CN108896519B - Double-spectrum flue gas mercury analysis device and corresponding method - Google Patents

Abstract

The present disclosure discloses a dual-spectrum flue gas mercury analysis device and a corresponding method. The dual-spectrum flue gas mercury analysis device includes: a light source, a gas chamber, a light detector and a control module, wherein: the gas chamber is used for storing The gas to be measured; the light source is placed on one side of the gas chamber to emit measuring light waves to illuminate the gas chamber; the photodetectors are two or more, placed on different sides of the gas chamber, It is connected with the control module for detecting the measurement light wave passing through the air chamber, and sends the detection data to the control module. The disclosed technical scheme comprehensively utilizes multiple measurement methods, can accurately measure the mercury content in the flue gas, has the advantages of simple structure, accurate measurement structure and the like, and can be widely used in the online detection of mercury content.

Description

Dual-spectrum flue gas mercury analysis device and corresponding method

technical field

The present disclosure relates to the technical field of analytical instruments, in particular to a dual-spectrum flue gas mercury analysis device and a corresponding method.

Background technique

Due to rapid industrial development, anthropogenic mercury emissions have gradually become a major source of atmospheric mercury in the environment. Coal is one of the energy and mineral resources, and it is an important material for economic and social development around the world. Industrial demand Globally burns a large amount of coal every year, and the mercury released from coal combustion accounts for a large proportion of the mercury released by human activities.

In October 2013, the "Mercury Treaty Diplomatic Conference" hosted by the United Nations Environment Programme in Kumamoto, Japan passed the Minamata Convention to control and reduce global mercury emissions. The representatives signed the convention, marking the first step in the global effort to reduce mercury pollution. The convention recognizes that small gold mines and coal-fired power plants are the largest sources of mercury pollution. Therefore, real-time monitoring of mercury in flue gas has become a necessary means.

In thermal power plants, the typical emission concentration of mercury is usually only 0.01ppm, which is 4-5 orders of magnitude lower _than that of SO2 or _NOx . Therefore, it is difficult to monitor mercury on-line. The existing flue gas mercury monitoring technology mainly adopts the flue gas to extract the sampling gas, and obtain the mercury concentration by optical monitoring after pretreatment. Different optical monitoring methods have a crucial impact on the construction of the overall system and the measurement accuracy. Therefore, the research on optical monitoring methods is the core of the online monitoring technology for elemental mercury.

At present, the optical monitoring methods of mercury mainly include cold vapor atomic absorption spectroscopy (CVAAS), cold vapor atomic fluorescence spectroscopy (CVAFS), atomic emission spectroscopy (AES), X-ray fluorescence X-ray fluorescence spectroscopy and Ultraviolet differential optical absorption spectroscopy (UV-DOAS). The most mature ones are cold atomic absorption spectroscopy and cold vapor atomic fluorescence Test equipment for atomic absorption spectroscopy.

General optical measurement methods use the characteristic that mercury atoms have a strong absorption effect on ultraviolet rays of 253.7 nm, and the concentration of mercury is obtained by measuring the changes of ultraviolet rays through mercury-containing flue gas. However, since coal-fired flue gas contains a large amount of impurities such as sulfur dioxide and nitric oxide, which also have a strong absorption effect on ultraviolet rays, the measurement of mercury content is generally carried out after desulfurization and denitration treatment. This process can remove most of the sulfur dioxide, nitric oxide and other gases in the flue gas. The above methods, except for the ultraviolet differential absorption spectrum, assume that there is no gas that can absorb ultraviolet rays. The ultraviolet differential method requires two independent gas chambers and measurement systems. If the reference gas is standard gas, the influence of impurity gas cannot be removed from the measurement results; if the reference gas is mercury-removed flue gas, then There is a possibility that the mercury cannot be completely removed, and the impurity gas may be removed at the same time, resulting in an inaccurate reference.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned problems in the prior art, the present disclosure utilizes the different characteristics of the measurement optical path by atomic absorption method and atomic fluorescence method, measures two values simultaneously in the same gas chamber, and removes the influence of impurity gas through numerical processing.

