Common Problems and Remedies
Whi
volur
ficulti
cineration systems can be very effective for
i. they have experienced operational dif-
scause of problems in furnace and support system
design. These difficulties have included inadequate dewater-
ing, equipment failure, excessive maintenance, and increas-
ed fuel consumption. Not only have these difficulties
resulted in increased costs for fuel, equipment replacement,
or repairs and labor, but in some cases installations have
Common problems encountered in the oper
perators
ii iy ic
blem:
United States December
Environmental Protection 1986
Agency
vvEPA
832R86108
Sludge
Incineration
Problems
and
Remedies
Sludge Incineration Problems and Remedies
Introduction
-in be an :.'
rig wastev ties are
adequa'
volume reduction pric addi-
rganic
mmarizes common problems
>r systems and provides sugges-
-or more detailed information the
tion ci
ice the
after-
cinerators. This evalu.
1985.
erway which will
:il informs*
EPA-OMPC (WH-595)
401 M Street SW
Washington DC 20460
(202) 382-7356
EPA-WERL
26 W. St. Clair Street
Cincinnati, OH 45268
(513) 569-7645
Mention of trade names or commercial products does not
constitute endorsement or recommendations for use.
Prepared by Engineering-Science, Inc.
CENTRAL SHAFT
COOLING STACK
COOLING AIR
EXHAUST DAMPER
FIGURE 1. SCHEMATIC OF MHF INCINERATOR SYSTEM
The multiple hearth furnace consists of a
cular steel shell with a series of horizontal h
and a rotating central shaft. Attached to the central
shaft are rabble arms which constantly move the
sludge on the hearths to aid in drying and combus-
tion. Sludge enters at the uppermost hearth for dry-
ing, then drops to lower hearths for combustion,
with the bottom hearth acting as an ash cooling
zone. Air for cooling and combustion is circulated
through the central shaft and rabble arms.
rFEEO I
COMBUSTION
ARM BLOWER
K
ASH TO
DISPOSAL
SHAFT COOLING
AIR FAN
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Applicability
The applicability of incineration systems is based on
economic, operational and public acceptability comparisons
with other sludge disposal options. For smaller wastewater
plants (less than 10 mgd), land application, landfilling, or
composting are usually more economical. Often, smaller
facilities do not have the professionally trained personnel,
adequate spare parts inventories, or training programs to
make the incinerator operation cost effective. For larger
wastewater plants located in urban areas, incineration may
be the most acceptable sludge management alternative due
to land use restrictions.
The applicability of an incineration system for a given
community may be dependent upon the individual features
of MHFs and FBFs. A comparison of the advantages and
disadvantages of the two systems is presented in Table 1.
Design and Operational Considerations
The proper selection of system components is essential
to ensure complete combustion, low maintenance, fuel effi-
cient operation and control of emissions. Process and sup-
port system design considerations should include: (1) defini-
tion of sludge feed rate and properties; (2) development of
heat and material balances; (3) establishment of an overall
sludge volume safety factor to avoid over-sizing units; (4)
provisions for matching and sizing of incinerator and support
equipment to the sludge feed rate and properties; (5) provi-
sions for incremental system expansion or multiple units in-
stead of oversizing the initial system; and (6), where feasible,
provisions for an energy recovery system to reduce plant-
wide energy consumption.
.s) must De supplied
;he afterburners. Heat
from the ^
jresent. Ti-
j the
3nd
minimize the product: . iirable gases ar
MHF
NTAQES
FBF
DISADVANTA
Less complicated sludge More complica!
feed system feed system
Less complex ash handling More complex ash handling
equipment equipment
Difficulty handling sludges
with low ash melting
temperatures
Less susceptible to corrosion Preheating equipment and
from excessive chlorides as other hot-side components
the temperature at which the are very susceptible to
acids condense is higher corrosion
due to the lower pressure
conditions in an MHF
DISADVANTAGES
ADVANTAGES
bute to maintenance cos!
Afterburner rnay be required High exhaust gas temper-
to meet new air emis; ature mav eliminate the need
regulations
for an afterburner
'up and shut-dow^ ;own
;an
litiori due to
of thermal
linings mass provided by the sand
Requires a,
during
'i or fuel required
* dusty Control of pr .-.hat
easier
P 9 ""PUI MATIP nc
rlUUnt /. ci^ntlvlMilw \Jf
INPINFRATOR CIYCTFVI
- Trrn
lure COniairtinQ a SanQ DeOf TlUlQIZiny 3n G.'/nC£S,
Dewatered sludge is pumped or carried by screw
snd combiifilinn of vo/pf/'/p ^o//rf^ r» ~ »/-.- The
- nhf\vf* thp* nift'itri /-ifrH*''s ' -'
.. tiieuia aiium> lui aepa' i i
tlnn nt fanrl Anframo/f in ach an/1 nrnvirlei rtoton T V
3 emramea in asnana proviaet, aewn
iion time for continued combustion The sand bed
h
so,8S«,n Wsempe,, «,,,,,
;
POM . N U
;:n ' "* ' p
r~i =/
iSES
~twf
ESftL
1
Problems and
Remedies
Problem and Consequences
General
Inadequate sludge
dewatering, resulting in
increased fue
sumption and decreased
capacity
Oversized furnace, in-
creasing unit operation and
maintenance costs
Varied feed sludge rate
and composition, affecting
power consumption
Slag and clinker formation,
increar mce
tenance
increasing mamtc
costs
Suggested Remedy
Replace or upgrade ex-
isting dewatering
equipr
Alter hearth use in existing
MHFs
Install multiple furnaces of
smaller size or furnaces
that can be modified
Install sludge equalization
and blending tanks
For MHFs, adjust excess
air, readjust rabble teeth,
change chemical con-
ditioning, shred dry sludge
cakes, provide poke holes
at perimeters, enlarge drop
holes, maintain com-
bustion zone temperature
below 1,650°F
For FBFs, adjust excess
air, maintain combustion
zone temperature below
1,650'F
Maintain steady sludge
feed
Use CO monitors i
> expert advice
Increase excess air
Con;
Inspection and
keeping to p"
problems
requirements. The s
jie to maii
orm air an
!e constant
Problem and Consc
Rabble arn
resulting in bending and
shortening of rabble arm
life
Rabble teeth cor; <
decreasing tooth life
Inadequate capac
improper orientation and
vibration of ID far
suiting
couples
replacement
FBFs:
Refractory dome
reducing dome life
if metal
Maintain steady sludge
feed
Provide adequate cooling
air
Use castable refractory
insulation
Provide temperature
control to reduce short
term high temperatures
Minimize ferric chloride
use
Use two-part looth
Replace fan and modify
duct work
Install automatic damper
Provide vibration isolators
Install vibration shut-off
switches
refractory c!
Use Incone
Limil temperature changes
to less than 50" F i
» Preheat fluidizing air
Improve dewatering to
reduce water content
* Minimize ferric c
rtunities for
A number
similar problems have .--ration
while simultaneously
cedure?
benefit
rature, an
bustier
ilute
improved
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