-
AM inGr t
CO2 rmemproce
Utilize
NaturThermal swing adsorption (TSA)unit
Removes heavy hydrocarbons
Serves three functions
Membranepretreatment
Feed gas dehydration
Sales gas hydrocarbondew pointing.
Background
General Considerations
Plant built and commissioned in1998 without TSA
membranepretreatment
Initial well tests indicated minimalamounts of heavy
hydrocarbons
Subsequently, found not to bethe caseMembrane separation and
Amine adsorption
Simplified process flow diagram isshown in Figure A-2.DOI:
1emoval process uses abrane/adsorption hybridss
s bothProcess overviewCO2 concentrations
Inlet: 30%
Outlet: 3%Indonesia: Case
Introduction
ConocoPhillips operates Grissik GasPlant (Figure A-1) on behalf
of itspartners:
Talisman Energy
Pertamina
BPMigas
Design basis
Gas feed: 310 MMscfdppendix Aembrane/Amissik Gas
Plan0.1016/B978-1-85617-982-9.00008-9Fed to the amine
absorptioncolumn where CO2 isremoved to about 3%.
Permeate rich in CO2 exits themembrane at near
atmosphericpressure.CO2 rich permeate is sent toan atmospheric
burner toproduce steam which is usedin the amine plant
forregeneration.
al gas exiting the membrane
Contains about 15% CO2e Hybrid,1,2,3 Sumatra,Study
Benefits of membrane/amine hybridprocess
Have a single stagemembrane and utilize thethermal value in the
permeatestream, thereby
Enjoying the simplicityof a membraneseparation processwithout
the use of arecycle compressorwhile
Still avoidinghydrocarbon losses.
-
158 Gas Sweetening and Processing Field ManualFIGURE A-1 Grissik
gas plant.First Commissioning
Membrane initially installed withpretreatment consisting of
Coalescing filter and
Nonregenerable absorptionguard bed.
At startup in 1998
Actual levels of heavyhydrocarbons (CO10,aromatics, and
napthenes)were higher than anticipated.
Raw feed300 MMSCFD 1140 PSIG 83 F 30% CO2
Retentate 230 MMSCFD 1100 PSIG 99 F 15% CO2
Perm
Gas/liquid separator
TSA
Note: Approximate flows and compositions shown.
120F
FIGURE A-2 Grissik process flowResulted in sharp reductionin
membrane capacity(declining to 2030% ofinitial capacity within in
amonth)
To maintain productioncapacity, the membraneelements were
beingfrequently replaced.
Installation of TSA
ConocoPhillips evaluatedheavy hydrocarbon removalprocesses
including
Membrane
Steam generator
Sales gas
Amine absorption column
Dehydration
eate
200 MMSCFD1087 PSIG 2% CO2
diagram.
-
Gas chilling process and
Regenerableadsorption process.
Gas chilling process
Deemed ineffective atthe plant operatingpressure, which wasnear
the cricondenbarof the feed gas phaseenvelope
Regenerable adsorptionprocess
Short cycle processfrom Engelhardwhich uses Sorbead
Designed toreduce C6components(includingaromatics andnapthenes)
sothat membraneperformance canbe maintainedfor an extendedperiod of
time
Designed withtwo separatetrains, each withfour adsorptionvessels
(refer toFigure A-3)
hydrocarbons for properpretreatment so as to yieldlong membrane
life.
FIGU l swing adso
Appendix A: Membrane/Amine Hybrid Grissik Gas Plant 159RE A-3
Engelhard thermasilica gel at elevatedtemperatures.
TSA was built andinstalled by Kvaener in2000Aromatics
Napthenes
Adsorption cycle isfollowed byregeneration of the(Silica Gel) as
theadsorbent
Uses multiple beds inparallel adsorption toremove
Heavyhydrocarbonsrption unit.TSA design andperformance
General Design
Considerations
Since feed gas was found to containhigh levels of heavy
hydrocarbons(C10, aromatics, and napthenes)
TSA had two functions and solvedtwo problems:
TSA removes heavy
-
Removal of heavyhydrocarbons allows the salesgas to meet
hydrocarbon dewpoint specs.
Since water is more strongly heldonto the Sorbead adsorbent
thanany of the hydrocarbons, the TSAsystem also dehydrates the
feedupstream of the membrane unit.
TSA Process Description
Each train was designed to treat225 MMscfd
Consiadsor
Refer(Figur
treated gas to thedownstreammembrane unit.
Balance of the feed gasbypasses the pressuredrop valve so as
toprovide the necessaryflow through thetowers being cooledand
heated.
Regeneration path containsthe
Tower being cooled
er ting Heliq
rem
diagram
160 Gas Sweetening and Processing Field Manualthrough the
two-phaseseparator, is split into twoparallel paths.
