The Acid Shower
A diluted nitric acid tank was positioned to feed a reactor through
gravity flow. The fluid level was monitored through a float sensor.
During routine operation the night shift manager was alerted by the
technician to the fact that the acid tank is empty -- per the board
indicator. The manager, a junior chemist, initiated an instrumentation
test, which came out clear. He then concluded that the tank must indeed
be empty, and went out to the plant to check it out. The tank was
placed on a third floor of a steel structure, and it was equipped with
a draining outlet close to its bottom. Mindlessly the chemist turned
open the drainage, and instantly recoiled as a gush of acid flushed
him. The acid poured all the way down the second and first floor. Since
it was the night shift there were no people on the path of the acid,
but the expensive instrumentation there was seriously damaged. The
careless chemist was briefly hospitalized.
It turned out that the old floater sprank a hole, was filled with
fluid, and sank to the bottom of the tank, sending the erronous signal
of an empty tank. The shift manager failed to conjecture this
possibility. He also failed to regard the fact that the acid could not
evaporate. If the tank has emptied, the acid must be somewhere!
Lastly, the manager was not trained in basic precautions of how to
position oneself when opening a drain valve.
Design lesson: critical storage tanks should be equipped with two
independent volume-meters, or with a visual lens for inspection.
The Mixing Blunder (a)
A veterinary pill was to be a mixture of seven ingredients. The chemist
and the vet who developed the formula administered the ingredients
separtely, and assumed it would be a simple engineering challenge to
premix the components. Alas, it turned out that for the ingredient mix
to be fluid it had to be heated to about 200F. However two of the
ingredients were mutually reactive at that temperature. The engineers
tried for several weeks to tinker with the mixing challenge, and
failed. When they lowered the temperature to prevent a reaction, the
viscosity climbed up, and the mixing became ineffective. The chemist
tried to solve the difficulty his way by searching for a de-catalytic
ingredient that would hinder the reaction. The working solution was not
mentioned because it was too expensive... The only way to insure proper
mixing was to mix the first six ingredients with the 7th one in a
powder form.
The Mixing Blunder (b)
Mixtures of large organic molecules (especially those with polymeric
tendencies) tend to be much more viscous then the premix fluids.
Viscosity affects mixing efficiency and determines the shape of blender
blades. This fact creates a big difference when a large number of such
molecules must be mixed to a rigorous tolerance. It makes a huge
difference which order to apply. The design of the mixing phase was
anticipated as a 1 week work, it lasted six months...
Lesson: mind your degrees of freedom when estimating design work!
The Packaging Foam
A group of chemists developed a nifty idea. Two organic chemicals
sprayed
together created a foam, which quickly dried out, and hardened. They
reasoned that their invention would be useful in packaging of fragile
cargo. The container box would be filled with that foam, and secure the
fragile cargo against rough road handling. When the chemistry was
perfected they deemed themselves to be done with the needed R&D. It
turned out that to build an industrial grade device to insure the right
proportions of the mixture, consistently is an expensive proposition.
Also, for large boxes it took too long for the light ingredient to
evaporate, and industrial shipper were too impatient. On the receiving
end, the foam was washed away with warm water. Shippers were reluctant
to apply. Over 2 million dollars in just the chemistry R&D were wasted
because the R&D team did not attack first the expected "cost mines".
Thermo-flow control dilemma
Two feeding fluids had to be kept in relatively high temperature to
facilitate
their smooth flow. The mixture had to be cooled off to hinder an
undesired side reaction. Alas, the desired reaction was exothermic and
the mixture was easily tipping off to the unwanted side reaction.
In a too low temperature the desired reaction was slowing down.
Accordingly raising the reactor temperature created an escalated
temperature increase, and reducing the reactor's temperature created a
non-linear de-escalation of the temperature. In addition, when the
side-reaction took over the feeding streams were cut down. The slower
flow increased the temperature of the feed (the heat exchanger was
unchanged), which in turn kept the side reaction cooking.
The design team decided to engineer the control strategy over the
production facility, and ended up wasting large amounts of the
expensive materials on trying various strategies. It was extremely
difficult to avoid unstable and oscilating control situation. They
spent another small fortune contracting out the modeling of the system.
Having never wrestled with trying to solve Navier-Stokes equations in a
non-adiabatic situation, did not realize how impractical this is, even
with numeric approximation. If the team had invested in a pilot they
could have developed a working strategy without wasting large amounts
of material. Control strategy scales up very well! In cases like
the above where a strategy is a matter of trial and error, pilot is a
must!
pollution delusion -- security reality
A chemistry research team has developed a pollution-reduction idea:
placing
an adsorption unit behind the radiator of vehicles. The sucked in air
would deposit air-pollution particles on the specially engineered
adsorption walls, and the air would come out cleaner. When the
adsoprtion surface is saturated, it is replaced with a fresh one.
According to compuation, if the unit was changed each time the car
stops for gas, the adsorption would continue uninterrupted. It worked
fine
in the lab. When they went out with their idea, the engineers in the
automotive firm have quickly calculated
that even if all the cars in America were equipped with this gizmo, the
effect on air pollution would have been negligible. In retrospect it
looked so incredibly naive on the part of the chemists. The
quantitative calculation was easy to make before the invested effort in
engineering the adsoprtion surface. The chemists argued that they had
no reliable data regarding miles-per-car per day, at which speed, and
times how many cars are on the road in a particular time of the day.
Alas, even a rough guess of these figures would have sifficed to
indicate the futility of the idea. Lesson: perform a critical
calculation even if you have pitiful little data to work from!
But the story does not end here. Years after having shelving this
pollution-delusion idea, it was resurrected. This time for a
completely different application: Security. Selected cars are
equipped with a classified version of this invention to adsorp air
particles. If the car rides in a suspected neighborhood, and adsorps
explosive particles, it becomes an important security asset. Lesson: don't kill your old ideas, however much
embarrasmment they have earned you. Their day might come!
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