Laser online detection device and method for alkali metal in flue gas

Abstract

The invention belongs to the field of flue gas detection, and particularly discloses a laser online detection device and method for alkali metal in flue gas, the device comprises a laser generation unit, a signal receiving unit and a data processing unit, the laser generation unit is arranged on one side of an observation inlet and forms at least one path of incident laser, and the signal receiving unit is arranged on the other side of the observation inlet; the laser emitter is used for emitting incident laser to the flue gas through the observation inlets, and one incident laser corresponds to one observation inlet; the signal receiving unit is arranged on one side of the observation outlet, is connected with the data processing unit and is used for receiving emergent light of the observation outlet and performing data analysis so as to perform on-line detection on alkali metal in the flue gas by utilizing laser-induced breakdown spectroscopy. According to the invention, online in-situ detection of flue gas can be realized, complex multiphase conversion behaviors of alkali metal in the combustion process can be conveniently obtained, and flue gas at different positions of the to-be-detected device can be detected by forming multiple paths of incident laser, so that multi-point detection of the to-be-detected device is realized.

Description

Technical Field

[0001] The present application belongs to the field of smoke detection, and more specifically, relates to a laser online detection device and method for alkali metals in smoke. Background Art

[0002] Zhundong coal, biomass and solid waste contain a large amount of alkali metal components, mainly sodium and potassium. For example, the sodium content of Zhundong coal, which is highly reserved in Xinjiang, my country, is greater than 2%, while corn stalks and rice husks in biomass fuels are potassium-rich biomass fuels with a potassium content of more than 1%, and the K content in urban solid waste is 0.95%.

[0003] During the combustion process, due to the relatively low melting point of alkali metal inorganic salts (such as alkali metal chlorides), alkali metal elements are easily released in gaseous form during the combustion process, which will also cause the ash to have a lower ash melting point. During the combustion process, some low-melting-point alkali metals are easily condensed, adhered and deposited on the heating surface of the boiler furnace after being released in gaseous form, causing a series of problems such as slagging, ash accumulation, and corrosion. On the one hand, slagging and ash accumulation will lead to reduced heat exchange efficiency and thermal efficiency; on the other hand, alkali metal gas phase condensates are prone to corrosion, causing damage to the heat exchange surface, causing leakage, and even causing major safety accidents.

[0004] In the prior art, the concentration measurement of alkali metals includes analytical methods based on flame / graphite furnace atomic absorption spectrometry, flame photometry, inductively coupled plasma emission spectrometry, etc., but these methods can only be used for offline detection, and cannot perform real-time in-situ detection of actual combustion flue gas. In addition, the collected samples need to be pre-processed to achieve experimental conditions, which is complicated and time-consuming. Furthermore, the offline detection method can only obtain the initial and final states, and cannot obtain the complex multiphase transformation behavior of alkali metals during the combustion process. Summary of the invention

[0005] In view of the defects of the prior art, the present application provides a laser online detection device and method for alkali metals in flue gas, aiming to solve the problem that the existing alkali metal concentration detection method cannot perform online in-situ detection of flue gas.

[0006] The present application provides a laser online detection device for alkali metals in flue gas, which specifically includes a laser generating unit, a signal receiving unit and a data processing unit, wherein: the laser generating unit is arranged on one side of an observation entrance and forms at least one incident laser, which is used to emit the incident laser to the flue gas through the observation entrance, and one incident laser corresponds to one observation entrance; the signal receiving unit is arranged on one side of the observation exit and connected to the data processing unit, which is used to receive the outgoing light of the observation exit and perform data analysis, so as to perform online detection of alkali metals in flue gas by using laser induced breakdown spectroscopy.

[0007] Through the above technical scheme conceived by the present application, compared with the prior art, since the present application applies laser induced breakdown spectroscopy to the detection of alkali metals in flue gas, it is possible to realize in-situ online testing of flue gas, and compared with offline detection, it is possible to obtain the complex multiphase transformation behavior of alkali metals in combustion engineering.

[0008] As further preferred, the laser online detection device also includes a microwave generating unit, which is arranged on one side of the observation entrance and is used to couple microwaves to the incident laser, thereby utilizing microwave-assisted laser-induced breakdown spectroscopy to improve detection accuracy.

