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Optimizing Operations of Finished Water Pumps and Protecting the Distribution System with Transient Modeling

This study aims to optimize operations and reduce O&M costs of finished water pumps and the distribution system by using surge modeling. The project background, surge modeling, field work, model calibration, air release valve analysis, economic analysis, recommendations, and summary are outlined.

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Optimizing Operations of Finished Water Pumps and Protecting the Distribution System with Transient Modeling

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  1. Optimizing Operations of Finished Water Pumps and Protecting the Distribution System with Transient Modeling 95TH Annual Conference | November 2015 | Raleigh Convention Center, Raleigh, NC

  2. Crystal Broadbent, Hazen and Sawyer Kelvin Creech, Town of Cary Michael Wang, Hazen and Sawyer Authors

  3. Outline • Project Background • Surge Modeling • Field Work • Model Calibration • Air Release Valve Analysis • Economic Analysis • Recommendations • Summary

  4. Purpose Surge Model used to identify problems affecting operations of finished water pumps, WTP, and distribution system Optimize operations Reduce O&M cost Protect critical infrastructure

  5. Background

  6. Background Staff suspect finished water pumps were adversely affected by entrained air left in the transmission main The WTP: 40 mgd WTP 9 finished water pumps 42-inch transmission main The challenges: After maintenance, unable to purge all air out of transmission main High-pitch sound emanating from existing air release valves

  7. Surge Model

  8. Surge Model2010 MDD Pumps Operating at MDD Two 1000 hp One 450 hp Q= 24.3 mgd Pressure = 161.4 psi

  9. High Service Pump Detail

  10. High Service Pumps in Surge Model Surge Relief Valve ADAMS Control Valve, typ. FWP-7 FWP-6 FWP-5 FWP-4 FWP-3 FWP-8

  11. 42-inch Transmission Line Profile CPZ Zone HSP

  12. Field Test

  13. Field Test – Logger Location Jenks & Apex Hwy 55 Between pumps and ADAMS valves Venturi Vault Green Level Church Rd

  14. Field Test • Work performed April 18th, 2013 • Evaluated a series of pump on and off configurations • Pump 6 start • Pump 5 start while Pump 6 operating • Pump 6 off while Pump 5 operating • Pump 3 on while Pump 4 operating • Pump 3 off while Pump 4 operating • Measured pressures at hydrants

  15. Pump 6 Start SCADA does not capture the pressure wave SCADA does not capture the pump start up

  16. Pump 5 Start Pump 6 Operating 25 psi difference A 25 psi difference between Pump 5 and Pump 6 & WTP Meter. This indicates that the ADAMS valve in front of Pump 5 is throttling flow and energy is being consumed.

  17. Pump 6 Off Pump 5 Operating

  18. Pump 3 On Pump 4 Operating Pressures are the same for Pump 4, Pump 3 and WTP Meter, as would be expected

  19. Pump 3 Off Pump 4 Operating 29 second closing: 62 psi pressure increase SCADA does not capture the pressure wave

  20. Model Calibration

  21. Surge Model Calibration to Field Test Results • Analyzed two scenarios • Pump 6 on • Pump 6 turns off while Pump 5 remains on • Graph • Field test results: dashed lines • Surge model results: solid lines • Different color for each location

  22. Model Matches Loggers

  23. Model Matches Loggers

  24. Air Valve Evaluation

  25. Basic Purposes of Air Valves • The Basic Premise • Allow air and gases to be released from a pipe • Allow air into a pipe under negative pressure conditions

  26. Behavior of Air “Air & Its Impact on a Water and Wastewater System”, Val-Matic; Air Valves Bulletin 1500; issue 3 volume 52 p 37-44

  27. Installation Guidelines • Air valve connection to the pipe needs to be correctly sized and located to capture the small air bubbles as well as larger pockets. • For air-release valves this is particularly important, since their function is to release these small bubbles and pockets. • Ideal (but not generally practiced in the U.S.): Connection to Pipe (d) Ratio to Pipe Diameter (D): d = D for D ≤ 12 inch d = 0.6D for D inch < D ≤ 60 inch d = 0.35D for > 60 inch

  28. Orifice Sizing: Air-release Valve • Difficult to predict quantity of air/gases that will come out of solution • Assume 2% solubility of air in water under standard conditions • Less is known about dissolved air properties in wastewater • “Choked orifice,” or “sonic flow” occurs when the ratio of low pressure (absolute) to high pressure (absolute) < 0.528 (for vacuum, avoid internal pressures below -5 psi gauge)

  29. Orifice Sizing: Air/Vacuum Valve • Pipeline Filling • Fill rate 1ft./sec. • Exhaust air at a rate = pumping rate or the design fill rate • Typically vented to atmosphere a differential pressure of < 2 psi. • Valves with anti-slam or slow-closing may have a differential pressure of 5 psi Air enters Orifice (3), travels through the annular space between the cylindrical floats (4), (5), and (6) and the valve Chamber Barrel (2) and discharges from the Large Orifice (1) into atmosphere

  30. Orifice Sizing: Air/Vacuum Valve, cont. • Pipeline Draining • Gravity flow based on pipe slope or drain valve • Determine maximum allowable negative pressure (usually -5 psi)

  31. Caution • Improper design of orifice size for an air/vacuum valve = • Release air too fast “air slam” Single stage 2 stage

