Corrosion Control on Amine Plants: New Compact Unit Design for High Loadings

Michel BONIS, TotalJean KITTEL, IFP

Gauthier PERDU, Prosernat

OAPEC IFP joint Seminar – 17th 19th June 2008

• Introduction

• Overview of corrosion likelihood in amine units Key factors of corrosion in amine plants An illustrative case Study

• From operating old CS units to handling high amine loadings More than 50 years REX The present operating basis High loadings - Lessons learnt from experience

• The use of stainless steels in amine sour units – the question raised by NACE

MR0175 / ISO 15156-3

• Main conclusions – a path to compacted designs

Outlook

Outlook

• Introduction

• Overview of corrosion likelihood in amine units Key factors of corrosion in amine plants An illustrative case Study

• From operating old CS units to handling high amine loadings More than 50 years REX The present operating basis High Loadings - Lessons learnt from experience

• The use of stainless steels in amine sour units – the question raised by NACE

MR0175 / ISO 15156-3

• Main conclusions – a path to compacted designs

• Total has operated and licensed amine units for more than 50 years: The 1st units :

– DEA units, sour gas, 16% H2S & 10% CO2, started in 1957 Now :

– 141 units licensed on 42 different locations over the world,– 75 DEA units,– 66 Selective or energized MDEA units,– 25 units operated by Total– Many of them have been debottlenecked for higher intensity operation

• Most are used for H2S removal, from 30 ppm to 50% H2S in, i.e. up to very high amine

loads!

• CO2 removal units mostly licensed during the last 10 years,

• Extensive use of CS with monitoring and aggregated feed back

• Prosernat - an IFP subsidiary is now the licensor

Five Decades of Operations Experience

A Typical Scheme of an Amine UnitWet sweet gas

Deminwater

Acid gasTank

LP steam

Reboiler

SourGas

Absorber

Exchanger RegeneratorFlash

drum

Flash gas

Amine Unit Corrosion: Key Factors

Intrinsic corrosivity of amine solution

Protectivity of sulfide / carbonate layer

Amine loading

pHtype of amine

& concentration

MEA > DEA ≥ MDEApH - Conductivity

Temperature

Thermalactivation

Oxygen entry

HSS

VelocityTurbulences

Inadequate designToo high flow rates

Uniform weight loss corrosion Erosion – corrosion Amine stress corrosion cracking

Wet Acid Gas Corrosion: Key Factors

Intrinsic corrosivity of condensed acid water

Protectivity of sulfide / carbonate layer

Flue gas compositionInadequate scrubbing

- H2S / CO2 ratio- Condensation

- Amine wall wetting- Condensation- Water accumulation

Inadequate designInadequate metallurgy (PWHT, sour grades...)Too low gas flow rates

Hydrogen cracking (HIC, SSC...)Weight loss corrosion

CO2 content in treated gas

Condensation in the treated gas lines

Main Corrosion Areas

Wet sweet gas

Deminwater

Acid gas

LP steam

SourGas

Corrosion of CS

reboiler coils

Wet Acid gas corrosion condensed water

Erosion – Corrosion

Wet sweet gas

Deminwater

Acid gas

LP steam

SourGas

Flash gas

AISI 410 (13% Cr)

Trays, valves & down-comers

CS shell

Illustrative Case Study: Sweet Gas Unit

Outlook

• Introduction

• Overview of corrosion likelihood in amine units Key factors of corrosion in amine plants An illustrative case Study

• From operating old CS units to handling high amine loadings More than 50 years REX with CS The present operating basis High loadings - Lessons learnt from experience

• The of use stainless steels in amine sour units – the question raised by NACE

MR0175 / ISO 15156-3

• Main conclusions – a path to compacted designs

Experience from Initial CS Units

More than 40 years after start-up some of the initial CS units

are still in operation today

Most encountered type of corrosion

• Erosion - corrosion in the rich amine route

Most susceptible areas

• Bottom of absorber (unappropriate design – Impingement...)

• Rich amine lines (too high velocities, degassing effects...)

• Top of the regenerator (unappropriate protection of walls)

CS Units: Lessons learnt to updated design

A combination of GOOD PRACTICE & selective replacement with CRA Efficient policy to minimize amine degradation

• prevent oxygen entry strict blanketing of amine tank deaeration of make-up water

• avoid high reboiler temperature

• control HSS concentration < 5000 mg/L Moderate velocities / reduced turbulences

• rich amine piping in CS: < 0.35 flow < 2 m/s // < 0.9 flow < 1.4 m/s

• bottom of Absorber / top of Regenerator Avoid jetting with CRA deflectors

Updated design to High Solvent Loadings

A combination of good practise & SELECTIVE

REPLACEMENT WITH CRA’s. Allows high intensity operation and debottlenecks

• Upgrade Bottom of Absorber & Top of Regenerator CRA cladding where appropriate or CRA weld overlay or CRA lining

• Select rich amine piping in CRA from Absorber to Regenerator allows Solvent Loadings > 0.9 & velocities > 2 m/s

High Amine Loadings : the Experience

More than 50 years of experience on various fields... AmineType

H2S (% v) CO2 (%v) Loading Start-up year

DEA 15.8 9.8 0.85 1957 (first unit)

