A soot detection method for tar-containing biomass gasification gas MILD combustion system

Abstract

The application discloses a tar-containing biomass gasification gas MILD combustion system carbon smoke detection method, and relates to the technical field of renewable low-carbon energy utilization and carbon smoke emission control. The application comprises the following steps: S1, installing a tar-containing biomass gasification gas MILD combustion system; S2, installing a carbon smoke detection system; and S3, detecting a carbon smoke generation process. The application realizes fuel supply of the tar-containing biomass gasification gas through a controllable mixing evaporator, guarantees that the tar participates in combustion in a gaseous form, detects the whole carbon smoke generation process under the MILD combustion by combining a thermal migration sampling system and an optical diagnosis system, solves the fuel supply problem caused by the tar, realizes the MILD combustion of the tar-containing biomass gasification gas, and further provides an effective detection method for the whole carbon smoke generation process under the MILD combustion, and provides a solution 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 in particular to a soot detection method for a tar-containing biomass gasification gas MILD combustion system. Background Art

[0002] Under the background of the “dual carbon” goal, renewable zero-carbon energy biomass energy has received extensive attention. Biomass gasification technology can absorb and efficiently utilize biomass waste. The biomass gasified gas (BGG) obtained by gasification can also fill the gas gap, and its importance is becoming increasingly prominent. Affected by the gasification raw materials, furnace type and medium, the composition of BGG is very complex. In addition to the combustible components CO, H2 and a small amount of C n H m In addition, it also contains a large amount of impurities such as non-combustible gases and tar, which leads to ignition difficulties, low combustion efficiency, unstable flames and NO under conventional combustion. x MILD (Moderate & Intense Low Oxygen Dilution) combustion is a combustion method achieved through high temperature preheating and low oxygen dilution, which can achieve low peak temperature and high average temperature in the furnace, thus having high thermal radiation efficiency and NO x The advantage of low emissions is that MILD combustion has been proven to reduce soot emissions from hydrocarbon fuel combustion. BGG's MILD combustion flame is stable and has good NOx reduction characteristics under all operating conditions.

[0003] Existing studies on the MILD combustion of BGG have only considered the simulated pure BGG gas and only focused on NO x and CO, two pollutants, but there is a lack of research on soot emissions caused by tar. Since tar will condense into a highly viscous liquid at room temperature, it is easy to adhere to and clog in pipelines and other transportation equipment, seriously affecting the transportation efficiency. At the same time, tar often participates in the combustion reaction in gaseous form during actual combustion. Currently, there is a lack of a fuel supply and transportation method for tar-containing biomass gasification gas, which mixes tar (or model compounds) of different concentrations with gasification gas in gaseous form for application in MILD combustion experiments or pilot studies. In addition, since the MILD combustion method has different temperature field and soot distribution characteristics from conventional combustion methods, its temperature field is usually more uniform, the temperature gradient is smaller, and the soot distribution is more dispersed in space and presents different particle size and concentration distribution characteristics. These characteristics make traditional single-point detection methods difficult to apply. Currently, there is a lack of a detection method for the entire process of soot generation under MILD combustion. Summary of the Invention

[0004] The present application mainly aims to provide a soot detection method for a tar-containing biomass gasification gas MILD combustion system, to realize accurate supply of the tar-containing biomass gasification gas, to ensure that the tar participates in combustion in a gaseous form, and to establish a tar-containing biomass gasification gas MILD combustion system by means of an oxygen-containing hot co-flow formed by a diffusion flat flame in an open space, to detect the whole process of soot from a gaseous precursor to soot particles by combining an invasive thermal phoresis sampling technology and an optical diagnosis technology of soot particles, and to study the generation and control mechanism of soot of the tar-containing biomass gasification gas in a MILD combustion mode.

