Simulation of high temperature raw materials processing using CFD- education and research
Benelux PHOENICS User Meeting – Eindhoven, May 24th 2005
Yongxiang YangResource EngineeringFaculty of Civil Engineering and Geosciences
Overview
• Introduction
• Examples of using CFD for raw materials processing• Simulation of hazardous waste combustion• Simulation of transient heating of dredging impellers
• Summary
Introduction
• History of using PHOENICS• Simulation of off-gas cooling in waste-heat boilers for
copper flash smelting process. (1992 – 1997 HUT)
• Simulation of gas flow and slab heating of steel reheat furnace. (1997 – 2000, HUT and TU Delft)
• Flow and combustion modeling of hazardous waste incineration in rotary kilns. (1999 – 2004, TU Delft)
• Predicting the fuel combustion and transient heating process of metal components. (2003 – 2004, TU Delft)
Introduction: history of using PHOENICS
Off-gas cooling & dust flow in WHBs
Sym m etric centerlineG as coo ling from 1370°C to586°C
2D view o f partic le tracks
50 m partic les , 20 injection po in ts
Y
Z
TEM1
181
281
380
480
580
679
779
879
978
1078
1178
1278
1377
1477
1577
Temperature distribution between the centerline and the side-wall (°C)
1477 1577
157712781377
1377
147712771178
127811781078
1078 1278181
Z
Y
Transient heat of steel slabs in re-heat furnace
0
200
400
600
800
1,000
1,200
1,400
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28
Furnace position in z- direction, m
Center temperature
Top surface temperature
Gas temperature near slab surface
Gas temperature 0.6 m above slab surface
Tem
per
atu
re (
°C)
Introduction
• Use of CFD in Raw Materials Processing at TU Delft• PHOENICS:
• Education (1998 -): “transport phenomena in raw materials processing” , Case studies in Computer Practicals.
• Steel flow in tundish, • Off-gas cooling in boilers, • Heat loss from furnaces and reactors, • Transient cooling of steel slabs
• MSc. thesis research: 5 students• Project research: modelling of hazardous waste incineration
• PhD research projects• Hot metal flow in an ironmaking blast furnace hearth (CFX)• Aluminium scrap melting in a rotary furnace (CFX)• Submerged arc furnace for phosphorus production (Fluent)
Example 1: Simulation of hazardous waste combustion in a rotary kiln• Key Issues and
challenges• Fuel stream modelling• Waste combustion modelling
(CFD)• Construction of cylindrical kiln
and rectangular secondary combustion chamber (SCC)
R otary k iln
S econdarycom bustioncham ber(S C C )
A shsum p
Waste combustion in the rotary kiln• Rotary kiln + secondary combustion chamber
(SCC)
• Waste supply • ~30 MW, 7.2 t/h• Main burner ~11.5 MW• Sludge burner ~4 MW• Solid burner ~11.5 • SCC burner ~3 MW• Fuel lances: non-regular
• Air supply• Load chute• Cooling ring• Air lances (SCC)
Rotary Kiln
Secondary Com bustionCham ber(S CC)
To RadiationChamberof W HB
A sh Sum p
Burner flame
Solid-waste flam e
Load chute
Main burner
Sludgeburner
SCC burner
Air lances(x 7)
A ir lances(x 7)
Off-gas
Slag
H O/air2
Kiln front-viewShreddedsolid-wasteburner
Approach Waste characterization
Virtual fuel definition
Inlet stream definition
(wastes/water, air)
CFD turbulent combustion
model (7-gas)
Temperature
validation
Species
validation
Post-processing
Statistical analysis
Parametric studies
Advice on operation
CFD combustion model
• Assumptions and physical models• Gas phase only (negligence of gasification and vapourisation)• Turbulence flow: k-model• Walls: adiabatic (small wall heat loss)• Radiation was neglected (adiabatic walls, no effect)• Kiln rotation: neglected
• Waste-combustion: • Global combustion model (SCRS, 3-gas model)
• Extended global combustion model (ESCRS, 7-gas model)
• Real gas/fuel compounds have to be used
7-Gas model: CmHn, H2, O2, CO, CO2, H2O, N2
1 Fuel Oxidant (1 ) Product Heatkg s kg s kg
Virtual fuel definition
Modelled virtual fuel
C3H4 87.37% 46.3 MJ/kg
CO 12.38% 10.1MJ/kg
H2 0.25% 120 MJ/kg
% C xH y % C O % H 2
A ssu m e d F u e l: C H1 .7
H ea t o f co m b u s tio n :42,000 kJ/kg
O ff g a s ca l cu la tio n s
C 1 02 H 1 31 O 11 0
H e a t o f c o m b u s tio nd e p e n d s o n c o m p .
