A seminal advance in vertical mill design by an integrated drive train

Cement production lines have seen considerable increase in capacities over the last several decades and the trend can be expected to continue in the future as owners continue to seek the benefits of the economies of scale such lines provide. Concurrent with this is the gradual phasing out of redundant, or backup, production equipment as exemplified by the increasing practice of having one raw and one finish mill for a production line. The production of cement requires about 110 kWh per ton of cement and comminution accounts for approximately 62 % of this energy; raw grinding taking 24 % and clinker grinding taking the balance, or 38 %. Comminution is increasingly being effected in vertical mills (also known as roller mills) which have seen similar size increases since their inception in the sixties. Unlike ball mills, the input rotation from the prime mover is orthogonal to the rotation of the grinding table and requires bevel gearing to accomplish the change in direction. The bevel gearing has generally been accepted as the weakest link in the total transmission drive. This paper will present a new design concept that eliminates the bevel gearing and combines the prime mover in an integral reducer to address future increases in power requirements and to provide greater reliability and hence increased mill availability.