Electric Drivers in LNG Liquefaction Plants: Design Aspects and Challenges

Over the past five decades within the liquefied natural gas (LNG) industry, there has been a notable evolution in the drivers employed to operate large compressors, encompassing a broad spectrum of solutions such as steam turbines, gas turbines, electric motors, and their combinations. The prevailing trend, influenced by the imperative to mitigate greenhouse gas (GHG) emissions, underscores a growing reliance on electric drives.Within an LNG liquefaction plant, the selection of the drivers for refrigeration compressors will significantly determine the overall plant emissions and energy consumption (also known as auto consumption) throughout the plant's life cycle. Utilizing electric motors to power large compressors can notably reduce the carbon footprint of an LNG liquefaction plant, particularly when clean and renewable energy sources (e.g., hydropower, solar, wind) are available.The increasing adoption of electric drivers for high-power LNG compressors necessitates that design engineers carefully consider various design aspects and address unique challenges. A novel concept is introduced for the first time in this paper that explains the torque versus speed capability curves for API 617 [1] specified operating points.A systematic categorization of commercially available high-power electric motors and electric drives based on their type or topology, along with a comparison of their respective performance, serves as a practical guide for selecting an appropriate driver system for LNG applications. Key considerations include grid integration, compatibility between motor and compressor, reliability, availability, and maintenance requirements. This paper delves into these topics in detail.