Simplicity = Freedom

Reducing Wiring Doesn't Just Save Labor, Time and Expenses

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Jim MontagueBy Jim Montague, Executive Editor

This is because those newly available hours can be filled up with other jobs. For instance, just one year ago, Southern States Chemical (www.sschemical.com) built and opened its new sulfuric acid plant in Wilmington, N.C. Its engineers used Emerson Process Management's two-year-old CHARacterization Modules (CHARMs) for Delta V electronic marshalling to simplify and streamline the entire project, according to Bryan Beyer, Southern's acid operations manager. He described Southern's efforts on Oct. 25 at the 2011 Emerson Global Users Exchange in Nashville, Tenn.

Though it runs other facilities as the largest East Coast supplier of sulfuric acid, Southern needed the new plant to meet growing demand for its products. Beyer reports that sulfuric acid is the world's most widely traded chemical commodity because practically every process application from pulp and paper to chemical production to brewing beer uses large amounts of it. The compact 120-ft x 100-ft plant was also needed to supply reliable, high-pressure steam to Invista's specialty chemical plant next door.

Sulfuric acid is made by combining sulfur and air in a furnace, producing SO2 gas, sending it to an absorbing tower, treating it in an SO2 to SO3 converter, and performing other steps, which have numerous I/O points for temperature, pressure, flow, conductivity and other values, and generate lots of data. "Temperature control of the SO2 converters is especially critical because they use a catalyst and have to make several passes, explained Beyer. "So we decided to install 10 CHARMs cabinets in areas with the highest I/O concentration."

Electronic marshalling eliminates all this work and leaves I/O subsystems unchanged. There's is no change to the I/O footprint.

Besides the modules, the cabinets have 24-V power, dual Ethernet connections, redundant CHARM I/O cards (CIOCs), RTDs, thermocouples and HART transmitters linked to a DeltaV controller. Control Southern and R.F. Mason helped Southern States design and integrate the new plant.

"By separating the I/O subsystem design from the control strategy design, the CIOC allows the field instrumentation design to begin long before the control strategy is finalized," states Emerson's original "DeltaV CHARMS Commissioning" white paper. "The CIOC replaces the physical cross-wiring between traditional marshaling terminals and the controller's I/O card. The I/O signals can be re-assigned as needed without affecting any physical wiring. This eliminates the need to add I/O hardware when adding a new controller. This can be a huge challenge with traditional, card-based I/O since the existing I/O cards are physically dedicated to the original controller. Electronic marshalling eliminates this work and leaves the I/O subsystem unchanged. Simply add the new controller and re-distribute the control modules as needed, along with their I/O channel assignments. There is no change to the I/O footprint and no wiring changes."

In the end, Beyer says his company saved about 50% on wiring and labor thanks to CHARMs and Emerson's other equipment. For example, instead of having to bring I/O signals 200 feet back to its control room, many could simply be tied into the existing  Ethernet backbone in just a couple of hours. "We were even able to secure some digital inputs, install a horn in the control room and have a plant evacuation system for just $2,000," added Beyer.

To get CHARMS and the rest of its new process control system up and running, Beyer adds that his team had to cope with Southern's long tradition of mostly manual control. "The company used very little automation before, so the operators weren't used to doing performing control functions in a control room," he added. "However, after two weeks of training, they found it was pretty easy to understand." 

Consequently, just as we can stand on the shoulders of giants and other predecessors, we can also be buoyed up and supported by our own good work, productive habits and efficiencies that we've built up over time.  

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