[0009] As a further preferred embodiment, the laser generating unit includes a digital delay, a laser generator and at least one first beam splitter, wherein the digital delay is connected to the laser generator and is used to control the laser generator to emit the incident laser at a timed interval; each of the first beam splitters is respectively arranged at a position close to an observation entrance and is used to reflect or transmit the incident laser so as to send the incident laser into each observation entrance respectively.

[0010] As further preferred, the microwave generating unit includes a microwave radiator and a microwave generator, one end of the microwave radiator is connected to the microwave generator, and the other end thereof is arranged at the outlet of the laser generator for coupling the microwave generated by the microwave generator with the incident laser.

[0011] As a further preferred embodiment, the signal receiving unit includes at least one second beam splitter and a focusing lens, a reflector, a spectrometer and an ICCD which are sequentially arranged along the light propagation direction, each of the second beam splitters is arranged near an observation outlet for reflecting or transmitting the outgoing light so as to sequentially send the outgoing light from each observation outlet into the spectrometer through the focusing lens; the ICCD is respectively connected to the spectrometer, the digital delay device and the data processing unit for converting the optical signal into an electrical signal and sending the electrical signal into the data processing unit.

[0012] As a further preferred embodiment, the observation outlet is provided with an optical processing module, which includes a first lens, a second lens, a reflector and a laser receiver. The first lens is used to collect incident laser light to excite flue gas to generate plasma. The plasma is collected by the second lens and then reflected by the reflector to form outgoing light and emitted from the observation outlet. At the same time, the laser receiver is arranged behind the first lens along the direction of light propagation to block and remove the remaining incident laser light.

[0013] As a further preferred embodiment, when detecting gaseous alkali metals in flue gas, the power of the microwave generating unit is 80W~120W, the laser intensity of the laser generating unit is 5mJ / pulse~10mJ / pulse, the gate width time of the signal receiving unit is 20ns~40ns, and the delay time is 1μs~5μs; when detecting the total amount of alkali metals in flue gas, the power of the microwave generating unit is 160W~200W, the laser intensity of the laser generating unit is 100mJ / pulse~240mJ / pulse, the gate width time of the signal receiving unit is 50ns~100ns, and the delay time is 5μs~10μs.

[0014] According to another aspect of the present application, a method for online laser detection of alkali metals in flue gas is provided, specifically: a preset number of observation inlets and observation outlets are opened on the device to be tested, the observation inlets and the observation outlets are symmetrically arranged, an incident laser is emitted to the flue gas in the device to be tested through the observation inlet, and the outgoing light is received at the observation outlet and data analysis is performed, and then the alkali metals in the flue gas are detected online using laser induced breakdown spectroscopy.

[0015] As a further preferred method, microwaves are coupled to the incident laser, thereby utilizing microwave-assisted laser-induced breakdown spectroscopy to improve detection accuracy.

[0016] As a further preference, when detecting gaseous alkali metals in flue gas, the microwave power is 80W~120W, the laser intensity of the incident laser is 5mJ / pulse~10mJ / pulse, the gate width time of the signal receiving unit is 20ns~40ns, and the delay time is 1μs~5μs; when detecting the total amount of alkali metals in flue gas, the microwave power is 160W~200W, the intensity of the incident laser is 100mJ / pulse~240mJ / pulse, the gate width time of the signal receiving unit is 50ns~100ns, and the delay time is 5μs~10μs.

[0017] In general, the above technical solutions conceived by this application have the following technical advantages compared with the prior art:

[0018] 1. The present application can apply laser induced breakdown spectroscopy to the measurement of alkali metals in flue gas by setting a laser generating unit, a signal receiving unit and a data processing unit. The sample does not need to be pre-processed, thereby realizing online in-situ detection of flue gas, and facilitating the acquisition of the complex multiphase transformation behavior of alkali metals during the combustion process. In addition, the present application can also detect flue gas at different positions of the device to be tested by forming multiple incident lasers, thereby realizing multi-point detection of the device to be tested;

[0019] 2. At the same time, considering the complex composition, uneven distribution, certain fluidity and low alkali metal content of flue gas, the present application proposes to set up a microwave generating unit, and couple microwaves to the incident laser at the observation entrance, so as to detect alkali metals in flue gas by microwave-assisted laser induced breakdown spectroscopy, which can effectively improve the detection accuracy;

[0020] 3. In particular, the present application optimizes the microwave power and the intensity of the incident laser according to the detection target, and can effectively utilize the coupling relationship between microwaves and lasers to improve the measurement accuracy, thereby accurately measuring the gas-phase alkali metals and the total amount of alkali metals in the flue gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the structure of the laser online detection device for alkali metals in flue gas provided in an embodiment of the present application.

