A gas and air mixing device and method incorporating an ejector

Abstract

The application discloses a kind of gas and air mixing device and mixing method combined with injection, gas flow passage is provided in the mixing device, including gas nozzle and injection structure in sequence according to the direction of gas flow passage, the injection structure is used to carry out partial premixing with gas and be injected air, including in sequence communication suction chamber, mixing section, diffuser section, outlet section, the gas nozzle is communicated with suction chamber, outlet section is provided with swirl device for generating swirl.The application utilizes the momentum of gas jet to inject atmospheric air, carries out partial premixing in advance in injection structure, realizes the sufficient premixing of gas and be injected air before being ejected, mixing distance is short, has the effect of helping to reduce nitrogen oxides emissions generated in industrial combustion process, conforms to the development trend of environmental protection.

Description

Technical Field

[0001] This invention relates to the field of combustion engine technology, and more particularly to a method for mixing fuel gas and air using a combined ejector method for low-NOx combustion engines. Background Technology

[0002] Air pollution is a major concern for the international community. Nitrogen oxides (NOx) are a collective term for compounds composed of nitrogen and oxygen, and are among the common air pollutants emitted during combustion processes. They include nitrous oxide (N₂O), nitric oxide (NO), nitrogen dioxide (NO₂), and nitrous oxide (N₂O₃), among others. NOx is considered a major air pollutant, and once it enters the atmosphere, it easily causes environmental problems such as acid rain, photochemical smog, ozone layer depletion, and global warming. Furthermore, NOx has varying degrees of toxicity; excessive inhalation can lead to acute lung injuries such as pneumonia and fulminant pulmonary edema.

[0003] Nitrogen oxides generated during combustion are mainly classified into thermal nitrogen oxides, transient nitrogen oxides, and fuel-based nitrogen oxides. Thermal nitrogen oxides are generated by the reaction of nitrogen and oxygen in the air at temperatures above 1500℃. Fuel-based and transient nitrogen oxides are closely related to the type of fuel. The main factors affecting nitrogen oxide formation during combustion are combustion temperature, air-to-fuel ratio, distribution of fuel and products, type of fuel, and degree of mixing between fuel and oxidant.

[0004] Low-NOx burners utilize the rational and rapid mixing of fuel and oxidant before combustion and control the maximum temperature of the combustion zone to produce very low nitrogen oxide emissions during combustion. They are used in industries such as chemical, energy, and food.

[0005] Existing burners emit large amounts of nitrogen oxides during combustion, which harms the atmospheric environment and human health. At the same time, the poor mixing effect of fuel and oxidant when they are introduced into the combustion chamber can lead to local high-temperature areas during combustion, resulting in the generation of large amounts of nitrogen oxides, which is not conducive to emission control. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a mixing device and method that combines ejector-driven combustion gas with air. The mixing device has no moving parts, a short mixing distance, and prevents backfire, thus ensuring high safety.

[0007] The present invention discloses a low-NOx burner with fuel ejector mixing. The mixing device has an airflow passage and includes a gas nozzle and an ejector structure in sequence according to the direction of the airflow passage. The ejector structure is used to partially premix the fuel gas with the ejected air and includes an intake chamber, a mixing section, a diffuser section, and an outlet section connected in sequence. The gas nozzle is connected to the intake chamber, and a swirling device for generating swirl is provided at the outlet section. The swirling device is directly connected to the ejector structure, the mixing distance is short, and the outer flow channel shell is directly connected to the periphery of the swirling device. The entire mixing device has no moving parts.

[0008] Preferably, an outer flow channel shell is provided around the outer periphery of the ejector structure along the airflow path direction, and the outer wall of the ejector structure shell and the inner wall of the coaxial outer flow channel shell together form an annular secondary air intake channel.

[0009] Preferably, the inlet of the suction chamber is a radial annular inlet, and the outlet of the suction chamber is connected to the inlet of the mixing section; the outlet of the mixing section is connected to the inlet of the diffuser section; the expanding shape of the diffuser section helps to diffuse and decelerate the mixed gas, and the outlet of the diffuser section is connected to the inlet of the outlet section; the outlet section has circumferentially arranged slits, which are used as outlets and connected to the secondary air intake channel. There are no particular limitations on the length ratio of each section of the mixing device. The relationship between the diameter of the gas nozzle and the diameter of the mixing section of the ejector device has a significant impact on the partial premixing effect. For different types of gas, this relationship needs to be adjusted to achieve the most ideal partial premixing effect.

