EPA/600/A-97/094
Paint Spray Booth Design
Using Recirculation/Partilioning Ventilation
By
Charles H. Darvin
U.S. Environmental Protection Agency
National Risk Management Research Laboratory
Research Triangle Park, NC 27711
David Proffitt
Acurex Corporation
P.O. Box 13109
Research Triangle Park, NC 27709
Jackie Ayer
Air Quality Specialists
2280 University Drive
Newport Beach, CA 92660
To be presented at AIChE Meeting, November 16-21, 1997, Los Angeles, CA
Session: Zero Discharge Manufacturing for Removal of Organics from Air -1,02g01
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Many spray painting facility operators have been attempting to reduce the discharge of volatile organic compounds (VOCs)
from paint spray booths to the atmosphere. Some have been able to convert to lower VOC containing paints and coatings
such as powder coating, waterborne coating, and radiation cured coatings. However, because of the functional requirements
of some painted surfaces, acceptable low polluting paints may not be available. Thus, these operations must continue to use
higher polluting paint formulations.
The control of emissions from paint booths has been considered not economically viable due to the cost of treating
the high volume of polluted air exhausted from these sources. However, studies conducted by EPA with various Department
of Defense (DoD) services have demonstrated that the cost of typical spray booth control can be significantly reduced through
the use of spray booth recirculation. Reductions of exhaust flow rates of up to 90 percent, when using recirculation, have
been achieved in properly designed and operated booths without concern for the industrial hygiene or fire safety issues often
mentioned when discussing recirculating booths. This paper presents the results of the design and demonstration program for
a full scale recirculating spray paint booth installed and operated at the U. S. Marine Corps (USMC), Marine Corps Logistics
Bases (MCLB) facility at Barstow, CA. It also summarizes the regulatory and safety design issues of recirculation spray
booths.
BACKGROUND
The recirculating spray paint booth concept operates by venting a portion of the exhaust, via a bleed-off stream to a
control system. The remaining exhaust air is returned to the booth after mixing with fresh air equal to the bleed-off stream
volume. Figure 1 is a schematic of a recirculation ventilation spray booth exhaust scheme. In 1981, the John Deere Company
patented a spray booth concept using recirculation [JJ. That recirculating design discharged the exhaust stream to hot water
heater burners to be used as combustion air, thus destroying the VOC content of the exhausted gases.
The use of air recirculation in spray booths has two major benefits. First, by reducing the exhaust volume significant
savings in energy needed for conditioning (heating and cooling) the booth and in some cases facility air, can be realized.
Second, both the capital and operating cost of the emissions control technology used to control the booth emissions can be
reduced. Unfortunately, even with these known benefits, recirculation has not been widely accepted as a booth design option
due to misinterpretation of Occupational Safety and Health Administration (OSHA) regulations and the pre-1985 National
Fire Protection Association (NFPA) code prohibiting recirculation of air from a paint spray booth [2.3].
In 1988, a series of studies were initiated by the U.S. Air Force (USAF) and EPA to characterize the booth
environment and emissions. The objectives of the studies were to dispel the safety concerns on the use of recirculation. The
studies were conducted at Hill Air Force Base (AFB), UT, and Travis AFB, CA. Using multiple sampling systems, the booth
environments were sampled along their lengths, heights, and widths to define the average concentrations in the various
regions of the booths during operation. The conclusions from those studies indicated that recirculation can be employed as a
method to reduce exhaust flow rates from spray booths without exceeding the exposure limits as defined by OSHA [4.5.6].
In addition, the studies also suggested a unique phenomenon in the exhaust flow patterns within and from the spray booths. A
concentration gradient at the exhaust face was formed as the pollutant flowed from the booth with the concentration relatively
high at the lower region of the booths and decreasing toward the ceiling.
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FRESH AIR
M A K EUP----
BYPASS
EXHAUST AIR
V ENTEO TO
APCS
INTAKE FILTER
EXHAUST FILTER
Figure 1. Exhaust Recirculation Spray Booth Ventilation
The evaporated solvents typically used in paints include: toluene, m,p,o-xylene, methyl isobutyl ketone, n-butyl
alcohol, ethyl benzene, and butyl acetate. Common paint solvents have specific gravities greater than air which results in a
tendency to settle to the floor of the booth. In addition, the average flow rate through a spray booth to comply with OSHA
will be at least 1.8 km/h for conventional spray booths and 1.08 km/h for booths using electrostatic painting equipment [2].
