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Research Papers: Gas Turbines: Turbomachinery

On the Combined Effect on Operating Range of Adjustable Inlet Guide Vanes and Variable Speed in Process Multistage Centrifugal Compressors

[+] Author and Article Information
Alberto Scotti Del Greco

GE Oil & Gas
via F. Matteucci 2,
Florence 50127, Italy
e-mail: alberto.scottidelgreco@ge.com

Libero Tapinassi

GE Oil & Gas
via F. Matteucci 2,
Florence 50127, Italy
e-mail: libero.tapinassi@ge.com

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 5, 2013; final manuscript received January 17, 2014; published online February 28, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(8), 082601 (Feb 28, 2014) (10 pages) Paper No: GTP-13-1293; doi: 10.1115/1.4026621 History: Received August 05, 2013; Revised January 17, 2014

Adjustable inlet guide vanes (IGVs) and variable speed drivers are known as providing process compressors with an effective regulation all throughout the operating envelope of the machine. A large amount of work exists in literature reporting the successful control of multistage centrifugal compressors by means of IGVs or speed separately, while a few studies document the combined use of both devices and their effect on compressor performance. The present paper details the off-design behavior of a multistage centrifugal compressor equipped with both types of control. It is shown that classical IGVs' advantage in extending the operating envelope of a fixed speed multistage compressor tends to reduce when speed regulation is active too. In this sense, the average level of peripheral Mach numbers inside the compressor may be interpreted as a sort of threshold since it deeply affects the stage mismatching at off-design conditions. This consideration is corroborated by a number of applications in a wide range of design peripheral Mach numbers. Based on those cases, the paper reviews the general effectiveness of the combined regulation, thus outlining some general rules of thumb for the choice of the optimal control device for a multistage centrifugal compressor.

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Figures

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Fig. 1

The sign of swirl is positive (in both absolute and relative frames) if the tangential component is oriented as the blade speed

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Fig. 2

Single stage equipped with IGVs. Contours of polytropic efficiency in the Hp-Q plane are reported for four different IGVs openings: 60 deg (almost closed IGVs), 40 deg, 20 deg, and −15 deg (fully open IGVs).

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Fig. 3

Multistage compressor equipped with IGVs. Contours of polytropic efficiency in the Hp-Q plane are reported for four different IGVs openings: 60 deg (almost closed IGVs), 40 deg, 20 deg, and −15 deg (fully open IGVs).

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Fig. 4

Maps with and without IGVs for a compressor where the first stage is taken at ϕ/ϕ* = 0.85 and the unregulated part is taken at ϕ/ϕ* = 1. The map on the background corresponds to the current selection (first stage at ϕ/ϕ* = 0.85) at IGV = 0 deg.

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Fig. 5

Maps with and without IGVs for a compressor where the first stage is taken at ϕ/ϕ* = 0.85 and the unregulated part is taken at ϕ/ϕ* = 1. The map on the background corresponds to the original selection (all stages at ϕ/ϕ* = 1) at IGV = 0 deg.

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Fig. 6

Two-stage compressor with MU = 0.85 for the first stage

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Fig. 7

Efficiency contours at IGV = 40 deg (dashed gray area) superimposed to the same map at IGV = 0 deg

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Fig. 12

Relative variations of flow coefficient (top) and polytropic head (bottom) for the each of the seven stages as the IGVs angle goes from 0 deg to 40 deg

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Fig. 11

Contours of flow coefficient for stages 1, 4, and 7 of the seven-stage compressor of Fig. 7

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Fig. 10

Plots of ϕ/ϕ* along turndown (top) and stability (bottom) paths for the compressor of Fig. 9

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Fig. 9

Turndown and stability superimposed to line at constant flow coefficient for the first (black) and the last stage (orange)

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Fig. 8

Red-dashed lines (contours of polytropic efficiency). Solid lines: contours of flow coefficient for the stages from the first one to the last one.

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