The new generation

The new generation

Siàƒ¢n Green

Senior Editor

The Bridgeport Energy plant in Connecticut is approaching combined cycle operation and is just one example of the many merchant power plants under development in the USA. Developed on an aggressive fast-track schedule, it also illustrates what can be achieved in a competitive market with the right resources.

In September 1997, Duke Energy Power Services and United Illuminating signed an agreement to construct a combined cycle natural gas fired merchant plant in Bridgeport, Connecticut. Just under one year later, in August 1998, the first units of the Bridgeport facility began supplying electricity to the New England grid.

When complete in July this year, the Bridgeport plant will supply New England with 520 MW of much-needed baseload power, selling all of its output into the wholesale market. Developed under a fast track schedule, the plant is the first merchant plant to be developed in New England, and among the first in the USA.

The plant is located at Bridgeport Harbour, Connecticut, on seven acres of land adjacent to an existing coal and oil-fired facility. Construction on the plant began in October 1997 and was undertaken in two stages. Phase one involved the installation of two gas turbines operating in simple cycle and was completed in August last year when the plant began supplying 340 MW to the grid.

Currently underway is the second phase, involving the installation of two heat recovery steam generators (HRSGs) and a steam turbine, providing an additional 180 MW. Duke Energy says that combined cycle operation will begin this summer in time for the expected peak demand. Projected annual output is 3600 GWh, and net generation at the end of 1998 was 237 GWh.

The $190 million plant is representative of developments in the US market, and of what an integrated energy company can achieve through a diverse set of capabilities. Deregulation, particularly in the New England region, has opened up the market to competition and to a new breed of generator – the merchant plant.

Merchant plants

Bridgeport embodies new project development trends in the USA – natural gas-fired merchant capacity constructed on a fast track schedule. In the last two years the country has seen an explosion in merchant plant activity, concentrated mainly in New England, Texas and California. Estimates suggest that there is over 50 000 MW of capacity in various stages of development.

The driving force is deregulation and the new strategy this brings for utilities and developers which seek to strengthen their market position and seize profit-making opportunities. The competitive advantage offered by the high efficiency combined cycle technology available is also a major incentive.

The risks associated with merchant plants are high, as by definition merchant plants sell most or all of their output into the wholesale market with no secure long-term power purchase contracts. Some developers are therefore willing to take large risks to gain market position ahead of others in a newly deregulated environment.

The New England independent system operator (ISO) was last year considering over 40 merchant plant proposals, including nine in Maine, 16 in Massachusetts, two in Rhode Island, 11 in Connecticut and five in New Hampshire.

In the case of Connecticut, the explosion in merchant activity has been driven by a number of other factors. Connecticut has a strong and growing natural gas supply. The Iroquois pipeline is one major source of natural gas for the state and more than $1.2 billion-worth of new pipeline is being constructed in the region. New England has also lost more than 3400 MW of baseload capacity through the forced permanent and temporary shutdowns of nuclear capacity.

In addition, the region`s present capacity is aging; more than 50 per cent of generation is from power plants which are more than 25 years old, and no significant new generating facilities have been constructed during the last decade. There are also significant transmission constraints into the northeast, which put a premium on capacity.

Nevertheless, the proposals for over 40 new merchant plants in New England, totalling around 23 000 MW, exceed the region`s needs. Analysts believe that only 3000 MW of additional capacity is required, even after expected nuclear plant retirements.

To be first out of the starting blocks was therefore important for Duke Energy, which took the project from announcement to simple cycle operation in just over one year. This enabled phase one to be completed in time for the summertime`s peak demand. The project underwent “parallel planning”, whereby the development, permitting, design and engineering activities were carried out simultaneously where possible, as opposed to a traditional “step by step” approach.

Project players

The Bridgeport facility is owned by Bridge- port Energy LLC, a company formed by Duke Energy Power Services (DEPS) and United Illuminating Co. The main equipment contractor is Siemens-Westinghouse.

DEPS, an affiliate of Duke Energy Corp., is the majority owner of the Bridgeport facility and has provided the financial backing for the project purely through its balance sheets. Duke Energy Corp., an integrated gas and electricity company, was formed in 1997 by the merger of Duke Power Co. and PanEnergy Corp. The company is utilizing several of its subsidiaries in various aspects of the project.

For example, its Energy Trading and Marketing unit will secure fuel supplies for the plant and will also market and sell the plant`s electricity. Duke Energy Field Services will help ensure fuel supply, while Duke Energy`s Energy Transmission Group will participate in transporting natural gas to the site. Duke/Fluor Daniel is the owner`s engineer and will assist in the operation and maintenance (O&M) of the plant.

