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.}

Our government is starting to limit NO_x emissions from cement kilns and the regulation, as I heard, was more severe than in the European countries. I think the best way for reducing NO_x emission with no further cost is to use fuels that contain the lower nitrogen content, especially coal and residual fuels. Am I correct?

The NO_x emissions arise from two sources: (i) the nitrogen in the fuel as you say, and (ii) "thermal" NO_x from the breakdown of atmospheric nitrogen at the high temperatures in the burning zone. Usually the thermal NO_x is much higher than the fuel NO_x and the best way to reduce NO_x emissions is to reduce this thermal NO_x. Low NO_x burners reduce the temperatures in the flame and produce less NOx by using less primary air. Low NO_x calciners burn some of their fuel in a depleted oxygen environment to cause NOx degradation by the following reaction: NO + CO -> 0.5N₂ + CO₂. These are the best way sto reduce the NO_x emissions of the kiln.