Automatic energy-saving tunnel type alkali smelting kiln and process for preparing zirconium oxychloride by alkali smelting method

Abstract

This invention belongs to the field of zirconium oxychloride process technology, specifically relating to an automated energy-saving tunnel-type alkali fusion furnace and a process for preparing zirconium oxychloride using the alkali fusion method. The automated energy-saving tunnel-type alkali fusion furnace of this invention includes a main tunnel kiln, which is sequentially divided into a preheating zone, an alkali fusion zone, a sand feeding reaction zone, a heat preservation zone, and a cooling zone, totaling 23 sections. A track is provided around the perimeter of the tunnel kiln. A transmission and sealing device is installed on the tunnel kiln, including an automatic dual-shaft carrier. A sand preheater is installed in the alkali fusion zone. The air outlet of the preheating zone is connected to the sand preheater via a pipeline, and the gas outlet of the sand preheater is connected to a waste heat boiler via a pipeline. An alkali feeding end and a material flushing end are respectively provided at both ends of the tunnel kiln. This invention also provides a process for preparing zirconium oxychloride using its tunnel kiln. The automated energy-saving tunnel-type alkali fusion furnace and the process for preparing zirconium oxychloride using the alkali fusion method of this invention solve the technical problems of zircon sand settling at the bottom, low production efficiency, and high energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of zirconium oxychloride process technology, specifically relating to an automated energy-saving tunnel-type alkali melting furnace and a process for preparing zirconium oxychloride by alkali melting. Background Technology

[0002] Zirconium oxychloride (ZrOCl2) Zirconium oxychloride (ZH₂O) is an important zirconium chemical, a raw material for the synthesis of zirconium dioxide and many zirconium salts. It can be used as a paint drying agent, rubber additive, refractory material, ceramic pigment, and lubricant. It has wide applications in ceramics, tanning, electronics, jewelry, metallurgy, catalysts, medical applications, and automotive exhaust purification. Furthermore, zirconium oxychloride is the raw material required for the wet separation of zirconium and hafnium. The alkaline fusion process for producing zirconium oxychloride features stable product quality, high equipment capacity, and low production costs. The current acid-alkali process for producing zirconium oxychloride is roughly as follows: alkaline fusion → flushing → water washing and transformation → acidification and water dissolution → crystallization. The purpose of the alkaline fusion stage is to decompose zircon sand with high-temperature molten sodium hydroxide to obtain easily decomposable sodium zirconate, and the purpose of the flushing stage is to transfer the material from the alkaline fusion pot with water.

[0003] The alkali fusion process uses a kiln to heat the material; common types include multi-hole single kilns, tunnel kilns, and rotary kilns. A typical process involves first heating preheated caustic soda flakes in the alkali fusion pot to approximately 650°C using a heat source, then adding zircon sand at room temperature. After the reaction is complete and the temperature is maintained, the alkali fusion pot is removed from the heating area and cooled. It is then transferred to the flushing stage using a hoist, where the material is flushed out with water. Finally, the empty alkali fusion pot is transferred back to the alkali fusion stage using a hoist again, starting the next cycle. This entire process has several shortcomings: firstly, the density of zircon sand is 4.6 g / cm³. 3 The density of molten sodium hydroxide is 2.13 g / cm³. 3The difference between the two is significant. When zircon sand is added to molten sodium hydroxide, it can only move with the convection generated by the heating of sodium hydroxide. Often, some large zircon sand particles will settle to the bottom of the alkali melting pot and not be alkali-dissolved. These large sand particles can even hinder the heat absorption of sodium hydroxide, resulting in incomplete reaction of the entire pot of material. The alkali dissolution rate is usually 97-98.5%, while for materials with sand settling, the alkali dissolution rate may not even reach 85%. Secondly, in pursuit of a higher alkali dissolution rate, zirconium oxychloride manufacturers generally try to increase the temperature of the molten sodium hydroxide when adding sand (600-650℃). Under the same equipment and environmental conditions, the higher the alkali temperature, the more heat is radiated to the outside, and the smaller the temperature difference with the heat source, the more time is required to raise the temperature, which means greater energy consumption. Thirdly, the alkali melting process uses natural gas for heating, while the flushing process uses water. Considering environmental and safety factors, these two processes are kept at a certain distance by each manufacturer. Operators use hoists to transfer the alkali-melted material to the flushing process, and after flushing, transfer the slurry and move the alkali melting pot to the alkali melting operation area. Throughout the process, a significant amount of time is wasted on heat preservation, cooling, and material and slurry transfer, severely hindering the alkaline lysis of zircon sand. Fourth, traditional tunnel kilns use flue gas to preheat materials, but lack suitable preheating equipment. Sodium hydroxide is typically placed in an alkaline melting pot, with the combustion exhaust gas flowing around it preheating the pot and the sodium hydroxide, making the preheating of zircon sand even more difficult.

[0004] For example, CN119680464A discloses a tunnel kiln that attempts to solve the problems of intermittent production and high energy consumption in traditional single kilns by continuously operating the kiln and utilizing combustion exhaust gas in stages. However, its automation is limited to temperature and atmosphere control and does not solve the problem of sand settling due to the density difference between zircon sand and alkali solution during feeding. In addition, it does not have an effective preheating device for zircon sand. When high-density zircon sand is instantly fed into the kiln, the contact between cold material and hot alkali will cause local temperature differences, exacerbating the risk of unreacted large-particle sand formation. CN102060326A discloses a horizontal kiln that designs a trough reactor and uses mechanical stirring to force the mixing of high-density zircon sand and molten alkali solution, improving the problems of sand settling and incomplete reaction in traditional static systems. However, the problem of separating the operating areas of natural gas and water remains unsolved, and material transfer relies on manual labor and lifting equipment. The heat loss during the lifting process not only drags down energy efficiency but also seriously restricts the production cycle. CN202912718U discloses a screw propulsion device that, combined with continuous feeding and discharging, solves the bottleneck of material transfer from a mechanization perspective. However, it has two inherent technical defects: First, the screw continuously rubs against the furnace body and the material, and wears out extremely quickly in a high-temperature and strong alkaline environment, which seriously affects the lifespan and operational stability of the device. Second, its plug-flow reaction mechanism is prone to back-mixing, resulting in insufficient reaction time for some materials and difficulty in ensuring the decomposition rate. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of high energy consumption and low alkali decomposition rate in the existing technology of alkali fusion of zircon sand, and to provide an automated energy-saving tunnel alkali fusion furnace and a process for preparing zircon oxychloride by alkali fusion, which solves the technical problems of zircon sand settling at the bottom, low production efficiency and high energy consumption.

[0006] The automated energy-saving tunnel-type alkali fusion kiln of the present invention includes a main tunnel kiln, a track, a transmission and sealing device, a sand preheater, an automatic metering device, a waste heat boiler, an automatic twin-shaft conveyor, a first gate, a second gate, and a third gate. The tunnel kiln is divided into 23 sections along its length: a preheating zone, an alkali fusion zone, a sand feeding reaction zone, a heat preservation zone, and a cooling zone. The track is fixedly installed on the ground on one side and both ends of the kiln body along its length for the movement of material cars, boiler cars, and frame cars. The transmission and sealing device includes a transmission... The system includes wheels, bearing mounting plates, motor mounting plates, drive motors, insulation cotton, refractory bricks, steel frames, and an alkali melting pot. The sand preheater is located next to the alkali melting zone. The exhaust gas outlet of the preheating zone is connected to the air inlet of the sand preheater via a pipeline, and the air outlet of the sand preheater is connected to the waste heat boiler via a pipeline. The automatic dual-shaft transporter is located outside the material feeding end of the tunnel kiln and is connected to the track. The first gate is located between the first preheating section and the alkali feeding end, the second gate is located between the sixth insulation section and the first cooling section, and the third gate is located between the sixth cooling section and the material car area.

[0007] More preferably, the 23 sections are: preheating section 1, preheating section 2, preheating section 3, preheating section 4, preheating section 5, preheating section 6, alkali melting section 1, alkali melting section 2, alkali melting section 3, alkali melting section 4, sand feeding reaction zone, heat preservation section 1, heat preservation section 2, heat preservation section 3, heat preservation section 4, heat preservation section 5, heat preservation section 6, cooling section 1, cooling section 2, cooling section 3, cooling section 4, cooling section 5, and cooling section 6.

