Page 78 - Wastewater Solids Incineration Systems

Combustion Technology 47

1.0 INTRODUCTION

Incineration is the most commonly used thermal oxidation process for treatment of
wastewater residuals. Other processes—such as plasma-assisted oxidation, pyrolysis,
and vitrification—are new processes that are not yet fully developed for this application.
Wastewater treatment plants (WWTPs) have used incineration for solids disposal
for more than 70 years. The first multiple-hearth furnace (MHF) was built in 1935 in
Dearborn, Michigan. Until the late 1960s, incineration using MHF was the thermal tech-
nique of choice. Today there are 250 to 260 aging MHFs in operation in North America.
In the 1970s, fluid bed incineration became the preferred thermal technique, pri-
marily because of tighter emission regulations and the increasing cost of auxiliary fuel.
The Lynwood, Washington, WWTP installed the first municipal fluid bed in 1962. It
was a small unit of 1.2 m (4 ft) internal freeboard diameter. Lynnwood was originally
sized for 91 kg/h (200 lb/hr) of dry solids. To accommodate plant expansion, the orig-
inal unit was replaced in 1989 with a 2.9 m (9.5 ft) diameter unit sized for 390 kg/h (860
lb/hr). Today, fluid bed technology has matured. Many larger fluid bed units can be
found, such as the St Paul, Minnesota facility. More recently, Lakeview, Ontario,
installed two units with dry feed capacities of approximately 3967 kg/h (8750 lb/hr) at
30% total solids and 4167kg/h (9187 lb/hr) at 27% total solids, respectively. With four
units of 4167 kg/h each under construction, the Lakeview plant of Region of Peel in
Ontario, Canada will become one of the largest fluid bed incineration plants in the
world (total installed dry-solids capacity of 400 metric tonne/d (441 ton/d). Since 1962,
more than 130 fluid bed incinerators have been installed in North America alone.
Since 1988, 53 new municipal fluid bed systems and one new multiple-hearth
system have been installed in North America. Of the fluid bed installations, 18
replaced existing MHFs.
This chapter focuses on fluid bed rather than multiple-hearth technology because
of the industry trend of installing fluid bed incinerators in new or replacement instal-
lations. Readers are encouraged to refer to the many publications available for infor-
mation on MHFs.

2.0 FLUID BED INCINERATION SYSTEM

This section addresses six specific fluid bed incinerator topics:
• Principles of fluidization, as applicable to incinerators.

• Principles of fluidization, specific to fluid bed incinerators.