CN114950283A - Fluidized reaction system for coating surfaces of ultrafine particles and using method thereof - Google Patents
Fluidized reaction system for coating surfaces of ultrafine particles and using method thereof Download PDFInfo
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- C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
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- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
- C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
- C23C16/442—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating using fluidised bed process
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- C30B28/00—Production of homogeneous polycrystalline material with defined structure
- C30B28/12—Production of homogeneous polycrystalline material with defined structure directly from the gas state
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Abstract
A fluidized reaction system coated on the surface of ultrafine particles and a using method thereof relate to the technical field of fluidized beds, and comprise a descending fluidized reaction zone and an ascending fluidized reaction zone, wherein the descending fluidized reaction zone comprises a fluidized bed reactor, a primary gas-solid separator, a secondary gas-solid separator and a product tank; the fluidization reaction system and the use method thereof aim at solving the fluidization problem existing in the superfine particle fluidization CVD coating technology, simultaneously eliminating the wall attachment reaction and improving the yield and the quality of the produced superfine powder material.
Description
Technical Field
The invention relates to the technical field of fluidized beds, in particular to a fluidized reaction system for coating the surface of ultrafine particles and a using method thereof.
Background
The fluidized bed reactor has the advantages of high heat and mass transfer efficiency, uniform bed layer temperature, large operation flexibility and the like, and is particularly suitable for heterogeneous reaction between fluid and fine powder particles; in the fluidization process, the particle size of fine powder is one of key factors influencing the fluidization performance of the fine powder, solid particles can be classified into A, B, C, D four types according to a Geldart particle classification method, wherein A type particles with the particle size of 30-100 mu m and B type particles with the particle size of 100-600 mu m are easy to fluidize, C type particles with the particle size of less than 20 mu m belong to superfine sticky particles, strong van der Waals force and electrostatic force exist among the particles, channeling, agglomeration, fluidization agglomeration or slugging phenomena are easy to generate in the fluidization process, bed pressure instability is caused, and the application of a fluidized bed in the field of superfine particles is greatly limited;
the Chemical Vapor Deposition (CVD) is a mature powder material preparation and surface modification technology, can coat the surface of powder particles to form a functionalized film or coating, and is widely applied to the development of new materials; in recent years, a fluidization technology is combined with a CVD coating process to form a novel fluidization CVD coating technology, but the fluidization CVD coating technology of ultrafine particles also faces the fluidization problem of C-type particles; to solve these problems, the following 4 types of methods are generally used: the 1 st type is an intrinsic method, namely, adding easy-to-fluidize A type or B type coarse particles into C type particles to improve the fluidization state of the particles, and the main defects are that products need to be further separated and the separation difficulty is high; the class 2 is a method for applying an external field force to a fluidized bed reactor, namely, the agglomerated structure among particles is destroyed by methods of vibration, stirring, centrifugation and the like, so as to achieve the purpose of uniform fluidization, and the method has the main defects that the device structure is complex and industrialization is difficult to realize; the method 3 is to break the particle channeling and agglomeration by arranging an inner member in a fluidized bed to improve the fluidization quality of the viscous particles, and has obvious effect on the low-adhesion ultrafine particles but poor effect on the high-viscosity ultrafine particles; class 4 is to improve the fluidization quality by increasing the operating pressure of the fluidized bed, with the disadvantage of increasing the equipment investment and operating costs;
in the production of solar grade polysilicon, a fluidized CVD coating technology is preferably adopted, high-purity polysilicon fine particles are added into a fluidized bed reactor as seed crystals, silane (SiH 4) and H2 are introduced from the bottom of the reactor, SiH4 undergoes a thermal decomposition reaction at the temperature of 600-800 ℃, and chemical vapor deposition occurs on the surface of a silicon seed crystal, so that the silicon seed crystal grows into approximately spherical particles with larger size; while the silane is deposited on the silicon seed particles in a chemical vapor phase, the silane is inevitably deposited on the inner wall of the reactor and internal components such as an air inlet nozzle or a gas distributor, and the like, which is called wall deposition reaction or wall attachment reaction, so that the nozzle or the gas distributor is blocked, and the normal production of the fluidized bed is influenced; meanwhile, as the thermal decomposition reaction of the silane is an exothermic reaction, the reaction is severe in a region with higher silane concentration, so that the local temperature is too high; in order to prevent the occurrence of the wall sinking reaction, Chinese patent No. CN 103495366A discloses a granular polysilicon fluidized bed reactor, a granular discharge port is arranged in the center of the bottom of the reactor, a plurality of circles of reaction gas distributors are distributed outwards along the discharge port, a distributor close to the inner wall of the reactor is a hydrogen distributor, and in the fluidized reaction process, the reaction gas and the wall of the reactor are separated by the hydrogen which goes upwards along the inner wall of the reactor, so that the occurrence of the silane wall-attached reaction is effectively reduced, but the reactor has the defect that the reactor is only suitable for the fluidized production of polysilicon granules with the granularity within the range of A class and B class and cannot be used for the stable production of C class granules;
in the research field of novel cathode materials of lithium ion batteries, a fluidized CVD coating technology is adopted to develop submicron superfine cathode materials with a core-shell structure, such as graphite-carbon coated particles or silicon-carbon coated particles, and the like, so that the capacity, stability, multiplying power and other properties of the lithium ion batteries can be greatly improved, but the problems of channeling, agglomeration or slug easily occur to C-type particles, the coating effect is seriously deteriorated, and the submicron superfine cathode materials become hot spots and difficulties in the research of the cathode materials of the current lithium ion batteries; US9279181 discloses the principle of thermal decomposition in a fluidized bed at high temperature using hydrocarbon gas as a carbon source to deposit a coating layer of pyrolytic carbon on a substrate, but does not illustrate the specific embodiment; US patent 6410087 discloses a process and apparatus for fluidized bed pyrolytic carbon deposition with detailed settings and constraints on the fluidized bed type structure and gas distribution plate, but again does not address the specific implementation; chinese invention patent CN112635733A discloses a negative electrode material of a lithium ion battery, a method for preparing the same, and a lithium ion battery, wherein a chemical vapor deposition method is utilized, a silane-hydrogen-inert gas three-component reaction system is adopted to deposit on a composite material synthesized by the patent with a particle size of less than 100nm in a fluidized bed reactor to form silicon particles, and then the silicon particles are subjected to carbon coating treatment in a rotary furnace to form the negative electrode material, wherein only parameters such as raw material composition, reaction conditions and the like of the silane vapor deposition method in the fluidized bed are provided, but no specific fluidized bed reactor structure and use method are mentioned; chinese invention patent CN111430692B discloses a lithium ion battery cathode material and a preparation method thereof, slurry containing SiOx is subjected to spray drying to obtain powder with the median particle size of 5-20um, heating fluidizing gas is introduced into a cavity of a fluidized bed reactor to enable the powder to be in a suspended state, then solution containing an organic carbon source is sprayed into the cavity of the fluidized bed reactor, and the temperature is reduced after the solution containing the organic carbon source completely reacts to obtain powder containing a coating layer, wherein the patent does not describe the specific form of the fluidized bed reactor; chinese patent CN111628162B discloses a porous silicon negative electrode material for lithium ion batteries and a preparation method thereof, wherein one of a vapor deposition furnace, a fluidized bed, a box furnace, a rotary furnace, a roller kiln and a pushed slab kiln is adopted, and an organic carbon source material is used for coating amorphous carbon with the average thickness of 10-2000 nm on the surface of porous silicon particles, and a specific implementation mode of the fluidized bed is not provided.
