A powder fluidized bed processing furnace

Abstract

A fluidized bed powder processing furnace, relating to the field of powder materials, is disclosed. It comprises a heating furnace, a fluidized bed, a gas circulation device, a gas preheater, and a tail gas cooling device. The fluidized bed is placed vertically, with a gas distributor at its bottom. The powder to be processed, packed in the fluidized bed, is agitated by an auxiliary gas distributor to establish a fluidized state, and then maintained by the main gas distributor of the gas circulation device. In the powder fluidized bed processing furnace, the high-temperature working gas is circulated back by the gas circulation device to maintain the fluid state of the ceramic powder in the fluidized bed. This high-temperature working gas circulation significantly reduces the consumption of working gas and heating energy, while improving the temperature uniformity inside the fluidized bed. Multiple gas distributors are installed at the bottom of the fluidized bed, each with independent gas supply, enabling accurate control of the fluidization state and simultaneous introduction of multiple gases, resulting in good process applicability. The tail gas cooling device is used to cool and vent the high-temperature gas discharged from the heating furnace.

Description

Technical Field

[0001] This invention relates to the field of powder materials, and in particular to a powder fluidized bed processing furnace. Background Technology

[0002] Ceramic powders have a wide range of applications in the processing and preparation of ceramic materials. High-performance ceramic powders are a prerequisite for the preparation of high-performance ceramic components. In the heat treatment of ceramic powders, such as sintering preparation and surface coating modification, ceramic powders can be divided into two types according to their fixed state: static stacking and dynamic flow. In static stacking, due to the long-term contact between ceramic powders, sintering and agglomeration at high temperatures cannot be avoided. The agglomeration of ceramic powders ultimately leads to a decrease in powder performance. In order to avoid the sintering and agglomeration of ceramic powders, dynamic flow methods such as fluidization, stirring, vibration or rotary kiln can be used in the heat treatment process to make the powder move and avoid the sintering and agglomeration caused by the long-term contact between ceramic powder particles [Wang Yong et al., Preparation of nano-silicon nitride powder by fluidized bed CVD method [J]. Journal of Inorganic Materials, 2006, 21(1):41-44]. Among the above-mentioned dynamic flow methods, the most common method is to use a fluidized bed to heat treat ceramic powder in a fluidized state. The fluidization process can use a single fluidized bed or a series of fluidized beds to achieve batch processing and continuous processing. When processing ceramic powder in a fluidized bed, a large carrier gas flow rate is usually required to keep the ceramic powder in a fluidized state. The working gas is discharged immediately after entering the fluidized bed, resulting in a huge consumption of working gas. Especially at higher temperatures, the preheating of a large flow rate of working gas consumes even more energy, which limits the further application of fluidized beds in the field of ceramic powder heat treatment. Summary of the Invention

[0003] The purpose of this invention is to address the aforementioned problems by providing a powder fluidized bed processing furnace. This furnace integrates a high-temperature gas circulation device to achieve partial recirculation of the working carrier gas at high temperatures. This saves energy consumption for the working gas and heating the working gas while meeting the requirements of fluidized bed operation, enabling low-cost, mass production of high-performance powders.

[0004] A powder fluidized bed processing furnace is provided with a heating furnace, a fluidized bed, a gas circulation device, a gas preheater, and a tail gas cooling device;

[0005] The heating furnace is used for heating and controlling the temperature; the fluidized bed and gas circulation device are located inside the heating furnace and are heated and maintained at the temperature by the heating furnace; the gas preheater and exhaust gas cooling device are located outside the heating furnace.

[0006] The fluidized bed is a vertically placed cylindrical body. A gas distributor is provided at the bottom of the fluidized bed. Gas blows the powder through the gas distributor and keeps it in a fluidized state. Different fluidization states of the powder can be adjusted by controlling the gas flow rate. A conical body with an increasing diameter from bottom to top is provided at the top of the fluidized bed. Powder leaving the cylindrical body and entering the conical body settles back into the cylindrical body due to the reduced gas flow rate.

[0007] The gas circulation device is located inside the heating furnace and operates at the furnace's operating temperature to maintain gas circulation. The high-temperature circulating working gas mixes with the newly introduced gas before entering the fluidized bed to agitate the powder. At least two gas distributors are provided, each supplying gas independently. The gas distributor connected to the gas circulation device is the main distributor, while the one directly connected to an external working gas supply is the auxiliary distributor. The main distributor provides the primary working gas for fluidizing the ceramic powder in the fluidized bed. The auxiliary distributor provides gas with the same or different composition as the main distributor, depending on the operating conditions, and is used to regulate the total gas flow rate of the main and auxiliary gas distributors to maintain a stable fluidization state of the ceramic powder in the fluidized bed. In the initial stage, the ceramic powder packed in the fluidized bed is agitated by the auxiliary gas distributor to establish a fluidized state, which is then maintained by the main gas distributor.

