Burner Development and Operability Issues Associated with Steady Flowing Syngas Fired Combustors

Abstract

This article addresses the impact of syngas fuel composition on combustor blowout, flashback, dynamic stability, and autoignition in premixed, steady flowing combustion systems. These are critical issues to be considered and balanced against emissions considerations in the development and operation of premixed combustors. Starting with blowout, the percentage of hydrogen in the fuel is suggested to be the most significant fuel parameter, which is more fundamentally related to the hydrogen flame's resistance to stretch induced extinction. Turning to flashback next, it is shown that multiple flashback mechanisms are present in swirling flows, and the key thermophysical properties of a syngas mixture that influence its flashback proclivity depend upon which flashback mechanism is considered. Flashback due to turbulent flame propagation in the core flow and the interaction of heat release with pulsations are less critical, whereas flame propagation in boundary layers and flashback due to the interaction of the heat release with vortex breakdown dynamics are most significant. Then, combustion instability is considered. The key flame parameter impacting the conditions under which instabilities occur is the spatial distribution of the flame. As such, fuel composition influences dynamics through impacts upon flame speed and the flame stabilization point. Furthermore, certain syngas fuel compositions are not more inherently stable than others – rather, each mixture has particular islands in the parameter space of, e.g., velocity and fuel/air ratio, at which instabilities occur. Changes in fuel composition move these islands around but do not necessarily eliminate or introduce instabilities. Relative to autoignition, measurements indicate that the ignition delay time exceeds typical premixer residence times, though by a substantially less margin than suggested by the calculations. Recent experiment work suggest that current detailed kinetic mechanisms developed for hydrogen/carbon monoxide ignition overestimate the ignition delay time, indicating the need for additional kinetic work in the low temperature, high pressure regime.