Spraytec particle size analyzer proves to be valuable tool in ALSTOM research on gas turbine injection nozzles

Researchers at ALSTOM Power Service (Baden, Switzerland) have used a Malvern Instruments’ Spraytec laser diffraction-based particle size analyzer to gain an improved understanding of high-fogging, a novel method of augmentation in gas turbines that facilitates significantly increased power output. The Spraytec system has proved to be a valuable tool in monitoring droplet size distribution and has allowed ALSTOM to both improve the efficiency and reduce the cost of its high-fogging systems.

High fogging is used to achieve increased power output by injecting a water-droplet “fog” into the air inlet of a turbine. These water droplets pass through the compressor of a gas turbine and evaporate causing inter-cooling. This increases the mass flow through the compressor and reduces parasitic compression work, enhancing power output. Of prime importance are size distribution and concentration of the water droplets contained within the fog as these define how rapidly the droplets evaporate within the compressor system.

The real-time, in situ measurements from the Spraytec system allowed an improved understanding of the dynamics of fog formation and aided the assessment of different injection nozzle types. Since the Spraytec system can be used directly on a gas turbine (rather than being sited in a laboratory) quantification of the effect of different droplet size distributions on the power of a gas turbine was possible for the first time.

Sasha Savic, senior engineer at ALSTOM Power Service said: “When we started work on the development of the high-fogging technology we needed a robust, reliable, accurate and flexible droplet sizer to perform measurements at different test rigs in our research laboratories. This is why we opted for a Spraytec. We found other droplet sizers were not capable of performing measurements directly on the gas turbine. Thanks to the flexibility of the Spraytec we were able to perform gas turbine experiments and we now know what other research labs can only estimate.”

ALSTOM now uses laser diffraction droplet size measurement to characterise specific nozzles for each individual installation of a high-fogging system. This is carried out in a wind tunnel, as part of a quality control process. Laser diffraction is also used to assess long-term operation of nozzles.

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