Soot detection method for tar-containing biomass gasified gas MILD combustion system

Abstract

The invention discloses a soot detection method for a tar-containing biomass gasified gas MILD combustion system, and relates to the technical field of renewable low-carbon energy utilization and soot emission control. Comprising the following steps: S1, installing a tar-containing biomass gasified gas MILD combustion system; s2, installing a soot detection system; and S3, detecting the soot generation process. Fuel supply of tar-containing biomass gasified gas is achieved through the controllable mixing evaporator, and it is guaranteed that tar participates in combustion in a gaseous form; a thermophoresis sampling system and an optical diagnosis system are combined to detect the whole soot generation process under MILD combustion; according to the method, the problem of fuel supply caused by tar is solved, MILD combustion of tar-containing biomass gasified gas is achieved, an effective detection means for the whole soot generation process under MILD combustion is provided, and a solution is provided for related experimental research.

Description

Technical Field

[0001] The present invention relates to the technical field of renewable low-carbon energy utilization and soot emission control, and particularly relates to a soot detection method for a Moderate&Intense Low Oxygen Dilution (MILD) combustion system of biomass gasified gas containing tar. Background Art

[0002] Under the background of the "dual carbon" goal, renewable zero-carbon energy biomass has received extensive attention. Biomass gasification technology can consume and efficiently utilize biomass waste, and the biomass gasified gas (BGG) obtained by gasification can also fill the gas gap, and its importance is becoming increasingly prominent. Affected by gasification raw materials, furnace types, and media, the composition of BGG is very complex. In addition to combustible components such as CO, H2, and a small amount of C n H m except, it also contains a large amount of non-combustible gases and impurities such as tar, which leads to a series of problems such as difficult ignition, low combustion efficiency, unstable flame, and difficult control of emissions of pollutants such as NO x and soot during conventional combustion. MILD (Moderate&Intense Low Oxygen Dilution) combustion is a combustion method achieved through high-temperature preheating and low-oxygen dilution, which can achieve a low peak temperature and a high average temperature in the furnace. Therefore, it has the advantages of high thermal radiation efficiency and low NO x emission, and MILD combustion has been proven to be able to reduce the soot emission of hydrocarbon fuel combustion. The MILD combustion flame of BGG is stable, and it has good NOx emission reduction characteristics in all working conditions.

[0003] In existing research on the MILD combustion of BGG, only the simulated pure BGG gas is considered, and only two pollutants, NO x and CO, are concerned, lacking research on soot emissions caused by tar. Since tar will condense into a liquid with relatively high viscosity at room temperature, it is easy to adhere to and block pipeline and other conveying equipment, seriously affecting the conveying efficiency. At the same time, tar often participates in the combustion reaction in a gaseous form during actual combustion. Currently, there is a lack of a fuel supply and conveying method for biomass gasified gas containing tar to mix different concentrations of tar (or model compounds) in a gaseous form with the gasified gas for application in MILD combustion experiments or pilot studies. In addition, due to the temperature field and soot distribution characteristics of the MILD combustion method being different from those of the conventional combustion method, its temperature field is usually more uniform, the temperature gradient is smaller, and the soot is more dispersed in space and shows different particle size and concentration distribution characteristics. These characteristics make the traditional single-point detection method difficult to apply, and currently, there is a lack of a detection method for the whole process of soot generation under MILD combustion. Summary of the Invention

[0004] The main object of the present invention is to provide a method for detecting soot in a MILD combustion system of biomass gasification gas containing tar, realizing the precise supply of biomass gasification gas containing tar, ensuring that tar participates in combustion in a gaseous form, establishing MILD combustion of biomass gasification gas containing tar through the formation of an oxygen-containing thermal coflow by a diffusion planar flame in an open space, and combining the intrusive thermophoretic sampling technology and optical diagnostic technology of soot particles to detect the whole process of soot from gas-phase precursors to soot particles, so as to study the formation and control mechanism of soot in the MILD combustion mode of biomass gasification gas containing tar.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A method for detecting soot in a MILD combustion system of biomass gasification gas containing tar, comprising the following steps:

