VSDs cap energy savings project at Lafarge

London - Lafarge Cement has completed a major energy efficiency programme at its Hope Works cement plant in Derbyshire with the installation of two final variable speed drives. The addition of Mitsubishi 132kW drives to two fans - used for cooling the clinker as it exits the kiln - means that all major axes within the plant are now speed-controlled, reducing total power consumption by 15% or more.

The fans were previously damper controlled, and so ran constantly at top speed, with the air-flow controlled by partially closing the dampers or baffles. The new drives mean that the motors can now have their speeds turned down to provide the exact air-flow required.

“Another big advantage of the new set up is that we can improve the accuracy of the airflow control loop,” said site engineer Mark Bramley. “The iris damper and actuator proved problematic. Now we can connect the inverters directly to a system controller to optimise the air-flow for maximising heat recovery in our clinker coolers.”

Hope Works, which has capacity to make up to 1.3 million tonnes of cement a year, uses Mitsubishi drives on the mill, the rotary kilns, pumps, fans, conveyors, feedwater, apron feeds and all other critical axes. Some of the 140 or more drives in use today are those originally installed up to 20 years ago.

Due to its location at the end of a lengthy electrical distribution network,  the plant can suffer from a significant voltage depression when starting up its large DOL synchronous machines.

This issue was one of the main reasons for installing the first big drives, inverters up to 375kW on the cooler and the kilns. By using the drives any spurious over- and under-voltages to the motors can be smoothed out, to get a more uniform running and reduce maintenance of the motors and running gear.