United States National Risk Management

Environmental Protection Research Laboratory

Agency Research Triangle Park, NC 27711

Project Summary

Research and Development EPA/600/SR-96/109 October 1996

This study evaluated several conventional and novel emission control

technologies that have been used or

could be used to treat styrene emissions from open molding processes in

fiberglass-reinforced plastics/composites (FRP/C) and fiberglass boat building facilities. Control costs for these

conventional and novel technologies

were developed and compared for

three hypothetical plant sizes. The results of this cost analysis indicate that

(1) preconcentration by adsorption followed by desorption for recovery or

oxidation appears to reduce the overall cost of styrene control, particularly

at the lower styrene concentrations

(less than 100 ppm) typically found at

these facilities, and (2) increasing the

styrene concentration (i.e., lowering

flow rate) of the exhaust streams can

significantly reduce cost per ton of

styrene removed for all technologies

examined, because capital and operating costs decrease with decreasing exhaust flow rate. Therefore, a company

should evaluate methods to increase

concentrations (i.e., reduce flow rates)

of the exhaust stream before considering any add-on control devices. This

report also presents air flow management practices and enclosure concepts

that could be used to create a concentrated exhaust stream while maintaining a safe working environment.

This Project Summary was developed

by EPA’s National Risk Management

Research Laboratory’s Air Pollution

Prevention and Control Division, Research Triangle Park, NC, to announce

Assessment of Styrene Emission

Controls for FRP/C and Boat

Building Industries

Emery J. Kong, Mark A. Bahner, and Sonji L. Turner

key findings of the research project

that is fully documented in a separate

report of the same title (see Project

Report ordering information at back).

Introduction

The fiberglass-reinforced plastics/composites (FRP/C) and fiberglass boat building industries have many alternatives for

reducing styrene emissions. Styrene emissions can be reduced by (1) using resin

materials and application equipment that

generate lower styrene emissions, (2) improving operator techniques to reduce

overspray, (3) changing from open- to

closed-molding processes, and (4) using

add-on emission control devices. The

amount of reduction achieved by these

alternatives, taken separately or in various combinations, can vary widely.

Lacking the regulatory mandates, addon pollution control systems are not often

used to reduce styrene emissions in the

FRP/C and boat building industries. Low

concentrations and high air flow rates also

have made conventional emission controls very expensive and, in some cases,

less efficient in destroying the emissions.

The FRP/C and boat building industries

need information on the applicabilities and

costs of conventional and emerging addon pollution control technologies so they

can make informed decisions about the

use of controls to reduce their emissions.

To meet this need, the cost and performance of several conventional and emerging add-on pollution control technologies

and air flow management practices potentially applicable to these industries were

evaluated.
2

This report summarizes the results of

literature reviews and control cost analyses. The report includes background information about the industries and the

characteristics of their emissions, assessment of various pollution control technologies, analyses of control costs, and an

evaluation of air flow management practices that may reduce worker exposure

and control costs. The appendixes include

costing procedures for various pollution

control technologies and a spreadsheet

cost model for these control technologies.

This report provides preliminary technical and cost information to FRP/C and

boat building companies for their use in

selecting add-on pollution control technologies. Companies should identify those

technologies that fit their production processes and contact the vendors of those

technologies for more accurate information on equipment costs.

Styrene Emission Control

Technologies

This report presents a technical evaluation of conventional, novel, and emerging

add-on pollution control technologies that

have been used or could be used to reduce styrene emissions from FRP/C and

boat building facilities.

Conventional Technologies

Conventional technologies include combustion (i.e., thermal and catalytic oxidation), adsorption, and condensation, which

have traditionally been used to treat volatile organic compound (VOC) emissions.

The effectiveness and the advantages/disadvantages of their application are presented for each conventional technology.

Novel Technologies

Novel technologies are those that have

been applied in the last decade to treat

low-concentration emissions. These technologies have been installed in European

and Japanese FRP/C or boat building facilities to treat styrene emissions or in the

U.S. to treat paint booth emissions or organic vapors from soil remediation. These

novel technologies include (1) hybrid systems that preconcentrate VOCs by adsorption, then desorb VOCs for recovery

by condensation or for destruction by thermal/catalytic oxidation; (2) a biofiltration

process that utilizes biodegradation to remove VOC emissions; and (3) a process

that applies ultraviolet (UV) light and ozone

in a wet system to disintegrate VOCs into

carbon dioxide and water, and removes

smaller organics in the exhaust gas by

adsorption.

Five preconcentration/recovery/oxidation

hybrid systems are evaluated: (1) MIAB

system, (2) Thermatrix PADRE system,

(3) Polyad system, (4) rotary concentrator

system by Durr Industries, and (5) fluidized-bed preconcentration system by

REECO/Environmental C&C.

