The drive to combat greenhouse gas emissions and seek eco-friendly energy solutions has led to a notable surge in the utilisation of Liquid Natural Gas (LNG) in marine applications. Recognised as a sustainable fuel, LNG has gained substantial traction as a viable alternative across various commercial transport sectors, including marine and shipping. With maritime traffic accounting for an estimated 3% of global CO2 emissions, the International Maritime Organisation (IMO) aims to reduce carbon emissions. While LNG offers a more environmentally friendly alternative to highly viscous diesel fuels commonly used in cruise liners and container ships, it poses notable challenges to fuel systems and pumps due to extreme cryogenic temperatures.
Overcoming the Hurdles
When it comes to LNG pumps, bearings play a critical role, enduring extreme temperatures while fully submerged in Liquid Natural Gas ranging from (-196ºC / -320ºF) or in Liquid Hydrogen at (-253ºC / -423ºF). Carter Manufacturing Ltd., based in Oxfordshire, is a renowned global supplier of precision bearings with a 20 years-rich heritage in providing reliable bearing solutions for cryogenic applications. As fuel systems approach near-zero operating temperatures, utilising liquid lubrication becomes increasingly challenging, necessitating the use of dry-running bearings. Conventional steel bearings, such as 52100 Chrome Steel are merely unproductive, leading to subpar performance, shorter service life, and unforeseen failures.
Apart from lubrication challenges, the material expansion and reduction within the bearing housings become crucial for optimal bearing efficiency. It is essential to carefully align the coefficient of thermal expansion with the chosen materials to ensure smooth operation.
In addition, achieving balance in the pump system to accommodate material contraction is quite important. Hence, partnering with a bearing supplier well-versed in the intricacies of cryogenic applications is paramount to overcome these challenges. Apart from addressing lubrication concerns, careful selection of bearing material and precise heat treatment procedures are also vital. By incorporating specialised cryogenic heat treatment and proprietary techniques, potential issues like non-linear contraction or warping of bearing components can be mitigated. This comprehensive approach ensures optimal results and enhances the overall performance of the bearings in extreme cryogenic conditions.
Selection of Correct Bearing Materials
To ensure optimal performance in cryogenic applications, careful selection of bearing cage design and material is essential. Common engineering plastics often become too fragile at cryogenic temperatures, making them unsuitable to use. Carter Manufacturing Ltd. specialise in utilising top-notch bearing materials tailored for extreme cryogenic conditions. These include cost-effective choices like PEEK and PTFE with custom additives, or specialised materials like PCTFE or Durafilm when required.
Furthermore, cage geometry is also of fundamental importance as materials become increasingly breakable at cryogenic temperatures. Carter’s cutting-edge innovation includes a proprietary two-piece riveted cryo cage design exclusively developed for deep groove ball bearings. This revolutionary design has significantly enhanced performance in cryogenic applications. As mentioned earlier, the use of standard 52100 bearing steel is insufficient for such demanding conditions. By collaborating with cryogenic experts like Carter Manufacturing Ltd., customers gain access to invaluable expertise and decades of experience, enabling them to leverage the full potential of cryogenic solutions.
Lubrication and Associated Challenges
In applications involving cryogenic temperatures, conventional bearings heavily rely on liquid lubricants that creates a thin film between the steel rolling components, reducing metal-to-metal contact and the associated risks of micro-welding adhesion. To overcome this challenge, Carter provide a reliable solution by offering ceramic bearings like silicon nitride, which eliminate the need for liquid lubricants while reducing mass and increasing speed capabilities. Additionally, the application of a dry film lubricant, such as tungsten disulphide (rated AMS2530), also plays a crucial role in the success of cryogenic bearings.
Inspection & Testing of Cryogenic Bearings
When it comes to cryogenic bearings, ensuring their suitability for your specific application and minimising risks is paramount. At Carter Manufacturing, they deeply understand the importance of testing at the manufacturing stage to ensure efficiency and mitigate risks. That’s why they have developed proprietary cryogenic testing procedures to validate the performance of their bearings even before they reach your site. Their rigorous testing involves fully submerging the bearings in Liquid Nitrogen at the temperature of -196ºC / -320ºF, providing a robust assessment beyond LNG submersion due to lower temperatures. Additionally, the bearings are examined for performance torque and dimensions to guarantee optimal performance tailored to your application’s requirements.
Carter Manufacturing is actively contributing to the drive for sustainable energy solutions and the reduction of greenhouse gas emissions, exemplified by their extensive involvement in the growth of LNG projects within the marine sector. LNG as a marine fuel not only aligns with the current regulations set by IMO and EU, but it also offers complete elimination of Sox and particles, along with a significant reduction of Nox emissions by up to 85%. Ultimately, this transition will lead to a substantial decrease in CO2 emissions, by a minimum reduction of 20%.
With a significant market share, Carter Manufacturing Ltd. offer an extensive inventory of cryogenic bearings, providing customers with a wide range of design and material choices tailored to their specific cryogenic applications. Moreover, Carter’s expertise is reflected in their established procedures, including proprietary heat treatment methods, rigorous testing protocols, and stringent internal quality controls. These factors contribute to Carter’s reputation as one of the leading suppliers of cryogenic bearings, delivering reliable and high-performance bearing solutions.
Source: Carter Bearings