Electrostatic precipitator hot galvanized cathode wire and method of making same

Abstract

The application provides a hot galvanized cathode wire of an electric dust collector and a preparation method thereof. The hot galvanized cathode wire comprises a support pipe and a plurality of thorn welded on the support pipe. The outer surface of the thorn is sequentially provided with a first galvanized layer and a second galvanized layer from inside to outside. The outer surface of the support pipe is provided with the second galvanized layer. The first galvanized layer comprises the following components: aluminum, tungsten, molybdenum, chromium, ZrO, MgO, rare earth oxide and Zn. The second galvanized layer comprises the following components: aluminum, molybdenum, chromium and Zn. The method that the thorn is welded on the support pipe and then the whole is hot galvanized can reduce the cost, improve the material utilization rate, improve the corrosion resistance and the corona discharge efficiency of the cathode wire. In addition, the welding position is hot galvanized as a whole, the corrosion resistance of the welding position is improved, and the thorn is not easy to fall off.

Description

Technical Field

[0001] The present invention relates to the technical field of flue gas pollutant treatment, in particular to a hot-dip galvanized cathode wire for an electrostatic precipitator and a preparation method thereof. Background Art

[0002] Electrostatic precipitation technology is a technology that supplies power through a high-voltage power supply, generates corona discharge on the cathode wire to charge the dust particles in the dust-containing gas, and collects the dust under the action of the electric field force. Electrostatic precipitators are the mainstream equipment for industrial flue gas dust removal, with the advantages of low pressure drop loss, no blockage, large flue gas treatment volume, and high dust removal efficiency. The power consumption distribution of existing electrostatic precipitators is as Figure 1 shown. Taking a medium-sized electrostatic precipitator supporting a 150MW unit as an example, the power consumption of the high-voltage power supply is about 500kW. The effective power consumption of the high-voltage power supply of the electrostatic precipitator is the secondary voltage multiplied by the secondary current. Only when the secondary voltage reaches a certain value (the corona starting voltage), can the cathode wire generate effective corona discharge. Therefore, reducing the corona starting voltage of the cathode wire can reduce the power consumption to a certain extent; the magnitude of the secondary current directly determines the space charge amount of the dust, and increasing the secondary current value can improve the electrostatic precipitation efficiency to a certain extent.

[0003] In the actual operation of electrostatic precipitators, the most common faults are cathode wire corrosion and breakage, vibration hammer falling off, ash hopper plugging, and insulator cracking, which are called the common "four major faults" of electrostatic precipitators. Among them, cathode wire corrosion and breakage are the main reasons affecting equipment safety and reducing dust removal efficiency. At present, electrostatic precipitators supporting flue gas from co-firing of coal and sludge, paper-making alkali furnaces, etc. generally have serious cathode wire corrosion problems, mainly manifested as corrosion of the welding points of barbs and connectors, barb corrosion, etc. Among them, after co-firing coal with sludge, the water content in the flue gas increases, the contents of Cl and S elements increase, the proportion of heavy metals rises, and the acid dew point temperature decreases, resulting in increased flue gas corrosivity. Cathode wire corrosion leads to barb shedding or even breakage, affecting the safe and stable operation of electrostatic precipitators. The Cl and S elements in coal and co-fired biomass are the main reasons for the corrosion of boilers and post-furnace environmental protection equipment. The Cl element mainly corrodes metal materials in the forms of HCl and Cl2. The Cl element enters the flue in the form of gaseous chlorides and undergoes a sulfation reaction with SO2 in the flue gas to generate HCl and Cl2, which react with metals to form FeCl2. In a reducing atmosphere, H2S can react with metals to form FeS under the action of C and CO, and in an aerobic environment, it is SO2 that corrodes metals.

