IX Maintenance and Troubleshooting 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 >10°C may affect resin operating capacity
(WAC & WBA particularly sensitive to low temperature) High temperature decreases silica removal.
Maintenance -Record Keeping 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 µS/cm. •
If the volume > 1.5 times the value for new resins, fouling or crosscontamination may have occurred and a cleaning should be made.
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
Maintenance -Monitor output • Conductivity • pH • Silica
• Throughput • Flows • Unusual incidents • Check rinse water consumption ~ every 15 cycles (for resin fouling)
DI Run Length vs. River Conductivity
700
230 220
600
)
3
210 500
m ( e 400 m u l o 300 V
200 190 180 170
200 160 100 0 Apr'93
150
Jun'93
Aug'93
DI Runs
Oct'93
Dec'93
Feb'94
140 Apr'94
River Conductivity
C o n d u c t i v i t y ( µ S / c m )
DI Run Length vs. River Conductivity
700
230 220
600
)
3
210 500
m ( e 400 m u l o 300 V
200 190 180 170
200 160 100 0 Apr'93
DI Runs
C o n d u c t i v i t y ( µ S / c m )
150
Jun'93
Aug'93
Oct'93
River Conductivity
Dec'93
Feb'94
140 Apr'94
Conductivity* DI Run Length (/1000)
Maintenance -Monitor output A n io
SAC y t i d i c A l a r e n i M e e r F
n e ff lu
Free Mineral Acidity e n
2 R’H + Ca++
R2Ca + 2 H +
d
n
R’H + Na+
R’Na +
ti
2 R’Na + Ca++
R2Ca + 2 Na+
c
t o u c v it y
H+
N a le
pH a k a
Na (anion effluent conductivity) End of rinse
Production run
Bedvolumes
e
g
In effluent: • H+ = key cation until exhaustion • All anions still present
Breakthrough
As exhaustion approaches, • • • •
[Na] increases. Free Mineral Acidity (FMA) e.g. HCl, H 2SO4, 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.
Maintenance -Monitor output 120
12 pH
60
120
12 pH
60
SBA
SBA 100
100
10
10 pH
pH 80
m c40 / S
a 60 c i l i S
y t i v i t c u d n o C20
L / g
40
4
Silica
20
0
µ
µ
6
Conductivity (increase due to acids)
0 End of rinse
Production run
If SBA breaks first => H2SiO3 , etc. in effluent
R’’OH + Cl –
R’’Cl + OH –
2 R’’OH + SO 4=
R’’2SO4 + 2 OH –
R’’OH+ HSiO3 –
R”SiHO3
2R”SiHO3 + SO4=
R’’2SO4 + HSiO3 –
2 Bedvolumes Breakthrough
a 60 c i l i S
40
y t i v i t c u d n o20 C
6
4
Silica
20
0
0
8
S
L / g
µ
µ
m 80 / c40
8
Conductivity (increase due to NaOH)
0 End of rinse
Production run
2 Bedvolumes
0
Breakthrough
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 + + OHH2O • 1st anion to break through = HSiO3 –
Monitoring Conductivity - Not Enough •
Silica being a weak acid does not have as high a conductance as Na
Silica, ppb
Conductivity, µS/cm
Sodium, ppb
Conductivity, µS/cm
10
0.0548
0.01
0.0548
40
0.0549
1
0.0550
160
0.0553
10
0.12
640
0.0566
100
1.1
1000
0.0576
1000
10.9
Monitoring pH pH out of each bed in a pretreatment system can give critical info especially when troubleshooting •
Weak Acid Cation Bed • • •
•
Cation Bed • •
•
Should be low <3 (depends on TDS) – understanding baseline is important Change upward from typical baseline pH indicates increase in cation leakage, should correspond to higher conductivity and pH out of anion resin
Weak Base Anion Bed • •
•
Should be low <4 for 10-30% of the run (depends on FMA) Will baseline at ~ 4.5 Change upward from 4.5 indicates breakthrough
Should be between 4 and 7 depending on alkalinity Drop in pH from baseline indicates exhaustion or channeling
Strong Base Anion Bed • • •
Should be between 7.5 and 9 Below 7 indicates exhaustion or channeling Higher than 9 indicates chemical hideout, leaky NaOH valve, or problem with SAC resin
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
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
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
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% – < 85 %
•
Increase testing; Plan to replace within ~12 months
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 CH3
CH3 N+ CH2 CH
Anion resin
3
CH2 CH2
CH2 CH2
CH2
O
CH3 N+ CH3 CH3 OO C
CH3 N+ O- CH CH3 3 O
C CH2
NH2 CH2
O O
CH2 CH2
O CH2
CH3
Organic acid
•
Symptoms: – Long rinse to conductivity – Reduced throughput to silica endpoint
O
C
O-
Effects of organic fouling Problems in plant operation •
During anion regeneration with NaOH – convert to -COONa
•
Rinse is long
•
Na leakage increases
•
SiO2 leakage increases
•
Capacity decreases
•
Moisture content decreases
60 50 SBA resin rinse
40
m c30 / S µ20
Long rinse
10
OK
0 0
2
4
6
8 10 12 14 16 18 20
Bedvolumes
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 50°C
•
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 CaSO 4 – 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? Anion Resin Surface
Cl
SO4
Surface Foulant negative charge
+ + + + +
+
+
++
++ + +
Anion Exchange Resin Bead
MTC Test Concept •
Flow through column test
•
Run on MB at flow rate simulating CPP, 50 gpm/ft 2 (120 m/h)
•
Bed depth set to get measurable leakage for new resin
•
Challenge the MB with inlet containing SO 4
•
Measure SO4 leakage (cation conductivity)
•
Calculate SO4 MTC using conditions of test – Be sure to include anion resin particle size
•
Now a standard test: – A S T M t e s t m e t h o d , D 6 3 02 -9 8
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, don’t wait for a major problem – Investigate possible causes of trend - We can help – Send resin samples to Dow for analysis