H e a t o f c o m b u s tio n :1 0 ,1 0 0 k J /k g
H e a t o f c o m b u s tio n :1 2 0 ,0 0 0 k J /k g
% C O 2 , O 2
G ene ra lize d fu e l:C xH yO z
B ette r defined Chem ically
Therm ally
Original waste
Less know n, p oorly de fined C h e m ic a lly
T h e rm a lly
From the incineration plant
Combustion model
Wat
er
Re-defined waste
Propyne Allene
Average off-gas composition: 7.5%O2, 69.5%N2, 9%H2O, 14%CO2
7-gas combustion model
• 1 primary reaction• 2 secondary reactions
• Turbulent combustion rate:• Eddy break-up model
• Dependent on turbulent mixing
• Fuel concentration + turbulence
• Regulated by CEBU constant (0.1 – 4.0 tested, 1.0 used)
3 4 2 21.5 3 2C H O CO H
2 22 2CO O CO
2 2 22 2H O H O
min , /mfu fu oxS CEBU m m sk
Stream definition
• Input streams• Waste streams: multi-fuel
streams
• Water content: mixed with wastes
• Combustion air: multi-feeding ports
• 2 stream constraint (code)• Fuel rich stream• Fuel lean stream
• Individual stream
Ash
sum
p
SCC
Air lances(7x2)
SCC burner
G asoutlet
Load chute
Sludge burner
Main burner
S-burner
FUEL RICH STREAM
Compound C3H4 O2 CO H2 CO2 H2O N2 Total
Percentage 21,64% 15,64% 3,09% 0,00% 0,75% 4,41% 54,47% 100,0%
FUEL LEAN STREAM
Compound C3H4 O2 CO H2 CO2 H2O N2 Total
Percentage 0,28% 20,97% 0,06% 0,00% 0,00% 5,64% 73,06% 100,0%
x% Fuel-rich + y% fuel-lean
Computational grid
• Cartesian grid• 230,000 – 360,000 cells• Using solid blockages to
form the kiln and SCC,• Difficult to set B.C. for
non-rectangular shapes.
• Burner definition• 2 stream approximation
Fuel-rich Fuel-lean
Example: main burner
Load chute
Cooling ring
Main burner
Sludge burner
Solid burner
Typical CFD predictions
Across the SCC burner
Across the m ain burner
Typical CFD predictions
SCC burner
So lid w asteburner
S ludgeburnerM ain
burner
SC C back w allS CC side w all
A cross SCC
burner plane
1098
1247
1396
1396
1247
1098
1247
1396
1247
1247
1098
1396
58
504
653
1998
1247
2139
2139
2139
2139
2139
1544
1544
1396
1693
1098
2139
1544
58
1098
1098
A shsum p
1098
Across the load-chute
Between the solid-waste burnerand the sludge burner
Across the main burner
Across the SCC-burner Near the outlet to WHB
Centra colder zone due to air injection lances
1247
1098
1247139 6
109 8
1247
1 396
154 41693
1247
1098
801
124715441 693
184 11 990
213 9
801653504
1841
1544
801653
1396
1247
1098
1247
1098
1396
154 41 693
1841
1693
1 544
2 139
653
801
18411 6931 990
2139
8 011247653
10981 544
1 098
950801
1247
12471396
1 3961 5441693
19002 139
21391 693
1693
5043552075 81 098
1 841
15441 247
801653
1 0986 53
124 71 396
1544
1 3961 544
109 8
130 1
128 3
1301
1319
13541372
1390
13371283
128 3
1 265
131 9
11401176
1194
1 229
12471265 126 5 1301 13191337
1372139 0
131 9
122 9
1354130 1
9 50
950
Temperature distribution
Typical CFD predictions
CO0.000 - 0 .054
0.0040.0080.01 2
0.0040.054 0.027
0.0160.00 4
0.016
~0.00
~0.00
0.016
Main burner axis (X-), m
Mas
s fra
ctio
n
CO2
O2
C3H4
H2O
CO
H2
Outside the SCC
Species distribution
Typical CFD predictions
C3H 40 .0 0 - 0 .16 8
C O0 .000 - 0 .0 54
CO 20 .0 0 0 .2 1
H2O0 .0 00 - 0 .1 05
Species distribution
N ear the top Z85: 0 - 1 .8x10 -6
B elow the topZ80: 0 - 3 .5x10
-6Above the a ir lances
Z 60: 0 - 1 .3x10-4
N ear the a ir lancesZ52: 0 - 4 .3x10 -4
A cross the S C C -bu rne rZ 40: 0 - 5 .2x10 -2
B elow the S C C burnerZ36: 0 - 3 .3x10 -4
N ear the O utle t X 570 - 2 .7x10
-6
CO overall range: 0 .00 - 0.071
Z85
Z80
Z60
Z52
3 6
Z40
Z20
Z10
Z1
X1
X15
X30
X57
SC C b u rne r
H igh
Low
H igh
Low
Low
H igh
H igh
H igh
H igh
H igh
H igh
H igh
Low
Low
H igh
H igh
H igh
H igh
H igh
H igh
H igh
H igh
H ighH igh
H igh
H igh
H igh
Low
Low
Low
Low
In term ed iate
H igh
H igh
Low
Low
Low
H igh
H igh
H ighH igh
H igh
Low
Low
Low
Model validation
• Temperature measurements
Ash
sum
p
S C C
A ir lan ce s(7 x2 )
G a so utle t
L o ad ch u te
S lu d g e b u rn er
M a in b u r n e r
S o lid b u r n e r
Ash
sum
p
S C C
A ir lan ce s(7 x2 )
G a so utle t
L o ad ch u te
S lu d g e b u rn er
M a in b u r n e r
S o lid b u r n e r5-m longWater-cooledThermocouple4-view ports
0
200
400
