Dewatering Optimization_Gupta
- 1. Optimization for Centrifuge Dewatering WEFTEC New Orleans, Louisiana Rashi Gupta, P.E. Steve Walker, CWP Carollo Engineers September 28, 2016
- 2. Filename.ppt/2 Questions to Answer Today… • Why is optimization important? • What should I consider within my dewatering process? • How do I systematically optimize the process?
- 3. Filename.ppt/3 Dewatering Costs a Lot Annual Dewatering Cost = $3.7M Case Study 1
- 4. Filename.ppt/4 Increasing Dryness Can Save on Hauling $ ~$80,000 between 20% and 22% per centrifuge at 250 gpm; 2% feed Case Study 1
- 5. Filename.ppt/5 Reducing Polymer Can Save on Chemical $ ~$20,000 between 38 lb act/DT and 40 lb act/DT per centrifuge at 250 gpm; 2% feed Case Study 1
- 6. Filename.ppt/6 Maximizing Dryness Not Always the Answer Case Study 2
- 7. Filename.ppt/7 Dewatering Costs – Case Study 1B from July 2011 to September 2014
- 8. Filename.ppt/8 Dewatering Performance – Case Study 1B Averages: 22.0% Cake 99% Capture 38.3 lb act/DT
- 9. Filename.ppt/9 Case Study 1B Dewatering Costs – Before and After • 2011-2014 Monthly Costs − $33,000 Hauling − $19,000 Polymer − $52,000 Total • 2015 Monthly Costs − $29,500 Hauling − $15,600 Polymer − $45,100 Total
- 11. Filename.ppt/11 Centrifuge Features Polymer Addition Sludge Feed Cake Discharge Centrate Discharge Centrifuge Main Drive Scroll Back Drive Ref: Centrisys
- 12. Filename.ppt/12 • Dewatered cake • Centrate • Sludge: − Anaerobically or aerobically digested − Primary sludge − Thickened waste activated sludge − Chemically enhanced • Polymer solution Centrifuge Inputs and Outputs Inputs Outputs
- 13. Filename.ppt/13 Operational Targets to Track Performance Criteria Units Importance Cake dryness %TS • Disposal costs • Water equals weight and takes up volume Centrate quality %TS or TSS, mg/L • Impact on liquid treatment processes • Re-treatment of solids (thickening, digestion and dewatering) • Impact of inert solids on activated sludge mass calculations Throughput lb/hr and gpm • Centrifuge capacity • Operations and hauling logistics Polymer dose Active pounds per dry ton • Operating costs
- 14. Filename.ppt/14 Dewatering Feed Characteristics Matter • Important Sludge Feed Characteristics − PS:TWAS ratio in digester feed, by mass Important because PS is MUCH easier to digest and dewater than TWAS The higher the PS:TWAS ratio, the better the dewaterability − Volatile solids content Generally, higher VS = More difficult to dewater − Biological phosphorous removal − Divalent cations (Ca2+, Mg2+) vs Monovalent (Na+, K+) − Sludge feed temperature
- 15. Filename.ppt/15 PS:TWAS Ratio Matters a Lot Case Study 1A Case Study 1B Case Study 1C Case Study 1D Highest PS:TWAS Lowest Polymer Most Dry
- 16. Filename.ppt/16 Understanding Polymer Basics Necessary to Assess Effectiveness • “Neat” polymer − Oil, surfactants, water, and polymer (emulsion as delivered) • “Active” − What’s doing the work − 40-50% typical for emulsion − 90%+ typical for dry
- 17. Filename.ppt/17 Many Pieces to the Polymer Puzzle • Procure the right polymer • Select right dilution concentration for polymer solution • Produce fully activated solution • Find best polymer injection location • Maintain req’d water pressure • Check water characteristics (chlorine, hardness, temperature) • Optimize polymer dose
- 18. Filename.ppt/18 • Loading rates (throughput) • Bowl speed (G-force) • Conveyor/scroll speed (differential speed) and torque − Newer centrifuges are controlled using a % torque or pressure setpoint − To achieve the desired torque/pressure, the PLC adjusts the scroll speed • Weir plates − Set the pool depth within the bowl Centrifuge Parameters that Affect Performance
- 19. Filename.ppt/19 Throughput • Need to stay within loading capacity • Changing solids concentration impacts loading
- 20. Filename.ppt/20 Throughput Case Study 1A: Data from January 2015 – April 2015