Majority of the gasflows through thepressure drop valve andthen
directly to twotowers on paralleladsorption.
Cycle time of thetowers is staggered by50% to allow for
acontinuous flow of
Wellhead
Regen heater
TSA tower cooling
TSAtowhea
Liquid
Pressure drop valve
FIGURE A-4 TSA process flowsts of four internally insulatedber
towers
Minimize the thermal massfor the short thermal cycle
Reduces heat load on thesystem
to TSA process flow diagrame A-4)
Feed gas, after passingTo membraneskids
TSA 2 towers adsorbing
avy uids
oved
.Wet feed gas is used as theregeneration medium, andbecause of
the pressure dropvalve, there is no need for acompressor to boost
thepressure of the spentregeneration gas.Cooling
AdsorbingEach tower is associated withsix valves that allow it
tochange functional positions
Adsorbing
Heating/regeneratingRegeneration heater
Tower being heated
Heat recovery heatexchangers, and
Spent regeneration gasseparator
-
components aredesorbed
Reas
In ordflowbed,funct
MaximdeterGrissitoweadsor
in parallel on adsorption is anequalized composition of
thetreate
In a s
Breakthrough
Appendix A: Membrane/Amine Hybrid Grissik Gas Plant
161regeneration gasrequirement.ons for Four Towers
er to maintain an acceptablevelocity across the adsorberthe
number of towers used is aion of
Flow rate and
Tower diameter.
um tower diameter wasmined by transport limits;k design resulted
in fourrs with two towers in parallelption.
Internal insulation was usedto minimize the amount ofthe process
where theheavy hydrocarbonsexit the system.Spent regeneration
gasstream containing water andC6 is then cooled and
Condensed liquidsremoved in theregeneration gasseparator.
This is the only place inDuring adsorption
Water and C6components areadsorbed at 1100 psigand 90140 F.
Prior to C6breakthrough, thetower position isswitched to
heatingmode and is completelyheated to 540 F.
Internal insulationallows heating of theadsorbent only and
notthe steel shell.
During heating, thewater vapor and C6Cycle times
Driven by the breakthroughbehavior of the C6components in the
towerdesign in order to meet thehydrocarbon specification ofthe
treated gas
Result of analysis and fieldobservations
Typical cycle consisted of(Refer to Table A-1)
Two-hour adsorbing
One-hour heating, and
One-hour cooling.
Heat Recovery Between
Cooling and Heating
System uses one tower heating andone tower cooling at a
time.composition betweenbeginning and end cycle,caused by the
breakout of theindividual components.
In a four tower system with twotowers on adsorption
There is an offset time of halfan adsorption cycle.
Gas composition of thecombined outlet gas is moreconstant than
from a singletower system.
Cycle Times andd gas.
ingle tower system
There is a difference in the gasHeating and cooling towers are
in aseries arrangement which alsoconserves the amount
ofregeneration gas required.
Additional benefit of having towers
-
Gas-t
adsorption bed and
ng
ating 1 h Coolingsorption 1 h Heatingoling 2 h Adsorptionating 1
h Cooling, 1 h adsorption
162 Gas Sweetening and Processing Field ManualHot gas is
cross-exchangedwith the gas upstream of theregeneration gas
heater(Refer to Figure A-4).
Exchanger is bypassed duringthe time when the gas exitingthe
tower on cooling is at ahigher temperature than thegas leaving the
tower in theheating step.Regento provide the requiredheating
gastemperature.
o-gas heat exchanger
It is used to capture the heatexiting the tower which isbeing
heated.temperature of the gasexiting the cooling tower
Drops so the heater hasDue to the entire towerbeing cooled the
gas isat the hot regenerationtemperature of 540 F
During the cooling cycle, theHot gas leaving the towerbeing
cooled flows throughthe heater in order to getadditional heat
in.
At the beginning of the cycle,gas exiting the tower oncooling is
almost at therequired heatingtemperature.
Results in nearly nomake-up heat beingrequired
Table A-1 Tower mode timi
Tower 1 2 h Adsorption 1 h HeTower 2 1 h Cooling 2 h AdTower 3 1
h Heating 1 h CoTower 4 1 h Adsorption 1 h Heeration heater
Direct-fired heaters
Size of the heater depends onthe regeneration gas flowrequired
to heat theshown.
Note the strong cutoff thatoccurs between C6 and C8.
Heavier hydrocarbons areessentially
completelyremoved.Tablhydr
TSA feTSA ouTable A-2.
Corresponding phaseenvelopes are shownin Figure A-5.
Figure A-6 shows the resultsof gas sampling done with amass
spectrometer whereboth the feed and exitstreams of the TSA
wereanalyzed dynamically.
Ratio of hydrocarbonconcentration in theoutlet versus inlet
isexcellent membraneperformance.