According to an aspect of the present disclosure, a dual-spectrum flue gas mercury analysis device is proposed, the dual-spectrum flue gas mercury analysis device includes: a light source, a gas chamber, a light detector, and a control module, wherein:

The gas chamber is used to store the gas to be tested;

The light source is placed on one side of the air chamber, and is used to emit measuring light waves to illuminate the air chamber;

There are two or more light detectors, placed on different sides of the air chamber, and connected to the control module, for detecting the measurement light waves passing through the air chamber, and sending the detection data to the control module.

Optionally, the light source is a low-pressure mercury lamp.

Optionally, the light source generates ultraviolet light at 253.7 nm.

Optionally, there are two light detectors, one is placed on the side of the air chamber opposite to the light source for detecting the absorption spectrum, and the other is placed on the side of the air chamber adjacent to the light source for detecting the absorption spectrum. Detect fluorescence spectra.

Optionally, the photodetector is a photomultiplier tube.

Optionally, the dual-spectrum flue gas mercury analysis device further includes a display module, the display module is connected to the control module and used to display the data sent by the control module.

According to another aspect of the present disclosure, a method for mercury analysis using the above-mentioned dual-spectrum flue gas mercury analysis device is also provided, the method comprising:

The mercury concentration measurement parameters are calibrated, wherein the mercury concentration measurement parameters include: incident light intensity, mercury concentrations of mercury-containing gases with different mercury concentrations, and corresponding fluorescence spectrum intensities;

Based on the calibrated mercury concentration measurement parameters, the estimated value of mercury concentration in the gas to be measured is measured by using the dual-spectrum flue gas mercury analysis device and the atomic fluorescence method;

Correct the estimated value of mercury concentration in the gas to be measured to obtain the concentration of mercury in the gas to be measured.

Optionally, the step of calibrating the mercury concentration measurement parameter includes:

Inject zero gas into the dual-spectrum flue gas mercury analysis device, and measure the light intensity of the zero gas absorption spectrum as the incident light intensity;

A first mercury-containing gas and a second mercury-containing gas are injected into the dual-spectrum flue gas mercury analysis device, and corresponding fluorescence spectrum intensities are obtained by measuring, wherein the mercury concentrations in the first and second mercury-containing gases different.

Optionally, the step of using the dual-spectrum flue gas mercury analysis device and the atomic fluorescence method to measure the estimated value of mercury concentration in the gas to be measured based on the calibrated mercury concentration measurement parameters includes:

injecting the gas to be measured in the dual-spectrum flue gas mercury analysis device;

Using the atomic fluorescence method to measure the fluorescence spectrum intensity of the gas to be measured;

Based on the calibrated mercury concentration measurement parameters and the fluorescence spectral intensity of the gas to be measured, an interpolation method is used to obtain an estimated value of the mercury concentration in the gas to be measured.

Optionally, the step of calibrating the estimated value of mercury concentration in the gas to be measured to obtain the concentration of mercury in the gas to be measured includes:

Use atomic absorption spectrometry to measure the absorption spectrum intensity of the gas to be measured;

A correction factor is calculated by using the incident light intensity and the absorption spectrum intensity of the gas to be measured;

The estimated value of mercury concentration in the gas to be measured is corrected by using the correction factor to obtain the concentration value of mercury in the gas to be measured.

The technical scheme of the present disclosure utilizes the different characteristics of measuring optical paths by cold atomic absorption method and cold atomic fluorescence method, and simultaneously measures two values in the same gas chamber, and finally removes the influence of impurity gas through numerical processing. The technical solution of the present disclosure can accurately measure the mercury content in the flue gas, has the advantages of simple structure, accurate measurement structure and the like, and can be widely used in the online detection of mercury content.

Description of drawings

1 is a schematic structural diagram of a dual-spectrum flue gas mercury analysis device according to an embodiment of the present disclosure;

2 is a schematic structural diagram of a dual-spectrum flue gas mercury analysis device according to another embodiment of the present disclosure;

3 is a schematic diagram of a cold atom fluorescence method according to an embodiment of the present disclosure;

FIG. 4 is a flowchart of a dual-spectral flue gas mercury analysis method according to an embodiment of the present disclosure.

