Compressors Flashcards
Describe the reciprocating piston compressor
May consist of 1-12 stages and is the only compressor capable of developing very high pressures
Describe sliding vane compressors
Positive displacement units in which high compression ratios are achieved by eccentric mounting of the rotor. The rotor is slotted to accommodate sliding blades. On rotation the blades move in and out, trapping the gas which is compressed during rotation and discharged at the delivery port
Describe Nash Hytor pump compressors
A positive displacement pump with specially shaped casing and a liquid seal which rotates with the impeller. The liquid leaves and re-enters the impeller cells like a piston
Describe lobe compressors
Compression is achieved by the rotation of two elements. These rotors turn in opposite directions so that, as each passes the inlet, it takes in air which is compressed between the impeller and the wall and is then expelled outward.
Describe centrifugal compressors
Depend on the conversion of kinetic energy into pressure energy
What happens when a compressor stalls or surges
- The flow of gas across the rotor stops or reverses
- The gas flowing backwards pushes the rotor backwards
- The rotor slides back and hits the thrust bearing which prevents axial movement of the rotor
- If the surge isn’t stopped, the bearing is deformed and the axial movement increases
- Eventually the spinning rotor will touch the stator and the compressor is destroyed
What can be done to prevent surging or stalling
- Install a recycle line with pressure control to allow more gas into the suction
- Lower the upstream pressure
Define the efficiency of a compressor
The ratio of the ideal work for a compression cycle divided by the actual work done
List the principal types of compressors
- Reciprocating piston
- Sliding vane
- Nash Hytor liquid pump
- Lobe
- Centrifugal
