Calculation and selection of electrical parameters of calcium carbide furnace

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The load, voltage and current of the calcium carbide furnace are important parameters for the operation of the electric furnace, which have a great impact on the efficiency of the calcium carbide furnace. In the calcium carbide production process, higher secondary voltages are generally preferred. Because the calcium carbide furnace operates at a higher secondary voltage and a smaller secondary current, it can obtain a higher power factor and higher electrical efficiency. In fact, because the quality of the raw materials in our factory is not that good, the quality of the equipment cannot meet the requirements, and the operator's technical proficiency is not good enough. When operating under this condition, although the power factor and electrical efficiency are improved, the thermal efficiency is not. * * decline, the overall efficiency will not only not improve, but will decline. According to the above situation, the specific performance of calcium carbide operation: (1) The electrode cannot be properly inserted into the furnace charge. Open arc operation results in large heat loss and a significant increase in unit power consumption. (2) The charge ratio is high and the electrode needs to be raised, so we have to produce calcium carbide with lower gas generation capacity. (3) The voltage of the rated capacity level cannot be used, so the operating load of the calcium carbide furnace is not high and the output is not high. (4) Due to the high position of the electrode and long-term open arc operation, the gas generation volume of calcium carbide is low, which causes the furnace bottom to rise and shortens the service life of the furnace. (5) In open arc operation, the temperature of the furnace surface is high, and the components on the electric circuit and the short net are susceptible to thermal corrosion and the degree of damage is aggravated. The result is low utilization of electric furnace equipment. Therefore, the electrical parameters must be improved, and the raw materials must be processed to increase the resistance of the charge. In this way, the electrode can be inserted into the material layer to an appropriate depth, the operation is relatively stable, and closed arc operation can basically be achieved. Therefore, various production technical and economic indicators have reached a good level. 1. Electrical parameters of calcium carbide furnace: The electrical parameters of the calcium carbide furnace include transformer capacity, secondary voltage, secondary current and current-to-voltage ratio, as well as the adjustable range of these parameters. Only when the capacity of the transformer and the geometric size of the calcium carbide furnace are reasonably matched can the transformer and calcium carbide furnace be used most effectively. The capacity of the transformer should also have a certain adjustment range, so that it can meet the needs of production without making the structure of the transformer too complex and bulky. ； When the secondary voltage is appropriate and has a certain adjustment range, and the current-to-voltage ratio is also appropriate, it can ensure stable electrode arc combustion and lay the foundation for high-temperature production in the furnace. When it can provide a current-to-voltage ratio that is suitable for raw material quality and operating level, it can ensure closed-arc operation and improve thermal efficiency, thereby achieving the goals of high quality, high output, and low consumption. 2. Calculation of the capacity of calcium carbide furnace transformer: The size of the calcium carbide furnace transformer capacity is determined based on the required annual output, calcium carbide power consumption, the power factor of the calcium carbide furnace operation, the current level of transformer utilization and the number of production days per year. The calculation formula is as follows: Ps=A·Q/8760·a1·a2·a3·a4·Cosψ where: Ps—Rated capacity of transformer (kilovolt amperes) A—Annual production capacity of calcium carbide furnace (tons/year) Q—Electric energy required per unit standard product (kWh/ton) a1—Regular maintenance time coefficient (0.985) a2—Intermediate maintenance time coefficient (0.98) a3—Overhaul time coefficient (0.94) a4—Equipment capacity utilization coefficient (0.95) Cosψ—power factor, changes due to transformer capacity. In order to meet the needs of calcium carbide production, the transformer capacity should have a certain adjustment range. As the transformer capacity increases, the required adjustment range also increases. Generally speaking, the apparent power adjustable range of transformers below 5,000 kVA is 90-100%, and the adjustable range of transformers between 6,000-15,000 kVA is (80-85)-100% ； 16500-40000 is (65-75)-100%. 