Motors compressor

For most of the rotary compressors in process service, the driver is an electric motor. Compressors in portable service, however, particularly the helical-lobe compressor, use internal combustion engines. Many of the rotary compressors require the high speed that can be obtained from a direct-connected motor. The dry type helical-lobe compressor is probably the main exception as the smaller units operate above motor speed and require a speed increasing gear which may be either internal or external (see Figure 4-1). The helical-lobe compressor is the most likely candidate for a driver other than the electric motor. Aside from the portables already mentioned, engines are used extensively as drivers for rotaries located in the field in gas-gathering service. Steam turbines, while not common, probably comprise most of process service alternate drive applications. 

A relatively new innovation for use in electric motor compressor drives is the variable frequency power source. Fundamentally, the power source converts an existing three-phase source into DC then uses an inverter to convert back to a variable frequency supply. Thyristors or transistors are used to switch the output at the required frequency. 

The low speed gear shaft and the housing must be designed to permit installation of a stub shaft for a torsiograph unit if an operational problem occurs. API 613 gives the details of the shaft end requirements for attaching a torsiograph. This should be done on all synchronous motor compressors and on multiple driver or multiple compressor case trains. 

Figure 14-1C. Engine-type synchronous motor. Compressor manufacturer furnishes the motor shaft and motor bearings. A solid hub is used for maximum mechanical strength. (Used by permission Bui. WMC-04A-94. TECO-Westinghouse Motor Co.)...

In this the refrigerant vapor is compressed mechanically. Two-stage motor compressors are used mostly in freeze-drying systems. This compressor is installed in a screwed-on housing together with an electric motor. 

EXTERNAL DRIVE - Term used to indicate a compressor driven directly from the shaft or by a belt using an external motor. Compressor and motor are serviceable separately. 

HERMETIC MOTOR - Compressor drive motor sealed within same casing which contains compressor. 

Inspection and testing of I. C materiel delivered to site as part of a packaged unit, such as a motor/compressor set for example, as well as connecting and integrating this materiel into the wider site systems... 

Because of the very small bearing clearances in gas bearings, dust particles, moisture, and wear debris (from starting and stopping) should be kept to a minimum. Gas bearings have been used in precision spindles, gyroscopes, motor and turbine-driven circulators, compressors, fans, Brayton cycle turbomachinery, environmental simulation tables, and memory dmms. 

Nuclear Radiation Effects. Components of a nuclear reactor system that require lubrication include control-rod drives, coolant circulating pumps or compressors, motor-operated valves, and fuel handling devices, and, of course, are exposed to varying amounts of ionising (14). 

Cooling. A compression refrigeration system, driven by an electric motor, suppHes cooling for either direct expansion or ice bank systems (Fig. 12). In the former, the milk is cooled by the evaporator (cooling cods) on the bulk tank liner opposite the milk side of the liner. The compressor must have the capacity to cool the milk as rapidly as it enters the tank. 

Space needs to be provided for the auxiliaries, including the lube oil and seal systems, lube oil cooler, intercoolers, and pulsation dampeners. A control panel or console is usually provided as part of the local console. This panel contains instmments that provide the necessary information for start-up and shutdown, and should also include warning and trouble lights. Access must be provided for motor repair and ultimate replacement needs to be considered. If a steam turbine is used, a surface condenser is probably required with a vacuum system to increase the efficiency. AH these additional systems need to be considered in the layout and spacing. In addition, room for pulsation dampeners required between stages has to be included. Aftercoolers may also be required with knockout dmms. Reference 8 describes the requirements of compressor layouts and provides many useful piping hints. 

Most rotating equipment includes electric motors or steam dryers that generate noise at a constant frequency. Air cooler fans are a source of noise that can be reduced by lowering the fan speed and increasing the number of blades. Pump motor noise can be reduced by including a shroud or fan cover that is accurately lined. Centrifugal compressor noise reduction can be achieved by blade design and the use of compressor pulsation noise reduction, silencers, and vibration isolation. 

