By Paul A. Wagner, P.E.
Athens Generating Company, L.P.
Athens, NY, USA

By the summer of 2003, Athens Generating Company L.P. will have built a 1080 MW power plant to supply much-needed power to New York’s grid. This will be the first major power plant to be built in the state in over ten years.

Athens Generating Company L.P. recently began construction of 1080 MW of electric generation to help increase competition and reliability in New York’s power grid.

Athens Generating expects to provide electricity by the summer of 2003, improving the reliability of the transmission system, bolstering the local economy as well as providing environmental benefits to the region. In addition to creating jobs and purchasing local goods and services, the project will provide a number of trust funds, educational programmes and land conservation projects to the local area.

The project, which is located in Athens, approximately 48 km south of Albany, New York, is comprised of a combined cycle power generation facility consisting of three W501G advanced combustion turbine generators, three heat recovery steam generators (HRSGs), three steam turbine generators, and associated balance-of-plant systems and facilities. The electric generating capacity rating of the facility will be a nominal 1080 MW. The primary fuel will be natural gas, and low sulphur (0.05 per cent) fuel oil will be used for back up.

The new facility will consist of three W501G advanced combustion turbine generators, three HRSGs, and three steam turbine generators
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Athens Generating Company, L.P. is the owner of the project and is a wholly owned indirect subsidiary of PG&E National Energy Group, Inc. (PG&E NEG). PG&E NEG is a wholly owned indirect subsidiary of PG&E Corporation.

Meeting demand

Athens Generating is one of the first projects to respond to New York’s emerging competitive market and will add much-needed generation to bolster the reliability of the transmission grid. As a merchant facility, this project will deliver wholesale energy through the New York Independent System Operator (ISO) to New York’s Mid-Hudson Valley, Southeastern New York and New York Metropolitan regions.

Athens Generating will be the first major generating facility built in New York in over ten years, at a time when nearly 75 per cent of the state’s fossil fuel generators are over 35 years old and the state has recorded record high demand for summer and winter peaks.

Fueled by natural gas, Athens Generating will produce enough electricity for approximately one million homes at up to double the efficiency of some older power plants.

Exceeding expectations

Since the project’s inception, Athens Generating has worked closely with regulators, the local government and the community to address environmental issues relating to the project. As a result, this project is expected to meet or surpass all the federal and state regulatory requirements in addition to addressing a number of local concerns.

The combined cycle, natural gas-fueled facility will recycle the heat produced in the combustion process and use that captured energy to produce more electricity through its steam generators. It will use fewer natural resources and produce fewer emissions per MW than traditional fossil fuel fired generating facilities.

The Athens Generating project will be complete by the summer of 2003, and will supply enough energy for one million homes
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Mitigation at this project has included the use of dry cooling technology, which virtually eliminates water plumes and also significantly reduces water consumption.

To address visual concerns, the project changed the location and design of the access road and the water pipeline route, reoriented the facility itself, incorporated directional lighting to reduce glare, and maintained tree buffer to help screen the facility with trees. Through additional environmental evaluations, the stack height was reduced to 55.9 m to minimize visual impact and eliminate the need for FAA lighting on the stacks.

Athens Generating is working to establish a Regional and Community Historic Preservation Benefit Plan which will provide funding for historic conservation and preservation in Columbia and Greene counties.

In addition, a Landscaping Planting and Restoration Plan has been set up by Athens Generating, which will provide funding for off-site landscape work in order to further screen the power project from private properties of historic significance. The company has also provided funds to revitalize the downtown historic district in Athens.

Project benefits

The power plant is expected to provide at least 600 construction jobs and will have an annual payroll of $2.5 million when the plant is operational. To promote local access to the plant’s specialized jobs, Athens Generating is partnering with Hudson Valley Community College to provide scholarships and curriculum upgrades for students interested in environmental studies or plant utilities technology.

Athens Generating is sponsoring many conservation and preservation plans in the local area, which include protection of the Hudson River and its aquatic resources. This featured prominently in the location, design and technology of this facility which is sited approximately 4.5 km from the river with a small pump house facility on the river’s edge. The location of the intake and discharge facility was chosen to avoid known spawning areas.

Athens Generating Company LP recently began construction on the new facility, which will run on natural gas and will have a nominal capacity rating of 1080 MW
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As an additional protective measure, 2 mm wire mesh screening will be installed on the intake pipes. Athens Generating’s water usage, at an average of 681 000 l of water per day, is far less than that of traditional generating facilities.

Efficient cycle

In the combined cycle arrangement, natural gas is fired in the combustion turbine for the production of power. Hot exhaust gas from each combustion turbine is passed through its HRSG to produce steam. Most of the steam produced will be high pressure (HP), which is sent to the reheat, single flow steam turbine for production of additional power output.

The cycle also contains a reheat cycle whereby after passing through the HP section of the steam turbine, the steam is returned to the HRSG for reheating, then forwarded to the intermediate pressure (IP) section and then to the low pressure (LP) section of the steam turbine for additional power generation.

In addition, heat absorbed from the combustion turbine rotor air produces steam in two separate rotor air coolers operating in parallel with the HRSG’s IP and LP pressure levels. The remaining steam, after being fully used by the steam turbine, will be condensed into boiler feedwater by the condenser. The condenser is air-cooled so that a vacuum is created at the outlet of the steam turbine. Feedwater from the IP steam drum is used to preheat the natural gas to the combustion turbines.

The combustion turbines are constant volume machines, so their electrical output varies with the density of inlet air, affected by temperature and humidity. Output will decrease in warm weather and will increase in cold. An inlet evaporative cooling system will help counter the decrease in output by cooling the inlet air during warm weather.

