You should restrict the PH outlet temperatures to less than 350 deg C at start up before feeding the kiln after a long stop.

During very short stops do not allow the PH outlet to go beyond 400 deg C

Some plants  inject 30 to 50  kgs of fine sand or clinker approx 4mm size in the down comer to reduce the speed of coating formation.

 

Hi

 Use of high sulphur fuel  encourages formation of cementious calcium sulphate which can form hard deposits on the ID fan blade. This is especially so if alkali sulphate ratio is off optimum range. In our plant I always associate use of high sulphur fuel with high Id fan vibration resulting largely from un even deposit on the fan blades. 

Most proven way to reduce ID fan vibration is to maintain the PH exit gas temperature about 200 deg.cent by water spraying in downcomer duct.If you are not able to control PH exit gas temperature around 200 degree cent. then best countermeasure is, whenever opportunity comes, clean the PH fan coating by "High Pressure water jet pump",you may clean the coating in less than 1 hour by the method.

There is a very good article on ID fan coating formation here:

http://cementamericas.com/mag/cement_solving_problem_buildup/ 

If nothing else can be done, active fan balancing technology can vastly increase the period between subsequent needed fan cleanings. For example of this technology:

http://www.concretemonthly.com/monthly/art.php?593

Best regards