Chemical Engineering May 2022 - 29

Tower Doctor
Should the Doctor Believe a Flowmeter?
Henry Kister shares lessons learned from troubleshooting distillation towers
M
any cooling-water systems
do not have flowmeters.
This is a tale
about a cooling-water
flowmeter that made a difference.
As a startup superintendent at
ICI Australia in the late 1970s, the
author was in charge of starting up
a new unit in the olefins plant that
produced polymer-grade propylene.
The main equipment was a C3 splitter
column, which at the time was
the biggest tower in Australia. It is
still in operation today, and can be
seen as one lands at Sydney Kingsford
Smith Airport. The auxiliaries
were a reboiler heated by waste heat
from the olefins quench-water system,
a water-cooled condenser, and
a reflux drum. Due to the very high
cooling load, a new cooling-water
system was added to service the
new unit alone, mostly the C3 splitter
condenser. The cooling tower was
some distance away from the unit,
and the large cooling-water pipes
were mostly underground to avoid
the need of a pipe rack. The equipment
was installed, and the author
was in the process of commissioning
and testing the unit, well before
hydrocarbons were introduced.
The author started up the cooling-water
system. The startup was
smooth
and
uneventful.
Everything
was fine, water flowed over
the cooling tower, the pump was
pumping with a discharge pressure
close to design. As the process side
was not commissioned yet, no heat
was exchanged.
The author walked around,
closely watching the system when
he noticed the cooling-water flowmeter
(Figure 1) reading zero. The
flowmeter was in a horizontal section
of pipe, with ample pipe diameters
before and after to give a reliable
reading. The dial was actually
hitting the stop pin below the zero
mark. The author called the plant
instrument foreman, who checked
the transmitter.
" This worthless transmitter is kaput. "
He said (using another word
for " kaput " ). " All that Engineering
have been giving
us in this
plant is junk
(again,
another
using
word
for " junk " ). Why
don't you tell
Engineering
to
provide us with
instruments
that work? "
This
statement
was true.
Many of the instruments
were
were
that
supplied
inoperative.
I passed
the message to
Alan, the Engineering
instrument
engineer.
" Again?
apologies.
Our
Let
me look into it. "
A couple of
hours later he
returned.
checked
" I
the
transmitter.
There is nothing
wrong with
it. It works. "
" So why is it
FIGURE 2. This diagram shows the cooling water system in the propylene purification
system as installed
reading zero? The pump is pumping
flat out, the water flowing, and
had the transmitter been any good,
it would not read zero. "
" Are you sure your cooling water
is not going backwards? " he asked.
I almost choked, then stared right
at him.
" Alan, if anybody else came up with
this nonsense, I would have thrown
him out of this door. But in your case,
I have a lot of respect for your expertise,
which incidentally, with this kind
of comment I am about to lose. But
just for old times sake, I will get this
nonsense out of your head. "
" How? " he asked
" Let's go. " We climbed up the condenser
platform. I pointed at the butterfly
valve at the condenser outlet. " I
will shut the valve and open the 1-in.
vent valve (Figure 1). What you will
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM MAY 2022
see is a water jet shooting up 30 ft in
the air, which will disprove your nonsense
idea. "
" Good deal, " he said.
I shut the butterfly valve, then
opened the vent. A water jet shot
up 30 ft in the air, just like I expected.
As I was getting ready to
shut the valve, the jet plunged, and
plunged, until it stopped. I shook
my head in disbelief.
" This is why the needle was hitting
the stop pin. It was reading
negative and tried to tell us something, "
he said.
I reopened the butterfly valve,
then repeated the test. Just in case I
was dreaming. The same happened
again. It was not a dream.
" I am taking it back, Alan. My respect
to your expertise has doubled.
This is an amazing catch. "
29
FIGURE 1. This diagram shows the cooling water system for the propylene purification
system as planned
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