[0007] S1. Install a MILD combustion system for biomass gasification gas containing tar;

[0008] S2. Install a soot detection system;

[0009] S3. Detect the soot generation process;

[0010] Among them, the combustion system in step S1 includes a controllable mixing evaporator for supplying biomass gasification gas containing tar, a heating pipeline for transporting biomass gasification gas containing tar, and a MILD burner for biomass gasification gas guided by an oxygen-containing thermal coflow formed by a diffusion planar flame in an open space. The controllable mixing evaporator evaporates tar into gas and mixes it evenly with the biomass gasification gas, and supplies it to the MILD burner for biomass gasification gas through the heating pipeline. The MILD burner for biomass gasification gas guided by a diffusion planar flame realizes the MILD combustion of biomass gasification gas by increasing the initial temperature, reducing the ignition delay time, and increasing the chemical reaction time through the thermal coflow;

[0011] The detection system in step S2 includes a thermophoretic sampling system and an optical diagnostic system. The thermophoretic sampling system collects soot particles at different positions in the flame, and the optical diagnostic system semi-quantitatively measures the concentrations of polycyclic aromatic hydrocarbons, hydroxyl groups, and soot in the open space flame;

[0012] During the detection in step S3, soot particle sampling, soot distribution detection, polycyclic aromatic hydrocarbon distribution detection, and hydroxyl group distribution detection are carried out in sequence.

[0013] Further, the controllable hybrid evaporator in step S1 includes a data control module, a liquid flowmeter, a hybrid evaporator, and a gas flowmeter. The liquid flowmeter, the hybrid evaporator, and the gas flowmeter are all electrically connected to the data control module. One end of the liquid flowmeter is connected to the hybrid evaporator through a pipeline, and the other end is connected to a toluene bottle through a pipeline. The toluene bottle is connected to a centrifugal pump through a pipeline. One end of the gas flowmeter is connected to the hybrid evaporator through a pipeline, and the other end is connected to a biomass gasification gas cylinder through a pipeline;

[0014] The toluene liquid in the toluene bottle is connected to the hybrid evaporator through the liquid flowmeter under the nitrogen pressure. The biomass gasification gas in the biomass gasification gas cylinder is connected to the hybrid evaporator through the gas flowmeter. Then, a heating pipeline is used to connect the outlet of the hybrid evaporator and the main fuel inlet of the biomass gasification gas MILD burner. Under the control of the data control module, the gas and liquid flow rates and the evaporation temperature are regulated to achieve the evaporation of different types of tar and different proportion mixing with the biomass gasification gas.

[0015] Further, the hybrid evaporator includes a heating cavity and a storage cavity. The heating cavity heats and mixes and evaporates the atomized gas and liquid mixture injected into it, and the storage cavity temporarily stores the gasified mixed gas;

[0016] The temperature of the heating cavity is not lower than 110.6 °C to ensure the evaporation of toluene.

[0017] Further, a heating tape is wound around the heating pipeline. The heating tape is tightly spirally wound, and its heating temperature is not lower than the boiling point of the evaporated liquid under the corresponding pressure to ensure that it will not condense into a liquid again and block the pipeline;

[0018] The heating tape includes a temperature control component, an electric heating tape, and a heat insulation layer. The temperature control component is used to regulate the temperature of the electric heating tape. The electric heating tape is a nickel-chromium alloy resistance wire with a silicone rubber outer layer, and the heat insulation layer uses fiberglass needle felt cotton.

[0019] Further, when installing the biomass gasification gas MILD burner in step S1, first position it and then fix it on the experimental bench;

[0020] The biomass gasification gas MILD burner is an open-space two-stage combustion system, including tar-containing biomass gasification gas as the jet main fuel and high-temperature heat recirculation. The high-temperature heat recirculation is formed by the lean combustion diffusion flame of CH4 / H2-air. The generated oxygen-containing flue gas is used as the oxidant of the biomass gasification gas to form a high-temperature and low-oxygen dilution combustion condition to achieve MILD combustion. The open space ensures good access to the optical system and the operability of invasive sampling operations;

[0021] Among them, the fuel with heat co-flow is a mixture composed of 50% CH4 and 50% H2, and the oxidizer is a mixture of O2 and N2.