[0008] In a further preferred embodiment, a square steel frame is placed inside each section of the kiln, and the alkali melting pot is placed in the middle of the steel frame and welded and fixed. The steel frame and the alkali melting pot are surrounded by insulation cotton, and the inner wall of the kiln is built with refractory bricks. Four steel fixed shaft drive wheels are installed on each side of each section. The drive wheels are installed on the steel structure of the kiln body through bearings and bearing fixing plates. The drive motor is fixed to the outside of the kiln body through the motor fixing plate and drives the drive wheels to rotate.

[0009] More preferably, the sand preheater is a carbon steel shell and tube heat exchanger, the main body of which consists of 1600 steel tubes with an inner diameter of 36mm, a wall thickness of 2mm, and a length of 3m. The upper part is a 3m×3m square sealing plate, and the perimeter is equipped with a 0.4m high sand baffle plate. The lower part is a square cone structure and is equipped with an electric sand discharge valve. The sand preheater is equipped with baffles inside, a sand inlet at the top, and a sand discharge outlet at the bottom.

[0010] In a further preferred embodiment, the automatic metering device is fixedly installed on the ground below the sand preheater and consists of four pressure sensors and an upper steel plate. The pressure sensors are Mettler Toledo TSC500kg. A sand weighing hopper with an insulation layer is placed above the automatic metering device, which works in conjunction with a tipping bucket elevator to achieve automatic metering, lifting, and sand feeding.

[0011] More preferably, the automatic dual-axis conveyor includes a tilting motor, baffle, bearing, and column, which can achieve a 100° side tilting action; the material pot is fed into the automatic dual-axis conveyor by the material cart along the track, and after the material is flushed, the empty pot flows back to the alkali feeding end via the frame car and the pot car along the track.

[0012] More preferably, the first gate, the second gate, and the third gate are all high-temperature resistant electric gates, including a gate body, an upper gate rail, a lower gate rail, a fixed pulley, and a traction motor; the upper and lower edges of the gate are provided with grooves to cooperate with the fixed pulley, and the horizontal opening and closing is achieved by the traction of the motor and the wire rope.

[0013] In a further preferred embodiment, an air outlet is opened on the cooling section of the kiln wall, which is connected to the air inlet of the insulation section through pipelines and a combustion fan, and the hot air is used as combustion air; an exhaust gas outlet is opened on the preheating section of the kiln wall, which is connected to the air inlet of the sand preheater through pipelines, so as to realize the cascade utilization of waste heat.

[0014] The process for preparing zirconium oxychloride in the alkali melting furnace includes the following steps: (1) Zircon sand is preheated to 200~300℃ by the high temperature tail gas of the kiln in the sand preheater; (2) Add the preheated zircon sand into the alkali melting pot. The temperature of the molten alkali in the pot is 520~580℃, the alkali-sand ratio is 1.2~1.4:1, and the reaction time is ≤10min; (3) The 23-section alkali melting pot is synchronously driven by the transmission wheel. Each section stays for 8-12 minutes and moves forward one station. (4) The gate automatically opens and closes to separate the temperature zones and ensure smooth movement of the pot body; (5) The ambient temperature air enters from the sixth cooling section and is heated to 280~330℃ to be used as combustion air; the tail gas of the kiln tail at 390~410℃ is used to preheat the sand and generate steam for the waste heat boiler. (6) The alkali melting pot enters the automatic dual-shaft carrier at the feeding end, tilts 100° to complete the feeding, and the empty pot is automatically returned; (7) The DCS system automatically controls temperature, sand feeding, transmission, gate, material flushing and reflux, so as to produce a batch of material every 10 minutes.

[0015] Further preferred, the 23 temperature ranges are as follows: Preheating stage 1: 390~410℃; Preheating stage 2: 430~450℃; Preheating stage 3: 460~480℃; Preheating stage 4: 490~510℃; Preheating stage 5: 520~540℃; Preheating stage 6: 540~560℃; Molten alkali stage 1: 560~580℃; Molten alkali stage 2: 580~600℃; Molten alkali stage 3: 600~620℃; Molten alkali stage 4: 620~640℃; Sand addition reaction zone: 640~660℃. 60℃; Insulation stage 1: 620~640℃, Insulation stage 2: 570~590℃, Insulation stage 3: 520~540℃, Insulation stage 4: 470~490℃, Insulation stage 5: 430~450℃, Insulation stage 6: 400~420℃; Cooling stage 1: 370~390℃, Cooling stage 2: 320~340℃, Cooling stage 3: 260~280℃, Cooling stage 4: 190~210℃, Cooling stage 5: 120~140℃, Cooling stage 6: 40~60℃.

[0016] The tunnel kiln is surrounded by tracks for guiding and conveying materials and pots. Specifically, the tracks are fixedly installed on the ground on one side and at both ends of the tunnel kiln along its length. Electric frame trolleys automatically transport empty pots along the tracks to their designated pot positions.

[0017] The steel frames and drive wheels are fitted together: all steel frames are pressed onto the drive wheels. When the drive motor starts, the drive wheels rotate, and friction pushes all the steel frames, along with the alkali melting pot on them, synchronously from left to right (from the preheating zone to the cooling zone) to one station. A horizontal track is installed on the corresponding position on the side wall of the tunnel kiln, with fixed pulleys inside. The gate is inserted into the track, and its side is connected to the motor via a steel wire rope. When the control system issues a command, the motor drives the gate to move horizontally along the track on the fixed pulleys, thus opening and closing the kiln and separating different temperature zones and operating areas.

[0018] Furthermore, a cold air inlet is provided at the cooling section, and a hot air outlet is provided at the insulation section. Specifically, an air inlet is opened at the top or side wall of the kiln in the cooling section as a cold air inlet, connected to a normal temperature high-pressure air source; an air outlet is opened at the top or side wall of the kiln in the insulation section as a hot air outlet. A high-temperature resistant air duct connects the hot air outlet to the combustion air inlet of the natural gas burners in each section of the molten alkali zone. No fan is installed inside the air duct; gas flow is achieved by utilizing the thermal pressure inside the kiln and the suction force of an external fan.

[0019] Furthermore, the preheating section is equipped with an exhaust gas outlet, which is connected to the hot gas inlet of a sand preheater via a pipeline. Specifically, an air outlet is opened on the kiln top or side wall of the preheating section and connected to the shell-side inlet of the sand preheater. The sand preheater is a carbon steel shell-and-tube heat exchanger, the main body of which consists of 1600 steel tubes with an inner diameter of 36mm, a wall thickness of 2mm, and a length of 3 meters. It has a 3×3m square sealing plate at the top, a 0.4m high sand baffle plate around the perimeter, and a square pyramidal slope at the bottom, with an electric sand discharge valve installed at the bottom. An automatic metering device is installed below the sand preheater, using a pressure sensor model such as, but not limited to, Mettler Toledo TSC500kg, which is fixedly installed on one side of the sand discharge valve at the bottom of the sand preheater to weigh the preheated zircon sand. In this field, the alkali-to-sand ratio in alkali-fusion reactions is generally around 1.3. If 20°C zircon sand is added when the alkali is heated to 620°C, the theoretical material mixing temperature is (620×1.3+20×1) / (1.3+1)=359°C. In this invention, 250°C zircon sand is added when the alkali is at 550°C, resulting in a theoretical mixing temperature of (550×1.3+250×1) / (1.3+1)=420°C, which is 61°C higher than the former. Microscopically, as soon as the high-temperature sand is added to the molten alkali, bubbles begin to appear on the outer surface of the sand. This is because the water vapor generated in the reaction rises rapidly in the high-temperature molten alkali at normal pressure, giving the zircon sand a strong upward driving force, preventing it from sinking. The on-site reaction results match the theoretical results, confirming that preheating the zircon sand can significantly reduce the temperature of the alkali when adding the sand, and can ensure a reaction time of less than 10 minutes and an alkali dissolution rate of around 99%.

[0020] This invention integrates the material feeding operation into the overall process, saving the time spent by overhead cranes hoisting materials back and forth, avoiding safety risks during operation, and ensuring that the time for transferring a batch of materials via the feeding belt is roughly equal to the reaction time, which can be controlled within 10 minutes. The time sequence of the traditional alkaline lysis of zircon sand is roughly as follows: Figure 8 As shown, the alkali fusion reaction time is about 15 minutes, while the material pouring and transfer takes about 30 minutes. Due to the long time required for heat preservation and cooling, there is a large amount of alkali fusion material waiting to be poured on site, which is equivalent to completing one batch of material in 1 hour, which seriously restricts the production process.

[0021] Furthermore, the gas outlet of the sand preheater is connected via a pipeline to the flue gas inlet of a waste heat boiler. The waste heat boiler is used to recover waste heat from the exhaust gas to generate steam.

