A method for rapidly detecting VOCs in incineration flue gas by photoionization time-of-flight mass spectrometer

Abstract

The application provides a method for rapidly detecting VOCs in incineration flue gas by using a photoionization time-of-flight mass spectrometer. The method first establishes a standard curve of each component of VOCs in the incineration flue gas by using the photoionization time-of-flight mass spectrometer, then the photoionization time-of-flight mass spectrometer is used for real-time sampling and detection of the incineration flue gas sample, the sample ions are transmitted to a high-resolution reflective time-of-flight mass analyzer through a radio frequency quadrupole and an electrostatic ion transmission system, and are separated and detected according to the time-of-flight difference to the detector. The mass spectrum of each component of VOCs in the detected incineration flue gas is compared with the mass spectrum of the standard gas of each component of VOCs in the incineration flue gas, and the actual concentration of each component of VOCs in the incineration flue gas is calculated according to the standard curve of each component of VOCs in the incineration flue gas. The method can realize high-sensitivity, high-accuracy and full-coverage online monitoring of VOCs in the flue gas in the industrial incineration site, does not need to collect, purify, concentrate and other steps for the flue gas sample, and can realize real-time feedback of VOCs in the incineration flue gas.

Description

Technical Field

[0001] This invention relates to the field of flue gas online monitoring technology, specifically to an online monitoring method for rapid detection of VOCs in incineration flue gas using photoionization time-of-flight mass spectrometry. By directly introducing the incineration flue gas into the photoionization time-of-flight mass spectrometer for analysis and detection, real-time in-situ online monitoring of VOCs is achieved. Background Technology

[0002] Volatile organic pollutants (VOCs) are the main precursors to the formation of ozone (O3) and secondary organic particulate matter (SOA), and are listed as key air pollutants for prevention and control. Monitoring and statistics of VOC emissions from incineration flue gas are of great significance for ecological protection and human health.

[0003] VOCs analysis and detection generally employs spectroscopic and mass spectrometric methods. Spectroscopy is an analytical method based on the structural and compositional characteristics of substances. However, it is an indirect analytical technique, requiring prior calibration of the model using standard methods to achieve qualitative and quantitative analysis of unknown samples. Furthermore, in complex systems, cross-interference between components and interference absorption from substances such as moisture, dust, and aerosols in the substrate can affect the accuracy of spectral measurements. Gas chromatography-mass spectrometry (GC-MS) is considered the gold standard for analysis and detection, offering accurate and reliable qualitative and quantitative results. However, it has a long analysis cycle and complex procedures, and cannot effectively detect highly volatile and easily convertible substances. The principle of chromatographic separation limits its ability to perform high-throughput online analysis while maintaining qualitative analytical capabilities. Even with the aid of automated enrichment and injectors, it only achieves quasi-continuous pulse injection, and the temporal resolution still cannot meet the requirements for continuous real-time analysis.

[0004] Photoionization (PI) is a threshold soft ionization technique that produces molecular or quasi-molecular ion peaks with almost no fragment ions and is unaffected by background gas interference. When combined with a high-throughput mass analyzer, it offers high resolution, fast response, and high sensitivity. PI-TOFMS, which requires no sample acquisition or pretreatment, is the most promising online mass spectrometry technique.

[0005] Developing online methods for VOCs in real incineration flue gas based on photoionization time-of-flight mass spectrometry is an effective means to achieve air pollution control and accurate emission estimation of VOCs in incineration flue gas. Summary of the Invention

[0006] In order to enable rapid, accurate, and in-situ detection of VOCs in incineration flue gas, the purpose of this application is to provide a method for rapid detection of VOCs in incineration flue gas using photoionization time-of-flight mass spectrometry.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for rapid detection of VOCs in incineration flue gas using photoionization time-of-flight mass spectrometry, the method specifically includes the following steps:

[0009] (1) Establish standard curves for each VOC component in flue gas. Select standard gases of different concentrations of VOC components in flue gas and sample them in real time into a photoionization time-of-flight mass spectrometer for detection. Obtain mass spectra of standard gases of different concentrations of VOC components in flue gas. Perform linear quantitative fitting between the peak areas of each VOC component in flue gas and the corresponding concentrations of each VOC component in flue gas to obtain standard curves for each VOC component in flue gas.

