I work in a ceramic industry where there are around 4000 ceiling fans which are run almost round the day.there is aregular problem with bearings and capaitors.the environment is heavily loaded with dust and moisture.can anyone suggest any remedies

You need to find a fan that can handle the dusty atmosphere, you may need to consult with the engineering dept of a manufacturer to be sure the bearings are sealed enough for your environment.

Here are a few:

Big A SS Industrial Ceiling Fans

I always thought the name was obnoxious, but they are the biggest fans I have ever seen.

Using these may reduce the total amount of units you need.

Action-Aire Inc.: Industrial Ceiling Fans

Northwest Envirofan - Industrial & Commercial Ceiling Fans