Method of making and using a 690 alloy electrode for joule heating ceramic furnaces

Abstract

A kind of 690 alloy electrode for joule heating ceramic furnace and its using method, including the mechanical processing of 690 alloy electrode, laser welding and high temperature annealing treatment, the long-term working temperature of the electrode is 1150 DEG C, up to 1200 DEG C at most, the electrode has the advantages of good cooling effect, small stress, corrosion resistance, long service life etc.

Description

Technical Field

[0001] This invention relates to the field of nuclear waste vitrification technology, specifically to the fabrication and application method of a 690 alloy electrode for a Joule-heated ceramic furnace. Background Technology

[0002] Glass has excellent physical and chemical durability and good containment capacity for actinides, strontium, cesium, zirconium and molybdenum, making it the preferred matrix for fixing long-lived and highly radioactive waste.

[0003] Since the 1950s, extensive and in-depth research has been conducted globally on the vitrification of radioactive waste. In 1978, France's first high-level radioactive waste vitrification plant began operation in Macour, employing induction heating crucible technology. Subsequently, vitrification plants in Germany, Russia, the United Kingdom, the United States, and other countries also commenced commercial operation, primarily using Joule-heated ceramic furnace technology.

[0004] Common electrode materials used in Joule-heated ceramic furnaces include molybdenum, tin oxide, and graphite, but all of them present challenges in resisting corrosion within molten glass. Especially with the increasing burnup of fuel rods in my country's nuclear power plants, higher requirements are being placed on the operating temperature, service life, and corrosion resistance of the electrodes.

[0005] Ni-Cr-Fe high-temperature alloy (690 alloy) has excellent corrosion resistance and can operate at a maximum temperature of 1200℃. With internal air cooling, its corrosion rate can be as low as 2 mm / year.

[0006] Alloy electrodes have the following problems during long-term service:

[0007] (1) The design of the cooling channel is unreasonable, which leads to poor local cooling effect of the alloy and short service life of the alloy;

[0008] (2) When the cooling channel uses traditional welding process, it is very easy to have uneven weld points, pinholes or impurities, which will cause corrosion on the back of the electrode and affect the long-term use of the electrode.

[0009] (3) Residual stress exists during machining, which causes the alloy electrode to deform when used at high temperature, resulting in excessive local current density and corrosion, affecting service life. Summary of the Invention

[0010] The purpose of this invention is to address the requirements of high temperature resistance and corrosion resistance in the vitrification of nuclear waste by designing a cooling gas path and using laser welding technology and high temperature annealing to produce a 690 alloy electrode for a Joule-heated ceramic furnace. This electrode has a long-term operating temperature of 1150℃ and can reach a maximum of 1200℃.

[0011] The technical solution of the present invention is as follows:

[0012] A method for manufacturing a 690 alloy electrode for a Joule-heated ceramic furnace, characterized by including machining, laser welding and high-temperature annealing of the 690 alloy electrode.

[0013] The machining of the 690 alloy electrode includes the fabrication of a 690 alloy electrode block, cooling channels, a 690 alloy cover plate, a 690 alloy electrode connecting pipe, and a 690 alloy inlet / outlet air pipe.

[0014] The 690 alloy electrode block is divided into a front and a back. The front contacts the molten glass, and the back is in close contact with the refractory brick.

[0015] The front surface of the 690 alloy electrode block is either a flat surface or a non-flat surface with a certain curvature, with most of them being flat surfaces.

[0016] The back of the 690 alloy electrode block has evenly distributed cooling grooves, and the cooling grooves are covered with 690 alloy cover plates.

[0017] The 690 alloy cover plate is a thin sheet produced by wire cutting and processing.

[0018] The 690 alloy electrode connecting tube includes a 690 alloy outer connecting tube and a 690 alloy inner connecting tube.

[0019] The 690 alloy inlet and outlet pipes are respectively connected to the inlet pipe and outlet pipe of the 690 alloy electrode external connecting pipe and the 690 alloy electrode internal connecting pipe.

[0020] The cooling channel is characterized in that the area of ​​the cooling channel occupies between 1 / 3 and 1 / 2 of the surface area of ​​the electrode block. If the area of ​​the channel is too small, the optimal cooling effect will not be achieved; if the area of ​​the channel is too large, the overall strength of the electrode will decrease.

[0021] The cooling channel is characterized in that the depth of the cooling channel is between 1 / 4 and 2 / 3 of the thickness of the electrode block. If the depth is too small, the optimal cooling effect will not be achieved; if the depth is too large, the service life of the electrode will be reduced.