[0022] Furthermore, the thermophoretic sampling system in step S2 includes a programmable time relay, an air compressor, a solenoid valve, a cylinder, a self-locking tweezer, a TEM copper mesh, and a lifting table. The self-locking tweezer holds the TEM copper mesh and is connected to the end of the cylinder. The cylinder is installed on the top of the lifting table, and the position of the cylinder is controlled by the lifting table to ensure that soot particles at different heights of the flame can be collected.

[0023] The air compressor provides the gas power for the cylinder. The programmable time relay controls the solenoid valve, and the solenoid valve controls the movement of the cylinder, so that the TEM copper mesh held by the self-locking tweezer enters the flame to sample the soot particles.

[0024] Furthermore, the optical diagnostic system in step S2 includes an ICCD camera, a double imager, a sheet light mirror group, a dye laser, a Nd:YAG laser, a timing trigger, an ICCD controller, and a filter group.

[0025] The Nd:YAG laser and the sheet light mirror group cooperate with the frequency doubling crystal group to generate the second harmonic, and output a laser with a wavelength of 532 nm, which is used to excite the incandescence signal of soot.

[0026] The Nd:YAG laser and the dye laser cooperate with the frequency doubling crystal group and the laser mirror group to generate two wavelengths of laser, 266 nm and 283 nm, which are used to excite polycyclic aromatic hydrocarbon and hydroxyl radical signals.

[0027] Furthermore, for the sampling of soot particles in step S3, by setting a program on the programmable time relay to control the solenoid valve and further control the cylinder, strictly control the residence time of the TEM copper mesh in the flame to ensure the accuracy of sampling and subsequent analysis. The obtained soot particles are analyzed for their morphological structure using a transmission electron microscope to obtain data on fringe spacing, fringe width, and fringe curvature.

[0028] For the detection of the distribution of polycyclic aromatic hydrocarbons, a 315 nm band-pass filter is selected to measure A1, a 400 nm band-pass filter is selected to measure A2 and A3, and a 492 nm band-pass filter is selected to measure A4. The above signals are captured and recorded by the ICCD camera, where A1 refers to benzene, A2 refers to dibenzene ring, A3 refers to tribenzene ring, and A4 refers to tetrabenzene ring.

[0029] For the detection of the hydroxyl distribution, the hydroxyl signal is processed by a band-pass filter of 300 - 320 nm and then captured and recorded by the ICCD camera.

[0030] Further, for the detection of soot distribution in step S3, the incandescence signal radiated by soot is filtered by 450 nm and 650 nm band-pass filters installed on the double image device, and then converted into two LII signals at specific wavelengths corresponding to pixel positions, which are captured and recorded by an ICCD camera. A band-pass filter with a central wavelength of 440 nm is used to eliminate the interference of polycyclic aromatic hydrocarbon groups on soot measurement, and the obtained LII signals are calculated using formulas (1) and (2) to obtain the temperature T p and volume fraction f v ,

[0031] Formula (1):

[0032]

[0033] Formula (2):

[0034]

[0035] In the formula, λ 1,2 is the central wavelength of the selected band-pass filter, h is Planck's constant, c is the speed of light, k is Boltzmann's constant, E(m λ ) is the soot absorption function at wavelength λ, V Exp is the signal intensity output by the ICCD, G Exp is the gain of the detection system, w b is the thickness of the laser sheet light, and η(λ) is the ratio of the output signal to the intensity of the irradiated light.

