Infrared light modulation technology-based synchronous measurement device and measurement method for concentration of particulate matters and gasTechnical Field
The invention relates to a synchronous measurement device for particulate matter and gas concentration based on a light scattering and spectroscopy technology, and further relates to a measurement method of the synchronous measurement device for particulate matter and gas concentration based on an infrared light modulation technology, belonging to the technical field of optical measurement.
Background
In recent years, with the increasing importance of the country on environmental protection and the need for ensuring the safe and efficient operation of industrial production, accurate monitoring of the concentrations of particulate matters and pollutant gas components has important significance for controlling air pollution emission. In order to facilitate the supervision and management of environmental protection departments to minimize the emission of pollutants, research and manufacture of techniques and equipment capable of accurately and rapidly measuring the concentration of gases and the concentration of particulate matters are urgent.
The existing methods applied to the measurement of the concentration of the pollutant gas are divided into two methods, namely a non-optical analysis method and an optical analysis method, according to the working principle. The non-optical analysis methods mainly include ultrasonic technology, gas-sensitive method, thermal catalysis method, gas chromatography, etc., but are very susceptible to environmental factors such as temperature, pressure, humidity, etc., and thus are difficult to apply to field gas analysis. An optical gas concentration analysis method is mainly based on the basic principle of spectroscopy, when the laser frequency is the same as the transition frequency of a gas absorption component, laser energy is absorbed, an absorption value along a light path can be obtained by comparing the incident light intensity with the transmitted light intensity, and then physical parameters such as gas temperature, gas concentration and the like are determined.
The spectroscopy mainly includes fourier transform infrared spectroscopy (FTIR), laser photoacoustic spectroscopy (PAS), tunable laser diode absorption spectroscopy (TDLAS), and the like. The FTIR technology is mainly based on the Michelson interferometer principle, and the infrared light source sends the parallel light after collimating by collimating lens, is received by the telescope system after the gaseous absorption of awaiting measuring, assembles the detector through the interferometer again to obtain the interference signal of the gaseous of awaiting measuring, can obtain the absorption spectrum information of gaseous under the different concentrations after Fourier transform, thereby calculate gaseous concentration. However, FTIR devices are bulky, have relatively slow response speed and are relatively expensive, and therefore will need to be developed in the future. The PAS technology is a gas concentration measuring method utilizing a photoacoustic effect, laser velocity energy emitted by a laser diode is absorbed by gas to be measured and then converted into heat energy, so that the temperature of local gas is changed, meanwhile, the change of gas pressure is caused, photoacoustic waves are generated, generated frontal sound waves are detected by a sound wave microphone, and the inversion of the gas concentration is completed according to the amplitude of the sound waves. However, the resonance mode is easily interfered by environmental noise, and the measurement precision is influenced. The TDLAS technology is a spectral measurement method based on the narrow linewidth characteristic of a semiconductor laser, can realize simultaneous measurement of multiple components and multiple parameters of mixed gas, has very strong universality and high measurement resolution, and can measure the concentration of trace gas by selecting a combined type characteristic absorption spectral line of gas to be measured.
The measurement methods of particulate matter concentration can be generally classified into two categories: sampling and non-sampling. The non-sampling method has been widely used because it does not need to sample the object to be measured, can directly measure the particulate matter, and does not generate disturbance to the object to be measured. The non-sampling method can be classified into a blackness method, a turbidity method, a light scattering method, and the like. The blackness method is also called the ringer-Mannheim method. The method is based on the fact that monitoring personnel visually observe the blackness of emitted particulate matters by using glass sheets with different black areas, then the blackness of the smoke to be detected is determined after the blackness is compared with the Ringelmann blackness (six levels in total), and then the smoke emission concentration is obtained according to a Ringelmann blackness level and particulate matter concentration comparison table. The turbidity method is mainly based on the Beer-Lambert law, and the transmitted light intensity is related to the size and concentration of particles so as to determine the mass concentration of the particles. The light scattering method is based on the principle of light scattering, when a light beam is incident on a particle, the light beam is scattered to the periphery of a space, and each scattering parameter of the light is closely related to the concentration of the particle. The light scattering method is widely applied to the measurement of the concentration of the particulate matters in the coal-fired power plant due to the advantages of high measurement sensitivity, low measurement lower limit and the like.
When particulate matter concentration is extremely low, scattering light intensity is minimum, receives external light source's influence easily, and light path shake, mechanical vibration and detector noise all can cause the influence to the detected signal to make the SNR can not satisfy the demand of measuring. Meanwhile, it is urgent to research and manufacture techniques and devices capable of accurately and rapidly measuring the gas concentration and the particulate matter concentration to meet the demand of on-site measurement. Therefore, it is important to develop a device and a method for synchronously measuring the concentration of particles and gas, which can reduce low-frequency noise and improve the signal-to-noise ratio.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to provide a synchronous measuring device for particulate matter and gas concentration based on an infrared light modulation technology.
