Liquids, storage open tanks

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 ... 

Design liquid storage so leaks and spills do not accumulate under tanks or process equipment Use open structures for plants using flammable or combustible materials Avoid buried tanks... 

Flame (flash) arrestor n. Devices utilized on vents for flammable liquid or gas tanks, storage containers, cans, gas hnes or flammable hquid pipelines to prevent flashback (movement of flame) through the line or into the container, when a flammable of explosive mixture is ignited. Wire screen of 40 meshes is utflized on smaller openings. On larger openings, parallel metal plates or tubes are more effective. 

Before any given test, weather data were measured and recorded and the transfer line and receiver tank purged with dry nitrogen gas. The 600 gallon liquid storage tank was pressurized to the predetermined pressure level. Then the hand valve and the downstream control valve were placed in the open position. 

The liquid storage tank shown in Fig. E2.13 has two inlet streams with mass flow rates w and W2 and an exit stream with flow rate 1V3. The cylindrical tank is 2.5 m tall and 2 m in diameter. The liquid has a density of 800 kg/m. Normal operating procedure is to All the tank until the liquid level reaches a nominal value of 1.75 m using constant flow rates w = 120 kg/min, W2 = 100 kg/min, and wn, = 200 kg/min. At that point, inlet flow rate wi is adjusted so that the level remains constant. However, on this particular day, corrosion of the tank has opened up a hole in the wall at a height of 1 m, producing... 

Two simple interlock systems are shown in Fig. 10.4. For the liquid storage system, the hquid level must stay above a minimum value in order to avoid pump damage such as cavitation. If the level drops below the specified hmit, the low-level switch (LSL) triggers both an alarm (LAL) and a solenoid switch (S) (or solenoid) that turns the pump off. For the gas storage system in Fig. 10.4b, the solenoid valve is normally closed. But if the pressure of the hydrocarbon gas in the storage tank exceeds a specified limit, the high pressure switch (PSH) activates an alarm (PAH) and causes the solenoid valve to open fully. 

Flammable gas detection is not usually required for open tank areas unless the potential for gas accumulation has been identified. (Storage tanks at upstream facilities usually contain stabilized cmde, nonvolatile combustible liquids.)... 

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. 

Storage Segregated storage Uncongested storage of combustibles gangways/adequate breaks Material stacked in the open should be away from windows Flammable liquids in properly designed storerooms bulk quantities in fixed, bunded, adequately spaced tanks... 

No particular industrial hazards are encountered in handling liquid alum. However, a face shield and gloves should be worn around leaking equipment. The eyes or skin should be flushed and washed upon contact with liquid alum. Liquid alum becomes very sick upon evaporation and therefore spillage should be avoided. Storage tanks may be open if indoors but must be closed and vented if outdoors. Outdoor tanks should also be heated, if necessary, to keep the temperature above 450F to prevent crystallization. Storage tanks should be constructed of type 316 stainless steel, FRP, steel lined with rubber, polyvinyl chloride, or lead. Liquid alum can be stored indefinitely without deterioration. 

An operator had to drain water from a 1,200-m spherical storage vessel nearly full of propane (Figure 8-1). He opened valves A and B. When traces of oil showed that the draining was nearly complete, he shut A and then cracked it to complete the draining. No flow came. He opened A fully. The choke—presumably hydrate, a compound of water and a light hydrocarbon with a melting point above 0°C—cleared suddenly, and the operator and two other men were splashed with liquid. The handle came off valve A, and they could not get it back on. Valve B was frozen and could not be moved. Access was poor because the drain valves were immediately below the tank, which was only 1.4 m above the ground. 

Where process, safety, and environmental considerations permit, vacuum protection may be provided by properly sized ever-open vents. Alternatively, active protective devices and systems are required. Vacuum breaker valves designed to open and admit air at a predetermined vacuum in the vessel are commonly used on storage tanks, but may not be suitable for some applications involving flammable liquids. Inert gas blanketing systems may be used if adequate capacity and reliability can be ensured. Where the source of the vacuum can be deenergized or isolated, suitably reliable safety instrumented systems (e.g, interlocks) can be provided. 

API (Venting Atmospheric and Low-Pressure Storage Tanks, Standard 2000, Washington, 1998) provides guidance for vacuum protection of low-pressure storage tanks. Where vacuum relief devices are provided, they should communicate directly with the vapor space in the vessel and should be installed so that they cannot be sealed off by the liquid contents in the vessel. Valves should be avoided in the inlets or outlets of vacuum relief devices unless the valves are reliably car-sealed or locked open, or excess relief capacity is provided (e.g., via multiple-way valves). 

---