Bridgeport is the first merchant plant project which Duke Energy has undertaken, and the company has since announced several other merchant plants, including projects in Maine, Texas and Missouri. A likely facility in a new region progressed in March 1999 when the Florida Public Service Commission (PSC) approved Duke Energy`s plans to build Florida`s first merchant power plant at New Smyrna Beach; this will be a 500 MW facility and, pending final approval from the state`s environmental Protection Department and the governor, will enter operation in 2001.

United Illuminating (UI) is a New Haven, Connecticut-based utility serving more than 310 000 customers in Greater New Haven and Greater Bridgeport. The company owns 4.2 per cent of Bridgeport Energy.

Bridgeport is being built adjacent to UI`s existing Bridgeport Harbour station which was built in 1957. The 80 MW Unit 1 of the four-unit facility has now been shut down, resulting in a 75 per cent decrease in total annual air emissions at the site.

Siemens-Westinghouse is the main contractor for the Bridgeport power plant, responsible for turnkey engineering, procurement and construction. It has supplied most of the major equipment, and, assisted by Duke/Fluor Daniel, the Siemens-Westinghouse Operating Company will undertake the O&M of the plant. The O&M contract includes all operations, minor maintenance and major inspections.

Natural gas for the facility is provided by an 18 km distribution pipeline recently constructed by Southern Connecticut Gas Co. (SCG). SCG will own and operate the pipeline, which interconnects with the Iroquois gas transmission line at Stratford, Connecticut. The natural gas will come from Canada, Oklahoma and the Gulf of Mexico.

Plant description

The design of Bridgeport power plant is based around a “two on one” power island consisting of two Siemens V84.3A gas turbine generators each rated at 170 MW ISO and a Siemens steam turbine generator rated at 180 MW. Two HRSGs supplied by Vogt-NEM extract waste heat from the gas turbine exhausts and feed steam to the steam turbine. Low-NOx burners and Selective Catalytic Reduction (SCR) control technology are used to lower emissions of nitrogen oxides. The overall heat rate of the facility is approximately 6500 Btu/kWh net.

In December 1997, the first of the two gas turbine-generators was delivered to the Bridgeport site, only four months after construction began. The second unit was delivered shortly after. Each turbine weighs 167 832 kg and is 4.6 m wide by 9.1 m long. Each generator weighs approximately 240 016 kg.

The plant uses salt water from Long Island Sound for once-through condenser cooling. The cooling water is taken from the Sound and conveyed through a 430 m intake pipe and is returned to the sound via a 490 m outfall pipe. The 3 m diameter pre-stressed concrete pipes, weighing 20 t per 6 m length, was supplied by Vianini Co. of New Jersey.

In total, 914 m of cooling water pipes were installed by O&G Industries Inc. of Torrington, CT, the main civil works subcontractor. O&G`s portion of the work included site, concrete, utility, building and environmental work. The company supplied around 10 000 m3 of concrete and 1100 t of structural steel. It erected the temporary stacks used for simple cycle operation, and is also constructing the permanent 40 m stack which will be used when combined cycle operation starts.

During peak construction, from May 1998 to March 1999, the site employed 300 workers. When the facility is fully commissioned, the plant will have a permanent work force of 20-25 people.

Environmental performance

A major benefit of the plant to the local surroundings is its environmental performance. The facility is one of the first electric generating facilities in the New England region to use gas-fired combined cycle technology, and in replacing older units such as the UI oil-fired Bridgeport Harbour Unit one, will help to reduce air emissions in the area considerably.

Even though the electricity output of the Bridgeport Energy facility will be 85 per cent greater than that of UI`s Bridgeport Harbour Unit 1, operating the new facility will result in a 75 per cent decrease in total annual air emissions when compared to Unit 1.

ࢀ¢ Nitrogen oxides: annual emissions of NOx will be reduced by 60 per cent, helped by the use of low-NOx burners and selective catalytic reduction technology.

ࢀ¢ Volatile Organic Compounds: VOCs will remain under 65 t per year and well within state and federal requirements.

ࢀ¢ Emissions of sulphur dioxide (SO): will be reduced by over 99 per cent by the closure of the oil-fired Bridgeport Harbour plant.

ࢀ¢ Particulate matter: The total annual emissions of soot will fall by 85 per cent by the time the plant is fully commissioned.

Commissioning of phase two of the project is currently in progress with the code boundary hydros completed and start-up of the balance of plant systems started. The turbines will go into outage in order to tie in the HRSGs, remove the temporary stacks and reconfigure the control systems for combined cycle mode. The plant is on schedule to enter combined cycle operation in July this year.

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Figure 2. Duke Energy is developing several merchant plants in the USA of which Bridgeport was the first to be announced and New Smyrna Beach the latest

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