Transitions - Sustainable Design: The Science of Sustainability and Green Engineering - page 131

Figure 3.9 Prototype of a liquid
injection system.
From U.S. Environmental Protection
Agency, “Locating and estimating air
emissions from sources of benzene,”
EPA/454/R-98/011, U.S. EPA, Research
Triangle Park, NC, 1998.

match the waste being handled with the combustion chamber as determined in
laboratory testing. The application is obviously limited to liquids that do not
clog these nozzles, although some success has been experienced with hazardous
waste slurries. Operating temperatures generally vary from 650 to 1650 ◦ C (1200
to 3000 ◦ F). Liquid injection systems (Fig. 3.9) are designed with residence times
of fractions of seconds as off-gases. The upward-moving off-gases are collected,
monitored for chemical constituents, and treated as appropriate prior to release
to the lower troposphere.

Fluidized Bed
Contaminated feedstock is injected under pressure into a heated bed of agitated
inert granular particles, usually sand, as the heat is transferred from the particles
to the waste, and the combustion process proceeds as summarized in Figure 3.10.
External heat is applied to the particle bed prior to the injection of the waste
and is applied continually throughout the combustion operation as the situation
dictates. Heated air is forced into the bottom of the particle bed and the particles
become suspended among themselves during this continuous fluidizing process.
The openings created within the bed permit the introduction and transport
of the waste into and through the bed. The process enables the contaminant
to come into contact with particles that maintain their heat better than, for
example, the gases inside a rotary kiln. The heat maintained in the particles
increases the time the contaminant is in contact with a heated element, and
thus the combustion process could become more complete with fewer harmful
by-products. Off-gases are collected, monitored for chemical constituents, and