A method and device for recovering waste heat from smelting flue gas of electrically fused magnesium oxide and preheating raw materials

Abstract

The application provides a method and device for recovering waste heat of smelting flue gas of electric smelting magnesium oxide and preheating raw materials, which comprises a stock bin, a cyclone dust collector, a furnace body of an electric arc furnace, a furnace cover and a bag-type dust collector. The furnace cover is arranged above the furnace body of the electric arc furnace and is provided with a dust removal rising pipe. The other end of the dust removal rising pipe is connected with the cyclone dust collector. The flue gas outlet of the cyclone dust collector is connected with the bag-type dust collector through a dust removal descending pipe. The material outlet of the cyclone dust collector feeds the electric arc furnace body through a cyclone downspout. The feeder at the bottom of the stock bin is connected with a feeding control valve. The feeding control valve feeds the electric arc furnace body through a first feeding downspout and is connected with the dust removal rising pipe through a second feeding downspout. The first feeding downspout or the second feeding downspout is selected according to the flue gas temperature of the dust removal rising pipe. The method and device for recovering waste heat of smelting flue gas of electric smelting of magnesium oxide and preheating raw materials have the advantages of remarkable energy-saving effect, simple structure, low investment, easy transformation and high automation degree.

Description

Technical Field

[0001] This invention relates to a method for smelting fused magnesium oxide, and more particularly to a method and apparatus for recovering waste heat from flue gas and preheating raw materials in fused magnesium oxide smelting. Background Technology

[0002] Fused magnesia is a high-purity magnesium oxide product obtained by high-temperature smelting of magnesite or other magnesium-containing raw materials in an electric arc furnace. Due to its advantages such as high melting point, high refractoriness, and good thermal stability, it is widely used in refractory materials, electrical insulation materials, and other fields. Large-crystal fused magnesia, in particular, requires high crystal size control and more stringent smelting process control.

[0003] In the traditional production process of large-crystal fused magnesia, raw material powder is directly fed from the upper silo into the smelting furnace below via a feeder. The smelting process generates a large amount of high-temperature, dust-laden flue gas, which is drawn away through dust collection pipes on the furnace lid side. The dust collection system typically includes a cyclone dust collector and a terminal bag filter: the cyclone dust collector effectively separates and collects coarse dust particles from the flue gas, and the collected dust flows back to the furnace from below the cyclone dust collector via a flap valve; the flue gas containing a small amount of fine dust is further drawn to the terminal bag filter for final purification.

[0004] The existing technology has the following problems:

[0005] (1) Serious energy waste. In the later stages of fused magnesium oxide smelting, the furnace temperature can reach 2500-3000℃, and the flue gas temperature is extremely high. The hot flue gas can even heat the steel plate of the flue pipe near the furnace cover to a red-hot state. This part of high-quality heat energy is not currently being effectively utilized and is being directly emitted, resulting in a large amount of energy waste. It is estimated that the waste heat carried away by the flue gas accounts for 15%-25% of the total energy consumption of smelting.

[0006] (2) Baghouse dust collectors are prone to damage. In the later stages of smelting, the temperature of the flue gas can exceed the withstand temperature of the baghouse dust collector filter bags (usually 180-260℃). High-temperature flue gas directly entering the baghouse dust collector will cause the filter bags to burn out and fail, seriously affecting the dust removal effect and production continuity. At present, the method of mixing cold air to cool down is often used, but this will further waste heat energy and increase the system load.

[0007] (3) Low raw material temperature. In traditional processes, raw material powder is directly fed into the furnace from room temperature, which requires a lot of electricity to heat the raw material from room temperature to the melting temperature, prolonging the smelting time and increasing electricity consumption.

[0008] In the prior art, CN112683059A discloses a preheating submerged arc furnace for producing large-crystal fused magnesia, which uses a chain grate system to preheat the raw materials. However, this solution requires the configuration of complex equipment such as chain grate machines, resulting in high investment costs, large floor space requirements, and high operation and maintenance costs for the chain grate machine system, making it difficult to implement at low cost on existing production lines.

