CN111141145A - Powder synthesis furnace based on low-temperature self-propagating combustion principle and synthesis method - Google Patents
Powder synthesis furnace based on low-temperature self-propagating combustion principle and synthesis method Download PDFInfo
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Abstract
Relates to a powder synthesis furnace based on a low-temperature self-propagating combustion principle, which comprises a middle shell, a plurality of combustion synthesizers, a blanking hopper, an airflow conveyor, a powder separator, a first-stage powder collecting barrel and a second-stage powder collecting barrel; the plurality of combustion synthesizers are respectively connected with the middle shell, the blanking hopper is connected to the lower part of the middle shell, and a cavity formed by the middle shell and the blanking hopper in a communicated mode is an inner cavity of the synthesis furnace; the blanking hopper, the airflow conveyor, the powder separator and the second-stage powder collecting barrel are sequentially connected, the upper end of the powder separator is communicated with the blanking hopper, and the first-stage powder collecting barrel is connected with the tail end of the airflow conveyor. The middle shell and a plurality of combustion synthesizers arranged on the periphery of the middle shell form a synthesizer unit. The synthesis furnace ensures the safety and controllability of the synthesis process, further simplifies the production flow, reduces the production energy consumption and improves the production efficiency. Also relates to a powder synthesis method based on the low-temperature self-propagating combustion principle, which can realize continuous and stable low-temperature self-propagating combustion.
Description
Technical Field
The invention belongs to the field of synthesis of superfine oxide powder, and particularly relates to a powder synthesis furnace and a synthesis method based on a low-temperature self-propagating combustion principle.
Background
A low-temp self-spreading combustion synthesis method for synthesizing superfine oxide powder features that the nitrate and complexing agent (citric acid, glycine, stearic acid, EDTA, etc.) dissolved in water are used as raw materials, and the superfine oxide powder with high dispersity is prepared through solution compounding, evaporating concentration, gel forming, drying, ignition and heat treatment. In the published data on low temperature self-propagating combustion synthesis of oxide powder, most of them need to go through gel formation and gel drying process, and then the block-shaped or ground xerogel is initiated to burn, and the method for initiating self-propagating combustion of xerogel to obtain the target product is also called sol-self-propagating combustion synthesis method or low temperature combustion synthesis method. In fact, the low-temperature self-propagating combustion synthesis method and the ordinary sol-gel method both need a violent redox reaction to obtain the product, and the difference is that: 1. the low-temperature self-propagating combustion synthesis method realizes the balance of the total amount of the oxidant and the reducing agent in the system by accurately calculating the dosage of the complexing agent (reducing agent) according to the total amount of the nitrate (oxidant), and ensures that the full combustion can be realized without depending on external oxygen in the combustion process. The nitrate is an efficient combustion improver, so that the low-temperature self-propagating combustion reaction is fast in speed and short in time, and the full reaction can be realized without continuous high-temperature heating; 2. in the sol-gel method, no matter a complexing agent-nitrate system or a complexing agent-metal alkoxide system, in order to ensure uniform dispersion and complexation of ions, the dosage of the used complexing agent is large, the reducing agent is obviously excessive in the combustion process, and the pure-phase oxide powder can be obtained only by continuously heating in an oxidizing atmosphere to ensure that the organic matter is fully decomposed. The low-temperature self-propagating combustion synthesis method develops the advantages of the sol-gel synthesis method, realizes the uniform mixing of the raw materials on the ion level, is suitable for synthesizing mixed-phase oxides of different elements or novel oxides containing multiple doping elements, and can obtain loose and highly dispersed superfine oxide powder. In contrast, the low-temperature self-propagating combustion synthesis method can reduce the amount of the complexing agent and remarkably reduce the production cost, and the obtained powder is often fluffy and the crystal grains are finer and uniform due to the violent and rapid reaction.
At present, in the industrial synthesis of ultrafine oxide powder, the application popularity of the low-temperature self-propagating combustion synthesis method is still low, and the high powder production cost is the root cause of the current situation. Besides the high cost of raw materials, the low-temperature self-propagating combustion method has many processes, the reaction speed is difficult to control, and continuous and large-scale production cannot be carried out, which is also an important reason for the overhigh production cost of products. At present, the low-temperature self-propagating combustion synthesis method still belongs to a common method for preparing a small amount of oxide powder under laboratory conditions, has low technical maturity and cannot be applied to industrial production. According to the related literature, when the powder is synthesized by a low-temperature self-propagating combustion synthesis method in a laboratory, a ceramic crucible is usually used for containing block-shaped xerogel or crushed gel powder, then the xerogel or the crushed gel powder is heated by a muffle furnace or ignited by flame at normal temperature, and after the ignition is successful, the combustion reaction is accelerated continuously due to more reaction heat release until the combustion reaction is stopped due to the exhaustion of materials. Because the nitrate and the organic matters are burnt violently, gel contained in the crucible cannot be excessive, otherwise, flame is easy to spray out to cause fire hazard. Since the self-propagating combustion reaction is difficult to control and has high risk, the enthusiasm of researchers using the method is low, and the technical development is slow.
