A coal-fired heavy metal detection and analysis device and method based on LIBS-LAAS

Abstract

The application belongs to the field of heavy metal detection, and discloses a coal-fired heavy metal detection and analysis device and method based on LIBS-LAAS, which comprises a pulsed laser excitation unit, a wavelength-tunable continuous laser resonance absorption unit, a coaxial signal acquisition unit, a paraxial signal acquisition unit, a control and analysis unit and a displacement detection platform; the pulsed laser excitation unit comprises a pulsed laser, which emits pulsed laser and ablates a sample to generate plasma; the wavelength-tunable continuous laser resonance absorption unit comprises a wavelength-tunable continuous laser for emitting continuous laser to the plasma; the coaxial signal acquisition unit comprises a first spectrometer, which acquires LAAS absorption spectrum information of the continuous laser passing through the plasma. Through the application, the interference of the spectrum line overlap of the LIBS detection of heavy metal elements can be broken through, the spectrum information of multiple heavy metal elements in the coal sample can be acquired at the same time, the rapid detection and analysis of the heavy metal elements can be realized, and the accuracy of the heavy metal detection and analysis result is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of heavy metal detection, and more particularly relates to a coal-fired heavy metal detection and analysis device and method based on LIBS-LAAS. BACKGROUND

[0002] Pollutants such as smoke dust, sulfur dioxide, nitrogen oxides and the like emitted by coal combustion have caused great harm to the ecological environment of China, and coal-fired power plants are the main emission source of coal combustion pollutants. With the increasing demand for the quality of the ecological environment, the emission and control of heavy metal pollutants in coal have gradually become the focus of attention. In recent years, with the completion of ultra-low emission transformation of coal-fired power plants, the coal power industry has made remarkable achievements in the control of conventional pollutant emissions, and the emission has been significantly reduced.

[0003] The whole-process monitoring of coal-fired heavy metal pollutants is an important means to deeply understand their emission status, master their form, structure and distribution law, and is also an important basis for developing heavy metal control technology. Due to the multiple types, low concentration and complex form of coal-fired heavy metal pollutants, the detection is difficult.

[0004] Laser-induced breakdown spectroscopy (LIBS) is a general in-situ analysis technology, which is widely used in Mars exploration, geological monitoring, water quality detection and the like. This technology can infer the element composition and content of a substance according to the wavelength and intensity information of element spectral information, has the advantages of rapidity, in-situ analysis, full-element analysis and the like, and plays an important role in the detection of heavy metal elements. However, due to the fact that the heavy metal elements in coal, soil and the like are rich, the laser-induced breakdown spectroscopy detection has serious spectral line overlap, and the spectral information of all heavy metal elements cannot be obtained, resulting in inaccurate detection and analysis results. SUMMARY

[0005] In view of the defects of the prior art, the present application provides a coal-fired heavy metal detection and analysis device and method based on LIBS-LAAS, aiming at solving the problem that the laser-induced breakdown spectroscopy detection of heavy metal elements has serious spectral line overlap, resulting in inaccurate coal-fired heavy metal detection and analysis results.

[0006] The application provides a coal-fired heavy metal detection and analysis device based on LIBS-LAAS, which specifically comprises a pulsed laser excitation unit, a wavelength-tunable continuous laser resonance absorption unit, a coaxial signal acquisition unit, a paraxial signal acquisition unit, a control and analysis unit, and a displacement detection platform for placing a sample; the pulsed laser excitation unit comprises a pulsed laser, which is used for emitting pulsed laser to the sample on the displacement detection platform to generate plasma; the wavelength-tunable continuous laser resonance absorption unit comprises a wavelength-tunable continuous laser for emitting continuous laser to the plasma, and the direction in which the continuous laser irradiates the plasma is perpendicular to the direction in which the pulsed laser irradiates the sample; the coaxial signal acquisition unit comprises a first spectrometer, which is used for acquiring LAAS absorption spectrum information of the continuous laser passing through the plasma; the paraxial signal acquisition unit comprises a second spectrometer, which is used for acquiring LIBS spectrum information emitted by the plasma; the control and analysis unit is connected with the pulsed laser, the first spectrometer, the second spectrometer, and the displacement detection platform, and is used for controlling the pulsed laser to emit pulsed laser, controlling the first spectrometer and the second spectrometer to acquire spectrum information and simultaneously analyzing the acquired spectrum information, and controlling the displacement detection platform to adjust the position of the sample.

