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Controlling particle size distribution for increased grinding efficiency: Stuart Barton, Xoptix (UK)

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

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Okay, so let's just start talking about really the subject of what I want to discuss which is the development and the improvements of technologies for measuring particle size and where we are today in this technology. Okay, I've got to find the button and should we try that. Hey, I'm almost in control now, I think we are going to be alright.

Okay. Well, one thing that was absolutely clear from Michelle Malkin and Xoptix was that of course the cement fineness and the size of the particles is critical for its performance and whether you, and it's always been monitored, it's always been a key monitoring point for the quality of the product and the salability and the use of the product and usability of the product in the various industries.

Now up until the last few years, this was exclusively in laboratories, that was the only way to do it and I think Xoptix allowed this, Blaine aparatus are used, Sieves are used and more recently but perhaps not quite so widely, laser diffraction has started to be used as a technology for measuring particle size. Now they are all used, all of these techniques are used because of course they give valuable information on the finished product, they tell you information on whether the finesse of your product whether it is appropriately ground but like all techniques, that are advantages and disadvantages to each technique. I was very grateful in a way to Xoptix because of course you will see if you come to our booth that's the technology that we are advocating is a laser diffraction.

Now, I can argue I think somewhere on my business card I've got the name sales and so I have to argue all of the sales points, I can argue that laser diffraction is a technique, it has advantages over the others but no techniques is perfect, there are advantages and disadvantages to any technique. I would suggest that some of the benefits and we'll talk about the benefits first of laser diffraction is the results are fast and reproducible, instead of a single parameter, you get a complete distribution of the particle size but actually, that's the only useful if you know what to do with it.

To a certain extent, less operator to operator dependency, but that again depends on the quality of the operators and the key points, the key advantage I guess that I want to talk about is the possibility to automate the process because you don't have computer generally attached to the Blaine apparatus, you don't have a computer attached to a safe generally, automation and tying it up with your process was not so possible but as soon as you've got computers involved they can talk to each other and automation becomes possible.

So, I said that are advantages and disadvantages of every technique, some of the disadvantages are, well we give a complete distribution instead of a single Blaine number, what does that mean? How does that compare with a Blaine analysis or with a sieve analysis, and another rather difficult situation I'll use my pen, if those two particles in the sieve are the same size, and yet they are different by other techniques, so different techniques will give different answers, for different reasons.

So with that, which parameters do we trust? Do we trust the Blaine? Do we trust sieves? Do we try and pull them all together and become particle size technology experts? No we want to make good cement, that's what we are interested, that's what you guys are interested in, I love particle size. I'm a very sad guy I live particle size but you guys are in making good cement and so, I guess we need to work out the best way to do that.

Now, nevertheless all of these technologies and they are pretty widely used, and laser diffraction has become reasonably well accepted. Okay, in the moves towards more automation, robotic labs were introduced and are still widely used, take advantages as it says here, potential for more frequent analysis because the samples can be taken automatically from the process, you can analyze more often, less operator intervention, less mistakes for you and me and I think especially him to make and it's possible to measure multiple parameters.

With this robotic lab system you're just not measuring particle size, you can XRF and XRD as well. So, these do have some benefits. With this sampling is still relatively infrequent, so it's difficult to have a fully closed loop feedback process and your robot is giving samples to laboratory instrumentation, which perhaps was not designed for such frequent operations, so more service ability to the laboratory systems and as I've said because of the the lack of the sampling still relatively infrequent it's still not really possible for close loop operation and another disadvantage was that it's very expensive, relatively speaking. But it's been world widely accepted, it's a useful techniques, really being critical about it. So the next move was to start putting instrumentation actually onto the process, so we're measuring in real time, and I'm going to jump about a little bit, I'm going to see if I can find a laser point, one of these and I'm afraid I can't point at both screens, so I will just try and point to one screen.

We have our main process, we have our 200 tones per hour coming down here, we take the sample out, a sub-sample which passes back in, and we take it even smaller sample and we pass it through the analyzer. In this technique, we are measuring every second, we are measuring in real time, and so the data can be fed back to the processed DCS or PLC and automatic decisions can be made on what is happening in your process, and very quickly if I can work out how to do this, this might not be seamless. Any of you who've been to the stand and have stood there will be very bored with this video already, but for those of you who haven't, it just explains more vividly the process. So, we have a process pipe where we have our 200 tonnes per hour flowing through and we turn valves on and we apply air and we start to take the sample through the instrument, so we're taking the sample in real time.

If we open up the instrument, we can see inside is a laser diffraction instrument and so we're actually measuring the sample every second, in fact we're measuring 2, 000 times a second, but I think every second is okay and we're measuring every second, we're feeding this information back into the process computers for close loop control .

