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Switching to solid fuels in cement plants – technical solutions and case studies: Suchismita Bhattacharya, Penta India Cement & Minerals Pvt. Ltd (India)

Filmed at Cemtech MEA 2015, 8-11 February, Grand Hyatt Dubai, UAE

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I work now with Penta India Cement & Minerals, and as an engineering firm we have dealt with our clients, many of them in the Middle East who've traditionally worked on fuels such as natural gas and LPA4 for the cement manufacturing. Lately we've realized how, while in India we mostly go with coal fueled firing for our cement manufacturing technologies, and these days we realized that there is a need out here in the Middle East as well as in Africa for switching to solid based fuels.

So solid fuels along with alternate fuels have, when you try to incorporate flexibility there are certain requirements and certain things one has to keep in mind, and that's going to be the focus of my presentation today. State of the art cement kilns today with the ILC systems, inline calciner systems, pre-heaters up to six stage consume around 700 kilo-calorie per kg of clinker. This specific heat consumption obviously depends upon technology, the older plants, wet process plants were higher, higher than 800, 900, some of the cement plants even with new technology when they're not functioning optimally, they have higher heat consumptions around 800 kilo-calories per kg.

When it comes to electricity consumption, the specific power consumption for per ton of OPC that is CEM I cement would be around 100 kilowatt hours per ton, and whereas the best performing plants have gone down to almost 80. As if you had more fly ash in your cement then obviously you'd achieve lowered consumptions as far as electricity is concerned as well as fuel.

A comparison of coal, fuel, oil and gas with respect to heating values, there is a range especially for coal because the range is wide because you have different types of coal and they have different properties which I will discuss in a bit. Why switch fuels? As most of you operating in this region are aware, there is fluctuating price of your traditional fuels, in some areas there is non availability of natural gas, I understand Egypt has had to shift to coal based firing in the last couple of years.

Also other causes could be social causes, economic causes may be even health issues or epidemics in certain areas where you don't have access to a certain fuel that you are having access to. So in today's day and age, it makes sense to have a flexibility with regarding to your fuel use in your cement manufacturing system.

So when you're trying to add in another kind of fuel or to switch to solid fuel, with respect to fuel what were the things you will need to consider? If it's coal you need to know what type of coal it is, how fine you need to grind your coal, whether it's pet coke or coal, there would be differences in volatility which in turn causes you to grind finer in one case. If it is alternative fuel as we've just seen earlier this morning, a lot of things need to be taken care of and with alternate fuels you have a separate waste, if you're doing a waste-based fuel or a waste-derived fuel, you would have a waste processing plant maybe as apart of your fuel-handling facility.

And most important, whenever you're dealing with this new entity, whether it is fine-ground coal or alternate fuel, you have safety requirement for fuel handling and transport. And this is something, what happens is you may put in the best systems but the people in your plant also need to be aware of all the hazards or all the new requirements, not necessarily you're going from a more difficult situation but it's a different situation and you need to train your workforce to deal with handling the different kind of fuel.

So these would be with respect to fuel. We'll move onto process considerations. Well let's say you have decided on a kind of fuel, you would make to make or tweak your pyro-processing slightly to get your cement clinker in the same quality. So what else would you have to deal with, there would raw mix design because now the coal will generate coal ash which will get incorporated in your clinker, and this is like another raw material that is added to your raw material mix, therefore you would have to work on raw mix design. Burner modifications, the burner has to be able to handle the different kind of fuel, calciner may need to be modified to provide for larger residence time. While you are operating with a different fuel, you may need to adjust the fuel split between calciner and the main burner and then we talk about the emissions to the environment.

We had some discussions earlier as well as this morning. Yes, there may be an effect on the composition of the gases that are emitted to the environment, you have to have your permits with respect to the new case that you will now have, you may also need permits for handling that particular fuel depending on where you're operating.

So these things all need to be taken care of when you embark on a fuel switching project. I will just talk a bit about, well I'm a Process Engineer I have to show you something that shows flow. So we are just talking about how SO3 is absorbed or evaporates and then emitted to the environment. You have sulphur coming in through raw materials to your fuels and within the rotary kiln calciner, some of it evaporates, some of it is absorbed back into the system.

At this point sulphide oxidation may also take place but the raw material that is coming in through your pre-heater has the ability to absorb some of this, ultimately this would be emitted to your stack. So this needs to be studied once you've changed your fuel depending on, sometimes pet coke has high, if you're changing to pet coke and it's sulphur content is higher, you may have to look into this sulphur, SO3 sulphur oxide evaporation and so this basically depends on the sulphur to alkali ratio, the material retention time in the burning zone, the flame shape, the temperature, burnability of the raw mix as also the required degree of clinkerization that is the free line.

