Gas roaster

Abstract

The invention provides a gas roaster. The gas roaster comprises a gas pipeline, a primary air pipeline and a secondary air pipeline, one end of the gas pipeline is provided with a gas inlet, and the other end of the gas pipeline is provided with a gas nozzle which is located on the same horizontal line with the gas inlet; a primary air inlet and a primary air nozzle are respectively formed in two ends of the primary air pipeline; a secondary air inlet and a secondary air nozzle are respectively formed in two ends of the secondary air pipeline; the fuel gas nozzles, the primary air nozzles and the secondary air nozzles are circumferentially and uniformly distributed from inside to outside by taking the same circle center as a reference; the fuel gas inlet, the primary air inlet and the secondary air inlet are arranged adjacently; the end parts of the gas pipeline, the primary air pipeline and the secondary air pipeline are connected with burners; and the burners are communicated with the gas nozzle, the primary air nozzle and the secondary air nozzle. Consistent contact time is guaranteed, and combustion reaction is more uniform and stable.

Description

Technical Field

[0001] The invention relates to the technical field of gas roasting start-up of aluminum electrolytic cells, in particular to a gas roaster. Background Art

[0002] The roasting process is a key step in aluminum electrolysis production. Its effect directly affects the service life of aluminum electrolysis cells, which in turn is closely related to the production costs of aluminum electrolysis enterprises. Currently, aluminum electrolysis cells are usually roasted and started by gas roasting or coke roasting. The gas roasting method is widely used because it cleans the electrolyte after startup, has a better roasting effect on the edge ramming paste, and has a lower cathode surface temperature gradient.

[0003] In traditional direct-fired burners, the flame comes into direct contact with the cathode and anode, easily causing the surface temperatures of the anode and cathode carbon blocks to overheat. Furthermore, due to incomplete oxygen consumption, oxidation reactions occur on the cathode and anode surfaces, leading to carbon block damage and shortening the life of the aluminum electrolysis cell. Furthermore, the uneven mixing of gas and air in traditional burners results in low combustion efficiency and poor flame stability, making it difficult to meet the high-efficiency and energy-saving requirements of modern aluminum electrolysis production.

[0004] For example, the carbon electrode or cathode baking furnace disclosed in the existing patent publication number CN110878940A uses a burner with automatic air distribution, ignition and fire detection. Its gas is ejected through a Venturi nozzle (main nozzle + fine nozzle), while air is indirectly introduced through the air outlet of the wind disk. The contact time between the two is inconsistent, which easily forms a rich fuel or oxygen-rich zone, resulting in uneven combustion. Summary of the Invention

[0005] The object of the present invention is to provide a gas roaster that makes the combustion reaction more uniform and stable.

[0006] The technical solution of the present invention is: a gas roaster, comprising a gas pipeline, a primary air pipeline coaxially mounted on the gas pipeline, and a secondary air pipeline coaxially mounted on the primary air pipeline, wherein one end of the gas pipeline is provided with a gas inlet, and the other end of the gas pipeline is provided with a gas nozzle coaxially mounted on the same horizontal line as the gas inlet; one end of the primary air pipeline is provided with a primary air inlet, and the other end of the primary air pipeline is provided with a primary air nozzle; one end of the secondary air pipeline is provided with a secondary air inlet, and the other end of the secondary air pipeline is provided with a secondary air nozzle;

[0007] The gas nozzles, primary air nozzles and secondary air nozzles are evenly distributed in a circle from the inside to the outside with the same center as the reference; the gas inlet, primary air inlet and secondary air inlet are arranged adjacent to each other; the ends of the gas pipeline, primary air pipeline and secondary air pipeline are connected to burners, and the burners are connected to the gas nozzles, primary air nozzles and secondary air nozzles.

[0008] In the above scheme, the gas pipeline, primary air pipeline and secondary air pipeline are set to a coaxial structure, and the inlet and outlet of the gas are on the same horizontal line, the contact time is consistent, and the combustion reaction is more uniform and stable.

[0009] Preferably, the primary air duct includes a first same-diameter pipe and a first reducing pipe, the first reducing pipe has a structure with a small diameter in the middle and large diameters at both ends, one end of the first reducing pipe is connected to the first same-diameter pipe, the other end of the first reducing pipe is provided with the primary air nozzle, and the primary air inlet is provided on the first same-diameter pipe.

