Process Control

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.

 

Read part 1 of our white paper- 2021 Power Generation and Renewable Energy Trends, to learn how fossil-based power generation technologies are rapidly evolving and renewable technologies are being scaled to meet the demands of the 21st-century market.

 

   
A brief history of gas turbine power 

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.  

 

How NGCC works 

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. 

 

Improvements to natural gas combined cycle efficiency 

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.  

 

NGCC benefits 

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. 

 

The annual energy outlook for NGCC in the US 

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.  

 

Managing NGCC operations and maintenance costs 

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.  

 

Rely on Parker Hannifin for NGCC plant maintenance needs 

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.

 

 To learn more about advancements in power generation, read our Power Generation and Renewable Energy Trends White Paper – Part 1.

  

This article was contributed by the Process Control Team.

 

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In onshore and offshore oil and gas, operators' demand for components that satisfy a reduction in leakage paths resulted in our designing the Monoflange valve, combining primary and secondary valves into one compact unit. Integrating piping and instrument valves into a single unit delivers cost and safety benefits to the oil and gas, petrochemical, and chemical markets.

The Monoflange has a needle valve primary and secondary rather than ball valves. The result is a lower system mass, which reduces loading and vibration stresses, further improving safety and reliability. Being smaller than a traditional double block and bleed valve, gives even more space and weight advantages. This ensures that the Monoflange valve is a cost-efficient option for both owners and operators.

 

How to safely replace a plugged Monoflange with uninterrupted production

Let's take a look step-by-step at how to safely remove a plugged Monoflange using our integrated Monoball solution to enable the processing pipeline to continue operation. For this example, the application is using a close-coupled Monoflange with an integrated Monoball. This enables the process pipeline and service to continue while the Monoflange is being serviced or replaced. This unique product combination allows the process to continue with no loss of production, increasing uptime.

 

Step 1 - To ensure the safe removal of the Monoflange valve, we will isolate the Monoball valve by turning the handle 90 degrees - this will prevent any process media from escaping to the atmosphere while the Monoflange is absent. 

 

 

 

 

Step 2 - To ensure all media is vented, open both the Monoflange block valves ( Primary and Secondary) and finally turn the vent on the Monoflange anticlockwise. This will remove the trapped volume of liquid or gas between the process and the instrument in a controlled manner. For substances such as H2S, an integral tube fitting and tube can be used to ensure safe removal.

 

 

Step 3 - Close the isolation vent on the Monoflange, two clockwise rotations. This will return the product to normal service-ready conditions. 

 

 

 

 

 

Step 4 - Remove the four top nuts and washers with a spanner/wrench. This will allow the operator to remove the Monoflange and transmitter from the Monoball for transfer to the service workshop to clean or replace the Monoflange. 

 

 

 

 

 

Step 5 - In the service workshop, the maintenance team will remove the transmitter and either clean or replace the Monoflange. 

 

 

 

 

 

 

 

Step 6 - Return the Monoflange and transmitter to the Monoball.

 

 

 

 

 

 

Step 7 - Retighten nuts with spanner/wrench.

 

 

 

 

 

 

 

Step 8 - Open the Monoball valve to return to normal working conditions. 

 

 

 

 

 

 

Watch this video and see all the steps to safely removing a plugged Monoflange valve by using a closed coupled Monoball valve arrangement. 

 

 

 

 

 

This helpful support content was contributed by the Instrumentation Products Division, Parker Hannifin 

 

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Small and mid-scale LNG plants are dramatically changing the application sphere for natural gas as an alternative fuel for transportation, both onland and for marine shipping use. They are helping drive adoption in various high horsepower applications and making gas capture and distribution from remote areas and wells without pipelines a reality.

LNG plant requirements drive need for smaller line and fittings

As the requirement for small and mid-scale LNG plants grows, so does the need for tube connection technology for smaller line sizes. In the past, connection technology was limited to either orbital welding or double ferrule compression fittings. Today, driven by cryogenic applications, there are four connection options in the less than two-inch space: instrumentation compression double ferrule fittings; instrumentation compression single ferrule fittings; O-ring face seal fittings; and permanent fittings.

