Cargoes consisting of mixtures with different vapour pressures should be not be cleaned by evaporation or hot pre-washed.. The evaporation of the light substances from the mixture will result in non-volatile residues which are very difficult to remove.
For cleaning LSHWFO tanks , first prewash with moderate warm water, followed by a recirc with gas oil.
After Slack Wax ( high MP paraffin ) , steam the tank hot, >20C above the MP of the wax, and then wash with hot sea water. Use Graco ( barrel pump) injection method with emulsifier. However with Refined Wax ( paraffin with low oil content ) , ensure the temp is < 20bdeg C above the MP of wax, or you will get white powdery residues. Use Graco injection method with emulsifier.
After mineral Lub Oils the best chemical to use would be a 75% emulsifier + 25% Surfactant mixture-like Sea Clean -with a low aromatic content , after a very hot prewash. . The first act would be to lower the BP of Lube oil from 250 deg C to less than 100 deg C.
After mineral Lub Oils the best chemical to use would be a 75% emulsifier + 25% Surfactant mixture-like Sea Clean -with a low aromatic content , after a very hot prewash. . The first act would be to lower the BP of Lube oil from 250 deg C to less than 100 deg C.
Do not give hot prewash to kerosene. For gasoil as warm prewash of < 50 deg C is the best .
When cleaning animal / veg oils use water and detergent. Or use Caustic Potash. Avoid Caustic Soda and sea water ( stubborn white deposits ).
When cleaning animal / veg oils use water and detergent. Or use Caustic Potash. Avoid Caustic Soda and sea water ( stubborn white deposits ).
Fatty acid oils is a difficult cargo to clean. For Palm oil Fatty acids, use hot FRESHWATER ( NEVER SEAWATER ) , 25 deg C above MP for prewash after steaming tank. If you don’t have FW use hardness treated seawater, to prevent white sticky residues of Calcium and Magnesium soaps . Heat increases these reactions: a 10°C increase in temperature doubles the chemical reaction rate. The best method for pre-cleaning is to prepare the required amount of freshwater in a separate and clean tank and to add a suitable water hardness remover. If seawater or untreated freshwater must be used for cleaning, the formation of white residues or a white powdery film cannot be avoided .
In SS tank the white sticky residues can be removed by diluted Phosphoric or Nitric acid.
An effective preclean method for non drying fats is to steam the tanks for a short time prior to tankcleaning with hotwater.
Chemicals that tend to polymerize (Isoprene, vinyl, vinylidene, acrylic, or carbonyl compounds, styrene, butadiene , ethylene oxide, propylene oxide, ethylene, propylene, isobutylene) require cold (ambient) water. Washing with hot water will result in stubborn polymeric residues left behind in tanks and lines. To avoid any polymerization by loss of inhibitor-protection, it is also recommended to wash immediately after discharge .
Styrene is soluble in Ethanol, Methanol, Ether and Carbon di Sulphide.
Lub oil additives : ECA, HITEC, OLOA, Paranox, TLA, LOA, Lubaol, Lubizol, Parabar, Sap etc. Avoid prewash with water after Lub oil additives , instead recirc 3 cum gas oil at 50C. Later do a hot butterworth at 80 deg C and then use a degreaser. If you use hot water first there will be a varnish Urethane residue.
Do not mix different grades of clay slurry. These are held in suspension and there will be a reaction between cationic and anionic products. If the slurry hardens and dries acid wash with 10% Nitric acid ( SS ).
Odour sensitive cargoes are Glycol, Glycerine, Veg oils, White spirit etc. Strong odour cargoes are Acrylates, Phenol, Fish oil, Molasses, Tall oil , Piridine etc.
Sea water has 33000 ppm of salt or chlorides. Or 2.8% by weight. For Methanol the WWT passes for chlorides at 2.0 ppm CL. For MEG FG ( UCC ) the passing limit is 0.249 ppm which is ridiculous indeed. But if you want to pass the test and load the cargo you have to comply with the specs.
