Abstract
Gas turbines performance losses are mainly due to the deposition of dirt on the compressor blades that needs to be periodically removed. This is the reason motivating the presence of water washing systems (WWS) in most of the compressor gas turbines. Water washing is generally achieved by installing a number of nozzles on the compressor casing and spraying water that clean the dirty surfaces of the compressor. The side effect of such a technique is the rising risk of erosion due to the impact of water droplets on the compressor blades which is even more pronounced when dealing with online water washing systems that is done while the unit is at normal load. The design of these systems must balance benefits and disadvantages associated to the process itself. The benefits can be measured in terms of water washing efficiency that is a quantity not uniquely defined. In previous works, the authors introduced some indices useful to evaluate the spatial cleaning coverage (the wet to the total surface) and the quantity of water mass actually impacting the dirty surfaces (the impacted to injected mass). On the other hand, water washing erosion is a complex phenomenon depending on several parameters, such as the mechanical properties of the blade material, the impact velocity and angle and the droplet diameter. For this reason, the WWS are strongly influenced by the adopted nozzles and by the injection conditions. The present paper aims at assessing water washing for six different injection conditions in the first stage of a real axial compressor. Two-phase CFD simulations are carried out with Ansys Fluent where a User Defined Function implemented by the authors is used to properly model water droplet erosion mechanism and to obtain all the quantities needed to evaluate the washing quality. Results confirm the strong influence of the injection conditions on the main features of the washing system. The study is part of an ongoing partnership between Baker Hughes and Sapienza University of Rome aiming at maximizing the washing of the compressor blades while maintaining the erosion under specific thresholds.
Highlights
As reported in the open literature, the loss of performance in a gas turbine engine is essentially related to compressor problems [1,2]
In the present paper we studied the effect of water flow rate on erosion damage and on water washing efficiency on the first-stage rotor of an axial compressor
A series of CFD simulations have been performed to better understand the complex phenomenon of the online water washing in a real full-rotor compressor geometry by varying the injection conditions
Summary
As reported in the open literature, the loss of performance in a gas turbine engine is essentially related to compressor problems [1,2]. The injection pressure affects the spray diameter, the cone angle and the injection velocity; all these parameters, together with the number and position of the injectors and the injection time, are linked to the water distribution in the machine, to the washing efficiency and to the risk of causing erosion on the blades [13,14,15,16,17,18]. Varying and optimizing these quantities result in a more or less efficient washing system, which in turn results in energy consumption, emission variation and duration of the blade life.
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