[0022] The present invention provides a process for preparing zirconium oxychloride by alkaline fusion using an automated, energy-saving tunnel-type alkaline fusion furnace, comprising the following steps: (1) Zircon sand preheating: Zircon sand is preheated by passing it through a sand preheater and using the combustion exhaust gas of an automated energy-saving tunnel alkali melting kiln. The preheating temperature reaches 200~300℃, preferably 240~260℃. (2) Alkali fusion reaction: The preheated zircon sand is put into the alkali fusion pot, which contains molten sodium hydroxide at a temperature of 520~580℃, preferably 540~560℃. The alkali-to-sand ratio is 1.2~1.4:1. The reaction time after adding sand is controlled within 10 minutes. The alkali hydrolysis rate can reach 98.5~99.5%. (3) Continuous alkali melting and transmission control: A tunnel-type alkali melting kiln is adopted. The kiln body is divided into multiple temperature sections, with a total of 23 sections from preheating to cooling. Each section is equipped with an alkali melting pot welded to a steel frame. The steel frame is synchronously driven by the transmission wheel and moves forward one station at a set time interval of 10 minutes. (4) Automatic gate separation control: Automatic gates are installed between the alkali feeding end and the preheating zone, between the heat preservation zone and the cooling zone, and between the cooling zone and the material cart zone. They open automatically after the reaction is completed and close automatically after the pot body is moved into place. (5) Cooling and waste heat recovery: The ambient temperature high pressure air enters from the end of the cooling zone (cooling section 6), and after flowing through the alkali molten material, it is heated to 280~330℃ and is used entirely as combustion air; the combustion exhaust gas preheats each section of the alkali molten pot in sequence, and finally preheats the first section before being discharged at a temperature of 390~410℃, and is then used to preheat zircon sand and generate steam in the waste heat boiler. (6) Automated feeding and empty pot return: After the reaction is completed, the alkali melting pot is moved to the feeding end and automatically tilted to feed. After the feeding is completed, the empty pot is automatically returned to the alkali feeding end and enters the next cycle. (7) Full-process automated control: The DCS system and infrared fiber optic thermometer enable automatic control of temperature monitoring, sand feeding, gate opening and closing, drive wheel start and stop, material feeding, and alkali melting pot body reflux, achieving continuous production of one batch of material every 10 minutes.

[0023] This invention is based on the principle of overall planning. The reaction is the most critical link in the network, and all other links should not exceed the reaction time and should all proceed synchronously with the reaction to optimize the efficiency of continuous alkali melting. Unlike traditional processes, this invention subdivides the entire alkali melting process into 26 small nodes, each node containing one pot. After approximately 10 minutes, all pots move to the next node, effectively completing one pot of material every 10 minutes, significantly improving work efficiency. The time node diagram of this invention is shown below. Figure 9 As shown. This invention uses a tunnel kiln as the main body of the production line, divided into 23 sections from a preheating section to a cooling section. Each section has a square steel frame, with an alkali melting pot placed in the middle of the steel frame and welded to it. Insulation cotton is installed around the perimeter to both seal the kiln body and keep it warm. A steel plate is installed at the junction of the kiln body and the steel frame. Four steel fixed shaft transmission wheels are installed on each side of each section. The drive motor can be programmed to start and stop synchronously, moving all the steel frames pressed on the wheels from left to right.

[0024] Furthermore, after the reaction in step (6) is completed, the alkali melting pot is moved to the automatic biaxial carrier at the feeding end, and the automatic biaxial carrier tilts the alkali melting pot 100° to the side.

[0025] Furthermore, while alkali-hydrolyzing 100t of zircon sand, 6-7t of 0.3MPa steam can be generated.

[0026] Furthermore, the process for preparing zirconium oxychloride via the alkali fusion method includes: alkali fusion → water washing, transformation → acidification → crystallization → acid washing → centrifugation, etc. This invention, by setting up a dedicated tubular sand preheater, utilizes high-temperature combustion exhaust gas to preheat zircon sand to 240-260℃, completely solving the technical problems of sedimentation and incomplete alkali dissolution caused by the large density difference between zircon sand and molten sodium hydroxide. In traditional processes, using zircon sand at room temperature (approximately 20℃) results in frequent sedimentation, with an alkali dissolution rate typically only 97-98.5%, sometimes even below 85%. This invention uses high-temperature sand at around 250℃; after mixing the high-temperature sand with molten alkali at 550℃, the theoretical mixing temperature can reach 420℃, which is 61℃ higher than the traditional process (620℃ alkali + 20℃ sand, mixing temperature 359℃). The water vapor generated by the instantaneous reaction on the surface of the high-temperature sand produces a strong buoyancy, preventing the zircon sand from sinking to the bottom. The reaction time is shortened to less than 10 minutes, and the alkaline hydrolysis rate is stably increased to about 99%, significantly reducing the raw material consumption per unit.

[0027] This invention achieves the cascade utilization of systematic energy, significantly reducing natural gas energy consumption and realizing waste heat recovery. Compared to traditional porous single-unit kilns (with a single-unit consumption of approximately 120m³), this invention... 3 Compared to traditional alkali-melting boilers (which do not produce steam), this invention has the following energy-saving features: First, ambient temperature high-pressure air enters from the end of the cooling zone, cooling the alkali-melting material while simultaneously heating itself to 280-330°C, and is entirely used as combustion air, thus recovering the sensible heat of the material; second, the high-temperature combustion exhaust gas preheats each section of the alkali-melting boiler sequentially, and the exhaust gas at approximately 400°C is then used to preheat the zircon sand; finally, the exhaust gas after preheating the zircon sand (approximately 230°C) enters the waste heat boiler to generate 0.3MPa of fresh steam. This invention can reduce the natural gas consumption per batch (800kg zircon sand) for alkali lysis to 78-81m³. 3 The process generates approximately 3.2 tons of steam per 12 hours, maximizing energy utilization and achieving significant energy savings. Currently, the process of alkaline pyrolysis of zircon sand using a tunnel kiln requires 20-30 minutes, or even longer, to heat the sand in the highest temperature zone (around 650℃). Furthermore, because room-temperature zircon sand is used, the sand feeding time is no less than 10 minutes, followed by continued heating until the reaction is complete. All these factors inevitably increase natural gas consumption. In contrast, this invention uses high-temperature sand, reacting immediately upon feeding. The reaction time from sand feeding to complete reaction is approximately 10 minutes, representing a significant improvement.

[0028] This invention, based on the principle of overall planning, modularizes and automates the entire alkali fusion process, constructing a continuous tunnel-type alkali fusion production line, significantly improving production efficiency and reducing labor. In traditional processes, the reaction (approximately 15 minutes) and material transfer (approximately 30 minutes) are severely disconnected, with long periods of ineffective operation time such as overhead crane hoisting, cooling, and transfer, resulting in only one batch of material being processed per hour. This invention subdivides the entire process into 26 nodes. Through the coordinated work of drive wheels, brakes, a DCS control system, and an automatic dual-axis conveyor, the dwell time of each segment is controlled to 8-12 minutes, allowing the reaction, cooling, material transfer, and empty pot recirculation stages to proceed synchronously and in parallel, achieving continuous production of one batch of material every 10 minutes. This invention can continuously process 66-71 batches of material in 12 hours, completely eliminating the overhead crane hoisting and handling process, significantly improving equipment utilization and per capita productivity.

[0029] Compared with the prior art, the beneficial effects of the present invention are: (1) The present invention designs a carbon steel tube heat exchanger as a special sand preheater, which uses the high temperature tail gas of about 400°C discharged from the tunnel kiln to preheat the zircon sand to about 250°C.

[0030] (2) The present invention divides the entire process of alkali melting and flushing into 26 nodes (23 heating / cooling sections + other auxiliary sections), with one alkali melting pot placed at each node. Through the cooperation of drive wheels and tracks, all pots advance one station at a time, so that the reaction, cooling, flushing, empty pot recirculation and other links can be operated in parallel, and the production cycle is shortened to 10 min / pot.

[0031] (3) The present invention utilizes the system energy in a cascade manner. The hot air (about 300°C) after cooling the material is used entirely as combustion air. The combustion exhaust gas is used to preheat the alkali melting pot and the zircon sand in sequence, and finally generates steam through the waste heat boiler, thus maximizing the recovery of heat. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of the automated energy-saving tunnel-type alkali melting furnace of the present invention.

