Combustion device for preparing high-sphericity powder by flame method

Abstract

The utility model discloses a combustion device for preparing high-sphericity powder by a flame method, which comprises a central gas spray pipe, a middle oxygen pipeline and an outer-layer material conveying pipeline which are coaxially arranged from inside to outside, and the gas outlet end of the central gas spray pipe is flush with the end face of the gas outlet end of the middle oxygen pipeline; the discharging end of the outer-layer material conveying pipeline extends to a flame jetting area covering the end of the center gas pipeline and the end of the middle oxygen pipeline, an annular protrusion corresponding to the gas outlet end of the center gas pipeline is arranged on the inner wall of the outer-layer material conveying pipeline, and a Venturi nozzle is defined by the annular protrusion. The design effectively solves the technical bottleneck that the retention time of particles is too short in the traditional hypersonic flame process, and is particularly suitable for the millisecond-level rapid melting-spheroidizing-quenching process requirements of ultrafine powder with the particle size smaller than 10 microns.

Description

Technical Field

[0001] This utility model relates to the field of powder material preparation technology, and more specifically, to a combustion device for preparing high sphericity powder by flame method. Background Technology

[0002] Supersonic flame spraying technology, as an important process in surface engineering, utilizes the high-temperature, high-speed flame generated by the combustion of combustible gas and oxygen to melt and accelerate the sprayed material. Traditional supersonic flame systems employ a De Laval nozzle structure, achieving flame velocities exceeding 2000 m / s and temperatures ranging from 2000 to 3000°C. However, the residence time of particles in the flame is typically only 0.1-0.3 milliseconds. This transient thermodynamic characteristic can effectively melt metal alloy powders with particle sizes greater than 20 μm, but when processing ultrafine powders at the 10 μm level, existing systems exhibit an inherent defect of insufficient flame residence time: particles pass through the flame zone before fully melting, leading to insufficient sphericity, increased satellite particles, and other process defects. Existing techniques that extend residence time by increasing gas flow rate or lengthening the flame can disrupt the jet momentum balance, causing particles smaller than 15 μm to penetrate and escape due to insufficient inertia, with measured escape rates exceeding 30%. Current mainstream equipment uses a mechanical powder feeding system to force the particles into the flame, but the problem of dynamically matching the powder feeding rate with the flame parameters can easily lead to particle agglomeration or uneven powder feeding, especially for ultrafine powders, which are prone to clogging of the powder feeding pipe.

[0003] In view of this, this utility model is hereby proposed. Utility Model Content

[0004] The purpose of this invention is to provide a combustion device for preparing high sphericity powder by flame method, so as to improve the above-mentioned technical problems.

[0005] The embodiments of this utility model can be implemented as follows:

[0006] In a first aspect, this utility model provides a combustion device for preparing high sphericity powder by flame method, which includes a central gas injection pipe, an intermediate oxygen pipe and an outer material conveying pipe arranged coaxially from the inside to the outside. The end face of the gas outlet of the central gas injection pipe is flush with the end face of the gas outlet of the intermediate oxygen pipe. The outlet of the outer material conveying pipe extends to the flame spray area covering the ends of the central gas injection pipe and the intermediate oxygen pipe. The inner wall of the outer material conveying pipe is provided with an annular protrusion corresponding to the gas outlet of the central gas injection pipe. The annular protrusion surrounds and forms a Venturi nozzle.

[0007] In an optional embodiment, a ceramic liner is provided on the inner wall surface of the outer material conveying pipe corresponding to the flame jet area, and the annular protrusion is a component of the ceramic liner.

[0008] In an optional embodiment, the ceramic liner is made of alumina ceramic.

[0009] In an optional implementation, for a machine with a thermal power of 100kW, the inner diameter of the central gas nozzle is 2.1mm~2.3mm and the wall thickness is 0.9mm~1.1mm.

[0010] In an optional implementation, for a machine with a thermal power of 100kW, the inner diameter of the intermediate oxygen pipe is 8.9mm~9.1mm.

