CN-120121551-B - Farmland ammonia emission monitoring system based on broadband cavity enhanced differential absorption spectrum

CN120121551BCN 120121551 BCN120121551 BCN 120121551BCN-120121551-B

Abstract

The invention discloses a farmland ammonia emission monitoring system based on broadband cavity enhanced differential absorption spectrum, which comprises a multi-pipeline acquisition unit, a light source unit, a gas absorption tank unit, a spectrum detection unit, a calculation unit and a calculation unit, wherein the multi-pipeline acquisition unit acquires gas to be detected at a plurality of sampling points through a plurality of pipelines and transmits the gas to be detected to the gas absorption tank unit, the light source unit emits detection light and is coupled with the gas absorption tank unit, the gas absorption tank unit adopts an absorption chamber inert to ammonia gas to carry out long-optical-path enhanced absorption on the gas to be detected, and simultaneously transmits the detection light passing through the gas to be detected and outputs the detection light, the spectrum detection unit acquires the detection light output by the gas absorption tank unit and forms cavity enhanced spectrum data, and the calculation unit performs ammonia concentration inversion and emission flux calculation based on the cavity enhanced spectrum data and combines a differential absorption algorithm. The system has ppb level detection sensitivity, has good passivation effect and detection accuracy on ammonia gas, has simple structure and simple and convenient operation, and is very widely applicable to the detection of farmland ammonia emission.

Inventors

LIU CHENG
WANG HONGFEI
XING CHENGZHI
WANG ZAIWEI
SUN ZHONGMOU

Assignees

中国科学技术大学

Dates

Publication Date: 20260508
Application Date: 20250311

Claims (8)

