Top Plant: John Twitty Energy Center Unit 2, Springfield, Missouri

Owner/operator: City Utilities of Springfield, Missouri

City Utilities of Springfield elected to add a 300-MW coal-fired plant to its fleet to meet rising demand for electricity. It was the first coal plant constructed by the utility since 1976. An extremely competitive construction market required the utility to adopt new contracting practices to meet a tight project schedule, an approach that proved very successful. The $555 million plant commissioned in January 2011 is expected to cover system growth at least through 2024.

Courtesy: City Utilities

City Utilities of Springfield (CU), Missouri, is a community-owned utility serving 110,000 customers in southwest Missouri with electricity, natural gas, and water services. The utility’s electricity generation resources include the 203-MW coal-fired Southwest No. 1 (renamed the John Twitty Energy Center [JTEC] Unit 1 in May 2011), which entered service in 1976, and the five-unit James River Power Station with a total nameplate of 255 MW, whose units entered service between 1957 and 1970. In addition, CU owns 359 MW of combustion turbines that satisfy the region’s peaking power requirements. The utility contracts for another 101 MW under long-term power purchase agreements. The CU 2010 net peak demand was 772 MW.

By 2003, increasing electrical demand from existing and new customers required CU to add additional generation, especially because its last plant had been constructed almost 30 years earlier. After considering several different generation alternatives, the decision was made to add a second coal-fired unit rated at 300 MW to the JTEC because it appeared to be the best life-cycle cost option. Construction of the $555 million (total construction and commissioning cost) project designed to burn low-sulfur western coal began in July 2006 with early construction of the chimney foundation. Unit 2 was formally dedicated on November 10, 2010, and in commercial operation in January 2011. CU doesn’t expect additional baseload generation will be needed until 2024 or later.

“With this new unit, we believe that a balance of reliable, affordable, and responsible power has been met,” said retired City Utilities General Manager John Twitty, after whom the plant was recently renamed (Figure 1). The new unit is expected to enhance the city’s ability to bring jobs to the area. “Springfield is open for business,” said Mayor Jim O’Neal. “And we’ve got the power to prove it.” A four-year time-lapse video of the plant’s construction is available at http://www.tinyurl.com/cus2010.

1. Same plant, new name. After completion of Southwest 2, City Utilities of Springfield in May renamed its energy complex the John Twitty Energy Center in honor of the utility’s retired general manager. The energy center has a combined gross output of 503 MW. Unit 2, the larger structure on the left, is rated at 300 MW. The 203-MW Unit 1, the smaller structure on the right, was completed in 1976. Courtesy: City Utilities

Designing a New Plant

Design of the new unit began in 2006. Stanley Consultants was retained as the owner’s engineer for the project with responsibility for the detailed design of the entire plant, cost estimating, scheduling, resident engineering services during construction, start-up services, and performance testing. Much of the design ran concurrent with construction because of the tight project schedule.

Lessening the plant’s environmental footprint was a key consideration. The design included the plant’s state-of-the-art emissions reduction technologies: activated carbon injection for mercury emissions control, a urea-based selective catalytic converter for NO_xcontrol, and an Allied Environmental dry fluidized bed desulfurization system with baghouse for SO₂ control, acid gas emissions reduction, and particulate control.

Many of the major equipment purchases were made by CU, including the steam turbine generator (Toshiba), condenser (Ecolaire), and the circulating, boiler feedwater, and condensate pumps (Flowserve). Oscar J. Boldt Construction was responsible for erection of the boiler island supplied by Foster Wheeler, and Cherne Contracting Corp. handled construction of the balance of plant. Alberici Constructors provided major equipment erection, including the turbine generator. Other major equipment suppliers included:

