IX Maintenance and Troubleshooting

Bill Carlin

Maintenance & Troubleshooting

Content

Maintenance

Record keeping Monitoring Vessel integrity Resin integrity

Resin analysis/Director services

Problematic Impurities

Maintenance

-Recordkeeping

Maintenance -Record Keeping

Changes in the following may affect running time or throughput :

Feed water composition:

Minor salinity increase: proportional reduce running time

x% more salinity means x% shorter cycle

Radical water composition changes: Re-assess whole plant

Feed water temperature:

Variations >10C may affect resin operating capacity

(WAC & WBA particularly sensitive to low temperature)

High temperature decreases silica removal.

5

Loss of capacity

After a long time in operation, gradual decrease of anion exchange resin capacity. May need to adjust running time or replace resin

Pressure drop

Pressure drops >2.5 bar (35 psi) should be avoided due to possible equipment or resin damage.

If the pressure drop in a vessel increases > 50 %, the resin should be backwashed to avoid channeling and resin damage.

Loss of resin replace immediately

Rinse water consumption

After regenerant injection, monitor the slow (displacement) rinse water volume required to reach 150 S/cm.

If the volume > 1.5 times the value for new resins, fouling or cross-contamination may have occurred and a cleaning should be made.

6

Maintenance -Record Keeping

Maintenance -Monitor Input

Feed water analysis & Temperature

Condition of the ion exchange resins

Resin height

Regenerant Conditions (level, concentrations, etc.)

Pretreatment Operating Data (residual Cl2, level of suspended solids, dosing chemical

consumption)

Maintenance log records routine maintenance, mechanical failures, equipment replacements,

calibration of gauges and meters, all IX cleanings

7

Conductivity

pH

Silica

Throughput

Flows

Unusual incidents

Check rinse water consumption ~ every 15 cycles (for resin fouling)

8

Maintenance -Monitor output

DI Run Length vs. River Conductivity

0

100

200

300

400

500

600

700

140

150

160

170

180

190

200

210

220

230

Apr'93 Jun'93 Aug'93 Oct'93 Dec'93 Feb'94 Apr'94

DI Runs River Conductivity

Volu

me (

m3)

Conductiv

ity (

S/c

m)

0

100

200

300

400

500

600

700

140

150

160

170

180

190

200

210

220

230

Apr'93 Jun'93 Aug'93 Oct'93 Dec'93 Feb'94 Apr'94

DI Runs River Conductivity Conductivity* DI Run Length (/1000)

DI Run Length vs. River Conductivity

Volu

me (

m3)

Conductiv

ity (

S/c

m)

Maintenance -Monitor output

11

As exhaustion approaches, [Na] increases. Free Mineral Acidity (FMA) e.g. HCl, H2SO4, HNO3, respectively decreases, with [Na

+]

pH at outlet of the SAC resin is low (2 to 4) until near exhaustion, then [H +] & pH Conductivity at the outlet of the SBA resin downstream reflects Na+ leakage from the

SAC resin: remains low until Na+ appear at the outlet of the cation column.

Production run

SAC

Fre

e M

inera

l A

cid

ity

An

ion

efflu

en

t co

nd

uc

tivity

Na

lea

kag

e

Bedvolumes

pH

Na (anion effluent conductivity)

Free Mineral Acidity

Break-through

End ofrinse

2 RH + Ca++ R2Ca + 2 H+

RH + Na+ RNa + H+

2 RNa + Ca++ R2Ca + 2 Na+

In effluent:

H+ = key cation until exhaustion All anions still present

12

End ofrinse

Production run

SBA

Co

nd

uc

tiv

ity

S/c

m

pH

Conductivity (increase due to acids)0

2

4

6

8

10

12 pH

0

20

40

60

0

20

40

60

80

100

120

Silic

a

g/L

Silica

Bedvolumes

Break-through

If SBA breaks first =>

H2SiO3 , etc. in effluent

End ofrinse

Production run

SBA

Co

nd

uc

tiv

ity

S/c

m

pH

Conductivity (increase due to NaOH)0

2

4

6

8

10

12 pH

0

20

40

60

0

20

40

60

80

100

120

Silic

a

g/L

Silica

Bedvolumes

Break-through

If SAC breaks first =>

NaOH, NaHSiO3 in effluent

In effluent:

