Page 127 - Wastewater Solids Incineration Systems

Combustion Technology 95

®
FIGURE 5.19 Thermal energy balance for GLASSPACK application at North Shore Sanitary
District, Zion, Illinois (Btu/hr 0.2931 W; Btu/lb 2.326 kJ/kg; lb/hr 0.4536 kg/h)
(courtesy of Minergy Vitrification LLC).

Waste Management Board, 2001). There are many variations in process operating
temperatures and pressures that will affect the byproducts, which may be in the form
of a syngas, char or slag, oils, and reaction water (Figure 5.20). Operating tempera-
tures may be in the range of 815 to 1815°C (1500 to 3300°F) and pressures may be 2800
kPa (400 psi). Process dynamics and products vary considerably depending on the
type of feed. Pilot testing is typically required to determine yields of the offgases and
residues. With WWTP solids, the process has proven to be expensive. Typically, the
economics of energy recovery are not positive because of low calorific value and high
moisture content of the feed cake, which must be heat dried before gasification. The
syngas produced generally has a relatively low heating value of approximately 4000
3
to 8000 kJ/m (105 to 210 Btu/cu ft) and needs to be combined with other higher
quality fuels, such as natural gas, before it can be used. The char and oils produced
will have less heating value than those produced in a pyrolysis system because of
partial combustion of the organics in the gasification process.
Gasification systems have been used more widely in Europe and Asia, both of
which use high calorific value feed stocks such as wood wastes. Advantages over