Application of Polymer Ratio Cryolite in 190kA Overhaul Starter

Practice has shown that the use of macromolecules than cryolite for roasting starts on the new starter tank, which can reduce the consumption of raw materials, is conducive to the stability of electrolysis technology parameters, and is conducive to the establishment of a stable and stable hearth, which is also favorable for extending the age of the tank.

Aluminum electrolysis; Polymer ratio cryolite; Ordinary cryolite; Technical parameters; groove age In recent years, with the continuous development of aluminum electrolysis technology, the current efficiency of Shanxi Guanlu Co., Ltd. has reached the international advanced level, the cost of tons of aluminum It is also leading the industry in the country, but the aluminum electrolytic cell life, which is the main equipment for aluminum electrolysis production, has always been the subject of Guan Aluminium research.

In order to further explore ways to extend the life of the electrolyzer, Shanxi Guan's Co., Ltd. has also reduced the production cost and reduced the labor intensity of the workers. For the first time, the giant electrolysis cell that was started for overhaul has selected the macromolecular cryolite of Jiaozuo Polyfluoride Chemical Co., Ltd. Conduct application tests. For a long time, Shanxi Guan Al has been using ordinary cryolite (molecule ratio 2.12.3) to roast and start the electrolytic cell. Because the molecular ratio is low, in order to make the roasting tank reach a sufficient temperature to establish a solid furnace formed by macromolecules than crystals, a large amount of solid 'base is required to be manually added during roasting and after the roasting to meet the production requirements. The polymer ratio cryolite, due to the high molecular ratio (2.8 or more), overcomes the deficiency of ordinary cryolite and can meet the requirements of the roasting start-up and later-stage management, and does not require the addition of solid base after the roasting start. Therefore, it is inevitable for the aluminum industry to develop the use of cesium molecules in the new starter tank compared to cryolite roasting.

1 requirements for cryogenic bath firing cryolite cryolite is the main component of the electrolyte, is dissolved A1203 flux, firing start slot to meet the absorption of sodium and the formation of polymer than the solid crystal of the furnace, so the requirements of cryolite Yes: cryolite has a low moisture content, which is conducive to the stability of the electrolysis process technology parameters; the molecular ratio is controlled at 2.8 or more to meet the requirements of the starter tank; macromolecules generally meet the above requirements, and common cryolites are far apart.

2 The roasting start The following mainly compares the 515 electrolysis cell (high molecular ratio cryolite) and the 512 electrolysis cell (common cryolite) after major repair, from the aspects of firing, start-up, and control of technical parameters.

2.1 Roasting According to the conventional furnace method, the raw materials used for charging the furnace are shown in Table 1. Table 1 190kA tank furnace material chute number Anode block cryolite coke solid call 16T (polymer ratio) no 2.2 start 2.2.1190kA electrolysis cell start condition : Neutral electrolyte height of 40cm, and the middle of the joint through the furnace temperature 900950'C electrolyte does not contain carbon; 4 The anode is not long and the work is normal (current distribution is even). From the roasting condition, the 512 roasting can basically meet the above requirements for three days (72 hours), while the 515 roasting for four days (96 hours) can reach the start-up requirement, which shows the mole ratio The cryolite melting point is low, the melting rate is slow, and the roasting time is long, which increases the power consumption.

Dry method is used to start without effect. From the beginning of lifting the anode, after the first 24h-48h, the aluminum is immersed in 8-10T and the voltage is kept at 5.5-6.0V. After AE and artificial AE voltage is 2030V, the electrolyzer is changed from "preheating" to 3 after starting for 15-20 minutes. Main technical parameters 3.1 Electrolyte levels After the electrolyzer is started, because the long furnace requires a lot of electrolyte, it is maintained. Higher electrolyte levels help provide the amount of electrolyte needed to form the furnace. See Table 2 (electrolyte levels for 10 consecutive days after start-up). Table 2 Electrolyte level tank numbers 10 days after start-up As can be seen from the table, to maintain a higher electrolyte level after start-up, both tanks are supplemented with cryolite. 5T, but from the measured data that: After the start of the polymer than cryolite, the electrolyte contraction is relatively slow, the loss is small, because of its low moisture content, can reduce the hydrolysis reaction of Na3AlF6, is conducive to the stability of the electrolyte composition Keep to meet production requirements. The normal cryolite shrinks relatively quickly and the electrolyte level is relatively unstable.

3.2 It is particularly important for the electrolyte molecules to maintain a higher molecular ratio (above 2.8) than after the electrolyzers were started. On the one hand, they can meet the needs of sodium sorption on the cathode of the electrolytic cell. On the other hand, the furnaces formed under the conditions of high polymer ratios are relatively stable and not easily melted.

