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Article # 0040

Reductions in Styrene Emissions from the CFA/UEF Emission Model

 

There are several assumptions utilized in calculating styrene emissions in the fiberglass manufacturing industry.  The Composite Fabricator’s Association (CFA)/United Emission Factor (UEF) table is the accepted emission factor model for calculating air emissions of styrene by both the Environmental Protection Agency (EPA) and the Texas Commission on Environmental Quality (TCEQ).  These factors are dependant upon styrene content and application method. While the assumptions underlying these factors are valid and are generally employed for emission calculations submitted to the TCEQ in the air permit application process, they are also conservative.  This article discusses some of the aspects of this conservatism and suggests a few methods for reducing styrene emission rates in calculations from fiberglass manufacturing.

 

CFA/UEF Emission Model Assumptions

 

General Overspray Assumptions for Thermoset Materials

 

On the average, overspray from the application of thermoset resin and gelcoat materials may generate waste totaling approximately 14% of the total amount of catalyzed material that was sprayed. (see Reference 1 - Controlled Spraying and Laser Touch® in the Fiber Reinforced Plastics Industry available at http://www.mntap.umn.edu/fiber/89-LaserTouch.htm).  This is consistent with the TCEQ’s generally-employed assumption of 20% overspray when high-volume low-pressure, high transfer efficiency spray guns are used for coating or thermoset material application.  When controlled spray techniques are utilized, the waste generation may drop to approximately 10% of the total amount of catalyzed material that was sprayed.

 

The Effect of Overspray on the CFA/UEF Emission Model

 

Overspray of thermoset materials increases process emissions due to the increased surface area of the oversprayed material.  Reduction of the amount of overspray has been found to affect the emissions of styrene from fiberglass manufacturing processes in a proportional manner. (Reference 2 - CFA Emission Models for the Reinforced Plastics Industries available at http://www.epa.gov/ttn/chief/efdocs/cfa_rpt3.pdf) 

 

The CFA/UEF emission model uses this proportional reduction for estimating emissions from processes using controlled spraying techniques.  (see Reference 3 - Unified Emission Factors for Open Molding of Composites available at http://www.dem.ri.gov/programs/benviron/air/pdf/uefs.pdf)   The reduction used in this table is an average of the percentage reduction seen in the overall model, as discussed in Reference 2. 

 

Controlled Spraying Techniques

 

As discussed in Reference 1 and in Reference 4 – Controlled Spraying Handbook (the industry standard published by the American Composites Manufacturing Association available at http://www.acmanet.org/ga/Controlled_Spray_Handbook.pdf), controlled spray techniques involve three elements to reduce overspray and thus emissions of styrene:

 

• Optimization of spray gun settings

• Capturing overspray at the mold perimeter

• Training operators

 

Operations employing these techniques are generally allowed by the TCEQ to take the reduction in emissions shown on the CFA/UEF emission factor table.

 

Resin Spray Guns

 

A typical resin application gun is Glas-Craft 23550-00.  This is an internal mix non-atomized spray gun.  Therefore, the CFA/UEF emission model for open molding operations with non-atomized mechanical resin application is used for the basis for emission calculations utilizing this type of application equipment.  These spray guns utilize fluid impingement technology which is defined in 40 CFR 63 Subpart WWWW (Fiberglass MACT Standard) as “a spray gun that produces an expanding non-misting curtain of liquid by the impingement of low-pressure uninterrupted liquid streams.”  This same subpart states that “Examples of nonatomized application include flow coaters, pressure fed rollers, and fluid impingement spray guns.”

 

Since this application method is “spraying” resin material, overspray is generated.  Reductions of the amount of overspray from these non-atomized guns through the utilization of controlled spray techniques should have the same proportional effect on the emissions of styrene as reduction in overspray from atomized spray guns.  Therefore, controlled spraying techniques are a useful emission reduction strategy to add to the effective reduction of styrene emissions from the resin spray guns utilizing fluid impingement technology.

 

This reduction is not employed on the CFA/UEF emission factor table, but could potentially be incorporated into the emission calculations submitted to the TCEQ for approval during the air permit application process.