[0036] Further, before performing step S1, the gas flow rate of the biomass gasification gas and the liquid flow rate of the tar are calculated according to the tar content of the required gasification gas.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] In view of the characteristics that the tar content of the biomass gasification gas containing tar is uncertain and easy to condense, the present invention realizes the fuel supply of the biomass gasification gas with different tar contents by accurately regulating the gas and liquid flow rates, evaporation temperature and mixing ratio through the coordinated operation of multiple modules of the controllable mixing evaporator, and ensures that the tar (or its model compound) participates in combustion in a liquid state;

[0039] In view of the characteristics that the open space staged combustor has convenient intrusive detection operation and good optical access, the present invention combines the thermophoretic sampling technology and optical diagnostic technology of soot particles to realize the detection of the whole process from gas-phase precursors to the formation of soot particles;

[0040] In view of the characteristics that under MILD combustion conditions, the flame temperature field is uniform, and the soot distribution is more dispersed in space and shows different particle size and concentration distribution characteristics, an optical diagnostic technique is selected to detect the soot distribution of the entire flame, avoiding the large errors caused by single-point sampling detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the controllable mixing evaporator of the present invention.

[0042] Figure 2 Schematic diagram of the thermophoretic sampling system of the present invention.

[0043] Figure 3 Schematic diagram of the optical diagnostic system of the present invention.

[0044] Description of reference numerals: 1 - data control module, 2 - liquid flowmeter, 3 - centrifugal pump, 4 - toluene bottle, 5 - heating tape, 6 - mixing evaporator, 7 - biomass gasification gas cylinder, 8 - gas flowmeter, 9 - programmable time relay, 10 - air compressor, 11 - solenoid valve, 12 - cylinder, 13 - self-locking forceps, 14 - TEM copper mesh, 15 - lifting platform, 16 - ICCD camera, 17 - double image device, 18 - biomass gasification gas MILD burner, 19 - sheet light mirror group, 20 - dye laser, 21 - Nd:YAG laser, 22 - timing controller, 23 - ICCD controller. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] The technical solutions of the present invention will be further described below with reference to the drawings and embodiments.

[0046] Refer to Figures 1 - 3 , this embodiment provides a soot detection method for a biomass gasification gas MILD combustion system containing tar, including the following steps:

[0047] S0. Calculate the gas flow rate of the biomass gasification gas and the liquid flow rate of the tar according to the tar content of the required gasification gas;

[0048] S1. Install a biomass gasification gas MILD combustion system containing tar;

[0049] S2. Install a soot detection system;

[0050] S3. Detect the soot generation process;

[0051] Among them, the combustion system in step S1 includes a controllable mixing evaporator for supplying tar-containing biomass gasified gas, a heating pipeline for transporting the tar-containing biomass gasified gas, and a biomass gasified gas MILD combustor 18 with an oxygen-containing thermal recirculation-guided diffusion planar flame formed in an open space. The controllable mixing evaporator evaporates tar into gas and mixes it evenly with the biomass gasified gas, and supplies it to the biomass gasified gas MILD combustor 18 through the heating pipeline. The biomass gasified gas MILD combustor 18 with a diffusion planar flame guide realizes the MILD combustion of the biomass gasified gas by increasing the initial temperature, reducing the ignition delay time, and increasing the chemical reaction time through thermal recirculation;

[0052] The detection system in step S2 includes a thermophoretic sampling system and an optical diagnostic system. The thermophoretic sampling system collects soot particles at different positions in the flame, and the optical diagnostic system semi-quantitatively measures the concentrations of polycyclic aromatic hydrocarbons, hydroxyl groups, and soot in the open space flame;

[0053] During the detection in step S3, soot particle sampling, soot distribution detection, polycyclic aromatic hydrocarbon distribution detection, and hydroxyl group distribution detection are carried out in sequence.

