Method for monitoring high-concentration total hydrocarbon

Abstract

The invention discloses a method for monitoring high-concentration total hydrocarbon, and relates to the technical field of chemical measurement, logarithmic amplification means that the amplitude of an output signal and the amplitude of an input signal are in a logarithmic function relation, signals are mainly converted into equivalent logarithmic values of the signals, and nonlinear operational amplification is involved: the characteristic equation is V = K * LOG (I); the linear transimpedance amplification means that the amplitude of an output signal and the amplitude of an input signal are in a linear function relationship, and the characteristic equation is V = K * I. The system adopts a one-to-two method for simultaneous measurement of two points, including a sampling state and an analysis state, to analyze intake air. The two sampling systems comprise an analysis system and a sampling system, the two independent analysis systems are integrated in one instrument, high-concentration monitoring of two point positions can be achieved at the same time, the gas enters one instrument through one pretreatment box, when the two point positions are monitored at the same time, sample gas does not interfere with each other, and the accuracy of respective detection results can be guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of chemical measurement, and in particular to a monitoring method for high-concentration total hydrocarbons. Background Art

[0002] The entire environmental monitoring system consists of a sampling platform, a constant temperature chassis, and an auxiliary gas unit. After being roughly processed by the platform sampling system, the sample gas is collected in the pretreatment box for further water removal and particle filtration, and then enters the internal gas path of the instrument. In the internal gas path, the valve assembly in the chassis controls the fourteen-way diaphragm valve to make the control gas path sample first, and temporarily store the sample gas in the quantitative loop. Then, the state of the diaphragm valve is changed to change its internal flow path, so that the carrier gas drives the sample gas in the quantitative loop into the detector.

[0003] However, during the implementation of the above technical solution, it was found that there were at least the following technical problems:

[0004] 1. Based on the national volatile organic compound (VOCs) emission limit standard, which is generally <80mg / m3, and local standards are more stringent, VOCs monitoring equipment is mainly used for waste gas monitoring at mg / m3 or even ug / m3 levels. The linear function is used to amplify the FID signal, which can accurately measure VOCs at low concentrations. However, when the VOCs waste gas to be monitored reaches the g / m3 level, the signal value will be too large, which further causes the data after function amplification to fail to accurately reflect the concentration of VOCs;

[0005] 2. Long-term detection of high-concentration VOCs exhaust gas that exceeds the measurement capacity of the instrument itself will not only make the data measured by the instrument inaccurate, but also damage the instrument's components and core components, affecting the instrument's service life. For this reason, we propose a monitoring method for high-concentration total hydrocarbons. Summary of the invention

[0006] 1. Technical issues to be solved

[0007] In view of the deficiencies of the prior art, the present invention provides a method for monitoring total hydrocarbons at high concentrations to solve the technical problems raised in the background technology.

[0008] (II) Technical solution

[0009] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0010] A method for monitoring total hydrocarbons with high concentrations, comprising: linear transimpedance amplification means that the output signal amplitude and the input signal amplitude are in a linear function relationship, and its characteristic equation V=K*I;

[0011] Logarithmic amplification means that the output signal amplitude is in a logarithmic function relationship with the input signal amplitude, mainly converting the signal into its equivalent logarithmic value, involving a nonlinear operational amplification: its characteristic equation V = K*LOG(I); logarithmic amplification is used instead of linear amplification.

[0012] Preferably, for chromatographic preamplifier circuits, most of them use logarithmic amplification. When the input signal is weak, it is a linear amplifier with a large gain; when the input signal is strong, it becomes a logarithmic amplifier, and the gain decreases with the increase of the input signal. The logarithmic amplifier circuit can convert the input signal into a voltage output within a super large dynamic range; it automatically provides dynamic compression, without the need for a control circuit, reducing subsequent processing; excellent DC accuracy. Therefore, we need to make a logarithmic amplifier circuit. Two independent analysis systems are integrated in one instrument, which can simultaneously realize high-concentration monitoring of two points.

[0013] The logarithmic amplifier circuit has the above advantages, and the use of the logarithmic amplifier circuit is more applicable.

