newtons(–more(than(just(agreat( 18,2014 snack ......2 6 #5 #1 8 6 point #5 submergence, point #1...

Novem

ber 1

8, 2014

BOB WIMMER AND ED KOBYLINSKI

NEWTONS – MORE THAN JUST A GREAT SNACK – THE KEY TO COMPARING MIXER TECHNOLOGIES

November 18, 2014

November 18, 2014

MIXING GENERAL: BASIC ISSUES

l  Want rapid blending of MLSS of two or more streams to intermix suspended solids

l  Want dissipaSon of incoming kineSc energy

l  Want rapid mixing of soluble rbCOD and nitrate l  Want shear to expose inner floc and acSve microbes to

rbCOD and nitrate l  High denitrificaSon rates only possible with high rbCOD

concentraSons

November 18, 2014

MIXING THEORY:TRADITIONAL

l  Pumping rate is a funcSon of impeller speed and diameter

l Q = Nq * RPM * Dia3

l  Nq = characterisSc pumping value unique to type of impeller l RPM = impeller rotaSng speed (revs/ minute)

l Dia = impeller diameter in feet

November 18, 2014

MIXING THEORY: TRADITIONAL

l  Pumping power is a funcSon of impeller speed cubed and diameter to the 5th power

l P = Np * spgr * RPM3 * Dia5 * 1.523*1013

l  Np = characterisSc pumping value unique to type of impeller

l RPM = impeller rotaSng speed (revs/ minute)

l Dia = impeller diameter in inches

November 18, 2014

OBJECTIVE

l  Input energy into tank and get liquid in moSon with the least amount of electrical energy

l  Meet process objecSves without transferring excessive amounts of oxygen

l Turnover of liquid will sSmulate oxygen transfer – Do Not Want Surface Turbulence

November 18, 2014

SUMMARY OF FIELD TESTING AT ROGERS ARKANSAS

FACILITIES • Tested new 4.7 mgd rated treatment train

• Anaerobic zone divided into 3 cells in series

• Anoxic zone divided into 3 cells in series

• 5 Hp top entering mixers -‐ axial flow down-‐pumping impellers

ANAEROBIC AND ANOXIC ZONE SCHEMATIC

Cell 1

Anaerobic/ FermentaSon

Cell 2 Cell 3

Cell 1 Cell 2 Cell 3

Anoxic MLSS recycle from aerobic zone

Influent plus RAS

Flow back to aerobic zone

ANAEROBIC ZONE

Baffle Wall Surface Port

Baffle Wall Submerged Port

Baffle wall submerged at above average flows

ANOXIC ZONE Baffle Wall Gap from Surface to Floor

MIXING TESTS

• Mixers designed at 34 rpm

• Mixers were run at three different speeds •  28 rpm 80% speed

•  16 rpm 50% speed

•  8 rpm 30% speed

• 69 inch diameter impeller-‐ down pumping

TOP ENTERING MIXERS

• At 28 rpm there is liple surface turbulence

• Liple surface vortexing

• Vortexing transfers oxygen

• Surface DO less than 0.4 mg/L

ANOXIC ZONE CELL #2 – SAMPLE LOCATIONS point #6 Submergence, sample ft below surface First Anoxic Zone

1 3 Cell #2 Cell #3 Point #2 Submergence, 2 6 2 ft sample # ft below surface3 9 1 34 12 #6 #2 2 6

point #4 ft below surface 2 ft 3 91 3 4 122 6 #4

point #3 ft below surface #31 32 6 #5 #1

8 6

Point #5 Submergence, Point #1 Submergence, sample # ft below surface sample # ft below surface

1 3 1 32 6 2 63 9 3 94 12 4 12

ANOXIC ZONE CELL #2 – MLSS PROFILE

3 6 9 121

3

5

3,4403,4603,4803,500

3,5203,540

3,560

3,580

3,600

3,620

3,640

MLSS, mg/L

Depth, ft

Location

123456

Anoxic Cell #2 - 28 rpm

Largest Variation - 120 mg/L3.35% variation


3 6 9 121

3

5

3,300

3,350

3,400

3,450

3,500

3,550

3,600

MLSS, mg/L

Depth, ft

Location

123456




3 6 9 121

3

5

3,250

3,300

3,350

3,400

3,450

3,500

3,550

MLSS, mg/L

Depth, ft

Location

123456



MIXING POWER TURNDOWN

• At 100% speed (34 rpm) mixers draw 5 Hp

• At 80% speed (28 rpm) mixers draw 2.8 Hp



• Mixer liquid pumping is proporSonal to rpm – 80% speed = 80% pumping capacity

November 18, 2014

MIXING PERFORMANCE

RPM gpm Hp Draw

Hp/Kft3

Turnovers/ minute

28 31,260 2.77 0.22 0.32

16 17,860 0.52 0.04 0.19

8 8,930 0.06 0.005 0.09

November 18, 2014

TEST DESIGN PROCEDURE

l  Set desired turnovers in mixing zone to get direct pumping rate – 0.2 turnovers/ minute

