DEPTH ANALYSIS AND POTENTIALITY EXPLOITATION ON ENERGY-SAVING AND

CONSUMPTION-REDUCTION OF ALUMINUM REDUCTION POT

Zhou Jianfei¹, Marc Dupuis², Yan Feiya¹, Huang Jun¹, Yi Xiaobing¹

¹CHALIECO GAMI Guiyang Guizhou China 550081

²GéniSim Inc., 3111 Alger St., Jonquière, QC, Canada, G7S 2M9

Keywords: aluminum reduction, prebaked pot, pot voltage, energy consumption

Abstract

Heat input

1. Current (variable)

In view of the existing status with aluminum overcapacity and

2. Voltage

lower aluminum price in China, many companies adopted various

2.1 Anode (constant)

measures to reduce the production cost and the energy

2.2 Cathode (constant)

consumption, but there has been no a normalization theory and

2.3 ACD

method as yet. Aimed at the existing status and the market

2.3.1 Bubble voltage drop (variable)

demand, this paper puts forward the evident effects of energy-

2.3.2 Bath voltage drop—ACD, bath ratio (variable)

saving and consumption-reduction in aluminum reduction pot

2.3.3 Back-EMF (constant)

using new thermal insulation pot lining design, application of

optimal cathode structure, reduction of horizontal current device,

Heat output

proper application of new lining materials and proper combination

1. Heat dissipation at pot top (internal cause: Topr )

of relevant process parameters based on the finite element

(External cause: material and thickness of anode covering

software ANSYS and using the thermal field simulation software

materials, flue gas velocity and sealing degree of pot hood)

of international simulation Prof. Mr. Dupuis as the calculation

2. Heat dissipation at pot side (internal cause: Tsuper)

method, combining the actual production data. Practice proves

(External cause: bath level, metal level, pot lining design)

that the above-mentioned method combining design, simulation

3. Heat dissipation at pot bottom (internal cause: Topr )

and experiment can become the effective and feasible way to

(External cause: material and thickness of cathode lining)

achieve low energy consumption, low cost and high profit.

The object of voltage reduction is the voltage combination in the

Introduction

heat input, the majority of which is voltage drop of ACD (anode

cathode distance).

In recent years, the nonferrous metal industry sets off a upsurge of

scientific and technological innovation activities on quality and

It should be pointed out that the high-temperature production

capacity increase, energy-saving and consumption-reduction as

during aluminum reduction mainly depends on the Joule heat

well as environment protection. The key technologies in

generated from current passing in the bath between the anode and

aluminum reduction area such as low-temperature reduction,

the cathode. The normal production shall be kept through the

intensifying current, on-line measurement of superheat,

“3-

dynamic balance of heat output and heat input during operation. If

variable ” control technology, anode slotting technology, irregular

the Joule heat generated from heat input is not enough to maintain

cathode technology, thermal insulation lining structure, cathode

the heat output, the pot shall get cool gradually, and the process

for horizontal current reduction, application of new lining

system shall be damaged.

materials, inert anode etc. are studied and developed, which raises

Chinese aluminum reduction technology to the world advanced

Therefore, the energy balance of pot is maintained by reducing the

level soon. Moreover, the consumption of energy and raw

heat dissipation in heat output combination as well as the voltage

material for aluminum reduction production is very high in recent

in heat input combination so as to reduce the voltage.

years, especially power consumption. With the energy crisis, the

aluminum reduction production costs must be reduced without

Analysis of potentialities and approaches on voltage

delay. For this, the most efficient method is to reduce the DC

reduction by heat dissipation of heat output

consumption by increasing current efficiency (CE) and reducing

cell voltage.

About half of the total power input in pot is used for aluminum

production and the other half is lost through heat dissipation, so

Analysis of mechanism and nature of pot work voltage

the focus of the pot voltage reduction is to reduce the heat

reduction based on energy balance principle

dissipation loss. The proper specification of the thickness of the

side ledge is at the core during voltage reduction. Both too thick

The pot energy balance was summarized by Warren Haupin in

ledge or too thin ledge have a negative effect on the pot stability

[1].

during production, thus affecting the voltage reduction effect and

the CE, even cause the pot leaking. Therefore, the reasonable heat

The heat input and output may be divided into the followings:

dissipation distribution and the proper side ledge formation are the

core of new thermal insulation lining optimization design.

Material and thickness of covering materials

Heat dissipation at pot top

The pot thermal balance shall be regulated by controlling the

The heat dissipation at the top of the pot accounts for about half of

alumina content as well as the thickness of covering materials. For

total heat output, so the focus of the heat output reduction is to

large-scale pots, it is necessary to take the insulation measures at

reduce the heat dissipation at this point. For the conventional pot,

the middle and end of pot, make use of the different thickness of

the top heat dissipation is in the range of 1.0V to 1.2V, and the pot

the covering materials to adjust the total thermal balance

voltage is required to be above 4.16V. However, based on the

uniformity of pot, thus guaranteeing the uniformity and regularity

statistics of the pots with different currents, the top heat

of the side ledge.

dissipation is below 0.98V for the pots with al voltage lower than

3.9V. This is to say that the top heat dissipation reduction

The material composition of the covering materials is relevant to

provides the larger space for the total heat dissipation reduction,

the alumina content and the bath crushing size in the covering

which contributes greater to the pot voltage reduction.

materials, it is shown as Figure 1.

