acid gastreatment & sulfur recovery

8/9/2019 Acid GasTreatment & Sulfur Recovery

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Gas Treatment& Sulfur Recovery

Process Engineer


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OutlineIntroduction

Some Definitions.Hazards of (H 2S).

Gas Treatment Amines. Amine Process.Operational Problems.

Sulfur RecoveryClaus Process.Interesting Aspect.


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Introduction

!at are t!e goals of "as #reatment ( "as s$eetening)%The goals are &

#o produce s$eet gas.

#o control corrosion and pre'ent poisoning of catal st indo$n stream facilities.#o meet consumer gas specification. #o meet en'ironmental re uirements and regulations.

!at about Sulfur *eco'er % #o reco'er t!e sulfur to beused in fertilizers industr .


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Definitions

Absorption &a separation process in'ol'ing t!e transfer of a substancefrom a gaseous p!ase to a li uid p!ase t!roug! t!e p!ase boundar .

Adsorption &t!e process b $!ic! gaseous components are adsorbedon solids because of t!eir molecular attraction to solid surface.

Sour "as & gas containing undesired uantities of ! drogen sulfide+carbon dio,ide+ and-or mercaptans.S$eet "as & gas $it!out sulfur content. Acid "as &feed stream to sulfur reco'er plant consisting of H 2 S+ CO 2 +H2 O+ and usuall less t!an 2 mol ! drocarbon.


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Hazards of H 2S

Hig!l to,ic colorless and flammable gas.

Hea'ier t!an air. At lo$ concentration+ it smells li/e 0rotten eggs1.Human sense of smell cannot be relied on todetect !azardous concentration of it.


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ppm Symptoms

3.333 Detected b odor

3 3.33 Occupational 4,posure 5e'el+ #!res!old 5imit 6alue(#56)

33 3.3 7ills sense of smell in 8 to 9 minutes. :a burn e esand t!roat.

233 3.32 7ills sense of smell rapidl . ;urns e es and t!roatafter one !our.

933 3.39 Dizziness+ loses sense of reasoning+ breat!ingceases in fe$ minutes. nconscious at once? follo$ed b deat!

!oncentration & Reaction "y Human "ody S l i g!

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Gas Treatment#$mines%

Types of $mines:onoet!anolamine #'($ %) HO! 2H*+H 2 ,rimary Diet!anolamine #D($%) #HO! 2H*%2+H Secondary:et! ldiet!anolamine #'D($%) #HO! 2H*%2+!H - Tertiary

'D($ is "etter) .hy/Highest selectivity for H2S over !O 2

Selectivity is defined as ratio of #mole percent of H 2S removedto mole percent of H 2S in feed gas% to #mole percent of !O 2 removed to mole percent of !O 2 in feed gas% .


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'D($

:ore Ad'antages&>seful in upgrading acid gas feed to sulfurreco'er unit.5o$ sol'ent losses due to lo$ 'apor pressure.Hig! resistance to degradation.Hig! energ efficienc .

5o$ capital and operating cost.5ess corrosi'e operation.


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$mine ,rocess Schematic


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,rocess DescriptionSour gas enters t!e base of t!e amine absorber+ $!ic! is s$eetened b t!e lean amineflo$ing do$n t!e absorber to$er. #!e s$eet gas lea'es t!e top for furt!er treatment.

*ic! amine lea'es t!e base flo$ing to t!e lo$ pressure amine flas! tan/+ $!ere t!edissol'ed gases and entrained ! drocarbon come off t!e solution.

#!e outgoing gas 0flas! gas1 can be s$eetened to be used as fuel gas.

#!e ric! amine lea'es t!e flas! tan/ to t!e ric!Blean e,c!anger to cool do$n t!e leanamine+ t!en continues to t!e amine regenerator.

H2 S and CO 2 are stripped off from t!e amine b t!e steam coming from t!e reboiler.#!e 'apor flo$ to t!e top of regenerator+ condensed b t!e condenser+ t!en proceed tot!e reflu, separator+ $!ere t!e gas is separated from t!e li uid.

#!e acid gas flo$s to t!e sulfur plant+ $!ile t!e condensed li uid is pumped bac/ to t!eregenerator as reflu,.

#!e regenerated amine solution flo$s to t!e ric!Blean e,c!anger to get cooled. It getsto t!e surge tan/+ cooled and pumped to t!e absorber to repeat t!e absorption process.


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Operational ,ro"lems

#!e usual problems in all amine s stems arerelated to&

Corrosion .Solution degradation.Solvent losses.Plugging and Fouling.

Foaming.


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!orrosion

Potential problem+ it is a function of temperature and li uid 'elocit .

Combination of H2S and CO 2 $it! $ater practicall ensures t!atcorrosi'e conditions $ill e,it in portions of t!e plant.

"as streams $it! high H2S to !O

2 ratios are less corrosi'e t!an

t!ose !a'ing lo0 H 2S to !O 2 ratios . ! %

H2S dissociate in $ater to form a $ea/ acid. #!e acid attac/s iron and form insoluble ironsulfide. #!e iron sulfide $ill ad!ere to t!e base metal and ma pro'ide some protectionfrom furt!er corrosion.

On t!e ot!er !and+ CO 2 $ill react $it! $ater to form carbonic acid . #!e acid attac/s t!eiron to form a soluble iron bicarbonate $!ic!+ upon !eating $ill release CO 2 and aninsoluble iron carbonate to iron o,ide.

H2S concentration in t!e ppm' (parts per million b 'olume) range$it! CO 2 concentration of 2 or more tend to be practicall corrosi'e.