TSA performanceregarding hydrocarbondew point wasimpressive,
seeplant in October 2000
Good TSA performanceremoving the heavyhydrocarbons led todesorb
the water andhydrocarbons within thedesign cycle time.
TSA performance
After recommissioning thee A-2 TSAocarbon dew point
ed gas 86 F at 1150 psigtlet gas 22 F at 1115 psig
-
Appendix A: Membrane/Amine Hybrid Grissik Gas Plant 163200
400
600
800
1000
1200
1400
1600Pr
essu
re [p
sig]
Bubble pointAir liquidemedalmembrane
General Considerations
Polyimide hollow fiber membraneelements (shown in Figure
A-7)provide for a high efficiencyseparation of CO2 fromhydrocarbon
streams.
Membrane system was fabricatedasmultiple skids (refer to Figure
A-8)operating in parallel.
0250 200 150 100
Temp
FIGURE A-5 TSA inlet and outlet
0
1
C4 C5 C6 C7
TS
A o
utl
et/in
let
FIGURE A-6 TSA hydrocarbon taiActual TSAinlet gasdew pt
Actual TSAoutlet gasdew pt
Dew ptpossibleby chillingEach skid contains multiplehorizontal
tubes.
Each tube contains multiplemembrane elements (refer toFigure
A-9).
Multiple elements areinstalled in a single tube.
Membrane elements areactually functioning in parallel.
More than 100membrane elementsare used in this plant.
50 0 50 100 150erature [F]
phase envelopes.
C8 C9 C10 C11
l.
-
164 Gas Sweetening and Processing Field ManualC1+CO2H2SH2OFeed
gas enters the tube near oneend and flows axially to all
themembrane elements by way of anannular clearance.
Each element is composedof several hundred thousand
CO2H2SH2O
FIGURE A-7 Air LiquideMEDAL
FIGURE A-8 Skid containing Air L
Feed
Permeate
FIGURE A-9 Multiple membraneC1+parallel hollow
polyimidefibers.
Feed gas enters the membraneelements on the fiber shell
insideand flows over the fibers, whereCO2 is removed, to a coaxial
tube in
Air liquide
natural gas membrane.
iquide membrane elements.
Residue
element flow arrangement.
-
the center of each element(retentate).
Retentate streams for each elementflow axially to exit at one
end of thetube.
CO2 selectively permeates intothe bore of the fibers and
thenflows axially to a collection pointat the end of each
element(permeate).
Permeate of each element is thencollected in the coaxial center
tubeand flows axially to exit the tube atthe opposite end from
theretentate.
Membrane Performance
Typical operating conditions
Permeate pressure is about10 psig which flows to thesteam
generator burners.
Hydrocarbon losses versus time
One of the major advantagesof the polyimide membrane isits
ability to maintain integrityindefinitely, even aging in
thepresence of heavyhydrocarbons.
As shown in Figure A-10,membrane integrity is solidand the
hydrocarbon losseshave decreased somewhatsince startup.
This trend of decreasinghydrocarbon losses indicatesno loss of
membraneintegrity and actually showsa slight increase in
apparent
Se
ca
Appendix A: Membrane/Amine Hybrid Grissik Gas Plant 1650.0
0.2
0.4
0.6
0.8
1.0
Aug-00 Mar-01
Hyd
roca
rbon
loss
es (
norm
aliz
ed)
FIGURE A-10 Membrane hydroMembrane skids are feddirectly from
the output ofthe TSA.
Feed temperatures varybetween 90 and 120 F.
Feed pressure is 1100 psig.
Feed gas contained 30%CO2.
1.2intrinsic membraneselectivity.
Such a selectivity increasewould be consistent with thechange in
permeability (seebelow).
Membrane capacity versus time
After TSA was commissionedin October 2000
p-01 Apr-02 Nov-02
Design losses
rbon losses versus time.
-
One membrane skidwas retrofitted withnew membraneelements and
itsperformance tracked.
Results shown in Figure A-11
Vertical axis is labeledRelative Capacity toRemove Moles ofCO2
which is thenormalized intrinsicmembranepermeability.
Initial capacity waswell above design,and after 10 years
ofoperation, the capacitystill remains abovedesign.
Membrane skids wereshut down andrestarted many timesfor
maintenanceof surroundingequipment or capacityturndown.
Start and stop, orpressurization anddepressurizationcycles have
no effecton membraneperformance, althoughcaution must be usedto
avoid reversepressurization.
Permeate/Acid GasUtilization
0.0
0.5
1.0
1.5
2.0
00 20,0 from start
tive
capa
city
to re
move
m
ole
s of C
O2
Design ca
FIGU city vers
166 Gas Sweetening and Processing Field Manual0 5000 10,000
15,0Hours
RE A-11 Membrane capaRel
aExact membrane lifecan be extrapolatedto be over 12
yearswithout replacement
Excellent operation ofthe TSA and membranehave resulted in
yearsof trouble freeoperation with zeromaintenance, that is,no
membranereplacements.00 25,000 30,000 35,000-up
pacity
us time.Two waste heat boiler units areinstalled.