[0010] Preferably, the secondary air duct includes a second same-diameter pipe and a second reducing pipe, the second reducing pipe has a structure with a small diameter in the middle and large diameters at both ends, one end of the second reducing pipe is connected to the second same-diameter pipe, the other end of the second reducing pipe is provided with the secondary air nozzle, and the secondary air inlet is provided on the second same-diameter pipe.

[0011] Preferably, an ignition tube and a flame detection tube are connected to the end face of the inlet end of the burner, and the ignition tube and the flame detection tube are arranged on both sides of the secondary air duct, and the axes of the ignition tube and the flame detection tube are parallel to the axis of the inlet end of the burner.

[0012] Preferably, a primary air cyclone is provided in the primary air duct, a secondary air cyclone is provided in the secondary air duct, the primary air cyclone is sleeved on the gas pipeline, and the secondary air cyclone is sleeved on the primary air duct.

[0013] Preferably, the primary air cyclone comprises a first shaft portion and a plurality of first blades uniformly distributed and inclined along the circumference of the first shaft portion, and the first shaft portion is sleeved on the gas pipeline.

[0014] Preferably, the secondary air cyclone includes a second shaft portion and a plurality of second blades uniformly distributed and inclined along the circumference of the second shaft portion, and the second shaft portion is sleeved on the primary air duct.

[0015] Preferably, the burner is formed by a curved circular cross-section tube with a bending angle of 70°-90°.

[0016] Preferably, the gas pipeline includes a straight pipe and a flared pipe, the flared pipe is a trumpet pipe with a small diameter at one end and a large diameter at the other end, the small diameter end of the flared pipe is connected to the straight pipe, the large diameter end of the flared pipe is connected to the burner, and the gas nozzle is provided on the large diameter end of the flared pipe, and the gas inlet is provided at the end of the straight pipe away from the flared pipe.

[0017] Preferably, the mass flow of primary air input to the burner through the primary air duct accounts for 60%-80% of the total air mass flow, and the mass flow of secondary air input to the burner through the secondary air duct accounts for 20%-40% of the total air mass flow.

[0018] Compared with the related art, the present invention has the following beneficial effects:

[0019] First, the present invention sets the gas pipeline, primary air pipeline and secondary air pipeline into a coaxial structure, and the gas inlet and outlet are on the same horizontal line, the contact time is consistent, and the combustion reaction is more uniform and stable;

[0020] Second, the present invention designs the primary and secondary air ducts as variable-diameter pipe structures to achieve the contraction and expansion Venturi effect, which can stabilize the airflow, prevent backfire, achieve full mixing of gas and air and efficient combustion, and effectively improve the stability and service life of the burner;

[0021] 3. The burner of the present invention adopts a circular cross-section design, which can improve combustion stability, reduce noise, and fully burn the gas in the burner. Compared with the traditional direct flame burner, it effectively reduces the problem of cathode and anode oxidation during the electrolytic cell baking and heating process;

[0022] Fourth, the present invention distributes the gas outlet, primary air nozzles, and secondary air nozzles uniformly around the same center of the circle from the inside out to ensure full mixing of air and gas within the burner. The number and diameter of the nozzles are linked to the gas flow rate to facilitate flow control.

[0023] 5. The present invention is equipped with air cyclones in both the primary and secondary air ducts, which can generate tangential vortexes, prolong the residence time of the gas, make combustion more complete, and achieve high temperature uniformity;

[0024] 6. The burner of the present invention is connected with the flame detection tube and the ignition tube, which ensures the stable ignition of the gas and enhances the safety of the system;

[0025] 7. The present invention can inhibit oxidation of the cathode and anode, improve combustion efficiency and temperature uniformity, reduce noise and shorten the baking cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The three-dimensional structure and cross-sectional schematic diagram of the gas roaster provided by the present invention;

[0027] Figure 2 The front view and cross-sectional view of the gas roaster provided by the present invention;

[0028] Figure 3 Schematic diagram of the structure of each nozzle;

[0029] Figure 4 It is a structural diagram of a primary air cyclone;

[0030] Figure 5 Schematic diagram of the structure of the secondary air cyclone;

[0031] Figure 6 It is a structural diagram of the burner;

[0032] Figure 7 This is the numerical simulation methane mass fraction cloud map;

[0033] Figure 8 This is a cloud diagram of oxygen mass fraction in numerical simulation;

[0034] Figure 9 This is the temperature cloud diagram of the flow field in the numerically simulated electrolytic cell;

[0035] Figure 10 Streamline diagram of the flow field in the numerical simulation electrolytic cell.

