Investigations of High Service Pump Failure Events and ...

Investigations of High Service Pump Failure Events and Actions to Prevent Future Failures

Marvin Gnagy, P.E., PresidentPMG Consulting, Inc.

Hall of Fame WorkshopAugust 15, 2019


Failures of existing turbine pumps Initial investigations of water chemistryChlorine contact clearwell operationsOperating data investigationsChemical feed point relocationResults and follow-up SCADA tuning effortsChanges in operating procedures

Agenda

2


• 90 mgd capacity• 99 mgd high service

pumping capacity• Ferric sulfate and

sulfuric acid pretreatment in Actiflo

• Lime pH adjustment• Ozonation and

biological filtration• NaOH pH adjustment

and free chlorine disinfection

• Pump to Tampa Bay Water

• Further pH adjustment

• Ammonia feed for chloramination

Scaling Events and Pump Failures

3

Tampa Bay Regional Surface Water Treatment Plant


Tampa Bay Regional Surface Water Treatment PlantHigh services pump failures occurred about once a month during a 3-year period

Locked up pumps and tripped breakersVarious random failures all six pumps Periods where multiple high service pumps out of service reducing reliability for pumping operationsPlant staff did not see any unusual water quality resultsMaintenance could not determine any electrical issues, but did notice scale build-up and pump shaft and impellersLifted pumps out of service with crane, had pump cleaned and rebuilt periodically with new bearingsAnnual maintenance and cleaning was costing about $75,000


4


Appeared to be direct correlations between water quality changes and scaling events that led to pump failures during 2015-2017

High alkalinity and high calcium levels with associated pH levels greater than 7.9 appeared to result in elevated LSI and CCPP valuesWater quality changes likely resulted in scale development

Pump scale analyzed at Bowser -Morner as predominantly CaCO3

Scale deposited on pump impeller and rotating components causing pump failure


5


Events in 2017 placed multiple pumps out of service at the same time

Reduced reliability of pumping operations and pumping capability35 events reported over 2015-2017

Temporary relocation of NaOH feed did not resolve the scaling issues

Moved about 20 feet upstream of weir wall

Secondary relocation of NaOH accomplished in October 2017

Moved 280 feet upstream of pumpsSince this chemical feed relocation no scaling events have occurred


6


Cursory review of water quality data did not reveal abnormal water qualityThree separate pump failure events reviewed in more detail during fall periods of similar water temperature

Water quality data reviewed 2015 - 2017Water pHChloridesSulfatesAlkalinityCalciumEquilibrium pH and AlkalinityLSICCPPBayliss curveCSMR (lead and copper impacts)

Scaling Period Evaluations

7

Some scale dissolved in acid, but minor


• Previous cleaning of scale at weir wall (after 6 years of operation)

• Scale 12-inches thick in some locations

• NaOH discharge lines completed blocked off


8


Monitoring of individual high service pump discharges Random increased pH up to 9.2 Scaling potential increased according to pH levels Possible channeling of NaOH feed depending on pumps operating Appeared that about 4 days of high pH induced scale build-up and

consequently pump failure Switching pumps slowed scale build-up, but failures kept occurring Water velocity known to impact CaCO3 scale deposits


9


Chlorine Contact Clearwell Operations

10



11

NaOH fed downstream of weir wall and about 52 feet upstream of high service

pumps



12

NaOH initially fed downstream of weir wall

and about 52 feet upstream of high service pumps

pH monitored before NaOH feed and after high

service pumps


Average chemical feed travel time to high service pumps less than one (1) minute at 70 mgd

NaOH/calcium reaction in water complete and reaches equilibrium after about 3 minutes to 4 minutesLikely chemical reactions occurring in pump suction and rotating impeller causing scale deposits (highest water velocity areas)Scale deposition increases pump friction and amp draw resulting in pump overheating leading ultimately to pump failure and tripped breakers


13


Investigations of operating data and water quality were made to:

Identify possible cause(s) of scale formations leading to pump failuresDefine water quality parameters that result in pump scalingDevelop means to reduce or eliminate pump scaling issuesEstimate water quality parameters and operating conditions to reduce or eliminate pump scalingImprove high service pump reliability

Data Investigations

14


2015 Pump Failures - LSI

15

0.30

0.33

0.35

0.38

0.40

0.43

0.45

0.48

0.50

0.53

0.55

0.58

0.60

0.63

0.65

0.68

0.70

7.75 7.80 7.85 7.90 7.95 8.00 8.05

Lang

elie

r Ind

ex

Finished Water pH, s.u.