l  Size top entering mixer for direct pumping

l  Set RPM maximum at 15

l  Want impeller diameter to fall within range of minimum of 25% of narrowest tank width and not more than 40% of

tank narrowest width

l  Basin Volume 19,490 r3

November 18, 2014

TEST DESIGN CONTINUED

l  Direct Pumping Rate = 3,899 r3/ min = 29,170 gpm l  Top entering Mixer Design

l  RPM = 12 l  Impeller Dia = 7.5 r l  Pumping Rate = 29,730 gpm l  Power Draw = 0.82 Hp or 0.04 Hp/ Kr3

l  Submersible Mixer SelecSon l  Pumping Rate = 13,160 gpm each use 2 units l  Power Draw = 12.8 Hp each (25.6 Hp Total) or 1.3 Hp/ Kr3

November 18, 2014

TEST DESIGN CONTINUED

l Conclusion – Submersible Mixer Claims for Induced Pumping must be correct!

l  We know we have installaSons at less than 1.3 Hp/ Kr3

l  Submersible mixer manufacturers have been claiming that our power inputs values are too high at 0.6-‐0.75 Hp/

Kr3

November 18, 2014

l FricSon occurs and a fast moving liquid will drag along the slower moving liquid. Net result is bulk liquid

movement l Need to view mixer as a pump imparSng energy into the

tank l  Top entering mixers pump water at a low velocity

relaSve to the bulk flow in the tank l  Submersible mixers generate a high velocity jet relaSve

to the bulk flow in the tank l  We have been trying to measure mixing by power input

not power transferred to the liquid phase

DIRECT PUMPING VERSUS INDUCED PUMPING

November 18, 2014

l  The energy imparted to liquid can be expressed as kineSc energy.

l  Liquid energy can be described through Momentum

DIRECT PUMPING VERSUS INDUCED PUMPING

November 18, 2014

MOMENTUM

l  Momentum is defined as a measure of the moSon of a body equal to the product of its mass and velocity

l  Momentum is a measure of the energy contained by mass that is in moSon and through fricSon that energy

can be imparted to other fluid mass l  So for the purposes of mixing, momentum imparted into the system will gradually induce other liquid into

moSon and liquid in moSon will keep solids in suspension

November 18, 2014

MOMENTUM CALCULATION

l  Top entering Mixer Design

l RPM = 12 l  Impeller Dia = 7.5 r = 44.18 r2 area l  Pumping Rate; Expressed as volume flow per second and mass flow per second = 29,730 gpm = 3,974 r3/ min = 66.23 r3/ sec = 247,948 lb/ min = 4,132.5 lb/ sec l  Velocity = 66.23 r3/ sec/ 44.18 r2 = 1.5 r/ sec

November 18, 2014


l  Momentum = 4,132.5 lb/ sec * 1.5 r/ sec = 6,199 r lb/ sec2

l  Momentum is energy input into system and becomes the reference point for comparison

between mixer types.

November 18, 2014


l Using data from Flygt calculate momentum from each mixer. Mixer impellers have different pitch resulSng different power draw and volume

of liquid pumped.

November 18, 2014

FLYGT MIXER DATA

Model 4660 4660 4660 4640 Hp 6.5 7.6 8.2 3.2 Nq 0.3113 0.3516 0.3717 0.432 Np 0.08212 0.096 0.1036 0.1222 RPM 580 580 580 860 Dia, ft 1.9 1.9 1.9 1.2 ft3/min 1,240 1,401 1,481 647 lb/ sec 1,290 1,457 1,540 673 Area, ft2 2.838 2.838 2.838 1.137 ft/ sec 7.284 8.227 8.697 9.484 Ft lb/ sec2 9,395 11,984 13,394 6,379

