Control method of mixed gas for metallurgical combustion and combustor thereof

Abstract

The invention discloses a control method of mixed gas for metallurgical combustion and a combustor thereof. According to the control method of the mixed gas for metallurgical combustion, three-time gas mixing control is formed through three sections arranged in a gas mixing area, so that mixing of combustion gas before combustion is completed. The combustor for metallurgical combustion comprises a gas mixing area and a combustion area connected with the gas mixing area. The gas mixing area is used for controlling the proportion of the mixed gas and forming tertiary mixing; the combustion area is used for rectifying incoming flow gas, blocking tempering and controlling and reducing nitric oxide in combustion. According to the control method of the mixed gas for metallurgical combustion and the combustor of the mixed gas, air and fuel gas can be mixed more sufficiently; the air-fuel ratio can be adjusted at will; the combustion stability is high, and emission of nitric oxide is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of premixed gas mixed combustion, and in particular relates to a control method for mixed gas for metallurgical combustion and a burner thereof. Background Art

[0002] For the mixing of gas and air, the most commonly used one is the Venturi mixer, which works by taking advantage of the pressure drop generated when the gas flows rapidly through the throat to draw in external gas and mix it with the air. However, the calculation of the pressure drop when the gas flows through the throat is relatively complicated, and it is also very inconvenient to control the amount of gas intake by relying on the pressure drop. However, for premixed combustion, it is very important to control the mixing ratio of fuel and air. Moreover, due to the influence of no wall slip, there is still a certain degree of premixing unevenness after the gas and air are mixed through the Venturi, which affects the subsequent combustion effect. Uneven combustion will lead to local high temperatures, which will accelerate the reaction rate of nitrogen and oxygen, thereby increasing the final nitrogen oxide content emitted.

[0003] The invention application with application number: CN201310044360.7 discloses "a multi-point introduction structure and flow control method of a venturi mixer". The venturi mixer includes a mainstream venturi tube and multiple inlet pipes connected to the venturi tube throat of the mainstream venturi tube; the multiple inlet pipes are arranged at 90 degrees to each other in the same cross-section of the venturi tube throat, or the first inlet pipe and the second inlet pipe are arranged at the upper end of the venturi tube throat, and the third inlet pipe and the fourth inlet pipe are arranged at the lower end, and the first inlet pipe and the second inlet pipe are arranged asymmetrically staggered with the third inlet pipe and the fourth inlet pipe; its flow control method adopts a pulse method to control the flow of the introduced fluid in the multiple inlet pipes; it can enhance the mixing of the introduced fluid and the mainstream fluid and improve the mixing efficiency of the venturi mixer; its flow control method can adjust the fluid flow rate at different introduction points, so that the venturi mixer is suitable for a wider range of flow ratios of the introduced fluid and the mainstream fluid.

[0004] The invention application with application number: CN201410219890.5 discloses "a new type of Venturi mixer", which includes a front section, a rear section and an intermediate section that coaxially connects the front section and the rear section. The front section includes a mainstream inflow pipe, a contraction section and a front half of the throat that are connected in sequence. The rear section includes a rear half of the throat, a diffusion section and a mainstream outflow pipe that are connected in sequence. The intermediate section includes a front section of a variable diameter connecting structure connected to the outer peripheral surface of the front half of the throat, a rear section of a connecting structure connected to the outer peripheral surface of the rear half of the throat and a space left between the rear half of the throat, and an internal connecting pipe connecting the front half of the throat and the rear half of the throat. Three rows of conical holes are opened on the internal connecting pipe along the mainstream flow direction. The flow rate of the introduced fluid is adjusted by inserting the rear half of the throat into the rear section of the connecting structure at different depths.

[0005] The invention application with application number: CN201810487914. discloses "a Venturi mixer containing a porous annular cavity and its application in the synthesis of cyanohydrin". The Venturi mixer includes a shell 1. a nozzle arranged in the shell 2. an annular cavity outside the shell; 3. the annular cavity is connected to the interior of the shell through multiple flow holes on the shell; the present invention adds an annular cavity to the Venturi mixer, improves the mixing of the mainstream fluid and the introduced fluid near the center line, destroys the boundary layer of the mixed fluid, improves the velocity distribution of the fluid cross section, avoids the problems of uneven mixing and low mixing efficiency caused by the high flow velocity of the mainstream fluid or the large flow rate of the introduced fluid, and makes the present invention applicable to a wider range of flow ratios of the introduced fluid and the mainstream fluid, and can achieve excellent mixing effects. Summary of the Invention

[0006] The purpose of the present invention is to achieve sufficient mixing and stable combustion of combustion gases in any proportion on the one hand, and to form emission reduction control of nitrogen oxides after combustion on the other hand.