[0036] In the accompanying drawings: 1. gas pipeline; 101. gas inlet; 102. flared pipe; 103. gas nozzle; 104. straight pipe; 2. primary air pipeline; 201. primary air inlet; 202. first reducer; 203. primary air nozzle; 204. first same-diameter pipe; 3. secondary air pipeline; 301. secondary air inlet; 302. second reducer; 303. secondary air nozzle; 304. second same-diameter pipe; 4. primary air cyclone; 41. first shaft; 42. first blade; 5. secondary air cyclone; 51. second shaft; 52. second blade; 6. burner; 7. ignition tube; 8. flame detection tube. DETAILED DESCRIPTION

[0037] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments. It should be noted that the embodiments and features of the embodiments may be combined unless they conflict. For ease of description, the words "upper," "lower," "left," and "right" appear below merely to indicate the directions of upper, lower, left, and right in the accompanying drawings and do not limit the structure.

[0038] like Figure 1 、 Figure 2 As shown, a gas roaster provided in this embodiment includes a gas pipeline 1, a primary air pipeline 2, a secondary air pipeline 3, a primary air cyclone 4, a secondary air cyclone 5, a burner 6, an ignition tube 7 and a flame detection tube 8.

[0039] The primary air duct 2 is coaxially mounted on the gas duct 1, and the secondary air duct 3 is coaxially mounted on the primary air duct 2. A gas inlet 101 is provided at one end of the gas duct 1, and a gas nozzle 103 is provided at the other end of the gas duct 1, aligned with the gas inlet 101. A primary air inlet 201 is provided at one end of the primary air duct 2, and a primary air nozzle 203 is provided at the other end of the primary air duct 2. A secondary air inlet 301 is provided at one end of the secondary air duct 3, and a secondary air nozzle 303 is provided at the other end of the secondary air duct 3.

[0040] The gas nozzles 103, primary air nozzles 203, and secondary air nozzles 303 are evenly distributed around the same center of the circle from the inside outward. The gas inlet 101, primary air inlet 201, and secondary air inlet 301 are adjacently arranged. The ends of the gas pipeline 1, primary air pipeline 2, and secondary air pipeline 3 are connected to a burner 6, which is in communication with the gas nozzles 103, primary air nozzles 203, and secondary air nozzles 303.

[0041] like Figure 3 As shown, the gas nozzles 103 are arranged in a circular array at equal intervals, with a number of 8-12 and a diameter of 5mm-7mm. The gas nozzles 103 penetrate the pipe wall along the axis of the gas pipe 1, with a penetration depth (hole length) of 2mm-4mm. The primary air nozzles 203 are arranged in a circular array at equal intervals, with a number of 14-18 and a diameter of 6mm-8mm. The primary air nozzles 203 penetrate the pipe wall along the axis of the primary air pipe 2, with a penetration depth of 2mm-4mm. The secondary air nozzles 303 are arranged in a circular array at equal intervals, with a number of 16-20 and a diameter of 6mm-8mm. The secondary air nozzles 303 penetrate the pipe wall along the axis of the secondary air pipe 3, with a penetration depth of 2mm-4mm.

[0042] like Figure 2 As shown, the gas pipeline 1 includes a straight pipe 104 and a flared pipe 102. The flared pipe 102 is a trumpet-shaped tube with a smaller diameter at one end and a larger diameter at the other. The smaller diameter end of the flared pipe 102 is connected to the straight pipe 104, while the larger diameter end of the flared pipe 102 is connected to the burner 6. The gas nozzle 103 is provided on the larger diameter end of the flared pipe 102. The gas inlet 101 is provided on the end of the straight pipe 104 away from the flared pipe 102.

[0043] like Figure 2As shown, the primary air duct 2 includes a first coaxial tube 204 and a first reducer 202. The first reducer 202 has a smaller diameter in the middle and larger diameters at both ends, forming a Venturi structure. One end of the first reducer 202 is connected to the first coaxial tube 204, and the other end of the first reducer 202 is provided with the primary air nozzle 203. The primary air inlet 201 is provided on the first coaxial tube 204.