Disclosure of Invention
Aiming at the technical problems in the prior art, the invention aims to: the powder synthesis furnace based on the low-temperature self-propagating combustion principle ensures the safety and controllability of the synthesis process, further simplifies the production flow, reduces the production energy consumption and improves the production efficiency.
The invention also aims to provide a powder synthesis method based on the low-temperature self-propagating combustion principle, which can realize continuous and stable low-temperature self-propagating combustion.
In order to achieve the purpose, the invention adopts the following technical scheme:
the powder synthetic furnace based on the low-temperature self-propagating combustion principle comprises a middle shell, a plurality of combustion synthesizers, a blanking hopper, an airflow conveyor, a powder separator and a secondary powder collecting barrel; the plurality of combustion synthesizers are respectively connected with the middle shell, the blanking hopper is connected to the lower part of the middle shell, and a cavity formed by the middle shell and the blanking hopper in a communicated mode is an inner cavity of the synthesis furnace; the blanking hopper, the airflow conveyor, the powder separator and the secondary powder collecting barrel are sequentially connected, and the upper end of the powder separator is communicated with the blanking hopper.
Preferably, the combustion synthesizer comprises a thermocouple, a resistance heating wire, a ceramic tube, a ceramic fiber heating sleeve and a ceramic fiber heat preservation felt which are sequentially arranged from inside to outside; the resistance heating wires are spirally arranged along the inner side wall of the ceramic fiber heating sleeve; one end of the ceramic tube is inserted into the middle shell, and the front end of the thermocouple extends to the inner side wall.
Preferably, one end of the ceramic tube, which is far away from the end inserted into the middle shell, is provided with a ceramic plug, and a gap is sealed between the ceramic plug and the ceramic tube through a high-temperature adhesive.
Preferably, the middle shell and the combustion synthesizers arranged on the periphery of the middle shell form a synthesizer unit, and the powder synthesis furnace comprises a plurality of synthesizer units which are sequentially connected in a stacked mode; the upper end of the middle shell of the synthesizer unit at the uppermost part is provided with a top cover, and the top cover is provided with a tail gas filter box. A 200-mesh stainless steel filter screen is additionally arranged between the tail gas filter box and the top cover, and high-temperature resistant filter cloth is filled in the tail gas filter box.
Preferably, the powder collecting device further comprises a primary powder collecting barrel, and the primary powder collecting barrel is connected with the tail end of the airflow conveyor.
Preferably, the airflow conveyor comprises a shell, a guide plate and a compressed air spray pipe; the two opposite ends of the shell are provided with valves, and the guide plate and the compressed air spray pipe are sequentially and oppositely connected to the inner wall of the shell between the two valves from top to bottom; the compressed gas spray pipe extends horizontally; the guide plate inclines and extends downwards, one end of the guide plate is connected with the inner wall of the shell, and the other end of the guide plate extends to the connecting end of the compressed air spray pipe.
Preferably, the powder separator comprises a shell and three layers of filter screens with different meshes, wherein the three layers of filter screens are horizontally arranged in the shell; the gas pipeline is positioned above the filter screen and communicated with the blanking hopper; the feeding pipeline is opposite to the nozzle of the compressed air spray pipe and is connected with the shell of the airflow conveyor.
Preferably, the powder synthesis furnace further comprises a feeding system, the feeding system comprises a feeding pump and a feeding pipeline, and the feeding pipeline is connected with one end, provided with a ceramic plug, of the ceramic pipe.
Preferably, the middle shell is provided with a viewing window.
Preferably, the combustion synthesizer is connected with the middle shell through bolts, so that the combustion synthesizer is convenient to disassemble, assemble, maintain and replace.
Preferably, the ceramic fiber heating jacket is made of aluminum silicate fibers, mullite fibers or zirconia fibers; the resistance heating wire is an iron-chromium heating wire or a nickel-chromium heating wire.
Preferably, the ceramic tube is a high-temperature-resistant, insulating, high-alumina, corundum, or quartz ceramic tube.
Preferably, the ceramic tube has a length of 20-40 cm, an inner diameter of 20-50 mm and a wall thickness of 3-15 mm.
Preferably, the length of the ceramic tube is larger than that of the ceramic fiber heating jacket, one end of the ceramic tube extends into the middle shell, and the other end of the ceramic tube is connected with a feeding pipeline of the feeding system.
Preferably, the master control box is provided with a temperature control meter, an ammeter, a feeding pump controller, a compressed air valve, an air pressure meter, a knob switch, an indicator light, an alarm and other parts, and has the functions of power distribution, temperature control, feeding start-stop and flow regulation, a compressed air switch, pressure indication, alarm and the like.
Preferably, the top cover and the middle shell, the two adjacent synthesizer units, the middle shell and the blanking hopper, and the blanking hopper and the airflow conveyor are connected by bolts and are additionally provided with sealing rubber rings.
Preferably, the air flow conveyor and the first-stage powder collecting barrel, the air flow conveyor and the powder separator, the powder separator and the blanking hopper, and the powder separator and the second-stage powder collecting barrel are connected by clamp quick connectors and are additionally provided with silica gel sealing rings.
