A gas analyzer and an analysis method thereof

Abstract

The application relates to a gas analyzer and an analysis method thereof. The gas analyzer comprises, in sequence along an air inlet direction, a sampling unit, a filtering unit, a flow control unit, a gas chamber, a pressure control unit, a gas pump and a tail gas treatment unit; further comprising a temperature control unit, a constant temperature unit, a light source, a detector, a signal acquisition unit and an analysis control unit, wherein the constant temperature unit comprises a circulating air duct, a circulating fan and a heater, the gas chamber, the circulating fan and the heater are located in the circulating air duct, a temperature sensor and a pressure sensor are arranged in the circulating air duct, the circulating fan and the heater are signal connected with the temperature control unit; the light source and the detector are arranged on two sides of the gas chamber respectively; the detector is signal connected with the signal acquisition unit; and the analysis control unit is signal connected with the sampling unit, the flow control unit, the pressure control unit, the gas pump, the temperature control unit, the light source, the signal acquisition unit, the temperature sensor and the pressure sensor. The application can effectively improve the detection precision.

Description

Technical Field

[0001] This invention belongs to the field of analytical testing technology, specifically relating to a gas analyzer and its analytical method. Background Technology

[0002] Currently, there are many types of analytical instruments based on spectroscopy, each with its own gas analysis technology. These include ultraviolet spectrophotometry, ultraviolet differential absorption spectrometry, non-dispersive ultraviolet, non-dispersive infrared, TDLAS, Fourier transform infrared spectroscopy, cavity ring-down spectroscopy, photoacoustic spectroscopy, ultraviolet fluorescence, and chemiluminescence. However, all gas analysis technologies based on spectroscopy are affected by factors such as gas flow rate, ambient temperature, and pressure.

[0003] Therefore, ensuring that the detection accuracy of analytical instruments remains within the error range is a pressing problem that instrument manufacturers urgently need to solve. Summary of the Invention

[0004] Based on the aforementioned shortcomings and deficiencies in the prior art, the purpose of this invention is to at least solve one or more of the aforementioned problems in the prior art. In other words, one of the objectives of this invention is to provide a gas analyzer and its analysis method that meet one or more of the aforementioned requirements.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0006] A gas analyzer includes a sampling unit, a filtering unit, a flow control unit, a gas chamber, a pressure control unit, a gas pump, and an exhaust gas treatment unit connected sequentially along the gas inlet direction.

[0007] It also includes a temperature control unit, a constant temperature unit, a light source, a detector, a signal acquisition unit, and an analysis and control unit. The constant temperature unit includes a circulating air duct, a circulating fan, and a heater. The gas chamber, the circulating fan, and the heater are located inside the circulating air duct. Temperature sensors and pressure sensors are also installed inside the circulating air duct. The circulating fan and the heater are signal-connected to the temperature control unit. The light source and the detector are respectively located on both sides of the gas chamber. The detector is signal-connected to the signal acquisition unit.

[0008] The analysis and control unit is connected to the sampling unit, flow control unit, pressure control unit, air pump, temperature control unit, light source, signal acquisition unit, temperature sensor, and pressure sensor.

[0009] As a preferred embodiment, a flow monitor is provided between the flow control unit and the gas chamber.

[0010] As a preferred embodiment, the gas chamber is provided with a heat insulation layer on its periphery.

[0011] As a preferred embodiment, the circulating air duct is provided with heat dissipation fins.

[0012] As a preferred embodiment, the circulating air duct is provided with an insulation layer.

[0013] As a preferred embodiment, the exhaust gas treatment unit employs a combination of activated carbon and an exhaust gas purification device.

[0014] The present invention also provides an analysis method for a gas analyzer as described in any of the preceding embodiments, comprising the following steps:

[0015] S1. Obtain the ultraviolet spectrum and preprocess the spectrum;

[0016] S2. Calculate the concentration of gaseous pollutants based on the preprocessed spectrum;

[0017] S3. Correct the concentration of gaseous pollutants.

[0018] As a preferred embodiment, in step S1, the spectral preprocessing includes:

[0019] The ultraviolet spectrum was subjected to dark background subtraction, nonlinear correction, smoothing, and averaging in sequence.