[0007] Compared with the prior art, the above technical scheme conceived by the application can overcome the problem that the spectral line overlap interference of LIBS detection of heavy metal elements affects the detection result, realize plasma spectrum spectral line decoupling by using the LAAS atomic selective absorption characteristic, detect the heavy metal elements with spectral line overlap, overcome the spectral line interference, can obtain the spectrum information of all heavy metal elements in the coal sample, and has the beneficial effect of improving the accuracy of heavy metal detection and analysis result.

[0008] As a further preferred, the pulsed laser excitation unit further comprises a first laser focusing mirror, and the pulsed laser is focused on the sample surface through the first laser focusing mirror.

[0009] As a further preferred, the wavelength-tunable continuous laser resonance absorption unit further comprises a second laser focusing mirror, and the continuous laser is focused on the plasma through the second laser focusing mirror, and the focal point of the continuous laser coincides with the focal point of the plasma generated by the pulsed laser.

[0010] As a further preferred, the coaxial signal acquisition unit further comprises a first acquisition focusing mirror and a first signal collection optical fiber, the first signal collection optical fiber is connected with the first spectrometer, and the continuous laser passing through the plasma is focused on the end face of the first signal collection optical fiber through the first acquisition focusing mirror.

[0011] As a further preferred, the paraxial signal collection unit further comprises a second collection focusing mirror and a second signal collection fiber, the second signal collection fiber is connected with the second optical spectrum analyzer, and the plasma emission light is focused on the end face of the second signal collection fiber through the second collection focusing mirror.

[0012] As a further preferred, the control and analysis unit comprises a timing controller and a computer, the pulse laser, the first optical spectrum analyzer, the second optical spectrum analyzer and the displacement detection platform are connected with the timing controller, and the first optical spectrum analyzer and the second optical spectrum analyzer are connected with the computer.

[0013] As a further preferred, the first laser focusing mirror, the second laser focusing mirror, the first collection focusing mirror and the second collection focusing mirror are all plano-convex lenses, and the planes are all directed to the displacement detection platform.

[0014] As a further preferred, the first signal collection fiber comprises a plurality of fiber cables inside.

[0015] As a further preferred, the incident end face of the first signal collection fiber is in a circular structure, and the exit end face is in a strip-shaped structure.

[0016] The application provides a coal heavy metal detection and analysis method based on LIBS-LAAS, which is realized by using the above detection and analysis device and comprises the following steps.

[0017] S1: a pulse laser emits pulse laser ablation to a sample to be detected to generate plasma;

[0018] S2: a second optical spectrum analyzer collects LIBS spectrum information generated by the plasma, and a control and analysis unit analyzes and compares the LIBS spectrum information to obtain spectrum information of part of heavy metal elements in the sample;

[0019] S3: the wavelength of continuous laser emitted by a wavelength-tunable continuous laser is determined according to one of the heavy metal elements whose spectrum information is not obtained, and the wavelength-tunable continuous laser emits continuous laser of the wavelength to the plasma;

[0020] S4: a first optical spectrum analyzer collects LAAS absorption spectrum information generated after the continuous laser passes through the plasma, and a control and analysis unit obtains the LAAS absorption spectrum information to obtain spectrum information of one of the heavy metal elements;

[0021] S5: a displacement detection platform adjusts the position of the sample to be detected, and a pulse laser emits pulse laser ablation to the sample to generate plasma;

[0022] S6: steps S3-S5 are repeated until spectrum information of all heavy metal elements to be detected in the sample is obtained, so as to complete the detection and analysis of the coal heavy metal.

[0023] Overall, compared with the prior art, the above technical solutions conceived by the present application mainly have the following technical advantages:

[0024] The present application aims at the problem that spectral line overlap interference will affect the detection result of LIBS detection of heavy metal elements, uses the atomic selective absorption characteristic of LAAS to realize plasma spectrum decoupling, detects heavy metal elements with spectral line overlap, overcomes the influence of spectral line interference, can obtain spectral information of all heavy metal elements in the coal sample, and improves the accuracy of heavy metal detection and analysis results.

[0025] The present application proposes multi-spectral fusion detection of heavy metal elements. In view of the limitation that LIBS can only obtain early emission spectrum of the plasma, the present application simultaneously collects multi-element emission and absorption spectrum of the laser-induced plasma by optical intelligent scanning absorption of the sample, compensates for the absence of the LIBS to the late signal of the plasma, thereby realizing mutual complementation of the early LIBS signal and the late LAAS signal of the plasma, forming cooperative detection of the plasma emission and absorption signals, and achieving the purpose of in-situ and rapid detection of heavy metal elements in the coal. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a schematic diagram of the overall structure provided by the embodiment of the present application.

