PDF《2.2 Sewage Sludge Incineration》

20 to

35 kilopascals (3 to

5 pounds per square inch gauge), simultaneously fluidizes the bed of hot sand and the incoming sludge. Temperatures of

750 to 925-C (1400 to 1700-F) are maintained in the bed. Residence times are typically

2 to

5 seconds. As the sludge burns, fine ash particles are carried out the top of the furnace. Some sand is also removed in the air stream;

sand make-up requirements are on the order of

5 percent for every

300 hours of operation. Combustion of the sludge occurs in two zones. Within the bed itself (Zone 1), evaporation of the water and pyrolysis of the organic materials occur nearly simultaneously as the temperature of the sludge is rapidly raised. In the second zone (freeboard area), the remaining free carbon and combustible gases are burned. The second zone functions essentially as an afterburner. Fluidization achieves nearly ideal mixing between the sludge and the combustion air and the turbulence facilitates the transfer of heat from the hot sand to the sludge. The most noticeable impact of the better burning atmosphere provided by a fluidized bed incinerator is seen in the limited amount of excess air required for complete combustion of the sludge. Typically, FBCs can achieve complete combustion with

20 to

50 percent excess air, about half the excess air required by multiple hearth furnaces. As a consequence, FBC incinerators have generally lower fuel requirements compared to MHF incinerators. Fluidized bed incinerators most often have venturi scrubbers or venturi/impingement tray scrubber combinations for emissions control. 2.2.1.3 Electric Infrared Incinerators - The first electric infrared f........