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Low-cost solutions for increasing production with alternative fuels: Tahir Abbas, Cinar Ltd (UK)

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

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Good afternoon everyone! So as Keith said, last time my presentation was very technical and still it's the same because the processes in the Cement industry are quite complex, especially the combustion and the interaction of combustion with the minerals. So I'll just start with some examples briefly. Cinar, Cinar was incorporated in 1988, so we have been providing services to the combustion and mineral industries for the last 26 years.

These are some of the clients, some very familiar ones at the top, but for the Asia and Africa, we have worked for UltraTech in India and also for Votorantim plant we're working on now. And Arabian cement - ACC, also for Chirag cement in Pakistan, and also for Riwal cement and Canakkale in Turkey, and also for [xx] team plant there, and AKRO plant in Sudan. For Holcim alone, we have completed over 30 projects including their largest plant 12,000 tons per day at St. Genevieve. So, when it comes to the upgrades and that was the question asked earlier on with the ID fan capacity, these are the general criteria to look at the maximum capacity which can be obtained from the plant. So cooler area 40-60, 60 on the upper side tons for day meter square, and then the burner zone thermal load 6 Mega Watt per meter square, cyclone cross section area where the material would flow 100 to maximum 120 tons per day meters square. Kiln volume, 6 tons per day meter cube, Kiln Fill, 10%. Kiln velocity at the pinch point upper limit to around 35 meters per second, Kiln Burner, 7-12 Newton per Mega Watt, but when it comes to calciner combustion and calcination in a calciner, so there's no fixed criteria. There are some

criterias of the residence time, and the velocities, but various manufacturers or technology providers are using different criterias. That's the AFR co-processing and that was the question asked before. Water, the effect of the water content on heat consumption? What will happen to heat consumption and also the production law.

So when the alternative fuels would have higher water and the ash content, then they have to be paid for or having a gate fee. Whereas the false air and Oxygen level can be optimized or reduced through the process and combustion improvement. So, these are four main criteria. This slide was presented before and heat consumption would normally go up and production would go down.

That's four trend plant, Holcim plant and they were firing chipped-tyres, and that's the area where the chipped-tyres were fired there, and it's very important to note, these calciners are designed for micro size particles, and not for two inch by two inch typical cheap sizes of the tires. So, any chipped-tyres fired over air and the velocities in this region are around 28-25 meters per second which are designed for sub-micron or micron particles.

So they would fall down and plant was absorbing build up in the hot kiln area, so they could not fire more than 20% of the thermal substitution of the chipped tires. So, a throat restriction was added there to suspend at least the smaller size chip particles or chip sizes of the tyres and the velocities in this area would be around 40-42 meters per second at the length of around 3 meters, and that would be just enough to revert these falling chips back up with the upward flow.

So that's the computational grid, I won't go through the details but just in this area, a venturi was added there to have minimum pressure drop and higher velocities in the localized areas, because the falling chip have to be de-accelerated and after reaching the zero velocity or the stagnation point then after losing weight, losing volatiles, and burning, they would be lifted up and then we can go to higher substitution rates.

So that's the plant feedback, a refractory throat restriction was added reducing the area from 7.2-5.4 meters square in the riser ducts in the earlier part of the duct, and chipped-tyre Thermal Substitution Rate was increased from 2-8 tons per hour, so that is from 20-65% of the calciner thermal input. And plant had to collect the wires after every 24 hours and with improving the chip quality, now they are doing 10 tons per hour.

So looking at the cost differential over here, the savings within the 10 net months for the operation were around U.S. $1.3 mealion and these are the study cost and that's the implementation cost, so the payback period was within a month or so. So the simulation tool, as we have seen some result from the CFD, it's a Mineral Interactive CFD, we developed and it's in-house developed tool, so we just don't use it, but we develop it and our group was one of the first one who started developing CFD course before some commercial ones became available.

