OCR Text |
Show If, however, the effectiveness of incinerators is limited by a problem that is chemical in nature, then there is an alternative to trying to improve the mechanical engineering: one should be able to improve the overall performance of the incinerator by improving its chemistry. The data in Figures 7 and 8 suggest possible way to make this improvement, i.e., Figures 7 and 8 show that addition of clean fuel can increase the extent to which a toxic organic is oxidized by a factor of up to 10,000. Thus, to improve the incinerator effectiveness one installs a set of injectors along the walls of the combustion chamber, i.e.,grid of pipes with holes distributed along their length so that one can inject a clean fuel into the postflame gases as they pass through the thermal oxidation zone. This raises the concentration of combustion materials in the flue gas to a level above threshold. Rapid oxidation can then occur destroying toxic organics. Of course in such a procedure one might wind up with some of the injected clean fuel being present in the gases which are discharged to the atmosphere. This is not a problem since there are many fuels such as natural gas whose emission at a level of a few ppm is quite acceptable. It is to be remembered that in the Thermal DeNOx process NO is reduced by injecting NHa into hot flue gas. The engineering problems involve in designing and installing a grid of pipes to inject NHa for Thermal DeNOx are essentially the same as those involved in improving incineration via clean fuel injection. Since the Thermal DeNOx process has been installed on more than 75 different combustion systems with generally excellent results it seems fair to say that the engineering problems of the Thermal DeNOx process have been well solved and that the very similar problems to be expected in developing a Clean Fuel Injection process should be very manageable. Costs for Clean Fuel Injection should be relatively modest. Thus, for example if one assumes an incinerator which produces a flue gas containing 5% Oe by burning a refuse whose heat of combustion per pound of oxygen consumed is the same as natural gas, and if one assumes a natural gas cost of $5/MBTUs, then the cost of injecting 2000 ppm natural gas will be $0. 13/MBTU. Since, however, the injected natural gas oxidizes, liberating its heat of combustion, there is a credit for this energy release. If energy produced within the incinerator is valued at $3/M8TUs (60% of the value of natural gas) then the net cost of the natural gas will be $0.052/M8TUs of waste burned. In addition to this fuel cost there is also a mixing cost, which may reasonably be estimated from the published costs of Thermal DeNOx. In Thermal DeNOx process there is a significant cost for carrier gas. i.e. in order get good mixing of the injected reagent with the flue gas one dilutes the reagent with a carrier such as compressed air, steam or recycled flue gas. This increases the amount of mass being injected and provides the jets of gas being injected with enough momentum to penetrate the flue gas and achieve good mixing. In reference 10 mixing 8 |