[0020] As a preferred embodiment, step S2 includes the following steps:

[0021] S21. Divide the pretreated spectrum by the standard gas spectrum and obtain the logarithm to calculate the absorbance of the gaseous pollutants.

[0022] S22. Perform Savitzky-Golay filtering on the absorbance of the gaseous pollutants to obtain the differential absorbance of the gaseous pollutants.

[0023] S23. Based on the differential absorbance of gaseous pollutants, the concentration of gaseous pollutants is obtained by least squares method.

[0024] As a preferred embodiment, step S3 includes the following steps:

[0025] S31. Obtain the pressure of the gas chamber, with the concentration of the sample gas before pressure correction as C0 and the concentration after pressure correction as C1: C1=f0(C0)=C0*P0 / P1; where f0 is the pressure correction function, P0 is the calibration pressure, and P1 is the measured pressure of the gas chamber.

[0026] S32. Obtain the temperature of the gas chamber and perform temperature correction. The concentration after temperature correction is C2: C2=f1(C1)=C1*(273+T1) / (273+T0); where f1 is the temperature correction function, T0 is the calibration temperature, and T1 is the measured temperature of the gas chamber.

[0027] S33. The concentration after the sliding algorithm is C3: C3=f2(C2)=C2(i) / N+C3(j-1)*(N-1) / N; C3(i) is the concentration corresponding to the i-th sample, C3(i-1) is the concentration corresponding to the (i-1)-th sample, f2 is the sliding algorithm function, and N is the number of sliding steps;

[0028] S34. Obtain the humidity RH of the sample gas, and the concentration after humidity correction is C4: C4=f3(C3)=C3 / (1-RH); where f3 is the humidity correction function;

[0029] S35. Calculate the gas concentration C5 of the actual sample gas: C5 = f4(C4) = C4 / R; where R is the proportion of the actual sample gas that is diluted.

[0030] Compared with the prior art, the beneficial effects of this invention are:

[0031] The gas analyzer of the present invention utilizes an analysis control unit to control a sampling unit, a flow control unit, a temperature control unit, and a pressure control unit to process the sampled gas, and to perform high-precision control on the uniformity of gas flow, as well as temperature and pressure stability, ensuring that the parameters change within 0.1% error, thereby achieving accurate signal analysis and measurement. Attached Figure Description

[0032] Figure 1 This is a structural diagram of the gas analyzer according to Embodiment 1 of the present invention;

[0033] Figure 2 This is a flowchart of the analysis method of the gas analyzer according to Embodiment 1 of the present invention. Detailed Implementation

[0034] To more clearly illustrate the embodiments of the present invention, specific implementation methods will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0035] Example 1:

[0036] like Figure 1As shown, the gas analyzer in this embodiment includes a sampling unit / calibration unit → a filtering unit → a flow control unit → a gas chamber → a pressure control unit → a gas pump (hereinafter referred to as the pump) → an exhaust gas treatment unit distributed along the gas path. It also includes a temperature control unit, a constant temperature unit, a light source, a detector, a signal acquisition unit, and an analysis control unit. The constant temperature unit includes a circulating air duct, a circulating fan, and a heater. The gas chamber, the circulating fan, and the heater are located in the circulating air duct. A temperature sensor and a pressure sensor are also provided in the circulating air duct. The circulating fan and the heater are signal-connected to the temperature control unit. The light source and the detector are respectively located on both sides of the gas chamber. The detector is signal-connected to the signal acquisition unit.

[0037] The analysis and control unit is connected to the sampling unit, flow control unit, pressure control unit, air pump, temperature control unit, light source, signal acquisition unit, temperature sensor, and pressure sensor.

[0038] The sampling / calibration unit processes the sample gas by removing dust, preheating, and sampling at a uniform speed to obtain a homogeneous pollutant gas; it filters the sample gas for large particulate matter to remove particles larger than 10μm to prevent blockage of the sampling gas path; it heats the gas to a suitable temperature according to the operating conditions to prevent the formation of crystals; it obtains the dilution ratio of the sample gas and controls the ratio to R; and it also obtains the humidity RH of the sampling unit.

[0039] This embodiment uses a pump as the power system to obtain a uniform intake volume, ensuring that the gas flow rate meets the monitoring requirements during long-term operation.

[0040] The filtration unit in this embodiment further performs more precise dust removal on the sample gas.

