 15 min at steel bar then grinding 30 min at ball grinding, and it will getting the maximum specific surface area, the smallest powder particle size and the the maximum activity index.

Optimizing the control system of cement milling: process modeling and controller tuning based on loop shaping procedures and process simulations

Based on a dynamical model of the grinding process in closed circuit mills, efficient efforts have been made to optimize PID controllers of cement milling. The process simulation is combined with an autoregressive model of the errors between the actual process values and the computed ones. Long term industrial data have been used to determine the model parameters. The data include grinding of various cement types. The M - Constrained Integral Gain Optimization (MIGO) loop shaping method is utilized to determine PID sets satisfying a certain robustness constraint. The maximum sensitivity is considered as such a criterion. Both dynamical parameters and PID sets constitute the inputs of a detailed simulator which involves all the main process characteristics. The simulation is applied over all the PID sets aiming to find the parameter region that provides the minimum integral of absolute error, which functions as a performance criterion. For each cement type a PID set is selected and put in operation in a closed circuit cement mill. The performance of the regulation is evaluated after a sufficient time period, concluding that the developed design combining criteria of both robustness and performance leads to PID controllers of high efficiency.

The modeling of dry grinding of quartz in tumbling media mills

The grinding of quartz sand to produce high purity silica flour was studied using ceramic balls, ceramic cylinders or flint pebbles in a laboratory mill and three full-scale closed circuit mills of 2.2, 2.3 and 2.8 m internal diameter. The primary breakage distribution determined in laboratory tests was the same for the three media types but the characteristic slope ( γ) was changed from 1.05 to 0.95 to fit the full-scale results. An approximate correction was used for non-first order breakage kinetics. Simulation models were developed for the air separator and the mills. Simulations indicated that a mill lining of smooth ceramic gave media slip and was less efficient than flint linings. Higher circulating loads reduced specific grinding energy even though the recycle of fine mill product to mill feed increased. Ceramic balls gave the lowest grinding energy, wear rate and cost per ton of product.

Determination of ball mill residence time distributions form tracer data taken in closed-circuit operation

Based on a method which searches on the parameter values for models, the possible one- and two-detection system tracer methods for the determination of ball mill residence time distributions from data taken on closed-circuit recycle systems are treated. Mathematical relationships for the most promising approaches are developed for both methods. This includes deriving, demonstrating, and verifying (with existing simple analytical models of closed-circuit mills) analytical models of tracer input and output based on the use of tanks-in-series and finite stage models with the convolution integral principle. Simulated results for typical processes are given and non-linear search methods are described and demonstrated for determining mill residence time distribution model parameters.

CAD of Closed Circuit Mills

Three models of different complexity are presented for CAD of closed circuit mills. The control and system engineering background of these models are discussed and compared in connection with the technology and the possible aims of CAD methods for cement mills. A programsystem is also presented on the basis of the developed theoretical and experimental results.

Effect of a material-flow model in prediction of particle-size distributions in open- and closed-circuit mills

A size-continuous breakage-kinetics model is postulated and supported with industrial grinding-mill data. It is shown that the kinetics parameters include the effects of possible classification at the mill discharge. The estimated parameters were then used in the kinetics model to simulate the behavior of a grinding mill in open- and closed-circuit operation. While material transport and kinetics are equally important in open-circuit operation, heavy recycle in a closed circuit makes a detailed material-transport model for grinding unnecessary. In effect, the mill can be considered as backmixed. This suggests that more emphasis should be placed on modelling the classifier than the development of detailed material-transport models for the grinding mill.

A note on limiting size distributions from closed circuit mills

A note on limiting size distributions from closed circuit mills

Control of a Closed Circuit Cement Mill

The design of a control system for a closed circuit mill is developed. The control strategy is to estimate the point of instability for the unit and to control the mill at a constant value away from this point.Several models of the mill are presented. The first is a high order model which is used to develop a simplified continuous model. This is discretized to yield a third order nonlinear model with measurement noise.The control is derived using a modified minimal variance control strategy. A Kaiman filter is used to estimate the point of instability.