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TECHNICAL PAPERS: Gas Turbines: Cycle Innovations

The Effect of Water Injection on Multispool Gas Turbine Behavior

[+] Author and Article Information
A. J. Meacock

Hopkinson Laboratory, Cambridge University Engineering Department,  Cambridge University, Trumpington Street, CB2 1PZ, UKajm83@cantab.net

A. J. White

Hopkinson Laboratory, Cambridge University Engineering Department,  Cambridge University, Trumpington Street, CB2 1PZ, UK

J. Eng. Gas Turbines Power 128(1), 97-102 (Mar 01, 2004) (6 pages) doi:10.1115/1.2032432 History: Received October 01, 2003; Revised March 01, 2004

Background: The injection of water droplets into industrial gas turbines is now commonplace and is central to several proposed advanced cycles. These cycles benefit from the subsequent reduction in compressor work, the increase in turbine work, and (in the case of recuperated cycles) reduction in compressor delivery temperature, which all act to increase the efficiency and power output. An investigation is presented here into the effect such water droplets will have on the operating point and flow characteristics of an aeroderivative gas turbine cycle. Method of Approach: The paper first describes the development of a computer program to study the effects of water injection in multispool industrial gas turbines. The program can operate in two modes: the first uses pre-determined nondimensional wet compressor maps to match the components and is instructive and fast but limited in scope; the second uses the compressor geometries as input and calculates the wet compressor operating conditions as and when required. As a result, it is more computationally demanding, but can cope with a wider range of circumstances. In both cases the compressor characteristics are calculated from a mean-line analysis using suitable loss, deviation and blockage models, coupled with Lagrangian-style droplet evaporation calculations. The program has been applied to a three-spool machine to address issues such as the effects of water injection on power output and overall efficiency, and the off-design nature of the compressor operation. Results: Preliminary results calculated on this basis show similar trends to predictions for single-shaft machines, namely that air mass flow rates and pressure ratios are increased by water injection, and that early stages of the compressor are shifted towards choke and rear stages towards stall. The LP compressor in particular operates at severely off-design conditions. Conclusions: The predicted overall performance of the three-spool machine shows a substantial power boost and a marginal increase in thermal efficiency.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Comparison between computational and experimental results and the shift in characteristics due to water injection

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Figure 2

Nondimensional compressor characteristics

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Figure 3

Layout of multispool gas-turbine showing labeling of axial locations

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Figure 4

Determining the compressor operating point from the dimensionless work characteristics

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Figure 5

Comparison between the dimensional and nondimensional methods for different water injection rates using 5‐μm-diameter droplets injected at inlet to the IP and HP compressors

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Figure 6

Effects of water injection location on the multispool characteristic with a 1.5% water injection rate and 5‐μm-diameter droplets

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Figure 7

Liquid water fraction during the compression process

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Figure 8

Variation of flow coefficient throughout the compressor

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Figure 9

Variation of overall efficiency with power output for several water injection rates (using 5‐μm-diameter droplets)

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