Screw compressor

Petrochemical Plant classes of equipment monomer plant gas compressors, screw conveyors, pumps, and other non-moving equipment ... 

Compressors, turbines, fans Centrifugal compressors Reciprocating compressors Screw compressors Turbines... 

Latex pump 2. Centrifugal pump 3. Heat exchanger 1 4. Extractor 5. Separator 6. Compressor (screw) 7. Heat exchanger 2... 

Compressors Screw, Lobe, Sliding Vane, Liquid-Ring... 

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. 

By contrast, the single-screw and double-hehcal screw compressors (Fig. 6) can operate at high or low pressure ratios. They can be appHed at pressure ratios below 2 1 and above 20 1 in a single stage. These compressors are suitable for use with higher pressure refrigerants such as CFC-12, HCFC-22, or ammonia. 

Fig. 6. (a) Single and (b) double-hehcal screw compressors (port areas shown as hatching). 

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... 

The first method is used most frequently. The next preference is for the last method, mostly used in small compressors due to problems with speed control of electrical motors. Other means of capacity control are very seldom utilized due to thermodynamic inefficiencies and design difficulties. Energy losses in a compressor, when capacity regulation is provided by lifting the suc tion valves, are due to fric tion of gas flowing in and out the unloaded cylinder. This is shown in Fig. 11-84 where the comparison is made for ideal partial load operation, reciprocating, and screw compressors. 

As compression occurs concurrently in both halves of the compressor, radial forces are oppositely directed, resulting in negligible net-radial loads on the rotor bearings (uuhke twin screw compressors), but there are some loads on the star wheel shafts. 

The suction gas which enters from the periphery is trapped by the scrolls. The closed volumes move radially inward until the discharge port is reached, when vapor is pressed out. The orbiting scroll is driven by a short-throw crank mechanism. Similar to screw compressors, internal leakage should be kept low, and is occurring in gaps between cylindrical surfaces and between the tips of the involute and the opposing scroll base plate. 

Similar to the screw compressor, the scroll compressor is a coustaut-vohime-ratio machine. Losses occur when operating conditions of the compressor do not match the built-in volume ratio (see Fig. 11-85). 

For ease of illustration we will consider the characteristics and behaviour of a centrifugal pump which is similar in behaviour to radial/axial flow fans and centrifugal/screw compressors. Figure 63 shows the mechanical connection of a flow valve to control the output of the pump or the discharge of the fluid through the throttle of the valve. Figure 6.39 illustrates the characteristics of the pump ... 

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