Soot Control During the Combustion of Polystyrene

This paper describes an experimental study on the control of soot formation during the combustion of polystyrene (PS). A stable, twodimensional flame generated by using a Wolfhard-Parker type diffusion flame burner was used to simulate practical combustion situations. The combustion characteristics, effects of operating conditions on soot formation, and the effectiveness of various metallic additives as soot suppressants were investigated. It was found that soot yield could not be significantly reduced by controlling the oxidizer (air) flow rate. Increasing the O₂ mole fraction of the oxidlzer increased soot yield under typical operating conditions. However, soot yield could be greatly reduced by adding small amounts of air into the pyrolysis zone of the flame. The additional air would probably increase the combustion reaction rate while decreasing the soot precursor formation rate, thereby causing the observed effect. It was thus suggested that effective soot control could be accomplished by improving mixing between air and the PS devolatilizatlon products In practical combustion situations. The metallic additives tested in this study were the salts of Na, K, Ca, and Ba. Among these salts, Ca was the least effective in reducing soot, and K and Na were nearly equally effective. Ba was much more effective than all the others, and Its effectiveness was strongly dependent on its addition rate.