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). 

The so-called propeUer-type fans with blades that are aerodynami-caUy designed (as seen in Fig. 10-68) can consist of two or more stages. The air in these fans enters in an axial direction and leaves in an axial direction. The fans usually have inlet guide vanes followed by a rotating blade, followed by a stationary (stator) blade. 

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. 

To reeap, a turboexpander is a radial inflow turbine. The expansion proeess is aeeomplished in two steps primary and seeondary expansion. Primary expansion oeeurs in the inlet guide vanes and seeondary expansion oeeurs in the radial wheel. The proeess is isentropie and thermally effieient with reeoverable eold energy. Turboexpanders used in dew point eontrol require the following ... 

Tail gas expander without or with adjustable inlet guide vanes (11) and guide vane setting motor (12), labyrinth shaft seals with air sealing... 

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.)...

Earlier ehapters explained tliat air separation expanders are mrbines that expand gases in two steps, using primary and seeondary gas expansion deviees. Inlet guide vanes (or inlet nozzles) are the primary expansion deviee. Their funetion is to eonvert almost half of... 

Eollowing initial installation in 1971, the Phase 1 expansion turbines have proven extremely reliable. The redesign effort of Phase 2 in 1992 incorporated improved aerodynamics and changed inlet guide vane profiles in the expansion turbines. This redesign yielded an additional. 40 to. 50 Bcf of gas per year without any increase in recompression horsepower. This translates to an increase in propane and butane production of an additional 3,600 to 4,500 bbl of liquid without an increase in electrical power consumption. 

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. 

The inlet guide vanes give eireumferential veloeity to the fluid at the indueer inlet. This funetion is ealled prewhirl. Figure 6-11 shows indueer inlet veloeity diagrams with and without IGVs. 

Malfunetion of hardware sueh as variable inlet guide vanes. 

The gas turbine eontrol loop eontrols the Inlet Guide Vanes (IGV) and the Gas Turbine Inlet Temperature (TIT). The TIT is defined as the temperature at the inlet of the first stage turbine nozzle. Presently, in 99% of the units, the inlet temperature is eontrolled by an algorithm, whieh relates the turbine exhaust temperature, or the turbine temperature after the gasifier turbine, the eompressor pressure ratio, the eompressor exit temperature, and the air mass flow to the turbine inlet temperature. New teehnologies are being developed to measure the TIT direetly by the use of pyrometers and other speeialized probes, whieh eould last in these harsh environments. The TIT is eontrolled by the fuel flow and the IGV, whieh eontrols the total air mass... 

The turbine eompressor effieieney and pressure ratio are elosely monitored to ensure that the turbine eompressor is not fouling. Based on these eomputations the turbine eompressor is water washed with mineralized water, and if neeessary adjustment of Inlet Guide Vanes (IGV) is earried out to optimize the performanee of the eompressor, whieh amounts to between 60-65% of the total work produeed by the gas turbine. 

Figure -55. Single-stage centrifugal with movable inlet guide vanes. Courtesy of A-C Compressor CorporatiorU...

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