[0027] In all the drawings, the same reference signs are used to represent the same elements or structures, wherein:

[0028] 1, pulsed laser excitation unit; 11, pulsed laser; 12, first laser focusing mirror; 13, laser reflecting mirror; 2, wavelength tunable continuous laser resonance absorption unit; 21, wavelength tunable continuous laser; 22, second laser focusing mirror; 3, coaxial signal acquisition unit; 31, first spectrometer; 32, first acquisition focusing mirror; 33, first signal collection optical fiber; 4, side-shaft signal acquisition unit; 41, second spectrometer; 42, second acquisition focusing mirror; 43, second signal collection optical fiber; 5, control and analysis unit; 51, time sequence controller; 52, computer; 6, displacement detection platform. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present application more clear and explicit, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0030] Material identification, classification, qualitative and quantitative analysis can be carried out by LIBS technology. Developing reliable laser-induced breakdown spectroscopy (LIBS) heavy metal detection technology has great application prospects in the field of pollution control. In the current LIBS coal heavy metal detection, there is no efficient and low-cost solution to the problem of incomplete heavy metal detection results caused by spectral line overlap. According to the research, laser ablation absorption spectroscopy (LAAS) uses resonance absorption characteristics to realize element selective detection, which has the advantages of rapidity, remote, low cost and so on. Therefore, the LIBS-LAAS detection technology is adopted in the application, and the LIBS detection result is assisted by LAAS detection to overcome the spectral peak interference problem between different elements.

[0031] The application discloses a coal heavy metal detection and analysis device based on LIBS-LAAS.

[0032] Reference Figure 1 A coal heavy metal detection and analysis device based on LIBS-LAAS is used for detecting and analyzing heavy metal elements in a coal sample, obtaining spectral information of the heavy metal elements, and analyzing content, characteristics and other data of the heavy metal elements. The spectral information of the heavy metal elements in the sample is obtained through the detection and analysis device, so that the composition and content of the heavy metal elements are analyzed according to the spectral information. The device comprises a pulsed laser excitation unit 1, a wavelength-tunable continuous laser resonance absorption unit 2, a coaxial signal acquisition unit 3, a side-shaft signal acquisition unit 4, a control and analysis unit 5 and a displacement detection platform 6 for placing a sample.

[0033] Firstly, the coal pressed sample is placed on the displacement detection platform 6, then the pulsed laser excitation unit 1 emits pulsed laser to ablate the coal pressed sample to generate plasma, the side-shaft signal acquisition unit 4 acquires LIBS spectral information generated by the plasma, the coaxial signal acquisition unit 3 acquires LAAS absorption spectral information generated after the continuous laser passes through the plasma, and the side-shaft signal acquisition unit 4 and the coaxial signal acquisition unit 3 transmit the acquired spectral information to the control and analysis unit 5. Since the survival time of the plasma is short, after the spectral detection of the first ablation point is completed, the control and analysis unit 5 controls the displacement detection platform 6 to move the sample to the next point, and the pulsed laser ablates to generate new plasma. Since the LAAS detection detects one element at a time, the wavelength of the continuous laser is adjusted to detect different heavy metal elements. Therefore, after the sample is moved, the wavelength of the continuous laser needs to be adjusted to detect new heavy metal elements. The wavelength of the continuous laser is determined according to the heavy metal elements to be detected. The side-shaft signal acquisition unit 4 and the coaxial signal acquisition unit 3 continue to acquire spectral information and transmit the spectral information to the control and analysis unit 5. The above process is repeated until the spectral information of the heavy metal elements in the sample to be detected is acquired.

[0034] The collected LIBS-LAAS signal is further analyzed and processed by the control and analysis unit 5, that is, the spectral information of the heavy metal element to be detected in the sample is obtained, and then the element composition and content of the substance are analyzed and inferred according to the spectral information; the non-overlapping spectral information can be obtained according to the LIBS spectral information, and the non-overlapping spectral information is compared with the heavy metal spectral information of the nist database to determine the spectral information of the corresponding heavy metal element in the non-overlapping spectral information; then the spectral information of the remaining heavy metal element is obtained according to the LAAS spectral information, and finally the content of the heavy metal element can be determined according to the spectral information.

