Analysis and modelling of boundary-layer flashback processes for hydrogen-rich gas-turbine combustion

Abstract

This thesis presents analysis and modelling of boundary-layer flashback processes for hydrogen rich gas-turbine combustion. The future use of industrial gas turbines will be dependent on lowering their carbon intensity, thus requiring flexible use of alternative fuels, such as those rich in hydrogen. Hydrogen has significantly different properties to traditional fuels, for example hydrogen shows an increased risk of flashback, where the flame propagates upstream from the combustion chamber into the premixing section of the gas turbine. Flashback is a significant safety concern which causes plant shutdowns and damage to equipment. The risk of flashback for hydrogen fuels, with their significantly higher flame speed, is particularly high in the case of boundary-layer flashback. Boundary-layer flashback has also been shown to be caused by an increase in swirl, which is particularly important for gas turbines where swirl is commonly used for flame stabilisation. To enable the use of hydrogen rich fuels in gas turbines it is therefore important to understand the physical mechanisms underlying boundary-layer flashback in swirling flows and to predict the effect of swirl on flashback speeds. This thesis describes models of flashback in channels and annuli using a Froude number to describe the effect of swirl. The predictions of flashback speed, and physical mechanisms underlying them, are validated using both two-dimensional laminar simulations and three-dimensional turbulent simulations in planar channels and annuli. In non-swirling flows, boundary-layer flashback is dominated by flame propagation that is enhanced by volumetric expansion through the flame. In swirling flows, it is shown that the radial pressure gradient, resulting from centripetal acceleration, causes flow diversion around the flame and results in pressure-driven flashback. These two physical mechanisms are described by models using a momentum balance over the flame, and an additive model that combines a flame-propagation and a pressure-driven term. The trend in flashback speed with swirl is validated using the laminar simulations and experimental data from previous investigations. Finally, the laminar simulations are used to investigate and develop empirical models for the effect of bulk velocity, channel height and boundary-layer development on flashback speed.

More information

Identifiers

ORCID for James Bailey: orcid.org/0000-0002-8784-4008

ORCID for Edward Richardson: orcid.org/0000-0002-7631-0377

Catalogue record

Export record