After dischg of drying oils like Soyabean or Linseed oil give a cold prewash. These drying oils if washed with hot water leave a stubborn varnish.
Always prewash inhibited cargoes with cold water. Products containing inhibitors must be washed thoroughly
Chemicals like Acetic acid, Benzene, Lun oils, Caustic soda, Paraffun, Molasses, Phenol, DINP, Fatty Alcohols, HMD, HITEC, WPAC, Butyl Acrylate, Creasote oil etc can be HOT prewashed.
For DOP and DIDP give ambient prewash.
Cargoes which cannot be washed with water are TDI, MDI, Slack wax, Coal tar, LO additives etc
Fresh water prewash is given for Wet phosphoric acid and Sulphuric acid.
After washing Esters / Acetates and halogenated HC which can form acids when mixed with water, the slops must not be allowed to stay in the tank.
After inhibited cargo eg Styrene, Acrylates etc always check PV valve. As cargo vapor can polymerise on flame screen/valve seat and also give off odour too.
Cargoes which are crystals in their pure form and are carried in solution such as caustic soda should be washed with a water temperature corresponding to, or slightly above, the discharge temperature.
Cargoes such as Alcohols and Ketones do not require extensive machine washing and can be cleaned by giving a short fresh water wash.
Cargoes such as Esters, Acetates and Halogenated hydrocarbons can form mineral or organic acids when mixed with water. To prevent any damage to coated tanks the water/slop must not be allowed to stay in the tank during or after the tank cleaning program.
Cargoes belonging to the Olefin, Phthalate, Adiptate, Fatty acid and Fatty alcohol categories are difficult to clean. When the subsequent cargo requires a high degree of cleanliness (wall wash), alternative stowages should be carefully evaluated.
Some lube additives contain organic acids which react with hot water. The introduction of hot water can also cause jells to form on the tank, pump and line systems.
Lube oils with low viscosities can be extremely hard to remove, especially from inorganic (zinc) coatings. Generally if the viscosity is less than 100 cst and the subsequent cargo is of high specification, it may be necessary to toluene float the tank. Obtain the viscosity at the load port to assist in cleaning the tank after discharge.
Ventilation procedures cannot be used for products which contain an inhibitor such as Vinyl acetate as the inhibitor does not evaporate.
White residues after amines can be removed by 3% Phosphoric acid plus 0.5% emulsifier.
After clay slurry recirc with dilute Nitric acid.
White residues after polyol can be removed by Acetone or MEK.
After dischg Isocyanate tanks have to be washed with non reactive solvent like chlorinated solvents and NEVER water. The urethane layer which forms will be very difficult to remove. Isocyanates (MDI/TDI) must never come into contact with water, nor must their residues, because the reaction product and insoluble urethane are very difficult to remove. MDI or TDI is cleaned best by Methylene Chloride.
Water reactive chemicals and products that must not come into contact with water must be washed with a suitable solvent which does not contain any water. Cleaning is carried out with a suitable solvent (e.g. butyl glycol ether, methanol, acetone, toluene, or 50/50 v/v mixtures of methanol and acetone)
After Latex, keep tank moist with steam before you can prewash with FW . NEVER EVER allow tank to dry. If it is difficult to peel off Latex, you can use Perchloroethylene.
After Coal tar prewash with Creosote at 60C . Then recirc Coal tar cleaner 1:5 . Further cleaning can be done with Toluene in inerted tank.
To remove lead of Leaded Gasolene from coatings use “lead clean” tank cleaning chemical
After hydrocracker, immediately fill up the tank with one foot water and then heat up to about 65 deg C. then wash with very hot water. Then use an emulsifier.
EDC discolouration can be removed by Phosphoric acid ..
Discoloration of the tank or the coating can be removed by the “dye out” method. It can be removed by spraying or recirculation with 0.5 to 2 percent sodium hypochlorite solution. If this does not work, steaming or solvent steaming could help.
Aldehydes and Ketones though water soluble leave traces in the vapor spaces and pipelines and are unsuitable prior cargoes like HMD.