Advanced technology

The W501G combustion turbine is a 3600 r/min, heavy-duty gas turbine. These combustion turbines are supplied as a complete package with all auxiliary components such as the excitation system, lube oil system, fuel gas system, controls and instrumentation, fire protection system, and water wash system for both on-line and off-line compressor washing.

Each combustion turbine is designed to deliver approximately 245 MW (nominal) of electric power based on the lower heating value (LHV) of natural gas firing and baseload operation. Each of the combustion turbines will utilize a hydrogen cooled generator.

Hot exhaust gas from the combustion turbines is directed to a three-pressure, natural circulation HRSG. The HRSG converts energy in the hot gas into HP steam which is used to generate additional electricity in the steam turbine. Additional space has been left in the HRSG to accommodate both additional SCR catalyst and CO catalyst if greater emissions reductions are required.

Combined cycle

The HP, IP and LP superheated steam from each HRSG is delivered to each steam turbine to generate additional electricity. The plant will use three single flow reheat, dual admission, axial exhausting condensing steam turbines suitable for sliding inlet pressure operation or operation under speed control. The steam turbines will be supplied complete with auxiliaries including electrohydraulic control, lube oil, turning gear, excitation, air-cooled instrumentation, and controls. Each steam turbine is designed to deliver approximately 126 MW (nominal) of electric power based on baseload operation of the combined cycle unit.

The steam cycle is designed to support operation of the combustion turbines in baseload operation at the average annual ambient conditions. A 100 per cent capacity feedwater pump will be provided for each HRSG. The feedwater pump will take suction from the LP drum of the HRSG and will supply water to the HP and IP sections of the HRSG.

The condenser will be air-cooled, A-frame type, supplied with a condensate tank and deaerator, and two-speed fans. The condenser will be designed for a turbine backpressure of 84.67 millibar, at an ambient temperature of 15°C.

One 100 per cent capacity condensate pump is provided to pump water from the condenser to the LP steam drum. Two holding steam jet air ejectors, each rated at 100 per cent capacity, are provided for normal operation along with a single stage non-condensing hogging steam jet air ejector to evacuate the turbine and condenser steam space when the unit is started.

The Athens project’s maximum water requirements will be supplied by an Intake/Discharge Facility (IDF), which is to be constructed on the western banks of the Hudson River, approximately 4 km southeast of the project site. The IDF will be interconnected with the project by an underground supply and return pipeline.

The project will obtain approximately 470 l/min of untreated water from the Hudson River, for steam cycle makeup and other uses. Demineralized quality make-up water is required to replace water used for steam cycle blowdown. The demineralized water system consists of leased reverse osmosis/EDI trailers to provide makeup for three demineralized water storage tanks, each providing steam cycle makeup to each combustion turbine/HRSG/steam turbine train.

A second demineralized water system consists of a leased trailer providing water for NOx injection when needed for combustion turbine oil firing. Potable water for the project will be provided by a single well drilled on site.

Fuelling the plant

The fuel gas supply at the interface with the supplier will be in the design ranges of 46 to 100 bar and 5 to 20°C. The natural gas system will be sized for the three combustion turbines full load gas flow, and includes an electric gas heater, gas scrubber and pressure regulation valves for each unit. The gas heaters will be sized to maintain a minimum 15°C gas temperature after the pressure reducing control valves. Gas compression will not be required for the project.

The combustion turbines will utilize DLN combusters to control NOx emissions, and each HRSG will be equipped with an SCR catalyst system. This uses aqueous ammonia injected into the HRSG to control NOx emissions from the stacks to below 2.0 ppmvd, while operating the project on natural gas.

The project will be supplied with a permanently installed Continuous Emissions Monitoring System (CEMS) to monitor the exhaust gas emissions from each HRSG stack and ensure that they meet air regulations.

Electrical power will be produced by a total of six electrical generators. All of the generators will be equipped with a static excitation system, automatic synchronization and neutral grounding equipment. The starting motors for the combustion turbines are powered from the unit auxiliary transformers. An isolated phase bus duct is used to connect each generator through a circuit breaker to the three-winding generator step-up (GSU) transformer.

The plant will be controlled through a distributed control system (DCS) designed to interface with equipment suppliers’ control systems for power plant control and automation. The DCS design will be engineered to provide safe and efficient start-up, operation and emergency shutdown of the plant.

The DCS will consist of redundant processors, operator CRT displays and keyboards, plant data highway, major system control interfaces, and data storage devices. The DCS provides control, monitoring and indicating functions for the control of the steam turbines, gas turbine generators, HRSGs, CEMS, balance of plant equipment, and related auxiliary equipment.

Power supply

The project’s 345 kV switchyard will be a ring bus configuration that bisects the existing transmission line between Niagara Mohawk Power Corporation’s (NMPC) Leeds substation and Con Ed’s Pleasant Valley substations. The switchyard will consist of five SF6 circuit breakers for the three GSU transformers.

The project will utilize approximately 550 m of interconnecting transmission lines to the existing NMPC Leeds transmission line. Revenue metering will be at the 345 kV switchyard and provided on the Pleasant Valley transmission line for inter-utility readings, and on each GSU 345 kV tie line for the project’s net power output.

To date, most of the engineering and preconstruction activities have been completed, including engineering design and site preparation. Procurement and delivery of site components has been steadily progressing with some major equipment already being delivered, such as the combustion turbines and HRSG modules. Work on the 4.5 km long water pipeline has commenced, with the river work and construction of the river pump house beginning in October 2001.