Dynamic machines centrifugal compressors

There are two general ways to compress gas in a refinery. Either a positive-displacement or a dynamic-type machine can be used. A reciprocating compressor is an example of a positive-displacement machine, whereas a centrifugal compressor is a dynamic machine. Centrifugal compressors are relatively ... 

The operating dynamics of centrifugal compressors are the same as for other centrifugal machine-trains. The dominant forces and vibration profiles are typically identical to pumps or fans. However, the effects ofvariable load and other process variables (e.g., temperatures, inlevdischarge pressure, etc.) are more pronounced than in other rotating machines. Table 8.1 identifies the common failure modes for centrifugal compressors. 

Dynamic machine Centrifugal pumps and centrifugal compressors are dynamic machines. They convert velocity imparted by the impeller to the fluid into fluid pressure. 

Centrifugal compressors are dynamic machines. They convert velocity, imparted to the gas by a spinning wheel, to poly tropic feet of head. The feet of head, multiplied by the density of the gas, equals the pressure boost produced by the centrifugal compressor. 

Dynamic compressors, like fans, are divided into two classes, centrifugal and axial, according to the direction of gas flow through the machine. A compression stage for a centrifugal compressor, shown in Figure 5.10, consists of a row of... 

Several typologies of blowers or compressors are potentially suitable for fuel cell application. In Fig. 4.4 a flow diagram of all compressor types is reported, distinguishing two main classes (dynamic and positive displacement) and different typologies for each (reciprocating and rotary as positive displacement devices, and centrifugal and axial as dynamic machines). 

Centrifugal compressors are dynamic compressors and are essentially constant pressure, variable volume machines and must be regulated in almost all applications. Before control can be discussed, the operating characteristics must be understood. The discussion to follow will be concerned with radial-flow compressors. Axial-flow compressors have similar characteristics curves, although the change in pressure rise is much greater with equivalent changes in compressor rotational speed. 

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. 

Reciprocating compressors have unique operating dynamics that directly affect their vibration profiles. Unlike most centrifugal machinery, reciprocating machines combine rotating and linear motions that generate complex vibration signatures. 

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