Drexel UniversityProf. Young I. Cho

April 2005choyi@drexel.edu

Physical water treatmentsin recirculating open cooling water system

2

The objective was to investigate

the efficiency of PWT technologies in preventing and controlling fouling

on heat transfer surfaces

in circulating open cooling-tower water systems.

3

Fouling Costs for Several Countries

0.154364New Zealand

0.15309463Australia

0.251,0002,500United Kingdom

0.251,9504,875Germany

0.254,00010,000Japan

0.255,67014,175United States

Fouling as % of

GNP

1992 GNP(billions U.S.

dollars)

Fouling in costs(million U.S.

dollars)

Country

Data from www.cpe.surrey.ac.uk/dptri/hms/fouling.htm

4

Objectives of the ASHARE research

To investigate the efficiency of physicalwater treatments (PWT)

1. To increase the cycle of concentration– water saving

2. To reduce fouling resistance – energy saving

5

Physical water treatment

• Permanent magnets• Solenoid coils • Electrostatic device• Catalytic alloys• Others

– (sudden pressure drop, vortex flows)

6

Permanent magnets

(Side view)

Flow

N S S N N S

(Cut view)

7

Solenoid-coils

Flow

Control Unit

Pulsating current

Solenoid coil

8

Electrostatic device

9

5 COC w/o EAF 5 COC w/EAF Make-up

a1 a2 a3 a4 a5

Conductivity (µS/cm) 450 2040 2150 2100 2150

pH 7.2 8.1 8.2 8.0 8.2

Calcium (mg/L) 150 520 512 558 544

Magnesium (mg/L) 50 244 240 234 236

Total hardness(mg/L) 200 764 752 792 780

Total alkalinity (mg/L) 78 176 188 180 188

Chloride (mg/L) 73 382 408 390 404

Langelier Saturation Index

(at 59oC) 0.36 2.02 2.1 1.95 2.1

Hard Water in a cooling tower

10

What is fouling in a heat exchanger?

Crystallization Fouling• Produce hardened scale deposits • Difficult to remove; need acid wash.

Particulate Fouling• Produces soft sludge scale coating • Can be removed if flow velocity is large.

+

-

+ -

+

-

+

-+

-+

-

+-

+

-

+

-

+-

++

+

-

++ -

+

-

11

Physics LawFouling in

Heat Exchanger

WaterChemistry

Challenges in physical water treatment

12

Proposed Mechanism of PWT for the Mitigation of Mineral Fouling

Bulk precipitation

13

Physical Laws behind PWT

• Permanent magnet - Lorentz force. E = V x B

• Solenoid coil - Faraday’s law:

E ds B dAt∂

⋅ = − ⋅∂∫ ∫

14

+–

Square wave current

∫∫ ⋅∂∂

−=⋅ ABsE dt

d

Faraday’s law

E = V x B

Lorentz force

-3

-2

-1

0

1

2

3

1 1.5 2 2.5 3

Time (msec)

Indu

ced

elec

trom

otiv

e fo

rce

(mV

)

B1

V

E1 = V x B1 B2

V

E2 = V x B2

flow

magnetic field perpendicular to flow

magnetic field changes direction E1

E2

+

–

Solenoide

Magnets

Physical Water Treatments

+–

15

Bulk precipitation

• External magnetic or electric fields precipitate mineral ions and form clusters in water.

• Clusters grow in size

• Particulate fouling soft sludge coating

• If sufficient flow velocity, the soft sludge coating is removed.

• Mineral fouling is mitigated.

16

The scope of the research

All tests were conducted with a biocide.

Determination of fouling resistance

Investigation of scale characteristics

Water Analysis

time-dependent images

SEM

X-ray diffraction

historical behaviors

scale characteristics

LSITitration

Heat transfertest

17

Acrylic cylinder

Compressed airCirculating water in

Circulating water to cooling tower via test

section

FillsPlastic wire

ball

Makeup water in

Air out with moisture

Solenoid valve

Float ball valve Signal in

Rectangular polyethylene tank

blowdown

Centrifugal fan

Air in

Laboratory Cooling Tower

18

Fouling Test Facility

Blowdown

Solenoid

Cooling tower

Make-up water

Microscope

Monitor & VCR

Hot side channel

24 kW water heater

Hot water to drain Hot water

Insulation

Copper plate

Circulating cooling water

Flow controller

Conductivitymeter

valve

Pump

flow

Air

Fan

Cold side channel

Floating valve

CCDcamera PumpPWT

device

Flow controller

HT test section: velocity = 1.2 - 1.5 m/s

19

Conductivity control and test procedure

Conductivity (µS/cm)