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

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

[0007] S1, installing a tar-containing biomass gasification gas MILD combustion system;

[0008] S2, installing a soot detection system;

[0009] S3, detecting a soot generation process;

[0010] In the step S1, the combustion system comprises a controllable mixing evaporator for supplying the tar-containing biomass gasification gas, a heating pipeline for conveying the tar-containing biomass gasification gas, and a biomass gasification gas MILD combustor guided by an oxygen-containing hot co-flow formed by a diffusion flat flame in an open space, the controllable mixing evaporator evaporates the tar into a gas and uniformly mixes the tar with the biomass gasification gas, the tar-containing biomass gasification gas is supplied to the biomass gasification gas MILD combustor through the heating pipeline, and the biomass gasification gas MILD combustor guided by the diffusion flat flame realizes MILD combustion of the biomass gasification gas by improving an initial temperature, reducing an ignition delay time, and increasing a chemical reaction time through the hot co-flow.

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

[0012] In the step S3, the detection is sequentially performed on soot particle sampling, soot distribution detection, polycyclic aromatic hydrocarbon distribution detection, and hydroxyl group distribution detection.

[0013] Furthermore, the controllable mixing evaporator in step S1 includes a data control module, a liquid flow meter, a mixing evaporator, and a gas flow meter, wherein the liquid flow meter, the mixing evaporator, and the gas flow meter are all electrically connected to the data control module, one end of the liquid flow meter is connected to the mixing evaporator through a pipeline, and the other end is connected to a toluene bottle through a pipeline, and the toluene bottle is connected to a centrifugal pump through a pipeline, one end of the gas flow meter is connected to the mixing 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 mixing evaporator through the liquid flow meter under nitrogen pressure, and the biomass gasification gas in the biomass gasification gas cylinder is connected to the mixing evaporator through the gas flow meter. Then, a heating pipeline is used to connect the outlet of the mixing 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 evaporation temperature are regulated to achieve the evaporation of different types of tar and mixing them with the biomass gasification gas in different proportions.

[0015] Furthermore, the mixing evaporator includes a heating chamber and a storage chamber, wherein the heating chamber heats and mixes the atomized gas and liquid mixture sprayed thereinto and evaporates the mixture, and the storage chamber temporarily stores the vaporized mixed gas;

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

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

[0018] The heating belt includes a temperature control component, an electric belt and an insulation 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 an outer layer wrapped with silicone rubber. The insulation layer is made of glass fiber needle-punched felt.

[0019] Furthermore, in step S1, when installing the biomass gasification gas MILD burner, it is first positioned and then fixed on the experimental table;

[0020] The biomass gasification gas MILD burner 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-burn diffusion flame. The generated oxygen-containing flue gas serves as an oxidant for the biomass gasification gas, creating high-temperature, low-oxygen, diluted combustion conditions to achieve MILD combustion. The open space ensures good optical system access and operability of invasive sampling operations.

[0021] The hot co-flow fuel is a mixture of 50% CH4 and 50% H2, and the oxidant is a mixture of O2 and N2.

[0022] Further, the thermal migration sampling system in step S2 comprises a programmable time relay, an air compressor, a solenoid valve, a cylinder, a self-locking forceps, a TEM copper net and a lifting platform, the self-locking forceps clamping the TEM copper net is connected to the end of the cylinder, the cylinder is installed on the top of the lifting platform, and the position of the cylinder is controlled by the lifting platform, so that carbon soot particles at different heights of the flame can be collected.

[0023] The air compressor provides gas power for the cylinder, the programmable time relay controls the solenoid valve, the solenoid valve controls the movement of the cylinder, and then the TEM copper net clamped by the self-locking forceps enters the flame to sample the carbon soot particles.

[0024] Further, the optical diagnosis system in step S2 comprises an ICCD camera, a double imager, a sheet mirror group, a dye laser, a Nd:YAG laser, a time sequence trigger, an ICCD controller and a filter group.

[0025] The Nd:YAG laser and the sheet mirror group cooperate with a frequency doubling crystal group to generate a second harmonic, and output laser with a wavelength of 532 nm for exciting incandescence signals of carbon soot.

[0026] The Nd:YAG laser and the dye laser cooperate with a frequency doubling crystal group and a laser reflector group to generate laser with two wavelengths of 266 nm and 283 nm for exciting polycyclic aromatic hydrocarbon and hydroxyl radical signals.

