How to Maximize Polymer Value for Improved Sludge Dewatering

Transcription

1 How to Maximize Polymer Value for Improved Sludge Dewatering Yong Kim, PhD Technical Director UGSI Solutions, Inc. (Gayle Corp, Koester Associates) NJ Water Environment Association Annual Conference Bally s Atlantic City, NJ May 16-20, 2016

2 Presentation Overview Characteristics of Polymer Effect of Mixing Energy/Strategy Two-stage Mixing in Mix Chamber Primary Mixing and Post-Dilution Mechanical vs. Hydraulic Mixing Weissenberg Effect Case Study at Fairfield-Suisun SD, CA 2

3 Coagulation and Flocculation Coagulation - Double-layer compression (charge neutralization) - Enmeshment (sweep coagulation) Clay suspension + Ferric chloride ( mg/l) Flocculation - Polymer Bridging Clay suspension + Ferric chloride + Polymer (< 1.0 mg/l) 3

4 Flocculation - Bridging by Polymer Molecules Extended cationic polymer molecule attracts negatively-charged suspended particles suspended particles How to prevent long-chain polymer molecules from being broken? 4

5 Polymer Structure Polymeric Flocculant, Linear Polymer, Polyelectrolyte Chained Structure by Repetition of Monomers. -CH 2 -CH-[CH 2 -CH] n -CH 2 -CH-... CO CO CO NH 2 NH 2 NH 2 Most polymers in water industry are acrylamide-based. If molecular weight of polymer is 10 million, the number of monomers in one polymer molecule, degree of polymerization n = 10,000,000 / 71 (mol. wt. of acrylamide= 71) = 140,850

6 Emulsion Polymer - 40% active d Hydrocarbon Oil: 30% Polymer Gel: Polymer 40% Water 30% d= µm 6

7 Storage of Emulsion Polymer Separation (stratification) * Drum (Tote) Mixer * Recirculation Pump M Separated Oil Settled Out Polymer Gels 7

8 Polymer Activation (Mixing, Dissolution) (I) Initial Wetting (Inversion) Sticky layer formed High-energy mixing -> No fisheyes (II) Dissolution Reptation* or Uncoiling Low-energy mixing -> No damage to polymer Oil Polymer (gel) Time Water (I) (II) Sticky Layer * de Gennes, P.G., J. Chem. Phys., 55, 572 (1971) 8

9 Development of Two-stage Mixer 1- stage mixer (EC) 2- stage mixer (PB) 1,700 1,100 4,000 G-value, mean shear rate (sec -1 ) 9

10 Mixing Effect on Polymer Activation Two-stage mixing significant increase in polymer solution viscosity stage mixer 2-stage mixer 18% up % up Anionic Polymer Cationic Polymer Viscosity of 0.5% Emulsion Polymer Solution, cp PolyBlend Technology

11 Why Primary Mixing followed by Post-Dilution? Inverting Surfactant helps to invert (or break) stable emulsion state d Hydrocarbon Oil: 30% Polymer Gel: Polymer 40% Water 30% Inverting (breaker) surfactant To enable inverting surfactant to work properly, make polymer solution at high concentration* * 0.75% -1.0% primarymixing * 0.25% - 0.5% secondary mixing (dilution) d= µm * AWWA Standard for Polyacrylamide (ANSI-AWWA B453-06), 11,

12 How to Accelerate Polymer Activation? Primary mixing at high % + Post-dilution to feed % Primary Mixing Ideal Design Polymer 1gph 1.0% Post-Dilution 0.5% solution Polymer 1gph Water 100 gph Primary Mixing 0.5% Water 100 gph 2x higher concentration of inverting surfactant leads to better polymer activation 0.5% solution Water 200 gph

13 Ideal Liquid Polymer System Two-stage Mix Chamber + Primary Mixing and Post-dilution Two-stage Mix chamber low-shear mixing baffle plate high-shear mixing Two-stage Mix chamber Secondary dilution water Primary dilution water

14 Mechanical or Non-mechanical (hydraulic) Mixing? Mixing Energy: G = (P / µv) 1/2 G: mean shear rate P: power delivered to fluid µ: viscosity V: mixing volume Mechanical Mixing P = 2 π N T N: rpm T: torque > Non-mechanical Mixing P ~ Q* P Q: flow rate P: pressure drop through mix chamber - G: irrelevant of water flow changes - Quantifiable mixing energy - Low P through mix chamber - Plant water pressure enough - G: varies as water flow rate changes - At low Q -not enough mixing energy - High P required for better mixing - Booster pump required

15 PolyBlend Dry Polymer System Components High Energy Mixing G = 15,000 sec -1 (3,450 rpm, < 0.5 sec) Low Energy Mixing (60 rpm, 20 min) (up to 0.75%) Post-dilution (0.1% - 0.2%) DD4 Disperser Mix and Hold Tanks Final Feed Skid

16 Dry Disperser (DD4) for Initial Wetting Very High-Intensity Mixing for Short Time G = 15,000 sec 3,450 rpm for < 0.5 sec Water in Solution Out Disperses Individual Polymer Particles * No Fisheye Formation * Shorter Mixing Time in Next Stage 16