600
800
1000
1200
1400
-300 -200 -100 0 100 200 300
Distance from SCC centreplane (mm)
Te
mp
era
ture
(°C
)
Measured3-gas model (no heat loss)
7-gas model (10% heat loss)7-gas model (no heat loss)
Waste energy input: 37 MWWaste mass input: 6.67 t/hAir supply assumed: 43.5 t/h atstoichiometric air/waste ratio 6.52.Excess air in the model: 75%(including leakage air)
SCC-burner side
Temperature profiles: statistical• Temperature averaging
• Area averaging (directly available in VR-Viewer)• Mass flow averaging: highly required for
heterogeneous flow
Average temperature weighted by mass, Kiln
100
300
500
700
900
1100
1300
1500
1700
1900
2100
2300
0 1 2 3 4 5 6 7 8 9 10 11
Flow direction, X (m)
T
( , , )T F x y zTmax
Tarea
Tmass
Tmin
Average temperature weighted by mass, SCC
0
200
400
600
800
1000
1200
1400
1600
1800
2000
0 2 4 6 8 10 12 14 16 18
Flow direction, z (m)
T
T_massT_areaTmaxTmin
Example 2: Simulation of transient heating of dredging impellers in a mobile furnace
• Fuel combustion• Oil (red diesel) simplified as gas,
3-gas model (CEBU=25)
• Radiation• IMMERSOL model (Ka=0.1, Kb=0.001)
• Metal surface emissivity: 0.05-1.0
• Wall emissivity: 0.8
• Conjugate heat transfer• CAD geometry for the impeller
Simulation of a heat treatment furnace
• Construction of furnace geometry and grid• Cylindrical furnace, curved
roof (spherical cap)• BFC or Cartesian?• Handling of furnace walls
and boundary conditions• Handling of furnace roof
• Using high conducting solids combined with normal refractories to form the cylindrical and curved walls
S and
Fan
Chimneyes
B urners (x4)
Simulation of a heat treatment furnace• Comparison of predicted and pre-set surface temperature profile on the dredging impeller• 3 steps of fuel supply• Varying excess air rate
Period(hour)
ExcessAir (%)
MixtureFraction
Fuel(kg)
Energy per burner (kW)
0-8 226% 0.02 214 80
8-10.5 160% 0.025 84 100
10.5-20.5 85% 0.035 356 85
Total - - 654 -
Temperature profile final model
0
100
200
300
400
500
600
700
800
900
1000
1100
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
Time (hour)
Tem
per
atu
re (
ºC)
980 oC
CFD modelling of a heat treatment furnace
• Transient heating process of a dredging impeller in a mobile furnace
End of the transient m odel s te a d y -s ta te m od e l
12600 seconds7200 seconds1800 seconds
240 seconds30 seconds
73800 seconds45000 seconds36000 seconds
18000 seconds
4 seconds 20 seconds
Temperature range: 25 -1175°C
SandSand
Simulation of a heat treatment furnace• Surface temperature evolution of the impeller (0-
20 hrs)
Simulation of a heat treatment furnace
• Energy balance• Heating: 50 – 10%• Wall loss: 0 – 15%• Off-gas: 50 – 75%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 2 4 6 8 10 12 14 16 18 20 22
Time (hrs)
En
erg
y d
istr
ibu
tio
n
solids
out offgas
Wall heat loss
Energy efficiency: LOW!
Simulation of a heat treatment furnace• Alternative heating source:
Using radiation plate• Substantially reducing heat loss
by off-gas• Easy to regulate and control• Energy saving:
• Oil: 43 MJ/kgx654 kg– 28 GJ• Radiation plates:
2233 kWh – 8 GJ (70% saving)
€ 178 vs € 520 (65% saving)
R a d ia tio n p la te
Im p e lle r
Time period Hours Energy setting Total energy
0-2 2 200 kW constant 400 kWh
2-8 6 75 – 105 kW linear 540 kWh
8-15 7 105 – 150 kW linear 893 kWh
15-20 5 80 kW constant 400 kWh
Total (0-20) 20 2233 kWh0
100
200
300
400
500
600
700
800
900
1000
1100
0 2 4 6 8 10 12 14 16 18 20 22
Time (hour)
Te
mp
era
ture
(ºC
)
Temperature impellermeasuredTemperature radiation 4inputs
Summary
• CFD is a useful and handy tool in education and research at universities, as well as in industrial design and process R&D.
• Various aspects of high temperature materials processing operations could be reasonably simulated.
• More insight understanding of the transport phenomena and process performance can be obtained.
• Still a lot of challenges: complex geometry, reactive and multi-phase flows in industrial applications.
• We need more functionality and power of the Code!
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