Raven plans DSI installations, coal switching at H.A. Wagner plant

The owner of the H.A. Wagner power plant in Maryland is planning a combination of dry sorbent injection installation and a switch from Central Appalachia bituminous coal to subbituminous coal for compliance with the federal Mercury and Air Toxics Standards (MATS) at Units 2 and 3.

H.A. Wagner LLC applied on Jan. 14 at the Maryland Public Service Commission for approval of these projects. H.A. Wagner LLC is a merchant generator and a wholly-owned subsidiary of Raven Power Holdings LLC. Raven is an investor-owned energy holding company, and it owns three Maryland generating stations that it bought in 2012 from Exelon (NYSE: EXC): Wagner, the adjacent Brandon Shores Generating Station, and the C.P. Crane Generating Station. All three plants fire coal.

The projects are for two approaches, useful separately or in conjunction, to reduce HCl emissions at Wagner Unit 2 and/or Unit 3. One approach is to use dry sorbent injection (DSI), a proven add-on control technology, to enable other existing emissions controls at Wagner to remove more acid gas from the combustion stream. The second approach is the combustion of subbituminous coal, either by itself or blended with bituminous coal.

“The content and characteristics of subbituminous coals are such that less chlorine is present in the coal and so less HCl will form and be emitted the boiler’s combustion than when using bituminous coals,” the application said. “The two approaches to reducing HCl can be used in conjunction, with less sorbent injected into blends containing higher ratios of subbituminous coals. Each approach also offers additional emissions reductions benefits. While the Applicant is seeking authorization for both Projects, it does not believe that both are ultimately necessary to achieve compliance with the MATS rule, and might not ultimately implement both Projects on both units.”

Compliance with the MATS HCl standards must be achieved for Units 2 and 3 by April 16, 2015. In order to meet the compliance deadline, the company is requesting expeditious review of the application, with a final decision by July 2014. This would allow it to begin final DSI system design and engineering this summer, with construction to follow shortly thereafter.

Projects would be used at Wagner’s only coal units

Wagner consists of four steam-electric generating units, a black-start combustion turbine and supporting facilities. The main generating units at Wagner and their current PJM Interconnection capacity ratings are as follows:

  • Unit 1, natural gas-fired (oil backup) unit, nominally rated at 126 MW (net), which began operation in 1956;
  • Unit 2, coal-fired unit, single wall-fired boiler type, nominally rated at 135 MW (net), which began operations in 1959;
  • Unit 3, coal-fired unit, opposed wall-fired dry-bottom boiler type, nominally rated at 305 MW (net), which began operations in 1966; and
  • Unit 4, oil-fired unit, nominally rated at 397 MW (net), which began operations in 1972.

Units 2 and 3 are each equipped with a cold-side electrostatic precipitator (ESP) for control of particulate matter (PM) emissions. Unit 2 is equipped with a selective non-catalytic reduction (SNCR) system for control of NOx emissions, while Unit 3 is equipped with a selective catalytic reduction (SCR) system for control of NOx. Each coal-fired boiler is equipped with an activated carbon injection system for control of mercury emissions and each boiler burns a refined coal, produced on site through the mixing of coal with two additives for emissions reduction.

As Units 2 and 3 are also subject to SO2 emission limits under the Maryland Healthy Air Act (HAA), the use of DSI and/or subbituminous coal (with its inherent lower sulfur content) will have the co-benefit of providing further flexibility for continued compliance with the HAA, said an environmental report on the project prepared by consultant Zephyr Environmental Corp.

The current primary coal type and source used in Units 2 and 3 is bituminous coal from Central Appalachia. Units 2 and 3 and their associated coal feeding equipment are already capable of accommodating subbituminous coals, the application noted. The company intends, however, to undertake additional minor measures to enhance safety when handling subbituminous coals. The use of subbituminous coal at Wagner 2 and 3 was previously tested and found technically feasible. Under the current schedule, the initial delivery of subbituminous coal to the plant is planned for October.

Testing of the DSI technology has already been performed at Wagner. This testing, when the plant was owned by Constellation Power Source Generation, was conducted in August 2011 and September 2012, and has been deemed a technically feasible option for HCl (and SO2) emissions control. A final vendor/design selection has yet to be made. The sorbent under consideration for the DSI system, hydrated lime, also referenced as calcium hydroxide, is a common, non-hazardous, alkaline compound.

“The use of subbituminous coal, including Indonesian Adaro coal, has also been evaluated at Wagner due to its lower chlorine content and associated lower HCl emissions,” the Zephyr report said. “Testing of subbituminous coal firing in Wagner Units 2 and 3 was conducted in May 2007 and June 2009. One benefit common to both DSI and subbituminous coal burning is the sulfur dioxide (SO2) emissions reduction.”

The report later added: “It is expected that the subbituminous coals will be sourced from either western locations in the United States (e.g., Powder River Basin (PRB) coal), or foreign countries (e.g., Indonesian Adaro coal).”

Wagner currently burns almost exclusively domestic medium-sulfur, low-fusion Central Appalachia bituminous coal. The average specifications of the coal now burned at the plant are approximately 12,168 Btu/lb, 12% ash, 0.8% sulfur, and 7% moisture. Based on previous testing, Raven thinks there is only about 20% of additional coal feed capacity that can be achieved with the subbituminous coal in both Unit 2 and Unit 3. Therefore, depending on the actual coal characteristics, these units might experience a minor derate since they can’t be fed enough of this low-Btu coal to maintain full capacity.

U.S. Energy Information Administration data shows coal out of West Virginia going to Wagner last year from these operations and suppliers: Hobet 21, Patriot Coal; Brooks Run, Alpha Natural Resources; Synergy, through Peabody Coal Trade; and Fork Creek, through EDF Trading.

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.