There is an important relationship between top heat dissipation

and pot voltage. Using the actual data from a 320 kA pot in a

Chinese smelter, this paper will try to explain it. A first type of

pot (Type A), with a thinner covering material, a voltage of 4.16

to 4.18V and a heat dissipation of 1.153V in the anode area, is

shown in Table 1.

Figure 1. Covering materials sample with above 93% Al2O3 left,

covering materials sample with below 13% Al2O3 and

0.5-8mm bath crushing size right

The thickness of covering materials has a major impact on the

heat dissipation at the top of the pot. Taking a 350 kA pot as an

example, its simulation is performed (bath content and alumina

content in the proportion of 1/1 in covering materials).

Table 1. Heat dissipation distribution (anode area) for a Type A pot

The second type of pot

(Type B), which presents a thicker

covering material, a pot voltage of

3.8 to

3.85V and a heat

dissipation of 0.98V in the anode area, is shown in Table 2.

Figure 2. 350 kA, covering materials with a thickness of 10 cm

Figure 3. 350 kA, covering materials with a thickness of 18 cm

As shown in Table 3, for the covering materials with alumina

content and bath content in the proportion of

1/1, when the

thickness is respectively 10 cm and 18 cm, the reduced voltage of

Table 2. Heat dissipation distribution (anode area) for Type B pot

heat dissipation is respectively 1.046V and 0.883V. This shows

that the voltage can be reduced by about

20 mV using the

covering materials.

Table 4. Relationship of optimal ledge thickness and bottom ledge

length

Table 3. Impact of different thickness covering materials on voltage

reduction

Table 5. Relationship among voltage, superheat and lining thermal

insulation

Application of new pot hood

Heat dissipation distribution calculation and actual measurement

The new energy-saving sealed pot hood has a layer of high

comparison between conventional lining and new thermal

temperature fire resistant and thermal insulation composites on the

insulation lining in 350 kA pot

hood internal face. This layer can prevent the heat in the pot from

transferring outside through the side hood, thus reducing a lot of

According to the results presented below for the comparison of

the heat loss, which complies with energy-saving goals. Through

cathode design: 1) conventional lining and insulation lining using

testing, the pot hood surface temperature shall be reduced by more

flat bottom cathode fit with conventional paste to connect steel bar

than 10°C and the reduced voltage shall be reduced by 5 to 15mV

and 2) irregular cathode fit with cast iron pouring to connect steel

using the new pot hood compared to the conventional pot hood.

bar.

Heat dissipation at pot side and pot bottom

The comparison of process parameters control in Table 6, shows

the following differences between the conventional lining and the

The heat dissipation at the pot side and bottom accounts for about

irregular cathode lining: 22 and 12 cm for the aluminum level, 5.4

half of the total heat output. The superheat is directly related with

and 4.5 cm for the ACD, and 8 and 7°C degrees for the superheat.

the heat dissipation, the principle of which is to maintain the

production under low voltage through lower superheat in order to

guarantee the energy balance. The pot lining design is indirectly

related with the heat dissipation. The purpose is to form a uniform

yet not excessive ledge thickness under low superheat in order to

guarantee a stable and effective production. Therefore, the pot

with a lower voltage must be running under the thermal balance

with a lower superheat. So the proper pot lining should be match

to guarantee a reasonable heat dissipation distribution and a

uniform yet not excessive ledge thickness.

Based on the technical features of Chinese aluminum reduction

and the market demand, the SIMULATION SOFTWARE OF

ENERGY BALANCE OF ALUMINUM REDUCTION POT is

currently developed by GAMI combining the thermal field

simulation software of international simulation Prof. Mr. Dupuis.

It aims at matching various-scale pots as well as the advanced

aluminum reduction technologies and process parameters using

the cathode model at pot side and at pot end as well as an anode

model in a three-in-one united method[3] based on reasonable

heat dissipation and proper ledge thickness after it has been

modified through years of checking and verification.

The relationship of optimal ledge thickness and bottom ledge

length is shown in Table

4 after numerous calculations and

monitoring validations (including 6, 160, 240, 300, 350, 400 and

500 kA pots) in recent years. Relationship among pot voltage,

superheat and lining thermal insulation structure in 160 to 450 kA

pots is shown in Table 5.

Table 6. Comparison of process parameter controls

Table 8. Comparison of heat dissipation distribution

For the economic benefit, with the prerequisite that efficiency loss

of insulation lining is 1-2% of the conventional lining, it can still

save 900 kWh/T of electric energy consumption.