[0027] Further, for sampling of the carbon soot particles in step S3, the program control solenoid valve is set on the programmable time relay to further control the cylinder, so as to strictly control the residence time of the TEM copper net in the flame, and ensure the accuracy of sampling and subsequent analysis, the obtained carbon soot particles are analyzed for morphology structure by a transmission electron microscope, and data of stripe spacing, stripe width and stripe curvature are obtained.

[0028] For 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, and the above signals are captured and recorded by the ICCD camera, wherein A1 refers to benzene, A2 refers to a two-ring benzene, A3 refers to a three-ring benzene, and A4 refers to a four-ring benzene.

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

[0030] Further, in step S3, for the detection of soot distribution, the incandescence signal radiated by soot is filtered by 450nm and 650nm bandpass filters installed on the double image device, and then converted into two specific wavelength LII signals corresponding to the pixel position, and recorded by the ICCD camera, a bandpass filter with a center wavelength of 440nm is used to eliminate the interference of polycyclic aromatic groups on soot measurement, and the obtained LII signal is calculated by using formula (1) and formula (2), so as to obtain the temperature T of the stimulated soot p And volume fraction f v ,

[0031] Formula (1):

[0032]

[0033] Formula (2):

[0034]

[0035] In the formula, λ 1,2 is the center 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 intensity output by the ICCD, G Exp is the gain of the detection system, w b is the thickness of the laser sheet, and η(λ) is the ratio of the output signal to the irradiation light intensity.

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

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

[0038] The present application is aimed at the characteristics of tar-containing biomass gasification gas that the tar content is uncertain and easy to condense, and through the precise regulation of gas and liquid flow, evaporation temperature and mixing ratio by the multi-module controllable mixing evaporator, different tar content of the biogasification gas fuel is realized, and the tar (or its model compound) is ensured to participate in combustion in liquid form;

[0039] The present application is aimed at the characteristics of the open space staged combustor that the invasive detection operation is convenient and the optical access is good, and combined with the thermal phoresis sampling technology and the optical diagnosis technology of soot particles, the detection of the whole process from the gas phase precursor to the soot particle generation is realized;

[0040] In view of the characteristics of MILD combustion conditions, where the flame temperature field is uniform and the soot distribution is more dispersed in space and presents different particle size and concentration distribution characteristics, the invention selects optical diagnostic technology 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] Fig. 1 Schematic diagram of the controllable mixing evaporator of the present invention.

[0042] Fig. 2 Schematic diagram of the thermophoresis sampling system of the present invention.

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

[0044] Explanation of the accompanying symbols: 1-data control module, 2-liquid flow meter, 3-centrifugal pump, 4-toluene bottle, 5-heating belt, 6-mixing evaporator, 7-biomass gasification gas cylinder, 8-gas flow meter, 9-programmable time relay, 10-air compressor, 11-solenoid valve, 12-cylinder, 13-self-locking tweezers, 14-TEM copper mesh, 15-lifting platform, 16-ICCD camera, 17-double imager, 18-biomass gasification gas MILD burner, 19-light mirror assembly, 20-dye laser, 21-Nd:YAG laser, 22-timing controller, 23-ICCD controller. DETAILED DESCRIPTION

[0045] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0046] Reference Figs. 1-3 This embodiment provides a soot detection method for a MILD combustion system of tar-containing biomass gasification gas, comprising the following steps:

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

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

[0049] S2. Install the soot detection system;

[0050] S3. Detecting the soot generation process;

[0051] The combustion system in step S1 includes a controllable mixing evaporator for supplying tar-containing biomass gasification gas, a heating pipeline for conveying tar-containing biomass gasification gas, and a MILD burner 18 for biomass gasification gas guided by oxygen-containing heat co-flow formed by a diffusion plane flame in an open space. The controllable mixing evaporator evaporates the tar into gas and mixes the gas with the biomass gasification gas uniformly, and supplies the gas to the MILD burner 18 through the heating pipeline. The MILD burner 18 for biomass gasification gas guided by the diffusion plane flame increases the initial temperature, reduces the ignition delay time, and increases the chemical reaction time by heat co-flow to achieve MILD combustion of the biomass gasification gas.

