Numerical Analysis of the Conceptual Design of Arrayed-Vanes Premixer for Gas Turbine Combustors Burning High-Hydrogen Fuels

Abstract

Using high-hydrogen fuels in industrial gas turbines is an effective way to achieve near-zero carbon emission power generation. Lean premixed combustion can effectively reduce NOx emission. However, due to the strong flashback and auto-ignition tendencies during fuel-air mixing, it is a challenge to use lean premix combustion mode of high hydrogen fuels under gas turbine operation conditions. An innovative conceptual design of arrayed-vanes premixer was proposed to achieve safe and uniform mixing of fuel and air. Inside the arrayed-vanes premixer, a cascade of mixing vanes is arranged in the axial annular air flow passage. Fuel-air mixing and flow field stretch are improved and well controlled by the arrayed vanes. The conditions of auto-ignition and flame stabilization inside the vanes are unsatisfied. Meanwhile the upstream flow disturbance will be inhibited by the arrayed vanes, which benefits combustion stability. The arrayed-vanes premixer was designed and its flow field was numerically simulated under the operation condition of F class gas turbine combustors. The flow and fuel-air mixing behavior was analyzed and compared with a typical swirl-based premixer now widely used in DLN combustors of F class gas turbines. The results show that the non-uniformity index of fuel concentration distribution at the exit plane of the arrayed-vanes premixer is 50% lower than that of the swirl-based premixer. The responses of flow field at the exit plane to the inlet flow disturbance was calculated and compared for the two types of permixer. The inlet flow disturbance includes the velocity distortion and the oscillation of the pressure. The results show that the arrayed-vanes premixer absorbs and damps the inlet flow disturbance better than the swirl-based premixer. And it exhibits highly monochromatic characteristic through the acoustic signature analysis. Furthermore, the tendencies of auto-ignition and flashback were investigated by examining the flow field and the flammability of hydrogen. The results show that there is a low risk of auto-ignition or flashback due to the short residence time and the high discharge velocity. The present study indicates that the arrayed-vanes premixer achieves ultra uniform fuel-air mixing, good adaptability to inlet flow disturbance and anti auto-ignition and flash back, which is benefit to DLN combustor designed for high-hydrogen fuels. This design will be possibly used in DLN combustors after future developments.