Energy-saving process method for changing AC submerged arc furnace into DC submerged arc furnace

Abstract

This invention relates to the field of submerged arc furnace smelting technology, and in particular to an energy-saving process method for converting an AC submerged arc furnace to a DC submerged arc furnace. This method overcomes the shortcomings of existing technologies, such as high AC power supply loss, difficulty in timely judgment of the submerged arc state, and delayed response to material replenishment and electrode adjustment, leading to insufficient smelting stability and energy-saving effects. This invention retains the original furnace body and auxiliary systems, and sets up a rectifier transformer, rectifier device, DC reactor, top cathode electrode, and segmented bottom anode to convert the AC power supply to a DC circuit. The submerged arc state is judged using the voltage fluctuation coefficient and power residual deviation rate. In case of an anomaly, current and voltage limiting, directional material replenishment, and step-by-step electrode relocation are executed sequentially. Once the parameters recover, the current is restored step-by-step. Simultaneously, waste heat recovery from flue gas and cooling water regulation are implemented to reduce power supply fluctuations, heat loss, and electrode wear, thereby improving smelting stability and energy utilization.

Description

Technical Field

[0001] This invention relates to the field of submerged arc furnace smelting technology, and in particular to an energy-saving process method for converting an AC submerged arc furnace to a DC submerged arc furnace. Background Technology

[0002] A submerged arc furnace is an industrial furnace that uses electrodes to input electrical energy into the furnace charge and relies on the heat of the electric arc and the resistance heat of the furnace charge to complete high-temperature reduction smelting. It is mainly used for the production of ferrosilicon, industrial silicon and other ferroalloy products. Existing submerged arc furnaces usually use three-phase AC power supply. Electrodes are embedded in the material layer to form a high-temperature reaction zone, which causes the ore to undergo a reduction reaction with carbonaceous reducing agents and achieves the separation of molten products from slag. Its function is to continuously provide the heat required for smelting and maintain the reduction, melting and heat preservation processes in the furnace.

[0003] Chinese patent CN113428863B discloses an energy-saving method for silicon carbide smelting and an energy-saving smelting furnace. The method involves constructing a U-shaped smelting trough below ground level using high-strength refractory bricks to create a furnace bed with ventilation channels. This ensures both the permeability of the smelting furnace and the necessary insulation, reducing heat loss. Traditional silicon carbide smelting requires at least four furnaces operating in a cycle, each connected to a transformer for both positive and negative voltage. This results in a large circulation loop with long busbar lines, significant losses, and substantial energy waste. This method addresses this by installing switches on each electrode in the large circulation loop, creating a smaller loop and reducing line losses. An energy-saving rectifier cabinet is used for end-to-end power supply, ensuring stable power and allowing for current adjustment based on weather and temperature conditions, saving energy and reducing power consumption by 100 kWh per ton of silicon carbide. Furthermore, the smelting furnace in this application collects and centrally treats the generated flue gas through a gas collection hood, avoiding environmental pollution caused by direct emissions.

[0004] The above-mentioned and existing related technologies often have the following drawbacks: existing energy-saving retrofits of electric arc furnaces are mostly focused on shortening power supply lines, reducing short-circuit losses, or stabilizing input current, making it difficult to take into account the low-cost DC retrofit of the original furnace body. At the same time, there is a lack of continuous judgment on the submerged arc coverage status during the smelting process. When there is a local shortage of material or the electric arc is exposed, manual material replenishment and electrode adjustment are usually required. The response is lagging, which can easily cause voltage fluctuations, power deviations and heat loss, and aggravate electrode wear, affecting the stability of the smelting process and the energy-saving effect. Summary of the Invention

[0005] The technical problem to be solved by this invention is that the existing technology has the disadvantages of high AC power supply loss, difficulty in timely judgment of the submerged arc state, and lag in the response of material replenishment and electrode adjustment, resulting in insufficient smelting stability and energy saving effect. To this end, we propose an energy-saving process method for converting AC submerged arc furnace to DC submerged arc smelting.