[0014] Preferably, many analytical instrument companies currently use logarithmic amplification for chromatographic preamplifier circuits, such as Agilent's latest environmental meteorological chromatograph 8890, Panno GC-1949 high-end gas chromatograph, Shimadzu's Nexis GC-2030, etc. All of their products use logarithmic amplifier circuits. From the current situation of these famous analytical instrument companies using logarithmic amplifier circuits, it can be determined that logarithmic amplifier circuits are a trend. The amplifier circuit currently used in FID products uses a linear transimpedance amplifier circuit, which is suitable for inputting signals with a narrow measurement dynamic range.

[0015] It is preferred, but when the input dynamic range of the signal is very large (such as picoampere-nanoampere level), it will not be able to cover the upper and lower limit signals, resulting in reduced performance. Although the gain is automatically controlled through software design, the gain control chip must be increased by increasing the cost. What's more important is that the dynamic range is not large enough, which is determined by the nature of the linear circuit.

[0016] Preferably, the relevant gas chromatograph analyzers of Panno, Shimadzu and Agilent have been investigated. Although the parameters and performance indicators of the specific instruments are known from their products and roughly compared, the single module indicators and performance parameters of the logarithmic amplifier board they use cannot be obtained. However, some relevant performance parameters can be obtained from ADI, TI, MAXIM and other logarithmic amplifier chip manufacturers. At present, these logarithmic amplifier chips are used as the starting point.

[0017] Although these indicators and performances belong to chip-level logarithmic operational amplifiers, not specific logarithmic amplifier circuits, the above parameters and indicators can be used as reference, and a series of indicators of the designed logarithmic amplifier circuit can be close to these chip-level logarithmic amplifiers.

[0018] When using, for this system we adopt a one-to-two method to measure two points simultaneously.

[0019] Preferably, sampling status:

[0020] The sample gas enters from port 1 of the 14-way valves V1 and V2, exits from port 14, passes through quantitative loops 1 and 3, enters from port 7 and exits from port 6, passes through quantitative loops 2 and 4, and then enters from port 3 and exits from port 2.

[0021] Carrier gas 1 and carrier gas 4 enter from port 13 and exit from port 12 of 14-way valves V1 and V2 respectively, pass through methane column 1 and methane column 3, and then enter from port 8 and exit from port 9 to purge methane column 1 and methane column 3.

[0022] Carrier gas 2 and carrier gas 5 enter from port 10 and exit from port 11 of 14-way valves V1 and V2 respectively, pass through methane column 2 and methane column 5, and then are discharged from the exhaust ports of detector 1 and detector 2.

[0023] Carrier gas 3 and carrier gas 6 enter from port 4 and exit from port 5 of fourteen-way valves V1 and V2 respectively, pass through total hydrocarbon column 1 and total hydrocarbon column 2, and are then discharged from the exhaust ports of detector 1 and detector 2.

[0024] Preferably, the analysis state is: the sample gas enters port 1 and is discharged from port 2 of the fourteen-way valves of V1 and V2 respectively, the carrier gas 1 and the carrier gas 4 enter port 13 and exit port 14 of the fourteen-way valves of V1 and V2 respectively to reach the quantitative ring 1 and the quantitative ring 3, pushing the sample gas in the quantitative ring to enter port 7 and exit port 8, pass through methane column 1 and methane column 3 for separation, and then enter port 12 and exit port 11 to reach methane column 2 and methane column 4 for separation again, and after separation, enter the detector for quantitative and qualitative analysis of methane under the push of the carrier gas, the carrier gas 3 and the carrier gas 6 enter port 3 from port 4 of the fourteen-way valves of V1 and V2 respectively to reach the quantitative ring 2 and the quantitative ring 4, pushing the sample gas in the quantitative ring to enter port 5 from port 6 to reach the total hydrocarbon column 2 and the total hydrocarbon column 4, and finally enter the detector under the push of the carrier gas for quantitative and qualitative analysis of total hydrocarbons.

