Simulation of a Mine Plants Presentation

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IAPG 2008

Simulation of Amine Plants: Fundamental

Models and Limitations

2das Jornadas Técnicas Sobre Acondicionamiento del Gas Natural

30 de Septiembre al 3 de Octubre de 2008El Calafate, Argentina

Jenny Seagraves

INEOS Oxide

GAS/SPEC Technology Group



IAPG 2008

Topics of Presentation

General history and overview of fundamental models

refer to paper and references in papers for more details

Case Studies

Important considerations or ideas for designing or optimizing anamine plant



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History and Fundamentals of

Amine Simulation Models



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Improved simulation model are developed as solventtechnologies evolve and amine plant become more

complex….

MEA Specialty

TEA DEA DGA Amine

1930 1940 1950 1960 1970 1980 & Beyond….

MDEA DIPA

Simple Models

(Hand Calculations)

Complex Computer

Models



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Simulation of MDEA and newer specialty solvents...

MDEA-based and specialty solvents more difficult to simulate

contain MDEA and sometimes blends of chemicals that yield specifictreating characteristics

have components with different reaction kinetics

MDEA solvent have different temperature profile than MEA or DEA.

Simplified computer calculations are dangerously misleading for MDEA and specialty amine designs



IAPG 2008

Improved Simulation is Needed asAmine Plant Designs Evolve...

While 20 trays absorber & regenerator designs are still mostcommon ….

We now are designing amine plants with

multiple feeds and side draws

Complex multi-staged flash to reduce energy

New mass transfer devices to get more capacity

» new packing material or trays

» or a combination of the two.



IAPG 2008

Example of Amine Plant with Multi-feeds and Flash

Syngas

Lean Amine

Rich Amine

Semi-lean

CO2

T = 130 F (50 C)

Reboiler

Absorber

Regenerator



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Definitions

Vapor Liquid Equilibrium (VLE)

Defines the solution chemistry / chemical species present

model determines the maximum limit of H2S and CO2 absorbed

Reaction Rates

Defines how quickly H2S and CO2 are absorbed

H2S react instantaneously with amines and CO2 react at various ratesdepending on type of amine.

Mass Transfer Rate

Define the surface area and how quickly the surface area is refreshedfor H2S and CO2 absorption



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Vapor Liquid Equilibrium

ionization of water

2 H2O H3O+ + OH- (eq. 1)

dissociation of hydrogen sulfide

H2O + H2S H3O+ + HS- (eq. 2)

dissociation of bisulfide

H2O + HS- H3O+ + S2- (eq. 3)

dissociation of carbon dioxide

2 H2O + CO2 H3O+ + HCO3- (eq. 4)

dissociation of bicarbonate

H2O + HCO3- H3O+ + CO32- (eq. 5)

dissociation of protonated alkanolamine

H2O + RR’R’’NH+ H3O+ + R’R’R’’N (eq. 6)

carbamate reversion to bicarbonate

RR’NCOO- + H2O RR’NH + HCO3- (eq. 7)



IAPG 2008

Vapor Liquid Equilibrium

The equations governing chemical equilibria for equations 1 to 7

may be written as:

K = i (xi i )i (eq. 8)

where, K is the equilibrium constant

xi is the mole fraction of species i

i is the activity coefficient of species i

i is the stoichiometric coefficient



IAPG 2008

Chemical Kinetics and Mass Transfer

Ni = Ei k°i,L a (yi interface - yi

Bulk ) (eq 8)

NI

= transfer rate

Ei = enhancement factor (accounts for chemical reaction)

k°i,L = Mass transfer coefficient

a = interfacial area

yiinterface= acid gas conc. at interface (from Henry’s law)

yi bulk = acid gas conc. in bulk (from VLE)



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Evolution of Amine Simulation

Pre 1980s - Equilibrium Stage

Approach was only method

Uses simplified estimates

Estimate chemical species insolution

Uses tray efficiencies lumpreaction and mass transfer rates

Adequate for simulation of MEA and DEA

Not accurate for MDEA,

specialty solvents, and complexamine mixtures

Still used in many commercialsimulators today

After 1980s - Mass Transfer

Rate Based Approach

More rigorous

Calculate exact chemicalspecies present in solution

Calculate reaction and masstransfer rates

Accurate for MEA, DEA,MDEA, and Specialty aminesolvents

Can be extended to systemswith heat stable salts and other components if data is available

Used in only a few simulators

Hi t f M T f R t B d Si l ti



IAPG 2008

History of Mass Transfer Rate Based SimulationApproach

Idea to combine mass transfer with chemical reactions in aminesimulation came about as a result of works by Astarita, Weiland,Katti, and others.

