EPA wants more emissions controls on Colstrip coal plant

The U.S. Environmental Protection Agency (EPA) is proposing a Federal Implementation Plan (FIP) to address regional haze in the state of Montana that would require new emissions controls on two units of the coal-fired Colstrip power plant, but would give the much smaller Corette coal plant nearby a pass.

EPA said in an April 20 Federal Register notice that it developed this proposal in response to the state’s decision in 2006 to not submit a regional haze State Implementation Plan (SIP) revision. This emissions control program is designed to assure reasonable progress towards the national goal of preventing any future and remedying any existing man-made impairment of visibility in mandatory Class I areas.

In addition, EPA is also proposing to approve a revision to the Montana SIP submitted by the state on Feb. 17. The state’s submittal contains revisions to the Montana Visibility Plan that includes amendments to the ‘‘Smoke Management’’ section, which adds a reference to Best Available Control Technology (BACT) as the visibility control measure for open burning as currently administered through the state’s air quality permit program. EPA will act on the remaining revisions in the state’s submittal in a future action.

Written comment on the proposed FIP and the state revisions is being taken until June 19, with a public hearing planned for May 1 in Helena and in Billings on May 2.

EPA in the FIP proposes these facilities as Best Available Retrofit Technology (BART)-eligible: Ash Grove Cement Co.; Cenex Harvest States Cooperative, Laurel Refinery; PPL Montana LLC, Colstrip Units 1 and 2; PPL Montana, Corette; Columbia Falls Aluminum Co. LLC; ExxonMobil Refining & Supply Co., Billings Refinery; Holcim (US) Inc.; Montana Sulfur & Chemical Co.; and Smurfit-Stone Container Enterprises Inc., Missoula Mill.

PPL Montana is a unit of PPL Corp. (NYSE: PPL). The Colstrip power plant, co-owned by PPL Montana and other parties, consists of four units. Of the four units, only Units 1 and 2 are subject to BART. Units 1 and 2 have a nominal gross capacity of 333 MW each. The boilers began commercial operation in 1975 (Unit 1) and 1976 (Unit 2) and are tangentially fired pulverized coal boilers that burn Powder River Basin (PRB) sub-bituminous coal from an adjacent mine of Westmoreland Coal (NASDAQ: WLB).

EPA looked at various emissions control options for each unit for three different pollutants; NOx, SO2 and particulates.

Colstrip Unit 1

NOx – the Colstrip Unit 1 boiler is a tangential-fired design with low-NOx burners and close-coupled overfire air (CCOFA). Originally, the unit operated with a NOx emission limit of 0.7 lb/MMBtu. In 1997, EPA approved an early election plan under the acid rain program (ARP) that included a 0.45 lb/MMBtu annual NOx limit. The early reduction limit expired in 2007 and the new annual limit of 0.40 lb/MMBtu under the ARP became effective in 2008. Normally, the unit operates with an actual annual average NOx emission rate in the range of 0.30 to 0.35 lb/MMBtu, accomplished with low NOx burners and CCOFA.

EPA identified that the following NOx control technologies are available: separated overfire air (SOFA), advanced separated overfire air (ASOFA), rotating opposed fire air (ROFA), rich reagent injection (RRI), selective non-catalytic reduction (SNCR), and selective catalytic reduction (SCR). EPA concluded that SOFA, SOFA+SNCR, and SOFA+SCR are all cost effective control technologies. The lesser cost of SOFA+SNCR ($1,564/ton) is justified when the visibility improvement is considered, EPA said.

“We propose that the NOx BART emission limit for Colstrip Unit 1 should be based on what can be achieved with SOFA+SNCR,” EPA wrote. “The proposed BART emission limit of 0.15 lb/MMBtu allows for a sufficient margin of compliance for a 30-day rolling average limit that would apply at all times, including startup, shutdown, and malfunction. … We propose a compliance deadline of five (5) years from the date our final FIP becomes effective because of the equipment installation and potential combustion modifications that will be required.”

SO2 – Colstrip Unit 1 is already controlled by wet venturi scrubbers for simultaneous particulate and SO2 control. The venturi scrubbers utilize the alkalinity of the fly ash to achieve an estimated SO2 removal efficiency of 75%. Based on emissions data for the baseline period 2008 through 2010, the average SO2 emission rate was 0.418 lb/MMBtu and the average SO2 emissions were 5,548 tons per year (tpy).

EPA concluded that the cost of lime injection with an additional scrubber vessel ($912/ton) is justified by the visibility improvement. The proposed BART emission limit is 0.08 lb/MMBtu. “We propose a compliance deadline of five (5) years from the date our final FIP becomes effective because of the equipment installation that will be required,” EPA wrote.