To neutralize the smell of some chemicals (Acrylates, Crude ‘Turpentine, NitroBenzene, Pygas etc), smell killers are used. Ex:-- P3/NA Henkel(CP), Airfresh (Vecom), Nilodor , bleach or an alcohol will help neutralize the smell. After the carriage of a product with a strong odor and prior to loading a sensitive cargoes the seals of tank and butterworth hatches maybe have to be renewed / exchanged. Odour will probably still be present after cleaning eg Acrylates, Butanol, Ethyl-Hexyl-Alcohols, Styrene etc so remove gaskets on tank hatch and tank cleaning hatches and clean in Toluene (or replace if bad condition. To remove strong odour from tank you can recirc with Caustic soda at 60 deg C. A smell killer can be used in combination with a emulsifier. The tank should be cleaned by recirculation to ensure full removal of the odour-producing cargo.
After Pyridine bases cargoes first hot wash, then recirc Caustic 2 %.
Toluene wiping of tanks must be done with chemical resistant sponges.
Metalbrite is phosphoric acid plus non ionic surfactants. For pickling of severely corroded surfaces use neat or 50%. When injected to remove white residue from epoxy 5%.
Ambient is < 30 C
Warm is < 60 C
Hot is > 60 C
For steam atomisation buy a small portable steam ejector. This is about 5 inches long.
Volatile substances are more soluble in cold water than in hot water. Do not allow tankcleaning chemicals to dry up on the tank bulkheads .
Some Lube oil additives requires wash with MDO < 50 deg C or kerosene or hot base oil > 60 deg C direct after discharge, before starting hot water wash. Sometimes a solvent is combined with an emulsifying cleaning agent (mixture of solvent, surface active agents and additives)
Some Lub oil additives react with hot water to leave a sticky residue all over. Test it inside a drained sample bottle. Some highly viscous cargoes (lube additives or polyols) , will have have undesired reactions at higher temperatures, hence it is necessary to pre clean with ambient water. .
Morocco Phosphoric Acid. After the usual washing, hard concrete like layers remain on horizontals which do not go with kew machine. Recirculation with diluted clean Phosphoric Acid will work—use filters to prevent clogging of BW machines.
Sodium silicate solutions should be washed only with Fresh water and NOT with seawater. Calcium and magnesium silicates formed with salt water are very difficult to remove.
Gas oil can be used to prewash luboil additives.
Fish Oil is an oxidizing oil, and a drying oil. It should never be prewashed hot. Commence prewash
as soon as possible after discharge. Remove hot interface.
After Slack Wax , steam the tank hot, > 20 deg C above the MP of the wax, and then wash with hot sea water.
Use Graco injection method with emulsifier. However with refines wax, ensure the temp is < 20C above the MP of wax, or you will get white powdery residues.
Coal tar and creosote is not an easy cargo to clean. Immediately after discharge do the mandatory
prewash. Long hot wash with very hot water is required. Use coal tar cleaner. Use Metal brite for
pipeline steaming.
Products which leave residue (crude products) should never be cleaned by evaporation. The NVM content in the specification of a chemical is a good indicator as to whether a product will leave residue
Chemicals with a low FP require the pre-cleaning temperature to be kept at least 10 C below FP to avoid flammable mixtures. If this is not possible, because the FP is lower than the ambient temperature, all ignition sources must be eliminated.
Water soluble and water miscible substances are easy to clean with water and the solubility of the substances might increase at higher temperatures. The use of a cleaning agent is only advisable for non-water soluble cargoes , to reduce the cleaning time or for odour removal . None of the veg oils are fats are soluble in water. Molasses is fully soluble in water.
Certain cargoes like acetic acid, benzene, luboils, caustic soda, paraffin, molasses, phenol, DINP, fatty alcohols, HMD , Hitec, WPAC, butyl acrylate , creosote etc can be hot pre-washed.
-------CAPT AJIT VADAKAYIL
( 30 YEARS IN COMMAND )