Aluminum electrolyzer cathode refractories are gradually destroyed and lose their protective effect on the underlying insulation material due to the infiltration of liquid electrolyte and steam, resulting in deterioration of the aluminum electrolyzer insulation performance, deterioration of production indicators, the bottom of the tank lift, Until destruction. The dry insulating material can form a dense vitreous nepheline layer with the permeated electrolyte, thereby preventing the continuous penetration of the liquid electrolyte and steam, ensuring that the insulating layer is not destroyed, on the other hand, the barrier layer has plasticity and the granular layer. Has a certain degree of compressibility, can effectively alleviate the bottom uplift and deformation of the tank shell. This article puts forward a trial scheme for the analysis of the status of the production of electrolyzers since the beginning of the operation of Shi-Al in 1998.
1 Analysis of current situation We analyzed 25 electrolyzers started from April 1998 to April 2000. 16 furnaces with high pressure drop at the hearth accounted for 64, and 13 units with higher pressure after the start, accounting for a high pressure drop at the bottom of the furnace. The number of slots 81 is due to: a. The quality of the carbon block is poor.
b. The electrolyte penetration is serious, the bottom of the tank is lifted, and the insulation is destroyed (the dry section electrolytic tank can be seen to lift the bottom of the tank by 20mm to 25mm).
c. Poor furnace quality.
The other three stations had lower furnace bottom pressure in the early stage of operation after start-up. As the running time increased, they increased rapidly, accounting for 19%. The main reasons were: (1) The electrolyte penetration at the bottom of the tank was severe and the insulation was destroyed.
(2) Poor operation management.
This article does not discuss the issue of operation management for the time being. It can be considered that the conditions for operation, furnace building, etc. will remain unchanged, and only ways to increase the resistance to infiltration at the bottom of the tank will be discussed.
2 Improve electrolytic cell penetration resistance test 2.1. Test plan In order to improve the bottom insulation and impermeability, formulate a test plan to see the plan to follow the following principles: a. Improve the bottom insulation b. Improve the bottom of the electrolytic tank anti-permeability , Stable production conditions c. Minimize the cost of repair d. Make full use of the existing inventory 2.2 Insulation anti-seepage material for testing Select 2 electrolyzers for testing, 22 for heat-proof and anti-seepage material. The HZG-type heat insulation material produced by the factory is used as an index.
Item Index Loose Bulk Density, t/m Bulk Density, t/m Permeation Resistance Depth 950°C×16h, mm Refractoriness, °C Chemical Composition, SiO Element Design Optimization Scheme Carbon Block Mat 440 Carbon Block 400 Fire Brick 132 Firebrick 65 Oxidation Aluminum 40 ~ 60 insulation anti-seepage material 127 insulation brick 198 asbestos board 10 calcium silicate board 40 asbestos board 10 asbestos board 2-3 anti-seepage mechanism with insulation anti-seepage material directly on the insulation brick, compaction, replace the aluminum oxide layer and Firebrick layer, insulating and anti-seepage material can form a dense vitreous nepheline layer with the permeated electrolyte, thereby preventing the continuous penetration of liquid electrolyte and steam, ensuring the insulation layer is not destroyed, and ensuring the bottom insulation stability is stable and prolonged. Slot life.
2.4 Advantages (1) Simplified furnace construction: Instead of laying alumina and refractory bricks with bulk materials, compaction and compaction can save manpower and build furnace time.
(2) The electrolyte penetration is blocked, the insulation layer is not destroyed, the bottom insulation performance is not changed, the life of the extension tank is long and the economic and technical indicators are stable during the operation (especially when it is running for 3 to 4 years). According to the information, the use of insulation anti-seepage material, the life of the tank can be extended by 1 year.
(3) After stopping the tank, after removing the carbon block part and the reaction layer of refractory material of refractory brick, dry planer shall add a small amount of insulation anti-seepage material, and the anti-seepage material can be kept below and the material cost can be saved.
3 Results Analysis 3.1 Pressure drop of furnace bottom Compared with the roasting of other tanks, the technical conditions and operation management are the same. After 5 months of operation, the pressure drop at the bottom of the furnace is compared with that in 1999 (10 tanks). .
Unit: mV Type Test Tank Average The start tank test tank in 1999 compared with the 1999 start tank can be seen from Table 1, the test tank bottom pressure drop 5 months average compared with the 1999 start tank compared to 20.8mV lower.
The pressure drop at the bottom of the test tank decreased with the extension of the operating time within 5 months of the test tank, and the change after 5 months became stable. The pressure drop at the bottom of the furnace increased with the running time in the 5 months of the 1999 operating tank. It should be said that the furnace The bottom insulation is unstable.
3.2 Insulation effect at the bottom We tested the temperature at the bottom of the two test tanks and one original design structure, with 8 tests per tank, 2 of which were tested at the bottom of the tank, respectively in the center of the tank and the center of the length to the edge. In the middle point, the tank lining is tested at 6 points, the groove center is tested at 3 points, and the centers are respectively, the center to the big surface is two-thirds, the center to the big surface is one third, the edges are 3 points and the center measures 3 points. correspond. The measurement interval is: a. During roasting start, every 3 hours (about 10 days) b. 10 days after 6 hours (about 10 days) c. 20 days after 12 hours (about 10 days) d After 1 month, test once a day for 2 months. Once a week, then once every week, f. After 1 month, once a month. To reduce the test cost and save money, we have repaired some old thermocouples except the bottom of the 76 tanks. The rest can meet the test requirements.
After 57 days of on-site testing, the results showed that the temperature of the test trough was 6.9°C lower than that of the bottom of the trough, indicating that the bottom of the test trough was better than the contrast trough, and the heat dissipation at the bottom of the trough was less.
3.3. Slot life At present, the test slot is in good condition and the slot life needs to be further observed.
4 Calculation of Economic Benefits 4-1 Comparison of Repairing Tank Costs The comparison of test tank and comparison tank repair costs is shown in Table 3 (in the table, the material prices are not including the tax price).
Material test trough Comparison trough amount, kg amount, Yuan dosage, kg amount, comparison amount of meta-test trough contrast trough, bottom refractories brick silica-calcium brick brick alumina heat insulation impervious material Other Total Description: a. Test trough and comparison The slots are calculated by one slot. b. The data in the table is the company's accounting for the slot.
4.2 Power Saving Calculation Substituting into (1) formula: The annual production capacity of the trough is 155t and the electricity price is 0.35 yuan/kWh, then the annual energy saving value is: 4.3 Overall efficiency (annual benefit) 5 Conclusions (1) The test optimization scheme achieves The purpose of enhancing the bottom insulation is to reduce the bottom temperature by 6.9°C and reduce the bottom pressure drop by 20.8mV. The scheme is feasible.
(2) By using this optimization scheme, the cost for repairing the groove can be reduced by 3009.43 yuan per unit, which is economically effective.
(3) The effect on the life of the tank needs further observation.
(4) The stability of the operation indicators of the electrolytic cell and the anti-seepage effect should be further observed.
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