United States
Environmental Protection
Agency
Industrial Environmental
Research Laboratory
Cincinnati OH 45268
Technology Transfer
v>EPA Capsule Report
Benefits o;f
M icroprocjessor Control
Of Curing Ovens
For Solvent-Based
Coatings
I
SOS.
IKI
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Technology Transfer
EPA 625/2-84-031
Capsule Report
Benefits of
Microprocessor Control
Of Curing Ovens
For Solvent-Based
Coatings
September 1984
This report was developed by the
Industrial Environmental Research Laboratory
Cincinnati OH 45268
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Prototype installation at Mack Trucks Inc., Allentown, Penna.
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1. THE SIGNIFICANCE
Solvent-based coatings are used in
the production jof automobiles, metal
furniture, trucks, paper, fabric, metal
coil, appliances, small metal parts,
tapes, labels, arid beverage cans.
The Environmental Protection
Agency (EPA) estimates that approxi-
mately 2 millior^ tons of organic
solvents (also known as volatile
organic compounds, or VOCs) are
emitted to the atmosphere annually
from the more than 15,000 coating
facilities in the United States.
Under the Clean Air Act of 1970 and
amendments toj the Act in 1977, EPA
promulgated regulations to control
VOC emissionsi from coating
industries. A survey of the
regulations for hew sources as of
the end of 1983 is shown in Table 1.
Many are typical of regulations for
existing plants as well.
Generally, any plant tnat can emit
100 tons or more of VOCs annually
must meet the emission level
specified for its industrial category.
Smaller facilities may also have to
meet regulations if the state or air
quality control region is not meeting
ambient air quality standards.
Curing ovens are a major source of
VOC emissions. The organic sol-
vents, or hydrocarbons, in the
coating are evaporated in the oven at
temperatures which range from
100°F to 700°F, depending upon the
curing properties of the coating and
the product. Because great volumes
of air containing low concentrations
of VOCs are involved, the fuel and
investment cost of controlling these
VOC emissions can be significant.
Table 1.
New Source Performance Standards (NSPS) for Solvent (VOC) Emitting Coating Operations
Source Category
Affected Operation
Emission Level
Monitoring Requirements
Metal furniture
All with organic coatings
0.7 kg/I of applied coating
solids
Firebox temperature of thermal
incinerator
Inlet and discharge temperature of
catalytic incinerator
Daily recovery rate of solvent in any
solvent recovery system
Automobile and light duty trucks Each guide coat operation
Graphic arts, industrial pub- Each printing press
licatign, rotogravure
<16% of total mass of VOC
solvent during one perform-
ance averaging period
Solvent, water usage
Solvent recovery
Industrial surfaces and large
appliances
Each surface coating operation
in a large appliance coating line
1.4 kg/I of applied coating
solids
No requirements
0.9 kg/I of applied coating
Firebox temperature of thermal
incinerator
Temperature monitoring before and
after the bed of any catalytic
incinerator
Metal coil
Each prime coat operation
Each finish coat operation
Combined prime and finish coat
operation when coatings are
applied wet on wet and cured
simultaneously
0.28 kg/I of coating solids
if no control device is used
0.16 kg/I of coating solids
or 90% control if control device
is used
Exit temperature of effluent gases
when thermal incinerator is used
Pressure sensitive tape and label Each coating line
0.2 kg/I of coating solids
Solvent usage
Solvent recovery
Firebox temperature of incinerator
Hooding and ventilation interlock
Beverage can
Each coating line
0.29 kg/I of exterior base coating
0.46 kg/I of overvarnish coating
0.89 kg/I of inside spray coating
Firebox temperature of incinerator
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Two approaches to controlling
curing oven emissions are available:
the use of low-solvent coatings and
the installation of pollution control
equipment. Low-solvent coatings
such as "high solids" or "water-
based" coatings have been success-
fully used in some cases to meet
emission levels. However, these
coatings frequently require that
extensive tests be conducted to
satisfy product quality demands and
may require the installation of new
coating application equipment.
The second approach, using add-on
pollution control equipment,
includes such control methods as
catalytic or thermal incineration,
carbon absorption, and vapor
condensation. The relative cost-
effectiveness of each of these
methods depends on site-specific
conditions.
