STORAGE TANKS & VESSELS - Floating Roof Storage Tanks PDF Print E-mail
Written by Norrie   
Monday, 24 May 2010 21:43
Article Index
STORAGE TANKS & VESSELS
Storage Tanks
Floating Roof Storage Tanks
Floating Roof Seals, Legs, Water Drain & Access Ladder
STORAGE OF HIGH PRESSURE GASES
1. SPHERICAL STORAGE (STORAGE SPHERES)
2. CYLINDRICAL STORAGE VESSELS
3. GAS CYLINDERS
STORAGE OF LOW PRESSURE GASES
All Pages

FLOATING ROOF STORAGE TANKS

A 'Floating Roof', as its name implies, actually floats on the surface of the liquid in the tank. As the liquid level changes the roof is designed to move up and down with the liquid level - i.e. Filling, Emptying, Expansion and Contraction due to temperature changes. This type of tank roof minimises the vapour space between it and the liquid surface. Since there is no large vapour space for the liquid to evaporate into, vapour losses are also minimised.

In its simplest form, the floating roof is merely a large, flat pan (or disc), slightly smaller in diameter than the tank shell. It is fitted with a system of flexible 'shoes' to close the space between the edge of the roof and the tank shell in order to minimise vapour loss.

In modern usage, there are two main designs of floating roof :

  1. The ' Pontoon ' roof
  2. The ' Double-Deck ' roof

1. The ' Pontoon ' Roof:

This consists of a series of pontoons - (closed compartments) around the outer edge of a central plate. This construction increases the floating stability. The roof is also sloped towards the centre to allow rain water to flow into a water drainage system.

2. The 'Double-Deck' Roof:

This is a development which employs two separate decks of steel plate over the entire tank area. The space between the upper and lower plates is divided into compartments. With this type, the liquid is never in contact with the underside of a plate whose top surface is directly exposed to the sun's rays, as is the centre section area of the pontoon roof and the full area of the pan type roof.

The double-deck roof therefore, has much lower evaporation losses than any other type of floating roof. Because of the very small vapour volume, ' breathing ' due to temperature change and vapour formation when pumping into the tank, is greatly reduced. Also, because the actual vapour space is so small, danger of fire is also minimised due to the liquid surface being entirely covered.



Last Updated on Monday, 24 May 2010 21:47