Rapid response
Yokogawa’s network-based control system replaces PLCs

The first installation of Yokogawa’s Stardom network-based controller in South Africa has revitalized an integrated compressor control system, replacing PLCs for high-speed compressor control while creating a unified operator interface through an existing DCS.
The compressor control upgrade project for polypropylene manufacturer Safripol in Sasolburg, South Africa, is a showcase for the philosophy of integrated control based around a single control room. The project integrated a fast Stardom Network-based Control System (NCS) for high-speed compressor control with an existing Yokogawa Centum CS distributed control system (DCS) for core process control.

The project began when Safripol decided to replace obsolete programmable logic controllers (PLCs) on four packaged compressor systems handling propylene, ethylene and nitrogen. The company wanted a system that could communicate with the DCS via Ethernet, giving an integrated control system with the “look and feel” of the existing one.

“As the old saying goes, you cannot control what you cannot measure,” says process control engineer Mike Dukas, Safripol. “But to get all these signals to and from the DCS using old technology, cabling, and junction boxes costs a lot of money. We decided to keep costs down by using modern technology that met all our requirements. A lot of options and product combinations were evaluated and Stardom with Ethernet communication came out to be the best for our business.”

“Making use of Yokogawa’s different control platforms having unique specifications but the same well-known operator interfaces allows us to avoid extensive operator training,” Dukas continues. “It also provides the right control philosophy on the plant floor, and makes use of the existing management information software tools.”

In choosing the new system, Dukas says, the company looked at cost; ease of integration with the DCS and with other PLCs; expandability; ease of setup, use and maintenance; reliability; and after-sales service. “We felt this system met all these criteria, so we decided to install the first Stardom network-based controller in South Africa,” says Dukas.

Safripol placed an order in March 2005, and three out of the four systems are now installed and running successfully. Each of the units has 112 I/O points, and communicates with the DCS via a Yokogawa gateway.

Minimum downtime

The compressors are critical to the polymerization process, so it was essential to keep expensive downtime to a minimum. This, in turn, meant a tight changeover schedule and accurate pre-testing.

The first unit was installed with the help of Yokogawa South Africa. Because of time pressure, this was done without official training. The controller was programmed with remote assistance from Yokogawa SCE in the Netherlands and Japan. “The changeover was virtually bumpless,” says Dukas. “Apart from the planned mini-shutdown time, we did not experience any additional downtime. The whole project was within time and budget.”

The system has certainly met the objective of being easy to program, maintain and expand, says process control engineer Bennie Coetzer: “Even without training on the system, it is simple to find your way and start with the first steps of programming. After a three-day training course one really feels the power and flexibility.”