Optimizing Wastewater Upgrade Projects with Improved Hydraulics

Transcription

1 Optimizing Wastewater Upgrade Projects with Improved Hydraulics Alden Webinar Series October 27, 2009 For audio, please dial 1 (866) , participant code

2 Housekeeping Questions and Audio Availability of slides and recording Q&A period For audio, please dial 1 (866) , participant code

3 Introduction Dave Schowalter, Alden Agenda Hydraulics and the Wastewater Industry Hagop Shahabian, Malcolm Pirnie Hydraulic Modeling 101 Andy Johansson, Alden Municipal Case Studies Sheldon Lipke, PVSC Q&A For audio, please dial 1 (866) , participant code

4 Introduction Aging infrastructure concerns ASCE report ARRA investment through state revolving funds $6B in total The role of hydraulics in implementing upgrades Pump stations Avoiding excess vibration, cavitation, air entrainment Clarifiers Residence time, flocculation Conveyance systems Odor control, throughput, solids control

5 Hydraulics and the Wastewater Industry Hagop Shahabian, PhD, PE Malcolm Pirnie

6 About Malcolm Pirnie One of largest U.S. firms focused on environmental & water issues 100+ years serving 5,000 public & private clients Provide environmental engineering, science and consulting services More than 1600 staff in over 60 offices As of July 2009, a wholly owned subsidiary of ARCADIS

7 Introduction Hydraulics is an Integral Part of all Aspects of Wastewater Systems Evaluations and Designs Collection Systems Wastewater Treatment Plants Pump Stations Outfalls

8 Purpose of Hydraulic Evaluations Determine Hydraulic Capacity Accommodate Flow Increases Incorporate New Processes Avoid Sewer or Treatment Plant Overflows Minimize Expenditures Maximize Treatment Efficiency Ensure Proper Flow Distribution Maintain Minimum Velocities Properly Size Pumping Systems Meet/Improve Process Goals

9 Methods of Analyses Not surprisingly, they vary depending on the goals of the evaluations: 1. Collection Systems: Usually One Dimensional Steady State or Time Varying Pipe Flow or Open Channel flow Full Equations of Motion or portions thereof Public and Commercially Available Models

10 Methods of Analyses, (continued) 2. Wastewater Treatment Plants: Usually One Dimensional Commercially Available & In-house Models Steady State Pipe Flow, Open Channel Flow and Control Points Continuity and Energy Equations Exceptions: Headworks (proper mixing or splitting of flows and solids, CFD or Physical models) Pump Stations Wet Wells (CFD or Physical Models)

11 Methods of Analyses, (continued) 3. Pump Station Systems Wet Wells: follow American Hydraulic Institute Standards CFD Models Physical Models as necessary Pumping Systems One Dimensional Pipe Flow Steady State Analysis for Capacity Transient Analyses for Safety

12 Methods of Analyses, (continued) 4. Outfalls: For Near Field: Steady State 3 Dimensional Agencies approved Models: PLUMES, CORMIX, For Far Field: Steady State or Time Varying 1, 2 or 3 Dimensional Agencies approved Models

13 WWTP Hydraulic Model Process Assemble Plant Physical/Operational Data Develop Draft Model Collect Field Data WWTP Model Calibrate Model

14 Example 1 Unexpected Blockage Grease accumulation in FST influent piping

15 Model Simulation Examples Determine Plant Hydraulic Capacity: Definition: Units in Service Minimum Freeboard Control point Submergence Increasing flows until capacity threshold is reached Identify Bottlenecks Simulate Alternative Improvements

16 Example 2 Undersized Piping Aeration effluent piping too small

17 Example 3 Undersized Conveyence Undersized Filter Bypass

18 Example 4 Hydraulic Bottleneck Sedimentation Tank Effluent piping too high

19 Example 5 Hydraulic Bottleneck Undersized effluent trough

20 Wastewater Treatment Plants Selected Critical Elements: Equal distribution among process units Baffling Systems in Reactors (eliminate/minimize backmixing) Pump Station Wet Wells

21 WWTP Influent Screen Channel

22 Consider Anoxic/Oxic Baffle Wall Q Q w Q Anoxic Oxic Q o Q = Q w + Q o Density differential Unaerated density > Aerated density

23 Q Anoxic/Oxic Baffle Wall Q b Q Anoxic Oxic Q o If resulting pressure differential is substantial Q o > Q Aerobic Q w negative - backflow will manifest (Q b )

