United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-86/102 Feb. 1987
i i
Project Summary
Costs of Air Pollution
Abatement Systems for
Sewage Sludge Incinerators
Gopal Annamraju, Yatendra Shah, and M. L Arora
Capital and operating costs were cal-
culated for applying six different air pol-
lution control systems to municipal
sewage-sludge incinerators that were
using multiple-hearth furnaces. The
systems involved three principal types
of air pollution equipment—wet scrub-
bers, fabric filters, and electrostatic pre-
cipitators—applied to three different
plant sizes (plants incinerating 36, 72,
and 300 tons of dry sludge per day in
one, two, and eight multiple-hearth fur-
naces, respectively). The six options
were (1) venturi/tray scrubber with a
40-in. pressure drop, (2) fabric filter sys-
tem operating at 500°F and equipped
with an upstream temperature control,
(3) fabric filter system operating at
500°F and equipped with a heat ex-
changer and a scrubber for SO2 reduc-
tion, (4) electrostatic precipitator (ESP)
with upstream limited temperature and
humidity control, (5) same as Option 4
but with an additional downstream wet
scrubber for SO2 reduction, and (6) ESP
with upstream temperature control and
an SO2 scrubber.
Results indicated that all three types
of controls could achieve a total partic-
ulate removal efficiency of 99 percent
but that the venturi/tray scrubber op-
tion entailed the lowest capital cost and
the highest annual costs.
This Project Summary was devel-
oped by EPA's Water Engineering Re-
search Laboratory, Cincinnati, OH, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
In the United States, wet scrubbing
devices are normally used to control
particulate emissions from multiple-
hearth furnaces designed for incinerat-
ing sewage sludge from municipal
wastewater treatment plants. Fabric fil-
ters and electrostatic precipitators
(ESP's) offer possible alternatives to
wet scrubbers. This report evaluates the
feasibility and associated costs of using
these three control devices.
Budget estimates were made for six
different system configurations involv-
ing three primary control devices, a sul-
fur dioxide (S02) scrubber, and ancillary
devices (e.g., heat exchangers) for ap-
plication at three different sizes of mu-
nicipal sewage sludge incineration
plants (i.e., plants processing 36, 72,
and 300 tons of dry sludge per day and
using one, two, and eight multiple-
hearth furnaces, respectively).
The report presents the feasibility of
using each of the three control devices,
the process for selecting a control sys-
tem, cost data, and detailed costing
methodology.
Emission Control System
Characteristics
The following factors must be consid-
ered when judging the practical appli-
cability of an emission control system
for sludge incinerators:
• The high degree of particulate re-
moval required (99 percent in this
study).
• The presence of condensable
fumes (requires that gas be cooled
as much as practical).
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• The temperature of the gas enter-
ing the control equipment.
• The high moisture content of the
gas.
• The presence of acid gases (such as
chlorides).
Wet Scrubbers
Wet scrubbers (generally venturi or
impingement type) have traditionally
been used to control particulate emis-
sions from multiple-hearth incinerators.
Though they have achieved compliance
with emission standards at many incin-
erators and have reduced odor prob-
lems, their power requirements are
high.
Fabric Filters
Fabric filters are used widely for par-
ticulate control in the metallurgical in-
dustry, where hot gasses and fine
fumes are encountered. A large fabric
filter system could be used at sludge
incinerators if emission gasses could be
cooled to at least 500°F. Cooling could
be accomplished by water spray or air
dilution. A smaller system could be
used if the gas were cooled to 200° to
SOOT, but some moisture condensation
might occur. Fabric filter systems are
rather large, however, and they do not
remove odors.
Electrostatic Precipitators
High-voltage ESP's have successfully
collected both solid and liquid particu-
late matter from smelters, steel fur-
naces, petroleum refineries, cement
kilns, acid plants, and many other oper-
ations. These devices can be operated
in the wet or dry mode (i.e., above or
below the gas dewpoint). Power con-
sumption is low on dry ESP's; but corro-
sion resulting from acid gases can be a
problem, and the system does not re-
duce odors. Wet ESP's also have low
power consumption. In addition, they
remove acid gases and soluble material
and reduce odor problems.
