Strong premixing combustion chamber for inhibiting combustion noise based on Helmholtz resonant cavity

Abstract

The invention discloses a strong premixing combustion chamber for restraining combustion noise based on a Helmholtz resonant cavity, and relates to the technical field of energy and power. Air and fuel enter the mixing cavity through corresponding connectors to be strongly premixed, premixed gas enters the hearth to be combusted through slit channels among water cooling channel branch pipes, a water cooling channel array can prevent backfire, the Helmholtz resonant cavity is connected with the hearth through a cavity neck and is provided with an air film cooling channel, the size of the Helmholtz resonant cavity needs to measure combustion noise, and a frequency spectrum is analyzed to obtain characteristic frequency. The neck length, the cross section area and the resonant cavity volume are calculated according to a Helmholtz resonance formula, and the sound absorption effect is verified in combination with a low-order thermoacoustic model. Combustion efficiency is improved through the strong premixing and slit water cooling design, tempering is prevented, NOx is reduced, the diffusion combustion problem is solved, the targeted design resonant cavity is matched with air film cooling, the defects that an existing silencing structure is large in size, poor in adaptation and low in high-temperature reliability are overcome, complex active control is not needed, cost is low, applicability is high, and the application range is wide. And cooperative control of high efficiency, low emission and unstable combustion is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy and power, more particularly, to a strong premixed combustion chamber for suppressing combustion noise based on a Helmholtz resonance cavity. BACKGROUND

[0002] Industrial boilers, as important heat power equipment, are widely used in power generation, heating, chemical industry, metallurgy and many other fields. With the change of fuel structure, natural gas is currently widely used as fuel in industrial boilers. In order to achieve low emission and efficient combustion, strong premixed combustion is usually adopted, that is, air and fuel are mixed in advance and then enter the combustion chamber for combustion. However, in the process of strong premixed combustion, due to the mutual coupling and positive feedback effect of fuel combustion heat release rate and sound pressure fluctuation, combustion instability is easy to occur, which is manifested as pressure oscillation increase and noise generation, and in severe cases, it may lead to flameout and combustion chamber structure damage, which has a great impact on the operation and safety of the actual industrial boiler combustion chamber.

[0003] Among the commonly used combustion instability control methods, there are active control technology and passive control technology. The active control technology is complex, high in cost, and has high requirements for the real-time performance and stability of the sound field environment. It is difficult to implement in the complex and variable combustion conditions and harsh environment (high temperature, dust) of industrial boilers, and its reliability and long-term stability are challenged. Therefore, developing a combustion noise control technology that is efficient, reliable, compact in structure and suitable for the high-temperature and harsh environment of industrial boilers has become a key problem to be solved in the field of industrial noise control. As a classic and efficient passive control technology structure, the Helmholtz resonance cavity has excellent sound absorption effect on narrow-band low-frequency noise. Its principle is to produce strong acoustic reactance at a specific frequency (resonant frequency) through a specific geometric shape (cavity + neck), which dissipates sound energy. It has potential advantages such as relatively simple structure, high sound absorption efficiency in the medium and low frequency band, and small influence on air flow resistance, providing a promising technical path for solving the problem of low-frequency combustion noise in industrial boilers.

[0004] Therefore, the present application "a strong premixed combustion chamber for suppressing combustion noise based on a Helmholtz resonance cavity" is born to overcome the shortcomings of the prior art. Through innovative design of the Helmholtz resonance cavity, optimization of the layout method and adaptability to the structure of the combustion chamber, efficient and targeted control of the low-frequency noise components in the combustion core of the industrial boiler is achieved, providing a more economical, practical and effective solution to the problem of industrial boiler noise pollution. SUMMARY

[0005] Therefore, the present application "a strong premixed combustion chamber for suppressing combustion noise based on a Helmholtz resonance cavity" is born to overcome the shortcomings of the prior art. Through innovative design of the Helmholtz resonance cavity, optimization of the layout method and adaptability to the structure of the combustion chamber, efficient and targeted control of the low-frequency noise components in the combustion core of the industrial boiler is achieved, providing a more economical, practical and effective solution to the problem of industrial boiler noise pollution.

