MODELLING OF RWGS FOR FTSYNTHESIS APPLICATIONS

Francisco Vidal Vázquez (Paco)

CONTENTS• Introduction to rWGS for FT applications.

• Experimental work for kinetic modelling

• Modelling&Simulation

– Parameter estimation.

– 1D stationary model.

– 1D dynamic model.

• Next steps

Introduction to rWGS for FT applications

• FT synthesis with Co-catalyst (Production of heavier HC): diesel and waxes.• High pressure (approx. 30 bar) reverse Water-Gas Shift reaction.

– Endothermic reaction, and equilibrium-limited process.– Advantage of high pressure: no need of compression in between rWGS and FT (cooling,

water removal, compression and reheating).– Disadvantage of high pressure is the methane production.

• Main reactions involved in the HP-rWGS:

rWGS FTsynthesis

+ 3 ⇄ + ∆ = −206.1

+ 4 ⇄ + 2 ∆ = −165.0

+ ⇄ + ∆ = +41.5

Methanationreactions(undesired)

Equilibrium of rWGS

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Temp. (degC)

1 bar

xCO2 eq (rWGS)

xCO2 eq (rWGS+CH4)

yCH4 eq (rWGS+CH4)

yCO eq (rWGS+CH4)

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Temp. (degC)

30 bar

Initial composition for thermodynamic calculations(N2=42.5%, H2=38.33%, CO2=19.17%)H2/CO2 ratio = 2

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Temp. (degC)

Any pressure

xCO2 eq (rWGS)

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450 550 650 750 850

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Temp. (degC)

1 bar

xCO2 eq (rWGS+CH4)

yCH4 eq (rWGS+CH4)

yCO eq (rWGS+CH4)

• Quartz tube inside the Inconel tube. Innerdiameter 6 mm.

• Sealing of the gap between the tubes bygraphite gasket cord on top and bottom ofthe tubes. SiC 100-200 µm placed in thegap between tubes to ensure nobypassing.

• Catalyst bed kept in place by SiC 710-850µm on the bottom of the tube to reducepressure drop.

• Relatively small blank activity.

0.6 cm

SiC (100-200 µm),outer wall

Catalyst dilutedwith SiC

TC

Heatingjacket

SiC (710-850 µm)

Graphitegasket

FLOW

Quartztube

Experimental apparatus (2nd tubular reactorconfiguration)

Experimental work• Fixed-bed tubular reactor.• Kinetic modelling:

• One catalyst: Ni/Al2O3 catalyst with ca. 2 w-% Ni. Particle size 400-500 µm.• Different SV (constant flow but different catalyst loadings) and H2/CO2 ratio.• Pressures 1, 15 and 30 bara and temperatures 500-800⁰C.

• Experimental results (after initial deactivation):– Catalyst loading 0.5 grams.

• 7 experimental points at 1 bar and H2/CO2 ratio 2.

– Catalyst loading 0.25 grams.• 7 experimental points at 1 bar and H2/CO2 ratio 2.• 6 experimental points at 30 bar and H2/CO2 ratio 2.• 7 experimental points at 15 bar and H2/CO2 ratio 2.• 4 experimental points at 1 bar and H2/CO2 ratio 3.• 2 experimental points at 30 bar and H2/CO2 ratio 3.

– Total useable experimental points for parameter estimation = 33.

Exp. results: 0.5 grams loading

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450 550 650 750 850

%

Temp. catalyst bed (degC)

1 bar

xCO2 eq (rWGS)

xCO2 eq (rWGS+CH4)

yCH4 eq (rWGS+CH4)

yCO eq (rWGS+CH4)

xCO2 exp

yCO exp

yCH4 exp

• Ni/Al2O3 catalyst with ca. 2 w-% Ni. Particle size 400-500 µm.• H2/CO2 ratio = 2

Exp. results: 0.25 grams loading

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100

450 550 650 750 850

%

Temp. catalyst bed (degC)

