2012 – summer Issue

Sands of Nebraska

When you think of sand and where you'll most likely find huge reserves of it, rural Nebraska probably isn't high on your list of sources. After all, there's no beach and no coast line. Surely no sand either. But that couldn't be further from reality.

For over 75 years, sand has been dredged from the Loup River producing a reserve of approximately 80 million tons of sand. The largest sand reserve of its kind in the country, it has a replenishment rate of approximately 2 million tons annually.

Our client, Preferred Sands, operates a silica sand processing plant just outside of Genoa, NE. The plant has capability to process 2 million tons of silica sand and 250,000 tons of resin-coated products annually. The wet plant process includes a washing system where unwanted particles are removed. The sand is then dried and screened into five different products according to client needs.

Preferred Sands was looking to upgrade their facility to add production capacity. To meet their process and quality requirements, they turned to Interstates for assistance with electrical engineering, automation, instrumentation and electrical construction. The Genoa Wet Plant Expansion project includes two startup phases. Phase 1 added 2,000 HP of motor loads to the facility and was completed in March 2012. Phase 2 added 3,700 HP of motor loads and was complete in June 2012. The project also includes upgrades to the control system and PLCs in order to have a fully automated facility. With the upgrades complete, the company will have capacity to double their production.

An existing 12.47kV distribution system was routed throughout the site using mostly overhead power lines for distances over a mile long. To accommodate the additional load, each of the two phases included installation of several new services at various locations throughout the facility. Three new transformers were installed with ratings of 1500, 2000, and 2500 kVA. Each service was installed with grounding resistors to create High Resistance Grounded systems.

Preferred Sands' unique process required installation of many large Variable Frequency Drives (VFD's). In fact, 2,900 HP of the new motor loads were installed on VFD's. The large proportion of VFD load made the presence of high levels of harmonics in the distribution system a concern. As a result of discussions with the local utility and referencing IEEE standards for acceptable levels of harmonic distortion, Interstates collaborated with the VFD manufacturers involved with the project for a solution. This led to identifying several large VFD's where harmonic filters were required and installed.

The facility also incorporated Smart MCC technology in order to monitor the running load of each motor. Because there is such distance between the motors and the control rooms, it is necessary to monitor for motor failure, damage to the motors, and mechanical loads. A sudden increase or decrease in current for an individual motor would indicate an abnormal condition. Electronic overloads which communicate over DeviceNet allow the plant operators to monitor motor loads from the control rooms.

"The system that we are providing at this location will allow the client to run more efficiently and with much better reliability," says Randy Noecker, Project Manager, Interstates Construction Services. "Unplanned downtime is the enemy for any processing facility. These system upgrades will allow the client to plan for maintenance and schedule downtime when it's time-appropriate. The added reliability will allow them to operate efficiently and prepare for their highproduction times."

"Our overall project experience with Interstates has been excellent," says Mark Harvey, Project Manager, Preferred Sands. "Interstates has done a great job in providing a turnkey project. We are eager to realize the productivity benefits of our newly automated system."