We would like to know the effect of removal of an ESP outside casing insulation if the prevailing ambient temperature is 40 degrees Centigrade and rainfall is scarce, ie dry weather, and is it possible to get a decrease in gas temperature inside the filter by this action or there are going to be some operational problems?

There will certainly be operational problems if you remove the insulation from your ESP. The temperature of the inner walls of the ESP will then become equal to the ambient temperature of 40 degrees C. This will be below the acid dew point of the gases passing through the ESP and you will have condensation on the inner walls and internal fittings of the ESP. You will then suffer from severe corrosion problems and will have to replace the internal fittings of the ESP on a regular basis.
My recommendation would be to adjust the raw mix chemistry to raise the LSF and AM and compensate for these changes. This will reduce the amount of baghouse fines required and therefore the ZnO additions. The mineralising effect of the ZnO will allow a higher LSF kiln feed to be combined in the kiln. At the same time C₃S and C_{3A content in clinker and cement will be increased offseting the retardation effects of the ZnO.}

I understand that flow of exit gases at preheater may be calculated by Q = velocity * cross sectional area of duct But I do not know the formula for velocity and density. Please explain the same. Secondly, please explain how an EP functions.

You need to study the Ideal Gas Laws to understand the relationships between gas volume, density and velocity. An EP works by inducing a strong electrical field between discharge and collection electrodes. Dust carried in the gas stream passing between these oppositely charged electrodes itself becomes charged and is collected on the collection electrode from where it is periodically knocked off into the collection hopper at the bottom of the EP by the rapping devices.