Self-venting

Assures complete self-venting and prevents vapor collection at the bearings. 

To reduce the risk of container failure, the pressure vessels are equipped with several safety features. These can include an effective self-venting system where unforeseen overpressure is released by a quick open-resealing step, or the use of safety disks which rupture when their pressure limit is reached. The small vials (0.2-20 mL) of some monomode reactors are protected by the pressure limit (20 bar) of the caps used, which is significantly lower than the operating limit of the vials themselves (40-50 bar). 

Unless otherwise specified, all pumps shall be provided with vent and drain connections. Vent connections may be omitted if the piunp is made self-venting by the arrangement of the nozzles. 

Where steam sterilization is required, the equipment must be self-venting and draining so that condensate drains to a single low point where it can be removed, and air which is trapped at high points can be displaced by steam. 

B). If downstream pressure is greater, then a barometric leg may be used to maintain a seal, as shown in Figure 3.5(C). The overflow line shown must be adequately sized to self-vent otherwise, it may begin to siphon. 

The 1991 revision included larger and self-venting tapered seal chambers, as well as conventional stuffing boxes, revised baseplate dimensions, witii a new identification numbering system, and a ductile material requirement for the bearing frame adapter if it clamps tiie rear cover plate to tiie casing. 

The following equations will calculate Froude numbers for both the liquid and gas phases. The computer program will print out a message indicating whether the vertical pipe is self-venting, whether pulsating flow occurs, or whether no pressure gradient is required. 

If FRNL <0.31, vertical pipe is SELF-VENTING else... 

The computer program PROG36 calculates the Froude numbers for the liquid and vapor phases. In addition, PROG36 will determine whether the pipe is self venting or whether pulsation flow is encountered. Table 3-13 shows the results for the 2-, 4-, and 6-inch (Schedule 40) pipes. Table 3-14 gives a typical input data and computer output for the 2-inch (Schedule 40) pipe. 

THIS PROGRAM WILL CALCULATE THE FROUDE NUMBERS OF VAPOR-LIQUID TWO-PHASE VERTICAL PIPE. IT FURTHER PRINTS OUT A MESSAGE IF THE PIPE IS SELF-VENTING, IF PULSATION FLOW OCCURS, OR IF NO PRESSURE GRADIENT IS NEEDED. 

TEST FOR SELF-VENTING, PULSE FLOW OR NO PRESSURE GRADIENT. 

FORMAT (lOX, LINE IS SELF-VENTING THEREFORE NO VIBRATION, ) WRITE (1, 200)... 

When vapor disentrainment is the controlling consideration, and it appears attractive to minimize the sump size, the liquid pipe downstream of the sump can be sized to provide a self-venting flow. In this case, the liquid residence time in the pipe contributes to the residence time requirement, and the sump itself can be designed for a smaller residence time. The high points on the self-venting lines should be vented back to the column. 

A short-cut correlation (354) for sizing self-venting lines is shown in Fig. 4.5. The author has had a lot of favorable experience with this correlation. With foaming systems, pipe diameter should be increased in proportion to the foaming factor (355). Caution with applying Fig. 

Vapor disentrainment is not required in a sump or draw pan used exclusively to feed a thermosiphon reboiler, because the reboiler can handle some vapor bubbles in its liquid supply. It is important to size the reboiler sump for self-venting flow otherwise vapor pockets may choke the reboiler sump. Figure 4.5 can be applied to determine the maximum allowable velocity through the reboiler sump. The pipe diameter on the y axis of the diagram is considered... 

When the bottom sump does not supply liquid to a reboiler (e.g., when a reboiler trapout pan is used, or when the column has a bottom feed and no reboiler), the design in Fig. 4.86 can be used with thermally unstable materials. This arrangement eliminates the need for a surge drum and self-venting lines, and immediately quenches liquid reaching the column base. 

Downcomer trapouts seldom provide sufficient residence time for vapor disentrainment, and the venting process must be completed downstream of the column outlet. The vent-retum nozzles must always be located above the tray s liquid level. Downstream piping must be designed for self-venting flow (Fig. 4.5). 

If no liquid level is maintained in the condenser, and the liquid is not substantially subcooled, vapor bubbles are likely to be entrained in the liquid condensate. The outlet line should therefore be sized for self-venting flow (Fig. 4.5). Moore (290) has suggested a slightly more conservative rule of thumb for gravity drainage of condensers (assuming no liquid accumulation)... 

The reactor slurry level is fixed by an overflow nozzle located on the shell of the reactor above the top of the draft tube. The resulting slurry, containing 29% P2O5 and 38%-40% solids, overflows through a self-venting pipe, which is sealed below the liquid level in the filter feed tank. The filter feed tank and a surge tank are between the reactor and filter. 

It would be desirable to add the acid and measure the pH in the piping between the cell room and the depleted brine receiver. However, the header should be designed to be self-venting, and even a horizontal section before the receiver may not run full of liquid. One alternative is to design the tank with a small baffled section for pH control. 

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