ISBN 9783843941075

978-3-8439-4107-5, Reihe Energietechnik

Christoph Carl Günther
Wet Compression − Considering non-equilibrium Thermodynamics

190 Seiten, Dissertation Helmut-Schmidt-Universität Hamburg (2018), Softcover, A5

Zusammenfassung / Abstract

A common method for increasing or adapting the power output of gas turbines is to inject water droplets. These water droplets are usually injected inside the intake duct. ’Wet compression’ is the term commonly used for the compression process with liquid water droplets as part of the compressed humid air, if these water droplets enter a gas turbine compressor. The water droplets entering the compressor evaporate during the compression process. Given a constant turbine inlet temperature, this phase change results in increased power output from the gas turbine.

To contribute to the understanding of wet compression and its influence on gas turbine operation, a thermodynamic model is developed. This generic gas turbine model contains an intake duct, a compressor, a combustor, and a turbine. For the conducted investigations, the generic system was loaded with 1% mass , 2% mass , and 3.5% mass of injected water with a droplet diameter of 28µm. The ambient temperatures vary between 288.15K and 318.15K.

For an initial evaluation, the intake duct is considered separately to get an overview of possible compressor inlet conditions. Furthermore, gas turbine operation under consideration of the upstream intake duct is analysed. For these investigations, the focus is on influences on the compressor. In a final step, analysis of the single gas turbine components is conducted, and influences on the Brayton cycle are presented.

Investigation of the compression process considering an upstream intake duct differs from those of previous publications. The results of the intake duct investigations show that supersaturation at the compressor inlet occurs for all chosen ambient conditions. Supersaturation can also occur if no water is injected.

The supersaturated fluid properties at the inlet to the compressor shift the beginning of the evaporation to later stages, and consequently, shift the impact of the evaporative cooling to later stages as well. A reduced load in the initial compressor stages can be observed. However, the effect of increased load on later stages is lower than that determined by previous authors.

An additional difference from previous publications is the effect of a reduced pressure ratio with increased amounts of injected water. Previous publications have reported an increase of mass flow and power output, with increased volumes of injected water.