Allen Combined-Cycle Plant
Owner: Tennessee Valley Authority
Lead Design Firm: Kiewit Engineering
EPC Contractor: Kiewit Power Constructors
Located five miles southwest of downtown Memphis, the Allen Combined-Cycle project was developed in response to the Tennessee Valley Authority’s commitment to expand fuel diversity. The facility replaces the project owner’s nearly 60-year-old Allen Fossil Plant, which is scheduled to be idled by the end of this year.
Completed in March 2018, the new Allen plant provides power to more than 650,000 Memphis-area homes and businesses. The 1,100-MW natural gas-fired facility’s state-of-the-art combustion turbine generators make it TVA’s most efficient plant, and among the most efficient in the world, according to Kiewit, the project’s EPC contractor. The new Allen plant also operates far cleaner than its predecessor, reducing carbon emissions by 60%, nitrogen oxides by 90% and sulfur dioxide by nearly 100%.
Through a partnership with the city of Memphis, the Allen plant taps methane gas from an adjacent wastewater treatment plant to generate approximately 5 MW of additional power. TVA invested $20 million in infrastructure that cleans, dries and transports methane to the new plant for use in an auxiliary boiler. TVA estimates that at peak production rates, the methane-fueled system could account for as much as 8 MW of the plant’s power output.
Collaboration across the integrated engineering, procurement and construction team helped optimize the project as each phase unfolded. When the project team discovered a potential clash between the placement of steel support columns and the new generators’ key access points, Kiewit worked with the turbine manufacturer’s steel supplier to eliminate the conflicts, resulting in a clean, efficient design that provides full access to all equipment.
The project team was also tasked with integrating a 3,000-panel solar array on a four-acre site adjacent to the combined-cycle plant. This scope of work was particularly unique in that the solar field is electrically connected to the balance of the plant’s 6,900-volt switchgear, presenting a potential issue with detecting operational problems. The design team upgraded the sensitivity of the DC-AC power inverter system, further enhancing the overall system’s ease of operation and monitoring capability.
As TVA’s largest self-built solar project in the Tennessee Valley area, the Allen plant’s $1.3-million solar installation will produce approximately 1 megawatt of renewable energy, enough electricity to power about 120 average homes.
Other project features include an enhanced layout in the steam turbine building with expanded access space for plant maintenance teams, and improved safety through the elimination of conventional “up and over” stairs across the pipe racks. The layout and size of the facility’s water treatment building allows all equipment to be located indoors. By routing all interconnecting piping and conduit beneath the building’s slab, the project team created a clean layout with generous maintenance and access space.
Complementing the project team’s design and construction successes were its efforts to ensure the day-to-day safety of the hundreds of workers involved with making the Allen plant a reality. A rigorous safety program, called Nobody Gets Hurt, stressed accountability for incident prevention by every individual on site, particularly craft workers. Full-time craft safety advisers (CSAs), selected based on experience and attitude, served as liaisons between craft workers and project management, and helped boost engagement and participation in all project safety efforts.
Another initiative was Craft Voice in Safety (CVIS), a formalized system for facilitating safety discussions and suggesting improvements to the management team. CVIS leaders were authorized to take time away from work to perform their duties, which included maintaining continuous communication with craft teams and mentoring newer workers.
The Nobody Gets Hurt approach lived up to its name. Workers on the Allen plant project amassed more than 2.7 million work-hours with zero lost-time incidents.
ENR Southeast’s Best Projects safety judges had high praise for what one panelist called a “grassroots approach to safety.”
“The obvious correlation and collaboration between craft workers and management is visible in the success of their program,” observed Deborah Hampton, corporate environmental, health and safety officer with Odebrecht, Coral Gables, Fla.
By carefully managing coordination between the TVA, General Electric and the city of Memphis, EPC contractor Kiewit was able to complete the project under budget and ahead of schedule.
“Continuous planning for tomorrow made today very manageable,” is how Dan Tibbs, TVA’s general manager for major projects and generation construction, projects and services, characterized the project’s team approach to handling the complexities of the plant. “It was seldom that the project was in a reactionary mode because of the continuous planning and preparation for what might happen.”
TVA was similarly satisfied with the contractor’s performance relative to the budget and schedule. Added Tibbs: “Excluding change orders initiated by TVA, there were almost no change orders and very little discussion of change orders by Kiewit, which was even better. (And) because of smart and continuous planning and a focus on execution, a fairly tight schedule was met with room to spare.”