Product promotion for Shandong Chenyang Carbon Co., Ltd Product promotion for Shandong Chenyang Carbon Co., Ltd

Research & Development of Low-consumption Carbon in Aluminum

Industry

Yu Yiru

Company profile

Project R&D

Project effectiveness

ContentContent

Basic theory

Experimental study

Technology evaluation

Industrial application test

Shandong Chenyang Carbon Co., Ltd established in 1987, is the largest wholly-owned

subsidiary of Jining Carbon Group Co., Ltd and is one of the national high-tech enterprises in

China. It has the R&D base for the production and technology of carbon anode used for

aluminum electrolysis, with output of carbon anode 500,000tpy. It is the leading enterprise in

the industry carbon used for aluminum electrolysis in China, the syndic units of China

Nonferrous Metals Industry Association and CHINALCO; the member of The National

Nonferrous Standardization Technical Committee; the vice-president unit of Carbon Branch;

Postdoctoral innovation experimental base of Wuhan University of Science and Technology;

Standard R&D demonstration base of carbon used for aluminum electrolysis; and it owns the

state-certified carbon testing laboratory and provincial enterprise technology center. It has

firstly passed the ISO9000 Quality Management System Certification, ISO14000 Environment

Management System Certification and OHSAS18000 Occupational Safety and Health

Management System Certification. The company with international reputation of the industry

was awarded as the Shandong Technological Innovation Enterprise, National High-tech

Enterprise and Shandong Star Enterprise of China’s Patent.

Company profileCompany profile

The company has always focused on the experiment & research of technology of carbon anode

used for aluminum electrolysis; tracking and being responsible for drafting the national and

industrial standards for a long term and conducting technical cooperation with scientific

research institutions at home and abroad. By cooperating with universities and employing

experts from home and abroad for technical guidance, with the bringing in, learning and re-

innovation, the company studied the new techniques of carbon anode used for aluminum

electrolysis, improved the performances of carbon anode continuously and then realized the

carbon creating perfectly from carbon producing. The company creates values for customers

by providing technology and services, and promotes the energy saving, consumption

reduction, emission reduction, benefits increase effectively in electrolytic aluminum

production, which improve the production technology of carbon anode, strengthen the

improvement of technology of carbon used for aluminum electrolysis and lead to the

continuous development of the whole industry.

Company profileCompany profile

The company has become the model of comprehensive utilization and circular economy. The

scientific and technological achievements of waste gas utilization and cogeneration founded the

beginning of the industry. For recent years, the company has achieved 10+ National Invention

Patents, 20+ utility model patents and 30+ innovations; it has drafted 30+ standards and 100+

papers as well. The company has compiled a series of professional publication “Carbon anode

production technology”, translated and publicly published many professional publications

including ”The technology of carbon anode used for aluminum electrolysis” , which have

promoted the carbon anode production technology progress in China.

During the period of 13th Five Year Plan, the company will make greater contributions to the

industry development and technology progress based on the principles of energy saving &

environmental protection, circular economy and sustainable development, to speed up the

pace of new carbon material series product R&D and industrialization.

Company profileCompany profile

Carbon anode, a material for making aluminum electrolysis, is hailed as the heart for

electronic tank, playing an important role of breakover in the whole process. The

carbon consumption is 334kg ／ t-A1 in theory while in practice it betweens 480—

530Kg/t-A1. The extra carbon

consumption is for overconsumption or just residuals. The reason that the process

consumed more carbon is related with the cell condition, temperature of electrolysis,

the shape of carbon anode, the quality and residual hardness. More anode consumed,

more electrolysis carbon discharged and it will undercut the electric current efficiency,

increase fuel consumption and CO2 emission which are bound to push up the

production cost.

Project developmentProject development

The project starts with influencing factors of carbon anode’s electrolysis

consumption in the tank, effect of the raw material nature and production parameter

setting. In addition, developing new technique, increasing pitch wetting and

adhesiveness for the carbon anode grain, enhancing thermal shock resistance of carbon

anode, improving roasting curve, decreasing reactivity of carbon anode and selective

oxidation, cutting slags discharge, boosting anti-oxidation performance, lowering

secondary reaction and extra consumption are all the goals the project intends to

achieve.

 

The project made huge contributions to the electrolytic aluminium industry concerning

energy saving, consumption cut, emission reduction and efficiency improvement.