[0025] (III) Beneficial effects

[0026] 1. Using logarithmic function to amplify FID signal can accurately measure VOCs at low concentrations, expand the concentration range monitored by the instrument, and enhance the instrument's ability to process data. When the input signal is strong, it becomes a logarithmic amplifier, and the gain decreases as the input signal increases. The logarithmic amplifier circuit can convert the input signal into a voltage output within a large dynamic range; it automatically provides dynamic compression, without the need for a control circuit, and reduces subsequent processing; excellent DC accuracy, so we need to make a logarithmic amplifier circuit.

[0027] 2. This detection system consists of two sampling systems including analysis and sampling. Two independent analysis systems are integrated in one instrument, which can realize high-concentration monitoring of two points at the same time. They pass through a pretreatment box and enter an instrument. There are two sets of non-interfering gas path systems and two independent detectors inside the instrument. Therefore, when monitoring two points at the same time, the sample gases will not interfere with each other, which can ensure the accuracy of each test result.

[0028] 3. It can be seen that after the scheme is changed, the pollutants that can be measured by the instrument reach g / m 3 , and when three different concentrations of standard gas, high, medium and low, are introduced, the data linearity is good. The data show that the instrument has good repeatability during the monitoring process, and the maximum relative indication error is 3.38%, which meets the national standard for indication error <5%. The instrument gas path is changed to reduce the amount of sample gas entering the FID detector, and the original 0.5ml quantitative loop is changed to a 0.1ml quantitative loop, so that it can reduce the load of the instrument while meeting the monitoring needs and increase the service life of the instrument parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings.

[0030] Figure 1 The sampling process of the monitoring method of high concentration total hydrocarbons of the present invention is as follows Figure 1 ;

[0031] Figure 2 The sampling process of the monitoring method of high concentration total hydrocarbons of the present invention is as follows Figure 2 ;

[0032] Figure 3 The analysis flow of a method for monitoring total hydrocarbons with high concentrations according to the present invention is as follows: Figure 1 ;

[0033] Figure 4 The analysis flow of a method for monitoring total hydrocarbons with high concentrations according to the present invention is as follows: Figure 2 ;

[0034] Figure 5A linear function diagram of the output signal amplitude and the input signal amplitude in a monitoring method for high-concentration total hydrocarbons of the present invention;

[0035] Figure 6 This is a high-concentration standard gas test diagram in a method for monitoring high-concentration total hydrocarbons of the present invention;

[0036] Figure 7 This is a test diagram of medium-concentration standard gas in a method for monitoring high-concentration total hydrocarbons of the present invention;

[0037] Figure 8 This is a low-concentration standard gas test diagram in a method for monitoring total hydrocarbons with a high concentration according to the present invention;

[0038] Fig. 9 This is a structural diagram of a support plate in a method for monitoring total hydrocarbons with a high concentration according to the present invention.

[0039] Legend: 1. Bookshelf; 2. Support base; 3. Sliding plate; 4. Telescopic rod; 5. Self-locking motor; 6. Placement table; 7. Traction rope; 8. Support plate; 9. Left side shelf; 10. Right side shelf; 11. Connecting rod; 12. Support rod. DETAILED DESCRIPTION

[0040] The embodiment of the present application solves the problem of excessively large data in the prior art by providing a method for monitoring total hydrocarbons at high concentrations, changes the signal processing method in the instrument, adopts logarithmic processing instead of traditional linear processing, expands the concentration range monitored by the instrument, and enhances the instrument's data processing capability.

[0041] Example 1

[0042] In the current conventional flame ionization detector (FID) detection, the span of the signal value collected by the detection end is very large, with the minimum being pA level and the maximum reaching mA level. Ordinary linear circuits must adjust the measurement range by switching the gain, and disturbances will occur when switching the gain. The current FID products need to input signals with a very large dynamic range (such as picoampere-nanoampere level) to cover the upper and lower limits of the signal while ensuring high DC accuracy.

[0043] The input current signal with a large dynamic range is converted into a voltage signal. The signal can be compressed and output according to a certain rule and covered to the upper and lower limits of the input signal without reducing the performance. At low frequencies, the logarithmic amplifier has a wide dynamic range and high DC precision. When a small signal is input, the logarithmic amplifier exhibits linear amplification characteristics and a large gain; when a large signal is input, it exhibits a logarithmic characteristic. The larger the signal, the lower the gain.