[0006] To achieve the above object, the present application adopts the following technical scheme:

[0007] A strong premixed combustion chamber based on Helmholtz resonance cavity for suppressing combustion noise, comprising a mixing cavity and a furnace connected in sequence;

[0008] An air interface and a fuel interface access the mixing cavity;

[0009] The inlet end of the furnace is provided with a combustion assembly, which comprises a water-cooled channel water inlet header, a water-cooled channel water outlet header, and a water-cooled channel array composed of a plurality of water-cooled channel branch pipes; the water-cooled channel array penetrates through the inlet end of the furnace, and the water-cooled channel water inlet header and the water-cooled channel water outlet header are respectively installed at both ends of the water-cooled channel array;

[0010] The furnace is connected with a Helmholtz resonance cavity, which comprises a cavity neck, a resonance cavity, and an air film cooling channel; one end of the resonance cavity is communicated with the wall surface of the furnace through the cavity neck, and the other end of the resonance cavity is provided with a plurality of air film cooling channels connected with an air cooling inlet.

[0011] Preferably, the water-cooled channel branch pipes are arranged in an array of round pipes or square pipes;

[0012] The cavity neck and the resonance cavity adopt a cylindrical structure.

[0013] Preferably, air and fuel enter the mixing cavity through the air interface and the fuel interface respectively, are fully mixed in the mixing cavity, and form a premixed gas;

[0014] The premixed gas enters the water-cooled channel array, flows through the slit channels between the water-cooled channel branch pipes into the furnace for combustion; wherein the cooling water of the water-cooled channel branch pipes cools the slit channel wall surface;

[0015] The noise generated during the combustion process is transmitted to the Helmholtz resonance cavity through the furnace wall, the Helmholtz resonance cavity resonates at the natural frequency, converts sound energy into heat energy and dissipates; at the same time, cooling air enters from the air cooling inlet, flows through the air film cooling channel, and forms a cooling air film on the inner wall of the resonance cavity;

[0016] The high-temperature flue gas after combustion is discharged from the gas outlet located at the outlet end of the furnace.

[0017] Preferably, the size of the slit channel ranges from 2 to 10 mm;

[0018] The gas outlet adopts a rectangular or circular cross-section outlet.

[0019] Preferably, the size design method of the Helmholtz resonance cavity comprises:

[0020] The combustion noise is measured by a dynamic pressure sensor arranged on the combustion chamber to obtain a sound pressure signal of the noise;

[0021] The sound pressure signal is subjected to a spectrum analysis to determine a target characteristic frequency to be suppressed;

[0022] According to the target characteristic frequency, dimensions of a neck length, a neck cross-sectional area and a volume of the resonant cavity are determined in combination with a formula of a natural frequency of the Helmholtz resonant cavity.

[0023] Preferably, the formula of the natural frequency of the Helmholtz resonant cavity is as follows:

[0024]

[0025] In the formula, f is the natural frequency of the resonant cavity, c0 is the sound speed in the combustion chamber, L is the neck length, V is the volume of the resonant cavity, and S is the neck cross-sectional area.

[0026] It can be known from the above technical solution that the application discloses a strong premix combustion chamber for suppressing combustion noise based on a Helmholtz resonant cavity, which has the following beneficial effects compared with the prior art:

[0027] (1) High efficiency of strong premix combustion:

[0028] Combustion modes are divided into diffusion combustion and premix combustion, and the diffusion combustion commonly used in current industrial boiler combustion is prone to cause incomplete combustion of fuel and air and low combustion efficiency, and the strong premix combustion of fuel and air is adopted in the application, that is, the premixing of fuel and air is enhanced through a mixing cavity to improve the combustion efficiency.

