The in-service date for the new Air Quality Control System on the coal-fired Big Stone plant in South Dakota has been pushed back to Dec. 1, even though the project is basically 100% completed, said Otter Tail Power in a quarterly project update filed Oct. 14 with the Minnesota Public Utilities Commission.
The delay is due to an extended outage due to the problems with the high pressure turbine. Currently, Otter Tail is expecting to declare the AQCS equipment in Commercial Operation on Dec. 1. “We will attempt to move this date earlier if conditions allow,” the utility added. In January 2012, the Minnesota commission granted advance prudence on this project.
“Actual construction on the project is now 100 percent completed, however there is the possibility that the start-up and tuning process may reveal minor modifications that will need to be made,” the company reported. “Also, the demolition of the old baghouse, ID fans, and ash silo still remain to be completed. The [third] quarter began with the plant still not running because of the extended outage for turbine repairs. The unit started up in early August but experienced problems that kept it from reaching full load until late in the month. AQCS equipment has been started and tuned whenever an appropriate load point could be maintained. Compliance testing started late in September.”
The original AQCS budget was $491 million, which was reduced in 2013 to $405 million and again reduced to $384 million in 2014. Even with the outage extension, the project still should finish on or under budget.
The EPA’s Mercury and Air Toxic Standards (MATS) require the Big Stone Plant to reduce mercury emissions, which can be controlled by adding Activated Carbon Injection (ACI) to the project. The estimated cost to add ACI as a stand-alone project is $5 million. Because of the synergies of installing the system at the same time as the AQCS, the owners decided to include the ACI system as part of the scope of the AQCS Project. That has only increased the projected cost of the AQCS Project by $2.1 million. Although the standard MATS rule compliance date is April 16, 2015, in August 2013 the South Dakota Department of Environment and Natural Resources granted a one-year compliance extension for Big Stone, putting the new compliance date at April 16, 2016.
The 475-MW Big Stone plant is majority owned by Otter Tail Power, with minority shares held by NorthWestern Energy and Montana-Dakota Utilities. The AQCS project includes a scrubber and selective catalytic reduction.
Otter Tail Power, a subsidiary of Otter Tail Corp. (NASDAQ Global Select Market: OTTR), is headquartered in Fergus Falls, Minnesota. It provides electricity and energy services to more than a quarter million people in Minnesota, North Dakota, and South Dakota.