[0006] To achieve the above objectives, this application adopts the following technical solution: an energy-saving process method for converting an AC submerged arc furnace to a DC submerged arc furnace, comprising the following steps: S1. After screening, drying, and batching, silica and carbonaceous reducing agent are fed into a submerged arc furnace, wherein the proportion of 10mm-30mm silica is ≥75%, the proportion of 5mm-20mm carbonaceous reducing agent is ≥80%, and the moisture content of the furnace charge is ≤3%. S2. Retain the original furnace body and the charging, unloading and cooling systems, remove the original AC furnace transformer, and install a rectifier transformer, rectifier device and DC reactor to form a DC circuit between the top cathode electrode, furnace charge, melting zone and bottom anode. S3. Start the arc with low current, and proceed with preheating, heat preservation and sintering in sequence. The DC load increases by 10% of the rated power every 8 hours. S4. Control the insertion of the cathode electrode into the material layer and melt in constant power mode. Calculate the voltage fluctuation coefficient and power residual deviation rate in a 5-10 minute time window. When the two are >8% and the absolute value is >6% respectively and last for more than 3 minutes, switch to current limiting and pressure limiting mode and add 1.2-1.5 times the material consumption of the corresponding electrode area. S5. Keep the electrode still during material replenishment. If the two parameters do not fall back to the recovery threshold, control the electrode to move down step by step in increments of 50-100mm. Re-evaluate after each 2-minute rest. After the parameters recover, increase the rated current by 2% every 2 minutes. When the rated value reaches more than 80%, release the voltage limit and resume constant power melting. S6. Complete slag-silicon separation, furnace pouring, flue gas dust removal and waste heat recovery, and adjust cooling water according to load and furnace temperature.

[0007] Preferably, in step S1, the proportion of silica, the proportion of carbonaceous reducing agent, and the moisture content of the furnace charge are all calculated as mass percentages, and the silica and carbonaceous reducing agent are screened and dried respectively before being mixed.

[0008] Preferably, in step S2, the furnace bottom anode adopts a segmented structure, with each segmented anode independently connected to a DC circuit and corresponding to the top cathode electrode.

[0009] Preferably, in step S3, the preheating, heat preservation, and sintering are respectively low-temperature preheating, medium-temperature heat preservation, and high-temperature sintering, and the next stage is entered after the furnace temperature and DC load of the previous stage are stable.

[0010] Preferably, in step S4, the voltage fluctuation coefficient is the ratio of the standard deviation of the electrode voltage to the average voltage within a continuous time window, and the power residual deviation rate is the percentage of the difference between the actual power after constant power compensation and the set power to the set power.

[0011] Preferably, in step S4, the absolute value of the residual power deviation rate is compared with the warning threshold, and the arc coverage is determined to be in failure only when the voltage fluctuation coefficient and the residual power deviation rate both exceed the corresponding warning threshold and continue for more than 3 minutes. The recovery threshold is lower than the corresponding warning threshold.

[0012] Preferably, in step S4, each top cathode electrode establishes a regional correspondence with the corresponding segmented anode and the fixed-point feeding port on the furnace top, and the feeding amount is 1.2-1.5 times the material consumption per unit time of the corresponding region.

[0013] Preferably, in step S5, after the directional feeding is completed, the electrode voltage, electrode current and actual power are collected, and the two parameters are recalculated according to the time window in step S4. The electrode is controlled to move down step by step only when the two parameters have not fallen back to the recovery threshold.

[0014] Preferably, in step S5, after each electrode is moved down and left to stand for 2 minutes, the two parameters are re-evaluated. When both parameters fall back to the recovery threshold, the electrode movement is stopped. Then, the current setting value is restored step by step, and the constant power mode is switched after the voltage limit is released.

[0015] Preferably, in step S6, the molten silicon liquid is successively poured, cooled and shaped and finished to obtain the finished product. The flue gas at the furnace mouth is collected under closed negative pressure and purified by dust removal before entering the waste heat recovery unit. The waste heat is recovered for furnace charge drying or waste heat power generation. The circulating cooling water system performs water cooling heat dissipation on the furnace body, electrodes and short grid respectively.

[0016] The technical effects and advantages of this invention are as follows: This invention forms a corresponding circuit between the segmented bottom anode and the top cathode electrode, and judges the arc submersion status by combining the voltage fluctuation coefficient and the power residual deviation rate. It can switch the current limiting and voltage limiting mode in time before the material layer coverage deteriorates, and sequentially perform fixed-point feeding and electrode step-by-step downward movement to reduce arc exposure, heat loss and electrode wear. After the arc is restored, the current is restored step by step. At the same time, it is combined with flue gas waste heat recovery and cooling water adjustment according to the load, which is conducive to improving smelting stability and comprehensive energy saving effect. Attached Figure Description