Project overviewProject overview

• Shape of electric tank/ anode size

• Current efficiency• Electrolyte temperature• Carbon anode fluting• Anode quality

Reactivity of CO2 Air reactive Thermal conduction

Basic theoryBasic theory

• 1. Electrochemical consumption (electrolytic reaction)

2 Al 2 O 3 + 3 C ＝ 4 Al + 3 CO 2

• 2. Chemical consumption

Chemical consumption which includes CO2 and air reactions is not only a

major factor that causes anode overload, but also an evaluation indicator for

carbon anode quality and performance.

CO2 reaction ： C ＋ CO2 ＝ 2CO

Air reaction ： C ＋ O2 ＝ CO2

• 3. Mechanical consumption

The mechanical consumption is partly due to the selective oxidation of

carbon anode. Because the carbon anode is anisotropic body, the reaction

first occurs in active points, and isolates the weak activated charcoal

granules, making them falling off into the electrolytic cell to form carbon

residue. The poor thermal shock resistance of carbon anode is another

cause. During electrolysis, carbon anode may fall off or broke as a result of

the arris defect, chip off-falling, fragmentation or even fracture.

Electrical consumption of carbon anodeElectrical consumption of carbon anode

In the electrolytic cell, the oxidation reaction mainly occurs on the top of the anode

which is exposed to the air and the lateral surface where the temperature is 400~600 . This ℃

reaction is not only associated with the quality of carbon anode, but also with the actual

operation during electrolysis, for example, the anode will be oxidized if the cell temperature is

too high, or the coverage of carbon anode isn’t good. And this kind of consumption accounts

for about 5%~10% of the total consumption. The reaction is as follows:

≤713℃

C + O2 CO2

＞ 713℃ 2C + O2 2CO

The chemical consumption of carbon anode: air reactionThe chemical consumption of carbon anode: air reaction

In the process of electrolysis, the composition of primary anode gas is almost pure

CO2, but the actual anode gas contains only 70% ~ 80% CO2, while the rest is CO,

which is no doubt the product of secondary reaction or even higher level reaction. CO2,

which is a primary reaction product, will precipitate on anode bottom palm, making

carbon anode surrounded by CO2, and the following reaction is bound to occur:

CO2 + C 2CO

This reaction is endothermic reaction, which occurs mainly on carbon anode where the

temperature is over 900 . With electrolytic process going on, carbon anode erosion ℃

which is caused by CO2 is becoming more and more serious, and the reaction occurs not

only on the surface of the carbon anode, but also deep into the internal anode 5 ~ 10cm.

This reaction does great harm to carbon anode, and makes up 2%-10% of the total

anode consumption.

The chemical consumption of carbon anode: CO2 reaction The chemical consumption of carbon anode: CO2 reaction

Oxidation resistance of anode is poor

Oxidation slag off

Increase carbon consumption of electrolysis

Oxidation slag off

Anode pressure drop rise, heating, promoting oxidation

Decrease conductive area

Increase electric current density

Increase the contents of electrolyte carbon slag

Resistance increases and voltage rise

High energy consumption, heat cells , instable of cells condition

Carbon slag accumulated and gathered at the bottom of anode

Isolate aluminaCause sudden effect, high energy consumption and instable of cells condition

Carbon slag accumulated and gathered

Anode has lumps, short circuit of the two poles, voltage swing, partial overheat

Reduce current efficiency and increase power consumption

The impact of anode carbon slag to electrolysis productionThe impact of anode carbon slag to electrolysis production

• Decrease bubble layer of anode bottom, reducing pressure drop of anode

• Enhance electrolyte movement in order to help alumina dissolve

• Decrease turbulent fluctuation of electrolyte causing by bubble and reduce

the surface metal vibration of electrolytic cell in order to reduce the noise

of electrolytic cell

After carbon anode slotting The resistance of the bubble may be reduced from 200-300mv to

10-100mV

Longitudinal slot is the center of material preparation for oblique

electrolytic cell, thus electrolyte can blend batter and alumina can

get better melting.

Carbon anode slottingCarbon anode slotting

Dense degree Dense degree

Mechanical strength Mechanical strength

Pore conditionsPore conditions

ConductivityConductivity

Heat-conducting property

Heat-conducting property

Cover material conditions

Cover material conditions

Electrolytic operation

Electrolytic operation

Chemical purity

Chemical purity

Chemical activity

Chemical activity

Chemical property of carbon anode

Electrolytic cell environment

Influence factors of carbon anode electrical consumptionInfluence factors of carbon anode electrical consumption

Thermal fieldThermal field

Magnetic fieldMagnetic field

Electrolyzing temperature

Electrolyzing temperature

Physical property of carbon anode

Based on experimental studies, production tooling control is improved; production

process parameters are optimized; petroleum coke blending scheme is tested;

production formula is studied; performance of asphalt wetting is promoted; baking curve

is optimized; technologies like reducing carbon anode reactions are improved;

performance of anodic anti-oxidation is enhanced; hardness of residual anode is

improved to reduce the anode electrolytic consumption.