Disclosure of Invention
In order to overcome the defects in the background technology, the invention discloses a fluidization reaction system for coating the surface of ultrafine particles and a use method thereof, aiming at solving the fluidization problem in the fluidization CVD coating technology of ultrafine particles, eliminating the wall attachment reaction and improving the yield and quality of the produced ultrafine powder material.
In order to achieve the purpose, the invention adopts the following technical scheme:
a fluidization reaction system coated on the surface of ultrafine particles comprises a downward fluidization reaction zone and an upward fluidization reaction zone coupled with the downward fluidization reaction zone; the descending fluidized reaction zone comprises a fluidized bed reactor, a primary gas-solid separator, a secondary gas-solid separator and a product tank; the upper end of the fluidized bed reactor is communicated with a fluidized bed feeder for feeding raw material powder and superheated carrier gas, the outer wall of the fluidized bed reactor is sequentially provided with a plurality of coolers at intervals from top to bottom, and feeding nozzles for feeding a coating agent are arranged on the outer walls of the fluidized bed reactor between the fluidized bed feeder and the uppermost cooler and between two adjacent coolers; the upper part feed inlet of the first-stage gas-solid separator is correspondingly communicated with the lower end of the fluidized bed reactor, the upper part feed inlet of the second-stage gas-solid separator is correspondingly communicated with the upper part gas outlet of the first-stage gas-solid separator through a pipeline, the upper part gas outlet of the second-stage gas-solid separator is provided with a filtering component, and the lower part solid material outlets of the first-stage gas-solid separator and the second-stage gas-solid separator are correspondingly communicated with the upper part feed inlet of the product tank through pipelines; the upward fluidized reaction zone comprises a riser reactor, the lower end of the riser reactor is communicated with a riser feeder, a gas feed port of the riser feeder is correspondingly communicated with a gas outlet at the upper part of the secondary gas-solid separator, a circulating powder inlet of the riser feeder is correspondingly communicated with a discharge port at the lower part of the product tank, the upper end of the riser reactor is directly communicated with the upper end of the fluidized bed reactor, and a riser heater is wrapped on the outer wall of the riser reactor.
Further, the fluidized bed feeder and the riser feeder are both arranged into venturi-shaped structures; the upper end of the fluidized bed feeder is provided with an overheating carrier gas inlet, and the throat part of the fluidized bed feeder is provided with a raw material powder inlet; the lower end of the riser feeder is provided with a gas feed inlet, and the throat part is provided with a circulating powder inlet.
Furthermore, the number of the coolers is three, namely a first cooler, a second cooler and a third cooler, the cooling medium of each cooler enters from bottom to top, and each cooler is provided with an independent cooling medium supply and temperature regulation system.
Furthermore, the feeding nozzles of the same cross section of the fluidized bed feeder are uniformly and annularly provided with at least three feeding nozzles, and the feeding nozzles of the same cross section are communicated with a coating agent feeding pipeline which is annularly arranged outside the corresponding wall of the fluidized bed feeder.
Furthermore, the lower parts of the primary gas-solid separator, the secondary gas-solid separator and the product tank are all arranged into cone structures, and mechanical stirrers are arranged in the cone structures.
Furthermore, a supercharger is arranged on a communicating pipeline between a gas feed port of the riser feeder and a gas outlet at the upper part of the secondary gas-solid separator.
Furthermore, a circulating powder secondary heater is arranged on a communicating pipeline between a circulating powder inlet of the riser feeder and a discharge hole at the lower part of the product tank.
