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Determination of Langmuir-Hinshelwood gasification kinetics

from integral drop tube experiments

Florian Keller, Felix Küster, Bernd Meyer

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I. Motivation & Background

II. Gasification experiments

III. Description of gasification reactivity

IV. Determination of gasification kinetics

V. Summary & Outlook

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Central Germanlignite

Production

Processing

HT-Conversion Syngas

LT-Conversion Olefins

Extraction Montan wax

I. Motivation & Background

Project ibi

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GMEQ

• Gasification Measurement Equipment

• Drop tube furnace reactor

• Lheated = 1,75 m

• Tmax = 1300 ˚C

• pmax = 6 bar

• mchar,max = 1.2 kg/h

• for CO2 and steam gasification

II. Gasification experiments

Gasification equipment

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M

Fuel feeder(char)

Rea

ctio

n t

ub

e (A

lO-c

eram

ics)

Shel

l sp

ace

Char

Reactant gasesPreheater

Elec

tric

hea

ters

Container for solid residues

Solid

s se

par

ato

r

Reaction gases

Filter Condenser

GC

Gas treatment equipment

Gas analyzer

N2

N2

N2

Preheater

Steam

Evaporator

CO2

CO

H2

N2

Ar

II. Gasification experiments

Gasification equipment

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Char preparation Gasification experiments

• Central German Lignite

• Pyrolysis in rotary kiln at 600 °C

• Crushed to particle size below 200 µm

• 66 experiments

• Mixtures of steam, CO2, CO, H2

• 6 bar total pressure

• 900 to 1100 °C

pCO2 pH2O pCO pH2 V̇Gas XC

[bar] [bar] [bar] [bar] [l(STP)/h] -

min 0.00 0.00 0.27 0.26 246 6%

max 3.74 3.91 1.77 1.61 543 71%

II. Gasification experiments

Experiment overview

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LH rate expression without inhibition1

𝑟𝐿𝐻 =𝑘11𝑝𝐶𝑂2

1 + 𝑘12𝑝𝐶𝑂2+

𝑘21𝑝𝐻2𝑂

1 + 𝑘22𝑝𝐻2𝑂

LH expression of shared active sites2

𝑟𝐿𝐻 =𝑘11𝑝𝐶𝑂2 + 𝑘21𝑝𝐻2𝑂

1 + 𝑘12𝑝𝐶𝑂2 + 𝑘13𝑝𝐶𝑂 + 𝑘22𝑝𝐻2𝑂 + 𝑘23𝑝𝐻2

LH expression of separated active sites2

𝑟𝐿𝐻 =𝑘11𝑝𝐶𝑂2

1 + 𝑘12𝑝𝐶𝑂2 + 𝑘13𝑝𝐶𝑂+

𝑘21𝑝𝐻2𝑂

1 + 𝑘22𝑝𝐻2𝑂 + 𝑘23𝑝𝐻2

d𝑋𝐶

𝑑𝑡= 𝒓𝑳𝑯 𝑅𝑃𝑀 𝜂

III. Description of gasification reactivity

• Reaction gas composition

• Reactant gas partial pressure

• Surface saturation (CO2, steam)

• Inhibition (CO, H2)

Langmuir-Hinshelwood rate equation

Reaction gas composition

1 N. M. Laurendeau, Progress in Energy and Combustion Science, 4(4):221–270, 1978.2 S. Umemoto et al., Fuel, vol. 103, pp. 14–21, Nov. 2013.

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Random Pore Model3

𝑅𝑃𝑀 = 1 − 𝑋𝐶 1 − 𝛹 ln 1 − 𝑋𝐶

d𝑋𝐶

𝑑𝑡= 𝑟𝐿𝐻 𝑹𝑷𝑴 𝜂

• Reaction gas composition

Langmuir-Hinshelwood rate equation

• Particle structure change

• Initial increase of reactive surface area

Random Pore model

III. Description of gasification reactivity

Particle structure change

3 S. K. Bhatia and D. D. Perlmutter, AIChE J., vol. 26, no. 3, pp. 379–386, 1980.

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• Reaction gas composition

Langmuir-Hinshelwood rate equation

• Particle structure change

Random Pore model

• Pore diffusion

• Reaction rate limitation at higher temperatures

Pore Effectiveness Factor

d𝑋𝐶

𝑑𝑡= 𝑟𝐿𝐻 𝑅𝑃𝑀 𝜼

Pore Effectiveness Factor4

𝜂 =1

𝜙

1

tanh 3𝜙−

1

3𝜙

Thiele modulus4

𝜙 = 𝐿𝑃

𝑟(𝐶𝐴𝑠

2 0

𝐶𝐴𝑠

𝐷𝑒 𝛼 𝑟 𝛼 𝑑𝛼

−12

ϕ = 𝐿𝑃

𝑚𝑐ℎ𝑎𝑟,0

𝑉𝐺𝑎𝑠

𝑥𝑐,𝑐ℎ𝑎𝑟,0 𝑅 𝑇

𝑀𝑐

1

2𝐷𝑒𝐴𝑘11

𝑘12𝑝𝐶𝑂2

1 + 𝑘12𝑝𝐶𝑂2 + 𝑘13𝑝𝐶𝑂

1

𝑘12𝑝𝐶𝑂2 − 1 + 𝑘13𝑝𝐶𝑂 ∗ ln(1 + 𝑘12𝑝𝐶𝑂2 + 𝑘13𝑝𝐶𝑂

III. Description of gasification reactivity

Pore diffusion

4 K. Bischoff, AIChE J., vol. 11, no. 2, pp. 351–355, 1965.

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Problems for determination of kinetic expressions