Waste heat boilers recoverwaste heat available in lowBTU
permeate gas stream(150250 Btu/scf) from themembrane units.
Utilizing waste heat in thepermeate stream meanssingle stage
membrane can
-
Appendix A: Membrane/Amine Hybrid Grissik Gas Plant 167be used
without thelimitations of a secondmembrane stage with
theaccompanying recycle gascompressor and still avoidhydrocarbon
losses.
Boilers are designed toincinerate the acidgases removed by
theamine unit.
Auxiliary fuel is utilized tomake up any inadequacy ofheating
value input and tostabilize the flame.
Furnace temperature ismaintained above 1600 Fprior to
introducing permeatefuel or acid gases.
Lower temperature leads toincomplete destruction of thecomponent
and results in theemission hazards.
Waste heat boilers arecontrolled by steam headerthat actuates
pressurecontrol valves on eachsteam drum.
Output of the steam headerpressure controller goesthrough flow
ratiocontrollers of permeategas, fuel gas, andcombustion air.
Fuel gas flow rate is setaround 10% of permeate gasflow rate
while combustionair is controlled to ensurestoichiometry and
completecombustion with 25%excess air.
Waste heat boiler producessteam up to 210,000 lbs/h at150 psig
and 348 F.
Biggest consumer of steamproduced is the aminesystem.
Condensing heat released bythe steam is used to removeacid gas
from amine solventat amine reboilers.Amine System
Amine system further reduces CO2and H2S to meet sales
gasspecification.
Residue gas from the membraneunit, containing 15% CO2,
Flows into the aminecontactors and
Contacted with lean amine(50%wt-activated MDEA).
CO2 absorption by activated MDEAis limited to a maximum loading
of0.5 mol acid gas/mol MDEA.
CO2 content in the treated gasvaries between 2% and 5% byvolume
(3%-vol average).
Rich amine is then flashed at75 psig, heated through a
lean/richamine exchanger, and regeneratedby the steam heated
reboiler.
The 150 psig steam used forregenerating amine is produced inthe
waste heat boiler that burnspermeate gas.
Several common problems of anamine system include
Reduced strength and abilityto absorb acid gas
Degradation
Foaming and
CO2 corrosion attack duringacid gas breakout inside
thereboiler.
Most problems found in an aminesystem are due to the presence
ofcontaminant in the amine solvent,including
Heat stable salts
Degradation products
Injected chemicals
Hydrocarbons and
Particulates.
Heat stable salts and degradationproducts are formed by
amine
-
solvents that decompose and/orreact with other contaminants.
TSA/membrane installed upstreamof the amine system has
mitigatedthe above problems to anacceptable level.
TSA unit removes heavyhydrocarbons from the feedgas and nearly
eliminatedthe foaming risk of aminesolvent.
An antifoam injection systemis provided to anticipate worstcase
conditions.
CO2 content reduction by themembrane unit
Breakout in the regenerationprocess
Lessons CO2 breakout in theregeneration process
Treated gas condition at the outletof the amine unit is normally
3%-volCO2 and 24 ppmv H2S, while salesgas contract specifies 5%-vol
CO2and 8 ppmv H2S.
One advantage from the highperformance of absorption is
anallowance to increase systemdeliverability by bypassing
someuntreated gas and blending withtreated gas while maintaining
thesales gas specification.
References
1. Anderson, C.L. and Siahaan, A.
Case study: Membrane CO2 re-
moval from natural gas, Grissik
gas plant, Sumatra, Indonesia,
Regional Symposium onMembrane
168 Gas Sweetening and Processing Field ManualReduces
contaminants thatmay trigger salt formation oramine degradation
Though contaminants couldalso be introduced bymakeup water or
evenmakeup amineScience and Technology, 2004,
Johor Bahru, Malaysia.
2. Malcolm, J. The Grissik gas plant,Hydrocarbon Asia, 2001.
3. Anderson, C.L. Case study: Mem-
brane CO2 removal from natural
gas, Regional Symposium on
Membrane Science and Technol-
ogy, 2004, Johor Bahru, Malaysia.
Membrane/Amine HybridGrissik Gas Plant,1,2,3 Sumatra,Indonesia:
Case StudyIntroductionProcess overviewBackgroundGeneral
ConsiderationsFirst Commissioning
TSA design and performanceGeneral Design ConsiderationsTSA
Process DescriptionReasons for Four TowersCycle Times and
BreakthroughHeat Recovery Between Cooling and Heating
Air liquide-medal membraneGeneral ConsiderationsMembrane
Performance
Permeate/Acid Gas UtilizationAmine System