24 Potential Corrective Measures 1. Eliminate bottom orifice: Q w = Q Need structural wall - higher cost Need to fill/drain each zone separately 2. Use Gates - higher cost 3. Provide physical barrier Higher headloss 4. Distribute Q w & Q o by design Anoxic Oxic

25 Hydraulic Modeling 101 Andy Johansson Alden

26 About Alden Oldest operating hydraulics lab in US 5 Areas of specialization, including hydraulics Calibration Environmental Services Air and Gas Flow Modeling Field Services Hydraulics

27 Hydraulic Modeling 101 Key focus area: pump intakes Common problems with pump station hydraulics Vortexing Swirl/pump performance Water level issues Considerations for other hydraulic equipment Screening and Grit Removal Efficiency, Head loss, Grit Deposition Diversion Boxes Flow Split, Head loss Clarifiers Flow patterns, Velocity distribution, Solid settling and re-entrainment

28 INTRODUCTION The design and hydraulic performance of pump intake structures is often evaluated using physical hydraulic models.

29 INTRODUCTION Typically a model study would include: i) Observation and documentation of flow patterns approaching and within the pump bays. ii) Observation and documentation of the location, strength, and frequency of any free surface and subsurface vortices. iii) Measurement of swirl at the pump inlet or suction pipe. iv) Measurement of velocity distribution at the pump inlet or suction pipe.

30 INTRODUCTION Additionally, the model study may evaluate other flow related concerns such as: Head loss associated with the intake structure. Silt deposition within the intake.

31 INTRODUCTION Over the past ten years, significant advancements in the field of pump intake modeling have resulted from: - Experience gained from numerous model studies. - Availability of the Hydraulic Institute American National Standard for Pump Intake Design,1998 (HIS). - Rapid development in the area of computational fluid dynamics (CFD). - Increased computerized data acquisition capabilities.

32 HYDRAULIC MODELING 101 When to Model New Intake Structures Guidance Provided by HIS - Intake or piping geometry that deviates from the design standards. - Approach flow to the pumps is non-uniform or non-symmetric. > Intake with significant cross flow (e.g. located on river) > Use of dual flow screens. - Pump flows > 40,000 gpm or total station flow > 100,000 gpm. - Pump operation is critical and pump repair, remediation of a poor design and the impacts of poor pump performance or failure together is > 10 x model study cost.

33 HYDRAULIC MODELING 101 When to Model Existing Intake - Correct an existing problem. - Equipment upgrades (pumps, screens, etc.).

34 HYDRAULIC MODELING 101 Model Boundaries and Details Include geometry that could influence the flow patterns at the pump intake forebay Proper simulation of screens and racks Downstream extent of the model will depend upon the type of pump and the suction arrangement

35 HYDRAULIC MODELING 101 Instrumentation and Data Acquisition Hydraulic modeling involves the measurement of: - Water surface elevations - Pump flows - Flow patterns - Swirl angle - Velocities - Surface and submerged vortices - Sediment behavior

36 HYDRAULIC MODELING 101 Instrumentation and Data Acquisition Virtually any instrument-based recording can be performed using a personal computer. Benefits: - Increased Accuracy - Increased Efficiency; Personnel is free to record visually based assessments Flow patterns Vortex activity

37 S W I R L A N G L E HYDRAULIC MODELING 101 Instrumentation and Data Acquisition Swirl meters: determine the swirl or pre-rotation at a location in the pump bell or suction pipe just upstream of the pump entrance TIME INDEX (seconds) Pump 1 Pump 2 A modern PC system and Swirl Meters, equipped with a sensing device, can be used to record the rate and direction of swirl. Several meters can be recorded simultaneously, which allows the dynamic interaction between adjacent pumps to be investigated.

38 HYDRAULIC MODELING 101 Instrumentation and Data Acquisition Digital photography and Video Benefits: Time Savings

39 HYDRAULIC MODELING 101 Acceptance Criteria Prior to the availability of HIS acceptance criteria, there was no single commonly accepted reference defining the acceptance criteria.

