INFLUENCE OF SLUDGE CAKE CONCENTRATION ON THE OPERATING VARIABLES IN INCINERATION BY DIFFERENT TYPES OF FURNACES

The influence of cake concentration on fuel consumption, air requireme nt and flue gas production in incineration of sewage sludge is discuss ed. Fluidized bed (FBF), multiple hearth (MHF) and rotary kiln (RKF) f urnaces are considered as alternatives together with the optional use of an afterburning chamber where exhaust gases are taken at 950 degree s C for 2 s with an oxygen concentration of 6% by volume. It clearly a ppears that, if an afterburning chamber is used, and total minimum fue l consumption can be achieved at an optimal value of cake concentratio n (45.9% for FBF and 32.5% for MHF) when autogenous conditions are rea ched in the furnace and air addition is no longer needed in the afterb urning chamber. At higher concentrations, abundant exhaust gas product ions, due to the dilution air needed in the furnace, can considerably increase fuel consumption in the afterburning chamber, especially in M HF operation. In the rotary kiln furnace, fuel requirement decreases o ver the whole range of cake concentration as no conditions for autogen ous combustion in the furnace can be achieved. (C) 1998 Published by E lsevier Science Ltd. All rights reserved.