[0054] In this embodiment, the controllable mixing evaporator in step S1 includes a data control module 1, a liquid flowmeter 2, a mixing evaporator 6, and a gas flowmeter 8. The liquid flowmeter 2, the mixing evaporator 6, and the gas flowmeter 8 are all electrically connected to the data control module 1. One end of the liquid flowmeter 2 is connected to the mixing evaporator 6 through a pipeline, and the other end is connected to a toluene bottle 4 through a pipeline. The toluene bottle 4 is connected to a centrifugal pump 3 through a pipeline. One end of the gas flowmeter 8 is connected to the mixing evaporator 6 through a pipeline, and the other end is connected to a biomass gasified gas cylinder 7 through a pipeline;

[0055] The toluene liquid in the toluene bottle 4 is connected to the mixing evaporator 6 through the liquid flowmeter 2 under the nitrogen pressure. The biomass gasified gas in the biomass gasified gas cylinder 7 is connected to the mixing evaporator 6 through the gas flowmeter 8. Then, a heating pipeline is used to connect the outlet of the mixing evaporator 6 and the main fuel inlet of the biomass gasified gas MILD combustor 18. Under the control of the data control module 1, the gas and liquid flow rates and the evaporation temperature are regulated to achieve the evaporation of different types of tar and different proportions of mixing with the biomass gasified gas.

[0056] Preferably, the mixing evaporator 6 includes a heating cavity and a storage cavity. The heating cavity heats and mixes and evaporates the atomized gas and liquid mixture sprayed into it, and the storage cavity temporarily stores the gasified mixed gas; the temperature of the heating cavity is not lower than 110.6 °C to ensure the evaporation of toluene.

[0057] Preferably, a heating tape 5 is wound around the heating pipeline. The heating tape 5 is tightly spirally wound, and its heating temperature is not lower than the boiling point of the evaporated liquid under the corresponding pressure to ensure that it will not condense into a liquid again and block the pipeline. The heating tape 5 includes a temperature control component, an electric heating tape, and a heat insulation layer. The temperature control component is used to regulate the temperature of the electric heating tape. The electric heating tape is a nickel-chromium alloy resistance wire with a silicone rubber outer layer, and the heat insulation layer is made of fiberglass needle felt cotton.

[0058] In this embodiment, when installing the biomass gasification gas MILD burner 18 in step S1, it is first positioned and then fixed on the experimental bench.

[0059] The biomass gasification gas MILD burner 18 is a two-stage combustion system in an open space, including tar-containing biomass gasification gas as the jet main fuel and high-temperature heat recirculation. The high-temperature heat recirculation is formed by the lean combustion diffusion flame of CH4 / H2-air, and the generated oxygen-containing flue gas is used as the oxidant of the biomass gasification gas to form a combustion condition of high temperature and low oxygen dilution to achieve MILD combustion. The open space ensures good access to the optical system and the operability of intrusive sampling operations.

[0060] Among them, the fuel of the heat recirculation is a mixture composed of 50% CH4 and 50% H2, and the oxidant is a mixture of O2 and N2.

[0061] In this embodiment, the thermophoretic sampling system in step S2 includes a programmable time relay 9, an air compressor 10, a solenoid valve 11, a cylinder 12, a self-locking tweezer 13, a TEM copper mesh 14, and a lifting table 15. The self-locking tweezer 13 holds the TEM copper mesh 14 and is connected to the end of the cylinder 12. The cylinder 12 is installed on the top of the lifting table 15, and the position of the cylinder 12 is controlled by the lifting table 15 to ensure that soot particles at different heights of the flame can be collected.

[0062] The air compressor 10 provides the gas power for the cylinder 12. The programmable time relay 9 controls the solenoid valve 11, and the solenoid valve 11 controls the movement of the cylinder 12, so that the TEM copper mesh 14 held by the self-locking tweezer 13 enters the flame to sample the soot particles.

[0063] The optical diagnostic system in step S2 includes an ICCD camera 16, a double imager 17, a sheet light mirror group 19, a dye laser 20, a Nd:YAG laser 21, a timing trigger 22, an ICCD controller 23, and a filter group.

[0064] The Nd:YAG laser 21 and the sheet light mirror group 19 cooperate with the frequency doubling crystal group to generate the second harmonic, and output a laser with a wavelength of 532 nm, which is used to excite the incandescence signal of the soot.

