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128 Wastewater Solids Incineration Systems

circulating water are removed continuously from the steam drum. Continuous blow
down often represents 3 to 5% of the total feedwater to the boiler.

4.5.5 Soot Blowers
Boiler efficiency is affected by the buildup of ash or soot on boiler tubes. Tubes can be
arranged to make cleaning easier. A high-pressure spray of air or steam can be used
to periodically blast each tube area that might be expected to show ash buildup. For
waste heat boilers, steam is the usual cleaning medium because it is available from
the boiler. A combination of inspection doors, automatic soot blowers, and hand
lance ports for manual cleaning are recommended. The frequency of soot blowing
operations must be determined for each installation and be timed to preserve heat
transfer capability and performance of the boiler. This is determined on a trial-and-
error basis. Soot blowers are intended to be used to keep tubes clean rather than to
remove baked on ash deposits after they have accumulated excessively and hardened
on tube surfaces.

5.0 SUMMARY

Although there are many options available for heat recovery, the most effective
method is recuperation and air preheating. Further, recovered energy as steam or
heated thermal fluids to thermally dewater feed cake to the incinerator is another
form of primary recovery and reuse that can dramatically reduce auxiliary fuel
requirements. After air preheating or thermal dewatering, options for secondary heat
recovery include heat exchangers for plume suppression, economizers, waste heat
boilers, or thermal oil heaters. Optimization of heat recovery is essential to efficient
energy operation of a plant; it is also what makes incineration with energy recovery a
bona fide form of beneficial use.

6.0 SUGGESTED READINGS
American Iron and Steel Institute (1979) High-Temperature Characteristics of Stain-
less Steel; American Iron and Steel Institute: Washington, D.C.
American Petroleum Institute (2003) Calculation of Heater Tube Thickness in Petro-
leum Refineries, 5th ed.; API Standard 530; American Petroleum Institute:
Washington, D.C.