Jet ejector

Two types of vacuum producing devices are used jet ejectors and mechanical pumps. Jet ejectors usually have lower initial costs, lower maintenance costs, but higher operating costs than equivalent mechanical systems. Mechanical pumps are more efficient users of energy. Jet ejectors require no moving parts and therefore are simplest of all vacuum producers. 

Current economics favor the use of mechanical vacuum pumps in most applications. Steam jet ejectors are economically superior to other pumping devices when their initial cost and simplicity compensate for their inherently low efficiency. 

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The collection of particles larger than 1—2 p.m in Hquid ejector venturis has been discussed (285). High pressure water induces the flow of gas, but power costs for Hquid pumping can be high because motive efficiency of jet ejectors is usually less than 10%. Improvements (286) to Hquid injectors allow capture of submicrometer particles by using a superheated hot (200°C) water jet at pressures of 6,900—27,600 kPa (1000—4000 psi) which flashes as it issues from the nozzle. For 99% coUection, hot water rate varies from 0.4 kg/1000 m for 1-p.m particles to 0.6 kg/1000 m for 0.3-p.m particles. 

MYERS Aboveground Storage Tanks POWER Steam Jet Ejectors for the Process Industries REID, PRAUSNITZ, POLING Properties of Gases and Liquids, Fourth Edition... 

Viscous Drag Jet (Ejector-boosted) Gas Lift Hydraulic Ram Electromagnetic Screw Centrifugal Rotating Casing (Pitot)... 

Uses of Ejectors For the operating range of steam-jet ejectors in vacuum applications, see the subsection Vacuum Systems. ... 

Steam-Jet (Ejector) Systems These systems substitute an ejector for a mechanical compressor in a vapor compression system. Since refigerant is water, maintaining temperatures lower than the environment requires that the pressure of water in the evaporator must be... 

Vacuum is applied to the chamber and vapor is removed through a large pipe which is connected to the chamber in a manner such that, if the vacuum is broken suddenly, the inrushing air will not greatly disturb the bed of material being dried. This line leads to a condenser where moisture or solvent that has been vaporized is condensed. The noncondensable exhaust gas goes to the vacuum source, which may be a wet or diy vacuum pump or a steam-jet ejector. 

Standards for Steam Jet Ejectors, 3rd Ed., Heat Exchange Institute, New York, N.Y. 

Here is a specification sheet for steam jet and liquid jet ejectors. It contains data needed by the manufacturer to design and quote an ejector for a specific application. 

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. 

The VPS overhead consists of steam, inerts, condensable and non-condensable hydrocarbons. The condensables result from low boiling material present in the reduced crude feed and from entrainment of liquid from the VPS top tray. The noncondensables result from cracking at the high temperatures employed in the VPS. Inerts result from leakage of air into the evacuated system. Steam and condensable hydrocarbons are condensed using an overhead water-cooled condenser. The distillate drum serves to separate inerts and non-condensables from condensate, as well as liquid hydrocarbons from water. Vacuum is maintained in the VPS using steam jet ejectors. 

Cracking imposes an additional penalty in a vacuum unit in that it forms gas which carmot 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. 

Replacement of the steam-jet ejector with a vacuum pump. The distillation operation will not be affected. The operating cost of the ejector and the vacuum pump are comparable. However, a capital investment of 75,000 is needed to purchase the pump. For a five-year linear depreciation with negligible salvage value, the annualized fixed cost of the pump is I5,000/year. 

E — Heat Exchanger, condenser, reboiler, etc. Ej — Jet Ejector Ex — Expansion Joint F — Fan... 

Figure 2-43. Evaluation curves for friction losses of air and steam flowing turbulently in commercial pipe at low pressures. By permission, Standards for Steam Jet Ejectors, 4th Ed., Heat Exchange Institute, 1988.

Thermocompressors are steam jet ejectors used to boost low pressure or waste steam to a higher intermediate pres-... 

Figure 6-7B. Chilled water refrigeration unit using steam jet ejectors. By permission, Croll-Reynolds Co., Inc.

Figure 6-11B. A typical relative comparison of various designs of steam jet ejectors. Based on same steam consumption, 100 psig steam pressure and 85°F water. Curves represent the capacity of ejectors designed for maximum air handling capacity at any one particular suction pressure. By permission, Graham Manufacturing Co.

Figure 6-110. Typical performance curves for steam jet ejectors, liquid ring pumps, and rotary piston oil-sealed pumps. By permission, Ryans, J. L. and Roper, D. L. [24],...

Figure 6-20B. Air and water vapor mixture data (Dalton s Law)—saturated, (continued). Reprinted by permission. Standards for Sfeam Jet Ejectors, 3rd. Ed., Heat Exchange Institute, 1956 [11].

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 ... 

Jackson, D. H., When to Use Steam Jet Ejectors, Bulletin CR-722, Croll-Reynolds Co. 

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