Mitigation to Abqaiq NGL Recovery Plant Corrosion Problem

Shadi Al-Adel, Saud Al-Mudaibegh & Vaughn GdulaProcess & Control Systems Department (P&CSD)

GPA - GCC Chapter Corrosion Management in Gas Processing Facilities

The Diplomat Radisson SAS Hotel, Kingdom of BahrainNovember 28, 2007

Background

•• Corrosion problems started with the Corrosion problems started with the introduction of the ethylene glycol (EG) introduction of the ethylene glycol (EG) hydrate inhibition system.hydrate inhibition system.

Stress Oriented Hydrogen Induced Cracking Stress Oriented Hydrogen Induced Cracking (SOHIC).(SOHIC).Localized pitting corrosion.Localized pitting corrosion.Piping and exchanger failures, which caused:Piping and exchanger failures, which caused:

•• Gas leaks.Gas leaks.

Background (contd.)

•• Corrosion Problem Source:Corrosion Problem Source:Elemental sulfur in the presence of free water. Elemental sulfur in the presence of free water. Caused from:Caused from:

Oxygen ingress.Oxygen ingress.Dissociation of hydrogen polysulfides at Dissociation of hydrogen polysulfides at temperatures below 120 temperatures below 120 °°F.F.

• Unique phenomena to Saudi Aramco.

H2S2 ⇔ S + H2S

NGL Recovery Plant Process Overview

Feed

60#Steam

C3

Feed Drum

Feed Chiller

Deethanizer

NGL C3+

Reflux Cond.

C3

Reflux Drum

Sour gas

LeanEG

LeanEG

Water &Rich EG

Water &Rich EG

Background (contd.)

•• Current EG injection system was Current EG injection system was susceptible to the corrosion problem.susceptible to the corrosion problem.

•• Need for alternative process to the Need for alternative process to the existing EG injection system.existing EG injection system.

Alternative Processes Evaluation

•• Process to remove elemental sulfur, Process to remove elemental sulfur, water or both.water or both.

•• New technologies evaluated:New technologies evaluated:CrystaSulfCrystaSulf for sulfur removal.for sulfur removal.TWISTER for gas dehydration.TWISTER for gas dehydration.Both processes were found to be impractical.Both processes were found to be impractical.

•• Conventional gas dehydration:Conventional gas dehydration:Molecular Sieves (MS).Molecular Sieves (MS).Triethylene glycol (TEG).Triethylene glycol (TEG).

Alternative Processes Evaluation (contd.)

•• Challenges with presence of elemental Challenges with presence of elemental sulfur within dehydration processes:sulfur within dehydration processes:

Presence of elemental sulfur not common.Presence of elemental sulfur not common.Effect of elemental sulfur not certain.Effect of elemental sulfur not certain.Feed temperature had to remain relatively high Feed temperature had to remain relatively high ((≈≈130 130 °°F)F) in order to minimize sulfur deposition.in order to minimize sulfur deposition.

•• Need for tests:Need for tests:Field.Field.Lab.Lab.

Abqaiq MS & TEG Field Tests

•• Test apparatus developed and Test apparatus developed and operated with the team effort by operated with the team effort by P&CSD, Research & Development P&CSD, Research & Development Center (R&DC) and Abqaiq Plants.Center (R&DC) and Abqaiq Plants.

•• Tests Objective:Tests Objective:Measure elemental sulfur in the feed gas and Measure elemental sulfur in the feed gas and through the MS and TEG cells.through the MS and TEG cells.Determine if elemental sulfur gets filtered by Determine if elemental sulfur gets filtered by MS and TEG.MS and TEG.Determine if hydrogen polysulfides carryover Determine if hydrogen polysulfides carryover from the filtered gas.from the filtered gas.

Abqaiq MS & TEG Field Tests (Contd.)

Test Apparatus Field LocationTest Apparatus Field Location

Abqaiq MS & TEG Field Tests (Contd.)

Apparatus Apparatus

Abqaiq MS & TEG Field Tests (Contd.)

Sulfur Measurement DeviceSulfur Measurement Device

Abqaiq MS & TEG Field Tests (Contd.)

•• Test Results:Test Results:Significant amounts of elemental sulfur existed Significant amounts of elemental sulfur existed

in the feed gas (more than 10 ppm).in the feed gas (more than 10 ppm).

Elemental sulfur was being filtered in MS.Elemental sulfur was being filtered in MS.