Emerging Technologies

Emerging technologies are those that

are just beginning to be explored via field

applications and pilot testing after undergoing several years of laboratory evaluations. Two emerging technologies are

evaluated: a membrane vapor recovery

technology and a photocatalytic oxidation

process that treat VOCs in the air at ambient temperatures in the presence of UV

light and a catalyst.

Control Cost Analyses

Total annualized costs for all control

technologies were calculated using the

general procedures outlined in the EPA

Office of Air Quality Planning and Standards (OAQPS) Control Cost Manual and

cost data collected from equipment vendors and other sources. A computer

spreadsheet model was developed to perform cost calculations. Based on the quantity of styrene emitted and the control efficiencies of these technologies, the costs

per ton of styrene removed were calculated from annualized costs. Control costs

for all control technologies were analyzed

for three hypothetical plants, treating 20,

100, and 400 tons* per year of styrene

emissions.

The cost analyses show that (1) costper-ton of styrene removed decreases as

the inlet concentration increases (i.e., exhaust flow rate decreases), and (2)

preconcentration technologies appear to

reduce the cost of styrene control, particularly at lower styrene inlet concentrations. The results of the cost analyses

suggest that reducing the inlet flow rates

to control devices is a good approach to

making any control technology more economically feasible.

Air Flow Management Practices

Current ventilation systems in FRP/C

and boat building facilities are primarily

designed to provide an environment that

is safe for workers and produces good

product quality. General ventilation, also

called dilution ventilation, supplies an

ample amount of makeup air to dilute the

contaminants to an acceptable air quality

level in the workplace. This common practice produces high-volume, low-concentration exhaust streams. The cost analysis indicates that these high-volume, lowconcentration exhaust streams make emission control systems more expensive. It is

also more expensive to heat or cool large

volumes of makeup air.

Proper air flow management would capture emissions at the point of generation

and prevent mixing contaminated air with

clean air. Thus, proper air flow management can maintain a safe environment for

operators, while significantly decreasing

exhaust flow rates. These reduced exhaust flow rates (increased concentrations)

can reduce control costs.

This report presents several air flow

management practices and concepts that

could be applied to minimize air flow volumes at FRP/C and boat building facilities. These practices and concepts include:

local air flow management, spray booth

modifications, and enclosures.

Local Air Flow Management

Local air flow management involves capturing air pollutants directly at the emission source; therefore, the amount of air

to be ventilated is minimized. In an open

space, this can be done by blowing

makeup air toward the emission source

and capturing the emission with an exhaust hood at the other end (a push/pull

ventilation system). Capture efficiency is

generally better for a push/pull system

than for an exhaust hood alone.

Spray Booth Modifications

Spray booths are commonly used in the

FRP/C and boat building industries, especially for gel coat and resin sprayup operations, and for parts (i.e., items being

manufactured) that can fit into a spray

booth. Using a spray booth can prevent

cross-contamination created by general

ventilation, because styrene emissions are

captured and exhausted directly.

 In a typical spray booth, a mold is

placed in the center of the booth. Air is

drawn into the front opening of the booth,

travels past the mold, and exits through a

filter bank at the rear of the booth. Dry

filter media are used to capture overspray,

and the media are replaced frequently to

protect the duct work and exhaust system. The captured emissions are vented

to the atmosphere or to an emission control device. Several modifications to spray

booth design could increase pollutant concentration and decrease exhaust flow, thus

making downstream emission controls

more cost-effective.

(*) For readers more familiar with metric units, 1 ton =

0.907 tonne.
3

Recirculation

The concept of recirculation had its origin in the spray painting industry, as a

means of lowering exhaust flow rates (and

therefore treatment costs) in paint spray

booths. Recirculation involves redirecting

a portion of the spray booth exhaust

stream back into the spray booth. The

recirculation stream may be reintroduced

at any location in the spray booth (e.g.,

near the inlet face, or at the center of the

booth). For a spray booth with recirculation alone, the increase in inlet concentration to a control device is directly related to the amount of recirculation. The

disadvantage of recirculation is the potential for increased worker exposure, unless fresh makeup air is provided to the

operator through a duct, or the operator

wears a respirator.

 Split-Flow Design

In a typical (horizontal-flow) spray booth,

the part being sprayed does not extend to

the full height of the spray booth. Therefore, most of the spraying and post-spraying emissions occur near the bottom of

the booth. A split-flow painting spray booth

design takes advantage of this fact. In this

design, higher-concentration exhaust air

from the bottom of the booth is directed to

an emission control device, while

lower-concentration air from the top of the

booth is recirculated. The main advantage

of a split-flow design is that it produces an

increase in VOC concentrations going to

a control device; however, the area to be

split must be specific to each spray booth,

based on the actual spraying pattern and

concentrations at various locations.

