EPA/600/A-97/056
CHOICES AND CHALLENGES - CONTROLLING VOLATILE ORGANIC
COMPOUNDS AND HAZARDOUS AIR POLLUTANTS FROM SPRAY
PAINTING FACILITIES
David Proffitt
Acurex Environmental Corporation
Durham, NC 27713
Charles H. Darvin
National Risk Management Research Laboratory
U. S. Environmental Protection Agency
Research Triangle Park, NC 27711
Jacqueline Ayer
Air Quality Specialists
2280 University Drive
Newport Beach, CA 92660
ABSTRACT
Acurex Environmental was contracted by the U.S. Environmental Protection Agency (EPA) to
demonstrate an advanced cost reduction strategy at a U.S. Marine Corps maintenance facility in
Barstow, California. One booth was modified and two new booths built to use the flow rate reduction
strategy, partitioned reeirculation. This is the first application in a high volume production
environment. Costs for controlling emissions from these facilities are high due to the large air volumes
required to produce the minimum face velocity required by the Occupational Safety and Health
Administration (OSHA). EPA desired to show that partitioned recirculation, developed over a number
of years and projects, could be designed and built as easily as existing non-recirculation booths by
using existing industry practices and a minimum of custom design.
At Barstow, partitioned recirculation and other techniques allowed a reduction in volatile organic
compound (VOC) control equipment cost by reducing the flow rate from approximately 142,000 to
43,000 cfm while achieving total exhaust treatment. The operating cost was also reduced significantly
due to the reduction in flow volume. A post-construction testing program confirmed the partition
height and fully characterized the painter environment during painting. Results confirmed that
recirculation is a reliable safe means of reducing VOC control costs.
This paper gives a detailed discussion of the various engineering and safety issues related to
accomplishing this project. Details discussed include hardware solutions to flow control, real-time
VOC level detection in the recirculated stream, maintenance intervals of multistage exhaust filters, and
hardware and software solutions to other unique process control challenges.
Application of coatings comprises one of the single largest stationary sources of organic pollutants.
In light of increasing attention paid to hazardous air pollutants (HAP) and VOC emissions, split flow
recirculation and other engineering strategies become increasingly important in identifying cost
reductions to treating these emissions. The success of this project is important to any base with
painting or depainting facilities.
INTRODUCTION
The primary challenge facing those controlling emissions of VOCs and HAPs from painting and
coating operations related to the large volumes of air normally used to convey these components from
the point of application to treatment. Regardless of the VOC control technology chosen, the costs are
driven by the overall exhaust flow rate to the control device. OSHA requires a minimum velocity of
-------
100 feet per minute (fpm) through a booth when using conventional spray equipment. This velocity,
combined with basic booth dimensions of length and width or height and width, results in a flow rate
determined by OSHA and The National Fire Protection Associaton (NFPA) to be the minimum
required for safely conveying paint overspray from the work area.
During 1988, EPA and the U.S. Air Force (USAF) began a joint research and development program
to control VOC and HAP emissions from paint spray facilities. The first study, conducted at
McClellan Air Force Base (AFB), led to a conclusion that control technologies can be more
economically applied to spray booths after modifications to permit recirculation of a portion of the
booth air. The concerns about health and safety for personnel in the booths (OSHA Regulation 29 CFR
1910.107)! were addressed in later studies at Hill AFB2. These tests demonstrated to the USAF and
OSHA that recirculation could be accomplished without exceeding NFPA code requirements or OSHA
workplace permissible exposure limits (PELs) of HAPs. Safety could be ensured by continuously
monitoring the recirculated stream.
The USAF and EPA work to characterize the painting environment inside normal paint booths
resulted in finding that stratification is a normal occurrence within cross flow paint booths where
particles and VOCs tend to leave the booth at heights at or below the point where applied. This
phenomenon can be used to partition booths into VOC-rich and -lean regions. Once filtered, the lean
region could be recirculated, freeing the control device from the burden of the full exhaust flow. The
method to separate these streams was patented under "Paint Spraying Booth with Split-Flow
Ventilation" Patent (5,221,230) (Darvin and Ayer) which is jointly held by EPA and Acurex
Environmental3.
This technology was successfully demonstrated by a study at Travis AFB4 where a booth was
baseline tested, modified to partitioned recirculation, and tested again. The first opportunity for a
permanent fully integrated booth and control system demonstration came with the Barstow Project,
where three existing booths were modified to reduce the cost of an innovative VOC control system
based on ultraviolet light and ozone. This project was funded by the Strategic Environmental Research
and Development Program (SERDP). This partitioned flow technique, combined with other
engineering and management techniques, reduced the flow from the three existing booths by an overall
71 percent. This saved more than $1.1 million in capital costs and more than 53 percent in operating
costs.