[0007] To achieve the above technical objectives, the present invention provides a method for controlling the nitrogen oxide content in metallurgical combustion and a burner thereof, the technical solutions of which are as follows:

[0008] A method for controlling mixed gas for metallurgical combustion, wherein three gas mixing controls are formed in three sections provided in a gas mixing zone to complete mixing of premixed gas before combustion;

[0009] The first gas mixing is completed by the gases introduced from different ports converging into a common flow channel and forming a first section of flow acceleration in the flow direction;

[0010] The second gas mixing passes through a second section following the first section and is completed in the second section;

[0011] The third gas mixing passes through the third section connected to the second section, and a backflow is formed from the third section. The backflow and the gas in the second section are arranged to form a reverse pressure gradient, thereby forming a flow boundary layer separation.

[0012] Further,

[0013] A double-layer combustion zone is formed by respectively setting a preheating zone and a tail flow zone in the combustion zone connected to the gas mixing zone;

[0014] The preheating zone is used to rectify the incoming gas flow and block the tempering;

[0015] The tail flow region is used to control and reduce nitrogen oxides during combustion.

[0016] Further,

[0017] A transition combustion zone is also set between the preheating zone and the tail zone;

[0018] The thickness of the transition combustion zone is set to 0.5mm-3.5mm.

[0019] Further,

[0020] The preheating zone is filled with a porous medium with a porosity of 0.35mm-0.45mm;

[0021] The tail flow area is filled with a porous medium with a porosity of 0.75 mm to 0.80 mm.

[0022] Further,

[0023] The mixing ratio is controlled by controlling the amount of gas introduced into different ports.

[0024] Further,

[0025] The first section, the second section and the third section are formed by providing a venturi mixer with a slowly changing flow area;

[0026] The introduction of air and gas is accomplished through a pair of openings symmetrically arranged in the inflow section of the venturi mixer.

[0027] Further,

[0028] The Venturi mixer with a slowly changing flow area comprises an inflow section (1), a gradually contracting forging (2), a throat (3), a gradually expanding section (4), a corner section (5), a reflux section (6) and an outflow section (7) which are arranged in sequence;

[0029] The inflow section (1), the tapered section (2), and the throat (3) constitute a first section;

[0030] The gradually expanding section (4) constitutes the second section;

[0031] The reflux section (6) constitutes the third section;

[0032] The corner section (5) forms an interface between the second section and the third section for generating a reverse pressure gradient.

[0033] A burner for metallurgical combustion includes a gas mixing zone and a combustion zone connected to the gas mixing zone;

[0034] The gas mixing zone is used to control the proportion of the mixed gas and form a tertiary mixture;

[0035] The combustion zone is used to rectify the incoming gas flow, block backfire, and control and reduce nitrogen oxides during combustion.

[0036] Further,

[0037] A venturi mixer with a slowly changing flow region is provided in the gas mixing zone, wherein the venturi mixer comprises an inflow section (1), a gradually contracting forging (2), a throat (3), a gradually expanding section (4), a corner section (5), a reflux section (6) and an outflow section (7) arranged in sequence;

[0038] A pair of openings are symmetrically provided in the inflow section (1) for respectively introducing air and gas;

[0039] The inflow section (1), the tapered forging (2), and the throat (3) constitute a first section for completing the first gas mixing;

[0040] The gradually expanding section (4) constitutes a second section for completing the second gas mixing;

[0041] The reflux section (6) constitutes a third section, and the gas entering the third section forms a reflux and forms a third gas mixing based on flow boundary layer separation with the gas in the second section through the reverse pressure gradient formed by the setting;

[0042] The corner section (5) forms an interface between the second section and the third section for generating a reverse pressure gradient.