[0022] The 690 alloy connecting pipe is characterized in that the ratio of the cross-sectional area of ​​the outer connecting pipe and the inner connecting pipe of the 690 alloy electrode is between 1.4 and 1.8. If the ratio of the cross-sectional area of ​​the outer connecting pipe and the inner connecting pipe of the 690 alloy electrode is too large or too small, it will affect the flow of the cooling medium, thereby adversely affecting the cooling effect of the alloy electrode.

[0023] The 690 alloy electrode block is characterized in that its four sides are chamfered with a radius of 0.5–1.5 mm. Adding chamfers around the edges prevents point discharge from the electrode, which could cause localized overheating and accelerate the corrosion rate of the alloy electrode.

[0024] The 690 alloy electrode block is characterized by a surface roughness better than 3.2 μm on its front side. Excessive surface roughness can cause preferential corrosion of the electrode surface by the high-temperature glass at processing defects such as pits and scratches, thus adversely affecting the service life of the alloy electrode.

[0025] The laser welding method described above is characterized in that the welding between the cooling channel and the 690 alloy cover plate, between the 690 alloy electrode connecting pipe and the 690 alloy electrode block, and between the 690 alloy inlet / outlet pipe and the 690 alloy electrode connecting pipe is laser welding.

[0026] The laser wavelength for laser welding is 1064nm or 532nm, preferably 1064nm;

[0027] The laser power for laser welding is 2 to 5 kW, preferably 3 to 4 kW;

[0028] The diameter of the laser spot used in the laser welding is 0.2–0.5 mm, preferably 0.3 mm;

[0029] The laser welding rate is 10-50 mm / s, preferably 30-40 mm / s.

[0030] The high-temperature annealing treatment is characterized by performing high-temperature heat treatment at a temperature of 600-800°C after the electrodes have been laser welded.

[0031] The method of using the 690 alloy electrode is characterized by the following steps:

[0032] 1) Install two 690 alloy electrodes from the side of the Joule furnace facing directly at a distance of 0-20cm above the furnace bottom. Fill the back with refractory bricks and connect them via the aforementioned 690 alloy electrode external connecting pipe or

[0033] The 690 alloy electrode internal connecting tube is connected to the electrode (copper busbar), and is connected to the cold gas (compressed air, nitrogen or argon) source through the inlet and outlet pipes, and is connected to AC power. The upper and lower limits of the glass liquid level are set, and the ratio of adding radioactive waste liquid and basic glass beads is set.

[0034] 2) Turn on the air conditioning and control the airflow rate to 2-10 m³ / h. 3 / h, pressure between 0.2 and 0.6 MPa;

[0035] 3) Use an auxiliary heater (silicon carbide rod) on the furnace top to raise the temperature inside the Joule furnace to above 800°C;

[0036] 4) Add starting glass beads or glass molten metal into the Joule furnace until the initial liquid level of the molten metal completely submerges the entire 690 alloy electrode block, and the liquid level is slightly higher than the uppermost edge of the 690 alloy electrode block.

[0037] 2-3cm;

[0038] 5) When the electrode temperature reaches above 500℃, connect the AC power and slowly increase the power or current, ensuring that the current density (electrode current / surface area of ​​the 690 alloy electrode front side) does not exceed 0.8A / cm². 2 ;

[0039] 6) Use current or power as the setpoint SV and glass melt temperature as the feedback signal PV to perform PID closed-loop control, ensuring that the glass melt temperature is controlled within the range of 1150℃±50℃.

[0040] 7) According to the set waste oxide inclusion rate in the cured glass, add radioactive waste liquid and basic glass beads or glass calciner into the Joule furnace for high-temperature glass melting;

[0041] 8) When the glass melt level reaches the upper limit, the Joule furnace begins to discharge the material;

[0042] 9) When the glass liquid level reaches the lower limit, return to step 7); after receiving the stop instruction, proceed to the next step;

[0043] 10) The Joule oven stops working.

[0044] Compared with the prior art, the beneficial effects of the present invention are:

[0045] 1) The 690 alloy electrode is designed with a cooling groove with appropriate groove area and groove depth to improve the cooling effect and uniformity of the cooling medium on the electrode. The temperature distribution on the front surface of the electrode is uniform, there is no local overheating, and the service life of the electrode is extended.

[0046] 2) Laser welding has advantages over traditional argon arc welding or other welding methods, such as high welding efficiency, uniform weld, fewer welding defects, low thermal stress, and small welding deformation.

[0047] 3) After machining and laser welding are completed, high-temperature heat treatment is performed to further eliminate the mechanical stress generated during machining and the thermal stress generated during laser welding. Attached Figure Description

[0048] Figure 1 This is a general view of the 690 alloy electrode of the present invention;

[0049] In the diagram: 1—690 alloy electrode block; 2—cooling channel; 3—690 alloy cover plate; 4—690 alloy electrode external connecting pipe; 5—690 alloy electrode internal connecting pipe; 6—690 alloy air inlet pipe; 7—690 alloy air outlet pipe.

