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Show Unmixed Combustion for Efficient Heat and American Flame Research Committee Mass Transfer in Chemical Processing Systems 1997 Fall International Symposium Under some circumstances, however, it is still possible for toxic or hazardous materials to escape the secondary oxidation chamber without being completely destroyed. The most notorious of these circumstances is known as a "puff'3. Puffing occurs in incinerators when something is introduced to the primary chamber that is unusually volatile and which rapidly overwhelms the oxygen capacity of the secondary chamber. A good example would be a sealed can of solvent that might be hidden in with other waste materials being fed to the incinerator. In the heat of the primary chamber, the solvent attempts to boil, but is confined in its container. At some point, however, the container ruptures, spewing the solvent onto the heated surfaces of the chamber. A s suggested by Figure 6b, the solvent then rapidly evaporates and rushes into the secondary chamber where either due to inadequate oxygen availability, or to the inability of the secondary air to mix completely with the it, the solvent cannot be entirely destroyed. Unmixed Combustion can be applied to this problem simply, as shown in Figure 7, by placing a packed bed full of copper oxide Unmixed Combustion catalyst into the exhaust stack of the incinerator, and sizing it to accommodate the effluent from the worst case puff imaginable. N o w, how exactly would this work? Consider the situation in Figure 7a where the incinerator is operating normally. In this case the exhaust from the incinerator is at about 1000 °C and contains excess oxygen. A s a result, the Unmixed Combustion catalyst is hot and fully oxidized. At some point (Figure 6b), a puff occurs in the primary chamber, and unoxidized gaseous organic compounds escape to the stack. A s these organic compounds pass through the Unmixed Combustion catalyst, they are oxidized completely, while some of the copper oxide is reduced to the metallic state. Within a minute or so, the puff subsides and the secondary chamber resumes normal operation. At this point, the metallic copper in the Unmixed Combustion catalyst is reoxidized and returns to its normal state. Table 2. Oxidation of surrogate toxic organic compounds by copper oxide. Compound Chlorobenzene Benzene Thiophene Pyridine Phosphonoacetic acid (pesticide and nerve gas surrogate) Formula C6H5CI CGHQ C4H4S C5H5N (HO)2POCH2COOH DRE >.99999 .99997 >.999999 .9999678 .99993 815 °C, 0.53 seconds gas phase residence time The effectiveness of Unmixed Combustion for incineration applications was demonstrated in an experimental apparatus similar to that shown in Figure 2 using copper/copper oxide as the unmixed combustion catalyst. The reactor was maintained at 815 °C and was exposed to gases containing surrogate toxic organic compounds with a characteristic gas phase residence time of 0.53 seconds. Results of these tests, shown in Table 2 illustrate that all compounds were Fairmont Hotel Chicago, Illinois September 21 -24 1997 Page 6 |