Barstow is an ideal site for this demonstration because it houses extensive priming and painting
operations for Marine Corps and other Department of Defense (DoD) vehicle and ground equipment.
The three paint booths are located in a single building, the Marine Corps Multi-Commodity
Maintenance Center (MC3). Booth 1 is a large drive-through vehicle booth primarily used for topcoat
application to armored personnel vehicles, Humvees, and other Marine equipment. The booth
dimensions are approximately 18 feet high, 20 feet wide, and 60 feet long. Ventilation air is
introduced through an intake plenum at the rear. 0f the booth and exits through filters at the front of the
booth. Booth 2 is a smaller (10 feet high, 30 feet wide, and 20 feet long) booth with an overhead
conveyor designed for painting small vehicle components. The critical parameter in determining
partition height was that significant wash-primer-containing hexavalent chromium was used in this
booth. Fresh air is introduced through a perforated plate into the ceiling plenum at the front of the
booth. Contaminated air exits through a filter bank covering the entire back wall. Booth 3 is similar to
Booth 2 (10 feet high, 22 feet wide, and 10 feet long) and is designed for painting pallet loaded
equipment. As with Booth 2, the wash primer was the primary driver in determining partition height.
One important goal for this project as defined by EPA was to design and install the spray booths
using as many standard approaches as possible to simplify its application to similar facilities and
industrial applications. By enforcing this throughout the design, EPA hoped to expedite the availability
of this to the general corrosion control industry, thereby providing economical approaches to
regulations driven by the Clean Air Act Amendments of 1990s. For those unable to meet emissions
limits by using reformulated paints, economical approaches will be needed for control technology. For
the vast majority of the design elements employed at Barstow, such as sheet metal, doors, and ducting,
-------
standard practices were applied that are presently used in spray booth construction. A number of
exceptions did require varying levels of custom design including:
* Constant flow rate through each booth: This will be needed for any booth with VOC
controls. Control equipment is sized for specific overall flow rates. Maintaining flow
rates consistent with OSHA's minimum required velocities saves considerable cost.
• Exhaust filter system: Many downstream elements are protected by application of high
performance paniculate filtering including ducting, VOC control equipment, and (in the
case of recirculation booths) operators.
* Coordination of paint booth/Air Pollution Control System (APCS) system operations:
Paint booths are relatively simple processes. VOC controlled booths are not. Close
coordination of the operations of the booths to the VOC control system is required to
maintain air regulation compliance. Multiple booths connecting to a single control
device increase the challenges of this requirement substantially.
" An. efficient, fully integrated safety monitoring system: Many variables affect booth
VOC concentrations and, therefore, operator exposure. The purpose of the safety
monitoring system is to ensure compliance with applicable OSHA exposure standards
without limiting booth operating schedules or process flexibility. A real-time VOC
measurement becomes an effective process window providing insight into booth or
operator problems such as high paint usage or paint equipment malfunctions.
These issues were of primary importance in developing an efficient and properly integrated Marine
Corps Logistics Base (MCLB) paint booth/APCS system, and are therefore discussed in detail.
ADVANTAGES OF FLOW CONTROL
Irrespective of recirculation considerations, booth ventilation rates should be controlled within set
limits for several reasons. Typical paint booth ventilation systems are designed with fixed drive fans
that are rated sufficiently high to ensure that the OSHA mandated 100 fpm requirement (for standard
spray guns) is met even under severe system operating conditions such as when the exhaust and/or
intake filters are heavily loaded with overspray paniculate. The conventional approach is to use fixed
drive fans which are typically sized with a large safety margin. This correspondingly produces
excessively high flow rates under "clean filter" conditions. While this approach ensures compliance
with applicable health and safety standards under all operating conditions, it also increases the capital,
installation, and operating costs of an APCS, because the capacity of the device must be sufficiently
large to process the highest flow rates generated, under "clean filter" conditions. Therefore, accurately
controlling the booth ventilation rates to continuously maintain the 100 fpm velocity reduces the air
pollution emission control costs. Another benefit is gained from ventilation rate uniformity. Higher
ventilation rates than required by OSHA can adversely affect paint application efficiency. Painters in
booths without control may have to make small continuous adjustments in technique to balance the
effect of varying face velocities. Flow controlled booths reduce face velocity changes to those created
by vehicle profile changes only. This permits painters to develop strategies and experiences for each
vehicle type that transfer paint smoothly to all other examples of that vehicle. Minimizing fan speeds
to OSHA requirements also saves energy. Controlling ventilation rate by fan speed is an approach
preferred by utility companies as opposed to energy inefficient methods such as control dampers or, in
the case of conventional booths, no flow control,
A final reason for controlling flow rates in recirculation/flow-partition systems is related to the need
to accurately and consistently partition the flow into exhaust and recireulated regions. Flow
partitioning takes advantage of constituent stratification patterns that typically occur in paint booths to
increase the recirculation rate to the greatest extent possible. The ventilation air that passes to the
-------
APCS therefore contains higher levels of overspray paniculate. Flow rate control balances the
differential loading that is imposed on the particulate filters thereby maintaining consistent face
velocities.