Pump 2 locked up due to scale

10/7/15

October 1 - 10, 2015


2015 Pump Failures - CCPP

16

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

8.5

9.0

7.75 7.80 7.85 7.90 7.95 8.00 8.05

CC

PP,

mg/

L as

CaC

O3


October 1 - 10, 2015


10/7/15



17

0.100.130.150.180.200.230.250.280.300.330.350.380.400.430.450.480.500.530.550.580.60

7.60 7.65 7.70 7.75 7.80 7.85 7.90 7.95 8.00 8.05 8.10 8.15 8.20 8.25 8.30 8.35 8.40

Lang

elie

r Ind

ex



10/24/16

October 18 - 27, 2016



18

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.60 7.65 7.70 7.75 7.80 7.85 7.90 7.95 8.00 8.05 8.10 8.15 8.20 8.25 8.30 8.35 8.40

CC

PP,

mg/

L as

CaC

O3


October 18 - 27, 2016


10/24/16



19

0.000.020.040.060.080.100.120.140.160.180.200.220.240.260.280.300.320.340.360.380.400.420.440.460.480.500.520.540.560.580.60

7.75 7.80 7.85 7.90 7.95 8.00 8.05 8.10 8.15 8.20

Lang

elie

r Ind

ex


Pumps 4, 5, 6 locked up due to

scale 9/20/17Pump 6 locked up due to scale

9/26/17

September 20 - 30, 2017



20

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

7.75 7.80 7.85 7.90 7.95 8.00 8.05 8.10 8.15 8.20

CC

PP,

mg/

L or

pH

eq, s

.u.


Pumps 4, 5, 6 locked up due to

scale 9/20/17

September 20 - 30, 2017


9/26/17


Information suggested insufficient reaction time between chemical feed and pumping operations

NaOH reacting with calcium producing CaCO 3like softening treatmentIncreased reaction time with relocation of chemical feed for pH adjustment might helpPossibly convert to lower strength NaOH to improve mixing into solution

Data suggested water pH target needs to be more closely matched with alkalinity and calcium parameters

Limit LSI and CCPP based on inlet water qualityPossibly suggest new target values for water pH, LSI, and CCPP to control pump scaling

Data Analysis

21

Previous scale build-up at weir wall


Needs for additional reaction time identified to reduce pump scaling issuesRelocated NaOH feed well upstream of weir wall in Pass 4 of the chlorine contact clearwell

Existing access hatch used as feed point location, added 280 feet of channel for reaction time

Chemical feed lines rerouted to new feed point

Diaphragm valves and rotameters used to control feed ratesPressure relief issue identified due to closed feed system

Pressure relief setting adjusted accordingly

Chemical Feed Relocation

22



23

Base feed point at access hatch

NaOH travel path through pass 4

and pass 5



24


Trim feed point at sample pumps



25


Trim feed point at sample pumps

pH monitored before NaOH feed and after high

service pumps

NaOH detention time at 70 mgd – 2.8 minutes


Scale formations appeared to be on bottom of clearwell rather than in the pumps (April 2018)In operation since October 11, 2017

No pump failures due to scaling since October 2017

Additional work suggested for permanent installation

Potential pipe loop and dosing control valvesPotential conversion to 25% caustic sodaSCADA fine tuning during backwashAdditional pH monitoring upstream of new chemical feed pointMore frequent CCC cleaning to remove scaleFinalization of CCC CT calculations (secondary barrier and future back-up)


26

NaOH feed line

Water flow



27

6.40

6.60

6.80

7.00

7.20

7.40

7.60

7.80

8.00

8.20

8.40

8.60

8.80

9.00

9.20

1115 1215 1315 1415 1515 1615 1715

Wat

er p

H, s

.u.

