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 Safety
in Solvent Extraction Plant |
Every industry has potential hazards associated with it.
Solvent Erection industry is no exception. There are three
areas where potential hazards exist.
These are:
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Mechanical accidents |
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Accidents due to the nature
of raw materials, products & chemicals handled
in the industry |
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Accidents due to the human
failure. |
It is the intention of this write-up to examine in detail
these potential hazards with respect to the solvent extraction
plant.
| Mechanical
Accidents |
Accidents of this type occur mainly due to a machine which
is in motion.
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The drives of all
the machines are a potential threat for accidents.
A moving belt can break and fly and hit a person
in the vicinity. Accidental insertion of hand or
foot between a driving chain and chain wheel or
between two gears will result in serious casualty.
Therefore, insist upon covering the moving parts
of a driving mechanism with properly designed guards. |
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Moving parts of
some machines themselves are potential threat for
accidents. Moving screw of a screw conveyor or moving
chain of a chain conveyor can cause accidents in
case they are not properly covered. Similarly moving
chain or belt of bucket elevator or moving screw
lift are potentials threats for accidents. |
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A frequent accident
spot in the preparatory section of a solvent extraction
plant is the space between two moving rolls of a
cracker or a flaker. Several operators have lost
their fingers by inserting a hand in these to catch
a flying nut or bolt or stone which has come along
with the feed material. Insist upon closing the
cover of the machine when it is running so that
the operator is not tempted to insert his hand. |
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The innocent looking
rotary valve in an extraction plant can be a deadly
source of accident. Many operators have lost their
arms by inserting their hand in the rotor of the
moving rotary valve. Therefore, the chutes at the
feed and discharge ends of a rotary valve should
be long enough so that a person cannot reach the
moving rotor by inserting his hand. |
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The inspection
doors in a hopper or chute of any machine shall
be so located that it is far enough from the moving
part of machine so that the hand inserted through
this door cannot reach the moving part. |
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All machines with
moving parts shall be provided with safety switches
for their motors. Thus when a machine is under repair
or maintenance its safety switch shall be in `OFF'
position, so that the motor cannot be started by
anybody accidentally pushing the starter button. |
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A main safety switch
in each operating floor of a plant and preparatory
and bagging sections shall be installed to switch
off the entire plant in case of an emergency at
any part of the plant. |
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Incidents of personnel
in a plant getting electrical shocks are well known.
This happens generally due to the incompetent people
meddling with electrical equipment such as starters,
fuses etc. where electrically live terminals and
wires are existing. Therefore, only competent electricians
shall be allowed to handle such equipment. |
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All the electrical
equipment in the plant such as motors, starters,
push buttons shall be well earthed to avoid electrical
shocks in case of short-circuiting of the power
anywhere. So also the entire plant shall be well
earthed. |
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Spillage of oil,
miscella etc. on the floor and, especially on the
staircases, shall be avoided and in case of any
such spillage, it shall be thoroughly cleaned immediately
to avoid slipping of foot of the personnel in the
plant. |
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| Mechanical
Accidents |
 In a Solvent Extraction Plant, the oil is extracted from
oilseeds or oilcakes by treating the same with normal
hexane and then distilling of the hexane from the resulting
solution of oil in hexane. The extracted material is also
heated to vapourise the hexane. All the vapours of hexane
from distillation and desolventisation are condensed and
reutilised for extraction. Normal hexane, being a highly
volatile and inflammable liquid, poses the greatest potential
for hazard in the plant. The oil/fat extracted is also
a source for fire hazard. So also is the oil-bearing raw
material.
Therefore, certain very important precautions are taken
in designing a Solvent Extraction Plant and operating
the same as enumarated below:-
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No naked fire is
allowed in the vicinity of a solvent extraction
plant. All the heating, necessary in the plant is
carried out by only steam and not by naked fire
or electrical fire, as the naked fire and electrical
heating are not controllable below the ignition
temperature of hexane and therefore, can cause the
fire. |
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For the ignition to occur in
a hexane atmosphere there must be a proper mixture
of oxygen (air) and hexane as well as ignition temperature.