Technical AssessmentTechnical Assessment

Industrial tests show that the carbon anode with low consumptions developed by the company is active in resistance to air and CO2 erosions, contains less carbon residues, performs well in hardness of residual anode and regularity and can withstand high current density with low consumption rate for electrolysis. The extension of one day for such kind of carbon anode can reduce 0.35-0.4 replacement period for anode. One ton of aluminum can lower carbon consumption by 15kg in electrolytic process and CO2 emissions from electrolytic aluminum by about 55Kg/t-Al, which is in accordance with the requirements of low carbon industrial policies and environmental protections, promoting the development of carbon anode technology in aluminum production and electrolytic aluminum industry.

Project resultsProject results

1. Low electrolytic consumption rate can prolong the life cycle by one day

More than 90% residues are left after the interaction between carbon anode of low consumption

with air and CO2 respectivity. Such carbon anode of low consumption performs excellently in

resistance to air and CO2 erosions with high inoxidizability and the consumption rate is better

than that of other common anodes.

Based on the same consumptions, its life cycle can be prolonged by one day. (0.4—0.6 mm/d)

2. The hardness of residual anode is better with high regularity

Low consumption carbon anode is powerful in resistance to air and CO2 erosions with no

oxidation dregs, blocks and anode pieces and etc. It belongs to hard residual anode with well

performance in shocking and washing and high regularity, which can withstand high power

currents and is favorable for the electrolytic operations with high currents.

3. The carbon consumption is low in the electrolytic process with less carbon residues.

Carbon anode of low consumption bears high inoxidizability and low chemical consumption and

the life cycle can be prolonged by one day with carbon consumption reduced by 15kg in

electrolytic process. In addition, it is also lower in selective oxidation with less carbon residues.

Project resultsProject results

1. Lower carbon consumption, lower production cost

Low consumption carbon anode could reduce 15kg carbon consumption for every ton of electrolytic

aluminum, indicating direct economic benefit of 3,000tpy of carbon anode consumption reduction for

a 200,000tpy electrolytic aluminum plant, which would certainly lower the production costs.

2.  Less carbon slag, lower fluoride salt consumption

Low consumption carbon anode features with a high anti-oxidization property, a low selective

oxidization property and generates less carbon slag, which could not only reduce the fluoride salt lose

in the carbon slag filtering process (according to test, carbon slag contains 60-70% of electrolyte) but

also let out less pollutants.

3.   Larger current density, more yields

The hardness of anode scrap endows it with high resistance against erosion and corrosion, as well as

good regularity, so that it could bear larger current density, which will strengthen the current and raise

the output of electrolytic aluminum.

Economic benefits Economic benefits

1. Lower labour intensity

Low consumption carbon anode requires 0.35-0.4 times fewer of anode

replacement frequency, indicating a 3,000-piece reduction of anode replacement

every year for a 200,000tpy electrolytic aluminum plant. Also, as it produces less

carbon slag, the difficulty of carbon slag processing has also been weakened.

2. Less heat lose and less pollution gas discharge

Low consumption carbon anode could effectively avoid the heat lose in anode

replacement and the discharge of fluorides and dust, which could reduce the

energy consumption and the air pollution of the process.

3. Less emission of Co2

Low consumption carbon anode could reduce 15kg carbon consumption and

55kg of Co2 gas emission for every ton of electrolytic aluminum, which will help

reduce the Greenhouse Effect.

C + O2 = CO2

44×15÷12=55 kg/tAl

C + O2 = CO2

44×15÷12=55 kg/tAl

Social benefitsSocial benefits

Research prospectResearch prospect

Taking the development of carbon industry as our own duty, base on the

development requirement of electrolytic aluminum production, Chenyang will conduct

deeper research and experiments, further develop the technology of low consumption

carbon anode for electrolytic aluminum use, produce more “green” products of low

carbon consumption, and make more contribution for the advance of aluminum use

carbon production technology and the development of the aluminum industry.