[0008] Both the main gas distributor and the auxiliary gas distributor have gas preheaters at their inlet sections. After preheating by the gas preheaters, the preheated main gas mixes with the gas in the heating furnace in the gas circulation device, and the preheated auxiliary gas enters the fluidized bed. The auxiliary gas is preheated to avoid interference with the temperature uniformity of the fluidized bed due to the low inlet temperature.

[0009] The exhaust gas cooling device is installed outside the heating furnace and is used to cool and vent the high-temperature gas discharged from the inside of the heating furnace.

[0010] The gas distributor can be provided in 2 to 4 units. Each gas distributor supplies gas independently.

[0011] The gas circulation device can be a jet pump, a centrifugal circulating fan, or a piston fan.

[0012] Both the main gas distributor and the auxiliary gas distributor are equipped with gas preheaters at their inlets. After preheating, the preheated main gas mixes with the gas in the furnace in a gas circulation device, and the preheated auxiliary gas enters the fluidized bed. Gas preheating avoids interference with the temperature uniformity of the fluidized bed caused by low inlet gas temperature.

[0013] The exhaust gas cooling device is installed outside the heating furnace, and the exhaust gas cooling device can be water-cooled, air-cooled, or other methods.

[0014] Advantages of this invention:

[0015] 1. The ceramic powder is fluidized at high temperature by using a high-temperature gas internal circulation method, which can greatly reduce the consumption of working gas and heating energy compared with the traditional working gas flow fluidization process.

[0016] 2. The internal circulation of high-temperature gas improves the temperature uniformity and stability inside the fluidized bed.

[0017] 3. By setting different gas distributors, accurate control of the fluidization state and simultaneous introduction of multiple gases can be achieved, resulting in good process applicability. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the functional structure of a powder fluidized bed processing furnace.

[0019] Figure 2 This is a schematic diagram of the structure of a powder fluidized bed processing furnace.

[0020] The markings in the figure are as follows: fluidized bed 1, powder inlet 101, powder outlet 102, jet pump 2, main gas distributor 3, vent hole 301 on the main gas distributor, auxiliary gas distributor 4, vent hole 401 on the auxiliary gas distributor, working gas preheater 5, auxiliary gas preheater 6, tail gas cooler 7, and heating furnace 8. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the following embodiments will be used in conjunction with the accompanying drawings to further illustrate the invention. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Matters not covered in this invention are common knowledge.

[0022] Example 1

[0023] In this embodiment, the fluidized bed furnace is used to pyrolyze high molecular weight polycarbosilane (HMPCS) powder in ammonia at high temperature to form silicon nitride powder.

[0024] like Figure 1 and 2 As shown, the powder fluidized bed processing furnace described in this embodiment includes a heating furnace 8, a fluidized bed 1, a jet pump 2, a working gas preheater 5, an auxiliary gas preheater 6, a gas auxiliary distributor 4, and a tail gas cooling device 7.

[0025] The heating furnace 8 provides the necessary high-temperature environment for the internal system, allowing HMPCS powder to pyrolyze and nitridate into silicon nitride powder. The furnace 8 is heated and its temperature is controlled by electric heating rods. Inside the furnace 8 is a fluidized bed 1 and a jet pump 2, which serves as a gas circulation device. The fluidized bed 1 is a vertically mounted cylindrical body, containing the heat-treated HMPCS powder. A main gas distributor 3 and an auxiliary gas distributor 4 are installed at the bottom of the fluidized bed 1. Gas is evenly distributed within the fluidized bed through these two distributors, keeping the powder in a fluidized state. A conical cylinder with a diameter increasing from bottom to top is installed above the fluidized bed 1. Powder leaving the cylindrical body and entering the conical cylinder settles back into the cylindrical body due to the reduced gas velocity. After being preheated by the working gas preheater 5, the main working gas ammonia is injected into the jet pump 2. As a gas circulation device, the jet pump 2 will simultaneously draw in the main working gas ammonia that has passed through the preheater 5 and the high-temperature ammonia-nitrogen mixture circulating inside the heating furnace 8. After the two gases are mixed in the jet pump 2, they are discharged into the main gas distributor 3, and then uniformly enter the fluidized bed 1 through the vent 301 on the main gas distributor 3.

