United States
Environmental Protection
Agency
Municipal Environmental Research *> W
Laboratory ' "'
Cincinnati OH 45268
Research and Development
EPA-600/S2-83-083 Nov. 1983
&ERA Project Summary
Plant-Scale Demonstration of
Sludge Incinerator Fuel Reduction
Albert J. Verdouw, Eugene W. Waltz, and Webb Bernhardt
A field research and demonstration
project was conducted to reduce fuel con-
sumption in sludge incinerators by using
a more fuel efficient incinerator operating
mode and improving instrumentation
and control systems. A low-capital-cost
approach to achieving major fuel reduc-
tion was operationally demonstrated by
the City of Indianapolis Department of
Public Works at its Belmont Wastewater
Treatment Plant Incineration Facility in
Indianapolis, Indiana, using eight
conventional multiple-hearth incinera-
tors.
The existing incinerators were upgraded
with modern instrumentation and
control systems for sludge flow rate,
fuel flow rate, fuel flow control, airflow
control, and exhaust oxygen analysis of
the combustion process. A more fuel
efficient operating mode was developed
from an extensive program of combus-
tion engineering measurement, testing,
and operational analysis. The incinerator
operators were then given a training
program on the new equipment and
operating mode. The new operating
mode with improved instrumentation
and control systems was also effective
in enabling the existing incinerators
(equipped with low-energy, cyclonic-
type scrubbers) to meet particulate
emission standards.
During an 8-month period of routine
operations, fuel consumption was
reduced 34 percent, thus saving more
than $900,000 per year. And because
all eight of the incinerators, using the
new operating mode, passed official
particulate emission tests, the city
saved more than $2 million in capital
costs that would have been required to
retrofit the incinerators with new
scrubbing equipment.
This Project Summary was developed
by EPA's Municipal Environmental
Research 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
Incinerating municipal sewage sludge
often uses large amounts of auxiliary
fuel. Increasing energy costs have made
incinerator fuel consumption a major
problem for many treatment plant opera-
tions. Using more fuel efficient operating
modes and improving existing instrumen-
tation and control systems can reduce
incinerator fuel consumption and prove
cost effective for municipal operators.
The City of Indianapolis Department of
Public Works developed a new, more
fuel-efficient incinerator operating mode
through extensive operational testing at
its Belmont Wastewater Treatment Plant
Incineration Facilities. These tests deter-
mined, and operationally verified, the
changes and improvements needed to
reduce fuel consumption and achieve
steady incinerator operation at reduced
operating temperatures. The operational
testing and analyses involved:
• A combustion engineering analysis of
the multiple hearth incinerator operat-
ing process.
• Extensively instrumenting one incin-
erator to measure (a) excess air, (b)
internal incinerator gas and sludge
temperatures, (c) flow rates of all
incinerator air supply sources and
exhaust gas locations, (d) exhaust gas
composition, and (e) total and burner-
specific fuel flow rates.
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• Parametric experimental testing to
determine the effect of the following
incinerator variables on fuel consump-
tion: (a)excess air, (b) sludge load rate,
(c) sludge moisture and volatile
content, (d) incinerator airflow, (e)
combustion zone location, (f) incinera-
tor temperature, (g) fuel burner
settings, (h) use of rabble arm cooling
air, and (i) sludge residence time.
• A comparative analysis of the
analytical and experimental data to
determine the relationship between
specific fuel consumption and key
incinerator operating variables.
• A kinetic incinerator analytical model
to predict the lowest possible fuel
consumption from optimum incinera-
tor operation. The model's predictions
of incinerator fuel requirements
provide a process-rate-determined
solution that accounts for the gas
temperatures, sludge composition,
and heat transfer rates that vary
throughout the incinerator volume.
• Using these test results and analyses
to specify a new, more fuel-efficient
operating mode.