[0029] (2) Anti-backfire and low emission capacity:

[0030] The strong premix water-cooled slit combustion proposed in the application can effectively prevent backfire and reduce pollutant emission, the slit channel between the water-cooled channel branch pipes is used to improve the outlet speed of the premix gas, the water-cooled channel branch pipes are used to control the temperature of the premix gas and the slit channel, and the backfire can be effectively prevented; through the strong premix combustion mode, the fuel and air are uniformly mixed, and the array distributed combustion flame is formed through the slit channel, the local high-temperature and high-residence-time area of combustion is effectively reduced, and the emission of NOx is reduced.

[0031] (3) Ability to suppress combustion instability:

[0032] The application adopts the Helmholtz resonance cavity to specifically suppress the combustion instability of the strong premixed combustion chamber, and proposes a size design method of the Helmholtz resonance cavity neck and the resonance cavity volume, specifically suppresses the combustion noise of the industrial boiler, and further proposes a resonance cavity design with gas film cooling, the input of the cooling gas can effectively dissipate the heat energy and acoustic energy in the resonance cavity, effectively protects the resonance cavity, and enhances the suppression ability of the resonance cavity to the combustion instability of the strong premixed combustion chamber. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only a part of the embodiments of the present application, and all other drawings obtained by those skilled in the art without creative labor based on the provided drawings are also within the protection scope of the present application.

[0034] Figure 1 The structure schematic diagram of the industrial boiler combustion chamber provided by the present application is shown in the figure.

[0035] Figure 2 The structure schematic diagram of the Helmholtz resonance cavity provided by the present application is shown in the figure.

[0036] Figure 3 The noise measurement result schematic diagram is shown in the figure.

[0037] Fig. 4(a) is a fast Fourier transform spectrum analysis diagram of the noise measurement result provided by the present application, and Fig. 4(b) is a short-time Fourier transform spectrum analysis diagram of the noise measurement result provided by the present application.

[0038] Figure 5 The size design flowchart of the Helmholtz resonance cavity is shown in the figure.

[0039] In the figure, 1 is an air interface, 2 is a fuel interface, 3 is a mixing cavity, 4 is a water cooling channel inlet main pipe, 5 is a water cooling channel branch pipe, 6 is a water cooling channel outlet main pipe, 7 is a furnace, 8 is a Helmholtz resonance cavity, 8001 is a furnace wall surface, 8002 is a cavity neck, 8003 is a resonance cavity, 8004 is a gas film cooling channel, 8005 is an air cooling inlet, and 9 is a fuel gas outlet. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0041] The embodiment of the present application discloses a strong premixed combustion chamber for suppressing combustion noise based on a Helmholtz resonance cavity, referring to Figures 1-2 , comprising a mixing cavity 3 and a hearth 7 connected in sequence.

[0042] The air interface 1 and the fuel interface 2 access the mixing cavity 3;

[0043] The inlet end of the hearth 7 is provided with a combustion assembly, which comprises a water-cooled channel water inlet main pipe 4, a water-cooled channel water outlet main pipe 6 and a water-cooled channel array composed of a plurality of water-cooled channel branch pipes 5; the water-cooled channel array penetrates through the inlet end of the hearth 7, and the water-cooled channel water inlet main pipe 4 and the water-cooled channel water outlet main pipe 6 are respectively installed at both ends of the water-cooled channel array;

[0044] The hearth 7 is connected with a Helmholtz resonance cavity 8, and the Helmholtz resonance cavity 8 comprises a cavity neck 8002, a resonance cavity 8003 and air film cooling channels 8004; one end of the resonance cavity 8003 is communicated with the hearth wall surface 8001 through the cavity neck 8002, and the other end of the resonance cavity 8003 is provided with a plurality of air film cooling channels 8004 connected with an air cooling inlet 8005.