[0011] In an optional embodiment, for a machine with a thermal power of 100kW, the inlet diameter of the Venturi nozzle is 21.5mm~22.5mm, the throat diameter is 14.5~15.5mm, the length from the inlet to the throat is 10.5mm~11.5mm, the outlet diameter is 19.5mm~20.5mm, and the length from the throat to the outlet is 16.5mm~17.5mm.

[0012] In an optional implementation, for a machine with a thermal power of 100kW, the length from the outlet end of the central gas nozzle to the inlet of the Venturi nozzle is 0mm to 5mm.

[0013] In an optional embodiment, the eccentricity of the central gas injection pipe, the intermediate oxygen pipeline, and the outer material conveying pipeline is <0.05mm, and the concentricity reaches ISO 1101 Grade 5.

[0014] And / or, the central gas injection pipe, the intermediate oxygen pipeline, and the outer material conveying pipeline are sealed with O-rings.

[0015] In an optional embodiment, the discharge end of the outer material conveying pipe is also connected to a centrifugal fan;

[0016] And / or, the outlet end of the outer material conveying pipe is also provided with a makeup air filter box for tangential injection of cold air.

[0017] In an optional embodiment, the outer material conveying pipe covering the outer wall of the flame jet area is further provided with a water-cooled jacket.

[0018] The beneficial effects of the combustion device for preparing high-sphericity powder by flame method provided in this embodiment of the invention include: by constructing a three-layer coaxial structure with the functions of "central subsonic gas jet - intermediate oxygen-enriched combustion aid - outer negative pressure suction", the ratio of gas jet momentum to material carrier gas momentum can be precisely controlled, thereby ensuring that particles can be effectively captured by the flame and avoiding penetration and escape. The negative pressure effect generated at the outer throat can efficiently transport particles to the core region of the flame without relying on a mechanical powder feeding device. This design effectively solves the technical bottleneck of excessively short particle residence time in traditional supersonic flame processes, and is particularly suitable for the millisecond-level rapid melting-sphericification-quenching process requirements of ultrafine powders with particle sizes less than 10μm. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this utility model and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the combustion device for preparing high sphericity powder by flame method provided in this embodiment.

[0021] Icons: 10 - Combustion device for preparing high-sphericity powder by flame method; 100 - Central gas nozzle; 101 - Gas inlet; 200 - Intermediate oxygen pipeline; 201 - Oxygen inlet; 300 - Outer material conveying pipeline; 301 - Venturi nozzle; 310 - Ceramic liner; 311 - Annular protrusion; 320 - Water-cooled jacket; 400 - Makeup air filter box; 410 - Makeup air proportioning valve; 500 - Powder collection device; 600 - Centrifugal fan. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. The components of the embodiments of this utility model described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0023] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0024] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0025] In the description of this utility model, it should be noted that if terms such as "upper," "lower," "inner," or "outer" are used to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship that the utility model product is usually placed in during use, they are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model.

[0026] Furthermore, the terms "first" and "second" are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0027] It should be noted that, where there is no conflict, the features in the embodiments of this utility model can be combined with each other.

[0028] The following describes in detail the overall structure, working principle, and technical effects of the combustion device 10 for preparing high sphericity powder by flame method provided by this utility model through embodiments and in conjunction with the accompanying drawings.

[0029] See Figure 1 This utility model provides a combustion device 10 for preparing high sphericity powder by flame method, which includes a central gas nozzle 100, an intermediate oxygen pipe 200 and an outer material conveying pipe 300 arranged coaxially from the inside to the outside. The end face of the gas outlet of the central gas nozzle 100 is flush with the end face of the gas outlet of the intermediate oxygen pipe 200. The material outlet of the outer material conveying pipe 300 extends to the flame spray area covering the ends of the central gas nozzle 100 and the intermediate oxygen pipe 200. The inner wall of the outer material conveying pipe 300 is provided with an annular protrusion 311 corresponding to the gas outlet of the central gas nozzle 100. The annular protrusion 311 surrounds to form a Venturi nozzle 301.

[0030] It should be noted that the relevant structural parameters of the combustion device 10 for preparing high sphericity powder by flame method in this embodiment are designed for a machine with a thermal power of 100kW. If it is for a machine with other thermal power, the size can be adjusted proportionally according to the ratio of thermal power ratio to pipe cross-section ratio.

