FIG. 10.9.3 Destruction efficiencies of various compounds as a function of temperature. (Reprinted, with permission, from Air pollution control at resource recovery facilities, 1984, California Air Resources Board [24 May].)

more than 99.9% of many effluent compounds, including dioxins and furans. Excessively high temperatures and extreme variations cause cracking and spalling, with rapid deterioration of refractories. The minimum burning temperature for carbonaceous waste to avoid the release of smoke is 1500°F (816°C). A temperature less than 1500°F permits the release of dioxins and furans.

Auxiliary burners can be added to maintain combustion efficiency. Reductions in combustion efficiency are usually due to one or more factors: start up and shutdown; large changes in moisture content, heat content, or the quantity of incoming refuse; and maladjustment of the air adjustment system. Auxiliary burners burn another, more uniform fuel (such as natural gas or oil). These burners are used when furnace temperature values fall below 1600°F, thereby stabilizing combustion by maintaining a minimum furnace temperature. Operators can increase residence time by reducing the amount of combustion air.

The design of the furnace interior affects combustion efficiency. Carefully placed protrusions from the furnace wall, called arches or bullnoses, can redirect the flow of air from the grate, guiding it into turbulent eddies within the furnace. Eddy currents maximize turbulence during the combustion of gases.

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