[0043] Further,

[0044] The mixing ratio is controlled by separately controlling the amount of gas introduced into different openings.

[0045] Further,

[0046] The combustion zone is composed of a preheating zone and a tail flow zone arranged in sequence to form a double-layer combustion zone;

[0047] The preheating zone is used to rectify the incoming gas flow and block the tempering;

[0048] The tail flow region is used to control and reduce nitrogen oxides during combustion.

[0049] Further,

[0050] A transition combustion zone is also set between the preheating zone and the tail zone;

[0051] The thickness of the transition combustion zone is set to 0.5mm-3.5mm.

[0052] Further,

[0053] The preheating zone is filled with a porous medium with a porosity of 0.35mm-0.45mm;

[0054] The tail flow area is filled with a porous medium with a porosity of 0.75 mm to 0.80 mm.

[0055] The present invention provides a control method for mixed gas for metallurgical combustion and a burner thereof. By setting the gas and air to enter from different inlets, the gas and air can be adjusted in any ratio to meet different process requirements. A second mixing is achieved by setting a gradual expansion section on the basis of normal Venturi mixing. Then, the gas enters a reflux section. In the reflux section, the mixed gas stops and meanders before further changing its flow direction and returns. The returned mixed gas is further mixed with the gas that continuously enters the corner section and undergoes boundary layer separation to form a third mixing. After these three mixings, the gas is fully mixed to form a better uniform mixed gas for combustion. Then, after entering the combustion zone, a porous medium with smaller pores is set in the preheating zone to prevent the combustion flame from backfireing on the one hand, and on the other hand, to complete the preheating and rectification of the incoming gas, so that the velocity distribution of the gas is relatively flat when flowing through the preheating zone, which is more conducive to the stability of the subsequent combustion flame; and by setting a large-aperture porous medium filling in the tail flow zone, the purpose of lowering the flue gas temperature after the combustion reaction can be achieved, thereby reducing the emission of nitrogen oxides; at the same time, a transition combustion zone with a smaller thickness is set between the preheating zone and the tail flow zone to strengthen the combustion reaction and make the combustion more complete. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is a schematic structural diagram of a burner for metallurgical combustion according to the present invention.

[0057] In the figure,

[0058] 1-inflow section;

[0059] 2-gradual forging;

[0060] 3-throat;

[0061] 4- Gradual expansion section;

[0062] 5-corner segment;

[0063] 6- reflux section;

[0064] 7-outflow section;

[0065] 8-Opening for air inflow;

[0066] 9-Opening for gas inflow;

[0067] 10- preheating zone of the combustion zone;

[0068] 11- Transition combustion zone of the combustion zone;

[0069] 12-Wake zone of the combustion zone. DETAILED DESCRIPTION

[0070] Hereinafter, a method for controlling a mixed gas for metallurgical combustion and a burner thereof according to the present invention will be further described in detail based on the accompanying drawings and specific embodiments.

[0071] Working principle and process description:

[0072] In order to achieve sufficient mixing and stable combustion of combustion gases in any proportion on the one hand, and to reduce and control the emission of nitrogen oxides after combustion on the other hand, the present invention provides a control method for mixed gas for metallurgical combustion and a burner thereof.

[0073] To achieve sufficient mixing, the technical solution is designed as follows: three gas mixing controls are formed in the three sections of the gas mixing zone to complete the mixing of the combustion gases before combustion; the first gas mixing is completed by the gases introduced from different ports converging into a common flow channel, and forming a first section in the flow direction where the flow is accelerated according to the Bernoulli principle; the Venturi mixer used to control and complete this setting concept is capable of arbitrarily adjusting the air-fuel ratio simply by providing openings for the introduction of air and gas in the inlet section of the Venturi mixer. The second gas mixing is completed by forming a reverse pressure gradient in the second section, which is connected to the first section, thereby forming flow separation; this setting concept is achieved by the corner section of the gradually expanding section connected to the Venturi mixer. The third gas mixing process occurs through a third section connected to the second section, where a return flow forms. This return flow creates an adverse pressure gradient at the interface with the gas in the second section, causing the incoming flow boundary layer to separate and further mixing the incoming and returning gases. This design concept is achieved through the coordination of the return flow section connected to the corner section and the corner section. The first section mentioned here is referred to as the throat section below, and the second section is referred to as the diverging section below.