Other Design Modifications

In a typical spray booth in an FRP/C

facility, a mold is placed in the center of

the booth. The arrangement of the mold

within the booth is such that higher concentrations are drawn through the center

of the filter bank, rather than through the

top or sides of the filter bank. A spray

booth can be modified to take advantage

of this spatial difference in concentrations.

Modification would involve constructing a

smaller, centrally located exhaust device.

The higher-concentration exhaust collected

by this device would be directed to an

emission control device. The lower-concentration exhaust could be vented to atmosphere or recirculated in the spray

booth.

In addition to spatial differences in emissions within spray booths, temporal (timerelated) variations in emissions can be

used to increase concentrations to the

emission control device. The centrally located exhaust device could be activated

to capture high-concentration exhaust during the spraying period. The main exhaust

of the spray booth would be operating

continuously during the nonspraying or

low-concentration period. Periods of high

emissions could be determined by concentration measurements, or high emissions could be assumed to occur during

any period of spraying (i.e., the small exhaust unit is activated by the spray-gun

trigger). Fresh makeup air can be supplied to areas occupied by the operator.

Enclosures

Enclosures provide a physical barrier

between the emissions and the surrounding environment, and they can reduce or

eliminate the dispersion of styrene vapors

from a production process. However, the

styrene concentration within the enclosure

must be kept below 2,500 ppm (25% of

the lower explosive limit) by ventilation. If

an enclosure is ventilated, the exhaust

concentration is inversely related to the

exhaust flow rate. Therefore, an enclosure can be used to confine emissions or

to create a low-flow-rate, high-concentration exhaust stream for destruction.

Conclusions and

Recommendations

Exhaust streams from open molding processes in the FRP/C and boat building

facilities are generally at low styrene concentrations and high air flow rates. General (dilution) ventilation is usually used to

ensure that worker exposure is less than

that allowed by Occupational Safety and

Health Administration (OSHA) standards.

Treating this low-concentration, high-airflow stream is more expensive than treating a low flow rate at higher concentration. Due to the general practice of dilution ventilation and the current lack of

specific regulations that require add-on

emission controls, these control devices

are not commonly used in the FRP/C and

boat building industries.

Of the limited number of add-on control

devices used in the FRP/C facilities in the

U.S., thermal and catalytic oxidation are

the most common. Costs of alternative

technologies have been compared, including biofiltration and preconcentration followed by recovery or oxidation, with

straight thermal and catalytic oxidation.

Preconcentration technologies followed by

recovery or oxidation appear to reduce

the cost of styrene control, particularly at

the lower styrene concentrations (less than

100 ppm) typically found at FRP/C and

boat building facilities. However, this apparent reduction in cost is significantly affected by the equipment cost assumptions used in this cost analysis. Therefore,

FRP/C companies should compare the

costs of competing technologies on a caseby-case basis.

The capital and operating costs of all

emission control devices are strongly related to the flow rate of the incoming

stream. Cost analyses indicate that, for all

control devices examined, cost per ton of

styrene removed decreases as styrene

inlet concentration increases (i.e., as the

air flow rate decreases). Therefore, it is

probably economical to concentrate the

exhaust air stream, using proper air flow

management practices or enclosures, before application of add-on emission control devices.

Proper air flow management techniques,

which capture emissions at the source, or

enclosures, which prevent plant air from

diluting styrene emissions, can reduce the

exhaust flow rate and increase styrene

concentration in the exhaust streams from

FRP/C and boat building facilities. These

approaches can maintain a safe working

environment and produce a high-concentration exhaust stream that makes add-on

emission control devices less expensive.
4

Emery J. Kong, Mark A. Bahner, and Sonji L. Turner are with Research Triangle Institute,

Research Triangle Park, NC 27709.

Norman Kaplan is the Project Officer (see below)

The complete report, entitled “Assessment of Styrene Emission Controls for FRP/C and

Boat Building Industries,” (Order No. PB97-104640; Cost: $31.00, subject to change) will

be available only from:

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

Telephone: 703-487-4650

The EPA Project Officer can be contacted at:

National Risk Management Research Laboratory

Air Pollution Prevention and Control Division

U.S. Environmental Protection Agency

Research Triangle Park, NC 27711

United States

Environmental Protection Agency

Center for Environmental Research Information (G-72)

Cincinnati, OH 45268

EPA/600/SR-96/109

Official Business

Penalty for Private Use $300

BULK RATE

POSTAGE & FEES PAID

EPA

PERMIT No. G-35