The most widely applied technolo-
gies for reducing VOC emissions
from curing ovens are incinerator
systems. The incinerator system can
include heat recovery equipment as
well as the incinerator itself. The
capital and operating costs for
incineration systems are a function
of the curing oven exhaust tempera-
ture, the total volume of air requiring
control, and the solvent concen-
tration. :
400
300
8 200
z
|
^ 100
10,000 20,000 30,000
AIR FLOW RATE (SCFM)
40,000
Most curing ovens operate at
ventilation air flow rates far in
excess of the rate required to cure
the product and to maintain the
solvent concentration below its
lower explosive limit (LEL). This over-
ventilation results in higher than
necessary investment costs for
pollution control equipment and high
fuel costs for both curing and
incineration.
As shown in Figure 1, reductions in
the volume of air can significantly
reduce capital costs. Operating
costs can also be significantly
affected by reduced air flow rates.
Figure 2 shows the energy saved by
reducing air flow rates for a range of
exhaust temperatures. The exhaust
temperature can be that of the
curing oven alone, of the curing oven
with its incineration system, or of
the system with heat recovery in the
incinerators. The energy savings for
any part or for the entire system are
still estimated based on its air flow
rate reduction and the final exhaust
temperature. For example, Figure 2
indicates that the energy saved by
reducing the air flow rate by 6,000
scfm is 4 million Btu/hr for a curing
oven with a stack temperature of
600°F. The same air flow reduction
for an incinerator with a final
exhaust temperature of 1,000°F
results in a savings of approximately
7.2 million Btu/hr.
Figure 1.
Capital Costs for Thermal Incinerators
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When heat recovery is a part of an
incinerator system, it is a major
contributor to the investment cost of
the incinerator system. However, the
size and therefore the capital costs
of the heat recovery system can be
reduced with lower air flow rates.
This also increases the solvent
concentrations and thus increases
the heat value of the air. Overall
operating costs can also be reduced
since less fuel is needed for the
overall system.
Jot'
Recognizing the potential for
reducing the fuel and investment
costs of meeting j/OC regulations,
the Chemical Coaters Association,
the Environmental Protection Agency
(Industrial Environmental Research
Laboratory), and the Department of
Energy (Office of Industrial
Programs) joined in a cooperative
program to develop a microcom-
puter-based system to control curing
oven ventilation by continually
monitoring and controlling operating
parameters (including solvent
concentrations and pressure). Such a
system can also monitor the
efficiency of pollution control
equipment.
This report highlights the results of
that program, the performance of a
prototype system at Mack Trucks,
and applications for other curing
operations.
= Oven or Incinerator System
Exhaust Temperature
Figure 2.
Energy Savings Achievable by Reducing Air Flow Rates
2000 4000 6000 8000
AIR FLOW REDUCTION (SCFM)
10,000
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2. THE CONCEPT
Oven or
Incinerator
The design and operation of
continuous curing ovens are based
on safety codes established by the
Factory Mutual Research Corpora-
tion, the National Fire Protection
Association (NFPA), and other
organizations. These codes require
that the ventilation air flow rate be
set so that the solvent concentration
is maintained belpw 25 percent of
the LEL inside the oven, or below 50
percent of the LEL when appropriate
analyzers and safpty systems are
installed. ;
The design ventilation air flow rate
for curing ovens is usually based on
the maximum solvent evaporation
rate expected that will keep the
solvent concentration below 25
percent of the LEL. Since many
facilities typically operate well below
this maximum solvent rate, most
ovens are operated at excessive
ventilation rates, for example, a
facility operating its curing oven at
an average of 5 percent of the LEL
may be using seven times more fuel
for air heating than if the curing
oven was operated at 35 percent of
the LEL.
In addition to satisfying LEL-related
requirements, the ventilation air flow
rate must also maintain the oven at
a slightly negative pressure to
prevent fumes from escaping to the
work area. The ventilation rate
required to maintain this pressure is
typically less than that required to
maintain 25 percfent of the LEL.
Microprocessor-based technology
was selected for controlling curing
oven ventilation systems because of
its ability to handle multiple control
and monitoring functions, particular-
ly those related to pressure, solvent
concentrations, temperature, and
operational status.
The basic components and functions
of the microcomputer-based control
system are illustrated in Figure 3.