FLOW CONTROL SYSTEM DESCRIPTION
The flow rate through each booth is controlled with a feedback loop composed of a flow
measurement probe, a transmitter, a process controller, and a variable frequency drive (VFD) equipped
fan motor. The probe is located in the duct and senses the flow. It then sends a pneumatic signal to the
flow transmitter which measures the signal and relays a flow proportional electrical signal to the
process controller which compares it to the desired or setpoint flow. The controller then decides which
way the flow needs to change to maintain the setpoint flow and communicates this electrically to the
variable frequency drive, which directly controls the fan motor speed.
Available flow rate metering devices include those defined by the American Society for Mechanical
Engineers (ASME) such as low loss flow tubes, Venturis, and orifice plates. In addition to these a
number of proprietary designs are available. Each of these methods presents different challenges to
design such as ducting arrangement and fan power losses. Some metering methods present lower
ultimate pressure losses reducing energy usage. Other probes yield greater signal amplification,
thereby increased accuracy, which may be necessary for low velocity systems. For Barstow, flow
sensing is done using pitot grid array probes that are manufactured specifically for heating, ventilation,
and air-conditioning (HVAC) and process flow applications. These probes deliver a signal
proportional to the square of the flow velocity and are designed to provide the accuracy of a full pitot
traverse such as described in EPA Method 2 . Two probes are installed in each duct to reduce error
attributed to cyclonic flow induced by elbows, fans, and other disturbances. Each flow probe pair is
connected in parallel to a high precision pressure transmitter. Measurement errors are minimized by
using high performance pressure transmitters that typically have combined errors of less than 0.1
percent of full scale. Duct velocities in the final design ranged from 2071 to 3019 feet per minute
(fpm) which resulted in consistent flow signals.
The transmitters employed are the "smart sensor" type; each is equipped with a calibration data table
that is stored in the sensor by the manufacturer and which supports field configuring. Errors for these
transmitters are typically expressed as a percentage of the configured upper range, which produces
substantially lower errors than transmitters having error rates expressed as a percentage of full range.
An additional feature of the transmitters installed on the MCLB paint booths is built-in temperature
detection and correction capability. By using these transmitters, flow measurement deviations are
estimated at less than 2 percent.
The flow controller, chosen for its accuracy and operational flexibility, is an important component of
the feedback control loop. The controller receives a signal from the transmitter, calculates the process
error, and generates a correction in its signal to the VFD. Of all components in the feedback control
loop, the flow controller requires the greatest effort to trim and configure to the system operation.
Loop tuning, which is required to provide smooth flow corrections without process overshoot or
undershoot, can be a long laborious process. To reduce loop tuning efforts, automatic (self tuning)
controllers were installed on the MCLB paint booths; this capability enabled the system programmer to
quickly establish estimated values for the proportional, integral, and derivative photoionization detector
(PID) settings (which define the controller response characteristics). After the approximate settings
were defined, the desired characteristics were manually adjusted. Final PID settings were established
after the booths were connected to the APCS by trimming the booth system responses to match the
APCS induced draft fan characteristics.
The VFD components were selected to be consistent with the APCS drives. Each drive accepts a 4-
20 mA signal from the controller. Each VFD is equipped with a number of diagnostic messages on the
front panel and many registers for customizing. A readout in Hz enables the user to monitor fan speed
as a function of fan flow.
-------
SAFETY MONITORING SYSTEM
To answer effectively the obvious questions of personal safety, the development plans of partitioned
recirculation included a real-time monitor to measure the quality of the air stream as it enters the booth.