[0010] (2) Real-time sampling and detection of incineration flue gas samples were carried out using photoionization time-of-flight mass spectrometry. The incineration flue gas was introduced into the photoionization time-of-flight mass spectrometer through the constructed flue gas pipeline for sampling. The sampled incineration flue gas samples were drawn into the photoionization time-of-flight mass spectrometer by a secondary sampling pump for real-time detection. Mass spectra of each VOC component in the incineration flue gas and real-time monitoring curves of each VOC component in the incineration flue gas were obtained, and the dynamic emission characteristics of each VOC component in the incineration flue gas were obtained.

[0011] (3) Compare the mass spectra of each VOC component in the detected flue gas with the mass spectra of the standard gas of each VOC component in the flue gas, and calculate the actual concentration of each VOC component in the flue gas based on the standard curve of each VOC component in the flue gas.

[0012] The standard gas for VOCs components in the incineration flue gas includes one or more of nitrogen, benzene, toluene, xylene, monochlorobenzene, vinyl chloride, dichloroethylene, tetrachloroethylene, and hexachlorobutadiene, with a concentration of 1-1000 ppb and a flow rate of 10-1000 ml / min.

[0013] The specific process for establishing the standard curve in step (1) is as follows: Five sets of standard gases of different concentrations of VOCs components in incineration flue gas were selected within the concentration range of 1-1000 ppb, with concentrations of X1 (ppb), X2 (ppb), X3 (ppb), X4 (ppb), and X5 (ppb), respectively. Five parallel samples were taken from each set, and the above five sets of standard gases of different concentrations were detected by photoionization time-of-flight mass spectrometry to obtain the corresponding peak areas, namely Y1, Y2, Y3, Y4, and Y5. The linear equation of the standard curve for the quantitative determination of VOCs components in the incineration flue gas was obtained by fitting: Y = a*X + b. The R value was obtained by fitting. 2 ≥0.99, where Y represents the peak area, X represents the concentration of VOCs in the flue gas, and R 2 This represents the goodness of fit of VOCs; a and b are constants.

[0014] The concentration of VOCs in the incineration flue gas is determined qualitatively using precise mass numbers and characteristic peaks of standard gas to identify the detected substances, and quantitatively using peak area and linear correlation curves to obtain the emission characteristics of VOCs concentration in the incineration flue gas.

[0015] The photoionization time-of-flight mass spectrometer described above uses a vacuum ultraviolet lamp ionization source, and the experimental conditions are as follows: vacuum ultraviolet lamp voltage of 1000–2000 V, and ionization region gas pressure of 4.0 × 10⁻⁶ V. 2 ~6.00×10 2 Pa, ion source temperature 100–200℃, MCP voltage 3700–4800V, detection zone gas pressure 7.00 × 10⁻⁶. -6 ~3.00×10 -4 Pa.

[0016] Specifically, VOCs in the flue gas are introduced into the VUV photoionization source via flue gas introduction, online pretreatment, and capillary negative pressure, directly ionizing sample molecules into molecular ions or quasi-molecular ions. The sample ions are then efficiently transmitted to a high-resolution reflective time-of-flight mass analyzer via a radio frequency quadrupole and electrostatic ion transport system. Ions accelerated to the same energy but with different mass-to-charge ratios are separated and detected based on their different flight velocities and arrival times at the detector. The ion signals are recorded by a high-precision time-to-digital converter (TDC) acquisition card and processed and analyzed in real time by data processing software.

[0017] The flue gas introduction includes a gas path system, a heat preservation system, and an automatic control module for gas path switching.

[0018] The purpose of the gas path system is to introduce flue gas from specific locations in the incineration system into the online monitoring cabin. During implementation, the length of the gas path system should be minimized, and the inner wall of the pipeline should be passivated.