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!orrosion

;ecause of t!e temperature relation to corrosion+ t!ereboiler+ t!e ric! side of t!e amineBamine e,c!anger+stripper o'er!ead condensing loop tend to e,perience

!ig! corrosion rates.H drogen sulfide stress crac/ing (SSC) is a critical formof corrosion during t!e fe$ mont!s of operation. It ta/esplace in pipes+ 'al'es and fittings. #!is is t picall t!e

outcome of improper material c!oice and noconsideration to stress relie'ing or critical piping.


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Some Guidelines to 'inimize The,ro"lem

>sing of corrosion in!ibitors in combination $it! operating practices+$!ic! $ill offer potential sa'ing in bot! capital and operating costs.

Some Guidelines are the follo0ing:aintain t!e lo$est possible reboiler temperature.:inimize solids and degradation products t!roug! reclaimer andeffecti'e filtration.

7eep o, gen out of t!e s stem b pro'iding a gas blan/et on allstorage tan/s and maintain a positi'e pressure on t!e suction ofall pumps.:onitor corrosion rates $it! coupon or suitable corrosion probes.

:aintain ade uate solution le'el abo'e reboiler tube bundle andfire tubes? a minimum submergence of 0 is recommended.


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1oaming

The most trou"lesome pro"lem on a day to day "asis).hen foaming occurs3 there is poor contact "et0een thegas and the chemical solution)

It reduces treating capacity and s0eetening efficiency3

possi"le to the point that outlet specification cannot "e met)

SymptomsSudden increase in differential pressure across thea"sor"er4regenerator)

$mine carry over)5nsta"le temperature in the a"sor"er and regenerator)5nsta"le flash tan6 level and flo0 to regenerator)5nsta"le acid gas flo0 to the Sulfur Recovery 5nit)


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1oaming

ReasonsSuspended solids.

Organic acids in t!e feed gas.

Condensed ! drocarbons.Corrosion in!ibitors.

:a/eBup $ater impurities.

Amine degradation products.5ube oil.

SoapBbased 'al'e greases.


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1oaming"uidelines

Contaminants from upstream operations can be minimizedt!roug! ade uate inlet separation.

Condensation of ! drocarbons in t!e absorber can usuall bea'oided be maintaining t!e lean solution temperature at least( 3 @) abo'e t!e ! drocarbon de$ point of t!e outlet gas.

#emporar upsets can be controlled b t!e addition of antifoamc!emicals ( silicon or longBc!ain alco!ol ).

@oaming tests s!ould be done to c!ec/ t!e compatibilit andeffecti'eness of ne$ antiBfoam before using t!em.


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Sulfur Recovery


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Sulfur RecoveryH2 S s!ould be con'erted to nonBto,ic and usefulelemental sulfur t!at can be used in fertilizerindustr .

Clause Process & a process in $!ic! -8 of t!eH2 S in t!e acid gas feed is burned to SO 2 $!ic!is t!en reacted $it! t!e remaining H 2 S toproduce sulfur.

#!e modified Claus process+ de'eloped b5ondon c!emist Carl @riedric! Claus in EE8


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!laus ,rocess

Sulfur is reco'ered

b 8 steps&Thermal )!atalytic )

!old 7ed $dsorption .


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!laus ,rocess Schematic


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!old 7ed $dsorptionSchematic


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!laus ,rocess

Thermal & #!e H 2 S is partiall o,idized $it! air+producing t!e H 2 S and SO 2 in a 2& ratio.#!is is done in a reaction furnace at !ig!temperatures ( 333B F33 C). Sulfur is formed+

but some H 2 S remains unreacted+ and someSO 2 is made.

H2S G 8-2 O 2 SO 2 G H2O ( )

2 H 2S G SO 2 8-n S n G 2 H 2O (2)

O'erall 8 H 2S G 8-2 O 2 8-n S n G 8 H 2O (8)

#!is step gi'es sulfur reco'er of about 3 .


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!laus ,rocess

!atalytic #!e remaining H 2S is reacted $it! t!e SO 2 atlo$er temperatures (about 233B893 C) o'er a catal st toma/e more sulfur.

2 H 2S G SO 2 8-n S n G 2 H 2O (2)

#!e most $idel used Claus catal st in sulfur reco'er units isnonBpromoted sp!erical acti'ated alumina+ suc! as Al 2O 8

Properties associated $it! optimum nonBpromoted Clauscatal st include !ig! surface area+ appropriate pore size

distribution+ and en!anced p! sical properties.#!is step gi'es sulfur reco'er of about 89 +so t!e o'erallsufur reco'er is 9 .


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!laus ,rocess!old 7ed $dsorption & #!e C;A reactor is operated at lo$temperature ( 2 B FE C) initiall so t!at it is belo$ t!e sulfurde$point of t!e reaction products+ #!e H 2S and SO 2 in t!e gas $illreact 'ia reaction (2) to form sulfur+ $!ic! condenses due to t!e lo$

operating temperature and is adsorbed on t!e catal st.4ac! C;A reactor contains a 8 BFE deep bed of sulfur con'ersioncatal st+ usuall aluminaBbased.

#!e tailgas from t!e second C;A reactor is routed to a #ailgas

#!ermal O,idizer to incinerate all of t!e sulfur compounds to SO 2 before dispersing t!e effluent to t!e atmosp!ere.

#!is step gi'es o'erall sulfur reco'er of about EB .


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Interesting $spect of !laus

#!e strange be!a'ior ofmolten sulfur.

#!e temperature ofmolten sulfur must becontrolled carefull . If t!esulfur is allo$ed to cool

too muc! it can begin topol merize.


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!haracteristic 8iscosity !urve $ssociated0ith 'olten Sulfur


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acid gastreatment & sulfur recovery

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