In early 1980s, GAS/SPEC funded a series of research projects todeveloped the first amine simulator that combined

rigorous vapor-liquid-equilibrium (VLE) modeling

with mass transfer and chemical reactions calculations

Mass Transfer Rate-based simulation has been used and refinedover the last 20+ years by the GAS/SPEC group

Available in certain simulators such as

GAS/SPEC APS Simulator (proprietary simulation program)

Commercially available ProTreat Simulator (Optimized Gas TreatingInc.)



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What is mass transfer rate-based?



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Example of GAS/SPEC APS Simulation



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Most Basic Amine Simulation Models

Predicted

Plant Performance

Simulation

Material Balance

Tray Efficiency

Phase Equilibrium

Properties

Use tray efficiencies toaccount for

•mass transfer

•reaction rates

Efficiencies are empirically

derived

Ignore tower internals

•use equivalent stages torepresent a given number

of trays or packing height



IAPG 2008

Mass Transfer Rate-based Simulations

Predicted

Plant Performance

Simulation Material Balance

Reaction Kinetics

Phase Equilibrium

Properties

Mass Transfer

(Tower internals)

More detailed approach

Avoid the use of efficiencies

Considers differences in

reaction rates of H2S and

CO2

Consider Mass Transfer rate

of absorption in differenttower internals (trays,

packing, etc.)



IAPG 2008

Advantages of MT Rate-based Models

Makes more rigorous and accurate prediction inside column

temperature profile

reaction or absorption zone

identify trouble area in thecolumn

» equilibrium limits

» areas of corrosion concernsdue to high temperatures

1

3

5

7

9

11

13

15

17

19

21

100 110 120 130 140 150

Temperature (F)

T r a y N u

m b e r

ProTreat

Actual

Example of Actual vs Predicted



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Equilibrium Stage Approach

No one-to-one correspondenceof theoretical stage with

position in column

3 trays per stage ? Or 4 trays per stage?…etc.

Difficult to locate exacttemperature and composition of feeds and side draws

Top Tray

Stage 3

Tray location? Stage 2

Tray location?

Temp?

Composition? Stage 1

Feed



IAPG 2008

M.T. Rate-based Approach

Know temperature andcomposition on every actualtray

Can accurately locateoptimum points for feeds and

side draws

Top Tray

Tray is known

Tray is known

Temp is known

Feed



IAPG 2008

Case Studies



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Case Study 1

High pressure coal bed methane gas

requires CO2 removal only

plant have ability to treat a portion of the natural gas and blend to meet3 mol% CO2 spec



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Case 1 - Flow Diagram

AMINE

COOLER

REFLUX

CONDENSER

REFLUX

ACCUMULATOR

LEAN /RICH

CROSS-EXCHANGER

FEED

FILTER TRAIN

TREATED GAS

REBOILER

ABSORBERREGEN

RICH AMINE

LEAN AMINE



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Benchmark Performance Tests

Test 1 Test 2 Test 3

Raw Gas

Flow (Nm3/h) 235500 232100 200900

Temperature (oC) 40 40 40

Pressure (kPa) 6881 6881 6881

CO2 (mol%) 4.29 4.29 4.21

Lean Solvent

Flow (m3/h) 227 186 227

Temp (oC) 40 43 39

Wt% MDEA 48 48 48



IAPG 2008

Performance Compared to Simulation


Solvent Rate (m3/h) 227 186 227

Gas Rate (Nm3/h) 235500 232100 200900

Treated Gas

Measured CO2 (mol%) 1.54 1.98 1.20Predicted CO2 (mol%) 1.57 1.95 1.20

Lean Amine

Actual mol/mol 0.008 0.008 0.007

Predicted mol/mol 0.0075 0.0059 0.0046

Rich Amine Predicted mol/mol 0.310 0.403 0.294



IAPG 2008

Actual versus Simulation Predicted Temperature

1

3

5

7

9

11

13

15

17

19

21

38 49 60 71

Temperature (°C)

T r a y N u m b e r

1

3

5

7

9

11

13

15

17

19 21

38 49 60 71 82

Temperature (°C)

T r a y N u m b e r

1

3

5

7

9

11

13

15

17

19 21

38 49 60

Temperature (°C)

T r a y N u m b e r

Test 1 - Absorber Test 2 - Absorber Test 3 - Absorber

Actual temperature measurements

Simulated Temperatures



IAPG 2008

Significance of Temperature Profile

Concern with Temperature Profile because

higher and broader profile have corrosion implications

outlet gas temperature increase load on downstream dehydrationequipment

high temperature may limit capacity or cause plant to go off spec -difficult to absorb CO2

» near equilibrium loading



IAPG 2008

Tower Temperature Profiles

GAS/SPEC technical service

engineers use these temperature

scans of towers to troubleshoot

amine plant. This is a method

to monitor performance

Poor liquid

distribution

Broad temperature

profile throughout



IAPG 2008

Options for More Capacity

Customer wants more capacity out of the plant

However CO2 level in inlet gas is rising!