 

The Effect of Surface Barriers on the CFA/UEF Emission Model

 

Vapor-suppressed resins are those which contain additives that migrate to the surface of the resin after it is applied to form a waxy barrier preventing the evaporation of styrene monomer during curing.  The function and effect of the barrier is essentially identical to the use of a covered cure.  A covered cure provides a film or barrier over the applied resin to prevent styrene evaporation.  (See Reference 5, available from www.epa.gov - Technical Discussion of the Unified Emission Factors for Open Molding of Composites, in particular pages 2-3, and 13-17).  As discussed in Reference 5, a barrier used in conjunction with a fiberglass manufacturing process utilizing resin sprayup and subsequent rollout will provide a proportional reduction of emissions during the curing phase from that expected from an identical process that does not utilize a barrier.  This reduction occurs due to the fact that a certain portion of the total emissions occurring during the manufacturing process occur during curing after sprayup and rollout.  This reduction is specified in References 5. 

 

It is possible that the manufacturing process utilized in some facilities may provide a physical barrier to styrene monomer evaporation during some steps of the open molding process.  If the resin application to the mold occurs in several layers (especially if the sprayed layer includes application of a layer of woven roven glass and subsequent resin rollout) and a layer is only partially cured before the next layer is applied, the next layer may provide a partial vapor barrier to the previous one.

 

Therefore, it may be appropriate to apply a reduction in emissions consistent with the derivation of emission factors for vapor suppressed resin and covered cure from the CFA/UEF model as discussed in the various references.

 

Biography 

Karen M. Bullard, P.E. is an Engineering Partner and the President of Bullard Environmental Consulting, Inc.   She has over 15 years experience in environmental engineering, compliance, and permitting.  She worked for the Texas Commission on Environmental Quality (TCEQ) for four years as an Air Permit Specialist in the Coatings and Combustion Section, where she developed a thorough understanding of the governmental procedures and policies in Texas.    Karen has a Bachelors of Science Degree in Chemical Engineering from the University of Texas at Austin.

Karen M. Bullard, P.E. No. 88449

Final Edition Completed June 27, 2008 from Previously Composed Material

 

 

Article # 0040         TEST QUESTIONS:

1.   What is the TCEQ?

  1. Texas Comity Evaluation Quorum

  2. Testing Cooperative for Environmental Quality

  3. Texas Committee on Emissions Quantity

  4. None of the above

2.   What is the CFA?

  1. Chlorofluoroacetone

  2. Composite Fabricator’s Association

  3. Consolidated Federal Air Standards

  4. None of the above

3.   What is the UEF?

  1. Unified Emission Fraction

  2. Ultimate Emission Formula

  3. United Emission Factor

  4. None of the above

4.   On average, what percentage of the total amount of sprayed, catalyzed material is wasted as overspray?

  1. 14%

  2. 22%

  3. 36%z

  4. 41%

5.   What is the TCEQ's assumption for the waste percentage when using high-volume low-pressure, high transfer efficiency spray guns?

  1. 10%

  2. 20%

  3. 30%

  4. 40%

6.   When controlled spray techniques are utilized, the waste generation may drop to approximately ____?

  1. 10%

  2. 20%

  3. 30%

  4. 40%

7.   Controlled spray techniques include which of the following to reduce overspray and thus emissions of styrene:

  1. Optimization of spray gun settings

  2. Training operators

  3. Computer Aided Spray Controls

  4. a and b

8.   ______  are those which contain additives that migrate to the surface of the resin after it is applied to form a waxy barrier preventing the evaporation of styrene monomer during curing.

  1. Vapor-suppressed resins

  2. Controlled cure cycle resins

  3. Low-volatile content resins

  4. Simulated covered cure by additive migration (SCCAM) resins

9.  An example(s) of nonatomized application include ______.

  1. pressure fed rollers

  2. flow coaters

  3. fluid impingement spray guns

  4. All of the above

10.   According to the article, overspray of thermoset materials increases process emissions due to the increased  ______ of the oversprayed material

  1. surface area

  2. volume

  3. waste

  4. All of the above

 

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