[0035] In this embodiment, the displacement detection platform 6 is a three-dimensional adjustable automatic displacement table, the sample is placed on the surface of the displacement table, the sample is moved on the X, Y and Z axes by the displacement table, the plane position of the sample to be detected is changed to ensure that the same position is not ablated repeatedly, and the height of the sample to be detected is changed to ensure that the pulsed laser is focused on the surface of the sample. The three-dimensional adjustable automatic displacement table uses a device commonly used in the art, and the principle thereof will not be described here.

[0036] In order to realize the emission of pulsed laser to the sample, the pulsed laser excitation unit 1 includes a pulsed laser 11 and a first laser focusing mirror 12. The pulsed laser 11 is used to emit high-energy pulsed laser to the sample on the displacement detection platform. The sample is ablated by the pulsed laser to generate plasma. The first laser focusing mirror 12 is located between the pulsed laser 11 and the sample. The pulsed laser is focused on the surface of the sample by the first laser focusing mirror 12, so as to realize sample ablation and generate plasma. The plasma emits light and generates LIBS spectral information.

[0037] In order to realize the emission of continuous laser to the sample, the wavelength tunable continuous laser resonance absorption unit 2 includes a wavelength tunable continuous laser 21 and a second laser focusing mirror 22. The wavelength tunable continuous laser 21 is used to emit continuous laser to the plasma. The second laser focusing mirror 22 is located between the wavelength tunable continuous laser 21 and the sample. The continuous laser is focused on the plasma by the second laser focusing mirror 22. The focus of the continuous laser coincides with the focus of the plasma generated by the pulsed laser, so that the ground state atoms resonate and absorb the continuous laser, and LAAS absorption spectral information is generated.

[0038] The direction of the pulsed laser irradiated on the sample is perpendicular to the direction of the continuous laser irradiated on the plasma. The continuous laser is arranged horizontally, and the pulsed laser is arranged vertically. The pulsed laser 11 is arranged above the wavelength tunable continuous laser 21 and arranged parallel to each other. The pulsed laser is reflected by the laser reflecting mirror 13 and irradiated on the sample, and acts vertically on the surface of the sample.

[0039] The coaxial signal acquisition unit 3 comprises a first spectrometer 31, a first acquisition focusing mirror 32 and a first signal collection optical fiber 33. The first signal collection optical fiber 33 is connected with the first spectrometer 31. The first acquisition focusing mirror 32 is located between the sample and the first signal collection optical fiber 33. The first acquisition focusing mirror 32 and the second laser focusing mirror 22 are located on the same axis. The continuous laser passing through the plasma is focused on the end face of the first signal collection optical fiber 33 through the first acquisition focusing mirror 32, so that the first spectrometer 31 acquires the LAAS absorption spectrum information. The incident end face of the first signal collection optical fiber 33 is in a circular structure. The outgoing end face of the first signal collection optical fiber 33 is in a strip-shaped structure. The first signal collection optical fiber 33 internally comprises a plurality of optical fiber cables, 19 200 μm optical fiber cables in this embodiment. The 19 200 μm optical fiber cables are arranged in a circular ring around the incident end face of the first signal collection optical fiber 33. The outgoing end face is in a 1x19 strip-shaped arrangement, so that the collected signal is stronger.

[0040] The paraaxial signal acquisition unit 4 comprises a second spectrometer 41, a second acquisition focusing mirror 42 and a second signal collection optical fiber 43. The second signal collection optical fiber 43 is connected with the second spectrometer 41. The plasma emission light is focused on the end face of the second signal collection optical fiber 43 through the second acquisition focusing mirror 42, so that the second spectrometer 41 acquires the LIBS spectrum information.

[0041] The first laser focusing mirror 12, the second laser focusing mirror 22, the first acquisition focusing mirror 32 and the second acquisition focusing mirror 42 are all plano-convex lenses of ultraviolet fused quartz. The planes are all directed to the displacement detection platform 6.

[0042] The control and analysis unit 5 is connected with the pulsed laser 11, the first spectrometer 31, the second spectrometer 41 and the displacement detection platform 6, and is used for controlling the pulsed laser 11 to emit pulsed laser, and is used for controlling the first spectrometer 31 and the second spectrometer 41 to collect spectral information and analyze the collected spectral information; specifically, the control and analysis unit 5 comprises a timing controller 51 and a computer 52, the pulsed laser 11, the first spectrometer 31 and the second spectrometer 41 are all connected with the timing controller 51, and the first spectrometer 31 and the second spectrometer 41 are both connected with the computer 52; the timing controller 51 controls the pulsed laser 11 to ablate the sample to generate plasma, the timing controller 51 controls the first spectrometer 31 and the second spectrometer 41 to collect spectral information at a specific time sequence, the computer 52 is used for reading and analyzing the emission and absorption spectral information, and the heavy metal elements in the sample to be detected are obtained, the displacement detection platform 6 is connected with the timing controller 51, and the displacement detection platform 6 is controlled to work by the timing controller 51, and the position of the sample is moved for detection again.

