Upgrading a process plant or migrating its controls can be challenging, but it doesn't usually involve shuttering an old facility for a couple of years, demolishing it, ripping out its equipment, reconsidering and rebuilding it 17 miles away.
However, this is exactly what PCS Phosphate underwent recently at its Suwannee River Chemical Complex in White Springs, Fla., with a crucial assist from the PlantPAx modern distributed control system, FactoryTalk and VantagePoint software, ControlLogix control systems and other solutions from Rockwell Automation.
"With PlantPAx our real-time data is displayed immediately, and this means much better and more timely decisions." David Klaas, senior electrical and controls engineer, PCS Phosphate.
"This was a 1970s-era green acid plant that had four different sub-processes with four different control platforms," said David Klaas, senior electrical and controls engineer, PCS Phosphate. "Ten months into the project and just 10 weeks before startup in August 2014, we were asked to implement electrical controls, so we took the P&IDs, and tried to think what we could come up with."Klaas presented "Installing PlantPAx and ControlLogix to consolidate controls and improve reporting" at the Process Solutions User Group (PSUG) conference this week in Atlanta.
Black to green
The plant that PCS Phosphate planned to move and rebuild is a refining system that takes black super phosphoric acid (BSPA) and refines it into green super phosphoric acid (GSPA). "This is done by removing the magnesium from the BSPA, and using diatomaceous earth and pressure to filter out impurities, creating a purified acid used in many food-grade and fertilizer products," explained Klaas. "We refer to this as low magnesium (lo-mag)."
Klaas reported that control systems at the former plant included:
- Primary system was an outdated APACS Moore PLC
- Secondary system was even more outdated, standalone SLC500;
- Tertiary system was a safety interlock system (SIS) using a standalone ControlLogix 5563 PLC, which was designed to protect the plant's ammonium nitrate from a runaway exothermic reaction
- Quaternary system operating the plant's pressure filter was completely standalone and analog
- Plantwide process monitoring and control by Wonderware InTouch HMI where available with full manual control elsewhere.
These controls ran Suwannee's three-stage process, which was widely spread over its former site, but now would be greatly consolidated and cleaned up in its new location. For example, where the old filter system used 4-20 mA drives, Klaas reported installing Allen-Bradley PowerFlex 755 drives from Rockwell Automation. He also integrated the new drives with the old plant's drives, which are still running today. For the SIS, he added ControlLogix 5573 controls. Finally, because PCS Phosphate wanted to standardize on ControlLogix controllers, Klaas was able to implement the PlantPAx DCS as the new plant's main control system.
New controls, better decisions
"It took a couple of months to transition the operators to the new HMI (human machine interface), but it was a pretty a seamless integration," said Klaas. "We started it up, and it’s been running flawlessly ever since."
In addition, while the plant's former controls and HMI ran as islands, Klaas reported that he implemented a new device-level ring topology network following ISA95 guidelines.
"This network allows us to send only what data IT and the business level needs through our demilitarized zone and firewalls," explained Klaas. "We're also using Stratix 5700 dual-redundant Ethernet switches and copper-fiber backbone as an independent distribution frame (IDF). This lets us monitor and manage the switches, but we can also click on any part of our network, and see a profile of any of our processes. We also built a widget for reporting when we remove the lo-mag from the BSPA to produce GSPA. Also, data is automatically collected and stored in FactoryTalk Historian, where it can be mined by our OSIsoft PI historian and FactoryTalk VantagePoint reporting tools."
The PlantPAx DCS and the rest of the plant's new controls and other support components occupy 16 physical hosts, which manage more than 150 virtual servers. Each of these virtual servers, in turn, handles more than 100 virtual nodes serving thin clients and production devices.
"We used to have to wait days or weeks for reports, but now our real-time data is displayed immediately, and this system can even do some adjustments automatically," added Klaas. "This means much better and more timely decisions. If you design a project like this right, it's so worth it. In fact, this was a $16-million project, and it paid for itself in just nine months. We're going to use PlantPAx on four other projects."
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