[0044] The technical solution in the embodiment of the present application is to solve the problem that the original solution linearly amplifies the signal sent back by the FID. The new solution uses a logarithmic function to amplify the FID signal so that it can detect g / m 3 When measuring the concentration of VOCs, the problem of too much data can be avoided. The general idea is as follows:

[0045] In view of the problems existing in the prior art, the present invention provides a method for monitoring total hydrocarbons in high concentrations.

[0046] as follows Figure 5 As shown, logarithmic amplification means that the output signal amplitude is in a logarithmic function relationship with the input signal amplitude, mainly converting the signal into its equivalent logarithmic value, involving a nonlinear operational amplification: its characteristic equation V = K*LOG(I);

[0047] as follows Figure 6 As shown, linear transimpedance amplification means that the output signal amplitude is in a linear function relationship with the input signal amplitude, and its characteristic equation is V=K*I.

[0048] Among them, the advantages and disadvantages of linear amplification and logarithmic amplification are compared in Table 1:

[0049]

[0050] Table 1

[0051] Most chromatographic preamplifier circuits use logarithmic amplification. When the input signal is weak, it is a linear amplifier with a large gain; when the input signal is strong, it becomes a logarithmic amplifier, and the gain decreases as the input signal increases. The logarithmic amplifier circuit can convert the input signal into a voltage output within a large dynamic range; it automatically provides dynamic compression, does not require a control circuit, and reduces subsequent processing; it has excellent DC accuracy, so we need to make a logarithmic amplifier circuit. Two independent analysis systems are integrated in one instrument, which can simultaneously realize high-concentration monitoring of two points.

[0052] The logarithmic amplifier circuit has the above advantages, and the use of the logarithmic amplifier circuit is more applicable.

[0053] At present, many analytical instrument companies use logarithmic amplification for chromatographic preamplifier circuits, such as Agilent's latest environmental meteorological chromatograph 8890, Panno GC-1949 high-end gas chromatograph, Shimadzu's Nex is GC-2030, etc. All of their products use logarithmic amplifier circuits. From the current situation of these famous analytical instrument companies using logarithmic amplifier circuits, it can be determined that logarithmic amplifier circuits are a trend. The amplifier circuit used in FID products currently uses a linear transimpedance amplifier circuit, which is suitable for inputting signals with a narrow dynamic range of measurement. However, when the input dynamic range is very large (such as picoampere-nanoampere level), it will cause the upper and lower limit signals to be unable to cover, resulting in reduced performance. Although the software is designed to automatically control the gain, the gain control chip must be increased by increasing the cost. And more importantly, the dynamic range is not large enough. This is determined by the nature of the linear circuit.

[0054] At present, we have investigated the relevant gas chromatographs of Panno, Shimadzu, and Agilent. Although we have learned the parameters and performance indicators of the specific instruments from their products and roughly compared them, we cannot obtain the single module indicators and performance parameters of the logarithmic amplifier board they use. However, we can obtain some relevant performance parameters from ADI, TI, MAXI M, and other manufacturers that design logarithmic amplifier chips. At present, we use these logarithmic amplifier chips as a starting point and make the following comparison as shown in Table 2:

[0055] Performance index parameters MAX4207(Maxim) ADL5304 (Analog Devices) LOG114 Dynamic Range 100dB 200dB 160dB Input current range 10nA-1mA 1pA-10mA 100pA-10mA Output voltage range 0-5.5V 0.5V-2.5V -4.4V -4.4V Default logarithmic slope 250mV / decade 200mV / decade 375mV / decade Operating temperature -40℃-85℃ -40℃-85℃ 0℃-70℃

[0056] Table 2

[0057] Although these indicators and performances belong to chip-level logarithmic operational amplifiers, not specific logarithmic amplifier circuits, the above parameters and indicators can be used as reference, and a series of indicators of the designed logarithmic amplifier circuit can be close to these chip-level logarithmic amplifiers.