Cost Estimates
Table 1 summarizes the capital and
annual costs for all six options at the
36-, 72-, and 300-mgd plants. The costs
are based on an arrangement in which
each incinerator has its own captive air
pollution control equipment (i.e., two
identical systems are required at a plant
with two incinerators, and eight identi-
cal systems are required at a plant with
eight incinerators). The capital cost
evaluations reflect the cost savings of
having more than one identical system
installed.
Conclusions
Technical feasiblity studies indicated
that all three types of controls (wet
scrubbers, fabric filters, and electro-
static precipitators) could theoretically
achieve the goal of 99 percent particu-
late removal.
The venturi/tray scrubber option en-
tailed the lowest capital cost, but annual
costs were highest for this option be-
cause of the pressure drop (40 in. of
water) thought to be necessary for 99
percent particulate removal resulted in
high energy costs. The advantages of
the wet scrubber are that it cools gas to
120°F, achieves compliance with emis-
sion standards, removes acid gases and
other soluble material, and reduces or-
ganics and odors. The venturi/scrubber
has been used for most sewage sludge
incinerators and has a history of suc-
cess.
The fabric filter with the sulfur dioxide
scrubber system has a capital cost dou
ble that of the venturi/scrubber systerr
and an annual cost nearly as high. This
system is known to provide excellen
particulate removal; however, the higf
moisture content and temperature
changes associated with a multiple
hearth sewage sludge incinerator coulc
easily cause a mud pack to be formec
on the bags and make the bags inopera
ble. Also, other research on a sid<
stream from an incinerator indicatec
particulate material was not removec
by the shaker system used to clean th(
bags, and it was necessary to brush th(
fly ash from the bags before returning
the bags to service.
The electrostatic precipitator pre
ceded by a sulfur dioxide removal sys
tem had a capital cost double that of thi
scrubber system, but had a lower an
nual cost than the venturi/scrubber sys
tem. Although this system (wet ESP) ap
pears to have the same capability as thi
scrubber/venturi system, it does no
have a proven record of performance.
Both the wet ESP and fabric filter syj
terns should require a backup scrubbe
system (in both cases, the sulfur dioxid
scrubber system) to ensure that the ir
cinerator can be operated with a polk
tion abatement system if the primar
system fails.
The full report was submitted in fulfil
ment of Contract No. 68-03-1821 b
James M. Montgomery Consulting Er
gineers. Inc. under the sponsorship c
the U.S. Environmental Protectio
Agency.
Table 1. Capital and Annual* Costs for Plants with One, Two, and Eight Multiple-Hearth Furnaces"1" (in thousands of mid-1985 dollars)
Option 1 —
venturi/tray
scrubbers
Option 2—
fabric filter
Option 3—
fabric filter
and SO2
scrubber
Option 4 —
ESP
Option 5 —
ESP followed
by SO2
scrubber
Option 6—
ESP preceded
bySO2
scrubber
Plant size
tons dry Number of Capital Annual Capital Annual Capital Annual Capital Annual Capital Annual Capital Anni
sludge/day incinerators costs Costs Costs Costs Costs Costs Costs Costs Costs Costs Costs Cos
36 1 $1,007 $ 595 $1,484 $ 547 $ 2,062 $ 547 $ 1,850 $ 404 $ 2,055 $484 $2,112 $4
72 2 1,757 1,141 2,598 781 3,613 1,018 3,243 740 3,601 881 3,701 8
300 8 6,448 4,452 9,531 2,463 13,247 3,895 12,074 2,828 13,408 3,375 13,781 3,4
"Consists of direct operating and maintenance costs and indirect costs including capital recovery.
+ Options 3, 5, and 6 have an additional scrubber for SO2 control. Gas flow from each incinerator is 19,053 scfm or 94,469 acfm at 1142°F. Avers
moisture content is 39.72 percent Capital recovery costs are based on 10 percent interest rate and a useful fife of 10, 20, and 20 years for vent
scrubbers, fabric filters, and electrostatic precipitators, respectively.
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Gopal Annamraju and Yatendra M. Shah are with PEI Associates, Inc..
Cincinnati. OH 45246; and Madan L Arora is with James M. Montgomery.
Consulting Engineers, Inc., Pasadena, CA 91109.
Howard Waft is the EPA Project Officer (see below).
The complete report, entitled "Costs of Air Pollution Abatement Systems for
Sewage Sludge Incinerators," (Order No. PB 87-117 743/AS; Cost: $13.95,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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