[0004] To address the above issues, existing cathode wires primarily utilize special metallic materials, such as 304, 316, and even 2205 stainless steel, leading to a significant increase in material costs and high pollution control costs. For example, utility model patent application number 201520977579.7 discloses a self-corrosion-resistant high-efficiency cathode wire, which solves the corrosion problem through material selection and addresses low discharge efficiency through structural shape, but at extremely high cost. Invention patent application number 201811514202.2 discloses a cobalt-thorium-tungsten alloy material for magnetron cathode coils and its preparation method. This material involves adding cobalt salt while doping blue tungsten with thorium nitrate. The cobalt element's grain-refining function improves the seismic resistance of the carbonized magnetron cathode coil, enhancing its strength, reducing brittleness, and improving seismic performance. Patent application number 201310513908.8 discloses a conductive catalytic electrode for a DC corona discharge gas purifier and its preparation method. This method improves the purification performance for volatile organic gases by coating the electrode substrate with a catalytic sol. While the materials disclosed in the aforementioned patent can improve the performance of the cathode wire to some extent, they significantly increase the cost of the cathode wire material, failing to economically and efficiently solve the problem of cathode wire corrosion failure. Furthermore, when the cathode wire uses low-carbon steel SPCC and stainless steel 304, 316, or 2205, the thermionic emission resistance is high during corona discharge, and the electron work function on the material surface is high, resulting in high high-voltage power consumption in the electrostatic precipitator. Summary of the Invention

[0005] The purpose of this invention is to solve the problems in the prior art by proposing a hot-dip galvanized cathode wire for electrostatic precipitators and its preparation method, which can improve the corrosion resistance and corona discharge efficiency of the cathode wire and reduce costs.

[0006] To achieve the above objectives, the present invention proposes a hot-dip galvanized cathode wire for an electrostatic precipitator, comprising a support tube and a plurality of barbs welded to the support tube. The outer surface of the barbs is provided with a first galvanized layer and a second galvanized layer from the inside to the outside. The outer surface of the support tube is provided with a second galvanized layer. The first galvanized layer comprises the following components: aluminum, tungsten, molybdenum, chromium, ZrO, MgO, rare earth oxides and Zn. The second galvanized layer comprises the following components: aluminum, molybdenum, chromium and Zn.

[0007] Preferably, the first zinc plating layer is composed of the following components in mass percentage: 0.15-0.25% aluminum, 0.01-0.02% tungsten, 0.02-0.03% molybdenum, 0.01-0.03% chromium, 0.008-0.02% ZrO, 0.05-1.2% MgO, 0.008-0.016% rare earth oxides, with the balance being Zn and unavoidable impurities.

[0008] Preferably, the rare earth oxides include La2O3, Y2O3 and CeO2, wherein the mass ratio of La2O3, Y2O3 and CeO2 is 2-5:3-5:3-6.

[0009] Preferably, the second zinc plating layer is composed of the following components in mass percentage: 0.12-0.2% aluminum, 0.01-0.02% molybdenum, 0.001-0.015% chromium, with the balance being Zn and unavoidable impurities.

[0010] Preferably, the contents of aluminum, molybdenum, and chromium in the second zinc plating layer are lower than those in the first zinc plating layer.

[0011] Preferably, both the support tube and the barbs are made of low-carbon steel SPCC.

[0012] This invention also proposes a method for preparing the above-mentioned hot-dip galvanized cathode wire for electrostatic precipitators, comprising the following steps:

[0013] S1. Press-shear forming: Press-shearing SPCC plates to form spiked flat plates;

[0014] S2. Pressing and molding: Pressing the spiked plate to form three-dimensional spikes;

[0015] S3. Preheating galvanizing: The pressed and formed barbs are subjected to a zinc bath, and a certain amount of aluminum, tungsten, molybdenum, chromium, ZrO, MgO and rare earth oxides are added to the zinc bath. After the zinc bath is removed, the first zinc coating layer is formed on the surface of the barbs.

[0016] S4. Welding and forming: Weld the preheated galvanized barbs to the connecting parts on both sides of the support pipe to form a cathode wire;

[0017] S5. Overall hot-dip galvanizing: The entire cathode wire is subjected to a zinc bath, and a certain amount of aluminum, molybdenum and chromium are added to the zinc bath. After the zinc bath is removed, a second zinc coating layer is formed on the surface of the barbs and support tube.

