Vapor compressors/compressor systems

Evaporators require a source of heat to operate. This heat may be supplied from a boiler, gas turbine, vapor compressor, other evaporator, or a combination of sources. Multiple effect evaporators are very popular when cheap, high pressure steam is available to heat the system. A Mechanical Vapor Recompression evaporator would use electricity or a gas turbine to drive a compressor that recycles the heat in the evaporator. 

All compressed air systems should always include a water-cooled aftercooler between the compressor and receiver tank. Properly designed and maintained aftercoolers, in normal summer conditions, condense at lOOpsig, up to 70 per cent of the vapor entering the system. Most of this condensation will collect in the aftercooler or the receiver tank. Therefore, both must be constantly drained. 

In a vapor-absorption refrigeration system, there are no moving parts. The added energy comes from a gas or liquid fuel burner or from an electrical heater, as heat. rather than from a compressor, as work. See Fig. 2. The refrigerant used in this example is ammonia gas. which is liberated from a water solution and transported from one region to another by the aid of hydrogen, The total pressure throughout the system is constant and therefore no valves axe needed. 

Vapor-Removal System. Water vapor may be removed from the freezer by several means a compressor, a steam ejector, a condenser, or absorption into a low vapor pressure solution. A water vapor compressor does not easily permit variable... 

To increase the value of the demonstration plant, features have been incorporated to permit operation under other than demonstration conditions. It will be possible to operate the evaporator at first-effect temperatures up to 300° F., thus almost doubling plant output if calcium sulfate scale can be prevented, and to use the acid method of scale prevention in place of the sludge method. Provisions have been made for later installation of a vapor compressor, which would convert the plant to a combination multiple effect-thermocompression system. This would add about 15% to plant output and would permit performance evaluation of vapor compressors in sea water service. 

A vapor-compression refrigeration system is conventional except that a countercurrent exchanger is installed to subcool the liquid from the condenser by heat exchange with the v stream from the evaporator. The minimum temperature difference for heat transfer is 10(°F). Amm is the refrigerant, evaporating at 22(°F) and condensing at 80(°F). The heat load on the evapo is 2,000(Btu)(s) . If the compressor efficiency is 75 percent, what is the power requirement ... 

Benfield LoHeat System (UOP) [677], The high thermal efficiency of this two-stage adsorption process using lean and semi-lean solvent is achieved by recompression of the flash steam with an injector or a mechanical vapor compressor. UOP has also developed a number of other process configurations [404], [669], [678] -[680], The diethanolamine promoter enhances the mass transfer by carbamate... 

A schematic of the system and the corresponding temperature-entropy diagram are shown in Figure 3. A schematic of the system is shown on the left side of the diagram. The equipment in this system are a gas compressor, compressor aftercooler, plate-fin heat exchanger, Joule-Thompson expansion valve and liquid-vapor separator. 

Vapor compression is carried out by mechanical compression (reciprocating compressor, lobe compressor, axial-flow or radial-flow compressor) with an electric motor or turbine as a propulsion system, or thermally by means of a vapor-jet compressor. 

Soil Vapor Extraction System. Once the air is injected into the saturated subsurface, it wiU migrate toward the surface due to the effect of buoyancy. Eventually the contaminated injected air will enter the vadose zone. At this point, a sou vapor extraction (SVE) system may be implemented. Soil vapor extraction applies a vacuum to the vadose zone to assist in collecting vapors. The vacuum will help vapor collection as well as assist in preventing unwanted off-site migration. Equipment used in a soil vapor extraction system is similar to that used in an air sparging system, except that a vacuum pump is used instead of an air compressor. Additionally, if the vapors being collected by the soil vapor extraction system are moist, a dewatering system may be employed (Johnson et al., 1993). 

Compressors come in a variety of styles and designs the most common being dynamic and positive displacement. Each of these designs is governed by standard scientific principles that should be well understood by process technicians assigned to these areas. Because compressors are so widely used, almost every process technician will come into contact with a compressor system. The compression of gases and vapors in the process industry is very important and is used in the following applications ... 

Cryopanels (Meissner traps) are cryocondensation surfaces in the deposition chamber that use large areas of cooled surfaces to freeze out vapors, particularly water vapor and solvent vapors. They are cooled by LN2 at — 196°C or refrigerants to about — 150°C from a closed-cycle refrigerator/compressor system. The vapor pressure of water at these temperatures is very low, as shown in Table 3.4. It takes about 780 watts to freeze one kilogram of water per hour and 11 kilograms of LN2 to freeze one kilogram of water. The ideal cryosurface should pump about 10 liters per second per square centimeter. 

Ammonia has low miscibility in mineral oils, alkylbenzenes, and polyol ester lubricants, particularly at low temperatures. A typical ammonia system uses a coalescing separator that removes all oil in droplet or aerosol form and drains it back to the compressor. Sometimes separators are equipped with some means of cooling the discharge gas to condense any oil that is discharged as a vapor. 

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