Study on the Operational Window of a Swirl Stabilized Syngas Burner Under Atmospheric and High Pressure Conditions

Abstract

Providing better fuel flexibility for future gas turbine generations is a challenge as the fuel range is expected to become significantly wider (natural gas, syngas, etc.). The technical problem is to reach a wide operational window, regarding both operational safety and low emissions. In a previous paper an approach to meet these requirements has already been presented. However, in this previous study it was difficult to exactly quantify the improvement in operational safety due to the fact that the flashback phenomena observed were not fully understood. The present continuative paper is focused on a thorough investigation of operational safety also involving the influence of pressure on flashback and the emissions of the proposed burner concept. To gain better insight in the character of the propagation and to visualize the path of the flame during its upstream motion, tests were done on an atmospheric combustion test rig providing almost complete optical access to the mixing section as well as the flame tube. OH* chemiliuminescence, HS-Mie scattering and ionization detectors were applied and undiluted H2 was used as fuel for the detailed analysis. To elaborate the influence of pressure on the stability behavior additional tests were done on a pressurized test rig using a downscaled burner. OH* chemiluminescence, flashback and lean blow out measurements were conducted in this campaign, using CH4, CH4/H2 mixtures and pure H2. The conducted experiments delivered the assets and drawbacks of the fuel injection strategy, where high axial fuel momentum was used to tune the flow field to achieve better flashback resistance.

Direct numerical simulation of premixed flame boundary layer flashback in turbulent channel flow

“…Among the important results obtained in these experiments is the conclusion that the critical velocity gradients at the wall required to avoid wall boundary layer flashback increase steeply as the pressure increases (Mayer et al 2011).…”

“…While boundary layer flashback has previously represented a minor issue for natural gas fired gas turbines, mounting evidence involving premixed combustion of hydrogen-rich syngas at gas turbine conditions (high pressure, high reactants' temperature) indicates that boundary layer flashback may constitute a key challenge (Mayer et al 2011) even in the presence of large quantities of diluent (Carroni 2006). …”

“…Finally, it is also important to mention that some recent experimental studies (Heeger et al 2010;Mayer et al 2011) have attempted to chart flashback behaviour under lean premix conditions for several different burner configurations and to shed light on the physical mechanisms behind near-wall upstream propagation of premixed flames using detailed laser diagnostics techniques with high spatial and temporal resolution. Among the important results obtained in these experiments is the conclusion that the critical velocity gradients at the wall required to avoid wall boundary layer flashback increase steeply as the pressure increases (Mayer et al 2011).…”

Effect of fuel composition and differential diffusion on flame stabilization in reacting syngas jets in turbulent cross-flow

“…One of the most serious operability issues often preventing modern combustors from operating in a safe, efficient, and reliable manner is flashback when the flame propagates upstream of the design position, where it is supposed to stabilize, and into the premixing duct [3]. Common flashback mechanisms include propagation of the turbulent flame in the core flow of the premixer duct or in its wall boundary layers, oscillations of the flame location due to combustion instabilities or combustion induced vortex breakdown [5]. Regardless of the initiating cause of flashback, once flashback occurs the flame will ultimately reach the fuel injection nozzles.…”

Experimental Investigation of the Effects of Central Fuel Injectors on Premixed Swirling Flames

“…Other works 3 have found that the increase in the diameter of the central injector will increase the thickness of the vortex cores and strengthens the axial flow velocity thus the vortex breakdown is shifted downstream producing better flame stability. Another groups 13 investigated two types of fuel injection, i.e. axial and trailing.…”