ENCYCLOPÉDIE DE LA RECHERCHE SUR L’ALUMINIUM AU QUÉBEC 2013 | Page 16

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PRODUCTION D’ALUMINIUM
ALUMINIUM PRODUCTION

Ventilation réduite du dessus des cuves
d’électrolyse : influence sur le bilan thermique
VENTILATION RÉDUITE DU DESSUS DES CUVES cuves et la salle des cuves
dans les D’ÉLECTROLYSE :
INFLUENCE SUR LE BILAN THERMIQUE DANS LES CUVES ET LA SALLE DES CUVES

REDUCED VENTILATION OF UPPER PART OF ALUMINUM
REDUCED VENTILATION IN THE UPPER PART OF ALUMINUM SMELTING POT :
SMELTING POT: INFLUENCE ON HEAT BALANCE IN POTS
INFLUENCE ON HEAT BALANCE IN POTS AND POTROOM
AND POTROOM
Ruijie Zhao1, Louis Gosselin1, Mario Farfard2, Donald P. Ziegler3
1Aluminium

Research Centre-REGAL and Departement of Mechanical Engineering
Université Laval, Québec, QC, G1V 0A6, Canada
2
NSERC/Alcoa Industrial Research Chair MACE3 and Aluminium Research Centre – REGAL
Université Laval, Québec, QC, G1V 0A6, Canada
3
Alcoa Global Primary, Metals Alcoa Technical Center, 100 Technical Drive,
Alcoa Center, PA 15069

Maintaining normal draft condition in the upper part of aluminum smelting cells requires significant amount of electricity for the operation of the fans. Assuming an average price of electricity of 0.05
US$/kWh, the annual cost of electricity for running pot ventilation system is 2.5 MUS$ in a plant such as ADQ (260,000 ton Al/y). If one can reduce by 50% the ventilation rate, the fan power can be
roughly reduce to ~1/8th of the current level. In the perspective of waste heat recovery, the reduction of pot ventilation can significantly increase the exhaust gas temperature (by 50-60˚C by reducing
50% of normal draft condition). Moreover, it will induce less moisture into the pot and reduce the HF emissions. Finally, once successfully implemented, it will allow to downsize the GTC.

9000

2. To estimate thermal condition in potroom: more heat
escapes from hoods and superstructure, so the
temperature in potroom should be verified, especially in
extremely hot weather.
3. To verify pot tightness in reduced pot ventilation: less
vaccum in pot cavity, tighter pots might be required.

qtop
qbath

8000
7000

q(W)

1. To maintain top heat loss: the heat transfer rate extracted
from the bath by the top of the cell is reduced by 10% as
the ventilation rate is reduced by half. (900 W missing per
anode)

6000

Problem 1
Top heat loss enhancement

qgas+rod
qgas

•

5000
4000

•

3000
0.0

0.5

1.0

1.5 2.0 2.5 3.0
3
Draft(Nm /s)

3.5

4.0

Figure 1. Heat transfer rate from
different components

Different scenarios tested: fins addition on anode
assemble, modification of gap geometry and change
of anode cover configuration

case c2

High efficiency: case c2 (exposing more stubs in
cavity), compensating almost 900 W

4.5

Reason: no interference of additional structure with
the radiation transfer, enhancement both in convection
and radiation
•

Moderate efficiency: case b2 (horizontal gap),
compensating 400 W

case b2

Reason: Convection enhancement reduces surface
temperature, and then reduces radiation heat transfer

Problem 1 (pot model A)
1.
2.

Problem 2

CFD model: 1/20 pot slice model, from the bath free
surface to the potroom, SST k-ω turbulence model.

1. Flow pattern under different ventilation conditions: streamline colored by temperature

Objectives:
To study the top heat loss in normal and 50% reduced
ventilation,
To obtain the heat losses from hoods, superstructure
and exhaust gas as the boundary conditions for
potroom model,
To estimate different design
maintaining top heat loss.

modifications

Schematic view of pot model A

for

Only buoyancy driven ventilation

Problem 2 (potroom model)
1. CFD model: a potroom slice model including two ½
pot, SST k- turbulence model.

With medium wind effect (10km/h)

2. Thermal conditions under different pot ventilation in extremely hot weather:
temperature field in potroom

2. Objectives:

Tamb=30˚C, Vwind=10 km/h from northwest

To study the flow pattern and temperature field under
different outdoor conditions (wind, temperature),
Schematic view of potroom model

To estimate the temperature in potroom under different
pot ventilation levels (normal and 50% reduction),

Ruijie Zhao
Louis Gosselin
Centre de recherche
sur l’aluminium - REGAL,
Département de génie
mécanique, Université Laval
Mario Fafard
Chaire de recherche
industrielle
CRSNG/Alcoa MACE3,
Centre de recherche
sur l’aluminium - REGAL,
Université Laval
Donald Ziegler
Alcoa Technical Center

To obtain the flow velocity, pressure and temperature
in the area near pots, which are used as boundary
condition for the model of problem 3.

Problem 3 (pot model B)
1. CFD model: 1/10 pot slice model and pot end model,
a large portion of potroom included in order to have
more accurate boundary conditions extracted from
potroom model

Normal pot ventilation

50% normal pot ventilation

2. Objectives:
To verify the efficiency of hoods and superstructure
under lower pot ventilation level,
Schematic view of pot model B

To modify current pot structure to achieve a better
tightness in low draft condition.

Pot model A

Top heat loss
enhancement

2. Optimizing the jet flow field is not enough to recover the reduction of top heat loss
under the low ventilation condition studied here.

Thermal condition
in potroom

Simulation Strategy

Thermal
BCs

Potroom
model

HF conc. in
potroom

1. In order to enhanc