[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 hydrocarbons distribution detection and hydroxyl distribution detection are sequentially performed.

[0054] In this embodiment, the controllable mixing evaporator in step S1 includes a data control module 1, a liquid flow meter 2, a mixing evaporator 6, and a gas flow meter 8. The liquid flow meter 2, the mixing 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 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 flow meter 8 is connected to the mixing evaporator 6 through a pipeline, and the other end is connected to a biomass gasification 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 flow meter 2 under nitrogen pressure, and the biomass gasification gas in the biomass gasification gas cylinder 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 mixing them with the biomass gasification gas in different proportions.

[0056] Preferably, the mixing evaporator 6 includes a heating chamber and a storage chamber. The heating chamber heats and mixes the mixture of atomized gas and liquid sprayed thereinto 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.

[0057] As preferred, the heating pipeline is wound with a heating belt 5, the heating belt 5 is tightly wound in a spiral shape, the 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 be condensed into liquid again to block the pipeline; the heating belt 5 comprises a temperature control assembly, an electric heating belt and a thermal insulation layer, the temperature control assembly is used to control the temperature of the electric heating belt, the electric heating belt is a nickel-chromium alloy resistance wire wrapped with silicon rubber, and the thermal insulation layer is glass fiber needle punching felt.

[0058] In the embodiment, when the biomass gasification gas MILD combustor 18 is installed in step S1, the biomass gasification gas MILD combustor 18 is first positioned and then fixed on the experimental table;

[0059] The biomass gasification gas MILD combustor 18 is an open space two-stage combustion system, which comprises a tar-containing biomass gasification gas as a jet main fuel and a high-temperature hot co-flow, the high-temperature hot co-flow is formed by a CH4 / H2-air lean diffusion flame, and the generated oxygen-containing flue gas is used as an oxidant of the biomass gasification gas, so as to form a high-temperature and low-oxygen dilution combustion condition, realize MILD combustion, and ensure the operability of the optical system access and the invasive sampling operation.

[0060] In the embodiment, the fuel of the hot co-flow is a mixed gas composed of 50% CH4 and 50% H2, and the oxidant is a mixed gas of O2 and N2.

[0061] In the embodiment, the thermal-phoresis sampling system in step S2 comprises a programmable time relay 9, an air compressor 10, an electromagnetic valve 11, a gas cylinder 12, a self-locking tweezers 13, a TEM copper net 14 and a lifting platform 15, the self-locking tweezers 13 clamping the TEM copper net 14 is connected to the end of the gas cylinder 12, the gas cylinder 12 is installed on the top of the lifting platform 15, the position of the gas cylinder 12 is controlled by the lifting platform 15, so as to ensure that the carbon soot particles at different heights of the flame can be collected.

[0062] The air compressor 10 provides the gas power of the gas cylinder 12, the programmable time relay 9 controls the electromagnetic valve 11, the electromagnetic valve 11 controls the movement of the gas cylinder 12, and then the TEM copper net 14 clamped by the self-locking tweezers 13 enters the flame to sample the carbon soot particles.

[0063] The optical diagnosis system in step S2 comprises an ICCD camera 16, a double image device 17, a sheet light mirror group 19, a dye laser 20, a Nd:YAG laser 21, a time sequence 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 a second harmonic, and output a laser with a wavelength of 532 nm, which is used to excite the incandescence signal of the carbon soot;

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

[0066] In this embodiment, the sampling of soot particles in step S3 is controlled by setting program control solenoid valve 11 on programmable time relay 9 to further control cylinder 12, strictly control the residence time of TEM copper mesh 14 in the flame, and ensure the accuracy of sampling and subsequent analysis. The obtained soot particles are analyzed by transmission electron microscope to obtain the data of stripe spacing, stripe width and stripe curvature;

[0067] For detection of polycyclic aromatic hydrocarbon distribution, 315 nm bandpass filter is selected to measure A1, 400 nm bandpass filter is selected to measure A2 and A3, and 492 nm bandpass filter is selected to measure A4. The above signals are captured and recorded by ICCD camera 16, wherein A1 refers to benzene, A2 refers to biphenyl ring, A3 refers to triphenyl ring, and A4 refers to tetraphenyl ring.

