Fuel flexibility with GE marine gas turbines

Mark Lipton's picture
Mark Lipton, Director of Commercial Applications, GE’s Marine Solutions (part of GE Aviation)
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LNG is gaining interest for marine propulsion applications thanks to its low emissions. In terms of performance and durability, LNG is the best fuel for gas turbines. What about using other fuels such as Liquid Petroleum Gas (LPG) or ethane for maritime propulsion? Is technology available today to allow ship owners to switch to burning hydrogen? GE’s marine gas turbines burn alternative fuels employing the same technology that has been used in the power generation and oil and gas sectors for 45 years.

Here is an overview of the impact of different pollutants on gas turbine performance and emissions in the marine sector. A key aspect in evaluating any gas as a fuel is its make-up. There is no single mixture that describes a gas make-up. Gas turbine technology uses the Modified Wobbe Index (MWI) as the main indicator of fuel gas composition; standard range of MWI is from 40 to 60. GE marine gas turbines have demonstrated operation burning diverse gas fuels including LNG, propane, ethane, and coke oven gas.

1. LNG is the easiest fuel for a gas turbine to accommodate since there are no operating restrictions. The gas turbine can be started without a pilot fuel and accelerated to full load with fuel switchovers automatically sequenced without loss in power. With LNG, CO2 emissions drop by >30% and NOx emissions drop by 70% while meeting Tier III requirements. GE’s proven Dry Low Emissions technology brings gas turbine NOx levels below Tier III levels. When using LNG, gas turbines maintain “unmeasurable” levels of unburned hydrocarbons, or “methane slip.” 

2. LPG is sometimes used to describe propane fuel. GE marine gas turbines can operate with commercial grade HD5 propane. However, when evaluating propane consider these key factors:

  • For the GE LM2500 family of gas turbines, a minor change to the fuel nozzle tip area is done.
  • Propane’s higher combustor flame temperature generates higher levels of NOx; GE gas turbines still can meet Tier III limits.
  • Careful consideration must be given to all safety and ventilation systems.

3. Ethane generates higher flame temperatures and has a heavier specific gravity thus requiring similar safety changes as propane. Overall, propane and ethane have very similar characteristics and impacts when used with a GE marine gas turbine.

4. Pure hydrogen as a fuel for a gas turbine has not yet been developed. Nonetheless, GE engines are used in other applications where high concentrations of hydrogen are produced. Even with significant challenges and various safety features, GE marine gas turbines have design capabilities to accommodate up to 85% hydrogen.

These case studies demonstrate the fuel flexibility of GE gas turbines:

  • The ConocoPhillips LNG plant in Darwin, Australia, uses two compressor trains of three GE LM2500+G4 gas turbines for each gas refrigeration step to produce 3.7 million tonnes of LNG per year.
  • The fast ferry Francisco, owned by Buquebus, operates on diesel when in port; once it clears the harbour, the ferry switches to LNG as the primary fuel.
  • GE, Hyun-Seong Marine Cruise Transport and its partners developed a propane-fueled ferry design using GE’s Combined Gas turbine Electric and Steam (COGES) solution. This ferry can switch to back-up diesel automatically if needed.
  • A coke oven gas site in Henan, China, has a high hydrogen content that powers two GE LM2500+G4 engines.

As the marine industry looks for alternate solutions to reduce pollutant levels, GE marine gas turbines are proven to operate on various fuels and provide options for shipbuilders and owners to meet current and future regulations.

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Image courtesy of GE Aviation