OCR Text |
Show of heavy metals in combination with high concentrations of organic compounds, care was taken in the design of the incinerator to ensure that it would not produce unacceptable levels of toxic emissions. To obtain the information needed to design an appropriate incinerator system for the wastes, a two phase program was devised based on the approach described above. First, theoretical models were used to identify the parameters which may have an impact on toxic emissions. Then, a series of bench-scale studies examining the impact of operating parameters on potential pollutant emissions were conducted. Finally, the results were used to characterize the required full-scale system. PRE-TEST MODELING The pollutants of concern in this example are toxic organic compounds and metals. The wastes did not contain pathogens. Acid gas emissions were not expected to be a problem. A model which can predict the behavior of metals in waste incinerators has been developed for the EPA1. This model was used to identify the parameters that should be examined in the bench-scale tests. Detailed analyses of organic emissions from incinerators have been conducted. However, because of the complexity of the reactions which occur during the destruction of organic compounds, a predictive model has not yet been developed. Thus, the bench-scale tests must take the lead role in the evaluation of potential organic emissions. Metals may exit a waste combustion system by any of several pathways. Figure 1 illustrates many potential pathways. Only a few of the pathways may apply to a given waste combustion system. Most of the metals in a waste pass through the incinerator unchanged and are found in the residual ash or grate siftings. The fly ash captured in the heat recovery and flue gas cleaning equipment will also contain some metals. A fraction of the metals originally in the waste may also be found in the exhaust gases emitted from the system. This division of metals between different emission streams is referred to as "partitioning." The metals partitioning model used consists of a group of computer submodels and analytical approaches structured as shown in Figure 21. These submodels simulate the physical and chemical mechanisms which may influence metals behavior in waste combustion systems. The phenomena simulated include: • Reactor thermal behavior • Particle entrainment • Metals reactions and vaporization • Aerosol dynamics Condensation Coagulation • Particle capture -3- |