[0045] Specifically, air and fuel enter the mixing cavity 3 through the air interface 1 and the fuel interface 2 respectively, are fully mixed in the mixing cavity 3, and form premixed gas;

[0046] The premixed gas enters the water-cooled channel array, flows through the slit channels between the water-cooled channel branch pipes 5 and enters the hearth 7 for combustion; wherein the cooling water of the water-cooled channel branch pipes 5 cools the slit channel wall surface;

[0047] The noise generated in the combustion process is transmitted to the Helmholtz resonance cavity 8 through the hearth 7 wall surface, the Helmholtz resonance cavity 8 resonates at the natural frequency to convert sound energy into heat energy and dissipate; at the same time, cooling air enters from the air cooling inlet 8005, flows through the air film cooling channels 8004, and forms a cooling air film on the inner wall of the resonance cavity 8003;

[0048] The high-temperature flue gas after combustion is discharged from the gas outlet 9 located at the outlet end of the hearth 7.

[0049] In the embodiment, the water-cooled channel branch pipes 5 are arranged in an array of round pipes or square pipes; the cavity neck 8002 and the resonance cavity 8003 adopt a cylindrical structure; the size of the slit channel ranges from 2-10mm; and the gas outlet 9 adopts a rectangular or circular cross-section outlet.

[0050] Further, as shown in Figure 5 , the size design method of the Helmholtz resonance cavity in the embodiment comprises the following steps:

[0051] S1. Measure the combustion noise by a dynamic pressure sensor arranged on the combustion chamber to obtain a sound pressure signal of the noise, as shown in Figure 3The following data are also acquired in this embodiment:

[0052] Combustion chamber structure size, i.e. the geometric shape, size of the combustion chamber and the space available for installing the resonant cavity.

[0053] Combustion chamber internal temperature, i.e. the temperature of the flue gas in the combustion chamber, which is used to calculate the local sound speed, a key parameter for determining the resonant frequency.

[0054] Cooling gas flow rate and temperature, which combines the influence of the flow rate and temperature of the cooling gas on the acoustic characteristics in the resonant cavity.

[0055] S2. Referring to FIGS. 4(a) and 4(b), the target characteristic frequency to be suppressed is determined by performing a spectral analysis on the sound pressure signal;

[0056] S3. According to the target characteristic frequency, the size parameters of the cavity neck length L, the resonant cavity volume V and the cavity neck cross-sectional area S are determined in combination with the Helmholtz resonant cavity natural frequency formula and the combustion chamber structure size.

[0057] The Helmholtz resonant cavity natural frequency formula is as follows:

[0058]

[0059] In the formula, f is the natural frequency of the resonant cavity, c0 is the sound speed in the combustion chamber, L is the cavity neck length, V is the resonant cavity volume, and S is the cavity neck cross-sectional area.

[0060] Specifically, the target characteristic frequency is substituted into the Helmholtz resonant cavity natural frequency formula as the natural frequency of the resonant cavity, and the size parameters of the cavity neck length, the cavity neck cross-sectional area and the resonant cavity volume are calculated to obtain the preliminary design parameters.

[0061] S4. The preliminary design parameters (S, L, V), the cooling gas parameters (flow rate, temperature) and the like are input into a low-order thermoacoustic model for computer simulation calculation, the sound absorption capacity of the resonant cavity based on the preliminary design parameters under the actual combustion temperature and cooling gas working conditions is evaluated, and the analysis dimensions include three items:

[0062] Pressure disturbance intensity amplitude: the attenuation effect of the resonant cavity on the pressure fluctuation in the combustion chamber at the target frequency is simulated, and if the amplitude attenuation rate is lower than a preset threshold, the geometric parameters need to be adjusted;

[0063] Temperature disturbance correlation: in combination with the combustion temperature and the cooling gas temperature, the influence of temperature change on the shift of the natural frequency of the resonant cavity is analyzed to ensure that the resonant frequency can still cover the target noise frequency within the temperature fluctuation range;

[0064] Sound absorption coefficient calculation: the absorption coefficient of the resonant cavity to the target frequency noise is calculated through the model, and if the preset condition is not met, the parameter adjustment link is entered.

[0065] S5. Determine whether the model output result of S4 meets the predetermined sound absorption requirement.

