CN101819140A - Continuous monitoring device and method of gaseous elemental mercury concentration - Google Patents

Abstract

The device and method for continuous monitoring of gaseous elemental mercury concentration relate to the field of gas concentration measurement, and solve the problems of low sensitivity, system complexity and high cost of the existing gaseous elemental mercury monitoring technology. In the device of the present invention, the mercury element lamp is placed in the magnetic field of the magnet, the output light is transmitted through the collimator lens to obtain parallel light, the parallel light enters the beam splitter after passing through the sample cell, and the transmitted light enters the first convex lens after passing through the reference cell, focusing to the first detector, the reflected light is incident on the second convex lens, and focused to the second detector, and the first detector and the second detector are connected with a data acquisition analyzer. The method of the present invention is specifically as follows: one, determine that the light intensity contrast M is the constant A corresponding to zero; two, depict the corresponding relationship curve between the light intensity contrast M and the concentration of the gaseous elemental mercury medium; three, measure the gaseous elemental mercury medium to be measured The contrast M of the light intensity is compared with the corresponding relationship curve to obtain the concentration of the gaseous elemental mercury medium to be measured. For monitoring gaseous mercury concentrations.

Description

Device and method for continuous monitoring of gaseous elemental mercury concentration

technical field

The invention relates to the field of gas concentration measurement, in particular to a device and method for continuously monitoring the concentration of gaseous elemental mercury.

Background technique

Mercury in combustion flue gas exists in three forms: gaseous elemental mercury, gaseous divalent oxidized mercury and particulate mercury. Among them, gaseous mercury is the main form. The total mercury content is measured by thermocatalytic or chemical conversion of other forms of mercury into gaseous elemental mercury. Among the currently applied continuous monitoring systems for mercury emissions, the most commonly used gaseous elemental mercury measurement techniques are cold vapor atomic absorption spectroscopy (CVAAS) and cold vapor atomic fluorescence spectroscopy (CVAFS) techniques based on the principle of spectroscopic detection. The former can directly measure the concentration of gaseous elemental mercury in the flue gas without the need for a carrier gas like the latter, so it is adopted by most continuous monitoring systems for mercury emissions. In most CVAAS-based systems, the mercury in the flue gas stream needs to be pre-concentrated and desorbed before being introduced into the optical detection system for analysis to improve measurement sensitivity and remove interfering gases. These two steps greatly reduce mercury emissions. The real-time nature of monitoring makes mercury monitoring only in a semi-continuous state.

At present, there are two main technologies that can continuously monitor gaseous elemental mercury: ultraviolet differential absorption spectroscopy (UV-DOAS) and Zeeman atomic absorption spectroscopy (ZAAS). Both of these technologies are based on the principle of absorption spectroscopy. Mercury is measured at 253.7nm, where mercury has the largest absorption cross-section. The response speed can reach the order of seconds, achieving real-time measurement in the true sense. The former uses a broadband emitting light source covering the ultraviolet to visible bands, but because mercury is a monatomic molecule, its absorption line width is very narrow, and it is difficult to obtain a large light intensity absorption ratio even with a filter, so it is difficult to obtain a higher Measurement sensitivity. The latter is a special case in CVAAS, which uses a narrow-band emitting mercury element lamp as a light source, and uses Zeeman background correction technology to eliminate interference and does not require pre-enrichment and desorption of mercury, but it has high requirements for the analysis system , which increases the complexity and cost of the system and cannot be widely used.

Contents of the invention

The invention aims to solve the problems of low sensitivity, complex system and high cost of the existing gaseous elemental mercury monitoring technology, thereby providing a continuous monitoring device and method for gaseous elemental mercury concentration.

A continuous monitoring device for the concentration of gaseous elemental mercury, which consists of a mercury element lamp, a magnet, a collimating lens, a sample cell, a beam splitter, a reference cell, a first convex lens, a first detector, a second convex lens, a second detector, and data acquisition The analyzer is composed of the mercury element lamp placed in the magnetic field of the magnet and set at the focal point of the collimating lens. The detection surface of the first detector coincides with the focal plane of the first convex lens, and the detection surface of the second detector coincides with the focal plane of the second convex lens. The focal planes of the convex lenses coincide, the output light of the mercury element lamp is incident on the collimator lens, and the parallel light is transmitted through the collimator lens. The parallel light is incident on the beam splitter after passing through the sample cell, and the parallel light is divided into reflected light by the beam splitter and the transmitted light, wherein the transmitted light enters the first convex lens after passing through the reference cell, and then focuses to the first detector through the first convex lens, and the reflected light enters the second convex lens, and then focuses to the second detector through the second convex lens, so The output end of the first detector and the output end of the second detector are respectively connected to the two access ends of the data acquisition analyzer, and the medium in the reference pool is elemental mercury gas with a saturated concentration.