Added to this monitor are alternate modes of booth operation to reduce VOC levels if needed. Initially,
studies concentrated on easily available, fully developed, monitoring devices such as those based on
the flame ionization detector (FID) and the PID. This type of monitor indicates VOCs by total carbon
counts. Its single readout must be qualified by response factor calculation based on many laboratory
calibration trials using mixtures of the process stream components. This works well for constant
streams of relatively few compounds. As the number of possible paints increases and the number of
compounds increases, determining accurate response factors becomes impractical. This led to
investigating another instrument based on the Fourier Transform infrared (FTIR) detector. Its greatest
advantage is its ability to measure and report concentrations of multiple compounds in a single stream.
By using comprehensive libraries of previously fingerprinted compounds, this instrument can easily be
reprogrammed to accommodate new paint formulations.
The safety system employs an FTIR to continuously monitor the recirculation stream organic
concentrations. This system assesses the quality of the recireulation air as it exits the paint booth on a
real-time basis performing a measurement approximately each minute. Each measurement includes the
concentrations of 12 separate compounds. These concentrations are combined with OSHA PEL data to
arrive at a combined exposure factor. This calculated value is compared to safety setpoints described
later to determine if adjustment is required. Booth 1 was equipped with a dedicated safety monitoring
system, and Booths 2 and 3 share a single monitoring system. This configuration was selected because
Booth 1 must be capable of full operation at all times, whereas Booths 2 and 3 were designed to
operate sequentially.
Each safety monitoring system is programmed with two alarm setpoints, or action levels, based on
the combined exposure level or OSHA factor, which modify the booth operation to reduce recirculation
stream constituent concentrations. If the recirculation duct organic concentrations measured by the
FTIR exceed the first action level, the paint delivery system is shut down, which immediately curtails
coating delivery to the paint gun, and stops the release of hazardous constituents. The paint delivery
system remains in the off mode until concentrations in the recirculation duct drop below the established
setpoint. If for some reason the concentration continues to increase to the second action level (such as
if a large quantity of paint is spilled in the booth), the booth control system activates dampers to
convert the booth to single-pass operation. Such action instantly reduces the in-booth hazardous
constituent concentrations. This alarm is latched, meaning that the alarm remains in effect until a
supervisor reviews the situation and intervenes, or resets the alarm. For the second action level as with
the first, the paint delivery system remains in the off mode until concentrations in the recirculation duct
drop below the established setpoint.
In practice the system has proven to be reliable, and high VOC excursions have become more and
more infrequent due to changes in painter practices. Typical practices that can result in excursions
include 1) pointing the spray gun up toward the recirculation filter face unnecessarily; and 2) mixing
paint with the fans off for extended periods, thus contributing to solvent vapor buildup in the booth
before turning on the fans.
The availability of real-time data has furthered our knowledge of paint booth recirculation, exhaust
emissions levels, and contributing factors such as painter technique and the effects of target profile. A
number of observations that have been made regarding the relationship between painter technique and
recirculated stream VOC concentrations include:
• The operator's technique contributes to booth VOC levels more than originally anticipated.
« Differences in application efficiency between operators are reflected in the VOC levels
reported by the FTIR.
-------
• Differences between operators can affect VOC levels in the booth more than differences in
target profile height,
• The operator's application efficiency can be increased through booth improvements such as
increased lighting or through training.
HIGH PERFORMANCE PARTICULATE FILTRATION
The coating operations in Booths 2 and 3 employ small quantities of a wash primer that contains
hexavalent chromium for which a very low PEL has been established. The Booth 2 and 3 partition
height calculations were influenced to a great extent by the potential presence of hexavalent chrome in
the overspray that is directed to the recirculation duct.
A 3-stage, high performance filtration system was selected for the MCLB application to minimize
the solid-phase hazardous compound concentrations in the recirculation duct and to reduce particle
fouling of the exhaust ducting and the APCS. This decision was reached after a series of tests to
determine characteristics such as pressure drop vs. paint loading rates for various coating materials and
included tests with samples of the coatings used at Barstow.
Typical booth paint filter systems that achieve moderate filtration efficiencies are designed with
single-stage media such as fiberglass or kraft paper that have clean pressure drop readings of less than
0.2 inch w.c., and which are replaced when the pressure differential across the media reaches 1 inch
w.c. or less. However, high efficiency, multistage filters tend to have relatively higher clean pressure
drop readings, and are also somewhat more expensive than traditional filter systems. As such, there is
an economic incentive to drive the filters to a reasonably high pressure drop prior to replacement.