[0009] Therefore, there is an urgent need to develop a method and device for recovering waste heat from molten magnesium oxide smelting flue gas and preheating raw materials that is simple in structure, requires low investment, is easy to modify, and has significant energy-saving effects. Summary of the Invention

[0010] This invention provides a method and apparatus for waste heat recovery and raw material preheating from flue gas in fused magnesium oxide smelting. It solves the problem of effectively recovering waste heat from high-temperature flue gas in fused magnesium oxide smelting without adding complex equipment, achieving raw material preheating, and simultaneously reducing flue gas temperature to protect the bag filter. The technical solution is as follows:

[0011] A waste heat recovery and raw material preheating device for fused magnesium oxide smelting flue gas includes a silo, a cyclone dust collector, a submerged arc furnace body, a furnace cover, and a bag filter. The furnace cover is located above the submerged arc furnace body and is equipped with a dust removal riser pipe for dust removal. The other end of the dust removal riser pipe is connected to the cyclone dust collector. The flue gas outlet of the cyclone dust collector is connected to the bag filter through a dust removal downcomer pipe. The material outlet of the cyclone dust collector feeds material to the submerged arc furnace body through a cyclone discharge chute. A feeder at the bottom of the silo is connected to a feed control valve. The feed control valve feeds material to the submerged arc furnace body through a first feed chute and is connected to the dust removal riser pipe through a second feed chute. The first or second feed chute is selected to be opened based on the flue gas temperature of the dust removal riser pipe. The first feed chute and the cyclone discharge chute pass through the furnace cover.

[0012] The feeder is a star-shaped feeder connected to the bottom of the hopper and equipped with a variable frequency speed control motor to achieve feeding speed adjustment from 0 to 500 kg / h.

[0013] The first and second feed chutes use steel pipes with the same diameter D1, while the dust removal riser uses steel pipes with a diameter D2, and 2D1≤D2≤4D1.

[0014] The cyclone dust collector adopts the CLT / A type cyclone dust collector, and the diameter D3 is the same as the diameter D2 of the dust collection riser pipe.

[0015] The furnace cover is provided with electrode holes through which three electrodes pass, and feed holes for passing through the first feed chute and the cyclone discharge chute; the side of the furnace cover is provided with a flue gas outlet, which is connected to a dust removal riser pipe to draw out the high-temperature dust-laden flue gas generated during smelting.

[0016] A first temperature sensor, which is a type K thermocouple, is installed at the inlet of the dust removal rising pipe, 1m from the inlet of the dust removal rising pipe; a second temperature sensor, which is also a type K thermocouple, is installed at the inlet of the dust removal falling pipe, 0.5m from the inlet of the dust removal falling pipe.

[0017] It is also equipped with a control device to control the operation of the feeder and the feed control valve based on the temperature of the first temperature sensor and the second temperature sensor.

[0018] A method for waste heat recovery and raw material preheating from molten magnesium oxide smelting flue gas includes the following steps:

[0019] S1: Determine whether the flue gas temperature generated by the submerged arc furnace body has reached the first set temperature T1. If it has not reached the set temperature, adjust the feeding control valve so that the magnesite raw material powder can directly enter the interior of the submerged arc furnace body through the first feeding chute.

[0020] S2: After the flue gas temperature reaches the first set temperature T1, the magnesite raw material powder is changed to enter the flue gas dust removal riser pipe through the second feed chute. After gas-solid heat exchange with the flue gas, it enters the cyclone dust collector. The cyclone dust collector sends the separated magnesite raw material powder into the furnace body through the cyclone discharge chute.

[0021] S3: The cyclone dust collector separates the flue gas and sends it into the bag filter through the dust collector downcomer. The control device continuously monitors the temperature of the cooled flue gas through the second temperature sensor installed at the inlet of the dust collector downcomer and adjusts the feeding speed according to the temperature of the cooled flue gas.

[0022] S4: After smelting is completed, remove the electrodes and reduce the feeding speed of the star feeder to keep the magnesite raw material powder entering the dust removal rising pipe through the second feeding chute; lift the furnace cover and remove the submerged arc furnace body. When the flue gas temperature is lower than the first set temperature T1, turn off the cyclone dust collector and the star feeder.

[0023] Furthermore, in step S3, the feeding speed is adjusted according to the temperature of the cooled flue gas, and the adjustment steps are as follows;

[0024] S31: Determine whether the temperature of the cooled flue gas has reached the second set temperature T2. If it has, increase the feeding speed.

[0025] S32: Determine if the temperature of the cooled flue gas has not reached the second set temperature T2, nor fallen below the third set temperature T3, and maintain the current feeding speed; wherein the third set temperature T3 is lower than the second set temperature T2;

[0026] S33: Determine whether the temperature of the cooled flue gas is lower than the third set temperature T3. If it is lower, reduce the feeding speed.

[0027] The temperature of the preheated raw material powder is 200-500℃, the temperature of the flue gas after heat exchange is reduced by 100-400℃, the second set temperature T2 is 260℃, and the third set temperature T3 is 200℃.

[0028] The method and apparatus for waste heat recovery and raw material preheating of fused magnesium oxide smelting flue gas is an energy-saving method and apparatus for preheating raw materials entering the furnace using high-temperature smelting flue gas, and is particularly suitable for the production process of large-crystal fused magnesium oxide.

