p.1 

OAR Box 1490 

Prepped by Charmelle Mathews 

Document Number: 

13) IV-B-13 

Docket Number: 

A-94-52 

Printed 8/4/2008 11:51:46 AM Sheet 13 of 273 
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MEMORANDUM 

TO: Docket 94-52, Reinforced Plastic Composites NESHAP 

FROM: Keith Barnett, Environmental Protection Agency and Ken Meardon, Pacific 

Environmental Services (PES) 

DATE: August 23, 2002 

SUBJECT: Evaluation of Composite Fabricators Association (CFA) comments on control of 

mixer emissions using covers. 

The CFA requested that we allow the use of covers to control emissions from mixing operations, 

rather than the 95 percent control requirements in the proposed rule. Their position was that 

covers were essentiality equivalent to 95 percent control without the adverse secondary impacts. 

We agreed to review their information. 

Pages 2 through 4 present an analysis prepared by PES ofthe CFA control estimates. Based on 

this analysis, we do not believe that it can be stated that 95 percent control and covering the 

mixers is equivalent. 

In the final rule, only mixing operations at new facilities must meet the 95 percent control 

requirement. At the floor facility, the mixers are covered, meeting the work practice requirements 

of Table 4 ofthe rule. The mixing room is then vented to the permanent total enclosure that 

encloses the production process. Therefore, the new source floor is covered mixers, with all 

mixer emissions venting to a control device that is 95 percent efficient. 
07/25/02 13:25 ©19199410234 PES RTP NC ©002/004 

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COVERS ON MIXERS 

Industry has requested that new source MACT require only covers on mixers rather than 

95% control. They have provided a spreadsheet analysis ofthe potential effectiveness of covers 

at 12 facilities (cases). Their results show a range of effectiveness from 85 to 96.9%. 

One ofthe basic assumptions used in their analysis is the uncontrolled emission factor of 

1%. This came from an agency-observed stack test on an open BMC mixer. We evidently used 

an emission factor of 0.5% (I do not know where this came from). 

Attached is a spreadsheet looking at two aspects ofthe potential effectiveness of mixer 

covers: 

1. The percent emission reduction achieved at various uncontrolled emission factors 

(1% down to 0.5%). 

2. The percent emission reduction achieved versus the type of paste mixed, the batch 

weight, and the mix time per batch. 

Observations 

1. The first observation, which should be obvious, is that as the uncontrolled emission 

factor drops, the estimated efficiency ofthe covers also drops. At 0.5%, the estimated efficiency 

range is 70 to 94%, with 11 of the 12 facilities having an emission reduction efficiency of less 

than 90%. Thus, it is critical to determine an appropriate uncontrolled emission factor or factors 

as the factor could (likely) vary with the type of paste being mixed, type of mixer used, HAP 

content ofthe paste, etc. 

2. Looking at the Paste Mixed column, the one thing that stands out is that four ofthe 

bottom five facilities are SMC and BMC mixes. 

3. Looking at the Batch Weight column, the one thing that stands out is that the heavier 

the batch, the better the estimated efficiency ofthe cover (excluding the SMC and BMC results). 

4. Looking at the Mix Time per Batch column, the one thing that stands out is that the 

longer the batch is mixed, the higher the estimated efficiency ofthe cover (almost even including 

SMC and BMC, but especially excluding them). 

What Does it Mean? 

I do not think a universal "adoption" of covers over 95% reduction is in order. If we 

consider adopting a covers only standard, it should be targeted to open molding mixing (i.e., 

conversely, do not include SMC and BMC in the exclusion) and to the length of time each batch 

is mixed (e.g., greater than 1 hour). 

We could have individual facilities conduct specific source tests of their mixers to 

develop specific emission factors and show on paper ala what Lipiro did that the estimated 

emission reduction is at least 95%. Of course, I think that the General Provisions might already 

allow this. 

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Covers on Mixers 

page 2 

OTHER THOUGHTS 

When I read Lipiro's analysis, one of my first thoughts is that this should not be an 

incremental analysis for new sources. Then I went and refreshed my memory as to what is being 

required of new sources for mixing. 

For new sources >100 tpy, we are requiring mixing: 

(1) to be controlled 95% [63.5805(c)] and 

(2) to use covers with no visible gaps present in the mixer covers and keep the 

mixers covers closed during mixing except when adding materials to the mixing 

vessels (Table 4). 

Looking at these requirements, I can see why one would conduct an incremental analysis. 

If mixers are required to be closed and they achieve 85 to 97% reduction already, then 63.5805(c) 

is only achieving up to another 10% of overall control. 

Scenario 1. Ifl have to control my mixers 95% by using an add-on control device, I am 

basically saying I need to capture my mixing emissions 100% and then reduce the captured 

emissions by 95%. But, the requirement in Table 4 allow from some escape of emissions when 

adding materials, resulting in less than 100% capture. So how can I achieve 100% capture? By 

placing all my mixers in a PTE (e.g., a room) and venting the PTE/room to the control device. 

But if I am doing that, then why do I need to put covers on my mixers? I am reducing the 

amount of styrene in the air and sending a more dilute stream to the control device. This says to 

me that requirements in Table 4 are not necessary for new sources. 

Scenario 2. Ifthe rule allows me to average all of my emissions for detennining 95% 

control, then I might be able to put covers on my new mixers (or even leave them uncontrolled) 

and control the remaining emissions (i.e., those from other processes) by more than 95% and still 

show at least 95% emission reduction overall. 

In summary, I am wondering: 

1. If we keep the 95% requirement, do we need the Table 4 requirements for mixers 

at all? 

2. If we should make it explicitly clear that ifa facility can demonstrate that covers 

achieve 95% reduction for their mixers, then they have meet the requirements of 

the rule (regardless of actual compliance with Table 4). 

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