[0074] In order to achieve stable combustion, in addition to fully mixing the mixed gas as mentioned above, the preheating zone is filled with small-pore porous media to block the backfire and rectify the incoming gas flow. At the same time, the transition combustion zone is also set to further enhance combustion.

[0075] Finally, in order to achieve the reduction of nitrogen oxide emissions, based on the idea of ​​the Arrhenius equation, specific control is established from the perspective of reducing the flue gas temperature, which is completed by setting up a filling with large-pore porous media.

[0076] The above arrangement allows the gas and air to enter from different inlets, thereby achieving the purpose of freely adjusting the mixing ratio of gas and air. By using the principle of the Bernoulli equation in fluid mechanics, the gas is made to pass through a narrow throat to accelerate the mixing of the gas and air, completing the first mixing through the first section in this technical solution. After passing through the narrow throat of the mixer, the air-gas enters a wider curved surface slowly changing flow area, which can be divided into a flow boundary layer separation area (i.e., the above-mentioned corner section, i.e., the interface between the second section and the third section) and a recirculation area (i.e., the above-mentioned recirculation section, i.e., the third section). The boundary layer separation area (i.e., the corner section, the interface between the second section and the third section) generates a reverse pressure gradient on the curved surface inside the mixer, thereby separating the boundary layer, thereby solving the problem of uneven air-gas premixing caused by the non-slip of the boundary layer, and completing the second mixing. After the gas flows through the recirculation zone, the reverse pressure gradient is generated, causing the gas flow boundary layer to separate. The gas flowing back from the recirculation zone mixes with the separated boundary layer gas, further promoting the full mixing of the air and gas, completing the third mixing. When the gas meets the continuously entering gas, the mixing degree of the air and gas will be further enhanced, making the air and gas premixed evenly. After the air and gas are fully mixed, the premixed gas enters the double-layer (the double layer here refers to the preheating zone and the wake zone) porous medium burner through the internal premixed gas inlet. The upstream preheating zone of the burner is filled with porous media with smaller pores. On the one hand, it prevents the combustion flame from flashing back. On the other hand, it preheats the incoming gas and rectifies the incoming gas, making the gas velocity distribution relatively flat when flowing through the preheating zone, which is more conducive to the stability of the subsequent combustion flame. The downstream combustion zone is divided into two areas: the transition combustion zone and the wake zone. The transition combustion zone is mainly the area where the combustion reaction between gas and air occurs. The transition combustion zone is not filled with any porous media. This is primarily because, due to the heat absorption effect of porous media, filling the combustion reaction zone with porous media would reduce the combustion temperature. According to chemical reaction kinetics, this lowered combustion temperature is detrimental to the rapid reaction between air and gas. Excessively high combustion temperatures in the wake zone also have adverse effects. After the gas and air react completely, the excessively high combustion temperature further promotes the reaction of excess nitrogen and oxygen in the air to form nitrogen oxides, thereby polluting the atmospheric environment. Furthermore, relevant chemical reaction mechanism research has shown that the amount of nitrogen oxides generated is closely related to temperature. Above 1500K, nitrogen oxides increase exponentially with increasing temperature. Therefore, controlling the combustion temperature downstream of the combustion is particularly necessary. Therefore, filling the wake zone with large-pore porous media aims to reduce the formation of nitrogen oxides by lowering the flue gas temperature after the combustion reaction. The underlying mechanism is: According to the Arrhenius equation, the relationship between the nitrogen oxide generation rate and reaction temperature is as follows:

[0077]

[0078] K: rate constant;

[0079] A: frequency factor;

[0080] Ea: reaction activation energy;

[0081] R: universal gas constant, 8.314 J / (mol·K);

[0082] T: temperature, unit: K.

[0083] According to the technical solution set up above, the beneficial effects are as follows: (1) Due to the secondary mixing caused by boundary layer separation during the mixing process, the air and gas can be mixed more thoroughly. (2) After the air and gas enter through different inlets, the air-fuel ratio can be adjusted to any proportion. (3) The transition zone of the combustion zone is not filled with any porous medium, which can promote the full reaction of gas and air. (4) The uniform mixing can improve the stability of combustion. (5) Since the air and gas can be mixed more thoroughly, the nitrogen oxide emissions during the combustion process can be reduced.

