LA Department of Water and Power (LADWP) has completed the repowering of its Scattergood Generating Station earlier this year.
“This involved the replacement of the almost 40-year-old Unit 3 with new gas turbines designed with faster start, faster ramp rates and well as many alarm features that would inform operation personnel of a problem before a component fails,” Sungly Chiu, Power Engineering Manager for LADWP told Gas to Power Journal.
Repowering refers to the rebuilding of power plants by taking old generating units out of commission, dismantling them and replacing them with modern units sited at the same facility. Drivers for repowering projects include the need to replace aging equipment, stiffening of environmental regulations, the needs of the local power grid, and policy changes that call for coal to be phased out and renewable sources of generation to be increased.
For an estimated project cost is $950 million, the repowering of Scattergood was done to achieve benefits such as:
• Reduce use of ocean water cooling to protect marine habitats
• Increase fuel efficiency, reduce greenhouse NOx emissions, improve reliability and lower fuel costs
• Heighten the utility’s ability to ramp up and down quickly in response to fluctuations in the availability of power from renewable sources
• Support at least 9,760 jobs annually and generate more than $2 billion in economic output and over $189.3 million in tax revenue
• Maintain the facilities generating capacity at 830 MW
• Meet federal and state air quality and environmental regulations.
“The new units include features that aid the LADWP in maintaining the power grid's reliability and efficiency in operation,” said Chiu.
Scattergood Generating Station is a 55-acre facility located just south of LA International airport. Built in the late 1950s, it originally consisted of three steam turbine generators that burn natural gas in boilers (capacity 830 MW). To meet air and water quality standards, Scattergood Unit 1’s capacity was lowered. Unit 3 was replaced by a more efficient combined-cycle generator. In addition, two smaller, simple cycle gas turbines were built.
The new turbines, known as Units 4, 5, 6 and 7, have a total generating capability of 534 MW. Units 6 and 7 are GE LMS100 simple cycle gas turbines and each has a 105.8 MW rating. Unit 4 is a GE 7FA.05 gas turbine with a 1 X 1 combined cycle configuration. It has a 214.4 MW rating. Unit 5 is a GE A650 steam turbine with a 107.2 MW rating. Additionally, a Vogt Triple Pressure Heat Recovery Steam Generator (HRSG) supplies steam to the steam turbine. Ocean water cooling usage was replaced at Scattergood with an air cooled condenser for the combined cycle unit and an air cooled heat exchanger for the smaller simple cycle units.
“Deploying an air-cooled steam condenser in place of using ocean water for cooling has reduced the cooling water usage by 55 percent,” said Chiu. “The new units have significantly faster start up and ramp rates, and the lowest NOx emission levels among all thermal generating units in the world.”
The 322 MW combined cycle plant can start within 88 minutes. Due to increased efficiency and improved emission performance, the combined cycle plant will be prioritized for service dispatch. One of the main drivers for the selection of the LMS100 aeroderivative gas turbine was quick response. With a generating capability of 110 MW and the ability to reach full load in 10 minutes, LADWP will use them as peakers to meet grid demands as well as to help integrate the variable output of renewable generating assets.
“The two LMS100s are equipped with a clutch system that allows the unit to provide greater stability and voltage support to our electrical transmission grid,” said Chiu.
The clutches are provided by SSS Clutch. They enable the LMS100 generators to operate as synchronous condensers as the clutch turns the generator into a synchronous motor which can produce or absorb varying degrees of reactive power. When the turbine rotor is separated by the clutch, it allows the generator to continue running as a synchronous motor without using natural gas, enhancing the fuel efficiency of our system. When power generation is again required, the turbine can then be accelerated to full speed and reconnected to the still rotating generator.
“One of the most valuable investments for the project is the inclusion of the clutch system for the Scattergood LMS100 units,” said Chiu. “The synchronous condensing feature is helpful in maintaining the overall grid stability and has proven to be effective.”