[0017] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts: Figure 1 This is a general flow chart of the energy-saving process method of the present invention; Figure 2 This is a flowchart of the process of furnace unloading, flue gas waste heat recovery, and circulating cooling water regulation in this invention; Figure 3 This is a flowchart of the workflow of the present invention. Detailed Implementation

[0018] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0019] Comparative Example S1. Silica and carbonaceous reducing agent are screened separately. Silica with a particle size of 20mm is selected, accounting for 85% of the total silica after screening. Carbonaceous reducing agent with a particle size of 12mm is selected, accounting for 88% of the total carbonaceous reducing agent after screening. Then, silica and carbonaceous reducing agent are dried and batched to make the moisture content of the furnace charge 2.5%. The prepared furnace charge is then sent to the storage silo and fed into the electric arc furnace through the furnace top charging device.

[0020] S2. Retain the original ore-fired furnace body, charging system, tapping system and cooling water system, remove the original three-phase AC furnace transformer, and install a rectifier transformer, rectifier device and DC reactor in sequence to form a DC conductive circuit between the top cathode electrode, furnace charge, melting zone and bottom anode.

[0021] S3. Start the arc with a low current, and then proceed with low-temperature preheating, medium-temperature heat preservation and high-temperature sintering in sequence. The DC load of each stage is gradually increased by 10% of the rated power every 8 hours until the furnace lining is sintered and meets the submerged arc melting conditions.

[0022] S4. Control the insertion of the top cathode electrode into the material layer and use constant power mode for melting. Continuously collect electrode voltage, electrode current and actual power, but do not calculate voltage fluctuation coefficient and power residual deviation rate. The operator judges the submerged arc state only by the state of the furnace flame, flue gas and instantaneous voltage change. When the arc is observed to be exposed or the voltage rises significantly, the operator replenishes the corresponding electrode area according to the experience of the operator. The amount of replenishment is not determined by the material consumption per unit time in that area. The power supply control still maintains constant power mode.

[0023] S5. During the feeding process, the electrode position is not kept unchanged. Instead, the top cathode electrode is directly moved down 75mm while feeding. After the electrode moves, no uniform resting time is set, and the submerged arc state parameters are not recalculated. When the furnace flame weakens or the electrode voltage drops, the electrode movement is stopped, and the original current setting value is directly restored. The control method of gradually restoring the current and delaying the release of the voltage limit is not adopted.

[0024] S6. After smelting, the furnace is tapped according to a fixed cycle to separate the molten silicon liquid from the slag. The molten silicon liquid is then poured, cooled and shaped, and finished to form the finished product. The high-temperature flue gas generated at the furnace mouth is collected under a closed negative pressure and purified by dust removal before entering the waste heat recovery unit. The circulating cooling water system cools the furnace body, electrodes, and short grid with water.

[0025] Example 1 Reference Figures 1-3 An energy-saving process method for converting an AC submerged arc furnace to a DC submerged arc furnace includes the following steps: S1. Silica and carbonaceous reducing agent are screened separately. Silica with a particle size of 20mm is selected, accounting for 78% of the total silica after screening. Carbonaceous reducing agent with a particle size of 12mm is selected, accounting for 82% of the total carbonaceous reducing agent after screening. The raw materials are then dried so that the moisture content of the furnace charge after batching is 2.8%. The furnace charge is then sent to the storage silo and fed into the electric arc furnace through the furnace top charging device.

[0026] S2. Retain the original blast furnace body, charging system, tapping system and cooling water system, remove the original three-phase AC furnace transformer, and install a rectifier transformer, rectifier device and DC reactor in sequence to convert AC power into low voltage high current DC power. The bottom anode adopts a segmented structure, and each segmented anode is connected to the corresponding top cathode electrode, so that the DC current passes through the top cathode electrode, furnace charge, melting zone and bottom anode in sequence to form a DC conductive circuit.

[0027] S3. Start the arc with a low current, and then carry out low-temperature preheating, medium-temperature heat preservation and high-temperature sintering in sequence. The DC load of each stage increases by 10% of the rated power every 8 hours until the furnace lining is sintered and meets the submerged arc melting conditions.

[0028] S4. Control the insertion of the top cathode electrode into the material layer and use constant power mode for melting. Continuously collect electrode voltage, electrode current and actual power. Calculate the voltage fluctuation coefficient and power residual deviation rate with a continuous time window of 5 minutes. When the voltage fluctuation coefficient is greater than 8% and the absolute value of the power residual deviation rate is greater than 6%, and the above parameters exceed the corresponding warning threshold at the same time and continue for more than 3 minutes, switch the corresponding electrode area to current limiting and voltage limiting mode, and replenish the furnace material in the area with 1.2 times the material consumption per unit time through the fixed-point feeding port.