They are:
Hydrocarbon sensors arid
analyzers, which measure the
hydrocarbon concentration at
various points within the oven as
percent of LEL. [Note: Most
curing ovens require multiple
analyzers because the area of
highest solvent release can
change depending on the coating
rate and coating type.]
Temperature sensors, which
monitor oven and incinerator
temperatures.
Pressure sensors, which measure
atmospheric pressure at several
points in the oven.
Microcomputer controller
software and hardware, which
collect information from the
sensors, control operating
conditions, and present such
information using printouts,
cathode ray tube (CRT) displays,
and alarms.
Pressure Sensing
Temperature Sensing
Hydrocarbon baiiiplnig
Emergency Backup Controls
Analyzer
Air Flow Control
Emergency Shutdown
Microcomputer
Controllers,
CRT&
Printer
Figure 3.
Basic Design Features of the Microcomputer Control System
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Although the number of sensors and
types of auxiliary equipment are site-
specific, the functions of the
microcomputer controller are based
on engineering principles, safety
codes, and operating conditions
common to the industry. Hence, the
microcomputer for every installation
performs the following functions:
Ventilation Air Flow Rate Control
As a result of changes in either
pressure or solvent concentrations,
the microcomputer controller opens
and closes dampers located in the
oven exhaust ducts. Whenever
solvent concentrations are below
their minimum LEL control set-point
the microcomputer automatically
maintains a slightly negative
pressure inside the oven based on
pressure sensor readings. When the
solvent concentration reaches a set-
point such as 35 percent of the LEL
inside the curing oven, the air flow
rate is increased by opening
damper(s) to maintain the set-point
concentration.
Safety Control If the solvent
concentration shqu Id exceed 50
percent of the LEL at any time, the
microcomputer controller provides
safety control features in order to
meet the NFPA codes. The micro-
computer will automatically increase
ventilation air flow rate to full, sound
an alarm, print anlalarm report, and
shut off the curing oven burners.
, Fail-Safe Control | In the event of a
control sensor failure or micro-
computer failure, the system reverts
to the ventilation air flow rate that
would maintain tl^e solvent concen-
tration below 25 percent of the LEL
for the maximum [solvent loading.
Therefore, a failurje of the control
system will not stop production.
Temperature Monitoring
Generally, the temperatures are
displayed on the (DRT for operator
information and energy demand data
analysis. Temperature data can be
recorded to satisfy monitoring
requirements of tjie New Source
Performance Standards.
Calculations of the Incinerator's
Destruction Efficiency The
destruction efficiency of the
incinerator is continuously
determined by monitoring the
solvent concentration with
incinerator inlet and exhaust
sensors. The comparison provides a
continuous measurement of
destruction efficiency and can be
used to set the operating tempera-
ture of the incinerator to meet the
required emission level.
Operational Flexibility The
microcomputer controller provides
visual displays of operating con-
ditions and alarm conditions, report
generation for data analysis, and
keyboard command capability. The
software is tailored to meet the site-
specific requirements of the operat-
ing personnel without compromising
control and safety functions. For
example, personnel can put the
microcomputer into either an auto-
matic or manual mode of operation
or can change control constants, but
cannot adjust set-points above
preprogrammed safety limits.
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SJWi PARTS LI( STATIS
, LBL SENSORS Ut STATES
6lP OVEN CONTROL POINT MMM ALARM
DIP OVCH EXHAUST
DIP OVEN RECIRC ZONE I
DIP OVCH RECIRC ZONE t
INCINERATOR INLET
INCINERATOR EXHAUST
AUXILIARY
<4«IENT: ,
INSTRUMENT AIR
PRIME OVCH EXHAUST
COLOR OVCH EXHAUST
LEL ANALYZER STATUS MNMSV
DIP OVEN CONTROLLER STATUS MONITOR Z
DIP 0«K eOMOITlOMS.