A method for using a fluidized reaction system coated with the surface of ultrafine particles comprises the following using processes: the first process, using overheating carrier gas AG to suck raw material powder S into a fluidized bed feeder through negative pressure generated by the fluidized bed feeder, and spraying the raw material powder S into a fluidized bed reactor after the raw material powder S and the fluidized bed feeder are uniformly mixed; in the second process, the coating agent F1 is sprayed into the fluidized bed reactor from feed nozzles arranged on different cross sections of the fluidized bed reactor in a gas phase form, and is mixed with the overheated carrier gas AG and the raw material powder S descending in the fluidized bed reactor to generate a pyrolysis reaction, and a coating layer is formed on the surface of the raw material powder S; meanwhile, the cooler is used for heating and insulating the fluidized bed reactor; the third process, the gas-solid mixture after reaction in the fluidized bed reactor enters a first-stage gas-solid separator downwards for sedimentation separation, the separated solid particles enter a product tank downwards, the separated gas phase carries a small amount of solid particles and enters a second-stage gas-solid separator connected with the first-stage gas-solid separator in parallel through a pipeline for filtration separation, the solid particles are intercepted by a filter assembly, collected at the lower part of the second-stage gas-solid separator and enter the product tank downwards through the pipeline, the gas phase component passes through the filter assembly upwards and flows out from the upper part of the second-stage gas-solid separator, one part of the gas phase component is taken as a gas product P2 outlet device, and the other part of the gas phase component is taken as dilution gas of an upward fluidization reaction zone II; mixing the diluent gas from the downward fluidization reaction zone I with a riser gas-phase feed F2, and then making the diluent gas go upward from a gas feed port of a riser feeder and pass through the riser feeder; one part of the powder flowing out of the product tank is taken as a coating product P1 and is discharged out of the device, and the other part of the powder is sucked into a riser feeder from a circulating powder inlet by negative pressure generated by ascending of a riser gas feed F2; and fifthly, after the gas-solid phases in the riser feeder are uniformly mixed, the gas-solid phases are upwards sprayed into the riser reactor, the gas-phase coating agent is subjected to thermal decomposition reaction in the riser reactor, so that the coating layer of the circulating powder is continuously thickened, and the gas-solid mixture in the riser reactor is completely downwards sprayed into the fluidized bed reactor from the upper end surface of the fluidized bed reactor to complete the circulating coating.
Furthermore, in the second process, the heat of the coolers arranged at intervals from top to bottom is determined according to the central temperature of each section in the corresponding fluidized bed reactor, and the central temperature of each section of the fluidized bed reactor is kept basically constant.
Further, in process one, the superheated carrier gas AG is an inert gas.
Due to the adoption of the technical scheme, the invention has the following beneficial effects:
firstly, a coupling mode of a descending fluidized bed reactor and an ascending riser reactor is adopted, so that the raw material powder can be circularly coated, and the coating efficiency and the product yield of the superfine powder are improved;
secondly, a combination form of a descending fluidized bed reactor, sectional feeding of a coating agent and sectional heat extraction is adopted, so that the problems of channeling, agglomeration and slugging of ultrafine particles caused by a traditional ascending fluidized bed can be avoided, the ultrafine particle raw material is in a good fluidized state in a bed layer, the phenomena of nonuniform coating and lump coating are overcome, and the operation stability of the fluidized bed reactor is improved; secondly, a coating agent sectional feeding mode is adopted, so that the local overheating phenomenon caused by the fact that the coating agent enters a bed layer at one time can be eliminated, and meanwhile, the uniform fluidization of ultrafine particles is facilitated; thirdly, a sectional cooling mode is adopted, the temperature of the bed layer of the fluidized bed reactor can be kept stable, the temperature of the inner wall of the fluidized bed reactor can be lower than the decomposition temperature of the coating agent, and the wall attachment reaction is prevented; fourthly, the powder particles pass through the fluidized bed reactor at one time, so that the problem of different coating thicknesses caused by particle back mixing of the traditional ascending fluidized bed reactor is solved;
thirdly, after a multi-stage gas-solid separation and filtration mode is adopted, the integral gas-solid separation efficiency can be enhanced, and the problem that the cyclone separator has poor separation efficiency on particles below 20 mu m is solved;
fourthly, the characteristics of fast flow speed, difficult agglomeration and weakened agglomeration tendency of coated particles of the riser reactor are utilized to carry out secondary coating in the riser reactor, so that the benefit of coating reaction can be obviously improved, and the running energy consumption of the device can be reduced;
fifthly, the fluidized bed feeder and the riser feeder are both designed into venturi-shaped structures, so that the problem that solid particle feeding is difficult to seal is solved, the operation pressure of the reactor is favorably improved, and superfine particles can be uniformly dispersed in a bed layer, so that good conditions are created for stable fluidization of the superfine particles;
sixthly, the mechanical loosening stirrer is arranged at the bottoms of the gas-solid separator and the production tank, so that the technical problems of secondary fluidization and difficult settlement of ultrafine particles caused by loosening wind adopted by a conventional fluidized bed can be solved;
in summary, compared with the prior art, the method solves the fluidization problems of channeling, caking, agglomeration, slugging and the like in the fluidized CVD coating technology of ultrafine particles, eliminates the wall attachment reaction in the decomposition process of the coating agent, and obviously improves the yield and quality of the novel ultrafine powder material produced by the fluidized CVD coating technology.
Drawings
FIG. 1 is a schematic diagram of an embodiment of the present invention;
FIG. 2 is a schematic view of a connection arrangement of the feed nozzles;
FIG. 3 is a schematic view of another connection arrangement of the feed nozzles.
In the figure: 1. a fluidized bed feeder; 1-1, a superheated carrier gas inlet; 1-2, raw material powder inlet; 2. a fluidized bed reactor; 3. a feed nozzle; 3-1, a first feed nozzle; 3-2, a second feed nozzle; 3-3, a third feed nozzle; 4. a cooler; 4-1, a first cooler; 4-2, a second cooler; 4-3, a third cooler; 5. a first-stage gas-solid separator; 6. a secondary gas-solid separator; 6-1, a filter component; 7. a product tank; 8. a circulating powder secondary heater; 9. a riser pipe feeder; 9-1, a gas feed inlet; 9-2, circulating powder inlet; 10. a supercharger; 11. a riser reactor; 12. a riser tube heater.
