Tanks self-emptying

Fig. 12.6. Self-emptying tanks (a, b) self-emptying by gravity (c) screw-conveyor self-anptying tank (screw conveyor is incorporated into the chute at the bottom of the tank) (d) rotating tank cake break-up and pomace...

After the wine is run off from the fermentor, the drained pomace is emptied from the tank and pressed. Self-emptying and automatic devatting fermentors are capable of executing this operation automatically (Section 12.3.3). Devatting can also be carried out manually, but this is laborious. 

In the stirred tank heater system shown in Figure 1.1, the flow rate F of the effluent stream is proportional to the square root of the liquid level h in the tank. Show that such a system is self-regulating (i.e., if the inlet flow rate increases or decreases by a unit, the tank will not overflow or empty completely). 

A pure capacitive process will cause serious control problems, because it cannot balance itself. In the tank of Example 10.3, we can adjust manually the speed of the constant-displacement pump, so as to balance the flow coming in and thus keep the level constant. But any small change in the flow rate of the inlet stream will make the tank flood or run dry (empty). This attribute is known as non-self-regulation. 

As we saw, Dave didn t encounter even mild depression until he d undergone three family crises and a major downturn at work. Jennifer, by contrast, was in the throes of fairly serious depression after relatively minor trouble at school and one upsetting incident with a friend. Clearly the levels in her tank had already fallen significantly before she ever experienced her first symptom. Indeed, her family history—a depressed mother and a father who might have self-medicated his depression by drinking—suggested that Jennifer may have been bom with a genetic predisposition to depression a small and easily emptied tank. 

Prefer static mixers to intensify (H). For systems where the viscosity increases with time (e.g. polymer reactors) prefer turbines to propellers because turbines are power self-limiting. Check shaft wobble to ensure that impeller will not hit vessel walls if turned on in an empty tank. Consider a foot bearing. 

A feedback optimizing controller must be used to hold minimum conductivity, but the process must be made self-regulating first. This can be accomplished by feeding solvent from one storage tank while flowing into another, switching when the feedtank is empty. 

Self-closing valves are used where failure to close a valve manually might permit flow of oil or gas into areas where a serious fire may result. The types of installation for which self-closing valves should be considered include water and chemical draws, vents, bleeders, drains, level cocks, sample points, and tank truck and barrel filling and emptying systems. 

Returning cylinders. Preparing Empty Cylinders for Eetum Be sure that the dust caps are ti tly screwed onto the male and female self-seaUng couplings and the nitrogen inlet caps are in place when the tanks are not in use. This is essential to prevent possible contamination and vapor leaks from the connectors. Make sure that the threads and internal body of all fittings are clean. 

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