[0033] Figure 2 The images show the front and top views of the sand preheater of the present invention, as well as a schematic diagram showing its position relative to the automatic metering device and the sand feeding reaction zone.

[0034] Figure 3 This is a schematic diagram of the three-view diagram of the peripheral transmission sealing device of the automated energy-saving tunnel alkali melting furnace of the present invention.

[0035] Figure 4 Schematic diagrams of an automated dual-axis vehicle from different perspectives.

[0036] Figure 5 This is a schematic diagram of the three-view structure of the transmission sealing device and the gate.

[0037] Figure 6 This is a schematic diagram of the frame cart from both the front and back.

[0038] Figure 7 This is a schematic diagram showing the front and back directions of the boiler car / material car.

[0039] Figure 8 This is a timeline diagram showing the traditional alkaline hydrolysis of zircon sand.

[0040] Figure 9 This is a sequence diagram of the time nodes of the continuous alkaline hydrolysis of the present invention.

[0041] Figure 1 Middle: 1. Preheating Zone; 11. Preheating Stage 1; 12. Preheating Stage 2; 13. Preheating Stage 3; 14. Preheating Stage 4; 15. Preheating Stage 5; 16. Preheating Stage 6; 2. Molten Soda Zone; 21. Molten Soda Stage 1; 22. Molten Soda Stage 2; 23. Molten Soda Stage 3; 24. Molten Soda Stage 4; 3. Sand Addition Reaction Zone; 4. Insulation Zone; 41. Insulation Stage 1; 42. Insulation Stage 2; 43. Insulation Stage 3; 44. Insulation Stage 4; 45. Insulation Section 5; 46. Insulation Section 6; 5. Cooling Zone; 51. Cooling Section 1; 52. Cooling Section 2; 53. Cooling Section 3; 54. Cooling Section 4; 55. Cooling Section 5; 56. Cooling Section 6; 6. Track; 7. First Gate; 8. Second Gate; 9. Third Gate; 10. Automatic Dual-Axle Carrier; 61. Sand Preheater; 62. Automatic Meter; 63. Waste Heat Boiler; Figure 2 In the middle section: 611, sand inlet; 612, baffle plate; 613, sand outlet; 614, air inlet; 615, air outlet; 621, sand weighing hopper; 622, insulation layer; 623, pressure sensor; 624, tipping bucket elevator; Figure 3 In the middle section: 64. Transmission wheel; 65. Bearing mounting plate; 66. Motor mounting plate; 67. Drive motor; 68. Insulation cotton; 69. Refractory brick; 610. Alkali melting pot; 6101. Steel frame; Figure 4 In the middle: 616, flip motor; 617, baffle; 618, bearing; 619, column.

[0042] Figure 5 In the middle: 1010, gate; 1011, upper rail of the gate; 1012, lower rail of the gate. Detailed Implementation

[0043] The present invention will be further described below with reference to specific embodiments.

[0044] like Figure 1As shown, the automated energy-saving tunnel-type alkali melting kiln of the present invention includes a main tunnel kiln, which is sequentially divided into a preheating zone 1, an alkali melting zone 2, a sand feeding reaction zone 3, a heat preservation zone 4, and a cooling zone 5; the preheating zone 1 is divided into 6 sections, the alkali melting zone 2 into 4 sections, the heat preservation zone 4 into 6 sections, and the cooling zone 5 into 6 sections, for a total of 23 sections; a track 6 is fixedly installed on the ground next to the tunnel kiln along the length of the kiln body, and the track 6 is used for the automatic movement of the material car, boiler car, and frame car; a transmission sealing device is installed on the tunnel kiln, which includes a transmission wheel 64, a bearing fixing plate 65, and a motor fixing plate 66. 6. Drive motor 67, insulation cotton 68, refractory bricks 69, steel frame 6101, alkali melting pot 610; An automatic dual-shaft conveyor 10 is independently installed on the outside of the material feeding end of the tunnel kiln, and the automatic dual-shaft conveyor 10 is connected to the track 6; A sand preheater 61 is installed in the alkali melting zone 2, and the air outlet of the preheating zone 1 is connected to the sand preheater 61 through a pipeline, and the gas outlet of the sand preheater 61 is connected to the waste heat boiler 63 through a pipeline; An alkali feeding end and a material feeding end are respectively set at both ends of the tunnel kiln; The material feeding end is connected to the cooling zone 5, the material car, and the automatic dual-shaft conveyor 10 in sequence to form a material output and empty pot return loop. The main tunnel kiln is built of high-alumina refractory bricks 69, and a sealing steel plate is installed at the junction with the insulation cotton of the steel frame to prevent flue gas leakage. The 23 sections are as follows: Preheating Section 11, Preheating Section 2, Preheating Section 3, Preheating Section 4, Preheating Section 5, Preheating Section 6, Molten Soda Section 1, Molten Soda Section 2, Molten Soda Section 3, Molten Soda Section 4, Sand Addition Reaction Zone 3, Insulation Section 1, Insulation Section 2, Insulation Section 3, Insulation Section 4, Insulation Section 5, Insulation Section 6, Cooling Section 1, Cooling Section 2, Cooling Section 3, Cooling Section 4, Cooling Section 5, Cooling Section 6, Cooling Section 6.

[0045] like Figure 3 As shown, a square steel frame 6101 is placed inside each section of the kiln, and the alkali melting pot 610 is placed in the middle of the steel frame 6101 and welded to the steel frame. Insulation cotton 68 is installed around the steel frame 6101 and the alkali melting pot 610. Refractory bricks 69 are built on the inner wall of the kiln. A sealing steel plate is installed at the junction of the kiln body and the steel frame. Four steel fixed shaft transmission wheels 64 are installed on each side of each section. The transmission wheels 64 are installed on the steel structure of the tunnel kiln through bearings and bearing fixing plates 65. The drive motor 67 is fixed to the outside of the kiln body through the motor fixing plate 66. The output shaft of the drive motor 67 is connected to the transmission wheels 64 and drives them to rotate synchronously.

[0046] like Figure 2 As shown, an automatic metering device 62 is fixedly installed on the ground below the side of the sand preheater 61. The automatic metering device 62 consists of four pressure sensors 623 and an upper steel plate. The pressure sensor model is Mettler Toledo TSC500kg. A sand weighing hopper 621 with an insulation layer 622 is placed above the automatic metering device 62. It works with a tipping bucket elevator 624 to realize automatic metering, lifting, tipping, and sand feeding.

[0047] like Figure 2 As shown, the sand preheater 61 is a carbon steel shell and tube heat exchanger, the main body of which consists of 1600 steel tubes with an inner diameter of 36mm, a wall thickness of 2mm, and a length of 3m. The upper part is a 3×3m square sealing plate, and the perimeter is equipped with a 0.4m high sand baffle plate. The lower part is a square cone-shaped inclined surface, and an electric sand discharge valve is installed at the bottom. The sand preheater 61 is equipped with a baffle plate 612 inside, a sand inlet 611 at the top, a sand discharge outlet 613 at the bottom, and an air inlet 614 and an air outlet 615 on the side.

[0048] like Figure 5 As shown, a first gate 7 is installed between the preheating section 11 and the alkali feeding end; a second gate 8 is installed between the insulation section 46 and the cooling section 51; and a third gate 9 is installed between the cooling section 56 and the material cart area. Each gate includes a gate 1010, an upper track 1011, a lower track 1012, a fixed pulley, and a traction motor. Grooves are formed on the upper and lower edges of the gate to engage with the fixed pulley. The track is fixed to the side wall of the tunnel kiln, and the gate is opened and closed horizontally by a motor and wire rope. All gates are high-temperature resistant electric gates. Their installation method is as follows: a horizontal track is opened at a corresponding position on the side wall of the tunnel kiln, with a fixed pulley inside the track. The gate is inserted into the track, and its side is connected to the motor via a wire rope. When the control system issues a command, the motor drives the gate to move horizontally along the track on the fixed pulley, thus opening and closing, thereby separating different temperature zones and operating areas within the kiln.

[0049] like Figure 4 As shown, the automatic dual-axis conveyor 10 includes a tilting motor 616, a baffle 617, a bearing 618, and a column 619, which can achieve a 100° side tilting action. The material pot is fed into the automatic dual-axis conveyor 10 by the material cart along the track 6. After the material is flushed, the empty pot is returned to the alkali feeding end by the frame car and the pot car along the track 6, forming a closed-loop automatic cycle.