w/o PWT w/ PWTbefore test

410

1990

a1

a2 a3 a4 a5

Time

2990b2 b3 b4 b5

3990 c2 c3 c4 c5

20

Heat transfer test section

21

inifouledf U

1U

1R −=

ciophoip TTcmTTcmQ )]([)]([ −=−= &&&

⎥⎥⎦

⎤

⎢⎢⎣

⎡

−−

−−−=∆

)()(

ln

)()(

,,

,,

,,,,

icoh

ocih

icohocihlm

TTTT

TTTTT

lmTAQU∆

=&

Fouling resistance

Overall heat transfer coefficient

Log-mean-temperature-difference

Energy balance

Calculation of Fouling Resistance

Test Results with Permanent Magnets

23

0.0E+00

2.0E-05

4.0E-05

6.0E-05

8.0E-05

1.0E-04

1.2E-04

1.4E-04

1.6E-04

0 50 100 150 200

Time (hours)

Foul

ing

Res

ista

nce

(m2 K

/W)

MWT-2.0 m/s

MWT-4.0 m/s

MWT-6.3 m/s

MWT-8.5 m/s

No treatment

2637

43

57 %

Permanent Magnet Test Results

24

Fouling resistance Rf (permanent magnet-1)

-2.0E-05

-1.0E-05

0.0E+00

1.0E-05

2.0E-05

3.0E-05

4.0E-05

5.0E-05

6.0E-05

0 50 100 150 200 250 300

Time (hour)

R f (m

2 K/W

)

No-treatmentPWT_V=2.3 m/sPWT_V=1.1 m/sPWT_V=1.7 m/sPWT_V=3.0 m/s

25

33

42

80%

(Side view)

Flow

N S S N N S

(Cut view)

25

Water quality data

2313.92015.15.7Silica, Total, as SiO2, ppm

0.60.90.90.61.2PO4, Ortho, as PO4

12213412612939Sodium, as Na, ppm

<0.05<0.05<0.05<0.05<0.05Iron, Total, as Fe, ppm

0.330.260.240.28<0.05Copper, Total, as Cu, ppm

24827128425858Magnesium, Total, as CaCO3, ppm

508581560565126Calcium, Total, as CaCO3, ppm

757853845824185Hardness, Total, as CaCO3, ppm

36941035638581Chloride, as Cl, ppm

23118431419554Sulfur, as SO4, ppm

19422918922870Alk, “M” as CaCO3, ppm

08.33.600Alk, “P” as CaCO3, ppm

1970203020101990525Sp Cond @ 25C, µmhos

8.48.38.48.37.7pH

PMSM V=3.0m/s

PMSM V=2.3m/s

PMSM V=1.7m/s

PMSM V=1.1m/s

MakeupBefore filtration

26

Percentage variations of Rf vs. flow velocity (through PM)

202530354045505560

0 2 4 6 8 10

Flow velocity (m/s)

Red

uctio

n of

foul

ing

resis

tanc

e (%

)

20

30

40

50

60

70

80

90

0 1 2 3 4

Flow velocity (m/s)

Red

uctio

n of

foul

ing

resis

tanc

e (%

)

27

Fouled surfaces after tests

No- treatment

Flow

Water Channel

PM-2.3 m/s PM-3.0 m/s

PM-1.7 m/s

28

SEM photographs: 3000x

No Treatment

29

SEM photographs: 3000x

PM-2.3 m/s

30

X-ray diffraction measurements of scale deposits

0

1000

2000

3000

4000

10 20 30 40 50 60 70 80 90Diffraction Angle, 2θ (deg.)

Inte

nsity

(cps

)

No treatment_2000No-treatment

0

1000

2000

3000

4000

10 20 30 40 50 60 70 80 90Diffraction Angle, 2θ (deg.)

Inte

nsity

(cps

)

PMD treatment_2000PWT – 2.3 m/s

0

1000

2000

3000

4000

10 20 30 40 50 60 70 80 90Diffraction Angle, 2 θ (deg.)

Inte

nsity

cps

)

Aragonite

Baseline

0

1000

2000

3000

4000

10 20 30 40 50 60 70 80 90

Inte

nsity

(cps

)

Calcite

Baseline

Diffraction Angle, 2θ (deg.)