The continuous monitoring method of gaseous elemental mercury concentration, the specific process is as follows:

Step 1. When the sample cell is filled with the gaseous elemental mercury medium to be measured, the data acquisition analyzer measures the transmitted light intensity I _R detected by the first detector and the reflected light intensity I _S detected by the second detector;

Step 2, calculate the light intensity contrast M of transmitted light and reflected light described in step 1 according to the following formula;

Wherein, A is the constant corresponding to the light intensity contrast M being zero when only air is contained in the sample cell;

Step 3: compare the light intensity contrast M obtained in step 2 with the corresponding relationship curve between the light intensity contrast M and the concentration of the gaseous elemental mercury medium to obtain the concentration of the gaseous elemental mercury medium to be measured.

The invention realizes the continuous and effective monitoring of the concentration of elemental mercury gas by using the Zeeman correlation spectrum technology, realizes the selective detection of gaseous elemental mercury by using the spectral information of the reference gas itself, and eliminates the pollution caused by gases such as sulfur dioxide and nitrogen dioxide. interference. The system is simple in composition, without the use of dispersion equipment such as spectrometers and complex polarization analysis equipment, and the cost is low. The minimum detection limit that can be achieved by the invention is lower than 1 μg/m ³ , which fully meets the requirements for monitoring mercury content in industrial waste gas emissions. It is suitable for the monitoring field of gaseous elemental mercury concentration requiring high sensitivity.

Description of drawings

Figure 1 is a schematic structural diagram of a continuous monitoring device for gaseous elemental mercury concentration. Fig. 2 is a flowchart of a continuous monitoring method for gaseous elemental mercury concentration. Fig. 3 is a graph showing the corresponding relationship between light intensity contrast and gas concentration to be measured in Embodiment 10.

Detailed ways

The specific embodiment one, present embodiment is described in conjunction with Fig. 1, the continuous monitoring device of gaseous elemental mercury concentration, it is made of mercury element lamp 1, magnet 2, collimating lens 3, sample cell 4, beam splitter 5, reference cell 6, the first Composed of a convex lens 7, a first detector 8, a second convex lens 9, a second detector 10, and a data acquisition analyzer 11, the mercury element lamp 1 is placed in the magnetic field of the magnet 2, and is arranged at the focal point of the collimating lens 3 , the detection surface of the first detector 8 coincides with the focal plane of the first convex lens 7, the detection surface of the second detector 10 coincides with the focal plane of the second convex lens 9, and the output light of the mercury element lamp 1 is incident on the collimator lens 3 , the parallel light is transmitted through the collimator lens 3, and the parallel light is incident on the beam splitter 5 after passing through the sample cell 4, and the parallel light is divided into reflected light and transmitted light by the beam splitter 5, wherein the transmitted light is incident after passing through the reference cell 6 to the first convex lens 7, then focus to the first detector 8 through the first convex lens 7, the reflected light is incident on the second convex lens 9, and then focus to the second detector 10 through the second convex lens 9, the first detector 8 The output end of the second detector 10 and the output end of the second detector 10 are respectively connected to the two access ends of the data acquisition analyzer 11, and the medium in the reference pool 6 is elemental mercury gas with a saturated concentration.

The medium in the sample cell 4 is the gaseous elemental mercury medium to be measured. The saturated concentration of elemental mercury gas in the reference cell 6 can make the light with a wavelength near 253.7nm be absorbed to the maximum extent.

Working principle: Mercury element lamp 1 emits ultraviolet light. Under the action of the magnetic field generated by magnet 2, its emission spectrum at 253.7nm is split into a series of Zeeman components with different wavelengths. The ultraviolet light after wavelength splitting is collimated After the lens 3, it becomes parallel light. After passing through the sample cell 4 equipped with the gas to be measured, it is divided into transmitted light and reflected light by the spectroscope 5. After the transmitted light passes through the reference cell 6 equipped with a saturated concentration of gaseous elemental mercury, it is at 253.7 The Zeeman component near nm is absorbed to the greatest extent, and the remaining Zeeman component is used as a reference light and then focused by the first convex lens 7 and then received by the first detector 8. The reflected light is sample light, and the reflected light directly passes through the second convex lens 9 After being focused, it is received by the second detector 10, and the signals generated by the first detector 8 and the second detector 10 are input to the data acquisition analyzer 11 for analog/digital conversion and data analysis, and the light of transmitted light and reflected light is collected strong message. When there is no gaseous elemental mercury in the sample cell 4, the light intensity contrast of the two paths of light is zero, and when gaseous elemental mercury appears in the sample cell 4, the light intensity contrast of the two paths of light increases with the increase of the mercury content, and There is a one-to-one relationship between light intensity contrast and mercury content.

