Tuesday, December 28, 2010

CLAY SLURRIES ON CHEMICAL TANKERS -- CAPT AJIT VADAKAYIL





KAOLIN CLAY SLURRIES

It is commonplace for the Framo pump cargo seals to leak en masse after you start recirculating Kaolin clay slurry at sea .  Experience has show that the leaks stabilize after the cargo is discharged. 

Discharging can be done with ships Framo pumps.  If the cargo does not go ( small deepwel risers ) , then the only alternative is to use a Framo portable screw pump .  A screw booster pump ashore is also needed.

IMPORTANT:   RECIRC AT SEA, IS ABOUT FAST JET MOTION IMPINGEMENT THROUGH SMALL DIA RECIRC NOZZLES FITTED ON DROPS AT BOTTOM. IT IS ABOUT ELECTROSTATIC CHARGES KEEPING THE SLURRY IN COLLOIDAL SUSPENSION.



Product Information:
Kaolin, ( China Clay ) in solid form are being shipped to ECC international, Colonial terminals, Savannah, processed and re-exported as slurry.

The slurries consists of 67 - 73 percent solids and 27 - 33 percent liquids and are used in the paper manufacturing industry.

In the receiving end, the product will go directly to the pulp mills without further processing.

There are presently 2 grades of slurry being shipped from Savannah, i.e.
 Capim GP formerly known as Hubergloss (Alphagloss) slurry
 WP Slurry formerly known as Nanaimo W.P. - Filler slurry

Common Chemical name           : Aluminum Silicate Hydroxide
Appearance                                  : White (Off White)
Specific Gravity                        : 1.73 - 1.81
Boiling Point                 : 100 C
Freezing Point               : Approx. O degr. C
MARPOL category/ OS

Shipping and Handling--

Before loading:

Cargo tanks:
Tanks should be cleaned from previous cargo to normal " water white " standard, ( i.e. no traces of previous cargo, no odor, no loose coating or particles present ).

Upon completion of normal cleaning, the tanks, pumps and lines should be thoroughly rinsed and flushed with fresh water, added with minimum 100 ppm Hydrogen Peroxide.

The slurry is extremely sensitive to bacteria, and may go off color and become unsuitable for its intended use if bacteria are allowed to grow.

This is one of the main concerns of the shippers, and bacterial tests of tanks may be carried out prior to loading.

The tanks presented for loading must furthermore be 100 percent coated, small areas with rust or pittings should be grinded and overcoated prior arrival at loading port. No particles, such as rust, coating flakes, grit or lint from wiping rags will be accepted, as these will appear as tears in the finished paper.

Cargo pumps: Frank Mohn recommend filling of  fresh water into pump cofferdams. All cofferdams should be filled 100 % prior to arrival at loading port.

After loading:

All cargo pipe lines must be thoroughly cleaned with fresh water as soon as possible upon completion of loading, not to allow drying of the product in any part of the line system, once dried it is virtually impossible to remove Make sure the water flushed through the lines is absolutely clear (not milky).  Check all drains and blanks.

(Recommended temp. of cleaning water: 40  50 degr. C )

Voyage
To avoid solids settling, it is necessary to recirculate the products during transit, this should be done via a hose from the pump stack through a tank cleaning hatch---bottom to top recirc, on ship's without recirc diffusers .

Diffusers build up a electrostatic charge which keeps the colloids from getting agglomerated/ flocculated and settling down on the bottom of tank toform a sediment which cements the deepwell pump impeller..
Shippers recommend pumps to be run at minimum speed during recirculation.

The fresh water level in the pump cofferdams must be controlled and maintained during this operation.

The solids in the Alphagloss product settle quickly, hence daily recirculation is necessary.  A similar problem has not been experienced with the other products, and recirculation once a week should be sufficient.

Should clogging, of impeller nevertheless occur, it is recommended to blow the pump stack with compressed air, to brake up solids forming in the impeller housing.

Discharging

Discharging can be done with ships Framo pumps. If the cargo does not go , then the only alternative is to use a Framo portable screw pump. A screw booster pump ashore is also needed.

Water level in cofferdams should be maintained during  discharge operation.

The discharge rate vary from grade to grade and is generally slow in the beginning, be patient, for once the cargo is flowing, the rate will gradually increase.

Shore line will be pigged between each grade.

The Alphagloss grade must be agitated ( recirculated ) prior to and during discharging,
experience has proved that this grade is extremely difficult to pump due to the high
content of solids, hence extra care is required.

The other grades does not require any agitation during discharging and will not represent any problem.

Upon completion of discharging, 2-3 cub. meter of unpumpable sediments will remain
in each tank hence sweeping is recommended. Tanks should be thoroughly ventilated
prior to entry, as the anti bacterial chemicals in the slurry can cause some irritation to the
eyes.

Cleaning with fresh water is advantageous as the clay dissolves easily, sea water should be avoided as the clay mixes poorly and solids settle quickly.

Lukewarm water was recommended by shippers, but not a must. Experience showed no difference whether cold or warm water was used.

Tank cleaning procedure after clay slurry.

1 ) Upon completion of discharging and sweeping of tank,  the tank should be closed  down to keep the clay from drying on the walls.

2) Cleaning should commence as soon as possible after the tank is empty, by using portable tank cleaning machines placed at the height of the cargo level.

3) Only fresh water should be used for washing, and the tank should be washed for 20 minutes, and washings transferred into slop tank.

4) Spot washing can be done with hand hose.

5) Flush cargo line from pumpstack to manifold and then to the slop tank.Open and flush all drain cocks on cargo line, stripping line, drop line and heat exchangers, blow all pump cofferdams by air to empty them from water.

6) Open and check all cargo lines for residues of clay, and flush by fresh water if  required. Final fresh water wash of tank of 30 min can be pumped overboard if the water is not milky. There is no pollution concern , but too much milkiness can cause sea to be stained white.

7) Open all drains , flanges etc and check for residue.

8) Steam lines.

Clay slurry reacts with Co2 in atmosphere  and hardens. Do not mix different grades of slurry in slop tank (reaction between different ionic type)—pump direct overboard if feasible. Since it swamps the bottom environment—take permission from local authority before pumping out in territorial waters.


This can be explained by this experiment. Take a Kaolin slurry watery mixture and pour it into a pit made in sand. Do NOT expect the water to drain, it will remain there. The clay colloids will immediately block the pores in the loose sand.

Ordinary slurries ( not clay ) react with CO2 and hardens. Avoid hot interface,a nd dump the washwater directly overboard—not into slops. Do not mix different grade slops, due to anionic/ cationic reaction.

-------CAPT AJIT VADAKAYIL

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