Option 1 - Continue to treat with MDEA

Treat to just below 3% CO2 specification

Option 2 - Upgrade to a Specialty Solvent

Treat CO2 to low levels of < 1000 ppm

then blend with untreated gas to meet 3% CO2 specification

M C i i h MDEA



IAPG 2008

Max Capacity with MDEA

0

100000

200000

300000

400000

500000

600000

3.5 4 4.5 5 5.5 6 6.5

Inlet CO2, mol%

G a s F l o w , N m 3 /

Treated

Bypassed

Combined

Pipeline Max

M C i i h S i l S l



IAPG 2008

Max Capacity with Specialty Solvent

0

100000

200000

300000

400000

500000

600000

700000

800000

900000

3.5 4 4.5 5 5.5 6 6.5

Inlet CO2, mol%

G a s F l o w , N m 3 /

Treated

Bypassed

CombinedPipeline Max

R lt ft C i



IAPG 2008

Results after Conversion

MDEA CS-2010

Flow to Absorber (Nm3/h) 235500 232100

Inlet CO2, mol% 4.29 4.5

Outlet CO2, mol% 1.54 < 0.1

Amine Flow, Nm3/h 227 202

Max Total Gas

Capacity (Nm3/h) 446400 502200

Currently limited by capacity of downstream pipeline

C l i C 1



IAPG 2008

Conclusions - Case 1

Demonstrates use of simulation tool to

accurately predict temperature and CO2 in the column.

identify opportunities for optimization of existing plant

make decision on how to best utilize assets for present and futuretreating conditions

C St d 2



IAPG 2008

Case Study 2

Offshore natural gas application

H2S and CO2 removal

Simulations used to

design original plant

modify plant to adapt to changing process conditions

C 2 Fl Di



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Case 2 - Flow Diagram

AMINE

COOLER

REFLUX

CONDENSER

REFLUX

ACCUMULATOR

LEAN /RICH

CROSS-EXCHANGER

FEED

FILTER TRAIN

TREATED GAS

REBOILER

ABSORBERREGEN

RICH AMINE

LEAN AMINE

O i i l D i T ti C diti



IAPG 2008

Original Design Treating Conditions

Inlet Gas Flow (Nm3/h) 502200

Inlet Gas Pressure (kPa) 7419

Inlet Gas Temp (°C) 49

Gas Composition:

CO2

(mol%) 3.25

H2S (mol%) 1.35

Treated Gas Specification:

CO2 (mol%) < 1

H2S (ppmv) < 4

K D i D i i



IAPG 2008

Key Design Decisions

Prior to INEOS involvement, customer decided on

30 tray absorber (3.35 meters diameter with 10 cm weir height)

design based on generic MDEA

plant was already designed with “Equilibrium Stage”-based simulator

Use of 30 trays is unusual in an offshore application due to weightconsideration

Sim lation Design Rate



IAPG 2008

Simulation - Design Rate

Gas Flow (Nm3/h) 502200Feed Tray from Top 30

MDEA Conc. (wt% ) 50%

Circulation Rate (m3/h) 545

Treated GasCO2 (mol%) 0.92

H2S (ppmv) < 1 ppm

Lean Loadings / Rich Loadings

H2S (mol/mol) 0.0002 / 0.13CO2 (mol/mol) 0.005 / 0.23



IAPG 2008

Variations operating conditions were alsosimulated...

Simulations for Changing Condition



IAPG 2008

Simulations for Changing Condition

Limited heat source at certain times

57% of design duty available

Plant will operate at reduced rate

Increased CO2 pickup at reduced rate

How to operate plant to minimize CO2 pickup

Alternatives for Operating at Reduced Rates



IAPG 2008

Alternatives for Operating at Reduced Rates

502200 Nm3/h

Reboiler Duty = X

30 trays

CO2 Out = 0.92 mol%

30 trays

279000 Nm3/h

340 m3/h of 50wt% MDEA

Reboiler Duty = 0.57 X

CO2 Out = 0.59 mol%

19 trays

279000 Nm3/h

340 m3/h of 50 wt% MDEA

Reboiler Duty = 0.57X

CO2 Out = 0.99 mol%

Scenario 1

Scenario 2

Outcome of Simulations



IAPG 2008

Outcome of Simulations

Feed points added to trays 30,24, 19 to allow for flexibilityunder changing conditions

Tray 30

Tray 24

Tray 19

Feed

ABSORBER

Prior to Startup



IAPG 2008

Prior to Startup

Plant needed lower CO2 level

Minimize corrosion in downstream pipeline

Old spec 1% CO2 ; New spec 1000 ppmv CO2

In order to maximize CO2 removal, customer has 2 options

Option 1 - Continue with MDEA

» Higher amine circulation rate, L/V

» Use all 30 trays

Option 2 - Specialty amine solvent

» Treat with less trays and less circulation

Customer decide to proceed startup with MDEA and then upgradeto a specialty solvent.