[0043] The application also discloses a coal heavy metal detection and analysis method based on LIBS-LAAS.

[0044] The application also discloses a coal heavy metal detection and analysis method based on LIBS-LAAS.

[0045] S1: the timing controller 51 controls the pulsed laser 11 to emit pulsed laser ablation to generate plasma, in the embodiment, the heavy metal elements to be detected in the sample include Cr, Pb, Cu, Cd, As, Se and Hg;

[0046] S2: the timing controller 51 controls the second spectrometer 41 to collect LIBS spectral information generated by the plasma and transmit the LIBS spectral information to the computer 52, the computer 52 analyzes and compares the LIBS spectral information to obtain spectral information of part of the heavy metal elements in the sample, specifically, the non-overlapping spectral information is compared with the heavy metal spectral information of the nist database to determine the spectral information of the corresponding heavy metal elements in the non-overlapping spectral information, such as Cr, Pb and Cu;

[0047] S3: after the LIBS spectral information is analyzed and compared according to step S2, one of the heavy metal elements (Cd, As, Se and Hg) whose spectral information is not obtained determines the wavelength of the continuous laser emitted by the wavelength tunable continuous laser 21, such as the continuous laser wavelength of 228.8nm when detecting Cd, and the timing controller 51 controls the wavelength tunable continuous laser 21 to emit the continuous laser with the wavelength to the plasma;

[0048] S4: The timing controller 51 controls the first spectrometer 31 to collect the LAAS absorption spectrum information generated after the continuous laser passes through the plasma and transmits the LAAS absorption spectrum information to the computer 52, and the computer 52 acquires the LAAS absorption spectrum information, which corresponds to the spectrum information of one heavy metal element;

[0049] S5: The timing controller 51 controls the displacement detection platform 6 to adjust the position of the sample to be detected, and the pulsed laser 11 emits pulsed laser ablation to the sample to generate plasma;

[0050] S6: Steps S3-S5 are repeated until the spectrum information of all heavy metal elements to be detected in the sample is acquired, so as to complete the detection and analysis of the heavy metals in the coal, that is, after the position of the sample is changed, new LAAS absorption spectrum information is collected to acquire the spectrum information of the next heavy metal element, so as to complete the acquisition of the spectrum information of all heavy metal elements to be detected, and the content of the heavy metal element can be determined according to the spectrum information.

[0051] It should be understood that the expressions such as "include" and "may include" used in the present application represent the existence of the disclosed functions, operations or constituent elements, and do not limit one or more additional functions, operations and constituent elements. In the present application, terms such as "include" and / or "have" can be interpreted to mean that specific features, numbers, operations, constituent elements, components or combinations thereof are present, but cannot be interpreted to exclude the existence or addition of one or more other features, numbers, operations, constituent elements, components or combinations thereof.

[0052] It should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0053] In addition, the terms "first" and "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first" and "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise specifically limited.

[0054] In this application, unless otherwise clearly indicated and limited, the terms "mounting", "connection", "connecting", "fixing" and the like should be interpreted broadly, for example, can be fixed connection, can also be detachable connection, or integrally connected; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0055] Those skilled in the art can understand that the above only describes the preferred embodiments of the present application, and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A LIBS-LAAS-based coal-fired heavy metal detection and analysis device, characterized in that, The device comprises a pulsed laser excitation unit (1), a wavelength-tunable continuous laser resonance absorption unit (2), a coaxial signal acquisition unit (3), a paraxial signal acquisition unit (4), a control and analysis unit (5), and a displacement detection platform (6) for placing samples. The pulsed laser excitation unit (1) comprises a pulsed laser (11) for emitting pulsed laser to samples on the displacement detection platform (6) to generate plasma. The wavelength-tunable continuous laser resonance absorption unit (2) comprises a wavelength-tunable continuous laser (21) for emitting continuous laser to the plasma, and the direction of the continuous laser irradiating on the plasma is perpendicular to the direction of the pulsed laser irradiating on the samples. The coaxial signal acquisition unit (3) comprises a first spectrometer (31) for acquiring LAAS absorption spectrum information generated by the continuous laser passing through the plasma. The paraxial signal acquisition unit (4) comprises a second spectrometer (41) for acquiring LIBS spectrum information generated by the plasma. The control and analysis unit (5) is connected with the pulsed laser (11), the first spectrometer (31), the second spectrometer (41), and the displacement detection platform (6), and is used for controlling the pulsed laser (11) to emit pulsed laser, controlling the first spectrometer (31) and the second spectrometer (41) to acquire spectrum information and analyzing the acquired spectrum information, and controlling the displacement detection platform (6) to adjust the position of the samples.