[0044] like Figure 2 As shown, the secondary air duct 3 includes a second same-diameter pipe 304 and a second reducer 302. The second reducer 302 has a small diameter in the middle (contraction section) and a large diameter at both ends (expansion section), forming a Venturi structure. One end of the second reducer 302 is connected to the second same-diameter pipe 304, and the other end of the second reducer 302 is provided with the secondary air nozzle 303. The secondary air inlet 301 is provided on the second same-diameter pipe 304.

[0045] The ratio of the cross-sectional area of the contraction section to the cross-sectional area of the expansion section of the first reducer 202 and the second reducer 302 is 1:1.5-1:2. The walls of the gas pipeline 1, the primary air pipeline 2, and the secondary air pipeline 3 are parallel to each other.

[0046] A primary air cyclone 4 is provided in the primary air duct 2. The primary air cyclone 4 is sleeved on the gas duct 1 and located at the connection between the first coaxial pipe 204 and the first reducing pipe 202. A secondary air cyclone 5 is provided in the secondary air duct 3. The secondary air cyclone 5 is sleeved on the primary air duct 2 and located at the connection between the second coaxial pipe 304 and the second reducing pipe 302.

[0047] like Figure 4 The primary air cyclone 4 includes a first shaft portion 41 and a plurality of first blades 42 uniformly distributed along the circumference of the first shaft portion 41 at an angle. The first shaft portion 41 is mounted on the gas pipeline 1. The number of first blades 42 is 12-16. The first blades 42 are uniformly distributed along the tangential direction, and each first blade 42 is inclined at an angle of 15°-30° relative to the axis of the primary air pipeline 2 to generate tangential swirl.

[0048] like Figure 5 As shown, the secondary air cyclone 5 includes a second shaft portion 51 and a plurality of second blades 52 uniformly distributed along the circumference of the second shaft portion 51 at an angle. The second shaft portion 51 is mounted on the primary air duct 2. The number of second blades 52 is 1216. The second blades 52 are uniformly distributed along the tangential direction, and each second blade 52 is inclined at an angle of 15° to 30° relative to the axis of the secondary air duct 3 to generate a tangential swirl.

[0049] The primary air and secondary air pass through corresponding cyclones to form rotating fluids. Combined with the Venturi structure, which first contracts and then expands along the direction of gas flow, the gas is accelerated. According to relevant tests, the pre-mixing time of gas and air is shortened by 20%.

[0050] like Figure 6 As shown, the burner 6 is formed from a curved circular cross-section tube with a bend angle of 70°-90°. Adjusting the bend angle of the burner 6 allows it to adapt to different electrolytic cell structures and production conditions, while also reducing operating noise and extending its service life. The bend angle of the burner 6 is preferably 70°. According to GB / T 3767-2016, "Acoustics - Determination of Sound Power Level and Sound Energy Level of Noise Sources by Sound Pressure Method in Approximate Free Field Above a Reflecting Surface," the noise reduction is 10 dB(A).

[0051] like Figure 6 As shown, the inlet end surface of the burner 6 is provided with two through holes, such as Figure 1 As shown, one through hole is connected to the ignition tube 7, and the other through hole is connected to the flame detection tube 8. The ignition tube 7 and the flame detection tube 8 are symmetrically distributed on either side of the inlet end, that is, the ignition tube 7 and the flame detection tube 8 are respectively arranged on either side of the secondary air duct 3. The axes of the ignition tube 7 and the flame detection tube 8 are parallel to the axis of the burner 6 inlet end.

[0052] The flow ratio of primary air to secondary air can be adjusted by a control system. The mass flow rate of primary air accounts for 60%-80% of the total air mass flow rate, and the mass flow rate of secondary air accounts for 20%-40% of the total air mass flow rate. In a preferred embodiment, the mass flow rate of primary air accounts for 80% of the total air mass flow rate, and the mass flow rate of secondary air accounts for 20% of the total air mass flow rate. In order to accurately adjust the input flow rate of primary air and secondary air through the control system. Gas is supplied through the gas nozzle 103 at the bottom of the gas pipeline 1. Under the premise that the total flow rate remains unchanged, the primary air provides a combustion-supporting effect during the combustion process, ensuring sufficient ignition of the gas and the initial heating effect; the secondary air optimizes the stability and completeness of the combustion during the combustion process, prevents excessive oxidation and improves combustion efficiency.