So why measure online? Why spend the extra money with already establishes, some people don't like the laser diffraction results because they don't understand the Blaine results and they don't want to do these things, and so, okay. In fact the biggest error in any measurement is not the instrument, oops!

I'm very sorry, how do I go back? The biggest error is not the instrument to instrument variations, the biggest error I'm afraid is user. Okay, all of you, I don't think it's me, is it? It might be me too, actually, yeah. The biggest error is human error, you take a sample from your process to the lab, you measure it, and you say, hmm!

Hey! That's a little bit out of spec, what do we do? Do we change the spec? No we don't, we're going to get another sample quickly, we measure it again, oh! it's alright, no problem, Okay? Because we get human error in the measurements, we get sampling errors in the measurements, okay? So by measuring online we reduce these errors completely. Okay, and the real benefit is because we're measuring in real time, we can see changes in the process, okay. So, it's very, very easy to see what's happening inside the process, we can see changes, we can either have this as manual information in our control room or we can have this information feeding back into the PLCs or DCS control systems that are controlling your cement plant, and okay, so why's that useful?

I told you that the biggest, in two slides ago, I said that the biggest error was me or you or, and I told you that online measurements are more accurate. This slide shows two things, the blue curve is the online measurement, okay, and the red curve is an offline measurement where some poor technician took 90 samples, you can see at bottom there, sorry, there are 90 measurement, you took 90 samples and measured them in the lab, okay and what it shows is two things, it shows first that online measurement is little lbit more precise, secondly lab measurement is a little bit more, you are going to get user errors. I don't know did you measure this sample size, sir.

Yeah, somebody measured those samples and the errors from sampling and from user measurement is not so precise. So we have more precision with online measurement. Another important thing about that slide, the offline measurements, 10 minutes per measurement, 15 minutes per measurement, took a very diligent technician two days to measure, two days to find this information was happening in the system and the online measurement took no time from anybody. Okay, but, if you take a laboratory instruments and you put it into a cement process, then you're going to have a very broken laboratory instrument quite quickly. So online systems must be more robust to cope with the more hostile production environments.

We want to calculate fast, 2000 times a second or we normally integrate over one second times so that we get real time feedback of what is happening in the process. You need OPC and other industrial standard communication protocols to feedback to your DCS, PLC computer systems and of course cement is a little bit abrasive, so you need to make sure that the components you use are very wear resistant so these instruments will last for years.

And minimum number of moving parts because you don't really want moving parts inside your cement mill which will wear out much faster. So, in fact this slide that you've seen before was actually very good. The only moving part was the auger which is pretty standard. Everything else, no other moving parts involved in the system, okay?

But let's remove the moving parts from the auger. We have just patented a new sampler with no moving parts. I don't have time here to explain all of the technical details of that sampler, but that sampler will sit in your process with no moving parts, diluting the sample representatively to the new, to the concentrations required for in-line measurements.

That simplifies this previous part. Removes the auger, no moving parts, completely reliable in-process system. So does it work? And these graphs show a typical output from an online system. So we have size, this is time along this axis and this is various parameters of size on the y-axis. So on the x-axis, we have size. This was the particle size using the conventional auger sampling, this was the particle size with the new sampler, and you can see there's absolutely no difference.

That they are either both wrong or they are both right, okay? No difference at all in the deviation. You cannot see from this distance, but this time scale is a very short time scale. That is a two hour period, so you can see that we're monitoring many, many times. This will, I think 5, we're monitoring every five seconds in this case. Okay, Real time in-process analysis is now able to be readily integrated into any cement process.

It's become much, much easier to integrate. The cost of the systems is now often lower than the single laboratory system, okay. So the cost of doing this is often lower than that and so what benefits do we get from it? We can increase the on-spec Product throughput, we can improve product specification tolerance on a recent, I'd have to read from this because I can't remember but on a recent installation, we increased throughput by 3%, just by installing this equipment and I will show you why in a little while.

We improve the 28 day strength and we also improved the 28 day strength standard deviation by a factor of four. So we optimize the consistency of the product. We can reduce the energy cost because we know what the size is, instantaneously we're measuring in real time, reduced waste and it's all about minimized production cost, so how do we do all that?

You remember this slide, this slide tells us one more thing. The vertical line at record 40 shows the point when we closed the loop, when we fed the information using a PID controller, into the DCS that controls the process to actually use the particle size to automatically adjust the parameters of the mill to control the particle size data and you've a two, what looks like completely different products. Everything else was possible offline, that's only possible to improve that quality and consistency of products can only be done by online measurement. So we've, it's all of these things are about cost and sometimes I say I can't remember whether it's $1 or $1 million, but what actually it is about, it's the payback time and in the recent case where I quoted, where we'd a 3% increase in throughput, just that 3% increase in throughput, paid for these instruments in three weeks. That's all I wanted to say at the moment.

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