So it's Multi-fuel firing capabilities so we can fire all these fuels at the same time in parallel, and combustion model is directly coupled with Calcination model and clinker formation chemistry. Especially for the Calciner, we have around 50% of CO2 which is released from the calcination, another 50% is from the combustion, and then we have endothermic reactions, so it's very important to have the Mineral Interactive part and not the CFD for the Calciner. And the model has been applied and tested over 150 kilns worldwide and calciners, and for the fuel switching in the calciner, I've just focused on the calciner, we have higher thermal substitution around 60%, sometimes 65%, and also we have hired AFR substitution rate 60%, 90%, or even 100% depending on the quality of the alternative fuels, the density and the heating value, and then we also have several injection ports available, injection location to inject these alternative fuels, and we can also find bigger size AFR, 50-60 mm than the kiln depending on again the density and the properties, and also the potential to reduce kiln generated CO and NOx, sometimes even 80% we can reduce kiln generated CO and NOx, especially in the inline calciners.

And potential of reducing kiln instabilities, we heard from [xx] earlier as three cycles and less build-ups and that is to having a maximum burn out of the fuel in the calciner and burn the fuel in suspension mode, and not falling down into the kiln [xx] of carry over to the cyclones and getting mix up with the meal. However, all these advantages needs to be tapped into and here, we see through one example, we're looking at the coal particles in Oxygen.

Maximum Oxygen here is 2.3% and the red in all the slides because more results are on the CFD, red is higher value and blue is lower value close to zero or as indicated. So we see, these are the coal particles trajectories from two burners placed in the riser ducts, so these particles are heated up and release volatiles. So over here we see,

most of all theOxygen which was coming in through the Kiln riser duct around 3% has been consumed, but some more of Oxygen becomes available so that is 21% Oxygen by volume coming in and that would push these particles toward side and also for some of the flow there, so we see more Oxygen available there.

But where these particles are travelling is narrow corridor here, for example, particles were ejected there and then moved because of the momentum of the tertiary air, which is around 50% of the momentum of the riser duct, so same strength mixing of the two streams, and then these particles keep on travelling in a narrow corridor where very little Oxygen is available, there's no cross flow mixing mechanism in the calciner.

So then if the particles are not burn earlier on, then the thermal deactivation would occur that means, the pores which have opened up with the release of the volatiles would close as the lack of the Oxygen. The heavier tyres would start simmering there and the temperatures in this region are lower also, as the temperature would be higher where the fuel particles would ignite earlier on the volatiles would burn.

And thus the Oxygen, which is not huge and that's why sometimes longer residence time are recommended or required in calciners, where fuel particles are not burning because Oxygen is not available although Oxygen is present. Just another example over her, we see tertiary air is divided into three parts, two over here and one over there, so those particles which are ejected there, and they do not burn, and they start burning quickly when we see this tertiary air coming in and mixing.

So these particles burn completely there and we stop tracking those particles, whereas those particles, coal particles which were injected there and going through the low Oxygen region will not burn until, or not fully burn, maybe around 90-95%, but these particles which see more Oxygen coming in from the upper tertiary air duct

would burn faster and better. And also the calciners are of different designs from 1.5 second to nearly 8 seconds, and various designs like auto speed design over there, and PSP, and various configuration, that is the tertiary air, and with the bends and the curves which also lead to the flow stratification that means Oxygen is away from the fuel particles, and we have to mix Oxygen with the fuel to burn completely, that's the flame, that's the oxidation principle where temperatures were minimized to reduce the formation of NOx, and give extra residence time of around 8 seconds. So flow stratification, hot-spots, Oxygen by passing not mixing with the fuel, retention time and temperature would directly affect the combustion or will burn out of the conventional fuels as well as alternative fuels CO or NOx.

So that's the case studies Calciner switching from natural gas to coal, that was the Calciner which was designed earlier on for natural gas firing, was later on converted 100% coal from 100% natural gas. So, we have two hot meals, a bypass kiln inlet over there, and then tertiary air is coming in there, riser duct burner, tertiary air burner towards the side of the tertiary air.

And then we have two Calciner burners, this is a 3D, so it's one here and the other one is on opposite side. So when we look at the velocity over here, we are looking at -10 to 60 meters per second upward component not the three components, and the streaks are the particles as they are moving up and the tertiary air is coming over there.

So here we have higher velocities and the outlet of the Calciner is on the opposite side to the tertiary air. With natural gas firing we would have earlier mixing taking place over there, but when it was converted to coal firing these particles were en-trained from all these four burners into this corridor having higher velocities so even less residence time for coal particles to burn.