EXHAUST TENPCRA'TURC
TONE TUNNEL TCW «T OVIN
INLET TO CATMLVST TEMP
DAMPER POSITION* - X OPEN
DIP OVEN EXHAUST DAMPER
DIP OVEM IHLET DAMPER
TO TURN ON DIP- OWN CONTROL PRESS t
DIP OVEN TO MANUAL CONTROL PHESS Z
TO TURN OFF THE *U*K HORN PRESS 3
TO GENERATE A PRINTED REPORT - PRESS 4
A typical CRT display
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3. THE PROTOTYPE
SYSTEM
The "514" assembly plant of Mack
Trucks Inc. in Alltentown, Pennsyl-
vania was selected for the testing
and installation of a prototype micro-
processor control system. The Mack
Trucks curing line was installed in
1977 using curing ovens and a
catalytic incinerator supplied by
Schweitzer Industrial Corporation.
This site was selected for a number
of reasons: solvept-based coatings
are applied at different rates to many
types of parts; the catalytic incinera-
tor permits an on-line determination
of destruction efficiency as well as
energy savings fijom reduced ventila-
tion air flow rates; the ovens are
typical multiple-zone conveyor ovens
with forced air rebirculation; a quality
assurance facility is available at
Mack Trucks to evaluate the effects
of reduced ventilation air flow rates
on product qualitV; and the range of
operating conditions permits an
evaluation of the [microcomputer
system under var able conditions.
The desired level for oven solvent
concentration (referred to as the set-
point) was chosen to be 35 percent
of the LEL This operating level
would result in significant fuel
savings and still conform to the
NFPA code requiring operation
below 50 percent of the LEL.
Figure 4 shows the layout of the
curing line involved in this project.
The prime, color, and dip overis are
two-zone ovens which use steam as
the source of heat to cure small
parts. The VOC-containing exhausts
from each curing oven are drawn by
an exhaust fan through a common
duct into the oil-fired catalytic
incinerator. (Prior to being
discharged to the atmosphere, the
exhaust gas from the incinerator
enters a heat exchanger which
preheats fresh air for another part of
the process.)
n_r
Figure 4.
General Layout of Mack Trucks Curing Line Involved in This Project
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Although an ideal system would
control all of the ovens at the plant,
this project was limited to the devel-
opment of a control system for a
single oven. The dip oven was
selected for control because its
solvent loadings and air flow rate are
normally higher than in the prime
and color ovens. However, since
there was a common exhaust fan for
the three ovens, a means of monitor-
ing the LEL and maintaining con-
stant ventilation air flow rates for the
color and prime ovens were
provided. Table 2 describes the
function of each of the sensors and
control devices.
The hydrocarbon analyzers were
supplied by Ratfisch Instruments
and consist of an eight-channel and
four-channel unit, which provide
continuous measurements for 12
sensing locations. The units have
adjustable high-level alarm outputs
that open dampers and sound
alarms if the solvent concentration
exceeds a preset percent of the LEL.
This alarm feature is used to provide
safety for the color and prime ovens
and also as a backup to the micro-
computer safety function for the dip
oven. The eight-channel unit is
shown in Figure 5.
The microcomputer, using an Intel
8086 controller as the central
processing unit, is .also shown in
Figure 5. The color CRT, keyboard,
and printer are shown in Figure 6.
The control system design offers
several benefits and features:
Table 2
Monitoring and Control Equipment
Equipment/Location
Purpose
Temperature
Dip ovon exhaust
Fume tunnel
Incinerator
Dip oven zones
Pressure
Dip oven
Hydrocarbon
Dip oven Inlet, Zone 1, Zone 2
and exhaust
Ambient air
Fume tunnel exhaust
Incinerator Inlet and exhaust
Prims oven Inlet and exhaust
Color oven Inlet and exhaust
DAMPERS
Dip oven Inlet
Dip oven exhaust
Color and prime ovens and fume
tunnel exhausts
FILTERS AND METERS
Condensate
Fuel oil
Calculate oven fuel demand
Maintain in-dratt at entry of dip oven
Monitor performance of incinerator, provide operational
information, calculate fuel demand
Provide operational information
Control oven pressure and make-up air rate
Air flow control and safety
Monitor for safety purposes
Monitor for safety purposes
Calculate destruction efficiency
Monitor for safety
Monitor for safety
Maintain pressure and safety
Control ventilation air flow rate
Maintain constant air flow rate
Monitor steam demand for dip oven
Monitor fuel demand for incinerator
Adjusts the ventilation air flow
rate by changing the position of
the exhaust damper based on the
set-point of 35 percent of LEL.