Figure 8. Conventional lining structure, profile of pot side ledge

Table 9. Comparison of economic benefit

Heat dissipation distribution comparison between conventional

lining and new thermal insulation lining

Figure 9. New thermal insulation lining structure, profile of pot side

ledge

From the comparison of the heat dissipation distribution, the main

realization of reduced of heat dissipation loss is in the cathode

area. The reduced heat dissipation quantity in the cathode area

corresponds to 300 mV and reduced heat dissipation in the anode

area corresponds to 50 mV. In the cathode area, the reduced heat

dissipation at lateral part accounted for the most, with

approximately

275 mV. The heat dissipation distribution

proportion, anode area and cathode area of conventional lining are

Table 10. Heat dissipation distribution comparison between the

conventional and the new thermal insulation lining

47.02%：52.98% and 54.16%：45.84% for the new thermal

insulation with irregular cathode lining. The proportions of the

According to Table 10, heat dissipation distribution proportion of

two linings are reverse.

cathode and anode for new thermal insulation with irregular

cathode lining is reverse the one observed for conventional lining.

The cathode area is decreased from 57% to 45%, the biggest

decrease (35% to 25%) being at the pot side.

Rational application of new lining insulation material

In the last two years, in the quest to decrease pot voltage and

introduce new thermal insulation lining, the application and

popularization of new insulation lining material have become the

focus for aluminum industry. Ceramics fiber, compound silica

acid magnesium aluminum type thermal insulation material are

now widely used at inner and outside insulation structure of pot.

Conclusions

[10]

Gui Yang Aluminium and Magnesium Design and Research

Institute and Aluminium Corp of China，Guangxi Branch.

From the above mentioned, by the way of lots of industrialized

“Comprehensive test report for physics field of

160 kA

experiments, testing at the site, computer simulation and

prebaked anode pot”, 2009.3.

comparisons, the ways and the methods to decrease energy

consumption through pot voltage reduction with respect to heat

[11]

Gui Yang Aluminium and Magnesium Design and Research

dissipation are as follows: material and thickness of anode

Institute and Aluminium Corp of China，Zuiyi Branch，

covering material, new-type thermal insulating lining and new-

“Comprehensive test report for physics field of

200 kA

type thermal insulating lining material.

prebaked anode pot”, 2009.3.

Comparing with the conventional pot, the reduced cell voltage is

[12]

Gui Yang Aluminium and Magnesium Design and Research

around 200-450 mV. The reduced energy consumption per ton

Institute and Aluminium Corp of China， Zuiyi Branch,

aluminum is around 640-1440 kWh/T based on the calculation of

“Comprehensive test report for physics field of

350 kA

93% current efficiency. The annual reduced energy consumption

prebaked anode pot”, 2009.3.

of the pot line is around 32*10⁷-72*10⁷kWh per year based on the

calculation of an annual capacity of

500 thousand tons. The

[13]

Jay N. Bruggeman, “Pot Heat Balance Fundamentals”, Proc.

operation cost savings are in the range of 160 to 360 million Yuan

6th Aust. Al. Smelting Workshop, 1998, 167-189.

per year as per 0.5 Yuan per kWh convertion for the power price.

References

[1]

Warren Haupin, Halvor Kvande

“Thermodynamics of

Electrochemical Reduction of Alumina”, TMS Light Metals,

2000, 379-384.

[2]

Jayson Tessier, Carl Duchesne, Claude Gauthier, Gilles

Dufour, “Image Analysis for Estimation of Anode Cover

Material Composition”, TMS Light Metals, 2008, 293-298.

[3]

Tian Yingpu, “Pot anode cathode distance composing model

and process energy consumption”, Light Metals, 2011.3.

[4]

Energy source science and engineering college of Central

South University and Aluminium Corp of China Guangxi

Branch ，“Comprehensive test report for physics field of

160 kA prebaked anode pot”, 2007.7.

[5]

Energy source science and engineering college of Central

South University and Aluminium Corp of China Guangxi

Branch， “Comprehensive test report for physics field of

320kA prebaked anode pot”, 2007.7.

[6]

Aluminium Corp of China， Zhengzhou Research Institute,

“Comprehensive test and energy-saving potential research

report for 320 kA pot”, 2008.6.

[7]

Aluminium Corp of China， Zhengzhou Research Institute,

“Comprehensive test report for related parameters

measurement for 400 kA pot”, 2008.3.

[8]

Aluminium Corp of China， Zhengzhou Research Institute,

“Comprehensive test and energy-saving potential research

report for 350 kA pot”, 2010.10.

[9]

Gui Yang Aluminium and Magnesium Design and Research

Institute and Aluminium Corp of China，Guizhou Branch,

“Comprehensive test report for physics field of

240 kA

prebaked anode pot”, 2008.7.