Tuesday, May 4, 2010
TOLUENE FLOATING ON CHEMICAL TANKERS-- CAPT AJIT VADAKAYIL
" TOLUENE SPRAY " MUST NEVER EVER BE DONE ON A CHEMICAL TANKER. If a sailor is forced to do this by his Captain , (like Methanol spray) , he must refuse .
MOST PARCEL CHEMICAL SAILOR DEATHS HAVE HAPPENED DUE TO " STATIC ELECTRICITY" EXPLOSION.
This method is usually used as a last resort say for Zinc tanks which had difficult insoluble cargoes and must be prepared for WWT as you do not have much of a choice.
Toluene floating can also be used to remove stubborn hydro-carbons, which may have been left from lub oils for example and the next cargo is wall wash. A lub oil/ additive tank is normally 'upgraded' to methanol standard via two or three intermediate cargoes of aromatics.
But the method works if the previous cargo is soluble in toluene!!. Better check it out yourself with a sample in the ships lab.
You must have sufficient toluene on board. Toluene floats in water with a clear interface ( density 0.86) and is insoluble.
The ships course must be altered so that the wind is not blowing into the accommodation.
Since it is the last resort it means that the tank is already clean and toluene floating is doing the final act. The ship must have no list and minimum trim. Rolling must not take place.
Put enough toluene in the empty tank using the ships loading drop so that there will be a 10 cm interface. Make sure the hoses you use are resistant to toluene.
Now introduce sea water into the tank via the sump or drop at 50 deg C. This temp is important to open the pores. Lift it up to the top of tank and then defloat. The water can be pumped out to sea. It is not safe to chase down the water with tankcleaning jets. Too much static is generated. After slow defloating the remaining toluene is transferred to next tank through a filter.
The toluene contact should be about 30 minutes. Then wash off with hot water injected with a surfactant. After the final hot wash , rinse with FW and steam.
The flotation method should only be used after first washing with cleaning chemicals. The method is then very effective, but it is less effective if cargo residues on the tank walls are of any appreciable thickness.
This flotation method might involve hazards as regards static electricity charges in the interface between the two liquids. It is wise to pump slowly in order not to exceed 1 m/s in the filling pipe.
The process should preferably be carried out with the tank inerted.
Toluene being a aromatic shows up in the UV test ashore. So if you do tankcleaning for MEG Fibre Grade using toluene ensure a final job is done with an UV neutral solvent like acetone, MEK , MIBK or Methanol.
PROPERTIES OF TOLUENE:--
A very good cleaning solvent ( aromatic, organic ) .
Static accumulator. If carried in deck tanks make sure the tank is electrically bonded to hull.
It shows up in a UV test.
Usually used in conjunction with steam, to remove heavier HC contamination from inaccessible areas like interior of pipelines.
For a tank size of 1000 cum use 50 litres toluene for steaming. Explosive limit is 1.2 to 7% by vol. if the LEL value ( 3.7 litres / 100 cum )is exceeded then the tank must be inerted. Fill up tank to above heating coils— then add toluene which will evaporate.
Pipelines can be steamed with eductor which sucks touene from a jerry can.
For toluene wiping use chemical resistant sponges.
Toluene is still potent even if it has been used many times over and is black in colour.
Toluene spray is not allowed — explosion due to static. Narcotic effect with severe fatigue , head ache and mental confusion due to central nervous system depression.
Rubber swells and softens. Stow away from Nitric acid.
Colourless liquid with a pleasant aromatic odour.
Dangerous fire hazard
Oil like substance
VP/ 30 mm hg at 20C
AH/ 38 C
TLV/ 100 ppm
Marpol Cat/ Y
Becomes unstable when heated
Toluene at 84% by volume, fueled all the turbo Formula 1 teams in the 1980s.
Inhalation of toluene fumes can be intoxicating, but in larger doses nausea-inducing
As toluene has very low water solubility, it cannot exit the body via the normal routes (urine, feces, or sweat). It must be metabolized in order to be excreted.
Toluene wiping of tanks must be done with chemical resistant sponges.
-------CAPT AJIT VADAKAYIL ( 28 YEARS IN COMMAND )