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1
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
[1] Alberta geology survey
ags.gov.ab.ca
Fig. Location of Athabasca oil sands [1] Fig.: Asphaltene rock
2
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
3
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
6
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
7
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
8
50µm
λ = 0.34 λ = 0.13
50µm
9
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
10
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
11
Gas profile in the reactor
12
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
13
Eulerian grid cell
Surrounding gas
14
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
15
Surrounding gas
Particle conversion steps: Temperatures
(I) Heating
(II) Melting (III) Pyrolysis
(IV) Burnout
Burnout
Pyrolysis
Meltin
g
Heating
16
Energy balance:
Virtual homogeneous reaction Zone
17
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
11
Energy balance: Particle
Burnout Pyrolysis
18
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
19
20
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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