Repowering South Mississippi Electric Power Association’s J.T. Dudley, Sr. Generation Complex

Repowering two units at the J.T. Dudley, Sr. Generation Complex added 180 MW of high-efficiency capacity to South Mississippi Electric’s portfolio. Now the cooperative can self-produce more than 50% of its electricity needs.

The J.T. Dudley, Sr. Generation Complex, owned and operated by South Mississippi Electric (SME), is located in Jones County, Miss. Originally installed in 1968 at what was then called the Moselle Generating Station were Units 1, 2, and 3, nearly identical 60-MW conventional steam plants. Units 4 and 5, General Electric (GE) 7EA simple cycle combustion turbines, were added in 1997 and 2005, respectively.

Today, the complex consists of five units capable of generating more than 500 MW. The additional capacity will pay long-term dividends to SME’s customers in the form of increased system reliability and more control over its production costs. The cooperative forecasts that as of 2013 it can self-generate 51% of its power needs; it purchases bulk power for the remainder.

The repowering project converted Units 1 and 2 into two, independent 1 x 1 combined cycle units. Both original gas-fired boilers were retired in place and the steam source for each unit was replaced with a new GE 7EA combustion turbine (CT) and a Vogt Power International (VPI) heat recovery steam generator (HRSG). The new power block is located approximately 400 feet from the existing powerhouse, with piping and cable tray routed along a three-level pipe rack between the HRSGs and powerhouse (Figure 1).

Construction began in August 2010. The commercial operation date (COD) for Unit 2 and Unit 1 combustion turbines in simple cycle operation was November and December 2011, respectively. The COD dates for Unit 2 and Unit 1 in combined cycle operation were May and November 2012, respectively.

Burns & McDonnell provided consulting, detailed design, procurement, construction management, and startup services. SME designed, procured, and installed the CT generator step-up transformer and interconnection power line, as well as the existing plant switchyard expansion.

A multi-phase and multi-contract approach was used on the remainder of the project. Beginning in August 2010, James Construction Group kicked off construction with site civil work and foundations, plus electrical and mechanical underground construction. Next, PCL Constructors followed in December 2010 with the combustion turbine and simple cycle portion of the construction project. The Saxon Group handled the final two major construction contracts: electrical and HRSG erection plus the combined cycle balance of plant, beginning work in January 2011 (Figure 2).

2. Refurbish instead of rebuild. The existing three conventional units are shown in the background (outdoor boilers with a
single steam turbine building located behind the boilers) with the two existing 7EA simple cycle combustion turbines (CTs) to
the right of the existing units. The new 7EA CTs are visible in the foreground. Between the new CTs and the three existing
boilers are the two HRSGs being assembled. Each 7EA-HRSG combination supplies steam to a single, existing steam
turbine. The HRSGs are Vogt Power International’s Enhanced Constructability Smart design. The design incorporates pressure parts, pressure part support steel, interconnecting piping, casing, and structural steel into only six shop-fabricated module boxes per HRSG, significantly reducing erection labor expense. The photo was taken during constructionin October 2011.  Courtesy: Burns & McDonnell

The engineering and design of the repowering project was performed with two goals in mind: increased operational flexibility and reuse of existing equipment, where feasible, to minimize project cost. Reused equipment included the steam turbine, boiler feed pumps, condensate pumps, condenser, cooling towers, deaerator, plant air system, and flash evaporator. Details about the major components and equipment used on the repowering project follow.

Combustion Turbines. The two new natural gas–fired GE 7EA CTs are equipped with dry low-NOx technology (DLN1) and each is rated at ~85 MW. Each CT is also equipped with evaporative cooling technology, which increases summer capacity by ~8 MW. At full load, the combustion turbines will provide a flow of 2,225,000 pounds per hour of exhaust gas at 1,022F to each HRSG (Figure 3).

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