OCR Text |
Show noted that the ultimate concentrations of all the organics are below the IO"15 mole fraction levels. The initial build up of HC1 is followed by significant decreases as it traverses the flame front. This decrease is reflected in an increase in the CI atom concentration. At the high temperature conditions in these calculations, the chlonne molecule is present in only insignificant amount. There are also considerable amounts of hydrogen molecules present. Apparently even with the excess oxygen all of the hydrogen is not being converted to water in the time scales displayed here. The hydrogen atom concentration ultimately decreases to a level that is much lower than that of the chlorine atoms. Figure 2 contains data on the concentration profiles for the case of fuel nch situation. As in the lean case there is drastic increases in temperature as one traverses the flame front. The intermediates first show an increase followed by a decrease. The chlonne atom concentration is at a considerably lower level than in the lean case. The hydrocarbon decomposition product, acetylene, levels are somewhat higher. Conversion to carbon monoxide is preferred in companson to degradation. Thus in order to have some hydrocarbon left to chlonnate, the composition of the mixture must be such that destruction of the hydrocarbons to carbon monoxide must be accounted for. Finally one notes the larger amounts of hydrogen molecules that is present. As in the case for the combustion of the lean mixture, although chlorinated organics are formed from the fuel, the destruction rate is so fast that essentially total destruction occurs. It will also be noted that the compounds with higher degrees of chlorination are always at lower concentrations than those with smaller amounts of chlorine. This is undoubtedly due to the high temperatures used in these simulations. It should be noted that there is a limit to how low a final temperature can be achieved with this scenario, since with ncher, or for that matter leaner, mixtures there will be problems of igniting the mixture. For such cases the plug flow model should be applied. The original intention was to quench the lean and rich mixtures whose compositions are given above and then mix the two packets of gas and examine the decree of chlorination. From the results given in Figure 1 and 2 it can be seen that over sufficiently long time even in the rich mixtures the hydrocarbons are all destroyed and there is indeed nothing to chlorinate. Thus chlorination can only occur at very short time. As a result w e consider the situation where some of the original fuel mixture, ethylene, is added to the product stream from the lean combustion system. In order to simplify the interpretation of the results w e have deliberately excluded the dichloromethane. Typical results for the case of a plug flow reactor can be seen in Figure 3. The ethylene that is added is at a concentration that is about a factor of three lower than all the available chlonnes in the quenched lean mixture. The necessity for quenching the mixture is that if the temperature were maintained the new fuel would simply be oxidized as before. We also found that it was necessary to quench the burnt mixture rapidly since a slow quench would favor H C 1 formation and there will be much less available chlorine. |