Liquid-draw nozzles

The vortex breaker is used in almost all liquid-draw nozzles. There are several types of vortex breakers used the most common one is shown as Figure 3.7. 

Many draw nozzles, especially those in the bottom of vessels, plug because of the presence of vortex breakers. Many designers routinely add complex vortex breakers to prevent cavitation in pumps. But vortex breakers are needed only in nozzles operating with high velocities and low liquid levels. Corrosion products, debris, and products of chemical degradation can more easily foul and restrict nozzles equipped with vortex breakers. 

Under normal service conditions, the liquid collector is a separate tray from any liquid distribution device. The basic collector is a chimney tray with a sump (Fig. 9). The chimneys provide passage for vapor rising through the tray. The sump(s) provides for liquid drainage into a draw nozzle (for product draw) or... 

For startup, a 2 or 3-inch diameter, gravity-flow by-pass is usually provided from the tower liquid space to a low point of the downcomer, at reboilers with high liquid draw-off nozzles. 

Liquid distribution can be a severe problem and a source of instability when more than one reboiler is used, and the reboilers share common inlet and outlet lines (237). It is best to provide separate liquid draw and vapor return nozzles on the column for each reboiler. 

Upon retray, the new trajrs were rotated to their original orientation. Internal piping was required from the new intermediate product draw sump to its draw nozzle and level gage. A flange on the internal draw line leaked, and starved the line of liquid. Poor separation resulted. The internal level gage lines plugged. 

I have a personal dislike of this widely used device. The idea of the vortex breaker is to prevent swirling liquid from conveying vapor into the draw-off nozzle. Sometimes though, trash lost in the tower during a turnaround gets caught on the vortex breaker. Since the draw nozzle typically is located in a sump below the seal pan, it may be hard to inspect. In some cases, it would be best to just cut off the vortex breaker. This is fine if the nozzle exit velocity is less than 3 or 4 ft/s. 

In this design, vertical baffles are used to break the vortex. The number of baffles used depends on the nozzle diameter. Table 3.11 is often used as a preliminary guideline to design a vortex breaker. The position of fhe draw nozzle is also important a vessel-flushed nozzle may not be always recommended, particularly if the incoming fluid contains inert or gummy material. The internal nozzle projection (50 to 100 mm) is often used to avoid draining of solids along with the liquid stream. 

Centrifugal pumps also rec]uire that the fluid be available to the pump s suction nozzle with sufficient energy. Centrifugal pumps cannot suck or draw the liquid into the pump housing. The principal pumping unit of a centrifugal pump is the volute and impeller. (See Figure 1-3). 

The pressure at point A in Fig. 10.4 was 13 psig. This means that the pressure drop in the vapor line from the stripper, back to the fractionator, was 3 psig. In order for the unstripped jet fuel, to flow out of the lower-pressure fractionator, and into the higher-pressure stripper, it had to overcome this 3-psig pressure difference. The 16-ft elevation difference between the draw-off nozzle on the fractionator and the stripper inlet provided the necessary liquid head driving force. 

If liquid is flowing through the nozzle, shown in Fig. 11.6, at, say, 9 ft/s, the pressure at point D will be lower than that at point B. Assuming the velocity in the draw-off sump to be close to zero, we can calculate the pressure at point D as follows head loss due to increased velocity = 0.34X92 = 28 in of water. 

Does this mean any frictional losses, due to external piping, at the same elevation as the draw-off nozzle, have to be added to the nozzle exit loss, in determining the liquid level in the sump Yes ... 

I once tried to increase the flow of jet fuel from a crude distillation column by opening the draw-off, flow-control valve. Opening the valve from 30 to 100 percent did not increase the flow of jet fuel at all. This is a sure sign of nozzle exit loss—or cavitation limits. To prove my point, I increased the level of liquid in the draw-off sump from 2 to 4 ft. Since flow is proportional to velocity and head is proportional to (veloc-... 

Lack of available NPSH may also be caused by high frictional loss in the suction piping. If this is the case, a small reduction in flow will not noticeably increase the pressure at the suction of the pump. A properly designed suction line to a centrifugal pump should have a frictional head loss of only a few feet of liquid. However, having a large-diameter suction line, and a relatively small draw-off nozzle, usually will lead to excessive loss of available NPSH. 

In contrast to writing, drawing, marking, and conventional printing methods, inkjet printing is a true primary, non-impact process. Liquid ink droplets are ejected from a nozzle under digital control and directed onto surfaces such as paper, plastics, metals, ceramics, and textiles to form a character or image [2,3],... 

Vacuum filling is commonly used for large liquid volumes because of easy adaptation to automation. A vacuum is produced in a bottle when the nozzle gasket seals against the lip of the bottle being filled. The vacuum draws the liquid from a reservoir through the delivery tube into the bottle. When the liquid level reaches the level of an adjustable overflow tube, the seal is mechanically loosened, and the vacuum is released. Any liquid drawn into the vacuum line is collected in a receiver and returned to the reservoir. 

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