[0065] The Nd:YAG laser 21 and the dye laser 20 cooperate with the frequency doubling crystal group and the laser mirror group to generate lasers with two wavelengths of 266 nm and 283 nm, which are used to excite the polycyclic aromatic hydrocarbon and hydroxyl radical signals.

[0066] In this embodiment, for the sampling of soot particles in step S3, the program control solenoid valve 11 is set on the programmable time relay 9 to further control the cylinder 12, strictly controlling the residence time of the TEM copper mesh 14 in the flame to ensure the accuracy of sampling and subsequent analysis. The obtained soot particles are analyzed for their morphological structure using a transmission electron microscope to obtain data on fringe spacing, fringe width, and fringe curvature.

[0067] For the detection of the polycyclic aromatic hydrocarbon distribution, a 315 nm band-pass filter is selected to measure A1, a 400 nm band-pass filter is selected to measure A2 and A3, and a 492 nm band-pass filter is selected to measure A4. The above signals are captured and recorded by the ICCD camera 16, where A1 refers to benzene, A2 refers to dibenzene ring, A3 refers to tribenzene ring, and A4 refers to tetraphenyl ring.

[0068] For the detection of the hydroxyl distribution, the hydroxyl signal is processed by a band-pass filter of 300 - 320 nm and then captured and recorded by the ICCD camera 16.

[0069] For the detection of the soot distribution, the incandescent light signal radiated by the soot is filtered by 450 nm and 650 nm band-pass filters installed on the double image device 17, and then converted into two specific wavelength LII signals corresponding to the pixel positions, which are captured and recorded by the ICCD camera 16. A band-pass filter with a central wavelength of 440 nm is used to eliminate the interference of polycyclic aromatic hydrocarbon groups on the soot measurement, and the obtained LII signals are calculated using formula (1) and formula (2) to obtain the temperature T p and volume fraction f v ,

[0070] Formula (1):

[0071]

[0072] Formula (2):

[0073]

[0074] In the formula, λ 1,2 is the central wavelength of the selected band-pass filter, h is Planck's constant, c is the speed of light, k is Boltzmann's constant, E(m λ ) is the soot absorption function at wavelength λ, V Exp is the signal intensity output by the ICCD, G Exp is the gain of the detection system, w bis the thickness of the laser sheet light, and η(λ) is the ratio of the output signal to the intensity of the irradiated light.

[0075] Supplementary description: The soot formation process includes 1. the formation of soot precursors (polycyclic aromatic hydrocarbons); 2. soot nucleation; 3. surface growth of particles; 4. oxidation and fragmentation of particles. The formation of the first benzene ring is a key step in the formation of soot precursors, and A4 is a key species in soot nucleation. Therefore, these substances need to be detected.

[0076] As described above, it is only a preferred embodiment of the present invention, and does not impose any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and decorations made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A soot detection method for a MILD combustion system of tar-containing biomass gasification gas, characterized in that: The following steps are involved: S1. Install MILD combustion system of tar-containing biomass gasification gas; S2. Install the soot detection system; S3, detecting the soot generation process; The combustion system in step S1 comprises a controllable mixing evaporator for supplying tar-containing biomass gasification gas, a heating pipeline for conveying tar-containing biomass gasification gas, and a biomass gasification gas MILD burner (18) guided by oxygen-containing heat co-flow formed by a diffusion plane flame in an open space, wherein the controllable mixing evaporator evaporates tar into gas and mixes it evenly with the biomass gasification gas, and supplies it to the biomass gasification gas MILD burner (18) through the heating pipeline, and the biomass gasification gas MILD burner (18) guided by the diffusion plane flame increases the initial temperature, reduces the ignition delay time, and increases the chemical reaction time through heat co-flow to achieve MILD combustion of the biomass gasification gas; The detection system in step S2 includes a thermophoresis sampling system and an optical diagnostic system, wherein the thermophoresis sampling system collects soot particles at different positions in the flame, and the optical diagnostic system semi-quantitatively measures the concentrations of polycyclic aromatic hydrocarbons, hydroxyl groups and soot in the open space flame; During the detection in step S3, soot particle sampling, soot distribution detection, polycyclic aromatic hydrocarbon distribution detection and hydroxyl distribution detection are performed in sequence.

