Pollutant Formation and Control in Flames

Pollutant Formation and Control in Flames Key combustion-generated air pollutants include nitrogen oxides (NOJ, sulfur oxides (principally SO9), particulate matter, carbon monoxide, and unburned hydrocarbons. 

Staged Burners As was pointed out earlier under Pollutant Formation and Control in Flames, the proper staging of fuel or air in the combustion process is one technique for minimizing emissions. Gas burners that achieve such staging are available. 

Turbulent Diffusion FDmes. Laminar diffusion flames become turbulent with increasing Reynolds number (1,2). Some of the parameters that are affected by turbulence include flame speed, minimum ignition energy, flame stabilization, and rates of pollutant formation. Changes in flame stmcture are beHeved to be controlled entirely by fluid mechanics and physical transport processes (1,2,9). 

Industrial flares and plumes represent a potentially significant source of air pollution that are poorly characterized and controlled. Conditions are ideal for post-flame thermal reactions and photolytic reactions at elevated temperatures (photothermal reactions). The elevated temperatures in flares and plumes (—50 to 600 °C outside of the visible flame) can result in accelerated rates of formation of oxy-PAH and nitro-PAH. At higher temperatures within the flame zone of combustors, oxy-PAH and nitro-PAH are likely to be destroyed, but under the relatively mild conditions of flares and plumes, the rates of formation can be accelerated without their subsequent destruction. The elevated temperatures and exposure to solar radiation can result in fast photothermal reactions that lead to the formation of both combustion-type pollutants and photochemical pollutants. Research has shown that at elevated temperatures, the rate of absorption of solar radiation and photochemical quantum yield can increase up to tenfold. 

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