17 Why Initial High-Energy Mixing is So Critical? Polymer dissolution time, t s ~ (diameter) 2 Tanaka (1979)* d Assume t s 1min 10*d t s 100 min Initial high-energy mixing No fisheye formation Significantly short mixing time * Tanaka, T., Fillmore, D.J., J. Chem. Phys., 70 (3), 1214 (1979) 17

18 Mixing Tank for Dissolution of Dry Polymer Patented Hollow-Wing Impeller No Weissenberg Effect Large Impeller, 70% of tank diameter Uniform Mixing Energy Low RPM, 60 rpm Low-intensity Mixing Minimize Damage to Polymer Chain Shorter Mixing Time Due to DD4 20 Minutes for Cationic Polymer 30 Minutes for Anionic Polymer Minimize Damage to Polymer Chain

19 Weissenberg Effect * Polymer solution exceeding critical concentration climbs up mixer shaft * Extremely non-uniform mixing * Critical factor for conventional polymer mix tank max 0.25% limit for HMW polymer extremely low mixing very high mixing extremely low mixing Water (Newtonian) Polymer Solution (Non-Newtonian, Pseudoplastic) 19

20 1 minute after mixing (Nalco TX series): 0.25%, 0.5%

21 10 minute after mixing (Nalco TX series): 0.25%, 0.5%

22 30 minute after mixing (Nalco TX series): 0.25%, 0.5%

23 Patented Mixing Impeller Prevents Weissenberg Effect PVC sleeve around mixer shaft separates mixer shaft from polymer solution PVC sleeve around mixer shaft prevents Weissenburg effect at high concentration, up to 0.75% Eye of impeller Hollow-bladed impeller Impeller / tank diameter > 0.7 Cationic Polymer 0.75%

24 Tips for Designing Efficient Dry Polymer Systems * High-Energy Initial Wetting (G = 15,000 sec -1 ) No fisheyes formed Shorter mixing time required Less chance of damaging polymer chains Smaller mix tanks * Preventing Weissenberg Effect (sleeve around mixer shaft) Enabling higher polymer solution concentration Less chance of damaging polymer chains Smaller mix tanks * Large Impeller in Mix Tanks (d / D > 0.7, 60 rpm) Low and uniform mixing energy Less chance of damaging polymer chains 24

25 Case Study: Fairfield-Suisan Sewer District, CA Solano County, CA, 40 miles North San Francisco Design capacity: 24 MGD tertiary treatment/ UV Population served: 135,000 Polymer use for dewatering (screw press) and thickening (GBT) Problems with existing polymer system Struggled to make proper polymer solution Polymer performance inconsistent Frequent maintenance issues FKC screw press runs at average 70 gpm of sludge (2% solids content)

26 Fairfield-Suisun Wastewater Treatment Plant Advanced Tertiary Treatment Facility Primary Clarifier Aeration Basin Secondary Clarifier Tertiary Filter UV Disinfection Headworks Polymer WAS RAS Final Effluent to Boynton Slough Gravity Belt Thickener Polymer Dewatering Screw Press Anaerobic Digester Biosolids to Landfill

27 Pilot Testing with Two Polymer Mix Equipment Existing Polymer System Initial wetting: educator-type hydraulic mixing Mixing: two (2) > 3,000 galmix/age tanks 1 hour mixing, 1 hour agingtime UGSI PolyBlend Dry Polymer System Initial wetting: high-energy mechanical mixing Mixing: two (2) 360 galmix tanks 20 min mixing, ~10 min holding time 27

28 Fairfield-Suisun SD Pilot Test Results Dewatering by Screw Press (3/21 4/21) Less polymer consumption * Daily usage from 255 lbs to 200 lbs * 22% polymer savings Better cake solids * 14% -16% to average 16.4% Thickening by GBT (4/24 5/23) Less polymer consumption Daily usage from 29 lbs to 20 lbs UGSI demo trailer at Fairfield SD 28

29 Various Forms of Polymer Solution Neat polymer Fisheyes due to poor initial wetting Ideal polymer chains by two-stage mixing Broken polymer chains by longer mixing time 29

30 How to Achieve this Results? initial high-energy mixing is critical Polymer dissolution time, t s ~ (diameter) 2 Tanaka (1979)* d Assume t s 1 min 10*d t s 100 min Initial high-energy mixing (DD4) No fisheye formation Significantly shorter mixing time Less damage to polymer structure Better quality polymer solution Polymer Savings * Tanaka, T., Fillmore, D.J., J. Chem. Phys., 70 (3), 1214 (1979) 30

31 Questions? Contact: Yong Kim, UGSI Sizing Online Program

32 Effect of Dilution Water Quality on Polymer Activation Ionic strength (Hardness): multi-valent ions hinders polymer activation - Soft water helps polymer molecules fully-extend faster -Hardness over400 ppm may need softener Oxidizer(chlorine): chlorine attacks/breaks polymer chains -Should be less than 3 ppm Temperature*: higher temperature, better polymer activation -In-line water heater for water lower than 40 o F -Water over 100 o F may damage polymer chains Suspended solids: strainer recommended if > 10 ppm ph: negligible effectwithin ph 3-10 *David Oerke (CH2M), et al., 2014 Biosolids Conf. -20% less polymer with warm water, 40% more polymer with 140 o F sludge 32