[0058] Example 2

[0059] Based on Example 1, the embodiment of the present application is to detect VOCs waste gas with a large concentration exceeding the measurement capacity of the meter for a long time. On the one hand, it will make the data measured by the meter inaccurate, and on the other hand, it will also damage the parts and core components of the meter. The overall idea is as follows:

[0060] When using, for this system we adopt a one-to-two method to measure two points simultaneously.

[0061] like Figure 1-2 As shown, sampling status:

[0062] The sample gas enters from port 1 of the 14-way valves V1 and V2, exits from port 14, passes through quantitative loops 1 and 3, enters from port 7 and exits from port 6, passes through quantitative loops 2 and 4, and then enters from port 3 and is discharged from port 2.

[0063] Carrier gas 1 and carrier gas 4 enter from port 13 and exit from port 12 of the fourteen-way valves of V1 and V2 respectively, pass through methane column 1 and methane column 3, and then enter from port 8 and exit from port 9 to purge methane column 1 and methane column 3.

[0064] Carrier gas 2 and carrier gas 5 enter from port 10 and exit from port 11 of fourteen-way valves V1 and V2 respectively, pass through methane column 2 and methane column 5, and are then discharged from the exhaust ports of detector 1 and detector 2.

[0065] Carrier gas 3 and carrier gas 6 enter from port 4 and exit from port 5 of fourteen-way valves V1 and V2 respectively, pass through total hydrocarbon column 1 and total hydrocarbon column 2, and are then discharged from the exhaust ports of detector 1 and detector 2.

[0066] like Figure 3-4 As shown, the analysis status:

[0067] The sample gas enters port 1 and is discharged from port 2 of the fourteen-way valves V1 and V2 respectively.

[0068] Carrier gas 1 and carrier gas 4 enter from port 13 and exit from port 14 of the fourteen-way valve of V1 and V2 respectively to reach quantitative loop 1 and quantitative loop 3, pushing the sample gas in the quantitative loop to enter from port 7 and exit from port 8, passing through methane column 1 and methane column 3 for separation, and then entering from port 12 and exiting from port 11 to reach methane column 2 and methane column 4 for separation again. After separation, the gas enters the detector driven by the carrier gas for quantitative and qualitative analysis of methane.

[0069] Carrier gas 3 and carrier gas 6 enter port 3 from port 4 of fourteen-way valve V1 and V2 respectively to reach quantitative ring 2 and quantitative ring 4, pushing the sample gas in the quantitative ring to enter port 5 from port 6 to reach total hydrocarbon column 2 and total hydrocarbon column 4, and finally enter the detector under the push of carrier gas for quantitative and qualitative analysis of total hydrocarbons.

[0070] The above three pictures are entered from top to bottom:

[0071] like Figure 7 As shown in Table 3, high concentration standard gas was introduced three times according to a1, b1 and c1: 1213445.5 mgC / m 3 Total hydrocarbons and 11303.5mgC / m 3 of methane;

[0072] serial number <![CDATA[Total hydrocarbons mg / m 3 > <![CDATA[methane mg / m 3 > a1 1212065.14 11292.71 b1 1212516.78 11298.88 c1 1207220.03 11294.77 average value 1210600.65 11295.45 Relative standard deviation / % 0.20 0.26 Relative indication error / % -0.23 0.07

[0073] Table 3

[0074] like Figure 8As shown in Table 4, the medium concentration standard gas is introduced three times according to a2, b2 and c2: 11625 mgC / m 3 of methane and 813589mgC / m 3 Total hydrocarbons;

[0075] serial number <![CDATA[Total hydrocarbons mg / m 3 > <![CDATA[Methane mg / m 3 > a2 819481.3 11692.54 b2 818475.52 11690.44 c2 817536.24 11693.72 average value 818497.6867 11692.23 Relative standard deviation / % 0.10 0.01 Relative indication error / % 0.60 0.58

[0076] Table 4

[0077] like Fig. 9 As shown in Table 5, low concentration standard gas is introduced three times according to a3, b3 and c3: 11250 mgC / m 3 of methane and 411428mgC / m 3 of total hydrocarbons.

