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A hybrid dephlegmator for incorporation into an air-cooled steam condenser

A hybrid dephlegmator for incorporation into an air-cooled steam condenser. Michael Owen Univ. of Stellenbosch/Dept. M&M Eng./STERG. Energy Postgraduate Conference 2013. Overview. Air-cooled condensers (ACCs): what, where, why? Hybrid (dry/wet) dephlegmator concept

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A hybrid dephlegmator for incorporation into an air-cooled steam condenser

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  1. A hybrid dephlegmator for incorporation into an air-cooled steam condenser Michael Owen Univ. of Stellenbosch/Dept. M&M Eng./STERG Energy Postgraduate Conference 2013

  2. Overview • Air-cooled condensers (ACCs): what, where, why? • Hybrid (dry/wet) dephlegmator concept • HDWD performance evaluation • Concluding remarks

  3. 3 ACCs: what, where, why?

  4. 4 ACCs: what, where, why? (cont.) • Wet cooling using evaporative condensers • Approximately ½ of all power plants in the U.S. use evaporative cooling¹ • 36 of the 37 major operating solar thermal power plants are wet cooled² • Water intensive: >30 000 litres per day per MW installed³ • Typically accounts for > 80 % of the water consumption at a plant4 The use of alternative means of cooling therefore holds the greatest potential for decreasing water consumption related to electricity production

  5. 5 ACCs: what, where, why? (cont.)

  6. 6 ACCs: what, where, why? (cont.) • ACCs use ambient air to cool and condense the process fluid • No water is directly consumed in the cooling process • ACCs are therefore an attractive option considering current global water security concerns • ACCs allow for flexibility in plant location • Location not constrained by proximity to water resources • Plants can be built nearer fuel/energy supplies or load centers → increased reliability and reduced transmission costs • ACCs experience a reduction in cooling effectiveness at high ambient temperatures • QαTv - Ta • A dynamic relationship exists between condenser and turbine performance • Reduced cooling effectiveness → decreased plant output on hot days

  7. 7 Hybrid (dry/wet) dephlegmator Conventional • Replace conventional dephlegmator with a HDWD • Originally proposed by Heyns and Kröger5 • 2 stages connected in series: • 1st stage – ACC (inclined finned tubes) • 2nd stage – hybrid plain tube bundle • 2nd stage operation: • Low ambient temperatures → DRY • High ambient temperatures → WET • Wet mode • Both latent and sensible heat transfer • Measurably enhanced air-side heat transfer coefficient Hybrid

  8. 8 HDWD performanceevaluation • 3 street ACC with a HDWD (operating wet) provides the same turbine output benefits as: • A 33% over-sized ACC (4 streets vs 3) - at a much reduced cost • A conventional ACC with spray cooling enhancement – while consuming 20 % - 30 % less water and avoiding fouling and corrosion issues

  9. 9 HDWD performance evaluation (cont.) • One-dimensional performance analysis to identify the best configuration for the 2nd stage HDWD bundle • More rows of smaller diameter tubes in a multipass arrangement with a single tube row in the final pass • Highest heat transfer rates (up to 35% increase for an ACC) • Lowest ejector loading • Slightly higher water consumption (although still negligible compared to an evaporative cooler) • Higher steam-side pressure drops 38.1 19.0 16 16 25

  10. 10 Concluding remarks • While ACCs offer water consumption advantages over evaporative cooling towers they experience decreased performance during hot periods • Alternative and enhancement strategies have thus far proven problematic • A novel hybrid dephlegmator concept is proposed that: • Offers enhanced cooling performance • While consuming only a small amount of water • Is able to reduce the load on the ejector • Simple and cost effective • Experimental data is required to fully quantify the exact performance characteristics of the HDWD

  11. 11 References • Carney B, Feeley T, McNemar A. NETL Power Plant Water Research Program. EPRI Workshop on Advanced Thermoelectric Cooling Technologies 2008; Charlotte NC. • NREL 2010: http://www.nrel.gov/csp/solarpaces/project_detail.cfm/projectID=6 • Gadhamshetty V, Nirmalakhandan N, Myint M, Ricketts C. Improving Air-cooled Condenser Performance in Combined Cycle Power Plants. J Energy Eng 2006; 132/2:81-88. • DiFilippo M., Reclaiming Water for Cooling at SCE’s Mountainview Power Plant, Presentation: EPRI workshop on Advanced Thermoelectric Cooling Technologies, Charlotte, 2008. • Heyns, J.A., Krӧger, D.G., Performance characteristics of an air-cooled steam condenser with a hybrid dephlegmator, R&D Journal of the South African Institute of Mechanical Engineers, Vol. 28, pp. 31-36, 2012.

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