40 HYDRAULIC MODELING 101 Remedial Modifications for Adverse Conditions Skewed Approach Flow Patterns Column Type Flow Distributors Energy Dissipators

41 HYDRAULIC MODELING 101 Remedial Modifications for Adverse Conditions Vortices

42 HYDRAULIC MODELING 101 Use of Computational Fluid Dynamics (CFD) CFD is a tool for solving flow problems numerically. Use of CFD for evaluating vortices is not yet acceptable due to difficulties in predicting the strength and persistence of free and subsurface vortices and resulting swirl or pre-rotation. In spite of its limitations CFD can complement physical models: - reducing the area to be modeled - reducing the number of test runs - compare alternative designs

43 Hydraulics in Other Equipment Clarifiers, Storm Water Separators - Flow patterns, Velocity distribution, Solid settling and re-entrainment, Removal efficiency

44 Hydraulics in Other Equipment Screening, Grit Removal, Diversion Structures - Flow patterns, Velocity distribution, Flow Split, Deposition, Removal efficiency, Head loss

45 Hydraulics in Other Equipment Contactors, - Flow patterns, performance/residence time, Concentrations

46 Hydraulics in Other Equipment: Clean out performance Sediment re-entrainment/deposition

47 Summary Physical and Numeric Hydraulic modeling can be a useful tool to evaluate hydraulics within wastewater treatment facilities and components Confirmation of a new design Correct adverse conditions in an existing design Benefits include both cost and time savings

48 CFD Modeling Experiences at PVSC Sheldon Lipke, P.E. Passaic Valley Sewerage Commissioners

49 INTRODUCTION The PVSC owns and operates a 330 MGD wastewater treatment plant serving approximately 1.2 million people, 260 significant industrial users and 5,000 commercial users. PVSC serves 48 towns and cities located in Bergen, Essex, Hudson, and Passaic counties, including Newark, Jersey City, Paterson and Passaic.

50 Topics of Discussion Headworks Modifications Forebay Grit sump Final Clarifier Improvements Flow modeling

51 HEADWORKS MODIFICATIONS FOREBAY

52 THE PROBLEMS Grit deposition in forebay Poor grit distribution among grit tanks Evidence of uneven flow distribution among grit tanks

53 Approach to Designing Solutions Model different technologies where possible Model headworks to address hydraulic and grit deposition/distribution problems Demonstrate full-size equipment at the plant

54 Hydraulic Modeling: Approach Computational Fluid Dynamics (CFD) Investigate design alternatives Select preferred design Improve design Physical Modeling Test design developed by CFD Develop further improvements Study grit deposition patterns

55 THE HEADWORKS

56 Existing Forebay Velocities

57 Channelized Forebay Consistently high flow velocities are maintained in active flow channels (> 1.0 fps, RED), however, velocities are low relative to the 2.0 fps rule of thumb for grit movement. Flow separation within forebay is minimized. Low-flow areas flush when other channels are activated.

58 Improved Channelized Forebay Results Consistently high flow velocities are maintained in active flow channels (about 2 fps during dryweather events) The flow rate through the South Forebay is greater than the flow rate through the North Forebay (54% passes through the South Forebay and 46% passes through the North Forebay)

59 Physical Model 1:9 scale Existing Condition: to compare with field data and new design (shown at right)

60 Physical Model

61 Physical Model 1:9 scale New Design: to test, study grit deposits, improve design (shown at right) Narrowed channels to increase localized velocities

62 HEADWORKS MODIFICATIONS GRIT PUMPING

63 Grit Pump Discharge Piping DIMENSIONS ARE PROTOTYPE INCHES MANIFOLDS NOT SHOWN FOR CLARITY

64 Velocity Contours with Vectors, Colored by Velocity Magnitude (red = 5 fps, violet = 0 fps)

65 Modeled Grit Sump Showing Grit Injection Push Beam

66 Model Run #3 - Grit Deposition in Sump: Peak Condition Both Pump and Manifolds Operating

67 FINAL CLARIFIER IMPROVEMENTS FLOW MODELING

68 Final Clarifier Diagram

69 Final Clarifier Effluent Launders: Modified (left) and Unmodified (right) Results Hydraulic modeling showed that the modified launder arrangement did not substantially improve effluent quality, which saved PVSC over $22 million.

70 Final Clarifier: Inlet Baffles

71 Final Clarifier: Stage Baffles

72 Final Clarifier: Stage Baffles

73 Summary Computational Fluid Dynamics (CFD) Preliminary design investigations Preferred design selection Initial design improvements Physical Modeling Test final design Develop final improvements Demonstration Project Test concepts in full-scale implementation

74 Webinar Conclusion Overview Hydraulics and the Wastewater Industry Hydraulics challenges in wastewater Hydraulic Modeling How and when to model Focus on pump stations Municipal Case Studies Forebay Grit pump discharge piping Clarifier

75 Questions Please use the Q&A tab in LiveMeeting Hagop Shahabian Andy Johansson Sheldon Lipke Dave Schowalter