Mills are widely used in the cement manufacturing processes, such as raw-material mill/ coal mill and cement mill. These loads are huge power consumption.
Fig.2 Mills in the cement plant
The effect of mill is used mechanical power to change big size of the material to small size in order to meet with cement plant requirement. For the big capacity cement plant, the mill rated power is very huge, maybe more than 5000kw. How to smoothly start without impact current and voltage, and how to adjust mill speed, are obstructing cement plant. Control them with VFDs results in the following benefits.
Advantages for INVT VFDs driving:
1.Extended lifetime and increased availability
VFDs provide accurate torque and speed control of mills. This reduces the stress on mechanical equipment such as gearboxes, especially during start-up and stopping, as same as during operation and maintenance. VFDs help to optimize the mill speed to match the material flow, thus minimizing the wear of the grinding mill.
2.Significant energy savings
Grinding mills can consume more than 60 percent of the plant’s total electrical energy. Control them with VFDs results in significant energy savings. VFDs are not running at full speed, the speed is changed with cement production. Compare with full speed running, there is lots of energy saving.
3.Smooth ramp up
Torque pulsations and peak torques, generated by mills during the starting phase, create high stresses on the network and mechanical equipment. VFDs provide a smooth ramp-up of the mill. They deliver high starting torque for the current drawn from the power plant system and have a programmed upper limit to reduce peak current during the start of the mill. The low starting currents and high starting torque enable a smooth start-up of the mill, even when fully loaded.
4.Optimized plant production
By controlling a mill with a medium voltage vfd, the speed of the mill is tuned for optimal grinding and maximum throughput, resulting in more efficient use of the grinding power. If up and downstream processes require a lower grinding throughput, the mill can be operated at partial load without having to stop the process. VFDs can adjust the speed according to charge volume.
Fig.3 INVT VFDs applied to VRM (Vertical roller mill) and ball mill