33 Effect of Chlorine (Oxidizing Chemical) When effluent is used for polymer mixing, chlorine should be < 3 mg/l Viscosity cp Cl2 mg/l 33

34 Effect of Dilution Water Hardness Soft water helps polymer chains to be fully extended Hardness, mg/l emulsion polymer, 0.5% Kim, Y.H., Coagulants and Flocculants: Theory and Practice, 43, Tall Oak Pub. Co. (1995/2014)

35 Comments on Viscosity (2/3) Relationship between Viscosity and Settling Rate Reduced Specific Viscosity Sakaguchi, K.; Nagase, K., Bull. Chem. Soc. Japan, 39, p.88 (1966)

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37 UGSI Demo Trailer Dry Polymer System (2) 360 gal Mix Tanks Dry Feeder DD4 (dry disperser)

38 Characteristics of High Molecular Weight Polymer Charge Type Anionic, Cationic, Nonionic Molecular Weight 5,000,000-25,000,000 Charge Density 0% to 40 % Physical Form Dry, Emulsion, Solution Concentration 5% - 100% Size of Polymer Particles Emulsion polymer: 0.1 µm - 2 µm Dry polymer: 0.1 mm - 2 mm 38

39 How Much Aging Time is Required for Dry Polymer? Well-designed equipment does not need additional aging stopped mixing 1.00% Viscosity (cp) stopped mixing 1.00% stopped mixing 0.86% Mix Time (min) Rao, M, Influents (WEA Ontario, Canada), Vol. 8, 42 (2013)

40 Aging for Conventional Dry Polymer Systems * Water Jet/Eductor: very low mixing energy at initial wetting -> fisheyes -> longer mixing time * Longer mixing time: damage to polymer, larger footprint * Small impeller diameter: non-uniform mixing -> damage to polymer * High impeller speed: damage to polymer * Air blower: polymer clogging Water Jet Feeder Mix Tank Air Blower * d / D = 0.2 * rpm * 1-2 hour mixing 40

41 Second-stage dry polymer mixing tank should not damage activated polymers: impeller diameter in relation to tank diameter d/d = 0.3 d/d = 0.5 Cutter (1966)* Non-Uniform Mixing Energy Okamoto (1981)** More Uniform Mixing Energy Impeller with large diameter provides low-energy uniform mixing energy, which is critical to prevent damaging polymer chains d: impeller diameter D: tank diameter * Cutter, L.A., AIChE J., 12 (1), 35 (1966) ** Okamoto, Y., Nishikawa, M., Hashimoto, K., Int. Chem. Eng, 21, 88 (1981)

42 Comparison - PolyBlend DP Systems vs. Others Features PolyBlend DP Other Dry Systems Feeder Shutter Polymer Feed Initial Wetting Mixing Tank Mixing Time Conc. Standard * no moisture into feeder Direct feed into DD4 * no blockage Mechanical Mixer high shear, short time no fisheyes Low shear mixing (60 rpm) no polymer damage Large Impeller (d/d = 0.7) uniform mixing no Weissenberg effect min > 1.0% ( % practical) None or optional moisture into feeder Transfer by Air Blower * transfer pipe blockage Venturi or Water injection very low shear always fisheyes High shear mixing (>400 rpm) polymer damage Small Impeller (d/d = 0.2) non-uniform mixing Weissenberg effect min < 0.3% (0.25% practical) Tank Size Smaller, < 20% 5-8 times larger Polymer Savings 20% - 30% N/A

43 Physical Forms of HMW Polymers Dry Polymer Cationic, anionic, non-ionic Molecular weight: up to 10 M (cationic), up to 20 M (anionic, non-ionic) > 95% active Polymer particle size: 0.1 to 1 mm Cost: high Emulsion Polymer Cationic, anionic, non-ionic Molecular weight: up to 10 M (cationic), up to 20 M (anionic, non-ionic) 30-60% active Polymer gel size: 0.1 to 2 µm Cost: very high 43

44 Non-mechanical (Hydraulic) Polymer Mixing Product A Mixing energy depends water flow rate & pressure drop (P ~ Q * ΔP) Inconsistent performance due to fluctuation of water flow & pressure 1 st stage : Not enough mixing energy for initial wetting 2 nd stage : Possible polymer build-up due to poor initial wetting * Hydraulic mixing: inconsistent mixing energy * Booster pump: must be required, not optional * No post-dilution: poor polymer activation, inverting surfactant works > 0.75% dilution 44

45 Mechanical Mixing with Too-Short Residence Time Product B Hydraulic/ Mechanical Mixing 1 st stage: Initial wetting fully dependent upon water pressure, not enough mixing energy 2 nd stage: lower energy than stage 3, not high enough mixing energy to prevent fisheyes. 3 rd stage: highest mixing energy at the last stage * Wrong mixing profile: low energy -> high energy * Too short mixing time: ~ gpm * No post-dilution: poor polymer activation inverting surfactant works > 0.75% dilution 45