Encyclopedie de la recherche sur l'aluminium au Quebec - Edition 2014 | Page 31

EFFICIENCY OF POT TIGHTNESS
PRODUCTION DE
UNDER DIFFERENT POT L’ALUMINIUM // ALUMINIUM PRODUCTION
DRAFT
CONDITIONS BASED ON CFD
EFFICACITÉ DE L'ÉTANCHÉITÉ DU POT SOUS DIFFÉRENTS
SIMULATIONS
COURANTS du pot sous SUR LA BASE DE SIMULATIONS CFD
Efficacité de l’étanchéité D'AIR DU POT
différents courants EFFICIENCY OF POT TIGHTNESS UNDER DIFFERENT POT
d’air du pot sur la
base de simulations CFD
DRAFT CONDITIONS BASED ON CFD SIMULATIONS

29

Ruijie Zhao1,2, Louis Gosselin1, Mario Farfard2, Donald P. Ziegler3
1Aluminium

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

Reduction of pot draft can result in potential benefits both in the perspective of waste heat
recovery and in terms of energy saving & emission reduction. However, the pot tightness, or the
vacuum in pot, is adversely influenced by the reduction in pot draft. An estimation of the pot
tightness is required for a proper control of the fugitive emissions under both normal and reduced
pot drafts. Several simplified analytic models and in-situ measurements, although providing

1.
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Influencing factors of pot tightness:
Pot draft level (2.4 Nm3/s vs. 1.2 Nm3/s)
Pot openings (gaps between hoods and around anode rod)
Wind condition (0, 10 km/h, 20 km/h outdoor wind)
Crust integrity (w/o holes)
Heat loss from crust and anode stubs (varied in 20%)
Air leakage from pneumatic system (not considered)

valuable insights on this issue, are either too simple to accurately analyse the situation or unable
to provide the detailed information everywhere. CFD simulation is employed and helps to
understand the mechanisms of fugitive emissions from pot shell. The simulation is confined to the
situation where all pot covers are put on position, i.e. no pot operation.

1. Pressure distribution in pot cavity

2. Mechanism of pot ventilation

Pot draft 1.2 Nm3/s

Pot draft 2.4 Nm3/s

Pot draft 1.2 Nm3/s, modified case

2. Pressure distribution on pot shell (1.2 Nm3/s)

3. CFD simulation strategy

Wind 0 km/h from tapping end

Wind 20 km/h from tapping end

3. Effect of the size of gaps between hoods

4. Model validation: flow path lines in potroom under different wind conditions (pot
draft 2.4 Nm3/s )

2 cm hood gaps, 1.2 Nm3/s

1 mismatch hood, 2.4 Nm3/s

4 cm hood gaps, 2.4 Nm3/s

4. Modifications of pot structure (1.2 Nm3/s)
0 km/h from tapping end

10 km/h from tapping end

20 km/h from tapping end

• Pot draft and gap size have the priority of influencing weight on the pot tightness, and
the wind influence in potroom will take place as the vacuum at the top of pot cavity
goes down to less than -1 Pa. A crust hole and an increased top heat loss cause very
limited influence on the pot tightness.
• Current pot structure with good hood placement can maintain enough pot tightness to
avoid fugitive emissions under the designed pot draft, 2.4 Nm 3/s.
• The width of gaps between hoods is recommended to less than 3 cm under 2.4 Nm3/s.
• Fugitive emissions is significant when the pot draft is reduced by half.
• The installation of brushes is an efficient way to reduce the fugitive emissions.
• The installation of lips along hood edges is the most efficient way to increase the
vacuum in pot under reduced pot draft conditions.
The authors greatly appreciate the financial support from FRQ-NT, and the collaboration
with Alcoa.

Installation of
brushes on
superstructure

2 cm hood gaps

2 cm hood gaps, 20 km/h, position 1

4 cm for 1 hood gap

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

Covering lower
half hood gaps
2 cm hood gaps

4 cm for 2 hood gaps

Journée des étudiants – REGALpot draft condition is promising for energy saving and waste heat
Reduction in

La réduction des gaz du pot est avantageuse pour l'économie d'énergie et la
18 novembre 2014
récupération de la chaleur perdue dans les cellules d'électrolyse de l'aluminium.
L’étanchéité du pot, ou le contrôle des émissions fugitives, est étudiée dans une
cellule de fusion avec une réduction des courants d'air à la moitié du niveau
standard sur la base de simulations CFD. Des modèles avec différentes échelles
de simulation ont été créés afin de définir de manière itérative des conditions
limites appropriées autour de la zone de fuite. Une analyse systématique de
l'étanchéité du pot est présentée en tenant compte de divers facteurs, tels que le
gaz du pot et le placement du panneau. Les résultats ont montré que, même dans
des conditions idéales, la structure actuelle du pot n’arrive pas à maintenir une
efficacité de panneaux de 100 % sous un gaz réduit de 50 %. Deux modifications
sont proposées et vérifiées et une étanchéité efficace est observée lors de la
couverture de la partie inférieure de l'écart entre les panneaux. Une estimation
primaire de la fuite de fluorure d'hydrogène est faite selon différents scénarios
afin de vérifier quantitativement les modifications.

recovery in aluminum smelting cells. Pot tightness, or control of fugitive emissions,
is investigated in a smelting cell with drafts reduced to half the normal level based
on CFD simulations. Models with different simulation scales are created in order to
iteratively define proper boundary conditions around the leaking area. A systematic
analysis on the pot tightness is presented by considering various factors, e.g., pot
draft, hood placement. The results have shown that the current pot structure, eve