The invention also aims to solve the technical problem of providing the measuring method of the device for synchronously measuring the concentration of the particulate matter and the gas based on the infrared light modulation technology, and the measuring method can greatly improve the signal-to-noise ratio of measurement and is suitable for synchronously measuring the low-concentration particulate matter and the gas.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a synchronous measuring device for particulate matter and gas concentration based on an infrared light modulation technology sequentially comprises a signal generating module, a particulate matter and gas measuring module, a signal receiving module and a signal processing module; the signal generation module comprises a function generator, a laser controller, a distributed feedback laser (DFB), an optical fiber beam splitter and an optical power amplifier; the particle and gas measuring module comprises an optical etalon, a heat tracing pipe belt, a measuring pool and a heating module wrapped outside the measuring pool; the signal receiving module consists of three photoelectric detectors; preheating particles to be measured and gas through a heat tracing pipe belt, and then, feeding the particles to be measured and the gas into a measuring tank, wherein a heating module enables the measuring tank to be maintained at a set temperature; the function generator inputs scanning superposition modulation signals into the laser controller, the laser controller tunes the output wavelength and light intensity of the distributed feedback laser, laser output by the distributed feedback laser is divided into three beams by the optical fiber beam splitter, one beam enters the measuring cell from the laser emission end through the optical power amplifier, is absorbed by gas to be measured and scattered by particles, is received by the photoelectric detector and is converted into an electric signal, and a scattered light intensity signal is obtained; one beam is received by a photoelectric detector after passing through an optical etalon to obtain an etalon signal; the other light signal is directly received by the photoelectric detector to obtain a background signal, and the three signals are transmitted to the signal processing module by the corresponding photoelectric detector to be processed.
The distributed feedback laser can continuously emit stable infrared laser, and the wavelength of the stable infrared laser depends on the gas to be measured.
The measuring method of the synchronous measuring device for the concentration of the particulate matters and the gas based on the infrared light modulation technology comprises the following steps:
step 1, inputting a scanning superposition modulation signal into a laser controller by a function generator, and tuning the output wavelength and light intensity of a distributed feedback laser by the laser controller;
step 2, dividing the modulated light in the step 1 into three beams through an optical fiber beam splitter, wherein one beam enters a measuring cell from a laser emitting end through an optical power amplifier, and a scattered light intensity signal is collected by a photoelectric detector; one beam passes through the optical etalon, and an etalon signal is collected by the photoelectric detector; the other beam is directly used for obtaining a background light intensity signal by a photoelectric detector;
step 3, obtaining a time-frequency response characteristic upsilon (t) from the etalon signal, and carrying out digital phase locking and low-pass filtering processing on the background light intensity signal and the scattered light intensity signal to obtain respective first harmonic signal and second harmonic signal;
step 4, further processing the first harmonic and the second harmonic of the scattered light intensity signal according to the Beer-Lambert law and the Lorenz-Mie theory, and calculating a gas concentration value according to the normalized second harmonic peak height and the time frequency response characteristic obtained in thestep 3;
step 5, calculating gas absorbance according to the time frequency response characteristics obtained in thestep 3 and the gas concentration value obtained in the step 4, subtracting the gas absorbance from the scattering light intensity signal measured in the step 2 to obtain a scattering light signal without gas absorption, and performing digital phase locking and low-pass filtering processing in thestep 3 to obtain a first harmonic signal thereof;
and 6, taking the mean value of the first harmonic signals obtained in the step 5 as a characteristic value for measuring the concentration of the particulate matters, wherein the characteristic value and the concentration of the particulate matters are in a linear relation, and obtaining the concentration value of the particulate matters through a calibration curve.
Compared with the prior art, the technical scheme of the invention has the beneficial effects that:
compared with the existing wavelength modulation spectrum technology, the method disclosed by the invention has the advantages that the light scattering measurement light path and the wavelength modulation measurement light path are coupled, the synchronous measurement of the concentration of the low-concentration particulate matter and the gas is realized, the low-frequency noise such as background dark current of a detector and the like is not additionally considered, the signal-to-noise ratio of the low-concentration particulate matter and the gas concentration measurement is effectively improved, the sensitivity is higher, and the detection lower limit of the existing particulate matter and the gas concentration is reduced, so that the technology disclosed by the invention has an important application value for realizing the synchronous online monitoring of the concentration of the particulate matter to be detected and the gas in a coal-fired power plant with an ultralow emission requirement.
Drawings
FIG. 1 is a schematic diagram of a system of a synchronous measuring device for particle and gas concentration based on infrared light modulation technology according to the present invention;
fig. 2 is a flow chart of the method for synchronously measuring the concentration of particulate matters and gas based on the infrared light modulation technology.
Detailed Description
The technical solutions of the present invention are further described below with reference to the accompanying drawings, but the scope of the claimed invention is not limited thereto.