- 22. Filename.ppt/22 Process Optimization • Achieve: − Desired cake dryness and centrate quality − Lowest polymer cost − Maximum throughput and efficiency • Balancing act: Maximize one or more of the process parameters, while keeping all others within their constraints
- 23. Filename.ppt/23 Parameters used for Optimization • Type of polymer • Polymer dose • Polymer dilution/solution concentration • Polymer injection point • Centrifuge torque/pressure • Centrifuge pond depth • Centrifuge bowl speed • Sludge feed (throughput) • Sludge characteristics
- 24. Filename.ppt/24 Process Optimization – Polymer Selection • Selecting the right polymer: − Site specific jar testing by different suppliers High molecular weight for centrifuge dewatering High charge density helps with dewatering of secondary sludges Cationic − Site specific full scale tests with promising polymers • Full scale tests can identify more effective polymers • Polymer effectiveness can be gauged through viscosity
- 25. Filename.ppt/25 Polymer Contract Flexibility • Establish Primary and Alternate supplies − Use two different suppliers rather than two different products from the same supplier • Determine if seasonal constraints support alternatives. For example: − An emulsion polymer may be more cost effective in winter months − A dry polymer may be more cost effective in the other months
- 26. Filename.ppt/26 Test Methodology – Phase 1 (Polymer Dose) • Batch polymer at preferred solution strength • Set sludge feed rate • Enter typical torque setpoint and bowl speed • Set lowest polymer feed rate • Run for a standard time (i.e., 45 minutes) • Sample feed, centrate and cake for TS/TSS. − Feed solids concentration used to calculate throughput • Run through sequence for at least 5 polymer feed rates • Calculate associated dose and plot results
- 28. Filename.ppt/28 Performance Curve - Polymer 80 82 84 86 88 90 92 94 96 98 100 10 15 20 25 30 35 1 2 3 4 5 6 lb/tonor%TS Dose v. % Recovery Dose, lb/ton Cake Recovery 24
- 29. Filename.ppt/29 Test Methodology – Phase 2 (Torque) • Set sludge feed rate • Set polymer solution feed rate for the “ideal” polymer dose • With sludge and polymer feed rates “locked in”, adjust % torque setpoint • Run for a standard time (i.e., 45 minutes) • Sample feed, centrate and cake for TS/TSS. • Run through sequence for at least 5 torque setpoint • Plot results
- 30. Filename.ppt/30 Performance Curve - Torque 80 82 84 86 88 90 92 94 96 98 100 10 15 20 25 30 35 40 45 50 1 2 3 4 5 6 %TSorTorque Torque v. % Recovery Torque Cake Recovery 39% Torque
- 31. Filename.ppt/31 Further Optimization • Choose variable to test − Polymer solution concentration or injection point − Throughput − Centrate weir location − Etc. • Run through same process as above, holding other parameters constant • Run through sequence with incremental changes to variable • Plot results
- 32. Filename.ppt/32 Optimize Upstream Processes • PS:TWAS ratio − If possible, modify upstream operations to favor PS in the digester feed • Dewatering feed temperature − Try minimizing storage or feeding from digesters • Track VS in dewatering feed • Plot these parameters and compare to performance Case Study 1A Case Study 1B Case Study 1C Case Study 1D
- 33. Filename.ppt/33 Outcomes of Regular Optimization • Determine what dose is effective under what conditions • Determine what torque is effective at what throughput • Determine impacts of upstream processes on dewatering • Provide general guidelines to dial in centrifuges and understand impacts of changes • If using more than one polymer, determine under what conditions each is most effective • Forecast usage to establish purchasing frequency and budget projections Consider a full range of testing at least every 6 months
- 34. Filename.ppt/34 Track Performance and Publish Results Relative to Targets
- 35. Filename.ppt/35 Continually Optimize to Address Changes
- 36. Filename.ppt/36 Optimization for Centrifuge Dewatering Thank you for being a wastewater treatment professional. Steve Walker swalker@carollo.com 303-635-1220 Rashi Gupta rgupta@carollo.com 714-593-5100