[0068] For detection of hydroxyl distribution, the hydroxyl signal is captured and recorded by ICCD camera 16 after being processed by 300-320 nm bandpass filter.

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

[0070] Formula (1):

[0071]

[0072] Formula (2):

[0073]

[0074] In the formula, λ 1,2 is the center 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 intensity output by ICCD, G Exp is the gain of the detection system, and w bFor laser sheet light thickness, η(λ) is the ratio of output signal and irradiation light intensity.

[0075] Supplementary explanation: The soot formation process includes 1. Soot precursor (polycyclic aromatic hydrocarbon) formation; 2. Soot nucleation; 3. Surface growth of particles; 4. Particle oxidation and fragmentation. The generation of the first benzene ring is the key step of soot precursor formation, and A4 is the key species of soot nucleation, so these substances are detected.

[0076] The above description is only the preferred embodiment of the present application, and does not limit the technical scope of the present application in any way, so any slight modification, equivalent change and modification of the above embodiment according to the technical essence of the present application still belongs to the scope of the technical solution of the present application.

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 includes a controllable mixing evaporator for supplying tar-containing biomass gasification gas, a heating pipeline for conveying tar-containing biomass gasification gas, and a MILD burner (18) for guiding oxygen-containing heat co-flow formed by a diffusion plane 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 (18) for biomass gasification gas through the heating pipeline. The MILD burner (18) for guiding the biomass gasification gas 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. The thermophoresis sampling system collects soot particles at different locations in the flame. 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 hydrocarbons distribution detection and hydroxyl distribution detection are sequentially performed.

2. The soot detection method for a MILD combustion system of tar-containing biomass gasification gas according to claim 1, characterized in that: The controllable mixing evaporator in step S1 comprises a data control module (1), a liquid flow meter (2), a mixing evaporator (6) and a gas flow meter (8), wherein the liquid flow meter (2), the mixing 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 mixing evaporator (6) through a pipeline, and the other end is connected to a toluene bottle (4) through a pipeline, and the toluene bottle (4) is connected to a centrifugal pump (3) through a pipeline, one end of the gas flow meter (8) is connected to the mixing evaporator (6) through a pipeline, and the other end is connected to a biomass gasification gas cylinder (7) through 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. The soot detection method for a MILD combustion system of tar-containing biomass gasification gas according to 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 atomized gas and liquid mixture 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 evaporation of toluene.

4. The soot detection method for a MILD combustion system of tar-containing biomass gasification gas according to 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 an outer layer wrapped with silicone rubber. The heat preservation layer is made of glass fiber needle-punched felt.

5. The 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), first 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-burn diffusion flame, and the generated oxygen-containing flue gas is used as an oxidant for the biomass gasification gas, forming a high-temperature, low-oxygen, diluted combustion condition to achieve MILD combustion. The open space ensures good optical system access and operability of invasive sampling operations; The co-current fuel is a mixture of 50% CH4 and 50% H2, and the oxidant is a mixture of O2 and N2.

6. The 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 tweezers (13), a TEM copper mesh (14) and a lifting platform (15), wherein the self-locking tweezers (13) clamp the TEM copper mesh (14) and are connected to the end of the cylinder (12), and the cylinder (12) is installed on the top of the lifting platform (15). 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 carbon soot particles.

7. The soot detection method for a MILD combustion system of tar-containing biomass gasification gas according to claim 6, characterized in that: The optical diagnostic system in step S2 includes an ICCD camera (16), a double imager (17), a light-sheet mirror assembly (19), a dye laser (20), an Nd:YAG laser (21), a timing trigger (22), an ICCD controller (23), and a filter assembly; The Nd:YAG laser (21) and the optical 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 the 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. The 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 sampling of soot particles, a program-controlled 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 morphology of the soot particles obtained is analyzed using a transmission electron microscope to obtain data on fringe spacing, fringe width and fringe curvature; For the detection of PAH distribution, 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), where 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. The 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 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, which are 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 after the soot is excited. p and volume fraction f v , Formula (1): Formula (2): Where 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 illumination light intensity.

10. The 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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