[0022] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0023] 1-microwave generator, 2-digital delay device, 3-laser generator, 4-microwave radiator, 5-first spectroscope, 6-device to be tested, 61-observation entrance, 62-observation exit, 7-optical processing module, 8-second spectroscope, 9-focusing lens, 10-spectrometer, 11-ICCD, 12-big data processing module, 13-computer, 14-incident laser, 15-first lens, 16-smoke, 17-laser receiver, 18-second lens, 19-reflector, 20-outgoing light. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0025] like Figure 1 As shown, the present application provides an alkali metal laser online detection device in flue gas, which specifically includes a laser generating unit, a signal receiving unit and a data processing unit, wherein: the laser generating unit is arranged at one side of the observation entrance 61 and forms at least one incident laser, which is used to emit the incident laser to the flue gas 16 through the observation entrance 61, and one incident laser corresponds to one observation entrance 61, and the laser generating unit includes a digital delay 2, a laser generator 3 and at least one first beam splitter 5, the digital delay 2 is connected to the laser generator 3, and is used to control the laser generator 3 to emit the incident laser at a fixed time; each first beam splitter 5 is respectively arranged at the position of the observation entrance 61, and each first beam splitter 5 is arranged in the same line in the vertical direction, and is used to reflect or transmit the incident laser, so as to send the incident laser to each observation entrance 61 respectively;

[0026] The signal receiving unit is arranged on one side of the observation outlet 62 and connected to the data processing unit, and is used to receive the outgoing light of the observation outlet 62 and perform data analysis, so as to use laser induced breakdown spectroscopy to perform online detection of alkali metals in the flue gas. The observation inlet 61 and the observation outlet 62 are symmetrically arranged on the left and right sides of the device to be tested 6 in the horizontal direction. In actual applications, a group of observation inlets 61 and observation outlets 62 can be opened at a certain interval as needed, so as to facilitate the detection of flue gas at different locations in the device to be tested 6.

[0027] The present application uses laser induced breakdown spectroscopy to detect alkali metals in flue gas, which can not only obtain the concentration of alkali metals in flue gas, but also realize online detection of alkali metal forms by adjusting the laser intensity. When measuring the concentration of gas-phase alkali metals in flue gas, low-intensity laser induced breakdown spectroscopy (LIBS) can be used for detection, and when measuring the total amount of alkali metals in flue gas, i.e., the sum of gas-phase alkali metals and particle-phase alkali metals, traditional LIBS can be used for detection.

[0028] Since the present application applies laser induced breakdown spectroscopy to the detection of alkali metals in flue gas, there is no need for pre-treatment of the flue gas, and the flue gas in the device to be tested can be directly tested in situ online. The detection process is fast and efficient, and compared with offline detection, it can obtain the changes in the concentration and form of alkali metals in the flue gas in real time, and then obtain the complex multiphase transformation behavior of alkali metals in combustion engineering.

[0029] Furthermore, considering that the laser promotes the high-temperature ionization of the sample and then generates plasma, so that it can be detected by the detector later, but the self-absorption effect will be generated due to the different temperature differences between the inside and outside of the plasma, and the microwave reduces the temperature difference between the inside and outside surfaces by heating the outer surface of the plasma, thereby reducing the self-absorption effect. Therefore, the present application proposes to use microwave-assisted laser-induced breakdown spectroscopy to detect alkali metals in flue gas. Therefore, the laser online detection device provided by the present application also includes a microwave generating unit, which is arranged on one side of the observation entrance 61, and is used to couple microwaves to the incident laser, thereby using microwave-assisted laser-induced breakdown spectroscopy to improve the detection accuracy. The microwave generating unit specifically includes a microwave radiator 4 and a microwave generator 1, one end of the microwave radiator 4 is connected to the microwave generator 1, and the other end thereof is arranged at the outlet of the laser generator 3, and is used to couple the microwaves generated by the microwave generator 1 with the incident laser, so that the incident laser coupled with the microwave is sent to the observation entrance 61 after reflection and transmission of the first spectroscope 5.