H+ = key cation unless SAC breaks first giving Na leakage Key anion = OH- until exhaustion H + + OH- H2O 1st anion to break through = HSiO3

ROH + Cl RCl + OH

2 ROH + SO4= R2SO4 + 2 OH

ROH+ HSiO3 RSiHO3

2RSiHO3 + SO4= R2SO4 + HSiO3

Maintenance -Monitor output

Silica being a weak acid does not have as high a conductance as Na

Silica, ppb Conductivity, S/cm

10 0.0548

40 0.0549

160 0.0553

640 0.0566

1000 0.0576

Sodium, ppb Conductivity, S/cm

0.01 0.0548

1 0.0550

10 0.12

100 1.1

1000 10.9

Monitoring Conductivity - Not Enough

Monitoring pH

pH out of each bed in a pretreatment system can give critical info especially when troubleshooting

Weak Acid Cation Bed Should be low

Maintenance

-Vessel integrity

Vessel Integrity

-Unit Distributor Inspection

Inlet Distributor

Flow Must be Evenly Distributed Across Bed

No Bent or Incorrectly Aimed Laterals

Splash Plates Intact

Regenerant Distributor

Flow Must be Evenly Distributed Across Bed

No Bent or Incorrectly Aimed Laterals

Outlet Distributor

If the Inlet Distributor is in Good Condition an Uneven Bed Surface After the Service Run Indicates Lower Distributor

Blockage.

M-16

Examples of Channeling

Concave Convex Diagonal

M-15

Vessel Integrity -Unit Lining Inspection

Check Walls, Base and Top for Tears or Bubbles

Check Wherever Laterals Enter Vessel or Are Braced

Check Walls of Vessel in Vicinity of Regeneration Lateral for Bubbles Caused by Regenerant

M-17

Maintenance

-Resin integrity

Analytical testing of resin

The purpose is to:

Troubleshoot

Track resin condition

Determine if resin needs to be replaced

Examine resin condition SEPARATE from the operating unit

Look for changes from new resin

Make INTERPRETATIONS about performance

Courtesy of The Dow Chemical Co All

rights reserved.

Sampling

Sample after regeneration and rinse Pre-regeneration samples maybe necessary for troubleshooting but

not routine testing.

Core samples preferred

Not necessary for mixed bed samples

Use clean, plastic container

Tape lid onto container to avoid spilling during shipment

Label container with paper label

Sharpie right on plastic container can get smudged

Make up demin resin analysis

Water Retention Capacity (WRC)

Total Capacity

Cation Resin Total Weight Capacity

Anion Resin Strong, Weak, Total Capacity

Fe Loading on Cation Resin

Organic Loading on Anion Resin

Bead Integrity - WUB

CPP resin analysis

WRC

Total Capacity Cation Resin Total Weight Capacity

%H and Na form sites

Anion Resin Strong, Weak, Total Capacity %OH, HCO3, Cl, SO4 form sites

Fe and Cu Loading on Cation Resin

Anion Resin Kinetics/MTC

Bead Integrity WUB

Special Testing

Water retention capacity

Problem: SAC Increase > 3%

Cause: Oxidation (decrosslinking)

Symptoms:

Softening of the resin

Decrease in particle density

Increased pressure differential

High resin makeup

Organic fouling of anion resin

Source of SULFATE in feed to boiler!!!

Total capacity

Tells you:

How many sites are present per unit mass or volume

Does not tell you:

How long your runs should be

Whether or not the capacity is accessible

Whether or not the resin is being adequately regenerated

Total capacity

Problem: SBA: loss of > 20% Total Cap SBA: conversion to Weak Base

Cause: Loss of chemical functionality

WB: cannot remove silica

Symptoms:

Loss of operating capacity

Short runs

Site analysis

Cation - % Na, % H

Anion - %OH, %HCO3, %Cl, %SO4, etc.

