TDLAS-based ammonia escape detection method

Abstract

The invention relates to the field of ammonia escape detection, and discloses a TDLAS (tunable diode laser absorption spectroscopy)-based ammonia escape detection method, which simultaneously solves three industrial problems of dust interference, light path offset and calibration dependence on the premise of not increasing hardware complexity. Under unpowered suction, to-be-measured flue gas is driven to be filtered by a filter at the front end of the in-situ sampling probe by using the internal and external pressure difference of the flue and then is introduced into the measuring cavity. A laser beam with a specific frequency is emitted by the laser emitting and receiving unit, is collimated by the collimator, then enters the measuring cavity, is absorbed twice by ammonia molecules in the flue gas, and then returns to the photoelectric detector. And the photoelectric detector converts the optical signal into an electric signal and transmits the electric signal to an analyzer for concentration inversion to obtain an ammonia escape concentration value. According to the method, a closed gas path is formed, so that flue gas is not in contact with the external environment in the whole process, and zero-emission detection is realized. The detection sensitivity and accuracy are effectively improved through a two-way absorption enhanced detection structure, and a reliable solution is provided for ammonia escape monitoring in the industrial process.

Description

Technical Field

[0001] The present invention relates to the field of ammonia escape detection, and in particular to a TDLAS-based ammonia escape detection method. Background Art

[0002] With the application of denitrification technology in thermal power plants, ammonia injection control and ammonia escape have a great impact on post-furnace equipment, such as air preheater blockage, electrostatic precipitator corrosion and other problems. Ammonia injection optimization control and ammonia escape measurement are particularly important.

[0003] Traditional ammonia slip measurement methods use laser beams on both sides of the flue to calculate the amount of ammonia slip based on the intensity of the ammonia slip absorption spectrum. However, flues are dusty and hot, which can lead to significant interference and data distortion. During unit operation, the flue expands unevenly as the boiler load increases or decreases, causing the laser beam to shift, requiring frequent re-alignment and increasing the workload.

[0004] Therefore, we proposed a TDLAS-based ammonia escape detection method to solve the above problems. Summary of the Invention

[0005] The present invention provides a TDLAS-based ammonia escape detection method, which solves the three major industry problems of dust interference, optical path deviation, and calibration dependence without increasing hardware complexity.

[0006] The first aspect of the present invention provides an ammonia escape detection method based on TDLAS, which includes: under the action of an unpowered suction device, the flue gas to be tested is filtered through a filter at the front end of an in-situ sampling probe, and the filtered flue gas is continuously passed into a measuring cavity; a laser beam of a specific frequency ν is emitted by a laser emitting and receiving unit, and the laser beam is collimated by a collimator and then shot into the measuring cavity. After the laser beam is absorbed by ammonia molecules in the flue gas in the measuring cavity, it reaches a reflector fixed at the front end of the measuring cavity. The laser beam reflected by the reflector passes through the flue gas again and is absorbed by the ammonia molecules, and finally returns to the photoelectric detector in the laser emitting and receiving unit; the photoelectric detector converts the optical signal into an electrical signal, transmits the electrical signal to an analyzer, performs concentration inversion, and obtains the ammonia escape concentration value in the flue gas; the flue gas that has completed concentration detection returns to the flue from the outlet of the measuring cavity.

[0007] Optionally, in a first implementation method of the first aspect of the present invention, it includes: utilizing the pressure difference between the inside and outside of the flue as the only power source to drive the flue gas to be measured in the flue into the inlet flow channel of the in-situ sampling probe; allowing the flue gas to pass through the filter for multi-stage dust interception to form filtered flue gas; introducing the filtered flue gas into the inlet of the measuring cavity, so that the flue gas forms a stable flowing gas medium to be measured in the measuring cavity.

[0008] Optionally, in a second implementation of the first aspect of the present invention, the flow path of the gas medium to be measured is orthogonal to the two-way absorption path of the laser beam.