1 bar

xCO2 eq (rWGS)

xCO2 eq (rWGS+CH4)

yCH4 eq (rWGS+CH4)

yCO eq (rWGS+CH4)

xCO2 exp

yCO exp

yCH4 exp

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100

450 550 650 750 850

%

Temp. catalyst bed (degC)

30 bar

• Ni/Al2O3 catalyst with ca. 2 w-% Ni. Particle size 400-500 µm.• H2/CO2 ratio = 2

Exp. results: cat. stability

1 barRun

05

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0 20 40 60 80

%

Time (hr)

xCO2 exp[%]

X CO2 eq

30 barRun

1 barRun

• Same check point:– Fixed SV and composition.– At 1 bar and ca. 500⁰C in the catalyst bed.

• 0.5 grams run sequences about 20 hr each: 1 bar, 30 bar and 1 bar again. Totaloperating time ca. 60 hr. The 30 bar run showed in this presentation was in between20 and 40 hr time on stream (cat. activity seemed not to be stable yet).

• 0.25 grams first 3 run sequences were the same as 0.5 grams. Total operating timeca. 130 hr. All the results showed in this presentation are over the 40 hr time onstream.

• Initial deactivation seem to be stronger at higher pressures.

0.5 grams

05

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%

Time (hr)

0.25 grams1 barRun

30 barRun

1 barRun

30 barRun

15 barRun

30 barRun

Modelling&Simulation work (using Matlab)

• Parameter estimation using experimental– 1D stationary model (isothermal and isobaric).– Xu and Froment (1989) kinetic model.– Own developed model.

• Assessment of reactor configuration options for rWGSusing 1D stationary model and 1D dynamic model:– Heat exchanger reactor.

• Co-current• Counter current.

– Adiabatic reactor/s: single reactor or reactor in series with“interheating”.

Modelling work (kinetic model)• Xu&Froment kinetic model was used for simulation with experimental input data. Xu&Froment results used NG

reforming catalyst Ni/Al2O3 with ca. 15 w-% Ni.

0

10

20

30

40

50

60

70

80

90

100

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%

Temp. catalyst bed (degC)

30 bar

0

10

20

30

40

50

60

70

80

90

100

450 550 650 750 850

%

Temp. catalyst bed (degC)

1 bar

xCO2 eq (rWGS)

xCO2 eq (rWGS+CH4)

yCH4 eq (rWGS+CH4)

yCO eq (rWGS+CH4)

xCO2 calc (Xu&Froment)

yCO calc (Xu&Froment)

yCH4 calc (Xu&Froment)

Modelling work (parameter estimation)

• Xu&Froment model has 14 parameter (too many).• Parameter estimation for 3-6 parameter.

Modelling work (parameter estimation)

Confidence interval and sensitivityanalysis still to be done. (debuggingof original Matlab script).

1,713e-05 3,387 3,343e-06 95,67 0,595

1D stationary model

• Species mass balance eq.:

=1

− +

• Velocity change by ideal gas eq. derivation:

= − +

• Heat balance eq.:

=1

−∆ −

2( − )

• Pressure drop by Ergun eq.• Assumptions:

– Plug-flow.– No radial gradients.

x1 xx xn

Initial values:- Velocity.- Concentration.- Temperature.- Pressure.

Reactor length

1D dynamic model• Species mass balance eq.:

= − − + +

• Momemtum eq. (Navier-Stokes eq. for compressible fluid):

= − −1

+43

• Velocity change by derivation based on eq. of state for ideal gas:

= − +

• Heat balance eq.:

=1

− − ∆ −2

( − )

• Pressure drop by Ergun eq.• Same assumptions as stationary model.