Detailed ways

Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement them. Also, for the sake of clarity, parts unrelated to describing the exemplary embodiments are omitted from the drawings.

In the present disclosure, it should be understood that terms such as "comprising" or "having" are intended to indicate the presence of features, numbers, steps, acts, components, parts, or combinations thereof disclosed in this specification, and are not intended to exclude a or multiple other features, numbers, steps, acts, components, parts, or combinations thereof may exist or be added.

In addition, it should be noted that the embodiments of the present disclosure and the features of the embodiments may be combined with each other under the condition of no conflict. The present disclosure will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

Considering that when there is an impurity gas in the flue gas that can affect the measurement of mercury, if the cold atomic absorption method is used for measurement, due to the absorption of ultraviolet rays by the impurity gas, the measured ultraviolet rays will be weakened, which will eventually make the mercury measurement result too large; If measured by cold atomic fluorescence method, the ultraviolet rays absorbed by mercury atoms are reduced due to the absorption of ultraviolet rays by impurity gas, and the generated fluorescence is also reduced accordingly, resulting in a small mercury measurement result. The present disclosure utilizes the cold atomic absorption method and the cold atomic fluorescence method to measure different optical paths, measures two values simultaneously in the same gas chamber, and finally removes the influence of impurity gas through numerical processing.

According to an aspect of the present disclosure, a dual-spectrum flue gas mercury analysis device is proposed. As shown in FIG. 1 , the dual-spectrum flue gas mercury analysis device includes: a light source, a gas chamber, a photodetector, and a control module, wherein:

The gas chamber is used to store the gas to be tested;

The light source is placed on one side of the air chamber, and is used to emit measuring light waves to illuminate the air chamber;

There are two or more light detectors, placed on different sides of the air chamber, and connected to the control module, for detecting the measurement light waves passing through the air chamber, and sending the detection data to the control module.

In an embodiment of the present disclosure, the light source adopts a low-pressure mercury lamp to generate ultraviolet rays of 253.7 nm.

Wherein, the air chamber is provided with an air inlet and an air outlet.

In an embodiment of the present disclosure, there are two light detectors, one is placed on the side of the air chamber opposite to the light source for detecting absorption spectra, and the other is placed in the air chamber adjacent to the light source. side, for detecting fluorescence spectra.

In an embodiment of the present disclosure, the photodetector is a photomultiplier tube.

In an embodiment of the present disclosure, the control module may be a Micro Control Unit (MCU).

In an embodiment of the present disclosure, the dual-spectrum flue gas mercury analysis device further includes a display module, the display module is connected to the control module, and is used for displaying data sent by the control module.

In an embodiment of the present disclosure, the display module may be a display device such as a display screen.

FIG. 2 is a schematic structural diagram of a dual-spectrum flue gas mercury analysis device according to another embodiment of the present disclosure. As shown in FIG. 2 , as in the previous embodiment, the dual-spectrum flue gas mercury analysis device includes: a light source, a gas chamber , light detectors, and control modules, where:

The gas chamber is used to store the gas to be tested;

The light source is placed on one side of the air chamber, and is used to emit measuring light waves to illuminate the air chamber;

There are two or more light detectors, placed on different sides of the air chamber, and connected to the control module, for detecting the measurement light waves passing through the air chamber, and sending the detection data to the control module.

In this embodiment, the air chamber is made of stainless steel as the base material. In addition, in order to prevent the reaction of the amalgam, the inner wall of the air chamber is also plated with Teflon.

The air chamber is provided with an air inlet and an air outlet, the air inlet and the air outlet are respectively connected with a heat tracing conduit, and the air inlet is connected to the mercury detection system and the pretreatment system through the heat tracing conduit. The air outlet is connected to the subsequent processing measurement devices such as flowmeter and air pump through the heat tracing pipe.

The photodetector is a photomultiplier tube (MPT).