• Boiler: Foster Wheeler
• Coal silos and mills: Foster Wheeler
• SCR catalyst: Ceram Environmental
• Air heater: Alstom Power
• CFB scrubber, baghouse: Allied Environmental
• PAC system: ADA-ES
• Chimney: Pullman Power
• Bottom ash and fly ash systems: United Conveyor Corp.
• Coal handling: Brahma Group (equipment and construction)
• Cooling tower: Midwest Towers (equipment and construction)

The coal pile was expanded to account for much-increased coal usage at the plant. Powder River Basin (PRB) coal is delivered by unit train using bottom dump railcars that arrive every 48 hours. Each delivery is about 18,000 tons of coal. Coal is unloaded from the railcars into hoppers, then to a transfer tower and stockout conveyors, and then deposited on the coal pile. Coal is reclaimed from the pile, crushed, and conveyed to Unit 2’s storage silos before delivery to the plant’s pulverizers. A “dead” storage pile is used to protect against interrupted or delayed deliveries. The Unit 2 boiler burns up to 170 tons per hour of PRB coal.

Challenges Abound

Compliance with all the environmental permits is often the critical path for these large construction projects. For JTEC Unit 2, the air permit required CU to begin construction prior to November 2006 or the permit would expire. Because the air permit defined the stack height and diameter, the foundation was designed based on past project experience. As seen in the video, construction began with drilling about 20 piers for the stack foundation, each more than 25 feet deep, followed by a continuous pour 10-foot-thick and 80-foot-diameter chimney foundation.

Procurement of major equipment and commodities, such as steel, took place in 2006 when marketplace activity was at historic highs and contractors had large backlogs. For example, when soliciting bids for the boiler island installation, of the three firms qualified to bid, two did not submit proposals. A negotiated contract with the remaining firm resulted.

Early procurement of major equipment, along with “open book” construction contracts, allowed significant owner involvement in the equipment selection and subcontracting processes. Often, nonstandard contracting approaches were required, such as accepting bond limits, incorporating target pricing for payment structures, and negotiating lump sum contracts with variable risk-sharing provisions. The cost risk was shared with the major construction contractors on market pricing for materials and equipment and on labor availability and productivity. City Utilities served as its own construction manager for the project.

A hybrid contracting approach was used for plant construction:

• Stand-alone work (such as chimney, coal handling, and cooling tower) used supply and erect contracts.
• Substructure work was separately contracted in phases.
• Separate contracts were signed for boiler erection and balance-of-plant construction.

Over 90% of the site construction labor was hired from a 100-mile radius of Springfield. Of $160 million spent on labor, 90% stayed in the region.

Unique Design Practices

Treated municipal wastewater from the Southwest Wastewater Treatment Plant (SWTP) is used for cooling water makeup and wet flue gas desulfurization sprays, saving approximately five million gallons per day of water that would otherwise have been supplied from underground aquifers. The water is pumped from SWTP, located about a mile away, through a 20-inch-diameter pipe to the plant. Water is stored on site in a 2.7 million gallon storage tank. The water quality, especially the chloride levels, required using SeaCure condenser tubes and titanium plates in other plant heat exchangers.

Emerson supplied its Ovation distributed control system for Unit 2. The plant makes extensive use of digital bus technologies with nearly 4,200 I/O points, more than 500 Foundation fieldbus devices, and more than 100 Profibus DP devices. The plant also uses Emerson’s Intelligent Device Manager to streamline installation and the configuration of each field device during start-up. In addition, the AMS Device Manager provides diagnostic and predictive maintenance information during plant operation.

Although not part of this project, Unit 1 controls were also recently upgraded to Emerson’s Ovation Expert digital controls. The new control room constructed for Unit 2 included sufficient room to house the control panels from both units.

The plant was designed using 3-D modeling software. This allowed a virtual check for interferences, particularly between structural steel, electrical cable tray and conduit, and piping. The software allowed users to take a virtual walk through the facility prior to beginning construction. Building information such as equipment tag numbers, valve numbers, and object specifications, were also collected in the 3-D model for future use.

— Dr. Robert Peltier, PE is POWER’s editor-in-chief.