  32. Air Valves for Burst and Draining • Each manufacturer uses its own set of calculations and some provide free sizing programs 4” 8” 8” 4” 4” 4” 4” 4” 3” 3”

  33. Existing Air Valves are 2 times too Small Velocity: 3-3.3 fps For 42 inch pipe Air Valve size is between a 4 and 6 inch Current Size Air Valves would be for ONLY a 16 to 24 inch pipe

  34. Economic Analysis

  35. Economic Analysis • Evaluated current operations for taking 42” offline and returning it to service • Determined effectiveness of existing air valves • Using model and field test • Determined existing restrictions in 42” transmission main • Energy cost due to restrictions in 42” transmission main

  36. Current 42” OperationNormally: 42” feeds CPZ (641’); 30” feeds WPZ (540’) • Operate valves to switch 30” from WPZ to CPZ • Drain 42” through blow off valves • Supply WPZ through PRVs from CPZ • Supply CPZ using • 3 WPZ pumps 400hp; 5.5 mgd @ 305 ft • 1 Swing pump 1000 hp; 9 mgd @ 450 ft • Supplement with Durham water • 24-72 hrs to refill 42” Main • Refill from NC 55 & Old Jenks Rd • 30” Main still providing supply to CPZ • Operate valves to switch 30” from CPZ to WPZ • Flush through hydrants • Return 42” Main to service Placing back into service Taking out of service

  37. Hydraulic Model Analysis* Evaluating 30” TM Supplying WPZ (typical operation) Supplying CPZ (when 42” offline) Average Day Demand CPZ: 16.2 mgd Swing Pump: operates 2 to 3 times a day: ~ 14hrs each day 9.6 MGD @ 424 ft; 85% Calculated HP: 840 WPZ Pumps operating: 1, 2 and 9 – operates continuously Each: 4.2 mgd @ 380 ft; 78% Calculated HP: 359 per pump Together, the WPZ pumps and swing pump can continue to meet average day demands • Average Day Demand for WPZ: 3.4 mgd • 1 WPZ Pump: 3 hrs a day • 6.3 MGD @ 271 ft; 78% • Calculated HP: 384 • Davis Drive & Waldo Rood Blvd PRV between CPZ and WPZ • 2.7 mgd • Setting 78 psi * hydraulic model received from CH2M’s

  38. WPZ Pump Pumping to WPZ Pumping to CPZ

  39. Cost Difference Between Supplying CPZ with 42” vs. 30”: Average Day Demand • 30” Supply CPZ • 3 WPZ pumps each: 359hp, 24hrs/day, 30days/month • Swing Pump: 840 hp, 14hrs/day, 30days/month • Total : 841,000 kwh/month • 42” Supply CPZ • Pump 3: 384 hp, 8.4hrs/day, 30days/month • Pump 5: 835 hp, 9.4hrs/day, 30days/month; 827 hp, 14.6hrs/day, 30days/month • Pump 6: 835 hp, 9.4hrs/day, 30days/month • Total : 720,000 kwh/month • Difference 121,000 kwh/month • kWh cost • $0.0535/kwh for all over 140,000 kWh per month, per kWh (duke energy) • Cost for using 30” verses 42” to supply CPZ • $1,600 cost/week $6,500 cost/month

  40. Effectiveness of Existing Air Valves • Surge model power loss result: Existing valves let in a greater volume of air and take longer to expel it than the proposed valves. • Larger volume of air is directly proportional to the headloss.

  41. Comparing Field Test to Model * Forcing the model to provide the exact flow as the field test Pumps are operating below the 20.2 inch impeller curve (shown in the next slides)

  42. Pump 6 Field Test Model

  43. Possible Restrictions: Throttled valve Air pocket Corrosion buildup* Biofilm* *City staff confirmed this is not the case

  44. Reduction of Pump Capacity –Air Pocket • Air pockets in the pipeline add additional head loss and restrict flow • Head loss is directly proportional to the size of air pocket • As high as 16% additional head loss • Extremely difficult to predict exact head loss • Determine entrained air by comparing the design capacity and actual capacity • Another way is to determine the actual friction value through field work and then recalculate capacity with new friction value to see if entrained air is an issue S J van Vuuren, M van Dijka and J N Steenkamp, Quantifying the Influence of Air on the Capacity of Large Diameter Water Pipelines and Developing Provisional Guidelines for Effective De-aeration. WRC Report No. 1177/2/03

  45. Potential Energy Savings: One Pump Evaluation • 818 hp, 24hrs/day, 30days/month • 439,000 kwh/month • 862 hp, 24hrs/day, 30days/month • 463,000 kwh/month • 24,000 kwh/month difference • Savings • $15,400 saving/yr Difference Model with No Restrictions Field Test

  46. Recommendation

  47. Suggested Sizing for 15 and 20 MGDfrom Manufacture Software 4” 8” 8” 4” 4” 4” 4” 4” 3” 3”/6” & 3” New Locations

  48. Hazen Recommendation Remains the same 4” 6” 6” 4” 4” 4” 3” 4” 3” New Locations

  49. Various Construction Cost Estimate for Valve Upgrade

  50. Recommended Modifying Pump Control Valves • Replace Actuators • More control of open/close times • Reduce operational cost by removing headloss through malfunctioning valve • ADAMS Valve

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