[0018] Preferably, in step S3, tungsten, molybdenum, chromium, ZrO, MgO, and rare earth oxides are added to the zinc bath in the following mass percentages: aluminum 0.15–0.25%, tungsten 0.01–0.02%, molybdenum 0.02–0.03%, chromium 0.01–0.03%, ZrO 0.008–0.02%, MgO 0.05–1.2%, rare earth oxides 0.008–0.016%, with the balance being Zn and unavoidable impurities.

[0019] Preferably, in step S5, aluminum, molybdenum, and chromium are added to the zinc bath in the following mass percentages: aluminum 0.12–0.2%, molybdenum 0.01–0.02%, chromium 0.001–0.015%, with the balance being Zn and unavoidable impurities.

[0020] Preferably, in step S3, during the zinc bath with barbed needles, the needles are rotated 90° along their axis until they are horizontal. After the zinc bath is completed, the needles are rotated again so that the needles face downwards when the zinc liquid is dispensed. After the zinc liquid is dispensed, the needles are cooled for 3-8 seconds while the remaining zinc is vibrated with the needles facing downwards.

[0021] The beneficial effects of this invention are:

[0022] 1. Compared to the method of integral pressing and forming of the barbs and intermediate tube, this invention uses a method of welding the barbs to the support tube and then hot-dip galvanizing the entire structure, which can reduce costs and improve material utilization. Furthermore, by applying overall hot-dip galvanizing to the welded area, this invention improves the corrosion resistance of the welded area and reduces the likelihood of barbs falling off.

[0023] 2. The cathode wire has a low corona initiation voltage, high discharge efficiency, high energy consumption, and high dust removal efficiency.

[0024] 3. It has strong structural adaptability and can meet the retrofit requirements of existing electrostatic precipitators, with low retrofit costs.

[0025] The features and advantages of the present invention will be described in detail through embodiments and in conjunction with the accompanying drawings. Attached Figure Description

[0026] Figure 1 This is a comparison chart of the power consumption distribution of existing electrostatic precipitators;

[0027] Figure 2 This is a comparison chart of the operating parameters of the discharge electrode of this invention and common discharge electrodes;

[0028] Figure 3 This is a photograph of the corona discharge of the hot-dip galvanized cathode wire of the present invention at 60kV;

[0029] Figure 4 These are images of the corona discharge of SPCC material barbed wire at 60kV.

[0030] Figure 5 This is a flowchart of a method for preparing a hot-dip galvanized cathode wire for an electrostatic precipitator according to the present invention;

[0031] Figure 6 This is a flowchart of the barbed zinc bath process for a hot-dip galvanized cathode wire of an electrostatic precipitator according to the present invention. Detailed Implementation

[0032] This invention discloses a hot-dip galvanized cathode wire for an electrostatic precipitator, comprising a support tube and a plurality of barbs welded to the support tube. Both the support tube and the barbs are made of low-carbon steel SPCC. The outer surface of the barbs is sequentially provided with a first galvanized layer and a second galvanized layer from the inside out. The outer surface of the support tube is provided with the second galvanized layer. The first galvanized layer consists of the following components by mass percentage: aluminum 0.15–0.25%, tungsten 0.01–0.02%, molybdenum 0.02–0.03%, chromium 0.01–0.03%, ZrO 0.008–0.02%, MgO 0.05–1.2%, rare earth oxides 0.008–0.016%, with the balance being Zn and unavoidable impurities. The rare earth oxides include La₂O₃, Y₂O₃, and CeO₂, wherein the mass ratio of La₂O₃, Y₂O₃, and CeO₂ is 2–5:3–5:3–6. The second zinc plating layer consists of the following components in mass percentage: 0.12-0.2% aluminum, 0.01-0.02% molybdenum, 0.001-0.015% chromium, with the balance being Zn and unavoidable impurities.

[0033] Furthermore, the content of aluminum, molybdenum, and chromium in the second zinc plating layer is lower than that in the first zinc plating layer. Because the tip of the barb requires corona discharge, this invention improves its discharge efficiency by adding tungsten and rare earth oxides. However, since the support tube has a large area and no corona discharge effect, to reduce costs, tungsten and rare earth oxides are not added during the overall hot-dip galvanizing process.

