Steam jets ejectors

In the above equations, T is the suction gas temperature in °C, MW is either MWqog or MWqwv and M is the molecular weight of suction gas (of water vapour for MWcwv or of suction gas other than water vapour for MWcog)- Water vapour and other components in the suction gas can be converted into DAE using the correction factors from Equations (11.2) to (11.5) and the following Equation (11.6), 

Pa and Pd are, respectively, the suction and discharge pressures in torr, and Py is the motive steam pressure in barg. For most cases, estimated by the above equation is 25% 

For condenser calculations involving air-and-water mixtures, the overall heat transfer coefficient, U W/(m K) can be estimated by using Equations (11.8)-( 11.9) developed based on the chart in Power (2005). Eor a gas-vapour mixture with non-condensable vapour mole percentage, NC, from 1 to 50%  

Induced draft fans are generally used in plants to maintain negative pressure so that gases may not leak out. Air ingress can occur in the plant and this should be considered while handhng inflammable gases. 

The impellers of such fans are suitably coated or protected against corrosion. Problems such as high vibrations when wet ash or dust carried with the gas sticks to the impellers can occur. In such cases, in situ cleaning, washing (by provision of cleaning window, water wash connection, etc.) and balancing should be possible. 

Such impellers are generally used for higher volumetric capacities induced draft fans for thermal power stations) but less discliaige pressures. Vendor may be asked to recommend the type of capacity control (e g. throtUing the suction, variable speed drive or by any other means) most suitable for the machine being supplied. 

Reciprocating compressors (for air supply to air-diy a plant of small capacity) these are to be procured when substantially constant low volumetric capacity is required at higher discharge pressures. Vendor may be asked to indicate the type of capacity control being provided (variable frequency drive or by aity other means) as well as pulsation suppression device for the discharge side. This may be in the form of dampening pots. 

Lobe-type blowers (positive displacement type) three lobe-types give less pressure pulsations on discharge side than twin lobe-type. 

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

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. 

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. 

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 6-20D. Air and water vapor mixture data (Dalton s Law)—saturated, (continued). Reprinted by permission, Standards for Steam 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. 

Although the thermal efficiencies of various mechanical vacuum pumps and even steam jet ejectors vary with each manufacturer s design and even size, the curves of Figure 6-34 present a reasonable relative relationship between the types of equipment. Steam jets shown are used for surf ace intercondensers with 70°F cooling water. For non-condensing ejectors, the efficiency would be lower. 

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