3. Calculation of secondary voltage of calcium carbide furnace transformer: The secondary voltage level, adjustment range, and adjustment method of the calcium carbide furnace transformer are determined based on the transformer capacity, size of the calcium carbide furnace, raw material quality, and operating level. First of all, it depends on the transformer capacity. Based on relevant data and my country's long-term experience in operating calcium carbide furnaces, an empirical formula for calculating the secondary voltage of calcium carbide furnace transformers is obtained.: U2=Ku·Ps1/3 where: U2—Secondary voltage of the transformer (volts) Ps—Rated capacity of the transformer (kilovolt amperes) Ku—Voltage coefficient of the transformer Relationship between the voltage coefficient Ku of the transformer and the capacity of the transformer: Transformer capacity (kvA) Voltage coefficient (Ku) 1000-50005.5-6.05000-165006.0-6.416500-400006.4-6.7 The secondary voltage calculated according to the above formula is the commonly used rated voltage during full load operation, but in actual production, the external voltage in many areas is lower than the rated value. In order to adapt to this situation, when designing the transformer, several more levels should be set above the commonly used rated voltage level to leave an appropriate margin. When the external voltage is lower than the rated value, the transformer can still be used to operate at full load at the commonly used level power. When the raw material quality and equipment conditions are good, and the operating level is high, the highest rated voltage and maximum rated current can be used to make the calcium carbide furnace operate overload under the conditions allowed by the transformer. Production practice has proved that when the calcium carbide furnace is operated at full load or overload, the electric furnace operates better and the production results are better. 4. Calculation of secondary current of calcium carbide furnace transformer: According to the maximum apparent power and common voltage rating of the transformer calculated by the above two formulas, the rated value of the secondary line current can be calculated. That is, I2=Psх1000/(J3хU2) It should be pointed out that there are two principles when designing calcium carbide furnace transformer: One principle is equal capacity, that is, when the secondary voltage is low, the secondary current is larger, and when the secondary voltage is high, the secondary current is smaller, but the apparent power of each stage remains unchanged. ； Another principle is equal current, that is, when the secondary voltage changes, the secondary current remains unchanged, and the apparent power of each stage increases as the secondary voltage increases. Small electric furnace transformers are often designed using one principle or mixed use. Large-scale electric furnace transformers often use the two principles to mix and use multiple times to try to obtain the arithmetic progression of transformer capacity changes. 5. Calculation of current-voltage ratio of calcium carbide furnace: The scientific definition of the current-to-voltage ratio of a calcium carbide furnace should be the ratio of the current on the electrode to the voltage from the electrode tip to the center of the furnace bottom. This is because this can basically reflect the size of the calcium carbide reaction zone and whether the electrode can penetrate deep into the furnace charge for closed arc production. When the short network voltage drop is unknown, because the electrode and the furnace bottom are connected in a Y shape, the transformer secondary line voltage can be divided by the voltage from the electrode to the center of the furnace bottom, and the transformer secondary line current can be used instead of the electrode current to estimate, which can still ensure relative accuracy. In fact, workers who have been operating calcium carbide furnaces for a long time * It is also relatively accurate to estimate the ratio of the secondary line current to the secondary line voltage of the transformer, which is more convenient for production personnel. A large number of calcium carbide production practices at home and abroad have proven that in order to achieve good results with high quality, high output and low consumption, the current-to-voltage ratio must increase with the increase in transformer capacity. The relationship between electric furnace transformer capacity and current-to-voltage ratio (I2/U2) optimal value =KGPS0.25 where: