New technology increases productivity
L. Chenna Krishnan, Dy.general manager, Refinery, AKS, says since the new ABB technology has been fitted, the refinery has benefitted from increased output, greater efficiency and improved reliability. “Previously the centrifuges were completing 22-24 cycles per hour but the new technology enables up to 30 cycles to be completed per hour. This means we can easily produce up to 7000 TPD, the figure before was around 5000-6000 TPD,” Krishnan recalls.” There is also less power lost. Before the centrifuges consumed 0.952 KWH per ton of massecuite which has been reduced quite significantly to 0.75 KWH per ton of massecuite. This equates to 22% energy saving.”
Traditionally, centrifugals were driven by single speed fixed frequency induction motors. These can’t regenerate power and are considered extremely inefficient – deceleration is generally by mechanical brake. To increase efficiency, two speed motors were developed to allow the low speed winding to regenerate from spin to approaching half speed, recovering about 10% of the motor energy used during acceleration, spinning discharging and feeding. Another improvement resulted from the introduction of three speed motors, using a single cage rotor in a double wound stator. Regenerative braking then occurs recovering 20-25% of the motor energy used during acceleration.
Regenerative drives are key
After a thorough study of customer requirements and expert support by the ABB factory in Finland, multi-drive system was designed to meet demanding motoring and regenerative cycle requirements operating 24 hours a day, 365 days a year.
This drive system comprised of three parallel operated Insulated Gate Bipolar Transistor (IGBT) supply units and 14 inverters to run ABB premium efficiency motors. IGBT Supply units help in regeneration of power, a feature required for this centrifugal application and facilitates low harmonic distortion and provides unity power factor.
Complete drive system was integrated by ABB's channel partner Blouden control system from Dubai, UAE. This company is the only partner in the Middle East to integrate the advanced ABB multi-drive system. ABB’s modular low voltage drives technology and documentation system facilitated channel partners to integrate these complex drive systems.