[0050] Figure 2 This is a diagram of the 690 alloy electrode block before welding the 690 alloy cover plate according to the present invention;

[0051] Figure 3 This is a diagram of the 690 alloy electrode block before welding the 690 alloy connecting pipe according to the present invention;

[0052] Figure 4 This is a diagram of the 690 alloy cover plate of the present invention.

[0053] Figure 5 Current and voltage operating curves for 690 alloy electrodes over 720 hours. Detailed Implementation

[0054] To enable those skilled in the art to better understand the present invention, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] The terms "first," "second," "third," "fourth," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may include steps or units not listed.

[0056] Please refer to Figure 1-4 As shown in the figure, the 690 alloy electrode includes a 690 alloy electrode block 1, a cooling channel 2, a cooling channel cover plate 3, an external electrode connecting pipe 4, an internal electrode connecting pipe 5, an air inlet pipe 6, and an air outlet pipe 7. The 690 alloy electrode block is divided into a front and a back. The front is in contact with the molten glass, and the back is close to the refractory brick. The front of the 690 alloy electrode block 1 is either a flat surface or a non-flat surface with a certain curvature, but mostly a flat surface is used.

[0057] The back of the 690 alloy electrode block has evenly distributed cooling channels 2, and the cooling channels are covered with 690 alloy cover plates 3.

[0058] The 690 alloy electrode connecting tube includes a 690 alloy outer connecting tube 4 and a 690 alloy inner connecting tube 5;

[0059] The 690 alloy inlet and outlet pipes are respectively connected to the inlet pipe 6 and outlet pipe 7 on the outer connecting pipe and inner connecting pipe of the 690 alloy electrode.

[0060] Example 1

[0061] The dimensions of the 690 alloy electrode are 200×100×50mm. The grooved area of ​​the cooling channel occupies 2 / 5 of the surface area of ​​the electrode block. The groove depth is 25mm, which is 1 / 2 of the electrode block thickness. The outer diameter of the 690 alloy electrode outer connecting pipe is 32mm, and the outer diameter of the 690 alloy electrode inner connecting pipe is 25mm. The 690 alloy electrode block is chamfered around its perimeter with a chamfer radius of 1mm. During processing, the surface roughness of the 690 alloy electrode block is ensured to be 1.6μm. Laser welding is used for the welding between the cooling channel and the 690 alloy cover plate, between the 690 alloy electrode connecting pipe and the 690 alloy electrode block, and between the 690 alloy inlet / outlet pipe and the 690 alloy electrode connecting pipe; the laser wavelength is selected as 1064nm, the laser power is 3kW, the laser spot diameter is 0.3mm, and the welding speed is 30mm / s.

[0062] After laser welding, the 690 alloy electrode is subjected to high-temperature heat treatment at 700℃ for 4 hours.

[0063] The method of using 690 alloy electrodes includes the following steps:

[0064] 1) Install the 690 alloy electrode in the Joule furnace at a distance of about 10cm from the bottom, fill the back of the electrode with refractory bricks, and connect the AC power.

[0065] 2) Turn on the air conditioning and control the airflow to 4m³ / h. 3 / h, pressure at 0.4MPa;

[0066] 3) Use an auxiliary heater (silicon carbide rod) on the furnace top to raise the temperature inside the Joule furnace to above 800°C;

[0067] 4) Add starting glass beads or glass molten material into the Joule furnace to ensure that the initial liquid level after melting is 2-3 cm higher than the upper edge of the 690 alloy electrode block;

[0068] 5) When the electrode temperature reaches above 500℃, connect the AC power and slowly increase the power or current, ensuring that the current density (electrode current / surface area of ​​the 690 alloy electrode front side) does not exceed 0.8A / cm². 2 ;

[0069] 6) Use current or power as SV (set value) and glass melt temperature as PV (feedback signal) to perform PID closed-loop control to ensure that the glass melt temperature is controlled within the range of 1150℃±50℃.

[0070] 7) According to the set waste oxide inclusion rate in the cured glass, add radioactive waste liquid and basic glass beads or glass calciner into the Joule furnace for high-temperature glass melting;

[0071] 8) When the glass liquid level reaches the upper limit, start feeding until the glass liquid level reaches the lower limit;

[0072] 9) Continue adding radioactive waste liquid and basic glass beads or glass clinker into the Joule furnace. When the glass liquid level reaches the upper limit, proceed to the next round of material discharge.

