Variable inlet guide vanes

Improved materials, coatings, and cooling techniques permit newer machines to operate at higher turbine inlet temperatures, yielding both increased output and efficiency. Further efficiency gains result from improved aerodynamics in the hot gas path, compressor, and turbine sections. Use is also made of variable inlet guide vanes (IGV). 

Depending on plant size, the hot gas expander is supplied either with (Figure 4-40) or without variable inlet guide vanes. Adjustment features are not required in small plants where throughput at eonstant or full-load eapaeity is antieipated. 

Figure 4-40. Two-stage radial inflow expander with variable inlet guide vanes (right). (Source Demag Delaval.)...

Malfunetion of hardware sueh as variable 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 first-stage 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. 

Throttling of the suction of centrifugal and axial compressors wastes less power than throttling the discharge. Even less power is wasted by adjustment of built-in inlet guide vanes with a servomechanism which is a feedback control system in which the controlled variable is mechanical position. Speed control is a particularly effective control mode, applicable to large units that can utilize turbine or internal combustion drives control is by throttling of the supply of motive fluids, steam or fuel. 

The inducer seen in Fig. 7 was a double helix vane convolution of variable pitch. The optimum degree of prerotation at the inducer inlet could only be speculated. An inlet bell was therefore provided with guide vanes for modification, as previously discussed. 

Variable guide vanes. These work by directing the gas flow with respect to blade rotation. Theoretically, there is no efficiency loss, but they tend also to act as inlet throttlers. Although excellent, this approach involves extra expense. 

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