CFD analysis of an uptake shaft with
slagging walls – the slag model
Bingzhi Li, Anders Brink, and Mikko Hupa
Combustion and Material Group, Process Chemistry Centre,
Åbo Akademi University, Finland
FINNISH-SWEDISH FLAME DAYS, January 28-29, 2009, Naantali, Finland
Outline
Background
Objective
Model description
Test case
Conclusions
Acknowledgement
FINNISH-SWEDISH FLAME DAYS, January 28-29, 2009, Naantali, Finland
Background (1/2)
Flash smelting process
Heat recovery boiler
(HRB)
Uptake shaft
• Smelter – a significant amount of dust particles
generated
• HRB – deposition causes performance decay
• Uptake shaft – herein the conditions affect the
deposition behavior of the dust particles
FINNISH-SWEDISH FLAME DAYS, January 28-29, 2009, Naantali, Finland
Background (2/2)
Nickel matte smelting slag
• Nickel matte smelting slag: FeO-Fe2O3-SiO2-MgO-CaO system
• MgO: increases liquidus temperature and, beyond certain level
raises viscosity of the slag
• CaO: added to overcome furnace accretion and tapping difficulties
• Liquidus temperature VS composition
• Viscosity-temperature relation VS composition
• Thermal conductivity, specific heat
FINNISH-SWEDISH FLAME DAYS, January 28-29, 2009, Naantali, Finland
Objective
Test the applicability of a slag model
by investigating slags with different compositions
which relevant to nickel matte smelting.
FINNISH-SWEDISH FLAME DAYS, January 28-29, 2009, Naantali, Finland
Model description (1/4)
Slag flow model
Running
slag layer
At steady state, F = G
d
dv
( ( x) )
dx
dx
F
X
v=0
(1)
(x) is the viscosity, dv/dx is the velocity gradient, and
is the slope of the wall, is the thickness of running slag
layer.
G
x=0
g cos
x=
dv/dx = 0
(x) can be obtained from the viscosity-temperature
relation (T) using a linear dependence of temperature
on position.
Boundary conditions
FINNISH-SWEDISH FLAME DAYS, January 28-29, 2009, Naantali, Finland
Model description (2/4)
Slag flow model
Exponential expression of visocity-temperature relation
Ae B / T
( x)
(
(2)
f ) exp(
x
)
ln( (0) / (
(3)
f
))
f
(1)
v( x)
g cos( )
(
m'
f
f )
2
Mass flow rate
2
e (
1
x
1
f
)
(
e
2
1
x
2
)
(4)
f
g cos( )
(
f )
3
f
e (
1
2
2
2
)
3
2
3
FINNISH-SWEDISH FLAME DAYS, January 28-29, 2009, Naantali, Finland
(5)
Model description (3/4)
Simplification of the heat balance
mdeposition
q flowin
m flow
q deposition
qradiation
qconduction
q radiation
q flow
qconduction
qdeposition
q flowin qradiation qdeposition
qconduction q flowout
q flowout
qradiation
qconduction
FINNISH-SWEDISH FLAME DAYS, January 28-29, 2009, Naantali, Finland
Model description (4/4)
Heat flux calculation
Tinner
Touter
Refractory
Tinner = liquidus temperature of the slag,
m’
q
Touter is solved with the thickness f,
heat flux
qconduction
Solid
Touter Tinner
f / kf
Fluid f
FINNISH-SWEDISH FLAME DAYS, January 28-29, 2009, Naantali, Finland
Test case (1/5)
Properties of nickel matte smelting slag and model inputs
Density (kg/m3)
Thermal conductivity k (W/m-K)
Specific heat Cp (J/kg-K)
2800
1
1200
Emissivity
0.8
Mass flow rate m’ (kg/s-m)
0.6
Gas phase temperature (K)
1700
These parameters are assumed to be the same for all the
slags considered. To assure that the gas phase temperature
is not lower than the liquidus temperature of the slags, it is
set to be higher than the normal actual temperature (~1500
K).
FINNISH-SWEDISH FLAME DAYS, January 28-29, 2009, Naantali, Finland
Test case (2/5)
Properties of nickel matte smelting slag –
Composition and liquidus temperature
Slag A, B, C: iron saturated artificial slags, Fe/SiO2 = 1.7
Composition (wt%)
Liquidus temperature (K)
Slag A
0 MgO, 0 CaO
1476
Slag B
6 MgO, 0 CaO
1616
Slag C
3 MgO, 3 CaO
1481
45.2 Fe, 28.1 SiO2,
5 Fe3O4, 5.6 MgO,
2.7Al2O3, 1.2 CaO
1566
Industrial
FINNISH-SWEDISH FLAME DAYS, January 28-29, 2009, Naantali, Finland
Test case (3/5)
Viscosity (Pa S)
Properties of nickel matte smelting slag - Viscosity
0.18
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
1450
Industrial
Slag A
Slag B
Slag C
1500
1550
1600
1650
1700
1750
Temperature (K)
FINNISH-SWEDISH FLAME DAYS, January 28-29, 2009, Naantali, Finland
Test case (4/5)
Viscosity (Pa s)
Properties of nickel matte smelting slag – Viscosity-temperaure relations
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
Industrial
Slag A
Slag B
Slag C
.
1450
1500
1550
1600
1650
1700
1750
Temperature (K)
4 * exp( 9 . 3715 e 3 / T ) SlagB :
SlagA :
1 . 2651 e
SlagC :
2 .6432 e 4 * exp( 7.6089 e3 / T )
Industrial :
4 . 4643 e
9 * exp( 2 . 622 e 4 / T )
4 . 5209 e
4 * exp( 8 . 9482 e 3 / T )
FINNISH-SWEDISH FLAME DAYS, January 28-29, 2009, Naantali, Finland
Test case (5/5)
Results –
thickness and the surface temperature of the running slag layer
Slag A
Slag B
Slag C
Industrial
TL (K)
1476
1616
1481
1566
Touter (K)
1543
1640
1540
1614
(mm)
0.55
0.48
0.47
0.68
q (kW/m2)
7.6
3.2
7.8
4.4
f
• Higher viscosity – thicker running slag layer
• Lower liquidus temperature (TL), fixed gas phase temperature – higher heat
flux
FINNISH-SWEDISH FLAME DAYS, January 28-29, 2009, Naantali, Finland
Conclusions
Three artifical slags and one industrial slag relevant to nickel matte
smelting were tested.
Thickness and surface temperature of the running slag layer were
calculated.
The magnitude of heat flux through the slagging wall is reasonable, which
proves the applicability of the model in the calculation for flash smelting
slags. The model can be implemented as a subroutine and be used in
CFD analysis of an uptake shaft.
FINNISH-SWEDISH FLAME DAYS, January 28-29, 2009, Naantali, Finland
Acknowledgement
This work has been part of the activities of the Åbo Akademi Process
Chemistry Centre funded by the Academy of Finland in their Centres of
Excellence Program. Financial support obtained from Outotec Oyj and by
the National Technology Agency of Finland in the research project
“INTER” is gratefully acknowledged
FINNISH-SWEDISH FLAME DAYS, January 28-29, 2009, Naantali, Finland