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Maritime Propulsion

March 30, 2023

MHI Develops Oilless, Nitrogen-Based Cryogenic ORC Generator

Oilless ORC generator (Source: Mitsubishi Heavy Industries)

Mitsubishi Heavy Industries has demonstrated a 100kW class cryogenic organic Rankine cycle (ORC) power generation system using a nitrogen-based, oilless cryogenic turbine generator.

ORC systems are able to harness lower-temperature heat than typical waste heat recovery systems, and MHI says the use of liquid nitrogen as the cryogenic energy source provides a stable refrigerant cycle and the specified regeneration output without freezing-induced clogging. It performs well even under conditions more severe than the low temperatures of conventional LNG cryogenic generation.

The generator rotates by extracting torque from the energy derived from the temperature differential created by vaporizing the refrigerant using seawater, and utilizing the resulting high-pressure steam as the rotational force. Oilless magnetic bearings and a hermetically sealed structure prevent refrigerant leakage outside the system.

MHI claims the design brings higher reliability, space savings and maintenance-free operation compared to earlier LNG-cooled steam turbines with open-end type, featuring forced-lubricated sleeve bearings.

Besides using liquid nitrogen (boiling point: approx.-196℃) in place of the conventionally adopted LNG (boiling point: -160℃), the test simulated actual LNG vaporization equipment such as a marine fuel gas supply system and offshore/onshore LNG vaporization equipment.

The testing expanded understanding the refrigerant cycle properties and the phase changes of cryo-temperature media such as LNG and liquid nitrogen and confirmed the system’s controllability. The results suggest there is further potential for stabilization and reliability in LNG refrigerant generation systems and support expectations of the use of hydrogen (boiling point: approx. -253℃), which is seen as a promising decarbonized fuel for cryogenic power generation.