[0031] Specifically, the central gas nozzle 100 adopts a straight pipe structure design, with a gas inlet 101 at one end. This gas inlet 101 is located at the end of the central combustion pipe, ensuring that the gas enters along the axial direction of the central combustion pipe. Through this design, the gas can form a subsonic jet within the central combustion pipe and ultimately exit from the outlet end opposite to the gas inlet 101 (i.e., the end port of the central gas nozzle). Regarding material selection, heat-resistant stainless steel, such as 310S stainless steel or other high-performance alloy materials, is recommended to meet the requirements for use under high-temperature conditions.

[0032] The central gas nozzle 100 uses natural gas with CH4 content > 95%, and the flow design standard is: gas flow rate V fuel =10.0 Nm 3 / h; Pipe size: Outlet inner diameter d fuel =2.2 mm, wall thickness δ1=1.0 mm; outer diameter D1=d fuel +2δ1=4.2 mm; Gas flow velocity v fuel =150 m / s (Mach number 0.45); Temperature: 300K (room temperature).

[0033] Among them, the outlet inner diameter d fuel The following formula is used for calculation:

[0034] .

[0035] The intermediate oxygen pipeline 200 adopts an integral straight pipe structure and is coaxially sleeved outside the central gas injector 100, forming an annular oxygen channel between its inner wall and the outer wall of the central gas injector 100. One end of the pipeline is sealed with an O-ring, and an oxygen inlet 201 is provided on the side wall adjacent to the sealed end; the other end forms an annular gap with the outer wall of the central gas injector 100, serving as an oxygen outlet channel.

[0036] The intermediate oxygen pipeline 200 supplies industrial oxygen with a purity greater than 93%, with a design flow rate of VO2 = 11.0 Nm³ / h (oxygen-fuel ratio 2.2:1). The pipeline dimensions are as follows: the annular inner diameter is D. 2,in (i.e., the outer diameter of the central gas nozzle 100): D 2,in =D1=4.2mm; outer diameter of the ring D 2,out =9.0mm; circumferential seam width w O2 =2D 2,out D 2,in =1.5mm, oxygen flow rate v O2 =180 m / s (slightly higher than the gas flow rate, forming a shear layer). The intermediate oxygen pipe 200 is made of 310S stainless steel with a wall thickness of 1.5mm.

[0037] The area A of the annular gap in the intermediate oxygen tube O2 The calculation formula is:

[0038] .

[0039] One end of the outer material conveying pipe 300 is provided with a connecting bend, which is sealed to the intermediate oxygen pipe 200 by an O-ring (not shown in the figure). It is coaxially arranged with the intermediate oxygen pipe, and the structure formed by the annular protrusion at the other end serves as a nozzle.

[0040] The outer material conveying pipe 300 conveys a mixture of <10μm powder and air. Its key parameters are the relevant dimensions of the Venturi nozzle 301. Throat inlet parameters: Carrier gas flow rate Q. air =25m³ / h (inlet throat section); carrier gas velocity v in =20m / s; Inlet diameter D 3,in =22mm; wall thickness δ3=3.5 mm (including 5mm ceramic liner 310). Throat parameters: throat diameter d throat3 =15 mm; throat flow velocity v throat =v in ×CR = 20 × 2.25 = 40 m / s; where CR is the shrinkage ratio, and CR is calculated as follows: Throat length L throat3 =0.7×d throat3 =11 mm. Expansion section parameters: Exit diameter D 3,out =20mm; Expansion half-angle θ _div =10°, length of expansion segment .

[0041] Among them, D 3,in The design formula is:

[0042] .

[0043] It should be noted that the inlet refers to the venturi inlet, i.e., the maximum dimension at the inlet end; the throat refers to the minimum dimension in the middle; and the outlet refers to the outlet of the extension section, i.e., the maximum dimension at the outlet end. The dimensions gradually decrease from the inlet to the throat, and gradually increase from the throat to the outlet.