[0029] The present invention has the following beneficial effects:

[0030] (1) Significant energy-saving effect. This invention preheats the raw materials entering the furnace from room temperature to 200-500℃, which significantly reduces the electrical energy required for heating the raw materials after they enter the furnace and shortens the smelting time. According to calculations, it can reduce smelting power consumption by 10%-20%. Based on an annual production of 10,000 tons of fused magnesium oxide, the annual power saving is about 1.5-3 million kWh.

[0031] (2) Protect the bag filter. Through heat exchange between the raw material and the high-temperature flue gas, the flue gas temperature can be reduced by 100 to 400°C, which effectively prevents the high-temperature flue gas from burning the filter bags of the bag filter, extends the service life of the filter bags by 2 to 3 times, and reduces the operation and maintenance costs.

[0032] (3) Simple structure and low investment. This invention only requires the addition of raw material feed pipe and related control valves to the existing flue gas pipeline. It does not require the configuration of complex chain grate machine, heat exchanger and other equipment. The investment for the renovation is only 10% to 20% of that of the traditional waste heat recovery scheme.

[0033] (4) Easy to modify and does not affect production. It can be quickly modified and implemented on existing production lines without the need for major production stoppages. The modification cycle is short and does not affect normal production.

[0034] (5) High degree of automation. Automatic control is achieved through temperature sensors and control devices, and the feeding speed is automatically adjusted according to the flue gas temperature, making operation simple.

[0035] (6) Improve the efficiency of cyclone dust removal. After the raw material powder enters the cyclone dust collector with the flue gas, the particle concentration in the cyclone dust collector increases, which improves the separation efficiency of the cyclone dust collector to a certain extent.

[0036] (7) Raw materials are fed into the furnace evenly. After being separated by a cyclone dust collector, the preheated raw materials are fed into the furnace evenly, which avoids the furnace temperature fluctuation caused by concentrated input of raw materials and is conducive to the formation of large crystals. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the waste heat recovery and raw material preheating device for fused magnesium oxide smelting flue gas;

[0038] Figure 2 This is a schematic diagram of the structure of the furnace cover;

[0039] Figure 3 This is a top view of the feeder.

[0040] Figure 4 This is a schematic diagram of the process for waste heat recovery and raw material preheating of the molten magnesium oxide smelting flue gas.

[0041] Explanation of markings in the diagram:

[0042] 1-Hopper; 2-Feeder; 3-Feeding control valve; 4-First feed chute; 5-Second feed chute; 6-Dust collector riser; 7-Cyclone dust collector; 8-Flap valve; 9-Cyclone discharge chute; 10-Submerged arc furnace body; 11-Furnace cover; 12-First temperature sensor; 13-Second temperature sensor; 14-Dust collector downcomer; 15-Bag filter; 16-Exhaust fan; 17-Sealing gasket; 18-Sealing ring; 19-Flue gas vent; 20-Electrode; 21-First discharge hole; 22-Second discharge hole; 23-Variable frequency speed control motor; 24-Rotor; 25-Blade. Detailed Implementation

[0043] like Figure 1 As shown, the waste heat recovery and raw material preheating device for fused magnesium oxide smelting flue gas includes a silo 1, a cyclone dust collector 7, a submerged arc furnace body 10, a furnace cover 11, and a bag filter 15. The furnace cover 11 is located above the submerged arc furnace body 10 and is equipped with a dust removal riser pipe 6 for dust removal. The other end of the dust removal riser pipe 6 is connected to the cyclone dust collector 7. The flue gas outlet of the cyclone dust collector 7 is connected to the bag filter 15 through a dust removal downcomer pipe 14. The material outlet of 7 feeds material to the furnace body 10 of the electric arc furnace through the cyclone discharge chute 9; the feeder 2 at the bottom of the silo 1 is connected to the feed control valve 3, the feed control valve 3 feeds material to the furnace body 10 of the electric arc furnace through the first feed chute 4, and is connected to the dust removal riser 6 through the second feed chute 5. The first feed chute 4 or the second feed chute 5 is opened by selecting the flue gas temperature of the dust removal riser 6. The first feed chute 4 and the cyclone discharge chute 9 pass through the furnace cover 11.