Preferably, the mounting bracket is made of angle steel or square steel through welding, and rollers are mounted at the bottom of the mounting bracket and are convenient for moving equipment.
The powder synthesis method based on the low-temperature self-propagating combustion principle comprises the following steps of:
(1) preparing a nitrate solution: calculating the required dosage of various nitrates according to the total amount of the required prepared powder, weighing the nitrates, adding deionized water, heating and dissolving to prepare a nitrate solution, and filtering the nitrate solution to remove insoluble impurities; or according to the amount of various nitrates calculated according to the total amount of the powder to be prepared, adopting oxides, hydroxides, carbonates and other raw materials to react with nitric acid to prepare aqueous solution containing the same amount of nitrates, and filtering the nitrate solution to remove insoluble impurities; (2) preparing a combustible solution: heating the nitrate solution obtained in the step (1) to 70-80 ℃, preserving heat, adding one or more of organic matters such as urea, polyethylene glycol, citric acid, glycine, cane sugar and the like as a combustion agent, and continuously heating to 70-90 ℃ for evaporation and concentration to obtain a combustible solution; (3) continuous self-propagating combustion: starting the powder synthesis furnace, setting the heating temperature of the combustion reactor to be 500-800 ℃, continuously inputting the combustible solution obtained in the step (2) into the combustion synthesizer after the temperature is stable, enabling the combustible solution to generate continuous self-propagating combustion in the ceramic tube, and enabling the powder generated by combustion to fall into a blanking hopper; (4) and (3) collecting powder: when the combustion products are fluffy powder, simultaneously opening upper and lower valves of the airflow conveyor, and enabling the powder to fall into a first-stage powder collecting barrel; when the combustion products contain slag, opening an upper valve of the airflow conveyor, keeping a lower valve closed, inputting compressed gas, conveying fluffy powder to the powder separator and falling into a secondary powder collecting barrel; (5) calcining treatment: the powder generated by self-propagating combustion is calcined by using a high-temperature kiln, and target powder which is easy to disperse and has nano, submicron or micron grain size can be obtained by adjusting the parameters of the calcination process.
Preferably, in the step (4), when the combustible solution is completely combusted in the synthesis process, the combustion product is uniform and fluffy flocculent powder and does not contain slag, simultaneously opening upper and lower valves of the airflow conveyor and stopping inputting compressed air, at the moment, the powder falls into the first-level powder collecting barrel, quickly closing the upper valve after the barrel is expected to be filled with the powder after a certain time, detaching and emptying the first-level powder collecting barrel, or directly replacing the first-level powder collecting barrel with an empty powder collecting barrel, and opening the upper valve again after the replacement is finished, so that the powder still falls into the first-level powder collecting barrel; when liquid drops fall due to insufficient combustion of a combustible solution or a small amount of slag is formed in a combustion product in the synthesis process, an upper valve of an airflow conveyor is opened, a lower valve is kept closed, compressed gas is input, fluffy powder is conveyed to a powder separator and falls into a secondary powder collecting barrel, after the secondary powder collecting barrel is expected to be filled with powder after a certain time, the input of the compressed gas is stopped, the upper valve of the airflow conveyor is closed, and the upper valve is opened and the compressed gas is input after the secondary powder collecting barrel is rapidly replaced; because the conglomeration formed by the slagging or the unburned solution is accumulated on the lower valve plate of the airflow conveyor, in order to prevent the conglomeration from being blown into the powder separator after the conglomeration is too much, the lower valve is required to be opened and closed at intervals of 5-10 min to enable the slagging or the conglomeration to enter the primary powder collecting barrel.
In summary, the present invention has the following advantages:
1. the invention ensures that the synthesis process is safe and controllable through process improvement and special equipment research and development, further simplifies the production flow, reduces the production energy consumption, improves the production efficiency, comprehensively reduces the powder production cost by matching with a low-cost raw material system, is beneficial to the popularization and application of the low-temperature self-propagating combustion synthesis method, and can promote the commercial production of various high-performance nano and submicron oxide powders.
2. The invention of the combustion synthesizer enables the realization of the continuous self-propagating combustion reaction to have a hardware basis, after the formula of the existing nitrate-citric acid powder synthesis raw material system is improved, the continuous self-propagating combustion can be initiated in the form of concentrated liquid without the processes of gel formation and gel drying, and the powder synthesis furnace provided with a plurality of sets of combustion synthesizers can carry out continuous production at the speed of kilogram per hour or even faster, which is an important technical breakthrough for applying the low-temperature self-propagating combustion synthesis process to industrial production.
3. The ceramic tube structure of the combustion synthesizer can concentrate heat generated by combustion of the resistance heating wire and the combustible solution, the process of continuous concentration, ignition and product separation of the input combustible solution in the combustion process is nearly seconds, the powder is cooled immediately after flowing out of the combustion synthesizer, and the concentrated combustible solution has low self-propagating combustion temperature and the product cannot obtain enough driving force to complete crystallization, so that the generated powder still keeps amorphous state, and in subsequent heat treatment, the grain size of the powder can be flexibly regulated and controlled by adjusting parameters such as heating rate, calcination temperature, heat preservation time and the like to obtain the required nano, submicron or even micron-sized powder.