Problems

High leakage

Low operating capacity

Causes

Poor Regeneration

Poor Separation

High Cl in NaOH

Physical integrity - Whole bead

Problem: Osmotic shock and physical attrition

Resin shrink and swell as they change forms

Osmotic stress on the resin is very strong

Shrink/swell too fast causes beads to break

Transfer to and from vessels causes physical attrition

WBA are particularly susceptible

Action Levels

85 to 90% Increase testing; Plan to replace within ~12 months

< 85 % Replace as soon as possible

Symptoms:

Loss of resin

Increased pressure drop

Channeling

High mixed bed Na leakage

RESIN ESCAPE: to next bed or to product

Separation problems in MB

Fouling/Precipitation (DI)

Types: Fe, Silica, Organic Compounds,

Calcium Sulfate, Barium Sulfate,

Mud, Dirt, Filth, Algae/Bacteria

Symptoms: Higher pressure drop

Channeling

Loss of operating capacity

Higher baseline leakage

Organic loading (DI)

Problem: Effective loss of Strong Base Capacity

Symptoms:

Long rinse to conductivity

Reduced throughput to silica endpoint

CH2

CH2

CH2

CH3

N+ N+

N+

CH2 CH2

CH2

CH3 CH3

CH3

CH3 CH3

CH3

CH3 CH3

OOO

O

CH2

CH2

CH2

NH2

CH2

CH2

CH3

O-

OC

O-OC

O-OC

Anion resin

Organic acid

Effects of organic fouling

During anion regeneration with NaOH

convert to -COONa

Rinse is long

Na leakage increases

SiO2 leakage increases

Capacity decreases

Moisture content decreases

Problems in plant operation

SBA resin rinse

0

10

20

30

40

50

60

0 2 4 6 8 10 12 14 16 18 20

BedvolumesS

/cm

Long rinse

OK

Poly-electrolyte fouling

Cationic or Anionic polyelectrolytes used in pre-treatment can be serious cause of resin surface fouling

Cationic polymers foul cation resin

See high leakage of Ca and Mg but not necessarily Na leakage

Not easy to detect by normal testing. Watch for the symptoms...

Recovering from fouling

SiO2

8% NaOH soak for at least 8 hrs

preferably at 50C

Natural Organic

10% NaCl/2% NaOH soak for at least 8 hrs

Repeat soaks may be necessary

Use frequently and routinely for high organic waters

Iron or CaSO4 10% HCl soak for at least 4 hrs

Repeat soaks may be necessary

Materials of construction must be compatible

Mass Transfer Coeficient (MTC)

Ion exchange processes are film diffusion limited

Measures the rate at which ions diffuse from the feed solution to the resin surface.

Reduction in MTC indicates resin fouling.

Why does anion MTC degrade with use?

35

+ +

+ +

+ +

+ + +

+ + + +

SO4

Cl

Anion Exchange Resin Bead

Surface Foulant

negative charge

Anion Resin

Surface

MTC Test Concept

Flow through column test

Run on MB at flow rate simulating CPP, 50 gpm/ft2 (120 m/h)

Bed depth set to get measurable leakage for new resin

Challenge the MB with inlet containing SO4

Measure SO4 leakage (cation conductivity)

Calculate SO4 MTC using conditions of test

Be sure to include anion resin particle size

Now a standard test:

ASTM test method, D6302-98

Take home message

Watch for the signs / trends

Your system will give warning signs before most major problems

Problems due to resin degradation typically develop over time

Sudden problems tend to indicate equipment issues or changes to feed water or regen conditions

Sample for resin analysis routinely

If you start to see a trend, dont wait for a major problem

Investigate possible causes of trend - We can help

Send resin samples to Dow for analysis

Thank You!

For more information please visit our web site or

contact your local Dow representative.

http://www.dowwaterandprocess.com/