2. A soot detection method for a MILD combustion system of tar-containing biomass gasification gas according to claim 1, characterized in that: The controllable mixed evaporator in step S1 comprises a data control module (1), a liquid flow meter (2), a mixed evaporator (6) and a gas flow meter (8), wherein the liquid flow meter (2), the mixed evaporator (6) and the gas flow meter (8) are all electrically connected to the data control module (1), one end of the liquid flow meter (2) is connected to the mixed evaporator (6) via a pipeline, and the other end is connected to a toluene bottle (4) via a pipeline, and the toluene bottle (4) is connected to a centrifugal pump (3) via a pipeline, one end of the gas flow meter (8) is connected to the mixed evaporator (6) via a pipeline, and the other end is connected to a biomass gasification gas cylinder (7) via a pipeline; The toluene liquid in the toluene bottle (4) is connected to the mixing evaporator (6) through the liquid flow meter (2) under nitrogen pressure, and the biomass gasification gas in the biomass gasification gas bottle (7) is connected to the mixing evaporator (6) through the gas flow meter (8). Then, a heating pipeline is used to connect the outlet of the mixing evaporator (6) and the main fuel inlet of the biomass gasification gas MILD burner (18). Under the control of the data control module (1), the gas and liquid flow rates and evaporation temperature are regulated to achieve the evaporation of different types of tar and the mixing of different proportions with the biomass gasification gas.

3. A soot detection method for a MILD combustion system of tar-containing biomass gasification gas as claimed in claim 2, characterized in that: The mixing evaporator (6) comprises a heating chamber and a storage chamber, wherein the heating chamber heats and mixes the mixture of atomized gas and liquid sprayed therein and evaporates the mixture, and the storage chamber temporarily stores the vaporized mixed gas; The temperature of the heating chamber is not lower than 110.6° C. to ensure the evaporation of toluene.

4. A soot detection method for a MILD combustion system of tar-containing biomass gasification gas as claimed in claim 2, characterized in that: A heating tape (5) is wound around the heating pipeline, and the heating tape (5) is tightly spirally wound, and its heating temperature is not lower than the boiling point of the evaporated liquid at the corresponding pressure, so as to ensure that the evaporated liquid will not condense into liquid again and thus block the pipeline; The heating belt (5) comprises a temperature control component, an electric belt and a heat preservation layer. The temperature control component is used to adjust the temperature of the electric belt. The electric belt is a nickel-chromium alloy resistance wire with a silicone rubber outer layer. The heat preservation layer is made of glass fiber needle-punched felt.

5. A soot detection method for a MILD combustion system of tar-containing biomass gasification gas according to claim 1, characterized in that: In step S1, when installing the biomass gasification gas MILD burner (18), firstly position it and then fix it on the laboratory table; The biomass gasification gas MILD burner (18) is an open space two-stage combustion system, including tar-containing biomass gasification gas as a jet main fuel and high-temperature heat co-flow, the high-temperature heat co-flow is formed by a CH4 / H2-air lean combustion diffusion flame, and the generated oxygen-containing flue gas is used as an oxidant for the biomass gasification gas to form a high-temperature, low-oxygen dilution combustion condition to achieve MILD combustion. The open space ensures good optical system access and operability of invasive sampling operations; The hot co-flow fuel is a mixture of 50% CH4 and 50% H2, and the oxidant is a mixture of O2 and N2.

