Project Scope

Graycor completed the Big Stone Plant Air-Quality Control System (AQCS) project near Milbank, South Dakota, for Otter Tail Power Company, owners’ agent, and plant co-owners NorthWestern Energy and Montana-Dakota Utilities Co. Graycor was awarded the contract as the project’s general contractor of the 475-megawatt power plant project site. Purchasing more than $20 million of additional equipment, Graycor’s team erected the AQCS, which included complete installation of all underground utilities, site grading, piling, concrete foundations, structural steel, ductwork, silos and dry scrubbers for two baghouses and two SCR (selective catalytic reduction) systems, including ACI (activated carbon injection).

Graycor also hired and managed the employees and subcontractors required to complete the project. The project provided nearly 600 jobs, and more than 2.2 million total OSHA hours were logged.

Graycor was chosen following an extensive evaluation process that began with 36 potential contractors. The basic criteria for contractor selection were price, commercial terms and technical specifications or work scope, which included safety performance.

Big Stone Plant’s AQCS, which must be installed according to Environmental Protection Agency regulations, includes about $490 million in retrofits to the plant and is expected to reduce both nitrogen oxide and sulfur dioxide by 80 to 90 percent.

Graycor has recently completed more than 20 air-quality control system projects for a variety of clients throughout the U.S. Additional information regarding the Big Stone Plant AQCS project is available at www.BigStonePlantAQCS.com.