As a result, we have coal burnout of around 82% which is very low, calcination around 88% and plant was observing spare buildup issues so they had to clean thoroughlly after every four hours, and the carbon in hot meal was very high, 0.3%, the recommended value is 0.005 or maximum 0.1%, and that would relate to a around burnout of 97%-98%. So plant was asked, was given a proposal to extend the calciner from the west and the east sides, and that would give extra residence time or more retention time by reducing the upward velocities, but as compared to the angle of the tertiary air, and the outlet on the opposite side, the comparative momentum of the tertiary air would increase and when we did this simulations for the plant, this idea was abandoned as the results showed even worse performance on the burnout of the coal particles as well as on calcination levels.

So after several simulations and since the parameter, burning parameters are highly non-linear, it's very difficult to assume the results or predict the results unless we compute and calculate, so that's the base case, and the simple solution which was for the plant was to move the burner from the side of the tertiary air towards this axis over there, so moving this burner to over there, and that will increase the coal burnout from 82% to 93% and calcination to 88-92% and that was the saving of 1.5 million US dollars for the plant by simply relocating the burner so we have tertiary burner over here so it's going through, more tertiary air is available for the particles to burn rather some of the tertiary air as we see higher concentration of the Oxygen there were passing through.

So, we can look at the film, so these black lines are the particles, so the Oxygen coming over there around 3% and these are the burners, and this is more Oxygen being consumed as these particles travel and some of the Oxygen consumed there, but which have Oxygen in this area, which is not consumed as low particles, coal particles are travelling through that area.

And when we look at the changing of the burner location so lower Oxygen there, around 3% and we'll have high Oxygen around 23% by mass, and that is being consumed. And since the this burner location has been changed so we see more of this Oxygen being utilized, so there we see all the Oxygen concentrations are around three.

And here we have very low Oxygen and high Oxygen. So that was for 1.5 second residence time when the calciner was converted from natural gas to 100% coal. So that's another example, we have calciner having poor burnout for two second residence time designed for coal firing, and then it was converted to 90% pro-fuel of firing. So this two twin tertiary air ducts, tertiary air is coming down and we have riser duct gases, and coal, two coal burners located in the riser duct, and then we have meal above the coal particles, which is a plausible solution and when it was designed, it was thought tertiary air coming down would mix better with the riser duct flow, but when we modeled, we saw some of the tertiary air was being forced and flown downward, and as a result the flow would be squeezed and the flow in the center, as we see from this velocity vectors, bigger vectors have higher velocity, so the flow would accelerate over there. So any coal particles which we see here, injected in the riser duct would accelerate because we have higher velocities in this area, and as a result, the burnout was very low around 70%.

So, we worked with the plant and we came up with this idea of modifying the tertiary inlets by making the horse shoe type tertiary, so tertiary it too that was modified. The tertiary air is coming from the two inlets and after heating this jets, and this is open from the inside so we have uniform tertiary air flow coming out and mixing, and that was the maximum which could be done for the 2 second residence time calciner.

So, when we look at the velocity vectors, we have after this tertiary air that's coming and the riser duct, so we have nice flow over here, more or less same size velocity vectors. So, tertiary air flow makes it quite well with the upward flow and also a venturi had to be added for a higher thermal substitution rate of pro-fuel, pro-fuel was a flop or the lighter version of the solid recovered fuel.

So, a venturi was added and these are the results from the plant before 2010 and after 2010, so clinker production was increased from 2,088 to 2,838 and also pro-fuel firing was increased from 6.8 times per hour to 8.2, and a pre-heater exit temperature was slightly reduced, and ID fan av Oxygen was also reduced, CO at the ID fan was also reduced, and also the fuel consumption which is Gigajoule per ton was also slightly reduced, so we're firing around 90% of the alternative fuel which is a lighter fraction and without losing on the fuel consumption, or the production of the clinker. So, that's a bit busy and it's quite a complicated slide I'm going to show, that's 40% pro-fuel, so when we're burning and these are the pro fuel particles, some of the bigger fraction would just fall and that is the Oxygen which went zero, blue is zero, and 23% by mass. And, below we're looking the meal particles and that is the mineral interactive computational fuel dynamics, so we can look at the meal particles. These purple color are the

