Page 94 - Wastewater Solids Incineration Systems

Combustion Technology 63

FIGURE 5.7 The Puerto Rico fluid bed incineration plant (6000 lb dry solids per
hour) (courtesy of Degremont Technologies – Infilco).

could be composed of heat exchangers for preheating the combustion and for plume
suppression or a waste heat boiler for steam generation, or both. The air pollution
control system could be either a dry-ash system or a wet-ash system.
A typical process flow diagram of fluid bed incineration system using a wet-ash
system with a hot wind box and heat recovery by heat exchangers is shown in Figure
5.8. Solids are dewatered using belt filter presses and pumped to the furnace via
piston pumps through two or four feed ports. no. 2 fuel oil or natural gas is used as
auxiliary fuel during startup and operation as needed. The freeboard operates at a
design temperature of approximately 843°C (1550°F). The reactor offers an expanded
freeboard to allow deceleration of the larger particles to minimize sand carry-over
and maximize carbon burnout. The bed makeup sand may be fed to the furnace
pneumatically during operation, if required. The hot wind box furnace in this
example is equipped with a refractory arch that supports the sand bed and evenly
distributes the air. To minimize auxiliary fuel use, fluidizing air is preheated to
approximately 675°C (1250°F) in an external tube and shell heat exchanger using the
exhaust flue gas of the reactor as a heat source. The air pollution control system