HELSINKI UNIVERSITY OF TECHNOLOGY
TKK, Energy Engineering and
Environmental Protection in ChemCom
Mika Järvinen, Ari Kankkunen, Pasi Miikkulainen and
Carl-Johan Fogelholm
Helsinki University of Technology
Anders Brink, Christian Mueller and Mikko Hupa
Åbo Akademi University
Contents
1. Black Liquor Spray Study in the Furnace
- Objectives
- Droplet measurements in the furnace
- First results
2. Development of the comprehensive DPM model for
black liquor
- Detailed droplet model, Järvinen et al. (2002)
- Description of the new simplified comprehensive
droplet model
- Sample results
Black Liquor Spray Study
in the Furnace
Introduction
• TKK, Laboratory of energy engineering and
environmental protection has long traditions in black
liquor spray research since 1990, Liekki I
– Small scale nozzles and substitute liquids
– Full scale nozzles in spray chamber
– Full scale nozzles in furnace (velocity, sheet
break-up mechanisms, spray appearance)
– Droplet size and shape in furnace 2006!
• Spraying results currently effectively utilized in
furnace conditions with ÅA
Objective
• Spray droplets properties in the furnace
• Droplet size and other spray properties was
measured in a test chamber earlier. Are results
applicable to a furnace?
• Droplet size and shape was documented inside a
furnace for the first time 2006
- Are droplets spherical inside the furnace?
- What is the relevant droplet size?
- What is the velocity of the droplets?
- What is the shape of the spray?
Furnace
Spray
Spray
Spray
Furnace
wall
Splashplate
nozzle
Splashplate
nozzle
2m
Splashplate
nozzle
2m
Conditions around spray
• Spray was directed along furnace wall
• The spray slightly hit the furnace wall in some test
cases
• Furnace temperature was 1100°C
• Downwards gas flow was detected near the
furnace wall
• Occasionally, burning particle flocks hit the spray
Spray at varying locations ( 4 m, 4 l/s)
above
center line
below
Development of the comprehensive
DPM model for black liquor
Introduction
• Droplet combustion modeling work was
initiated 1996, furnace studies
• Development of the detailed single droplet
model 1999-2002, Järvinen (2002),
TEKES/CODE
• Simplification of the detailed model on physical
basis (Post-Doc, Academy of Finland 2003-4)
• Development of the simplified comprehensive
DiscreteParticeModel model 2005- (ChemCom)
Detailed droplet model
Järvinen et al. 2002
Detailed droplet model - Internal profiles
180
900
120
600
60
300
0
40
20
0
1250
150
1000
H2 O + C
CO2 + C
O2 + C
CO + H2O
100
50
750
500
0
250
-50
0
0
0.2
0.4
0.6
0.8
Radial coordinate (r/rs)
0
1
200
1
r
10
Temperature and
reaction profiles
during char
combustion
0.2
0.4
0.6
0.8
Radial coordinate, r/rs
1
50
40
3
0.2
0.4
0.6
0.8
Radial coordinate (r/rs)
H2O + C
O2 + C
CO2 + C
30
R i (mol/m s)
3
50
0
0
R i (mol/m s)
Temperature and
reaction profiles
during pyrolysis
3
1200
Temperature (°C)
3
R i (mol/m s)
Pyro
Temperature (°C)
Dry
240
Ri
60
1500
R i, mol/m s
300
O2 + Na2S
M2CO3 + 2 C
M2SO4 + 2 C
30
20
10
0
0
0.2
0.4
0.6
0.8
Radial coordinate (r/rs)
1
Important observations from the detailed
model
• Overlapping drying and devolatilization stages in thin cores with
characteristic temperatures: Tb ~ 150°C, Tp ~ 250-300°C
• Intraparticle thermal radiation is important aR ~ 850 1/m
• During drying and devolatilization, temperature profile approaches
quasi-steady state profile
• Char conversion occurs simultaneously with drying and
devolatilization
• During ”pure” char combustion stage particle is almost isothermal
• No single dominating char reaction
The simplified comprehensive droplet
model
Tg
Ts(t)
Tp= const
Tb= const
H2O(l)
C(s)
N(s)
MCl(s)
DS
M2S(s)
M2SO4(s)
M2CO3(s)
+ DS
- only Ts(t) + 8 tracked
species mi(t) solved
- const. Tb, Tp
- Na + K => M
Reactions in the simplified model
• Drying, shrinking core heat transfer model
• Pyrolysis, shrinking core heat transfer model
• Overlapping char and sulfide oxidation
- C(s) + 0.5O2 → CO
Smith 1982
- M2S(s) + 2 O2 → M2SO4(s)
-”-
• Char gasification
- C(s) + H2O → CO + H2
Li et al. 1991
- C(s) + CO2 → 2 CO
• Inorganic reactions
- M2CO3(s) + 2 C(s) → 2 M + 3 CO
Li et al. 1991
- M2SO4(s) + 2 C(s) → Ma2S(s) + 2 CO2
Wåg et al., 1995
Towards a sub-model for CFD
• Developed C-source code of the stand-alone droplet
model delivered to ÅA by TKK
• Conversion of source code to Fluent UDF and
implementation into Fluent at ÅA
• Fluent UDF in use at ÅA and TKK, common test
case
• Sensitivity analysis, comparison and application of
all single droplet/particle models developed at TKK
and ÅA at well defined conditions
First application of the sub model
Droplet data from
measurents
u = 12 m/s
X = 7.44 mm (RR)
q = 2.5
First application of the sub model
Solids content
Surface temperature
First application of the sub model
Initial results for computational Demand, CPU-time [s]
• 10 droplets from one liquor gun, 50 stochastic tries
500 droplet trajectories
• ÅA Furnace Model: 9 s
• Comprehensive SDM: 109 s
• Increase in computational time per DPM iteration: ~ factor 12
• This factor has decreased after further development and
simplification
Summary
• A new comprehensive single black liquor droplet combustion
sub-model has been implemented into FLUENT software and
is currently in use at TKK and ÅA
• Simplified model is based on the experimentally validated
detailed model, using the most essential physical and
chemical mechanisms observed by simulations and
experiments
• Close co-operation between Helsinki University of
Technology and Åbo Akademi University has been essential
for effectively combining the knowledge on detailed model
development, combustion experiments and CFD model
implementation
• The project has been definitely a “Win- Win deal” for both
sides
Acknowledgement
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TEKES
Andritz Oy
Kvaerner Power Oy
Foster Wheeler Energy Oy
Vattenfall Utveckling AB
Metsä-Botnia Oy
International Paper
Mill Personel