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| David W. Spitzer, P.E.
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Last month we
considered the economic value of steam flow measurements. Liquid flows
are typically more common, so let’s take a look at an example of their
economic impact here.
Assuming the average liquid flowrate is one kg/min valued at
$1.00 per liter operating all year, the flowmeter would pass
approximately $525,600 of liquid per year (1 liter/min * 60 min/hr *
8760 hrs/yr * $1.00/liter).
Think about this for a minute … a small flow of a reasonably
priced liquid results in over $500,000 of liquid passing through the
flowmeter each year. In custody-transfer applications, purchasing a
flowmeter that performs 1 percent better can reduce the measurement
error by $5000 per year. This value is much larger in many
custody-transfer applications, so reducing the magnitude of flow
measurement error can be used to justify better (and more costly) flow
measurement devices.
While justification for improved (and more costly) flow
measurement devices is relatively easy in custody-transfer
applications, how many times have you had to fight (tooth and nail) to
purchase a more expensive flowmeter for process applications? Did you
ever calculate the value of the material passing through the flowmeter?
You might be surprised with the results.
For example, a flowmeter operating year round at 100 liters per
minute will pass over $25 million of liquid per year if the liquid is
valued at $0.50 per liter. This may not be economically important in
many process applications, such as recycle, cooling, or spray flows
where the flow need only be higher than a minimum value. However, it
can be of extreme importance in other process applications, such as
reactor feeds, where addition of the proper amounts of reactants can
drastically affect chemical reactions, process yield, and the economics
of the operation.
The majority of process flow measurements typically fall between
these two extremes and can exhibit a detrimental effect on process
economics. For example, the flowmeter detailed here might be the slave
process variable in a cascade level control. There could be a
discussion (fight?) as to whether to buy a flowmeter for $2700 or a
superior flowmeter for $3300. Put in another perspective — should one
spend an additional $600 to better measure $25 million of liquid per
year?
You decide.
David W. Spitzer,
P.E., is a regular contributor to Flow Control. He has more than 30
years of experience in specifying, building, installing, startup, and
troubleshooting process control instrumentation. He has developed and
taught seminars for over 20 years and is a member of ISA and belongs to
the ASME MFC and ISO TC30 committees. Mr. Spitzer has written a number
of books concerning the application and use of fluid handling
technology, including the popular “Consumer Guide” series, which
compares flowmeters by supplier. Mr. Spitzer is currently a principal
in Spitzer and Boyes LLC, offering engineering, product development,
marketing, and distribution consulting for manufacturing and automation
companies. He can be reached at 845 623-1830.
www.spitzerandboyes.com
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