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
Symmetric centerline
Gas cooling from 1370°C to586°C
2D view of particle tracks
50 m particles, 20 injection points
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
Te
mp
era
ture
(°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)
Rotary kiln
Secondarycombustionchamber(SCC)
Ashsump
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 CombustionChamber(SCC)
To RadiationChamberof WHB
Ash Sump
Burner flame
Solid-waste flame
Load chute
Main burner
Sludgeburner
SCC burner
Air lances(x 7)
Air 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-e 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
%CxHy %CO %H2
Assumed Fuel: CH1.7
Heat of combustion:
42,000 kJ/kg
Off gas calculations
C102H131O110
Heat of combustiondepends on comp.
Heat of combustion:10,100 kJ/kg
Heat of combustion:120,000 kJ/kg
% CO2, O2
Generalized fuel:
CxHyOz
Better defined
ChemicallyThermally
Original waste
Less known, poorly defined
ChemicallyThermally
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
e
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 s
um
p
SCC
Air lances(7x2)
SCC burner
Gasoutlet
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 main burner
Typical CFD predictions
SCC burner
Solid wasteburner
Sludgeburner
Mainburner
SCC back wallSCC side wall
Across 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
Ashsump
1098
Across the load-chute
Be tween the solid-waste burnerand the sludge burner
Across the main burner
Across the SCC -burner Near the outlet to WH B
Centra colder zone due to air injection lance s
1247
1098
1247
139 6
109 8
1247
1 396
154 4
16931247
1098
801
124715441 693
184 11 990
213 9
801
653504
1841
1544
801653
1396
1247
1098
1247
1098
1396
154 4
1 693
1841
1693
1 544
2 139
653
801
1841
1 693
1 990
2139
8 011247
653
10981 544
1 098
950
801
1247
12471396
1 3961 5441693
19002 139
21391 693
1693
5043552075 8
1 0981 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
1140
1176
1194
1 229
12471265
126 51301
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 fr
ac
tio
n
CO2
O2
C3H4
H2O
CO
H2
Outside the SCC
Species distribution
Typical CFD predictions
C3H40.00 - 0.168
CO0.000 - 0.054
CO20.00 0.21
H2O0.000 - 0.105
Species distribution
Near the top
Z85: 0 - 1.8x10 -6
Below the top
Z80: 0 - 3.5x10-6
Above the air lances
Z60: 0 - 1.3x10-4
Near the air lances
Z52: 0 - 4.3x10 -4
Across the SCC-burner
Z40: 0 - 5.2x10 -2
Below the SCC burner
Z36: 0 - 3.3x10 -4
Near the Outlet X57
0 - 2.7x10-6
CO overall range: 0.00 - 0.071
Z85
Z80
Z60
Z52
36
Z40
Z20
Z10
Z1
X1
X15
X30
X57
SCC burner
High
Low
High
Low
Low
High
High
High
High
High
High
High
Low
Low
High
High
High
High
High
High
High
High
HighHigh
High
High
High
Low
Low
Low
Low
Intermediate
High
High
Low
Low
Low
High
High
HighHigh
High
Low
Low
Low
Model validation
• Temperature measurements
Ash
sum
p
SCC
Air lances(7x2)
Gasoutlet
Load chute
Sludge burner
Main burner
So lid burner
Ash
sum
p
SCC
Air lances(7x2)
Gasoutlet
Load chute
Sludge burner
Main burner
So lid burner
5-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
)
Measured
3-gas model (no heat loss)
7-gas model (10% heat loss)
7-gas model (no heat loss)
Waste energy input: 37 MW
Waste mass input: 6.67 t/h
Air supply assumed: 43.5 t/h at
stoichiometric 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 z%
Tmax
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
Sand
Fan
Chimneyes
Burners (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)
Excess
Air (%)
Mixture
Fraction
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
pera
ture
(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 model steady-state model
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)
Radiation plate
Impeller
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 impellermeasured
Temperature 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!
Top Related