[0050] Transmission wheels 64 and drive motor 67: On each side of each section of the tunnel kiln, four steel transmission wheels 64 with fixed shafts are installed. The transmission wheels 64 are mounted to the steel structure of the tunnel kiln via bearings and bearing mounting plates 65. The drive motor 67 is mounted on the outside of the tunnel kiln via a motor mounting plate 66, and its output shaft is connected to the transmission wheels 64 to provide driving force. The drive motor 67 is a programmable synchronous motor capable of controlling the start and stop of all transmission wheels 64.

[0051] The steel frame 6101 and the transmission wheel 64 are matched: all steel frames 6101 are pressed on the transmission wheel 64. When the drive motor 67 starts, the transmission wheel 64 rotates and relies on friction to push all the steel frames together with the alkali melting pot on them from left to right (from the preheating zone 1 to the cooling zone 5) synchronously to one station.

[0052] The automatic dual-axis conveyor 10 is installed at the feeding end of the tunnel kiln and is used to side-tilt the alkali fusion pot that has completed the reaction and moved there. Its specific model is "YZX-10T type dual-axis side-tilting conveyor". The material cart is equipped with rollers at the bottom. After receiving the alkali fusion material, the cart can move along the ground track to the left side of the dual-axis conveyor, and the alkali fusion pot is sent into the dual-axis conveyor via drive wheels. Then, a tilting motor rotates the conveyor and pot 100°. After feeding, the inspector resets the conveyor and alkali fusion pot and sends the empty pot to the frame car. The electric frame car automatically sends the empty pot along track 6 to the side of the pot car position, and the empty material cart automatically returns to the side of the cooling section 6 position 56.

[0053] An air outlet is opened on the top or side wall of the cooling section 51. The air outlet is connected to the air inlet of the insulation section 41 via pipeline and combustion fan, and the hot air is used as combustion fan. The fan of the preheating section 11 sends the exhaust gas into the sand preheater 61 from the upper air inlet. The hot air is fixed in direction by the baffle plate 612 in the sand preheater 61, repeatedly heating the sand storage pipe and the zircon sand therein. Finally, the exhaust gas is discharged from the air outlet at the bottom of the sand preheater 61. An automatic metering device 62 with a Mettler Toledo TSC500kg pressure sensor is installed diagonally below the sand preheater 61 to weigh the preheated zircon sand. The gas outlet of the sand preheater 61 is connected to the flue gas inlet of a waste heat boiler 63 via pipeline. The waste heat boiler 63 is used to recover the waste heat of the exhaust gas to generate steam.

[0054] In the process of preparing zirconium oxychloride by alkali fusion of this invention, during normal continuous alkali fusion operation, the alkali fusion stage 21 to the heat preservation stage 43 are heated by natural gas in each alkali fusion pot. When the infrared fiber optic thermometer detects that the temperature of the molten alkali in the fusion pot reaches 550°C, the central control operator remotely clicks the "sand addition" button to add sand. Two minutes later, the sand is added, and the sand hopper is automatically returned to the weighbridge. The central control operator observes that when the reaction ends, the fire is stopped first, then the air intake is stopped, and then the DCS system sends an "open" signal to the first gate 7, the second gate 8, and the third gate 9. The three gates are then automatically opened by motor drive. After opening to the correct position, the proximity switch corresponding to each gate sends a "position" signal to the system. Upon receiving this signal, the system stops the gate motor. Simultaneously, the DCS system sends a "start" signal to all drive wheel motors 64. The drive wheel 64 begins to rotate in the set direction and speed, pushing the steel frame pressed against it from left to right, advancing all the pots from the alkali feeding end to the cooling section 56 by one position. A proximity switch is installed on the far right of the material cart section. Once the steel frame is in place, it sends a "positioned" signal to the system. Upon receiving this signal, the system issues a "deceleration and braking" command to all the motors of the drive wheels 64. After all pots are in place, the system automatically closes the first gate 7, the second gate 8, and the third gate 9. After closing, the proximity switch sends a signal to the system. Upon receiving the signal, the system automatically opens the air intake and ignites the furnace. This is the control process of the drive wheel 64 and the gates.

[0055] From "Preheating Section 11" to "Sand Feeding Reaction Zone 3" and then to "Cooling Section 6" (Section 56), the kiln temperature first rises and then falls. A typical temperature sequence is 400℃, 440℃, 470℃, 500℃, 530℃, 550℃, 570℃, 590℃, 610℃, 630℃, 650℃, 630℃, 580℃, 530℃, 480℃, 440℃, 410℃, 380℃, 330℃, 270℃, 200℃, 130℃, and 50℃. The material remains in each section for 10 minutes. During normal operation, the production line is equipped with three automatic gate valves.

[0056] The ambient temperature high-pressure air enters from the sixth cooling section 56 and exits from the first cooling section 51. While cooling the alkali molten material, it is also heated to about 300°C and then used entirely as combustion air.

[0057] From the molten alkali stage 21 to the insulation stage 41, natural gas burners and high-temperature combustion air ducts are installed on both sides of each stage, and the valve openings can be controlled programmatically. The combustion exhaust gas sequentially heats the preheating stages 11, 12, 13, 14, 15, and 16, exiting at approximately 400°C from the preheating stage 11. Processing 70 batches of molten alkali material over 12 hours produces approximately 62,000~65,000 m³ of exhaust gas. 3 The exhaust velocity is approximately 5100~5400 m / s. 3 / h.

[0058] The combustion exhaust gas is then sent to the sand preheater 61. After preheating the zircon sand, the exhaust gas temperature drops to 230℃, and then it is sent to the waste heat boiler 63 to generate some fresh steam at 0.3MPa. Finally, the exhaust gas is discharged at a temperature of about 140℃. Throughout the process, the heat from the natural gas combustion is fully utilized. For the alkaline hydrolysis of one batch of feed (800kg of zircon sand), approximately 80m³ of natural gas is used. 3 The process involved alkali hydrolysis of 70 pots of zircon sand over 12 hours, simultaneously generating approximately 3.3 tons of fresh steam at 0.3 MPa.

[0059] The system then performs the following operations: (1) The boiler car returns to its original position from the alkali feeding position; (2) Transfer the empty pot from the frame car to the pot car; (3) The boiler car returns to the alkali feeding position, and the operator feeds alkali (1040kg). (4) The empty frame car automatically resets.

[0060] On the other end, the system simultaneously performs the following operations: (1) The material cart transfers the material pot to the automatic dual-axle conveyor 10; (2) After the material is in place, the automatic dual-shaft carrier 10 tilts the alkali melting pot 100° to the side, and the flushing device automatically flushes the alkali melt material clean and transfers it. (3) After the material is flushed, the inspector resets the alkali melting pot and sends the empty pot to the frame car. The electric frame car automatically sends the empty pot to the side of the pot car along track 6; (4) The empty material car automatically returns to the side of position 56 of the sixth cooling section.

[0061] In addition, after the gate is closed, the system automatically adds 800 kg of hot zircon sand to the weighing hopper and lifts the weighing hopper above the sand feeding hopper for later use.

[0062] The central control operator operates remotely from the control room, while on-site operators prepare materials; the entire process is repeated continuously. In case of abnormalities, both the system interface and the on-site personnel have emergency stop buttons for easy handling.

[0063] A traditional intermittent multi-hole single-unit kiln has only one heating port and 2-3 preheating ports. Five kilns can perform alkali calcination on 60 batches of zircon sand in 12 hours. Similarly, alkali calcining one batch (800 kg of zircon sand) requires approximately 120 cubic meters of natural gas. 3 It does not produce steam as a byproduct.

[0064] Example 1 Zirconium oxychloride is continuously prepared using the automated energy-saving tunnel-type alkali melting furnace described in this invention, following the steps below.

[0065] (1) Preheating of zircon sand: Zircon sand is preheated by passing it through a tubular sand preheater and using the approximately 400°C combustion exhaust gas discharged from the first stage of the tunnel kiln. After preheating, the temperature of the zircon sand reaches 250°C.

[0066] (2) Alkali fusion reaction: When the infrared fiber optic thermometer detects that the temperature of the molten sodium hydroxide in the alkali fusion pot has risen to 550℃, the DCS system automatically controls the sand addition. 800kg of preheated zircon sand is added to each pot, which contains 1040kg of molten alkali (alkali-to-sand ratio 1.3:1). The sand addition process is completed within 2 minutes, and the material reacts at 640~660℃ (temperature of the sand addition reaction zone). The total reaction time (from the start of sand addition to the end of the reaction) is 9 minutes.

