if on increasing the feed rate , if more CO2 is getting formed then volume of the exhaust gas should increase and consequently , the fan power should increase.

But in our plants we have observed that as soon as feed is increased, the load on the gas is increased and therefore the preheater exit draft also increases and consequently fan power increases. Can you throw more light on this?

Do you have any automatic control loops? Is there any water injection responding to changing gas temperatures? Without more intimate knowledge of the particular kiln it is almost impossible to diagnose these things.

Actually, we have got two FLS make Simulators at our place. One is having ILC Kiln and another is having SLC Kiln.

In the ILC Kiln, the fan draft is in the manual mode by keeping the set pt for the fan speed at 89.1% for which fan power indicated is 1810 KW. The feed rate is in manual mode. Between the preheater exit and ID Fan there is water sprinkling system which cools the preheater exit gas and works in auto mode .The Kiln speed can be operated either in automatic mode or manual mode. In the automatic mode , if kiln speed is increased , then automatically kiln feed rate is increased , i.e both are related to each other by some factor of (0.008 * Feed rate = Kiln speed). The fuel rate to kiln is in the manual mode and to the calciner in the automatic mode. In the automatic mode, fuel rate to the calciner is increased or decreased to maintain calcination temperature of the calciner at 880 degree centigrate.

Now in the ILC Kiln ,case (a).when I keep the Kiln speed constant(manual mode), kiln fuel rate constant, calciner fuel rate constant(i.e in manual mode), water injection at the exit in manual mode and increase the feed rate , following happens:-

There is a increase in the gas draft at the preheater exit and an decrease in the fan power Kw.

case (b).However, if i keep all other above parameters same and in manual mode except for water injection system which is run in auto mode then

There is increase in the fan draft and a decrease in gas draft at the preheater exit.

Now in the SLC Kiln, keeping in view of the same description for the ILC Kiln except for the separate line calciner, if we increase the feed rate in the same manner as for the ILC Kiln then for the case(a). it is observed that gas draft at the preheater exit Increases and fan power  decreases. case (b). it is observed that gas draft at the preheater exit decreases and fan power decreases.

Now I want to clarify that the impact of increasing the feed rate should remain the same irrespective of the type of kiln we are using. Fundamentally what should be the impact of increasing the feed rate on the fan power and the Preheater exit gas draft for the cases mentioned above for both the types of Kiln.