Table 3 The number of consecutive molecular ratios after the start of the electrolysis cell The cell number can be seen from the table. The ratio of the electrolyte molecules obtained after the melting of the macromolecular cryolite is relatively slow, which can meet the requirement of the new start cell to the molecular ratio. Ordinary cryolite in order to maintain a high molecular ratio, to meet the production requirements, after the start of the need to manually add alkali to meet the production requirements. (Note: After start-up, add 1,500 tons of alkali in 515 tanks; add 2.00 tons of alkali in 512 tanks; the molecular ratio takes a sample every 4 days) 3.3 Electrolyte temperature The electrolysis cell maintains a relatively high electrolyte temperature after startup, in order to form high-temperature crystals. Furnace, after being transferred to normal production, is not easily melted at low electrolyte temperatures.

Table 4 Electrolyte cell start-up for 10 consecutive days Electrolyte iQuenti As can be seen from the above table, the use of a macromolecule can be reasonably maintained after the start of calcination, and the temperature of the electrolyte can be reasonably maintained. The temperature change can meet the production requirements.

4 other trial results 4.1 Cathode current distribution Cathode current distribution is uniform or not, can directly reflect the furnace bottom condition is good or bad, Table 5 is the cathode current distribution measured after 515 and 512-slot roasting start.

It can be seen from the table that the 515 cathode current distribution is relatively uniform with respect to 512, indicating that the bottom of the 515 trough tank is clean and free of sediment.

4.2 Cathodic sodium absorption after the start of the electrolyzer, 515 four feeding mouth consistent flame, no yellow flame, indicating that the cathode absorbs sodium evenly, the temperature inside the tank is even, and 512 due to artificially added solid alkali, due to the increase in the local overheating caused by shouting, individual under Yellow flame appears at the material port, so the use of polymer than cryolite to start the roasting process can solve the key problem that affects the service life of the tank due to the uneven absorption of sodium at the cathode.

Table 5 Cathodic current distribution test comparison 5 The application of macromolecular cryolite for the study of the life of the bath The main reason for the early damage of the electrolysis bath is due to the uneven absorption of sodium at the cathode, which causes the sodium to infiltrate into the cathode carbon block to lift the hearth and the cathode carbon block. Peel off and so on. Ordinary cryolite due to artificially added alkali after the start caused by local concentration of alkali, resulting in non-uniform cathode absorption, and polymer than cryolite due to its high molecular ratio to solve the phenomenon of uneven absorption of sodium cathode, to lay a solid shelf life to lay a solid Foundation.

Compared to cryolite in the early stage of electrolyzer startup, because of its high melting point, electrolytes with higher melting temperatures are formed in the gaps of the linings, blocking the etch channels of aluminum in the lining of the tanks, effectively compensating for the lining of the cathodes. The defects prevent early damage of the lining of the cell and create favorable conditions for extending the service life of the cell lining.

6 Economic Benefits Through the use of two types of cryolite, it is known that the use of cryogenic polymers from cryogenic polycrystalline Coking Co., Ltd. in Jiaozuo not only satisfies the electrolytic production requirements, but also has significant benefits.

Compared with cryolite, the polymer has better physical properties than the cryolite, and the price is also slightly lower than or equal to that of ordinary cryolite, which can reduce the production cost; the use of macromolecules than the cryolite roasting can reduce the amount of solid alkali, each slot Alkali 2 - 3T can be saved, calculated according to 丨 100 yuan/ton, each slot can directly create economic benefits of 2200-3300 yuan; use of polymer than cryogenic calcining to start the electrolytic cell, the stability of the various technical parameters conducive to control, will It is beneficial to the prolongation of the life of the electrolyzer and can create more considerable economic benefits.

7 advantages and disadvantages of polymer than cryolite 7.1 advantages 1 can meet the electrolytic production process requirements, the technical parameters are stable and easy to control, etc.; can make the cathode absorb sodium evenly, the temperature distribution is uniform, which will help to prolong the service life of the tank, and at the same time the next phase of electrolysis The normal operation of the tank creates favorable conditions; the electrolyzer is in normal flame, the cathode current is evenly distributed, and the bottom of the furnace is clean; the amount of alkali can be reduced, and at the same time, it avoids the possibility of local overheating caused by large amounts of alkali during start-up; and reduces the labor intensity of operating workers. Satisfy the environmental protection requirements; 5%, reduce the consumption of materials and reduce costs.

7.2 Disadvantages The use of macromolecules than cryolite for roasting, due to its high melting point, melting rate, so a long calcination time, power consumption is slightly higher than ordinary cryolite; after the use of polymer than the start, the separation of the carbon slag in the electrolyzer is not good ; 3 The polymer has weaker ability to dissolve A1203 than cryolite, and the following material interval should be reasonably maintained.

8 It is recommended that the aluminum electrolytic cell be started using a high molecular ratio of cryolite for calcination, which not only can reduce the production cost, but also it is beneficial to the control of the electrolysis production process parameters, which creates the conditions for the future stability of production and improvement of economic indicators. , And to solve the uneven absorption of sodium cathode, leading to early damage to the furnace, to further extend the life of the tank to lay a solid foundation.