[0010] Preferably, the tail end of the outlet section has a conical cavity structure.

[0011] Preferably, the gas nozzle extends into the suction chamber at the front end of the ejector structure, and the swirling blades of the swirling device are disposed upstream of the tail slit of the ejector structure, located between the outer flow channel shell and the shell of the ejector structure.

[0012] Preferably, when methane is used as fuel, the ratio R of the inner diameter D of the straight mixing section of the ejector structure to the inner diameter d of the gas nozzle is in the range of 6 to 12, and the premixed gas equivalence ratio after complete mixing within the ejector structure is in the range of 2.9 to 7.5. It should be noted that different types of gaseous fuels will result in different premixed equivalence ratios.

[0013] A method for mixing fuel gas and air using an ejector, according to the aforementioned mixing device, includes the following steps: Step 1, fresh fuel gas is injected into the suction chamber of the ejector structure through a fuel gas nozzle, forming a high-speed jet and creating a low-pressure suction environment. Air from the atmospheric environment is drawn into the suction chamber, and the ejected air and the fuel gas jet enter the mixing section together to form a partially premixed gas; Step 2, the partially premixed gas in the mixing section enters the diffuser section for deceleration and diffusion, and then enters the outlet section, where it is injected into the secondary air flow channel through a radial slit; Step 3, secondary air is introduced from the inlet of the secondary air flow channel, flows through the swirl vanes to form a swirling flow, and the swirling flow is mixed with the fuel-rich partially premixed gas ejected from the opening behind the swirl vanes, and then introduced downstream to supply the combustion chamber for combustion.

[0014] Preferably, the gas delivered by the gas nozzle is methane, natural gas, ethane, or methane or ethane diluted with an inert gas; the oxidant is primary air and secondary air.

[0015] A low-NOx burner includes the aforementioned mixing device. Beneficial effects

[0016] (1) Compared with the traditional direct jet mixing of gas and air, the present invention utilizes the momentum of the gas jet to entrain the ambient air and performs partial premixing in the entraining structure, so as to achieve full premixing of gas and entrained air before they are ejected from the slit. (2) The present invention uses swirl blades to create a secondary air swirl and mix it with a partially premixed gas jet that flows in a relatively vertical direction. This allows the secondary air and the partially premixed gas to be fully mixed within a short distance, which helps to improve the combustion environment and reduce nitrogen oxide emissions during the combustion process. (3) The fuel-rich premixed gas in the mixing device of the present invention is far from the chemical stoichiometry of the combustion reaction, and the flow area of ​​the slit at the tail of the ejector structure is small, which makes the jet velocity of the slit high. Both of these have the effect of preventing the combustion flame from spreading into the ejector structure, and the combustion safety performance is good. (4) The mixing device of the present invention has no moving parts, has a simple structure, low maintenance cost, and low manufacturing cost. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a burner structure according to an embodiment of the present invention; Figure 2 This is a schematic cross-sectional view of a burner structure according to an embodiment of the present invention; Figure 3 This is a schematic diagram of a burner ejector structure according to an embodiment of the present invention; Figure 4 This is a diagram illustrating the fuel mixing effect of a burner numerical simulation according to an embodiment of the present invention.

[0018] Reference numerals: 1-Ejector structure, 2-Swirl device, 3-Outer flow channel shell, 4-Suction chamber, 5-Mixing section, 6-Diffuser section, 7-Outlet section, 8-Gas nozzle, 9-Slit, 10-Suction inlet, 11-Gas inlet, 12-Secondary air inlet. Specific implementation methods

[0019] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0020] like Figure 1 , Figure 2 , Figure 3 As shown, the main structure of the mixing device of the present invention includes: an ejector structure 1, a swirling device 2, and an outer flow channel shell 3.

[0021] like Figure 2 , Figure 3 As shown, the ejector structure 1 is used to partially premix the fuel gas and the ejected air. It includes an intake chamber 4 with a radially annular inlet. The center of the inlet is connected to a fuel gas nozzle 8 for introducing fuel gas, meaning the fuel gas nozzle 8 extends into the intake chamber 4 before the ejector structure 1. The outlet of the intake chamber 4 is connected to a straight pipe, which serves as the inlet of the mixing section 5. The outlet of the mixing section 5 is connected to a conical pipe, which serves as the inlet of the diffuser section 6. The outlet of the diffuser section 6 is connected to the outlet section 7. To enhance the mixing effect between the air introduced from the secondary air inlet 12 and the partially premixed gas in the ejector structure 1, a circumferentially distributed array of slits 9 is provided at the tail of the outlet section 7 of the ejector structure 1. These slits 9 serve as the outlet and connect to the external secondary air flow channel.

