Tanks design

A distributor is frequently installed at the top of the column for use during backwash. It collects water evenly and prevents resin from escaping the column should unexpected surges develop in the water flow during backwash. Columns lacking an upper distributor or screen to prevent loss of resin should have an external system to prevent resin from being lost to the drain. It is referred to as a resin trap and may consist of a porous bag that fits over the outlet pipe or a tank designed to lower the linear velocity. Resin drops to the bottom of the tank and is returned to the column when convenient. 

Fig. 15. Wet drum low intensity magnetic separator tank designs (a) concurrent, (b) counter-rotation, and (c) countercurrent (6) (d) shows the operating...

Most tanks store Hquid rather than gases or soHds. Characteristics and properties such as corrosiveness, internal pressures of multicomponent solutions, tendency to scale or sublime, and formation of deposits and sludges are vital for the tank designer and the operator of the tank and are discussed herein. Excluded from the discussion are the unique properties and hazards of aerosols (qv), unstable Hquids, and emulsions (qv). A good source of information for Hquid properties for a wide range of compounds is available (2). 

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. 

Miscellaneous Properties. Other properties such as viscosities, solidification temperature, pour poiat, and cubical rate of thermal expansion are aH important for the tank designer or operator to consider and understand. 

Low Pressure Tanks. Low pressure ia the coatext of tanks means tanks designed for a higher pressure than atmospheric tanks. In other words, these are relatively high pressure tanks, designed to operate from atmospheric pressure up to 15 psig (101.4 kPa). 

When the design temperatures are significantly below ambient temperature, the primary threat to tank integrity is failure of the material by britde fracture. The tank design codes usually provide thorough treatment of this topic to prevent catastrophic failure. Additionally, there is the consideration of corrosion allowance, defined as extra thickness added beyond that required for strength. Corrosion allowance is not discussed herein. 

A further development in the process is the use of universal refrigerant-cooled tanks, designed to ferment, age, and finish beer in a single tank without the usual transfers. The Uni-Tank has a shallow cone bottom rather than the typical steep cone shape of usual fermenting tanks. Fermentation and maturation of the beer within a single vessel take approximately two to three weeks. 

Rotation speeds to 40 r/min are possible with cakes typically 3 to 6 mm (0.12 to 0.24 in) thick. Filter sizes range from 930 cm to 19 m (1 to 207 ft") with 93 percent of the area active. The slurry is fed into a conical feed tank designed to prevent solids from settling without the use of mechanical agitators. The proper hquid level is maintained by overflow, and submergence ranges from 5 to 70 percent of the drum circumference. 

A basic stirred tank design is shown in Fig. 23-30. Height to diameter ratio is H/D = 2 to 3. Heat transfer may be provided through a jacket or internal coils. Baffles prevent movement of the mass as a whole. A draft tube enhances vertical circulation. The vapor space is about 20 percent of the total volume. A hollow shaft and impeller increase gas circulation (as in Fig. 23-31). A splasher can be attached to the shaft at the hquid surface to improve entrainment of gas. A variety of impellers is in use. The pitched propeller moves the liquid axially, the flat blade moves it radially, and inclined blades move it both axially and radially. The anchor and some other designs are suited to viscous hquids. 

FIG. 23-30a A basic stirred tank design, not to scale, showing a lower radial impeller and an upper axial impeller boused in a draft tube. Four equally spaced baffles are standard. H = beigbt of liquid level, Dj = tank diameter, d = impeller diameter. For radial impellers, 0.3 < d/Dt < 0.6. 

FIG. 23-30 Basic stirred tank design and selected lands of impellers, (h) Propeller, (c) Turbine, (d) Hollow, (e) Anchor,... 

ANG tank design and the adsorbent materials chosen can help to minimize these problems. However, these alone may not provide a total solution to the... 

Flow equalization system A device or tank designed to hold back or store a portion of peak flows for release during low-flow periods. 

Tanks designed to hold hygroscopic corrodants should be well sealed to prevent their breathing damp air. 

A condensible blowdown tank, designed on a similar basis to that described above for phenol, may be provided in other services where a conventional condensible blowdown drum would not be acceptable (e.g., due to effluent water pollution considerations). Examples of such cases are methyl ethyl ketone (MEK) and dimethyl formamide (DMF). A suitable absorbing material is specified (e.g., a lube oil stock for MEK water for DMF), and the design must include consideration of maximum permissible operating temperatures to prevent excessive vapor evolution or the boiling of water. 

In fact, the vent on the tank was choked. The gauge air pressure (75 psi or 5 bar) was sufficient to burst the tank (design gauge pressure 5 psi or 0.3 bar). Originally the tank had a 6-in.-diameter vent. But at some time this was blanked off, and a 3-in.-diameter dip branch was used instead as the vent. 

Tank design pressure 6 inches WC positive and 2 inches WC negative... 

The system is a storage tank designed to hold a flammable liquid under a low positive nitrogen pressure (see Figure 5.1). This pressure is controlled by PICA-1. A relief valve is fitted which operates if overpressurization occurs. Liquid is fed to the tank from a tank truck, and is subsequently supplied to the process by the pump P-1. 

For water spray protection over tlie entire surface area of tlie tank designed witli a density of 0.25 gpni/ft or more F=0.3. For an approved fire resistant installation, F=0.3. For an underground or buried tank, F=0.3. For water spray witli good drainage F=0.15. 

The use of these settlers is not usually practical for most situations. The diameters or cross-section areas become too large for the handling of anything but the very smallest of flowing vapor streams. In general, gravity settlers of open box or tank design are not economical for particles smaller than 325 mesh or 43p [23]. 

For tank design per API Standard 650 with weak roof to shell designs (roof lifts up) the venting requirements of API-Std-2000 do not apply for emergency venting to atmosphere or elsewhere. 

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