Our plant has four cement mills (closed circuit with first generation seprator) - we use about 20 per cent slag , the output is 100tph ,the dimension of every mill is 15.5 x 4.4, the liners in the first chamber are lifting and in second chamber classifier. Are there any ways to increase mill production? How about for a raw mill?

There are numerous ways to increase the production from your cement mills. In the short term use of grinding aids combined with optimisation of the ball charge and drafting would be the best method. Longer term (and at greater cost) you could upgrade the separators to third generation or install a roll press to pre-crush the clinker ahead of the mills. With regard to raw mills you can again use grinding aids or install pre-grinding equipment.

I have two questions: What is the effect of NO_x and SO_x in controlling the burning zone temperature and what other parameters like kiln torque, kiln inlet oxygen or if anything else affects the kiln operation.
Secondly, how to improve the ventilation in ball mills, as we observe the coating formation on the balls is on the high side.

NO_x and kiln torque are both good indicators of the temperature in the burning zone of the kiln. This is key to ensuring stable operation and good combination of the clinker. Kiln inlet oxygen is a good indicator of the combustion conditions in the kiln where a small excess of oxygen is necessary to ensure burning in oxidising conditions. SO_x rises if there is reductive burning and CO present in the burning zone therefore this reinforces the kiln inlet oxygen measurement.
To improve the ventilation in the ball mill you need to increase the speed of the induced draft fan. However if you are suffering coating of the media this is more likely related to temperature control in the mill. This is a function of the clinker temperature, ventilation and the cooling with water injection.