[0067] (3) Continuous alkali melting and transmission control: The tunnel kiln is divided into 23 sections (preheating section 1 to cooling section 6), each containing an alkali fusion pot welded to a steel frame. All steel frames are pressed onto drive wheels. After the reaction, the DCS system first shuts off the fire and combustion air, then automatically opens the first, second, and third gates. Once the gates are in position, the drive motor starts, and the drive wheels rotate synchronously, using friction to push all the steel frames, along with the alkali fusion pot, from left to right (from the alkali feeding end to the cooling end) to one station. The dwell time for each section is set to 10 minutes. After moving to the correct position, the gates automatically close, and air intake and ignition resume heating.

[0068] (4) Automatic gate separation control: The first gate is located between the preheating section and the alkali feeding end, the second gate is located between the insulation section and the cooling section, and the third gate is located between the cooling section and the material cart area. The three sets of gates open and close automatically in the order described in step (3) to ensure the separation of temperature zones inside the kiln and the smooth movement of the kiln body.

[0069] (5) Cooling and waste heat recovery: High-pressure air at ambient temperature enters from the sixth cooling section, flows through the alkali-melting material, and is heated to 300°C. All of this air is then piped to the natural gas burners in each section of the molten alkali zone as combustion air. The combustion exhaust gas passes sequentially through each section of the preheating zone and the insulation zone, finally exiting from the first preheating section at a measured temperature of 405°C. This exhaust gas first enters the sand preheater to heat the zircon sand. After exiting the sand preheater, the exhaust gas temperature drops to 230°C, then enters the waste heat boiler to generate 0.3MPa steam, with a final exhaust gas temperature of approximately 140°C.

[0070] (6) Automated feeding and empty pot return: After the reaction is complete, the alkali fusion pot, which is then moved to the end of the sixth cooling stage, is transported by a material cart along a track to an automatic dual-axis conveyor. The automatic dual-axis conveyor tilts the alkali fusion pot 100° to its side, and the flushing device automatically flushes the alkali fusion material in the pot into the water washing tank. After flushing, the empty pot is automatically returned to the alkali feeding end via a frame car and a pot car along a track, entering the next production cycle.

[0071] (7) Full-process automated control: The DCS system and infrared fiber optic thermometer enable automatic control of processes such as temperature monitoring, sand feeding, gate opening and closing, drive wheel start and stop, material feeding, and pot reflux. A batch of material is continuously produced every 10 minutes.

[0072] The system operated continuously for 12 hours, processing 68 batches of zircon sand (800 kg per batch), with a total alkaline hydrolysis volume of 54.4 tons. Four composite samples of the alkali-melted material were taken, and the hydrolysis rates were tested according to industry standard methods. The results were 99.13%, 99.38%, 98.89%, and 99.18%, with an average hydrolysis rate of 99.15%. The total natural gas consumption was 5448 m³, with a natural gas consumption of 80.12 m³ / batch. The waste heat boiler produced 3.2 tons of 0.3 MPa steam in 12 hours.

[0073] Example 2 Zirconium oxychloride is continuously prepared using the automated energy-saving tunnel-type alkali melting furnace described in this invention, following the steps below.

[0074] (1) Preheating of zircon sand: Zircon sand is preheated by passing it through a tubular sand preheater and using the approximately 400°C combustion exhaust gas discharged from the first stage of the tunnel kiln. After preheating, the temperature of the zircon sand reaches 240°C.

[0075] (2) Alkali fusion reaction: When the infrared fiber optic thermometer detects that the temperature of the molten sodium hydroxide in the alkali fusion pot has risen to 540℃, the DCS system automatically controls the sand addition. 800kg of preheated zircon sand is added to each pot, which contains 1040kg of molten alkali (alkali-to-sand ratio 1.3:1). The sand addition process is completed within 2 minutes, and the material reacts at 640~660℃ (temperature of the sand addition reaction zone). The total reaction time (from the start of sand addition to the end of the reaction) is 10 minutes.

[0076] (3) Continuous alkali melting and transmission control: The tunnel kiln is divided into 23 sections (preheating section 1 to cooling section 6), each containing an alkali fusion pot welded to a steel frame. All steel frames are pressed onto drive wheels. After the reaction, the DCS system first shuts off the fire and combustion air, then automatically opens the first, second, and third gates. Once the gates are in position, the drive motor starts, and the drive wheels rotate synchronously, using friction to push all the steel frames, along with the alkali fusion pot, from left to right (from the alkali feeding end to the cooling end) to one station. The dwell time for each section is set to 11 minutes. After moving to the correct position, the gates automatically close, and air intake and ignition resume heating.

[0077] (4) Automatic gate separation control: The first gate is located between the preheating section and the alkali feeding end, the second gate is located between the insulation section and the cooling section, and the third gate is located between the cooling section and the material cart area. The three sets of gates open and close automatically in the order described in step (3) to ensure the separation of temperature zones inside the kiln and the smooth movement of the kiln body.

[0078] (5) Cooling and waste heat recovery: High-pressure air at ambient temperature enters from the sixth cooling section, flows through the alkali-melting material, and is heated to 300°C. All of this air is then piped to the natural gas burners in each section of the molten alkali zone as combustion air. The combustion exhaust gas passes sequentially through each section of the preheating zone and the insulation zone, finally exiting from the first preheating section at a measured temperature of 402°C. This exhaust gas first enters the sand preheater to heat the zircon sand. After exiting the sand preheater, the exhaust gas temperature drops to 228°C, then enters the waste heat boiler to generate 0.3MPa steam, with a final exhaust gas temperature of approximately 140°C.

[0079] (6) Automated feeding and empty pot return: After the reaction is complete, the alkali fusion pot, which is then moved to the end of the sixth cooling stage, is transported by a material cart along a track to an automatic dual-axis conveyor. The automatic dual-axis conveyor tilts the alkali fusion pot 100° to its side, and the flushing device automatically flushes the alkali fusion material in the pot into the water washing tank. After flushing, the empty pot is automatically returned to the alkali feeding end via a frame car and a pot car along a track, entering the next production cycle.

[0080] (7) Full-process automated control: The DCS system and infrared fiber optic thermometer enable automatic control of processes such as temperature monitoring, sand feeding, gate opening and closing, drive wheel start and stop, material feeding, and pot reflux. A batch of material is continuously produced every 11 minutes.

[0081] The system operated continuously for 12 hours, processing 66 batches of zircon sand (800 kg per batch), with a total alkaline hydrolysis volume of 52.8 tons. Four composite samples of the alkali-melted material were taken, and the hydrolysis rates were tested according to industry standard methods. The results were 98.95%, 99.16%, 99.18%, and 99.42%, with an average hydrolysis rate of 99.18%. The total natural gas consumption was 5341 m³, with a natural gas consumption of 80.92 m³ / batch. The waste heat boiler produced 3.1 tons of 0.3 MPa steam in 12 hours.

[0082] Example 3 Zirconium oxychloride is continuously prepared using the automated energy-saving tunnel-type alkali melting furnace described in this invention, following the steps below.

[0083] (1) Preheating of zircon sand: Zircon sand is preheated by passing it through a tubular sand preheater and using the approximately 400°C combustion exhaust gas discharged from the first stage of the tunnel kiln. After preheating, the temperature of the zircon sand reaches 260°C.

[0084] (2) Alkali fusion reaction: When the infrared fiber optic thermometer detects that the temperature of the molten sodium hydroxide in the alkali fusion pot has risen to 560℃, the DCS system automatically controls the sand addition. 800kg of preheated zircon sand is added to each pot, which contains 1040kg of molten alkali (alkali-to-sand ratio 1.3:1). The sand addition process is completed within 2 minutes, and the material reacts at 640~660℃ (temperature of the sand addition reaction zone). The total reaction time (from the start of sand addition to the end of the reaction) is 8 minutes.

[0085] (3) Continuous alkali melting and transmission control: The tunnel kiln is divided into 23 sections (preheating section 1 to cooling section 6), each containing an alkali fusion pot welded to a steel frame. All steel frames are pressed onto drive wheels. After the reaction, the DCS system first shuts off the fire and combustion air, then automatically opens the first, second, and third gates. Once the gates are in position, the drive motor starts, and the drive wheels rotate synchronously, using friction to push all the steel frames, along with the alkali fusion pot, from left to right (from the alkali feeding end to the cooling end) to one station. The dwell time for each section is set to 9 minutes. After moving to the correct position, the gates automatically close, and air intake and ignition resume heating.

[0086] (4) Automatic gate separation control: The first gate is located between the preheating section and the alkali feeding end, the second gate is located between the insulation section and the cooling section, and the third gate is located between the cooling section and the material cart area. The three sets of gates open and close automatically in the order described in step (3) to ensure the separation of temperature zones inside the kiln and the smooth movement of the kiln body.

