Thread Content
Research, Development, and Production Practice of 400kA Pre-baked Anode Aluminum Electrolysis Cells Yang Xiaodong, Liu Yafeng, Zhu Jiaming, Sun Kangjian (Shenyang Aluminum and Magnesium Design and Research Institute, Shenyang 110001, Liaoning) Abstract； The Shenyang Aluminum and Magnesium Design and Research Institute (SAMI) has applied a number of technological innovations to develop the SY400 electrolyzer comprehensive technology, and installed 16 400kA test cells in the SY350 series at Chinalco’s Lanzhou branch. The SY400 test tank was put into operation in May 2007, and its technical specifications have continued to improve; the current intensity reaches as high as 403 kA, with a current efficiency of 94.16%. The tests on the SY400 electrolyzer were **successful**, and its overall technology has reached the world’s advanced level. Keywords: 400kA ； Aluminum electrolyzer ； Technology Development. Chinese Library Classification Number: TF821; Document Code: B; Article Number: 1002—1752(2008)07—23～4. The development and application of 400kA prebaked anode pot technology. YANG Xiao-dong, LIU Ya-feng, ZHU Jia-ming, SUN Kang-jian (Shenyang Aluminum and Magnesium Engineering and Research Institute, Shenyang 110001, China). Abstract: SAMI has developed the SY400 pot technology, which incorporates many innovative elements, and has installed 16 pilot units at the Chalco Kouou Branch. The performance of these SY400 pots has been continuously improving since their operation began in May 2007; the current current rating has reached 403kA, with an efficiency of 94.16%. The SY400 pot technology is successful, and its performance is at the world-class level. Keywords: 400kA ； aluminium dectrolys~s pot ； In 2007, China produced 12,607 kt of primary aluminum, maintaining its position as the world’s largest producer of such metal. In 2007, the world’s production of primary aluminum was approximately 32,000 kt, with electrolyzers of large capacity (160 kA to 350 kA) being the dominant type. Internationally, Pishine continues to upgrade the AP30 electrolyzer by employing a range of optimization techniques to increase the anode current density and improve thermal balance, thereby raising the current capacity of the AP30 electrolyzer. It competes in the international market under the AP35 name. Additionally, Pishine is currently the only company in the world that possesses technology for 500kA-class electrolyzers. It is through active optimization, as well as promotion of the large-cell technologies AP3X and AP50 with high anode current densities, that Pischne has maintained its technical leadership in the global aluminum industry. To meet the demands of the domestic market and international competition, Shenyang Aluminum-Magnesium Design and Research Institute set out to develop a new type of comprehensive aluminum electrolysis technology that is efficient, energy-saving, environmentally friendly, capable of improving labor productivity, and reducing the investment per ton of aluminum produced. Based on the SY350 electrolyzer, further improvements and optimizations were carried out; while maintaining the original design parameters of the electrolyzer’s structure, the SY400 electrolyzer with a higher anode current density was developed. Sixteen such experimental electrolyzers were installed in the 350kA electrolysis series at the Lanzhou branch. After more than half a year of testing, the current in the test tank remained stable at 403 kA, with an average current efficiency of 94.16%. 1 Installation configuration of the SY400 test cells. The SY350 electrolysis series at China Aluminium Corporation’s Lanzhou branch consists of two electrolysis workshops, with a total of 288 electrolytic cells installed. Among these, 16 400kA test cells are located at the output end of the electrolysis series, on the side close to the rectifier station. To meet the power supply requirements of the 400kA electrolyzer, it is attached to the side of the test cell. To meet the power supply requirements of the 400kA electrolyzer, two smaller generators were added to the test cell; their maximum power supply current is 50kA, and they operate in parallel with the 350kA current source to supply power to the 16 test cells. See Figure 1. To explore the impact of different cathode carbon block materials on extra-large electrolyzers, SAMI conducted industrial tests using 4 types of cathode carbon blocks. Four test cells are grouped together, and industrial tests are conducted using four different types of polar carbon block materials. Slots 6001#–6004# use domestically produced graphitized cathode carbon block materials, while slots 6005#–6008# employ imported graphitized cathode carbon blocks. Slots 6009#–6012# use domestically produced all-graphite cathode carbon blocks, and slots 6013#–6016# utilize 30% semi-graphitic cathode carbon blocks, the same type as those used in 350kA series electrolyzers. The SY400 pre-baked anode electrolyzer is shown in Figure 2. 2 Technical features of the SY400 pre-baked anode electrolyzer 2.1 The current intensity reaches 403 kA, with an anode current density of 0.82 A/cm2. Previously, the maximum current intensity of electrolyzers in China was 350 kA, with an anode current density of 0.713 A/cm2. By optimizing the design of the SY350 electrolyzer, SAMI was able to increase the current intensity to 403 kA without altering the basic structural parameters of the electrolyzer; the anode current density reached 0.82 A/cm2. Ten months of operation have shown that all technical specifications meet world-class standards. 