1. A farmland ammonia emission monitoring system based on broadband cavity enhanced differential absorption spectrum is characterized by comprising a multi-pipeline acquisition unit, a light source unit, a gas absorption tank unit, a spectrum detection unit and a calculation unit; the multi-pipeline collecting unit collects the gas to be tested at the multi-sampling points through a plurality of pipelines and transmits the gas to the gas absorption tank unit; the light source unit emits detection light and is coupled into the gas absorption cell unit, wherein the light source unit comprises a deuterium lamp light source, strong continuous light with the short ultraviolet wavelength of 185-400nm is emitted as detection light, and the detection light is coupled into the gas absorption cell unit after being collimated by the convex lens, so that the optical power signal is maximized; the gas absorption cell unit comprises an absorption cell with a cavity structure, the inner side of the absorption cell is coated with a passivation coating inert to ammonia gas, a resonant cavity is formed by coupled detection light and a high reflector in a cavity inert to the ammonia gas, long-optical-path enhanced absorption is carried out on the gas to be detected, and meanwhile the detection light is output; the spectrum detection unit collects detection light output by the gas absorption cell unit and forms cavity enhancement spectrum data; The calculation unit is based on the cavity enhancement spectrum data and combines a differential absorption algorithm to reverse the ammonia concentration and calculate the emission flux, and specifically comprises a data processing module, an inversion calculation module and a dynamic flux automatic calculation module; the data processing module is used for performing polynomial fitting, noise reduction and filtering on the cavity enhancement spectrum data to obtain a differential absorption section; The inversion calculation module is used for data preprocessing and ammonia initial concentration prediction, the predicted initial concentration prediction is substituted into the calculated optical density, the real effective absorption optical path is corrected through repeated iteration based on the optical density, a least square method is adopted to fit a differential absorption section determined by the effective absorption optical path and a differential absorption spectrum, an LSTM residual error model is adopted to train and optimize concentration residual error constructed based on the least square method, ammonia inversion concentration is obtained, the iterative stop condition is that the concentration difference of two iterative inversion is smaller than the error of spectrum fitting, and a loss compensation coefficient is introduced, so that final inversion ammonia concentration is obtained; The dynamic flux automatic calculation module is used for calculating the emission flux based on the ammonia concentration.
2. The farmland ammonia emission monitoring system based on broadband cavity enhanced differential absorption spectroscopy according to claim 1, wherein the multi-pipeline acquisition unit comprises a multi-pipeline control module, a flow control module, a temperature and humidity acquisition module, a constant temperature control module, an air pump control module and a gas filtering module; The multi-pipeline control module comprises multiple-input-output electromagnetic valves for controlling the sampling time resolution, and the multiple-pipeline electromagnetic valves are respectively connected with different flux boxes through pipelines to collect gas to be tested at multiple positions; the flow control module is used for controlling the collection flow of each pipeline; the temperature and humidity acquisition module is used for acquiring the ambient temperature and humidity and visually displaying the ambient temperature and humidity in real time; the constant temperature control module is used for performing constant temperature control on the inside of a module accommodating cavity of the multi-pipeline acquisition unit, and the control precision reaches +/-0.1 ℃; The air pump control module is used for controlling an air pump arranged on each pipeline to realize air extraction and sampling of the pipeline; the gas filtering module is used for arranging a particle filter and a drying device on a pipeline leading to the gas absorption tank unit, so that aerosol and water vapor in the gas to be detected are effectively removed.
3. The farmland ammonia emission monitoring system based on broadband cavity enhanced differential absorption spectrum according to claim 1, wherein the gas absorption tank unit further comprises optical connection components arranged at the input end and the output end of the absorption tank, the absorption tank is connected with the optical connection components at the two ends through threads, each optical connection component is further connected with an optical fixing piece through threads, the bottom of each optical fixing piece is provided with a fixing thread, a reflector adjusting lens barrel is arranged along the direction of an optical path and embedded into the optical fixing piece, the reflector adjusting lens barrel comprises a high reflector arranged along the optical path, and a sealing ring which surrounds the outer side of the reflector adjusting lens barrel and plays an interference fit when embedded into the optical fixing piece, and the elasticity of the sealing ring can realize micro-angle adjusting effect on the reflector adjusting lens barrel, so that the optical path is convenient to adjust.
4. The farmland ammonia emission monitoring system based on broadband cavity enhanced differential absorption spectroscopy according to claim 3, wherein the optical fixing piece is further provided with a threaded through hole and a nitrogen purging pipeline connected with the threaded through hole, and the nitrogen purging pipeline is used for performing nitrogen purging so as to protect lenses of the high-reflection mirror; the absorption tank is provided with an air hole, a precise pressure gauge is arranged on a pipeline connected with the air hole, the pressure indication inside the absorption tank is displayed in real time, and the absorption tank is clamped by two clamping pieces; the left optical connecting component and the right optical connecting component are provided with air holes which are respectively used as an air inlet and an air outlet, and a pipeline connected with the air holes is provided with an air extracting pump to control the inlet and the outlet of the gas in the absorption tank.
5. A farmland ammonia emission monitoring system based on broadband cavity enhanced differential absorption spectroscopy according to claim 3, wherein said passivation coating inert to ammonia gas comprises SilcoNert < 2000 > passivation coating, polytetrafluoroethylene coating.
6. The farmland ammonia emission monitoring system based on broadband cavity enhanced differential absorption spectrum according to claim 3, wherein the absorption tank is in a pipeline form, the pipeline length is 500 nm-1000 mm, and the pipeline inner diameter is 25.4 mm-50.8 mm.
7. The farmland ammonia emission monitoring system based on broadband cavity enhanced differential absorption spectroscopy according to claim 1, wherein the spectrum detection unit comprises a lens, a detection optical fiber and a spectrometer, and the detection light emitted from the gas absorption cell unit is received by the detection optical fiber after being focused by the lens and then transmitted to the spectrometer through the detection optical fiber, so that the cavity enhanced absorption spectroscopy is formed in the spectrometer.
8. The broadband cavity enhanced differential absorption spectroscopy-based farmland ammonia emission monitoring system according to claim 1, wherein a transducer model is used for initial concentration prediction of ammonia gas.

