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Maritime Forum

TOPIC: Double bottom tank construction for storage of liquid

Double bottom tank construction for storage of liquid 24 Jun 2016 10:04 #4540

Describe the pumping arrangement for a double bottom tank. What methods are used to :
1.Ensure against air locks
2.Ensure complete drainage
3.Measure the content of tank
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Double bottom tank construction for storage of liquid 28 Jun 2016 03:43 #4549

The pumping arrangement for a double bottom tank is not much different from that in any other tanks, but following factors makes a difference and are considered while designing the pipe work:

1. The ship's are mostly down by stern
2. The bottom plate is in touch of sea-water from outer side and thus will cool the liquid(fuel or ballast water).

Thus considering these factors following arrangements are done to ensure against air locks & complete drainage:

1) The suction opening is bell mouth and is located in the Aft of the tank, to take advantage of Ship's aft trim.This will ensure maximum amount of liquid to be sucked from it.For Ballast tanks the pumping arrangement is aided with the Eductor system also, along with the Centrifugal Pump(could be having self priming arrangements, as well). While the Fuel tank's pumping system has Positive displacement pump, to ensure maximum transfer.
2) The pipe line should be so designed so that it has less amount of bends and does not have slops which will cause air-locking. This include putting the Transfer pumps(Ballast water pump and Fuel transfer pumps) at the bottom platform of the Engine Room.
3) The Fuel tanks are heated with steam coils so that the liquid remain in pumpable condition. The ships (like ice class) which operate in colder seas also has heating coils in the ballast tanks for this reason.
4) Air-pipes to atmosphere is fitted in the forward of the tank which keeps the pressure inside the tank,atmospheric, which lets the pumping to work in normal condition.(Air pipes are to be fitted at the opposite end of the tank to that which the filling pipes are placed and at the highest part of the tank.)

Arrangements to measure content

1) The soundings are to be taken as near the suction pipes as practicable.

2) An approved level gauge or remote reading level device may be accepted in lieu of a sounding pipe.

3) Where fitted, sounding pipes are to be as straight as practicable and if curved to suit the structure of the ship, the curvature is to be sufficiently easy to permit the ready passage of the sounding rod or chain.

4) Striking plates of adequate thickness and size are to be fitted under open ended sounding pipes.

5) Where slotted sounding pipes having closed ends are employed, the closing plugs are to be of substantial construction.
Last Edit: 28 Jun 2016 08:00 by anandgardener.
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