[0019] The insulation system has a total pipeline insulation and heat tracing temperature of 180℃, which effectively prevents sample loss during transmission, prevents sample adsorption and deposition on the pipe wall, and controls the sample loss rate to within 5%.

[0020] The online pretreatment system includes an online filtration device and an online dehumidification device.

[0021] The online filtration device employs a two-stage filtration system, with a secondary 0.45μm pore size filter combined with multi-pulse backflushing technology, enabling automatic online dust removal from samples and ensuring effective removal of particulate matter.

[0022] The online dehumidification device uses high-temperature Nafion tube dehumidification technology to dry flue gas samples at 100°C, which can effectively remove water vapor and highly corrosive gases from the flue gas and prevent the water vapor in the flue gas from affecting the analytical instruments.

[0023] The analysis and detection were performed using a photoionization time-of-flight mass spectrometer, and the connection interface between the instrument and the gas path system was a self-designed supporting module.

[0024] The qualitative analysis employs a vertically accelerating reflective structure and high-field extraction technology. After correcting the mass axis with standard gas, the molecular formula of VOCs can be directly determined by using precise mass number information and referring to the characteristic peaks of VOCs standard gas.

[0025] The VOCs in the incineration flue gas include, but are not limited to, benzene series compounds, halogenated hydrocarbons, aromatic hydrocarbons, alkanes, alkenes, alkynes, alcohols, aldehydes, ketones, ethers, esters, phenols, organic amines, and organic sulfur compounds. The standard gas concentration is selected from 10 to 1000 ppb, and the standard gas flow rate is controlled from 10 to 1000 ml / min.

[0026] The quantitative analysis involves determining the target analyte based on the qualitative analysis results, switching the instrument analysis and detection mode to the standard gas detection mode, and performing online quantitative calculations of the target analyte in the flue gas based on the target analyte standard.

[0027] The purpose of residual purging is to prevent the memory effect from interfering with the analysis and detection of flue gas samples during continuous online monitoring. Specifically, this can be achieved by switching the instrument's analysis and detection mode to purging mode and using a large flow of purging gas to clean the instrument's pipelines and detection system.

[0028] The purging gas includes, but is not limited to, high-purity nitrogen and compressed air.

[0029] The purging flow rate is 100-1000 ml / min.

[0030] This application has the following beneficial technical effects:

[0031] 1. This application enables highly sensitive, accurate, and comprehensive online monitoring of VOCs in flue gas at industrial incineration sites. It eliminates the need for flue gas sample collection, purification, and concentration, and provides real-time feedback on VOCs in incineration flue gas. This allows for synergistic effects of pollution reduction and carbon reduction in industrial production processes, while saving labor costs and reagent consumption.

[0032] 2. This application enables the simultaneous analysis and detection of hundreds of VOCs in incineration flue gas, with a detection time as low as 1 minute and a detection limit as low as 0.1 ppt. No sample collection or pretreatment is required, significantly reducing pretreatment time and instrument analysis and detection time. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the solid waste incineration system structure of this application.

[0034] In the attached diagram, the numerical codes represent: ①-boiler, ②-reaction tower, ③-bag filter, ④-SCR, ⑤-chimney.

[0035] Figure 2 This is a schematic diagram of the online monitoring system for incineration flue gas in this application.

[0036] In the attached diagram, the numbers represent: 1-sampling point, 2-flue gas pipeline, 3-photoionization time-of-flight mass spectrometer, 4-client, 5-control system, and 6-environmental protection department.

[0037] Figure 3 This is the mass spectrum of VOCs detected in flue gas in Example 1 of this application.

[0038] Figure 4 This is a standard curve diagram of eight representative VOCs in the flue gas of this application.

[0039] Figure 5 This is the mass spectrum of VOCs detected in flue gas in Example 2 of this application.

[0040] Figure 6 This is a mass spectrum of VOCs in the inlet flue gas of the SCR device ④ in Embodiment 3 of this application.

[0041] Figure 7 This is a mass spectrum of VOCs in the flue gas outlet of the SCR device ④ in Embodiment 3 of this application. Detailed Implementation

[0042] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0043] Instrument: Photoionization Time-of-Flight Mass Spectrometry (PI-TOFMS5020), detection sites are Figure 1 Any position before or after device ① to ⑤.