4. The invention adopts a modular design concept, combines a plurality of sets of combustion synthesizers and the middle shell into the synthesizer unit, can expand the capacity of the synthesis furnace through the superposed synthesizer unit, has large capacity upgrading potential, and can better meet the requirement of industrial production.
Drawings
Fig. 1 is a main structure diagram of a powder synthesizing furnace in an embodiment.
Fig. 2 is a schematic diagram of a synthesizer unit.
Fig. 3 is a schematic diagram of the internal structure of the combustion synthesizer.
Fig. 4 is a partial longitudinal cross-sectional view of a combustion synthesizer.
Fig. 5 is a schematic view of the structure of the air flow conveyor.
Fig. 6 is a schematic view of the structure of the powder separator.
The reference numbers and corresponding part names in the figures are: 1-mounting a bracket; 2-a middle shell; 21-an observation window; 3-a combustion synthesizer; 31-ceramic fiber heating jacket; 311-nickel chromium heating wire; 32-corundum ceramic tubes; 321-corundum ceramic plug; 33-ceramic fiber insulation felt; 34-ceramic insulated terminals; 35-a thermocouple; 4-a top cover; 41-tail gas filter box; 5-a trapezoidal blanking hopper; 6-an air flow conveyor; 61-housing of the air flow conveyor; 62-an upper valve; 63-a deflector; 64-compressed gas jet pipe; 65-lower valve; 7-first-level powder collecting barrel; 8-a powder separator; 81-housing of the powder separator; 82-a filter screen; 9-a secondary powder collection barrel; and 10-a master control box.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited to these examples.
The inventor considers that the continuous and stable supply of reaction materials is a prerequisite for realizing the controllable self-propagating combustion, and is a key for determining whether the low-temperature self-propagating combustion synthesis method can be applied to continuous production. Through a large number of experimental researches, the inventor proves that the reaction materials capable of initiating the self-propagating combustion are not limited to xerogel, and the concentrated aqueous solution of the metal nitrate and organic matters such as citric acid, glycine, glucose, urea, polyethylene glycol and the like can also generate continuous and stable self-propagating combustion. If the concentrated solution is used as reactant, the solution can be continuously and stably input into the reaction area at a certain flow rate by using corrosion-resistant pumps such as peristaltic pumps, diaphragm pumps and the like, and continuous and stable self-propagating combustion can be smoothly realized. The feeding in the form of a concentrated solution has the following outstanding advantages: 1. compared with xerogel, the solution contains excessive water, the water evaporation process is firstly carried out after the solution enters the reaction zone, the solution can be ignited after being continuously evaporated and concentrated to a certain degree, and the combustion flame can not reversely ignite materials which do not enter the reaction zone along the feeding pipeline; if the xerogel is used for continuous feeding, the combustion reaction cannot be completely cut off, the materials outside the reaction area are easy to ignite, and the potential safety hazard is great; 2. when the solution is combusted, the gas generated by combustion and a large amount of steam are generated, the generated gas amount is more than that of xerogel combustion reaction, and the obtained solid combustion product is more fluffy and is more favorable for preparing superfine and highly dispersed oxide powder; 3. the water is vaporized to absorb the heat generated by combustion, which is beneficial to reducing the temperature of combustion flame, and the combustion product can keep amorphous state, thereby being convenient for regulating and controlling the grain size of powder by adjusting the parameters of the subsequent heat treatment process. On the basis of solution feeding, the inventor uses a ceramic tube with a heating component attached to the outside to perform an experiment, reaction solution is pumped into the ceramic tube to initiate combustion, and in the experiment process, a solid product after combustion continuously gushes out from the other end of the ceramic tube under the pushing of reaction gas. In the experiment, the continuous feeding, stable combustion and continuous separation of products from a combustion area are realized, the continuous production of a low-temperature self-propagating combustion method is preliminarily realized, and various nano and submicron oxide powders are prepared. Therefore, the control system, the reactor, the feeding system and the product collecting system are integrated to manufacture the integrated low-temperature self-propagating combustion powder synthesis furnace, the scheme is feasible, and the invention of the equipment can greatly promote the industrial application of the low-temperature self-propagating combustion method.
A powder synthesis furnace based on a low-temperature self-propagating combustion principle is shown in figure 1 and comprises a middle shell, a combustion synthesizer, a trapezoidal blanking hopper, a top cover, a tail gas filter box, an airflow conveyor, a powder separator, a first-stage powder collecting barrel, a second-stage powder collecting barrel, a mounting bracket, a feeding system and a master control box.
