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Scalable sampling solutions for in-process particle size monitoring: Stuart Barton, Xoptix (UK)

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

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Okay, I want to just talk a little bit about particle sizing in cement. It's a fairly obvious first statement that the fineness of cement is critical for its performance and it's always been monitored ever since cement was first produced, therefore it's probably obvious from that, that the closer and the tighter the control and the better that we can monitor the furnace, the better the quality and the consistency of the cements that we can produce.

Now until recently this fineness has been carried out by various techniques in the laboratory, blaine apparatus, sieves, and actually this must be a very old slide because I've said more recently laser diffraction. Actually laser diffraction has been used in cement plants for more than 25 years.

Okay all these techniques give valuable information, otherwise they wouldn't be used I think that's another fairly obvious statements. I was at the cement plant in the UK a few months ago when I was speaking to the laboratory manager and she hated the laser diffraction instrument, because it gave different answers to the other techniques.

Now, what I said to her is that she should be worried if it didn't give different answers, different techniques by definition, will give different answers. We take for example I need a drink, I'm sorry if I lose my voice halfway through this presentation, I think I'm going down with a cold so that's if I could open this, this is a good start.

Right, okay, that particle has just changed its properties. It's almost the same dimension, but the absorption of that particle by blaine apparatus will be completely different. Different techniques will give different answers, and it's what you do with those answers that define the quality of the data that you receive.

Okay, some of the reasons that laser diffraction has become popular. The measurements are fast and reproducible, instead of one or two parameters, you can get a complete distribution of the particle size. Arguably less operator to operator dependency although some people would dispute that, but of course because a computer is attached to it, computers are very clever things they can crunch numbers very well, it's possible to alternate the system. Some of the disadvantages I spoke about one of them, it's going to give different answers to the some of the techniques.

It's no a do agree so which is correct? Is the safe correct, is the blaine measurement correct, is the laser diffraction correct? The are two possible answers to that, they are all correct or none of them are correct, you choose which one you want for that. So more training is required but the technology is not pretty widely used.

In some cases robotic labs are used for automation and you take the human out of the equation and this potential for more frequent analysis. Obviously, less operated intervention and of course one very important thing, it's possible to measure multi-parameters not just size, you can measure XRF, XRD and particle size, in the same laboratory.

While it's almost online it's not really online, the sampling is still relatively infrequent. So typically every 20 minutes. You're then making more frequent measurements in laboratory instrumentation which was designed not to be used as frequently and hence the reliability of less ragged laboratory equipment was questionable and so not possible to close the loop because of the infrequency of the measurement and it's actually very very expensive.

Okay, now in-process systems have been available for some time, and in this case we use an augur screw to extract the sample, and then the sample is taken through the instruments and if we and I don't know how we play that no, no. Okay, well it's not working very well. I never worked with animals, children and PowerPoint presentations, no worries, it's OK, it's not so important, I can jump about in point.

The sample is taken out of the main process, diverted by an augur, and then a sub sample is taken through the particle sizer, and fed back into the process. And so we're actually measuring in real time. The sample data can be sent to the process DCS or PLC to close the loop, for particle size analysis. And because we are now seeing changes just immediately, it's now actually possible to, this scale is time, and this is particle size, it's now actually, it's possible to see the changes in the process, as they happen, and so it's possible to respond to issues, the problems within the process in real time.

Okay this graph is, oop! I'm very sorry, this graph is 90 measurements at one minute intervals. In fact the online system is capable of measuring every second, but this was 90 measurements at one minute intervals. And the blue plot was the online instrument and the pink plot was the lab instruments.

And the graph below, shows two things, online and offline measurements agree very well with each other, there is a difference, you will get a difference between any two instruments, between two manufacturers and the difference is not great but online measurement is actually more precise than labaratory measurement.

And why would that be? Well, this slide is taken from a 30 year old text book on particle sizing. And it said, that for any instrument, you will get a variation comparing one instrument with another instrument, there is going to be some variations. That is not good news and they are very expensive and why should there be a 2% variation? That, how we put the sample into the instruments gives an even bigger variation, which is also not good news.

Sampling, a lot is talked about sampling in measurement, if we don't take a good sample from our cement process, we can't take any good information from that analysis. And I guess maybe to explain that, in my pocket I've carried some strange things, I've got some ball bearings of different sizes. In that bag, there's only one biggest ball, okay? I've only got, one in here is the biggest.

If I take the biggest one in my sample, if I take one 10% of this, if I tak eit, I assume that they're 10 of them. If I don't take it, I assume there are none. So sampling is very very important. But the biggest error, is him or me, or you. Okay, the user to user variation. Now, this looks like very bad news, and standard operating procedures can get rid of a lot of these.

You know this is head line news, it's not real life, these issues are still there. And the reason that online measurement is more accurate, is that we can get rid of those three errors out of the process. Those three errors can be removed from the equation. Okay, going back to this graph, another benefit, the offline measurements took a very diligent technician two days, between one and two days to measure and collate.

The online measurements took no time from anybody. So we have less labor intervention. So what's important for in process? The equipment must be tough. I have been in some wonderfully clean cement plant, but I've also been in some pretty horrible cement plants, and the environment is not the best for instrumentation.

We need fast calculations, we want to measure every second, we want to see what's happening with our process. We need standard OPC outputs that can talk to the PLC and DCS's of the process plant. And the intro needs to be robust but wear resistance ceramic linings so that the instrument doesn't need constant maintenance.

And of course a minimum number moving parts to ensure trouble free operations. This solution ticks most of those boxes, but we have the moving parts of the organ. So that is not completely ideal, this have been known to to fail and in most environments to block. It would be a much simpler installation if we could use just a very simple sample pro to take the sample out to the process.

However, representative sampling is such that at 200 tones per hour pipe, this is not a viable proposition. We have recently patented a sampling probe which actually get around these full processes up to about a 120 tonnes per hour and by adding an interstitial jacket around the sample probe, we can control the air to that probe and sampling is much, much more tightly controlled.

Just to show that blown up, by controlling the input air into here we can take, we can control how the sample is taken. It's just as simple as a standard probe, minimal additional setup, abrasive resistant parts and suitable for smaller scale output up to about 120 tones per hour.

For larger scale, we have another patented multi stage dilution probe which also dilutes the sample with no moving parts. So we can then take a diluted sample out of the process and this fits directly into the process again, it is abrasion resistant for long life and we can sample in processes of up to 300 tones per hour.

These plots are particle size, this is time, a long this scale, particle size on this scale and this shows the plots for conventional order sampling and for the new sampler, the results are the same. The sampling is robust, the sampling does work. So, we can now much more easily integrate real time analysis, in process analysis into any cement process.

The cost of doing this now, is often lower than conventional laboratory equipment. Okay and what benefits can we see? What are the benefits. All of these, maximum on- spec throughput. The quality of the product can be improved. The energy cost can be reduced, completely reduce waste because we see what is happening when it's happening.

In the end it's all about saving money. As I said at the beginning of the presentation, the fineness has always been monitored. You need laboratory systems. You need plane operators, you need sieves. You need laser diffraction systems in your laboratory. You don't need online monitoring.

If it doesn't save money, it is of no use to you. Another benefit, we've seen this graph a few times. This vertical line of record number 40, shows the point that the PID controller was started. This was feeding the particle size data back into the DCS, to automatically adjust the classifier, to control the particle size.

So the improved quality of the product is only possible within process measurement. We have a case study which was published in May's edition of International Cement Review, where one customer had a pay back time to return on investment, for less than three weeks. We would normally see that the improved performance would mean return on investment certainly in weeks rather than months.

And that's about everything that I wanted to say.

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