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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/