As shown in fig. 2, the middle case is a square structure, a hole is opened on the front side of the middle case and a transparent glass is embedded as an observation window, and 2 sets of combustion synthesizers are respectively installed on the left, right and rear sides. The intermediate housing and 6 sets of combustion combiners connected to the intermediate housing constitute a combiner unit. In this embodiment, the powder synthesizer includes 2 synthesizer units up and down. The middle shell is used for installing the combustion synthesizer and forms a closed space together with the upper part assembly and the lower part assembly, the upper middle shell and the lower middle shell are connected through bolts and are additionally provided with sealing rubber rings, the upper end of the middle shell on the upper portion is provided with a sealing top cover, and the top cover and the middle shell are connected through bolts and are additionally provided with the sealing rubber rings. The top cover is provided with a hole and is provided with a tail gas filter box, a 200-mesh stainless steel filter screen is additionally arranged between the tail gas filter box and the top cover, and the tail gas filter box is internally filled with high-temperature resistant filter cloth. The synthesizer unit is arranged in a modularized mode, so that equipment is convenient to install and maintain, the synthesizer unit can be directly additionally arranged on the upper part of the synthesizer unit according to actual production requirements to upgrade the capacity of the equipment, and the adaptability of the equipment in industrial production is improved.
The lower part of the middle shell at the lower part is connected with a trapezoidal blanking hopper by adopting a bolt and is additionally provided with a sealing rubber ring, and the trapezoidal blanking hopper is fixed on a mounting bracket. In this embodiment, the cavity formed by the two middle shells, the top cover and the trapezoidal blanking hopper is an inner cavity of the synthesis furnace.
As shown in fig. 3-4, the combustion synthesizer comprises a corundum ceramic tube, a ceramic fiber heating jacket, a ceramic fiber heat preservation felt, a shell, a thermocouple, a nickel-chromium heating wire and a corundum ceramic plug which are arranged in sequence from inside to outside; the shell is of a square structure and is made by bending and welding a stainless steel sheet; a nickel-chromium heating wire with certain power is embedded in the inner side wall of the ceramic fiber heating sleeve, and the nickel-chromium heating wire is spirally arranged along the inner side wall of the ceramic fiber heating sleeve; one end of the corundum ceramic tube is longer than the ceramic fiber heating sleeve and is inserted into the middle shell, and the other end of the corundum ceramic tube is provided with a corundum ceramic plug and a gap is sealed by using a high-temperature adhesive; the corundum ceramic plug penetrates out of the shell of the combustion synthesizer and is connected with a feeding pipeline of a feeding system. The ceramic fiber heat preservation felt can reduce heat loss and reduce equipment energy consumption, a ceramic insulation wiring terminal is installed on the inner side of a combustion synthesizer shell and used for being connected with a nickel-chromium heating wire and a heating power supply, a hole is formed in the center of the upper end face of the combustion synthesizer shell, a thermocouple is inserted into the hole, the front end of the thermocouple penetrates through a gap of the nickel-chromium heating wire and is close to a corundum ceramic tube, and a signal wire of the thermocouple is connected into a temperature control meter installed in a master.
When the combustion synthesizer is used, firstly, a temperature control meter in a master control box sets the working temperature (preferably 500-900 ℃, and flexibly adjusted according to a reactant system and the concentration degree), after the heating to the set temperature and the stabilization, concentrated solution is input into the corundum ceramic tube from a middle hole of the corundum ceramic plug, the solution is combusted in the corundum ceramic tube, wherein gas generated by vaporization and combustion of water in the solution and powder produced in flame gush out of the corundum ceramic tube and enter an inner cavity of the synthesizer and fall into a powder collecting barrel under the action of gravity, and the concentrated solution undergoes the processes of further concentration, ignition, completion of combustion, separation and the like in the corundum ceramic tube with limited length. In the process, if the ignition or combustion completion link fails, the liquid raw materials fall into the trapezoidal blanking hopper, and if powder generated by combustion cannot be smoothly separated under the pushing of gas, the reaction is stopped because the corundum ceramic tube is blocked by product accumulation. Therefore, the oxidant/reducing agent ratio and the concentration degree of the concentrated solution introduced into the combustion synthesizer are determined by theoretical calculation in advance, and then the self-propagating combustion process adaptability test is carried out on the machine.
As shown in fig. 5, the air flow conveyor comprises a shell, a guide plate and a compressed air nozzle, the shell is a square tube formed by welding, and valves are arranged at two ends of the square tube. One end of the guide plate is a connecting end and is connected to the middle part of the inner side of the square pipe; the other end is a free end, and the guide plate inclines towards the lower end along the upper end of the square tube (namely, the connecting end of the guide plate is positioned above the free end when in use); the compressed gas spray pipe is installed at the inner side of the square pipe, is positioned at the opposite side of the guide plate and is positioned below the free end of the guide plate, and the free end (namely the tail end) of the guide plate is far away from the nozzle of the compressed gas spray pipe. When the airflow conveyor designed by the invention is operated according to the method, the slagging in the combustion products with a certain probability is higher in speed when falling along the guide plate due to higher mass, and can fall into the bottom of the cavity of the airflow conveyor so as to be far away from the action area of the compressed air jet flow, the lower valve is intermittently opened and closed according to a certain time, and the accumulated slagging falls into the primary powder collecting barrel, so that the separation of high-fluffy powder and slagging can be realized, and the synthesis of high-dispersity ultrafine powder is facilitated.
