Ejector System Specifications

Figure 6-25 presents estimated steam requirements for several ejector systems. Exact requirements can be obtained only from the manufacturers, and these will be based on a specific performance. 

Demolding Gate separation Ejector system (incl. ejector, design, and tolerance specifications)... 

Cracking imposes an additional penalty in a vacuum unit in that it forms gas which cannot be condensed at the low pressures employed. This gas must be vented by compressing it to atmospheric pressure. This is accomplished by means of steam jet ejectors. Ideally, it would be possible to operate a vacuum pipe still without ejectors, with the overhead vapors composed only of steam. In practice, however, leakage of air into the system and the minor cracking which occurs make it necessary to provide a means of removing non-condensibles from the system. In addition to the distillation of atmospheric residuum, the lube vacuum pipe still is also used for rerunning of off specification lube distillates. 

It is necessary to consult manufacturers for final and specific selecdons. However, the followang guide data is reliable and should serve to check recommendations or to specify a system. It is advisable to try to accomplish the specific operation wth as few ejectors as possible, because this leads to the most economical operation and lowest first cost in the majority of cases. Figures 6-9A, B, and C are a basic comparison guide for vacuum systems. 

Combinations of steam jet ejectors operating in conjunction th mechanical pumps can significandy improve the overall s) stem efficiency, especially in the lower suction pressure torr range of 1 torr to 100 torn They can exist beyond the range cited, but tend to fall off above 200 torr. Each system should be examined indhadually to determine the net result, because the specific manufacturer and the equipment size enter into the overall assessment. Some effective combinations are ... 

There is no vacuum source that is the best choice for every application. The technology for protecting mechanical pumps from process upsets and abuse is highly developed. This technology can be used effectively in designed vacuum systems to meet specific requirements. In several applications, mechanical pumps have demonstreted reliability comparable with, or superior to, liquid-ring pumps or steam jet ejectors. 

For creating a continuous jet we used a conical-cylindrical nozzle 8 mm in diameter for a drop-type jet we used hydropneumatic and ejector nozzles " The size of the drops was determined by trapping them with a sticky compoimd. (The median diameter of the drops obtained after emerging from the hydropneumatic nozzle was 275 M.) The specific pressure over the cross section of the jet was measured by means of a system of detectors and an MPO-2 oscillograph. 

---