The reflected light path and the transmitted light path behind the beam splitter 5 can be reversed, that is, the reflected light is incident on the first convex lens 7 after passing through the reference cell 6, and then focused to the first detector 8 by the first convex lens 7, and the transmitted light is incident on the second convex lens 9 , focus to the second detector 10 through the second convex lens 9 .

Embodiment 2. This embodiment is described with reference to FIG. 1 . The difference between this embodiment and Embodiment 1 is that the beam splitter 5 is a semi-reflective and semi-transmissive beam splitter.

Specific Embodiment 3. This embodiment is described with reference to FIG. 1 . The difference between this embodiment and Embodiment 1 is that the saturation concentration of elemental mercury gas per meter in the reference cell 6 is 0.2-20 mg/m ³ .

Embodiment 4. This embodiment is described with reference to FIG. 1 . The difference between this embodiment and Embodiment 1 is that the magnetic induction generated by the magnet 2 is 1-3T.

Specific embodiment five, illustrate present embodiment in conjunction with Fig. 2, the continuous monitoring method of gaseous elemental mercury concentration, concrete process is as follows:

Step 1, the sample cell 4 is filled with the gaseous elemental mercury medium to be measured, and the data acquisition analyzer 11 measures the transmitted light intensity I _R detected by the first detector 8 and the reflected light intensity I _S detected by the second detector 10;

Step 2, calculate the light intensity contrast M of transmitted light and reflected light described in step 1 according to the following formula;

Wherein, A is the constant corresponding to the light intensity contrast M being zero when only air is contained in the sample cell 4;

Step 3: compare the light intensity contrast M obtained in step 2 with the corresponding relationship curve between the light intensity contrast M and the concentration of the gaseous elemental mercury medium to obtain the concentration of the gaseous elemental mercury medium to be measured.

Embodiment 6. This embodiment is a further description of Embodiment 5. In step 2, the sample pool 4 only contains air, and the constant A corresponding to the light intensity contrast M being zero is obtained by the following method:

Step 2M, when the sample cell 4 only contains air, the data acquisition analyzer 11 measures the transmitted light intensity I _R0 detected by the first detector 8 and the reflected light intensity I _S0 detected by the second detector 10;

Step 2N, obtaining the light intensity contrast M of the transmitted light described in step 2M and reflected light is the constant A corresponding to zero;

Among them, the light intensity contrast M is obtained by the following formula:

.

Specific embodiment seven, this embodiment is a further description of specific embodiment five, the corresponding relationship curve of the light intensity contrast M described in step 3 and the gaseous elemental mercury medium concentration is obtained by the following method:

Step 3M, the sample cell 4 is filled with the gaseous elemental mercury medium of known concentration, and the data acquisition analyzer 11 measures the transmitted light intensity I _R detected by the first detector 8 and the reflected light intensity I _S detected by the second detector 10;

Step 3N, calculate the light intensity contrast M of the transmitted light and reflected light described in step 3M according to the following formula;

Wherein, A is the constant corresponding to the contrast of zero when the sample cell 4 does not contain the gas to be measured;

Step 3P, repeat step 3N until the light intensity contrast M of n groups of gaseous elemental mercury medium concentration is obtained, and the horizontal axis is the gaseous elemental mercury medium concentration, and the light intensity contrast M is the vertical axis to depict the light intensity contrast M and the gaseous state Corresponding relationship curve of elemental mercury medium concentration.

Embodiment 8. This embodiment is a further description of Embodiment 5. The corresponding relationship curve between the light intensity contrast M and the concentration of the gaseous elemental mercury medium in step 4 is a straight line.

Embodiment 9. This embodiment is a further description of Embodiment 5. In step 4, measure the concentration of n gaseous elemental mercury media and the light intensity contrast M is 5-12 values.

Specific embodiment ten, in conjunction with Fig. 3 illustrate this embodiment, present embodiment adopts the device described in specific embodiment one and the method described in specific embodiment five to measure the concrete example of gaseous elemental mercury concentration to be measured, select following parameter:

The magnetic field intensity generated by the magnet 2 is 1T, and the saturation concentration per meter of the elemental mercury gas in the reference cell 6 is 1 mg/m ³ .