The chemical and physical properties of the pollutants in the exhaust and the relatively slow air movement in the booth result
in the formation of a region of high pollutant concentration in the lower levels of the booth. Thus, by taking advantage of
this phenomenon, it was speculated that the basic spray booth recirculation design (Figure 1) could be further enhanced by
partitioning (dividing) the exhaust into two streams and allowing the removal of a large percentage of the total pollutant
volume in a smaller exhaust stream from the lower region of the booth. Figure 2 is a conceptual schematic of the
recirculating/partitioned paint spray booth defined from the results of those studies.
FRESH
MAKEUP
A IR
BYPASS
P A RTIT1O N
EXHAUST AIR
APCS
INTAKE FILTER
EXHAUST FILTER
Figure 2. Recirculation/Partitioned Spray Booth Ventilation
The Impact of Codes and Regulations On Spray Booth Design
The design and operation of paint spray booths is governed by codes and regulations established by consensus
organizations and the various State and Federal regulatory agencies. They include OSHA, NFPA, and the American
Conference of Governmental Industrial Hygienists (ACGIH). The pre-1985 NFPA 33 Standard for Spray Painting Using
Flammable and Combustible Materials prohibited the use of recirculation in paint spray booths [2]. This prohibition was
incorporated into the OSHA regulation and applied to industrial hygiene safety. However, the original intention of the code
was to prevent the formation of concentrations approaching the explosive level of VOCs and was due primarily to the lack of
reliable and accurate monitoring equipment to ensure that VOC concentrations in the booth and exhaust did not exceed the 25
percent lower explosive limit (LEL) for the volatile constituents. In 1985, the NFPA code was revised to permit recirculation
and includes strict provisions for monitoring and controlling air movement in the booth.
The volatile concentration needed to support combustion, however, is several orders of magnitude higher than the
concentration found in typical spray booths even when operating in a recirculating mode. Thus, the deciding factor and the
most important design criterion for a manned recirculating booth atmosphere is not whether the booth will reach 25 percent
LEL, but will the booth atmosphere approach the established personnel exposure limits (PELs) as defined in OSHA 29 CFR
Part 1910, subpart z Toxics and Hazardous Substances [&]. Similar limits are also recommended by ACGIH guidelines. In
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1989, OSHA issued a policy directive accepting the use of recirculation in spray booths when operated under the established
PEL [9J. In 1992, ACGIH concurred on the use of recirculation in spray booths when designed and used properly. The
procudure is presented in the ACGIH Manual of Recommended Practice QOJ.
Recirculating/Partitioned Booths Demonstration at USMC Facility. Barstow. CA
In 1993, a joint demonstration project sponsored by the Strategic Environmental Research and Development
Program (SERDP) was initiated by the EPA and the USMC. The objectives of the program were to define the degree of
exhaust flow reduction that can be achieved by dividing a booth's exhaust stream into two flows, or partitioning the booth:
one stream a rich pollutant stream, and the other a lean stream, recirculated back to the booth. The study of the
recirculation/partitioning design would permit an evaluation of the impact of the design on industrial hygiene safety within the
booth. The demonstration included three modified booths, and an end-of-pipe control system processing exhaust from all
three booths. Each booth used the partitioned design concept shown in Figure 3 which allowed for the removal of the greatest
volume of pollutant in the least volume of air exhausted. Table 1 presents each demonstration booth's dimensions.
Table 1. Demonstration spray booth dimensions
Booth No.
1
2
3
Depth, m
18.2
6.1
3.0
Width, m
6.1
9.1
6.7
Height, m
5.5
3.0
3.0
Partition Height, m
2.7
2.0
2.0
Booth Design
Operator safety is the paramount consideration in the design and operation of a manual recirculating spray booth.
The pollutant concentration limits that drive the spray booth design are codified in OSHA 29 CFR 1910.1000 and OSHA 29
CFR 1910.107 which govern booth ventilation and worker exposure requirements [L21- The ACGIH threshold limit values
(TLVs) can also be used since they are typically more conservative than OSHA PELs. The demonstration booths at the
Barstow facility used the TLV limits which resulted in a somewhat higher exhaust flow rate than would be used if the PELs
are used for each compound. Based on the PEL or TLV values which limit the allowable toxic pollutant concentraion in the
recirculating stream, the booth design and partition heights were determined.