[0044] Example 1

[0045] This application provides a method for online monitoring of VOCs in boiler outlet flue gas, including the following steps:

[0046] (1) Before the experiment, a VOCs standard curve was established using the online dilution method. Specifically, 1 ppm VOCs standard gases were prepared, including benzene, toluene, xylene, trimethylbenzene, tetramethylbenzene, phenol, methylphenol, and dimethylphenol. High-purity nitrogen was used, and a high-precision mass flow meter was employed. The standard gases were diluted to 1 ppb, 5 ppb, 10 ppb, 50 ppb, and 100 ppb, respectively, according to the concentration from low to high. After the signal reached equilibrium at each concentration, five parallel tests were performed, the average value was taken, and the relative standard deviation was calculated to establish the relative relationship curve between the peak area and concentration of each standard gas. The specific standard curve is shown below. Figure 4 As shown, V1-V8 represent benzene, toluene, xylene, trimethylbenzene, tetramethylbenzene, phenol, methylphenol, and dimethylphenol, respectively.

[0047] (2) A sampling point is taken between boiler ① and reaction tower ②. Using a two-stage sampling pump, a multi-channel sampling system and automatic analysis control software, the flue gas sample is sent through a sampling probe, a full-process high-temperature heat tracing (180℃) pipeline and a high-temperature dehydration (120℃) module to the photoionization time-of-flight mass spectrometer.

[0048] (3) After the detection begins, the pre-set online monitoring sequence is automatically executed. First, the purging mode is entered, and the pipeline is purged with clean high-purity nitrogen at a rate of 300 ml / min to prevent sample residue. The purging time is 13.5 min. After the purging is completed, the system automatically switches to the detection mode. The incineration flue gas is stably introduced into the analytical instrument at a rate of 100 ml / min. After the flow rate stabilizes for 30 s, the introduced incineration flue gas is monitored online for 300 s. The detection conditions for the photoionization time-of-flight mass spectrometer are shown in Table 1. After the detection is completed, the system switches to the calibration mode. The standard gas concentration is selected as 100 ppb, and the standard gas flow rate is controlled at 100 ml / min. After the standard gas flow rate stabilizes for 30 s, the standard gas is used for signal correction and mass axis calibration to obtain the mass spectrum of VOCs in the incineration flue gas, as shown in Table 1. Figure 3 As shown.

[0049] (4) Based on the characteristic peaks of each VOCs component in the incineration flue gas standard gas, the precise mass numbers of benzene, toluene, xylene, trimethylbenzene, tetramethylbenzene, phenol, methylphenol and dimethylphenol were used to qualitatively determine the spectral peaks in the spectrum: 78.04695, 92.0626, 106.07825, 120.0939, 134.10955, 94.04187, 108.05752 and 122.07317. The peak areas in the spectrum were substituted into the pre-calculated standard curve to obtain the concentration values ​​of benzene, toluene, xylene, trimethylbenzene, tetramethylbenzene, phenol, methylphenol and dimethylphenol in the flue gas as 0.6 ppbv, 2.8 ppbv, 11.7 ppbv, 0.4 ppbv, 1.0 ppbv, 1.2 ppbv, 1.5 ppbv and 2.8 ppbv, respectively.

[0050] Table 1. PI-TOFMS instrument parameters for online monitoring of VOCs in flue gas

[0051] parameter numerical values VUV lamp voltage 1400V ExtractV1 voltage 16V FocusV2 voltage 14V Skimmer1 voltage 10V Q-offset voltage 4V Skimmer2 voltage 2V Lens1 voltage 120V Lens3 voltage 100V P-offset voltage 25V MCP voltage 4250V Vacuum level (ion source) 584V Vacuum level (detector) <![CDATA[5.2×10 -4 In]]> Heat tracing pipe temperature 150℃ Ion source temperature 100℃