meal particles, so where we have some of these particles from the, or chips from the pro-fuels which have fallen down, we see some high temperatures there, but after releasing volatiles, becoming lighter there and train upwards with the flow going up. But when the pro-fuel was increased from 40-70%, so we saw a bigger, bigger fraction of this AFR, pro-fuel particles, or chips falling down and then after releasing weight, releasing volatiles becoming lighter and are trained up, but their trajectories have changed. But the meal particles are still travelling in this areas, so that's where these pro-fuels particles are travelling and we have very higher temperatures over there.

And when we go even further with 90% pro fuel firing conditions, it becomes even worse. So a lower meal, 50/50 meal split was done for the plants, so we see from the lower meal, these meal particles are travelling in this area and these higher temperature regions are eliminated over here and this one, so for 90% pro-fuel firing plant had to split the meal into two not keeping with the one meal inlet. Just last example to increase the clinker production and that was the project which we did together with PM Technologies from 2,880 to 3,200 tons per day.

These are various pictures for the GUIDE VANE installation and the bid which we had together with the PM Tech was cheaper as compared to the other bidders, because we did not increased the volume of the calciner as was the offer by other companies, so these are the erection and, so I'll come to the calciner.

That's the four gas burners, two oil burners, and one single meal inlet, and four natural gas burners, and single meal inlet and two oil burners which had the provision to fire but were not being used by the plant, and when we look at the upward velocity component, again, very dark, blue is -5 meters that is downwards and then zero is light blue color, so there's tertiary air coming in a cyclonic motion, and then when it comes to the narrow area, that is the higher velocity as tertiary would take the area in the periphery outer area.

And then we have these four spikes that's where the natural gas burners are because of the combustion and the change in the density, we have increase in the velocities over there. And, when we look at the Oxygen, more Oxygen, red areas over there, and then this red area disappears as coal as natural gas burners are consuming the Oxygen there, so we've more Oxygen available towards the center.

And when we look at the temperature that is even worse, so we have these meal particles purple which are also being twisted because of the cyclonic movement of the tertiary air. We see very high temperature regions at the larger area. So the solution has been for additional meal inlet and also moving two natural gas burners from the top to the bottom.

So we have two burners there and two burners at the top, and by moving these two burners and having extra meal inlet or splitting the meal, it was 60/40 split. We see these, high temperature regions have been disappeared because these meal particles are travelling from that area which was higher at temperatures, and we look at the Oxygen. Also the higher Oxygen regions have been eliminated as we have more uniform distribution of the fuel as the meal particles, and that was the case before so comparing this temperature distribution to this one, we see a mark change by splitting the meal into two inlets.

So, that was the upgrade. So the residence time, retention time of the meal particles also increase from 4.6 to 5.1 seconds, so that is again of a half a second for the calcination for the meal particles without having to increase the volume of the calciner, and that is feedback from the plant, so we gain on the calcination around 8%, and then on the clinker output around 18%, and the target was 3,200 before, given to the plant and plant operated at 3,400 tons per day.

So, just some comments on the presentation, it's higher clinker production and higher thermal substitution of alternative fuels via combustion and process optimization. We are at the end of the chain because there's a lot of effort going into lobbing, permitting, and preparation of the alternative fuels, and then the feeding, shrading, and then it comes to the combustion so we have to maximize the advantages of the AFR fuels by combustion and process optimization, and also focusing on the lower Capex solutions and the shorter paybacks.


But however, there has been other non-linear parameters which we have to look into, especially the fuel AFR injection strategies where these fuels are injected with references to where the meal particles are travelling, and from where the tertiary air is coming and how these fuels are burning. And the flow stratification issues, if the Oxygen is not closer to where the fuel particles are, and if required, the use of venturi for bigger size AFR chips, needs to be burned otherwise around 20-25%.

Thermal substitution rate can be achieved without stopping the bigger size chips falling down, and also the meal splits to curb these hot spots, but all these variables are highly non-linear, so one has to use computational techniques to solve these fundamental equations numerically and produce results more representative of what is happening in a real calciner and the kiln.

Thank you!

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