Power Generation Gas Turbine Systems
How Metal Seals Help “Power” Productivity & Reliability In Natural Gas Turbines
By Alex Josephson (May 2021)
Enormous changes to the world’s energy systems are being implemented today due to climate concerns. As such, there has been a concentrated push to use “clean energy” in more homes and businesses for their environmentally-friendly impact and cost-effective nature. Other alternative sources of energy such as natural gas resources have also proven to be a major asset as gas-fired power plants are a natural complement for renewable energy, providing electricity when outputs from wind and solar are low. As the power generation industry looks to further increase efficiency and reduce emissions, seals play an integral part - particularly metal seals - as the seals need to handle higher temperatures and pressures to optimize performance and ensure reliability.
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According to a report by Fortune Business Insights, the world’s gas turbine market should rise annually and reach $10.23 billion by 2026. A natural gas turbine is a type of internal combustion (IC) engine, converting the heat produced by natural gases into mechanical energy. This energy is then supplied to power generators that produce electricity for residential and industrial use. Gas turbines are used to power aircraft, trains, ships, electrical generators, pumps, gas compressors, and tanks. There are three significant manufacturers: General Electric of the US, Siemens of Germany and Mitsubishi Hitachi Power Systems of Japan.
Metal seals are increasingly being considered in natural gas power generation.
Metal seals are increasingly being considered in natural gas power generation.
How Do Seals Ensure Greater Productivity?
From honeycomb and labyrinth seals, advanced polymers, to shroud seals (our expertise), a variety of different seals and materials are typically used in turbines for the power generation industry. Today, these seals need to address higher temperatures and pressures to strive for higher efficiencies. Natural gas turbines can become as hot as 1427°C (2600°F); therefore, the need for robust, high temperature seals is imperative to the efficiency of the turbine. As industry statistics indicate, a one percent increase in turbine efficiency can equate to $1 million in savings for energy producing customers as well as reduce thousands of tons of CO2 emissions per year. With more efficient turbines, blades must spin faster to output more energy. A tight seal must also address many rigors and ensure that fuel supplies, as well as air flow, are properly sealed to ensure the turbine is operating at its highest possible efficiency.
Another important factor in productivity is the reliability of seals in certain sections of the turbine. For instance, even with safeguards in place, a seal failure in the combustion system could lead to fuel leakage and combustion, resulting in damaged hardware that could cost millions of dollars to repair, not to mention the cost of downtime, which can quickly escalate. Our technical team performs several tests and analyses in order to ensure that each seal design will function properly in the environment it is meant to seal.
How Do Metal Seals Work In The Combustion System & Turbine?
Metal seals are increasingly being considered in natural gas power generation to address higher temperatures, pressures, and reliability. These seals are often used in two of the three main parts of gas turbines: the combustion system and turbine.
Combustion System – This is where air and fuel are mixed and combusted to create the high temperature, high pressure gas stream that is used to turn the turbine. As such, this is also often the place where the highest pressures and temperatures are experienced. Metal face E-Seals, spring-energized C-Seals, axial lip seals, as well as proprietary seals are frequently used to handle these high pressures and temperatures.
Turbine – The turbine section uses the high pressure, high temperature gas stream from the combustion system to drive the turbine blades, thus converting chemical energy into mechanical energy. Segmented E-Seals, V-Seals, and turbo seals are just a few of the seals used to seal the shroud sections of the turbine. Segmented seals vary by size and are typically supplied in 2, 4, or 6 segments for easier installation. They are installed against the turbine shrouds, sealing any open joints and limiting the amount of high velocity air that escapes.
Metal seals are being used more regularly to seal the outer casing of the turbine, replacing rubber and metal rope seals. The introduction of metal seals to these locations further enables the turbine to reach higher pressure, temperature and efficiency.
What Are Other Challenges Turbine Seals Face?
In addition to needing to address high temperatures and pressures, metal seals in the turbine must also address a number of other challenges.
Sealing the Cavity – A major challenge for seals, due to the amount of heat and pressure, is that as the turbine heats up, joints and seals often experience a lot of separation/liftoff as a result. As the joints expand, seals need to have the flexibility necessary to adjust to this type of movement while maintaining the same level of leakage. Large segmented E-Seals and Multi-Convoluted E-Sealsprovide this type of flexibility while also providing a high temperature, high pressure sealing solution.
Our team has never encountered a cavity that could not be sealed using a variety of unique designs. As just one example, we helped a customer seal a cavity with a width of 0.210 inches and a depth of 0.450 inches. This seal needed to be able to handle drastic joint separation at high temperature and pressure while also ensuring that the seal would be capable of accommodating multiple compressions and decompressions throughout the lifetime of the seal.
Wear - With the higher pressures, temperatures and vibrations experienced during turbine operation, the metal-to-metal contact between the seal and the mating hardware can result in wear and galling. To prevent wear, we leverage a proprietary, electroplated coating, called NCCM that is applied to the seal. The unique characteristic of NCCM is that not only does the plating protect the seal, but over time, the plating transfers to the mating hardware, preventing wear on both surfaces. This cuts down on the need to replace costly mating hardware. It also reduces time and costs associated with turbine overhaul.
Custom Designs - One challenge is that often metal seals in turbines must be designed in unique shapes, sizes and orientations, making custom designs and manufacturing methods a necessity. Shroud seals often tend to be large, varying in size from 20 to 150 inches in diameter. We also have the capability to manufacture standard seals ranging from 0.250 to 150 inches in diameter, giving the customer a broad range of sizes that works best for their application.
Cross Platform - One growing trend from customers in power generation is that they are looking for seals that can be used across platforms. Developers are often looking at one design that can be used across every model and temperature range versus having to reengineer a new seal each time. Leveraging a single design helps to reduce costs, increases convenience, and can help to ensure reliability with less chance of leakage.
Our metals seals today are used in various gas turbine frames, including in some of the most efficient turbines in the industry.
With unique solutions for extreme environments, metal seals can address:
Pressures ranging from vacuum to 100,000 psi (6895 bar) depending on the seal design
Temperatures ranging from cryogenic to 1010°C (1850°F) depending on the seal material
Various mating hardware materials and shapes
Obstacles from vibration, separation, and thermal expansion
Our team has extensive application engineering experience to address custom designs, in-house testing and qualification services and also focuses on being customer centric. Since 1971, we have earned a reputation for quality, reliability, and integrity.
Could metal seals be a fit for your gas turbine application? Contact us today to learn more about power generation seals and other energy solutions.