By Steve Blankinship, Associate Editor
The Big Bend Power Station is a coal-fired facility with a generation capacity of over 1,800 MW. Owned by Tampa Electric, Big Bend is on Tampa Bay in southeastern Hillsborough County. The 1,500-acre plant site is divided into several major areas: steam plant, coal field, byproducts, flue gas desulfurization (FGD) scrubbers, waste water pond systems and combustion turbines.
Big Bend consists of four pulverized coal-fired steam units and three distillate fueled combustion turbines (peaking units). The coal-fired units are equipped with FGD scrubbers and electrostatic precipitators. They currently are undergoing the addition of selective catalytic reduction (SCR) systems. The Unit 4 SCR retrofit was completed in June 2007. The remaining SCR systems are scheduled for completion by 2010. In conjunction with the SCR additions for Units 1-3, the boiler draft systems will be modified to a balanced draft design to accommodate the increased pressure drop associated with the new systems. Unit 1 began service in 1970; Units 2 and 3 were added in 1973 and 1976; and Unit 4 was added in 1985 as the station expanded during the 1970’s and 1980’s.
Karen A. Sheffield, P.E. (right) is Big Bend Plant general manager. She has been with Tampa Electric Co. for 31 years. Karen O. Zwolak (left) is senior environmental coordinator. Photo courtesy Tampa Electric.
Karen A. Sheffield, P.E., is Big Bend Plant general manager. She has been with Tampa Electric Co. in the Energy Supply area for 31 years. Karen O. Zwolak, Big Bend senior environmental coordinator, has been with Tampa Electric Co. for 17 years.
The units at Big Bend Station are all pulverized coal units with nominal ratings between 425 and 485 MW. Each unit is fired with a blend of high sulfur bituminous coal and up to 20 percent (by weight) of petroleum coke. Units 1-3 are Riley Stoker Turbo Furnace, wet bottom, pressurized draft units. Unit 4 boiler is a Combustion Engineering, tangentially fired, balanced draft dry bottom boiler. The FGD systems are wet limestone systems with forced oxidation and produce a commercial-grade gypsum byproduct.
The Big Bend Power Station has approximately 400 employees. Another 60 contractors work at the plant on a routine basis. During major outages, Big Bend may add 300 to 500 contractor workers.
Tampa Electric and the Big Bend Station have taken on numerous improvement projects to reduce environmental impacts associated with air emissions, as well as storm water control, groundwater protection, byproduct reuse and beneficial reuse of plant wastewater and county sewage treatment plant effluent. Unit 4 was the first of Tampa Electric’s fleet designed and built with a flue gas desulfurization system to reduce SO2 emissions.
Tampa Electric engineers developed a means to scrub two units with one system, thereby reducing SO2 emissions on Unit 3 by integrating Unit 3 with the Unit 4 existing scrubber. With the Title IV requirements of the Clean Air Act, Tampa Electric built a second FGD system to scrub SO2 from its remaining coal-fired Units 1 and 2 four years later, in 1999. Currently, the scrubbers remove between 93 percent and 95 percent of SO2 emissions from the flue gas streams.
With the Department of Justice and EPA new source review enforcement actions in late 1999 and 2000, Tampa Electric agreed to improve the existing pollution control equipment for SO2 and particulate matter, as well as install pollution control technology to reduce NOX emissions. This included optimizing the station’s FGD systems for SO2 removal, installing low NOX burners and SCR technology on all units for NOX emission reductions and improving particulate matter removal through development of best operation practices, best available control technology improvements and installation of new particulate matter CEM technology. By 2010, the SCR projects are expected to reduce NOX emissions at Big Bend by roughly 85 percent from 1998 levels.
The station is also exploring ongoing issues, most notably dissolved oxygen in its cooling water outfall and 316(B) studies for impingement/entrainment of microorganisms in its circulating water intake. Units 3 and 4 have fine mesh screen technology and organism return systems. EPA is evaluating the possibility of developing new effluent guidelines to address impacts to U.S. waters from SO2 and NOX removal technologies. Big Bend was chosen as a sampling site for data collection.
The SCR project requires retrofitting a vintage plant with new technology. Construction is on base load units with limited space. During the preliminary design phase, a team consisting of engineering, construction and plant operations personnel was assembled to develop the most efficient design possible by using innovative construction methods. Special consideration was given to maximize pre-outage installation. This allowed some pre-outage start-up activities and also enabled the team to maximize the use of resources during the SCR tie-in outage. In essence, over 90 percent of the Unit 4 SCR construction was completed prior to the tie-in outage, while the unit was in operation.
As a part of the engineering phase of the project, 3-D computer models were developed to determine constructability due to the tight clearances present at the site. The models were used to understand spatial constraints to determine tie-in coordination activities and the physical fit of the SCR equipment. Detailed sequencing and planning to avoid interferences, construct amid tight clearances and utilize prefabrication of ductwork, was made possible with use of the 3-D model.