November 18, 2014

FLYGT MIXERS

Model 4640

RPM 860

Impeller Dia 1.2 ft

Power draw 3.2 Hp

Pumping rate 4,840 gpm

Impeller angle 9

Momentum 6,379 ft lb/ sec2

Power per unit volume = 0.16 Hp/ Kr3

November 18, 2014

FLYGT MIXERS

l  The 0.16 Hp/Kr3 power input is a liple low based upon our current experience but is in a

range that Flygt claims is more correct for mixing

November 18, 2014

MIXING COMPARISON: CASE 2

l  Let’s look at a equivalent mixer sizing for to 80% speed condiSons at Rogers

l  80% speed equaled a turnover rate of 0.32 turnovers/ min

l Oren fall in between mixer sizes for Flygt

November 18, 2014

TOP ENTERING MIXER CALCULATION

Basin Volume 19,493 ft3

Turnover/ min 0.28 Pumping rate 5,458 ft3/ min RPM 12 Impeller Dia 100 inches Pumping Rate 40,781 gpm Power draw 1.4 Hp Impeller area 54.54 ft2

Velocity 1.67 ft/ sec Momentum 9,443 ft lb/ sec2

Power per Unit volume = 0.07 Hp/ Kr3

November 18, 2014

FLYGT MIXERS

Model 4660

RPM 580

Impeller Dia 1.9 ft

Power draw 6.5 Hp


Impeller angle 3


Power per unit volume = 0.33 Hp/ Kr3

MOMENTUM CONVERSION TO THRUST

• Divide momentum by the gravitaSonal constant 32.174 lbm r/ sec2

• This converts momentum to lb force or lbf

• 1 Newton = 0.2248089 lbf • Divide lbf value by 0.2248089 to get Newtons

TARGET THRUST VALUES

• Target Momentum for lower intensity = 6,199 r lb/ sec2 = 875 Newtons

• Target Momentum for higher intensity = 9,443 r lb/ sec2 = 1,306 Newtons

• SI momentum units = Thrust

• Kg meter/ sec2 = Newtons

November 18, 2014

MIXING COMPARISON – LOWER INTENSITY

Units Top Entering

Flygt

Aqua DDM Wilo/ EMU

Impeller, ft 7.5 1.2 0.958 4.917

RPM 12 860 1,200 31

Hp 0.82 3.2 2.7 1.34

gpm 29,730 4,840 3,557 19,989

ft lb/ sec2 6,199 6,379 5,434 6,517

Thrust, Newtons

857 882 751 900

November 18, 2014

MIXING COMPARISON – HIGHER INTENSITY

Units Top Entering

Flygt

Aqua DDM Wilo/ EMU

Impeller, ft 8.3 1.9 0.958 1.967

RPM 12 580 1,200 366

Hp 1.4 6.5 4.5 5.23

gpm 40,780 9,280 4,520 9,360

ft lb/ sec2 9,440 9,395 8,760 8,931

Thrust, Newtons

1,306 1,299 1,211 1,250

www.bv.com

© Black & Veatch Holding Company 2012. All Rights Reserved. The Black & Veatch name and logo are registered trademarks of Black & Veatch Holding Company.

CONCLUSIONS

• Thrust/ Momentum is proper way to compare mixers on equal fooSng except for INVENT

• For INVENT compare direct flow with axial down pumping mixers

November 18, 2014

MIXING COMPARISON

• Aqua DDM appears out of line but based upon basin volume the right momentum/ Thrust value falls in between the 3 and 5 hp units and between the 5 and 7.5 Hp units

• This will be true of all units. Proper size can fall in between two standard sizes.

November 18, 2014

COLLECTION SYSTEM ISSUES

RAS

Influent

Overflow Underflow

Overflow

Deniter gate MLSS Recycle

Slot in Wall Top to Floor

3 Anaerobic Cells in series

MLSS Return Flow

November 18, 2014

AQUA AEROBICS

Model 3 Hp 5 Hp 20 Hp 75 Hp Hp 2.7 4.5 18 67.5 Nq 0.4506 0.5721 0.673 0.5794 Np 0.118313 0.1972 0.3075 0.19676 RPM 1,200 1,200 900 900 Dia, ft 0.958 0.958 1.375 1.958 ft3/min 475 604 1,575 3,914 lb/ sec 494 628 1,637 4,070 Area, ft2 0.7208 0.7208 1.485 3.011 ft/ sec 10.99 13.96 17.67 21.67 ft lb/ sec2 5,434 8,760 28,937 88,191

November 18, 2014

AQUA AEROBICS: CASE 1 CONDITIONS

• We want to match a 6,200 r lb/ sec2 momentum value • Momentum falls between the 3 Hp and 5 Hp Aqua DDM units

• Assume we use the 3 Hp DDM unit • Hp/ Kr3 = 0.1385 or 18.5 Hp/ MG – lower power per volume than Aqua Recommends – They recommend 30 Hp/ MG for MLSS applicaSons

November 18, 2014

MIXER DESIGN COMPARISON

l  Next comparison is using the same example based upon Rogers but using the Aqua Aerobics

