Effect of Nozzle Geometry on the Performance of Non-Assist Flares

TL;DR

This paper uses large-eddy simulations to analyze how different nozzle shapes affect combustion efficiency, mixing, and blowout resistance in non-assist methane flares, highlighting the advantages of cornered geometries.

Contribution

It systematically evaluates five nozzle geometries, revealing that cornered shapes improve efficiency and blowout resistance compared to streamlined designs.

Findings

Cornered nozzles enhance recirculation and mixing.

Square nozzles maintain >96.5% efficiency under high crosswinds.

Sharp-edged nozzles increase blowout resistance.

Abstract

This study employs large-eddy simulations with a flamelet progress variable approach to systematically quantify the influence of nozzle geometry on combustion efficiency, mixing, and blowout resistance in non-assist methane flares. Five canonical nozzle shapes-circle, low aspect ratio ellipse, high aspect ratio ellipse, diamond, and square-were evaluated under relevant industrial flare conditions. Results demonstrate that cornered geometries enhance near-field recirculation, promote mixing, and sustain flame attachment, resulting in up to a 5% improvement in combustion efficiency compared with streamlined nozzles. The square nozzle performed best irrespective of the wind direction (orientation) and maintained a combustion efficiency greater than 96.5% even at the highest tested crosswind velocities, while other streamlined designs exhibited early flame lift-off, reduced recirculation, and efficiency losses. Analysis of mixing and vorticity reveals that sharp-edged nozzles accelerate scalar homogenization and buffer flames against crosswind-induced strain, directly translating to increased blowout resistance.