Compact incinerator afterburner concept based on vortex combustion

Abstract

A design concept for a compact incinerator afterburner based on actively controlled vortex combustion was developed and tested at ≈ 5 kW and ≈ 50 kW. Acoustic control of fluid dynamics was used to enhance mixing and increase the DRE (destruction and removal efficiency) for a waste surrogate. A detail study of the concept of utilizing vortex combustion for incineration was undertaken in a small-scale flame using advanced laser diagnostics to elucidate and optimize the fluid dynamic mechanisms. The system was then scaled up by ≈ 10, optimized, and evaluated for performance. The open loop active control methodology is based on the concept of combustion in periodic axisymmetric vortices. Acoustic excitation was, used both to stabilize coherent vortices in the central jet air flow and to control circumferential gaseous fuel and waste injection into the shear layer at the right time during vortex formation. The gaseous-fueled actively controlled 4.5 kW incinerator was able to surpass 99.997% DRE even when the gaseous benzene waste surrogate constituted 66% of the total combustible content and the combustible to total air ratio (ø) was 0.974; lowering ø below this increased the DRE to beyond our detection limit. The DRE for gaseous benzene exceeded 99.999% in the 50-kW system when combustible to air ratios were kept below 0.78. Parameters found critical to maintenance of high DRE at both energy scales were the fraction of circumferentially entrained air, the entrainment geometry, the forcing levels, and the phase angle of fuel injection with respect to the vortex roll-up. The 50-kW combustor was also evaluated for stack emissions and combustion efficiency. The controller improved combustion efficiency and lowered emissions: CO dropped from 2900 ppm to as low as 2 ppm. Unburned hydrocarbons were also reduced. Under some conditions the controller also reduced NO x levels down to as low as 12 ppm.