350kA电解槽系列的发展

THE ADVANCEMENT OF NEW GENERATION SY350 POT

Zhu Jiaming1, Yang Xiaodong1, and Liu Yafeng1, SunKangjian1

1Shenyang Aluminum & Magnesium Engineering & Research Institute (SAMI); 184 Hepingbei St.

Shenyang, Liaoning 110001, China

Keywords: SY350 Pot, SY400 Pot, Numerical Modelling, Pot Design,

Abstract

SAMI’s high amperage SY350 pot technology was developed in 2002. Presently, there are three SY350 potlines in operation in China and nine more in design phase. Over the years, SAMI has made further improvement on the SY350 pot technology and has since increase the pot amperage up to 378kA.

SAMI has also developed the SY400 pot technology and has installed a total of 16 trial pots at one of SAMI’s latest designed potline. The trial pots are currently operating at 402kA and have been in operation successfully for more than 14 months. Good performance obtained from the trial pots with high current efficiency and low energy consumption. Presently, there are two SY400 potlines under design.

This paper will introduce the SY350 pot technology and describe some of the key advancements of the technology to date, including aspects of the SY400 trial pots.

Introduction

Shenyang Aluminium & Magnesium Engineering & Research Institute (SAMI) has developed 160kA, 190/200kA, 230/240kA, 280kA, 300kA PFPB technologies based on the effective numerical simulation model and summarizing the successful and failing engineering and operation experience from 1996 to 2002. All above successful projects are praised as “miracles” in the aluminum industry of China.

In 2002, SAMI developed its 350kA pot technology called SY350 that has saved investment compared to its previous technologies and higher productivity. The first SY350 potline began operation in June 2002 in Henan province [1]. In the past five years, SAMI has been active in optimizing its SY350 technology and has made vast improvement. The Lanzhou SY350 potline was started in 15th May 2007 in Lanzhou branch CHALCO. Sixteen trial pots in this potline have increased to 402kA by the end of 2007. There is a total of 4 pots that utilize the same structure (include the cell, lining and superstructure) as the rest of the pot design of the potline.

The SY350 Technology Development

In 2002, SAMI developed its first generation SY350 pot technology and used the technology in the Henan Shenhuo smelter. The potline was started up in Aug 2005. The new generation SY350 was started in 15th May 2007 in Lanzhou branch CHALCO.

The goal of the new generation SY350 pot is to increase the anode current density and at the same time improve the pot technology performance (current efficiency, DC power consumption, etc). Further development work of the pot technology has led to the new generation SY350 pot technology, which was implemented at the Lanzhou branch CHALCO. The new generation SY350 pot

was preheated in 15th May 2007. Presently, the potline is running

at amperage of 378kA. The potline has high current efficiency and

lower energy consumption. SAMI and Lanzhou has planned to increase the line current to 400kA in the near future.

Figure 1: The first generation SY350 pot in Henan Shenhuo

smelter.

Figure 2: The new generation SY350 pot in Lanzhou branch

CHALCO.

SAMI has spent more than two years in pot modulating, pot operation practice, pot control system to improve the pot performance and increase the potline current. A lot of measurements such as pot shell temperature, shell deformation, magnetic fields, current distribution etc. have been performed

since the first SY350, SY300 pots start up.

Light Metals 2009 Edited by: Geoff Bearne TMS (The Minerals, Metals & Materials Society), 2009

The SY400 Pot Technology

There are 16 SY400 trial pots in the Lanzhou SY350 potline in

which additional current was added to the trial pots. Figure 3

shows a schematic diagram of SY400 trial pots section busbar

arrangement.

Figure 3. External busbar arrangement for the SY400kA trial pots.

The SY400 pot was preheated in June 2007. The current was

increased to 400kA in August 2007. After four months of

operation, the pots show high current efficiency and low energy

consumption. The pots are presently operating at 402kA. In the

future, the pot current will be increased to 420kA.

New Generation SY350/SY400 Pot Design

SAMI has been continuously optimizing the SY350 pot design

during the past 5 years according to the pot numerical modelling

and industrial tests.

Busbar

Pot operation has proven that correct and successful design of the

busbar in the first SY350 potline has been achieved in which the

busbar system was designed in an asymmetrical arrangement for

compensation of magnetic induction of adjacent pots. However,

SAMI has optimized the busbar arrangement to reduce the busbar

voltage and get more reasonable MHD stability in the subsequent

SY350 potlines. The SY350/SY400 pots have also shown high

stability in pot operation.

Figure 4. SY350 MHD modelling

Anode and Anode Assembly

There are 24 anode assemble blocks in each SY350/SY400 pot.

