Tanks, types floating-roof tank

These tanks must have a seal between the roof and the tank shell. If not proteeted by a fixed roof, they must have drains for the removal of water, and the tank shell must have a wind girder to avoid distortion. An industry has developed to retrofit existing tanks with floating roofs. Mueh detail on the various types of tank roofs is given in manufaeturers literature. Figure 12-14 shows types. These roofs eause less eondensation build up and are highly reeommended. 

These tanks are designed to reduce evaporation and vapor emission. Two distinct designs are those with and those without an additional fixed roof. Of the former types, known as internal floating roof tanks, various provisions... 

The open-top floating roof tank design eliminates the potential for BLEVE. Further, the material being handled has no potential for chemical reactions or for condensed-phase explosions. Thus, these types of explosions can also be eliminated from consideration. 

There are several technologies of linear heat detectors, most designed to monitor air temperature and a few that detect radiant heat. This type of detection is wire or plastic tubing and can be used where other types of detectors are difficult to install. Generally, they are used to supplement other forms of detection in difficult areas, such as heavily congested areas, rim area of floating roof tanks, on pumps, etc. Linear types can be pneumatic, electrical, or optical. Electrical linear heat detectors come in three types that ... 

Fluoroprotein and alcohol resistant type AFFF concentrates are suitable for seal protection of open top floating roof tanks. Foam may be applied from fixed chambers in an "over-the-top" fashion or by discharge from "foam chambers" located at the top of the tank shell allowing the foam to run down the inside wall of the tank shell onto the seal area. Subsurface foam on floating tanks is generally not recommended as a sunken roof would block the foam distribution. Typical protection is shown in Table 7-10. 

The foam concentrate used with subsurface systems should be a fluoroprotein type for best results, although some AFFF foams are listed for substitutable application (because of their "fuel shedding" properties). The minimum foam solution rate should be 0.3 gpm/ft (12 Ipm/m ). The supply of foam liquid should be adequate to operate the system for 20 minutes. The foam injection point must be above the level of any residual water in the bottom of the tank. Subsurface foam application is not recommended for open or covered floating roof tanks or cone roof tanks with internal floating covers. 

Internal (or covered) floating-roof tanks Vent fire Overfill ground fire Obstructed rim seal fire Obstructed full liquid surface fire Many fires in this type of tank occur as a result of overfilling. Tank will be extremely difficult to extinguish if entire liquid surface becomes involved. Fires in tanks with pan type covers can be expected to develop into obstructed full liquid surface fires. 

Type of Design Approx. Number in Use in United States Cost (for 40-ft Floating Roof Tank with Temperature Measurement) Measures Accuracy Maintenance Required... 

The most vulnerable storage tanks are primarily atmospheric floating roof tanks followed by conic roof tanks. Both tank types are often used for the storage of petroleum, oil and diesel. Floating roof tank shunts are used to conduct stray electrical energy but in fact they... 

Two types of designs are commonly applied. For cone top tanks or internal floating roof tanks with other than pontoon decks, multiple foam makers are mounted on the upper edge of the tank shell. These systems are designed to deliver and protect the entire surface area of the liquid of the tank. For open and covered floating roof tanks with pontoon decks, the foam system is designed to protea the seal area. Foam makers are mounted on the outside of the tank shell near the rim and foam is run down inside to the seal area that is provided with vertical barrier adjacent to the seal area i.e., a foam dam to hold the foam in the seal area. This method tends to cause the movement of cooler product to the surface to aid in extinguishment of... 

External Floating Roof Tank—This is an open top cylinder shaped base with a pontoon type roof that floats on the liquid surface as the contents raise and lower with tank operation. The top of the tank is open to the... 

An effective way of preventing vent loss is to use one of the many types of variable-volume tanks. These are built under API Standard 650. They may have floating roofs of the double-deck or the singledeck type. There are hfter-roof types in which the roof either has a sldrt moving up and down in an annular hquid seal or is connected to the tank shell oy a flexible membrane. A fabric expansion chamber housed in a compartment on top of the tank roof also permits variation in volume. 

A cone roof tank with an internal floating roof that does not meet these criteria or uses plastic foam for flotation, even if encapsulated in metal or fiberglass, should be fire protected by side wall foam chambers suitable for the full (surface) area of the tank. This type of internal floating-roof installation is not recommended, particularly for flammable liquids. 

Floating Roof A special type of storage tank roof which floats on the surface of the oil in storage. This helps to eliminate tank venting and reduces evaporative loss. 

A variety of symbols are used to illustrate the different type of tanks and vessels found in the chemical processing industry, including bins, drums, and dome, cone, open-top, floating-roof, and spherical tanks. Process symbols are designed to graphically display the vessel as it appears in the field. Common pump and tank symbols are shown in Figure 7-8. 

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