[0030] Furthermore, the signal receiving unit includes at least one second beam splitter 8 and a focusing lens 9, a spectrometer 10 and an ICCD 11 which are sequentially arranged along the light propagation direction. The second beam splitter 8 is arranged at a position close to the observation outlet 62, and each second beam splitter 8 is arranged in the same line in the vertical direction, and is used to reflect or transmit the emitted light, so as to periodically send the emitted light of each observation outlet 62 into the spectrometer 10 in sequence through the focusing lens 9. When working, the emitted light of each observation outlet 62 can be separated and periodically sent into the spectrometer 10 by controlling the working mode of each second beam splitter 8; the ICCD 11 is respectively connected to the spectrometer 10, the digital delay 2 and the data processing unit, and is used to convert the optical signal into an electrical signal, and send the delay data of the digital delay 2 and the electrical signal together to the data processing unit for processing.

[0031] Furthermore, the observation outlet 62 is provided with an optical processing module 7, which includes a first lens 15, a second lens 18, a reflector 19 and a laser receiver 17. The first lens 15 is used to converge the parallel incident laser 14 to one point to excite the flue gas 16 to generate plasma. The plasma radiated in all directions is converged by the second lens 18 to become parallel light and is reflected by the reflector 19 to form an output light 20 to be emitted from the observation outlet 62. At the same time, the laser receiver 17 is arranged behind the first lens 15 along the propagation direction of the light to block and remove the remaining incident laser 14.

[0032] Furthermore, the number of the first beam splitter 5 and the second beam splitter 8 is the same. The more the number of the first beam splitter 5 and the second beam splitter 8 is, the richer the detection data obtained is, which is more conducive to exploring the distribution of flue gas alkali metals in the device to be tested. However, too many first beam splitters 5 and second beam splitters 8 will lead to a sharp increase in cost. Therefore, the number of the first beam splitter 5 and the second beam splitter 8 is preferably 2 to 6 respectively.

[0033] Furthermore, considering that too much laser energy will lead to a stronger self-absorption effect, while too little laser energy will fail to excite the signal, too much microwave power will lead to too high a sample surface temperature, while too little microwave power will lead to too low a sample surface temperature, and will also produce a self-absorption effect. At the same time, considering that optimizing the gate width time and delay time of the signal receiving unit can also play a role in suppressing the self-absorption effect, the present application optimizes the laser intensity, microwave power, gate width time and delay time in the gas phase alkali metal detection and the total amount of alkali metal detection process, respectively, and can achieve adaptive coupling of laser and microwave for different test targets, effectively improving the measurement accuracy. Among them: when detecting gas phase alkali metals in flue gas, the power of the microwave generating unit is 80W~120W, the laser intensity of the laser generating unit is 5mJ / pulse~10mJ / pulse, the gate width time of the signal receiving unit is 20ns~40ns, and the delay time is 1μs~5μs. When detecting the total amount of alkali metals in flue gas, the power of the microwave generating unit is 160W to 200W, the laser intensity of the laser generating unit is 100mJ / pulse to 240mJ / pulse, the gate width time of the signal receiving unit is 50ns to 100ns, and the delay time is 5μs to 10μs.

[0034] Furthermore, the data processing unit includes a big data processing module 12 and a computer 13. The big data processing module 12 is used to process data, which can realize online monitoring and prediction of alkali metal distribution data within a certain range. The computer 13 is used to record and display monitoring data.

[0035] According to another aspect of the present application, a method for online laser detection of alkali metals in flue gas is provided, specifically: a preset number of observation entrances 61 and observation exits 62 are opened on the device to be tested 6, and the observation entrances 61 and the observation exits 62 are symmetrically arranged, and an incident laser is emitted to the flue gas in the device to be tested 6 through the observation entrance 61 by a laser generating unit, and the outgoing light is received by a signal receiving unit at the observation exit 62 and sent to a data processing unit for data analysis, and then the alkali metals in the flue gas are detected online by laser induced breakdown spectroscopy.