[0052] Example 2

[0053] exist Figure 1 A sampling point was taken at the middle of the chimney (⑤), and the other steps were the same as in Example 1 to obtain the mass spectrum of VOCs in the incineration flue gas, such as... Figure 5 As shown, according to Figure 5 The precise mass numbers of the spectra (78.04695, 92.0626, 106.07825, 120.0939, 134.10955, 94.04187, 108.05752, 122.07317) were used to qualitatively determine the positions of the spectral peaks. Substituting the peak areas into a pre-calculated standard curve, the concentrations of benzene, toluene, xylene, trimethylbenzene, tetramethylbenzene, phenol, methylphenol, and dimethylphenol in the flue gas were obtained as 0.9 ppbv, 3.1 ppbv, 3.7 ppbv, 0.3 ppbv, 0.7 ppbv, 1.3 ppbv, 1.2 ppbv, and 1.9 ppbv, respectively.

[0054] Example 3

[0055] This application provides a selective catalytic reduction (SCR) denitrification device. [1] A separate online monitoring method was used for the inlet and outlet flue gas of the SCR device ④. Sampling points were taken at the inlet and outlet locations. A two-stage sampling pump, a multi-channel sampling system, and automatic analysis and control software were used to guide the flue gas samples through a sampling probe, a fully high-temperature heated pipeline, and a high-temperature dehydration module before entering the analytical instrument. First, the flue gas pipeline was switched to the SCR inlet, and the online monitoring of the SCR inlet flue gas was performed according to the steps in Example 1 to obtain the mass spectrum of VOCs in the incineration flue gas, such as... Figure 6As shown, in Figure 6 Based on the precise mass numbers 78.04695, 92.0626, 106.07825, 120.0939, 134.10955, 94.04187, 108.05752, and 122.07317 in the spectrum, the peaks in the spectrum were qualitatively determined. Substituting the peak areas in the spectrum into the pre-calculated standard curve, the concentrations of benzene, toluene, xylene, trimethylbenzene, tetramethylbenzene, phenol, methylphenol, and dimethylphenol in the incineration flue gas were obtained as 0.4 ppbv, 0.8 ppbv, 46.4 ppbv, 0.2 ppbv, 0.8 ppbv, 1.2 ppbv, 2.6 ppbv, and 2.3 ppbv, respectively.

[0056] Using a sampling pump, flue gas valves, and supporting control software, the flue gas pipeline was switched to the outlet of SCR unit ④, and the flue gas at the outlet of SCR unit ④ was monitored online according to the steps in Example 1. Mass spectra of VOCs in the incineration flue gas were obtained, such as... Figure 7 As shown, in Figure 7 The spectral peaks in the spectrum were qualitatively determined based on their precise mass numbers of 78.04695, 92.0626, 106.07825, 120.0939, 134.10955, 94.04187, 108.05752, and 122.07317. The peak areas in the spectrum were then substituted into a pre-calculated standard curve to obtain the concentrations of benzene, toluene, xylene, trimethylbenzene, tetramethylbenzene, phenol, methylphenol, and dimethylphenol in the incineration flue gas as 0.5 ppbv, 1.5 ppbv, 2.4 ppbv, 0.2 ppbv, 0.7 ppbv, 1.3 ppbv, 1.1 ppbv, and 1.4 ppbv, respectively.

[0057] Further comparison of the VOCs composition and concentration in the flue gas at the SCR inlet and outlet revealed that the SCR device promoted the removal of benzene, toluene, and phenol by 25.5%, 92.3%, and 8.2%, respectively. The removal efficiency of the SCR device for xylene, trimethylbenzene, tetramethylbenzene, methylphenol, and dimethylphenol was 94.8%, 14.8%, 19.0%, 56.5%, and 36.2%, respectively.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. References:

[0059] [1] Ren Meihui, Fan Yun, Wang Sheng, Xu Liang, Zhang Ning, Zhang Xueping, Chen Jiping, Zhang Haijun, Synergistic removal of PCDD / Fs, PCBs and PCNs from coke oven gas combustion exhaust gas by SCR device [J]. Environmental Science, 2019, 40(1): 143-148.