The anode pins used in the new generation pots are bigger than

the previous generation. Higher and slotted anodes are used in the

latest potline as well. The anode current density has increased to

0.815 A/cm2

Lining

Combined silicon nitride bonded silicon carbide bricks are used as

sidewall material for good heat dissipation and easier formation of

side ledge in all SY350/SY400 pots. The new generation SY350

pots utilize 35% graphitic cathode blocks. The SY400 trial pots

use three different cathodes, 35% graphitic, 100% graphitic, full

graphitized cathode blocks. The pot cavity of new generation

SY350/SY400 is much deeper than previous generation for the

purpose of automatic anode effect termination and more heat

emission area.

Pot Shell

The ship shape steel shell with cradle design was used in all

SY350/SY400 potlines, which was validated to supply enough

strength and reduce deformation for the pots. All the cradles and

heat dissipation fins were welded to the shell in the later

SY350/SY400 potline for more efficient heat dissipation to form

sufficient amount of ledge. The pot shell design of later

SY350/SY400 pots is deeper to give a deeper cavity and thicker

cathode blocks. These improvements ensured the reduction of

thermal load on the pot shell, and thus upgrades mechanical

behavior such that it has less maintenance.

Table 1 The technological comparison between the new and old generation SY350 pot technologies.

Item/smelter Old generation SY350

(Henan Shenhuo)1

New generation SY350

(Lanzhou branch CHALCO)

Start up 2004,8 2007,5

Number of SY350 pots 156 288

Operating current (kA) 348~356 378

Current efficiency (%) 94.15 >94%

DC power consumption kWh/t 13474 <13200

Anode effects per pot and per day < 0.3 0.08

Figure 5. Shell thermo-stress modelling.

Superstructure

A center point feeding system with a total of 5 feeders is installed on the SY350/SY400 pots. Feed volume has been reduced to 0.9 liter from 1.8 liter, which has been found to be advantageous for alumina dissolution. Pot hood and fume extraction are improved for greater efficiency.

Process Control

SAMI has developed the automatic control system called fuzzy control for nearly ten years. Adjustments are made and optimized accordingly to the different pot designs. Up till now, the pot control functions such as alumina concentration control, molar ratio control and bath temperature control are improved and optimized, so that the alumina concentration is controlled accurately in 1.5-2.5% range and AE coefficient is below 0.1 AE/pot/day. The fuzzy control has contributed significantly on the pot performance.

Pot Room

The pot room ventilation in the later SY350/SY400 potlines has been improved by new pot room architecture and higher operation floor. Optimizing these features has improved the air flow between pots and heat emission from the side of the pots for better working conditions in the pot room.

Figure 6.Potroom ventilation modeling.

Pot preheat and operation

Pot Preheat and Start-Up

The new generation SY350/SY400 pot technology uses resistor coke-bed to preheat pot. After 72 hours of preheating, the cathode bottom temperature would have increased to 850~950degrees Celsius in which then 12t of bath is poured into the pot cavity. Then 24 hours later, about 16t of liquid aluminium is added into the pot. Normal pot operation will commence about three months after start-up.

Lanzhou SY350 potline is divided into three sections, with each section comprising of 98pots. On the 15th May 2007, the first group (six pots) was started up using coke bed to preheat. The first group used dry-start method and the rest used wet-start method to start-up the pots. The first two sections was successfully started up in two months.

Line Current Increase and Pot Operation

The trial SY400 pots were started up from 350kA. After about three months, the line current was increased to 400kA in 15th September 2007. Four months into operation, the trial pots showed good stability. The shell temperature is less than 320degrees Celsius. The next target is to increase the trial pot to 420kA.

The SY350 pots were started up from 350kA. After about three months, the line current was increased to 378kA. An additional set of transformer and rectifier system was installed in order to provide the whole potline with the capacity of 400kA current.

Contrast to the western technology, the traditional Chinese pot has lower anode current density, reasonable technology performance. The high anode current density is more sensible. SAMI have done research on the SY400 pot operating practice. Some operating method and thoughts have been realized in order to get better pot performance. From eight months of tapping data, the current efficiency is about 94.16% and the average DC power consumption pot is below 13250kWh/t.

New SPC control software has been used to analyse the daily data. The foreman can get the information easily and carry out actions according to the new operation manual. Also, the manager can easily identify the status of the work operation.

Conclusion

SY350 technology has been improved and optimized since 2002 by SAMI. The latest SY350 potline is operating at 378kA. The SY400 trial pots have successfully been in operation for more than 4 months now.

The new SY350/SY400 technology is now validated and available for its performance and economy. SAMI will launch a new campaign to increase more current in the latest SY350/400 potline in the next year.

Reference

[1]Cheng Xiang, Jia Xinwu, Shen Shanming “Baking start-up and operation practice of SY350 pot ”, Page Light metal(china)

2005-3,32~35