[0029] S5. During the feeding process, keep the position of the top cathode electrode unchanged. After the feeding is completed, continue to collect the electrode voltage, electrode current and actual power. If the voltage fluctuation coefficient and power residual deviation rate do not fall back to the recovery threshold, control the top cathode electrode to move down step by step in increments of 50mm. After each movement, let it stand for 2 minutes and then re-determine the parameter status. After the parameters are restored, restore the current setting value at a rate of 2% increase of the rated current every 2 minutes. When the current is restored to 80% of the rated value, release the voltage limit and restore constant power submerged arc melting.

[0030] S6. After smelting, slag and silicon are separated and the furnace is tapped at a set time. The molten silicon liquid is successively poured, cooled and shaped and finished to form the finished product. The high-temperature flue gas at the furnace mouth is collected by a closed negative pressure and purified by dust removal before entering the waste heat recovery unit. The recovered waste heat is used for drying the furnace charge. The circulating cooling water system adjusts the cooling water flow and supply pressure according to the DC smelting load and furnace temperature.

[0031] Example 2 Reference Figures 1-3 An energy-saving process method for converting an AC submerged arc furnace to a DC submerged arc furnace includes the following steps: S1. Silica and carbonaceous reducing agent are screened separately. Silica with a particle size of 20mm is selected, accounting for 85% of the total silica after screening. Carbonaceous reducing agent with a particle size of 12mm is selected, accounting for 88% of the total carbonaceous reducing agent after screening. The raw materials are then dried so that the moisture content of the furnace charge after batching is 2.4%. The furnace charge is then sent to the storage silo and fed into the electric arc furnace through the furnace top charging device.

[0032] S2. Retain the original blast furnace body, charging system, tapping system and cooling water system, remove the original three-phase AC furnace transformer, and install a rectifier transformer, rectifier device and DC reactor in sequence to convert AC power into low voltage high current DC power. The bottom anode adopts a segmented structure, and each segmented anode is connected to the corresponding top cathode electrode, so that the DC current passes through the top cathode electrode, furnace charge, melting zone and bottom anode in sequence to form a DC conductive circuit.

[0033] S3. Start the arc with a low current, and then carry out low-temperature preheating, medium-temperature heat preservation and high-temperature sintering in sequence. The DC load of each stage increases by 10% of the rated power every 8 hours until the furnace lining is sintered and meets the submerged arc melting conditions.

[0034] S4. Control the insertion of the top cathode electrode into the material layer and use constant power mode for melting. Continuously collect electrode voltage, electrode current and actual power. Calculate the voltage fluctuation coefficient and power residual deviation rate with 8 minutes as a continuous time window. When the voltage fluctuation coefficient is greater than 8% and the absolute value of the power residual deviation rate is greater than 6%, and the above parameters exceed the corresponding warning threshold at the same time and last for more than 3 minutes, switch the corresponding electrode area to current limiting and voltage limiting mode, and replenish the furnace material in the area with 1.35 times the material consumption per unit time through the fixed-point feeding port.

[0035] S5. During the feeding process, keep the position of the top cathode electrode unchanged. After feeding is completed, continue to collect the electrode voltage, electrode current and actual power. When the voltage fluctuation coefficient and power residual deviation rate have not fallen back to the recovery threshold, control the top cathode electrode to move down step by step in a single step of 75mm. After each movement, let it stand for 2 minutes and then re-determine the parameter status. After the parameters are restored, restore the current setting value at a rate of 2% of the rated current every 2 minutes. When the current is restored to 80% of the rated value, release the voltage limit and restore constant power submerged arc melting.

[0036] S6. After smelting, slag and silicon are separated and the furnace is tapped at a set time. The molten silicon liquid is successively poured, cooled and shaped and finished to form the finished product. The high-temperature flue gas at the furnace mouth is collected under closed negative pressure and purified by dust removal before entering the waste heat recovery unit. The recovered waste heat is used for waste heat power generation. The circulating cooling water system adjusts the cooling water flow and supply pressure according to the DC smelting load and furnace temperature.

