Do you think that pre-dedusting in a raw mill circuit by means of cyclone with a separation efficiency of 91-93 will have negative influence on the raw mill bag filter or ESP in regard to the fact that after pre-dedusting only rather fine grain and rather low quantity of dust will enter the filter? Could it become difficult to clean the bags due to fine dust getting deeper into the pores of the filter bag and could the fine dust have negative influence on the ESP?

I cannot foresee that reduces the load of dust entering a filter will have any detrimental effect on its performance. Certainly no problem with an ESP. Your point regarding fine dust blinding the cloth of fabric filters maybe valid, but I would be surprised.

Our ESP on our long dry kiln (2520tpd) is out of order. A certain company has recommended instead of the ESP to install a water fogging system(droplet size = 10 micron) into the riser pipe of this kiln claiming that 80 per cent of dust passing with exit gases before the ID fan can be suppressed that way. Can you advise us on the merits and/or disadvantages of such a system.

I am afraid I cannot see many merits to this suggestion. It is common practice to condition (humidify and cool) the gases before entering the ESP by spraying droplets of water into the gas stream in a conditioning tower. This might indeed lead to 80 per cent of the dust load dropping out in the conditioning tower. However in your kiln, the suggestion is not to spray into a tower that will act as an expansion chamber but into the gas riser. You will also cool and contract the volume of the gases which will have the effect of increasing the draft at the kiln inlet leading to the possibility of higher dust losses from the kiln. I could not advise such a modification and believe that a much more detailed examination of the problem is required.