Printech Archives, July 1997: Re: Vapor Pressure and VOC Emissions

Re: Vapor Pressure and VOC Emissions

Jeff Adrian (
jeffadrian@johnroberts.com)
23 Jul 1997 15:00:18 -0500


Jim:

I believe the following, excerpted from a letter written in 1993, will be
useful to you to understand the demonstrable results of shifting to lower
vapor pressure solvents.

You have requested that I forward to you data illustrating results we obtained
with vapor pressure reduction of the cleaning solvents we use for the cleaning
of printing presses. I believe the data enclosed will demonstrate the benefits
of such solvent vapor pressure reductions. Though it is difficult to select a
single factor with which to relate our company's growth over the last few
years, I will provide you with enough parameters so as to have some measure of
this growth.

Briefly, I'll review significant reductions in vapor pressure of our cleaning
solvents. At John Roberts Company, we made two major changes, the first in
January of 1990 and the second in September of 1992. In 1989, we were using a
highly volatile solvent blend with a vapor pressure of 105.2mm Hg at 68#251#
F. Engineering calculations at the time indicated more than 50% of the solvent
purchased never did any work for us, it merely evaporated. The new substitute
blend initiated at that time lowered the vapor pressure to 45.5mm Hg at
68#251# F. Continued testing of substitute blends over the next two years
helped us find our current solvent blend which has a vapor pressure of 3.5mm
Hg at 68#251# F. This blend is the one we have used since September of 1992.
All blends are virtually 100% VOC content.

Each time we lowered the vapor pressure of our solvent blend(s), we
experienced gains. First off, we found that in spite of company growth, we
significantly reduced the total amount of cleaning solvents purchase.
Secondly, with the 1992 reduction, we found that we increased dramatically the
total amount of waste solvents recovered from soiled shop towels (using our
centrifuge recovery system). These recoveries of waste solvents are documented
with our hazardous waste manifests. Considering the VOCs these solvent
recoveries represent, they are significant in that if they are in the drum,
then they are not in the atmosphere. Up until October of 1993, recovered waste
solvents were fuel blended for disposal in a cement kiln. In October of 1993,
we began a distillation program that closes the recycling loop to our own
facility.

The results of all this effort are as follows. In 1989, our company purchased
194 drums (55-gallon) of solvent, or 73,305 pounds. In 1990, that fell to just
146 drums, or 58,336 pounds, a 20.5% reduction of VOCs. This change occurred
at the same time we initiated our program of solvent recovery from soiled shop
towels. Again, in 1992, on a calendar year basis, purchase of solvents
amounted to 172 drums, or 68, 676 pounds. In calendar year 1993, purchases
were again reduced to just 154 drums, or 59,466 pounds a 13.5% reduction of
VOCs.
However, because the second major change in solvent blends occurred in
mid-September of 1992, perhaps more telling of these reductions would be a
comparison of solvent usage and recoveries occurring over the period of
September 1991-1992 with September 1992-1993. In the 91-92, we purchased 197
drums of solvent and recovered 77 drums of waste solvent. In 92-93, we
purchased 168 drums and recovered 99 drums. Thus, purchased solvents were
reduced by 14.8% while solvents recovered increased by 28.5%. Using the old
recovery rate, we would have expected to recover just 66 drums of waste, not
the 99 we actually recovered. Based upon 6.79 pounds of VOC per gallon, the
additional 33 drums recovered represent recapture of 36,969 pounds of VOCs!

Along with selection of lower vapor pressure solvent blends, the company has
benefited from cleaner indoor air quality. Clearly, comments by our employees
expressing their pleasure with reduced pressroom odor is tied to this
substitution of cleaning solvents. In reducing the company's overall emissions
(after recoveries and destruction) from a total of 29.88 TPY in 1992 to just
15.06 TPY for 1993, the largest part of this reduction by far was from the
change in cleaning solvents to a lower vapor pressure blends. The results, I
believe, speak for themselves.


Regards,
Jeff Adrian
--------------------------------------
Has anyone seen published fugitive emissions measurements that compared
emissions when different blanket washes were used?

I am aware of the ACT emission factor (<10 mm Hg = a 70% VOC reduction);
however, it'd be nice to (semi) quantify the potential benefit of
switching to lower VOC content or vapor pressure washes.

For instance, how much benefit is gained by switching from say xylene
(paint thinner, 8 mm Hg 68 F, 100% VOC) to a 12 carbon naphtha (0.2 mm
Hg, 100% VOC) or to a vegetable ester wash (<0.1 mm Hg, <1% VOC).


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