As shown in fig. 6, the powder separator includes a cylindrical housing and three layers of stainless steel screens radially arranged in the housing, the mesh numbers of the three layers of screens from bottom to top are respectively 40 meshes, 80 meshes and 200 meshes, the upper part of the housing is provided with a gas pipeline, and the lower part of the housing is provided with a feeding pipeline; the gas pipeline is positioned above the filter screen and communicated with the trapezoid blanking hopper; the feeding pipeline is opposite to the nozzle of the compressed air spray pipe and is connected with the airflow conveyor.
The lower part of the trapezoid blanking hopper is connected with the head end of the airflow conveyor through a bolt, a sealing rubber ring is additionally arranged, the tail end of the airflow conveyor is connected with the first-level powder collecting barrel, a feeding pipeline of the powder separator is connected to the airflow conveyor and is just opposite to a nozzle of a compressed air spray pipe, the bottom of the powder separator is connected with the second-level powder collecting barrel, and a gas pipeline of the powder separator is connected with the trapezoid blanking hopper. The air flow conveyor and the first-stage powder collecting barrel, the air flow conveyor and the powder separator, the powder separator and the trapezoidal blanking hopper, and the powder separator and the second-stage powder collecting barrel are connected by clamp quick connectors and are additionally provided with silica gel sealing rings. The master control box is arranged on the mounting bracket and keeps a certain distance with the combustion synthesizer and the trapezoidal blanking hopper.
The working process of the airflow conveyor is as follows:
(1) when liquid drops fall due to insufficient combustion of the combustible solution or a small amount of slag is formed in combustion products in the synthesis process, the valve at the lower part is kept closed, the valve at the upper part is opened to a certain angle, and the compressed air spray pipe sprays the filtered and purified air. The powder gathered by the trapezoid blanking hopper falls into the containing cavity of the air flow conveyor, the powder is gushed along one side of the nozzle far away from the compressed air spray pipe under the guide of the guide plate, and the jet flow formed by the compressed air drives the powder to enter the powder separator which is arranged right opposite to the nozzle of the compressed air spray pipe. After the powder enters the shell of the powder separator along with the airflow, because the shell body of the powder separator is larger than the inner diameter of the feeding pipeline, when the powder reaches the shell body, the airflow speed is reduced, part of the powder immediately falls into the second-stage powder collecting barrel, the other part of the powder falls into the second-stage powder collecting barrel after moving upwards and being blocked by the filter screen, and the filtered gas enters the inner cavity of the synthesis furnace along a gas pipeline connected with the trapezoid dropping hopper. Because the adopted compressed gas is air after filtration and purification, part of oxygen in the air participates in the self-propagating combustion reaction to reduce the carbon residue of combustion products, and the input air can also take away part of heat of the inner cavity of the synthesis furnace to reduce heat accumulation.
(2) When the combustible solution is completely combusted in the synthesis process, the combustion product is uniform and fluffy flocculent powder and does not contain slag bonding, the upper and lower valves of the airflow conveyor are simultaneously opened and the input of compressed air is stopped, and at the moment, the powder falls into the first-stage powder collecting barrel.
The feeding system comprises a feeding pump and a feeding pipeline. The feeding pipeline of the feeding system is connected with one end of the corundum ceramic pipe of the combustion synthesizer, which is provided with the corundum ceramic plug. Feeding a combustible solution to the combustion synthesizer.
The total control box is provided with a temperature control meter, an ammeter, a feeding pump controller, a compressed air valve, a barometer, a knob switch, an indicator light, an alarm and other parts, and has the functions of power distribution, temperature control, material feeding start-stop, flow regulation, compressed air switch, pressure indication, alarm and the like. The specific style and the installation position can be flexibly determined, but the combustion synthesizer can be independently or in groups powered, and the combustion synthesizer has the functions of power supply indication, work indication, alarm, temperature display, current display, infusion pump start-stop, forward and reverse rotation control, rotating speed control, compressed air switching, pressure display and the like, and electrical elements necessary for the functions, and the specific installation arrangement of the combustion synthesizer is determined by persons in the field.
The tail gas filter cartridge that the top cap installed additional should be used for waste heat recovery with collect the comdenstion water with multistage heat exchanger series connection, and tail gas processing apparatus should be connected to last one-level heat exchanger export, reduces the nitrogen oxide that incomplete combustion reaction leads to and discharges, and above-mentioned heat exchanger and tail gas processing apparatus do not belong to the powder synthetic furnace based on low temperature self-propagating combustion principle that this embodiment provided, and its concrete form and mounting means this embodiment do not limit.
The powder synthesis method based on the low-temperature self-propagating combustion principle is used for synthesizing 1.0mol of LaCrO in the embodiment3The powder is taken as an example and comprises the following steps:
(1) preparation of nitrate solution
The nitrate solution can be prepared by a nitrate dissolving method: the dosage of various raw materials is calculated according to the components of the target product, nitrate solution is prepared by dissolution, and insoluble impurities in the solution are removed by filtration. By direct use of nitrates toWhen the raw materials are used, 0.5mol of Cr (NO) is respectively taken3)3·9H2O and 0.5mol La (NO)3)3·6H2And O, adding 100g of deionized water, heating and dissolving at 50-80 ℃ to prepare a nitrate solution, and filtering to remove insoluble impurities possibly existing in the raw materials.