[0084] Example

[0085] Taking methane-air as an example, the following figures illustrate the process of methane-air being fully mixed in the burner of this technical solution and efficiently burning in the inert porous medium burner. The specific steps are as follows. Figure 1The following steps are performed: (1) A certain amount of methane enters from the gas inlet 9; (2) At the same time, under the condition of an excess air coefficient of 1.2, the required air volume is calculated based on the excess air coefficient and the combustion reaction of methane and air, and the required air volume is simultaneously introduced from the air inlet 8. (3) Methane and air pass through the Venturi mixer in sequence, the inflow section 1, the gradually contracting section 2, the throat 3 and the gradually expanding section 4; at the throat 3, due to the reduction of the throat area, according to the Bernoulli equation of incompressible fluid, the gas-air mixture is quickly mixed at the throat, and preliminary mixing (i.e., the first mixing) is performed. (4) After the methane and air are mixed in the throat, the mixed gas enters the slowly varying flow area, and the flow rate of the mixed gas gradually decreases at this time. (5) When the mixed gas flows through the boundary layer separation area (i.e., the corner section 5), due to the existence of the adverse pressure gradient, the boundary layer of the mixed gas separates, causing the air and methane close to the wall to mix for the second time. (6) After the mixed gas passes through the boundary layer separation area, it enters the recirculation section 6. In the recirculation section 6, the mixed gas further changes its flow direction after stopping and winding, and the returned mixed gas and the mixed gas that continuously enters the boundary layer separation area are further mixed. This is the third mixing of the mixed gas. (7) After the mixed gas is mixed three times, it enters the porous medium burner from the premixed gas inlet (i.e., the outflow section 7). There is also a slow-changing flow area in the burner as a rectification area for the premixed gas, which can reduce the flow rate of the mixed gas entering the porous medium burner, thereby facilitating the stability of subsequent combustion. (8) In addition, when the mixed gas enters the porous medium preheating area 10, due to the obstruction of the porous medium, a certain amount of turbulent pulsation will be generated in the slow-changing flow area, which is conducive to the heat exchange between the mixed gas and the porous medium in the preheating area when entering the preheating area, further preheating the mixed gas. (9) After being preheated in the preheating area, the mixed gas enters the transition combustion area 11 and is further ignited, causing a violent combustion reaction between methane and air in this area. Since the thickness of the flame of the combustion reaction is very thin, the thickness of the combustion area can be designed to be relatively narrow (generally set to a thickness between 0.5mm and 3.5mm), and it is only necessary to allow the methane and air premixed gas to fully react. (10) After the premixed gas fully reacts in the combustion area 8, the flue gas after combustion and the large-pore porous medium in the tail flow area 12 undergo heat exchange, which can slow down the flow rate of the flue gas on the one hand, and on the other hand, allow the fuel that has not been completely burned in the combustion area to further react, thereby facilitating the full reaction of the fuel. On the other hand, the rapid heat exchange between the porous medium and the high-temperature flue gas will reduce the flue gas temperature, thereby inhibiting the further reaction of oxygen and air, thereby reducing the generation of nitrogen oxides.Furthermore, the porous medium is inert. In practice, a porous medium with a certain catalytic effect can also be used to further suppress the reaction between oxygen and air. For example, a porous medium made of metal fibers can be used. Under high temperature conditions, oxygen reacts with the active metal in the metal fibers, thereby suppressing the reaction between oxygen and nitrogen oxides. The preheating zone is filled with a porous medium with a porosity of 0.35mm-0.45mm; the tail flow zone is filled with a porous medium with a porosity of 0.75mm-0.80mm.

Claims

1. A method for controlling mixed gas for metallurgical combustion, characterized in that: Three gas mixing controls are formed respectively by three sections arranged in the gas mixing area to complete the mixing of the premixed gas before combustion; The first gas mixing is completed by the gases introduced from different ports converging into a common flow channel and forming a first section of flow acceleration in the flow direction; The second gas mixing passes through a second section following the first section and is completed in the second section; The third gas mixing is completed by passing through a third section connected to the second section, and a backflow is formed from the third section. The backflow and the gas of the second section are set to form a reverse pressure gradient, thereby forming a flow boundary layer separation.