Reactor length

Method of Lines

t1

tx

tn

= + + +

x1 xx xn

= [… ]

= [… ]

BCs BCs

1D dynamic model• Species mass balance eq.:

= − − + +

• Momemtum eq. (Navier-Stokes eq. for compressible fluid):

= − −1

+43

• Velocity change by derivation based on eq. of state for ideal gas:

= − +

• Heat balance eq.:

=1

− − ∆ −2

( − )

• Pressure drop by Ergun eq.• Same assumptions as stationary model.

1D Dynamic model• Mass balance with momentum equation applying velocity change

(du/dl) eq. (450 degC and 1 atm):• First second of simulation only axial dispersion:

t=0.01 sec t=1 sec

1D Dynamic model• Mass balance with momentum equation applying velocity change

(du/dl) eq.(450 degC, 1 atm):

t=1.01 sec t=1.1 sec

1D Dynamic model• Mass balance with momentum equation applying velocity change

(du/dl) eq.:• Velocity continues to grow without finding an steady state…

t= 3 sec

Next steps

• Complete FD dynamic model.• Apply finite volume method for 1D dynamic

case.• Assess reactor configurations with 1D models.• Article writing.

NEO-CARBON ENERGY project is one of the Tekes strategic researchopenings and the project is carried out in cooperation with Technical Research

Centre of Finland VTT Ltd, Lappeenranta University of Technology LUT andUniversity of Turku, Finland Futures Research Centre FFRC.

TECHNOLOGY FOR BUSINESS

http://www.neocarbonenergy.fi/

Blank test Quartz tube

Packed tube withonly SiC as shown inprevious slide

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Temp. catalyst bed (degC)

1 bar

xCO2 eq (rWGS)

xCO2 eq (rWGS+CH4)

yCH4 eq (rWGS+CH4)

yCO eq (rWGS+CH4)

xCO2 exp

yCO exp

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%

Temp. catalyst bed (degC)

30 bar

Exp. results: 0.25 grams loading• Ni/Al2O3 catalyst with ca. 2 w-% Ni. Particle size 400-500 µm.• H2/CO2 ratio = 3

No visiblecarbon formationIn the catalyst.However, carbonformation around thethermocouple

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%

Temp. catalyst bed (degC)

1 bar

xCO2 eq (rWGS)

xCO2 eq (rWGS+CH4)

yCH4 eq (rWGS+CH4)

yCO eq (rWGS+CH4)

xCO2 exp

yCO exp

yCH4 exp0

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%

Temp. catalyst bed (degC)

30 bar

Exp. results: 0.25 grams loading

No visiblecarbon formationIn the catalyst.However, carbonformation around thethermocouple

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100

450 550 650 750 850

%

Temp. catalyst bed (degC)

1 bar

xCO2 eq (rWGS)

xCO2 eq (rWGS+CH4)

yCH4 eq (rWGS+CH4)

yCO eq (rWGS+CH4)

xCO2 exp

yCO exp

yCH4 exp

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100

450 550 650 750 850

%

Temp. catalyst bed (degC)

30 bar

• Ni/Al2O3 catalyst with ca. 2 w-% Ni. Particle size 400-500 µm.• H2/CO2 ratio = 2

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100

450 550 650 750 850

%

Temp. catalyst bed (degC)

15 bar

Modelling work• Xu&Froment kinetic model compared to experimental data. Both own experiments and Xu&Froment results used

NG reforming catalyst Ni/Al2O3 with ca. 15 w-% Ni. (THIS IS NOT THE SAME CATALYST AS THE PREVIOUSRESULTS).

0

10

20

30

40

50

60

70

80

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100

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%

Temp. catalyst bed (degC)

30 bar

0

10

20

30

40

50

60

70

80

90

100

450 550 650 750 850

%

Temp. catalyst bed (degC)

1 bar

xCO2 eq (rWGS)

xCO2 eq (rWGS+CH4)

yCH4 eq (rWGS+CH4)

yCO eq (rWGS+CH4)

xCO2 exp

yCO exp

yCH4 exp

xCO2 calc (Xu&Froment)

yCO calc (Xu&Froment)

yCH4 calc (Xu&Froment)