DEA 34.6 6.1 0.90 1972

DEA 8.5 9.5 0.77 1980

DEA 21.5 14.7 0.82 1987 (first train)

DEAMDEA 4.2 6.0 0.64 1984

Formulated MDEA

Traces 9.2 0.72 1996

MDEA 4.0 5.6 0.71 2001

... Mostly with CS, to extended lifecycle, with reduced

investments and energy costs … without major

corrosion problems…

High Amine Loadings – Corrosion Impact

High Loadings

Enhanced corrosivity to CS

Stable protective layerNo Corrosion

Enhanced flashing

Unstable or mechanically damaged layer Severe erosion - corrosion

Unit design• Too high velocities• Turbulences• Impingement

High Amine Loadings : Lessons Learned

High Loadings

Enhanced corrosivity to CS

Stable protective layer

Enhanced flashing

Unstable or mechanically damaged layer Severe erosion - corrosion

Unit design• Too high flow rates• Turbulences• Impingement

Good design &good practises: No degradation, Flow < 1.4 m/s

CRA:

- Rich Amine Lines- Bottom Abs. + Top Reg.

No CorrosionLoading up to > 0.9 High velocities (> 2 m/s)Compact designsReduced maintenance

Outlook

• Introduction

• Overview of corrosion likelihood in amine units Key factors of corrosion in amine plants An illustrative case Study

• From operating old CS units to handling high amine loadings More than 50 years REX with CS The present operating basis High Loadings Lessons learnt from experience

• The use of stainless steels in amine sour units – the question raised by NACE

MR0175 / ISO 15156-3

• Main conclusions – a path to compacted designs

Use of CRA's in sour amine units: the NACE

• Recommended limits of use of austenitic grades (304, 316, 321) 60°C, pH2S > 15 psi

60°C, 15 psi > pH2S > 50 psi, Chlorides (Cl-) must be < 50 mg/L

Strict application of standard would drastically restrict the use of austenitic CRA’s in

amine units

NACE MR 0175/ISO 15156-3 "Petroleum & natural gas industries –Materials for use in H2S

containing environments in oil & gas production – Part 3: Cracking-resistant CRAs and other

alloys" (2003)

CRA's in Sour Amine Units : the Experience A specificity of many sour amine environments

• 304L and 316L have been used in sour amine units for several

decades

• A practical experience of austenitic CRA in operation with chlorides

up to 2000 mg / litre in highly sour service

• Should-be-sensitive material are commonly present: Lean / Rich cross heat exchanger plates, 0.6-0.7 mm thick / SS316L No internal failure

• Additional laboratory tests have been performed at IFP over a long

period:Amine Solvent load T° Cl- Steel type Result

DEA 4N 10 bar H2S

7 bar CO2

110°C 6 g/L AISI 321 No cracking-No pitting

MDEA 40% 4.7 bar H2S

1.8 bar CO2

110°C 6 g/L AISI 304LAISI 316L

No cracking- No pittingNo cracking- No pitting

NACE and Sour Amine Service

• The U-bend test :

• A detailed view : no cracking – no pitting

Strict application of NACE MR0175/ISO 15156 is questioned from Lab Tests and Long Term Monitoring of amine gas plants with Cl-

NACE MR0175/ISO 15156 is based on acidic systems data which does not fit the alkaline pH of liquid amine solvents

Outlook

• Introduction

• Overview of corrosion likelihood in amine units Key factors of corrosion in amine plants An illustrative case Study

• From operating old CS units to handling high amine loadings More than 50 years REX with CS The present operating basis High loadings - Lessons learnt from experience

• The of stainless steels in amine sour units – the question raised by NACE

MR0175 / ISO 15156-3

• Main conclusions – a path to compacted designs

Main Conclusions – 1

Corrosion control in DEA and MDEA amine units is a simple combination of: • A few key operating practices

Avoid amine degradation – careful blanketing + deO2 of Make-up Water and Nitrogen +

controlling heat flux to reboiler Avoid high velocities with CS

• A consistent design Carefully manage turbulences & impingement areas with dedicated

arrangements Use CRA at selected locations (Bottom of absorber, top of regenerator, rich

amine lines)

Successful results with high amine concentrations and high amine loading ( > 0.9 mol/mol)

An Up-Dated Design of High Loadings Sour UnitsWet sweet gas

Fluid monitoring

HSS < 5000 mg/lCl- < 500 mg/l

HSS < 5000 mg/lCl- < 500 mg/lPrevent oxygen entries

Blanketting

Deminwater

Acid gas

LP steam

Flash gas

> 300k.cm

Controlled chloride

Use of 316L stainless steel

Main Conclusions – 2

Present design and operating practice are based on more than 50 years of positive experience

Rely on extended use of the 316L SS on corroded sensitive areas

No cracking in sour media, documented by Feed Back & Lab Tests

Keep all flexibility to any future process change or solvent swap

Keep the possibility for upgrading during scheduled maintenance phases to allow operation with higher loadings

Use specific design rules for sweet service units

Thank you very much for your attention

OAPEC IFP joint Seminar – 17th 19th June 2008