[0036] Furthermore, the device to be tested 6 may be any device into which flue gas is introduced, including but not limited to a boiler outlet, an economizer outlet, a heat exchanger inlet, and the like.

[0037] Furthermore, microwaves can be coupled to the incident laser, thereby utilizing microwave-assisted laser-induced breakdown spectroscopy to improve detection accuracy.

[0038] Furthermore, when detecting gaseous alkali metals in flue gas, the microwave power is 80W~120W, the laser intensity of the incident laser is 5mJ / pulse~10mJ / pulse, the gate width time for receiving the output light is 20ns~40ns, and the delay time is 1μs~5μs; when detecting the total amount of alkali metals in flue gas, the microwave power is 160W~200W, the intensity of the incident laser is 100mJ / pulse~240mJ / pulse, the gate width time is 50ns~100ns, and the delay time is 5μs~10μs.

[0039] The technical solution provided in this application is further described below based on specific embodiments.

[0040] Example 1

[0041] Taking the flue gas generated by the combustion of Zhundong coal as an example, an observation inlet 61 and an observation outlet 62 are set at the boiler outlet and the provincial gas outlet. Microwave-assisted laser induced breakdown spectroscopy (MA-LIBS) is used to detect alkali metals in the flue gas, and the parameters of the laser generator 3, the digital delay device 2 and the microwave generator 1 are adjusted. The laser light source of the multi-point LIBS technology is respectively a laser intensity of 6.2mJ / pulse (low-intensity LIBS), an output wavelength of 1064nm and a laser intensity of 140mJ / pulse (conventional LIBS), and a wavelength of 355nm. According to the potassium (K) line (766.49nm and 769.897nm) and the sodium (Na) line (588.995nm and 589.592nm) in the measurement results, after data processing by the same computer 13, the real-time concentrations of particulate potassium, gaseous potassium, particulate sodium, and gaseous sodium in the flue gas are obtained.

[0042] Under low pulse intensity, the laser measures the concentration of gas phase potassium and gas phase sodium in the flue gas at the corresponding position, while the power of the microwave generating unit is 90W, the gate width time of the signal receiving unit is 26ns, and the delay time is 3μs; under high pulse intensity, the laser measures the concentration of particulate phase potassium, gas phase potassium, particulate phase sodium, and gas phase sodium in the flue gas at the corresponding position, while the power of the microwave generating unit is 180W, the gate width time of the signal receiving unit is 70ns, and the delay time is 7μs. As mentioned above, the observation entrance 61 and the observation exit 62 are opened at different positions, and the corresponding laser information can be obtained and data processing can be performed through experiments with different laser intensities, so as to know the real-time concentration of alkali metals in different states at the corresponding sites.

[0043] In the Zhundong coal flue gas exported from the boiler, the gas phase potassium element accounts for 30.1%, the particle phase potassium element accounts for 69.9%, the gas phase sodium element accounts for 29.8%, and the particle phase sodium element accounts for 70.2%.

[0044] Example 2

[0045] Taking the flue gas generated by biomass combustion as an example, an observation inlet 61 and an observation outlet 62 are set at the boiler outlet and the front section of the heat exchanger. Microwave-assisted laser induced breakdown spectroscopy (MA-LIBS) is used. The parameters of the laser generator 3, the digital delay device 2 and the microwave generator are adjusted, and the laser light source of the multi-point LIBS technology is respectively used as the laser light source of the laser intensity 7mJ / pulse (low-intensity LIBS), the output wavelength 1064nm and the laser intensity 180mJ / pulse (conventional LIBS), and the wavelength 355nm. According to the potassium (K) line (766.49nm and 769.897nm) and the sodium (Na) line (588.995nm and 589.592nm) in the measurement results, after data processing by the same computer 13, the real-time concentrations of particle phase potassium, gas phase potassium, particle phase sodium, and gas phase sodium in the flue gas are obtained.

