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State-of-art cement grinding technology: from micro to macro scale: Marco Goisis, Italcementi SpA (Italy)

Filmed at Cemtech Europe 2015, 20-23 September, Intercontinental Hotel, Vienna, Austria.

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Thanks for the kind introduction to the speaker, to the chairman and good morning to everybody. My speech is on the state of the art of cement grinding technology, and I will move from a first part dealing with basics and fundamentals, and going through some aspects arriving there to grinding technologies and industrial applications.

Just as it was on a framework communition is dated back to many centuries to the pallolit period was used motorand parcel, and the minismascal power was used for many time with different solutions such as the Armer System finally, mankind is called at the animal muscle power, such as bajerano and the power of water.

So water mills and finally electricity, with the proposition of a bowl milling in 1890 and vertical roller mills, for vertical roller mills where proposal for raw materials grinding and the the proposal of a high pressure grinding rollers. The question is why communication is so important for mankind? The answer is that the coarse particles cannot be easily handled and processed and more over they react slowly, a poor radiation and entering properties in composite application and are more likely to have a spatial variation of the properties so where we get the higher specific surface area, we permit to speed up chemical reactions.

To speed up mass transfer operations to enhance us physical affinity of the material such as part of this solution, filtering and absorption and also to create a better bond between the particle and matrix and also to give to final product is solid, better mechanical stability.

Let us move now to the fundamentals. It is well known that grinding the combination of materials needs energy to be done. And when Vatica law was taken in 1937 by worker is general grind ability low. Which says that the required energy for the reduction, the differential reduction of size is proportional the size changer, and inversely proportional to the initial size to stamp our end all the other laws which are present in the literature department and so on, suggest rating as for postulate, Kicks Law and Bond's Law are particular cases of this general law, the mathematical expression of the other laws is exactly the same, what differs is also the value of the exponent end just a few words on grind ability.

Grind ability is the the attitude of the material, the resistance that the material fuses against the action of grinding. It is usually expressed by energy consumed to grind to a sorting finess. There are different equipment that are used to predict a grindability such as born miller size and miller agrov miller, but what is the most important concept is that grind ability is not an inner enter property of the material, if the property of the system, so equipment plus material so be careful when you give a look at grind ability values to compare with different papers is possible only if the system grinder and material is the same, a very wise, it's easy to make some misunderstanding.

Article Site Distribution is generally in cement sector expressed by the plain number. The plain number is a well established value coming from a well established procedure. But the limit of plain number, is that it is a singer figure. And we cannot express by a single figure distribution.

Distribution of particle is generally drafted by an instagram. In the cement sector we do not use an instagram We prefer to use a cumulative fraction so a particle size distribution expressed in this way. And the value on the epsinon axis on the ordinate axis expresses the cumulative fraction by percentage of particles that are smaller than the relative value on the X axis.

As regard model to modernize size distribution, several empirical equations have been proposed over time. Two of them are the so called [xx] are the most use and even if today larger scattering de fraction of particles, they meet relatively easy to have a good particle size distribution.

They are still used because they allow a first evaluation of particle size distribution with only two points and the first and the last correlation of weak chemicals and processed parameters. What is important in this equation is the co-efficient N, N is the slope of a straight line, and the N higher, N tighter, the particle size distribution, but why N the slope is so much important in cement grinding.

Because N depends on the path on the fines present in the material. More fines means lower values of N and the fines have dramatic impact on water demand, increasing on certain time decreasing on the degree of hydration increasing it release strength as regard refresh between 3 and 32 micro-chromes and on the microstructure of interstitial and seasons on, so the zone between aggregate and bulk of the material.

Moreover N so important because of it's effect on performance of cement is different it depends on the grinder generally speaking bowl mills have a value of N, lower than that of vertical roller mills and still lower than high pressure grinding rollers. The reason is that in bowl mill, residence time is much higher than a vertical roller mills 20, 30 times more and the particles can impact repeatedly and they generate a higher proportion of fines which compel to lower down the curve and the N value.

The separator influences to critical extent of particle size distribution. To characterize the separator [xx] is a generally used it shows the performance of a classifier we have a graphical representation of a probability of the even the size of particle in the separator returning the miller a reject. Tom Carver is a generally many parameters describing it but one of the most important is the sharpness of the separation.