[0044] like Figure 2As shown, the lower end of the submerged arc furnace body 10 is fixed on a trolley. The submerged arc furnace body 10 is a conventional electric arc furnace for fused magnesium, with a capacity of 1000 kVA. A furnace cover 11 is placed on top of the submerged arc furnace body 10. A ceramic fiber sealing gasket 17 is provided between the lower part of the furnace cover 11 and the top of the submerged arc furnace body 10. The top of the furnace cover 11 is a refractory material prefabricated component with electrode insertion holes. The gap between the electrode 20 and the electrode insertion hole is sealed with a ceramic fiber sealing ring 18. The opening of the ceramic fiber sealing ring is approximately the same size as the diameter of the electrode and is placed close to the electrode. The furnace cover 11 is also provided with a flue gas hole 19 and a discharge hole. The flue gas hole 19 is connected to the dust removal riser pipe 6 and is used to draw out the high-temperature dust-laden flue gas generated during smelting. There are two sets of discharge holes, namely a first discharge hole 21 and a second discharge hole 22, which are used to insert the first feed chute 4 and the cyclone discharge chute 9, respectively.

[0045] The silo 1 is installed above the furnace body 10 of the submerged arc furnace and is used to store magnesite raw material powder to be fed into the furnace. A feeder 2 is located at the bottom; the feeder 2 is a star-shaped feeder connected below the silo 1 and equipped with a variable frequency speed control motor, which can adjust the feeding speed from 0 to 500 kg / h. Figure 3 As shown, the working principle of the star-shaped feeder (also known as a rotary feeder or rotary valve) is as follows: A variable frequency speed-regulating motor 23 drives the main shaft through a reducer, causing a rotor 24 equipped with several blades 25 to rotate uniformly within the cylindrical housing. Material falls from the upper hopper (feed inlet) into the spaces (chambers) between the rotor blades by its own weight. As the rotor rotates, the carried material moves to the lower discharge port and is discharged by gravity or system pressure, thus achieving continuous and uniform material conveying. By adjusting the rotor speed, the feeding amount can be precisely controlled, achieving quantitative or real-time feeding. The rotor speed can be constant or variable. The star-shaped feeder is existing technology and will not be described in detail further.

[0046] The feeding control valve 3 has one inlet and two outlets. The inlet is connected to the material outlet of the feeder 2, and the two outlets are connected to the first feeding chute 4 and the second feeding chute 5, respectively. The feeding control valve 3 has an internal electrically controlled valve to control the selection of the two outlets of the first feeding chute 4 and the second feeding chute 5, ensuring that material can only flow out through one of the outlets. The chutes used for the first feeding chute 4 and the second feeding chute 5 are made of steel pipe with a diameter of Φ80mm. One end of the first feeding chute 4 is connected to one outlet of the feeding control valve 3, and the other end passes through the furnace cover 11 and enters the interior of the submerged arc furnace body 10, serving as a raw material feeding channel in the early stages of smelting. When the flue gas temperature is low (such as in the early stages of smelting), material can be fed directly into the submerged arc furnace body 10 through the first feeding chute 4. One end of the second feeding chute 5 is connected to the other outlet of the feeding control valve 3, and the other end extends into the dust removal riser pipe 6.

[0047] The dust removal riser pipe 6 is made of steel pipe with a diameter of Φ300mm, which is more than twice the diameter of the second feed chute 5. One end is connected to the flue gas outlet on the side of the furnace cover 11, and the other end is connected to the inlet of the cyclone dust collector 7. The connection point between the dust removal riser pipe 6 and the second feed chute 5 is 0.5 to 3m away from the furnace cover 11. Furthermore, the dust removal riser pipe 6 is connected to the flue gas hole 19 of the furnace cover 11 through a flue gas pipe, which is horizontally arranged and has a length of 20-50mm.

[0048] The cyclone dust collector 7 is a CLT / A type cyclone dust collector with a diameter of Φ600mm. Its inlet is connected to the dust collection riser pipe 6, and a flap valve 8 is installed at the bottom. The outlet of the flap valve 8 is connected to the cyclone discharge chute 9, which leads to the interior of the submerged arc furnace body 10. When the flap valve 8 sends the magnesite raw material powder collected by the cyclone dust collector 7 into the cyclone discharge chute 9, the magnesite raw material powder enters the submerged arc furnace body 10 through the cyclone discharge chute 9 for electrofusion.

[0049] The waste heat recovery and raw material preheating device for fused magnesium oxide smelting flue gas selects to open either the first feed chute 4 or the second feed chute 5 based on the flue gas temperature of the dust collector riser pipe 6. A temperature sensor needs to be installed in the dust collector riser pipe 6. Furthermore, a first temperature sensor 12, which is a K-type thermocouple, is installed at the inlet of the dust collector riser pipe 6, 1m from the inlet. A second temperature sensor 13, also a K-type thermocouple, is installed at the inlet of the dust collector fallr pipe 14, 0.5m from the inlet.

