MD&A’s Advanced Sealing System (with Guardian Packing Rings & Vortex Shedder Spill Strips)
Seals within a steam turbine serve a very important purpose: to prevent steam from leaking between the rotating and stationary components and to keep air out. Learn about MD&A’s Advanced Sealing System with two successful case studies.
Over time, seals deteriorate, and components become distorted. This could lead to excessive clearance, which reduces turbine efficiency. Conversely, clearances may become too tight, causing turbine rubs and operational problems. To avoid these issues, it’s important to have a system inspected regularly, and for seals to be properly replaced before smaller issues become much larger costlier ones.
While the temptation may be to “simply” replace a seal with the OEM part, in reality, you’ll need one that’s designed for the specific turbine that is being serviced. Why? No two systems will wear the same way, thus requiring a sealing solution that’s designed and manufactured for the specific conditions of the unit. In fact, in an impulse steam path design, conventional seals & shaft-packing can attribute to leakages up to 29% loss of stage efficiency!
There are two common distortions that will cause efficiency and operational issues over time. These include:
- Elliptical Bore Distortion – where components such as diaphragms, blade rings, and gland cases become elliptical from years of service. This distortion alters the seal radial clearances, resulting in seal rubs, wear, and increased seal clearances. In turn, sealing efficiency and overall turbine efficiency and output is decreased.
- Dishing Distortion of the Diaphragm – The axial relationship between seal teeth and the turbine rotor is critical to a smooth-running and properly sealed turbine. As a turbine ages, the interstage diaphragms/nozzles may creep axially due to differential steam pressures. This changes the relationship between the stationary seal teeth and the rotor. If the change becomes too great, the rotor will rub the seal teeth, causing vibration and increased seal clearances.
MD&A’s Innovative Advanced Sealing System
Leveraging decades of experience with inspecting and repairing steam turbines from dozens of manufacturers, MD&A has developed specialty products designed to address these various sealing challenges: Guardian® packing rings and Vortex Shedder® tip seals.
Guardian packing rings will replace virtually any conventional OEM packing ring, without requiring modifications to either the holder or the rotor. They are constructed of a patented, non-galling, low coefficient of friction material. Guardian packing rings are set with a radial clearance 0.005” less than the conventional teeth. They will perform in any location, at any temperature, pressure, or flow condition.
Keep in mind that during normal turbine operation, nothing should be touching. You should have a uniform seal ring around the circumference. However, if a rub condition is about to occur, the Guardian’s posts will push the seal teeth away from the rotor. This protects the delicate teeth from potential damage and maintains the efficiency and integrity of the seal. Unlike other packing designs, Guardian Packing rings maintain a positive radial seal during start-up, shutdown, turning gear, and unit operation. Since seal efficiency and longevity are increased, the unit heat rate between overhauls is better maintained.
Vortex Shedder tip seals work by creating vortices at the admission side of the seal. These vortices create a pressure barrier at the tooth, lowering the change in pressure across it, which reduces leakage and increases seal efficiency and longevity. These seals can also be installed in any location on any OEM steam turbine.
The Vortex Shedder has been proven to increase unit efficiency above design, by 1.5% to 4.5%. It also helps lower EPA emissions per megawatt. The overall increased unit efficiency results in lower operating costs.
The Vortex Shedder operates on a reaction steam path design where you can apply to the rotating seal strip and the stationary seal strip. This reduces the pressure drop resulting in lower flow and less leakage across the seal. This also means improved stage heat rate performance for the turbine.
Success Stories at a Glance
Case #1: Guardian/Vortex Installed in HP/IP
Turbine OEM: GE® D11 Steam Turbine, 1050F/1800psia, nominal 200MW
For this installation, the expected HP Efficiency with new conventional seals was 2.1%. After installation of our products, efficiency was measured at an impressive 3.5%, giving the customer 1.4% incrementally improved efficiency.
Case #2: Guardian/Vortex Installed in HP/IP
Turbine OEM: Toshiba® Steam Turbine, nominal 200MW
With this system, the expected HP efficiency with new conventional seals was 1.9%. After our solution was installed, efficiency was measured at 2.8%, giving the customer 0.9% incrementally improved efficiency.
Custom On-Site Installation Services
MD&A Parts Division offers custom design, manufacture, and installation of any packing ring or tip seal. Our specialized crews are highly experienced in the installation of turbine seals and follow our time-tested, proven process.
It begins with a comprehensive measurement and assessment phase where our technicians come in and carefully measure all relevant aspects of your equipment. They also collect performance data that will help us design, manufacture, and install seals to your system’s exact specifications.
Our design engineers then closely review all of the collected measurements and data, then modify our products to perform optimally in your equipment.
Our installation team then expertly installs the seals and will even correct out-of-round conditions, thanks to our containerized machine shop. Our goal is to have your systems up and running at a performance level that exceeds where you were prior to the service.
A major benefit of having custom on-site installation is that our experts will go above and beyond just replacing the seals. They will make adjustments during design or installation to compensate for issues such as holder distortion, dished diaphragms, misalignment issues, and bowed rotors, just to name a few.
Increase Efficiency and Lower Operational Costs
Our innovative advanced sealing system has been installed in over 350 units to date over an extensive roster of major turbine manufacturers. Our customers are always pleased with the many benefits of installing our precisely engineered, innovative sealing solutions. In fact, when Guardian and Vortex are combined as a system, unit efficiency is proven to perform above design by 1.5%-4.5%. When efficiency increases, systems last longer, and operation costs are lowered, all leading to improved bottom lines.
Contact our MD&A Parts Division at +1 (518) 885-3199 or use our contact form.Tags:
Email This article | Print This Article