|The H.F. Lee Plant, a 920-MW combined cycle power plant in North Carolina, began commercial operation in December 2012 and is owned and operated by Duke Energy. The plant features three SGT6-5000F gas turbines from Siemens. Photo courtesy of Duke Energy.|
By Russell Ray, Managing Editor
Squeezing more power from the fuel used to generate it is an ongoing battle for all power generators.
So far, the industry’s best weapon is combined cycle gas turbine (CCGT) technology. Combined cycle power plants are highly efficient, allowing power producers to ring much more power from the same amount of natural gas. The energy conversion rates for CCGT plants are high, ranging from 50 to 60 percent.
Meanwhile, natural gas-fired generation is projected to grow 3.1 percent a year through 2038, adding 348,000 MW of gas-fired capacity to the U.S. grid, according to a report released last month by Black & Veatch. Most, if not all, of that capacity will be met with CCGT technology. Natural gas-fired combined cycle plants are expected to account for 50.5 percent of U.S. power production by 2038, up from 25 percent this year, according to the report. By 2038, coal’s share of the generation pie will drop to 21 percent, down from 39 percent in 2014.
In its 2014 outlook, the Energy Information Administration said natural gas will overtake coal as the dominant source of power generation by 2035. That’s a significant change compared with EIA’s 2013 outlook, which projected coal would account for most of the nation’s power production through 2040.
The transition to CCGT technology is being driven by low gas prices, stricter regulation for coal plants, and the integration of growing amounts of renewable power.
Combined cycle plants compliment wind and solar power because they can start and stop quickly, and are thus capable of offsetting the fluctuations in renewable power.
In addition to rapid-response times, combined cycle plants emit significantly fewer emissions of carbon dioxide (CO2), sulfur dioxides (SO2), nitrogen oxides (Nox) and other air emissions. CO2 emissions from power plants using combined cycle technology are about 50 percent lower than most coal-fired plants. Emissions of NOx and SO2 are 80 to 90 percent lower.
The increasing use of CCGT technology has led to a sharp reduction in overall air emissions from U.S. power plants, according to a study performed by the National Oceanic and Atmospheric Administration’s Cooperative Institute for Research in Environmental Sciences at the University of Colorado. According to the study, CO2 emissions from U.S. power plants in 2012 were 23 percent lower than 1997 levels, thanks to the shift to CCGT technology. Reductions in NOx and SO2 emissions were even greater, dropping 40 percent and 44 percent, respectively.
Combined cycle power plants feature gas and steam turbines. The gas turbine generates electricity using natural gas, while the steam turbine generates electricity using waste heat from the gas turbine.
The process is highly efficient because the exhaust heat, which would otherwise be lost in the stack, is re-used in the steam turbine to generate additional electricity. The exhaust heat is sent to a heat recovery steam generator (HRSG), where the heat is absorbed by heat exchanger tubes containing hot water to create steam for the steam turbine.
What follows is a summary of five modern power projects equipped with CCGT technology.
Cape Canaveral Clean Energy Center
Some of America’s greatest innovations were realized at Cape Canaveral, home of the Kennedy Space Center. It’s fitting that this historic site is now home to one of the most advanced power plants in the world.
|The Cape Canaveral Clean Energy Center, a 1,200-MW combined cycle power plant in central Florida, began commercial operation in April 2013 and is owned and operated by Florida Power & Light. Construction was completed more than a month ahead of schedule and about $140 million under budget. Photo courtesy of Siemens.|
Florida Power & Light’s Cape Canaveral Next Generation Clean Energy Center, a 1,200-MW combined cycle plant equipped with three SGT6-8000H turbines from Siemens, began commercial operation April 24, 2013, one month ahead of schedule and more the $140 million under its $1 billion budget. Zachry Inc. engineered and built the project, which replaced a two-unit, dual-fuel facility built in 1965.
