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User experiences of VRM grinding and optimisation at Indocement: Jean-Marc Reginster, HeidelbergCement Technical Centre (Indonesia)

Filmed at Cemtech Asia 2015, 21-24 June, Grand Hyatt, Bangkok, Thailand

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I will talk today about our experience in Heidelberg Cement, I will not go into too much detail because we don't have a lot of time for that, but I will explain to you what is our feeling about vertical mills, and what we think about it. So we'll talk about three vertical mills. There's one Gebr. Pfeiffer mill with six rollers, there is one Loesche mill with three plus three rollers, and there is OK mill that we operate in Citeureup Indonesia.

So we will go quickly through the characteristics of the mills, there is also a sheet with the separate characteristics, the types of products, what we produce in Port Kembla and Jency, and then the separate experience with the various mills. So basically, these are the characteristics of the mills, Port Kembla it's 6 meter diameter table, Jency is 5.3 meter diameter mill, in the Indocement is OK mill, 5.6 diameter mill and then we're going to start three new mills from Russia, 5.6 table diameter , these means are not yet in operation. We're erecting them and we should be in operation by the end of this year.

So these are the main characteristics, airflow and type of separator, these are all high efficiency separator, and then these mills are producing OPC or slag, and for example in Port Kembla there is mixing of the products after the mill, in the Loesche mill and Jency we are producing OPC but feed fly ash in the top of the mill that is mixed directly in the production unit. In Citeureup we're feeding material clinker, gypsum, limestone and truss together on the table, and it's grind directly in the mill and goes to the finished product. Indocements P14 will be the same, the same working the same way, also producing OPC. So these are the types of components we're using, so Port Kembla we're using clinker, gypsum and limestone, and then we're grinding slake and gypsum separately, and these two products are mixed.

Jancy, it's basically clinker, gypsum that is ground and fly ash fed in the other separator . In Indocement, we use mainly PCC which is 72% clinker, 3% gypsum, limestone and truss. We go up to 20% truss. So in all the installation we have achieved the guarantee figure given by the OEM, the milln supplier we are able to maintain this quality and the throughput. So this is the Pfeiffer mill at the Port Kembla. This is a multiple drive mill which is quite a new technology.

This technology is really very interesting because you have a much more simple transmission system. One of the main advantage, here you see the balll that is under the table, in the classical system, you have a gear box that is usually much more narrow than the table, which mean that this balll, are submitted to a lot of forces, and prone to developing some cracks. Here we can have the ball that has some vertical walls on the top of the drive system which means it's much less sensitive to crack and much easier to manufacture for the foundry..

Their is no gear box, their is just a gas gear, and some pin ons that are driving these gas gear, which is much safer than a classical gear box, that you find under the older classical system. So in Port Kembla there is a particular device, here we have a hot gas generator, later under special crusher for the gypsum, which means that we can crash the gypsum under given a specific heat treatment.

In a normal vertical mill you are limited in temperature inside the vertical mill otherwise you'll have full setting in the silo, so you cannot have the optimum properties of the gypsum. So in Port Kembla we have this special device, that enables to give a specific heat treatment to the gypsum, which means you can optimize the effect of the gypsum, outside the vertical mill.

So you can keep the temperature in the vertical mill just to have sufficient drying. So you can go to lower temperature in the silo without having the problem of lower re-activity of the gypsum. so this feature is working quite well, and it is really an advantage and I think it is also quite unique. So multiple drive, there is no problem of synchronization, the system is working perfectly, we have had faced when we had to 35 millimeter wear on the roller.

This we had about 10-15 tonnes per less throughput with the wear on the roller and on the table, which is acceptable for us, and then after rebuilding table and rollers we could go back to the normal throughput. To follow properly the wear profile, is really key to keeping the castings and and the wear parts, into good shape.

If you work too much, then you might have too much material to rebuild, and it can lead to cracks of the parts. Also when you buy these wear parts, it's important to keep in mind what you'll do after, because if you go too high in hardness in the base metal, you will have difficulties to hard face.

So Ni-Hard is somehow a very good solution because you can hard face with no too much risk, okay the material that is not the hardest available on the market, but it's safe to hard face. Ni-Hard is also quite easy to manufacture. So it is a good solution. So in this mill we have no major issue. Jancy is a Loesche mill with supporting rollers and grinding rollers, there is no particular problem with the this mill, in fact here it is grinding OPC because most of the fly ash is fine enough, so fly ash is just going to the finished products, we add a vertical mill, only a small fraction of it is to be ground. One of the important factor as well, when you grind with the vertical mill if you have different sources of clinker, the machine can be quite sensitive to the variation in clinker quality. So it is very important that the operators have a very close follow up, and in some case if the clinker is really way to fine, then it is difficult to maintain the machine into the normal production level. So as I have explained, it's a classical Russia mill, classical solution, there's really no issue with this production unit.

The Loesche mill for cement grinding, is a solution that is, since many years in operation, the difference between these three types of mill, that's the OK mill and the Gebr Pfeifer, they have a ball type of table, which means that the material is naturally retained on the table. With the Loesche mill the table is flat, and you have a very high retainer ring. When I say very high it's in the range of 450 mm, when in the other mill the retainer ring is only 100 mm. To keep the production, sometimes you have to play with the retainer ring height, it's an exercise that can take some time. So it's very important to maintain the wear on the roller and table, in order not to have to modify the retainer ring height. That's the material we are grinding in the OK mill, that's an average moisture of around six person, we did not face any problem for the drying, we do not face any problem to keep the the quality of the cement, but if we have large variation of clinker quality, then it is a bit difficult to operate the machine. In Citeurep we have nine different kilns, so we have to be sure that the quality of the clinker is rather constant. When you are using your ball-mill, whatever is the quality of the clinker, you will find quite easily your solution to operate the mill with stable condition, the time the material to be ground is in the vertical mill is very short, which means that you don't have any chance to recovery if you have something wrong in the feed. So this is the type of mill, here we have have two rotary valves, we have two inlets, one inlet for dry materials and one inlet for wet material.

