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I'm doing an article on a company whose Title V Operating Permit is currently under review by state regulators. (See biographical note below.) See also my specific questions, numbered below. Most important are #4 & #7 & #8.

So I'm trying to arrive at some measure of the company's baghouse filtration efficiency. The company melts heavy metals such as Cd, Cr, As & Pb in a batch heated in a 2500F furnace. The company and state regulators agree that 98% of the Cr that is emitted is Cr(VI).

There were several stack emission tests done for various HAPs; I'm focused on Cr. There are two issues at hand that may have underestimated the facility's Cr emissions for different products on an on-going basis. One is the fact that, violating the state's instructions, the company made a test product that used only ~10% of the Cr used in its most Cr-heavy product. That's one way the emissions test underestimates the company's potential actual production emissions of Cr going forward. It makes products colored with ten-times more Cr.

The second problem is that the emissions test used chromium oxide (Cr2O3), a very refractory type of Cr that is subject to forming unmelted "stones" in the batch. Thus, some significant amount of the Cr neither entered into solution nor was potentially vaporized and off-gassed off the melt to enter baghouse filtration -- some small portion of that to be emitted to ambient air. The company also uses sodium dichromate (Na2Cr2O7) as a coloring agent. In fact, it had many hundreds of pounds of Na2Cr2O7. on-site as reflected in state Fire Marshal data. But instead of using the far less refractory and more soluble Na2Cr2O7 for the test melt, it used Cr2O3. The fact that Cr2O3 remains 'inert,' in effect, in the unmelted stones, also potentially underestimates the amount of Cr emitted when Na2Cr2O7 is melted.

Such was the test-melt that yielded stack emissions data. Through the application of U.S. EPA's AEROMOD modler to arrive at dispersion levels, such low-ball emission data may have yielded an artificially high chromium daily use allowance. And, in fact, the company has already received permission to use more than 350 lb/day of chrome. Which seems like a lot for the single furnace that uses most of the Cr. (Should the company protest that it won't use 350 lb/day, note that its formal request to regulators was for permission to use almost 600 lb/day of chrome. And, to repeat, it's agreed that any emissions are Cr(VI), a rampant carcinogen.

Such is the context in which I query the good experts of Stack Exchange. Here's my questions: Is it possible, given the data in the public documents I link to below, to arrive at some estimate of the company's baghouse filtration efficiency?

The documents linked just below include the source test report, the dispersion modeling report and especially the company's Usage Rate Request -- that one is DOCUMENT A. Does that data permit you to arrive at a viable estimate for its filtration system's efficiency rating?

The 'semiotics' of everything I've encountered in my past month of research suggest that the filters are at most MERV 16. And MERV 16 filtration would not reassure neigbors justly concerned about Cr6, Cd, Pb & As, etc.

Note that the documents below are all public documents.

The Cr test used 8.05 lbs of pure chrome, Cr2O3.

According to the chrome-use request (DOCUMENT A), the lb CR VI emitted/lb Cr used = 7.59 X 10-6 lb/per lb used. It would seem we could multiply that number by 8.05 for the total amount of Cr6 emitted in the test. CORRECT?

DOCUMENT A: See the consultant's request for allowable chrome use here -- see here, page 3 for the equations.

DOCUMENT B: Here's DEQ's review of the source test -- see here, Cr data, page 2. Page 3 contains data on baghouse pressure drop and the like.

DOCUMENT C: Here's DEQ's discussion of the air modeling report -- see here.[3]

DOCUMENT D: Here's the Title V Operating Permit application -- see here. It's worth noting that on page 17, the company states the Efficiency Rating for Baghouse West (which controls 18 separate 2500F furnaces) is "99+%." To my understanding, that statement doesn't really work. That is, a MERV 16 filter is 95% effective, perhaps a bit more. And the next step up, a HEPA filter is 99.97%. So 99+% has no real standing with any group establishing efficiency standards.And, again, at a public meeting and in documents, the company has never claimed HEPA filters on its baghouse. Had it spent to the money for HEPA, it certainly would have been shouting it from the rooftops. Also see pgs 75 to 77 of DOCUMENT D linked in this paragraph for more hard data.

  1. Given the data in these documents, can you state (within some range) the facility's baghouse filtration efficiency rating?
  2. The permit application -- DOCUMENT D above, pg. 17 -- notes a 99+% Efficiency Rating. But, as has been pointed out to me, in the absence of sizing of the PM to be filtered, is that sort of a meaningless statement? (After all, the cheapest filter can have 99+% rating if it's asked to stop large rocks or some such.) So does that "99+%" rating have no real meaning?
  3. What is the aerodynamic diameter -- approximately -- of a chromium particle off-gassing off a 2500F glass-melt? A range? An estimate of the size? Way down in nanometers?
  4. Or is question #3 the wrong question since the chromium coming off the melt will be vaporized into a gas? Will the vapor phase gaseous Cr pass through the baghouse and be emitted into the air?
  5. Or is the system designed so that the gaseous Cr will condense to particulate form?
  6. If so, can we estimate the size of the PM? A few dozen nanometers perhaps?
  7. If many pounds of Cr are used per day, according to Fire Marshal data, a lot of it will be Na2Cr2O7, which is more volatile and less refractory than the Cr2O3 used in the test melt. Either way, do nearby receptors, of which there are many, including schools and day-care centers, have reason for concern? (Almost entirely all the Cr emitted is CrVI.)
  8. How much would it cost to boost this baghouse filtration system up to a HEPA level?
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  • $\begingroup$ I suggest editing the questions to be concise. Currently it is too long to read. $\endgroup$ – Mahendra Gunawardena Feb 10 '20 at 12:21
  • $\begingroup$ Are you asking us to do your research for you? $\endgroup$ – morbo Feb 11 '20 at 12:40
  • $\begingroup$ Currently wallowing through a stack of print-outs, yes, a foot high, including full texts of 30 journal articles. I've read the 250-page stack emissions report & 100-page permit applicatoin. Emailed dozens of professors, heard back from a few. Reached out to the corporate sector, including Parker-Hannifin, the baghouse makers. (They ain't talking.) The query above indicates a non-technical person's 7 weeks of scrounging for data, the company involved a black-box, state regulatros wary. After weeks of research, such as I'm able, I sought expert advise. Scott below helped. Thanks, Daniel. $\endgroup$ – Daniel Forbes Feb 11 '20 at 15:19
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The only way to determine baghouse efficiency would be a particulate sample at the inlet and outlet.

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