The new plant was recognized by Power Engineering magazine as the Project of the Year for gas-fired projects in 2013. The same H-class turbine used at Cape Canaveral set a world record for combined cycle efficiency of 60.75 percent in May 2011 at the Irsching Power Station in Bavaria, Germany.
The new plant is 33 percent more fuel efficient than the plant it replaced. What’s more, despite a 50-percent increase in capacity, carbon dioxide(CO2) emissions are 50 percent lower and NOx and SOx emissions are more than 90 percent lower versus emissions from the old plant. In addition, the new plant generates enough electricity to power 250,000 Florida homes and businesses, nearly double the original plant, without using additional water or land.
FPL, Florida’s largest electric utility, said the improved fuel efficiency will save its customers “hundreds of millions of dollars” in fuel costs. “Investments in efficient power plants like this are one of the reasons why FPL’s typical residential customer bills are lower than the national average and the lowest of all 55 electric utilities in Florida,” the utility said.
FPL’s investments in combined-cycle, natural gas power plants since 2001 have cut the utility’s fuel costs by more than $6 billion through 2012, and all of that savings have been passed on to customers, the utility said.
Colusa Generation Station
The Colusa Generation Station, about 70 miles northwest of Sacramento, Calif. near the town of Maxwell, began generating power in December 2010. The two-unit, combined cycle power plant has a generation capacity of 660 MW, enough to power more than half a million homes in Northern California.
The plant is loaded with environmental technologies, including a “dry cooling” system that uses 97 percent less water than a conventional cooling system. What’s more, the plant is equipped with a Zero Liquid Discharge system, which recycles and cleans wastewater for reuse throughout the plant. The ZLD equipment was supplied by Aquatech under a contract with Gemma Power Systems, the project’s primary contractor. Worley Parsons served as the project’s design engineer.
Cleaner-burning turbines and the latest air-quality-control technologies mean Colusa’s CO2 emissions are 35 percent lower than older gas-fired power plants. Moreover, the plant is designed to reduce its output quickly when wind and solar power are readily available, a feature that allows the utility to accommodate the growing amount of renewable power in California. The plant’s ability to start and stop quickly will be increasingly critical as PG&E secures more renewable power to meet demands for cleaner power.
“This plant was designed to be among the cleanest in PG&E’s fleet,” said Randy Livingston, PG&E’s vice president of power generation. “It turns out to be the cleanest operating plant in all of California.”
Southcentral Power Project
Alaska’s most efficient power plant began commercial operation in February 2013, serving customers in southcentral Alaska, including Anchorage. After 22 months of construction, the Southcentral Power Project was completed several months ahead of schedule at a cost of $359 million.
Fuel efficiency was a high priority for the project’s owners, Chugach Electric Association and Municipal Light & Power. Alaska has an abundant supply of natural gas, but power producers in the region struggle to meet demand because of insufficient pipeline capacity. A pipeline outage or strong demand can be problematic for a state that produces more than half of its power from natural gas.
In addition, the grid serving southcentral Alaska, from Fairbanks to Anchorage, is isolated from the large, interconnected grids in Canada and the Lower 48 states. As a result, purchasing additional power from producers outside the region during times of peak demand is not an option. About 90 percent of Alaskan communities rely on consumer-owned electric cooperatives for power.
Although the 183-MW combined cycle plant is small, it is equipped with three highly efficient aeroderivative gas turbines from General Electric. The GE LM6000PF turbines, rated at 48 MW each, were chosen for their fuel efficiency and their ability to reach full capacity in just minutes. The new plant consumes 25 percent less gas, cutting the utility’s natural gas consumption by 3 billion cubic feet a year, which translates to significant savings in fuel costs. What’s more, the plant emits 25 percent less CO2 and 95 percent less carbon monoxide and nitrous oxide.
SNC-Lavalin designed and built the project. The project’s 39-MW steam turbine was furnished by Mitsubishi Power Systems Americas. At the peak of construction, the project employed more than 400 workers. The combined-cycle project was completed in January 2013, five months ahead of schedule.
