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Re: level of effort for mass balance?



Bob et al,
Please differentiate between a detailed chemical mass balance (which is
what the Nat'l Academy of Sciences did) and the much more commonly used
materials accounting process. Materials accounting is straightforward
chemical engineering and while it does take some time and effort (not
unlike the estimates per chemical from Burt below), it has been shown to
be well worth the effort in NJ and Mass. Here in NJ, for every dollar
spent to do P2 Planning (including process level materials accounting),
facilities found 3-8 dollars in savings. The other 2 big bonuses: 20-80%
of all environmental releases were "discovered" and had gone
unpermitted, and of course, production managers had a chemical use
efficiency measure that they could track as frequently as they wished.
I would never recommend a chemical mass balance unless a facility had
no idea of what chemical tranformations took place in their processes.
Melinda Dower
Research Scientist
NJ Dept. of Environmental Protection

>>> Robert Pojasek <rpojasek@sprynet.com> 01/08/03 01:13PM >>>
Under one of the RCRA re-authorizations, Congress required the National

Academy of Engineering to prepare a report that answers this very 
question.  The results of the report (I cannot remember the year) were
very 
interesting.  They recommended that the US EPA should NOT require mas 
balances.  This is where they derived the term "resource accounting." 
Mass 
balances require many measurements to be taken so there is an exact
balance 
prepared.  Some of the sampling is very expensive and could take a
month or 
more to perform and verify at each point in the process.  There was a
mass 
balance performed on the Amoco refinery (it is a small refinery) for
the 
EPA project and the cost was over $1 million.  They had to design,
test, 
calibrate and use a special flux chamber to make measurements on the 
dissolve air filtration system.  I believe the cost for three readings
on 
this one unit process was about $250,000.  It was money well spent,
because 
they showed the actual benzene emissions represented a 750% reduction
from 
what the API estimate was.

A colleague of mine is certified for the use of the UNIDO P2
methodology 
used by the National Cleaner Production Centers.  She tells me that the

Brazil National Cleaner Production Center is having difficulty finding

companies to use their services because of the difficulty of doing the

required mass balance up front.  It cost the company quite a bit of
money 
in analytical and personnel costs.  Besides the data needs to be
completely 
redone the following year.

I think that if you did a Total Cost Analysis (figuring in company 
personnel time at a fully burdened rate, lost production time,
analytical 
costs, engineering costs, and management review) for the complete
facility 
that you will find mass balance to be an extremely expensive option - 
orders of magnitude greater in cost than what you are proposing here.

The alternative would be to do what I call, just in time mass balance;

i.e., only do mass balances around the process map steps that you are 
seeking to improve.  Resource accounting will help determine the flow
of 
resources through the operation.  Eco-effizienz in Germany has a great

method for doing this.  The combination of resource accounting and 
just-in-time mass balance should satisfy even the most devoted
chemical, 
industrial or mechanical engineer.  Resource accounting is widely used
in 
Europe, Japan and the USA.  I hope they will consider the findings of
the 
National Academy of Engineering report.  I am sure it is still
available 
through their book store.

Bob Pojasek
Harvard University

>I have been asked by person in the environmental agency here to
provide
>estimates about what level of effort is needed to do a mass balance
for a
>company.  They are considering making a mass balance analysis a
requirement
>for a particular environ regulation.
>
>Obviously this depends on the number of processes being considered.  I
have
>not done process mass balances for several years, not being an
engineer, and
>would appreciate any insights.  Here are my basic estimates for a
"typical"
>production process.  I am making these pretty generous.  Also I am
assuming
>there is some data around already.
>
>Preparation of process flow diagram:  3 hours
>
>Collection of input-output data for each step:  1 hour per step in
the
>process
>
>If we estimate that a process has about 5 major steps, this would be 5
hours
>
>Preparation of the mass balance for key factors:  2 hours
>
>So roughly I would estimate for a "generic" company, that it would
take an
>engineer about a day to prepare a mass balance for one production
process.
>Another day to summarize results from all the processes, and maybe
another
>day to work out the bugs.
>
>I realize this is grossly simplified and the world is much more
complex.  If
>any of you hotshot engineers can comment on these estimates I will be
>grateful, and also I think the regulators will be interested to know
your
>ideas too since mass balance for processes is pretty basic for most
P2
>analyses.
>
>and Happy New Year to all!
>
>Burt Hamner
>Univ de Pacifico


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