[0041] The flow control unit is equipped with a flow monitor between itself and the gas chamber. The gas chamber is surrounded by a heat insulation layer. The circulating air duct is equipped with heat dissipation fins and an insulation layer is installed outside the circulating air duct.

[0042] The exhaust gas treatment unit in this embodiment uses a combination of activated carbon and an exhaust gas purification device.

[0043] In this embodiment, the gas flow rate is set by a flow control unit to further control the accuracy of the flow rate, ensuring more precise flow and a control accuracy of 0.03%, before the gas enters the gas chamber.

[0044] In this embodiment, the pressure entering the gas chamber is kept constant at a fixed value with an accuracy of 0.02% through a pressure control unit.

[0045] In this embodiment, gas is extracted from the gas chamber by an air pump, and then the waste gas is treated by activated carbon and a tail gas purification device.

[0046] The temperature control unit of this embodiment is described in detail below:

[0047] (1) Wrap the gas chamber being measured evenly with insulating cotton;

[0048] (2) The temperature of the heater is set by the temperature control unit, the air in the constant temperature unit is heated and then circulated out through the heat dissipation fin air duct; the air is blown out from the left and right sides through the circulating air duct structure, and then circulated through the entire constant temperature unit by the suction action of the fan after passing through the gas chamber.

[0049] (3) The outer layer of the constant temperature unit is made of 10mm thick heat insulation foam to separate the outside temperature from the heating box temperature, making the system temperature more stable.

[0050] (4) The heater adopts a more complex PID control process;

[0051] (5) A high-sensitivity temperature sensor is used to monitor the gas chamber temperature in real time, which can control the temperature accuracy within 0.002℃ temperature fluctuation;

[0052] The pressure control unit in this embodiment is described in detail below:

[0053] (1) A combination of flow controller and pressure controller is used (back pressure type EPC method can be used), and the pressure control accuracy can be controlled to 0.02%;

[0054] (2) By using a pump as a fixed power system, the pressure can be controlled in real time within a low pressure range and the pressure accuracy can be controlled within 0.02% atm pressure fluctuation.

[0055] like Figure 2 As shown, the analysis method of the gas analyzer in this embodiment includes the following steps:

[0056] S1. Obtain the initial ultraviolet spectrum and perform spectral preprocessing;

[0057] The obtained initial ultraviolet spectrum needs to be processed by dark background subtraction, nonlinear correction, averaging, and smoothing.

[0058] Specifically, the initial spectrum SP1 is obtained by first subtracting the dark background from the spectrum, where SP1(i) = SP light (i)-SP background (i);

[0059] Where i is the number of spectral data points, SP light For the spectrum under luminescent conditions, SP background The spectrum was collected under dark conditions;

[0060] Furthermore, perform nonlinear correction SP2: SP2(i) = SP1(i) * (a + b * i + c * i) 2 Correcting the nonlinearity introduced by the photodetector;

[0061] Furthermore, the smoothed spectrum SP3 is obtained by performing a spectral moving average M times: SP3(i) = SP2(i) / M + SP2(i-1)*(M-1) / M;

[0062] Furthermore, the spectrum is averaged N times to obtain the average spectrum SP4: SP4(i)=∑SP3(i) / N;

[0063] Comprehensive spectrum: SP4(i) =

[0064] ∑{[SP1(i)*(a+b*i+c*i 2 )] / M+[SP1(i-1)*(a+b*(i-1)+c*(i-1) 2 )]*(M-1) / M} / N;

[0065] S2. Calculate the concentration of the sample gas based on the preprocessed spectrum;

[0066] Divide the spectrum under nitrogen or zero gas background with the spectrum under standard gas conditions and take the logarithm to obtain the absorbance A_SP(i);

[0067] Then, Savitzky-Golay type filtering is performed to obtain differential absorption spectra;

[0068] Further differential spectra D_SP(i) of different gases (NO, SO2, NO2) are obtained, where i = A:B (the spectral selection range is from pixel A to pixel B). Subsequent analysis will take length L as an example:

[0069] Set the filter window function width to U = 2v + 1; the measurement points are i = (-v, -v + 1, -v + 2, ..., -1, 0, 1, ..., v - 1, v); and use a k-1 degree polynomial (k is set according to requirements) to fit the data points within the window.

