Ejector 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... 

The secondaiy ejector systems used for removing air require steam pressures of 2,5 bar or greater. When the available steam pressure is lower than this, an electrically driven vacuum pump is used for either the final secondaiy ejector or for the entire secondaiy group. The secondary ejectors normally require 0,2-0,3 kg/h of steam per kW of refrigeration capacity,... 

Precondensers are recommended for any ejector system when the pressure conditions and coolant temperature will allow condensation of vapors, thus reducing the required design and operating load on the ejectors. This is usually the situation when operating a distillation column under vacuum. The overhead vapors are condensed in a unit designed to operate at top column pressure, with only the non-condensables and vapors remaining after condensation passing to the ejector system. 

When the ejector system consists of one or more ejectors and intercondensers in series, the volume as pounds per hour of mixture to each succeeding stage must be evaluated at conditions existing at its suction. Thus, the second stage unit after a first stage barometric intercondenser, handles all of the non-condensables of the system plus the released air from the water injected into the intercondenser, plus any condensable vapors not condensed in the condenser at its temperature and pressure. Normally the condensable material tvill be removed at this point. If the intercondenser is a surface unit, there wall not be any air released to the system from the cooling w ater. 

An evacuation booster or hogging ejector is sometimes used to remove air from a system on start-ups. Its capacity is set to bring the system pressure down to near operating conditions before the continuous operadng ejector system takes over. Figure 6-23 illustrates the instal-ladon of such a unit. 

Once a. system has been evacuated to normal operating conditions, it is possible for capacity to fall to almost zero when the only requirement is air inleakage or small quantities of dissolved gases. Under these conditions, it is important to specify an ejector system capable of stable operation dow n to zero load or shut-off capacity. The curve of Figure 6-24 represents such a system. 

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. 

As a guide, the follotving is a suggested procedure for rating and selecting an ejector system for vacuum operation. 

Example 6-12 Temperatures at Barometric Condenser on Ejector System... 

Figure 6-32 illustrates ejector systems with large condensable loads which can be at least partially handled in the precondenser. Controls are used to maintain constant suction pressure at varying loads (air bleed), or to reduce the required cooling water at low process loads or low water temperatures [2]. The cooler W ater must not be throttled below the minimum (usually 30%-50% of maximum) for proper contact in the condenser. It may be controlled by tailwater temperature, or by the absolute pressure. 

Figures 12-51-12-55 are summaries of the common types of shaft seals. For some seals it is preferable to connect the vent opening between the seals to an area of low pressure, such as an ejector system, in order to draw the leaking gases out of the seal, in preference to pressurizing the seal with contaminating oil, air, or other gas.

Dusts, particle sizes, 225 Dusts, hazard class, 521-523 Explosion characteristics, 524 Efficiency, centrifugal pumps, 200 Ejector control, 380 Ejector systems, 343, 344, 351 Air inleakage, table, 366, 367 Applications, 345 Calculations, 359-366 Chilled water refrigeration, 350 Comparison guide, 357, 375 Evacuation lime, 380, 381 Charts, 382 Example, 381 Features, 345... 

FIGURE 4.39 Fuel jet ejector system for premixed fuel—air burners. 

T0233 Ejector Systems, Inc., VESTRIP T0236 Electrokinetic Remediation—General T0238 Electrokinetics, Inc., Electrokinetic Soil Cleaning T0239 Electro-Petroleum, Inc., Electrokinetic Treatment... 

T0233 Ejector Systems, Inc., VESTRIP T0236 Electrokinetic Remediation—General... 

VESTRIP is a system designed for the in situ treatment of soils contaminated with volatile organic compounds (VOCs) benzene, toluene, ethylbenzene, and xylenes (BTEX) and other contaminants that are amenable to soil vapor extraction (SVE). The vendor, Ejector Systems, Inc. (ESI) has combined the key components of SVE systems with an air stripper to form a product that performs the functions of both. The name, VESTRIP, is a contraction of VES (vapor extraction system) and air stripping. 

There is little danger, in injecting a controlled amount of water into a furnace inlet, when using a properly designed metering pump. Such pumps typically have a capacity of 1 to 10 GPM and provide a set flow, regardless of the discharge pressure. The injected water flashes immediately to steam inside the furnace tubes. Vfe have retrofitted several vacuum and delayed coker heaters with condensate injection systems, with no adverse downstream effects. Water from the hot well of a vacuum ejector system is our normal source of condensate for this environmentally friendly modification. 

Vacuum Pumps. The function of these pumps is to evacuate the drying chamber quickly without allowing the prefrozen material to melt—and thereafter to reduce the pressure progressively to the desired vacuum and maintain it at Ihis level by removing the noncondensablc gases. The vacuum equipment can be cither an oil-sealed rotary vacuum pump, or a multistage stream-ejector system. 

If the gas is particularly corrosive the steam ejector system shown in Fig. 6.59e may be employed to sample gases at temperatures of up to 450 K (e.g. flue gases). The possibility of corrosion occurring in the sample lines when the steam/gas sample cools to the dew point is much reduced due to the dilution of the corrosive condensate by the condensed steam. 

An ejector system is required to remove inerts from the plant at the lowest pressure point in the system. For the plant shown in Figure 2, this point is the deaerator. Suitable instruments are required in the plant to control liquid flows, temperatures, and levels. The process and controls have been described in detail (3). 

The vacuum sulphuric acid concentrator consists of a single stage evaporator. The vacuum is maintained by a two-stage steam ejector system utilizing shell and tube inter-and after-condensers. Most of the heat required to reconcentrate the sulphuric acid is recovered as sensible heat from the reaction and is contained in the spent acid. The balance is added through a tantalum bayonet heater immersed in the evaporator body. 

In practice, the vapor that is to be condensed sometimes contains noncondensible gases such as air. The presence of these noncondensible gases can significantly lower the heat transfer rate from that which would exist under the same circumstances with a pure vapor. A common example is the build-up of air in power plant condensers. These condensers usually operate at a substantial vacuum and some air entrainment is unavoidable. The continuous removal of air by specially designed ejector systems is essential to maintain the condenser vacuum and to maintain acceptable condensation rates. In some chemical plants, the separation of constituents is sometimes produced by condensing one gas from a mixture of gases and in such cases the presence of a noncondensible gas is unavoidable. 

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