Compressor vanes

Typical uses of polyimide include electronic applications, sleeve bearings, valve seatings, and compressor vanes in jet engines. Other uses include aircraft and aerospace applications with high performance requirements. They are used for printed circuit boards in computers and electronic watches for both military and commercial uses. Polyimides are used in the insulation of automotive parts that require thermal and electrical insulation, such as wires used in electric motors, wheels, pistons, and bearings. 

Compressor vanes. Polyamide-imide compounds are being used in a number of rotating industrial equipment apphcations. One particular area of interest is in rotary vane compressors. Previously the vane materials were made from a phenolic composite construction. Although more expensive from a material of construction perspective, a polyamide-imide compound was chosen due to a dramatic extension in life and a lower lubrication requirement, both of which reduce maintenance and the overall operating cost of the compressor. In addition the compressors can operate at a higher discharge pressure due to polyamide-imide s higher-temperature capability. 

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). 

The two principal elements of evaporator control are evaporation rate a.ndproduct concentration. Evaporation rate in single- and multiple-effect evaporators is usually achieved by steam-flow control. Conventional-control instrumentation is used (see Sec. 22), with the added precaution that pressure drop across meter and control valve, which reduces temperature difference available for heat transfer, not be excessive when maximum capacity is desired. Capacity control of thermocompression evaporators depends on the type of compressor positive-displacement compressors can utilize speed control or variations in operating pressure level. Centrifugal machines normally utihze adjustable inlet-guide vanes. Steam jets may have an adjustable spindle in the high-pressure orifice or be arranged as multiple jets that can individually be cut out of the system. 

Air compressor (axial or centrifugal type) without or with adjustable guide vanes (8) and guide vane setting 19... 

Caution should be taken to prevent excessive acceleration. One solution is to provide for opening of the compressor discharge vent valve to increase the compressor flow and increase blower horsepower. This is effective with a centrifugal compressor, however, not with an axial compressor unless the compressor is provided with adjustable stator vanes that are reliable. This can be seen from the performance curve. The head versus flow curve for a given vane setting is extremely steep and opening the vent valve is ineffective. However, if the vanes operate fully open and the vent valve opens, the combined effect is satisfactory. The vent valve must not be oversized. 

Figure 4-81. Axial compressor antisurge and guide vane control.

Most ethylene plants operate continuously with the expander functioning at or near design point. However, by using inlet guide vanes, the expander can still provide optimum performance at off-design conditions. Also, the expansion process generates power, which is used by the compressor. The ethylene enters the expanders at approximately 26 bar (377 psia) and exits at approximately 6 bar (87 psia). The expanders generate over 2,000 hp for gas compression. 

This chapter examines the overaii performance characteristics of compressors and turbines. This materiai is presented here to famiiiarize the reader with the behavior of these machines, ciassified under the broad term tur-bomaciiinery. Pumps and compressors are used to produce pressure turbines produce power. These machines have some common characteristics. The main eiement is a rotor with biades or vanes, and the path of the fluid in the rotor may be axiai, radiai, or a combination of both. 

Most centrifugal compressors in service in petroleum or petrochemical processing plants use vane less diffusers. A vaneless diffuser is generally a simple flow channel with parallel walls and does not have any elements inside to guide the flow. 

The sliding-vane compressor uses a single rotating element (see Figure 1-8). The rotor is mounted eccentric to the center of the cylinder portion of the casing and is slotted and fitted with vanes. The vanes are free to... 

Figure 1-8. Cross section of a sliding vane compressor. Courtesy ofA-C Compressor Corporation)...

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