| OCR Text |
Show show that as the pressure is increased, the destructive efficiency decreases for pressures up to about 10 atm and then increases (100 atm was the highest pressure considered). These stirred reactor calculations do not indicate any advantage in improved destructive efficiency of operating at high pressures (at least up to 100 atm). The predictions of the model at high pressure are tentative since many of the pressure dependencies of reaction rates involving chlorinated species have not been investigated. We investigated the addition of methane and ethane to the chloroethane-air mixture and its effect on destructive efficiency. The addition of methane is of interest because it constitutes a large fraction of natural gas that might be used to help incinerate chlorinated hydrocarbons. We performed calculations of chloroethane reacting with an equal amount of either methane or ethane in air. The calculations assumed a stoichiometry of one, a residence time of 0.1 sec, a pressure of 1 atm, and a temperature of 1200 K. With the addition of methane-air, the destructive efficiency was reduced from 99.989 to 99.979%. With the addition of ethane-air, the destructive efficiency decreased significantly from 99.989% to 99.916%. Thus, these preliminary stirred reactor calculations did not indicate any benefit of adding methane-air or ethane-air with respect to the destructive efficiency of chloroethane. Sensitivity We used sensitivity analysis to provide insight into how individual reaction rate constants affect the destructive efficiency of chloroethane. The PSR code provides first-order sensitivity coefficients of species concentration with respect to rate constants. The sensitivity of the chloroethane concentration (and thus the destructive efficiency) to the rate constants is given for the most sensitive reactions in Fig. 6. These results show that the reactions that exhibit the highest sensitivity are those associated with the H2/CO submechanism. This finding is not surprising because Warnatz has shown that hydrocarbon flames give similar sensitivity results [24]. Almost all the reactions involving chlorinated species that give large sensitivities involve the fate of the Cl atom. The most highly ranked of these reactions are C2HSCI + Cl => CH2ClCH2 + HCl C2HSCI + Cl => CH3CHCl + HCl (189) (191) These reactions exhibit negative sensitivities which means that increasing their rate decreases the concentration of C2HSCI (and increases the destructive efficiency). They are the primary reactions consuming chloroethane under conditions near an equivalence ratio of one. In general, reactions which compete with the above reactions for Cl atoms give positive sensitivities and decrease the destructive efficiency. This trend can be seen in the sensitivities for the following reactions (Fig. 6): HCO + Cl => co + HCl (3S) Cl + OH + M => CIOH + M (28) Cl + H02 => HCl + O2 (9) . - S- |
