Transitions - Sustainable Design: The Science of Sustainability and Green Engineering - page 132

Figure 3.10 Pressurized
fluidized-bed system.
From U.S. Department of Energy, TIDD
PFBC Demonstration Project, U.S. DoE,
Washington, DC, 1999.

PRESSURIZED
FLUIDIZED-BED BOILER
PRESSURE
VESSEL
COMPRESSED
AIR

AIR

GAS
TURBINE

GEN.

CLEAN
HOT GAS

DOLOMITE/
LIMESTONE

BED
VESSEL

STEAM

COAL
WATER

GEN.

STEAM
TURBINE
FEED
WATER

CYCLONES

WASTE
HEAT
REDOVERY

BED
PREHEATER

CONDENSER

ELECTROSTATIC
PRECIPITATOR

ASH
COOLER

STACK

FLY ASH

CYCLONE
ASH

BED ASH

FEED WATER
INLET

TO DISPOSAL

treated as appropriate prior to release, and the falling ash is collected, monitored
for chemical constituents, and subsequently treated prior to ultimate disposal.
Most organic wastes can be incinerated in a fluidized bed, but the system is
best suited for liquids. Operating temperatures generally vary from 750 to 900 ◦ C.
Liquid injection systems 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.

Multiple-Chamber System
Contaminants are turned into a gaseous form on a grate in the ignition chamber
of a multiple-chamber system. The gases created in this ignition chamber travel
through baffles to a secondary chamber where the actual combustion process
takes place. Often, the secondary chamber is located above the ignition chamber
to promote natural advection of the hot gases through the system. Heat may be
added to the system in either the ignition chamber or the secondary chamber, as
required for specific burns.
The application of multiple-chamber incinerators generally is limited to solid
wastes, with the waste entering the ignition chamber through an open charging
door in batch, not continuous, loading. Combustion temperatures typically hover
near 540 ◦ C for must applications. These systems are designed with residence
times of minutes to hours for solid hazardous wastes as off-gases are collected,