Evaluation of Nox Emissions Associated to Non-Premixed Combustion of H2/Natural Gas Blends in a 40 MW Heavy-Duty Gas Turbine

Abstract

The tightening in the international regulations is leading the energy production sector towards the usage of hydrogen, which is a zero-carbon energy carrier. In the field of gas turbine lifetime extension, a non-premixed approach including hydrogen blending with conventional fuels is the most promising. However, high-temperature spots might occur, thus increasing thermo-mechanical stresses and NOx emissions. Therefore, a reliable evaluation of the impact of hydrogen blends in combustors characterized by non-premixed flames is necessary. In the present work, a 40MW heavy-duty multi-can combustor belonging to EthosEnergy is investigated by means of steady, reactive simulations by using the ANSYS® FLUENT® solver. The combustor geometry is simplified by removing the casing volume, being the flow split among the holes already available. Such simplification allows for paying major attention to the chemical kinetics thanks to the use of the extended reaction mechanism for natural gas developed by NUI Galway. Simulations include the assessment of the natural gas base load configuration together with hydrogen blends up to 50% in volume, while maintaining unaltered the turbine inlet temperature. The obtained data provide some retrofitting guidelines in the field of hydrogen usage in non-premixed combustion and prove for a modified temperature field in the combustor core and close to the basket. A linear increase in NOx emission is also associated to hydrogen addition, thus suggesting the need for NOx abatement technologies (e.g., water injection).