[0070] Y = b0 + b1X + b2X 2 +b k-1 X k-1 Y is the fitted curve;

[0071] The filter value of Y for Savitzky-Golay type filtering can be obtained by performing a k-variable linear equation analysis on the absorbance X = A_SP(i).

[0072]

[0073] Where err is the error function.

[0074] This embodiment utilizes least squares to solve for the value of b, and then obtains the filtered value sequence Y. The specific process of the Savitzky-Golay type filtering in this embodiment can be referred to the existing technology, and will not be elaborated here.

[0075] Thus, the differential absorbance is obtained: D_SP(i)=A_SP(i)-Y(i); the differential absorbances of NO, SO2 and NO2 gases are D_SP_NO, D_SP_SO2 and D_SP_NO2, respectively;

[0076] Real-time calculation of the raw absorption signals of gaseous pollutants (NO, SO2, NO2);

[0077] Assume the standard gas concentrations of NO, SO2, and NO2 (SPAN) are 50*10. -6 The basic vectors P_NO, P_SO2, P_NO2, and P_other (the sum of vectors for the unknown gases) can be obtained separately, and each standard gas spectrum and absorbance corresponds to a concentration value:

[0078] C_NO = D_SP(i) * P_NO(i);

[0079] C_SO2 = D_SP(i) * P_SO2(i);

[0080] C_NO2 = D_SP(i) * P_NO2(i);

[0081] When the concentration of the standard gas is the same as that of the sample gas, C_NO=C_SO2=CNO2=SPAN;

[0082] The least squares algorithm is used to obtain the gas concentrations C_NO, C_SO2, and C_NO2 from the differential absorbance. The calculation process is as follows:

[0083] D_SP(i)=C_NO*D_SP_NO+C_SO2*D_SP_SO2+C_NO2*D_SP_NO2+

[0084] D_SP_other;

[0085]

[0086] S3. Correct the concentration of gaseous pollutants as follows:

[0087] (a) Obtain the gas chamber pressure and determine whether the gas chamber pressure is within the normal pressure range; if so, perform pressure correction on the concentration, taking the NO concentration before pressure correction as C0 and the concentration after pressure correction as C1.

[0088] According to the standard gas equation: PV=NRT, when the volume remains constant and the pressure increases, the gas concentration per unit volume will also increase. Therefore, the gas concentration C1 is corrected to correct the deviation caused by the pressure.

[0089] C1 = f0(C0), where f0 is the pressure correction function, which can be found in the standard condition equation:

[0090] C1 = f0(C0) = C0 * P0 / P1;

[0091] Where P0 is the calibration pressure and P1 is the measured pressure of the gas chamber.

[0092] (b) Obtain the temperature of the gas chamber and determine whether the gas chamber temperature is within the normal temperature range; if so, perform temperature correction on the concentration, and the concentration after temperature correction is C2.

[0093] C2 = f1(C1);

[0094] Where f1 is the temperature correction function, which can be referenced from the standard condition equation. The temperature unit is degrees Celsius. T0 is the calibration temperature, and T1 is the measured temperature of the gas chamber. When the volume is constant, the gas concentration decreases as the temperature increases.

[0095] C2=f1(C1)=C1*(273+T1) / (273+T0).

[0096] (c) Concentration data sliding processing algorithm, concentration C3 after sliding algorithm:

[0097] C3 = f2(C2), where f2 is the sliding algorithm function;

[0098] To obtain more stable data results, the data can be slid N times;

[0099] The gas concentration after sliding is C3 = f2(C2) = C2(i) / N + C3(i-1)*(N-1) / N; where C3(i-1) is the concentration corresponding to the (i-1)th sampling, and N is the number of sliding times;

[0100] (d) Obtain the humidity RH (in %) of the sample gas and determine whether the humidity is within the normal humidity range; if so, perform humidity correction on the concentration to obtain the concentration C4: C4 = f3(C3); where f3 is the humidity correction function;

[0101] Due to humidity, the gas concentration in the sample gas will be diluted, C4 = f3(C3) = C3 / (1-RH);

[0102] (e) Concentration conversion to obtain the actual sample gas concentration C5: C5=f4(C4)=C4 / R; where R is the proportion of the actual sample gas that is diluted.