2. A method for controlling a mixed gas for metallurgical combustion according to claim 1, characterized in that: A double-layer combustion zone is formed by respectively setting a preheating zone and a tail flow zone in the combustion zone connected to the gas mixing zone; The preheating zone is used to rectify the incoming gas flow and block the tempering; The wake zone is used to control and reduce nitrogen oxides during combustion.

3. The method for controlling a mixed gas for metallurgical combustion according to claim 2, characterized in that: A transition combustion zone is also provided between the preheating zone and the wake zone; The thickness of the transition combustion zone is set to 0.5mm-3.5mm.

4. The method for controlling a mixed gas for metallurgical combustion according to claim 2, characterized in that: The preheating zone is filled with a porous medium with a porosity of 0.35 mm to 0.45 mm; The wake zone is filled with a porous medium with a porosity of 0.75 mm to 0.80 mm.

5. The method for controlling a mixed gas for metallurgical combustion according to claim 1, characterized in that: The mixing ratio is controlled by controlling the amount of gas introduced into different ports respectively.

6. The method for controlling a mixed gas for metallurgical combustion according to claim 1, characterized in that: The first section, the second section and the third section are formed by providing a venturi mixer with a slowly changing flow area; The introduction of air and gas is accomplished through a pair of openings symmetrically arranged at the inflow section of the venturi mixer.

7. A method for controlling a mixed gas for metallurgical combustion according to claim 6, characterized in that: The Venturi mixer with a slowly changing flow area comprises: an inflow section (1), a gradually contracting forging (2), a throat (3), a gradually expanding section (4), a corner section (5), a reflux section (6) and an outflow section (7) which are arranged in sequence; The inflow section (1), the tapered section (2), and the throat (3) constitute a first section; The gradually expanding section (4) constitutes the second section; The reflux section (6) constitutes the third section; The corner section (5) forms an interface between the second section and the third section for generating a reverse pressure gradient.

8. A burner for metallurgical combustion, characterized in that: It includes a gas mixing zone and a combustion zone connected to the gas mixing zone; The gas mixing zone is used to control the proportion of the mixed gas and form a tertiary mixture; The combustion zone is used to rectify the incoming gas flow, block backfire, and control and reduce nitrogen oxides during combustion.

9. A burner for metallurgical combustion according to claim 8, characterized in that: A venturi mixer with a slow-changing flow area is arranged in the gas mixing area, wherein the venturi mixer comprises: an inflow section (1), a gradually contracting forging (2), a throat (3), a gradually expanding section (4), a corner section (5), a reflux section (6) and an outflow section (7) arranged in sequence; A pair of openings are symmetrically provided in the inflow section (1) for respectively introducing air and gas; The inflow section (1), the tapered forging (2), and the throat (3) constitute a first section for completing the first gas mixing; The gradually expanding section (4) constitutes a second section for completing the second gas mixing; The reflux section (6) constitutes a third section, and the gas entering the third section forms a reflux and forms a third gas mixing based on flow boundary layer separation with the gas in the second section through the reverse pressure gradient formed by the setting; The corner section (5) forms an interface between the second section and the third section for generating a reverse pressure gradient.

10. A burner for metallurgical combustion according to claim 9, characterized in that: The mixing ratio is controlled by respectively controlling the amount of gas introduced into different openings.

11. A burner for metallurgical combustion according to claim 8, characterized in that: The combustion zone is composed of a preheating zone and a wake zone arranged in sequence to form a double-layer combustion zone; The preheating zone is used to rectify the incoming gas flow and block the tempering; The wake zone is used to control and reduce nitrogen oxides during combustion.

12. A burner for metallurgical combustion according to claim 11, characterized in that: A transition combustion zone is also provided between the preheating zone and the wake zone; The thickness of the transition combustion zone is set to 0.5mm-3.5mm.

13. A burner for metallurgical combustion according to claim 11, characterized in that: The preheating zone is filled with a porous medium with a porosity of 0.35 mm to 0.45 mm; The wake zone is filled with a porous medium with a porosity of 0.75 mm to 0.80 mm.

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