Fixed Versus Floatin Roof Tank Selection ?

[salehy]

Hi every one:

i am wondering if there are any charts or selection curves that indicate the approperaite selection of tank roofing type, i.e, floating versus fixed against the emmission control, the size of the tak, the ambient conditions and of course the bulk material? so do we have such guidelines telling up to certain size or evaporation losses, you shall select the floating type?

 

[JStephen]

In many cases, it will be regulated by law, although you may still have some options as to how to achieve the intended result.

 

[vesselguy]

Salehy,

As far as I know, there is no one magic curve or chart that tells you if tank needs a floating roof or fixed roof. If you find one, please post it here so we can all share in on this.

With fixed roof, you could have a vapour recovery system (closed system) to have zero emission and recover your products. Alternatively, you could go with a floating roof to "minimize" the vapour loss.

JStephen is correct in that whether you use floating tank roof or not is dictated largely by the local government Environmental agency rules on emission control. Search the web or contact your local state gov body to find out the rules.

To help you a bit, here is an excerpt from the Washington State Dept of Ecology specification for oil storage tanks:

Tank Types
This is a vertical cylindrical tank with a cone or dome or umbrella roof which is either self supported off the shell or supported with one or more interior columns resting on the tank bottom plates.
This type of tank is common for low vapor pressure fluid, such as diesel oil, when the loss of fluid by vaporization into the atmosphere is not a concern.

Open Top, Floating Roof
This is a vertical cylindrical tank with a floating roof that floats on top of the tank fluid. Vapor leakage is minimized between the periphery of the float and the tank shell by means of a flexible seal. A roof drain has to be provided. This type of tank is used for higher vapor pressure fluids (such as condensate) which will readily evaporate into the atmosphere.
9-1
This type of tank will leak small amounts of vapor to the atmosphere, depending on condition of the seals. Rain and snow may also impair the operation of the float.