[0009] Optionally, in a third implementation method of the first aspect of the present invention, it includes: generating a narrow-linewidth laser beam of a specific frequency ν that matches the absorption spectrum of ammonia molecules; converting the narrow-linewidth laser beam into a parallel beam through a collimator, and directionally injecting it into a measurement cavity; allowing the parallel beam to penetrate the gas medium to be measured along a first optical path in the measurement cavity, and be absorbed by the ammonia molecules to form a primary attenuated laser beam; controlling the primary attenuated laser beam to reach a reflector fixed at the front end of the measurement cavity, and forming a reverse-propagating reflected laser beam after reflection; allowing the reflected laser beam to penetrate the same gas medium to be measured again along a second optical path, and be absorbed by the ammonia molecules for the second time to form a secondary attenuated laser beam; and accurately guiding the secondary attenuated laser beam into the photoelectric detector of the laser transmitting and receiving unit.

[0010] Optionally, in a fourth implementation of the first aspect of the present invention, the first optical path overlaps with the second optical path and the total length is equal to 2L, where L is the length of a single-pass absorption path, constituting a double-pass absorption enhanced detection structure.

[0011] Optionally, in a fifth implementation of the first aspect of the present invention, the method includes: converting the light intensity signal of the secondary attenuated laser beam into an initial current signal through a photodetector; performing logarithmic amplification processing on the initial current signal to generate a voltage signal that is proportional to the laser transmittance τ(ν); based on the voltage signal, extracting the gas absorption characteristic harmonic component through a phase-locked amplifier to generate an ammonia molecule absorption line function The absorption line function of the ammonia molecule Perform integration operation to obtain the equivalent absorption area A; according to the equivalent absorption area A, the known single-pass absorption path length L and the gas temperature and pressure parameters, the concentration inversion formula is used Calculate the ammonia escape concentration value;

[0012] Where X is the concentration of the gas to be measured, S(T) is the intensity of the characteristic spectrum line of ammonia molecules at temperature T, and P is the total pressure of the gas in the measurement chamber.

[0013] Optionally, in a sixth implementation of the first aspect of the present invention, it includes: connecting the outlet of the measuring cavity with the reflux channel of the in-situ sampling probe to form a closed gas path; using the pressure difference generated by the negative pressure of the flue as a driving force to make the flue gas after detection pass through the reflux channel; setting an acceleration structure at the interface between the reflux channel and the flue to make the flue gas return to the flue in a jet flow state; controlling the flow direction of the jet flow flue gas to be consistent with the original flue airflow direction to avoid local turbulence interference.

[0014] Optionally, in a seventh implementation of the first aspect of the present invention, the closed gas circuit prevents the flue gas from coming into contact with the external environment throughout the entire process, thereby achieving zero emission detection.

[0015] The mechanism of the present invention is as follows:

[0016] The basic physical principles of TDLAS are deeply integrated with the denitrification operating constraints of thermal power plants. Through the three-in-one innovation of single-end dual-pass absorption structure + in-situ closed-loop flow path + calibration-free physical inversion, the three major technical bottlenecks of traditional ammonia escape detection are broken through.

[0017] Beneficial effects:

[0018] Ammonia slip is measured using the TDLAS technique. When a monochromatic laser beam with a frequency of v passes through a length of L in the gas medium being measured, the laser is absorbed by the characteristic spectral lines of the gas molecules. Analysis of the laser intensity after absorption by the gas molecules reveals parameters such as the temperature, pressure, and concentration of the gas being measured. Using an in-situ measurement system, the flue gas is filtered through a filter at the front end of the in-situ sampling probe and enters the measurement chamber. After measurement is complete, the gas enters the flue. Once the equipment is commissioned, frequent alignment is unnecessary, resulting in minimal maintenance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the TDLAS technology measurement principle of the TDLAS-based ammonia escape detection method in an embodiment of the present invention;

[0020] Figure 2 Schematic diagram of the in-situ sampling technology of the ammonia escape detection method based on TDLAS in an embodiment of the present invention;

[0021] Figure 3 This is a diagram of a one-to-four distributed ammonia escape rate monitoring solution based on the TDLAS ammonia escape detection method in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] An embodiment of the present invention provides an ammonia escape detection method based on TDLAS, which solves the three major industry problems of dust interference, optical path offset, and calibration dependence without increasing the complexity of hardware. The terms "first", "second", "third", "fourth", etc. (if any) in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way are interchangeable where appropriate, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "including" or "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or apparatus.