Detailed Description
In the following description, the technical solutions of the present invention will be described with reference to the drawings of the embodiments of the present invention, and it should be understood that, if there is an orientation or positional relationship indicated by terms such as "upper", "lower", "front", "rear", "left", "right", etc., it is only corresponding to the drawings of the present invention, and for convenience of describing the present invention, it is not necessary to indicate or imply that the indicated devices or elements have a specific orientation:
the fluidization reaction system for coating the surfaces of the ultrafine particles, which is described in conjunction with the attached drawings 1-3, comprises a descending fluidization reaction zone I and an ascending fluidization reaction zone II coupled with the descending fluidization reaction zone I;
the descending fluidized reaction zone comprises a fluidized bed reactor 2, a first-stage gas-solid separator 5, a second-stage gas-solid separator 6 and a product tank 7; the upper end of the fluidized bed reactor 2 is communicated with a fluidized bed feeder 1 used for feeding raw material powder and overheated carrier gas, the lower port of the fluidized bed feeder 1 is arranged corresponding to the center of the upper end face of the fluidized bed reactor 2, so that the raw material can be uniformly dispersed after entering, and the descending fluidized bed reactor 2 is adopted, so that the problems of channeling, agglomeration and slugging of ultrafine particles caused by a traditional ascending fluidized bed can be avoided, the ultrafine particle raw material is in a good fluidized state in a bed layer, the phenomena of coating unevenness and agglomerate coating are overcome, the operation stability of the fluidized bed reactor 2 is improved, in addition, the powder particles downwards pass through the fluidized bed reactor 2 at one time, and the problem of different coating layer thicknesses caused by particle backmixing of the traditional ascending fluidized bed reactor is also solved; according to the requirement, the fluidized bed feeder 1 is arranged into a Venturi tube-shaped structure, the uppermost end is arranged into an overheating carrier gas inlet 1-1, and the throat part is provided with a raw material powder inlet 1-2, so that the design structure has two advantages, one is to solve the problem that solid particle feeding is difficult to seal, and is beneficial to improving the operating pressure of the reactor, and the other is to realize the uniform dispersion of ultrafine particles in a bed layer and create good conditions for the stable fluidization of the ultrafine particles;
the outer wall of the fluidized bed reactor 2 is sequentially provided with a plurality of coolers 4 at intervals from top to bottom, the temperature of the bed layer of the fluidized bed reactor 2 can be kept stable by adopting a sectional cooling mode, the temperature of the inner wall of the fluidized bed reactor 2 can be lower than the decomposition temperature of a coating agent, and the occurrence of wall attachment reaction is prevented; according to the requirement, the number of the coolers 4 is three, namely a first cooler 4-1, a second cooler 4-2 and a third cooler 4-3, cooling media of each cooler 4 are all fed in and fed out from the bottom, and each cooler 4 is provided with an independent cooling medium supply and temperature regulation system, so that the cooling temperature is controllable in a segmented mode, and the cooling efficiency is greatly improved; the outer walls of the fluidized bed reactors 2 between the fluidized bed feeder 1 and the uppermost cooler 4 and between the two adjacent coolers 4 are respectively provided with a feeding nozzle 3 for feeding the coating agent, when the number of the coolers is three, the feeding nozzles 3 are also sequentially divided into a first feeding nozzle 3-1, a second feeding nozzle 3-2 and a third feeding nozzle 3-3 from top to bottom, and by means of the segmented feeding of the coating agent, the local overheating phenomenon caused by the fact that the coating agent enters the bed layers of the fluidized bed reactors 2 at one time can be eliminated, and meanwhile, uniform fluidization of ultrafine particles is facilitated; according to the requirement, at least three feeding nozzles 3 with the same cross section of the fluidized bed feeder 2 are uniformly and annularly arranged, if three feeding nozzles are arranged, the feeding nozzles are distributed at intervals of 120 degrees, and if four feeding nozzles are arranged, the feeding nozzles are distributed at intervals of 90 degrees; the plurality of feeding nozzles 3 with the same cross section are communicated with a coating agent feeding pipeline which is annularly arranged outside the corresponding wall of the fluidized bed feeder 2, when three feeding nozzles 3 with the same cross section are arranged, namely three first feeding nozzles 3-1 are connected to the same annular coating agent feeding pipeline through radial connecting pipes, the three second feeding nozzles 3-2 and the three third feeding nozzles 3-3 of the lower layers are also in a similar connection mode, and the spraying speed, the spraying range and the spraying amount of the three feeding nozzles 3 of each layer can be kept basically consistent;
the upper part feed inlet of the first-stage gas-solid separator 5 is correspondingly communicated with the lower end of the fluidized bed reactor 2, the upper part feed inlet of the second-stage gas-solid separator 6 is correspondingly communicated with the upper part gas outlet of the first-stage gas-solid separator 5 through a pipeline, the upper part gas outlet of the second-stage gas-solid separator 6 is provided with a filtering component 6-1, the lower part solid material outlets of the first-stage gas-solid separator 5 and the second-stage gas-solid separator 6 are correspondingly communicated with the upper part feed inlet of the product tank 7 through a pipeline, the filtering component 6-1 can adopt a cylindrical filtering device with an upper port as a gas outlet, the upper end of the cylindrical filtering device is arranged at the upper part gas outlet of the second-stage gas-solid separator 6, the lower end of the cylindrical filtering device extends into the second-stage gas-solid separator 6, the filtering area is enlarged, the filtering efficiency is improved, and the integral gas-solid separating efficiency can be enhanced after adopting multi-stage separating and filtering modes, the problem that a cyclone separator is poor in separation efficiency on particles below 20 mu m is solved; according to the requirement, the lower parts of the primary gas-solid separator 5, the secondary gas-solid separator 6 and the product tank 7 are all arranged in a cone structure, and mechanical stirrers are arranged in the cone structure, so that the technical problems of secondary fluidization and difficult sedimentation of ultrafine particles caused by loosening wind adopted by a conventional fluidized bed can be solved;
the ascending fluidized reaction zone comprises a riser reactor 11, the lower end of the riser reactor 11 is communicated with a riser feeder 9, the riser feeder 9 can be set to be a Venturi tube-shaped structure as with the fluidized bed feeder 1, the lower end of the riser feeder 9 is set to be a gas inlet 9-1, the throat part is provided with a circulating powder inlet 9-2, the gas inlet 9-1 of the riser feeder 9 is correspondingly communicated with an upper gas outlet of a secondary gas-solid separator 6, the circulating powder inlet 9-2 of the riser feeder 9 is correspondingly communicated with a lower discharge hole of a product tank 7, the upper end of the riser reactor 9 is directly communicated with the upper end of the fluidized bed reactor 2, the outer wall of the riser reactor 9 is wrapped with a riser heater 12, and the characteristics of high flow speed, difficult agglomeration and weakened agglomeration tendency of the wrapped particles are utilized, the secondary coating is carried out in the riser reactor 9, so that the benefit of the coating reaction can be obviously improved, and the operation energy consumption of the device is reduced; in addition, a booster 10 is arranged on a communicating pipeline between a gas feed port of the riser feeder 9 and a gas outlet at the upper part of the secondary gas-solid separator 6, and is used for pressurizing the gas product with reduced pressure of the secondary gas-solid separator 6; in addition, a circulating powder secondary heater 8 is installed on a communicating pipeline between a circulating powder inlet of the riser feeder 9 and a discharge port at the lower part of the product tank 7, and the coated product with the temperature reduced in the product tank 7 is subjected to preheating treatment.