However, establishing a reasonable filter life cycle involves the consideration of several related
factors. For instance, less frequent filter replacements require higher pressure differentials which in
turn require higher fan and motor capacities as well as sturdier, heavier exhaust plenums, ducting, and
dampers. One of the first tasks was to establish the limits of the MCLB paint booth exhaust plenums,
as well as the selected 3-stage high-efficiency filter system. The results of this evaluation indicated
that the plenums are capable of withstanding a 3 inch w.c. pressure drop, whereas the filters can easily
handle a 7 inch w.c. pressure drop (or more).
The operating life of each stage of the 3-stage filter system varies as a function not only of the filter
material, but also of the painting operation characteristics such as workpiece configuration, aerosol size
distributions, coating transfer efficiency and dropout, and operator habits. To establish the replacement
frequency of each of the filter stages in the MCLB paint booths, two representative filter elements were
selected (one above the partition in the recirculation zone, and one below the partition in the exhaust
zone), and pressure differential gages were installed across each stage of these representative elements.
The elements were selected to reasonably represent the median particulate loading level in each of the
two zones. By installing a static pressure probe between stages 1 and 2 and one between stages 2 and 3
and referencing these to booth and plenum pressures, respectively, three discrete pressure signals are
available from each representative element. The probes are connected to manometer gages mounted on
the exterior of the booth, thus providing a means of measuring the pressure differential across each
stage. These gages provide information for determining whether the first, second, or third stage needs
replacing when the overall pressure exceeds 2.5 inch w.c.
Clean filter pressure drop is directly proportional to the linear face velocity through the filter.
Therefore, controlling the flow rate through each booth produces the added benefit of reducing the
clean pressure drop insofar as possible. For booths 2 and 3, the face velocity through the exhaust filters
is 134 fpm, which corresponds to a clean filter pressure differential of approximately 0.5 inch w.c.
across all three stages. The original Booth 1 exhaust face was configured such that, even with the flow
rate reductions achievable by flow control, a 200 fpm face velocity would be generated after the retrofit
modification. This was considered too high to achieve reasonable filter replacement intervals, thus the
-------
exhaust system was redesigned to accommodate an additional row of filters. This successfully reduced
the linear face velocity through the Booth 1 exhaust filters to 167 fpm, which corresponds to a clean
filter pressure differential of 0.87 inch w.c.
For each booth, the pressure gages provide input to the booth control panel, and notify the operator
of impending filter replacement requirements via a 2-level warning system. The first level is triggered
at a 2.5 inch w.c. pressure drop, and notifies the operator to schedule a filter change. The second level,
which occurs at 3.0 inch w.c., disables the booth fans, thereby maintaining a reasonable pressure
differential in the plenums and ductwork. This 0.5 inch w.c. margin was provided in an effort to
reasonably extend filter life and minimize operating costs.
Day-to-day operation revealed much about operating with 3-stage filtration that was not apparent
during design. Our design included roll media for the first stage to save money and replacement time.
The first filter rack used for retaining this stage was cumbersome and formed a less-than-satisfaetory
seal. As a result of early experiences, the booth contractor, Spray Booth Systems, Inc., redesigned the
rack, which was installed during a subsequent visit. This new retention design includes a 0.5 in.
channel perimeter around each rack of panel filters which form the second and third stages. This
channel accepts the first-stage roll media, which is rapidly installed using a special rotary disk tool.
Each panel, ranging from 33 to 55 ft2, is installed in minutes, and the first stage is tightly sealed to
prevent particles from bypassing to later stages.
The replacement intervals for 3-stage filters are much more difficult to determine than when single-
stage filters are used. Instrumenting each filter stage with separate gages is helpful, but the decision of
when to replace a particular stage is not obvious at a glance. Rules and guidelines have yet to be
established to guide the operator or technician responsible for. filter changing. Future designs will
address this by integrating modern process controls to provide guidance on optimal changeouts,
FINAL FLOW RATES
The results of the Baseline Study indicated that significant flow reductions could be achieved for the
MCLB paint booths. The initial, projected, and actual booth exhaust flow rates achieved are
summarized in Table 1. The data presented in Table 1 in the Final Configuration column reflect actual
operating conditions that currently exist and which were established as a result of the Phase n retrofit
efforts.
