Advancing Industrial Smokeless Flaring: Experimental and Computational Studies into Swirl Air-Assist Burners

Abstract

The flame thermal radiation characteristics of two prototype swirl air-assist burner designs, associated with industrial smokeless flaring, were experimentally and computationally studied. The work was driven by two main interests: first, to explore the potential of swirling air-assist flare tips in reducing thermal radiation levels, decreasing soot emission, and stabilizing flames in cross-wind; second, to develop an affordable Reynolds Averaged Navier-Stokes (RANS) based computational fluid dynamics (CFD) methodology validated with these specific flames to facilitate further burner designs. The experimental investigation involved two burner configurations. The first burner, named the accelerating swirl burner, was evaluated using two-phase propane at rates of 3 kg/min and 6 kg/min. Compared to an open flare and the burner setting without assist air, the burner with a moderate active assist air supply effectively reduced the visible flame area and emissive power, while also enhanced flame stability in cross-wind. The second burner, called the diffusing swirl burner, equipped with two powerful centrifugal fans, was tested under assist-air to fuel ratio (AAFR) ranged from low, moderate, high to maximum. An increase in AAFR introduced recirculation regions near the burner outlet, led to reductions in visible flame area, emissive power, and radiative heat flux. CFD simulations of both swirl burners in ANSYS Fluent captured the general trends observed in experiments, such as decrease in flame size and emissive power. For the diffusing swirl burner, however, the flame shape responsiveness to AAFR changes in CFD lagged behind that in experimental observations, with flame area discrepancies ranging from 11%-42% compared to the flame contours observed at 800 K. Predictions of emissive power deviated from the experimental values by 3%-67%. Regarding soot production, the model predicted a maximum 84% reduction in soot volume fraction, closely aligning with the observed transition from slightly sooty to smokeless flames in experiments.