During the past 60 years, the use of the natural gas combined cycle (NGCC) process for electricity generation has grown to make it one of the world’s leading sources of power. Along the way, natural gas combined cycle efficiency has improved because of engineering advancement.
This blog offers an overview of NGCC. It includes a brief look at its history, covers the advantages of NGCC over other power generation types, and discusses some of the challenges engineers still are confronting as the technology moves to the future.
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The history of natural gas turbines to generate electric power starts in 1940. In that year, a plant in Switzerland came online and produced 4 MW of power by passing superheated gas through a turbine; a process now known as a “simple cycle.” This was the first time a natural gas turbine had been used to supply the public with electricity. Larger plants were built in the decades that followed. In 1960, a simple cycle plant in British Columbia, Canada became the first to generate 100 MW of electricity.
A year later, a newer gas technology arrived: Natural Gas Combined Cycle (NGCC). The world’s first combined-cycle power plant, a 75 MW facility in Austria, started operation in 1961. By the time of its retirement in 1974, and thanks to combined cycle efficiency improvements, NGCC had established itself as “the most efficient and low-cost route to electricity production,” according to an article in International Turbomachinery. Today, NGCC is one of the leading natural gas power technologies in the world.
To understand how NGCC works, it’s helpful to understand the ways it’s different from simple cycle technology.
In a simple cycle gas turbine plant, hot gas is burned and propelled at high pressure through a single turbine. The turning of the turbine is used to generate electricity. Wasted heat is simply lost in this design, and the overall efficiency of such a plant is approximately 35 to 40 percent.
An NGCC plant improves on this design, leveraging that waste heat and an additional generator cycle to maximize overall plant efficiency.
In the first cycle of an NGCC plant, natural gas is burned to directly power a generator that produces electricity. The hot exhaust that would otherwise be lost in a simple cycle plant is instead captured for a second cycle. That heat energy is delivered to a boiler and used to generate steam from water. This, in turn, is used to power a steam turbine generator that produces additional electricity. The steam then condenses back into liquid water and is recycled for further use. With these multiple cycles, overall efficiency is boosted to around 50 to 60 percent. Today’s NGCC plants range in size, with the largest producing more than 1,500 MW.
NGCC technology has evolved over the years, and plants have been built with increasing capacities. Global and U.S. capacity for gas-fired electricity has continued to grow steadily in recent decades. Natural gas plants (all types) now supply more than half of the energy for both residential and commercial use, and 41% of the energy used by U.S. industries. And as consumers and industries alike become more aware of the broader impact of their energy use, they can rest easier knowing that natural gas plants produce significantly fewer emissions than the average coal-fired plant.
An article in the journal Science Direct lays out several key advantages for NGCC technology.
Boosted electrical efficiency. NGCC plants have an efficiency of between 50 to 60% of fuel used. This is the highest efficiency currently available among power plant generating technologies; it compares to an efficiency of 30 to 35% for a coal-fired plant. A large, simple cycle, natural gas plant has an efficiency of 35 to 40%, according to Bridgestone Associates.
Lower capital costs. The capital cost of an NGCC plant larger than 200 MW ranges from $450 to $650 per kW. A smaller plant ranges from $650 to $1,200 per kW. Additionally, a large NGCC plant can be built in less than 24 months.
Lower emissions and environmental impact. NGCC plants have the lowest emissions of unburnt hydrocarbons, nitrogen oxides, and carbon monoxide of any current thermal power plant technology. NGCC plants also have a more compact footprint than other major power plant types, further lessening their impact on the environment.
The highest recorded efficiency for an NGCC plant is 63.08%. This was achieved at the 1,190 MW Chubu Electric Nishi Nagoya plant in Japan, according to a 2018 article in POWER magazine.
According to another analysis, prepared in 2019 by the consulting firm Sargent & Lundy for the U.S. Energy Information Administration, a 1,100 MW NGCC plant would have an estimated capital cost of $958 per kW. A 240 MW simple cycle gas plant would have a total capital cost of $713 per kW. A 650 MW coal-fired plant without carbon capture, meanwhile, would have an estimated total capital cost of $3,676 per kW. Adding incremental levels of carbon capture technology to the coal-fired plant would increase this cost correspondingly.
The Science Direct article also predicts that:
These (NGCC) plants will displace coal in the power generation sector by 2050, under a model scenario where industrialized nations reduce CO2 emissions by 2050 through carbon emission pricing. Large emerging economies such as Brazil, China, and India will reduce CO2 emissions by 2070.
According to the U.S. Energy Information Administration, NGCC first surpassed coal-fired plants for producing electricity in late 2015 and early 2016 when natural gas prices were very low. This trend reversed itself when gas prices rose, until February 2018. As of 2020, NGCC is responsible for 26% of electricity generation in the U.S., making it the clear leader. With the growing number of NGCC plants and the retirement of more coal-fired plants, the technology should be the leading source of power in the U.S. for the foreseeable future.
Compared to other types of power generation, operations and maintenance costs for NGCC plants are relatively low. Data from the International Energy Agency show that NGCC has an average O&M cost of $25 per kW. This matches solar photovoltaic ($25 per kW), and beats coal ($43 per kW), onshore wind ($46 per kW), hydropower ($53 per kW), and nuclear ($198 per kW).
Nevertheless, plant operators are smart to take a planful approach to maintenance, especially for NGCC plants used in applications with frequent starts and stops.
Parker Hannifin offers a wide range of solutions for power plants. These include products for automation, filtration, fluid connections, hydraulics, instrumentation, and sealing. One utility company managing a 790 MW NGCC plant was able to increase the life of its electrohydraulic service valves from 3,100 hours to more than 60,000 hours, simply by switching to Parker's solution.
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This article was contributed by the Process Control Team.
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