A method for using a fluidized reaction system for coating the surfaces of ultrafine particles, which adopts the thermal decomposition reaction (namely fluidized CVD coating technology) of a coating agent F1 in a descending fluidized bed reactor 2 and the thermal cracking reaction in an ascending riser reactor 11 to lead raw material powder S and circulating powder to be circularly coated between the two reactors, and qualified coated products are discharged from a product tank 7 in the descending fluidized reaction zone, and concretely comprises the following using processes:
firstly, overheating carrier gas AG is used for rapidly passing through a Venturi type fluidized bed feeder 1 from an overheating carrier gas inlet 1-1 from top to bottom, a negative pressure area is formed at the throat part of the Venturi type fluidized bed feeder 1, raw material powder S preheated to a preset temperature is sucked into the inner cavity of the fluidized bed feeder 1 from a raw material powder inlet 1-2, and the raw material powder S are uniformly mixed and then downwards sprayed into a fluidized bed reactor 2; the superheated carrier gas AG is an inert gas, preferably nitrogen, as required;
in the second process, a coating agent F1 is sprayed into the fluidized bed reactor 2 from the feeding nozzles 3 arranged on different cross sections of the fluidized bed reactor 2 at a certain temperature, and is mixed with the overheated carrier gas AG and the raw material powder S descending in the fluidized bed reactor 2 to generate a thermolysis reaction, a solid phase generated by the decomposition of the coating agent generates heterogeneous deposition on the surface of the raw material powder S, and a coating layer is formed on the surface of the raw material powder S; meanwhile, the cooler 4 carries out heat taking and heat preservation on the fluidized bed reactor 2; a plurality of coolers 4 which are arranged at intervals from top to bottom in sequence according to requirements, wherein the heat taking amount of the coolers 4 is determined according to the central temperature of each section in the corresponding fluidized bed reactor 2, and the central temperature of each section of the fluidized bed reactor 2 is kept basically constant;
it should be noted that, in order to prevent the occurrence of the coanda reaction and to maintain the absence of local hot spots in the descending fluidized bed reactor 2, two measures are taken, one is to control the flow rates of the cooling media C-1, C-2 and C-3 of the first to third coolers on the outer wall of the fluidized bed reactor 2 respectively so that the temperature of the inner wall of each section of the reactor is lower than the thermal cracking temperature of the coating agent; secondly, the flow of the coating agent feeding nozzle is adjusted, so that the central temperature of the fluidized bed reactor bed layer is basically kept unchanged;
thirdly, the gas-solid mixture after reaction in the fluidized bed reactor 2 downwards enters a primary gas-solid separator 5 for sedimentation separation, the separated solid particles downwards enter a product tank 7, the separated gas phase carries a small amount of solid particles and enters a secondary gas-solid separator 6 connected with the primary gas-solid separator 5 in parallel through a pipeline for filtration separation, the solid particles are intercepted by a filter assembly 6-1 and are collected at the lower part of the secondary gas-solid separator 6 and downwards enter the product tank 7 through the pipeline, the gas phase component upwards passes through the filter assembly 6-1 and flows out from the upper part of the secondary gas-solid separator 6, one part of the gas phase component is taken as a gas product P2 outlet device, and the other part of the gas phase component is taken as a diluent gas of an upwards-flowing fluidized reaction zone II; in order to prevent the solid particles collected in the first-stage gas-solid separator 5, the second-stage gas-solid separator 6 and the product tank 7 from bridging, mechanical loose stirrers positioned in the cone sections of the first-stage gas-solid separator, the second-stage gas-solid separator and the product tank can be respectively started;
taking partial gas from a secondary gas-solid separator 6 in a descending fluidized reaction zone I as diluent gas, pressurizing the diluent gas by a supercharger 10, mixing the diluent gas with riser gas-phase feeding F2 before a gas feeding inlet 9-1 of a Venturi type riser feeder 9, and ascending the diluent gas from a gas feeding inlet 9-1 of the riser feeder 9 to pass through the riser feeder 9; one part of the powder flowing out of the product tank 7 is taken as a coating product P1 and is discharged out of the device, the other part of the powder is taken as circulating powder after being heated by a circulating powder secondary heater 8, and the circulating powder is sucked into a riser feeder 9 from a circulating powder inlet 9-2 by negative pressure generated by ascending of a riser gas feed F2;
fifthly, after gas-solid phases in the riser feeder 9 are uniformly mixed, the gas-solid phases are upwards sprayed into the riser reactor 11, the gas-phase coating agent is subjected to thermal decomposition reaction in the riser reactor 11, so that the coating layer of the circulating powder is continuously thickened, and the gas-solid mixture in the riser reactor 11 is completely downwards sprayed into the fluidized bed reactor 2 from the upper end face of the fluidized bed reactor 2 to complete circulating coating; the temperature of the riser reactor 9 is controlled by a riser heater 12; the operating speed of the riser reactor 9 is much higher than that of the ordinary fluidized bed reactor 2, so that the harm of the coanda reaction is greatly reduced;
it should be noted that if the thickness of the coating layer formed by the raw material powder needs to be controlled, the circulation amount and the circulation times of the circulating powder can be adjusted; the circulation quantity and the circulation times of the circulating powder are increased, the thickness of the coating layer is increased, and otherwise, the thickness of the coating layer is reduced.
