Combined Cycle : The Preferred Option

Combined Cycle : The Preferred Option

03/16/2015

By Russell Ray

Chief Editor 

By Russell Bay, Chief Editor

Most new generation in the U.S. is being fueled with natural gas, and the most dominant technology being used to burn the fule is ombined cycle.

Combined cycle power plants are highly efficient, allowing power producers to wring much more power from the same amount of natural gas. The energy conversion rates for combined cycle gas turbine (CCGT) plants are high, ranging from 50 to 60 percent.

The number of combined-cycle project is expected to increase 3.1 percent a year through 2038, according to a report from engineering firm Black & Veatch.

In 2014, the U.S. added 15,450 MW of new generation. More than half of that capacity -7,902 MW - was fired by natural gas. What's more, CCGT technology accounted for 92 percent of the gas-fired generation that was brought online last year.

In 2035, power fueled with natural gas is expected to surpass coal-fired power as the dominant source of power generation in the U.S., according to the Energy Information Administration (EIA), the statistical arm of the U.S. Department of Energy (DOE). After 2020, power plants fueled with natural gas will account for 70 percent of all new generation capacity, according to EIA.

By 2040, renewable power capacity will grow 69 percent, which means gas-fired plants must be fast and flexible t accomodate the growing amount of intermittent generation.

The transition to CCGT technology is being driven by low gas prices, stricter regulation for coal plants, and the intergration of growing amount of renewable power. Combined cycle plants compliment wind and solar power because they can start and stop quickly, and thus are capable of offsetting the fluctuations in renewable power.

The increasing use of CCGT technology has led to a sharp reduction in overall air emissions from U.S. power plants. In addition to rapid-response times, combined cycle plants emit significantly fewer emissions of carbon dioxide (CO2), sulfur dioxide (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. Emission of NOx and SOx are 80 to 90 percent lower.

Combiend cycle power plants feature gas and steam turbines. The gas turbine generates eletricity using natural gas, while the steam turbine generates electicity 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 generation (HRSG), where the heat is absorbed by heat exchanger tubes containing hot water to creat steam for the steam turbine.

One of the biggest developers of combined cycle power plants in the U.S. is Dallas-based Panda Power Funds. The company recently announced plan to build a third combined cycle plant in Pennsylvania.

Panda Power Funds has two Marcellus gas-fueled power plants currently under construction in Bradford and Lycoming counties. The 829-MW Liberty power plant is expected to begin commercial operations in early 2016. The 829-MW Patriot power plant is scheduled to begin operations in the second quarter of 2016. Last year, the company began commercial production at the 758-MW Panda Sherman plant and the 758-MW Temple plant in Texas.

What follows is a summary of four modern power projects equipped with CCGT technology.

Panda Sherman

Panda Sherman.

Photo courtesy : Panda Power Funds

Built to support Texas' vast amount of wind power capacity, the 758-MW Panda Sherman combined cycle power plant is one of the fastest starting power plants of its kind. The combustion turbines provided by Siemens Energy can begin producing power in 10 minutes and can achieve maximum power production in less than 60 minutes. The fast ramping capability allows power producer to offset the loss of intermittent wind power when the wind stop blowing.

Siemens privided engineering, procurement and construction services for the project, which began commercial production in July 2014. Construction began in July 2012.

Equipped with advanced emissions control technology, the Panda Sherman plant is one of the cleanest power plants in the U.S., with carbon monoxide emission less than 10 parts-per-million (ppm) and nitrogen oxide emission less than 2.0 ppm.

"The plant's advanced technology enables the plant to produce higher power output on higher temperature days, which is important in this region," said Martin Tartibi, senior vice president at Siemens Energy Solutions Americas.

The plant can supply enough power for 758,000 Texas homes.

The Panda Sherman plant uses "Flex-Plant" technology from Siemens. It's the second Flex-Plant in commercial operation in Texas. Flex-Plants offer high efficiency and operational flexibility. Innovative design features enable fast start and fast ramping up and down across a large operating window from low plant turn-down to high plant output.

Each unit features an SGT6-5000F gas turbine. In addition to the gas turbines, Siemens provided one SST6-5000 steam turbine, two SGen6-1000A generators, one SGen6-2000H generator, the SPPA-T3000 instrumentation and control system as well as two Benson heavy duct-fired heat recovery steam generators.

