Holding vessel size

Reactors are now little more than holding vessels for the reactor cyclones. With efficient riser separators, reactor velocities of up to 3.5 Ft/S are not uncommon. A new reactor would be sized for about 2.5 Ft/S. Cyclone inlets are normally placed at least 15 Ft above simple riser turndowns to allow for any catalyst disengagement that might take place. 

Mixing in Agitated Vessels Agitated vessels may frequently be used for either batch or continuous service and for the latter may be sized to provide any holding time desired. They are useful for liquids of any viscosity up to 750 Pa s (750,000 cP), although in contacting two liquids for reaction or extraction purposes viscosities in excess of 0.1 Pa s (100 cP) are only rarely encountered. 

This form is partieularly appropriate when the gas is of low solubility in the liquid and "liquid film resistanee" eontrols the rate of transfer. More eomplex forms whieh use an overall mass transfer eoeffieient whieh ineludes the effeets of gas film resistanee must be used otherwise. Also, if ehemieal reaetions are involved, they are not rate limiting. The approaeh given here, however, illustrates the required ealeulation steps. The nature of the mixing or agitation primarily affeets the interfaeial area per unit volume, a. The liquid phase mass transfer eoeffieient, kL, is primarily a funetion of the physieal properties of the fluid. The interfaeial area is determined by the size of the gas bubbles formed and how long they remain in the mixing vessel. The size of the bubbles is normally expressed in terms of their Sauter mean diameter, dj, whieh is defined below. How long the bubbles remain is expressed in terms of gas hold-up, H, the fraetion of the total fluid volume (gas plus liquid) whieh is oeeupied by gas bubbles. 

To apply the mass transfer equation for design, the interfacial area, a, and mass transfer coefficient kL must be calculated. The interfacial area is dependent upon the bubble size and gas hold-up in the mixing vessel as given by ... 

Size the vessel to restrict the carryover of liquid droplets. The liquid hold-up time need not be considered, as the liquid level will be a function of the thermal design. 

An example of a sequential operation is (1) charging benzene to a vessel at a specific rate through a specific line of known size, (2) charging methanol and toluene through two different lines at different rates, (3) holding the batch for a specified time, and (4) discharging the batch through a different line at a specified rate. If the line sizes, rates, and materials of construction are known, the potential hazard of each step of the operation can be estimated. 

Measurement of autoignition temperature can vary based on the size of the vessel (i.e., the test apparatus) holding the vapor and the strength of the ignition source. Because of these factors, there is often some variability in quoted autoignition temperatures. The convention is to use the lowest value found in literature. 

Document that the reservoir conforms to purchase specification and invoice. Verify and document that the vessel meets or exceeds the pressure rating (vacuum) specified in the purchase specifications. Perform vacuum hold tests on the tank and document. Acceptance ID tests will vary with the size of the system. A positive pressure test is often done in order to find leaks. Perform and document cleaning procedures used prior to placing the vessel in service. This completes the normal testing done on the tank prior to joining it to the vacuum system. 

Tho vessel holding the solution is of any convenient form, and is provided with agitators of all shapes and sizes, depending upon the whim or caprice of each... 

Determination of the washability characteristics of coal by the float and sink (float-sink) method can be applied to coal of any particle size provided suitably large vessels to hold the larger lumps are available. Air-dried coal, not dry coal, should be used since the separation depends partly on the difference in specific gravity of the clean coal and dirt particles, and the specific gravity, in turn, is dependent on the moisture content of the coal. If the coal is dried before the test is carried out, the conditions will then differ from those in commercial washers, and the results will be at variance with those obtained in practice. 

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