[0046] Under low-intensity LIBS laser intensity, the laser measures the concentration of gaseous potassium and gaseous sodium in the flue gas at the corresponding position, while the power of the microwave generating unit is 100W, the gate width time of the signal receiving unit is 35ns, and the delay time is 4μs; under traditional LIBS laser intensity, the laser measures the concentration of particulate potassium, gaseous potassium, particulate sodium, and gaseous sodium in the flue gas at the corresponding position, while the power of the microwave generating unit is 190W, the gate width time of the signal receiving unit is 85ns, and the delay time is 8μs. As mentioned above, by opening an observation entrance 61 and an observation exit 62 at different positions, the corresponding laser information can be obtained and data processing can be performed through experiments with different laser intensities, so as to know the real-time concentration of alkali metals in different states at the corresponding sites.

[0047] In the biomass flue gas at the boiler outlet, the gas phase potassium element accounts for 48.9%, the particle phase potassium element accounts for 51.1%, the gas phase sodium element accounts for 50.1%, and the particle phase sodium element accounts for 49.9%.

[0048] Example 3

[0049] Taking the flue gas generated by the combustion of solid waste as an example, an observation inlet 61 and an observation outlet 62 are set at the boiler outlet and the economizer gas outlet. Microwave-assisted laser induced breakdown spectroscopy (MA-LIBS) is used. The parameters of the laser generator 3, the digital delay device 2 and the microwave generator 1 are adjusted, and the laser light source of the multi-point LIBS technology is respectively used as the laser light source of the laser intensity 9.5mJ / pulse (low-intensity LIBS), the output wavelength 1064nm and the laser intensity 230mJ / pulse (conventional LIBS), and the wavelength 355nm. According to the potassium (K) line (766.49nm and 769.897nm) and the sodium (Na) line (588.995nm and 589.592nm) in the measurement results, the gate width is set to 50ns, and after data processing by the same computer 13, the real-time concentrations of particle phase potassium, gas phase potassium, particle phase sodium, and gas phase sodium in the flue gas are obtained.

[0050] Under low-intensity LIBS laser intensity, the laser measures the concentration of gaseous potassium and gaseous sodium in the flue gas at the corresponding position, while the power of the microwave generating unit is 120W, the gate width time of the signal receiving unit is 35ns, and the delay time is 5μs; under traditional LIBS laser intensity, the laser measures the concentration of particulate potassium, gaseous potassium, particulate sodium, and gaseous sodium in the flue gas at the corresponding position, while the power of the microwave generating unit is 195W, the gate width time of the signal receiving unit is 90ns, and the delay time is 9μs. As mentioned above, the observation entrance 61 and the observation exit 62 are set at different positions, and through experiments with different laser intensities, the corresponding laser information can be obtained and data processing can be performed, so as to know the real-time concentration of alkali metals in different states at the corresponding sites.

[0051] In the solid waste flue gas at the boiler outlet, the gas phase potassium element accounts for 60.3%, the particle phase potassium element accounts for 39.7%, the gas phase sodium element accounts for 58.7%, and the particle phase sodium element accounts for 41.3%.

[0052] In the description of the present application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the feature. In the description of the present application, "plurality" means two or more, unless otherwise clearly and specifically defined.

[0053] In addition, references throughout this specification to "one embodiment"; "one embodiment", "an example" or similar language indicate that a particular feature, structure, or characteristic described in conjunction with the embodiment is included in at least one embodiment of the present application. Thus, appearances of the phrase "in one embodiment"; "in one embodiment" and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0054] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A laser online detection device for alkali metals in flue gas, characterized in that: The laser online detection device specifically comprises a laser generating unit, a signal receiving unit and a data processing unit, wherein: the laser generating unit is arranged at one side of an observation inlet (61) and forms at least one incident laser, which is used to emit the incident laser to the flue gas (16) through the observation inlet (61), and one incident laser corresponds to one observation inlet (61); the signal receiving unit is arranged at one side of an observation outlet (62) and connected to the data processing unit, which is used to receive the output light of the observation outlet (62) and perform data analysis, so as to perform online detection of alkali metals in the flue gas by using laser induced breakdown spectroscopy.

2. The laser online detection device for alkali metals in flue gas according to claim 1, characterized in that: The laser online detection device also includes a microwave generating unit, which is arranged on one side of the observation entrance (61) and is used to couple microwaves to the incident laser, thereby utilizing microwave-assisted laser-induced breakdown spectroscopy to improve detection accuracy.

