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Kiln Assistant
The Kiln Assistant is a computer control system carrying out the daily task of running a cement kiln. The Kiln Assistant makes a complete calculation of the gas flow, fuel flow, heat balance and necessary changes to the kiln operation. All calculations are performed using only high reliability measurements. Since the kiln gas flow is measured by the ID fans, we are able to determine the thermal power introduced into the kiln. This makes the Kiln Assistant independent of having the correct burning values and accurate measuring of the fuel feeds, which is important when using alternative fuels.
Seen from the operators screen, the main picture looks like below (taken from a FLS ILC-E kiln):
In this picture the operator can select the production, the oxygen percent and the specific heat consumption (kcal/kg clinker) or he can leave it to the system and just select maximum possible production and automatic kcal/kg control. The minimum O2 makes the system do a correlation between the CO level and the oxygen and select the lowest possible oxygen percent to get a certain CO level. Normally the operators select as above and therefore receives the values for production and kcal/kg from the pictures shown below.
The Kiln Assistant will then adjust the kiln speed, rawmeal feed, ID fan speed and all the fuels to achieve the kiln torque the operators want.
Below this picture you have 4 more detailed pictures, which you reach by pressing one of the buttons: Production - here you set up limitations controlling the production. Emission - here you can set the limitations controlling the oxygen level (at present). Heat Consumption - where you control kcal/kg. Fuel Mixing - where you set up how the fuels should be mixed.
If we take the pictures one by one, starting with Production:
The operator here inserts the limitations the Kiln Assistant
should obey with respect to the production level. Only the value
(recalculated as production) closest to the limit
will have influence. You can have as many limitations as needed. Using the gasflow as the limiting factor can be advantageous if you have
excessive rawmeal recirculation from the lowest cyclone stage, like in this kiln at the time when the
snapshot was taken. The limitations has big influence on how the system will
react to changes. If, like above we are running on one of the gasflow
related limits, changes in the needed kcal/kg will be carried out by
changing the kiln speed and feed. If we were in production limit, the same
change would be done by changing fanspeed and fuel. If we were close to both
limits, part would be done by changing fanspeed and fuel and the rest by
changing kiln speed and feed.
At present you can insert the desired CO level and the system will then make a correlation between the CO level and the O2 setpoint will be changed so the CO level will be close to the desired. In the picture above can be seen that if we want an average CO level of 0.1% the system will suggest 4.1% oxygen setpoint. This value is transferred to the main picture, only if emission control is switched on.
If you go back to the main picture and press Heat Cons, you will get:
In this picture you enter the kiln torque you want in the upper left part. The system then adjusts the specific heat consumption needed to reach this. The NOx and cyclone temperature levels automatically adapts the the levels needed to get the desired torque. In the situation above it can be seen that the kiln has been slightly too hot and the kcal/kg has therefore slowly reduced. If the operator wants quick action, for instance while heating up, he can enter the kcal/kg directly. How the heat balance should be made is selectable by the operator. Above he has deselected to have compensation for both exhaust gas and clinker loss (perdidas means loss in Portuguese). If you have a good correlation between the FCaO and the combined temperature indicators, this correlation can be used to directly manipulate the setpoint. If a good kiln camera picture is available, this can also be included.
During operator training we let the operators insert the kcal/kg manually to get used the the kiln reaction.
Again from the main picture, if you press Fuel Mixing, you will get the below picture:
The picture shows fuel mixing for an ILC-E kiln, where we keep the ratio between the riser pipe fuel and the main burner fuel constant (15%). The operator has selected control of the petcoke in each firing location, and consider the rest of the feeders as measured disturbances (see the tick marks in the control column). This means variations in the riser pipe alternative fuel will be compensated in the riser pipe petcoke and variations in the main burner alternative fuels will be compensated in the main burner. This also means that the fuel feeders can start and stop as they like (and they do!) - it is immediately compensated.
The fuel system can have as many fuel feeders as you like. The ratios between firing locations are using the t/h and burning values of the individual fuels, but the overall energy is determined by gas flow, chemical composition of the fuels and oxygen consumption. This has proven superior to trusting the fuel feeders.
If the individual fuels has a content of something you want to have a limit, like Chloride, you can, by telling the system the Chloride content of each fuel, make the fuel mixing deviate from the operators choice of mixing, in case this would lead to a too high total Chloride content.
If you want immediate compensation compensation of the combustion air and energy when the fuel mix changes, we need an ultimate coal analyse of each fuel like the one shown below:
The analyses are used to calculate the average fuel composition and the necessary combustion air to achieve the needed thermal power. They do not have to be precise since deviations are automatically compensated in the kcal/kg.
Comments:
Most of the Kiln Assistant is pure physics. Only the control of kcal/kg has some religious aspects. How much action do we want to take if the torque is 1% below the target? This is a matter of temper and has to be agreed with the operators. The rest is pure calculations - and some experience.
During commissioning we go through all externally involved control loops to make sure they are as good and stable as they should be. After commissioning we follow each Kiln Assistant for around a year with near daily remote checks of the performance.
Should you like more information, please contact us. 
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