Printech Archive
Re: Blanket wash


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From: Jeff Adrian (jeffadrian@johnroberts.com)
Date: Thu Mar 09 2000 - 08:29:00 CST


                      Re: Blanket wash 3/9/00
Robb:

Certainly answering the questions raised by Gary Jones in reply to your original
question will increase the accuracy of any calculated emissions.
if, however, what you are measuring is the mixture collected after the cleaning
operations, be they hand cleaning or automatic cleaning, some general
observations regarding the nature of your solvent blend still hold true.

Based upon my experience with a similar solvent blend (percentage of aliphatic
and aromatic hydrocarbons), I would (safely) specualate that your blend has a
vapor pressure of 3.6 or so. Experience with solvent blends with vapor pressures
in this range indicates comparitively little evaporative (fugitive) losses
provide good management techniques are employed (closed shop towel collection
bins, screened bench cans, closed containers, etc.).

If you utilize any active form of recovery of residual solvents in shop towels,
for example a centrifuge or mechanical wringing, recovery of solvents can be as
much as 91% of solvents purchased and brought into the plant. Our own studies
have measured this, and when US EPA reserachers visited our facility to do their
own research on solvent recovery, their figures confirmed ours.

If, on the other hand, you do not use an active form of solvent recovery from
soiled shop towels, our experience and measurements indicate that you would miss
recovery of another 9-10 % of solvents that are residual in the shop towels.
This would reduce your over-all recoveries to approximately 81% of solvents
brought into the facility. It is very important to note that the numbers stated
above would hold true ONLY if your soiled shop towels were like ours at the
point of collection. Our shop towels are not wet like a face cloth. For
virtually every towel, you would not be able to get any solvent to drip out of
them during hand wringing. If yours are wetter, than you can still calculate the
residual solvent left in shop towels going to the laundry.

You can do your own measurements of solvent retention in shop towels. Weigh 20
dry towels and compare that weight to the weight of 20 soiled shop towels (using
a postage scale from your shipping department). Dividing by 20, and then
calculating the weight increase you can determine the "soil weight" of you shop
towels. While, admitedly, this process does not account for the weight of the
ink in the towels, our experience is that it provides a very close measure of
solvent retention, and the results are quite consistent in repeated tests.

Since we collect our spent solvent in drums, which are in turn sent out as a
hazardous waste (flammable) to a TSDF, we have iron-clad documentation of our
recoveries and take that credit against potential air emissions. By the way, in
our case, the recovered solvents are distilled at the TSDF, the distillate is
shipped back to the original vendor who brings it back into specification
(re-adding surfactants), re-packages and re-labels the solvent and ships it back
to our facilty, closing the re-cycling loop.
I hope this provides you with some useful ideas in measuring your recovered
solvents.
Regards,
Jeff Adrian
Director, Environment & Safety
The John Roberts Company

RobLindsay wrote:
>
>
>I have a question on calculating VOC emmissions from a lithographic press. We
>use a water and blanket wash mixture. Example - If we use 60 gallons of blanket
>wash and 40 gallons of water and after cleaning operations the waste is
>collected. How much of the blanket wash voc's have been consumed? Obviously I
>don't want to report 60 gallons of voc's being released.
>
>Any help would be appreciated.
>
>
>Oh, the blanket wash we are using is 74% aliphatic petroleum distallates
>cas#64742-88-7
> 20% aromatic petroleum distallates cas#64742-94-5
> 12% aliphatic petroleum distallates cas#8042-47-5
> 1.8% napthalene cas# 91-20-3
>
>My background is occupational safety and industrial hygiene, so please don't
>assume I have any working knowledge of the press. LOL
>
>
>
>
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