[0026] The gas-assisted distributor 4 is used to uniformly distribute the auxiliary gas (nitrogen) into the fluidized bed 1 to help maintain the fluidization state of the fluidized bed;

[0027] The working gas preheater 5 is used to preheat the main working gas (ammonia) to a suitable temperature so that it can be mixed with the high-temperature gas in the jet pump 2;

[0028] The auxiliary gas preheater 6 is used to preheat the auxiliary working gas (nitrogen) to bring its temperature close to that in the heating furnace 8, so as to maintain the temperature stability and uniformity in the fluidized bed. After passing through the auxiliary gas preheater 6, the auxiliary nitrogen gas enters the gas auxiliary distributor 4, and then enters the fluidized bed 1 evenly through the vent 401 on the gas auxiliary distributor 4. The HMPCS powder in the fluidized bed 1 is blown up by the working gas and auxiliary gas entering the fluidized bed and kept in a fluidized state.

[0029] The exhaust gas cooling device 7 is installed on the exhaust port of the heating furnace 8. The exhaust gas cooling device 7 adopts water cooling and can cool the exhaust gas discharged from the heating furnace 8 to below 200°C and then discharge it into the air.

[0030] In the initial stage, the HMPCS powder being treated and packed in the fluidized bed 1 can first be blown up by the auxiliary gas distributor 4 to establish a fluidized state, and then switched to the main gas distributor 3 to maintain its fluidized state.

[0031] In fluidized bed 1, the HMPCS powder is gradually nitrided into silicon nitride powder under heating in a furnace. The main working gas, ammonia, is preheated in the main gas distributor 5 and then mixed with the high-temperature gas in the furnace in the jet pump 2. The auxiliary working gas, nitrogen, is also preheated in the auxiliary gas preheater 6. All gas temperatures are close to those in the furnace 8 to improve the stability and uniformity of the gas flow temperature in the fluidized bed and to avoid interference from low inlet gas temperature on the temperature of the HMPCS powder in fluidized bed 1.

[0032] A powder inlet 101 is provided at the top of the heating furnace. HMPCS powder is fed into the fluidized bed 1 through the powder inlet 101. Raw materials can be easily replenished through the powder inlet 101 for continuous or batch processing. A powder discharge port 102 is provided at the bottom of the fluidized bed 1 to discharge the silicon nitride powder generated in the reaction. In this embodiment, the gas-assisted distributor 4 and the plug of the powder discharge port 102 are the same component. When installed on the powder discharge port 102, it functions as a gas-assisted distributor 4 to ensure uniform gas distribution. When this component is removed, the powder discharge port 102 is opened, allowing the silicon nitride powder generated in the reaction to be discharged from the fluidized bed 1. This design not only simplifies the equipment structure but also improves the flexibility and efficiency of operation, making the entire fluidized bed processing furnace system more practical and efficient.

[0033] Example 2

[0034] In this embodiment, the fluidized bed furnace is used to heat silicon powder to 1300°C in nitrogen atmosphere to prepare silicon nitride powder.

[0035] This embodiment includes a heating furnace 8, a fluidized bed 1, a gas circulation device (centrifugal fan) 2, a gas distributor 3, 4, and a tail gas cooling device 7;

[0036] The heating furnace uses electrically powered carbon rods for heating and is equipped with a temperature control system to ensure precise temperature control. The internal space of the heating furnace is used to accommodate the fluidized bed and gas circulation device.

[0037] Fluidized bed 1 is a vertically placed cylindrical body with gas distributors 3 and 4 at the bottom. A cone with a diameter increasing from bottom to top is located at the top of fluidized bed 1 to ensure that the powder can smoothly settle back into the cylindrical body when the gas flow rate decreases. The fluidized bed is made of graphite.

[0038] The gas circulation system uses a centrifugal circulating fan to maintain nitrogen circulation at the furnace's operating temperature. The high-temperature circulating gas, mixed with the newly introduced nitrogen, enters the fluidized bed, ensuring uniform heating of the silicon powder within the fluidized bed.

[0039] There are three gas distributors: one main distributor and two auxiliary distributors. Each gas distributor supplies gas independently. The main distributor provides the primary working gas for fluidizing silicon powder in the fluidized bed. The auxiliary distributors, depending on the operating conditions, provide the same nitrogen as the main distributor or gases such as argon or hydrogen to dilute the nitrogen concentration. They are also used to regulate the total gas flow rate of the main and auxiliary gas distributors to maintain a stable fluidization state of the silicon powder and the formed silicon nitride in the fluidized bed. Specifically, the main distributor supplies nitrogen; the first auxiliary distributor supplies nitrogen; and the second auxiliary distributor supplies argon and hydrogen.

[0040] Both the main gas distributor and the auxiliary gas distributor have gas preheaters at their inlet sections. After preheating by the gas preheaters, the preheated main gas mixes with the gas in the furnace in a gas circulation device, and the preheated auxiliary gas enters the fluidized bed. Gas preheating avoids interference with the temperature uniformity of silicon powder and silicon nitride powder in the fluidized bed due to low inlet gas temperature. The preheating temperature is 1100–1300℃.