[0034] Since the principle of electrostatic precipitators is to charge dust particles through corona discharge and then separate them from the flue gas through an electric field, the front-end electric field of the electrostatic precipitator needs to charge the dust particles. The larger the charge, the more beneficial it is for dust removal. High voltage is beneficial to dust removal efficiency but has little impact, although it leads to high power consumption. Therefore, the front-end electric field needs a low-voltage, high-current discharge electrode. Developing a low-voltage, high-current discharge electrode can improve dust removal efficiency while reducing power consumption. The corona initiation voltage of the hot-dip galvanized cathode wire of this invention compared with several common discharge electrodes under normal atmospheric conditions is shown in Table 1 below. The corona initiation voltage of the most commonly used discharge barbed wire and needle-punched wire is 15kV (the materials are generally SPCC, 304, and 316, and the corona initiation voltages of these materials are not significantly different), while the corona initiation voltage of the hot-dip galvanized cathode wire of this invention is 13kV.

[0035] Table 1

[0036]

[0037]

[0038] This invention uses tungsten, ZrO, MgO, and rare earth oxides (La2O3, Y2O3, CeO2) as active materials to reduce the electron work function of the material, improve its thermionic emission capability, and reduce the corona initiation voltage of the electrostatic precipitator. Furthermore, molybdenum and chromium metals improve the resistance of the spikes to chloride ion corrosion, and tungsten further enhances corrosion resistance. The principle behind this is that tungsten has a high melting point and low work function (around 4.5 eV). The addition of rare earth oxides, acting as active materials, further reduces the work function. La2O3 and Y2O3 have the most significant effect. During the corona discharge operation of the electrostatic precipitator, La2O3 is reduced by the heated flue gas, forming a La monoatom film on the surface of the discharge point, reducing the work function of the composite material by approximately 0.2 eV, thus forming an activation layer for efficient corona discharge. In addition, the addition of Y2O3 catalyzes the formation of dense blue tungsten on the surface of the discharge point in a high carbon dioxide flue gas environment, which improves the stability of tungsten and avoids the high-temperature volatilization loss of tungsten. Under the normal operating flue gas conditions of electrostatic precipitator, the theoretical wear life can reach 8 years.

[0039] Conventional cathode wires begin to corona discharge at 15kV, while the cathode wires using the material of this invention, after hot-dip galvanizing, begin to corona discharge at 13kV. Under the same corona discharge efficiency, the electrostatic precipitator operates at a lower voltage; under the same operating voltage, the electrostatic precipitator has a higher current density and a higher dust charge, thus improving the corona discharge efficiency and achieving energy saving and emission reduction.

[0040] Material cost comparison, taking a 1000MW unit as an example, with the support pipe and barbs thickness calculated at 0.6mm:

[0041] The prices of commonly used cathode wires in the market (excluding tax rates and other factors due to significant fluctuations in steel and labor costs) are as follows:

[0042] 316L monolithic barbed wire: 37 yuan per meter;

[0043] 316L barbed welding wire: 28 yuan per meter;

[0044] 304 stainless steel barbed wire: 23 yuan per meter;

[0045] 304 stainless steel barbed welding wire: 18 yuan per meter;

[0046] SPCC overall barbed wire: 11 yuan per meter;

[0047] SPCC barbed welding wire: 9 yuan per meter;

[0048] Note: 316L integral barbed line means that both the intermediate tube and the barbs are made of 316L stainless steel, and the barbs and intermediate tube are integrally pressed into shape. 316L welded barbed line means that both the intermediate tube and the barbs are made of 316L stainless steel, the barbs and intermediate tube are pressed into shape separately, and then the barbs are welded to the intermediate tube. The other models follow the same principle.

[0049] Corrosion resistance comparison: 316L integral barbed wire > 316L barbed welded wire > 304 integral barbed wire >> 304 barbed welded wire > SPCC integral barbed wire >> SPCC barbed welded wire.