Time Intervals

Intermediate pH Finished pH

Stabilized finished water pH at 70 mgd production

74 mgd production to

fill clearwell for backwash, pH

stable

Filter backwash,pH spiked then

quickly stabilized to established

Initial feed adjustment at

11:20 am

October 2017



28

6.40

6.60

6.80

7.00

7.20

7.40

7.60

7.80

8.00

8.20

8.40

8.60

8.80

9.00

9.20

1115 1215 1315 1415 1515 1615 1715

Wat

er p

H, s

.u.

Time Intervals

Intermediate pH Finished pH

Stabilized finished water pH at 70 mgd production

74 mgd production to

fill clearwell for backwash, pH

stable

Filter backwash,pH spiked then

quickly stabilized to established

Initial feed adjustment at

11:20 am

6 hours for clearwell pH and finished pH to converge



29R² = 0.9906

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

6.90 7.00 7.10 7.20 7.30 7.40 7.50 7.60 7.70 7.80 7.90

Hyd

raul

ic D

eten

tion

Tim

es P

rodu

ced

Intermediate Water pH, s.u.

Hydraulic retention suggested adequate reaction time to produce stable water pH under laminar flow

conditions

140 detention times to reach

steady state


Notable pH spikes observed during backwash cycles

Backwash pump draws significant flow from production for filter washesSignificant reduction in flow to CCC during backwashNaOH feed was not altered for the changes in flow to the contact clearwells (flow pacing based on high service production)Resulted in a slug of NaOH that created a spike in pH after backwashpH spikes may contribute to pump failures due to scaling

SCADA Backwash Fine Tuning

30


Backwash Fine Tuning of SCADA

31

Initial trial with

NaOH at access hatch

spikes during backwash cycles up to

0.6 pH units



32

pH dip during backwash cycles up to 0.4 units with NaOH

turned off during backwash



33

pH dip during backwash cycles up to 0.25 units with NaOH speed at 50% and 2-minute offset from

backwash cycle



34

pH more consistent during backwash cycles – NaOH speed at 70%

and 2-minute offset from backwash cycle



35

y = 0.000167x2 - 0.033274x + 1.685889R² = 0.997053

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

30.0%

35.0%

40.0%

45.0%

50.0%

55.0%

60.0%

65.0%

70.0%

40 50 60 70 80 90 100

NaO

H S

peed

Red

uctio

n D

urin

g B

ackw

ash

Finished Water Flow, mgd



36

y = 0.000167x2 - 0.033274x + 1.685889R² = 0.997053

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

30.0%

35.0%

40.0%

45.0%

50.0%

55.0%

60.0%

65.0%

70.0%

40 50 60 70 80 90 100

NaO

H S

peed

Red

uctio

n D

urin

g B

ackw

ash

Finished Water Flow, mgd

28% NaOH speed reduction during backwash at 60 mgd

production rate. Flow pacing now enabled according to flow

being treated.



37

Insignificant pH variations during

backwash


CT compliance generally met in ozone contactorsCT reviews for chlorine contact clearwell made as secondary barrier and as back-up

Revised clearwell volume based on relocated NaOH feed pointVerified state approved baffling factorDeveloped CT model with new configurations to determine worst -case scenarioModel predictions meet CT if ozone contactor out -of-service

Review of CT Calculations

38



39

Proposed disinfection areas in blueProposed pH adjustment with NaOH relocation in red



40

2

99 34,373 7.00 20.0 7.5 2.80 11.6 30.1 2.58

PEAK HOURLY TREATMENT FLOW EACH

CHAMBER, gpm

HIGHEST WATER pH

LOWEST WATER TEMP.

oC

CALCULATED CT mg/L-minutes

REQUIRED CT FROM TABLES

mg/L-min.

