The corn-processing plant in Fort Dodge, Iowa, has been part of Cargill’s food and agriculture business since the facility was purchased from Tate & Lyle in 2011. It produces ethanol and feed stock, but also pioneered a digital transformation for Cargill that lowered costs and improved safety.
The corn-refining process involves inspecting, cleaning, steeping and separation. Steeping is a very important continuous-batch process. “We soak it in a water-and-chemical solution,” explained John Krueger, instrumentation, process control and automation lead, North America, Cargill, who spoke at the 2019 Emerson Global Users Exchange in Nashville, Tennessee. “If you don’t soak it long enough, the corn is brittle. If you soak it too long, it becomes mush. This hurts our value stream.”
The problem Cargill needed to address involved the screens at the bottom of the tanks that would plug up with corn periodically, making it difficult to read levels. The manual process necessary to clean the screens once they were plugged was time-consuming and dangerous.
“There’s a ring header on the bottom of the tank to flush the screens,” said Krueger, “but plugging of the screens by corn particles presented a challenge. They would create a mat layer, and that would overflow the steeps, creating a problem with our level reader. It was a manual process to unplug the screens.”
Because the steeping process didn’t take place close to the control room, someone would have to take a five-minute walk to get there and then use a ladder to get in there and try to break up what was on the nozzle.
“It was overall not a very good design for a manual process,” said Krueger, “and the valves were being left open.”
The facility’s leadership challenged engineers to automate the 30 ring-header valves and set up a control scheme. This required a solution for applying water at the correct intervals to keep screens clean, reducing line plugging, optimizing water flows throughout the steep and reducing the need for manual intervention. “And they challenged us to do it in two weeks,” said Krueger.
Works like a CHARM
The traditional scheme for this implementation would have called for individual solenoids, but the control system was point-limited. “We only had 10% spare capacity for I/O,” explained Krueger. “And wiring hardware, locations and timing all added to costs. The plant already had DeltaV hardware, and we had been looking at the ASCO 580 with CHARMs. We received drawings and were able to modify the existing cabinet for the 32-valve bank easily.”
Each CHARM I/O card (CIOC) can accommodate up to 96 I/O channels. In this case, 32 solenoids and 64 characterization modules (CHARMs) were connected via the manifold to DeltaV using two cables. “Once the cabinets were modified, we were ready to commission,” said Krueger.
“One advantage the module gives us is diagnostics because it’s tied to the DeltaV,” explained Mike Unterreiner, business development manager, process-hydrocarbon, fluid & motion control, Emerson. “If a coil has a short circuit, it will show up as an error message in DeltaV. Another diagnostic is for the bus cables. Each manifold is connected to the CHARMs baseplate.”
But the big advantage of the ASCO CHARMs approach was the cost. It was 30-40% lower than the traditional approach, and completely eliminated the need for a third-party Profibus network. Installation was simplified because of the DIN-rail mounting in cabinet. “It took very little time to commission once it was installed,” said Unterreiner. “DeltaV automatically senses that is it connected to the solenoid bank and auto-configures. The solenoid valves are labeled on the solenoid ports, and, when commissioning, a light on the solenoid comes on to show it’s being signaled.” Water flow management was improved, and the new system reduced the need for manual screen-cleaning intervention, so workers weren’t being sprayed with steep or running the risk of falling off of a ladder. And, best of all, the project was completed within the two-week period set by management.
Standard bearer
The system was modified slightly and then standardized regionally for Cargill. “Fort Dodge found it so helpful, they took it to the region for a standard consideration,” explained Krueger. It was standardized using ASCO 503s, replacing the existing solenoid-bank design. “We also standardized on the four-way valve, instead of the three-way,” said Krueger. “When we look at our new design, there was a cost savings. It wasn’t as great as the Fort Dodge plant, but not all of our plants are DeltaV, so we have a solution that will meet those needs, as well.”