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Gasification of Athabascan asphaltenes in a drop tube furnace: experimental and modeling results

A. Bader1, V. Kurian2, P. Nikrityuk2, R. Schmidt1,3, J. Friedemann1,

R. Gupta2 , B. Meyer1

1 IEC, TU Bergakademie Freiberg, Germany, 2 CME, Uni. of Alberta, Canada 3 AIR LIQUIDE, Germany

Andre.Bader@iec.tu-freiberg.de

[1] Alberta geology survey

ags.gov.ab.ca

Fig. Location of Athabasca oil sands [1] Fig.: Asphaltene rock

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Asphaltenes:

Melting temperature

150 – 250°C

Proximate Analysis, kg/kg

Fixed carbon: 0.28

Volatile matter: 0.71

Ash content: 0.01

Ultimate analysis, kg/kg:

C: 82.17;

H: 8.18;

N: 1.17;

S: 7.45;

O: 1.03

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Content

1. Experimental setup

2. CFD Modeling

3. Subgrid Modeling

4. Conclusion

Reactor design

Fig.: Reactor scheme [2]

4 [2] Vejahati, F.; Katalambula, H.; Gupta, R.:

Energy & Fuels, 2011

Drop tube furnace:

• Length: 1.5 m

• Diameter: 6.5 cm

• Electrical wall heated: 1573 K

• Atmospheric pressure

• Nitrogen as carrier gas for the

asphaltene particles

Fig.: Nozzle

Reactor design

5

Fig.: Cross section of the reactor top

Reacto

r w

all

Nozzle Inlet: fuel

Inlet: gasification agent

Particle size determination

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Fig.: CAMSIZER measurement principles [3]

Data generation:

Image processing with pulsed LED source

X-Fall X-Jet

[3] Figures from Brochure:

Retsch Technology, CAMSIZER XT,

0

0,2

0,4

0,6

0,8

1

1,2

0 100 200 300 400 500 600 700 800 900

Pro

ba

bil

ity d

en

sit

y f

un

cti

on

, %

,µm

d, µm

X-Fall X-Jet

Particle size of the feed particles

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50µm 50µm

Agglomeration effects!

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

0 100 200 300 400 500

Pro

ba

bil

ity d

en

sit

y f

un

cti

on

, %

,µm

d, µm

Feed (X-Fall) λ=0.34 (X-Fall) λ=0.13 (X-Fall)

Feed (X-Jet) λ=0.34, (X-Jet) λ=0.13, (X-Jet)

Particle size of the feed and char particles

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50µm

λ = 0.34 λ = 0.13

50µm

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CFD model

• Ansys Fluent 14.0

• 2D-axisymmetric geometry

• k-ω-SST turbulence model

• P-1 radiation model

• Incompressible ideal gas

• Euler-Lagrange approach

Gas profile in the reactor

Fig.: Contour of oxygen in kg/kg, with as stoichiometric air-fuel ratio. The left represents the

top and the right the bottom of the reactor. Reactor length is 1.5 m

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Gas profile in the reactor

Fig.: Contour of methane in kg/kg, with as stoichiometric air-fuel ratio. The left represents the

top and the right the bottom of the reactor. Reactor length is 1.5 m

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Gas profile in the reactor

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Fig.: Contour of carbon monoxide in kg/kg, with as stoichiometric air-fuel ratio. The left

represents the top and the right the bottom of the reactor. Reactor length is 1.5 m

Advanced model concept

Subgrid model: Mass transfer

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Eulerian grid cell

Surrounding gas

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Subgrid model: Heat transfer

Standard model concept Advanced model concept

Eulerian grid cell Eulerian grid cell

Surrounding gas Surrounding gas

Particle conversion steps: Temperatures

Burnout

Pyrolysis

Meltin

g

Heating

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Surrounding gas

Particle conversion steps: Temperatures

(I) Heating

(II) Melting (III) Pyrolysis

(IV) Burnout

Burnout

Pyrolysis

Meltin

g

Heating

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Energy balance:

Virtual homogeneous reaction Zone

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Burnout Pyrolysis

Meltin

g

Heating

Surrounding gas

Figure 5: Contour of oxygen in kg/kg determined by the CFD model, with as stoichiometric air-fuel ratio (experiment 1 and 2 with = 0 34 and

0.13, respectively). Thecaseconditionsaresummarized in Tab. 5. The left represents the top and theright thebottom of thereactor. Reactor length

is 1 546m.