[0073] Figure 5 The graph shows the current and voltage operating curves of the 690 alloy electrode after 720 hours. It can be seen from the graph that the electrode operating parameters are normal, and no obvious corrosion was observed on either electrode after the furnace was shut down.

Claims

1. A method of making a 690 alloy electrode for a joule heated ceramic furnace, characterized by: The method comprises the following steps: 1) the mechanical processing of the 690 alloy electrode, including the manufacture of a 690 alloy electrode block (1), a cooling channel (2), a 690 alloy cover plate (3), a 690 alloy electrode outer connecting pipe (4), a 690 alloy electrode inner connecting pipe (5), a 690 alloy gas inlet pipe (6) and a gas outlet pipe (7), the 690 alloy electrode block (1) being divided into a front surface and a back surface, the front surface being in contact with the glass liquid and the back surface being in close contact with the refractory brick; the front surface of the 690 alloy electrode block (1) being a flat surface or a non-flat surface with a certain curvature, the surface roughness of the front surface of the 690 alloy electrode block (1) being better than 3.2 μm; the back surface of the 690 alloy electrode block (1) being provided with uniformly distributed cooling channels (2), the opening area of the cooling channels (2) accounting for 1 / 3-1 / 2 of the surface area of the front surface of the electrode block, the opening depth of the cooling channels (2) accounting for 1 / 4-2 / 3 of the thickness of the electrode block, and the cooling channels (2) being covered with the 690 alloy cover plate (3); the 690 alloy cover plate (3) being an integral piece after wire cutting and processing; 2) the gas inlet pipe (6) and the gas outlet pipe (7) being respectively connected with the outer connecting pipe (4) and the 690 alloy electrode inner connecting pipe (5) by laser welding between the cooling channels (2) and the 690 alloy cover plate (3), the cross-sectional area ratio of the 690 alloy electrode outer connecting pipe (4) and the 690 alloy electrode inner connecting pipe (5) being 1.4-1.8; 3) after the completion of laser welding of the electrode, high-temperature heat treatment is performed at a temperature of 600-800 °C.

2. The method of claim 1, wherein: the 690 alloy electrode block (1) being chamfered around, and the chamfering radius being 0.5-1.5 mm.

3. The method of claim 1, wherein: the laser wavelength of the laser welding being 1064 nm or 532 nm; the laser power of the laser welding being 2-5 kW; the laser spot diameter of the laser welding being 0.2-0.5 mm; and the welding speed of the laser welding being 10-50 mm / s.

4. The method of claim 1, wherein the method further comprises: the laser wavelength of the laser welding being 1064 nm; the laser power of the laser welding being 3-4 kW; the laser spot diameter of the laser welding being 0.3 mm; and the welding speed of the laser welding being 30-40 mm / s.

5. The method of using a 690 alloy electrode for a joule-heated ceramic furnace according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: 1) two 690 alloy electrodes are respectively installed from the two opposite sides of the Joule furnace at a position of 0-20 cm above the furnace bottom, the back surface is filled with refractory bricks, and the electrodes are connected with the electrodes through the 690 alloy electrode outer connecting pipe (4) or the 690 alloy electrode inner connecting pipe (5), connected with the cold gas source through the gas inlet pipe (6) and the gas outlet pipe (7), and connected with the alternating current, the upper and lower limit values of the glass liquid level are set, and the proportion of the added radioactive waste liquid and the base glass beads is set; 2) Turn on the cooling gas, the flow of which is controlled at 2-10 m 3 / h, and the pressure at 0.2-0.6 MPa. 3) the temperature in the Joule furnace is raised to above 800 °C by using the auxiliary heater at the top of the furnace; 4) Add starting glass beads or glass frit into the Joule furnace until the initial liquid level after melting of the frit completely submerges the whole 690 alloy electrode block and the liquid level is 2-3 cm higher than the uppermost edge of the 690 alloy electrode block; 5) When the electrode temperature reaches 500°C or above, turn on the AC power, slowly increase the power or current, and make sure the current density does not exceed 0.8 A / cm 2 ; 6) Use current or power as the set value SV and the glass liquid temperature as the feedback signal PV to perform PID closed-loop control to ensure that the glass liquid temperature is controlled within the range of 1150℃±50℃; 7) According to the set waste oxide containment rate in the solidified glass, add radioactive waste liquid and base glass beads or glass frit into the Joule furnace to perform high-temperature glass melting; 8) When the glass liquid level reaches the upper limit, the Joule furnace starts to discharge; 9) When the glass liquid level reaches the lower limit, return to step 7); when the instruction to stop is accepted, proceed to the next step; 10) The Joule furnace stops working.

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