3. The laser online detection device for alkali metals in flue gas according to claim 2, characterized in that: The laser generating unit comprises a digital delay device (2), a laser generator (3) and at least one first beam splitter (5); the digital delay device (2) is connected to the laser generator (3) and is used to control the laser generator (3) to emit incident laser light at a fixed time; each of the first beam splitters (5) is respectively arranged at a position close to an observation entrance (61) and is used to reflect or transmit the incident laser light so as to send the incident laser light into each observation entrance (61).

4. The laser online detection device for alkali metals in flue gas according to claim 3, characterized in that: The microwave generating unit comprises a microwave radiator (4) and a microwave generator (1); one end of the microwave radiator (4) is connected to the microwave generator (1), and the other end of the microwave radiator (4) is arranged at the outlet of the laser generator (3) for coupling the microwave generated by the microwave generator (1) with the incident laser.

5. The laser online detection device for alkali metals in flue gas according to claim 1, characterized in that: The signal receiving unit comprises at least one second beam splitter (8) and a focusing lens (9), a spectrometer (10) and an ICCD (11) which are sequentially arranged along the light propagation direction. Each of the second beam splitters (8) is arranged at a position close to an observation outlet (62) and is used to reflect or transmit the outgoing light so as to sequentially send the outgoing light from each observation outlet (62) through the focusing lens (9) into the spectrometer (10); the ICCD (11) is respectively connected to the spectrometer (10), the digital delay device (2) and the data processing unit and is used to convert the optical signal into an electrical signal and send the electrical signal into the data processing unit.

6. The laser online detection device for alkali metals in flue gas according to claim 5, characterized in that: The observation outlet (62) is provided with an optical processing module (7), and the optical processing module (7) comprises a first lens (15), a second lens (18), a reflector (19) and a laser receiver (17). The first lens (15) is used to collect incident laser light (14) to excite flue gas (16) to generate plasma. The plasma is collected by the second lens (18) and then reflected by the reflector (19) to form output light (20) and is emitted from the observation outlet (62). At the same time, the laser receiver (17) is arranged behind the first lens (15) along the light propagation direction to block and remove the remaining incident laser light (14).

7. The laser online detection device for alkali metals in flue gas according to claim 2, characterized in that: When detecting gaseous alkali metals in flue gas, the power of the microwave generating unit is 80W to 120W, the laser intensity of the laser generating unit is 5mJ / pulse to 10mJ / pulse, the gate width time of the signal receiving unit is 20ns to 40ns, and the delay time is 1μs to 5μs; when detecting the total amount of alkali metals in flue gas, the power of the microwave generating unit is 160W to 200W, the laser intensity of the laser generating unit is 100mJ / pulse to 240mJ / pulse, the gate width time of the signal receiving unit is 50ns to 100ns, and the delay time is 5μs to 10μs.

8. A laser online detection method for alkali metals in flue gas, characterized in that: The laser online detection method specifically comprises: providing a preset number of observation inlets (61) and observation outlets (62) on a device to be tested (6), wherein the observation inlets (61) and the observation outlets (62) are symmetrically arranged, emitting incident laser light to the smoke in the device to be tested (6) through the observation inlets (61), receiving the emitted light at the observation outlets (62) and performing data analysis, and then performing online detection of alkali metals in the smoke using laser induced breakdown spectroscopy.

9. The laser online detection device for alkali metals in flue gas according to claim 8, characterized in that: Microwaves are coupled to the incident laser, thereby utilizing microwave-assisted laser-induced breakdown spectroscopy to improve detection accuracy.

10. The laser online detection device for alkali metals in flue gas according to claim 9, characterized in that: When detecting gaseous alkali metals in flue gas, the microwave power is 80W~120W, the laser intensity of the incident laser is 5mJ / pulse~10mJ / pulse, the gate width time of the signal receiving unit is 20ns~40ns, and the delay time is 1μs~5μs; when detecting the total amount of alkali metals in flue gas, the microwave power is 160W~200W, the intensity of the incident laser is 100mJ / pulse~240mJ / pulse, the gate width time of the signal receiving unit is 50ns~100ns, and the delay time is 5μs~10μs.

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