[0041] The exhaust gas cooling device is installed outside the heating furnace. It cools the high-temperature gas discharged from the furnace before venting, ensuring that the temperature of the emitted gas does not harm the environment. The exhaust gas cooling device uses water cooling, and the cooled exhaust gas temperature ranges from 60 to 200°C.

[0042] The work process is as follows:

[0043] 1) Start-up phase: Turn on the electric heating element and set the heating temperature to 1100℃. Start the gas circulation device, ensuring normal gas circulation, and set the airflow to 1500m³ / h. 3 / h.

[0044] 2) Filling the powder: Fill 200 kg of ceramic powder into the fluidized bed.

[0045] 3) Initial fluidization: The ceramic powder is agitated by an auxiliary gas distributor to establish a fluidized state, with the gas flow rate set to 500 m³ / h. 3 / h.

[0046] 4) Maintain fluidization: The main gas distributor starts supplying gas, and the gas flow rate is set to 1000 m³ / h. 3 / h, maintaining the fluidized state of the ceramic powder. Adjust the gas flow rate of the auxiliary gas distributor as needed, setting it to 500m³ / h. 3 / h, to ensure stable temperature and gas flow rate within the fluidized bed.

[0047] 5) Cooling and venting: After processing, turn off the electric heating rod and stop gas circulation. The high-temperature gas is cooled to 100°C by the exhaust gas cooling device before being vented.

[0048] Example 3

[0049] Similar to Example 2, the gas circulation device in this example uses a piston fan, and there are two gas distributors: one main distributor and one auxiliary distributor. The exhaust gas cooling device uses a combination of water cooling and air cooling.

[0050] This invention is applicable to the heat treatment process of materials such as ceramic powders and has broad application prospects.

[0051] The above embodiments are merely preferred embodiments of the present invention and should not be considered as limiting the scope of the present invention. All equivalent variations and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A powder fluidized bed processing furnace, characterized in that... It is equipped with a heating furnace, fluidized bed, gas circulation device, gas preheater and exhaust gas cooling device; The heating furnace is equipped with a temperature control heating device for heating the fluidized bed, gas circulation device and powder being processed inside the heating furnace. The fluidized bed is a vertically placed cylindrical body. A gas distributor is provided at the bottom of the fluidized bed. The gas distributor blows the powder up and keeps it in a fluidized state. The different fluidization states of the powder are adjusted by controlling the gas flow rate. A conical body with a diameter that increases from bottom to top is provided at the top of the fluidized bed. Powder that leaves the cylindrical body and enters the conical body settles back into the cylindrical body due to the reduced gas flow rate. The fluidized bed and gas circulation device are located inside the heating furnace, which heats and keeps the temperature. The gas circulation device operates at the working temperature of the heating furnace to maintain gas circulation. The high-temperature working gas is circulated back by the gas circulation device, mixed with the newly entered gas, and then enters the fluidized bed to maintain the fluid state of the ceramic powder in the fluidized bed. The gas distributor is provided with at least two units, each supplying gas independently. The gas distributor connected to the gas circulation device is the main distributor, and the one directly connected to the external working gas supply is the auxiliary distributor. The main distributor provides the main working gas for the fluidization of ceramic powder in the fluidized bed, and the auxiliary distributor provides gas with the same or different composition as the main distributor according to the working conditions. It is also used to adjust the total gas flow rate of the main gas distributor and the auxiliary gas distributor to maintain the fluidization state of the ceramic powder in the fluidized bed. In the initial stage, the ceramic powder packed in the fluidized bed is blown up by the auxiliary gas distributor to establish the fluidization state, and then blown up by the main gas distributor to maintain its fluidization state. The gas preheater and exhaust gas cooling device are located outside the heating furnace; the exhaust gas cooling device is used to cool the high-temperature gas discharged from the inside of the heating furnace before venting it. Both the main gas distributor and the auxiliary gas distributor have gas preheaters at their inlet sections. After preheating by the gas preheaters, the preheated main gas mixes with the gas in the heating furnace in the gas circulation device, and the preheated auxiliary gas enters the fluidized bed. The auxiliary gas is preheated to avoid interference with the temperature uniformity of the fluidized bed due to the low inlet temperature.

2. The powder fluidized bed processing furnace as described in claim 1, characterized in that... The gas distributor is provided in 2 to 4 parts, each gas distributor supplies gas independently, and one of the gas distributors is connected to the gas circulation device.

3. The powder fluidized bed processing furnace as described in claim 1, characterized in that... The gas circulation device employs a jet pump, a centrifugal circulating fan, or a piston fan.

4. The powder fluidized bed processing furnace as described in claim 1, characterized in that... The exhaust gas cooling device is either water-cooled or air-cooled.

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