After Startup



IAPG 2008

After Startup

After startup, the plant experienced foaming

Plant had difficulty treating at high capacity

Not making the 1% CO2 spec with MDEA

Problem was caused by

Hydrocarbon coming into the plant

High amine flow and high tray count required by MDEA seem toworsen foaming problem

» operate with only 19 trays

» over-circulate to keep the CO2 level down

Conversion to Specialty Solvent



IAPG 2008

Conversion to Specialty Solvent

After operating with MDEA for 5 months, customer converted to

GAS/SPEC* CS-2000 solvent

Running conversion.

Now plant treating at full capacity of 450 MMSCFD

Meeting < 1000 ppmv CO2

spec

Only the bottom 19 trays were needed

Reduction in foaming tendency

» better separation / filtration

» higher loading decrease HC solubility




IAPG 2008


Ideally want to design a plant with fewer trays and higher rich

loadings

to reduce capital cost

to minimize hydrocarbon absorption

Simulation used to determined alternative feed points to improve plant flexibility

Simulations helped adapt plant to new treating requirements witha specialty solvent

Case Study 3



IAPG 2008

Case Study 3

Natural gas plant

plant faced with rising CO2 composition

Originally 7.8 mol%

CO2 is now over 10%

Plant operation was unstable because high outlet CO2 causedcoldbox to freeze

Goal is to increase capacity and stabilize plant operations

Operating Conditions versus Simulated



IAPG 2008


Flow (Nm3/h) 34600

Temperature (°C) 11

Pressure (kPa) 4440Inlet CO2 (mol%) 10.2

Actual CO2 Out (ppm) 10

Predicted CO2 Out (ppm) 10

Lean SolventFlow (m3/h) 82


Wt% GAS/SPEC CS-2020 50

Rich SolventTemperature (°C) 79 to 81

Predicted Temp (°C) 81




IAPG 2008


Flow (Nm3/h) 34600


Pressure (kPa) 4440Inlet CO2 (mol%) 10.2

Actual CO2 Out (ppm) 10

Predicted CO2 Out (ppm) 10

Lean SolventFlow (m3/h) 82


Wt% GAS/SPEC CS-2020 50

Rich SolventTemperature (°C) 79 to 81

Predicted Temp (°C) 81

Effect of Rate on CO2 Concentration



IAPG 2008

Effect of Rate on CO2 Concentration

1

3

5

7

9

11

13

15

17

19

21

23

1 10 100 1000 10000 100000

CO2 in Vapor, ppmv

T r a y # ( T o p d o w

n )

36800 Nm3/h

35700 Nm3/h

34600 Nm3/h

Effect of Rate on CO2 Loadings



IAPG 2008

Effect of Rate on CO2 Loadings

1

3

5

7

9

11

13

15

17

19

21

23

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45

Loading, mol/mol

T r a y # ( T o p d o w n )

36800 Nm3/h

35700 Nm3/h

34600 Nm3/h

Little CO2

absorption

Effect of Rate on Column Temperature



IAPG 2008

Effect of Rate on Column Temperature

1

3

5

7

9 11

13

15

17

19 21

23

120 130 140 150 160 170 180 190 200 210

Temperature, °F

T r a y # ( T o p d o w

n )

36800 Nm3/h

35700 Nm3/h

34600 Nm3/h

Outcome - Case 3



IAPG 2008

Outcome Case 3

Plant personnel confirmed maximum rate of 34600 Nm3/h

Client considering upgrading pumps and exchangers in order toincrease/maintain capacity as inlet CO2 rises




IAPG 2008

Conclusions Case 3

MT Rate based simulation gave insight on effect of gas rate on

treat and temperature profile

Allows plant to make informed decisions for future

Conclusions



IAPG 2008

Conclusions

Discussed the advantages of Mass Transfer Rate Based Simulation

over other simulation methods

Case studies have shown

accuracy of column temperature/composition prediction

effect of mass transfer (tray count) on performance

how to use simulator to design/modify in changing conditions

the importance in considering temperature effects

Acknowledgement



IAPG 2008

Acknowledgement

Ulises Cruz - INEOS

Andy Sargent - INEOS

Ralph Weiland - Optimized Gas Treating, Inc.

* GAS/SPEC and CS-2000 are trademarks of INEOS Oxide

TM ProTreat is a trademark of Optimized Gas Treating, Inc.



IAPG 2008

QUESTIONS?

Simulation of a Mine Plants Presentation

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