Chugach is Alaska’s largest electric utility, serving more than 30,000 customers in the Anchorage area.
The site now known as the H.F. Lee Energy Complex near Goldsboro, N.C., has been producing power since 1951. The 382-MW pulverized coal plant that started it all was retired in September 2012, which was followed by the retirement of four oil-fueled combustion turbine units in October 2012.
In their place, Duke Energy built a three-unit, 920-MW combined cycle power plant, which began commercial operation Dec. 31, 2012. The $700 million project, which was engineered and built by Kiewit and ITC, features three Siemens SGT6-PAC 5000F gas turbines with a rated capacity of 206 MW each. The turbines include a dual fuel, ultra-low NOx combustion system, extended outage interval parts and low carbon monoxide turndown.
From a complete shutdown, the plant can reach full capacity in about four hours, according to Duke Energy.
Three Vogt heat recovery steam generators (HRSG) are used to capture the exhaust heat from the three gas turbines. A 400-MW steam turbine generator from Toshiba harnesses the steam from the HRSGs to produce more power without consuming more fuel, thereby boosting efficiency.
Compared with the old coal-fired plant, the new combined cycle gas plant produces 60 percent less CO2, 90 percent less mercury, 95 percent less nitrogen oxides, and nearly 100 percent less sulfur dioxides, according to Duke Energy.
To supply gas to the site, Piedmont Natural Gas constructed a 32-mile, 20-inch pipeline that stretched from Clayton, N.C., to Goldsboro. The new 920-MW plant and the 863-MW Wayne County Energy Complex, which features five combustion turbines built in 2000, were combined to create the H.F. Lee Energy Complex, with a total generation capacity of 1,783 MW.
El Segundo Energy Center
If you could snap a picture of the future of power generation, this is what it might look like.
Billed as one of the most energy efficient and responsive power plants in the nation, the new 550-MW El Segundo Energy Center (featured on the cover) illustrates how far the power generation industry has come in the last 50 years.
Nestled between a cliff and the Pacific Ocean in a well-known beach community, this advanced combined cycle plant consumes 30 percent less natural gas than the units it replaced and uses rapid-response technology to provide critical backup power for intermittent forms of generation such as wind and solar power. What’s more, the project eliminates the need to use seawater for cooling the turbines. Instead, this two-unit plant uses 32 large horizontal fans to dry cool the machinery. As a result, the plant uses 90 percent less water than conventional water-cooled technology.
In addition to slashing overall NOx, SO2 and CO2 emissions, the plant’s start-up emissions are more than 89-percent lower thanks to a rapid-response technology from Siemens that mitigates stack emissions while ramping up or down.
The plant’s fast-start capability is perhaps its most valuable feature, especially in California, where utilities and grid managers struggle to maintain a balanced load amid a growing source of intermittent electricity. California law requires power providers to generate 33 percent of their power from renewable resources by 2020. The plant can ramp up to 300 MW in less than 10 minutes and be at full capacity (550 MW) within one hour. That compares to 14 hours to reach full capacity with the old units.
The plant’s owner, NRG Energy, retired and demolished two old gas-fired boiler units at the original plant. The new two-unit plant uses “Flex-Plant” technology from Siemens. Each unit features an SGT6-5000F gas turbine, an SST-800 steam turbine, an SGen6-1000A generator, an SGen6-100A-2P generator, a heat recovery steam generator (HRSG), and an air-cooled heat exchanger. Siemens also supplied the complete electrical equipment and the SPPA-T3000 power plant instrumentation and control system.
The SGT6-5000F turbine is integrated with a single-pressure, non-reheat bottoming cycle. Together, with an air-cooled heat exchanger for steam condensing, the plant provides a net efficiency of nearly 49 percent, making it “the most efficient peaking plant technology available today,” Siemens said.
The plant began commercial operation Aug. 1, 2013. All of the output is delivered to Southern California Edison under a 10-year power purchase agreement.
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