KG—Flow-pressure ratio coefficient (31-33.6) For a calcium carbide furnace with the same capacity, the current-to-voltage ratio is large, which will make the electrode easy to penetrate into the furnace material and cause closed-arc production, and the thermal efficiency is high. However, if the current-to-voltage ratio is too large, the electrode will be inserted too deep into the furnace charge, reducing the height and volume of the molten pool and reducing the output. At the same time, it is easy to burn the furnace bottom. Practice has proved that thermal efficiency has a greater impact on the overall efficiency than electrical efficiency. Therefore, the correct operation method should be to increase the specific resistance of the charge. Under the conditions of ensuring that the electrode can be properly inserted into the charge and closed-arc production, a slightly higher secondary voltage should be appropriately selected so that the current-voltage ratio is not too large. Under the condition of higher thermal efficiency, higher electrical efficiency can be obtained at the same time, so that the total efficiency of the calcium carbide furnace can be maximized. 6. Electrical parameter control and analysis: Take the transformer capacity 6400kvA as an example: The statistical results of production records in May 2003 are as follows:: Date Apparent Power Secondary Voltage Secondary Current Current Voltage Ratio Gas Production Production (T) Remarks 5.1 6062 111.22 31469.16 282.95 280 28 5.2 6122.62 111.59 31783.85 284.83 281.6 28.3 5.3 6183.24 111.96 31886.39 284.80 285 29 5.4 6243.86 112.33 32092.94 285.7 284 30 5.5 6304.48 112.69 32301.00 286.64 290 29.8 5.6 6395.41 113.23 32610.62 288.00 292 30.5 5.7 6401.47 113.26 32632.87 288.12 295 31 5.8 6425.72 113.41 32713.16 288.45 300 31.2 5.9 6456.03 113.58 32818.28 288.94 302 32 5.10 6486.34 113.76 32920.18 289.38 302.5 31.5 5.11 6516.65 113.94 33021.77 289.82 303 31 5.12 6546.96 114.12 33123.03 290.25 303.2 30.6 5.13 6577.27 114.29 33226.88 290.72 304 29 5.14 6607.58 114.47 33327.51 291.15 304.3 29.2 5.15 6637.89 114.64 33430.74 291.61 305 29 5.16 6668.2 114.82 33530.74 292.03 304.8 28.8 5.17 6680.32 114.88 33574.14 292.25 306 28 5.18 6686.4 114.92 33593.00 292.32 310 28.5 According to the data provided in the production record sheet, we can see that the gas generation amount of calcium carbide increases as the current-to-voltage ratio increases. Therefore, the analysis results of actual production data are consistent with the results of theoretical calculations. We can see that the yield increases as the current to voltage ratio increases. After reaching the maximum value, the output decreases as the current-to-voltage ratio increases. Since the gas generation volume increases with the increase of the current-to-voltage ratio, the maximum value point of the output is the optimal control point we want. At this point, the gas generation volume and output reach the optimal level. Therefore, the electrical parameters at this point are what we want to choose. 7. Benefit analysis of the best control point: The control of the electrical parameters of the calcium carbide furnace is crucial to ensuring high quality, high output, and low consumption. The electrical parameters are controlled reasonably so that the electrode can be inserted into the material layer to an appropriate depth, the operation is relatively stable, and the closed arc operation can be achieved, thereby ensuring that various production technical indicators reach a good level. It can be seen from the production record table in May that if we control the apparent power at 6456kvA, the secondary voltage at 113.58V, and the secondary current at 32818.28A, then the calcium carbide quality will reach 302g/L and the output will reach the highest. The average output is 2T per day. According to the current market price of 2,000 yuan per ton, the profit can be made in one year: 2 * 2000 * 30 * 10 (month) = 120,000 yuan. At the same time, due to better control of various technical indicators, production is more stable, which reduces the amount of equipment maintenance and improves equipment utilization. Although we have theoretically found the best electrical control parameters, there are still some gaps in the actual application process. Due to the unstable quality of our raw materials, low proficiency of workers, aging of equipment, etc., the control of electrical parameters always deviates from the optimal control point. Therefore, we need to continue to work hard, have an innovative spirit, raise awareness, sum up experience, reverse the current production situation of our factory, and strive to achieve high-quality, high-yield, and low-consumption production goals.