[0023] For ease of understanding, the specific process of the embodiment of the present invention is described below. Figure 1 In one embodiment of the present invention, a method for detecting ammonia escape based on TDLAS includes:

[0024] 101. Under the action of the unpowered suction device, the flue gas to be measured is filtered through the filter at the front end of the in-situ sampling probe, and the filtered flue gas is continuously passed into the measuring cavity;

[0025] It is understood that the execution subject of the present invention can be a TDLAS-based ammonia escape detection device, or a terminal or a server, which is not limited here. The embodiment of the present invention is described by taking the server as the execution subject as an example.

[0026] It should be noted that:

[0027] a) Using the pressure difference between the inside and outside of the flue as the only power source, the flue gas to be tested in the flue is driven into the inlet flow channel of the in-situ sampling probe;

[0028] b) passing the flue gas through the filter to perform multi-stage dust interception to form filtered flue gas;

[0029] c) introducing the filtered flue gas into the inlet of the measurement cavity, so that the flue gas forms a stable flowing gas medium to be measured in the measurement cavity;

[0030] The flow path of the gas medium to be measured is orthogonal to the double-pass absorption path of the laser beam in the subsequent laser detection step.

[0031] 102. A laser beam of a specific frequency v is emitted by a laser emitting and receiving unit. The laser beam is collimated by a collimator and then emitted into the measurement cavity. The laser beam is absorbed by ammonia molecules in the flue gas in the measurement cavity and then reaches a reflector fixed at the front end of the measurement cavity. The laser beam reflected by the reflector passes through the flue gas again and is absorbed by ammonia molecules, and finally returns to the photodetector in the laser emitting and receiving unit.

[0032] It should be noted that:

[0033] a) generating a narrow linewidth laser beam of a specific frequency ν that matches the absorption line of ammonia molecules;

[0034] b) converting the narrow linewidth laser beam into a parallel beam through a collimator and injecting the parallel beam into the measurement cavity in a directionally controlled manner;

[0035] c) allowing the parallel light beam to penetrate the gas medium to be measured along a first optical path in the measurement cavity and be absorbed by ammonia molecules to form a primary attenuated laser beam;

[0036] d) controlling the once-attenuated laser beam to reach a reflector fixed at the front end of the measurement cavity, and forming a reverse-propagating reflected laser beam after reflection;

[0037] e) causing the reflected laser beam to penetrate the same gas medium to be measured again along a second optical path, and to be absorbed by ammonia molecules for the second time to form a secondary attenuated laser beam;

[0038] f) accurately directing the secondary attenuated laser beam into a photodetector of a laser transmitting and receiving unit;

[0039] The first optical path and the second optical path overlap and the total length is equal to 2L (L is the length of a single-pass absorption path), forming a double-pass absorption enhancement detection structure.

[0040] 103. The photoelectric detector converts the optical signal into an electrical signal, transmits the electrical signal to the analyzer, performs concentration inversion, and obtains the ammonia escape concentration value in the flue gas;

[0041] It should be noted that:

[0042] a) converting the light intensity signal of the secondary attenuated laser beam into an initial current signal through a photodetector;

[0043] b) performing logarithmic amplification processing on the initial current signal to generate a voltage signal proportional to the laser transmittance τ(ν);

[0044] c) Based on the voltage signal, extracting the gas absorption characteristic harmonic component through a lock-in amplifier to generate an ammonia molecule absorption line function

[0045] d) the absorption line function of the ammonia molecule Perform integration operation to obtain the equivalent absorption area A;

[0046] e) calculating the ammonia escape concentration value using the concentration inversion formula X=A / [S(T)·P·L] based on the equivalent absorption area A, the known single-pass absorption path length L, and the gas temperature and pressure parameters;

[0047] Where X is the ammonia escape concentration, S(T) is the characteristic spectral line intensity of ammonia molecules at temperature T, and P is the total gas pressure in the measurement chamber.

[0048] 104. The flue gas that has completed concentration detection returns to the flue from the outlet of the measuring chamber.

