The Rise of Sealed Compressors

Sealed compressors leverage compactness, low maintenance requirements, and emissions-free operation to enable solutions across the ongoing energy transition. Across the energy industry, requirements are shifting: Emission limits are becoming stricter, available space offshore and onshore is limited, and there is a growing need for solutions that can be operated remotely. Sealed—or hermetically sealed—compressors address these challenges. They are compact, oil-free, and operate without shaft seals, offering reliability and flexibility in applications where conventional compressors face constraints. What Makes a Compressor “Sealed”? The word hermetic is indirectly related to the Greek god Hermes, known as the messenger of the gods. The hermetic seal itself comes from alchemy in the tradition of Hermeticism, which was named after Hermes Trismegistus, a legendary figure who, according to the Hermeticists, invented the process of making a glass tube airtight with a secret seal. More commonly, the term “hermetically sealed” is used to describe a container so tightly closed that liquids or gases can neither enter nor escape. Applied to compressors, “sealed” or “hermetically sealed” refers to centrifugal compressors with an electric motor driver inside the same housing as the compressor bundle. Impellers and motor armature are mounted on a common shaft, supported by magnetic bearings, which means there are no COMPRESSORS penetrations through the housing for lube oil supply or drain ports. Motor and bearings are cooled by a stream of process gas extracted from within the compressor itself. The absence of shaft seals makes the entire system more compact and less complex, ideally suited for applications where leakage, maintenance, or footprint are critical concerns. The development of sealed compressors began in the 1980s, when they were first applied in natural gas pipeline boosting. The motor-driven pipeline compressor (MOPICO) featured one or two overhung stages arranged in series or parallel, achieving either high flow rates of up to 30,000 m3 per hour or discharge pressures of 150 bar in a compact, sealed package. Around the same time, magnetic bearings were being tested as an alternative to lube and seal oil systems. In 1985, Nova Corp. of Alberta installed a prototype magnetic bearing system in a centrifugal compressor, marking an early step toward fully oil-free designs. The breakthrough came in 1991 with the introduction of the high-speed oil-free integrated motor compressor (HOFIM). Combining a high-speed induction motor, a multi-stage centrifugal compressor, and active magnetic bearings within a sealed casing, the HOFIM eliminated the need for a gearbox and oil systems. Operating at pressures up to 303 bar (4,400 psi) and power levels of 18,000 kW (24,000 HP), these machines offered a smaller footprint, lighter weight, and high flexibility. Originally developed for gas transmission and storage, the technology soon proved its value in a wide range of other applications. From Urban Pipelines to Subsea Compression Pipeline compressors are traditionally driven by gas turbines operating at 3,600 rpm and optimized for barrel compressors. Turbines often burn natural gas directly from the pipeline, but even modern units produce CO2 and NOx emissions. In densely populated areas, noise and emissions limits make such stations difficult to permit. Here, electrically driven sealed compressors offer a clean and quiet alternative. With no exhaust, no oil system, and low vibration, they can be directly integrated into the grid and placed where conventional stations would not be feasible. A milestone for sealed compressor technology came in 2016 with the world’s first subsea gas compression system at the Åsgard field in Norway. Operated by Equinor, the system features two subsea HOFIM units that have accumulated over 100,000 operating hours without intervention. By boosting pressure directly on the seabed, the system extends production from declining reservoirs while avoiding the need for large offshore platforms. The compressors are qualified for wet gas operation, eliminating the need for additional separation equipment and simplifying the subsea process significantly. Industrial-Scale Heat Pumps A relatively new use for sealed compression technology can be found in industrial-scale heat pumps. By using a trans-critical CO2 cycle to amplify an ambient or waste heat source for use in hot water district heating systems, a heat pump incorporating a sealed compressor can replace conventional heating systems such as coal- or gas-fired boilers. When a green electricity source is available, an industrial-scale heat pump system using a sealed compressor can claim zero emissions, in addition to consuming a fraction of the energy required by a conventional heating system. In addition, the characteristics of a sealed compressor provide a very rapid startup, typically three minutes or less. This is particularly valuable for systems designed to provide heating or cooling (or both) in response to variable demand. A prominent reference case is the Esbjerg project in Denmark, where the world’s largest CO2-based heat pump is now in operation. Using seawater as the heat source, the plant supplies climate-neutral heat to around 100,000 residents. The system has replaced a coal-fired power plant and avoids around 120,000 tons of CO2 emissions annually. Looking ahead, sealed compressors could become a cornerstone technology for unmanned offshore platforms. Their compact design does not require auxiliary equipment such as gearboxes and lube-oil or seal-oil systems, resulting in major savings in both footprint and weight. Just as importantly, they eliminate the need for routine manual checks such as oil-level inspections or valve leak monitoring. This makes them particularly attractive for installations where no permanent personnel are present. A major order for Aker BP’s Yggdrasil area illustrates this trend: two HOFIM compressors will be deployed on the unmanned Munin platform and controlled entirely from shore via Everllence’s integrated digital solution. Real-time monitoring, predictive maintenance, and digital-twin functionality enable reliable, autonomous performance with minimal on-site intervention. This project highlights how sealed compressors are evolving into fully digital, remotely operated assets that redefine the future of offshore gas production. Hydrogen compression represents another promising field. Pure hydrogen is notoriously difficult to contain, and leaks can pose severe safety risks. A hermetically sealed compressor design minimizes leakage potential, offering a safer and more reliable solution for this challenging application. Technical Highlights Today’s sealed high-speed compressors cover a wide range of operating conditions. Power levels range from 1 MW (1,300 HP) up to 18,000 kW (24,000 HP), with discharge pressures reaching 303 bar (4,395 psi). Units can be configured in series or tandem arrangements to extend their operating range. MECOS active magnetic bearings are digitally controlled and can operate reliably even when the control panel is located hundreds of meters away. In one Canadian installation, the control room is over 3,000 km from the compressor station. Touchdown bearings protect the rotor at standstill, with a preloaded design that prevents inner-race rotation when the shaft is supported by the magnetic bearings. Variable-speed drives provide efficient, low-harmonic operation while enabling flexible capacity control. Åsgard, Norway: World-first subsea compressor (2016) Ivar Aasen, Norway: First offshore platform HOFIM (2017) Jansz-Io, Australia: Most powerful subsea compressor North Sea Projects: Valhall, Hugin, and Munin (2027) Americas: Stagecoach (USA), Lachenaie (Canada), Stealth Stations From pipelines to subsea to district heating, sealed compressors have evolved from a niche concept into a proven technology. Their compactness, low maintenance requirements, and emission-free operation make them an enabling solution for the energy transition. With future applications in hydrogen and unmanned offshore platforms, the full potential of hermetically sealed compressors is only beginning to unfold. Kevin Kisor is the Senior Technical Advisor at Everllence USA Inc. 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