Tank roof

To reduce these losses, the crude oils are stored in floating roof tanks. 

Storage of Flammable Materials. The preferred storage for flammable Hquids or gases is in properly designed tanks. Floating roof tanks frequently are used in the petroleum industry for flammable cmdes and products (see Tanks and pressure vessels). The vents on cone roof tanks should either be equipped with flame arrestors or the vapor space above the contents should be inerted with a nonflammable gas or vapor, unless the flash point is weU above the maximum ambient temperature, the contents are not heated above the flash point, and the tank is not exposed to other tanks containing flammable Hquids. 

Fig. 4. Fixed-roof tanks (a) self-supported cone roof (b) center-supported cone roof (c) column-supported cone roof and (d) dome or umbrella roof...

Cone-Roof Tanks. Cone-roof tanks are cylindrical shells having a vertical axis of symmetry. The bottom is usually flat and the top made ia the form of a shallow cone. These are the most widely used tanks for storage of relatively large quantities of fluid because they are economic to build and the market supports a number of contractors capable of building them. They can be shop-fabricated ia small sizes but are most often field-erected. Cone-roof tanks typically have roof rafters and support columns except ia very small-diameter tanks when they are self-supporting (see Fig. 4b and c Table 3). 

Umbrella- and Dome-Roof Tanks. UmbreHa-roof tanks are similar to cone-roof tanks, but have roofs that look like umbreHas. They are usuaHy constmcted to diameters not much larger than 60 ft (18 m). These tank roofs can be self-supporting, ie, having no column supports that must be mn to the bottom of the tank (see Fig. 4d). 

Dome-roof tanks are similar to umbrella-roof tanks except that the dome more neatly approximates a spherical surface than the segmented sections of an umbrella roof... 

Aluminum geodesic dome roof tanks are becoming popular. These are often the economic choice. They offer superior corrosion resistance for a wide range of conditions, and are clear span stmctures not requiring internal supports. They can also be built to any required diameter. However, domes caimot handle more than a few inches of water column internal or external pressure. 

EFR tanks have no vapor space pressure associated with them and operate strictly at atmospheric pressure. IFR tanks, like fixed-roof tanks, can operate at or above atmospheric pressure in the space between the floating roof and the fixed roof. 

Polyurethane. Polyurethanes (pu) are predominantly thermosets. The preparation processes for polyurethane foams have several steps (see Urethane polymers) and many variations that lead to products of widely differing properties. Polyurethane foams can have quite low thermal conductivity values, among the lowest of all types of thermal insulation, and have replaced polystyrene and glass fiber as insulation in refrigeration. The sprayed-on foam can be appHed to walls, roofs, tanks, and pipes, and between walls or surfacing materials directly. The slabs can be used as insulation in the usual ways. 

Specifications. Eor fuel-grade MTBE, the typical specification of merchant product is 95 wt % minimum purity ia the United States and 98% minimum ia Europe. The maximums for impurities are usually 0.5 wt % for methanol, and 0.15 wt % for water. To maintain quaUty, fuel-grade MTBE is normally stored ia fixed-roof tanks, to keep rain water out, with internal floaters, to minimise vapor losses. 

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. 

Vapor recovery systems floating roof tanks pressure tanks vapor balance painting tanks white Cyclones-precipitator-CO boiler cyclones-water scrubber multiple cyclones Vapor recovery vapor incineration Smokeless flares-gas recovery... 

Dome-roof tank -self-supported roof... 

McAllister gives the following equation for the vapor formed when filling a tank. This must be known when sizing the vapor piping for a manifolded expansion-roof tank system. 

Cone roof and floating roof tanks are usually correlated using vs. volume, w ith materials of construction as another variable. The cost of internal heat exchangers, insulation, unusual corrosion allowance, and special internals should be separated from the basic cost of the tank in the correlations. 

Inert gas is used to blanket certain fixed-roof tanks for safet. Here is how to determine the inert gas requirements. Inert gas is lost in two ways breathing losses from day/night temperature differential, and working losses to displaee changes in active level. 

Example A fixed-roof tank D = 128 ft Height = 36 ft Avg. outage = 12 ft Annual throughput = 300,000 bbl Location = New Orleans Detennine monthly inert gas usage Solution ... 

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... 

Any source of ignitable hydrocarbons, such as separators or floating roof tanks, should be at least 60 m from the base of the flare stack. 

Workers should not go onto floating-roof tanks to extinguish rim ThiJ6t< tiF3il.dfgcffliMi isnte)fip, e i lMT 2 ft... 

Figure 5-15. Oil trapped in the leg of a floating-roof tank caught fire during demolition.

When the tank was refilled with warm crude oil at 37°C. vapor was pushed out into the space above the floating roof and then out into the atmosphere through vents on the fixed-roof tank (Figure 5-16). This vapor was ignited at a boiler house some distance away. 

Do not take floating-roof tanks off-float except when they are being emptied for repair. 

An explosion and fire occurred on a fixed-roof tank that was supposed to be blanketed with nitrogen. After the explosion, it was found that the nitrogen supply had been isolated. Six months before the explosion the manager had personally checked that the nitrogen blanketing was in operation. But no later check had been carried out [8]. 

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