[0050] The material and manufacturing cost of 316L barbed wire is approximately 37 yuan per meter. The total length of cathode wire for one unit is about 150,000 meters, with a cost of 5.55 million yuan.

[0051] The material and manufacturing cost of the hot-dip galvanized barbed wire (hot-dip galvanized cathode wire) of this invention is about 12 yuan per meter. The cathode wire length of a single unit is about 150,000 meters, and the cost is 1.8 million yuan.

[0052] The material and manufacturing cost of 304 barbed wire is approximately 13 yuan per meter. The total length of cathode wire for one unit is about 150,000 meters, with a cost of 1.95 million yuan.

[0053] The corrosion resistance of the material of this invention is higher than that of 316L, and the discharge efficiency is higher than that of 316L. Therefore, based on the same corrosion resistance, the cost of a 1000MW unit electrostatic precipitator using the cathode wire of this invention can be reduced by approximately 3.6 million yuan, while other costs such as installation and transportation remain the same. Furthermore, the discharge efficiency is improved, energy consumption is reduced, and dust removal efficiency is increased.

[0054] Example 1:

[0055] In this embodiment, the first zinc plating layer comprises the following components by mass percentage: 0.15% aluminum, 0.02% tungsten, 0.02% molybdenum, 0.01% chromium, 0.02% ZrO, 1.0% MgO, 0.016% rare earth oxides (including 0.005% La2O3, 0.005% Y2O3, and 0.006% CeO2), with the balance being Zn and unavoidable impurities. The second zinc plating layer comprises the following components by mass percentage: 0.12% aluminum, 0.01% molybdenum, 0.001% chromium, with the balance being Zn and unavoidable impurities.

[0056] In practical engineering applications of electrostatic precipitators (ESPs), those equipped with conventional barbed wire exhibit high dust removal efficiency when burning high-quality coal or operating at low loads in coal-fired power plants. To reduce energy consumption, the power supply is typically adjusted to its minimum. To achieve the minimum secondary current value, the secondary voltage generally needs to be adjusted to 30kV, and the secondary current density to 0.1mA / m. 2The current corresponding to a power supply is approximately 300mA / m. 2 (The values ​​vary depending on the electric field magnitude), corresponding to an effective power of 9kW. Compared to conventional cathode wires, using the cathode wire of Example 1 in this embodiment, to achieve the minimum secondary current value, the secondary voltage only needs to be adjusted to 20kV, and the secondary current density can reach 0.1mA / m. 2 The current corresponding to a power supply is approximately 300mA / m. 2 The corresponding effective power is 6kW.

[0057] Therefore, by using the cathode wire of this invention in the front-end electric field of the electrostatic precipitator, the required secondary current density can be achieved at a lower secondary voltage, thereby reducing energy consumption by more than 30% while ensuring dust removal efficiency. For example... Figure 2 As shown.

[0058] Similarly, when the unit needs to operate at full load or when burning low-quality coal, a large current discharge is required in the front-end electric field of the electrostatic precipitator to ensure dust removal efficiency. At 60kV, the secondary current of the barbed wire (hot-dip galvanized cathode wire) of this invention can reach 0.5mA / m. 2 Compared to the secondary current of 0.4 mA / m in the barbed wire of conventional SPCC material, 2 The corona discharge photographs of the barbed wire (hot-dip galvanized cathode wire) and the SPCC material barbed wire of the present invention at 60kV are shown below. Figure 3 , Figure 4 As shown. Therefore, by using the hot-dip galvanized cathode wire of the present invention, the dust removal efficiency of the electrostatic precipitator is higher.

[0059] Example 2

[0060] In this embodiment, the first zinc plating layer comprises the following components by mass percentage: 0.25% aluminum, 0.01% tungsten, 0.03% molybdenum, 0.03% chromium, 0.02% ZrO, 1.0% MgO, 0.01% rare earth oxides (including 0.002% La2O3, 0.003% Y2O3, and 0.005% CeO2), with the balance being Zn and unavoidable impurities. The second zinc plating layer comprises the following components by mass percentage: 0.15% aluminum, 0.015% molybdenum, 0.015% chromium, with the balance being Zn and unavoidable impurities.