[0044] Furthermore, in this embodiment, a ceramic lining 310 layer is provided on the inner wall surface of the outer material conveying pipe 300 corresponding to the flame jet area, and the annular protrusion is a component of the ceramic lining 310 layer.

[0045] The ceramic lining layer 310 is made of alumina ceramic. The thickness δ of the remaining portions, excluding the annular protrusion, is... ceramic =5mm (close to the inner metal wall), its thermal conductivity λceramic ≈25W / (m·K), temperature resistance: long-term >1800°C, instantaneous >2000°C, take the maximum temperature resistance T. flame =2800°C, where the temperature of the external metal substrate is <300°C, and the temperature of the metal shell is taken as T. shell =300°C, metal shell thickness δ metal =3.5mm, thermal conductivity λ of metal casing metal =16 W / (m·K), thermal resistance q is calculated as follows:

[0046] ;

[0047] Heat dissipation from the casing: Internal surface area A inner ≈π×0.022×0.03=0.0021m², heat flow Q=q×A=12.5kW (accounting for only 12.5% ​​of the heat power, which is acceptable).

[0048] In this embodiment, the length from the outlet end of the central gas nozzle 100 to the inlet of the throat of the venturi nozzle 301 is 0mm to 5mm. Preferably, the distance L from the gas outlet to the throat inlet is... gap3 =(1.2 1.3)×d throat3 =18~20 mm, to ensure that the flame core zone is formed 5 mm before the throat inlet.

[0049] In this embodiment, the outer wall of the outer material conveying pipe 300 covering the flame jet area is also provided with a water-cooling jacket 320 to ensure that the outer shell is <300°C.

[0050] Furthermore, the eccentricity of the central gas nozzle 100, the intermediate oxygen pipeline 200, and the outer material conveying pipeline 300 is <0.05mm, and the concentricity reaches ISO 1101 Grade 5, in order to avoid uneven circumferential temperature caused by eccentricity, which would result in large differences in spheroidization.

[0051] The complete calculation process for the 100kW system in this embodiment is demonstrated below:

[0052] Step 1, Gas flow rate V fuel calculate

[0053]

[0054] Where P is the target power of the system, LHV is the net calorific value, η is the combustion efficiency, and V fuel Rounded to 10 Nm³ / h, corresponding to a power of 92 kW (with an 8% margin).

[0055] Step 2, the outlet inner diameter d of the gas nozzle fuel :

[0056]

[0057] Step 3, Oxygen pipe circumferential seam area A O2 :

[0058] Oxygen-fuel mass ratio 2.2:1 → Oxygen mass flow rate m O2 =7.2×2.2=15.84 kg / h.

[0059] , where ρ O2 For oxygen density, v O2 This refers to the oxygen flow rate.

[0060] Step 4: The throat inlet diameter D of the outermost pipe 3,in :

[0061] Carrier gas speed 20 m / s, flow rate 25 m³ / h:

[0062]

[0063] Step 5: Optimization of throat diameter

[0064] Contraction ratio CR = 2.2 (balancing negative pressure and flow velocity), throat diameter d throat3 :

[0065]

[0066] Step 6: Verification of the thermal protection of the ceramic lining 310

[0067] Flame-side heat flux density q:

[0068] q=hc(Tg Tw)=500×(2800 2000) = 400kW / m 2 .

[0069] In the formula for calculating heat flux density q, hc is the convective heat transfer coefficient, Tg is the mainstream fluid temperature, and Tw is the wall temperature.

[0070] Ceramic outer surface temperature T ceramic,out :

[0071]

[0072] Ceramic outer surface temperature T ceramic,out In the calculation formula, T ceramic,in The temperature of the inner surface of the ceramic is given by q, where q is the heat flux density on the flame side, and δ is the temperature of the inner surface of the ceramic. ceramic λ is the thickness of the ceramic portion excluding the annular protrusion (close to the inner metal wall). ceramicis the thermal conductivity of the ceramic.

[0073] Metal casing temperature T shell :

[0074]

[0075] Metal casing temperature T shell In the calculation formula, T ceramic,out Let δ be the temperature of the ceramic outer surface, q be the heat flux density on the flame side, and δ be the temperature of the ceramic outer surface. metal λ is the thickness of the metal shell. metal is the thermal conductivity of the metal casing.

