Juliana Pohlmann, Antônio Vilela e Eduardo Osório Laboratório de Siderurgia (LASID)/UFRGS

Angeles Borrego e Maria Diez

Instituto Nacional del Carbón (INCAR)/Espanha

Pulverized coal injection (PCI)

Unburnt char is carried from the combustion zone to the shaft;

Gasification in CO2-rich atmosphere;

Coal/char characteristics are important in combustion efficiency (burnout) and gasification;

Flexibility as regards the utilization of several carbonaceous materials and different gaseous compositions/ratios.

At current time, the coals typically used in PCI in Brazil are exclusively imported from many countries;

Alternative: coal mined in Rio Grande do Sul;

Top Gas Recycling:

Mathmatical models;

CO2 injection in BF: cooling effect and fuel-rate increase;

CO2 injection is possible when combined with oxygen enrichment.

Oxy-fuel combustion

Coal is burnt in a N2-free atmosphere and oxygen is usually diluted by recycled flue gas rich in CO2 (O2/N2 O2/CO2);

CO2 capture and storage;

Application in power plants.

Bilateral cooperation INCAR (Spain) and LASID-UFRGS (Brazil);

To study differences between chars obtained in O2/N2 and O2/CO2 atmospheres aiming at oxy-fuel application in BF;

To compare a brazilian coal with imported coals of different ranks, analyzing the possibility to use this material in ironmaking.

Coal Símbol Origin Classification

Butiá Leste B3 Brazil Low rank coal

Black Water BW Australia Medium rank coal

Jellinbah JB Australia High rank coal

Proximate and ultimate analysis of the coals.

B3 BW JB

Ash % db 10.1 9.5 9.8

VM

% daf

38.6 26.5 15.9

C 79.0 83.4 87.2

H 5.2 4.3 3.8

N 1.2 2.0 1.9

O 9.5 10.6 5.6

S 0.9 0.7 0.7

Char preparation in DTF

• Heating rate = 104–105°C.s-1

• Temperature = 1300°C

• Feeding rate = 1 g.min-1

• Particle size = 36-75 μm

• Residence time = 200 ms

• Flow rate = 300 and 900 l.h-1

2 step samples = to assess the combustion of chars without volatiles interference.

Coal

2.5% O2 in N2 Char

5-10% O2 in N2 Char

5-10% O2 in CO2 Oxy-char

5% O2 in N2 Ref-char

5% O2 in CO2 Ref-oxy

10% O2 in CO2 Ref-oxy

1 Step chars

2 Steps chars

100100

1001(%)

.

.

.

.

combchar

combchar

coal

coal

Ash

Ash

Ash

AshBurnout

Chars characterization:

Morphology/structure in optical microscope

Surface area:

▪ Mesopores: N2 adsorption isotherms at – 196°C (pore size range 0.4-250 nm); BET theory.

▪ Micropores: CO2 adsorption isotherms at 0ºC (pore size range 0.4 – 1 nm); D-R theory;

• CO2 reactivity in thermobalance.

• 1st step: The sample was heated up to 1000°C under N2 flow at a heating rate of 30°C.mim-1;

• 2nd step: Isotherm in CO2 until weight stabilization;

• Reaction rate rate:

R50% = -1/w0 (dw/dt)50%

• To simulate the solution loss reaction out of the raceway.

NETZSCH STA 409 PC Luxx

Combustion tests in DTF: Coal burnouts in different atmospheres in one (a) and two steps (b).

(a) (b)

Chars appearence in optical microscope

A 2.5

B 2.5

C 2.5

A 10

B 10

C 10

50 µm

• Structures typical of high heating rates;

• Different textures due to different ranks;

• The majority of the particles exhibited swelling forming rounded particles with abundant secondary porosity within the walls.

• 2 steps chars: abundant fragments and more reacted surfaces.

50 μm

Meso (SBET) and microporosity (SCO2) of chars (m2.g-1)

n.d. not determined; af = ash-free.