[0087] (5) Cooling and waste heat recovery: High-pressure air at ambient temperature enters from the sixth cooling section, flows through the alkali-melting material, and is heated to 300°C. All of this air is then piped to the natural gas burners in each section of the molten alkali zone as combustion air. The combustion exhaust gas passes sequentially through each section of the preheating zone and the insulation zone, finally exiting from the first preheating section at a measured temperature of 408°C. This exhaust gas first enters the sand preheater to heat the zircon sand. The exhaust gas temperature drops to 232°C upon exiting the sand preheater, then enters the waste heat boiler to generate 0.3MPa steam, with a final flue gas temperature of approximately 140°C.

[0088] (6) Automated feeding and empty pot return: After the reaction is complete, the alkali fusion pot, which is then moved to the end of the sixth cooling stage, is transported by a material cart along a track to an automatic dual-axis conveyor. The automatic dual-axis conveyor tilts the alkali fusion pot 100° to its side, and the flushing device automatically flushes the alkali fusion material in the pot into the water washing tank. After flushing, the empty pot is automatically returned to the alkali feeding end via a frame car and a pot car along a track, entering the next production cycle.

[0089] (7) Full-process automated control: The DCS system and infrared fiber optic thermometer enable automatic control of processes such as temperature monitoring, sand feeding, gate opening and closing, drive wheel start and stop, material feeding, and pot reflux. A batch of material is continuously produced every 9 minutes.

[0090] The system operated continuously for 12 hours, processing 71 batches of zircon sand (800 kg per batch), with a total alkaline hydrolysis yield of 56.8 tons. Four composite samples of the alkali-melted material were taken, and the hydrolysis rates were tested according to industry standard methods. The results were 99.32%, 98.86%, 99.18%, and 99.07%, with an average hydrolysis rate of 99.11%. The total natural gas consumption was 5549 m³, with a natural gas consumption of 78.15 m³ / batch. The waste heat boiler produced 3.4 tons of 0.3 MPa steam in 12 hours.

[0091] Example 4 Zirconium oxychloride is continuously prepared using the automated energy-saving tunnel-type alkali melting furnace described in this invention, following the steps below.

[0092] (1) Preheating of zircon sand: Zircon sand is preheated by passing it through a tubular sand preheater and using the approximately 400°C combustion exhaust gas discharged from the first stage of the tunnel kiln. After preheating, the temperature of the zircon sand reaches 250°C.

[0093] (2) Alkali fusion reaction: When the infrared fiber optic thermometer detects that the temperature of the molten sodium hydroxide in the alkali fusion pot has risen to 580℃, the DCS system automatically controls the sand addition. 800kg of preheated zircon sand is added to each pot, which contains 960kg of molten alkali (alkali-to-sand ratio 1.2:1). The sand addition process is completed within 2 minutes, and the material reacts at 640~660℃ (temperature of the sand addition reaction zone). The total reaction time (from the start of sand addition to the end of the reaction) is 9 minutes.

[0094] (3) Continuous alkali melting and transmission control: The tunnel kiln is divided into 23 sections (preheating section 1 to cooling section 6), each containing an alkali fusion pot welded to a steel frame. All steel frames are pressed onto drive wheels. After the reaction, the DCS system first shuts off the fire and combustion air, then automatically opens the first, second, and third gates. Once the gates are in position, the drive motor starts, and the drive wheels rotate synchronously, using friction to push all the steel frames, along with the alkali fusion pot, from left to right (from the alkali feeding end to the cooling end) to one station. The dwell time for each section is set to 10 minutes. After moving to the correct position, the gates automatically close, and air intake and ignition resume heating.

[0095] (4) Automatic gate separation control: The first gate is located between the preheating section and the alkali feeding end, the second gate is located between the insulation section and the cooling section, and the third gate is located between the cooling section and the material cart area. The three sets of gates open and close automatically in the order described in step (3) to ensure the separation of temperature zones inside the kiln and the smooth movement of the kiln body.

[0096] (5) Cooling and waste heat recovery: High-pressure air at ambient temperature enters from the sixth cooling section, flows through the alkali-melting material, and is heated to 300°C. All of this air is then piped to the natural gas burners in each section of the molten alkali zone as combustion air. The combustion exhaust gas passes sequentially through each section of the preheating zone and the insulation zone, finally exiting from the first preheating section at a measured temperature of 410°C. This exhaust gas first enters the sand preheater to heat the zircon sand. The exhaust gas temperature drops to 235°C upon exiting the sand preheater, then enters the waste heat boiler to generate 0.3MPa steam, with a final flue gas temperature of approximately 140°C.

[0097] (6) Automated feeding and empty pot return: After the reaction is complete, the alkali fusion pot, which is then moved to the end of the sixth cooling stage, is transported by a material cart along a track to an automatic dual-axis conveyor. The automatic dual-axis conveyor tilts the alkali fusion pot 100° to its side, and the flushing device automatically flushes the alkali fusion material in the pot into the water washing tank. After flushing, the empty pot is automatically returned to the alkali feeding end via a frame car and a pot car along a track, entering the next production cycle.

[0098] (7) Full-process automated control: The DCS system and infrared fiber optic thermometer enable automatic control of processes such as temperature monitoring, sand feeding, gate opening and closing, drive wheel start and stop, material feeding, and pot reflux. A batch of material is continuously produced every 10 minutes.

[0099] The system operated continuously for 12 hours, processing 69 batches of zircon sand (800 kg per batch), with a total alkaline hydrolysis yield of 55.2 tons. Four composite samples of the alkali-melted material were taken, and the hydrolysis rates were tested according to industry standard methods. The results were 99.01%, 98.92%, 99.10%, and 98.85%, with an average hydrolysis rate of 98.97%. The total natural gas consumption was 5520 m³, with a natural gas consumption of 80.00 m³ / batch. The waste heat boiler produced 3.3 tons of 0.3 MPa steam in 12 hours.

[0100] Comparative Example 1 Alkali fusion is performed using a traditional multi-hole single kiln, without the use of a sand preheater, automatic transmission device, or automatic material flushing and return system. The zircon sand is at room temperature (25℃), while the molten alkali temperature needs to be heated to 650℃ for alkali fusion. The sand feeding process is manual, and iron utensils are used to stir the sand to prevent sedimentation. The reaction time is approximately 15 minutes, followed by a 20-minute heat preservation period. Material flushing and transfer rely on overhead cranes.

[0101] Each boiler processes 800 kg of zircon sand at an alkali-to-sand ratio of 1.3:1. Continuous operation for 12 hours (with 5 kilns operating simultaneously) yielded 60 boilers, producing 54.0 tons of alkaline hydrolysis. The hydrolysis rates were 98.35%, 98.18%, 98.56%, and 99.02%, with an average of 98.53%. Total natural gas consumption was 7200 m³, with a single boiler consumption of 120.0 m³. No steam was produced.

[0102] Comparative Example 2 The same tunnel kiln structure as the present invention is adopted, but the sand preheater and zircon sand preheating step are eliminated (zircon sand is added at room temperature of 25°C), the cooling air recovery pipeline used as combustion air is eliminated, and the waste heat boiler is not installed. Other automated devices such as transmission, gate, and automatic material return are retained.

[0103] The process was run continuously following steps similar to those in Example 1, with the only differences being: in step (1), the zircon sand was not preheated (25°C); in step (5), the cooling air was directly discharged, and the combustion air used was ambient temperature air, with no waste heat boiler. The process ran continuously for 12 hours, processing a total of 65 batches of material, with 52.0t of alkali hydrolysis. Due to the ambient temperature of the zircon sand, localized settling occurred after sand addition, reducing the alkali hydrolysis rate. The measured rates were 97.2%, 96.8%, 97.5%, and 97.0%, with an average of 97.1%. The total natural gas consumption was 7150 m³, with a single consumption of 110.0 m³ / batch. No steam was produced.

[0104] As can be seen from the above embodiments, this invention uses air to cool the material while simultaneously providing air temperature, which is then used as combustion air, thus reducing energy consumption. Using high-temperature combustion exhaust gas to preheat the alkali increases the alkali temperature, shortens the alkali melting time, and reduces energy consumption. Using a tube heat exchanger to preheat the zircon sand with combustion exhaust gas increases the zircon sand temperature, significantly reducing the alkali temperature during sand addition, shortening the heating time, accelerating the reaction rate, and reducing energy consumption. It also eliminates zircon sand settling, increases the alkali hydrolysis rate, and reduces raw material consumption per unit area. Using a waste heat boiler to generate steam from combustion exhaust gas recovers energy and reduces energy consumption. Modularizing and automating the alkali melting and flushing process enables smooth continuous alkali melting operation, reduces labor, eliminates the need for overhead cranes to lift and transport materials, and significantly improves production efficiency.

