| OCR Text |
Show There is great concern about not only destroying the organics in the waste stream, but ensuring that no toxic organics are formed as trace byproducts that escape the system. Data exist which indicate that MSW incinerators can be operated in such a manner that they produce relatively high concentrations of highly toxic cogeners of chlorinated dibenzo-p-dioxins (CDD) and furans (CDF). The data have further indicated that such emissions are controllable via the combustion process, but this must be ensured under all normal and abnormal occurrences. Recent studies have also indicated that dry scrubbers - fabric filter combinations can remove CDD/CDF, but the transference to the fly ash may make the solid residues hazardous8. Combustion control of the emission of trace organic species (such as chlorinated dioxin) from MSW and HW combustors is based upon the generation of high temperature, fully mixed, oxygen rich combustion products. Gas cofiring could be used to improve the combustion environment within the furnace over a range of steady and unsteady conditions so as to ensure control of trace organics. Also, gas fired afterburners could be used downstream of the waste firing zone to destroy unreacted components . . The high temperature well mixed conditions designed to reduce organic and CO emi ssi ons wi 11 favor the formati on of tJOx. The term IINOx -Co tradeoffll is sometimes used to refer to this inverse relationship between the emissions of NOx and unburned material. There are a number of combustion modification techniques that are suitable to control NOx including flue gas recirculation, staging of air and staging of fuel. In particular, reburning with natural gas is a technique in which natural gas is introduced downstream of the main heat release zone in a controlled manner to effect a reduction in NOx• This technique has shown to achieve greater than 50 percent reduction in NOx (Ref. 9) while still being compatible with conditions suitable for control of unburned material. The residuals that remain after the combustion of municipal and hazardous waste must be disposed of in an environmentally acceptable manner. Toxic heavy metals contained in the residuals can be leached from solids and migrate into groundwater if the residuals are not stabilized properly and if 3 |
