In recent years, in order to further improve the economic benefits of enterprises, the international aluminum electrolysis industry has generally increased aluminum output by strengthening the series current density of electrolysis. Increasing production efficiency by increasing current efficiency has little effect, while long-term construction periods for new and expanded investments are long. In contrast, using enhanced current methods to increase output can achieve low investment and quick results. It can make full use of existing site, public and auxiliary facilities to increase aluminum production and current efficiency in electrolytic cells and reduce production costs. In particular, the current price of alumina is relatively low, and the profits of electrolytic aluminum companies have been relatively high. Under the stimulation of these factors, electrolytic aluminum enterprises have all raised their output below the full capacity of the equipment.
In 2005, the output of electrolytic aluminum in China reached 7.8 million tons, reaching 9.35 million tons in 2006. There are 43 aluminum plants with a current intensity of 157 kA, and the production volume accounts for about 82% of the national output. The anode current density of these electrolytic cell designs is relatively low, generally less than 0.73 A/cm2, and all have the feasibility of strengthening the current. However, the anodic current density of the pre-baked cells modified by the original 60kA self-baked cell is relatively high, generally 0.80A/cm2~0.88A/cm2, and the feasibility of the enhanced current is small. After deducting the production capacity of the pre-baking cell converted from the baking tank, the new pre-baking cell with a capacity of 160 kA accounts for more than 60% of the total output. If this pre-bake cell current is enhanced by 10%, the output can be increased by 550,000 annually after current fortification. Tons, the investment cost for newly-built electrolytic aluminum in China is 11,000 yuan/ton to 13,000 yuan/ton, while the investment required for the electrolytic aluminum to increase the current output is only 0 to 30% of the investment in the new project, which can save about 80% of the investment. , Strengthen current and increase output of 550,000 tons of electrolytic aluminum can save 5 billion yuan in investment. In addition, the increase in the output of the electrolytic aluminum plant enables the fixed cost per ton of aluminum to be reduced by about 10%, ie, a cost savings of about 55 yuan per ton, and a savings of 3,321.10 million yuan in the whole country. It can be seen that the aluminum electro-refining current is of great significance. Therefore, it is said that the intensified current is an effective measure to save production of electrolytic aluminum.
The feasibility of strengthening the current
1. Domestic successful case of strengthening current. The domestic aluminum electrolyzer strengthens the current in 2002, but the magnitude of the intensified current is relatively small, generally 1% to 5%. In recent years, the magnitude of the intensified current has increased. Chinalco Guangxi Branch and Qinghai Branch successfully used the extended eccentric anode to successfully intensify the current in the 160kA pre-baked cell to 180kA and increase the series current by 12.5%. The Guangxi Branch's 2006 test cell further intensified the current to 190kA; Lanzhou Aluminum In 2006, without increasing the size of the anode, the current of the 200kA series of prebaked cells was enhanced to 220kA, the test cell was strengthened to 230kA, and the intensity of the intensified current reached 10% to 15%; Zhengzhou Research Institute in the original 280kA prebaked anode electrolysis. The tank is based on a strengthening current up to 300kA. The above successful cases of intensified current have achieved good economic and social benefits. Both have passed the appraisal of domestic authoritative professional technologies, and industrial production practices show that they can be applied.
2. Strengthen current and anode current density and current efficiency. At the 6th Electrolytic Aluminum Technology Conference held in Australia in November 1999, a new series of 200kA pre-baked cells in the Dubal aluminum plant in New Zealand, the anode current density is as high as 0.88A/cm2, and the current efficiency reaches 95.5 for 1 year. %, the result proves that the electrolyzer operates stably.
Aldrich Aluminum Plant, Norway, 1 series 150kA enhanced to 159kA, current efficiency increased from 88.9% to 93.2%, 11 series 160kA enhanced to 169kA, current efficiency increased from 90.5% to 93.4%; French Pischne company 180kA enhanced to 210kA The current efficiency increased from 94.8% to 94.9% to 95.3%. The anode current density design value of domestic 160 ~ kA200kA pre-baked cell is about 0.72A/cm2, the current efficiency is about 92% ~ 93%, after the strengthening current, the anode current density is 0.75A/cm2 ~ 0.83A/cm2, the current efficiency is improved. About 0.2 percentage points, the overall view of domestic currents after the strengthening of current efficiency change is not.
3. Strengthen the feasibility of current. The anode current density of the original 60kA self-baked cell was earlier as high as 1.0A/cm2. After many times of anode widening, the anode current density is still above 0.82A/cm2. The foreign prebaked cell anode current density is generally 0.8A/cm2 ~ 0.9A/cm2, with the anode production technology is mature, the anode quality continues to increase, on the anode carbon material physical and chemical properties, allowing the current density to increase To a certain level, the anode current density can be increased to 0.9 A/cm2 to achieve normal aluminum electrolytic production.
From the above several examples, we can see that the experience of strengthening the current is successful, and the current efficiency has been improved to different degrees after strengthening the current, indicating that the current density increases with the anode and the corresponding technical measures are taken after the strengthening of the current. The current efficiency will be improved. The higher the research density, the higher the current efficiency. However, the current efficiency tends to be constant when the anode current density reaches a certain value (1.57 A/cm2). As far as China's large-scale pre-baking cells are concerned, current-enhancement of 10% to 20% is possible where the anode current density is less than 0.73 A/cm2.
Intensified current solutions and major technical measures
1. Enhanced current solution. The aluminum electrolyzer enhances the electric current, involves many technical problems such as aluminum electrolyzer lining material, electric heat balance, magnetic field influence and so on. The main technologies include anode and cathode technologies. After the simulation calculation of electricity, current and magnetic field, the investment costs required after the increase of the load are estimated, and a better plan is analyzed and selected.
The intensified current is carried out under the same size of the electrolytic cell tank shell and the main structure. At present, there are mainly two schemes for strengthening the current: the front, increasing the area of ​​the anode, so that the anode current density increases less after the current is strengthened; second, the anode size does not change, so that the anode current density is higher after the strengthening of the current. No matter which scheme is used, it is better to carry out computer simulation analysis and comparison of the magnetic field, thermal field and material balance after strengthening the current through specialized departments. In particular, after the series current is increased by 10% to 30%, the influence of heat balance may become a key issue, and the technical solution is determined on the basis of simulation analysis.
Aluminum electrolytic strengthening current production is prudently implemented. First, a small number (5 to 10 units) of production tanks should be selected for industrial testing, control cables in the test tanks and solution of the electrolytic tank heat balance, and process technology plans, etc., only on the basis of successful tests. Above the full range of current enhancement can be promoted.
2. The main technical measures.
(1) Power supply. The test tank needs a small external circuit, and the current is strengthened by adding a supply of a movable DC power supply. When the entire series is enhanced, the original rectifier system has a capacity to meet the increased load of the enhanced current. Otherwise, it needs to increase according to the required load. Power supply facilities. With the increase of current, the load on the power supply system and its auxiliary facilities is increased, and the reliability of the power supply facilities is more demanding. A certain amount of spare parts needs to be reserved for overhaul.
(2) Flue gas purification system.
(3) Heat balance.
(4) Material balance.