-------
Table I:
Summary of Flow Rate Reductions Achieved for MCLB Paint Booths3
Booth
1
2
3
Total
Initial Volume
Flow Rate
m3/m (cfm)
1,500
(53,000)
1,783
(63,000)"
778
(27,500)c
4,061
(143,500)
Projected from Baseline Study
Volume Flow
mVm (cfm)
1,019
(36,000)
906
(32,000)
623
(22,000)
2,548
(90,000)
Exhaust Flow
m3/m (cfm)
566
(20,000)
580
(20,500)
393
(13,900)
1,539
(54,400)
Final Configuration
Volume Flow
m'/m (cfm)
962
(34,000)
906
(32,000)
623
(22,000)
2,491
(88,000)
Exhaust Flow
m3/m (cfm)
572
(20,210)
604
(21,330)
415
(14,660)
1,176
(41,540)a
Overall Flow
Reduction
Achieved
%
62
66
47
71b
* Booths 2 and 3 arc not operated simultaneously; the highest booth exhaust flow rate to the control device is 20,210 +
21,330 = 41,540 dm,
b Based on maximum flow allowed in APCS.
c Based on 125 fpm estimated face velocity.
The significant flow reduction achieved in the MCLB paint booth retrofit efforts is attributed to the
following design factors:
1) Flow Control - With the VFDs, a constant flow rate is maintained in each booth, which
ensures compliance with OSHA requirements while minimizing exhaust flow rates. Of the
flow reduction achieved, 32 percent is attributed to the flow control feature.
2) Recirculation/Flow-Partitioning - Through installation and operation of recirculation/
flow-partitioning, the exhaust flow rate to the APCS was reduced by an additional 31
percent. Note that the level of flow reduction achieved by recirculation/flow partitioning
was limited primarily by a conservative decision to establish large safety margins for the
recirculation duct OSHA factor. Greater flow reductions may be achieved via recirculation
for facilities that either employ more stringent protective equipment, or adopt an approach
that is less conservative.
3) Booth 2 Enclosure - Booth 2 was originally configured as an open face booth, and
therefore operated at a significantly higher flow rate than is necessary for a fully enclosed
booth of similar size. By enclosing Booth 2, the flow rate vented to the APCS was reduced
by an additional 23 percent.
4) Production Schedule Management - By alternating the operating schedules for Booths 2
and 3, the volumetric flow rate.vented to the APCS was reduced an additional 14 percent.
The sequential operation of Booths 2 and 3 is controlled from a single interface panel. Although
each booth is internally equipped with full operating capabilities, the circuitry is designed such that
only one booth can be run at a time. The operating booth is selected via a front panel switch, which is
locked for supervisor control. The safety monitor is devoted to whichever booth is operating, and the
sample inlet direction is controlled with a 3-way valve connected to the panel-mounted switch.
8
-------
PAINT BOOTH/APCS SYSTEM INTEGRATION REQUIREMENTS
The MCLB paint booth operating schedules are frequently demanding and generally variable. The
two booth areas, 11 (Booths 2 and 3) and 18 (Booth 1) are managed by different supervisors. Booths 2
and 3, which cannot be operated simultaneously, are designed for sequential operation due to the flow
capacity of the APCS. Given the process constraints and area management structure, the importance of
adequately linking booth ventilation systems with APCS operation was apparent. To develop the
necessary system coordination procedures and handshake signals between the booths and the APCS,
various startup and operation strategies were identified through a detailed "what if analysis.
The APCS design included a Management Information System (MIS) in its original design which
included a comprehensive network of data handling modules and controllers. A personal computer is
used as the operator interface. The booths were designed primarily as standalone components
including the minimum control logic necessary for VOC alarms, door interlocks, and paint gun
interlocks. It was apparent that to successfully link the booths to the APCS required significant data
sharing and passing of handshake, or initialization, signals. During design, the booths were then
added to the APCS network to permit data sharing between the two systems. This network provides
the APCS startup control over the booths. If the APCS is down for maintenance, booth operation is
suspended or is prevented from stalling. Depending on which booth starts and whether a booth is
currently online, the APCS refers to pre-programmed responses. This provides tighter control over
critical system parameters such as induced draft pressure.
The startup strategy was developed based on the premise that the booths and the APCS form an
integrated process, thus all painting operations rely on proper functioning of the APCS. Booth
operators must be able to detect at a glance whether the APCS is available for service, or is down for
maintenance. After this is determined, and the start button is pressed, startup becomes a series of
automatically executed steps that include several system condition tests. The booth ventilation system
and APCS operations are activated only after these checks are satisfactorily completed to ensure
simultaneous, smooth, and safe system integration.
ANNISTON PRO JECT
Building on the experience of Barstow, several important improvements are planned for a facility for
the Anniston Army Depot. Two truck-sized drive-through booths are being installed with a dedicated
regenerative thermal oxidizer (RTO) for each. The inside dimensions of each booth are 40 feet long,
24 feet wide, and 18 feet high.
