Most burner technologies reported in past oxy-combustion studies were incapable of operating at the high levels of exhaust-gas recirculation required in the oxyfuel combustor of the Allam cycle for zero-emission power production. This present study has thus experimentally investigated utilizing the exceptionally stable and flexible micromixer gas-turbine technology, coupled with hydrogen enrichment, to present an oxyfuel combustor that is capable of sustaining highly-diluted flames for application in the Allam cycle. Gas-turbine micromixers have never been tested under oxyfuel combustion conditions, which highlights the novelty of the present study. The operability window of a premixed micromixer burner holding hydrogen-enriched oxy-methane flames was quantified over ranges of fuel hydrogen fraction and oxidizer oxygen fraction. The micromixer burner showed superior stability, allowing for the reduction of oxygen fraction down to 21% (by vol.) without hydrogen enrichment, which satisfies the dilution requirements (23%) of the primary reaction zone within the Allam-cycle combustor. By comparison, swirl-based burners from past studies exhibited a \~30% minimum threshold. Enriching the fuel with hydrogen boosted flame stability and allowed for reducing the oxygen fraction further down to a record-low value of 13% at a hydrogen fraction of 65% (by vol.) in the fuel mixture. Under these highly-diluted conditions, the adiabatic flame temperature is 990 °C (1800 °F), which is substantially lower than the lean blowout limit of most known technologies of lean premixed air-fuel combustion in gas-turbine applications. The CO~2~ flow inside the Allam-cycle combustor can thus be split differently to increase the dilution of the primary reaction zone and reduce the secondary CO~2~ stream used for liner cooling, which results in a more uniform exit temperature profile. The effective stabilization mechanism of the micromixer technology is described here by visualizing how few lit core jets act as a pilot to stabilize the majority of unlit outer jets, especially near the blowout limit. The results also showed that hydrogen enrichment has minimal effect on the adiabatic flame temperature and combustor power density (MW/m^3^/atm), which facilitates great operational flexibility in adjusting the hydrogen fraction to sustain flame stability without affecting the Allam cycle peak temperature or impacting the turbine health. Micromixer combustion with hydrogen enrichment is thus a recommended technology for controlled-emission, fuel/oxidizer-flexible combustion in gas turbines.


Micromixers and Hydrogen Enrichment: The Future Combustion Technology in Zero-Emission Power Plants

Division / Sponsors: 
Power Division & Nuclear Engineering Division (NED)

Power Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2020/volume/83747

International Conference on Nuclear Engineering
Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE2020/volume/83761

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