Motor-driven, multistage reciprocating compressors have reportedly been the most popular choice for aeroderivatives. Motor-driven, oil-fiooded screw compressors are also used in some cases. High horsepower, multistage centrifugal compressors, similar to those used at many pipeline compressor stations, may be required for the newer heavy-duty units if the distribution pipeline pressure is insufficient (see Pipelines). Gas turbines have more stringent fuel-gas specifications in terms of cleanliness than do gas-fired boilers. Thus oil- and water-knockout systems, coalescing filters, and fine-mesh filters are used. 

On a typical pipeline, compressor stations are located at 81—161-km intervals and may contain up to 15 compressors. These stations may use either gas-turbine, reciprocating-engine, and/or motor-driven centrifugal compressors capable of boosting pipeline pressure and keeping gas moving at an average speed of about 24 km/h. Gas-turbine-driven units are the most popular. 

Power Take-Off From Engine or Transmission. This type of system is limited to tmcks and there are several take-off means available. Most are some form of electric power generation equipment, belt-driven from the engine crankshaft, which produces either a regulated a-c voltage or rectified direct current for the compressor and fan motors in the body. 

Babbitt ahoys ate suitable for hundreds of types of iastahations involving the movement of machinery, eg, the main, crankshaft, connecting tod big end, camshaft, and journal bearings associated with marine propulsion, tailtoad and automotive transportation, compressors, motors, generators, blowers, fans, rolling-mill equipment, etc. 

Eig. 7. Schematic flow diagram of a basic horizontal-tube vapor compression (VC) desalination plant, shown (a) with a mechanical, motor-driven compressor and (b) with a thermocompressor, using an ejector, where (------) represents vapor (—), brine and (-), product. 

The compressor can be driven by electric motors, gas or steam turbiaes, or internal combustion (usually diesel) engines. The compressor can also be a steam-driven ejector (Fig. 7b), which improves plant reUabiUty because of its simplicity and absence of moving parts, but also reduces its efficiency because an ejector is less efficient than a mechanical compressor. In all of the therm ally driven devices, turbiaes, engines, and the ejector mentioned hereia, the exhaust heat can be used for process efficiency improvement, or for desalination by an additional distillation plant. Figure 8 shows a flow diagram of the vertical-tube vapor compression process. 

From equation 60 one can obtain a theoretical power requirement of about 900 kWh/SWU for uranium isotope separation assuming a reasonable operating temperature. A comparison of this number with the specific power requirements of the United States (2433 kWh/SWU) or Eurodif plants (2538 kWh/SWU) indicates that real gaseous diffusion plants have an efficiency of about 37%. This represents not only the barrier efficiency, the value of which has not been reported, but also electrical distribution losses, motor and compressor efficiencies, and frictional losses in the process gas flow. 

Compressors up to around 75 kW (100 hp) usually have a single center-throw crank, as illustrated in Fig. 10-83. In larger sizes compressors are commonly of duplex construction with cranks on each end of the shaft (see Fig. 10-87). Some large synchronous motor-driven units are of four-corner construction i.e., they are of doubleduplex construction with two connecting rods from each of the two crank throws (see Fig. 10-88). Steam-driven compressors have one or more steam cylinders connected directly by piston rod or tie rods to the gas-cyhnder piston or crosshead. 

Motor-driven compressors usually operate at constant speed, and other methods of controlhng the capacity are necessary. On reciprocating compressors discharging into receivers, up to about 75 kW (100 np), two types of control are usually available. These are auto-matic-start-and-stop control and constant-speed control. 

Motor-driven reciprocating compressors above about 75 kW (100 hp) in size are usually equipped with a step control. This is in reality a variation of constant-speed control in which unloading is accomplished in a series of steps, varying from full load down to no load. Three-step eontrol (full load, one-half load, and no load) is usually accomplished with inlet-valve unloaders. Five-step eontrol (fuU load, three-fourths load, one-half load, one-fourth load, and no load) is accomphshed by means of clearance pockets (see Fig. 10-91). On some machines, inlet-valve and clearance-control unloading are used in combination. 

Using other criteria, compressors are classified as open, semiher-metic accessible), or hermetic. Open type is characterized by shaft extension out of compressor where it is coupled to the driving motor. When the electric motor is in the same housing with the compressor mechanism, it could be either hermetic or accessible (semihermetic). Hermetic compressors have welded enclosures, not designed to be repaired, and are generally manufac tured for smaller capacities (sel-... 

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