Many VOC control technologies were considered during the proposal stages including adsorption
based, thermal based, .and hybrids such as rotary zeolite adsorber/thermally desorbed. The procurement
of this facility included a requirement for estimated maintenance costs over a 20 year lifetime. This
drove the choice to use RTOs for VOC controls because of their inherent design simplicity and energy
efficiency. The basic design of these units has been improved over a number of years, arriving at the
latest multibed units which bring 95 percent thermal efficiency with 99 percent or more VOC
destruction. This design maturity is advantageous to production painting facilities which cannot afford
unplanned down time.
The complexity of integrating paint booth and APCS operations can be effectively handled by many
different types of hardware. The Barstow booths employ local relay logic control and standalone
process controllers, and the APCS is managed by a network of distributed control. A more integrated
control system offers many advantages. For Anniston Army Depot, programmable logic controller
(PLC) processors will be used to control both the booth operation and the RTO operation. PLCs have
gained wide industry acceptance for small to medium size process control installations. By using
identical control hardware on the major components, diagnostics can be performed by any person
familiar with this industry standard approach. For each booth/RTO pair, the two processors
communicate and share signals via a local network connection; both processors will be available by
-------
telephone connection. The primary advantage of this system is that the telephone link will allow
diagnosing any signal line of the processors. These will include such signals as:
1. Thermocouple sensors in the RTO
2. RTO poppet valve function
3. Alarm modes for the RTO
4. Recirculation flow rates
5, Exhaust flow rates
6. Filter pressure drops in the booth
7. Fan motor power
The RTO and booth share a single blower, preventing the need to match two competing fans. RTO
and recirculation blowers will be flow-rate controlled and the heating makeup air unit will be
controlled using booth static pressure.
Other advantages to more thoroughly linking booths with VOC control hardware include the ability
to support more complex modes of operation. For example, Anniston's control processors will be
programmed to support a standby mode which will be used to throttle the booths and the RTOs down
during extended breaks and preparation periods when paint guns are idle. Energy use will drop below
a quarter of that needed during painting operation. Another possibility will be a timed ramp down
mode to be used at the end of shift to prevent the loss of VOCs flashing off the day's final work. By
linking the FTIR to these modes of operation, personal exposure data will need to be collected only
during painting modes, preventing the accumulation of volumes of data when guns are turned off.
7. CONCLUSION
The partitioned recirculation paint spray booth system can address emissions from a significant
portion of DoD's aircraft and vehicle service sector, which can be considered a leading toxic materials
usage area. Such a solution is important to DoD's adherence to the 1995 National Emissions Standards
for Hazardous Air Pollutants for Source Categories: Aerospace Manufacturing and Rework Facilities7
and existing requirements for VOC emissions in ozone non-attainment areas.
Broad application of advanced split-flow recirculation paint spray booth systems can have a major
impact on reducing energy usage and regulated emissions from DoD facilities. Aircraft servicing is a
significant generator of toxic emissions with 5 of the top 10 toxic compounds found in the paints used
at typical aircraft maintenance facilities.
Most spray coating facilities can be retrofitted with partitioned recirculation ventilation to reduce the
cost of controlling VOC emissions, whether vented to a conventional or advanced control system.
Because this technology operates separately from the APCS, it is compatible with all emission control
systems. Fiscal analysis indicates that a booth similar to the Barstow installation with a 32-percent
recirculation will yield a 25- to 30-percent reduction in the typical total capital and operating cost of
$1.5 million over a 10-year lifetime. Because the degree of flow reduction is a function of many
parameters, each booth operation must be individually assessed. For example, the flow rate reduction
in a large hanger operation exhausting 250,000 cfm in which two or three paint stations are used, could
be 80 percent or higher. Conversely, the flow reduction in a small booth may be as low as 20 percent,
but in practically all cases translates into cost savings.
Even in locations which are not required to control the VOC emissions, the application of this
technology may provide substantial cost savings by reducing the heating or cooling load required to
condition large volumes of air. This can be a critical concern for facilities located in less temperate
zones of the country or in foreign installations.
10
-------
Table 2:
Metric Conversion
To convert from
Feet (ft)
Feet/minute (fpm)
Inch w.c. (in. H2O, 60° F)
Inch (in.)