Claims

1. An automated, energy-saving tunnel-type alkali melting furnace, characterized in that: The main tunnel kiln is divided into a preheating zone (1), a melting zone (2), a sand feeding reaction zone (3), a heat preservation zone (4), and a cooling zone (5). The preheating zone (1), melting zone (2), heat preservation zone (4), and cooling zone (5) are divided into multiple sections. The tunnel kiln is surrounded by a track (6), and a movable frame car is installed on the track (6). A sand preheater (61) is installed in the melting zone (2). The air outlet of the preheating zone (1) is connected to the sand preheater (61) through a pipeline. The gas outlet of the sand preheater (61) is connected to the waste heat boiler (63) through a pipeline. The tunnel kiln is connected to the alkali feeding end and the material flushing end. The tunnel kiln is equipped with a transmission sealing device. An automatic double-shaft carrier (10) is independently provided at the material flushing end. The automatic double-shaft carrier (10) is connected to the track (6). The material flushing end is located at the end of the cooling zone (5) and is connected to the automatic double-shaft carrier (10), the material car and the track (6) in sequence. The alkali melting pot (610) output from the cooling zone (5) is sent to the automatic double-shaft carrier (10) via the material car along the track (6) to complete the side-turning material flushing. The empty pot is returned to the alkali feeding end via the frame car and the pot car along the track (6).

2. The automated energy-saving tunnel-type alkali melting furnace according to claim 1, characterized in that: The preheating zone (1) is divided into 6 sections, the alkali melting zone (2) is divided into 4 sections, the heat preservation zone (4) is divided into 6 sections, and the cooling zone (5) is divided into 6 sections, for a total of 23 sections. Each section is equipped with a steel frame (6101), and an alkali melting pot (610) is placed in the middle of the steel frame (6101). Insulation cotton (68) is provided between the steel frame (6101) and the alkali melting pot (610). The steel frame (6101) is set on the transmission device on the refractory bricks (69) in the direction inside the tunnel kiln.

3. The automated energy-saving tunnel-type alkali melting furnace according to claim 1, characterized in that: The sand discharge port (613) at the bottom of the sand preheater (61) is connected to the automatic metering device (62) on the side through a pipeline. The automatic metering device (62) receives materials from the sand feeding reaction zone (3) through the tipping bucket elevator (624).

4. The automated energy-saving tunnel-type alkali melting furnace according to claim 1, characterized in that: The tunnel kiln is specifically divided into 23 sections as follows: Preheating Section 1 (11), Preheating Section 2 (12), Preheating Section 3 (13), Preheating Section 4 (14), Preheating Section 5 (15), Preheating Section 6 (16), Molten Alkali Section 1 (21), Molten Alkali Section 2 (22), Molten Alkali Section 3 (23), Molten Alkali Section 4 (24), Sand Feeding Reaction Zone (3), Insulation Section 1 (41), Insulation Section 2 (42), Insulation Section 3 (43), Insulation Section 4 (44), Insulation Section 5 (45). The insulation section is divided into six sections (46), cooling section one (51), cooling section two (52), cooling section three (53), cooling section four (54), cooling section five (55), and cooling section six (56). A first gate (7) is provided between the preheating section one (11) and the alkali feeding end, and a second gate (8) is provided between the insulation section six (46) and the cooling section one (51). The cooling section six (56) is adjacent to the material car area and a third gate (9) is provided between the cooling section six (56) and the material car area.

5. The automated energy-saving tunnel-type alkali melting furnace according to claim 4, characterized in that: An air outlet is provided at the cooling section (51), and the air outlet is connected to the air inlet of the insulation section (41) through a pipeline. The preheating section (11) is connected to the sand preheater (61) through a pipeline.

6. The automated energy-saving tunnel-type alkali melting furnace according to claim 1, characterized in that: The transmission sealing device includes a transmission wheel (64), a bearing fixing plate (65), a motor fixing plate (66), and a drive motor (67). The transmission wheel (64) is installed on the steel structure of the tunnel kiln via the bearing and the bearing fixing plate (65). The drive motor (67) is fixed on the outside of the kiln body via the motor fixing plate (66). The output shaft of the drive motor (67) is connected to the transmission wheel (64).

7. The automated energy-saving tunnel-type alkali melting furnace according to claim 1, characterized in that: The sand preheater (61) is a carbon steel shell and tube heat exchanger. The main body consists of 1600 steel tubes with an inner diameter of 36mm, a wall thickness of 2mm, and a length of 3m. The upper part has a square sealing plate of 3×3m, a surrounding sand baffle plate of 0.4m high, and a square cone-shaped inclined surface at the bottom. An electric sand discharge valve is installed at the bottom.

8. A process for preparing zirconium oxychloride by alkaline fusion using the automated energy-saving tunnel-type alkaline fusion furnace according to any one of claims 1 to 7, characterized in that, Includes the following steps: (1) Preheating of zircon sand: Zircon sand is preheated by passing it through a sand preheater and using the combustion exhaust gas from an automated energy-saving tunnel-type alkali melting furnace to reach a preheating temperature of 200~300℃. (2) Alkali fusion reaction: The preheated zircon sand is put into an alkali melting pot containing molten sodium hydroxide at a temperature of 520~580℃. The alkali-to-sand ratio is 1.2~1.4:1, and the reaction time after adding the sand is controlled within 10 minutes. (3) Continuous alkali melting and transmission control: The tunnel-type alkali melting furnace is adopted. The furnace body is divided into multiple temperature sections, totaling 23 sections from preheating to cooling. Each section contains an alkali melting pot welded to a steel frame. The steel frame is synchronously driven by a transmission wheel and moves forward one station at a set time interval. (4) Automatic gate separation control: Automatic gates are installed between the alkali feeding end and the preheating zone, between the insulation zone and the cooling zone, and between the cooling zone and the material cart area. They open automatically after the reaction is completed and close automatically after the pot body moves into place. (5) Cooling and waste heat recovery: Normal temperature high pressure air enters from the end of the cooling zone, and after flowing through the alkali molten material, it is heated to 280~330℃ and is used entirely as combustion air; the combustion exhaust gas preheats each section of the alkali molten pot in sequence, and finally exits at a temperature of 390~410℃, and is then used to preheat zircon sand and generate steam in the waste heat boiler. (6) Automated feeding and empty pot return: After the reaction is completed, the alkali melting pot is moved to the feeding end and automatically tilted by an automatic dual-shaft carrier (10) to feed the material. After the feeding is completed, the empty pot is automatically returned to the alkali feeding end and enters the next cycle. (7) Full-process automated control: The DCS system and infrared fiber optic thermometer enable automatic control of temperature monitoring, sand feeding, gate opening and closing, drive wheel start and stop, material feeding, and alkali melting pot body return process, achieving continuous production of one batch of material every 8 to 12 minutes.

9. The process for preparing zirconium oxychloride by alkali fusion according to claim 8, characterized in that: In step (3), there are 23 stages from preheating to cooling, with the following temperature sequence: Preheating stage 1: 390~410℃; Preheating stage 2: 430~450℃; Preheating stage 3: 460~480℃; Preheating stage 4: 490~510℃; Preheating stage 5: 520~540℃; Preheating stage 6: 540~560℃; Molten alkali stage 1: 560~580℃; Molten alkali stage 2: 580~600℃; Molten alkali stage 3: 600~620℃; Molten alkali stage 4: 620~640℃; Sand addition reaction zone: 640~660℃. The insulation temperature ranges as follows: Section 1: 620-640℃; Section 2: 570-590℃; Section 3: 520-540℃; Section 4: 470-490℃; Section 5: 430-450℃; Section 6: 400-420℃. The cooling temperature ranges as follows: Section 1: 370-390℃; Section 2: 320-340℃; Section 3: 260-280℃; Section 4: 190-210℃; Section 5: 120-140℃; Section 6: 40-60℃. The material remains in each section for 8-12 minutes.

10. The process for preparing zirconium oxychloride by alkali fusion according to claim 8, characterized in that: After the reaction is completed in step (6), the alkali melting pot is moved to the automatic biaxial carrier at the feeding end, and the automatic biaxial carrier tilts the alkali melting pot 100° to the side.

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