Phosphate Plant Reconstructed with a Modern DCS

Phosphate Plant Reconstructed with a Modern DCS

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 at its Suwannee River Chemical Complex in White Springs, Florida, with a crucial assist from the PlantPAx® modern distributed control system and other solutions from Rockwell Automation. PlantPAx DCS enabled real-time data to display immediately, allowing operators and management to make better and timelier decisions.

The 1970s-era green acid plant had four different sub-processes and control platforms. Ten months into the project and just 10 weeks before startup in August 2014, the staff was challenged to implement electrical controls.

Black to Green

The former PCS Phosphate plant refined black super phosphoric acid (BSPA) into green super phosphoric acid (GSPA) by removing the magnesium from the BSPA, and using diatomaceous earth and pressure to filter out impurities. This created a purified acid known as low magnesium (low mag), used in many food-grade and fertilizer products. Control systems at the former plant included:

  • A primary system and secondary system using outdated, standalone control
  • A tertiary system was a safety interlock system (SIS) using a standalone PLC, which was designed to protect the plant's ammonium nitrate from a runaway exothermic reaction
  • A quaternary system operating the plant's pressure filter was completely standalone and analog
  • Plantwide process monitoring and control 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 greatly consolidated and cleaned up in its new location. Allen-Bradley® PowerFlex® 755 drives were installed where the old filter system used 4-20 mA drives.

The new drives were integrated with the old plant's drives, and SIS controls were added. Because PCS Phosphate wanted to standardize on Rockwell Automation controllers, PlantPAx DCS was implemented as the new plant's main control system.

New Controls, Better Decisions

After a few months the operators were seamlessly integrated to the new HMI (human machine interface) and operated flawlessly. While the plant's former controls and HMI ran as islands, the new device-level ring topology network was implemented following ISA95 guidelines.

The network allows operators to send only what data IT and the business level need through the demilitarized zone and firewalls. The plant uses Stratix 5700 dual-redundant Ethernet switches and copper-fiber backbone as an independent distribution frame (IDF). This allows monitoring and management of the switches, but also gives access to click on any part of the network to see a profile of any process.

A widget for reporting was also built to remove the lo-mag from the BSPA to produce GSPA. Data is able to be collected and stored where it can be mined by OSIsoft PI historian and PlantPAx DCS 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. While reports previously took weeks to prepare, real-time data is can now be displayed immediately and adjustments can be made automatically.

This allows for much better and timelier decision making. The $16-million project paid for itself in just nine months and PCS is planning on using PlantPAx on four other projects.

Find out more about the PlantPAx modern DCS from Rockwell Automation.

PCS Phosphate presented this case study at the Process Solutions User Group (PSUG) in Atlanta, Georgia.

This blog is based off an article from the editors of Control.

Jim Montague
Posted July 21, 2017 By Jim Montague, Executive Editor, Control
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