Square Feet (ft2)
Cubic feet/minute (ft3/min)
to
Meter (rn)
Meter/sec (m/sec)
Pascal (Pa)
Meter (m)
Square meter (m2)
Liter/sec [m3/see]
multiply by:
0.3048
0.00508
249
0.0254
0.093
0.472 [0.000472]
ACKNOWLEDGMENTS
The authors wish to thank Dr, Joseph Wander of the Environics Directorate of Armstrong
Laboratory at Tyndall Air Force Base, Florida, and the Marine Corps Logistics Branch in Barstow, CA,
and in Albany, GA.
REFERENCES
1. U.S. Department of Labor, Occupational Safety and Health Administration (OSHA), CFR 29
1910.107, "Spray finishing using flammable and combustible materials," 1987 Edition,
2. Ayer, J., and Hyde, C, "VOC Emission Reduction Study at the Hill Air Force Base Building
515 Painting Facility." EPA 600/2-90-051 (NTIS ADA198092), April 1990.
3. Patent No. 5.221,230, (Darvin and Ayer), "Paint Spraying Booth with Split-Flow Ventilation."
Jointly held by U.S. Environmental Protection Agency and Acurex Environmental Corporation.
4. Hughes, S., J.Ayer, and R. Sutay, "Demonstration of Split-Flow Ventilation and Recirculation
as Flow-Reduction Methods in an Air Force Paint Spray Booth, Volume I,"
EPA 600/R-94-214a (NTIS ABA 286807), July 1994.
5. U.S. Environmental Protection Agency. PL 101-549: Clean Air Act Amendments of 1990.
6. U.S. Environmental Protection Agency. 40 CFR 60, Appendix A, Method 2:Stack Gas Velocity
and Volumetric Flow Rate.
7. Jordan, B.C. 1994. National Emission Standards for Hazardous Air Pollutants for Source
Categories: Aerospace Manufacturing and Rework Facilities; Background Information for
Proposed Standards. EPA 453/R-94-036a (NTIS PB94-192648), May 1994.
11
-------
NRMRL-RTP-P-218
TECHNICAL REPORT DATA
(Please readlKslructions on the reverse before completi
T. REPORT NO.
EPA/600/A-97/056
2.
3. I
4. TITLE ANDSUBTITLE
5. REPORT DATE
Choices and Challenges—Controlling Volatile Organic
Compounds and Hazardous Air Pollutants from Spray
Painting Facilities ,
6. PERFORMING ORGANIZATION CODE
7.AUTHOR(si D.Proffitt (A cur ex), C. Darvin (EPA), and
J. Ayer (Air Quality Specialists)
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Acurex Environmental Corp. Air Quality Specialists
P. O. Box 13109 Newport Beach, CA 9266(
Res. Tri. Pk, NC 27709
10. PROGRAM ELEMENT NO.
Hi, CONTRACT/GRANT NO.
68-D4-0111
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Presented paper; 10/95-1/97
14. SPONSORING AGENCY CODE
EPA/600/13
is.sui»LeMe«TARYNOTesAppCDproject officer is Charles H. Darvin, MD~6l, 919/541-
7633. Presented at 1997 DOD/lndustry Aerospace Coatings Conference, Las Vegas,
NV, 5/12-15/97.
s. ABSTRACT
paper gives a detailed discussion of the various engineering and safety
issues related to the demonstration of an advanced cost reduction strategy at a U. S.
Marine Corps maintenance facility in Barstow, CA. Details discussed included hard-
ware solutions to flow control, real-time volatile organic compound (VOC) level de-
tection in the recirculated stream, maintenance intervals of multistage exhaust fil-
ters, and hardware and software solutions to other unique process control challen-
ges. One paint booth was modified and two new booths were built to use the flow rate
reduction strategy, partitioned recirculation. This is the first such application in a
high-volume production environment. Costs for controlling emissions from these
facilities are high due to the large air volumes required to produce the minimum
face velocity required by the Occupational Safety and Health Administration (OSHA).
EPA desired to show that partitioned recirculation, developed over a number of
years and projects, could be designed and built as easily as existing non- recircula-
tion booths by using existing industry practices and a minimum of custom design.
At Barstow, partitioned recirculation and other techniques allowed a reduction in
VOC control equipment cost by reducing the flow rate from about 142,000 to 43,000
cfm (67 to 20 cu m/sec) while achieving total exhaust treatment.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.iDENTlFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Pollution
Emission
Painting
Circulation
Organic Compounds
Volatility
Pollution Prevention
Stationary Sources
Paint Booths
Partitioned Recircula-
tion
Volatile Organic Com-
oounds (VOCs)
13 B
14G
13 H
07C
20M
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
------- |