Mehran Sugar Mills, located around 250 kilometers from Karachi in the south of Pakistan, is one of the country’s oldest and most important sugar mills. Every year, the facility crushes over 1.5 million tons of cane to produce the well-known Chashnik brand of granulated sugar.
But a few years back, it started to suffer from an issue with process downtime that was causing production losses running at $4,000 an hour. The issue was with the Programmable Logic Controller, PLC that controls the operation of one of the facility’s six sugar centrifuges.
Centrifuging is a key stage in the refining process in which the syrup resulting from the crushing, evaporation and crystallization phases is spun at speeds up to around 1,000 rpm.
This forces out the liquid to leave behind sugar crystals. The significant downtime caused by the faulty PLC was a major concern since the sugar cane harvesting season runs for only five months of the year, from November to March.
“The sugar season in Pakistan is short, so sugar mills demand the highest levels of availability and reliability,” explains Muhammad Kazim, ABB project leader for the sugar centrifuge PLC revamp project at Mehran Sugar Mills.
“Sugar processing companies can only operate for around 130 days a year, so they cannot tolerate one single hour of stoppage during the harvesting season.”
As the PLC makers’ local support team was not able to troubleshoot their own PLC, Mehran Sugar Mills decided it was time to call on ABB for help.
The reason for the decision was that they had been doing business with ABB since 2008 and already had a large installed base of ABB motors and drives in different applications.
And most recently, in 2013, ABB had installed a PLC to upgrade the control logic on another sugar centrifuge that was operating without missing a beat.
ABB replaces equipment in record time
One of the main requirements from Mehran Sugar Mills was that the delivery would be fast and that the implementation of the new PLC would restore their machine in record time. ABB’s engineers de-signed an ABB compatible solution for the old PLC system, based on the AC500 PLC while using the existing instruments and cabinet.
A Human Machine Interface was provided for operator control. A major challenge was that the existing PLC program was locked. Therefore, ABB developed a complete new program for the sugar centrifuge to meet the facility’s specific operational needs as well as making it as easy to use as possible for the machine operators.
ABB implemented the PLC replacement project in only two months. All the sugar centrifuges are now working perfectly, with not a single hour of downtime recorded.
Muhammad Anwar Khanzada, Assistant General Manager Electrical at Mehran Sugar Mills, is pleased with the work from ABB:
“ABB’s AC500 PLC/HMI has been working well on our Silver Weibull refining centrifuge for the last two years with absolutely no issues.”
The sticky air is no problem for ABB’s PLCs
One of the main requirements from Mehran Sugar Mills was that the delivery would be fast and that the implementation of the new PLC would restore their machine in record time. ABB’s engineers de-signed an ABB compatible solution for the old PLC system, based on the AC500 PLC while using the existing instruments and cabinet.
A Human Machine Interface was provided for operator control. A major challenge was that the existing PLC program was locked. Therefore, ABB developed a complete new program for the sugar centrifuge to meet the facility’s specific operational needs as well as making it as easy to use as possible for the machine operators.
ABB implemented the PLC replacement project in only two months. All the sugar centrifuges are now working perfectly, with not a single hour of downtime recorded.
Muhammad Anwar Khanzada, Assistant General Manager Electrical at Mehran Sugar Mills, is pleased with the work from ABB:
“ABB’s AC500 PLC/HMI has been working well on our Silver Weibull refining centrifuge for the last two years with absolutely no issues.”
The sticky air is no problem for ABB’s PLCs
One reason for the success of the ABB PLCs is that they are very robust. This includes the capability to operate in the harsh environment without problems caused by the moist sugar-laden atmosphere.
In some cases, it is possible for sugar dust to penetrate the equipment enclosure and then form deposits on the internal electronics that cause short circuits. ABB has prevented this possibility by the use of a special coating that protects the electronics.
Farzand Ali, Assistant General Manager at Mehran Sugar Mills Instrumentation department has been satisfied with the cooperation with ABB on the project:
“ABB supported us during hard times when we were suffering from unplanned downtime due to the malfunction of the PLC on the refine machine. We are very satisfied with the performance of AC500 based PLC system. We consider this refine machine as the most reliable and robust one among our refine centrifugal fleet.”
Another success factor is how well the PLC communicates with the HMI through the Ethernet connection.
Preparing the plant to sell power to the national grid
Mehran Sugar Mills has also just started its fourth mill electrification project with ABB. Its objective is to generate electricity and sell surplus power to the national grid. Previously, all the cane-crushing machinery at the plant has been driven by steam produced by burning bagasse, which is the fibrous waste product left after sugar cane is processed.
Now, with electrification, that steam is used to turn turbines that generate electricity which can power the plant, with any available surplus sold on to the national grid. ABB is providing a complete electrification solution to Mehran Sugar Mills.
The latest project includes IEC type HXR motors rated at 850 KW, ACS880-37 low harmonic variable speed drives (VSDs), multiple process house motors, electrical panels and a Unitrol 1000 AVR (Automatic Voltage Regulator) for the 3000 kilovolt-amp (kVA) steam turbine generator.
When all 10 mills are electrified, Mehran Sugar Mills will produce a surplus of 2 megawatt (MW) of electricity during the sugar cane harvest season. This will be sold to the national grid to bring in an added income of around $4,000 per day.