[0050] One end of the dust collection downcomer 14 is connected to the flue gas outlet of the cyclone dust collector 7, and the other end is connected to the bag filter 15. The inlet of the bag filter 15 is connected to the flue gas outlet of the cyclone dust collector 7 through the dust collection downcomer 14, and the flue gas from the cyclone dust collector 7 enters the bag filter 15 through the dust collection downcomer 14. The bag filter 15 is a pulse jet bag filter with a filtration area of ​​120 m², and the filter bag material is PTFE membrane filter media with a temperature resistance of 260℃. An induced draft fan 16 is installed at the other end of the bag filter 15. The induced draft fan 16 is located at the rear end of the bag filter, and the purified flue gas is discharged through the induced draft fan 16, realizing the induced draft treatment of the bag filter 15.

[0051] Furthermore, the waste heat recovery and raw material preheating device for fused magnesium oxide smelting flue gas is equipped with a control device. The control device adopts a PLC control device and is connected to the feeder 2, the feed control valve 3, the first temperature sensor 12, the second temperature sensor 13, etc., to realize automatic control. The operation of the feeder 2 and the feed control valve 3 is controlled according to the temperature of the first temperature sensor 12 and the second temperature sensor 13.

[0052] like Figure 2 As shown, the method for waste heat recovery and raw material preheating of fused magnesium oxide smelting flue gas includes the following steps:

[0053] Step S1: The control device uses the first temperature sensor 12 inside the dust removal riser pipe 6 to determine whether the temperature of the flue gas generated by the submerged arc furnace body 10 has reached the first set temperature T1. If it has not reached the set temperature, the feeding control valve 3 is adjusted, and the magnesite raw material powder enters the submerged arc furnace body 10 directly through the first feeding chute 4.

[0054] In the early stage of molten magnesium oxide smelting, the flue gas temperature generated by the submerged arc furnace 10 is relatively low (about 200 to 400°C). That is, when the flue gas temperature detected by the first temperature sensor 12 is lower than the first set temperature T1 (such as 400°C to 600°C, preferably 500°C), the control device adjusts the feeding control valve 3, and the magnesite raw material powder enters the interior of the submerged arc furnace 10 directly through the first feeding chute 4.

[0055] The initial feeding speed V1 is 100 kg / h, which shall not exceed the feeding speed V2 when switching to the second feeding chute.

[0056] Step S2: When the flue gas temperature generated by the submerged arc furnace body 10 reaches the first set temperature T1, adjust the feeding control valve 3. The magnesite raw material powder enters the flue gas dust removal riser pipe 6 through the second feeding chute 5. After gas-solid heat exchange with the flue gas, it enters the cyclone dust collector 7. The cyclone dust collector 7 sends the separated magnesite raw material powder into the interior of the submerged arc furnace body 10 through the cyclone discharge chute 9.

[0057] Specifically, it includes the following steps:

[0058] S21: When the temperature of the flue gas generated by the furnace body 10 of the electric arc furnace reaches the first set temperature T1, the feeding control valve 3 switches the discharge port to the second feeding chute 5.

[0059] In the later stages of fused magnesium oxide smelting, when the flue gas temperature generated by the furnace body 10 of the submerged arc furnace reaches the preset first set temperature T1, that is, when the flue gas temperature detected by the first temperature sensor 12 reaches the first set temperature T1, the control device adjusts the feeding control valve 3 to change the raw material powder to be fed into the furnace into the second feeding chute 5, and feeds it from the hopper 1 into the flue gas dust removal riser 6 near the furnace cover.

[0060] The second feeding chute 5 is connected to the flue gas dust removal riser 6 at a distance of 0.5 to 3 meters from the furnace cover 11, preferably 1 to 2 meters. At the same time, the feeder 2 is started with an initial feeding speed V2 of 200 kg / h to feed material into the dust removal riser 6.

[0061] S22: Magnesite raw material powder undergoes gas-solid heat exchange in the dust removal rising pipe 6;

[0062] The raw material powder is dispersed and suspended by the high-temperature flue gas entering the dust removal riser duct 6. The suspended raw material powder and the high-temperature flue gas are in full contact within the dust removal riser duct 6, and gas-solid heat exchange occurs, causing the raw material temperature to rise and the flue gas temperature to fall. The temperature of the preheated raw material powder is 200–500°C. The flue gas temperature decreases by 100–400°C after the heat exchange.

[0063] S23: The magnesite raw material powder after heat exchange enters the cyclone dust collector 7, is separated and then sent into the interior of the electric arc furnace 10.

