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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

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

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

slide5

5

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

slide6

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
slide7

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

slide8

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
slide9

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

slide10

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
references

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.