Particulate Matter (PM) – Colstrip Unit 1 currently has the wet venturi scrubbers designed to control PM emissions. The venturi scrubbers at Unit 1 are designed to have at least 98% control efficiency and have shown control efficiencies approximating 99.5%. The present filterable particulate emission rate is 0.047 lb/MMBtu. EPA proposes to base the BART emission limit on what Colstrip Unit 1 is currently meeting.

Colstrip Unit 2

NOx – The Colstrip Unit 2 boiler is of tangential-fired design with LNB and OFA. The current annual limit is 0.40 lb/MMBtu. Normally, the unit operates with an actual annual average NOx emission rate in the range of 0.30 to 0.35 lb/MMBtu, accomplished with the low NOx burners and CCOFA. As with Unit 1, EPA found that the cost of SOFA+SNCR ($1,571/ton) is justified when the visibility improvement is considered and set a five-year compliance deadline after FIP approval.

SO2 – Colstrip Unit 2 is already controlled by wet venturi scrubbers, which are identical to the Colstrip Unit 1 scrubbers, for simultaneous particulate and SO2 control. The Colstrip Unit 2 venturi scrubber equipment currently achieves greater than 50% removal of SO2. EPA again concluded that lime injection and lime injection with an additional scrubber vessel are both cost effective control technologies. EPA proposes an SO2 emission limit based on installation of this equipment.

PM – Colstrip Unit 2 currently has the venturi scrubbers designed to control PM emissions. They are designed to have at least 98% control efficiency and have shown control efficiencies approximating 99.5%. The present emission rate is 0.0525 lb/MMBtu. EPA founded that the BART emission limit can be achieved through the operation of the existing venturi scrubbers.

Corette plant gets a pass based on current low emissions

PPL Montana’s Corette plant, located in Billings, consists of one generating unit. Corette’s boiler has a nominal gross capacity of 162 MW. It began commercial operation in 1968 and is a tangentially fired pulverized coal boiler that burns PRB coal. Although the gross capacity of Corette is below the 750 MW cutoff for which use of the BART Guidelines is mandatory, EPA nonetheless followed the guidelines as they provide useful advice.

NOx – The Corette boiler is a tangential-fired unit with existing low-NOx burners and CCOFA. The unit is subject to an annual NOx emission limit of 0.4 lb/MMBtu. EPA found that any of the control options would have a positive impact on visibility; however, the cost of controls is not justified by the visibility improvement. It proposes a BART emission limit of 0.4 lb/MMBtu, the same as the current one.

SO2 – The Corette boiler currently burns very low-sulfur PRB coal with a sulfur content of 0.3% by weight. The boiler is subject to a fuel sulfur limit of 1 lb/MMBtu (as fired) on a continuous basis and an annual emission limit of 9,990,00 lbs/calendar year. EPA concluded that dry sorbent injection (DSI) is a cost effective control technology, but decided no technology is worth the scant visibility improvements.

PM – Corette currently has an electrostatic precipitator (ESP) for particulate control, and considering scant visibility improvements from any further controls, EPA proposes basing the BART emission limit on what Corette is currently meeting. The units are exceeding a PM control efficiency of 99%.

PPL managed to argue Colstrip Units 3-4 out of plan

Said PPL Corp. about this rulemaking process in its Feb. 28 annual Form 10-K report: “In Montana, the EPA Region 8 is developing the regional haze plan as the Montana Department of Environmental Quality declined to develop a BART state implementation plan at this time. PPL submitted to the EPA its analyses of the visibility impacts of sulfur dioxide, nitrogen oxides and particulate matter emissions for Colstrip Units 1 and 2 and Corette. PPL’s analyses concluded that further reductions are not warranted. The EPA responded to PPL’s reports for Colstrip and Corette and requested further information and analysis. PPL completed further analysis and submitted addendums to its initial reports for Colstrip and Corette. In February 2009, PPL received an information request for data related to the non-BART-affected emission sources of Colstrip Units 3 and 4. PPL responded to this request in March 2009.”

In November 2010, PPL Montana received a request from EPA Region 8, under the Reasonable Further Progress goals of the Regional Haze Rules, to provide further analysis with respect to Colstrip Units 3 and 4, the Form 10-K noted. PPL completed a high-level analysis of various control options to reduce emissions of SO2 and PM for these units, and submitted that analysis to the EPA in January 2011. The analysis showed that any incremental reductions would not be cost effective and that further analysis is not warranted. PPL also concluded that further analysis for NOx was not justifiable as these units installed controls under a Consent Decree in which the EPA had previously agreed that, when implemented, would satisfy the requirements for installing the BART for NOx.
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.