Claims

1. A method for rapid detection of VOCs in incineration flue gas using photoionization time-of-flight mass spectrometry, characterized in that, The specific steps include: (1) Establish standard curves for each VOC component in flue gas. Select standard gases of different concentrations of VOC components in flue gas and sample them in real time into a photoionization time-of-flight mass spectrometer for detection. Obtain mass spectra of standard gases of different concentrations of VOC components in flue gas. Perform linear quantitative fitting between the peak areas of each VOC component in flue gas and the corresponding concentrations of each VOC component in flue gas to obtain standard curves for each VOC component in flue gas. (2) Real-time sampling and detection of incineration flue gas samples were carried out using photoionization time-of-flight mass spectrometry. The incineration flue gas was introduced into the photoionization time-of-flight mass spectrometer through the constructed flue gas pipeline for sampling. The sampled incineration flue gas samples were drawn into the photoionization time-of-flight mass spectrometer by a secondary sampling pump for real-time detection. Mass spectra of each VOC component in the incineration flue gas and real-time monitoring curves of each VOC component in the incineration flue gas were obtained, and the dynamic emission characteristics of each VOC component in the incineration flue gas were obtained. (3) Compare the mass spectra of each VOC component in the detected flue gas with the mass spectra of the standard gas of each VOC component in the flue gas, and calculate the actual concentration of each VOC component in the flue gas based on the standard curve of each VOC component in the flue gas.

2. The method for rapid detection of VOCs in incineration flue gas using photoionization time-of-flight mass spectrometry according to claim 1, characterized in that: The standard gases containing VOCs in incineration flue gas include one or more of the following: nitrogen, benzene, toluene, xylene, monochlorobenzene, vinyl chloride, dichloroethylene, tetrachloroethylene, and hexachlorobutadiene.

3. The method for rapid detection of VOCs in incineration flue gas using photoionization time-of-flight mass spectrometry according to claim 1, characterized in that: The specific process for establishing the standard curve in step (1) is as follows: Five sets of standard gases of different concentrations of VOCs components in incineration flue gas were selected within the concentration range of 1-1000 ppb, with concentrations of X1 (ppb), X2 (ppb), X3 (ppb), X4 (ppb), and X5 (ppb), respectively. Five parallel samples were taken from each set, and the above five sets of standard gases of different concentrations were detected by photoionization time-of-flight mass spectrometry to obtain the corresponding peak areas, namely Y1, Y2, Y3, Y4, and Y5. The linear equation of the standard curve for the quantitative determination of VOCs components in the incineration flue gas was obtained by fitting: Y = a*X + b. The R value was obtained by fitting. 2 ≥0.99, where Y represents the peak area, X represents the concentration of VOCs in the flue gas, and R 2 This represents the goodness of fit of VOCs; a and b are constants. The concentration of VOCs in the incineration flue gas is determined qualitatively using precise mass numbers and characteristic peaks of standard gas to identify the detected substances, and quantitatively using peak area and linear correlation curves to obtain the emission characteristics of VOCs concentration in the incineration flue gas.

4. The method for rapid detection of VOCs in incineration flue gas using photoionization time-of-flight mass spectrometry according to claim 1, characterized in that, The photoionization time-of-flight mass spectrometer described above uses a vacuum ultraviolet lamp ionization source, and the experimental conditions are as follows: vacuum ultraviolet lamp voltage of 1000–2000 V, and ionization region gas pressure of 4.0 × 10⁻⁶ V. 2 ~6.00×10 2 Pa, ion source temperature 100–200℃, MCP voltage 3700–4800V, detection zone gas pressure 7.00 × 10⁻⁶. -6 ~3.00×10 -4 Pa.

5. The method for rapid detection of VOCs in incineration flue gas using photoionization time-of-flight mass spectrometry according to claim 1, characterized in that, The VOCs in the incineration flue gas include, but are not limited to, benzene compounds, halogenated hydrocarbons, aromatic hydrocarbons, alkanes, alkenes, alkynes, alcohols, aldehydes, ketones, ethers, esters, phenols, organic amines, and organic sulfur compounds.

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