To determine the most efficient booth partition height, a mass balance is developed around Figure 2. The equations
assume steady state booth operation, which will result in the most conservative (worst case) results. The mass balance is
defined by: qrcr + qm Cm = qb cb . (1)
where:
qr = volume flow rate of recirculated air
cr = hazardous constituent concentration in recirculated air
qm = volume flow rate of fresh makeup air
cm = hazardous constituent concentration in fresh makeup air
qb = volume flow rate through paint booth
cb = hazardous constituent concentrations in air upstream of painter location
Since it can be assumed that the booth makeup air is free of hazardous constituents, Equation (1) at the booth inlet becomes:
qr cr = qb Cb
(2)
The mass balance equation at the booth exhaust face is defined as:
qb cb + mg = qrcr + qece (3)
where:
mg = hazardous constituent mass generation rate from paint application process
qe = volume flow rate of exhaust air vented to the air pollutant control system (APCS)
c, = hazardous constituent concentrations in exhaust air vented to.the APCS
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The left side of Equation (3) represents the mass flow rate at the booth intake face plus the mass of pollutant
generated by the spray gun in the booth during painting. The right side of Equation (3) defines the mass flow rate exiting the
booth into the recirculation duct and the exhaust duct, respectively. Based on previous studies of spray booth exhaust
characteristics, the exhaust concentration profile is not uniform across the exhaust face, and forms a non-linear decreasing
concentration gradient from the bottom to the top of the exhaust filter face [5.61. Figure 3 shows the general concentration
profile at the exhaust face. The shaded area of Figure 3 represents the pollutant mass that enters the exhaust duct at the
exhaust face below the partition height s.
on
V
Si
7
s
I
Pollutant Concentration
Figure 3. Total VOC Concentration Profile at the Exhaust Face
It is possible; therefore, to take advantage of this profile by strategically locating the exhaust duct to the APCS. The location
of the flow partition is determined experimentally by testing and developing a concentration profile of the exhaust face of the
booth. Thus, an additional element is added to Equation (3) that defines the impact of the partitioning of the booth flow to the
recirculation and exhaust ducts. When incorporated into Equation (3), it locates the exhaust duct and correlates the pollutant
mass flow rate to the exhaust stream at the exhaust face. That relationship is defined by:
qece = mg(l - X) + cbqb(s/H) (4)
where:
X = percent of hazardous constituents generation in the booth exiting above height s.
s = partition height
H = exhaust filter height
Substituting Equation (4) into Equation (3) yields:
qrcr = qbcb(l-s/H) + mg X (5)
The qb cb(l - s/H) term in Equation (5) represents the hazardous constituent mass flow rate in the recirculation
stream that is reintroduced at the intake face. The third term in Equation (4) represents the mass of pollutant that is
introduced into the recirculation duct by the painting operation. The mathematical expression that defines the relationship
between the constituent concentrations in the recirculation stream and the partition height therefore becomes:
cr = (mg X)/qr (s/H) (6)
The partition height and corresponding recirculation rate that yield acceptable hazardous constituent concentrations in the
booth intake stream may then be derived iteratively from Equation (6).
RESULTS AND CONCLUSIONS
The spray booth installations at the Barstow facility met all operating and safety design requirements projected at
the beginning of the program. Continuous monitoring and discrete testing of the booth operation and exhaust were conducted
over a 1 month period to confirm that predicted recirculation and exhaust stream concentrations levels were achieved. First,
the pollutant concentrations within each booth were not significantly increased with the use of recirculation. There was no
apparent degradation in booth atmosphere compared to pre-modification levels. It was found that the resulting flow patterns
in the modified booths improved the overall atmosphere of the booth. Second, test results for each booth validated the
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presence of a pollutant concentration gradient as found in previous studies. For example. Figures 4 and 5 below show the
metal and organic mass distribution at the exhaust face. The pollutant mass is primarily concentrated at the lower region of
the booth. The concentration gradient is important for maximizing the amount of pollutant exiting the booth in the partitioned
stream to the APCS, thus achieving the flow reduction capability of the design. In figures 4 and 5, over 70 percent of the of
the generated pollutant exits the booth at or below the 9 foot (2.7 meter) level of the 18 foot (5.5 meter) high exhaust filter.
Table 2 presents a summary of the flow reductions achieved with the new or modified booths.
IS
S 10
£
o
i s
20 40 60
PERCENT BELOW HEIGHT
80
100
Figure 4. Cumulative Distribution of Metals at Various Heights in Booth 1.
