Speed Controller
A speed controller is needed in conjunction with the surge control system. A new head-capacity curve is established for each speed, as shown in Figure 10-14.
Inlet Guide Vanes
The performance curve can also be shifted to match the process requirements by variable inlet guide vanes. Located at the compressor inlet, these vanes change the direction of the velocity entering the firststage impeller. By changing the angle at which these vanes direct the flow at the impeller, the shape of the head capacity curve can be changed. As more velocity change is added to the inlet gas, the performance curve steepens with very little efficiency loss. Extreme changes in process conditions cannot be accommodated. The high cost of inlet guide vanes limits use to very large compressors where small improvements in efficiency can bring large rewards.
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