• Linear regression not possible

Changing gas composition

CO2 and steam gasification

• Impact of gas phase reaction on gas composition

Fitting concept

• Modeling of gasification process

• Determination of deviation between model and experiments

• Minimization of deviation by adjustment of kinetic parameters

IV. Determination of gasification kinetics

Advantages of drop tube furnace experiments

• Single particle behavior

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• Heterogeneous water gas reaction

𝐶𝑓 + 𝐻2𝑂 → 𝐶𝑂 + 𝐻2

• Boudouard reaction

𝐶𝑓 + 𝐶𝑂2 → 2 𝐶𝑂

• Homogeneous water gas reactions

𝐶𝑂 + 𝐻2𝑂 → 𝐶𝑂2 + 𝐻2

𝐶𝑂2 + 𝐻2 → 𝐶𝑂 + 𝐻2𝑂

IV. Determination of gasification kinetics

Considered reactions

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Isothermal 1D plug flow gasification model

2 x 𝑑𝑋𝐶,𝑖

𝑑𝑡• Langmuir-Hinshelwood model

• Random pore model

• Effectiveness factor

(CO2, H2O)

4 x 𝑑 𝑛𝑖

𝑑𝑡• Heterogeneous gasification reactions

• Homogeneous gas phase reaction(CO2, CO, H2O, H2)

1 x 𝑑𝑙

𝑑𝑡• Gas velocity

• Particle sinking velocity (Stokes)

2 x 𝜂𝑖 • Thiele modulus approach (CO2, H2O)

Differential algebraic equation system with 9 equations and 14 kinetic constants

• Solved in MATLAB

• Initial condition: experimental conditions

• Termination criterion: length of reaction tube

IV. Determination of gasification kinetics

Gasification process model

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0

100

200

300

400

500

600

700

800

0%

10%

20%

30%

40%

50%

60%

70%

80%

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Tota

l gas v

olu

me f

low

[l(

ST

P)/

h]

Ga

s v

ol. f

ractio

n /

ca

rbo

n c

onve

rsio

n X

C

Reactor length [m]

X C

x (CO2)

x (CO)

x (H2O)

x (H2)

Gas flow

IV. Determination of gasification kinetics

Example model course

Reaction gas partial pressure [bar] Initial gas flow

[l (STP) /h]

Temperature

[°C]CO2 CO H2O H2 Ar N2

2.10 1.12 1.15 0.34 0.33 0.96 507.4 1100

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Experimental results

Design (14 constants)

Optimized Design

Gasification Model (MATLAB)

for 66 experiments

Average deviation (CO2, CO, H2)

Optimization Algorithm

(ModeFRONTIER)

Validation of Effectiveness Factor

IV. Determination of gasification kinetics

Fitting procedure

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Relative mole flow deviation

CO2 H2 CO C

16,6% 18,4% 7,5% 4,4%

𝑑𝑋𝐶

𝑑𝑡= 1 − 𝑋𝐶 1 − 𝛹 ln 1 − 𝑋𝐶

𝑘11𝑝𝐶𝑂2 + 𝑘21𝑝𝐻2𝑂

1 + 𝑘12𝑝𝐶𝑂2 + 𝑘13𝑝𝐶𝑂 + 𝑘22𝑝𝐻2𝑂 + 𝑘23𝑝𝐻2

Optimization results

Kinetic expression: LH with inhibition > LH without inhibition > n-th order

Concept of active carbon site competition has no significant effect

Effectiveness factor does not improve fitting quality

IV. Determination of gasification kinetics

Results

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IV. Determination of gasification kinetics

Results

0%

10%

20%

30%

40%

50%

60%

70%

0 10 20 30 40 50 60

Vol.-

fractio

n C

O

Experiment number

Experiments Simulation

900 C 1100 C1000 C

0%

10%

20%

30%

40%

50%

60%

0 10 20 30 40 50 60

Vol.-f

raction H

2

Experiment number

Experiments Simulation

900 C 1100 C1000 C

0%

10%

20%

30%

40%

50%

0 10 20 30 40 50 60

Vo

l.-fr

act

ion C

O2

Experiment number

Experiments Simulation

900 C 1100 C1000 C

0%

10%

20%

30%

40%

50%

60%

70%

80%

0 10 20 30 40 50 60 70

Ca

rbo

n c

onve

rsio

n X

C

Experiment number

Experiments Simulation

900 C 1000 C 1100 C

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Summary

• Gasification experiments with lignite char in PDTF at 6 bar,

up to 1100 C in atmosphere of steam, CO2, H2, CO

• Isothermal 1D plug flow gasification model

• Determination of kinetic parameters by model fitting

V. Summary & Outlook

Example model course

Outlook

• Comparison of DTF kinetics to TGA derived kinetics

• Method application under more sever reaction conditions

• Integration of methanation reaction, film diffusion

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Thank you for your attention!

Acknowledgment:

The ibi project was supported by the

Federal Ministry of Education and

Research (BMBF)

(project ID: 03WKBZ06C)