## material retention time in a ball mill & vrm - page 1 of 1

DEAR ALL
CAN ANYBODY SUGGEST ME HOW TO CALCULATE THE MATERIAL RETENTION TIME IN A CLOSED CIRCUIT BALL MILL IN EACH COMPARTMENT?
SIMILARLY FOR A VERTICAL MILL .
WHAT IS THE USE TO CALCULATE THE SAME?
IS IT HELPFUL FOR OPTIMISATION LIKE IN KILN ?
PLEASE DO REPLY
RAJ

You could do thatby measuring the material flowrate Q[tons/h] through the mill as well as the quantityM[tons] of material that accumulates within the mill. The retention time, also called residence time, is the ratio (M/Q) [h] .The flowrate Q could be measured from the production P[tons/h] and the circulating load C and given by Q[tons/h] = C P[tons/h] . The circulating load could be obtained by measuring the particle size distribution of the feed, the product and the reject, and by thenusing the Koulen method. (see this post)The material M accumulated within the mill could be observed by measuring the level of the material within the mill, deducting the volume occupied by the balls and assuming a reasonable value for the material density. Alternatively, you might empty the mill and weight what comes out. Another method uses fluorescein injection.See the Cement plant operations handbook B4.8 .See also page 33 3in this Mapei document .

You could do thatby measuring the material flowrate Q[tons/h] through the mill as well as the quantityM[tons] of material that accumulates within the mill. The retention time, also called residence time, is the ratio (M/Q) [h] .

The flowrate Q could be measured from the production P[tons/h] and the circulating load C and given by Q[tons/h] = C P[tons/h] . The circulating load could be obtained by measuring the particle size distribution of the feed, the product and the reject, and by thenusing the Koulen method. (see this post)

The material M accumulated within the mill could be observed by measuring the level of the material within the mill, deducting the volume occupied by the balls and assuming a reasonable value for the material density. Alternatively, you might empty the mill and weight what comes out.

## cement grinding in ball mills and vortex layer devices - globecore. oil purification systems

Cement and concrete are the second most used substances in the world, after water. On average, the per capita consumption of cement is one ton. This material is widely used as a binder in the production of concrete, reinforced concrete and various construction mixes. The demand for cement in construction of new buildings, repairs and reconstruction is always high.

The process of cement production includes several stages and concludes by grinding clinker with the addition of gypsum. Grinding precision is an important characteristic of cement, since it defines the amount of material capable of hydration. The rate of hydration and strength increase also depends on this parameter. Grinding processes are quite energy intensive, with up to 20% of the worlds energy production consumed by grinding equipment. Clinker grinding accounts for approximately 70% of energy costs in cement production. The objectives of the cement production industry at the modern stage are therefore as follows:

The principle of the ball mill operation is simple: it consists of a rotating drum and grinding media (cylinders, balls etc). The material is placed into the drum which starts rotating. The grinding media and the substance both come in circular motion and at a certain point drop from the walls the bottom of the drum. The grinding is achieved by attrition (particles of the ground substance and the grinding media move relative to each other) and impacts. Ball mills are most commonly used in cement factories to grind the raw material and finely grind the cement.

The use of ball mills in cement grinding is due to several factors, among which are relatively simple design and high processing rate. However, these machines have certain limitations as well. It is known that only 2 to 20% of the energy is consumed by the grinding proper, while the rest is expanded on overcoming friction, on vibrations and is dissipated as heat. Ball mills also are material-intensive due to high wear of the components. These mills are also very noisy.

The vortex layer device is, in a sense, similar to the ball mill, but the effect on the processed material is different in principle. The first similarity is the chamber, where the material is ground. However, the chamber of the vortex layer device is stationary, smaller than a drum and is always made of a non-magnetic material. The second similarity is the presence of grinding media (which, in the case of the vortex layer device, are cylindrical and made of ferromagnetic material). While the grinding media in the ball mill is put into motion by the motion of the drum, in the case of the vortex layer device, the grinding media moves along complex trajectories under the influence of a rotating electromagnetic field. This field is generated inside the chamber by electromagnetic induction coils. In fact, the design of the machine is similar to a short-circuited cage motor without the rotor (the rotor being replaced with a tube, i.e. the processing chamber).

Mean power of these effects is such that not only cement is ground and activated, but the process is sharply intensified as well. Every ferromagtnetic particle is both a grinding and mixing medium. Moving along complex trajectories, these particles cover the entire volume of the chamber another important distinction of the vortex layer device from a ball mill. If the process takes tens of minutes and hours in other mills, the required retention time in vortex layer devices is measured in seconds or minutes.

Vortex layer devices are superior to ball mills in several respects. Specifically, vortex layer devices are multifunctional. Unlike the ball mills, they can grind cement extremely fine without loss of efficiency, while at the same time activating the material with the electromagnetic field. All the processes occur a lot faster. E.g., increasing the mean surface area from 2800 to 6800 cm2/g is achieved as soon as within 120 seconds of processing. The noise output of the device is negligible, as compared to the ball mill. Cement can be activated even without ferromagnetic particles, simply passing it through process chamber. In this case, the processing capacity increases severalfold.

Brief processing of cement in the vortex layer device ensures a reduction of concrete hardening time under natural conditions, a reduction of cement consumption or improved concrete grade, as well as achievement of high mix plasticity. The use of activated cement in all cement compounds ensures high physical and mechanical characteristics of the products.

The vortex layer device can also magnetize water for concrete mixes. Using magnetic water for mixing significantly improves the product strength. Regular water involves a lengthy period of cement crystallization, whereas in the case of magnetic water, the plastic strength starts growing almost immediately after mixing.

The conclusion is that the vortex layer device used for cement grinding addresses three main issues of the cement production industry: it increases grinding fineness and reduces the energy costs of the process, while at the same time remaining simple and reliable in operation.

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## optimization of continuous ball mills used for finish-grinding of cement by varying the l/d ratio, ball charge filling ratio, ball size and residence time - sciencedirect

During the last decade, semi-finish-grinding plants have been used more and more for the energy efficient grinding of high-quality cement. In 1999, it was found that by decreasing the ball charge filling ratio it was possible to lower the specific energy demand for grinding significantly.

It was obvious, too, that the L/D ratio influences the specific energy demand and the mill throughput as well. Therefore, a huge test program was carried with a semi-industrial ball mill, which was operated in closed circuit. The mass-specific surface area of the two feed materials (intermediate product) used were quite typical for industrial semi-finish grinding plants. The values were 2200 and 3000 cm2/g according to Blaine. The product finenesses were 3000 and 3800 cm2/g, respectively. The L/D ratio of the ball mill was varied in four steps of 1.75, 2.1, 2.79 and 3.49, and the ball charge filling ratio was varied in three steps of 15%, 20% and 25%. The experiments clearly indicated that the optimal L/D ratio and the optimal ball charge filling ratio are different for each feed fineness.

The influence of the ball charge grading on the specific energy demand, characterised by the average ball diameter, was tested by means of a discontinuous laboratory ball mill. The results showed that by using a finer ball grading the specific energy demand could be lowered considerably.

The obtained results can be explained well by theoretical considerations regarding the ruling stress intensity and the number of stress events. The stress intensity expressed as the power input per ball is dependent on the ball diameter to the third power and only slightly dependent on the inner diameter of the mill. The number of stresses can be characterised by the average retention time of the ground material inside the mill if the ball charge grading remains unchanged. The optimal retention time depends not only on the feed material and the desired comminution result but also on the ball charge filling ratio and particularly on the L/D ratio. On the basis of the present results and considerations, a specific optimisation of ball mills in semi-finish-grinding plants can be done.