Applications of Aqueous Process Modeling to Petroleum Refinery Corrosion Control

Jim FeatherExxonMobil Research & Engineering

OLI 23rd User ConferenceOctober 5-6, 2005

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Presentation Outline

• Challenges with corrosion prediction• Application Overview• Example Applications• Looking Ahead

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Refinery Corrosion Analysis

• Corrosion control applications often focus on a particular section of a process unit

• Complex modeling tools aren’t easily applied to routine operating envelope management

• Chemistry of corrosion environment remains complex

• Corrosion rates at complex conditions or across a process may not be easily predictable

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Analyzers Bring Modeling Tools to the Corrosion Engineer

• OLI Analyzers are facilitating evaluations of conditions important to aqueous corrosion– Aqueous phase dew point– Aqueous phase condensation profile– Application of corrosion control methods

• Changes in operating conditions readily evaluated for their impact on chemistry

• Effectiveness of corrosion control measures more readily evaluated

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General Application of Analyzers to Corrosion Prediction• Tools used in several ways to improve corrosion

predictions– Model chemistry and use other tools for

corrosion rate predictions– Model chemistry and compare with operating

envelope constraints– Direct estimation of corrosion rate with Corrosion

Analyzer• Assess the impact of changes or mitigation

measures in the process on corrosion– Water wash & chemical treatment programs– Validation of 3rd party corrosion inhibitor

programs

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Example Refinery Applications

• Common applications of interest– Crude distillation unit overhead – Acid

condensate corrosion, water wash application– FCCU overhead systems – Sour water corrosion,

Carbonate stress corrosion cracking, water wash application

– Coker overhead systems – Sour water corrosion– Hydrotreater reactor effluent systems – Sour

water corrosion, water wash application• Estimation of corrosivity of environments without

readily available corrosion data

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Application to Crude Distillation Unit Overhead

Naphtha

CRUDEFEED

DESALTER

Acidic WaterCondensate

INHIBITOR

NEUTRALIZER

Steam Reduced Crude

Kerosene

Light Gas Oil

Heavy Gas Oil

Acidic WaterCondensate

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Conditions of Untreated Overhead

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More Corrosive Conditions at Dewpoint

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Est. Corrosion through Condensation Range

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Impact of Neutralizer Addition in CDU Overhead

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Effect of Neutralizer During Condensation

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Controlling Corrosion in FCCU Overheads

• Carbonate stress corrosion cracking in non-stress relieved carbon steel piping is a growing problem – May be associated with operations which

increase NH3 & CO2 in overhead water while unit feed sulfur is being reduced by hydroprocessing

– Greatest likelihood of cracking occurs:• pH < 9.0 and CO3 > 100 ppm

• pH between 8.0 and 9.0 and CO3 > 400 ppm

– Direct measurement of carbonate is not straightforward

• General corrosion control also an important issue, often managed by water wash

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Carbonate SCC

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Conditions promoting SCC in FCCU’spH

Log CO3, ppm

SCC Not Likely

SCC Possible

SCC Likely

From NACE C/90 Paper 206, Kemetz & Truax

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Analyzer Used to Evaluate FCCU OH

• Analyzer used to model changes in operations with other model as input

• Outputs pH & carbonate ion concentration to support cracking likelihood assessment

• Benefit of corrosion & cracking control mitigation measures evaluated– General corrosion – balance corrosion vs

operational issues with excess water– Model impact of measures taken to reduce

tendency for cracking• Dilution • pH adjustment

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Looking Ahead

• Prediction of salt deposition a needed capability– Corrosive NH4Cl salt forms in refinery

processes• Crude distillation• Hydroprocessing• FCCU’s & Cokers

– Amine chloride salt important in neutralizer applications

– Corrosion predictions “nice to have” but modeling of deposition more important