Performs safety functions in the
event of microcomputer or LEL
analyzer failure or in the event of
solvent excursion above 50
percent of the LEL. Safety func-
tions include opening dampers to
increase air flow, sounding an
audible alarm, printing an alarm
report, and stopping the conveyor.
Provides safety checks of
instrument air and hydrogen to
the LEL analyzers.
Provides color display of
operating conditions and the
status of control sensors and
alarms.
Allows keyboard changes of the
concentration and pressure set-
points within allowable ranges.
Stores operating data for reports
on production, alarm conditions,
and destruction efficiency.
Accepts keyboard commands to
generate reports, to turn off the
audible alarm, and to place the
system in automatic or manual
control.
Displays readings of all major
operating conditions.
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Figure 5.
Microcomputer and Hydrocarbon Analyzer
Figure 6.
Production and Alarm Printer, CRT, and Keyboard
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4. PERFORMANCE OF
THE SYSTEM
The installation of the
microcomputer controller and
auxiliary hardware and sensors was
completed in September 1981 and
the system was started up the
following month. Under automatic
control, the ventilation air flow rate
from the dip oven was reduced by 86
percent from 3,400 scfm to an
average of 490 scfm. The ventilation
air flow rates from the color and
prime ovens were maintained at their
original rate of 2,000 scfm each; the
air flow rate from the fume tunnel
was maintained at 1,840 scfm. As a
result, the combined air flow
entering the incinerator was reduced
to 6,330 scfm, a reduction of 31
percent. Had the ventilation air flow
rate from each of the prime and
color ovens been reduced to 490
scfm as well, the combined air flow
requiring incineration would have
been 3,310 scfm, a reduction of an
additional 33 percent. A summary of
the average operating conditions
measured during test periods under
manual and automatic control is
shown in Table 3.
Table 3
Baseline and Automatic Curing Line Operating Conditions:
Mack Trucks Inc.
Operating Conditions
Baseline "
(Oct. 5-16)
Automatic
(Oct. 26 to Nov. 6)
Dip Oven (controlled)
Air flow, scfm
Exhaust temp, °F
Total Fuel consumption,'million Btu/hr *
Prime and Color Ovens (Total) (not controlled)
Air flow, scfm
Exhaust temp, °F
Fume Tunnel (not controlled)
Air flow, scfm :
Exhaust temp, °F
3400
252
1.74
4000
250
1840
70
490
282
0.77
4000
250
1840
70
Catalytic Incinerator
Total air flow, scfm
Average VOC at inlet, ppm
Average VOC exhaust, ppm
Inlet temp, °F
Temp, at exit of catalyst tjed °F
Destruction efficiency, %c
Fuel consumption, million Btu/hr
Fuel Savings
Fuel consumption in dip oven and incinerator, million Btu/hr
Hourly fuel saving for dip oven and incinerator, million Btu/hr
Projected annual fuel cost saving in dip oven and incinerator^
9240
140
20
257
787
85
4.72
»6.46
6330
160
10
281
828
93
4.16
4.93
1.53
$60,800
Data supplied by Mack Trucks; fuel demand based on meter readings including air heating, radiation
losses, and parts heating.
"The system was in place but the sensors operated only to provide data for a subsequent
evaluation of the system, not to provide data for manually adjusting the operating conditions.
* Includes energy for curing paint, heating the product, heat losses to the work space, and air
heating.
c Based on difference between inlet and exhaust solvent concentrations with the incineration
temperature at the catalyst bed held constant.
'/Based on fuel oil cost of $6.98/million Btu and annual operating time of 5,690 hours.
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I
The observed performance of the
control system during its first six
months of operation and the initial
control test period as shown in
Table 3 leads to the following
conclusions:
The microprocessor technology
proved capable of automatically
controlling air flow rates and
monitoring temperatures, solvent
concentrations, pressure, and
incinerator destruction efficiency.
The control system achieved the
objective of reducing the air flow
to the maximum extent possible
given pressure constraints,
thereby achieving the maximum
oven fuel savings possible. (At
this minimum air flow rate, the
maximum solvent concentration
inside the dip oven reached only
12 percent of the LEL because of
low production rates and frequent
product changes.)
All LEL control and safety
features were dynamically tested
and satisfied the NFPA codes.
The operation of the control
system had no detrimental effects
on the operation of the curing
oven and incinerator.
