Chemical Engineering August 2018 - 38

Cover Story
Effective Agitator
Operation and
Maintenance
Agitators play key roles in chemical processing. Their proper operation and
maintenance can improve process reliability, leading to reduced downtime and costs
Jason R. Hora,
Eric Janz and
Eric A. Wiget
National Oilwell Varco
Kevin J. Myers
University of Dayton
IN BRIEF
AGITATOR COMPONENTS
GETTING OFF TO A GOOD
START
GETTING UP AND
RUNNING
KEEPING A GOOD THING
GOING
WHEN THE GOING GETS
TOUGH
HAVING SPARES ON THE
SHELF
FINDING RENEWED
PURPOSE
A
gitators, which are relied
upon to dependably
and cost-effectively
meet production goals,
are commonly used throughout
the chemical process industries
(CPI). Despite their prevalence
and importance, agitators are
rarely the focal point of process
hardware. In fact, a properly functioning
agitator is usually a case
of " out of sight, out of mind. " It is
when an agitator is not working
properly that it garners the most
(unwanted) attention. The purpose
of this article is to outline
best practices for agitator operation
and maintenance to ensure
reliability and reduce the costs
and headaches associated with
process downtime.
Agitators share significant characteristics
with other rotating equipment, particularly
pumps. The most apparent similarity between
pumps and agitators is the production
of fluid motion via impeller rotation.
However, the scope of process objectives
to be accomplished by agitators is much
broader than that of pumps. While the primary
purpose of pumping is to transport material
from point A to point B, agitators are
used to achieve numerous objectives that
include blending miscible liquids, increasing
mass transfer rates between immiscible
phases, contacting reactants, suspending
and dispersing solids in liquids and aiding
process control by promoting heat transfer.
To meet these objectives, an agitator
must be designed, installed, operated and
maintained properly.
A key point that should be made at the
36
FIGURE 1. Typical agitator components are shown. On the left is a parallelshaft
drive unit, and the image on the right displays a right-angle drive unit
loutset is that equipment vendors provide
detailed instructions via installation, operation
and maintenance (IOM) manuals, and
these documents should serve as the primary
information source to ensure safe, reliable
and effective agitator operation. Furthermore,
adherence to vendor guidelines
is required to avoid invalidating the manufacturer's
warranty. Such specific information
as provided in IOM manuals will not be
presented here; rather, the focus will be on
general practices that promote dependable
agitator performance.
Agitator components
Figure 1 illustrates the components of a typical
agitator. The agitator induces liquid motion
through the rotation of an impeller system
within the liquid. The impeller is mounted
on a shaft connected to the agitator drive
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Chemical Engineering August 2018

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