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Publication Date: 2012-May-08
Document File: 22 page(s) / 1M

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Yacine Amrouche, Chaitali Dave', Kamal Gursahani, Rosabella Lee, Lisa Montemayor KBR

  The skyline is continuously changing across the nation as chemical plants are constructed to improve the quality of our lives. As we drive down roads and bridges we see facilities where storage tanksare used to store valuable products that we use on a daily basis. This paper is intended to provide a developing engineer with a fundamentalunderstanding of storage tanks. It was written by a small group of developing engineers who belong to KE3R's young professional network, which is known as IMPACT. This is the second paper in a new series of introductory articles sponsored by KBR. This particular paper will focus on the process design and operational considerationsof vertical aboveground, atmospheric-pressure storage tanks,which are most commonly used in the chemical process industry (CPI).

  By definition, an atmospheric tankhas a design pressure less than 2.5 psig'. Atmospheric tankscan be equipped with a fixed roof or a floating roof. A vertical fixed roof tankconsists of a cylindrical metal shell with a permanently affixed roof (see Figure 1). The roof may vary in design from flat to cone- shaped to dome-shaped. Fixed roof tanks are used to store materials with True Vapor Pressures (TVP) less than 1.5 psia. Fixed roof tanks are less expensive to construct and are generally considered the minimumacceptable equipment for storing chemicals.

There are two types of floating roof tanks,External Floating Roof (EFR) tanksand Internal Floating Roof (IFR) tanks. EFR tanks consist of an open-topped cylindrical shell with a roof that floats on the surface of the stored liquid (see Figure 2). These types of tanks are used to store materials with TVP's from I.$psia to 11 pia. The floating roof, w k hrises and fa& with the €iq&&€eveb

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with a seal system that is attached to the roof perimeter, sealing the annular space between the roof and the tank wall. AnIFR tank has both a permanent fixed roof and a floating deck inside (see Figure 3).

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The floating roof in the IFR tankrises and falls with the liquid level, and either floats directly on the liquid service (contact deck) or rests on pontoons several inches above the liquid surface (noncontact deck). Internal floating roof tankswith an external fixed roof are used in areas of heavy accumulations of snow or rainwater on the floating roof, which affect the operating buoyancy of the roof, or to minimize contact of the vapor with the atmosphere. In such cases, the vapor space above the liquid must be purged with an inert gas
Design of Storage Tanks:
Factors to consider in storagetankdesign include:

0 Process design considerations,

0 Mechanical design aspects,

0 Environmental requirements,

0 Structural requirements,and

0 Operational and control considerations. Process Design Considerations

   One process design aspect of storage tanks is deter...