The control system required only
minimal operator attention
(primarily to put the system in
automatic control, to respond to
alarms when they occurred, and
to calibrate the analyzers before
start-up of the curing line).
The reduction in ventilation air
flow rate did not affect the
product quality of the cured parts.
The 86 percent reduction in air
flow in the dip oven led to a
measured fuel savings in the dip
oven of 44 percent; the difference
results from the: energy used to
cure paint, to heat the product,
and for heat losses.
Measured fuel savings for the
incinerator were
13 percent. (This
was lower than expected due to
cycling of the te'mperature
controller.)
Given a total projected annual
fuel saving of $60,800 as a result
of reducing the air flow in the dip
oven only, it can, be assumed that
if the flow from jthe prime and
color ovens were also reduced
from a total 4,00^0 scfm to a total
980 scfm, the projected annual
fuel savings would be $125,500
per year or more depending on
such factors as the added fuel
value of the solvent, and better
temperature control of the
incinerator. I
The destruction 'efficiency of the
catalytic incinerator improved by
approximately 8 [percent (from 85
percent to 93 percent) when the
curing oven was) controlled and
when the incineration temperature
at the catalyst b^d was held
constant.
The highest solvent
concentrations were frequently
found to be as much as 200
percent higher inside the curing
oven than in the oven exhaust
duct. Hence, control of the
ventilation air flow rate should be
based on the highest solvent
reading in the curing oven rather
than on measurements from the
exhaust duct alone.
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5. INDUSTRIAL
APPLICATION AND
BENEFITS
The technology demonstrated at
Mack Trucks is directly applicable to
continuous curing ovens throughout
the coating industry. The safety
controls and methods for reducing
ventilation air flow rates are generic
to all curing oveps and incinerators.
Site-specific requirements, of course,
will determine the exact computer
software and hardware, and
therefore costs, 'required to match
the process conditions at each site,
and the number of sensors and type
of auxiliary equipment necessary.
Energy savings will also be
dependent on site-specific
conditions.
A survey of a wide variety of
industrial curing ovens indicates that
most curing ovens are operated at 7
percent of the LEL Since solvent
concentrations of up to 50 percent
of the LEL are permissible, signifi-
cant reductions Jin air flow rates can
be achieved. This control system can
continuously monitor and adjust
ventilation air flow based on
pressure and solvent concentrations
inside the oven and can thus reduce
costs of curing and VOC pollution
control without Compromising safety
or product quality.
The benefits of using such a control
system for continuous curing ovens
are:
Curing Oven and Incinerator Fuel
Savings The microcomputer
control system will reduce the
fuel costs for air heating in the
curing oven in direct proportion to
the reduction in ventilation air
flow rate. In addition, for plants
presently using incinerators, their
fuel demands will decrease in
direct proportion to the reduction
in total ventilation air flow rate to
the incinerator. The fuel savings
are based on the reduction in
ventilation air flow and the
average exhaust air temperature
from the curing oven. For
example, as was shown in Figure
2, a reduction of the ventilation
air flow rate by 5,000 scfm in an
oven with an exhaust temperature
of 500 °F can reduce fuel demand'
by 2.7 million Btu/hr. In an
incinerator with an exhaust
temperature of 1400°F, an air flow
reduction of 5,000 scfm can result
in a reduction in fuel demand of
8.8 million Btu/hr for both the
curing oven and the incinerator.
Incineration Destruction Effi-
ciency Destruction efficiency
can be monitored and recorded
continuously to assure compli-
ance with VOC regulations. By
monitoring the incinerator
temperature and holding it to
maintain the required destruction
efficiency, a fuel savings can also
be achieved. For example, a
100°F decrease in the incinerator
exhaust temperature could pro-
duce a fuel savings of approxi-
mately 1.4 million Btu/hr for a
thermal incinerator operating with
10,000 scfm of air.
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Lower Emission Control Invest-
ments As was shown in Figure
1, the total installed costs for
controlling VOC emissions from
curing ovens using thermal
incinerators is directly propor-
tional to the ventilation rate.
Similar investment savings are
achievable for catalytic
incinerators, carbon absorption
systems, and other VOC control
technologies.
Safety Most curing ovens
operate at constant ventilation air
flow rates. However, they may
apply coatings at different
application rates from day to day.