[0053] The combustion of burner 6 was numerically simulated under an implementation scheme in which the primary air mass flow rate accounted for 80% of the total air mass flow rate and the secondary air mass flow rate accounted for 20% of the total air mass flow rate. The model used a steady-state calculation method, ignoring the formation of nitrogen oxides. The computational domain simplified the model, excluding the cyclone structure, gas pipeline 1, primary air pipeline 2, and secondary air pipeline 3. It included the flow field area of burner 6, the lining and superstructure of the aluminum electrolytic cell, and the internal flow field area of the electrolytic cell formed by the anode and cathode cavities of burner 6. The model used an unstructured polyhedron mesh. After verifying mesh independence, the deviation of the temperature calculation results was less than 1% when the number of grid cells was increased to 600,000.

[0054] Burner 6 has a design power of 60 kW. The model simulates inlet boundary conditions using mass flow. The gas inlet is set to 0.001245 kg / s with a 100% volume fraction of methane; the primary air inlet is set to 0.017 kg / s with a composition of 21% oxygen and 79% nitrogen; and the secondary air inlet is set to 0.00429 kg / s with a composition of 21% oxygen and 79% nitrogen. The gas outlet boundary condition is set to a pressure outlet, modeled as a 100 mm diameter circular tube, which is considered to be approximately equivalent to the flue gas outlet during the roasting process. The turbulence model uses the ke Realizable model, the combustion model uses the ED model, and the radiation model uses the Do model.

[0055] like Figure 7 、 Figure 8 、 Figure 9 and Figure 10 As shown, from the fuel mass fraction cloud map, it can be seen that methane is concentrated near the gas nozzle and is sprayed in a conical shape in the combustion chamber 6. The mass fraction gradually decreases and no obvious uneven diffusion occurs. From the oxygen mass fraction cloud map, it can be seen that the oxygen concentration drops rapidly in the combustion chamber 6, and the oxygen content outside the combustion chamber 6 is extremely low, indicating that the oxygen has been fully consumed. From the temperature cloud map, it can be seen that the flame generated by the burner combustion has a moderate width, and a large high-temperature zone is formed in the middle of the anode and cathode, reaching the temperature required for the start of aluminum electrolysis (950℃-960℃). From the streamline diagram, it can be seen that the nozzle of the combustion chamber 6 generates two vortex circulation areas in the center of the flow field through strong swirl. The generation of vortex circulation areas is conducive to strengthening the heat transfer between the high-temperature flue gas and the tank body, thereby shortening the time required for roasting.

[0056] Finally, the area-weighted average parameters of the flow field outlet and cathode surfaces were calculated. The results showed that the high-temperature zone on the flow field outlet reached 1223°C, while the cathode surface temperature stabilized at 955°C ± 5°C after heat dissipation through the cell body. This temperature met the requirements of T / CNIA 0026-2019, "Technical Specifications for Startup of Gas-fired Roasting of Aluminum Electrolytic Cells." The outlet methane mass fraction was less than 0.05%, and the oxygen mass fraction was less than 1%.

[0057] Numerical simulation results show that methane and oxygen are fully mixed in the combustion chamber, the flame temperature is evenly distributed, there is no dead zone in the flow field, and there is no backfire phenomenon, which verifies the inhibitory effect of the present invention on combustion efficiency and anode and cathode oxidation.

[0058] As shown in Table 1:

[0059] Table 1: Performance comparison between the gas roaster of the present invention and the conventional gas roaster

[0060]

[0061] The present invention improves smooth temperature uniformity, promotes complete combustion of fuel, and reduces noise. The temperature non-uniformity coefficient is calculated by the following formula:

[0062]

[0063] Where n is the number of measuring points;

[0064] t i ——temperature at each measuring point;

[0065] ——The arithmetic mean of the temperatures at each measuring point.

[0066] In summary, the innovation of the present invention lies in achieving sufficient mixing of gas and air and efficient combustion by optimizing the nozzle design of gas, primary air and secondary air, and combining the swirler structure and the Venturi structure, thereby improving the stability and service life of the burner.