The first embodiment of the method comprises the following steps:
coating a silicon shell layer on the surface of the ultrafine graphite particles;
the raw material powder S to be coated is spherical natural graphite particles, the particle size of D50 is 10 mu m, and the preheating temperature is 800 ℃; the coating agent F1 is a mixture of SiH4 and hydrogen, and the molar ratio is 0.20; the overheating carrier gas AG is nitrogen with the purity of 99.999 percent;
nitrogen preheated to 780 ℃ is passed from a superheated carrier gas inlet 1-1 of the fluidized bed feeder 1 at a flow rate of 1200NL/h from top to bottom; raw material powder S preheated to 800 ℃ is uniformly sucked into the fluidized bed feeder 1 from a raw material powder inlet 1-2 at a flow rate of 8kg/h, and is sprayed downwards into the fluidized bed reactor 2 from a fluidized bed feeder outlet after being uniformly mixed; because the thermal decomposition reaction of the silane belongs to an exothermic reaction, the cooling media of the three coolers 4 adopt hot water of 80 ℃, and the temperature of the inner wall of the fluidized bed reactor 2 is kept at not higher than 400 ℃ and lower than the thermal decomposition temperature of the silane by controlling the flow of the cooling media C-1-3, so that the occurrence of wall-attached reaction is avoided; the central temperature of the bed layer of the descending fluidized bed reactor 2 is controlled at 650 +/-5 ℃, and the operating pressure is controlled at 50 +/-3 KPaG; the feeding temperature of the coating agent F1 is 390 ℃, the total feeding speed is 1600NL/h, the coating agent F1 is respectively sprayed into a reactor bed layer from a first feeding nozzle 3-1, a second feeding nozzle 3-2 and a third feeding nozzle 3-3 according to the flow rates of 800NL/h, 500NL/h and 300NL/h, silane is contacted with overheated carrier gas and preheated raw material powder in the bed layer, heat and mass transfer are carried out, thermal decomposition reaction is carried out, elemental silicon and hydrogen are generated, and the elemental silicon is deposited on the surface of graphite particles to form a coating layer; when the gas-solid mixture runs to the bottom of the fluidized bed reactor 2, the gas-solid mixture enters a primary gas-solid separator 5 together downwards for gas-solid settlement separation, the separated once-coated graphite particles fall into a lower cone section of the separator for short, the rotating speed of a stirrer of the primary gas-solid separator 5 is kept at 5rpm, and the once-coated graphite collected in the primary gas-solid separator 5 flows downwards into a product tank 7; the gas phase separated by the primary gas-solid separator 5 is mainly nitrogen and hydrogen and carries a small amount of ultrafine particles, and enters the secondary gas-solid separator 6 through a pipeline, wherein the aperture of a filter component 6-1 is not more than 5 mu m, the solid particles entering the secondary gas-solid separator 6 are intercepted, collected in a cone section at the lower part of the secondary filter 6 and downwards enter a product tank 7 through a connecting pipeline; in order to prevent the graphite particles from bridging, the rotating speed of the stirrer of the secondary gas-solid separator 6 and the rotating speed of the stirrer of the product tank 7 are also kept at 5 rpm; the gas passed through the filter module 6-1 was passed from the upper part of the secondary gas-solid separator 6 at a flow rate of 3120NL/h, and divided into two parts, wherein the gas at a flow rate of 1620NL/h was passed out of the apparatus as gaseous product P2 and the remaining 1500NL/h was used as a diluent gas for the upflowing fluidized reaction zone II;
the flow rate of the diluent gas introduced into the upstream fluidization reaction zone II from the downstream fluidization reaction zone I is 1500NL/h, and the feeding temperature is 650 ℃; the gas phase feeding F2 of the riser is SiH4, the preheating temperature is 350 ℃, and the molar ratio of SiH4 to released gas is 0.20; controlling the reaction temperature of the riser reactor 11 to be 650 +/-5 ℃ and the operation pressure to be 60 +/-3 KPaG;
pressurizing the dilution gas to 100KPaG by a supercharger 10, mixing the dilution gas with SiH4 preheated to 350 ℃ in front of a Venturi type riser feeder 9, and passing through the riser feeder 9 from bottom to top from a gas feed inlet 9-1; part of the primary coated graphite particles flowing out of the product tank 7 are used as circulating powder, the flow rate is controlled to be 4kg/h, the circulating powder is preheated to 650 ℃ by a circulating powder secondary heater 8, the circulating powder is sucked into a cavity of a lifting pipe feeder 9 from a circulating powder inlet 9-2 at the throat part of the lifting pipe feeder 9, and gas-solid phases are uniformly mixed and then are upwards sprayed into a lifting pipe reactor 11; maintaining the reaction temperature of the riser reactor 11 at 650 +/-5 ℃ and controlling the operation pressure at 60 +/-3 KPaG; the coating agent SiH4 is subjected to thermal decomposition reaction in the riser reactor 11, so that the coating layer of the circulating powder is continuously thickened; the reacted gas-solid mixture is all sprayed into the fluidized bed reactor 2 downwards along the outlet of the riser reactor 11, and the circulation of the graphite particles to be coated between the downstream fluidization reaction zone I and the upstream fluidization reaction zone II is completed;
the yield of the coated product after one cycle of this example was 8.60 kg.