When the ratio D25, D75 is equal to one we have an ideal separation, so there right to corner. In the other case we are more or less closer to the ideal situation and we talk of a good or poor separation. High intensity separator so are giving much improvement in the efficiency of grinding equipment.

Since they increase the ball mill output they can decrease the specific energy consumption during grinding may decrease the entire mill temperature improve the control of separator, we've zero stop of mill to adjust fineness they improve ability to accept process here and some other advantages.

Let us give a look at [xx] forces which are present during grinding. In high pressure grinding role we have compression forces in vertical roller mill we have compression plus sharing forces in ball mill we have, compression, sharing, and impact forces, we with fundamental we can move to the grinding technologies and well understand of the importance of some of the previews parameters.

First of all the actual trend grinding plants especially vertical roller mills are gradually substitution the ball mills. The reason is that the specific energy efficiency as of vertical roller mill is much less than that of ball mills, it depends if grinding cement or if grinding is lead, but anyway these is the situation.

Ball mill has been used for 100 years and still accounted for almost 50% of all cement needs. It's important to note that ball mill is often revamped to is often optimized and revamped with conversion to high [xx] separators and that sometimes it is used as a stand mill and by mills for vertical roller mills.

Ball mill is simple to operate, it is reliable, it has simple maintainers, no more the mechanical part, tolerant to variation mill feed and more over it is the benchmark for the particle size distribution. The limit of a ball mill is it's low energy efficient, and the anticipation of the input energy in a heater vibration we are baller, we are and so on.

Many parameters can be optimized to improve the efficiency of a bowl meal such as below the level control the grinding bowl grading, the lining design, the specific diagrams we know is census we've done stream frequencies and analysis on rotating Michelle and so on. Vertical roller miller are can say that also today they represent a breakthrough, but they were introduced initially in 1930 which are the reasons for such delay in application in cement technology.

The reasons depends on the property of a cement from the point of view of customer cement quality was not in enough making the market requirement cement properties means what are the demand and the cement strength. Actually the basic equipment for verti carola is we have a roller able to roll freely without the table and the other to move at the table.

The basic principle is that we have to compact the material, which are also under the roller and between the roller and the table and to high rate a bit. Different solutions are present to get these results, the so-called to rollers technology, in which a sleeve roller prepare the material before entering under the main roller, and the dual lob design of rollers with a low and high pressure zone, the low zone prepare the material and the high pressure zone makes the grinding. Vertical roller mill has an energy consumption advantage of less to a ball mill estimated about 20-40% is able to grind higher quantity than the ball mill, and in a single unit it's able to dry grind and classify the material.

Moreover, it is less sensitive to possible high humidity content of the material. Here we have some figures illustrated comparison between the two types of mill the residence time of a ball mill is much higher than vect of the vertical roller mill 20-40 times higher. The clashing before the separation is nearly uncountable for ball mill and only limited to 1-3 for the vertical roller mill.

The circulation factor is higher for a vertical roller mill to compensate a lower residence time and the wear weight is higher for the ball mill. Which is the limit of a vertical roller mill. The limit is that a smaller energy input is given to the material each of passer within the roller and the table and so large number of passes are required and higher internal material separation effective, but moreover the most important basic is the particle size distribution which is a steeper then in the ball mill, so different solution has been a addressed by the manufacturer to arrive to a particle size distribution, so to a value value of N of a slope N similar to a that of the ball mill.

So perhaps increasing of the grinding pressure, increasing of the A of the damaringer[sp?] at the outlet of the table and adjusting some processes during the running. I got just a one slide more which only advances in vertical roller mill. With table driven machine we have three problems, one is the demand for grinding is given higher and higher, it's compass increasing the dimension of cement mill and it's a challenge for drives as the ability and [xx] Russians.

The second is vibrations transferred that from the grinding to the mortor, and third is the failure which cause the stopping of the mill. Solution has been addressed by manufacturer, we've for example rollers driven a by-single mortors, so not giving the vibration to the basic mortor of the equipment, or drive system with multiple mortors and gear box with milling also the coupling study of geometry of a roller table.

Just about there. If it was on the high pressure grinding roller, is roller which can implement very well the capability of ball mill, and it can be used as a pre-grinder for primary grinding, prompt grinding system with ball mill. The limiter is that the particle size the solution is narrow and the time for the deliver of the spare parts is sometimes is very high.

Thank you for your attention.

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