[0078] serial number <![CDATA[Total hydrocarbons mg / m 3 > <![CDATA[Methane mg / m 3 > a3 397105.27 11091.82 b3 398012.13 11092.24 c3 397434.01 11089.96 average value 397517.13 11091.34 Relative standard deviation / % 0.09 0.01 Relative indication error / % -3.38 -1.41

[0079] Table 5

[0080] In summary, it can be seen that after the scheme is changed, the pollutants that can be measured by the instrument reach g / m 3 , and when three different concentrations of standard gas, high, medium and low, are introduced, the data linearity is good. The data show that the instrument has good repeatability during the monitoring process, and the maximum relative indication error is 3.38%, which meets the national standard for indication error <5%. The instrument gas path is changed to reduce the amount of sample gas entering the FID detector, and the original 0.5ml quantitative loop is changed to a 0.1ml quantitative loop, so that it can reduce the load of the instrument while meeting the monitoring needs and increase the service life of the instrument parts.

[0081] Finally, it should be noted that: Obviously, the above embodiments are only examples for clearly explaining the present invention, and are not intended to limit the implementation methods. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the scope of protection of the present invention.

Claims

1. A method for monitoring high concentration total hydrocarbons, comprising: Linear transimpedance amplification means that the output signal amplitude is in a linear function relationship with the input signal amplitude, and its characteristic equation is V = K*I; The characteristics are as follows: logarithmic amplification means that the amplitude of the output signal is in a logarithmic function relationship with the amplitude of the input signal, mainly converting the signal into its equivalent logarithmic value, involving a nonlinear operational amplification: its characteristic equation V = K*LOG(I); logarithmic amplification is used instead of linear amplification.

2. A method for monitoring high concentration total hydrocarbons as claimed in claim 1, characterized in that: When used as described, for this system we adopt a one-to-two method to measure two points simultaneously, including sampling state and analysis state to analyze the intake air.

3. A method for monitoring high concentration total hydrocarbons as claimed in claim 2, characterized in that: The sampling status: The sample gas enters from port 1 of the 14-way valves V1 and V2, exits from port 14, passes through quantitative loops 1 and 3, enters from port 7 and exits from port 6, passes through quantitative loops 2 and 4, and then enters from port 3 and exits from port 2. Carrier gas 1 and carrier gas 4 enter from port 13 and exit from port 12 of 14-way valves V1 and V2 respectively, pass through methane column 1 and methane column 3, and then enter from port 8 and exit from port 9 to purge methane column 1 and methane column 3. Carrier gas 2 and carrier gas 5 enter from port 10 and exit from port 11 of 14-way valves V1 and V2 respectively, pass through methane column 2 and methane column 5, and then are discharged from the exhaust ports of detector 1 and detector 2. Carrier gas 3 and carrier gas 6 enter from port 4 and exit from port 5 of fourteen-way valves V1 and V2 respectively, pass through total hydrocarbon column 1 and total hydrocarbon column 2, and are then discharged from the exhaust ports of detector 1 and detector 2.

4. A method for monitoring high concentration total hydrocarbons as claimed in claim 2, characterized in that: The analysis states: The sample gas enters and is discharged from port 2 of the 14-way valves V1 and V2 respectively. Carrier gas 1 and carrier gas 4 enter from port 13 and exit from port 14 of 14-way valve V1 and V2 respectively to reach quantitative loop 1 and quantitative loop 3, pushing the sample gas in the quantitative loop to enter from port 7 and exit from port 8, passing through methane column 1 and methane column 3 for separation, and then enter from port 12 and exit from port 11 to reach methane column 2 and methane column 4 for separation again. After separation, the sample gas enters the detector driven by the carrier gas for quantitative and qualitative analysis of methane. Carrier gas 3 and carrier gas 6 enter port 3 from port 4 of fourteen-way valve V1 and V2 respectively to reach quantitative ring 2 and quantitative ring 4, pushing the sample gas in the quantitative ring to enter port 5 from port 6 to reach total hydrocarbon column 2 and total hydrocarbon column 4, and finally enter the detector under the push of carrier gas for quantitative and qualitative analysis of total hydrocarbons.

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