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Re: level of effort for mass balance?



Burt,

There is much variability in the time required, mostly based on the 
company's accounting systems. If the company does a good of managing 
its inventory, raw material purchases and sales (all on a weight 
basis), then the only difficulty is figuring out the waste 
quantities. This is particularly a problem when a company uses lots 
of water, particularly if they do evaporative cooling. Companies 
never put water meters on their cooling towers, so you have to guess 
how much evaporates. Usually this is done by counting up everything 
else, subtracting outputs from inputs and figuring the difference is 
evaporation, weighing errors, meter inaccuracies, etc. If this is the 
case, you may be looking at 1 to 2 person-days to do the materials 
balance. Simple operations may shorten the time, complex 
operations-and poor accounting practices / systems lengthen it.

Warren

>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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-- 

Warren Weaver
PENNTAP
Penn State University
PO Box 5046
York, PA 17405

Ph: (717) 848-6669
Fax: (717) 854-0087
E-mail: wjw5@psu.edu
Web Address: www.penntap.psu.edu

Registered ISO 14000 Auditor: #E051734

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