Now these are process aspects that need to be studied the moment your fuel changes. Once, these are problems or these would be issues that could be dealt with by changing some other things in your system. It's nothing that is difficult. It's just something that needs to be paid attention to. Again you've got a new entity in your system, you need to look at the layout considerations.

Bear in mind, if you are switching to fuel obviously it's a brownfield project. So there are, as with other brownfield projects maybe alternate fuel or waste heat recovery, there are some certain constraints of the existing facility within which you have to design this new material handling facility. So you have to pay attention to fuel receipt, handling and storage then you have a certain safety consideration at the same time you have to optimize distances so that your operating power costs are kept within certain limits.

There are traffic, on-going traffic constraints your project execution related issues, so you have to ensure that your plant is in operation while you are putting in the new coal handling system and obviously there would be with respect to fine coal you would need coal firing bins, an intermediate storage and a firing modification for the burner pipe which brings the fuel into the calciner or the kin.

Just a look at pet coke, bituminous coal, lignite and anthracite and I have just tabulated some of the properties of the different kind of fuel that were considered by one of our clients and this interesting case, when the client wanted to use Nigerian coal which was lignitic in nature and it had a lot of moisture that couldn't be dried way, also their volatility were different, compared to what they had initially thought they were wanting to use South African and we know instances in India where people have gone up to 100 persons like lignite as well. However this client, he asked us to look in to what the OEM was providing and the OEMs design finally could accept only a certain amount of lignite because of the high moisture that would remain in the cold once even after drying and grinding. So as a result the extent to which he can actually replace with lignite is limited because of the process limitations.

So the these things needs to be evaluated upfront when you decide on what kind of fuel mix you're going to work on. This kind of data would form the design basis for your fuel switching project. Here is another trick that, depending on the volatility of the fuel, you require certain fineness and if it was the calciner fuel we would go by this line and then if you had 20% volatile, you would decide that you wanted to grind to a certain fineness and if it were around 8% or 10% volatilities, your fineness of grinding that is residue of 90 microns and residue on 45 microns were differ. So this is kind of a normal graph that can be used to decide how fine you have to grind the fuel when you are deciding on a particular type and it would differ with respect firing and in the kiln firing in the calciner.

This is where we have perfect coke and for other coal and also the specific power consumption. Please bear in mind that if you put, if you are now substituting liquid fuel or natural gas for coal, you would have added operating cost with respect to coal grinding or pet coke grinding and this gives an idea of the specific power consumption at different fineness for coal and pet coke in the VRM. Of course different manufacturers would have slightly different number here but this is kind of an average for specific power consumption for grinding of coal and pet coke. Now I come to a case study where one of our clients has placed or added coal grinding and coal firing to almost one, two, seven of his facilities and one more, there's an eighth one as well and what they have had to do therefore.

This is just to give you an idea of what the project would entail and typically this was the clinkerization amount for each line, and I'm going by the heat consumptions that they are observing right now. This is four stage pre-heater systems and these are 5 stage, if I am not mistaken. This is the calorific value of the coal they intend to use.

This is the coal consumption they have projected and as a result, this is the milling capacity and this is the crusher capacity that would be required and finally these were the mills that they chose to buy around these capacities and these are the crushers that they have had to install in their existing cement producing locations. Sometimes if you have multiple lines, you can have a single crusher area which check out, mandates the requirement of your multiple cement kiln lines.

A typical layout or rather a flow sheet would have the coal storage areas, from there you would go to the hoppers, these hoppers and there's a crusher, and from the crusher, you can got to the hoppers, from the hoppers you would go to the coal grinding section and this is finally the fine coal beads.

Again, layout would be project specific if they were brownfield, of course if they were greenfield, it would be easier to get your, if you wanted flexibility you could do that and have multiple fuels right decided at the beginning of your project. With fine coal, there are safety issues that need to be taken care off with respect to using inertization and having proper census in place to be aware of whether unsafe conditions with regarding to fire or sparks are occurring and you always have to ensure that these safety requirements are also taken care of.

So therefore, typically what we recommend if you are at the existing installation and you want to include coal, therefore, you would, or a solid fuel and this could also be applicable to you if you were doing alternate fuel project with regards to the system project requirements. I think you will hear one more talk on alternate fuels now and one later on in the next session.

So a feasibility study to figure out exactly what the project entails, the environmental permits that are required for handling new material that could be important. Optimum system design, project scheduling to match with your down times or if you are taking a regular down time in your cement manufacturing so that you can tie in at the correct time, of course there will be an impact on your specific power consumption and that you have to bear in mind up front and the logistics for the new fuel that is something that you would want to be prepared to deal with.

So I am done with what I wanted to speak to you about and if you have any questions I'd be ready to take.

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