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Improved Caustic Tower Operationby Complex System Evaluation
Hua Mo, David DixonBaker Hughes Incorporated
Sugar Land, TX 77478
Agenda
• Introduction of caustic tower
• Caustic tower fouling mechanism
• Identify caustic tower fouling mechanism
• Treatment summary
• Conclusion
Acid Gas Removal• Acid gas
- Organic acids
- Carbon dioxide (CO2)
- Hydrogen sulfide (H2S)
• Acid gas removalRCOOH OH- H2ORCOO-
2H2S OH- H2OS2-
CO2 2 OH - CO32- H2O
Caustic Tower Design
Fouling Mechanism (1)• Aldol condensation
• Diels Alder reaction
Red Oil
R1CH2CHOH- -
R1
-H2O
R2CH2CHR1CHCH R2CH2CHCHCH
R1
R2CH2CH=CCH
Fouling Mechanism (2)• Free radical polymerization
Keys Questions
• Why does the caustic tower foul?
• What chemical treatment(s) can be used tomitigate the fouling?
Test Protocols
• Pre-treatment system evaluation
• Skim oil analysis
• Deposit analysis
• Caustic reflux test
Pre-treatment System Evaluation
Filterable Solids(ppm)
Soluble Polymer(ppm)
Strong Section 329 490
Weak Section 1986 1895
Skim Oil Analysis
• Aldol condensation
- Aldehyde
• Free radical polymerization
- Vinyl monomer
• Solvent help to mitigate the fouling
- Aromatic components
Deposit Analysis• Organic foulants
• Hydrogen/Carbon mole ratio similar to aldol polymer
• Precursor of free radical polymerization trapped indeposit matrix
- Styrene, Indene, etc
• Deposits matrix contained:– products of free radical polymerization
– Diels Alder reaction products
– aldol polymer
Summary
• All reaction mechanism involved in the caustictower fouling
How to treat it?
Treatment Recommendation
• Aldol condensation inhibitor
- POLYFREE™ 305C additive
• Free radical polymerization inhibitor
- POLYFREE 300R1 additive
• Antifoulant for controlling Diels Alder fouling
- POLYFREE 350 additive
POLYFREE is a trademark of Baker Hughes Incorporated
Caustic Reflux Results
Chemical Additives Percentage inhibition (%) *
Blank 0
POLYFREE 300R1 Additive 18.9
POLYFREE 305C Additive 27.9
POLYFREE 300R1 /POLYFREE 305C Additives
81.5
*Percentage Inhibition (%)=[(Foulants with additive) – (Foulant without additives)]/(Foulant without additives) x 100
Treatment Results (1)• Soluble Polymer
• Skim Oil Quality
Before Treatment (ppm) After Treatment (ppm)
1895 640
Treatment Results (2)• Process Data
y = 0.013x - 529.19
y = 0.0076x - 305.68
2
3
4
5
6
7
8
9
12/23/11 4/1/12 7/10/12 10/18/12 1/26/13 5/6/13 8/14/13
Cau
stic
Tow
er
DP
Date
Before Treatment After Treatment Linear (Before Treatment) Linear (After Treatment)
Treatment Summary
• The POLYFREE treatment program wassuccessful
• The column run length extended to 18+months
– It reached turnaround
Conclusion
• A complex proprietary caustic tower system evaluationcan identify fouling mechanisms
• Free radical polymerization, Aldol condensation andDiels Alders reaction mechanisms are involved incaustic tower fouling
• From the analysis, a successful POLYFREE chemicaltreatment program was recommended
• Field test data indicates fouling was controlled
• The caustic tower run length was significantly extended
• A costly unplanned outage was avoided
Acknowledgement
• The analytical group in Baker Hughes
• Unit personnel for their collaboration,communication and discussions of caustictower operations
Questions ?