[0067] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A gas roaster, comprising a gas pipeline (1), characterized in that: It also includes a primary air duct (2) coaxially mounted on the gas duct (1), and a secondary air duct (3) coaxially mounted on the primary air duct (2), wherein one end of the gas duct (1) is provided with a gas inlet (101), and the other end of the gas duct (1) is provided with a gas nozzle (103) on the same horizontal line as the gas inlet (101); one end of the primary air duct (2) is provided with a primary air inlet (201), and the other end of the primary air duct (2) is provided with a primary air nozzle (203); one end of the secondary air duct (3) is provided with a secondary air inlet (301), and the other end of the secondary air duct (3) is provided with a secondary air nozzle (303); The gas nozzles (103), the primary air nozzles (203) and the secondary air nozzles (303) are uniformly distributed on a circumference from the inside to the outside with the same center as the reference; the gas inlet (101), the primary air inlet (201) and the secondary air inlet (301) are arranged adjacent to each other; the ends of the gas pipeline (1), the primary air pipeline (2) and the secondary air pipeline (3) are connected to a burner (6), and the burner (6) is in communication with the gas nozzles (103), the primary air nozzles (203) and the secondary air nozzles (303).

2. The gas roaster according to claim 1, characterized in that: The primary air duct (2) comprises a first same-diameter pipe (204) and a first reducing pipe (202); the first reducing pipe (202) is a structure with a small diameter in the middle and large diameters at both ends; one end of the first reducing pipe (202) is connected to the first same-diameter pipe (204); the other end of the first reducing pipe (202) is provided with the primary air nozzle (203); and the primary air inlet (201) is provided on the first same-diameter pipe (204).

3. The gas roaster according to claim 1, characterized in that The secondary air duct (3) comprises a second same-diameter pipe (304) and a second reducing pipe (302); the second reducing pipe (302) is a structure with a small diameter in the middle and large diameters at both ends; one end of the second reducing pipe (302) is connected to the second same-diameter pipe (304); the other end of the second reducing pipe (302) is provided with the secondary air nozzle (303); and the secondary air inlet (301) is provided on the second same-diameter pipe (304).

4. The gas roaster according to any one of claims 1 to 3, characterized in that: An ignition tube (7) and a flame detection tube (8) are connected to the end surface of the inlet end of the burner (6). The ignition tube (7) and the flame detection tube (8) are respectively arranged on both sides of the secondary air duct (3), and the axes of the ignition tube (7) and the flame detection tube (8) are parallel to the axis of the inlet end of the burner (6).

5. The gas roaster according to any one of claims 1 to 3, characterized in that: A primary air cyclone (4) is provided in the primary air duct (2), a secondary air cyclone (5) is provided in the secondary air duct (3), the primary air cyclone (4) is sleeved on the gas duct (1), and the secondary air cyclone (5) is sleeved on the primary air duct (2).

6. The gas roaster according to claim 5, characterized in that: The primary air cyclone (4) comprises a first shaft portion (41) and a plurality of first blades (42) uniformly distributed and inclined along the circumference of the first shaft portion (41); the first shaft portion (41) is sleeved on the gas pipeline (1).

7. The gas roaster according to claim 5, characterized in that: The secondary air cyclone (5) comprises a second shaft portion (51) and a plurality of second blades (52) uniformly distributed and inclined along the circumference of the second shaft portion (51); the second shaft portion (51) is sleeved on the primary air duct (2).

8. The gas roaster according to any one of claims 1 to 3, characterized in that: The burner (6) is formed by a curved circular cross-section tube with a bending angle of 70°-90°.

9. The gas roaster according to any one of claims 1 to 3, characterized in that: The gas pipeline (1) comprises a straight pipe (104) and an expanded pipe (102); the expanded pipe (102) is a bell pipe with a small diameter at one end and a large diameter at the other end; the small diameter end of the expanded pipe (102) is connected to the straight pipe (104); the large diameter end of the expanded pipe (102) is connected to the burner (6); the gas nozzle (103) is provided on the large diameter end of the expanded pipe (102); and the gas inlet (101) is provided at one end of the straight pipe (104) away from the expanded pipe (102).

10. The gas roaster according to any one of claims 1 to 3, characterized in that: The mass flow of the primary air inputted from the primary air duct (2) to the burner (6) accounts for 60%-80% of the total air mass flow, and the mass flow of the secondary air inputted from the secondary air duct (3) to the burner (6) accounts for 20%-40% of the total air mass flow.

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