The Technical Challenges of Dissolved Oxygen Enhancement

Transcription

1 The Technical Challenges of Dissolved Oxygen Enhancement B.Papillon EPRI-DOE Conference on Environmentally-Enhanced Hydro Turbines Washington DC May 19, 2011

2 Agenda 1st topic 2nd topic 3nd topic 4nd topic 5nd topic 6nd topic 7nd topic Introduction - The DO Issue Aeration methods Effects of aeration Aeration on model and transposition to prototype Prediction of aeration performances Parameters influencing oxygen dissolution Possible areas of R&D Conclusion The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 2

3 Introduction The DO issue Cs (mg/l) T (degré C) In warm region: Reservoir thermal stratification Low upstream reservoir DO level Warm water temperature DO saturation The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 3

4 Introduction - The DO issue The dissolved oxygen (DO) level has a direct impact on aquatic life : Total dissolved gas concentrations in water should not be higher than 110%. Concentrations above this level can be harmful to aquatic life. Fish in waters containing excessive dissolved gases may suffer from "gas bubble disease. This is very rare to reach that level mg/l : maximum level of DO in 0 C water at 100% saturation 9.0 mg/l : average level in good fishing waters (for 20 C water) Note : max. solubility of oxygen in 20 C water at 100% saturation = 9.07mg/L 5.0 mg/l : stress level for fish 2.0 mg/l : moribund fish at the surface "gasping" for oxygen ("piping behaviour). 1 2 mg/l : during few hours = large fish kills The dissolved oxygen (DO) criteria is recognized as the 0 mg/l : no life most important criteria of water quality for aquatic life The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 4

5 Introduction The DO issue Criterion often requested: DO > 5mg/L. In the South of the US, during summer and fall, this criterion is often not respected downstream hydroelectric powerplants (DO content of incoming water often lower than 1 mg/l). Mainly a concern in US. Begin to appear in other part of the world. The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 5

6 Introduction The DO issue Possible solutions Aeration weirs Bubble diffusers Surface water flow pumps Air admission through turbine Generally the cheapest method Effective solution Cost: Efficiency Power output The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 6

7 Agenda 1st topic 2nd topic 3nd topic 4nd topic 5nd topic 6nd topic 7nd topic Introduction - The DO Issue Aeration methods Effects of aeration Aeration on model and transposition to prototype Prediction of aeration performances Parameters influencing oxygen dissolution Possible areas of R&D Conclusion The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 7

8 Aeration methods Air Admission Objectives Safety Vacuum breaker Stability Reduction of pressure fluctuations at low and high loads. Noise reduction Needs typically an air flow of 1% of the turbine discharge. Environmental Increase of the dissolved oxygen («DO») in water This is needed mostly in warm regions like the south of the US. Needs typically an air flow up to 4% of the turbine discharge (and even more). The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 8

9 Aeration methods Natural air admission requires low pressure zones CFD calculations help to determine lower pressure zones Runner tip Runner periphery Runner outlet The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 9

10 Aeration methods Central air admission Center of runner cone, runner cone baffles or tube Typical for stability DO: more efficient at low loads 1 The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 10

11 Aeration methods Peripheral air admission (discharge ring, draft tube cone) Runner outlet DO: more efficient at medium to high loads The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 11

12 Aeration methods Typical aeration system (here through the head cover) The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 12

13 Effects of aeration Piping system installation The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 13

14 Agenda 1st topic 2nd topic 3nd topic 4nd topic 5nd topic 6nd topic 7nd topic Introduction - The DO Issue Aeration methods Effects of aeration Aeration on model and transposition to prototype Prediction of aeration performances Parameters influencing oxygen dissolution Possible areas of R&D Conclusion The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 14

15 Effects of aeration Increase DO concentration in water The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 15

16 Effects of aeration The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 16

17 Effects of aeration Modify turbine performance Flow rate, power output and efficiency Efficiency change (%) Runner cone center Runner cone baffles Discharge ring Qair/Qwater (%) The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 17

18 Effects of aeration Turbine Efficiency (%) Turbine efficiency without aeration Turbine efficiency with aeration Predicted turbine efficiency without aeration Ratio air flow / turbine discharge (%) 88 Ratio air flow / turbine discharge Turbine Output (HP) The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 18