[0049] It should be noted that:

[0050] a) connecting the outlet of the measuring cavity to the reflux channel of the in-situ sampling probe to form a closed gas path;

[0051] b) using the pressure difference generated by the flue negative pressure as a driving force to make the detected flue gas pass through the reflux channel;

[0052] c) providing an acceleration structure at the interface between the return channel and the flue to allow the flue gas to return to the flue in a jet flow state;

[0053] d) controlling the flow direction of the jet-like flue gas to be consistent with the original flue gas flow direction to avoid local turbulence interference;

[0054] The closed gas path prevents the flue gas from coming into contact with the external environment throughout the entire process, thus achieving zero emission detection.

[0055] The measurement technology of the present invention is advanced and can accurately measure ammonia escape data based on TDLAS. The in-situ measurement technology solves the problems of high dust and high temperature in the flue, large interference in measurement, and data distortion. When the boiler increases or decreases load, the flue expands unevenly, the laser irradiation is offset, and frequent alignment is required, which requires a lot of maintenance.

[0056] In an embodiment of the present invention, an ammonia escape rate monitoring instrument realizes distributed online monitoring of ammonia concentration in flue gas after denitrification based on tunable diode laser absorption spectroscopy (TDLAS) technology combined with an in-situ sampling method.

[0057] The TDLAS measurement principle is as follows Figure 1 As shown in the figure, when a monochromatic laser beam with a frequency of v passes through the gas medium to be measured with a length of L, the laser is absorbed by the characteristic spectral lines of the gas molecules. Then, by analyzing the intensity of the laser after being absorbed by the gas molecules, the temperature, pressure, concentration and other parameters of the gas to be measured can be obtained.

[0058] When the laser passes through the gas medium to be measured, the ratio of the transmitted light intensity to the incident light intensity can be described by the Beer-Lambert absorption law:

[0059]

[0060] According to the above simplification, we can get

[0061] Where τ(v) is the laser transmittance; I0 and I t Represent the incident light intensity and transmitted light intensity of the laser respectively; P [atm] is the total pressure of the gas in the measurement chamber; S (T) [cm-2atm-1] is the intensity of the characteristic spectrum line, and its magnitude is only related to the gas temperature T; X is the escape concentration of the gas to be measured; L [cm] is the transmission distance of the laser in the gas to be measured; is the absorption line function of ammonia molecules, which satisfies

[0062] In-situ sampling measurement principle Figure 2 As shown in the figure, the solid arrow is the gas flow line, and the dotted arrow is the laser measurement line. The entire measuring device adopts an integrated structural design, which mainly includes a laser transmitting and receiving unit and an in-situ sampling probe. Under the action of the unpowered suction exhaust device, the flue gas is filtered through the filter at the front end of the in-situ sampling probe and then enters the measuring cavity. After the measurement is completed, it enters the flue. During the measurement process, the laser emitted by the laser transmitting and receiving unit is collimated and then shot into the measuring cavity. After being absorbed by the gas, it reaches the reflector at the front end of the measuring cavity for reflection. After being absorbed by the gas again, it reaches the laser receiving module in the laser transmitting and receiving unit for photoelectric detection, and is finally transmitted to the analyzer to realize concentration inversion.

[0063] A distributed online monitoring solution for ammonia escape rate based on in-situ sampling technology is as follows: Figure 3 As shown, the flue after the denitrification outlet is divided into zones, and in-situ sampling and measuring probes are installed at the center of each zone. The laser is split in the analyzer according to the number of measuring probes required. The split laser is transmitted to the measuring probes respectively. After the measurement is completed, the photoelectric detector signal detected is transmitted to the analyzer to complete data acquisition, concentration inversion and signal transmission. At the same time, the analyzer is equipped with a control module to perform regular purge of the measuring probes, thereby realizing synchronous online monitoring of multi-point ammonia escape concentration.

[0064] The present invention also provides a computer-readable storage medium, which may be a non-volatile computer-readable storage medium or a volatile computer-readable storage medium. The computer-readable storage medium stores instructions, which, when executed on a computer, cause the computer to execute the steps of the TDLAS-based ammonia escape detection method.

[0065] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0066] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), magnetic disk or optical disk, etc., various media that can store program code.