[0064] After heat exchange, the flue gas carries the preheated raw material powder upward into the cyclone dust collector 7, which separates the preheated raw material powder from the flue gas. The separated preheated raw material powder is added into the interior of the electric arc furnace body 10 through the flap valve at the bottom of the cyclone dust collector 7 and the cyclone discharge chute 9.

[0065] Step S3: The cyclone dust collector 7 separates the flue gas and enters the bag dust collector 15 through the dust removal downcomer 14. The control device continuously monitors the temperature of the cooled flue gas through the second temperature sensor 13 installed at the inlet of the dust removal downcomer 14, and adjusts the feeding speed according to the temperature of the cooled flue gas.

[0066] After cooling, the flue gas enters the bag filter 15 through the dust collector downcomer 14 for final purification, and is then discharged into the atmosphere by the induced draft fan 16. The control device monitors the temperature of the cooled flue gas using the second temperature sensor 13 installed at the inlet of the dust collector downcomer 14 to adjust the feeding speed. The adjustment steps are as follows:

[0067] S31: Determine whether the temperature of the cooled flue gas has reached the second set temperature T2. If it has, increase the feeding speed.

[0068] The second set temperature T2 is used to determine whether the temperature entering the bag filter is too high. If the temperature is too high, it will damage the device. If the temperature is high, the feeding speed can be increased to achieve the purpose of cooling by exchanging heat with the powder. The feeding speed can be increased by increasing the rotation speed of the variable frequency motor of the feeder 2.

[0069] S32: Determine if the temperature of the cooled flue gas has not reached the second set temperature T2, nor fallen below the third set temperature T3, and maintain the current feeding speed; wherein the third set temperature T3 is lower than the second set temperature T2;

[0070] S33: Determine whether the temperature of the cooled flue gas is lower than the third set temperature T3. If it is lower, reduce the feeding speed.

[0071] Normally, as the temperature rises, the feeding speed is increased to lower the temperature detected by the second temperature sensor 13; correspondingly, if the flue gas temperature is lower than the third set temperature T3, the rotation speed of the variable frequency motor of the feeder 2 is reduced.

[0072] In this embodiment, the second set temperature T2 is 260°C and the third set temperature T3 is 200°C. When the temperature of the cooled flue gas is between the two, i.e., within the range of 200°C to 260°C, the current feeding speed is maintained.

[0073] Furthermore, by adjusting the feeding speed to control the temperature drop of the flue gas, the temperature of the flue gas entering the bag filter can be controlled between 50 and 200°C.

[0074] Step S4: After smelting is completed, remove the electrodes and reduce the feeding speed of the star feeder to keep the magnesite raw material powder entering the dust removal rising pipe 6 through the second feed chute 5; lift the furnace cover and remove the submerged arc furnace body 10. When the flue gas temperature is lower than the first set temperature T1, turn off the cyclone dust collector and the star feeder.

[0075] After smelting, electrode 20 is raised and extended out of the furnace cover. During the electrode raising process, the feeding speed of the star feeder can be reduced. At this time, the feeding speed V3 of the star feeder is half of the initial feeding speed V1. By continuing to feed material into the dust removal rising pipe 6, heat exchange between the material and the flue gas continues.

[0076] Furthermore, when raising the furnace cover, the feeding speed of the star feeder is gradually reduced. After the furnace cover 11 is raised, the submerged arc furnace body 10 is removed. At this time, when the flue gas temperature is lower than the first set temperature T1, the cyclone dust collector 7 and the star feeder 2 can be turned off.

[0077] In this embodiment, the waste heat recovery and raw material preheating device for fused magnesium oxide smelting flue gas includes a silo 1, a feeder 2, a feed control valve 3, a pre-feed chute 4, a post-feed chute 5, a dust removal riser 6, a cyclone dust collector 7, a flap valve 8, a cyclone discharge chute 9, a furnace body 10, a furnace cover 11, a first temperature sensor 12, a second temperature sensor 13, a dust removal downcomer 14, a bag filter 15, and an induced draft fan 16.

[0078] The method for recovering waste heat from molten magnesium oxide smelting flue gas and preheating raw materials using the above-mentioned device is as follows:

[0079] (1) Initial stage of smelting;

[0080] At the start of smelting, the flue gas temperature is relatively low (approximately 200–400°C). The control device adjusts the feed control valve to allow the raw material powder to be directly added into the furnace body 10 through the first feed chute.

[0081] (2) The middle and late stages of smelting;

[0082] When the first temperature sensor 12 detects that the flue gas temperature reaches 500℃, the control device automatically executes the following: adjusting the feeding control valve 3, changing the raw material inlet channel to the second feeding chute 5, and starting the feeder 2 to feed material into the dust collector riser pipe 6 at an initial feeding rate of 200kg / h. The raw material powder is dispersed and suspended in the dust collector riser pipe 6 by the high-speed flowing high-temperature flue gas.

