Emission characteristics of organic and heavy metal pollutants in fluidized bed incineration during the agglomeration/defluidization process

Abstract

The accumulation of adhesive materials may generate agglomerates during incineration. These agglomerates affect fluidization behavior and cause the formation of secondary pollutants. However, the impact of agglomeration on the emission of organics and heavy metals has seldom been investigated. Accordingly, this work focuses on the preparation of different synthetic wastes to simulate the generation of agglomerates, as well as the effects of various alkali metals, alkaline earth metals, and operating temperatures on the formation of pollutants. The experimental results indicate that defluidization time declines as the concentration of sodium increases, and that alkaline earth metals (Mg and Ca) inhibit agglomeration. Concentrations of organic pollutants gradually increase with operating time, indicating that the size of the agglomerate gradually increases, reducing the quality of fluidization and the efficiency of combustion. After defluidization, the temperature on the surface of the sand bed increases, thereby reducing the concentrations of organics, but it remains higher than that of blank operation (without Na addition). Furthermore, concentrations of three volatile metals (Cd, Pb, Cr) follow similar trends with operating time. Independent of whether the agglomerate is formed, the concentrations of emitted heavy metals are similar. After defluidization, the emitted concentration increases, because the system is transformed to the phase of the fixed bed. The abundant silica sand does not capture the heavy metals released from waste combustion. The increasing temperature of the surface of the sand bed significantly enhances the emission of heavy metals. Accordingly, the emitted organic and heavy metal pollutants behave differently during agglomeration and defluidization.