As shown in fig. 1, the device for synchronously measuring the concentration of particulate matter and gas based on the infrared light modulation technology sequentially comprises a signal sending module 1, a particulate matter and gas measuring module 2, asignal receiving module 3 and a signal processing module 4; the signal generation module 1 comprises a function generator 5, alaser controller 6, a distributed feedback laser (DFB)7, an opticalfiber beam splitter 8 and an optical power amplifier 9; the particle and gas measuring module 2 comprises anoptical etalon 10, a heat tracing pipe belt 13, a measuring cell 11 and a heating module 12 wrapped outside the measuring cell 11; thesignal receiving module 3 is composed of threephotoelectric detectors 15; preheating particles to be measured andgas 14 through a heat tracing pipe belt 13, then entering a measuring cell 11, and maintaining the measuring cell 11 at a set temperature through a heating module 12; the function generator 5 inputs scanning superposition modulation signals into thelaser controller 6, thelaser controller 6 tunes the output wavelength and light intensity of the DFB laser 7, laser emitted by the DFB laser 7 is divided into three beams by the opticalfiber beam splitter 8, one beam enters the measuring cell 11 from a laser emitting end after passing through the optical power amplifier 9, and scattered light with gas absorption signals is received by thephotoelectric detector 15 and converted into electric signals to obtain scattered light intensity signals; one beam passes through theoptical etalon 10 and is received by thephotoelectric detector 15 to obtain an etalon signal; the other light signal is directly received by thephotoelectric detector 15 to obtain a background signal; the three signals are all transmitted to the signal processing module 4 for processing.
As shown in fig. 2, the method for synchronously measuring the concentration of particulate matter and gas based on the infrared light modulation technology of the present invention comprises the following steps:
step 1, the function generator sets the scanning frequency to be fsSignal superimposed modulation frequency fmInputting the signal into a laser controller, and tuning the output wavelength and light intensity of the DFB laser by the laser controller;
step 2, dividing the modulated light in the step 1 into three beams through an optical fiber beam splitter, enabling one beam to pass through an optical power amplifier and enter a measuring cell filled with gas and particles from a laser emitting end, and collecting scattered light intensity signals through a photoelectric detector
One beam passes through the optical etalon and the etalon signal is collected by the photoelectric detector
The other beam is directly collected by the photoelectric detector to obtain the background light intensity signal
Step 3, using the etalon signal
Obtaining a time frequency response characteristic upsilon (t) and a background light intensity signal
And scattered light intensity signal
Carrying out digital phase locking and low-pass filtering processing with the same parameter setting to obtain corresponding first harmonic signal and second harmonic signal:
in the formula (1), the reaction mixture is,
as a background light intensity signal
The corresponding first and second harmonic x and y components,
respectively, scattered light signals
The corresponding first and second harmonic x and y components, and F is a low pass filter.
In the formula (2), the reaction mixture is,
as a background light intensity signal
The first and second harmonic signals of (1),
for scattering optical signals
First and second harmonic signals.
And 4, according to the Beer-Lambert law and the Lorenz-Mie theory, the relationship between the scattered light signals and the concentrations of the particles and the gas can be expressed as follows:
in the formula (3), V is the volume of the flue gas to be measured, theta is a scattering angle, r is the distance between an observation point and scattering particles, rho is the density of the particles in the flue gas to be measured, and X
particleIs the mass concentration of particulate matter, i
1(θ, upsilon, D, n) and i
2(θ, upsilon, D, n) is a scattering intensity function, f
r(D) As a function of the particle size distribution, D
min、D
maxRespectively the lower limit and the upper limit of the particle size, n is the refractive index of the particles, P is the total pressure of the gas, T is the temperature of the gas, and X is
gasIs the gas concentration and L is the optical path length. Phi (upsilon) is a linear function, S (T) is the line intensity of transition spectral line,
the light intensity signal is an original light intensity signal without influence of gas absorption and particle scattering.
Background-subtracted intensity signal
Normalized second harmonic signal of
Can be expressed as:
the normalized second harmonic signal withholds the influence of the fluctuation of the concentration of the particulate matter on the light intensity signal, and the influence is on the center upsilon of the spectral line
0At its peak height
With gas concentration X
gasAnd (4) correlating. For experimental measurement signals, the normalized second harmonic peak heights at different gas concentrations were simulated from the HITRAN2016 spectral database under known temperature conditions
The measured gas concentration is obtained after interpolation calculationDegree X
gas。
And 5, calculating gas absorbance tau (upsilon) according to the time-frequency response characteristic upsilon (t) obtained in thestep 3 and the gas concentration value obtained in the step 4:
v(υ)=exp{-PS(T)Φ[υ(t)]XgasL} (5)
the scattered light intensity signal measured in the step 2 is processed
Deducting gas absorbance tau (upsilon) to obtain scattered light signal without gas absorption
Will be provided with
Carrying out digital phase locking and low-pass filtering processing by adopting the same parameters in the
step 3 to obtain a first harmonic signal thereof
Can be expressed as:
in the formula (7), G is the gain coefficient of the detector, i1The first order modulation amplitude of the light intensity.
And 6, taking the mean value of the first harmonic signals obtained in the step 5 as a characteristic value for measuring the concentration of the particulate matters, wherein the characteristic value and the concentration of the particulate matters are in a linear relation, and obtaining the concentration value of the particulate matters through a calibration curve.