[0061] Compared to Example 1, although the discharge performance of Example 2 is slightly reduced, the cost is lower and the corrosion resistance is better. Compared to Example 1, by using the cathode wire of Example 2, the secondary voltage only needs to be adjusted to 25kV to achieve the minimum secondary current value, and the secondary current density can reach 0.1mA / m. 2 The current corresponding to a power supply is approximately 300mA / m. 2 The corresponding effective power is 7.5kW.

[0062] See Figure 5 This invention discloses a method for preparing the above-mentioned hot-dip galvanized cathode wire for an electrostatic precipitator, comprising the following steps:

[0063] S1. Press-shear forming: Press-shearing SPCC plates to form spiked flat plates;

[0064] S2. Pressing and molding: Pressing the spiked plate to form three-dimensional spikes;

[0065] S3. Preheating and Galvanizing: The pressed and formed barbs are placed in a zinc bath, and a certain amount of aluminum, tungsten, molybdenum, chromium, ZrO, MgO, and rare earth oxides are added to the zinc bath, using the following mass percentages: aluminum 0.15-0.25%, tungsten 0.01-0.02%, molybdenum 0.02-0.03%, chromium 0.01-0.03%, ZrO 0.008-0.02%, MgO 0.05-1.2%, rare earth oxides 0.008-0.016% (including La2O3 0.002-0.005%, Y2O3 0.003-0.005%, CeO2 0.003-0.006%), with the balance being Zn and unavoidable impurities; after exiting the zinc bath, a first zinc coating layer is formed on the surface of the barbs; see reference. Figure 6 During the zinc bath with barbs, rotate the barbs 90° along their axis until they are horizontal (corresponding to...). Figure 6 (b. Zinc bath state), after the zinc bath is complete, rotate the barb again so that the needles face downwards when the zinc liquid is discharged (corresponding to...). Figure 6 c. The state of zinc liquid exiting (the purpose is to make the condensation state of the zinc liquid consistent with the direction of the barb tip, so as to improve the efficiency of corona discharge. After exiting the zinc liquid, cool for 3-8 seconds and keep the barb needles pointing downwards to vibrate the remaining zinc.

[0066] S4. Welding and forming: Weld the preheated galvanized barbs to the connecting parts on both sides of the support pipe to form a cathode wire;

[0067] S5. Overall hot-dip galvanizing: The cathode wire is subjected to a zinc bath, and a certain amount of aluminum, molybdenum and chromium are added to the zinc bath, using the following mass percentages: aluminum 0.12~0.2%, molybdenum 0.01~0.02%, chromium 0.001~0.105%, with the balance being Zn and unavoidable impurities; after exiting the zinc bath, a second zinc coating is formed on the surface of the barbs and support tube.

[0068] Because the barbs have a small surface area and the central tube has a large area, preheating and galvanizing the barbs can reduce the amount of zinc liquid used, thus lowering costs. Preheating and galvanizing improves discharge efficiency and gives the cathode wire higher corrosion resistance. Depending on environmental requirements, different formulations are used for the preheating and galvanizing of the barbs and the overall hot-dip galvanizing of the cathode wire to reduce costs and achieve the desired effects. This invention employs a two-stage process of preheating and galvanizing the barbs and the overall hot-dip galvanizing, which can achieve the required performance targets at a low cost. Furthermore, under different flue gas conditions of the electrostatic precipitator (such as flue gas from coal-fired sludge co-firing, paper mill alkali furnaces, and high-moisture coal), different proportions of the two galvanizing layers can be used to adapt to the corrosive effects of different flue gas components.

[0069] The above embodiments are illustrative of the present invention and are not intended to limit the present invention. Any simple modifications to the present invention are within the scope of protection of the present invention.