6. A soot detection method for a MILD combustion system of tar-containing biomass gasification gas according to claim 1, characterized in that: The thermophoresis sampling system in step S2 comprises a programmable time relay (9), an air compressor (10), a solenoid valve (11), a cylinder (12), a self-locking tweezer (13), a TEM copper mesh (14) and a lifting platform (15), wherein the self-locking tweezer (13) clamps the TEM copper mesh (14) and is connected to the end of the cylinder (12), the cylinder (12) is installed on the top of the lifting platform (15), and the position of the cylinder (12) is controlled by the lifting platform (15) to ensure that soot particles at different heights of the flame can be collected; The air compressor (10) provides gas power for the cylinder (12), the programmable time relay (9) controls the solenoid valve (11), and the solenoid valve (11) controls the movement of the cylinder (12), thereby allowing the TEM copper mesh (14) clamped by the self-locking tweezers (13) to enter the flame to sample the carbon smoke particles.

7. A soot detection method for a MILD combustion system of tar-containing biomass gasification gas as claimed in claim 6, characterized in that: The optical diagnostic system in step S2 comprises an ICCD camera (16), a double imager (17), a light sheet mirror group (19), a dye laser (20), a Nd:YAG laser (21), a timing trigger (22), an ICCD controller (23) and a filter group; The Nd:YAG laser (21) and the light-sheet mirror group (19) cooperate with the frequency-doubling crystal group to generate a second harmonic and output a laser with a wavelength of 532 nm, which is used to excite the incandescent signal of carbon smoke; The Nd:YAG laser (21) and the dye laser (20) cooperate with a frequency doubling crystal group and a laser reflector group to generate lasers with two wavelengths of 266nm and 283nm, which are used to excite polycyclic aromatic hydrocarbons and hydroxyl free radical signals.

8. A soot detection method for a MILD combustion system of tar-containing biomass gasification gas as claimed in claim 7, characterized in that: In step S3, for the sampling of soot particles, a program-controlled electromagnetic valve (11) is set on the programmable time relay (9) to further control the cylinder (12), strictly control the residence time of the TEM copper mesh (14) in the flame, and ensure the accuracy of sampling and subsequent analysis. The morphology structure of the obtained soot particles is analyzed by a transmission electron microscope to obtain the stripe spacing, stripe width and stripe curvature data; For the detection of the distribution of PAHs, a 315 nm bandpass filter was selected to measure A1, a 400 nm bandpass filter was selected to measure A2 and A3, and a 492 nm bandpass filter was selected to measure A4. The above signals were captured and recorded by an ICCD camera (16), wherein A1 refers to benzene, A2 refers to diphenyl ring, A3 refers to triphenyl ring, and A4 refers to tetraphenyl ring; For the detection of hydroxyl distribution, the hydroxyl signal was processed by a 300-320 nm bandpass filter and then captured and recorded by an ICCD camera (16).

9. A soot detection method for a MILD combustion system of tar-containing biomass gasification gas according to claim 7, characterized in that: In step S3, for the detection of soot distribution, the incandescent signal radiated by the soot is filtered by the 450nm and 650nm bandpass filters installed on the dual imager (17), and converted into two LII signals of specific wavelengths corresponding to the pixel position, and captured and recorded by the ICCD camera (16). A bandpass filter with a central wavelength of 440nm is used to eliminate the interference of polycyclic aromatic hydrocarbon groups on the soot measurement, and the obtained LII signal is calculated using formulas (1) and (2) to obtain the temperature T of the soot after stimulation. p and volume fraction f v , Formula (1): Formula (2): In the formula, λ 1,2 is the central wavelength of the selected bandpass filter, h is Planck's constant, c is the speed of light, k is the Boltzmann constant, E(m λ ) is the soot absorption function at wavelength λ, V Exp is the signal strength output by ICCD, G Exp is the gain of the detection system, w b is the optical thickness of the laser sheet, and η(λ) is the ratio of the output signal to the irradiated light intensity.

10. A soot detection method for a MILD combustion system of tar-containing biomass gasification gas according to claim 1, characterized in that: Before performing step S1, the gas flow rate of the biomass gasification gas and the liquid flow rate of the tar are calculated according to the required tar content of the gasification gas.

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