The inlet for wet material is heated and it is quite a sensitive issue. The maintenance of these rotary valve is really critical, because you can have a lot of false air if they are not properly maintained, and it's quite critical. So a lot of attention has to be drawn on this valve. There are some periodical adjustments, their cleaning scrap are inside them, so it is quite a sensitive equipment.

So this is the sketch of one the shoot for wet material. We have designed this shoot specially so that it can be opened quickly and cleaned very quickly. At the beginning when we were operating we had very frequent blockage of this shoot, and in order not to have too much downtime, you must have a design that enables you to clean it very quickly, this is the type of cement we're producing.

We are maintaining the throughput without any difficulties. We had faced some problems because we have hard faced or rebuild the rollers a bit too late in time. So when the wear was too much, then we had the difficulties to keep the throughput. When you have too much wear on the roller for example, the material bed depth is becoming very thin, and as this material bed depth is coming very thin then you go into a vibration problem, and sometimes roller system heating those top ring, so really special care has to be taken, to do maintenance on due time.

So when we can discuss about ball mill and vertical mill, these are really different type of equipment's, if you a farmer, if you are using a old Massey Ferguson type of tractor, it is very easy to drive, very easy to maintain, nothing complicated, nothing sophisticated. If you have a John Deere last generation with GPS, all the hydraulics and so on, it needs really different operator and different maintenance people.

For a ball mill maintenance is very easy. You can easily predict the life time, you can know six months in advance when to replace the shell liner and you can plan there's no difficulty. For the vertical millls, you have to react much faster and you have to for see much more. So the machine require much more attention than a ball mill.

When you operate the ball mill you have 30 minutes to react, because when the material enter in the mill and the material goes out, it's about 30 minutes. When you are in a vertical mill it's much lower than one minute. So if you have something wrong in the feed, you have almost no time to react. In terms of maintenance, in the ball mill as I said it's you speak in terms of years, in a vertical mill, you speak in terms of months. If you grind slack, you might have to hard face only after 2000 hours. So you have really to foresee, and to be well ahead of what is going to happen.

Vertical mill advantage it's a very compact machine, easy to grind and dry together. For example in a ball mill, basically when you enter into the grinding chamber, you must be below one person moisture, otherwise you will have all kind of problems. In the vertical mill as the time the materials stays in the machine is very short, the humidity has no time to react with the clinker. So you can grind very wet material, without affecting much the quality. You can grind a very wide range of products, meaning you can grind very coarse and grind very fine, and the transition time is very short. As the material is not staying for very long in the machine, you can change quality within a short period of time. Of course it is recommended to work by campaign, you cannot change too many times the quality. Otherwise it will effect your productivity. The new type of drives give possibility for much higher capacities, because you are not linked any more to this heavy gear box, you are working with the gas gear or with roller driven. So in such cases you can have much higher install power. What is really also very important, when you have let's say quite local quality cement, there is no not much problem. When you are selling to a very matured market, sorry, then you need to to really focus under quality and with a ball mill there is not much to be done to keep up a very high quality. It is very very important for a vertical mill to play with all the different factors, to address the quality. It is possible to produce constant and very high quality, in vertical mill, but it requires quite a lot of efforts. From the production people, from the followup of the raw material, meaning clinker, truss and so on, and you can achieve, but it is more difficult, to have constant quality and high quality is more difficult than with ball mill. Also in the vertical mill, what is very very important is the water injection, and the use of grinding aids. What enables you to stabilize the belt, and to have proper material entering into the rollers, is the water spray and the use of grinding rates.

It is a very sensitive issue, because if you spray too much water, you will loose in early strengths and you will loose in cement quality. So the aim is to reduce the minimum water injection. So there is a lot to be done, how to put the water spray, where to put it, and there's quite a lot of knowledge in that, Also the grinding rate, you cannot use simply the same grinding rate as for a ball mill. You need also to do, some investigation about the grinding rate to use. So as I was explaining before, when you operate a vertical mill, you need really to have the people that are sharp and that are focused, from production as well as from maintenance.

So the mill is quite sensitive to the feed quality variation, the machine has a very fast reaction, and it's very sensitive to detail. So as I was mentioning, keeping running element profile, and to work on water spraying and grinding rate. Regarding maintenance, you have to be very focused on false air, and for example rotary ceiling at the feed system,

grinding elements, profile maintenance and you need hydraulic competence. So if you don't have someone really specialized in hydraulics, you might face some problems for maintenance. Let's say because of it's characteristics, we are in favor of vertical mill in the new units, especially now that most of the cement plant are grinding mixed products, clinker, I would say maximum 70% clinker and additives, so vertical mill has a lot of advantages.

Some new technologies are coming on the market, for example the roller driven mill, which have really a lot of advantages. In a table driven mill, if the mill starts to vibrate you have to play with water injection, with the feed and it is quite difficult to control. With a roller driven mill, you have a variation speed for the rollers, and you can straight influence the speed of the table, so a lot of vibration problem can be very easily avoided by varying the speed of the table. So you can slow down the table very quickly, and then you can go back to the normal speed without stopping the mill. As with a classical table driven mill, you have much less fast action on the grinding. So it's more sensitive to vibration.

So as first summary I would say, vertical mill is a very good machine for grinding cement, but you must be prepared, which means you must dedicate time to train the operator and to train the mechanics, and you must be sure that when the machine is in production, the people are aware of these challenges that they will face.

Thank you.

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