SCO2 Oxy-Combustion Technology Group

SCO2 Oxy-Combustion Technology Group
Meeting Minutes
December 11, 2017
Presentation by Dr. Pete Strakey

 

Agenda
  • 1:05p – Introduction / Meeting Outline / Objectives
  • 1:15p – Strakey presentation on NETL R&D activities
  • 2:00p – Q&A
  • 2:15p – General Discussion
  • 2:30p – Conclude

Meeting Outline/Objectives
An introduction from the Working Group host:

  • Seth Lawson - NETL
    • Federal Project Manager in Advanced Energy Systems Team
  • Currently several projects in the NETL portfolio related to SCO2 oxy-combustion
  • SCO2-based power cycles are a transformational technology
    • Direct fired cycles – a major challenge is oxy-combustion
  • Working Group plans to meet on a bi-monthly basis
    • Meeting is open to the public
    • WebEx meeting
    • A volunteer speaker will present on a relevant topic followed by Q&A
    • Open discussion on SCO2 oxy-combustion will be encouraged
    • Meeting minutes and presentation will be shared following the meeting

Presentation

  • Pete Strakey –Thermal Science Group in the NETL Research and Innovation Center (RIC)
  • Title: “Oxy-Combustion Fundamentals for Direct Fired Cycles”
  • Presented on NETL R&D activities in SCO2 oxy-combustion
    • Designed a generic 50 MWth (P=300 bar) combustor with SSME preburner type combustor with 21 coaxial injectors
    • Simulated Two limiting cases using CFD:
    • The 70% CO2 case yielded conventional looking turbulent flame
    • The 91% CO2 case appear to have autoignition characteristics
    • Both cases yielded the same average temperature at the combustor exit
    • CO2 production in each case was predicted using Dynamic Smagorinksy 17-species skeletal mechanism
      • The 70% CO2 case yielded 2.6% CO at combustor exit while the 91% CO2 case yielded >0.1% CO at combustor exit
    • Thermo-acoustic instabilities were modeled with LES using the Aramco 17 skeletal model with 75% CO2 by mass
      • Radial mode thermoacoustic instability at 3kHz was observed
      • Peak-to-peak pressure oscillation was 60% of the mean combustor pressure
    • General Conclusions include:
      • Oxy-combustion at 300 bar with CO2 diluent is somewhat uncharted territory
      • Accurately predicting CO levels for combustor design to minimize CO at the turbine inlet is critical to maximizing cycle efficiency. For every mole % of CO that enters the turbine a cycle efficiency penalty of 1% is expected
      • These findings suggest that thermos-acoustic instability is a major issue. Strakey plans to explore the effect of CO2 concentration on instability. Hypothesis: The propensity for instability will decrease as oxygen concentration decreases
      • Because selecting appropriate combustion models is critical to accurately modeling combustion with CFD, there is a need for validated detailed chemical kinetic mechanisms and corresponding reduced mechanisms
      • Perhaps the greatest research need currently is experimental data from oxy-combustion of natural gas and/or syngas at relevant conditions. This data will play a critical role in validating reduced order kinetic mechanisms and CFD models

    Q&A

    Q&A followed the presentation, with some highlights below of Pete’s responses to the questions:

    • Used the mean exit temperature from the combustor model (~1550K) as the turbine inlet condition.
    • Used Aramco-derived 17-species skeletal mechanism in CFD combustor simulations
    • Expect lower CO levels for the lower O2 cases.
    • Transport properties from kinetic theory modeling
    • Haven’t yet looked at thermoacoustic instabilities at other CO2 concentrations, but instability is expected to improve at high
    • Expect propensity for thermoacoustic instability to go down with lower O2 concentration.
    • Have not yet looked at combustor equivalence ratio
    • In simulations, don’t see any unburned hydrocarbons – all converted to CO2 and CO.
    • Flame instability quite a bit worse for low O2 case.

    General Discussion

    • Important to understand CO levels at the combustor exit and entering the turbine.
    • Nate Weiland described some of NETL cycle modeling work:
      • Evaluated cycle efficiency as a function of CO mole fraction out of combustor
      • Approximately 1% reduction of cycle efficiency per mole % CO in combustor exhaust
      • If geometry doesn’t have good mixing, could have higher CO in combustor exhaust
      • Effect of excess O2
        • Most simulations done at ~1% excess O2
        • Didn’t do corresponding cycle analysis but expect slight (1.5%) excess O2
        • Will report this work at upcoming SCO2 Power Cycles Symposium
    • Need for a combustor test stand to experimentally validate the models
    • Modeling/systems analyses work at NETL is valuable to industry
    • SwRI has a current DOE-funded project to build/test an oxy-combustor test stand
      • They plan to adapt SunShot test loop for oxy-combustor testing
      • Seth indicated he spoke with Jacob Delimont at SwRI about presenting on this work at a future Working Group meeting.
    • Sought any comments on this Working Group meeting format. Feedback is highlighted below:
      • Excellent format to discuss the issues.
      • More likely to get people to contribute using this format.
      • Could we do the whole meeting on WebEx, not using phone line?
    • Is the bi-monthly meeting frequency appropriate?
      • Group agreed this is a good frequency for the meeting.
    • Any volunteers to present at next meeting?
      • No responses
    • Potential opportunities for face-to-face meetings for the Working Group
      • 6th International SCO2 Power Cycles Symposium
      • Turbo Expo - Norway

    Planning Discussion for Future Meetings
    Discussion on planning future meetings:

    • Next meeting will be in February 2018.
    • Can we share the attendee list – names and organizations?
      • Seth will check on this.
    • Do we have a mission statement/mandate?
      • Seth indicated the objective is to provide a forum for participants from industry, government, and academia to share insights and address oxy-combustion technology gaps for commercialization of direct fired SCO2 power cycles
    • Anyone who has suggestions on how to improve the working group meeting or on the focus/objective of the working group, please email Seth Lawson (seth.lawson@netl.doe.gov).