2. The LIBS-LAAS-based coal-fired heavy metal detection and analysis device according to claim 1, characterized in that, The pulsed laser excitation unit (1) further comprises a first laser focusing mirror (12), and the pulsed laser is focused on the surface of the samples through the first laser focusing mirror (12).

3. The LIBS-LAAS based coal-fired heavy metal detection and analysis device according to claim 2, wherein, The wavelength-tunable continuous laser resonance absorption unit (2) further comprises a second laser focusing mirror (22), and the continuous laser is focused on the plasma through the second laser focusing mirror (22), and the focal point of the continuous laser coincides with the focal point of the plasma generated by the pulsed laser.

4. The LIBS-LAAS-based coal-fired heavy metal detection and analysis device according to claim 3, characterized in that, The coaxial signal acquisition unit (3) further comprises a first acquisition focusing mirror (32) and a first signal collection optical fiber (33), the first signal collection optical fiber (33) is connected with the first spectrometer (31), and the continuous laser passing through the plasma is focused on the end face of the first signal collection optical fiber (33) through the first acquisition focusing mirror (32).

5. The LIBS-LAAS based coal-fired heavy metal detection and analysis device according to claim 4, characterized in that, The paraxial signal acquisition unit (4) further comprises a second acquisition focusing mirror (42) and a second signal collection optical fiber (43), the second signal collection optical fiber (43) is connected with the second spectrometer (41), and the light emitted by the plasma is focused on the end face of the second signal collection optical fiber (43) through the second acquisition focusing mirror (42).

6. The LIBS-LAAS-based coal-fired heavy metal detection and analysis device according to any one of claims 1-5, characterized in that, The control and analysis unit (5) comprises a timing controller (51) and a computer (52), the pulse laser (11), the first spectrometer (31), the second spectrometer (41) and the displacement detection platform (6) are connected with the timing controller (51), and the first spectrometer (31) and the second spectrometer (41) are connected with the computer (52).

7. The LIBS-LAAS based coal-fired heavy metal detection and analysis device according to claim 5, wherein, The first laser focusing lens (12), the second laser focusing lens (22), the first collection focusing lens (32) and the second collection focusing lens (42) are all plano-convex lenses, and the planes are all directed to the displacement detection platform (6).

8. The LIBS-LAAS based coal fired heavy metal detection and analysis device as claimed in claim 4, wherein, The first signal collection optical fiber (33) comprises a plurality of optical fiber cables.

9. The LIBS-LAAS based coal-fired heavy metal detection and analysis device according to claim 8, wherein, The incident end face of the first signal collection optical fiber (33) is in a circular structure, and the outgoing end face is in a strip-shaped structure. 10.A coal heavy metal detection and analysis method based on LIBS-LAAS, which is implemented by using the detection and analysis device according to any one of claims 1-9, and comprises the following steps: S1: the pulse laser (11) emits pulse laser ablation to the sample to be detected to generate plasma; S2: the second spectrometer (41) collects LIBS spectrum information generated by the plasma, and the control and analysis unit (5) analyzes and compares the LIBS spectrum information to obtain spectrum information of part of heavy metal elements in the sample; S3: according to one of the heavy metal elements whose spectrum information is not obtained, the wavelength of the continuous laser emitted by the wavelength-tunable continuous laser (21) is determined, and the wavelength-tunable continuous laser (21) emits continuous laser of the wavelength to the plasma; S4: the first spectrometer (31) collects LAAS absorption spectrum information generated after the continuous laser passes through the plasma, and the control and analysis unit (5) obtains the LAAS absorption spectrum information to obtain spectrum information of one kind of heavy metal element; S5: the position of the sample to be detected is adjusted by the displacement detection platform (6), and pulse laser ablation is emitted to the sample by the pulse laser (11) to generate plasma; S6: steps S3-S5 are repeated until the spectrum information of all heavy metal elements to be detected in the sample is obtained, so as to complete the detection and analysis of the coal heavy metal.

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