15
I 10
H
0
20 40 60
PERCENT BELOW HEIGHT
80
100
Figure 5. Cumulative Distribution of Organic Mass at Various Heights in Booth 1.
Table 2. Summary of volumetric flow rate reduction achieved at Marine Corps Logistics Bases
Booth No.
1
2
3
Total
Initial Exhaust
Flow Rates
rrrVmin
1,500
1,783
778
4,061
Projected Exhaust
Flow Rates
m3/min
566
580
393
1,539
Final Exhaust Flow
Rates to APCS
mVmin
572
604
415
1,591
Percent Exhaust
Flow Reduction
to APCS
62
66
47
61
jaint booths.
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LITERATURE CITED
1. U.S. Patent No. 4,266,504, "Paint Spraying Assembly," Deere & Company, Moline, IL, (May 12, 1981).
2. U.S. Department of Labor, Occupational Safety and Health Administration (OSHA), CFR 29, 1910.107, "Spray
Finishing Using Flammable and Combustible Materials," (1987).
3. "Standard for Spray Finishing Using Flammable and Combustible Materials," NFPA No. 33, (1969).
4. Ayer, J. and C.D, Wolbach,"Volatile Organic Compound and Particulate Emission Studies of Air Force Paint Booth
Facilities: Phase I." EPA-600/2-88-071 (NTIS ADA 198092), (December 1988).
5. Ayer, J, and C. Hyde, "VOC Emission Reduction Study at the Hill Air Force Base Building 515 Painting Facility,"
EPA-600/2-90-051 (NTIS ADA 198092), (September 1990).
6. 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).
7. U.S. Department of Labor, Occupational Safety and Health Administration (OSHA), 29 CFR 1910.94, Subpart G,
"Ventilation," (1974).
8. U.S. Department of Labor, Occupational Safety and Health Administration (OSHA), 29 CFR 1910.1000, Subpart Z,
"Toxics and Hazardous Substances," (1987).
9. U.S. Department of Labor, Occupational Safety and Health Administration, "OSHA Computerized Information
System, Exhaust Air in Spray Operation," (November 3,1989).
10. Industrial Ventilation. A Manual of Recommended Practice, 21st Edition ACGIH, Cincinnati, OH, (1992).
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NRMRL-RTP-P-258
TECHNICAL REPORT DATA
(Please read Imsottctions on the reverse before eomplei
1. REPORT NO.
EPA/600/A-97/094
4. TITLE AND SUBTITLE
Paint Spray Booth Design Using Recirculation/
Pardoning Ventilation
5. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
C. H. Darvin (EPA), D. Proffitt (Acurex), and J.Ayer
(Air Quality Specialists)
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Acurex Corporation Air Quality Specialists
P. O. Box 13109 2280 University Drive
RTP, NC 27709 Newport Beach, CA 92660
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-D4-0111 (A curex)
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 flEPORT AND PERIOD COVERED
Published paper; 10/95-1/97
14. SPONSORING AGENCY CODE
EPA/600/13
is. SUPPLEMENTARY NOTES APPCD project officer is Charles H. Darvin, Mail Drop 61, 919/
541-7633. Presented at AIChE Conference, Los Angeles, CA, 11/16-21/97.
16. ABSTRACT
The paper gives results of a design and demonstration program for a full-
scale recirculating spray paint booth installed and operated at the U. S. Marine
Corps, Marine Corps Logistics Bases facility at Barstow, CA. It also summarizes
the regulatory and safety design issues of recirculation spray booths. The control of
emissions from paint booths has been considered to be not economically viable due to
the cost of treating the high volume of polluted air exhausted from these sources.
However, studies conducted by EPA with various Department of Defense services
have demonstrated that the cost of typical spray booth control can be reduced signi-
ficantly through the use of spray booth recirculation. Reductions of exhaust flow
rates of up to 90% when using recirculation have been achieved in properly designed
and operated booths without the industrial hygiene and fire safety problems often
mentioned when discussing recirculating booths.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lOENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution
Spray Painting
Ventilation
Emission
Pollution Prevention
Stationary Sources
Spray Booths
Recirculation/Partition-
ing
13B
13H
13A
14G
18. DISTRIBUTION STATEMENT
Release to Public
19.SECURITY CLASS (ThisReport/
Unclassified
21. NO, OF PAGES
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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