DDM floaSng mixer

l  It is a down pumping mixer

l  Fixed speed unit with Hp sizes varying from Nominal 3 Hp (2.7 Hp draw) to 75 Hp (67.5 Hp

draw)

November 18, 2014

WILO/ EMU MIXER DATA

Mixer Impeller Dia,

inches

RPM Flow, gpm

Power, Hp

Thrust, Newtons

TR50 19.7 476 7,614 7.24 1,180

TR60 23.6 366 9,360 5.23 1,250

TR90 35.4 168 13,484 3.08 1,140

TR215 59 31 19,989 1.34 900

November 18, 2014

WILO/ EMU MIXERS

• Target Momentum for lower intensity = 6,199 r lb/ sec2

• Target Momentum for higher intensity = 9,443 r lb/ sec2

•  I did not give WILO the target momentum values. Was looking for their recommendaSons.

November 18, 2014

WILO/ EMU MIXERS LOWER INTENSITY – TARGET = 6,199 FT LB/ SEC2

Model TR215

RPM 31

Impeller Dia 4.917 ft

Power draw 1.34 Hp (0.07 Hp/ Kft3)



Thrust 900 Newtons

November 18, 2014

WILO/ EMU MIXERS HIGHER INTENSITY– TARGET = 9,443 FT LB/ SEC2

Model TR60

RPM 366

Impeller Dia 1.967 ft

Power draw 5.23 Hp (0.27 Hp/ Kft3)



Thrust 1,250 Newtons

November 18, 2014

AQUA AEROBICS: CASE 2 CONDITIONS

• We want to match a 9,440 r lb/ sec2 momentum value • Momentum falls between the 5 Hp and 7.5 Hp Aqua DDM units

• Assume we use the 5 Hp DDM unit = 8,760 r lb/ sec2 momentum value

• Hp/ Kr3 = 0.2308 or 30.8 Hp/ MG – Aqua recommends 30 Hp/ MG for MLSS applicaSons

November 18, 2014

AQUA AEROBICS

• Aqua bases their claims for mixing based upon operaSon of about 1,000 SBR systems using an anoxic fill cycle

• While we do not have direct confirmaSon of their SBR performance, they are similar mixing demands

November 18, 2014

NITRATE AND SOLUBLE COD PROFILE

Nitrate and Soluble COD Profile 2/16/2009

0.4

10.97.8 8.0 7.7 6.4

36.8

11.6 10.0 8.5 10.06.2

0.05.0

10.015.020.025.030.035.040.0

AN Eff MLR AX1 Eff AX2 Eff AX3 Eff Final Eff

Location

Con

cent

ratio

n, m

g/L

NO3-N

COD

November 18, 2014

NITRATE AND BIODEGRADABLE SOLUBLE COD PROFILE

Nitrate and Biodegradable Soluble COD Profile 2/16/2009

0.4

10.98.72 7.8 8.0 7.7 6.4

30.6

5.4

10.4

3.8 2.3 3.80.0

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

AN Eff MLR AN Eff+MLR AX1 Eff AX2 Eff AX3 Eff Final Eff

Location

Con

cent

ratio

n, m

g/L

NO3-N

COD

November 18, 2014

NITRATE REMOVAL

• Soluble COD consumed in first Anoxic Cell

• DenitrificaSon in Cells #2 and #3 is driven by endogenous oxygen demand

•  It rained the night before tesSng began •  Incoming carbon affected by fermentaSon in the sewer – high sewer flow strips off slime

• Mixing versus denitrificaSon rate was inconclusive because of insufficient carbon

November 18, 2014

WILO/ EMU MIXERS

• Wilo was in for a presentaSon and I gave them the same tank volume used in the previous examples and asked for their mixing recommendaSons

• Basin Volume 19,490 r3

• They responded with 4 different mixer sizings but provided impeller diameter, RPM, direct pumping and power data on each mixer selecSon

November 18, 2014

INVENT MIXERS

•  Just received sizing informaSon for St Cloud

• Data include pumping rate, dia impeller, RPM and power draw

• Calculated Np and Nq values for two different INVENT impeller sizes

November 18, 2014

THRUST

• Per meeSng with Flygt Momentum = Thrust

• The momentum generated by the mixer pumping the fluid can be measured by the thrust (force) generated by the mixer on the mixer mounSng