400

600

800

1000

1200

1400

1600

1800

2000

0.01 0.1 1

T,K

t, s

I II III IV

Tp

Th

T f

T

Figure 6: Transient temperatures determined with the subgrid model

and reference case conditions. Period (I): inert heating, period (II):

melting, period (III): pyrolysis, period (IV): char burnout

ticle (Eq. (7)) and the VHRZ (Eq. (10)) are shown in392

Fig. 7 and 8. The reaction rates at the particle surface393

and in thehomogeneous reaction zone layer aregiven in394

Fig. 11 and Fig. 9 - 10, respectively. The particle con-395

version is categorized into four parts representing the396

periods which are (I) inert heating, (II) particle melting397

(III) pyrolysis and (IV) heterogeneous char reactions.398

Inert heating (I). During period (I) the particle con-399

sumes heat from the environment and heats up over400

400K within the first 0 01s. The inert heating period401

continues until Tp reaches the melting temperature (at402

0 02s). The particle heating net rate Q̇p is determined403

by the convective heat transfer from the ambient Q̇con p404

with 80% and the radiation Q̇rad with 20%, see405

Fig. 7.406

Theparticle temperature isthecoldest of all four tem-407

peratures, as the particle is initially cooler than the am-408

bient. Theparticle isheated up by theheat transfer from409

the ambient during period (I), see Eq. (8). Hence Th410

is warmer than Tp and colder than T as it represents411

-0.2

-0.1

0

0.1

0.2

0.3

0.01 0.1 1

Q̇,W

t, s

I II III IV

Q̇p

Q̇rad

Q̇con p

Q̇R s

Q̇pyro

Q̇sen

Q̇m

Figure 7: Transient heat fluxes of Eq. (7) representing the particle

energy balancedetermined with referencecaseconditions. Period (I):

inert heating, period (II): melting, period (III): pyrolysis, period (IV):

char burnout.

heat transfer coefficient weighted mixture between Tp412

and T (see Eq. (15)), when no reactions occur like in413

period (I) and (II). The temperature T f (see Sec. 2.1.9)414

is applied for ignite the VHRZ and is warmer than Th415

as the heat transfer coefficient between the ambient and416

the VHRZ is increased if no Stefan flow occurs like in417

period (I) and (II).418

Melting (II). During the melting process the particle419

still consumesheat. Theparticle temperature keepscon-420

stant because of the consumed fusion enthalpy during421

the liquefaction, see Eq. (29). The convective and radi-422

ant heat transfer onto the particle isused for the particle423

fusion which leads to a zero particle heating rate, see424

Fig. 7. Because of the melting, all other temperatures425

keep constant, as Tp is constant and no reactions heat is426

released as no reactions take place in period (I) and (II)427

like it can be seen in Fig. 11 - 10.428

Pyrolysis (III). The third period is governed by pyrol-429

ysis. During the pyrolysis the volatile matter ignites in430

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Energy balance: Particle

Burnout Pyrolysis

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Surrounding gas

t,s

nu

mbe

r o

f p

arc

els

0.4 0.6 0.8 1.0 1.2 1.4

02

040

60

Fig: Carbon conversion Fig: Particle residence time

Validation: Carbon conversion at the reactor end

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Summary and Outlook

• The experimental gasification of Athabascian asphaltenes can be simulated with

CFD and stand-alone subgrid models with good agreement.

• Particles enters the drop to furnace as clusters of single particles.

• Advanced particle transformation model for size and shape are needed.

• The “virtual homogeneous reaction zone model” shows a significant energy

feedback from the vicinity around the particle onto the particle.

Thank you for your attention!

Literature concerning previous VHRZ subgrid model development steps:

S. Schulze, M. Kestel, P.A. Nikrityuk, D. Safronov, From detailed description of

chemical reacting carbon particles to subgrid models for CFD, Oil Gas Sci. Technol.

Rev. IFP Energies nouvelles 68 (2013) 1007–1026.

S. Schulze, R. Schmidt, P. Nikrityuk, Gasification Processes - Modeling and

Simulation: Subgrid Models for Particle Devolatilization-Combustion-Gasification,

WILEY (2014).

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