[0067] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features thereof can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A TDLAS-based ammonia escape detection method, characterized in that: The TDLAS-based ammonia escape detection method includes: Under the action of the unpowered suction device, the smoke to be measured is filtered through the filter at the front end of the in-situ sampling probe, and the filtered smoke is continuously passed into the measurement cavity; A laser beam of a specific frequency v is emitted by a laser transmitting and receiving unit, collimated by a collimator, and then emitted into the measurement cavity. The laser beam is absorbed by ammonia molecules in the flue gas in the measurement cavity, and then reaches a reflector fixed at the front end of the measurement cavity. The laser beam reflected by the reflector passes through the flue gas again and is absorbed by ammonia molecules, and finally returns to the photodetector in the laser transmitting and receiving unit. The photoelectric detector converts the optical signal into an electrical signal, transmits the electrical signal to the analyzer, performs concentration inversion, and obtains the ammonia escape concentration value in the flue gas; The flue gas that has completed concentration detection returns to the flue from the outlet of the measuring chamber.

2. The ammonia escape detection method based on TDLAS according to claim 1, characterized in that, include: The pressure difference between the inside and outside of the flue is used as the only power source to drive the flue gas to be tested in the flue into the inlet flow channel of the in-situ sampling probe; Passing the flue gas through the filter to perform multi-stage dust interception to form filtered flue gas; The filtered flue gas is introduced into the inlet of the measuring cavity, so that the flue gas forms a stably flowing gas medium to be measured in the measuring cavity.

3. The ammonia escape detection method based on TDLAS according to claim 2, characterized in that, The flow path of the gas medium to be measured is orthogonal to the double-pass absorption path of the laser beam.

4. The ammonia escape detection method based on TDLAS according to claim 1, characterized in that include: Generate a narrow linewidth laser beam with a specific frequency ν that matches the absorption line of ammonia molecules; The narrow linewidth laser beam is converted into a parallel beam by a collimator and directed into the measurement cavity; The parallel light beam is made to penetrate the gas medium to be measured along the first optical path in the measuring cavity and is absorbed by ammonia molecules to form a primary attenuated laser beam; Controlling the once-attenuated laser beam to reach a reflector fixed at the front end of the measurement cavity, and forming a reverse-propagating reflected laser beam after reflection; The reflected laser beam is made to penetrate the same gas medium to be measured again along the second optical path, and is absorbed by the ammonia molecules for the second time to form a secondary attenuated laser beam; The secondary attenuated laser beam is precisely guided into the photoelectric detector of the laser emitting and receiving unit.

5. The ammonia escape detection method based on TDLAS according to claim 4, characterized in that, The first optical path and the second optical path overlap and the total length is equal to 2L, where L is the length of a single-pass absorption path, forming a double-pass absorption enhancement detection structure.

6. The ammonia escape detection method based on TDLAS according to claim 1, characterized in that, include: converting the light intensity signal of the secondary attenuated laser beam into an initial current signal through a photodetector; Performing logarithmic amplification processing on the initial current signal to generate a voltage signal that is proportional to the laser transmittance τ(ν); Based on the voltage signal, the gas absorption characteristic harmonic component is extracted through a phase-locked amplifier to generate an ammonia molecule absorption line function. The absorption line function of the ammonia molecule Perform integration operation to obtain the equivalent absorption area A; According to the equivalent absorption area A, the known one-way absorption path length L and the gas temperature and pressure parameters, the concentration inversion formula Calculate the ammonia escape concentration value; Where X is the concentration of the gas to be measured, S(T) is the intensity of the characteristic spectrum line of ammonia molecules at temperature T, and P is the total pressure of the gas in the measurement chamber.

7. The ammonia escape detection method based on TDLAS according to claim 1, characterized in that: include: Connecting the outlet of the measuring cavity to the reflux channel of the in-situ sampling probe to form a closed gas path; Using the pressure difference generated by the flue negative pressure as a driving force, the detected flue gas passes through the reflux channel; An acceleration structure is provided at the interface between the return channel and the flue to allow the flue gas to return to the flue in a jet flow state; The flow direction of the jet-like flue gas is controlled to be consistent with the original flue gas flow direction to avoid local turbulence interference.

8. The TDLAS-based ammonia escape detection method according to claim 7, characterized in that: The closed gas path prevents the flue gas from coming into contact with the external environment throughout the entire process, thus achieving zero emission detection.

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