Page 337 - Wastewater Solids Incineration Systems

298 Wastewater Solids Incineration Systems

sludge. Gross heat input includes not only the heat of combustion of the sludge
volatiles but also the sensible heat in the preheated combustion air. Autogenous com-
bustion is achieved at zero percent (0%) availability. When availability is less than
0%, additional heat input is required to bring the products of combustion to temper-
ature. In some cases this can be done by increasing inlet air temperature, reducing
exhaust temperature, or reducing the XS air level, all within certain limits. When this
is not possible because of process or mechanical considerations, it is necessary to pro-
vide auxiliary fuel to the combustion system. When availability is greater than 0%,
either the exhaust temperature or XS air must be increased or the inlet air tempera-
ture must be reduced to achieve a thermal balance. Changes in sludge solids below
the autogenous point have a pronounced effect on availability. However, increasing
the percent sludge solids above the autogenous value can be characterized by dimin-
ishing returns.