High-Speed Centrifugal Compressors: How Rotational Speed Impacts Sealing Solutions

In an ever-accelerating industrial landscape, high-speed centrifugal compressors are pushing operating limits to meet the changing demands of energy and process industries. However, an increase in speed presents complex challenges for mechanical engineers, which poses a critical question: how can compressor manufacturers and contractors overcome these challenges and unlock the potential of high-speed compression?

John Crane is leveraging decades of experience to push the boundaries of turbomachinery solutions. Read on to explore the dynamics of high-speed rotational sealing.

Understanding What Makes an Application "High-Speed"

Compression supports a range of mission-critical process industries, including oil and gas, chemical manufacturing, petroleum refining, power generation and pharmaceutical production. However, determining whether an application operates at “high-speed” is not straightforward; there is no universal definition.

Mechanical seal suppliers have their own approach to assessing the duty condition. Two main aspects of a compressor duty affect a seal: rotational speed and shaft diameter. John Crane assesses the impact of the speed by calculating the circumferential velocity at the seal's balance (hydraulic) diameter.

New energy processes involving hydrogen compression require specialised compressors. Hydrogen is the lightest molecule and compressing hydrogen gas requires some of the fastest rotation relative to other processes to achieve the same pressure ratio without a significant design change of the compressor. For other fluids that support new energy, such as methane, CO₂, supercritical CO₂ (sCO₂), ethylene and nitrogen, high-speed compression or expansion may or may not be needed. The energy transition is evolving and a clear trend is not yet visible.

Controlling emissions at faster speeds requires sealing solutions engineered for reliability and efficiency. The process starts with a thorough engineering review.

Matching Dry Gas Seal Design to Performance Needs

Dry gas seals are a reliable solution for emissions control in rotating equipment. Sealing technology offers numerous benefits, including efficiency, extended life and safety.

Sealing technology is constantly progressing and, in today's energy landscape, changing performance needs can push the limits of centrifugal compressors. As demands increase, the impacts on seal design and engineering can translate to increased circumferential speeds.

The complex interplay between seal design and rotational speed poses distinct challenges that deserve meticulous consideration.

Heat Generation

Heat causes expansion for most materials, not just metal. Since all materials in the seal expand, and by different amounts, heat expansion must be included in seal design. There are several sources of heat to consider; one of the most basic is the heat generated by friction between moving and static components. Another is shearing or churning of a fluid, such as air, where power loss is transformed into heat, due to close clearance rotation of cylindrical components.

These heat inputs combine to create thermal energy, raising the temperature of the equipment. The faster a compressor's rotor spins, the more heat the system generates and the more it affects a seal's propensity to control emissions.

Sometimes, it's necessary for compressor manufacturers to push engineering to new limits when designing high-speed equipment. By partnering with an experienced sealing solutions provider like John Crane, OEMs can help protect assets that matter in the long run. Regarding considerations such as heat distribution within a seal, John Crane's engineers take a comprehensive design approach, leveraging years of experience and running simulations aimed toward replicating operating conditions in the field.

Hoop Stress

High-speed rotation creates intense forces in a dry gas seal, and mechanical engineers must ensure the materials used can handle the increased hoop, or centrifugal stress generated by compressor operation. For the seal rotor John Crane's standard material choices include stainless steel grades such as 410 and 316, while nickel-chromium-based superalloys, offer higher strength material properties for the higher speeds.

The rotating sealing ring (the mating ring) also must withstand the increased hoop stresses at high speed. These are typically offered in silicon or tungsten carbide.

Where hoop stresses push the boundaries of material science, John Crane's engineers work with customers to ensure that mechanical seal components are appropriate for the application, for example, hydrogen service. New materials are being developed to withstand the rigorous demands for modern sealing solutions.

Seal Gas Film Thickness

The groove design is fundamentally important for the reliable operation of the seal, which, when combined with rotational speed provides the necessary hydrodynamic lift and affects the thickness of the gas layer between the seal faces. If there is too much lift, the generated fluid film is thicker, and process gas leakage becomes excessive. But if the gas layer is too thin, the seal's seat and face make contact and cause damage. Therefore, optimising the gas film thickness is crucial to avoid face contact and minimise the seal leakage. Typically, the ideal layer thickness is no larger than a few microns.