[0103] The stability factors such as pressure, temperature, and flow rate in the control parameters are all within 0.02%, which greatly improves the accuracy of the above measurements.

[0104] The final test results are shown in Table 1. The zero-point fluctuation range was reduced to within 0.1, which effectively improved the detection accuracy.

[0105] The above description is merely a detailed explanation of preferred embodiments and principles of the present invention. For those skilled in the art, there may be changes in specific implementation methods based on the ideas provided by the present invention, and these changes should also be considered within the scope of protection of the present invention.

[0106] Table 1 Test Results

[0107]

Claims

1. An analytical method for a gas analyzer, characterized in that, The gas analyzer includes a sampling unit, a filtering unit, a flow control unit, a gas chamber, a pressure control unit, a gas pump, and an exhaust gas treatment unit connected sequentially along the air inlet direction; it also includes a temperature control unit, a constant temperature unit, a light source, a detector, a signal acquisition unit, and an analysis control unit. The constant temperature unit includes a circulating air duct, a circulating fan, and a heater. The gas chamber, circulating fan, and heater are located within the circulating air duct, which also contains a temperature sensor and a pressure sensor. The circulating fan and heater are signal-connected to the temperature control unit. The light source and detector are located on opposite sides of the gas chamber. The detector is signal-connected to the signal acquisition unit. The analysis and control unit is connected to the sampling unit, flow control unit, pressure control unit, air pump, temperature control unit, light source, signal acquisition unit, temperature sensor, and pressure sensor. The analytical method includes the following steps: S1. Obtain the ultraviolet spectrum and preprocess the spectrum; S2. Calculate the concentration of gaseous pollutants based on the preprocessed spectrum; S3. Correct the concentration of gaseous pollutants; In step S1, the spectral preprocessing includes: The ultraviolet spectrum was sequentially subjected to dark background subtraction, nonlinear correction, smoothing, and averaging. Step S2 includes the following steps: S21. Divide the pretreated spectrum by the standard gas spectrum and obtain the logarithm to calculate the absorbance of the gaseous pollutants. S22. Perform Savitzky-Golay filtering on the absorbance of the gaseous pollutants to obtain the differential absorbance of the gaseous pollutants. S23. Based on the differential absorbance of gaseous pollutants, the concentration of gaseous pollutants is obtained by least squares method; Step S3 includes the following steps: S31. Obtain the pressure of the gas chamber, using the concentration of the sample gas before pressure correction as... C 0, the concentration after pressure correction is C 1: C 1= f 0( C 0)= C 0* P 0 / P 1; among which, f 0 represents the pressure correction function. P 0 represents the calibrated pressure. P 1 represents the measured pressure in the gas chamber; S32. Obtain the temperature of the gas chamber, perform temperature correction, and the concentration after temperature correction is: C 2: C 2= f 1( C 1)= C 1*(273+ T 1) / (273+ T 0); where, f 1 represents the temperature correction function. T 0 represents the calibration temperature. T 1 represents the measured temperature of the gas chamber; S33, The concentration after the sliding algorithm is: C 3( i ): C 3( i )= f 2( C 2)= C 2 / N + C 3( i -1)*( N -1) / N ; C 3( i ) is the first i The concentration corresponding to the next sample. C 3( i -1) is the first i -1 concentration corresponding to the sampling f 2 represents the sliding algorithm function. N The number of slides; S34. Obtain the humidity (RH) of the sample gas, and the concentration after humidity correction is: C 4: C 4= f 3( C 3)= C 3 / (1-RH); where, f 3 represents the humidity correction function; S35. Calculate the gas concentration of the real sample gas. C 5: C 5= f 4( C 4)= C 4 / R ;in, R This represents the proportion by which the actual sample gas was diluted.

2. The analytical method according to claim 1, characterized in that, A flow monitor is installed between the flow control unit and the gas chamber.

3. The analytical method according to claim 1, characterized in that, The gas chamber is surrounded by a heat insulation layer.

4. The analytical method according to claim 1, characterized in that, The circulating air duct is equipped with heat dissipation fins.

5. The analytical method according to claim 1, characterized in that, An insulation layer is provided outside the circulating air duct.

6. The analytical method according to claim 1, characterized in that, The exhaust gas treatment unit employs a combination of activated carbon and an exhaust gas purification device.

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