LMS100 cuts water use, improves flexibility of LA plant

LMS100 being delivered to LA plant[/caption]

One of the earliest and most enthusiastic adopters of the GE LMS100 has been LA Department of Water and Power (LADWP). It ordered these machines for several of its plants along the California coast. Now that they have had a couple of years of operation, how are they doing in the real world?

“The LMS100s are the most efficient and quick response simple cycle units available today with a generating capability of 100 MW and can reach full load in 10 minutes,” said Sungly Chiu, Power Engineering Manager for LADWP. “The six LMS100s at our Haynes facility have been successful in meeting peak power demands and providing a quick response to unscheduled loss of transmission or generation assets.”

Water Intake Woes

LADWP placed generating stations such as Hayes along the Pacific shoreline to minimize cooling costs. That enabled them to take all the water they needed for cooling purposes in a process known as once-through cooling (OTC). Back in the day, the ocean was seen as an endless source of cooling water.

But Haynes and other LADWP coastal facilities fell afoul of the Federal Clean Water Act. Section 316(b) mandated that power plants minimize danger to wildlife and fish populations by use of cooling water from rivers, lakes and the sea. Policy set by the California State Water Resources Control Board called for all existing power plants using ocean water for OTC to slash water usage by a whopping 93%.

Enacted at the start of the decade, those regulatory changes set in motion a multi-billion dollar program by LADWP to repower its coastal generating stations. As well as greatly reducing water usage, the goal was to create more efficient and flexible generation, and continue its ongoing clean energy push with the goal of achieving 33% renewables within its energy mix by 2020.

The first station to undergo an extensive repowering project in alignment with Section 316(b) was the Haynes Generating Station in Long Beach, California. Built in the 1960's, Haynes had six natural gas/steam units producing a total of 1600 MW. In 2005, Units 3 and 4 were repowered with a 575 MW 2x1 combined cycle power block using large frame gas turbines (this became known as Units 8 thru 10). That power block was 40% more efficient and had 94% fewer emissions than the aging boilers it replaced.

The plan for Units 5 and 6 was initially to introduce another combined cycle block of similar size using large GT frame units. But the once through cooling rule called for a shift in approach. That led LADWP to opt for six 100 MW GE LMS 100 fast-start, simple-cycle gas turbines rather than one large combined cycle unit. At full capacity, the combined cycle block would be more efficient, but the LMS 100s were a better overall fit based on real-world usage patterns and the specific needs of the utility.

Each LMS 100 can go from 0 to 100 MW in 10 minutes and can operate down to half load. This offered the Haynes plant the ability to rapidly respond to system fluctuations, operating anywhere from zero to all six turbines. In other words, the utility could ramp up to 600 MW in ten minutes, and could ramp that back in a multitude of increments all the way down to running only 50 MW (one gas turbine running at half load and the rest offline). Plant managers preferred the configuration of six fast-start 100 MW units in terms of ramp up and ramp down capacity, versus having a 600 MW power block which only offered a very limited ramp range and would be slower to bring on and offline.

In late September 2011, the LADWP broke ground on the Haynes repowering project. The major equipment started arriving in the spring of 2012. Three 190-ton turbines, 182-ton generators and 100-ton dry cooling towers were delivered to the site, with the other three units arriving later than summer. Testing and tuning took place into 2013 to allow the turbines to be ready for the summer season.

Chiu explained that the LMS100 units at Haynes are used as peakers. As the load on the system rises, the units can be brought online one by one to the amount of power required.

“On a typical day, a unit may be placed online around 2 pm and could operate until 8 pm,” said Chiu. “The LMS100s would also be used more often when other units such as the combined cycles are down due to outages.”

Now that the utility has had three years of use out of these machines, it finds itself utilizing them more than originally envisioned.

“The overall usage of the Haynes generating units has increased significantly over the life of the units,” said Chui. “Most of our LMS100s have averaged over 90 starts per year.”

Grid Stability

In addition to cutting water use, improving energy efficiency and adding flexibility, Haynes had to also provide enough reactive power to support the grid and allow the importation of power from remote renewable sources. This reactive power support issue didn’t exist with the old units as one or more of them were always kept running by LADWP to provide spinning reserve and grid inertia, as the older machines were slow to start up.

The switch to fast start GTs, then, solved several problems. But system engineers at LADWP still had to find another way to provide voltage support. With a single large frame unit continuously operating, the generator would provide the necessary reactive capability to help pull in power from remote generating stations. But the LMS 100s were not to be run whenever there were enough renewable power sources providing the required volume of power to LADWP customers.

The utility, therefore, had two of its LMS 100s equipped with clutches from SSS Clutch. These overrunning clutches would sit between the turbine and the generator so that those units would be able to operate as synchronous condensers and supply the needed reactive support.

“The synchronous condensing feature is helpful to support system voltage and to maintain stability in the power grid, and has proven to be very effective,” said Chiu. “It is also well commended by other agencies as LADWP has a significant capability to help maintain a stable grid.”

Chiu explained that its synchronous condensers are composed of a complex system with a clutch that transforms the generator of the LMS100 into a synchronous motor which can absorb varying degrees of reactive power. This allows it to maintain control of the local transmission grid's Volt Ampere Reactive (VAR) flow and voltage.

When the generator initially fires up, the clutch forms a connection so that it drives the generator. When no longer needed for generation, the turbine can be ramped down. The clutch automatically disconnects the turbine from the generator, and the generator keeps spinning, synchronized to the grid and providing the necessary voltage support. Later, when active power is needed, the unloaded turbine fires up and the clutch automatically reconnects the two.

“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,” said Chiu. “When power generation is again required, the turbine can then be accelerated to full speed and reconnected to the still rotating generator.”

While the other LMS100s average over 90 starts per year, the two clutched units have been running continuously in synchronous condensing mode with approximately 30 to 60 starts a year, said Chiu. Typically, the operators start whichever unit has the least operating hours as a way to ensure equal run times among the two units providing voltage support service.

During extremely slow periods, LADWP has the ability to go all that way down to zero generation and just keep the generator synchronized and giving the system voltage support and overall flexibility.

“One of the most valuable investments for the Haynes Repowering Project was the inclusion of the clutch system for the LMS100 units,” said Chiu.