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| Sulphuric Acid on the WebTM | Technology Manual | DKL Engineering, Inc. |
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Knowledge for
the Sulphuric Acid Industry Introduction
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Introduction The following procedure is applicable to air unloading of tank cars or tank
trucks. The procedure is general in nature and must be adapted to the specifics of
each unloading facility and to the operators own procedures and rules. Personnel Attendance by a qualified person during the entire unloading procedure should
be required. This person must be thoroughly familiar with the hazards of sulphuric
acid and all operating, emergency, safety and first aid procedures recommended for its
safe handling. Safety and Preparation Water in large quantities should be immediately available at the unloading
site to wash down any acid that may be spilled. A safety shower is recommended along with a signal system designed to get
assistance if an emergency should arise. The signal system and safety showers should
be tested routinely. Signs restricting access to the area should be used. The slow attack of sulphuric acid on mild steel results in the formation of
hydrogen sulphide gas which is flammable and can form explosive mixtures with air.
Smoking or other sources of ignition should not be permitted near acid tank cars, and cars
fittings should never be hammered or chiseled. Unloading Procedure Note: Tank Truck Unloading - In some cases, the truck driver will
normally connect the customer's transfer equipment to his the vehicle. Unloading of
the tank truck is the responsibility of the consignee. Locating the Container For tank cars, the train or engine crew should accurately spot the car at the
unloading line. The brakes should be set, and the wheels blocked by standard wheel
clamps. Blue warning flags and derails should be placed at least 1 1/2 car-lengths
away. For tank trucks the driver should position the truck accurately on the
unloading line. The vehicle should be switched off, the brakes set, and the wheels
blocked. Verification of Tank Contents Verify the contents of the container by checking the shipping papers and
container stenciling. Make sure the receiving storage tank has sufficient outage to
hold the contents of the container being unloaded. Inspect Shipping Container Inspect the shipping container for leaks or damage which could interfere with
safe unloading. Venting Shipping containers as received will frequently be under pressure either
because of thermal expansion of the acid or slow hydrogen generation. Carefully open the air connection valve and vent any pressure in the
container. If there is no air connection, the safety vent should be removed. If no venting occurs, check to make sure the air connection and valve are
unobstructed. Carefully loosen the fill hole cover bolt (do not disengage), and pry
up slightly. If any pressure is present, let it bleed off slowly until no pressure
is in the tank, then open the fill hole cover.
Caution: All pressure must be vented before any container
fittings are removed because of the danger of acid spray. Do not remove the cap from
the liquid eduction pipe until it is definitely known that all pressure has been vented
from the container, and that the valve is closed (if so equipped). Sampling Samples of the acid should be taken after the container has been
depressurized, if required. The locking hinge which holds the filling hole cover in
position should then be loosened and the cover swung back. The gas space must then
be left to vent to atmosphere for 15 minutes before sampling is done. A hydrogen-enriched atmosphere can develop in the dome of containers which
have been in transit for long periods in hot weather. If a sampling device is
lowered through the filling hole immediately on opening the cover, there is a risk that a
stray spark could trigger an explosion. The risk is eliminated by allowing the gas
to escape through the opened cover for a few minutes. After sampling, the filling hole cover must be closed and the retaining clamp
tightened to reseal the cover. Acid Connections Only after the container has been depressurized, then the acid connection can
be made. Close the liquid eduction valve (if so equipped), and carefully remove the
cap from the valve, or from the liquid eduction pipe (if no valve is provided).
Inspect the condition of the threads, gaskets and liquid eduction pipe carefully.
Pipe threads in sulphuric acid service deteriorate rapidly, especially when exposed to
acid and atmospheric moisture. Connect the acid line to the eduction pipe. Air Connections The air supply must be non-contaminated, free from oil, moisture and foreign
matter. A suitable inert gas may be substituted for the unloading air if desired.
Caution: The air supply should never be connected before the
acid unloading is connected. The air supply must have a shut-off valve, a check valve, a pressure reducing
valve (set at 172-193 kPag (25-28 psig)), a pressure gauge, a safety relief valve (set at
207 kPag (30 psig)), and a bleed off connection and valve. Connect the air supply to
the rail car. Storage Tank Ensure that the storage tank is ready to receive the acid. The tank
vent should be checked to ensure that it is open. Final Check Close the fill hole cover and inspect the system to be sure it is tight, and
that all vent and bleed valves on the unloading line are closed, and all valves properly
positioned to receive acid. Pressurization Slowly apply air pressure to the container by opening the isolation valve on
the air supply line. Care should be taken not to exceed 193 kPag (28 psig) air
pressure. If the air pressure is too high, the safety relief valve on the air supply
will open. If pressure cannot be maintained, check for leaks or a broken bursting
disc on the shipping container. Unloading Unloading of the acid in the container to the storage tank should now be
underway. If any leaks should develop in the acid line, the air should be turned off
and the air pressure released from the car before attempting to correct the leaks.
If it is necessary to break connections on the unloading line, extreme care should be
taken in draining acid from the line, particularly from low spots. If leaks develop or acid is spilled, promptly wash down any surface where
acid has spilled with an excess of water being extremely careful to avoid getting water
into the container, piping or into large accumulations of acid in holes or trenches. Termination of Unloading When the container is empty, a drop in the pressure and the sound of air
rushing through the discharge pipe will be heard. Shut off the air supply, then shut
off the valve in the unloading line near the connection point. Allowing some air to
flow through the unloading line will help to clear the acid from the line. Depressurization Vent all pressure from the shipping container through the air supply line
bleed valve. Carefully open the fill hole cover and inspect the container to insure
unloading is complete. Disconnect the air supply line. Disconnect Loading Line When the unloading line has been completely drained, carefully disconnect the
line from highest point first. If the unloading line is not equipped with a drain
and vent valve, acid should be expected at the disconnect points. Sealing of Container Close the fill hole cover tightly and replace the caps on the air connection
valve and liquid eduction line. Replace the valve covers. Inspect the
container and place proper DOT required placards on the container for the return shipment. |
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Copyright© 2005,
2006, 2007, 2008 DKL
Engineering, Inc., All Rights Reserved |