The gas turbines, steam turbines and generators were manufactured at the Siemens North American manufacturing hub in Charlotte, North Carolian.

Riveria Beach

Riviera Beach

Photo courtesy : Siemens

In June 2011, the smokestacks of the oil-fired Riviera Beach power plant were demolished. In their place, Florida Power & Light built a more efficient plant fueled with cleaner-burning natural gas.

The Riviera Next Generation Clean Energy in Florida began commercial operation in April 2014. The $1.3 billion project uses three H-class gas turbines from Siemens. Zachry Engineering was the EPC contractor on this historic project. The 1,250-MW combined cycle plant produces enough power for 250,000 Florida homes.

The combined cycle plant is expected to save FPL customers hundreds of millions of dolloars over its 30-yeaer lifetime. The Riviera facility is 33 percent more fuel efficient than the plant it replaced. In addition, CO2 emissions are 50 percent lower than NOx and SOx emissions are more than 90 percent lower.

The same turbine used at Riviera Beach set a world record for combined cycle efficient of 60.75 percent in May 2011 at a power plant in Bavaria, Germany. Siemens has sold 40 H-class gas turbines worldwide. Eleven are in commercial operation with more than 100,000 equivalent operation hours.

Siemens supplied three of its SGT6-8000H gas turbines to the Riviera Beach project, each delivering an electrical generating capacity of 274-MW. The plant entered commercial operation on April 1.

La Caridad

La Caridad

Photo courtesy : Siemens

Minera Mexico, a subsidiary of Grupo Mexico, the country's largest mining company and one of the world's largest copper producers, wanted to produce most of its power in-house. La Caridad I and II, a 500-MW combined cycle plant in northen Mexico, is part of the company's plan to generate 90 percent of its power in-house.

The two 1x1 combined cycle units feature two Siemens SGT6-5000F gas turbines. The units are rated at 258.1MW net output and 56.9 percent efficiency.

Siemens also provided the steam turbines, air-cooled generators, heat recovery steam generators and the instrumentation and control technology. Black & Veatch provided engineering services for the project.

Unit I was commissioned in September 2013 and Unit II was commissioned in April 2014.

Producting its own power with Siemens' high-efficiency F-class technology, the mining company will be able to reduce its production costs. The $580 million project allows the company to cut its electricity costs by 40 percent to 6 cents per kWh. The project also helps the state of Sonora and the country by supplying reliable power of the grid.

What's more, it will allow the company to reduce the cost of producing copper to 89 percent a pound, down from 93 cents.

The La Caridad I and II power project created more than 1,000 jobs during construction and more than 50 direct jobs for day-to-day operation.

The plant produces about two thirds of its electricity from the gas turbines. The rest comes from exhaust heat which then heats water to create vapor that powers a second steam turbine. By capturing the heat, 33 percent addition electricity is produced.

Ninemile 6

Ninemile 6.

Photo courtesy : Entergy

Entergy Louisiana completed construction of Ninemile 6, a 560-MW combined cycle unit, in December 2014. Built in Westwego and serving New Orleans and southeast Louisiana, it is the first power plant the utility has constructed in nearly 30 years.

The need for more generation equipped with modern technologies was critical. The retirement of Unit 1 and 2, the looming retirement of Unit3, and a growing economy created a crucial need for replacement generation.

"Adding Ninemile 6 to our portfolio gives us an opportunity to meet that new need, while satisfying our customers' expectation of safe, reliable and affordable energy," said Phillip May, president and chief executive officer of Entergy Louisiana.

The new unit features dual-feul GE 7FA gas turbines, a heat recovery steam generator from Vogt Power International, and a steam turbine from Toshiba. CB&I provided engineering, procurement and construction services for the project.

In addition to natural gas, Ninemile 6 is equipped to burn fuel oil, an important capability in the event of a hurricane cutting off supplies of natural gas.

Without a supply of gas, the plant ca continue producing power with fuel oil from on-site tanks.

The unit was completed at a cost of $655 million, well below its original budget of $721 million.

The project employed 750 people during construction and created 21 full time jobs for day-to-day operation.

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