CONTRIBUTING RE.ENGINEER
KnightHawk Engineering
www.knighthawk.com
CHALLENGE
Background: Thermal Oxidizers are widely applied in industry for air pollution control, specifically for the destruction of waste gases and liquids containing hazardous pollutants. These pollutants are thermally destroyed to a high efficiency, oxidized mainly to CO2 and H2O before release to atmosphere under strict environmental control permit conditions. KnightHawk has extensive experience in the troubleshooting, failure analysis and optimization of thermal oxidizers.
The challenge: A Thermal Oxidizer experienced problems under certain operating conditions, waste gas & liquid flows and compositions. The operators observed high vibrations and flame instabilities. Liquid injections were not adequately entrained and destroyed resulting in dropout, rundown and corrosion of walls and piping. Particulate matter and VOC emissions exceeded permit limits.
SOLUTION
KnightHawk engineering developed CFD models including for the reaction kinetics to (i) establish the Root Cause, (ii) Trouble Shooting and (iii) Solution Development. The models were calibrated and verified against process data measurements such as temperatures and emissions, proving a very good correlation. Physical models applied included for an air-methane burner, swirling and turbulence model, radiation, mixture compositions, discrete phase droplet injections and species transport by reactions. By visualing temperatures, velocities, species fractions and streamlines over section planes and quantifying in linearized XY plots, the problems were evident. Flame impingement by waste products; Poor mixing of waste streams with hot flue gases; low residence times and injections of atomized droplets in low heat/low velocity regions were identified.
RESULT
Solutions were developed to ensure a shielded flame front, effective mixing of waste products with hot flue gases and long enough residence times to ensure boiling and vaporization of droplets and complete thermal destruction of volatiles and organics.