November 18, 2014

INVENT MIXERS

Impeller Dia, ft

RPM Hp gpm Np Nq Thrust, Newtons

6.558 22 1.4 44,205 0.952 0.663 2,031

7.55 18 1.5 54,985 0.949 0.642 2,729

November 18, 2014

COMPARISON TO AXIAL FLOW MIXER – MATCHED FLOWRATES – LOW INTENSITY

Imp Dia, ft

RPM Hp gpm Thrust, Newtons

Invent 7.03 12 0.32 29,702 849

Axial 7.5 12 0.82 29,730 857

November 18, 2014

COMPARISON TO AXIAL FLOW MIXER – MATCHED FLOWRATES – HIGHER INTENSITY

Imp Dia, ft

RPM Hp gpm Thrust, Newtons

Invent 7.25 15 0.73 40,723 1,302

Axial 8.33 12 1.4 40,781 1,306

November 18, 2014

ANOXIC ZONE CELL #1 SAMPLE LOCATIONS

Anaerobic Cell #3 First Anoxic ZoneFlow to Anoxic Cell #1 Cell #1

6 7 1

43

2

5

MLSS Recycle FlowFrom Ditch thru

deniter gate

November 18, 2014

ANOXIC ZONE CELL #1 MLSS PROFILE

3 6 9 121

3

5

7

3,200

3,250

3,300

3,350

3,400

3,450

3,500

MLSS, mg/L

Depth, ft

Location

1234567

Largest VariaSon -‐ 125 mg/L 3.65% variaSon

Anoxic Cell #1 Mixer Speed 28 rpm

November 18, 2014

ANOXIC ZONE CELL #1 MLSS PROFILE

3 6 9 121

3

57

3,100

3,150

3,200

3,250

3,300

3,350

3,400

3,450

3,500

3,550

MLSS, mg/L

Depth, ft

Location

1234567

Largest VariaSon -‐ 290 mg/L 8.63% variaSon

Anoxic Cell #1 -‐ 16 rpm

November 18, 2014

M

l 

Anoxic Cell #2 Mixer at 8 rpm. NoSce MLSS floc size and some clear liquid zones

Anoxic Cell #3 Mixer at 16 rpm. More uniform floc at surface

November 18, 2014


November 18, 2014

COMPARISON TO AXIAL FLOW MIXER

• Thrust calculaSon very much influenced by assumpSon of radial flow area

• Area of flow is not as straight forward as for Axial downpumpers

•  I first assumed a 1 r width of flow off of the radial end of the impeller. Velocity was higher than axial flow so thrust was higher.

•  Increased width of flow Sll thrust matched and got a 2.5 to 3 r band between the two units

November 18, 2014

COMPARISON TO AXIAL FLOW MIXER -‐ CONCLUSIONS

• Match direct flow pumping rate

• Hp sizing is in the same range and much lower than other mixers

• Must seple flow area issue to be able to compare on a thrust basis

November 18, 2014


l  At 80% mixer speed based on the Rogers data, the comparison between the top entering mixer, Flygt mixer, Aqua DDM mixer and Wilo mixer

looks reasonable. l  The key is to set the right reference point for

level of mixing for the calculaSon of the pumping rate from the top entering mixer.

November 18, 2014


l  Top entering mixer design should always use a large impeller turning at not more than 15 RPM.

l  This approach produces a low power consumpSon design

l  Opportunity for mixing energy to impact denitrificaSon rate requires a facility with plenty

of excess carbon.

November 18, 2014


l  This approach will level the playing field for the various mixer types.

l  Invent is radial pumping versus axial pumping and unSl we get field data on the area of flow off the edge of the impeller we should compare it to

the axial pumpers based upon direct flow.

November 18, 2014

MIXER DESIGN UNKNOWNS

l  The issue of shear and floc size reducSon is sSll up in the air.

l  For floc shearing rather than mix the whole zone at a higher energy input should we focus agitaSon in a small

area and rip the floc apart? l  Is VFA/ BOD uptake/ absorpSon fast enough to allow a

shear zone to be effecSve?

November 18, 2014

MIXER DESIGN RESEARCH

l  SSll need to look for opportunity or do this in lab, to explore mixing energy versus denitrificaSon rate.

l  Keep rbCOD constant and nitrate constant and vary mixing energy

l  Use same mixing energies and vary starSng rbCOD to see which has bigger impact – Carbon or energy

November 18, 2014

ANOXIC ZONE CELL #1 – TOUGHEST MIXING APPLICATION

• Surface entry from Anaerobic Zone Cell #3

• MLSS recycle up to 4 Smes influent – full depth

• Both flows are opposing

Anaerobic Influent

MLSS Recycle

November 18, 2014

DENITER GATE

• Gate controls MLSS recycle

• 3 r wide channel, 18 r deep

MLSS Recycle

Ditch flow to aerator

newtons(–more(than(just(agreat( 18,2014 snack ......2 6 #5 #1 8 6 point #5 submergence, point #1...

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