A highly diluted oxy-fuel micromixer combustor with hydrogen enrichment for enhancing turndown in gas turbines

Most burner technologies in past studies were incapable of operating at the high CO₂-dilution levels required in the oxy-fuel combustors of zero-emission power cycles. The present study addresses this gap by utilizing the micromixer gas-turbine technology, coupled with hydrogen enrichment, to present an oxy-fuel burner that is capable of sustaining highly diluted flames for application in the zero-emission Allam power. Gas-turbine micromixers have never been tested under oxy-fuel combustion conditions before, which highlights the novelty of the present study. The operability window of the present burner was quantified experimentally over ranges of fuel (CH₄/H₂) hydrogen fraction and oxidizer (O₂/CO₂) oxygen fraction. It was found that the micromixer delivers superior stability, allowing for operation at oxygen fractions as low as 21% (by vol.) without hydrogen enrichment, which satisfies the nominal dilution requirements (23%) of the primary reaction zone within the Allam-cycle combustor. Micromixers are thus the technology recommended for oxy-fuel combustion in zero-emission power plants. Enriching the fuel with hydrogen was found to boost flame stability, which allowed for reducing the oxygen fraction further down to a record-low value of 13% at a hydrogen fraction of 65% (by vol.). This offers great operational flexibility and pioneering improvement in the turndown and low-load capabilities of the cycle. The results also showed that hydrogen enrichment has minimal effect on flame temperature and combustor power density (power per unit volume), which facilitates additional operational flexibility in adjusting the hydrogen fraction to sustain flame stability without influencing cycle peak temperature or turbine health.