CHLORINE CONTACT

CHAMBER FREE CHLORINE CONC. mg/L

PLANT PRODUCTION

RATE, mgd

TAMPA BAY REGIONAL SURFACE WATER TREATMENT PLANTCT CALCULATIONS MODEL FOR CHLORINE CONTACT CHAMBERS

Chlorine contact chambers in service (1 or 2)

LOWEST CHLORINE CONTACT CHAMBER

OPERATING LEVEL, ft.

CT RATIO

CT model developed for Tampa Regional plant


1

99 68,746 7.00 20.0 7.5 2.80 11.6 15.0 1.29

PEAK HOURLY TREATMENT FLOW EACH

CHAMBER, gpm

HIGHEST WATER pH

LOWEST WATER TEMP.

oC

CALCULATED CT mg/L-minutes

REQUIRED CT FROM TABLES

mg/L-min.

CHLORINE CONTACT

CHAMBER FREE CHLORINE CONC. mg/L

PLANT PRODUCTION

RATE, mgd

TAMPA BAY REGIONAL SURFACE WATER TREATMENT PLANTCT CALCULATIONS MODEL FOR CHLORINE CONTACT CHAMBERS

Chlorine contact chambers in service (1 or 2)

LOWEST CHLORINE CONTACT CHAMBER

OPERATING LEVEL, ft.

CT RATIO


41

CT model developed for Tampa Regional plant


Further Data Evaluations LSI

42

0.200.230.250.280.300.330.350.380.400.430.450.480.500.530.550.580.600.630.650.680.70

120 140 160 180 200 220 240 260 280

Lang

elie

r Ind

ex

Calcium, mg/L as CaCO3

Average Finished Water pH - 7.932015-2017

Apparent LSI to avoid pump failures


Further Data Evaluations CCPP

43

0.00.51.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.09.5

10.0

120 140 160 180 200 220 240 260 280

CCPP

, mg/

L as

CaC

O3


Average Finished Water pH - 7.932015-2017

Apparent CCPP to avoid pump failures


Data Evaluations LSI and Lower pH

44

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

120 140 160 180 200 220 240 260 280

Lang

elie

r Ind

ex


Finished Water pH average 7.75 or less

Apparent LSI to avoid pump failures


Data Evaluations CCPP and Lower pH

45

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

120 140 160 180 200 220 240 260 280

CCPP

, mg/

Las C

aCO

3


Finished Water pH average 7.75 or less

Apparent CCPP to avoid pump failures


Maintain finished water pH levels at 7.75 or lessTarget pH 7.5 to pH 7.75 Maintain LSI values less than 0.27 Maintain CCPP values less than 3.0 mg/L

Expected to nearly eliminate pump failures due to scale formations and improve high service pump reliability near 100%

Annual CCC cleaning suggested to remove scale from channels upstream of weir wall and pumpsInitial cleaning observed about 6 -inches of soft scale along floor and walls after 8 months of operation

Suggested Control Parameters

46


Conversion to 25% NaOH for treatmentImproved mixing in contact clearwell since specific gravity is closer to sodium hypochloriteCrystallization point is 1oF rather than 54oF (heat tracing not needed)No increase in costs (NaOH cost based on dry weight)

Costs verified by chemical supplierIncreased operating speed of the feed pumps (12% to 24%) and provided more reliability and flexibility in chemical feed75,000 gallons storage available

Projected usage at 75,000 gallons per month at 64 mgd

pH adjustment SOP re-written once details finalized

Suggested Control Parameters

47


Reduced target pH to no more than 7.75 LSI and CCPP continue to be monitored, but no longer a primary

goal

Converted to 25% NaOH Feed pump operating in nearer to middle capacity range

SCADA fine tuning maintaining water pH ±0.11 units SOP revised to target pH levels and operating conditions Discusses pump failures due to scale Discusses SCADA tuning to maintain pH during backwash Outlines target parameters to avoid pump scaling

Changes in Operating Procedures

48


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