United States Environmental Protection Agency National Risk Management Research Laboratory Research Triangle Park, NC 27711 Research and Development EPA/600/SR-96/109 October 1996 &EPA Project Summary Assessment of Styrene Emission Controls for FRP/C and Boat Building Industries Emery J. Kong, Mark A. Bahner, and Sonji L. Turner This study evaluated several con- ventional and novel emission control technologies that have been used or could be used to treat styrene emis- sions from open molding processes in fiberglass-reinforced plastics/compos- ites (FRP/C) and fiberglass boat build- ing facilities. Control costs for these conventional and novel technologies were developed and compared for three hypothetical plant sizes. The re- sults of this cost analysis indicate that (1) preconcentration by adsorption fol- lowed by desorption for recovery or oxidation appears to reduce the over- all 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 operat- ing costs decrease with decreasing ex- haust flow rate. Therefore, a company should evaluate methods to increase concentrations (i.e., reduce flow rates) of the exhaust stream before consid- ering any add-on control devices. This report also presents air flow manage- ment practices and enclosure concepts that could be used to create a concen- trated exhaust stream while maintain- ing a safe working environment. This Project Summary was developed by EPA's National Risk Management Research Laboratory's Air Pollution Prevention and Control Division, Re- search Triangle Park, NC, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction The fiberglass-reinforced plastics/com- posites (FRP/C) and fiberglass boat build- ing industries have many alternatives for reducing styrene emissions. Styrene emis- sions can be reduced by (1) using resin materials and application equipment that generate lower styrene emissions, (2) im- proving 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 vari- ous combinations, can vary widely. Lacking the regulatory mandates, add- on pollution control systems are not often used to reduce styrene emissions in the FRP/C and boat building industries. Low concentrations and high airflow rates also have made conventional emission con- trols 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 add- on 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 perfor- mance of several conventional and emerg- ing add-on pollution control technologies and air flow management practices poten- tially applicable to these industries were evaluated. ------- This report summarizes the results of literature reviews and control cost analy- ses. The report includes background in- formation about the industries and the characteristics of their emissions, assess- ment of various pollution control technolo- gies, analyses of control costs, and an evaluation of air flow management prac- tices 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 techni- cal and cost information to FRP/C and boat building companies for their use in selecting add-on pollution control technolo- gies. Companies should identify those technologies that fit their production pro- cesses and contact the vendors of those technologies for more accurate informa- tion on equipment costs. Styrene Emission Control Technologies This report presents a technical evalua- tion of conventional, novel, and emerging add-on pollution control technologies that have been used or could be used to re- duce styrene emissions from FRP/C and boat building facilities. Conventional Technologies Conventional technologies include com- bustion (i.e., thermal and catalytic oxida- tion), adsorption, and condensation, which have traditionally been used to treat vola- tile organic compound (VOC) emissions. The effectiveness and the advantages/dis- advantages of their application are pre- sented for each conventional technology. Novel Technologies Novel technologies are those that have been applied in the last decade to treat low-concentration emissions. These tech- nologies have been installed in European and Japanese FRP/C or boat building fa- cilities to treat styrene emissions or in the U.S. to treat paint booth emissions or or- ganic vapors from soil remediation. These novel technologies include (1) hybrid sys- tems that preconcentrate VOCs by ad- sorption, then desorb VOCs for recovery by condensation or for destruction by ther- mal/catalytic oxidation; (2) a biofiltration process that utilizes biodegradation to re- move 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) fluid- ized-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 under- going several years of laboratory evalua- tions. Two emerging technologies are evaluated: a membrane vapor recovery technology and a photocatalytic oxidation process that treat VOCs in the air at am- bient 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 Stan- dards (OAQPS) Control Cost Manual and cost data collected from equipment ven- dors and other sources. A computer spreadsheet model was developed to per- form cost calculations. Based on the quan- tity of styrene emitted and the control effi- ciencies of these technologies, the costs per ton of styrene removed were calcu- lated 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) cost- per-ton of styrene removed decreases as the inlet concentration increases (i.e., ex- haust flow rate decreases), and (2) preconcentration technologies appear to reduce the cost of styrene control, par- ticularly at lower styrene inlet concentra- tions. 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 eco- nomically 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 (*) For readers more familiar with metric units, 1 ton = 0.907 tonne. contaminants to an acceptable air quality level in the workplace. This common prac- tice produces high-volume, low-concen- tration exhaust streams. The cost analy- sis indicates that these high-volume, low- concentration exhaust streams make emis- sion control systems more expensive. It is also more expensive to heat or cool large volumes of makeup air. Proper air flow management would cap- ture emissions at the point of generation and prevent mixing contaminated air with clean air. Thus, proper air flow manage- ment can maintain a safe environment for operators, while significantly decreasing exhaust flow rates. These reduced ex- haust 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 vol- umes at FRP/C and boat building facili- ties. These practices and concepts include: local air flow management, spray booth modifications, and enclosures. Local Air Flow Management Local air flow management involves cap- turing air pollutants directly at the emis- sion 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 ex- haust 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, espe- cially for gel coat and resin sprayup op- erations, 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 sys- tem. The captured emissions are vented to the atmosphere or to an emission con- trol device. Several modifications to spray booth design could increase pollutant con- centration and decrease exhaust flow, thus making downstream emission controls more cost-effective. ------- Recirculation The concept of recirculation had its ori- gin 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 recircula- tion alone, the increase in inlet concen- tration to a control device is directly re- lated to the amount of recirculation. The disadvantage of recirculation is the po- tential for increased worker exposure, un- less 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. There- fore, most of the spraying and post-spray- ing 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 con- centrations 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-con- centration exhaust could be vented to at- mosphere or recirculated in the spray booth. In addition to spatial differences in emis- sions within spray booths, temporal (time- related) variations in emissions can be used to increase concentrations to the emission control device. The centrally lo- cated exhaust device could be activated to capture high-concentration exhaust dur- ing 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 con- centration measurements, or high emis- sions could be assumed to occur during any period of spraying (i.e., the small ex- haust unit is activated by the spray-gun trigger). Fresh makeup air can be sup- plied to areas occupied by the operator. Enclosures Enclosures provide a physical barrier between the emissions and the surround- ing 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 enclo- sure can be used to confine emissions or to create a low-flow-rate, high-concentra- tion exhaust stream for destruction. Conclusions and Recommendations Exhaust streams from open molding pro- cesses in the FRP/C and boat building facilities are generally at low styrene con- centrations and high air flow rates. Gen- eral (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-air- flow stream is more expensive than treat- ing a low flow rate at higher concentra- tion. Due to the general practice of dilu- tion 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, includ- ing biofiltration and preconcentration fol- lowed 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 ap- parent reduction in cost is significantly af- fected by the equipment cost assump- tions used in this cost analysis. Therefore, FRP/C companies should compare the costs of competing technologies on a case- by-case basis. The capital and operating costs of all emission control devices are strongly re- lated 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, be- fore application of add-on emission con- trol 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-concen- tration exhaust stream that makes add-on emission control devices less expensive. ------- 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 ofStyrene Emission Controls for FRP/C and Boat Building Industries,"(Order No. PB97-104640; Cost: $31.00, subjecttochange)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. 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