[0083] (3) Gas-solid heat exchange process;

[0084] The suspended raw material powder comes into full contact with the high-temperature flue gas in the dust removal riser pipe 6, and gas-solid heat exchange occurs. The temperature of the raw material powder rises from room temperature to 300-500℃, while the temperature of the flue gas decreases from 500-700℃ to 100-200℃.

[0085] (4) Gas-solid separation process;

[0086] After heat exchange, the flue gas carrying the preheated raw material powder enters the cyclone dust collector 7. The cyclone dust collector 7 uses centrifugal force to separate solid particles from the flue gas. The separated preheated raw material powder is periodically added into the furnace body 10 through the flap valve 8 and the cyclone discharge chute 9.

[0087] (5) Flue gas purification process;

[0088] After cooling, the flue gas enters the bag filter 15 through the dust removal downcomer 14 for final purification, and is then discharged into the atmosphere by the induced draft fan 16.

[0089] (6) Automatic control process;

[0090] The control device continuously monitors the signal from the second temperature sensor 13: when the temperature is above 260°C, the feeding speed is increased; when the temperature is below 200°C, the feeding speed is decreased; when the temperature is within the range of 200°C to 260°C, the current feeding speed is maintained.

[0091] An industrial application test was conducted at an fused magnesia plant in Liaoning Province. The test results showed that:

[0092] (1) The power consumption per ton of product decreased from 2850 kWh to 2380 kWh, saving 16.5% of electricity;

[0093] (2) The smelting time has been reduced from 8.2 hours to 7.1 hours;

[0094] (3) The temperature of the flue gas entering the bag filter drops from 350-450℃ to 50-200℃;

[0095] (4) The filter bag replacement cycle is extended from 3-4 months to 10-12 months;

[0096] (5) The investment in equipment modification is about RMB150,000, and the investment payback period is less than 5 months.

[0097] The present invention has the following beneficial effects:

[0098] (1) Significant energy-saving effect. This invention preheats the raw materials entering the furnace from room temperature to 200-500℃, which significantly reduces the electrical energy required for heating the raw materials after they enter the furnace and shortens the smelting time. According to calculations, it can reduce smelting power consumption by 10%-20%. Based on an annual production of 10,000 tons of fused magnesium oxide, the annual power saving is about 1.5-3 million kWh.

[0099] (2) Protect the bag filter. Through heat exchange between the raw material and the high-temperature flue gas, the flue gas temperature can be reduced by 100 to 400°C, which effectively prevents the high-temperature flue gas from burning the filter bags of the bag filter, extends the service life of the filter bags by 2 to 3 times, and reduces the operation and maintenance costs.

[0100] (3) Simple structure and low investment. This invention only requires the addition of raw material feed pipe and related control valves to the existing flue gas pipeline. It does not require the configuration of complex chain grate machine, heat exchanger and other equipment. The investment for the renovation is only 10% to 20% of that of the traditional waste heat recovery scheme.

[0101] (4) Easy to modify and does not affect production. It can be quickly modified and implemented on existing production lines without the need for major production stoppages. The modification cycle is short and does not affect normal production.

[0102] (5) High degree of automation. Automatic control is achieved through temperature sensors and control devices, and the feeding speed is automatically adjusted according to the flue gas temperature, making operation simple.

[0103] (6) Improve the efficiency of cyclone dust removal. After the raw material powder enters the cyclone dust collector with the flue gas, the particle concentration in the cyclone dust collector increases, which improves the separation efficiency of the cyclone dust collector to a certain extent.

[0104] (7) Raw materials are fed into the furnace evenly. After being separated by a cyclone dust collector, the preheated raw materials are fed into the furnace evenly, which avoids the furnace temperature fluctuation caused by concentrated input of raw materials and is conducive to the formation of large crystals.

Claims

1. A device for waste heat recovery and raw material preheating from fused magnesium oxide smelting flue gas, characterized in that: The system includes a hopper, a cyclone dust collector, a submerged arc furnace body, a furnace cover, and a bag filter. The furnace cover is located above the submerged arc furnace body and is equipped with a dust removal riser pipe. The other end of the dust removal riser pipe is connected to the cyclone dust collector. The flue gas outlet of the cyclone dust collector is connected to the bag filter through a dust removal downcomer pipe. The material outlet of the cyclone dust collector feeds material to the submerged arc furnace body through a cyclone discharge chute. The feeder at the bottom of the hopper is connected to a feed control valve. The feed control valve feeds material to the submerged arc furnace body through a first feed chute and is connected to the dust removal riser pipe through a second feed chute. The first or second feed chute is selected to be opened based on the flue gas temperature of the dust removal riser pipe. The first feed chute and the cyclone discharge chute pass through the furnace cover.