TEG absorbed elemental sulfur. TEG absorbed elemental sulfur.

Elemental sulfur was detected downstream of Elemental sulfur was detected downstream of

the cells.the cells.

Indicated hydrogen polysulfides carryover.Indicated hydrogen polysulfides carryover.

Lab Tests

•• MS Lab Tests:MS Lab Tests:Fresh sour gas resistant desiccants from CECA Fresh sour gas resistant desiccants from CECA

(SILIPORITE RA) and UOP (SF(SILIPORITE RA) and UOP (SF--1087). 1087).

Accelerated Degradation & Crush Strength.Accelerated Degradation & Crush Strength.

•• TEG Lab Tests:TEG Lab Tests:With presence of sulfur, water and chlorides:With presence of sulfur, water and chlorides:

WeightWeight--loss corrosion test.loss corrosion test.

Online corrosion monitoring test.Online corrosion monitoring test.

Lab Tests (Contd.)

•• Lab Test Results:Lab Test Results:MS desiccant tests concluded the acceptance MS desiccant tests concluded the acceptance

of both desiccantof both desiccant’’s performance. s performance.

TEG corrosion tests revealed normal corrosion TEG corrosion tests revealed normal corrosion

rates and no major corrosion concerns.rates and no major corrosion concerns.

Recommended Process

•• TEG dehydration system with TEG dehydration system with

metallurgical upgrades and special metallurgical upgrades and special

filtering to essentially eliminate the sulfur filtering to essentially eliminate the sulfur

pitting corrosion.pitting corrosion.

Recommended Process (Contd.)

Supporting Conclusions:Supporting Conclusions:Dehydration with TEG achieves the gas water Dehydration with TEG achieves the gas water dew point requirements.dew point requirements.MS dehydration has higher operating and capital MS dehydration has higher operating and capital cost (cost (≈≈ $ 17 MM)$ 17 MM) than the TEG system.than the TEG system.Proper TEG filtering can remove solid Proper TEG filtering can remove solid contaminants including elemental sulfur.contaminants including elemental sulfur.There are sour gas TEG dehydration systems There are sour gas TEG dehydration systems operating with carbon steel equipment.operating with carbon steel equipment.

Recommended Process (Contd.)

•• TEG Dehydration System Design:TEG Dehydration System Design:

Feed gas Flow 280 MMSCFD, 131 Feed gas Flow 280 MMSCFD, 131 °°F & 385 psig.F & 385 psig.

Dry gas water dew point was set at approx. 35 Dry gas water dew point was set at approx. 35 °°F.F.

Special metallurgy was recommended where Special metallurgy was recommended where

potential corrosive environment exists.potential corrosive environment exists.

Special filtering was included to handle the Special filtering was included to handle the

presence of elemental sulfur.presence of elemental sulfur.

Conclusion

•• Elemental sulfur, along with free water, Elemental sulfur, along with free water, was the main source of pitting corrosion.was the main source of pitting corrosion.

•• TEG dehydration system was TEG dehydration system was recommended to essentially eliminate recommended to essentially eliminate corrosion and restore design operating corrosion and restore design operating conditions.conditions.

•• The proposed TEG system included The proposed TEG system included special metallurgy and filtering.special metallurgy and filtering.

•• Cost savings for selecting TEG over MS Cost savings for selecting TEG over MS was approximately $ 17 MM.was approximately $ 17 MM.

Acknowledgments

•• Special thanks to team members Special thanks to team members from:from:

Abqaiq Plants Department.Abqaiq Plants Department.Research and Development Center.Research and Development Center.Facilities Planning Department.Facilities Planning Department.Consulting Services Department. Consulting Services Department. Southern Area Producing.Southern Area Producing.

•• Also supporting departments such Also supporting departments such as:as:

Pipelines Department.Pipelines Department.Oil Supply Planning & Scheduling (OSPAS).Oil Supply Planning & Scheduling (OSPAS).ShedgumShedgum Gas Plant.Gas Plant.TanajibTanajib Plants.Plants.

Thank you!Thank you!

Questions

Field Testing Apparatus Schematic DiagramField Testing Apparatus Schematic Diagram

Water outlet

Water inlet

Gas outlet

Gas inlet

H2S2 ⇔ S + H2S

Sulfur Measurement Methodology

Sulfur probe used with pressure and Temperature reduction in gassampling lines.