From: anthony ungerer (firstname.lastname@example.org)
Date: Fri Dec 10 1999 - 10:21:57 CST
I am in agreement with you on the vapor pressure / recovery issue. I can see it no other way than if it doesn't evaporate (low VP) then it would remain in the rags. Makes sense to me.
You may be aware that regarding air emissions in Wisconsin, lithographic printers have been allowed to take a rag retention credit of 50% for products having VP less than 10 mmHg and < 30% VOC, and 60% for products with VP > 10 mmHg. Previous to these applied credits, VOC credits were taken for the balance left in disposed rags or solvent waste. Having performed a comparison between the two, it is generally true that the acceptable rag retention credit (50 or 60%) is more favorable for the printer than an actual waste credit (. . .but not always) from an air emissions standpoint.
There's my two cents! - Tony
Jeff Adrian wrote:
> Re: Printing Rag Practices 12/7/99
> I would like to add to the other responses you have already received as I believe we were one of the first companies to practice recovery of residual solvents from soiled shop towels through the use of a centrifuge. You don't indicate the size of the printing organization or the number of shop towels used per week, but our experience and those of others would tie the return on investment (for a centrifuge) to weekly shop towel usage.
> We were able to justify a quick payback with about 7000 towels per week when we installed our centrifuge in 1990. Our shop towels, prior to centrifuging are not wet like a face cloth would be but in fact wouls yield no liquids by hand wringing. In 1993, the recovered solvents (about 2 1/2 to 3 1/2 gallons per load of 250 shop towels) were redirected from disposal through fuel blending to distillation, where the distillate was shipped from the licensed Treatment, Storage & Disposal facility back to the original vendor, who would bring the blend back into virgin specifications (mostly re-adding the surfactant package of the blend), re-package and re-lable the recycled solvent and ship it back to the John Roberts Company on an as-needed basis. Elimination of disposal costs for this former waste stream saves us about $28,000/year net!
> One observation from our own testing that differs from Lyle's experience is that the LOWER the vapor pressure of the solvent blend, the GREATER the amount recovered in the centrifuge process. Our experience in recovery rates has been borne out by US EPA research teams conducting their own testing at our site (comparing recovery rates for low and high vapor pressure solvents). So I'm a bit confused by Lyle's experience.
> Also, keep in mind that recovery of residual solvent s can possibly help with air permitting issues. If the solvent, and thus the VOCs are "in the drum", than the same cannot be said to be in the air, can it? Precisely! And so the facility may be able to take credit (as we have) for the VOCs not released through fugitive emissions. That may allow for a more flexible level of air permitting for the facility.
> Hope this helps.
> Jeff Adrian
> Director, Environment & Safety
> The John Roberts Company
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