Sweetening

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Synergas Technologies In c. 1 Natural Gas Sweetening Wayne Monnery

description

gas sweetening concept

Transcript of Sweetening

  • Natural Gas SweeteningWayne Monnery

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  • Natural Gas SweeteningVarious ProcessesRegenerable Chemical Solvents (amines, potassium carbonate)Physical and Hybrid Solvents (Solexol, Sulfinol)Direct oxidation liquid redox (LoCat)Dry Bed Processes (mole sieve)Non-Regenerable chemical (scavenger)Membrane permeation

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  • Natural Gas SweeteningProcess SelectionH2S, CO2 concentrations in sour gasSales gas specificationsRaw gas composition: hydrocarbon content, COS, CS2, mercaptansPressureAcid gas and waste products disposal

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  • Natural Gas SweeteningSweetening Process Selection

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  • Natural Gas SweeteningRegenerable Chemical Solvents (amines)

    MDEADEAMEA

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  • Natural Gas SweeteningAmines - Basic chemistry

    H2O H+ + OHH2S H+ + HS-CO2 + H2O HCO3- + H+ RNH2 + H+ RNH3+RNH2 + CO2 RNHCOO- + H+ COS + H2O CO2 + H2S

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  • Natural Gas SweeteningRegenerable Chemical Solvent Process

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  • Natural Gas SweeteningAmines - MEAAdvantages:Efficient at low pressureExcellent acid gas removal capacityRemoves COS, CS2, mercaptans

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  • Natural Gas SweeteningAmines - MEADisadvantages:Degraded by CO2, COS, CS2Reclaimer requiredRelatively higher corrosion limited soln concn, limited rich loadingRelatively higher circ rateRelatively high vap press high vap lossesRelatively higher regen heat reqdNot selective

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  • Natural Gas SweeteningAmines - DEAAdvantages:Less corrosive than MEALower circ rate than MEA @ P > 300 psigLow vap press low vap soln lossLower reqd regen energy than MEA (lower op cost)Low degradation by COS, CS2

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  • Natural Gas SweeteningAmines - DEADisadvantages:Degraded by CO2, requires vacuum distillationInefficient at low pressuresNot selective

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  • Natural Gas SweeteningAmines - MDEAAdvantages:Selective absorptionLower regen energy than MEA, DEA (lower op cost)Relatively efficient at low pressuresLess corrosive than MEA, DEA higher soln concn, loadingLower circ rate in most casesRelatively resistant to degradation

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  • Natural Gas SweeteningAmines - MDEADisadvantages:Higher erosional corrosionHigher foaming potentialRequires high contact time in non-selective casesResidue gas lower BTUsDegrades, corrosion with elemental sulphur

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  • Natural Gas SweeteningAmines - DGAAdvantages:Efficient at high temp, low pressExcellent acid gas removal capacityLess corrosive than MEA higher soln concnLower circ rate than MEARemoval of COS, mercaptans

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  • Natural Gas SweeteningAmines - DGADisadvantages:Not well known and accepted compared to MEA, DEA, MDEADegraded by CO2, COS; requires reclaimer

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  • Natural Gas SweeteningAmines - Mixed (MDEA + )Advantages:Selective, customizableLower regen energy reqd than MEA, DEA (lower op cost)Relatively efficient at low pressuresLess corrosive than MEA, DEA higher soln concn, rich loadingLower circ rate in most casesRelatively resistant to degradation

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  • Natural Gas SweeteningAmines - Mixed (MDEA + )Disadvantages:Higher erosional corrosionHigher foaming potentialReliance on vendorRelatively expensive

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  • Natural Gas SweeteningAmines - Recommended Solvent Concn:

    SolventRecommended wt%MEA10 - 20DEA25 - 35MDEA40 - 50DGA40 - 70

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  • Natural Gas SweeteningAmines - Recommended Rich Loadings:

    SolventMax. Rich mole/moleLow H2S/CO2High H2S/CO2MEA0.250.50DEA0.450.70MDEA0.400.60DGA0.250.45

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  • Natural Gas SweeteningAmines - Contactor temp profile

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  • Natural Gas SweeteningAmines - TemperaturesContactor Feed: 60 - 110 F (15 - 43 C)Contactor Bulge < 190 F (88 C)Stripper Feed: 180 - 220 F (82 - 104 C)Stripper Reboiler < 260 F (127 C)Stripper Ovhd 195 - 210 F (90 - 99 C)Stripper Condenser 100 - 110 F (38 - 43 C)

