Tanks, storage vaporizers, pressurized

Emerson Gumming, Inc. eventuaUy bought the rights to the Sohio process and produced a variety of microspheres. Union Carbide was Hcensed to produce the phenoHc microspheres offered under the name PhenoHc MicrobaUoons (Table 16). When PhenoHc MicrobaUoons are introduced into a cmde-oU storage tank, they form a fluid seal that rises and faUs with the level of the oU. A continuous vapor-barrier seal is formed, which reduces evaporational losses up to 90%. Tests have been conducted under various mechanical and weather conditions and with cmde oUs of varying vapor pressure. 

Vapor pressure has also become a means of regulating storage tank design by the EPA. Because increasing vapor pressure tends to result ia an iacrease ia volatde emissions, the EPA has specific maximum values of vapor pressure for which various tank designs may be used. 

LPG. LPG could be a principal alternative transportation fuel if its other uses were displaced by natural gas. A significant number of LPG fueling stations are located throughout the United States. LPG is a Hquid fuel and does not suffer the same driving range problem as natural gas. Because LPG vapor pressure is high, the storage tank has to withstand 2800 kPa (400 psi). 

Storage tanks are generally designed based upon the vapor pressure of their contents, and can range from low pressure (API-type) tanks to high pressure tanks for compressed gases or pressurized liquids. 

In some cases the decision whether storage vessels will be equipped with a vapor recovery system has been determined by the United States Environmental Protection Agency (EPA). In 1973 it set the standards4,5 for all petroleum liquids that are stored in vessels of mcae than 65,000 gal (245 m3). It states that if the vapor pressure is greater than 11.1 psia (570 mm Hg) a vapor recovery system or its equivalent must be installed on any new tanks. If the vapor pressure is between 1.52 psia (78 mm Hg) and 11.1 psia (570 mm Hg), a floating head tank may be used or a vapor recovery system may be installed. Since the former is cheaper it will usually be selected. Below 1.52 psia (78 mm Hg) only a conservation vent or its equivalent is required. 

A liquid with a viscosity of 5cP, density of 45 lbm/ft3, and vapor pressure of 20 psia is transported from a storage tank in which the pressure is 30 psia to an open tank 500 ft downstream, at a rate of 100 gpm. The liquid level in the storage tank is 30 ft above the pump, and the pipeline is 2 in. sch 40 commercial steel. If the transfer pump has a required NPSH of 15 ft, how far downstream from the storage tank can the pump be located without danger of cavitation ... 

Calculate the mass flux (kg/m2 s) for the following tank leaks given that the storage pressure is equal to the vapor pressure at 25°C ... 

A critical safety issue of using diesel-ethanol blends relates to flashpoint and flammability. E-diesel blends containing 10-15% ethanol have the vapor pressure and flammability limits of ethanol. This means that ethanol concentrations in enclosed spaces such as fuel storage and vehicle fuel tanks are flammable over the temperature range 13-42 °C. Thus, there are higher risks of fire and explosion than with diesel fuel, or even gasoline. Other vehicle performance-related concerns are (a) a decreased maximum power (b) an increased incidence of fuel pump vapor lock and (c) a reduced fuel pump and fuel injector life due to the decreased lubricity of ethanol. 

Safety Considerations Design and location of storage tanks, vents, piping, and connections are specified by state fire marshals, underwriters codes, and local ordinances. In NFPA 30, Flammable and Combustible Liquids Code, 2003 (published by the National Fire Protection Association, Quincy, Ma.), liquid petroleum fuels are placed in Class I through Class III B based on their flash point, boiling point, and vapor pressure. 

LPG (liquefied petroleum gas)— propane or (less commonly) butane, obtained by extraction from natural gas or from refinery processes. LPG has a vapor pressure sufficiently low to permit compression and storage in a liquid state at moderate pressures and normal ambient temperatures. Pressurized in metal bottles or tanks. LPG is easily handled and readily lends itself to a variety of applications as a fuel, refrigerant, and propellant in packaged aerosols. LPG is also called LP gas and bottled gas. See natural gas liquids. 

On-off control is used to keep the vapor pressure within limits in both the fuel (hydrogen) and oxidant (02) tanks. The LH2 storage tank vapor space, for example, is held between 32 and 34 psig. Below 32 psig a GH2 supply valve is opened to the tank at 33 psig this valve closes, and at 35 psig a relief valve is opened. The same type of on-off control is applied to keep the 02 tank pressure between 20 and 22 psig. Similarly, to control the propellant flows, the 17 in. control valves are pneumatically operated. 

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