[0066] If the requirement is met, the design is completed and can enter the processing and manufacturing stage. If not, return to S2 and then re-perform the simulation calculation of S3. This process is repeated until the design meets all performance indicators.

[0067] The various embodiments described in this specification are presented by way of example, and each embodiment describes a specific feature of the application that is independently useful. Each embodiment is intended to contribute to the broader understanding of the application, and should be interpreted as such. The same part in different embodiments is mutually referred to. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the relevant part is referred to the method part.

[0068] The above description of disclosed embodiments enables a person skilled in the art to implement or use the application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the application. Therefore, the application will not be limited to these embodiments shown herein, but will conform to the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A highly premixed combustion chamber for suppressing combustion noise based on a Helmholtz resonant cavity, characterized in that, Includes a mixing chamber and a furnace connected in sequence; The air interface and fuel interface are connected to the mixing chamber; A combustion assembly is provided at the inlet end of the furnace. The combustion assembly includes a water-cooled channel inlet main pipe, a water-cooled channel outlet main pipe, and a water-cooled channel array composed of several water-cooled channel branch pipes. The water-cooled channel array passes through the inlet end of the furnace, and the water-cooled channel inlet main pipe and the water-cooled channel outlet main pipe are respectively installed at both ends of the water-cooled channel array. The furnace is connected to a Helmholtz resonant cavity, which includes a cavity neck, a resonant cavity, and a film cooling channel. One end of the resonant cavity communicates with the furnace wall through the cavity neck, and the other end of the resonant cavity is provided with several film cooling channels connected to an air cooling inlet.

2. The strongly premixed combustion chamber based on a Helmholtz resonant cavity for suppressing combustion noise according to claim 1, characterized in that, The water-cooling channel is arranged in an array of round or square tubes. The cavity neck and the resonant cavity adopt a cylindrical structure.

3. The strong premixed combustion chamber based on Helmholtz resonant cavity for suppressing combustion noise according to claim 1, characterized in that, Air and fuel enter the mixing chamber through air and fuel interfaces respectively, and are thoroughly mixed in the mixing chamber to form a premixed gas. The premixed gas enters the water-cooled channel array, flows through the slit channels between the water-cooled channel branches, and enters the furnace for combustion; wherein the cooling water of the water-cooled channel branches cools the walls of the slit channels. The noise generated during combustion is transmitted to the Helmholtz resonant cavity through the furnace wall. The Helmholtz resonant cavity resonates at its natural frequency, converting sound energy into heat energy and dissipating it. At the same time, cooling air enters from the air cooling inlet, flows through the gas film cooling channel, and forms a cooling gas film on the inner wall of the resonant cavity. The high-temperature flue gas after combustion is discharged from the gas outlet located at the furnace outlet end.

4. A strong premixed combustion chamber based on a Helmholtz resonant cavity for suppressing combustion noise according to claim 3, characterized in that, The slit channel size ranges from 2 to 10 mm; The gas outlet has a rectangular or circular cross-section.

5. A strong premixed combustion chamber for suppressing combustion noise based on a Helmholtz resonant cavity according to claim 1, characterized in that, The method for designing the dimensions of the Helmholtz resonant cavity includes: Combustion noise is measured by a dynamic pressure sensor installed on the combustion chamber to obtain the sound pressure signal of the noise; Perform spectral analysis on the sound pressure signal to determine the target characteristic frequencies that need to be suppressed; Based on the target characteristic frequency and combined with the Helmholtz resonant cavity natural frequency formula, the dimensional parameters of the cavity neck length, cavity neck cross-sectional area, and resonant cavity volume are determined.

6. A strong premixed combustion chamber for suppressing combustion noise based on a Helmholtz resonant cavity according to claim 5, characterized in that, The formula for the natural frequency of a Helmholtz resonator is as follows: In the formula, f is the natural frequency of the resonant cavity, c0 is the speed of sound in the combustion chamber, L is the length of the cavity neck, V is the volume of the resonant cavity, and S is the cross-sectional area of ​​the cavity neck.

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