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Effect of temperature on carbon deposition

during integrated coal pyrolysis−tardecomposition over low grade iron ore

ISIJ Conference

March 2014

1

Rochim B. Cahyono, Naoto Yasuda, Takahiro Nomura,Tomohiro Akiyama

Hokkaido University

Fuel 89 (2010) 1784 –

1795

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2

Years

   P   i  g   i  r  o  n  p  r  o   d  u  c   t   i  o  n ,

   1   0   3   M   t

Adapted from World Steel Association, 2011.

Ironmaking industry

World Steel Association, 2011. Steel statistical yearbook 2011, world steel Committee on Economic Studies-BRUSSELS,

2011. World Steel Association, p. 101; The Japan Iron and Steel federation

Highly required

alternative ofreduced agent and

iron ore sources

Raw materials : Coal (HG) = 690 kg/ton-pig ironIron ore (HG) = 1390 kg/ton-pig iron

Consumes around 5% of the total world energy

Energy recovery : 25.3 % input energy

CO2 emission: 1519 kg-CO2/ton-pig iron

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3

Tar decomposition VS carbon deposition

Tar decomposition/cracking:

Carbon deposition:

Catalytic process

Endothermic reaction

High conversion at elevated

temperature

The purposes:

(1) To obtain the optimum temperatures forboth the pyrolysis and tar decomposition

processes for high carbon deposition

(2) To understand the main factors in the

carbon deposition process with different

contents of combined water (CW)

Required high surface area/pore

volume

High deposition at lower

temperature

Carbon gasification at hightemperature

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4

Dehydration process

(a)

Micropore

Macropore

Mesopore

Removing H2O during dehydration process

created porous ore with layer by layer structure

The micropore/mesopore was predominat in the

dehydrated ore

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3.0

3.5

4.0

4.5

0

15

30

45

60

75

90

400 500 600 700 800 900

   C  a  r   b  o  n  y   i  e   l   d   [   %  m  a  s  s  -   C   ]

Pyrolysis temp [oC]

   C  a  r   b  o  n  y   i  e   l   d   [   %  m  a  s  s  -   C   ]

Char 

Gas

Tar 

Deposited -C

H ore; tar decomposition temp : 600 oC

Coal pyrolysis

 At elevated temperature,

char amount decreased

while volatile matter (gas

and tar) increased due to

thermal cracking

Products distribution

Beside large deposited carbon, clean gas with small tar

was resulted at high pyrolysis temperature

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Thermal cracking athigh pyrolysis

temperature enhanced

the volume of H2 and

CO

Beside large carbondeposition, high

pyrolysis temperature

resulted also extra

heating value

]CH[%volx396.1 

]H[%volx110.2CO][%volx127.1)(MJ/NmLHV

4

2

3

Lower Heating Value

4

6

8

10

12

0

40

80

120

160

400 500 600 700 800 900

   G  a  s  v  o   l  u  m

  e   [   N  c  m   3   /  g  -  c  o  a   l   ]

Pyrolysis temp [oC]

   L   H   V

   [   M   J   /   N  m   3   ]

H2

CH4

CO2

CO

LHV

H ore; tar decomposition temp : 600 oC

Coal pyrolysis

6

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0

20

40

60

80

100

400 500 600 700 800

   C  a  r   b  o  n  y   i  e   l   d   [   %  m  a  s  s  -   C   ]

Tar decomposition temp [oC]

Gas Deposited carbon tar Unreacted tar  

H ore, Pyrolysis temp : 800 oC

Tar decomposition

Tar product distribution

 CnhydrocarbolightotherCHCOCOHTar  422  

kJ172.48HCO2CCO2  

0.5

1.0

1.5

2.0

1

2

3

4

300 400 500 600 700 800 900

   C

  a  r   b  o  n  c  o  n   t  e  n   t   [   %  m  a  s  s   ]

Tar decomposition temp [oC]

Deposited carbon

Total volume

   G  a  s  v  o   l  u  m  e   [   L   ]

Pyrolysis temp = 800 oC

Lignite coal

7

 At constant pyrolysis temperature, the maximum carbon content was

obtained at tar decomposition of 600 oC.

 At high temperature, deposited carbon decreased due to high tar activity

and carbon gasification to produce larger gas product

Highest

deposition

Unreacted tar 

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 A higher temperature resulted in a

large reduction degree because ofindirect reduction of CO and fast

reduction rate.

FeO was found at high

temperature; this is consistent with

the phase diagram.

30 40 50 60 70 80

2θ [degree]

   I  n   t  e  n  s   i   t  y   [  a .  u

   ]

400 oC

500 oC

600 oC

700 oC

800 oC

Dehydrated ore

Fe2O3 Fe3O4 FeOH ore; pyrolysis temp : 800oC

(b)

0

0.2

0.4

0.6

0.8

1

400 500 600 700 800 900 1000

Tar decomposition temp [oC]

Fe

Fe3O4

FeO   P   C   O

   P   C   O

   +   P   C   O   2

   [  -   ]

Fe2O3

H ore; pyrolysis temp : 800 oC

(a)

2

243

24332

COFeCOFeO

CO3FeOCOOFe

;COO2FeCOO3Fe

Tar decomposition

8

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0

20

40

60

0 5 10 15

   P  o

  r  e  s   i  z  e   d   i  s   t  r   i   b  u   t   i  o  n

   [   1   0  -   6  m   3   /  n  m   /   k  g   ]

Pore size [nm]

DH

400600

800

: Dehydrated ore (DH)

: Tar decomposition at 400o

C: Tar decomposition at 600 oC

: Tar decomposition at 800 oC

H ore;

Pyrolysis temp: 800 oC

86.7

21.9 20.3

2.8

DH 400 600 800

BET surface

area [m2/g]

Tar decomposition temp [oC]

3.15

3.89

1.94

400 600 800

Carbon deposition [%mass]

Tar decomposition temp [oC]

Tar decomposition

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Smallest carbon deposition

but largest deceasing of

surface are and pore

distribution, why??

The amount of carbon deposition should be

proportional with the decreasing of surface

area and pore size distribution.

The melting point of the iron ore (Fe2O3) was

1733 K(=1460oC)

Sintering process

[14] HSC chemistry 7.0; [15] Canovaa, IC. et.al. Materials Research Vol. 2, No. 3, (1999) 211-217

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Conclusions

 At constant temperature of tar decomposition, high pyrolysis temperature

resulted large deposited carbon and clean gas with extra heating valueThe highest deposited carbon was obtained at pyrolysis temperature of

800 oC and tar decomposition temperature of 600 oC.

 At elevated temperature, the amount of deposited carbon decreased due

to carbon gasification.

 At tar decomposition temperature of 800 oC, the FeO was found but the

sintering phenomena was started

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