We've been faced with a problem that the collecting efficiency of the electrostatic precipitators lowers remarkably since having started to use sewage sludge as the secondary material. I'm not sure where the cause is from. Is there any possibility of causing such problem by using sewage sludge, and which kind of components that sewage contains can affect the performance of ESP? As the reference, we've been experienced in the same problem when we used TPA sludge(Telephtalic Acid) two years ago.

I have not heard of this phenomenon before. The resistivity of the dust exiting the preheater must be changed when burning these sludges. I hope all the sewage sludge is being burnt in the kiln and the problem is not caused by organic residues entering the ESP. If so then the problem can only be associated with volatiles derived from the sludge entering the ESP with the dust. The most likely source is chlorides from the sludge. You should also check carefully that the problem is not caused by mercury from the sludge. If so then you have a big problem.

I'm working in a cement plant established at 1984, two lines with dry processing technology, the plant faces so many conflicts, major parts are not from the source company, for example the dust separator doesn't work at all, so many efforts carried out with no result, also the computerised analysis system with daily production reports does not work either. The plant uses oil for heating up, there is a factor normally set at 1.64 which is a standard in cement production, but now it has been elevated to 1.90. After how many years how could the 1.64 could be increased to 1.90.

The factor of 1.64 you refer to is the raw mix to clinker factor taking into consideration dust losses from the preheater. If you have very high dust losses then this factor might need to be higher. However to justify a factor of 1.90 the dust losses will need to be in the region of 30 per cent of the feed to the top of the preheater. If this is the case and your dust collector is not working the pollution must be terrible.