The second method embodiment:
coating an amorphous carbon shell on the surface of the ultrafine graphite particles;
the raw material powder S to be coated adopts spherical natural graphite particles which are completely the same as those in the second embodiment, and the coating agent adopts the mixture of methane and hydrogen, wherein the molar ratio of the methane is 0.10;
because the thermal decomposition of methane belongs to endothermic reaction and the tendency of the coanda reaction is weaker, in the embodiment, the cold wall state does not need to be kept in the running process of the descending fluidized bed, cooling media are not introduced into the three coolers 4, and the cooling vacuum degrees are kept at-97 kPa in order to prevent the heat loss of the bed layer; otherwise, the operation process of the second embodiment is the same as that of the first embodiment;
the specific operating conditions of example two were:
nitrogen preheated to 750 ℃ was passed through the fluidized bed feeder 1 from its inlet 1-1 for superheated carrier gas at a flow rate of 900NL/h from top to bottom; raw material powder S preheated to 750 ℃ is uniformly sucked into the fluidized bed feeder 1 from a raw material powder inlet 1-2 at a flow rate of 6kg/h, the raw material powder S and the raw material powder S are uniformly mixed and then are downwards sprayed into the fluidized bed reactor 2 from an outlet 1-3 of the fluidized bed feeder 1, and the operating pressure of the fluidized bed reactor 2 is controlled to be 80 +/-5 KPaG; the feeding temperature of the coating agent F1 is 800 ℃, the total feeding speed is 1800NL/h, the coating agent F1 is respectively sprayed into a reactor bed layer from a first feeding nozzle 3-1, a second feeding nozzle 3-2 and a third feeding nozzle 3-3 according to the flow rates of 800NL/h, 500NL/h and 500NL/h, methane is contacted with overheated carrier gas and preheated circulating powder in the bed layer, heat and mass transfer are carried out, thermal decomposition reaction is carried out, simple substance carbon and hydrogen are generated, and the simple substance carbon is deposited on the surface of graphite particles to form a coating layer; when the gas-solid mixture runs to the bottom of a descending fluidized bed reactor 2, the gas-solid mixture enters a primary gas-solid separator 5 together downwards for gas-solid settlement separation, the separated once-coated graphite particles fall into a lower cone section of the separator for short, the rotating speed of a stirrer of the primary gas-solid separator 5 is kept at 3rpm, and the once-coated graphite collected in the primary gas-solid separator flows downwards into a product tank 7; the gas phase separated by the first-stage gas-solid separator 5 is mainly as follows: nitrogen and hydrogen with a small amount of ultrafine particles enter a secondary gas-solid separator 6 through a pipeline, wherein the aperture of a filter component 6-1 is not more than 5 mu m, the solid particles entering the secondary gas-solid separator 6 are intercepted, collected in a lower cone section of the secondary filter 6 and downwards enter a product tank 7 through a connecting pipeline; in order to prevent the graphite particles from bridging, the rotating speed of the stirrer of the secondary gas-solid separator 6 and the rotating speed of the stirrer of the product tank are also kept at 3 rpm; the gas passing through the filter assembly 6-1 was passed from the upper part of the secondary gas-solid separator 6 at a flow rate of 2880NL/h, dividing it into two parts, wherein the gas at a flow rate of 880NL/h was passed out of the apparatus as gaseous product P2 and the remaining 2000NL/h was used as dilution gas for the upflowing fluidized reaction zone II;
the flow rate of the diluent gas introduced into the upward fluidization reaction zone II from the downward fluidization reaction zone I is 2000NL/h, and the feeding temperature is 750 ℃; the riser gas-phase feed F2 is methane, the preheating temperature is 750 ℃, and the molar ratio of methane to released gas is 0.10; the reaction temperature of the riser reactor 11 is kept at 750 +/-5 ℃, and the operation pressure is controlled at 100 +/-5 KPaG;
pressurizing the diluted gas to 120KPaG by a supercharger 10, mixing the diluted gas with methane preheated to 800 ℃ in front of a Venturi type riser feeder 9, and passing through the feeder 9 from bottom to top from a gas feed inlet 9-1; part of the primary coated graphite flowing out of the product tank 7 is taken as circulating powder, the flow rate is controlled at 3.5kg/h, the circulating powder is preheated to 750 ℃ by a circulating powder secondary heater 8, the circulating powder is sucked into a cavity of a lifting pipe feeder 9 from a circulating powder inlet 9-2 at the throat part of the feeder, and gas-solid phases are uniformly mixed and then are upwards sprayed into a lifting pipe reactor 11; maintaining the reaction temperature of the riser reactor 11 at 750 +/-5 ℃ and controlling the operation pressure at 100 +/-5 KPaG; the coating agent methane generates thermal decomposition reaction in the riser reactor 11, so that the coating layer of the circulating powder is thickened continuously; the reacted gas-solid mixture is all sprayed into the fluidized bed reactor 2 downwards along the outlet of the riser reactor 11, and the circulation of the graphite particles to be coated between the downstream fluidization reaction zone I and the upstream fluidization reaction zone II is completed;
after one cycle, the yield of the coated product is 6.19 kg.
The invention is not described in detail in the prior art, and it is apparent to a person skilled in the art that the invention is not limited to details of the above-described exemplary embodiments, but that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof; the present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein, and any reference signs in the claims are not intended to be construed as limiting the scope of the claims concerned.
Claims (10)
1. A fluidized reaction system for coating the surface of ultrafine particles is characterized in that: comprises a downward fluidization reaction zone and an upward fluidization reaction zone coupled with the downward fluidization reaction zone;
the downward fluidized reaction zone comprises a fluidized bed reactor (2), a primary gas-solid separator (5), a secondary gas-solid separator (6) and a product tank (7); the upper end of the fluidized bed reactor (2) is communicated with a fluidized bed feeder (1) for feeding raw material powder and superheated carrier gas, the outer wall of the fluidized bed reactor (2) is sequentially provided with a plurality of coolers (4) at intervals from top to bottom, and feeding nozzles (3) for feeding a coating agent are arranged on the outer wall of the fluidized bed reactor (2) between the fluidized bed feeder (1) and the uppermost cooler (4) and between two adjacent coolers (4); the upper part feed inlet of the primary gas-solid separator (5) is correspondingly communicated with the lower end of the fluidized bed reactor (2), the upper part feed inlet of the secondary gas-solid separator (6) is correspondingly communicated with the upper part air outlet of the primary gas-solid separator (5) through a pipeline, the upper part air outlet of the secondary gas-solid separator (6) is provided with a filtering component (6-1), and the lower part solid material outlets of the primary gas-solid separator (5) and the secondary gas-solid separator (6) are correspondingly communicated with the upper part feed inlet of the product tank (7) through pipelines;
the upward fluidization reaction zone comprises a riser reactor (11), the lower end of the riser reactor (11) is communicated with a riser feeder (9), a gas feed port (9-1) of the riser feeder (9) is correspondingly communicated with a gas outlet at the upper part of the secondary gas-solid separator (6), a circulating powder inlet (9-2) of the riser feeder (9) is correspondingly communicated with a discharge port at the lower part of the product tank (7), the upper end of the riser reactor (9) is directly communicated with the upper end of the fluidized bed reactor (2), and a riser heater (12) is wrapped on the outer wall of the riser reactor (9).