Connection in a cryogenic application should focus on five critical areas:

• Safety
• Leakage and fugitive emissions
• Ease of assembly
• Longevity
• Code compliance

Safety first

Safety is critical in small and mid-scale LNG plants. In these complex plants, electricity, gas and water will often coexist in close proximity. Add cryogenic temperatures to the mix and the environment becomes extreme.

The most important rule of safety in an LNG plant is to keep the media contained. Good tube connections prevent catastrophic failure at connection points. A failure mode and effect analysis reveal the threat that a bad connection – or a poorly made one – can pose to a plant. In addition to explosion leaks, the danger of frostbite exists with cryogenic temperatures. A good connection is a first defense in preventing exposure and harm to personnel.

Leakage and fugitive emissions

Leakage of methane, a greenhouse gas -- while still not regulated -- is a major concern in LNG plants. Overall, fugitive emissions will become increasingly important; keeping hundreds and thousands of connections in an LNG plant from leaking will be key.

As a basic requirement, ensure bubble-tight connections that follow appropriate leak specifications to future-proof against fugitive emissions while not limiting solely to safe exposure levels. Apart from methane leaks, cryogenic fluid leaks can cause frostbite and major freezing hazards. A small, seemingly safe leak is also a loss of revenue and efficiency. Leak-tight connections can add up to savings and notable percentage points of efficiency.

Ease of assembly

A big challenge for small-scale, modular LNG plants is the flexibility to connect on-site to a dispensing system or a point-of-use system. This often means a lot of field connections and the capability to carry out repairs. Other times it means making certain connections at the time of installation. While welding sometimes seems to be the most straightforward strategy for a permanent joint, finding certified and trained welders may not be simple or easy.

Longevity

With the operational life of an LNG plant in the range of 15 to 25 years or more, it is critical to select corrosion-resistant, robust and reliable connection technologies that outlast the moving parts. Longevity can be achieved by choosing materials that resist corrosion from environmental sources and that are compatible with the media or fluid being transported.

Code compliance

Finally, it is essential to consider applicable codes of construction that, in some environments, may include marine standards such as those for ABS or DNV GL. Code compliance helps ensure that all the above topics are covered. Codes to consider include:

• In the US: NFPA 59A
• In Europe: EN 1473:2007 and EN 13645
• Globally: ISO (draft) 116901, ISO TC 67, ISO 18638, ISO TC 252

The end-use must take into account all possible interface points such as vehicles, tankers, vessels or rail cars to define application standards.

Connection technology challenges and advantages

• The double ferrule compression fitting is a well-known component to most fitters in the industry. A single ferrule fitting allows the use of the same skill set as a double ferrule fitting but reduces the risk of making a wrong connection since one ferrule is eliminated. Both types provide good field make-and-break capability.
• The O-ring face seal fitting and flanged tubes may be tightened and remade many times, and to set torque, provide zero-clearance tube entry. Additionally, the metal seal ensures LNG compatibility.
• Finally, the permanent fitting can replace a normally welded joint or a fitting joint that typically would never need to be reopened in the field. A permanent fitting can also be made much faster and without field orbital welding.

Better protection against fugitive emissions

In both single and double ferrule fittings, stainless steel parts that rub together under high pressure have a strong tendency to cold weld and seize, leaking to leaks and the resulting fugitive emissions.

Using fittings coated with molybdenum disulfide can avoid this problem. Solid molybdenum disulfide readily adheres to surfaces, is noted for its lubrication and anti-seizing properties, and does not squeeze out under extreme pressure. The result is low assembly torque and consistent, leak-free performance, even with repeated remakes.

Many fittings manufacturers also combat fitting leaks – and the resulting possibility of fugitive emissions – through proprietary ferrule-hardening processes designed to heighten corrosion resistance. For example, Parker treats its ASTM 316 stainless steel, single and double ferrule fittings with Suparcase®. The chemical process provides greater resistance to pitting, as well as excellent stress corrosion performance to provide longer, leak-free service life.

 

Article contributed by the Process Control Team. Original article published at LNG Industry in September 2015.  

 

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