[0037] Example 3 Reference Figures 1-3 An energy-saving process method for converting an AC submerged arc furnace to a DC submerged arc furnace includes the following steps: S1. Silica and carbonaceous reducing agent are screened separately. Silica with a particle size of 20mm is selected, accounting for 92% of the total silica after screening. Carbonaceous reducing agent with a particle size of 12mm is selected, accounting for 94% of the total carbonaceous reducing agent after screening. The raw materials are then dried so that the moisture content of the furnace charge after batching is 1.8%. The furnace charge is then sent to the storage silo and fed into the electric arc furnace through the furnace top charging device.

[0038] S2. Retain the original blast furnace body, charging system, tapping system and cooling water system, remove the original three-phase AC furnace transformer, and install a rectifier transformer, rectifier device and DC reactor in sequence to convert AC power into low voltage high current DC power. The bottom anode adopts a segmented structure, and each segmented anode is connected to the corresponding top cathode electrode, so that the DC current passes through the top cathode electrode, furnace charge, melting zone and bottom anode in sequence to form a DC conductive circuit.

[0039] S3. Start the arc with a low current, and then carry out low-temperature preheating, medium-temperature heat preservation and high-temperature sintering in sequence. The DC load of each stage increases by 10% of the rated power every 8 hours until the furnace lining is sintered and meets the submerged arc melting conditions.

[0040] S4. Control the insertion of the top cathode electrode into the material layer and use constant power mode for melting. Continuously collect electrode voltage, electrode current and actual power. Calculate the voltage fluctuation coefficient and power residual deviation rate with 10 minutes as a continuous time window. When the voltage fluctuation coefficient is greater than 8% and the absolute value of the power residual deviation rate is greater than 6%, and the above parameters exceed the corresponding warning threshold at the same time and continue for more than 3 minutes, switch the corresponding electrode area to current limiting and voltage limiting mode, and replenish the furnace material in the area with 1.5 times the material consumption per unit time through the fixed-point feeding port.

[0041] S5. During the feeding process, keep the position of the top cathode electrode unchanged. After feeding is completed, continue to collect the electrode voltage, electrode current and actual power. When the voltage fluctuation coefficient and power residual deviation rate have not fallen back to the recovery threshold, control the top cathode electrode to move down step by step in increments of 100mm. After each movement, let it stand for 2 minutes and then re-determine the parameter status. After the parameters are restored, restore the current setting value at a rate of 2% increase of the rated current every 2 minutes. When the current is restored to 80% of the rated value, release the voltage limit and restore constant power submerged arc melting.

[0042] S6. After smelting, slag and silicon are separated and the furnace is tapped at a set time. The molten silicon liquid is successively poured, cooled and shaped and finished to form the finished product. The high-temperature flue gas at the furnace mouth is collected under closed negative pressure and purified by dust removal before entering the waste heat recovery unit. Part of the recovered waste heat is used for drying the furnace charge, and the rest is used for waste heat power generation. The circulating cooling water system adjusts the cooling water flow and supply pressure according to the DC smelting load and furnace temperature.

[0043] Comparison table of process effects between the examples and comparative examples

[0044] As shown in the comparison table of process effects between the examples and the comparative examples, Examples 1, 2, and 3 all judge the arc coverage status by combining the voltage fluctuation coefficient and the power residual deviation rate, and adjust according to the order of current limiting and voltage limiting, directional feeding, step-by-step electrode movement, and step-by-step current recovery. Compared with the comparative example, which relies on manual observation and experience-based adjustment, it can identify arc anomalies in advance and reduce voltage and power fluctuations. Example 1 has a faster response speed, but its shorter calculation window is easily affected by instantaneous fluctuations. Example 3 has higher judgment stability, but its response speed is relatively slower. Example 2 maintains a good balance between anomaly identification speed, judgment accuracy, feeding amount, and electrode movement amplitude, thus exhibiting better overall smelting stability and energy-saving effect.

