Chemical Engineering December 2016 - 45

or it could be intended to serve as a
longterm mini-plant used for continuous
improvement and experiments
that cannot be done effectively in
the larger plants. In many ways,
these plants are similar to small
commercial plants in their design
and the methods used to engineer
and construct them. In these cases,
traditional methods of estimating are
likely to be quite appropriate.
For a small startup company,
academia, or for very early development,
a pilot plant may mean a small
bench-scale unit producing a few
grams per minute. These systems are
often built in a small laboratory using
off-the-shelf items, and they are frequently
operated with considerable
manual intervention. Often, these
systems can be estimated rather
easily based on equipment quotes
and a rough estimate of a technician's
time to build (if the process of
estimating the costs is even of value
at all). In these cases, the following
discussion should still be considered,
as it may still be applicable to
this situation.
In the author's experience, the term
pilot plant has most often meant an
intermediate scale of operation -
something larger than a laboratory
bench, but certainly smaller than a
standalone plant. For the purposes
of this article, this is the definition
which will take the major focus.
These pilot
facilities are typically
designed to provide a wealth of information,
including: engineering
design data; validation of process
models; process studies, including
the impact of recycles on the
process and product quality; and
validation of continuous operations
at a reasonable scale. They often
have column diameters in the 2- to
6-in. range and reactors designed
to provide sound scaleup information.
Production rates commonly
run between one and a few hundred
pounds per hour, depending on the
nature of the process. Although
these pilot plants can be either
skid-mounted or stick-built, this article
will focus primarily on stick-built
units constructed within an existing
structure and that take advantage of
available infrastructure, such as control
rooms, utilities and sometimes
control systems. These are typically
cost-effective designs, and the type
that would most likely require engineers
to develop their own cost estimate.
Stick-built plants are those
assembled on-site from individual
pieces, including the piping and
controls, as opposed to modular
construction, where skids or racks
are used to assemble large portions
of the plant off-site and are shipped
to the final location.
Pilot versus commercial scale
As mentioned, there are some very
important differences between
pilot and commercial facilities that
will impact the cost and the estimating
methods. The more critical
differences are discussed in the
following sections.
Field instrumentation. Perhaps the
most important difference for cost
estimating stems from an area in
which there is actually very little difference
between commercial and
pilot operations. Field instrumentation
- the instruments on the equipment
that tie back into the control
system - are often very similar in
scope for both types of facilities.
Whether a reactor is 20,000 gallons
or 2 gallons in size, both are likely
to have a level transmitter, pressure
transmitter,
thermocouples,
feed
flow control and some level of safety
shutdowns. In many of these cases,
the instruments will even be the
same make and model, or they will
at least be comparable in price (Figure
1). Therefore, instrumentation is
an area that simply doesn't scale up
in most cases. In other words, you
cannot assume that a pilot plant
that is a hundred times smaller than
a commercial plant will have some
predictably smaller scope or cost
for instrumentation. Oftentimes, the
two will be very comparable, and in
some cases, the pilot plant instrumentation
may actually be more
expensive if the plans include collecting
extensive design data for the
commercial plant.
Analytical systems. The analytical
plan for a pilot plant is another area
that can have a huge impact on its
cost. Usually, one of the key drivers
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Chemical Engineering December 2016

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