Performance evaluation of water collecting systems with a hybrid dephlegmator

[摘要] ENGLISH ABSTRACT: Water collection systems are used in wet-cooling towers (WCTs) with fill overwhich water to be cooled flows and in evaporative air-cooled heat exchangers(EACHEs) having deluged tube bundles over which water flows to transfer heatfrom the tubes. They collect and remove water falling from the bottom of the fillor heat exchanger tube bundle while allowing air to pass with limited flowresistance. There are basically two types of collection systems, categorized astrough and basin systems. Trough systems comprise of multiple, evenly spacedparallel troughs extended in one direction with inclined capture plates to directwater into the troughs. The water collects in the troughs and drains under gravityto a collecting tank or manifold from where it is pumped to the sprayers. In basinsystems water falls directly into an open basin under gravity where it is collectedand can be pumped to the sprayers. The hybrid (dry/wet) dephlegmator (HDWD)for air-cooled steam condensers, which is being developed at StellenboschUniversity as discussed by Heyns (2008), Owen (2013) and Anderson (2014),requires a more effective water collection system with a lower pressure drop thanwhat current designs have to offer.In this thesis, an existing trough system is systematically evaluated by means ofvarious high speed camera and flow experiments to determine its performancecharacteristics and to find ways to improve its catchment effectiveness. Amodification is proposed which increases the effectiveness from approximately92% to 100 % with a relatively small increase in pressure drop, by adding a smalldeflector plate and reducing the spacing between adjacent troughs. Experimentaldata and CFD models are used to determine the performance characteristics of themodified trough system for design purposes.For comparison, various basin system designs are proposed and investigated usingCFD, where the baseline model is validated by means of experimental data ofrectangular cooling tower inlets by Kröger (2004). Rectangular cooling towerinlets are relevant as they have a similar re-circulating flow pattern to what is seenwith the water basin inlets at the vicinity of the inlet wall. The numerical data iscorrelated to determine empirical relations for the flow performancecharacteristics.The comparison between the modified trough and the different basin systemsyields that the trough system requires significantly less fan and pumping powerthan basin systems and the costs are also expected to be less.

[发布机构] Stellenbosch University