[0076] In this embodiment, the discharge end of the outer material conveying pipe 300 is also provided with a makeup air filter box 400 for tangential injection of cold air, and a makeup air proportioning valve 410 is provided at the outlet of the makeup air filter box 400; the spheroidized powder can be rapidly cooled by secondary air to avoid thermal melting and agglomeration.

[0077] Furthermore, the discharge end of the outer material conveying pipe 300 is also connected to a centrifugal fan 600 to provide collection power to the powder collection device 500 at the rear end and supplement negative pressure, which enables the throat to generate a static pressure of -800Pa, so that the particles can be sucked into the core area of ​​the flame without mechanical powder feeding.

[0078] The above description is only a specific embodiment of this utility model, but the protection scope of this utility model is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this utility model should be included within the protection scope of this utility model.

Claims

1. A combustion apparatus for preparing high-sphericity powder by flame method, characterized in that, It includes a central gas nozzle, an intermediate oxygen pipe, and an outer material conveying pipe arranged coaxially from the inside to the outside. The outlet end of the central gas nozzle is flush with the end face of the outlet end of the intermediate oxygen pipe. The outlet end of the outer material conveying pipe extends to the flame jet area covering the ends of the central gas nozzle and the intermediate oxygen pipe. The inner wall of the outer material conveying pipe is provided with an annular protrusion corresponding to the outlet end of the central gas nozzle. The annular protrusion surrounds and forms a Venturi nozzle.

2. The combustion apparatus for preparing high-sphericity powder by flame method according to claim 1, characterized in that, A ceramic lining is provided on the inner wall surface of the outer material conveying pipe corresponding to the flame jet area, and the annular protrusion is a component of the ceramic lining.

3. The combustion apparatus for preparing high-sphericity powder by flame method according to claim 2, characterized in that, The ceramic lining layer is made of alumina ceramic.

4. The combustion apparatus for preparing high-sphericity powder by flame method according to claim 1, characterized in that, For a machine with a thermal power of 100kW, the inner diameter of the central gas nozzle is 2.1mm~2.3mm and the wall thickness is 0.9mm~1.1mm.

5. The combustion apparatus for preparing high-sphericity powder by flame method according to claim 4, characterized in that, For a machine with a thermal power of 100kW, the inner diameter of the intermediate oxygen pipeline is 8.9mm~9.1mm.

6. The combustion apparatus for preparing high-sphericity powder by flame method according to claim 5, characterized in that, For a machine with a thermal power of 100kW, the inlet diameter of the Venturi nozzle is 21.5mm~22.5mm, the throat diameter is 14.5~15.5mm, the length from the inlet to the throat is 10.5mm~11.5mm, the outlet diameter is 19.5mm~20.5mm, and the length from the throat to the outlet is 16.5mm~17.5mm.

7. The combustion apparatus for preparing high-sphericity powder by flame method according to any one of claims 1 to 6, characterized in that, For a machine with a thermal power of 100kW, the length from the outlet of the central gas nozzle to the inlet of the Venturi nozzle is 0mm to 5mm.

8. The combustion apparatus for preparing high-sphericity powder by flame method according to any one of claims 1 to 6, characterized in that, The eccentricity of the central gas injection pipe, the intermediate oxygen pipeline, and the outer material conveying pipeline is <0.05mm, and the concentricity reaches ISO 1101 Grade 5. And / or, the central gas injection pipe, the intermediate oxygen pipeline, and the outer material conveying pipeline are sealed with O-rings.

9. The combustion apparatus for preparing high-sphericity powder by flame method according to any one of claims 1 to 6, characterized in that, The discharge end of the outer material conveying pipeline is also connected to a centrifugal fan; And / or, the outlet end of the outer material conveying pipe is also provided with a makeup air filter box for tangential injection of cold air.

10. The combustion apparatus for preparing high-sphericity powder by flame method according to any one of claims 1 to 6, characterized in that, The outer material conveying pipeline covering the outer wall of the flame jet area is also equipped with a water-cooled jacket.

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