Gas turbines

Task 5 pertains to the use of combustion in gas turbine engines for power generation, and represents the required enabling step that completes the CCS value chain on the Norwegian Continental Shelf, throughout Europe and worldwide.

The overall objective is to assess and improve the stability and operability of gas turbine combustion systems facing issues related to novel and unconventional fuel mixtures. Specific focus and significant efforts are aimed at the characterisation of “reheat” hydrogen combustion, which is a firing layout that relies on the longitudinal staging of the combustion system that is divided into two combustion zones arranged in sequence: a first “conventional” dry low-emission burner and a second “reheat” dry low-emission burner.

Ultimately, Task 5 aims to assess the overall impact on power generation, thermodynamic efficiency, and pollutants emissions in order to reduce costs related to clean and efficient energy conversion in gas turbines, and improve their safety and robustness.

Andrea Gruber
Task leader: Andrea Gruber

Results 2021

In 2021, the research work built upon the significant findings and fundamental insights about hydrogen combustion acquired in 2017-2020 to investigate more applied topics of increasing relevance to the development of fuel-flexible gas turbines.

The characteristics of hydrogen flames at reheat combustion conditions that are present in Ansaldo’s GT36 gas turbine have been investigated by SINTEF using a computationally intensive numerical modelling approach named Large Eddy Simulation (LES), in order to accurately represent the reactive flow, combined with a detailed representation of the chemical reaction kinetics.

Scientific illustration
A hydrogen reheat flame (green isosurface) stabilised in a dump combustor at combustion conditions (25 bar, flame temperature > 1800K), which corresponds to full-load of the Ansaldo GT36 gas turbine. The vorticity structures of this strongly turbulent reactive flow are visualized by yellow and purple isosurfaces (rotating in opposed directions).

Results from the LES calculations have provided important information for combustion conditions corresponding to part- and full-load operation of the GT56 gas turbine about the response of hydrogen reheat flames to prescribed variations of the reactants’ temperature. The calculations revealed a robust, stable and predictable behaviour of hydrogen reheat flames in high-pressure conditions, which is relevant to gas turbine applications.

Hydrogen/methane flames ignition and stabilization for different back-pressure conditions.

Interestingly, a very different flame behaviour, characterised by a strong tendency of flame instability in response to temperature fluctuations, was observed for atmospheric pressure conditions. However, these are irrelevant in the context of reheat combustion. This knowledge is key to assessing and improving the robustness of gas turbine combustors that aim for stable and clean operation based on pure hydrogen firing, and will speed up combustor development by OEMs.

In parallel to the computational activity at SINTEF, the experimental activity performed at NTNU has focused on the ignition dynamics and its effect on the flashback tendency of hydrogen-enriched flames (hydrogen-methane blends). The experimental work, conducted by the PhD student Tarik Yahou under the supervision of Professor James Dawson, and in collaboration with Thierry Schuller of IMFT Toulouse, revealed that the ignition dynamics cannot be fully described by classical kinematics arguments and proposed a new mechanism to explain the empirical observations.

The NCCS-sponsored KSP “Reheat2H2” complements Task 5’s research activities by investigating combustion dynamics (thermo-acoustic instabilities) of hydrogen reheat flames and, based on numerical simulation and experimental measurement, is building a low-order model that can represent the flames’ response to unsteady effects emerging from the surroundings (acoustic waves, reactants temperature fluctuations, heat loss etc).