19 Effects of aeration The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 19

20 Agenda 1st topic 2nd topic 3nd topic 4nd topic 5nd topic 6nd topic 7nd topic Introduction - The DO Issue Aeration methods Effects of aeration Aeration on model and transposition to prototype Prediction of aeration performances Parameters influencing oxygen dissolution Possible areas of R&D Conclusion The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 20

21 Aeration on model and transposition to prototype Aeration model test Objectives Effect of aeration on performances (efficiency, power output, flow rate) Effect of aeration on pressure fluctuations Pressure measurements at the air injection location Effect of aeration on DO (not an easy one) Allows to test multiple devices The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 21

22 Aeration on model and transposition to prototype The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 22

23 Aeration on model and transposition to prototype The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 23

24 Aeration on model and transposition to prototype The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 24 Q ED /Q EDopt =1.00

25 Aeration on model and transposition to prototype Aeration model test The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 25

26 The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 26 Aeration on model and transposition to prototype Alstom similitude rules: air flow ensuring homologous vortex cores 1 2 2,, + = γ m p m p m air p air E E D D m m 2 +1 = γ φ φ m p m p E E

27 Aeration on model and transposition to prototype Limitations of model Closed-circuit type: degassing is needed periodically to be able to measure DO. Dissolution in the tailrace not modelled on the test rig. Transposition is difficult (air flow, performances and DO even more). Based on empirical constants, function of test conditions of a particular project. Just field testing confirms air flow, impact on performance and DO uptake. The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 27

28 Agenda 1st topic 2nd topic 3nd topic 4nd topic 5nd topic 6nd topic 7nd topic Introduction - The DO Issue Aeration methods Effects of aeration Aeration on model and transposition to prototype Prediction of aeration performances Parameters influencing oxygen dissolution Possible areas of R&D Conclusion The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 28

29 Prediction of aeration performances Do Prediction Methods: Analytical and Physical Model CFD Calculations One and two phase flow Past experience Model Test The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 29

30 Prediction of aeration performances DO calculation: much higher level of uncertainty when compared to hydraulic calculations without aeration. DO uptake is function of many parameters Conditions at site (DO upstream, water temperature ) DO measurements locations. Tailrace mixing Tuning between DO uptake and performances has to performed on prototype. The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 30

31 Agenda 1st topic 2nd topic 3nd topic 4nd topic 5nd topic 6nd topic 7nd topic Introduction - The DO Issue Aeration methods Effects of aeration Aeration on model and transposition to prototype Prediction of aeration performances Parameters influencing oxygen dissolution Possible areas of R&D Conclusion The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 31

32 Parameters influencing oxygen dissolution Possible areas of R&D Parameters influencing oxygen dissolution Water temperature Incoming DO concentration Local pressures in water passageways Bubbles size Turbulence Velocity Residence time Air modifies local pressure, velocity and global density of the fluid. Bubbles can break and coalesce. Size bubbles vary in time due to local pressure and dissolution of gas in water Very complex phenomenon The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 32

33 Parameters influencing oxygen dissolution Possible areas of R&D Even though some interesting numerical model exist, there is a need to improve these models or to design new ones: Reduce need to calibrate numerical model with prototype measurements Better accuracy needed. Consider breakup and coalescence Predict bubbles size distribution Understand the basic physics of the air entrainment in a reduced scale model Define DO testing standards or guidelines in Codes (IEC or ASME). The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 33

34 Agenda 1st topic 2nd topic 3nd topic 4nd topic 5nd topic 6nd topic 7nd topic Introduction - The DO Issue Aeration methods Effects of aeration Aeration on model and transposition to prototype Prediction of aeration performances Parameters influencing oxygen dissolution Possible areas of R&D Conclusion The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 34

35 Conclusion Turbine aeration is an efficient method to increase DO Turbine aeration modifies DO but also turbine performance Design of aeration devices to achieve a certain DO level while predicting required air flow and impact on performances is a challenge: Complex physical process. Numerical model still not so accurate. Limitations of model test Field testing very important More R&D required in this field Better numerical models and understanding of the physics Partnership with Universities Defining guidelines in Codes Better standardization would help this technology to progress. The Technical Challenges of Dissolved Oxygen Enhancement - 23/05/ P 35

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