This can result in localized high
solvent concentrations inside the
oven, possibly causing fires pr
explosions. Continuous moni-
toring of the solvent concentra-
tions inside the oven enables the
control system to detect such an
emergency situation and respond
by increasing ventilation to the
maximum, hence shutting off
burners and stopping the curing
line.
The investment cost for a micro-
computer control system varies
depending on the number of
pressure, temperature, and
hydrocarbon sensors required, as
well as the costs of modifying the
curing ovens to achieve control of
the air flow rate. The cost is
independent of the present ventila-
tion air flow rate. For plants with
VOC emission control equipment
already in place, the economic
benefits of the microcomputer
system will be derived from fuel
savings alone. For p ants without
VOC control equipment, the system
will also result in lo\jver pollution
control investment costs.
The initial evaluation of the VOC
pollution control equipment begins
with an accurate determination of
the current curing oven conditions.
This evaluation includes
measurements of all sources of air
entering and leavingithe curing oven,
as well as air temperatures and
solvent concentrations (as a percent
of the LEL) inside the curing oven
and in each exhaust! duct. This
information establishes the basis for
the design of VOC control
equipment and for projections of
operating costs and
flow reduction achievable.
ventilation air
Table 4
Example Cases of Investment and Operating Cost Savings
New Incinerator Systems
Estimated investment and operating
costs for VOC pollution control
equipment and a microcomputer
system for fabric and coil coating
facilities are presented in Table 4. In
these two cases, the microcomputer
system included the microcomputer
controller itself; for the controlled
oven, a hydrocarbon analyzer and
sensor for each zone, two pressure
sensors, and control dampers for
make-up and ventilation air; and for
the incinerator, temperature sensors
for the inlet and exhaust, and hydro-
carbon sensors for the continuous
monitoring of the destruction
efficiency of the thermal incinerator.
The major cost differences in the
control systems used to make these
estimates are the number of
sensors, the modifications required
to install the microcomputer control
system on the curing oven, and the
ductwork and field-erection for the
incinerator.
These examples illustrate that the
microcomputer control system can
reduce the total installed investment
cost for VOC emission control while
at the same time reducing the total
fuel costs for curing and
incineration, even taking into
account the cost of the
microcomputer.
T
ith Microcomputer Control
Fabric Coating Facility
Coil Coating Facility
Uncontrolled
Ovenj
Controlled
Oven
Uncontrolled
Oven
Controlled
Oven
Number of oven zones
Curing Oven Conditions
Air flow, scfm
Exhaust temperature, °F
Fuel demand for air heating, million Btu/hr
Thermal Incinerator Conditions
Exhaust temperature, °F
Design air flow, scfm
% of primary heat recovery
Fuel demand for air heating, million Btu/hr
Summary of Fuel and Investment Costs
Total fuel demand for air heating, million Btu/hr
Total annual air heating cost*
Savings per year
Total investment for incineration
Total investment for microcomputer system
Total installed investment
Savings investment costs
14,40q
300
5.0
1,400
15,00q
0
7.0
12.0
$2/0,000:
$230,OOOJ
$230,000;
$171,000
$ 20,000
5,200
300
1.8
1,400
6,000
0
2.6
4.4
$ 99,000
$ 90,000
$120,000
$210,000
15,400
480
8.1
1,400
17,000
80
2.2
10.0
$252,000
$550,000
0
$550,000
$151,000
$100,000
4,500
480
2.4
1,300
6,000
0
2.1
4.5
$101,000
$120,000
$330,000
$450,000
'Fuel costs of natural gas $5.00/million Btu, annual operating hours 4,500.
-------
This report was prepared for the U.S. Environmental Protection Agency by
the Centec Corporation, Reston,Virginia, and JACA Corp, Fort Washington,
Pennsylvania. Charles Darvin of the EPA Industrial Environmental Research
Laboratory coordinated the project. Photographs were provided by Mack
Trucks Inc.
Additional information or reference material may be requested from:
Mr. Charles Darvin
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
This document has been reviewed in accordance with U.S. Environmental
Protection Agency policy and approved for publication. Mention of trade
names or commercial products does not constitute endorsement or
recommendation for use.
* U.S. GOVERNMENT PRINTING OFFICE 1984-761-919
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