The air chamber is provided with three optical windows, and the optical windows are sealed with silica glass, wherein, one end of the air chamber is provided with a first optical window, and a low-pressure mercury lamp light source is placed on the outside of the first optical window. , as a test light source; the other end of the gas chamber is provided with a second optical window, and a first photomultiplier tube is placed on the outside of the second optical window for measuring atomic absorption spectroscopy; one side of the gas chamber, A third optical window is provided in the direction perpendicular to the gas chamber, and a second photomultiplier tube is placed outside the third optical window for measuring atomic fluorescence spectrum.

In addition, in order to avoid the influence of other background light, a color filter needs to be set between the three optical windows, the light source and the photomultiplier tube, so as to ensure that only the measurement light of 253.7nm passes through.

The control module is a Micro Control Unit (MCU).

The dual-spectrum flue gas mercury analysis device further includes a display module, which is connected to the control module for displaying data sent by the control module, and the display module may be a display device such as a display screen.

Wherein, the length of the air chamber is 20cm.

According to Beer's law, the light intensity measured by atomic absorption spectrometry has a relationship with the incident light intensity as shown in the following formula:

Among them, I ₁ is the light intensity measured by atomic absorption spectrometry; I ₀ is the incident light intensity; ε _Hg is the absorption coefficient of mercury per unit length and unit concentration medium; c _Hg is the concentration of mercury; L is the entire measuring cell length.

In the actual flue gas, in addition to mercury atoms that absorb ultraviolet rays, there are other impurity gases that also absorb ultraviolet rays, such as SO ₂ , NO _x , etc. Therefore, according to the additive principle, formula (1) can be modified as:

中ε_i表示测量气体中第i种杂质气体单位长度和单位浓度介质的吸收系数，c_i表示测量气体中第i种杂质气体的浓度，N表示测量气体中杂质气体的种类数量，令

则式(2)可表示为：in,

where ε _i represents the absorption coefficient of the i-th impurity gas per unit length and unit concentration medium in the measurement gas, c _i represents the concentration of the i-th impurity gas in the measurement gas, N represents the number of types of impurity gases in the measurement gas, let

The formula (2) can be expressed as:

In addition, as shown in Figure 3, for the cold atomic fluorescence method, in any small layer in the gas chamber, the following relationship exists:

为荧光效率，where I _x represents the fluorescence generated on a small layer in the gas cell, I _i ′ is the light intensity absorbed by mercury on this small layer,

is the fluorescence efficiency,

In the formula, I _i represents the incident light intensity on this small layer, and x is the starting distance of the small layer from the light cell.

Since the impurity gases do not generate resonance fluorescence except SO ₂ , integrating equation (5) over the entire measurement length, we can get:

Combining formula (3), we can get:

2.303(ε _Hg c _Hg +k)=ln(I ₀ /I ₁ ) (7)

Substitute equations (3) and (7) into equation (6) to get:

It can be obtained by formula (8):

When there is no impurity gas (standard gas) that absorbs the measured light wave in the flue gas, that is, k=0, it can be obtained from formula (6):

进行泰勒展开，得到：Will

Perform Taylor expansion to get:

Since the mercury content in the flue gas is very small, the higher-order terms in equation (11) can be ignored, so we can get:

Substitute into equation (10) to get:

From formula (13), we can get:

Substitute into equation (9) to get:

则式(15)可以改写为：definition

The formula (15) can be rewritten as:

It can be obtained from equation (16) that when using cold atomic fluorescence method to measure mercury in flue gas, it can be assumed that the flue gas does not contain any gas that affects the measurement, and then the correction factor k is calculated by cold atomic absorption method to finally remove effects of other gases.

According to another aspect of the present disclosure, a method for mercury analysis using the dual-spectrum flue gas mercury analysis device is proposed. As shown in FIG. 4 , the method includes steps S401 to S403:

In step S401, the mercury concentration measurement parameters are calibrated, wherein the mercury concentration measurement parameters include: incident light intensity I ₀ , mercury concentrations of mercury-containing gases with different mercury concentrations, and corresponding fluorescence spectrum intensities;

In step S402, based on the calibrated mercury concentration measurement parameters, the estimated value of mercury concentration in the gas to be measured is measured by using the dual-spectrum flue gas mercury analysis device and the atomic fluorescence method;

In step S403, the estimated value of mercury concentration in the gas to be measured is corrected to obtain the concentration of mercury in the gas to be measured.

