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New high capacity bucket elevator developments: Fernando Libonati, Aumund (Germany)

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

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So we'll be talking about the new high-capacity bucket elevator developments from AUMUND. We have around 7400 bucket elevators being sold worldwide, and between belt and chain. So we'll first start talking about the belt, and the new developments on belt, then we will shift to chain, and the new developments in chain, and then finally we'll end up with the technical and commercial benefits.

So regarding the Belt Bucket Elevators. We have 3900 units installed, and we can reach capacities of up to 2000 tonnesnes per hour, for fine material, up to 10 mm. Now we've belts with strengths of 4200 newtonnes per mm, and we can reach lifting heights of up to to 200 meters. We found the opportunity to develop this belt bucket elevator, not only for fine material, but also for coarse material.

Coarse material we mean up to, majority 80 mm. Now not only, did we want to develop for coarse material, but also high capacity. So first we tried using single wide bucket of 1400 , 1600 mm wide, which is possible to use, but you need special reinforcement to the buckets. So we found that the best configuration, is to use a double or triple bucket configuration. Now, the limit here, is the width of the belt which can be found in the market is maximum 2.4 meters. So with these 2.4 meters and a triple bucket configuration we can reach capacities of up to 3000 tonnesnes per hour. Now the tricky part here, is to on the feeding section, because we have three buckets, so we need even feeding of these three buckets, and we'll talk about this later on.

So we'll just go through the steps, of investigation through this new development with the belt bucket elevator for course material. So first we started with the discrete element analysis, so with this we would feed up the boot completely to start at a critical situation,and here we can see the behavior of the feeding into to the buckets. We started out with a 10mm which was our experience, and went up to a 100 mm, and with this analysis, we could check, the forces acting on the fixings.

So, this was a very important first step. So, another important aspect to look at was the discharge, because if you have a different bucket configuration, different bucket design, with different protrusion, you need to insure that you have a correct discharge of material, so the right material projection, because if you're too fast or too slow, you can end up having your material, all to the boot. Then we went to the test elevator.

This test elevator is located in our head quarters in Germany and Limburg. So, this is a closed circuit. We have a belt, a bucket elevator, and we used for this test, several different types of grain size going from 20 up to 100mm. And in each one of these groups, we did tests for 100 hours. Now with these 100 hours, we could get exactly the data we wanted. If you run it more than 100 hours, you start having degradation of material. A really important aspect here was to use the hydraulic cylinders on the tail drum, because these are approximately nine meters center distance elevators, so we needed to simulate higher lifting heights up to 100 meters, so we could do that with the hydraulics cylinders.

Regarding the bucket design, we went through several different designs to till we reached the ideal one. So all these different designs were used in the test elevator, from five to ten buckets, we would change the design and we could see the behavior which with each one of them, till we had our ideal bucket design.

The final test was regarding fatigue, and here we wanted to ensure safety on the bucket attachment. So this in critical situations of scooping, so we wanted to be sure what's the maximum force needed to rip these fixings out of the belt, and the results were per fixing two tonnes . Here we have two different critical situations. When elevator stops, full of material in the buckets, and when you've excessive filling by flushes. So here we've the old version, and the new development, and we can see on the red circle there, that the material is completely in contact with the belt, and behind the buckets, this will definitely damage the belt. And on the new development, you can see that the material is restricted to the buckets, so it has no contact with the belt, and this is also an advantage regarding temperature. Let's say if you've a material temperature of 130 degrees Celsius. As you have no contact to the belt, only 80 degrees Celsius will be transferred to the belt, so you can have a longer life time of your belt. So AUMUND applied for a pattent, and the pattent is pending for this new development.

Another point that I would like to point out is, when the buckets go through the pulleys, you still have 12-15 millimeter gap. If you're working with dry materials, this is no problem because this fine material will come out. But if you're handling sticky and material with high moisture, it will be trapped here, and later on, will damage the belt. So what we did in this case was to improve the sealing, so we have extra rubber profiles which are attached to the buckets, and here we can ensure that no material even if sticky or moist will get trapped and damage your belt, and with this, we improve the lifetime of the belt.

Experience we have with materials with high moisture, we have used use these ceramic friction liners, which increase the grip. So, we have experience with coal at 15% moisture, and this works without any problem. So we can say that up to 80 mm, we can use a belt, and this is more competitive solution than chain. So you have a 20% saving there. But if you handling a majority of grain size, which is higher than 80 mm, then we do recommend to go with the chain. But not only the grain size dictates the type of elevator. So we also need to take into account the process conditions, so this means mill type, re-circulation rate, frequency of flushes. So, looking to a cement plan.

Where are the two critical places where we can find these high capacity elevators that could have, process problems is in the re-circulation of raw material, and re-circulation of cement mill. And especially when we take into account applications with roller press, where the capacity of elevators are five times the mill capacity.

So for example actual situations, we have mill capacities of 400 tonnes per hour, so this means the re-circulation bucket elevator will reach 2000 tonnes per hour. These are high capacities, and the future requirements say that the mills are even higher capacities, so above 500 tonnes per hour. This means we would need bucket elevators for even higher capacity than 2500 tonnes per hour.

