Composite behavior is sometimes an explanation for the observed results, i.e., a model consisting of a plug-flow reactor followed by one or more CSTRs.

In all combustion reactions, some CO is always formed. The following two-step global model accounts for this formation:

VOC^CO-

where, assuming excess oxygen, the following equations apply:

Qualitatively, the resulting concentration dependence is of the form shown in Figure 5.21.3. Under typical incinera-

key:

c = Concentration at time t or exit concentration C0 = Initial concentration k1t= Product of rate coefficient x time, where t can be taken as the residence time at a given temperature

FIG. 5.21.3 Qualitative relationship between VOC, CO, and CO2 concentration as a function of kjt.

tion conditions, the preceding chemical sequence is irreversible. Using Cvoc (t = 0) = CvOC,i and Cœ,i = Cœ2,i = 0, the solution of Equations 5.21(7) to 5.21(9) is as follows:

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