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  • Natural Gas SweeteningAmines - Recommended Lean Loadings:

    SolventH2S (mole/mole)CO2

    MEA0.020.10DEA0.01 0.05 - 0.08MDEA0.004 - 0.0080.006 - 0.012DGA 0.01 - 0.02 0.04 - 0.08(for P/L spec gas)

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  • Natural Gas SweeteningAmines: Recommended reboiler duties:

    SolventDuty (BTU/USgal)

    MEA1100 - 1300DEA 900 - 1100MDEA 800 - 1000DGA1200 - 1400

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  • Natural Gas SweeteningAmines - Operating Problems:CorrosionFoamingSolution degradationVolatility and entrainment lossesGoing Sour

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  • Natural Gas SweeteningAmines - Operating Problems:Corrosion: 3 typesWet acid gas corrosionAmine solution corrosionErosion corrosion

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  • Natural Gas SweeteningAmines - Operating Problems: Corrosion

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  • Natural Gas SweeteningAmines - Operating Problems:Wet acid gas corrosionOvhd. section of regen - minimize by 0.5% amine in refluxbottom of contactor - minimize by acid gas introduction in distributor below liq. Level or allowing amine to weep around bottom tray

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  • Natural Gas SweeteningAmines - Operating Problems:Amine solution corrosion factorshigh temphigh acid gas loadingsH2S/CO2 in acid gasamine type and soln concndegradation products and heat stable salts

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  • Natural Gas SweeteningAmines - Operating Problems:Amine solution corrosionbottom of stripperpiping between contactor LCV to flash drumrich soln side of L/R exchangerpiping from flash drum LCV to stripperMinimize by appropriate materials of const., limit rich loadings (circ rate) and limit lean loadings (stripping steam)

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  • Natural Gas SweeteningAmine - Operating Problems:Erosional corrosionPiping from contactor LCV to flash drumPiping on hot, rich side of L/R exchanger from flash drum LCV to stripperLean amine pumpMinimized by limiting velocities in equip. and piping, designing to minimize turbulence and dissipate turbulent energy

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  • Natural Gas SweeteningAmines - Operating Problems:Materials of construction carbon steel with stainless:Rich soln piping from contactor LCV to flash drumRich soln piping from flash drum LCV to stripperL/R exchanger bundle or platesUpper half of stripper cladStripper ovhd. piping?, condenser?, reflux drum?Stripper reboiler bundle, vapor return?Stripper trays?, bottom contactor trays?

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  • Natural Gas SweeteningAmines - Operating Problems:Cracking: 4 typesSulphide Stress Cracking (SSC)Hydrogen Induced Cracking (HIC)Stress Oriented Hydrogen Induced Cracking (SOHIC)Alkaline Stress Corrosion Cracking

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  • Natural Gas SweeteningAmines - Operating Problems:SSC from atomic H in metal lattice embrittlementSSC found in welds in bottom of contactor, rich side of L/R exchanger, top of regen and regen ovhdMinimize by stress relieving

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  • Natural Gas SweeteningAmines - Operating problems:HIC/SOHIC caused by H atoms combining to H2 in metal lattice blistering, crackingHIC minimized by HIC-resistant metal, stress relieving helps SOHIC but does not prevent it

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  • Natural Gas SweeteningAmines - Operating Problems:Alkaline stress corrosion cracking caused by amine solution corrosion cycleMinimized by stress relievingStress relieving recommended for all metals in contact with sour gas, acid gas, lean and rich amine but not for SS

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  • Natural Gas SweeteningAmines - Operating Problems:FoamingResults in off-spec gas, amine lossesCaused by contaminants: liq. Hydrocarbons, suspended solids (iron sulphide), degradation products (HSS), feed gas contaminants (corrosion inhibitors from field), make-up water contaminants, other contaminants (filter treatment oils, surfactants, turnaround)Also caused by gas overloaded contactor

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  • Natural Gas SweeteningAmines - Operating Problems:Foaming SymptomsGoing SourHigh/erratic differential press across contactorHigh amine lossesOpaque solution>10% HSS; failure of foaming testSolids accumulation in regen ovhd, plugged instrumentation

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  • Natural Gas SweeteningAmines - Operating problems:Foaming PreventionGood inlet separationCheck gas h/c dew pt., lean amine temp = gas temp + 10 FFiltrationSolution reclaimingHydrocarbon skimming