New Operating Mode and
Control System
The new operating mode and control
system improvements were used in full-
scale plant operations. The operating
mode included specific, detailed settings
for optimizing the combustion zone
location, airflow management, fuel
burner use profiles, and air and fuel flow
rate guidelines for various sludge cake
load ranges and moisture and volatile
characteristics. The key features of the
operating mode involve operational
settings to maintain:
(1) a steady sludge cake feed rate,
(2) the lowest possible incinerator draft
to reduce air leakage,
(3) the proper oxygen level associated
with a given load rate and cake
moisture and volatile content to
maintain the most efficient excess air
level,
(4) the minimum required fuel flow rate
for a given load rate and cake
moisture and volatile content (see
Figure 1 for an example),
(5) control of combustion zone location
with burner use firing profiles and air
flow management, and
(6) optimum throughput rate with proper
center shaft speed.
These guidelines and other equipment-
specific techniques and instructions
were included in an operational manual
400
300
I
.2 200
o
"S
100
Figure 1.
60 65 70 75
Moisture (%)
Fuel flow guidelines in liters of
oil per hour for 6.4 metric tons
(7 tons} of sludge cake per hour.
for training and instruction programs for
the operators.
The older instrumentation and control
systems of the Indianapolis operation
were also upgraded to enable a greater
degree of remote control by the operator
in conjunction with the new operating
mode. New systems were designed and
installed for (1) air flow control, (2) fuel
flow control, (3) oxygen analysis, (4) fuel
flow rate measurement, and (5) sludge
cake load rate measurement.
The total cost for the engineering
design, purchase, and installation of
these new systems averaged $20,000
per incinerator.
Results
Fuel Consumption
A full-scale plant demonstration deter-
mined that $900,000 per year of fuel was
saved by using a more fuel efficient op-
erating mode and upgrading the incinera-
tor control systems. The 8-month opera-
tional test period from November 1980
through June 1981 was compared with
the baseline operational year for 1977,
the last full calendar year of operations
before any changes were initiated in the
incinerator operating mode or control e-
quipment. Plant operational records for
both periods were used to obtain fuel con-
sumption, load rates, incinerator operat-
ing hours, and sludge cake moisture and
volatile data for comparative analysis.
The principal measure used for com-
paring fuel consumption was the specific
fuel consumption (SFC) defined as liters
of oil per dry volatile metric ton of sludge
cake incinerated. The SFC is also directly
related to the absolute ratio of sludge
cake moisture to volatile content (kg/kg).
An accurate comparison of SFC must ac-
count and correct for the moisture to vola-
tile (M/V) ratio of the sludge cake being
incinerated to avoid a distorted compari-
son. For this reason, the relationship of
the daily average SFC and the sludge cake
M/V ratio for the demonstration period
was computed and compared with the
same relationship recorded for the 1977
baseline operations.
A least squares regression analysis
was made for the SFC versus sludge cake
M/V ratios for both time periods. The
computed regression straight lines,
drawn to reflect the overall changes
observed, can be compared (Figure 2).
Table 1 shows the respective averages of
the other operational variables for the
two time periods.
As shown in Figure 2, the average
sludge cake M/V ratio was higher for the
demonstration period than in 1977; this
reflects dewatering process changes that
occurred between the two periods. The
SFC was reduced, as was the basic
relationship between SFC and M/V as
reflected by the decreased rate of
increase of SFC with M/V ratio. At the
low M/V ratio of 6, the SFC difference
was 27%, and at the high M/V ratio 8.5,
the difference was 41% (Figure 2). The
SFC difference corresponding to the
average sludge cake M/V ratio for the
demonstration period was 34%. This
result does not represent the full fuel
reduction potential since four out of the
eight incinerators were notfully equipped
with the new control systems until 3
months after the demonstration period
began. Even so, the 34% demonstrated
fuel reduction average represents annual
fuel savings, or cost avoidance, of over
$900,000 per year based on oil prices of
$ 1.00 per gallon. A 2-day test period after
the project was completed demonstrated
that additional savings were possible.
When technical supervision was present
at the operation for 24 hours per day
coverage, a 70% average decrease in SFC
was demonstrated (Figure 2).
An analysis of operational data avail-
able from other cities shows that 20% to
50% fuel savings are possible if these ci-
ties use the fuel efficient mode of opera-
tion.
