Conducting Tracer Studies to Demonstrate Plug Flow Characteristics in an Ozone Pipeline Contactor

Transcription

1 Conducting Tracer Studies to Demonstrate Plug Flow Characteristics in an Ozone Pipeline Contactor California-Nevada Section AWWA Annual Fall Conference 3 October 2013 Sacramento, California Craig Thompson 1, Julia Lund 1, Jason Yim 2, and Elizabeth Sobczak 2 1 Kennedy/Jenks Consultants, San Francisco, California 2 Castaic Lake Water Agency, Santa Clarita, California

2 Overview Castaic Lake Water Agency Background Rio Vista WTP Method Results Discussion Recommendations Summary and Conclusions

3 Castaic Lake Water Agency Rio Vista WTP

4 Background Operating Permit Requirements Pipeline Contactor Tracer Test Determine Pipeline T 10 to HDT Ratio LT2 ESWTR Toolbox Guidance Manual Ozone CT Credit Requires [O3] 0.05 mg/l [O 3 ] depends on ozone decay rate and time T 10 to HDT ratio may depend on L to D ratio Each segment s T 10 to HDT ratio should be determined

5 Example Fluoride Concentration Curve for Ozonated Water Ideal Plug Flow Response

6 Rio Vista WTP

7 Pipeline Contactor Tracer Sample Stations Tracer Injection Point

8 Ozone Injector Station

9 Ozone Sample Station (typical)

10 Pipe Length to Diameter Ratios Tracer Test Sample Points Sample Station 3 (SA3) SA4 SA5 SA6 Ozone/Tracer Injection Station (OIS) to Sample Stations OIS to SA3: 16 to 1 (L to D ratio) OIS to SA4: 29 to 1 OIS to SA5: 41 to 1 OIS to SA6: 188 to 1

11 Method Step input tracer test (tracer added continuously) Tracer added to injector water at Ozone Injector Station 55 gallon drum of 23% hydrofluosilicic acid LMI Metering Pump (25 gph) Water samples collected at sample stations (SA3 6) Account for injection and sample time delays: Between tracer injection and raw water pipeline (10 seconds) Between ozone contactor and each sample station tap (5 6 sec)

12 Tracer Chemical Addition Ozone Injector System Mixing Energy (G) >1,200 sec -1 at each pair of nozzles Tracer added via Injector #1 nozzles Additional dispersion due to Injector #2 nozzles Ozone added using Injector #3 nozzles

13 Sample Collection Times Based on estimated Hydraulic Detention Time (HDT) at each Sample Station (SA) Samples collected at frequent intervals for a period equivalent to 3 HDTs to create ascending curve Samples collected at same intervals between 3 HDT and 6 HDTs to create descending curve Descending curve sample times based on completing 3 HDT at SA6

14 Sample Station HDTs (minutes) Plant Flow Rate (MGD) 60 (Max) 30 (Avg) 15 (Min) SA3 1:15 2:30 5:00 SA4 2:20 4:40 9:20 SA5 3:24 6:48 13:36 SA6 16:06 32:12 64:24

15 Sample Collection Intervals SA Station to 15 seconds SA Station to 30 seconds SA Station 5 15 to 60 seconds SA Station 6 45 seconds to 6-½ minutes

16 Results Once sample analysis was completed, ascending and descending F-curves were generated for each of the sample stations

17 Ascending F Curve for 15 MGD

18 Ascending F Curve for 30 MGD

19 Ascending F Curve for 60 MGD

20 Receding F Curve for 15 MGD

21 Receding F Curve for 30 MGD

22 Discussion A pipeline contactor with L to D ratios between 16 to 1 and 188 to 1 appears to provide a T 10 to HDT ratio of 1.0 to 1 (plug flow conditions) RVWTP Pipeline Contactor Reynolds Numbers: 15 MGD: 30 MGD: 250,000 (dimensionless) 490,000 (dimensionless) 60 MGD: 1,020,000 (dimensionless)

23 Discussion (#2) These data indicate that there are benefit(s) of using pipeline contactors for ozone disinfection CT credit. Pipeline contactors tend to be about twice as costly (per unit volume) as reinforced concrete structures BUT a smaller volume is required for the same T 10. A pipeline contactor with a T 10 to HDT ratio of 1.0 to 1 can provide the same T 10 time as a baffled, over-under reinforced concrete contactor with twice the volume and a T 10 to HDT ratio of 0.5 to 1. One set of tracer data (SA6) was compromised due to un-expected injector pump failure(s) (repeated) during the 60 MGD test period.

24 Lessons Learned & Recommendations Two individuals needed to collect samples at 3 to 7 second intervals timer and sampler Future pipeline contactor tracer tests should collect samples more frequently around 1 HDT to better demonstrate pipeline s perfect plug flow characteristics (T 10 to HDT ratio is 1.0 to 1) If using injector pump to disperse tracer chemical, disable injector water flow meter and pump shutdown alarm signal during tracer addition/injection period.

25 Summary and Conclusions Pipeline shows perfect plug flow condition RVWTP tracer test data demonstrates that T 10 to HDT ratio is 1.0 to 1 for pipelines with L to D ratios between 16 to 1 and 188 to 1 when operating with Reynolds Numbers between 250,000 and 1,000,000. Pipeline contactors with similar L to D ratios operated at the range of Reynolds Numbers tested should be given a T 10 to HDT of 1.0 to 1 (plug flow) for disinfection CT credit calculations.

26 Acknowledgements Castaic Lake Water Agency Gary Haggin Rafael Pulido Mik Mizniak Richard Kreiger Paul Halushka Jeff Koelewyn Wayne Rowley Dirk Hare Chester Nigra Todd Grubber Brian Folsom Kennedy/Jenks Consultants Megan Plumlee Catrina Paez Doug Henderson Joe Drago

27 References Surface Water Treatment Rule (SWTR) (FR 54: 124: 27486) Guidance Manual for Compliance with the Filtration and Disinfection Requirements for Public Water Systems using Surface Water Systems, 1990, EPA Contract No , October. Surface Water Treatment Staff Guidance Manual, Office of Drinking Water Department of Health Services, May 15, Long Term 2 Enhanced Surface Water Treatment Rule Toolbox Guidance Manual, 2010 EPA 815-R published by United States Environmental Protection Agency, April

28 Questions?