There are also various methods for preparing the nitrate solution, such as by reacting oxides, hydroxides, carbonates with nitric acid, and for the same purpose, 0.25mol of La may be used2O3Or 0.5mol La (OH)3/La2(CO3)3Reaction of xH2O with nitric acid to introduce 0.5mol Cr (NO)3)3·9H2O, 0.5mol of Cr (OH) can be used3Dissolving in nitric acid or sucrose to reduce 0.5mol of CrO30.5mol of Cr (NO) is introduced3)3·9H2O, the amount of nitric acid used in each reaction is determined by the equation of the reaction, and the specific operation and conditions are within the ordinary skill in the art.
(2) Preparation of combustible solution
Heating the nitrate solution obtained in the step (1) to 70-80 ℃, preserving heat, adding one or more of organic matters such as urea, polyethylene glycol, citric acid, glycine, cane sugar and the like as a combustion agent (refer to 'propellant chemical theory'), and fully combusting the nitrate and the organic matters to generate solid oxide and CO2、H2O、N2In the embodiment, three organic matters of glycine, urea and glycol are selected as the combustion agents, specifically 0.67mol of glycine, 1.0mol of urea and 0.9mol of glycol, and the addition amount of the combustion agent in the proportion is relatively excessive by 20%. And continuously heating the solution to 70-90 ℃, evaporating and concentrating the solution to a certain degree to obtain a combustible solution, transferring the combustible solution to a heat-preserving container, and preserving the heat at 50-80 ℃.
(3) Continuous self-propagating combustion
And (3) starting the powder synthesis furnace, setting the heating temperature of the combustion synthesizer to be 500-800 ℃, starting the feeding pump to continuously input the concentrated combustible solution prepared in the step (2) into the combustion synthesizer after the temperature is stable, wherein the flow rate of the concentrated combustible solution input into the combustor is 20-60 mL/min, and in the embodiment, the flow rate is 40 mL/min. The concentrated combustible solution is subjected to continuous self-propagating combustion in the corundum ceramic tube, and powder generated by combustion falls into the trapezoid blanking hopper.
(4) Powder Collection
In the embodiment, the upper valve is opened by the airflow conveyor, the lower valve is kept closed, the compressed air after filtration and purification is input through the compressed air spray pipe, at the moment, fluffy powder is conveyed to the powder separator and falls into the second-stage powder collecting barrel, and the lower valve of the airflow conveyor is switched at intervals of 5min to enable slag or agglomerates mixed in the powder to fall into the first-stage powder collecting barrel.
(5) Calcination treatment
The powder generated by self-propagating combustion is calcined by using a high-temperature kiln, and target powder which is easy to disperse and has nano, submicron or micron grain size can be obtained by adjusting the parameters of the calcination process.
In the embodiment, the combustion products collected in the secondary powder collecting barrel are subjected to heat treatment by adopting a high-temperature muffle furnace, heated to 900 ℃ at the heating rate of 10-20 ℃/min and kept for 30min, and the LaCrO can be obtained3And (3) nano powder.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (10)
1. The powder synthesis furnace based on the low-temperature self-propagating combustion principle is characterized in that: comprises a middle shell, a plurality of combustion synthesizers, a blanking hopper, an airflow conveyor, a powder separator and a secondary powder collecting barrel; the plurality of combustion synthesizers are respectively connected with the middle shell, the blanking hopper is connected to the lower part of the middle shell, and a cavity formed by the middle shell and the blanking hopper in a communicated mode is an inner cavity of the synthesis furnace; the blanking hopper, the airflow conveyor, the powder separator and the secondary powder collecting barrel are sequentially connected, and the upper end of the powder separator is communicated with the blanking hopper.
2. The powder synthesis furnace based on the low-temperature self-propagating combustion principle according to claim 1, characterized in that: the combustion synthesizer comprises a thermocouple, a resistance heating wire, a ceramic tube, a ceramic fiber heating sleeve and a ceramic fiber heat preservation felt which are sequentially arranged from inside to outside; the resistance heating wires are spirally arranged along the inner side wall of the ceramic fiber heating sleeve; one end of the ceramic tube is inserted into the middle shell, and the front end of the thermocouple extends to the inner side wall.
3. The powder synthesis furnace based on the low-temperature self-propagating combustion principle according to claim 2, characterized in that: and a ceramic plug is arranged at one end of the ceramic tube far away from the end inserted into the middle shell, and a gap is sealed between the ceramic plug and the ceramic tube through a high-temperature adhesive.
4. The powder synthesis furnace based on the low-temperature self-propagating combustion principle according to claim 1, characterized in that: the powder synthesis furnace comprises a middle shell and a plurality of combustion synthesizers arranged on the periphery of the middle shell, wherein the middle shell and the plurality of combustion synthesizers are formed into a synthesizer unit; the upper end of the middle shell of the synthesizer unit at the uppermost part is provided with a top cover, and the top cover is provided with a tail gas filter box.