So, for this reason AUMUND made a new development on the chain bucket elevators, for extreme high capacities, and we will show this later. So which are the typical conditions for a raw mill re-circulation? We have capacities up to 2500 tonnes per hour depending on the mill type, temperatures up to 130 degrees celsius, grain size up to 150 millimeters, you can see a photo there, then density 1-1.8 ton per cubic meter, now this depends if you're using a roller press for example you get the material is compacted so you higher density, so it depends on the mill type, flushes into the boot depend on the process conditions, and build up and caking, now this depends on moisture and humidity. So if you have high air humidity, and a lot of fines, this starts building in and the casing and that's what it looks like, here we can also see a picture. So specifically for the roller press, why is it critical here, the bucket elevators?

Because we will handle extremely high capacities, and we have no control of the reject feed. The reason for this we have no feeder, before the bucket elevator. So everything goes directly to the boot of the elevator in case you have a flush. You also get a higher density of material compacted by the rollers, and if you have a malfunction in the roller press, the rollers open, and then you can easily get these flushes, and then higher dynamic stress and the strength. So for this reason, with the chain can withhold, this high stress. Now going into the chains, we have 3500 units installed worldwide, with possibility to reach capacities up to now, of 2400 tonnes per hour, for coarse material up to 150mm.
Now the standard, single strand chain bucket elevator, reaches 1500 tonnes per hour, the double bucket strand, reaches 2400 tonnes per hour, and now the new development is this triple strand bucket elevator, WWT, and it can reach 4000 tonnes per hour, with only one elevator.

Now for this new development we also use some of the features, of the previous elevators, which have proven to be very good, so why not use it for the new development? So we consider also central chain, the advantages if you are using double chain, when you have elongation of the links, you can have misalignment, bending of the links, bending of the buckets, so with central chain you don't have this problem.

Another feature which we continue to use is the patented connection between the buckets and the chain. We use angular brackets, and these brackets have loose connection with the bolt from the chain. So this means the vibration is compensated and not transmitted directly to the buckets, so you don't get bucket cracks.

Another feature we use which is also very nice, we don't have sprockets, we use drive ring which is straight. Now for this, in order to get the right grip, we need the four point support. We use the two links, and the two bushes that create the necessary grip to make the elevator turn. Now with this, we can reduce also the wear on the bushes, and it's a homogeneous wear on the rim as well, because you don't have the teeth, and you are not only hitting the same spot.

This is the chain family, that we have, going from steel plate chains up to forged link chains, and we have breaking loads of 400 kilo-newtons up to 2450 kilo-newtons. And these chains all come from Germany. Now under the new requirements say that, we need higher capacities and even higher center distance. So for this reason we also had to develop a new stronger chain.

Now we came up with a AU 19.3, with the breaking load of 2450 kilo-newtons, this is the strongest chain in the market. Now to reach this chain we also needed to go through the same process with fined element, method analysis, then with tensile strain test, fatigue test, and fill test with strain gauges.

So going in to the references, Aumund has 200 chain bucket elevators, for capacities from a 1000-2000 tonnes per hour. 160 from these are for mill applications, and from these 110 are located in Asia. So we can see how important our market here is. Just to give you an example, this was a high capacity bucket elevator delivered to a housing plant in India in 2013. So just to have a look at the capacity, here we can see this is for 1900 tonnes per hour.

So, we are dealing with really high capacities. And now even more because we can reach 4000 tonnes per hour, so here when we look at the drive station of this triple bucket elevator, we can see that they share the same shaft, and the advantage here is that we use four bearing supports, so we don't need really large diameters of shaft and we have a double drive.

So these bucket elevators have buckets of 800 - 1100 millimeters width, with speeds from 1.6 - 1.9 meters per second. On the tension side, we also used the same system from the previous bucket elevators, but different from the drive unit, it's completely independent. So we have this gravity tensioning box, which are independent because you have different chain lengths, so they can tension independently.

Also for the bearing, we use the maintenance free Ni-Hard bearings. What we mentioned in the beginning about the triple shoot to feed these three buckets, this was also Aumund design, and here we wanted to be sure that there are no moving parts that involve maintenance, so it's completely maintenance free.

So we came up with two different solutions, one for lateral feed, which needs a little bit more height, and one for in-line feed. So the advantage of the lateral feed is the flexibility in arrangement. So you can have a feeder or conveyor coming from any direction. Now here, we can see this development, I can show you through this graph application for 3, 300 tonnes per hour, where each color represents one of the outlets. So here we can see in each one of the outlets, we get approximately 1100 tonnes per hour. So even distribution. OK, coming to our conclusion, the technical and commercial benefits. The technical benefits. We have a machine now, elevator to deal with extreme heavy duty applications like roller press. We can reach capacity of 4000 tonnes per hour with only one elevator.

We can reach also sensor distance with chain up to 70 meters, with a really strong chain. We also delivered for 90 meters, but it was a smaller bucket width. We have a less footprint compared to three independent elevators, and optimal bucket filling. So on the commercial side, it's much cheaper option to have one machine instead of three, and it's a more simple and closer compact arrangement, which involving feeding the dusting everything is more simple. So here we can see that if you have three independent elevators, you need a certain spacing between each of them and then the feeding point needs to be much higher than that, so, you can see the difference here, the messages, instead of three, we can have only one bucket elevator for very high capacities. Thank you very much.

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