How can the efficiency of clinker cooler be increased without any modifications?

Cooler efficiency is a function of the amount of air that is blown into the cooler for cooling the clinker. You might improve the efficiency by reducing the amount of cooling air. However, you need to develop a model of the cooler to ensure that you have the optimum balance between thermal efficiency and cooling performance.

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.