2.2 The busbar configuration is reasonable. The magnetohydrodynamic stability of the electrolyzer has reached a new level. As the current intensity increases, the complexity of busbar configuration rises. The SY400 electrolyzer utilizes optimized electromagnetic and flow field models for simulation, taking full account of the shielding effects from adjacent electrolyzers, surrounding electrolyzers, and the electrolyzer casing. By adopting an asymmetric busbar configuration, it effectively addresses the challenge of magnetohydrodynamic stability in large-scale electrolyzers. At the same time, the design of the busbar is also cost-effective; the current distribution across the cathode steel rods is even, and the busbar does not experience overload under normal operating conditions or in the event of a short circuit. The bus configuration is simple, making it easy to install. Tests conducted by the Zhengzhou Light Metal Research Institute of Chinalco showed that the current distribution at the cathode and anode of the 400kA electrolyzer was uniform, with good magnetic field performance. 2.3 Good thermal balance design: In its designs, the Shenyang Aluminum and Magnesium Design Institute adopted a concept that combines ventilation in the electrolysis hall with the overall thermal balance of the electrolyzers. By using advanced computer simulation techniques to model the ventilation in the electrolysis hall, and combining this with simulations of the thermal balance of the electrolyzers, it was possible to optimize the thermal balance of the SY400 electrolyzers. This approach addressed the challenge of controlling the thermal balance in large electrolyzers with high current densities, improved the working conditions in the electrolysis workshop, and created favorable conditions for the stable and efficient operation of the electrolyzers. The main optimization measures are as follows: *Increase the operating height in the electrolysis workshop, add partition walls inside the factory building, and optimize the layout of ventilation windows in the electrolysis workshop ； *The electrolyzer shell and the cradle frame are connected by welding ； *Weld heat sinks to the side walls of the tank shell ； *The tank shell features a bandless design ； * Install a cradle frame on the small side of the electrolyzer and provide cooling holes in the surrounding panel ； *Optimized-sized ventilation grills are used between the tank shell and the workshop floor, and in combination with the layout of the electrolysis workshop, this creates effective natural ventilation currents on the sides of the electrolytic cells. 2.4 The SY400 electrolyzer’s exhaust duct is designed with a 5-segment upper gas collection system. Dividing the entire electrolyzer into 5 sections for segmented gas collection **improves the uniformity of the negative pressure within the electrolyzer, which helps to enhance its gas collection efficiency as well as its environmental purification capabilities. 2.5 Cathode carbon blocks with a width of 660 mm are used. Large-scale electrolyzers in domestic aluminum plants typically use anode carbon blocks with a width of 660 mm, which does not correspond to the projection dimensions of cathode carbon blocks with a width of 515 mm. The SY400 electrolyzer uses cathode carbon blocks with a width of 660 mm, whose orthogonal projection overlaps substantially with that of the anode carbon blocks. This reduces the generation of horizontal currents during electrolysis, contributes to a more uniform distribution of current at the cathode, and enhances the magnetohydrodynamic stability of the electrolyzer. 2.6 Different types of cathode carbon block materials: Industrial tests were conducted on SY400 electrolyzers using three types of cathode carbon blocks (semi-graphitic, graphitic, and graphitized), with a current intensity of 403 kA in all cases; the anode current density was 0.82 A/cm2, and the operation was successful. Tests were conducted using three types of cathodes (semi-graphitic, graphitic, and graphitized) primarily to verify the performance of the electrolyzers corresponding to different cathode carbon blocks. Tests showed that the temperature of the shells of all 400kA electrolyzers was between 280 degrees and 300 degrees, with the thickness of the furnace walls being 10 cm to 12 cm. Practice has shown that 400kA electrolyzers using graphitized cathode carbon blocks have, compared to those using semi-graphitic cathode carbon blocks: a lower bottom-of-furnace voltage drop of 20–30 mV, which reflects their energy-saving effect. — —The heat dissipation at the bottom is about 2% higher, reflecting the use of its high thermal conductivity in the design. — —With a pole pitch of 2 mm or 3 mm, it indicates that it still has the potential to further increase the current intensity; it should be possible to raise the current by another 10 kA to 20 kA, bringing the current intensity to the range of 410 kA to 420 kA, thus fully leveraging the advantages of using its graphitized cathode carbon blocks as designed. 2.7 A comprehensive control system for electrolyzers was established. Taking into account the internationally recognized health, environmental protection, and safety standards for electrolyzer operation (EHs), the Shenyang Aluminum and Magnesium Design and Research Institute developed a comprehensive control and standardized operation system for electrolyzers. This system enabled effective control of the thermal and material balances in the electrolyzers, resulting in the creation of a set of technical guidelines for the operation of 400kA electrolyzers, which ensured that these electrolyzers achieved excellent technical performance.