Description

Farmland ammonia emission monitoring system based on broadband cavity enhanced differential absorption spectrum Technical Field The invention belongs to the technical field of intersection of spectral absorption measurement and instrument automation, and particularly relates to a farmland ammonia emission monitoring system based on broadband cavity enhanced differential absorption spectrum. Background Ammonia is colorless and has a pungent smell, and can cause great harm to cardiovascular nerves and immune systems of human bodies. Agricultural sources are the most major sources of ammonia, such as animal husbandry and chemical fertilizer use, and react with acid gases in the atmosphere to form particulate nitrates, which increase the concentration of PM2.5 particulates in the air, affect air quality, and reduce atmospheric visibility. It is therefore very important to develop a highly sensitive detection technique for detecting ammonia concentration and discharge flux in farmland. At present, ammonia detection in farmlands has various analysis methods, wherein the main analysis methods include an electrochemical method, a colorimetry method, a chromatographic analysis method, a tunable diode laser absorption spectrometry method and the like, and all the analysis methods have defects. The electrochemical method has the defects of short service life of the sensor, need to replace the sensor every year and poor anti-interference capability when various gases exist in the environment, the colorimetric method is a classical analysis method, needs various chemical reagents for reaction, can meet the measurement requirement only by collecting a large amount of air samples when the ammonia concentration in the environment is low, has the defects of time and labor waste, has complex operation procedures and huge volume, and is a tunable diode laser absorption spectrometry method which has high detection precision, but has large equipment volume, complex control instrument and high cost, is mainly suitable for laboratory measurement and is not easy to be widely used for measuring ammonia volatilization detection in agricultural production, so that the development of a farmland ammonia emission automatic detection instrument which has high precision sensitivity, is portable, has simple device and is stable in long-term work without manual frequent calibration is very important. The cavity enhanced absorption spectrum technology can obtain a long effective absorption optical path in a limited space, greatly improves the detection sensitivity and resolution, and has the advantages of simple device, small volume, easy operation and good robustness. Is a method which is very suitable for real-time, dynamic continuous and online gas detection and measurement. The differential absorption spectroscopy (DOAS) is characterized by identifying gas components by utilizing the narrow-band absorption characteristics of gas molecules in the air, inverting the concentration of trace gas according to the narrow-band absorption intensity, and having the characteristics of high precision, short period and quick response. Because ammonia has active chemical properties and strong adsorptivity, an absorption peak is narrower in a near infrared band, and ammonia is extremely easily interfered by moisture and the like in the band, the detection of ammonia by utilizing a spectrum absorption technology has been challenging. Disclosure of Invention In view of the above, the invention aims to provide a farmland ammonia emission monitoring system based on broadband cavity enhanced differential absorption spectrum, which has ppb level detection sensitivity, good passivation effect and detection accuracy on ammonia gas, has simple system structure and simple and convenient operation, and is very widely applicable to farmland ammonia emission detection. In order to achieve the aim of the invention, the farmland ammonia emission monitoring system based on broadband cavity enhanced differential absorption spectrum provided by the embodiment comprises a multi-pipeline acquisition unit, a light source unit, a gas absorption tank unit, a spectrum detection unit and a calculation unit; the multi-pipeline collecting unit collects the gas to be tested at the multi-sampling points through a plurality of pipelines and transmits the gas to the gas absorption tank unit; the light source unit emits detection light and is coupled with the air inlet body absorption cell unit; The gas absorption cell unit adopts the coupled detection light to form a resonant cavity with a high reflector in a chamber inert to ammonia gas, carries out long-optical-path enhanced absorption on the gas to be detected, and outputs the detection light; the spectrum detection unit collects detection light output by the gas absorption cell unit and forms cavity enhancement spectrum data; The calculation unit is used for calculating the ammonia concentration and the emission flux based on th