[0022] The ejector structure 1 has a conical concave cavity structure at the tail end of the outlet section 7. The purpose is to ensure that the flow velocity of the slit jet at the rear does not decrease too much, thus ensuring the performance of preventing flame flashback.

[0023] The ratio R of the inner diameter D of the straight mixing section of ejector structure 1 to the inner diameter d of the gas nozzle has a significant impact on the equivalence ratio of the fuel-rich premixed gas within the ejector structure. When methane is used as fuel, if the R value is in the range of 6 to 12, the equivalence ratio of the fully mixed fuel-rich premixed gas within the ejector structure is in the range of 2.9 to 7.5. This ensures that the equivalence ratio is far from the stoichiometric ratio of methane fuel combustion, thus protecting the ejector structure from flame spread, while also preventing the premixed gas equivalence ratio from being too high, which would be detrimental to subsequent ignition and combustion.

[0024] The swirling device 2 is used to generate swirling flow. It consists of 12 fan-shaped blades and is located outside the outlet section 7 of the ejector structure 1, near the upstream of the tail slit of the ejector structure 1. Specifically, it is located in front of the slit 9 of the outlet section 7, between the outer flow channel shell and the ejector structure shell.

[0025] The outer flow channel shell 3 is connected to the periphery of the swirl device 2. The inner wall surface of the outer flow channel shell 3, together with the outer wall surface of the diffuser section 6 and the outlet section 7 of the ejector structure 1, forms an annular secondary air flow channel for introducing secondary air. The outer flow channel shell 3, the ejector structure 1, and the swirl device 2 are coaxial.

[0026] The present invention also discloses a low-NOx burner, including the above-mentioned mixing device.

[0027] The present invention also discloses a method for mixing ejected combustion gas with air, based on the above-mentioned mixing device, comprising the following steps: Step 1: The supplied fresh gas is injected into the suction chamber of the ejector structure through the gas nozzle, forming a high-speed jet and creating a low-pressure suction environment. Air in the atmospheric environment is drawn into the suction chamber, and the injected air and the gas jet enter the mixing section together to form a partially premixed gas.

[0028] Step 2: Part of the premixed gas in the mixing section enters the diffuser section for deceleration and diffusion, and then enters the outlet section, where it is injected into the secondary air flow channel through the radial slit.

[0029] Step 3: Secondary air is introduced from the secondary air channel inlet, flows through the swirl vanes to form a swirling flow, and mixes with the fuel-rich premixed air injected from the openings behind the swirl vanes. The mixture is then introduced downstream to supply the combustion chamber for combustion.

[0030] The working principle of this invention: to Figure 3 Gas is introduced through the gas inlet 11, and a high-speed gas jet is injected into the suction chamber 4 of the ejector structure 1 through the gas nozzle 8, creating a low-pressure suction environment in the suction chamber 4. Figure 3 The intake port 10 draws in air from the atmospheric environment. The drawn-in air and the gas jet enter the mixing section 5 together for mixing to form a partially premixed gas. Then, it passes through the diffuser section 6 for diffusion and deceleration, and finally reaches the outlet section 7.

[0031] The matching relationship between the inner diameter D of the mixing section in ejector structure 1 and the inner diameter d of the gas nozzle 8 will directly affect the equivalence ratio of the partially premixed gas formed in ejector structure 1.

[0032] In one embodiment, when methane is used as fuel, and the ratio of the inner diameter D of the mixing section 5 of the ejector structure 1 to the inner diameter d of the gas nozzle 8 is 6 to 12, the equivalence ratio of the premixed gas is in the range of 2.9 to 7.5, resulting in a fuel-rich premixed gas that is far from the stoichiometric ratio of the combustion reaction. The equivalence ratio of the premixed gas is kept within a reasonable range, which has the effect of preventing flame flashback, while not affecting the subsequent ignition and combustion process.

[0033] The pre-mixed fuel-rich gas is injected from the slit 9 at the tail of the outlet section 7 into the outer flow channel, which is composed of the outer flow channel shell, the transition section 6, and the outer shell of the outlet section 7. The jet slit 9 on the outlet section 7 of the ejector structure 1 has the effect of preventing backfire. At the same time, the fuel-rich pre-mixed gas mixed in the ejector structure 1 is far away from the stoichiometric ratio of the combustion reaction, which also has the effect of preventing the flame from spreading into the ejector structure 1.