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  • Natural Gas SweeteningAmines - Operating Problems:Solution degradationMEA+CO2 oxizoladone HEEDMEA+COS similar (only 20%)Irreversible, loss of solution capacity; reclaim solutionNo contribution to corrosion if loadings reasonableCS2 and most COS removal by hydrolysis

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  • Natural Gas SweeteningAmines - Operating Problems:Solution degradationDEA+CO2 THEED PiperazineDegradation contributes to corrosionMinimize by operation with lowest practical temps and lower concentrations; truck vacuum reclaimingNo COS degradation (70-80% removal by hydrolysis)

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  • Natural Gas SweeteningAmines - Operating Problems:Solution degradationDGA+CO2 BHEEUDGA+COS similarIrreversible, loss of solution capacity; reclaim solution

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  • Natural Gas SweeteningAmines - Operating Problems:Solution degradationMDEA does not react irreversibly, not degraded by CO2 or COS; does not react with CS2Oxygen+amines carboxylic acids HSS; minimize by blanketing tanks with fuel or inert gas

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  • Natural Gas SweeteningAmines - Operating Problems: Solution Testing:Organic Acids, HSSAmine wt%Iron SulphideLiquid hydrocarbonsWaterRich/Lean Loadings; Foaming TestVisual check

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  • Natural Gas SweeteningAmines - Operating Problems: Make Up Water Check:Check for:Total hardnessTotal dissolved solidsIronSodium/PotassiumChlorides

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  • Natural Gas SweeteningAmines - Operating Problems:Volatility losses caused by high vapour press; 0.5-2.0 lb/MMscf for MEA, lower for other aminesEntrainment losses caused by overloading contactor, inefficient mist extraction or foaming; 0.2 lb/MMscfStripper volatility losses 0.1 lb/MMscf for MEA, lower for other amines; minimal entrainment losses

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  • Natural Gas SweeteningAmines - Operating ProblemsGoing SourSolution circ rate too lowInadequate regenerationSolution concn too lowGas flow too highContactor press too low or temp too highFoamingDP cell leak; L/R exchanger leak

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  • Natural Gas SweeteningOther processes:Potassium carbonate (similar to amine except hot contact)Physical solventsEquilibrium solubilityRegen by flashing, inert gas or thermal strippingLow regen energy reqdSelectivity; COS, CS2 and mercaptan removalHeavy hydrocarbon co-absorptionMany flow schemes

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  • Natural Gas SweeteningOther processes:Hybrid (physical + chemical solvent)Sulfinol Advantages:High degree of COS, CS2 and some mercaptan removal; can be selectiveLower circ rateLower foaming tendency; low corrosion

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  • Natural Gas SweeteningOther processes:Sulfinol disadvantages:Expensive license fee and solventReclaimer may be requiredCo-absorption of heavy hydrocarbonsInefficient at low pressureHigh viscosity, low thermal conductivityProcess same as amines

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  • Natural Gas SweeteningOther Processes:Dry Processes (Mole Sieve) can remove H2S, CO2 and waterProcess similar to dehydration, requiring one bed on adsorption and one regenerating with hot gas, details in notes

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  • Natural Gas SweeteningOther processesNon-regenerable chemical H2S scavengers

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  • Natural Gas SweeteningOther processes:Non-regnerable chemical H2S scavengersMost economic when sulphur < 300 lb/dSour gas bubbled through vessels (parallel or lead-lag) or direct injection of liquidMost popular dry is Sulfa Treat and most popular liquid is Sulfa-Scrub; details in notes

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  • Natural Gas SweeteningCalculations:AminesHeat and material balance can be done manually (cumbersome) or using computer softwareKey parameters estimated:Circ Rate = K(MWam)(Qg)(yag)/[(PU)(SGs)(Xs)]Reboiler duty to obtain lean loadings, as previous

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  • Natural Gas SweeteningCalculationsAmines - Equipment Shortcutrelated to circ rate (USgpm)

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  • Natural Gas SweeteningCalculationsAmines - Equipment Shortcutrelated to circ rate (USgpm)

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  • Natural Gas SweeteningCalculationsAmines - Equipment Shortcut

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  • Natural Gas SweeteningCalculationsAmines - Equipment Shortcut

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  • Natural Gas SweeteningCalculationsAmines - Piping VelocitiesLiquid 3-5 ft/s (1.0-1.5 m/s) CS; 6-8 ft/s (1.8-2.4 m/s) SSGas 60-100 ft/s (18-30 m/s)Other equipment, see notesProcess Simulation, see notesOther processes: vendors, some simplified calcs in Maddox and Morgan (1998)

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