Liquids, storage pressure tanks

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. 

Commercial grades Available in three grades refinery (50-70%), chemical (90-92%), and polymer (99%) grade. The remaining percentage in each case is mainly propane. It is shipped as a liquid in pipelines, tank cars, tank trucks, and steel cylinders. Storage is as a liquid at pressures of about 200 psi. 

Crude dichlorobenzene is pumped from a storage tank to a distillation column. The tank is blanketed with nitrogen and the pressure above the liquid surface is held constant at 0.1 bar gauge pressure. The minimum depth of liquid in the tank is 1 m. 

Vertical cylindrical tanks, with flat bases and conical roofs, are universally used for the bulk storage of liquids at atmospheric pressure. Tank sizes vary from a few hundred gallons (tens of cubic metres) to several thousand gallons (several hundred cubic metres). 

A storage tank is 10 m high. At a particular time the liquid level is 5 m high within the tank. The tank is pressurized with nitrogen to 0.1 bar gauge to prevent a flammable atmosphere within the tank. The liquid in the tank has a density of 490 kg/m3. 

Where relief valves are provided on liquid storage tanks or vessels, where there is a possibility of liquid release, i.e., liquid slug, careful evaluation of the release disposal system (e.g., flare header) needs to be undertaken. In some cases, a liquid slug may block a header from releasing pressure and defeat the purpose of the pressure release system. 

Where enclosed spaces may produce overpressures blow out panels or walls are provided to relieve the pressure forces. The connections of the panel are specified at a lower strength that normal panels so it will fail at the lower level and relieve the pressures. Similarly, combustible or flammable liquid storage tanks are provided with weak roof to shell seams so that in case of an internal explosion, the built-up pressure is relieved by blowing off the roof and the entire tank does not collapse. 

A pressurized tank (10 bar) is used for the storage of distilled water fed to the reactor. To feed liquid water, a specific mass flow controller (Quantim, Brooks) is used. 

Propane can be stored as liquid in pressurized (approximately 15 atmospheres) storage tanks and/or at cold temperatures and vaporizes to a gas at atmospheric pressure and normal temperatures. This makes it possible to store a large volume of propane as a liquid in a relatively small volume propane as a vapor occupies 270 times the volume of propane in liquid form. This makes liquid propane an ideal fuel for transport and storage until needed. 

Tanks are used in innumerable ways in the chemical process industry, not only to store every conceivable liquid, vapor, or solid, but also in a number of processing applications. For example, as well as reactors, tanks have served as the vessels for various unit operations such as settling, mixing, crystallization (qv), phase separation, and heat exchange. Herein the main focus is on the use of tanks as liquid storage vessels. The principles outlined, however, can generally be applied to tanks in other applications as well as to other pressure-containing equipment. 

Ethylene oxide storage tanks are pressurized with inert gas to keep the vapor space in a nonexplosive region and prevent the potential for decomposition of the ethylene oxide vapor. The total pressure that should be maintained in a storage tank increases with liquid temperature, since the partial pressure of ethylene oxide will also increase. Figure 5 shows the recommended minimum storage pressures for liquid ethylene oxide under nitrogen or methane blanketing gas. 

LP gas, or propane, is the alternative fuel used in highest volume in the U.S. at present. Propane is unique among alternative fuels in that it is a pressurized liquid, i.e., a modest pressure (under 43.5 kPa [300 psi]) will maintain it in the liquid state. Propane fuel tanks must thus be built to pressure vessel codes like CNG and LNG tanks, but propane is transferred using pumps because pressure differentials are low and the pressure cannot be manipulated as it can for LNG. Propane is sometimes stored in refrigerated containers which lowers the storage pressure significantly, though such containers are rarely if ever used to store propane intended for use in vehicles. 

Storing H2 in aqueous NaBH4 solutions compares favorably to other H2 storage methods. For example, the volume required to store 5 kg of liquid H2 in cryogenic containers is —110 liters. In pressurized tanks, storing 5 kg H2 at 34 MPa (5000 psi) requires 220 liters. However, storing 5 kg of H2 in 35 wt % NaBH solutions requires only 65 liters. 

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