Higher areas for the lower rank coal chars;

SBET (m2g-1)af SCO2 (m2g-1)af

B3 BW JB B3 BW JB

Char 2.5% 176,9 12,7 12,2 449,3

161,08 150,5

Char 5-10% 289,5 40,7 23,6 492,5

Oxy-char 5-10% 567,5 n.d 22,7 526,5

Ref-char 5% 125,8 20,3 14,0 505,0

Ref-oxy 5% 317,5 20,9 n.d 482,2

Ref-oxy 10% 205,1 n.d 20,1 839,8

Differences due to oxy-fuel atmospheres were only found for the low rank coal chars (higher SBET for O2/CO2 chars).

Evolution of BET surface area with burnout

Solid symbols: 1 step combustion, void symbols: 2 step chars.

Increase in surface area with burnout due to micropores coalescence or widening;

2 step chars: higher burnouts but lower SBET: surface more reacted, reducing area;

0,0E+00

5,0E-04

1,0E-03

1,5E-03

2,0E-03

Char

2,5%

Char 5-

10%

Oxi-char

5-10%

Ref-char

5%

Ref-oxi

5%

Ref-oxi

10%

R5

0%

C

O2

(.s-1

)

B3

BW

JB

Reactivity in CO2 in thermobalance

Higher reactivities as lower the rank;

BW and JB: R50% O2/N2 chars similar to R50% O2/CO2 chars

B3 1 step: R50% O2/N2 chars < R50% O2/CO2 chars

B3 2 steps: R50% O2/N2 chars > R50% O2/CO2 chars

-5,0E-04

5,0E-18

5,0E-04

1,0E-03

1,5E-03

2,0E-03

Char

2,5%

Char 5-

10%

Oxi-char

5-10%

Ref-char

5%

Ref-oxi

5%

Ref-oxi

10%

R5

0%

C

O2

(.s-1

)

B3

BW

JB

Reactivity in CO2 in thermobalance

Higher reactivities as lower the rank;

BW and JB: R50% O2/N2 chars similar to R50% O2/CO2 chars

B3 1 step: R50% O2/N2 chars < R50% O2/CO2 chars

B3 2 steps: R50% O2/N2 chars > R50% O2/CO2 chars

-5,0E-04

5,0E-18

5,0E-04

1,0E-03

1,5E-03

2,0E-03

Char

2,5%

Char 5-

10%

Oxi-char

5-10%

Ref-char

5%

Ref-oxi

5%

Ref-oxi

10%

R5

0%

C

O2

(.s-1

)

B3

BW

JB

Reactivity in CO2 in thermobalance

Higher reactivities as lower the rank;

BW and JB: R50% O2/N2 chars similar to R50% O2/CO2 chars

B3 1 step: R50% O2/N2 chars < R50% O2/CO2 chars

B3 2 steps: R50% O2/N2 chars > R50% O2/CO2 chars

Reactivity X Burnout: influence of coal combustibility in gasification

Positive evolution of reactivity with burnout due to the increase in BET surface area of the samples;

Higher SBET facilitate the diffusion of the gas in chars particles.

Effect of the coal rank:

Higher burnouts, BET surface areas and reactivities were reached as the coal rank decreased.

CONCLUSIONS

Effect of burnout:

Increasing in BET surface area and in CO2 reactitivity with burnout;

Effect of O2/CO2 atmosphere:

There was no effect in burnout, surface areas and reactivity because of the N2 replacement (conventional atm.) by CO2 (oxy-fuel atm.) for the imported coal chars (BW and JB);

Differences were only found between the conventional and oxy-fuel conditions for the brazilian coal chars;

CONCLUSIONS

CONCLUSIONS

Effect of O2/CO2 atmosphere: brazilian coal chars

Burnout

The burnout of the O2/CO2 samples was higher than the O2/N2 ones;

Reactivity and surface area

The oxy-fuel sample was more reactive than the conventional one for the 1 step chars because of the higher BET surface area;

The reactivity of the 2 steps char obtained in O2/CO2 atm. was slightly lower than the O2/N2 char.

The greater combustibility, surface area and reactivity

showed by the brazilian coal and the relatively narrow range of values obtained for both O2/N2 and O2/CO2 atmospheres could be positive for its utilization for PCI.

CONCLUSIONS

To better correlate the char behavior in the BF shaft, its necessary to make combustion tests in conditions closer to those found in the raceway (atmosphere, temperature and pressure).

To achieve this, the study will continue with new tests conducted in a raceway simulator (injection rig). This equipment is going to be built at LASID with the financial support of the Brasilian Coal Net.

THANK YOU!!!!!