Liquids, storage fixed roofs

Fixed-roof atmospheric tanks require vents to prevent pressure changes which would othei wise result from temperature changes and withdrawal or addition of liquid. API Standard 2000, Venting Atmospheric and Low Pressure Storage Tanks, gives practical rules for vent design. The principles of this standard can be applied to fluids other than petroleum products. Excessive losses of volatile liquids, particularly those with flash points below 38°C (100°F), may result from the use of open vents on fixed-roof tanks. Sometimes vents are manifolded and led to a vent tank, or the vapor may be extracted by a recov-eiy system. 

With proper safety precautions and operating procedures the occurrence of explosions in the vapor space of fixed roof storage tanks are a very rare event. A frequency estimate of an explosion once in every 1,000 years, per tank, has been stated. Explosive mixtures may exist in the vapor space of a tank unless precautions are taken. Any vapor will seek an ignition source, so prevention of ignition cannot be guaranteed. This is especially true with liquids that have low conductivity that... 

Fixed (cone) roof tanks Vent fire Overfill ground fire Unobstructed full liquid surface area Obstructed full liquid surface fire if frangible roof remains partially in tank For volatile liquids, the rich vapor space typically prevents ignition within the tank. Environmental regulations typically prevent storage of Class 1 flammable liquids in larger fixed roof tanks. 

Large-scale methanol storage usually uses cylindrical tanks similar to those used for petroleum products. A floating-roof design is usually the choice. If a fixed-roof tank is used, an inert gas pad must be used to prevent the possible formation of an c q)losive mixture above the liquid. Tanks in a tank farm are usually enclosed by dikes and protected by water cannons and fire-extinguishing systems. 

Large cylindrical steel storage tanks with a height/diameter ratio between 0.2 and 2. The roof can be welded to the shell (fixed conic roof) or floating over the contained liquid. The operating volume varies from some tens to 200000 m. The bottom plate is circular and placed directly on a granular backfill. When they are full filled, part of the... 

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