Caustic Tower System_AICHE_final version

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 ?