A lime kiln drive from DC to AC

The conversion of a lime kiln drive from analog DC to digital AC is examined in detail. The existing two-motor DC drive system suffered from old age and had a history of insufficient starting torque and extreme torque imbalance. The imbalance prematurely wore out the kiln ring gear, which required replacement. Alternatives such as DC drive retrofits, digital DC drives and hydraulic drives were higher in installed cost and required more maintenance. The AC drive was lowest in installed cost and offered tremendous advantages in simplicity, reliability, performance and the lowest maintenance. The new two-motor AC drive system was installed and tested before the original drive was taken out of service. Torque sharing between drives is coordinated through a dedicated communication link. The benefits of the conversion were impressive. Starting torque was increased, eliminating stall conditions, and enabling emergency single drive starts. Torque balance induced mechanical wear was eliminated. The speed control precision increased noticeably and maintenance was virtually eliminated. The DC drive to AC drive conversion outlined in this case study achieved excellent results in a cost-effective manner.