[0034] External secondary air is introduced through secondary air inlet 12, and then passes through swirl device 2 to form a swirling flow. The secondary air swirling flow then impacts and mixes with the mixed air jet ejected from the tail slit 9 of the outlet section 7. They are fully mixed in a short distance and flow downstream together for subsequent organization of ignition and combustion.

[0035] In one embodiment, at a point on the downstream axial direction of the outlet section where the distance x from the outlet section end face is 0.69 to the maximum diameter H of the outer flow channel shell 3, the part of the fuel-rich premixed gas ejected from the slit 9 of the outlet section 7 and the secondary air introduced into the outer flow channel achieve a good mixing effect.

[0036] The numerical simulation results of the embodiments show the mixing effect of methane fuel with air as follows: Figure 4 As shown (darker colors indicate higher methane concentration), the simulated background consists of methane gas introduced through a 3mm diameter nozzle at a velocity of 120m / s, and secondary air introduced at a flow rate of 15g / s. Figure 4 It can be seen that after part of the fuel-rich premixed gas is injected into the secondary air flow channel from the slit 9 at the tail of the ejector structure 1 outlet section 7, it is fully mixed with the surrounding secondary air within a very short distance.

[0037] The present invention is only described with reference to the above embodiments. The structure, position and connection method of each component can be varied. Based on the technical solution of the present invention, any improvements and equivalent transformations made to individual components according to the principles of the present invention should not be excluded from the protection scope of the present invention.

Claims

1. A device for mixing fuel gas and air using an ejector, characterized in that, The device includes a mixing device with an airflow passage. Following the direction of the airflow passage, it includes a gas nozzle and an ejector structure. The ejector structure is used to partially premix the gas with the ejected air. It includes a sequentially connected intake chamber, mixing section, diffuser section, and outlet section. The gas nozzle is connected to the intake chamber. A swirling device for generating a vortex is provided at the outlet section. One end of the swirling device is directly connected to the shell of the ejector structure, and the other end is directly connected to the outer flow channel shell. An outer flow channel shell is provided around the outer periphery of the ejector structure along the airflow passage direction. The outer wall of the ejector structure shell and the inner wall of the outer flow channel shell together form an annular secondary air intake channel. The outlet section is provided with circumferentially arranged slits, which serve as the outlet and are connected to the secondary air intake channel. The tail end of the outlet section has a conical cavity structure.

2. The blending apparatus according to claim 1, characterized in that, The outer flow channel shell, ejector structure, and swirling device are coaxial.

3. The blending apparatus according to claim 1, characterized in that, The gas nozzle extends into the suction chamber at the front end of the ejector structure, and the swirling blades of the swirling device are positioned upstream of the tail slit of the ejector structure.

4. The blending apparatus according to any one of claims 1-3, characterized in that, When methane is used as fuel, the ratio R of the inner diameter D of the straight mixing section of the ejector structure to the inner diameter d of the gas nozzle is in the range of 6 to 12, and the equivalent ratio of the partially premixed gas after complete mixing in the ejector structure is in the range of 2.9 to 7.

5.

5. A method for mixing ejected combustion gas with air, characterized in that, The device for mixing gas and air by combining ejection according to claim 1 includes the following steps: Step 1: The supplied fresh gas is injected into the suction chamber of the ejector structure through the gas nozzle, forming a high-speed jet and creating a low-pressure suction environment. Air in the atmospheric environment is drawn into the suction chamber, and the injected air and the gas jet enter the mixing section together to form a partially premixed gas. Step 2: Part of the premixed gas in the mixing section enters the diffuser section for deceleration and diffusion, and then enters the outlet section, where it is injected into the secondary air flow channel through the radial slit. Step 3: Secondary air is introduced from the secondary air channel inlet, flows through the swirl vanes to form a swirling flow, and mixes with the fuel-rich premixed air injected from the openings behind the swirl vanes. The mixture is then introduced downstream to supply the combustion chamber for combustion.

6. The blending method according to claim 5, characterized in that, The gas nozzle delivers methane, natural gas, or ethane, or methane or ethane diluted with an inert gas.

7. A low-NOx combustion engine, characterized in that, Includes a gas-air mixing device combined with an ejector as described in claim 1.

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