Engineers consider the effects of speed when designing the seal face groove technology that controls the lift, ensuring the dry gas seal minimises leakage even with high-speed operation.

Centring

The precise centring of the seal on a compressor's rotor shaft helps maintain balance, which minimises vibrations during operation. It is equally important to ensure all the seal components are centred, the more accurate the fit to true centre, the better the compressor's performance, especially at high speeds.

While a seal provider supplies their product's mass and centre of gravity to the compressor manufacturer for design purposes, the rotor's mass typically overshadows any centring concerns from the much lighter rotating parts of a dry gas seal. But this isn't always the case.

With integrally geared compressors, it's common for the impeller and seal to overhang the bearing. As such, the mass and balance of the seal can become more critical at high speeds. John Crane supports OEMs by engineering sealing solutions that work harmoniously amid an application's unique centring dynamics.

Intermittent Operations

Renewable energy sources like solar and wind are key levers in reaching net zero emissions. Although these options enable carbon-free hydrogen production, one of their challenges is inconsistency, as it isn't always sunny or windy.

Dry gas seals function most efficiently during constant operation and transient operations, whether due to renewable power or any other reason, increases the likelihood of contact and therefore wear. High-speed operations are subject to the challenges of intermittent operations, however, applying special technology can make the seal face or seat more resistant to wear caused by contact.

John Crane's Type 28XP standard dry gas seal is engineered for rotational speeds up to 140 m/s (460 fps) at balance-diameter, it is suitable for temperatures ranging from -40°C to 200°C (-40°F to 392°F) and for gauge pressures up to 180 bar (2610 psi). However, several of John Crane's dry gas seals already exceed these operating parameters to support higher speed applications.

Pushing Compressors to Higher Speeds

Hydrogen is becoming widely used in today's industrial landscape, yet it is still realising its full potential as a clean-burning fuel or energy carrier to support the energy transition. The International Energy Agency (IEA) sees hydrogen demand increasing to reach more than 150 Mt by 2030, with nearly 30% of that demand coming from new applications.

The shift toward cleaner energy sources — for example, “lighter” gases like hydrogen and hydrogen blends — could drive demand for high-speed compressors. Accordingly, seals and bearings capable of supporting equipment at higher speeds will be necessary to strengthen the new energy value chain.

When it comes to compressor speeds and sealing solutions at high speeds, it's a matter of levelling up together. Pushing operating limits presents both challenges and opportunities for OEMs. John Crane is committed to providing sealing solutions and services that support OEM customers as they address and anticipate the requirements of new energy applications.

Here's just one example of how John Crane supports OEMs: A leading compressor manufacturer proposed John Crane's solutions and services for enhancing its hydrocracker capacity at one of Canada's most efficient hydrocarbon processing sites. Our engineers provided dry gas seals and support systems that increased the hydrocarbon processing site's reliability in capturing CO₂.

For more details, read the full case study.

Protecting What Matters

John Crane has the experience and expertise to protect and optimise mission-critical turbomachinery assets. Our innovative solutions and services help prevent downtime and uphold compressor reliability and efficiency.

Real-time data collection with John Crane Sense® and John Crane Sense® Monitor provides insight into compressor seal and asset performance, enabling timely decisions that safeguard equipment, people and operations.

The John Crane Dry Gas Seal Refurbishment program is a turnkey solution for increasing equipment reliability and lifetime, while our ongoing Asset Management Solutions provide data-driven maintenance management tailored to operational needs.

Explore John Crane's Sealing Solutions

Overcoming the challenges posed by high-speed compressor operation takes ambition and the right sealing solutions partner. An industry leader with a legacy of technology leadership, innovative solutions and global service excellence, John Crane has the expertise to help address the unique challenges posed by high-speed compression.

From oil and gas to fertiliser production to new energy, John Crane has a long history of improving compressor efficiency and reliability to help organisations meet their decarbonisation targets. We're continuing this legacy in the new energy era — a time in which the need for high-speed compression operations is increasing. We're investing in sealing solutions that help enable reliable compressor performance today and in the future.

Contact John Crane today to speak to one of our experts.