An Automated Cash Crop in the Heartland
The amber waves of grain have been more than a song lyric to Iowa’s farmers since the 1800s, but farming techniques in the 21st century bear little resemblance to those of horse-drawn plows. Modern technology is helping small towns compete with grain storage and distribution facilities in far larger cities.
Goldfield, Iowa’s population may barely break 600, but the local Gold-Eagle Cooperative collects and distributes 34 million bushels of produce for farmers in north central Iowa. It uses the corn it receives for its ethanol and feed processing plants, while soybeans typically are stored for distribution to processors.
Gold-Eagle recently modernized its facilities to respond to changes in the way farmers bring crops to its facilities. “We don’t get pickups towing trailers these days,” coop officials explain. “Now, during harvest season, huge semis arrive by the dozen, forcing us to process grain faster and store more than ever before—all while increasing reliability, cutting energy consumption, reducing labor costs, and simplifying maintenance.”
The company chose to expand, increasing the size of existing plants and building additional facilities. During 2010 and 2011, new grain storage facilities were constructed in nearby Thor, Corwith, Renwick, and Titonka, Iowa. All four facilities were equipped with identical Siemens switchboards, Motor Control Centers (MCCs), PLC-based controls, and Profibus networking.
Grain storage and distribution facilities consume a lot of electricity. In this case, they house some 80 to 90 motors generating roughly 2,700 hp. In each bin, motors operate fans and conveyors with about 550 hp. Motors in the receiving pit, chain drags, and bucket elevators account for another 300-500 hp.
To distribute the power, two 1,600-Amp Siemens switchboards (Figure 2) were installed at each facility. Each switchboard is fitted with Siemens VL and Sentron molded case circuit breakers for distributing incoming power and with Siemens PAC 3100 meters to monitor incoming power on utility feeds. Power is distributed from the switchboard to the MCCs. The electrical equipment—switchboard, MCCs, PLC, and I/O—is all in the same location.
To maximize reliability, the local utility installed redundant step-down transformers at each plant. In this main-tie-main switchboard configuration, each transformer supplies power to the switchboard. Should one transformer fail, a mechanical key interlock system can be used to transfer all power to the other transformer.
The new systems have reaped a number of benefits. Most notably, variable frequency drives (VFDs) resolved an expensive issue with the coop’s electric utility demand charge. Previously, all six fans in each storage bin started at once. Even soft starts drew 1,200 A, causing the plant to exceed its peak demand and incur a penalty charge for the month. Now, VFDs are tightly controlled via Profibus so starting up the six fans draw only 400 A peak current.
Other benefits include:
- Heightened efficiency. Unloading several trucks simultaneously in multiple receiving pits might not have a downside to those whose primary job is the smooth, fast operation of a plant. However, the impact of such activity could generate an unacceptably high electrical load and corresponding utility demand charge. The monitoring capabilities of the HMI and PLC ensure that the system always runs at an acceptable load and that no equipment will start if the action would incur an unwanted demand charge.
- Enhanced diagnostics. In addition to its other tasks, the HMI system also performs Profibus diagnostics, identifying problems and alerting operators. Siemens MCCs and ET200S motor controls automatically detect and report such problems as excessive temperatures or voltage draws, blown fuses, or equipment failure. Siemens SIMOCODE pro smart overloads on the MCC motor starter buckets provide motor current and other critical information such as current imbalance and estimated motor temperature.
- Improved safety. Better diagnostics also help increase operator safety. Workers no longer need to climb towers, inspect hundreds of feet of conveyors, or open cabinets and access panels to find and identify a malfunction. Diagnostics pinpoint problems such as a slipping belt or bad motor bearing and tell the operator how to fix it.
- Lower costs. Labor costs at the coop have dropped because the PLC handles all equipment start-ups and operational sequences. No equipment is operated manually, reducing the possibility of costly human error. All of the new systems have proven reliable and require minimal maintenance.
Automating processes, improving operations
Each plant is controlled through a Siemens S7 PLC and a PC-based HMI. The PLC controls motors, fans, and related equipment through hardwiring and the Profibus network. The HMI features a 19-in. touchscreen (Figure 5) that runs Siemens WINCC Flexible software. Through the HMI, operators manage the movement of grain from trucks to silos, handle the drying process, monitor operations, review diagnostics, direct the grain to unloading stations for transport to customers, and monitor and control all other plant automated plant systems.
Results of the upgrade have been impressive. Power costs are lower, the plants are safer, and maintenance is simpler. The coop is planning to add more storage, essentially doubling current capacity at some locations. The effort will require more motors, MCCs, and motor controls—but no additional PLCs, HMIs, or switchboards.
Read more about Gold-Eagle Cooperative by visiting the coop website at www.goldeaglecoop.comHave an Inquiry for Siemens about this article? Click Here >>