The contrast between the two light intensities was calculated by the formula, and the concentration of gaseous elemental mercury in the sample cell was determined according to the different light intensity contrasts obtained. The results are shown in Figure 3. The horizontal axis is the concentration of the gaseous elemental mercury medium; the vertical axis is the light intensity contrast. the

Claims (9)

1. The device for continuously monitoring the concentration of the gaseous elemental mercury is characterized by comprising a mercury element lamp (1), a magnet (2), a collimating lens (3), a sample cell (4), a spectroscope (5), a reference cell (6), a first convex lens (7), a first detector (8), a second convex lens (9), a second detector (10) and a data acquisition analyzer (11), wherein the mercury element lamp (1) is arranged in a magnetic field of the magnet (2) and is arranged at the focal point of the collimating lens (3), a detection surface of the first detector (8) is superposed with a focal plane of the first convex lens (7), a detection surface of the second detector (10) is superposed with a focal plane of the second convex lens (9), output light of the mercury element lamp (1) enters the collimating lens (3) and is transmitted by the collimating lens (3) to obtain parallel light, and the parallel light enters the collimating lens (5) after passing through the sample cell (4), the parallel light is divided into reflected light and transmitted light through the spectroscope (5), wherein the transmitted light is incident to the first convex lens (7) after passing through the reference pool (6), and then is focused to the first detector (8) through the first convex lens (7), the reflected light is incident to the second convex lens (9), and then is focused to the second detector (10) through the second convex lens (9), the output end of the first detector (8) and the output end of the second detector (10) are respectively connected with two access ends of the data acquisition analyzer (11), and the medium in the reference pool (6) is elemental mercury gas with saturated concentration.

2. The continuous monitoring device of gaseous elemental mercury concentration according to claim 1, characterized in that the beam splitter (5) is a half-reflective and half-transmissive beam splitter.

3. The continuous monitoring device of gaseous elemental mercury concentration according to claim 1, characterized in that the saturated concentration per meter of elemental mercury gas in the reference cell (6) is 0.2-20 mg/m³。

4. The device for continuously monitoring the concentration of gaseous elemental mercury according to claim 1, characterized in that the magnetic induction generated by the magnet (2) is 1-3T.

5. The continuous monitoring method using the continuous monitoring device of gaseous elemental mercury concentration according to claim 1, characterized by the following specific procedures:

step one, filling a sample cell (4) with a gaseous elementary mercury medium to be detected, and measuring the transmitted light intensity detected by a first detector (8) by a data acquisition analyzer (11)I _R And the intensity of the reflected light detected by the second detector (10)I _S ；

Step two, calculating the light intensity contrast of the transmitted light and the reflected light according to the following formulaM；

Wherein,Athe contrast of light intensity is only when the sample cell (4) contains airMA constant corresponding to zero;

step three, the light intensity contrast obtained in the step twoMContrast with light intensityMAnd comparing with the corresponding relation curve of the concentration of the gaseous elementary substance mercury medium to obtain the concentration of the gaseous elementary substance mercury medium to be detected.

6. The method according to claim 5, wherein the sample cell (4) in step two contains only air and has a light intensity contrastMConstant corresponding to zeroAIs obtained by the following method:

step two M, when the sample cell (4) only contains air, the data acquisition analyzer (11) measures the transmitted light intensity detected by the first detector (8)I _R0 And the intensity of the reflected light detected by the second detector (10)I _S0 ；

Step two N, the light intensity contrast ratio of the transmission light and the reflection light in the step two M is obtainedMConstant corresponding to zeroA；

Wherein the contrast of light intensityMThe following equation is used to obtain:

。

7. the method of claim 5, wherein the step three of continuously monitoring the concentration of gaseous elemental mercury is characterized by a light intensity contrastMThe corresponding relation curve with the concentration of the gaseous elementary mercury medium is obtained by the following method:

step three M, filling the sample cell (4) with gaseous elementary mercury medium with known concentration, and measuring the transmitted light intensity detected by the first detector (8) by the data acquisition analyzer (11)I _R And the intensity of the reflected light detected by the second detector (10)I _S ；

Step three N, calculating the light intensity contrast of the transmitted light and the reflected light in step three M according to the following formulaM；

Wherein,Ais a constant corresponding to the contrast being zero when the sample cell (4) does not contain the gas to be measured;

step three P, repeatedly executing step three N until obtaining the light intensity contrast of N groups of gaseous elementary mercury medium concentrationMAnd the concentration of the gaseous elementary mercury medium is taken as the horizontal axis, and the light intensity contrast ratioMPlotting intensity contrast for the vertical axisMAnd (4) a corresponding relation curve with the concentration of the gaseous elementary mercury medium.

8. The method of claim 5 or 7, wherein the method comprises continuously monitoring the concentration of gaseous elemental mercury by light intensity contrastMThe curve of the corresponding relation with the concentration of the gaseous elementary substance mercury medium is a straight line.

9. The method according to claim 7, wherein the step three P comprises obtaining the light intensity contrast of the concentrations of n groups of gaseous elemental mercury mediaMTo obtain 5-12 sets of light intensity contrastMNumerical values.

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