5. The powder synthesis furnace based on the low-temperature self-propagating combustion principle according to claim 1, characterized in that: the device also comprises a primary powder collecting barrel, and the primary powder collecting barrel is connected with the tail end of the airflow conveyor.
6. The powder synthesis furnace based on the low-temperature self-propagating combustion principle according to claim 1, characterized in that: the airflow conveyor comprises a shell, a guide plate and a compressed air spray pipe; the two opposite ends of the shell are provided with valves, and the guide plate and the compressed air spray pipe are sequentially and oppositely connected to the inner wall of the shell between the two valves from top to bottom; the compressed gas spray pipe extends horizontally; the guide plate inclines and extends downwards, one end of the guide plate is connected with the inner wall of the shell, and the other end of the guide plate extends to the connecting end of the compressed air spray pipe.
7. The powder synthesis furnace based on the low-temperature self-propagating combustion principle according to claim 6, characterized in that: the powder separator comprises a shell and three layers of filter screens with different meshes, wherein the three layers of filter screens are horizontally arranged in the shell; the gas pipeline is positioned above the filter screen and communicated with the blanking hopper; the feeding pipeline is opposite to the nozzle of the compressed air spray pipe and is connected with the shell of the airflow conveyor.
8. The powder synthesis furnace based on the low-temperature self-propagating combustion principle according to claim 3, characterized in that: still include feeding system, feeding system includes feed pump and feed line, and feed line is connected with the one end that ceramic pipe was equipped with ceramic end cap.
9. The powder synthesis method based on the low-temperature self-propagating combustion principle is characterized by comprising the following steps of:
(1) preparing a nitrate solution: calculating the required dosage of various nitrates according to the total amount of the required prepared powder, weighing the nitrates, adding deionized water, heating and dissolving to prepare a nitrate solution, and filtering the nitrate solution to remove insoluble impurities;
or according to the amount of various nitrates calculated according to the total amount of the powder to be prepared, adopting oxides, hydroxides, carbonates and other raw materials to react with nitric acid to prepare aqueous solution containing the same amount of nitrates, and filtering the nitrate solution to remove insoluble impurities;
(2) preparing a combustible solution: heating the nitrate solution obtained in the step (1) to 70-80 ℃, preserving heat, adding one or more of organic matters such as urea, polyethylene glycol, citric acid, glycine, cane sugar and the like as a combustion agent, and continuously heating to 70-90 ℃ for evaporation and concentration to obtain a combustible solution;
(3) continuous self-propagating combustion: starting the powder synthesis furnace, setting the heating temperature of the combustion reactor to be 500-800 ℃, continuously inputting the combustible solution obtained in the step (2) into the combustion synthesizer after the temperature is stable, enabling the combustible solution to generate continuous self-propagating combustion in the ceramic tube, and enabling the powder generated by combustion to fall into a blanking hopper;
(4) and (3) collecting powder: when the combustion products are fluffy powder, simultaneously opening upper and lower valves of the airflow conveyor, and enabling the powder to fall into a first-stage powder collecting barrel; when the combustion products contain slag, opening an upper valve of the airflow conveyor, keeping a lower valve closed, inputting compressed gas, conveying fluffy powder to the powder separator and falling into a secondary powder collecting barrel;
(5) calcining treatment: the powder generated by self-propagating combustion is calcined by using a high-temperature kiln, and target powder which is easy to disperse and has nano, submicron or micron grain size can be obtained by adjusting the parameters of the calcination process.
10. The method for synthesizing powder based on the low-temperature self-propagating combustion principle according to claim 9, characterized in that: in the step (4), when the combustible solution is completely combusted in the synthesis process, and the combustion product is uniform and fluffy flocculent powder and does not contain slag bonding, simultaneously opening upper and lower valves of the airflow conveyor and stopping inputting compressed gas, and at the moment, the powder falls into a first-stage powder collecting barrel; after a certain time, quickly closing the upper valve after the barrel is expected to be filled with powder, detaching and emptying the primary powder collecting barrel, or directly replacing the primary powder collecting barrel with an empty powder collecting barrel, and opening the upper valve again after the replacement is finished, so that the powder still falls into the primary powder collecting barrel;
when liquid drops fall due to insufficient combustion of a combustible solution or a small amount of slag is formed in a combustion product in the synthesis process, an upper valve of an airflow conveyor is opened, a lower valve is kept closed, compressed gas is input, fluffy powder is conveyed to a powder separator and falls into a secondary powder collecting barrel, after the secondary powder collecting barrel is expected to be filled with powder after a certain time, the input of the compressed gas is stopped, the upper valve of the airflow conveyor is closed, and the upper valve is opened and the compressed gas is input after the secondary powder collecting barrel is rapidly replaced; and (4) performing lower valve opening and closing operation at intervals of 5-10 min to enable the slag or the agglomerates to enter the primary powder collecting barrel.
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