[0045] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. An energy-saving process method for converting an AC submerged arc furnace to a DC submerged arc smelting process, characterized in that, Includes the following steps: S1. After screening, drying, and batching, silica and carbonaceous reducing agent are fed into a submerged arc furnace, wherein the proportion of 10mm-30mm silica is ≥75%, the proportion of 5mm-20mm carbonaceous reducing agent is ≥80%, and the moisture content of the furnace charge is ≤3%. S2. Retain the original furnace body and the charging, unloading and cooling systems, remove the original AC furnace transformer, and install a rectifier transformer, rectifier device and DC reactor to form a DC circuit between the top cathode electrode, furnace charge, melting zone and bottom anode. S3. Start the arc with low current, and proceed with preheating, heat preservation and sintering in sequence. The DC load increases by 10% of the rated power every 8 hours. S4. Control the insertion of the cathode electrode into the material layer and melt in constant power mode. Calculate the voltage fluctuation coefficient and power residual deviation rate in a 5-10 minute time window. When the two are >8% and the absolute value is >6% respectively and last for more than 3 minutes, switch to current limiting and pressure limiting mode and add 1.2-1.5 times the material consumption of the corresponding electrode area. S5. Keep the electrode still during material replenishment. If the two parameters do not fall back to the recovery threshold, control the electrode to move down step by step in increments of 50-100mm. Re-evaluate after each 2-minute rest. After the parameters recover, increase the rated current by 2% every 2 minutes. When the rated value reaches more than 80%, release the voltage limit and resume constant power melting. S6. Complete slag-silicon separation, furnace pouring, flue gas dust removal and waste heat recovery, and adjust cooling water according to load and furnace temperature.

2. The energy-saving process method for converting an AC submerged arc furnace to DC submerged arc smelting as described in claim 1, characterized in that: In step S1, the proportions of silica, carbonaceous reducing agent, and furnace charge moisture are all calculated as mass percentages. The silica and carbonaceous reducing agent are screened and dried before being mixed.

3. The energy-saving process method for converting an AC submerged arc furnace to DC submerged arc smelting as described in claim 1, characterized in that: In step S2, the furnace bottom anode adopts a segmented structure, with each segmented anode independently connected to a DC circuit and corresponding to the top cathode electrode.

4. The energy-saving process method for converting an AC submerged arc furnace to DC submerged arc smelting as described in claim 1, characterized in that: In step S3, the preheating, heat preservation and sintering are respectively low-temperature preheating, medium-temperature heat preservation and high-temperature sintering. After the furnace temperature and DC load of the previous stage are stable, the next stage is entered.

5. The energy-saving process method for converting an AC submerged arc furnace to DC submerged arc smelting as described in claim 1, characterized in that: In step S4, the voltage fluctuation coefficient is the ratio of the standard deviation of the electrode voltage to the average voltage within a continuous time window, and the power residual deviation rate is the percentage of the difference between the actual power after constant power compensation and the set power to the set power.

6. The energy-saving process method for converting an AC submerged arc furnace to DC submerged arc smelting as described in claim 5, characterized in that: In step S4, the absolute value of the residual power deviation rate is taken and compared with the warning threshold. Only when the voltage fluctuation coefficient and the residual power deviation rate both exceed the corresponding warning threshold and continue for more than 3 minutes is it determined that the buried arc coverage is about to fail, and the recovery threshold is lower than the corresponding warning threshold.

7. The energy-saving process method for converting an AC submerged arc furnace to DC submerged arc smelting as described in claim 1, characterized in that: In step S4, each top cathode electrode establishes a regional correspondence with the corresponding segmented anode and the fixed-point feeding port on the top of the furnace, and the feeding amount is 1.2-1.5 times the material consumption per unit time of the corresponding region.

8. The energy-saving process method for converting an AC submerged arc furnace to DC submerged arc smelting as described in claim 1, characterized in that: In step S5, after the directional feeding is completed, the electrode voltage, electrode current and actual power are collected, and the two parameters are recalculated according to the time window in step S4. The electrode is controlled to move down step by step only when the two parameters have not fallen back to the recovery threshold.

9. The energy-saving process method for converting an AC submerged arc furnace to DC submerged arc smelting as described in claim 8, characterized in that: In step S5, after each electrode is moved down and left to stand for 2 minutes, the two parameters are re-evaluated. When both parameters fall back to the recovery threshold, the electrode movement is stopped. Then, the current setting value is restored step by step, and the constant power mode is switched after the voltage limit is released.

10. The energy-saving process method for converting an AC submerged arc furnace to a DC submerged arc furnace as described in claim 1, characterized in that: In step S6, the molten silicon liquid is successively poured, cooled and shaped and finished to obtain the finished product. The flue gas at the furnace mouth is collected under closed negative pressure and purified by dust removal before entering the waste heat recovery unit. The waste heat is recovered for furnace charge drying or waste heat power generation. The circulating cooling water system performs water cooling heat dissipation on the furnace body, electrodes and short grid respectively.

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