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Source: M. Henmi, K. Okazawa, and K. Sota, 1986, Energy saving in sewage sludge incineration with indirect heat drier, National Waste Processing Conference, Denver, 1986 (ASMER).

Note: Values in parentheses are average values. All units are in metric (SI).

Source: M. Henmi, K. Okazawa, and K. Sota, 1986, Energy saving in sewage sludge incineration with indirect heat drier, National Waste Processing Conference, Denver, 1986 (ASMER).

Note: Values in parentheses are average values. All units are in metric (SI).

porting it. As the air flow increases, the bed expands and becomes fluidized. The solid waste in the sludge can be destructed by either combustion or pyrolysis.

During combustion the organic material is turned into carbon dioxide:

The heat of combustion helps maintain the fluidized bed at a temperature of about 1400°F (760°C).

In the pyrolysis process, the sludge is decomposed in the presence of inert gases at 1400°F (760°C), which yields hydrogen, methane, carbon monoxide, and carbon dioxide. For pyrolysis, auxiliary heat is required to maintain the fluidized bed at the high reaction temperature:

The operation of the fluidized-bed incinerator is optimized by control of the airflow rate and the bed temper ature. Since reaction rates are related to bed mixing and the source of agitation is the fluidizing air, operators can adjust reaction rates by changing the airflow supply. The bed temperature is usually maintained between 1300 and 1500°F (704 to 815°C). For complete combustion (odor-free operation), about 25% excess air is needed (Rabosky 1974).

Organic material can be deposited on the sand particles (agglomerative mode) and removed by continuous or intermittent withdrawal of excess bed material. An alternative mode of operation (nonagglomerative) combines the organic ashes with exhaust gases and collects them downstream with dust collectors.

The main advantages of fluidized-bed incinerators include the uniformity of the bed, the elimination of stratification and hot or cold spots, the high rate of heat transfer for rapid combustion, the elimination of odor and the need for afterburners, and the low maintenance requirements of the process. The disadvantages include the high operating-power requirement, the need for auxiliary fuel

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