Incineration, furnace design

Selective catalytic reduction (SCR) and selective noncatalytic reduction processes (SNCR) are widely employed in large industrial and utility boiler plants, as well as in municipal waste incineration plants and other combustion processes. They are used to complement mechanical improvements (such as low NOx burners and furnace design modifications) as an aid to reducing the emission levels of NOx, S02, and other noxious gases into the atmosphere. 

The types of incinerators used are listed in Table 3. Municipal solid-waste furnace designs have evolved over the years, with the newer waste incinerators being waste-to-energy plants that produce steam for electric power generation. 

These techniques are applied in other industrial sectors, such as steel and non-ferrous metal production and waste incineration. Judging on a technical basis, they may be transposed to foundry furnace types that show a risk of dioxin formation cupola, rotary and electric arc furnaces melting iron and steel (Section 3.8.2). For new and existing installations primary dioxin reduction measmes, such as efficient combustion, furnace design modifications and scrap quality control have to be taken into consideration on a case-by-case basis, before turning to secondary measures. 

Elaborate on the incineration process. What are the basic design parameters to consider in building an incineration furnace ... 

The design eost will be a function of the incinerator cost plus installation which is normally in the range of 4 to7%. This cost should be doubled to include engineering services during project construction. It should be noted that with the electric furnace, the power needed to start up results in a large connected load. In areas of the country where there are high demand charges for electric power, this system can be economically impractical. 

These may be horizontal or vertical shell boilers or watertube boilers. They would be designed to suit individual applications ranging through gases from furnaces, incinerators, gas turbines and diesel exhausts. The prime requirement is that the waste gases must contain sufficient usable heat to produce steam or hot water at the condition required. 

One incinerator that has been evaluated rather extensively and for which test results have been reported is the liquid chemical waste incinerator facility owned by the Metropolitan Sewer District (MSD) of Greater Cincinnati, Ohio (1 ). The MSD facility uses a rotary kiln and liquid injection cyclone furnace to incinerate a wide variety of liquid industrial chemical wastes. The total design heat release rate is 120 million kJ/h (114 million Btu/h). Tests conducted over a wide temperature range ( 900°C to 1300°C) for six Appendix VIII chemicals (carbon tetrachloride, chloroform, hexachlorobenzene, hexachlorocyclo-pentadiene, and hexachloroethane) have shown DREs equal to or very near 99.99%. 

Our statistician colleague did some work, he looked into the records of crematoria in Germany during the last war, and it would appear that the authorities there were presented with a similar problem - that they came up against a thermal barrier. They could not design a furnace that reduced the mean incineration time to a very practical effective level. So we started to look at why there is this thermal barrier with human tissues."... 

Incineration is another reclamation technique in use. The multiple-hearth furnace can operate under designed conditions for years with low maintenance and low energy consumption (108). The fluid-bed incinerator is also very effective (108). Tests have shown that all organic compounds are decomposed and most carbon residue oxidized. The ash is of high nickel value being predominately... 

Proper design and operation of an incinerator require attention to temperature, turbulence of the mixture being combusted, and residence time at the incineration temperature, generally referred to as the 3rs of combustion. To achieve efficient combustion, every part of the waste stream must reach an adequately high temperature for a sufficient period of time, and there must be adequate mixture of waste and oxygen. Cool spots can occur next to the furnace s walls where heat is extracted such as in boiler-type furnaces. Cold spots are less likely in refractory lined furnaces, such as in cement kilns. 

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