EPA offers Sundt Unit 4 coal-to-gas switch as haze option

The U.S. Environmental Protection Agency said Jan. 28 that it is proposing pollution controls at six facilities in Arizona, including a coal-to-gas switch at Unit 4 of the Sundt power plant.

EPA is proposing a federal implementation (FIP) under its regional haze program to limit emissions such as NOX and SO2 tailored to six facilities: Tucson Electric Power’s Sundt plant in Tucson; Chemical Lime Nelson in Peach Springs; ASARCO’s Hayden Smelter; Freeport McMoran’s Miami Smelter; Phoenix Cement Co.’s Clarkdale plant; and CalPortland Cement Co.’s Rillito plant.

As a part of this process, EPA also evaluated other sources but is not proposing to require any additional controls on these other sources at this time. EPA estimates that this proposal would reduce SO2 by almost 30,000 tons per year and NOX by 3,100 tons per year.

EPA said it will hold public hearings on Feb. 25 in Phoenix and on Feb. 26 in Tucson and will accept comments for 45 days after publication of this proposal in the Federal Register. A final determination will be made by June 27.

EPA is proposing a FIP to address those elements of the state’s Regional Haze Plan that were disapproved in July 2013. Under the terms of a consent decree, the FIP must be proposed by Jan. 27 and finalized by June 27.

At Sundt Unit 4, EPA is proposing a NOx emissions level that is consistent with a selective non-catalytic reduction (SNCR) level of control technology. The proposed SO2 limit is meetable with dry sorbent injection (DSI) technology. A particulate level is based on an existing fabric filter baghouse installation.

EPA said it is also proposing a coal-to-gas switch as a “better-than-BART” alternative. BART stands for best available retrofit technology. Tucson Electric has submitted to EPA an alternative to BART based on the elimination of coal as a fuel source for Sundt Unit 4 by Dec. 31, 2017, the agency noted.

Sundt is a power plant located in Tucson, Arizona, and operated by Tucson Electric. The plant consists of four steam electric boilers and three stationary combustion turbines for a total net generating capacity of about 500 MW. Sundt Unit 4 is a steam electric boiler that was manufactured in 1964 and placed into operation in about 1967. Unit 4 is a dry bottom wall-fired boiler with a maximum gross capacity of 130 MW when firing coal. Originally designed to fire natural gas and fuel oil, Sundt Unit 4 was converted to also be able to fire coal in the early 1980s as a result of an order issued by the Department of Energy. The unit now fires both coal and natural gas. As part of the coal conversion, the unit was equipped with a fabric filter for particulate matter control. Unit 4 was upgraded in 1999 with low Nox burners (LNB) and overfire air (OFA) designed to meet Phase II Acid Rain Program requirements.

Tucson Electric has indicated that the generating capacity of Sundt Unit 4 while firing coal is reduced compared to its capacity using natural gas. As reported to the Energy Information Administration (EIA), Unit 4 has a 173 MW nameplate capacity while firing natural gas. However, the maximum gross capacity at which the unit could operate for a sustained period of time while burning coal is about 130 MW. This is due primarily to the fact that the amount of coal that can be introduced to the boiler is limited by the size of the boiler. Excess coal injection causes the flame to impinge on the back wall of the boiler which damages the boiler tubes, EPA said.

A November 2013 presentation from Tucson Electric as part of its preparation for its 2014 integrated resource plan shows that a preliminary estimate to retrofit Sundt Unit 4 with air controls to meet haze needs would be about $130m. The IRP document assumes that the unit will be switched to fire gas at the end of 2017. The plan notes that the Sundt units reconstructed outside of the BART time frame (1962-1977) are not BART eligible.  

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.