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Investigations on char gasification kinetics under CO2atmosphere at mid pressures

Victor Gonzalez. IEC. TU-FreibergSascha Rußig, Martin Schurz, Mark Zink, Stefan Guhl, Steffen Krzack, Bernd Meyer

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Content:

Motivation

Equipment description

Experimental matrix

Evaluation and results

Summary

Outlook

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Motivation:

VIRTUalization of High temperature CONversion processes

Generation of property and process data and for gasificationprocesses

Numerical simulation of processes by validated models

Improving the basic understanding and optimization of the processes

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Equipment description:

Pressure up to 100 bar

Temperature up to 1100°C

CO2, steam, CO, H2 and Ar/N2

Quench sampling system for char

Real time GC and FTIR gas analysis

Optical char feed monitoring system

Gas sampling ports in the heating room

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Measurementpoint

Position [mm]

1 02 1853 4144 6455 8756 11057 13348 15639 1795

10 202411 225412 2657

Equipment description:

Nickel based alloy reactor tube L: 2657 mm ID: 60 mm

12 gas sampling ports OD: 6 mm Flow: 0.5 l/min (STP) Gas velocity: 50 m/s

48 Temp. measurement points 4 per sampling tube

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Equipment description:Concentration profiles along the reactor (20 bar, 900°C 25 vol.% CO2 )

0

20

40

60

80

100

0 500 1000 1500 2000 2500 3000

Con

cent

ratio

n [v

ol.%

]

Length along the reactor [mm]

Ar

N2

CO

CO2

Measurement relative error:Ar: 0.4%N2: 2.0%CO: 2.6 %CO2: 2.7 %H2: 2.5 %

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Equipment description:Stability of the system (20 bar, 1000°C, 25 vol.% CO2)

4

6

8

10

12

14

16

18

20

11:16 11:24 11:31 11:38 11:45

CO

con

cent

ratio

n. P

oint

12

[vol

. %]

Time [hh:mm]

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Experimental matrix:

Boudouard reaction Total pressure: 20 bar Feeding rate: 10 g/min Flow rate ≈ 100 l/min (STP) Test duration per setting≈ 4 h Gases preheated to set temperature

Partial pressure of CO2 [bar] at 20 bar total

Temperature [°C] 5 10 15

900

1000

1100

2 2C C O C O

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Experimental matrix: The raw material

Char produced from a german brown coal

Particle size distribution:

d50: 105.8 µm

Specific area:

N2 adsorption, 77 K, BET: 289 m2/g

Hg-porosimetry:

Macropores: 43.4%

Mesopores: 8.3 %

Micropores: 48.3 %

Comp. [wt.%]Water 1.09Ash 8.37Volatiles 4.56Cfix 85.98Total 100

Porosity: 53.4 vol. %

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Evaluation and results:Temperature profile (set temperatures) based on 48 measurement points

Set T [°C] Average T [°C]900 844

1000 9411100 1027

900 °C 1000 °C 1100 °C

Leng

th[m

m]

Tem

pera

ture

[°C

]

Ti

Ti+1

21

iii

TTT

Li

n

i T

ii

LTLT

1

Length weighed T average

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Evaluation and results: Residence time

GPGGP uuu ,,

Section Points Lenght [mm] Residence time [s]

1 0 - 185 185 0.68

2 185 - 414 229 0.86

3 414 - 645 231 0.86

4 645 - 875 230 0.86

⁞ ⁞ ⁞ ⁞

11 2254 - 2657 406 1.55

Total [s] 10.04

2, 9

2P

G

GPGP Rgu

Particle velocity uP,F: Stokes‘ law

G

GG A

Vu.

Gas velocity uG: Gas flow

PT: 20 bar, 844°C , 25 vol.% CO2

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Evaluation and results:

Random pore model[1]:

Spherical particles

Cyl. pores/unevendiameter

xLnxKdtdx

xLn

SL

xLnxSS

RPM

111

1122

14

111

max

20

00

0

feededC

reactedC

COPCOreactedCcharfeededcharfeededC

m

mx

RTPV

mCmm

,

,

,,,, 2678.0

0,0

0,2

0,4

0,6

0,8

1,0

0 500 1000 1500 2000 2500 3000

Con

vers

ion

[-]

Lenght along the reactor [mm]

[1]Bhatia, S. K. and Perlmutter, D. D. (1980), A random pore model for fluid-solid reactions: I. Isothermal, kinetic control. AIChE J., 26: 379–386.

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Evaluation and results:

0,0

0,2

0,4

0,6

0,8

1,0

0 4 8 12

Con

vers

ion

[-]

844 °C

941 °C

1027 °C

Effect of the temperature. 20 bar, 25 vol. % CO2

Effect of the partial pressure of CO2 20 bar, 941°C

0,0

0,2

0,4

0,6

0,8

1,0

0 4 8 12

Con

vers

ion

[-]

25% CO2

50% CO2

75% CO2

Residence time [s] Residence time [s]

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Evaluation and results: Kinetic parameters. RPM

Parameter Units ValueΨ - 3.5n - 0.34A0 1/s 39.6 Ea kJ/mol 70.4

Ψ: reported values between 1 and 26 [2]

n: reported values between 0.2 and 0.5Ea: reported values between 29-300 kJ/mol [3]

[2]Kajitani (2006): Gasification rate analysis of coal char in entrained flow coal gasifier. Fuel 85: 163-169.[3]Cakal (2007) : Physical and chemical properties of selected turkish lignites and their pyrolysis and gasification ratesdetermined by thermo-gravimetric analysis. J. anal. Appl. Pyrol 80: 262-268

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Evaluation and results: Validation (941°C)

0,0

0,2

0,4

0,6

0,8

1,0

0 2 4 6 8 10 12

Con

vers

ion

[-]

Residence time [s]

EXP, 25 % CO2

EXP, 50% CO2

RPM, 25% CO2

RPM, 50% CO2

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Summary:

Construction and successful operation of a drop tube reactor up to 100 bar

Concentration profile for all the components along the reactor length in a single test In situ

Real time temperature profile during the process

Good reproducibility and stability of the process

Particle residence time estimated taking into account changes in the gas flow and flow area

Neglectable dead time between sample taking and gas analysis

Kinetic parameters Ea: 70.4 kJ/kg, n: 0.34

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Outlook:

Elimination of the cold spots along the reactor by optimized design

New feeding system

Gasification with CO2 at higher pressures (40 bar)

Gasification experiments with steam

Include inhibition reactions due to CO and H2

Experimental validation of the estimated residence time

Connect experiments with CFD modelling for CFD-validation and for estimation of residence time, recirculation, …

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This research has been funded by the Federal Ministry of Education and Research of Germany in the framework of VirtuhconProject Number 03Z2FN12 and HITECOM II Project Number 03Z2F512

Victor GonzalezInstitut für Energieverfahrenstechnik und ChemieingenieurwesenFuchsmühlenweg 9, 09599. Freiberg+49 3731 39 4233Victor.Gonzalez@iec.tu-freiberg.de