New air controls being tied into Big Stone coal plant during outage

Actual construction on an Air Quality Control System (AQCS) project at the coal-fired Big Stone power plant was as of the end of March 94% completed, with the plant shut down as of Feb. 27 for the start of the outage to “tie-in” all of the AQCS equipment.

“The outage also signals the start of the large amount of boiler work that is part of the AQCS project,” said Otter Tail Power in a quarterly project update filed on April 13 at the Minnesota Public Utilities Commission, which had approved the project in 2012. “During the last quarter the focus has started to shift from construction to commissioning and start-up activities.”

Examples of accomplishments in the first quarter of this year include:

  • All inlet ductwork to the Flue Gas Desulfurization (FGD) system has been set in place with the exception of the ducts that need to be installed during the tie-in outage.
  • All ductwork from the FGD outlet to the Induced Draft (ID) Fans and then to the stack is complete except for the ducts that need to be placed into the stack during the tie-in outage.
  • Baghouse bags and cages are being installed.
  • Selective Catalytic Reduction (SCR) has had all the catalysts loaded.
  • The oil system for the ID Fans has been completed and has been placed into service. The fans are in the process of being commissioned and run for the first time.
  • Commissioning work is well underway with the control system changes being implemented.

The tie-in outage has begun with the focus on the demolition work that needs to be done. All ductwork that needs to be removed has been removed. The contractor working on the boiler is well into the removal of the boiler sections that need to come out.Boiler work is approximately 35% complete at this time.

The updated noted: “As described in previous quarterly reports, the project budget was reviewed in early 2013 and then again in early 2014. Following both reviews the projected project budget was reduced. The original project budget was $491M; it was reduced in 2013 to $405M and again reduced to $384M in 2014. As the tie-in outage progresses we will again assess the cash flow needed to complete the project so that budget projects can be refined for the balance of the project.

“The EPA has issued the Mercury and Air Toxic Standards (MATS) rule, also known as the utility Maximum Achievable Control Technology (MACT) rules, which require control of hazardous air pollutants. While the final rule has been issued, several petitions for review have been filed in United States Court of Appeals for the D.C. Circuit which could ultimately delay its effective date. The rule as issued requires 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 standalone project is $5M. Because of the synergies of installing the system at the same time as the AQCS, the owners have decided to include the ACI system as part of the scope of the AQCS Project; we have only increased the projected cost of the AQCS Project by $2.1M to account for the ACI system. Although the standard MATS rule compliance date is April 16, 2015, on August 27, 2013 the South Dakota Department of Environment and Natural Resources granted a one year compliance extension for Big Stone Plant, such that the new compliance date is April 16, 2016.”

The 475-MW plant is located at Big Stone City, South Dakota, and it burns sub-bituminous coal. It is owned 54% by Otter Tail Power, 23% by NorthWestern Energy and 23% by Montana-Dakota Utilities.

Otter Tail said in an April 3 statement that this tie-in outage is scheduled to last until June 9. “This will be the longest scheduled outage in Big Stone Plant’s history,” said Tom Hrdlicka, Site Manager for the AQCS project. “During this outage the back third of the existing boiler must be replaced to increase the surface area. Babcock and Wilcox (B&W), the general contractor for the boiler project, is on site along with stacks and stacks of new boiler tubes. Graycor, the general contractor, is wrapping up construction. Commissioning of various components is in full swing and going well. Demolition of old equipment that no longer will be needed when the AQCS goes into service is beginning. Perhaps the most visible work being completed is covering outside areas with insulation and lagging.”

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.

About Barry Cassell 20414 Articles
Barry Cassell is Chief Analyst for GenerationHub covering coal and emission controls issues, projects and policy. He has covered the coal and power generation industry for more than 24 years, beginning in November 2011 at GenerationHub and prior to that as editor of SNL Energy’s Coal Report. He was formerly with Coal Outlook for 15 years as the publication’s editor and contributing writer, and prior to that he was editor of Coal & Synfuels Technology and associate editor of The Energy Report. He has a bachelor’s degree from Central Michigan University.