Prsentation PowerPoint

Gas Sweetening Unit (Amine Unit)5/11/2015111. Scope Amine systems have three main functions:

Treatment of feed streams to meet product specifications in terms of acidiccomponent loadings.

CO2 removal from gas streams to prevent freezing in downstream cryogenicprocesses.

H 2S removal from fuel gas to avoid SOx production.

5/11/2015221. ScopeTYPES OF AMINE SOLUTION USED FOR ACID GAS REMOVALChemicals usually used in amine systems are:

Monoethanolamine (MEA), Diethanolamine (DEA), Triethanolamine (TEA), Methyldiethanolamine (MDEA),

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5/11/20154Amine ContactorSour GasSweet GasAmine RegeneratorRich AmineLean Amine42. Gas Sweetening Process

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52. Gas Sweetening ProcessUntreated natural gas containing carbon dioxide (CO2) and hydrogen sulfide (H2S) flows into the amine contactor where it contacts a downward-flowing amine-water solution. The amine solution chemically absorbs CO2 and H2S from the gas stream. As the amine solution is re-circulated, rich amine solution collects at the bottom of the absorber and level controlled to a flash tank. The rich amine is then cross exchanged with lean amine. Rich amine solution is further treated in a stripper or still. The still has an external, indirect heating system that heats the rich amine solution. As it is heated, steam from heating the amine rises as rich amine flows downward through the still column, stripping out the CO2 and H2S. The lean amine solution accumulates at the bottom of the still. CO2, H2S and water vapor separated in the amine still are cooled in air exchange coolers. Condensed water is returned to the amine still. CO2 and H2S exit the system at low pressure. Lean amine solution is cycled through the absorber to repeat the process.5/11/2015662. Gas Sweetening ProcessMajor Problems Occurring in the Amine Unit:Wet H2S Damages (Blistering/HIC/SOHIC/SSC)Ammonium Bisulfide CorrosionErosion/Erosion-CorrosionAmine Stress Corrosion CrackingAmine Corrosion

5/11/2015773. Wet H2S Damages (Blistering/HIC/SOHIC/SSC)Wet H2S Damages (Blistering/HIC/SOHIC/SSC)

5/11/20158Sulfide Stress CorrosionBlisteringHydrogen Induced CrackingStress-Oriented Hydrogen Induced Cracking Hydrogen blisters may form as surface bulges on the ID, the OD or within the wall thickness of a pipe orpressure vessel. The blister results from hydrogen atoms, that diffuse into the steel, and collect at a discontinuity in the steel such asan inclusion or lamination

Flat cracking due to hydronic diffusion (Blistering or SWC Stepwise CrackingParticular form of the HIC in existence of residual or applied stress. Cracking are perpendicular to the surfaceSulfide Stress Cracking (SSC) is defined as cracking of metal under the combined action of tensilestress and corrosion in the presence of water and H 2S

83. Wet H2S Damages (Blistering/HIC/SOHIC/SSC)5/11/20159Blistering

Hydrogen Induced Cracking

93. Wet H2S Damages (Blistering/HIC/SOHIC/SSC)5/11/201510Sulfide Stress Corrosion

Stress-Oriented Hydrogen Induced Cracking

103. Wet H2S Damages (Blistering/HIC/SOHIC/SSC)5/11/201511Affected Equipment: Amine regenerator overhead systems are especially prone to wet H2S damage because of generally high concentrated acid gas solutions.

Materials & Remedies: See Next Table113. Wet H2S Damages (Blistering/HIC/SOHIC/SSC)5/11/201512Materials & RemediesDamageHIC/BlisteringSOHICSSCMaterials (Carbon steel and low alloy steels) and RemediesCladdings and CoatingsSpecialized Corrosion InhibitorsStainless Steel HIC-Resistant Carbon Steels(NACE Publication 8X194)

PWHT

PWHT & Design Reviewing

Limiting the hardness of welds to 200 HB max by PWHT.

125. Amine Stress Corrosion Cracking5/11/201513Amine Stress Corrosion Cracking: Corrosion. Tensile/Residual Stress.

Affected Equipment: Carbon Steel and low allow carbon steel and non-PWHT carbon steel (Weldments). Rich side of Lean/Rich Amine Exchanger.Materials & Remedies: Cladded Carbon Steel and 300 Series SS are highly resistant.134. Ammonium Bisulfide CorrosionAmmonium Bisulfide Corrosion: Aggressive Type of Corrosion due to the formation at high temperature of NH4HS. (Corrosion above 2wt%).

Affected Equipment: High Concentration of NH4HS may be found in Amine Regenerator Reflux Unit.

Remedies and Materials: 300 Series SS, Duplex SS, Determine the NH4HS content , Review Velocities

5/11/201514145. Amine CorrosionAmine Corrosion : General/localized CO2 Corrosion (Dissolved acid gas in the aqueous amine solution).

Affected Equipment: Regenerator Reboiler (High T and Turbulence). Rich side of Lean/Rich Amine Exchanger.

Materials & Remedies: Carbon Steel and 300 Series SS are highly resistant.5/11/201515155. Amine CorrosionErosion / Erosion-Corrosion: Erosion-corrosion is a description for the damage that occurs by a combined action of erosion and corrosion.

Affected Equipment: All types of pipes materials

Materials & Remedies: Reviewing velocities (About 1.5 m/s), Improvements in design involve changes in shape, geometry and materials selection

5/11/201516162. Inlet System Damages

5/11/201517Sour GasSweet GasAmine ContactorRich AmineLean Amine(Aqueous Solution)Inlet/ Filter CoasterOutlet SeparatorWet Co2/H2S CorrosionWet H2S Damages&Amine CrackingErosion/Erosion-Corrosion & Amine Corrosion CO2/H2S Corrosion & Wet H2S Damages172. Regeneration system Damages

5/11/201518Amine RegeneratorCondenserLean FilterRich AmineFlash TankFlash GasRich AmineRich/Lean ExchangerAmine ReboilerReflux SeparatorAcid GasCoolerWet H2S and Amine CrackingWet H2S Damages&Amine CrackingErosion-CorrosionAmine Corrosion & CrackingWet H2S Cracking & Ammonium Bisulfide corrosionAmine CrackingAmine Corrosion &Erosion18X. Material Selection for Inlet System

5/11/201519Equipment ItemMaterialCommentInlet FilterStainles SteelAmine ContactorShell: Carbon SteelInternal: Stainless SteelOutlet SeparatorCarbon SteelPipe (Inlet->Contatcor)Stainless SteelPipe (Contactor->Regeneration)Stainless SteelCarbon Steel Pipe (Contactor-> Outlet Separator)Carbon SteelPeriodic Exchange19X. Material Selection for regeneration system

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Comment

RegeneratorShell: Stainless SteelInternal: Stainless SteelRegenerator Reflux drum

Shell: Stainless SteelTubes: Stainless SteelLean/Rich exchangerTubes: SS or CS+CladShell: Carbon SteelRegenerator ReboilerShell: Stainless Steeltubes: Stainless SteelLean amine CoolerCarbon Steel202. Gas Sweetening Process

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