VFD Upgrade for Alcoa Petroleum Coke Bunkers

Control of three-phase AC induction motors for petroleum coke bunker feeders.

Alcoa Wenatchee Works
Malaga, WA
Visit project
September 2015

Alcoa Wenatchee Works is a smelting plant where aluminum ore is reduced to metal. The smelting plant was constructed as a result of a request by the Office of Defense Mobilization.  The request was to increase the domestic production of aluminum in a defense oriented economy. Responding to this government demand, the facility began producing metal in 1952. Wenatchee Works was the first smelter built in the Pacific Northwest after World War II.

The original production of primary aluminum at Wenatchee Works was 85,000 tons per year. Two major expansions in the 1960s increased the output to more than 210,000 tons per year. Today the facility provides high purity and commodity grade aluminum products for aircraft, automobile, and other manufacturing industries.

Why VFD Upgrades Were Needed

There are many processes that go into the smelting and refining of aluminum at Wenatchee Works. For each process, there is a requirement to be met for clean air and greenhouse emissions. Since the facility is built next to the Columbia River, there are clean water regulations to consider as well.

One aluminum smelting process is the production of anodes. Anodes are large carbon blocks which act as conductors to allow for electricity and heat to enter the smelting pots.

Anode production begins in an area of the smelter called the “green mill”. Here, an anode mix is produced from blended petroleum cokes (p-cokes), pitch and recycled anode butts that have been returned from the smelting process. The materials are mixed together in heated mixer boxes and conveyed to a series of mechanically vibrated molds. The formed anodes, or “green anodes”, are then conveyed to the Carbon Bake where they will undergo another process.

Before getting to the green mill, the p-coke comes in by rail-car and stored in large bunkers. It is then fed into a conveyor system that moves it into an injection scrubber system inside the green mill. Particulate matter from the p-coke is a large concern each time it is moved, especially since the facility is so close to the Columbia River. The p-coke scrubbing system includes mixer vents, conveyors below the mixers, and conveyors to the anode forming room. All of these system components are subject to specific particulate emission standards and Alcoa proceeded with the compliance upgrades.

VFD Upgrade Engineering for Alcoa

The primary engineering consultant for the VFD upgrade was Wenatchee-based Z-Engineers. Z-Engineers provides engineering services for two distinct but related disciplines of electrical and control systems. Both elements are typically applied to their projects, resulting in a complete and integrated design solution. They worked directly with Alcoa and ControlFreek Inc  to meet this project’s VFD upgrade needs.

CFI used Allen-Bradley Powerflex 700 VFD technology to control three-phase AC induction motors for the petroleum coke bunker feeders. The feeders move the p-coke from the bunkers into the mixers. This VFD upgrade panel controlled 10 bunker feeders in total. The Powerflex VFD’s was a fine choice for the feeders because of their excellent torque production and regulation. Fast update times of torque inputs made it suitable for this high performance application.