Claims

1. An electrostatic precipitator hot galvanized cathode wire comprising a support tube and a plurality of spines welded to the support tube, characterized in that: The outer surface of the thorn is sequentially provided with a first galvanized layer and a second galvanized layer from inside to outside, the outer surface of the support pipe is provided with the second galvanized layer, the first galvanized layer comprises the following components: aluminum, tungsten, molybdenum, chromium, ZrO, MgO, rare earth oxide and Zn, and the second galvanized layer comprises the following components: aluminum, molybdenum, chromium and Zn.

2. An electric dust precipitator hot galvanized cathode wire as defined in claim 1, characterized in that: The first galvanized layer is composed of the following components in mass percentage: aluminum 0.15-0.25%, tungsten 0.01-0.02%, molybdenum 0.02-0.03%, chromium 0.01-0.03%, ZrO 0.008-0.02%, MgO 0.05-1.2%, rare earth oxide 0.008-0.016%, and the balance of Zn and inevitable impurities.

3. An electric dust precipitator hot galvanized cathode wire as defined in claim 2, characterized in that: The rare earth oxide comprises La2O3, Y2O3 and CeO2, and the mass ratio of La2O3, Y2O3 and CeO2 is 2-5:3-5:3-6.

4. An electric dust precipitator hot galvanized cathode wire as defined in claim 1, characterized in that: The second galvanized layer is composed of the following components in mass percentage: aluminum 0.12-0.2%, molybdenum 0.01-0.02%, chromium 0.001-0.015%, and the balance of Zn and inevitable impurities.

5. An electric dust precipitator hot galvanized cathode wire as defined in claim 1, characterized in that: The content of aluminum, molybdenum and chromium in the second galvanized layer is lower than that in the first galvanized layer.

6. An electric dust precipitator hot galvanized cathode wire as defined in claim 1, characterized in that: The material of the support pipe and the thorn is low-carbon steel SPCC.

7. A method of producing an electric dust precipitator hot galvanized cathode wire as claimed in any one of claims 1 to 6, characterized in that: The method comprises the following steps: S1. Press-shear forming: SPCC plates are press-sheared into thorn-shaped flat plates; S2. Press forming: the thorn-shaped flat plates are pressed to form three-dimensional thorns; S3. Preheating galvanizing: the press-formed thorns are subjected to zinc bath, and a certain amount of aluminum, tungsten, molybdenum, chromium, ZrO, MgO and rare earth oxide is added in the zinc bath, so that the first galvanized layer is formed on the surface of the thorn after the zinc liquid is discharged; S4. Welding forming: the thorn after preheating galvanizing is welded with the connecting portions on both sides of the support pipe to form a cathode wire; S5. Overall hot galvanizing: the cathode wire is subjected to zinc bath, and a certain amount of aluminum, molybdenum and chromium is added in the zinc bath, so that the second galvanized layer is formed on the surface of the thorn and the support pipe after the zinc liquid is discharged.

8. A method of making an electric dust precipitator hot galvanized cathode wire as defined in claim 7, characterized in that: In step S3, the following mass percentages of tungsten, molybdenum, chromium, ZrO, MgO and rare earth oxide are added in the zinc bath: aluminum 0.15-0.25%, tungsten 0.01-0.02%, molybdenum 0.02-0.03%, chromium 0.01-0.03%, ZrO 0.008-0.02%, MgO 0.05-1.2%, rare earth oxide 0.008-0.016%, and the balance of Zn and inevitable impurities.

9. A method of making an electric dust precipitator hot galvanized cathode wire as defined in claim 7, characterized in that: In step S5, the following mass percentages of aluminum, molybdenum and chromium are added in the zinc bath: aluminum 0.12-0.2%, molybdenum 0.01-0.02%, chromium 0.001-0.015%, and the balance of Zn and inevitable impurities.

10. A method of making an electric dust precipitator hot galvanized cathode wire as defined in claim 7, characterized by: In step S3, when the thorn is subjected to zinc bath, the thorn is rotated by 90° along its axis to a horizontal state, and the thorn is rotated again after the zinc bath is completed, so that the needle of the thorn faces downward when the zinc liquid is discharged, and the thorn is vibrated for 3-8 seconds after the zinc liquid is discharged to keep the needle of the thorn facing downward.

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