31

COC effect (permanent magnets-2)

-2.0E-05

-1.0E-05

0.0E+00

1.0E-05

2.0E-05

3.0E-05

4.0E-05

5.0E-05

6.0E-05

7.0E-05

0 50 100 150 200 250 300

Time (hour)

Rf(

m2

K/W

)

84 %

2,000 µS/cm

-1.5E-05

-5.0E-06

5.0E-06

1.5E-05

2.5E-05

3.5E-05

4.5E-05

5.5E-05

6.5E-05

0 50 100 150 200 250

Time (hour)

Rf(

m2

K/W

) 57 %

3,000 µS/cm

40 %

-2.0E-05

-1.0E-05

0.0E+00

1.0E-05

2.0E-05

3.0E-05

4.0E-05

5.0E-05

6.0E-05

0 50 100 150 200 250

Time (hour)

Rf(

m2

K/W

)4,000 µS/cm

Flow

N S S N

N S S N

32

Need for multiple magnets: Rf vs. time

-2.0E-05

-1.0E-05

0.0E+00

1.0E-05

2.0E-05

3.0E-05

4.0E-05

5.0E-05

6.0E-05

7.0E-05

0 50 100 150 200 250 300

Time (hour)

Rf (

m2 K

/W)

No treatmentType II-AType II-B

84%

5%

2,000 µS/cm

(a) Type II-A

(b) Type II-B

N S

N S

N NS SN NS S

N NS SN NS S

Ring magnet

Permanent magnet-3

33

Effects of strength and frequency

-5.0E-05

0.0E+00

5.0E-05

1.0E-04

1.5E-04

2.0E-04

2.5E-04

3.0E-04

3.5E-04

4.0E-04

4.5E-04

0 50 100 150 200

Time (hour)

R f (m

2 K/W

)

SCED-0.7A,3.5 kHzSCED-7.0A,3.5 kHzSCED-0.7A,0.5 kHzNo-treatmentSCED-7.0A,0.5 kHz 33

20

53%

No-treatmentSCI-0.7A, 0.5kHzSCI-0.7A, 3.5kHzSCI-7.0A, 0.5kHzSCI-7.0A, 3.5kHz×

3,000 µS/cm

• Solenoid-coil device

Flow

Control Unit

Pulsating current

Solenoid coil

34

Why measure surface tension of water?

If PWT produces bulk precipitation, surface tension should decrease.

Results can be used as indirect support for the bulk precipitation hypothesis

35

Surface tension measurement method

Ruler

Water sample

Capillary tube

Positioning lift

36

Surface tension of water treated by solenoid coil

Hard water (3000 µS/cm)

0.06

0.062

0.064

0.066

0.068

0.07

0 1 2 5 10 30

No. of pass through solenoid-coil

Surf

ace

tens

ion

(N/m

)

37

Computer-controlledMicro-syringe pump

Water sample

Needle

Dye

Camera

Dye-drop tests for surface tension effect

syringe

38

Dye-drop test: water treated by solenoid coil (3,000 µS/cm)

no-treatment (2) (10)

In untreated water, dye rapidly spread over.

In treated water,dye fell vertically.

39

Using Filtration Together With PWT

Using filtration together with descaling generates a synergetic effect.

40

Using Filtration Together With Descaling

100

200

300

400

500

600

700

Pre

ssur

e D

rop

(Pa)

0 4 8 12 16 20 24 28 32 36 40

Time (hr.)

No treatmentFilter only

EAFT+FilterEAFT only

Scientific validation was published in the International Journal of Heat and Mass Transfer.

No Treatment

Filtration Alone

Filtration Plus Descaling

Descaling Alone

41

Comprehensive Cooling Water Treatment Program

Chiller

Pump

Sump

Cooling Tower

PWT Unit

Biocontrol Unit

High Efficiency Filtration Unit

Side-stream Loop

42

Filtration for Particulate

Control

Mineral Fouling Control Bio-Control

System Monitoring &

Control

Water Treatment Program Areas

43

Conclusions

• Mechanism of physical water treatment (PWT).

– The PWT produces a bulk precipitation in water.

– As the solubility of treated water decreases inside HT equipment, the small seed particles grow in size, resulting in particulate fouling.

– If water flow can remove the soft sludge coating from HT equipment, then, the PWT can mitigate mineral fouling.

44

Remarks

Validation of your PWT device

The validating test service is available.