2. The waste heat recovery and raw material preheating device for fused magnesium oxide smelting flue gas according to claim 1, characterized in that: The feeder is a star-shaped feeder connected to the bottom of the hopper and equipped with a variable frequency speed control motor to achieve feeding speed adjustment from 0 to 500 kg / h.

3. The waste heat recovery and raw material preheating device for fused magnesium oxide smelting flue gas according to claim 1, characterized in that: The first and second feed chutes use steel pipes with the same diameter D1, while the dust removal riser uses steel pipes with a diameter D2, and 2D1≤D2≤4D1.

4. The waste heat recovery and raw material preheating device for fused magnesium oxide smelting flue gas according to claim 3, characterized in that: The cyclone dust collector adopts the CLT / A type cyclone dust collector, and the diameter D3 is the same as the diameter D2 of the dust collection riser pipe.

5. The waste heat recovery and raw material preheating device for fused magnesium oxide smelting flue gas according to claim 1, characterized in that: The furnace cover is provided with electrode holes through which three electrodes pass, and feed holes for passing through the first feed chute and the cyclone discharge chute; the side of the furnace cover is provided with a flue gas outlet, which is connected to a dust removal riser pipe to draw out the high-temperature dust-laden flue gas generated during smelting.

6. The waste heat recovery and raw material preheating device for fused magnesium oxide smelting flue gas according to claim 1, characterized in that: A first temperature sensor, which is a type K thermocouple, is installed at the inlet of the dust removal rising pipe, 1m from the inlet of the dust removal rising pipe; a second temperature sensor, which is also a type K thermocouple, is installed at the inlet of the dust removal falling pipe, 0.5m from the inlet of the dust removal falling pipe.

7. The waste heat recovery and raw material preheating device for fused magnesium oxide smelting flue gas according to claim 1, characterized in that: It is also equipped with a control device to control the operation of the feeder and the feed control valve based on the temperature of the first temperature sensor and the second temperature sensor.

8. A method for waste heat recovery and raw material preheating from fused magnesium oxide smelting flue gas, characterized in that, Includes the following steps: S1: Determine whether the flue gas temperature generated by the submerged arc furnace body has reached the first set temperature T1. If it has not reached the set temperature, adjust the feeding control valve so that the magnesite raw material powder can directly enter the interior of the submerged arc furnace body through the first feeding chute. S2: After the flue gas temperature reaches the first set temperature T1, the magnesite raw material powder is changed to enter the flue gas dust removal riser pipe through the second feed chute. After gas-solid heat exchange with the flue gas, it enters the cyclone dust collector. The cyclone dust collector sends the separated magnesite raw material powder into the furnace body through the cyclone discharge chute. S3: The cyclone dust collector separates the flue gas and sends it into the bag filter through the dust collector downcomer. The control device continuously monitors the temperature of the cooled flue gas through the second temperature sensor installed at the inlet of the dust collector downcomer and adjusts the feeding speed according to the temperature of the cooled flue gas. S4: After smelting is completed, remove the electrodes and reduce the feeding speed of the star feeder to keep the magnesite raw material powder entering the dust removal rising pipe through the second feeding chute; lift the furnace cover and remove the submerged arc furnace body. When the flue gas temperature is lower than the first set temperature T1, turn off the cyclone dust collector and the star feeder.

9. The method for waste heat recovery and raw material preheating of fused magnesium oxide smelting flue gas according to claim 8, characterized in that: In step S3, the feeding speed is adjusted according to the temperature of the cooled flue gas. The adjustment steps are as follows; S31: Determine whether the temperature of the cooled flue gas has reached the second set temperature T2. If it has, increase the feeding speed. S32: Determine if the temperature of the cooled flue gas has not reached the second set temperature T2, nor fallen below the third set temperature T3, and maintain the current feeding speed; wherein the third set temperature T3 is lower than the second set temperature T2; S33: Determine whether the temperature of the cooled flue gas is lower than the third set temperature T3. If it is lower, reduce the feeding speed.

10. The method for waste heat recovery and raw material preheating of fused magnesium oxide smelting flue gas according to claim 9, characterized in that: The temperature of the preheated raw material powder is 200-500℃, the temperature of the flue gas after heat exchange is reduced by 100-400℃, the second set temperature T2 is 260℃, and the third set temperature T3 is 200℃.

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