2. The ultrafine particle surface-coated fluidized reaction system according to claim 1, wherein: the fluidized bed feeder (1) and the riser feeder (9) are both of Venturi tube-shaped structures; the upper end of the fluidized bed feeder (1) is provided with an overheating carrier gas inlet (1-1), and the throat part is provided with a raw material powder inlet (1-2); the lower end of the riser feeder (9) is provided with a gas feed inlet (9-1), and the throat part is provided with a circulating powder inlet (9-2).
3. The ultrafine particle surface-coated fluidized reaction system according to claim 1, wherein: the number of the coolers (4) is three, namely a first cooler (4-1), a second cooler (4-2) and a third cooler (4-3), cooling media of each cooler (4) are fed in and discharged out from the lower part, and each cooler (4) is provided with an independent cooling medium supply and temperature regulation system.
4. The ultrafine particle surface-coated fluidized reaction system according to claim 1, wherein: the feeding nozzles (3) of the fluidized bed feeder (2) with the same cross section are uniformly and annularly provided with at least three feeding nozzles, and the feeding nozzles (3) with the same cross section are communicated with a cladding agent feeding pipeline annularly arranged outside the corresponding wall of the fluidized bed feeder (2).
5. The ultrafine particle surface-coated fluidized reaction system according to claim 1, wherein: the lower parts of the first-stage gas-solid separator (5), the second-stage gas-solid separator (6) and the product tank (7) are all arranged into cone structures, and mechanical stirrers are arranged in the cone structures.
6. The ultrafine particle surface-coated fluidized reaction system according to claim 1, wherein: and a supercharger (10) is arranged on a communicating pipeline between a gas feed port of the lifting pipe feeder (9) and a gas outlet at the upper part of the secondary gas-solid separator (6).
7. The ultrafine particle surface-coated fluidized reaction system according to claim 1, wherein: and a circulating powder secondary heater (8) is arranged on a communicating pipeline between a circulating powder inlet of the lifting pipe feeder (9) and a discharge hole at the lower part of the product tank (7).
8. A method for using the fluidized reaction system for coating the surface of the ultrafine particles according to claim 1, which comprises: comprises the following using processes:
the first process is that the raw material powder S is sucked into a fluidized bed feeder (1) by using superheated carrier gas AG through negative pressure generated by the fluidized bed feeder (1), and the raw material powder S and the fluidized bed feeder are uniformly mixed and then are downwards sprayed into a fluidized bed reactor (2);
in the second process, the coating agent F1 is sprayed into the fluidized bed reactor (2) from the feeding nozzles (3) arranged on different cross sections of the fluidized bed reactor (2) in a gas phase form, and is mixed with the overheated carrier gas AG descending in the fluidized bed reactor (2) and the raw material powder S to generate a thermal decomposition reaction, so that a coating layer is formed on the surface of the raw material powder S; meanwhile, the cooler (4) is used for heating and insulating the fluidized bed reactor (2);
thirdly, the gas-solid mixture after reaction in the fluidized bed reactor (2) enters a primary gas-solid separator (5) downwards for sedimentation separation, the separated solid particles enter a product tank (7) downwards, the separated gas phase carries a small amount of solid particles and enters a secondary gas-solid separator (6) connected with the primary gas-solid separator (5) in parallel through a pipeline for filtration separation, the solid particles are intercepted by a filter component (6-1), the solid particles are collected at the lower part of the secondary gas-solid separator (6) and enter the product tank (7) downwards through the pipeline, the gas phase component flows upwards through the filter component (6-1) and flows out from the upper part of the secondary gas-solid separator (6), one part of the gas phase component is taken as a gas product P2 outlet device, and the other part of the gas phase component is taken as a dilution gas of an ascending fluidized reaction zone II;
fourthly, after the diluent gas from the downward fluidization reaction zone I is mixed with the gas-phase feeding F2 of the riser, the diluent gas ascends from a gas feeding hole (9-1) of the riser feeder (9) and passes through the riser feeder (9); one part of the powder flowing out of the product tank (7) is taken as a coating product P1 and discharged out of the device, and the other part of the powder is sucked into a lifting pipe feeder (9) from a circulating powder inlet (9-2) by negative pressure generated by lifting pipe gas feed F2;
and fifthly, after gas-solid phases in the riser feeder (9) are uniformly mixed, the gas-solid phases are upwards sprayed into the riser reactor (11), the gas-phase coating agent is subjected to thermal decomposition reaction in the riser reactor (11), so that the coating layer of the circulating powder is continuously thickened, and the gas-solid mixture in the riser reactor (11) is completely downwards sprayed into the fluidized bed reactor (2) from the upper end surface of the fluidized bed reactor (2) to complete the circulating coating.
9. The method of using the fluidized reaction system coated with the surface of the ultrafine particles as set forth in claim 8, wherein: in the second process, a plurality of coolers (4) are arranged at intervals from top to bottom, the heat taking amount of the coolers is determined according to the central temperature of each section in the corresponding fluidized bed reactor (2), and the central temperature of each section of the fluidized bed reactor (2) is kept basically constant.
10. The method of using the fluidized reaction system coated with the surface of the ultrafine particles as set forth in claim 8, wherein: in process one, the superheated carrier gas AG is an inert gas.
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