Once the oxidation (burning) of hexane starts the
reaction is highly exothermic and produces enough
heat to continue the reaction (i.e. burning) and
the fire quickly spreads. The reaction produces
(mainly carbon dioxide) are released in great volumes
creating the pressure inside the burning enclosures
and the explosion results. Therefore, to avoid fire
and/or explosion in a solvent plant it is necessary
to see that the air and hexane vapours do not exist
in explosive limits. The explosive limits for hexane
and air are below 6.9% and above 1.2% hexane in
air by volume. In a plant which is working normally,
the atmosphere inside the equipment is full of saturated
vapours of hexane containing negligible amount of
air. And hence, it does not constitute a dangerous
atmosphere. But, during the starting and stopping
of a plant, the proportion of air inside the equipment
is much higher and that may pose a potential hazard.
Therefore, during this period it is necessary to
ensure that no ignition temperature is reached in
any part of the plant. A safe plant design shall
take this into consideration. |
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While the atmosphere inside
the equipment is free from hazard in a working plant,
any leak of solvent vapours from the equipment constitutes
a serious hazard. The leaking vapours meet with
enough amount of atmospheric air just outside the
leaky spot and can catch fire in case of ignition.
Therefore, it is absolutely necessary to block all
the leaks in a plant, not only to prevent hazards
but also to reduce hexane loss. The potential leaky
areas are: |
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| • Flanges
not properly tightened |
| • Damaged
packings between the flanges. |
| • Welding
leaks due to inferior workmanship |
| • Screw
joints not properly tightening |
| • Damaged
mechanical seals |
| • Pump
glands |
| • Glands
of valves in process lines |
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It is good practice to take hydraulic test of the plant
periodically to locate any such leaks and plug them.
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| Accidents
by Human Failure |
 In spite of all the precautions taken in designing a solvent
extraction plant, an accident can occur due to what is
called human failure. This is essentially due to the lethargy
on the part of the operators to observe a few well established
and simple safety rules and sidetrack the same to `SAVE'
some work. Therefore, the following guidelines shall be
strictly enforced in a solvent extraction plant to avoid
accidents due to human failure:-
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Putting hands and
limbs into running machinery is a common mode of
accidents. The operators of plants shall be strictly
warned that no machine shall be run without the
covering of moving parts in place. Many a times
operators take out the guards and covers for maintenance
or repairs, but do not replace them before starting
the machine. This should strictly not be allowed. |
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The operators shall be strictly
prohibited from taking any matches, candles, cigarettes,
and naked flames in any form inside the solvent
plant area, including preparatory section, bagging
section and oil storage tanks. Warning signs in
regard to the same shall be exhibited at such restricted
areas. |
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The plant operators shall be
thoroughly made to understand the potential hazards
involved and their causes as explained under A and
B above to evolve safety consciousness in them. |
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People who are not authorised
to work in the solvent plant area shall not be allowed
to enter there. |
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'NO SMOKING' signs shall be
exhibited at as many spots as possible to repeatedly
remind the people not to smoke and about the consequent
fire hazard in case of smoking. |
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Many a times the plant personnel
are tempted to `Dry Clean' their clothes using the
hexane available in the plant. To avoid detection
they do so in the electrical cabin which is the
only enclosed room available for such clandestine
activity. This is most dangerous to do as there
are continuous electrical sparks in the panel board
and the hexane vapours generated may get ignited.
There are instances of electrical cabin blowing
off with the personnel inside. The plant personnel
must be thoroughly educated in this regard and the
hazard involved must be impressed upon them. Using
hexane for washing clothes shall be totally disallowed. |
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Normal-Hexane is a slightly
toxic substance and continuous and heavy inhaling
of hexane vapours can render a person `Drunk'. Therefore,
no personnel shall enter the extractor or any other
equipment in the plant when there are heavy hexane
vapours. The equipment shall be properly desolventised
before entering. In conclusion, it can be stated
that if all the safety precautions enumerated above
are diligently implemented, a solvent extraction
plant can be as safe as or even safer then any other
INDUSTRY. |
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