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Table 1. Daily Average Values of Key Operating Variables for Baseline and Demonstration Periods
Operating
Variable
1977
(12 Months)
Daily Average Value
8-Month
Demo Period
Percent
Difference
Cake Load:
Wet
Metric Tons
Dry Volatile
Metric Tons
Percent Moisture
Percent Volatiles
Moisture/ Volatile
Ratio
Incinerator Hours
Load Rate
(Wet Metric Tons/
Incinerator/Hour)
767.8
781
64.1
29.6
6.13
115
6.76
817.3
83.5
71.7
37.3
7.07
116
7.04
+6.5
+6.9
+11.9
+26
+ 15
+4
c
•
u. «
1 1
to O
560
480
400
320
240
160
80
1977 Average
8-Month Demo Average
Two Day Demo A verage
5 6 7 8
Sludge Cake Moisture to Volatile Ratio(M/V)
Figure 2. Comparison of specific fuel consumption for the 1977 baseline and the 8-month
demonstration period.
Particulate Emissions
The impact of the new operating mode
and control systems on incinerator
paniculate emissions was also assessed.
The Indianapolis incinerators are equipped
with low energy cyclonic stack gas
scrubbers with no impingement trays for
particulate removal. When the incinera-
tors were tested before this project
began, they were in violation of the
emission standard with readings as high
as 0.6 g of particulate per kilogram of dry
exhaust gas corrected to 50% excess air.
AM eight incinerators were officially
tested using the new operating mode and
control systems. The average emission
level of these tests was 0.135 g per
kilogram of exhaust gas; this represented
a 75% reduction in emission levels.
Because all eight incinerators were
brought into official compliance, a $2
million bond issue, needed to fund
retrofitting the incinerator scrubbing
system, was avoided.
Conclusions
The principal conclusions from this in-
plant research and demonstration project
were:
• Incinerator auxiliary fuel consumption
can be significantly reduced by using
more fuel efficient operating modes
and improving existing operating
control systems.
• Fuel reductions can be easily and
quickly achieved through operational
mode changes alone in current
incinerator facilities without having
to make major or high cost equipment
changes.
• The use of more fuel efficient operat-
ing modes will also reduce mainte-
nance costs and incinerator downtime.
• Significant reductions in participate
emissions loadings to the stack gas
scrubbers are achieved when fuel
efficient operating modes are used.
• A 34% fuel reduction was achieved
over an 8-month, plant-scale demon-
stration period representing a savings
of over $900,000 per year. Limited
analysis of operational data from
other cities shows similar potential
savings from 20% to 50% are possible.
• Costs for upgrading instrumentation
and control systems and operator
training totaled approximately $20,000
per incinerator with a payback period
in fuel savings or cost avoidance of
less than 3 months.
Recommendations
• Most municipal sludge incinerator
operations are still experiencing high
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fuel consumption rates as a result of
using improper incinerator operating
modes. Incinerator operating modes
should be technically investigated to
identify inefficient practices, instru-
mentation and control inadequacies,
and special operator training needs
so they can be cost effectively
corrected to achieve significant fuel
savings.
• Operational tests are critically needed
to further verify the interrelationship
of incinerator operating modes with
particulate emissions and pollution
control equipment. Such tests are
essential to correct a serious void that
currently exists in the analytical and
operational understanding of how
incinerator operating modes affect
particulate emissions. This informa-
tion would help municipal operators
comply with incinerator particulate
emission standards.
• Operational tests should be conducted
to determine the effect of fuel
efficient operating practices on hydro-
carbon or odor emissions.
The full report was submitted in
fulfillment of Cooperative Agreement No.
S806248 by City of Indianapolis Depart-
ment of Public Works, Indianapolis, IN
46204, under the sponsorship of the U.S.
Environmental Protection Agency.
Albert J. Verdouw and Eugene W. Waltz are with Indianapolis Center for
Advanced Research, Indianapolis, IN 46204; and Webb Bernhardt is with the
City of Indianapolis, Department of Public Works, Indianapolis, IN 46204.
Howard O. Wall is the EPA Project Officer (see below).
The complete report, entitled "Plant-Scale Demonstration of Sludge Incinerator
Fuel Reduction," {Order No. PB 83-259 697; Cost: $11.50, 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:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati. OH 45268
AUS GOVERNMENT PRINTING OFFICE 1983-659-017/7215
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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