Rotary compressor

Installation requirements for rotary positive-displacement compressors are similar to any rotating machine. Review the installation requirements for centrifugal pumps and compressors for foundation, pressure-relief, and other requirements. As with centrifugal compressors, rotary positive-displacement compressors must be fitted with pressure-relief devices to limit the discharge or inter-stage pressures to a safe maximum for the equipment served. 

Rotary Compressors Rotary compressors are machines of the positive-displacement type. Such units are essentially constant-volume machines with variable discharge pressure. The volume can be varied only by changing the speed or by bypassing or wasting some of the capacity of the machine. The discharge pressure will vary with the resistance on the discharge side of the system. A characteristic curve typical of the form produced by these rotary units is shown in Fig. 10-93. 

Figure 3.24. Control of positive displacement compressors, rotary and reciprocating, (a) Flow control with variable speed drives, (b) Pressure control with bypass to the suction of the compressor, (c) Reciprocating compressor. SC is a servomechanism that opens some of suction valves during discharge, thus permitting stepwise internal bypass. The clearance unloader is controllable similarly. These built-in devices may be supplemented with external bypass to smooth out pressure fluctuations.

Note Count must be limited to major equipment i.e., pumps, agitators, and compressors. Rotary valves, chemical feed pumps, and the like must not be included. 

COMPRESSOR, ROTARY BLADE - Mechanism for pumping fluid by revolving blades inside cylindrical housing. 

A laboratory or pilot-scale conveying system comprising hoppers, air compressor, rotary feeder, polyvinyl chloride (PVC) conveying pipe, control valves, pressure transducers, rotameter, and electronic weight indicator. Polypropylene granules of different size, as testing material. 

It was concluded in 1975 that centrifugal secondary compressors with a dehvery pressure of 200—250 MPa (29,000—36,000 psi) would be feasible for ethylene capacities of more than 100,000 kg/h. However, in order to replace the primary compressor with a centrifugal machine, it would be necessary to increase the throughput to 200,000-250,000 kg/h (176). Rotary machines have yet to be used in LDPE plants. 

Compressors used in a typical refrigerator/freezer are of the positive displacement type, utilizing either reciprocating or rotary motion (Eig. 5) and... 

In some cases, blade-type rotary compressors are used in low temperature appHcations as high volume, low stage, or booster compressor (Fig. 9). These booster compressors are appHed at suction conditions varying from —87 to —20°C with compression ratios of 7 1 using CFC-12, HCFC-22, or ammonia. 

Many users consider rotaiy compressors, such as the Rootes -type blower, as turbomachines because their behavior in terms of the rotor dynamics is very close to centrifugal and axial flow machineiy. Unhke the reciprocating machines, the rotary machines do not have a veiy high vibration problem but, like the reciprocating machines, they are positive displacement machines. 

Screw-Type This type of rotary compressor, as shown in Fig. 10-80, is capable of hancmng capacities up to about 4.248 X lO" m m (25,000 fF/min) at pressure ratios of 4 1 and higher. Relatively small-diameter rotors allow rotative speeds of several thousand rev/min. Unhke the straight-lobe rotary machine, it has male and female rotors whose rotation causes the axial progression of successive sealed cavities. These machines are staged with intercoolers when such an... 

FIG. 10-78 Approximate performance curves for a rotary positive-displacement compressor. The safety valve in discharge line or bypass must he set to operate at a safe value determined hy construction. 

Rotary compressors are also PDC types, but where refrigerant flow rotates during compression. Unhke the reciprocating type, rotaiy compressors have a built-in volume ratio which is defined as volume in cavity when the suc tion port is closed (V = m vj over the volume in the cavity when the discharge port is uncovered (V = m vj). Built-in volume ratio determines for a given refrigerant and conditions the pressure ratio which is ... 

While the foregoing examples have dealt with applications on centrifugal pumps, the same sort of analysis can be made for reciprocating pumps, reciprocating compressors, or other rotary users hke cooling-tower fans. 

Agitators and mixers (variable density) Blowers, exhausts and fans (over 75 kW) Rotary compressors and pumps (other than centrifugal)... 

API Std 619, Rotary-Type Positive Displacement Compressors for Petroleum, Chemical, and Gas Industry Services, 3rd Edition, June 1997... 

The dry helical lobe rotary compressors nonlubricated cylinder types of compressors are used for injecting of the fuel in gas turbines at the high pressure needed. The gas turbine application requires that the compressor be dry. This standard is primarily intended for compressors that are in special purpose application and covers the minimum requirements for dry helical lobe rotary compressors used for vacuum, pressure, or both in petroleum, chemical, and gas industry services. This edition also includes a new inspector s checklist and new schematics for general purpose and typical oil systems. 

Compressors using the intermittent compression mode are referred to as positive displacement compressors, of which there are two distinct types reciprocating and rotary. Continuous-mode compressors are also characterized by two fundamental types dynamic and ejector. 

The rotary compressor portion of the positive displacement family is made up of several compressor configurations. The features these compressors have in common are ... 

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