In an embodiment of the present disclosure, the step S401 includes steps S4011-S4012:

In step S4011, zero gas is injected into the dual-spectrum flue gas mercury analysis device, and the light intensity of the zero gas absorption spectrum is measured and obtained as the incident light intensity I ₀ , wherein the zero gas refers to the absence of Mercury and other impurity gases, such as pure nitrogen;

In step S4012, inject a first mercury-containing gas and a second mercury-containing gas into the dual-spectrum flue gas mercury analysis device, and measure the corresponding fluorescence spectrum intensities, wherein the first mercury-containing gas and the second mercury-containing gas are The mercury concentration in the mercury gas is different, the mercury concentration of the first mercury-containing gas is denoted as c _a , the corresponding fluorescence spectrum intensity is denoted as I _a , and the mercury concentration of the second mercury-containing gas is denoted as c _b , Its corresponding fluorescence spectral intensity is denoted as I _b .

In actual operation, in order to improve the measurement accuracy, it is necessary to re-calibrate the mercury concentration measurement parameters every preset time, such as 1-2 weeks.

In an embodiment of the present disclosure, the step S402 includes steps S4021-S4023:

In step S4021, inject the gas to be measured in the dual-spectrum flue gas mercury analysis device;

In step S4022, using the atomic fluorescence method to measure and obtain the fluorescence spectral intensity I ₂ of the gas to be measured;

In step S4023, based on the calibrated mercury concentration measurement parameters and the fluorescence spectral intensity I ₂ of the gas to be measured, an interpolation method is used to obtain an estimated value of the mercury concentration in the gas to be measured

In an embodiment of the present disclosure, the interpolation method is a linear interpolation method.

In an embodiment of the present disclosure, the step S403 includes steps S4031-S4033:

In step S4031, using atomic absorption spectrometry to measure the absorption spectrum intensity I ₁ of the gas to be measured;

In step S4032, the correction factor k is calculated by using the incident light intensity I ₀ and the absorption spectrum intensity I ₁ of the gas to be measured:

In step S4033, the estimated value of mercury concentration in the gas to be measured is corrected by using the correction factor to obtain the concentration value of mercury in the gas to be measured:

According to the above technical scheme, the present disclosure comprehensively utilizes multiple measurement methods to accurately measure the mercury content in the flue gas, and has the advantages of simple structure and accurate measurement structure. The dual-spectrum flue gas mercury analysis device disclosed in the present disclosure can be used as an important component of on-line detection of mercury content in coal-fired power plants.

The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present disclosure in detail. It should be understood that the above-mentioned specific embodiments are only specific embodiments of the present disclosure, and are not intended to limit the present disclosure. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present disclosure should be included within the protection scope of the present disclosure.

Claims (7)

1. a method for dual-spectrum flue gas mercury analysis, characterized in that, a dual-spectrum flue gas mercury analysis device is used, and the dual-spectrum flue gas mercury analysis device comprises: a light source, a gas chamber, a light detector and a control module, wherein : The gas chamber is used to store the gas to be tested; The light source is placed on one side of the air chamber, and is used to emit measuring light waves to illuminate the air chamber; There are two light detectors, one is placed on the side of the air chamber opposite to the light source for detecting absorption spectra, and the other is placed on the side of the air chamber adjacent to the light source for detecting fluorescence spectra, and connect with the control module, and send the detection data to the control module; The method includes: The mercury concentration measurement parameters are calibrated, wherein the mercury concentration measurement parameters include: incident light intensity, mercury concentrations of mercury-containing gases with different mercury concentrations, and corresponding fluorescence spectrum intensities; Based on the calibrated mercury concentration measurement parameters, the estimated value of mercury concentration in the gas to be measured is measured by using the dual-spectrum flue gas mercury analysis device and the atomic fluorescence method

; Correcting the estimated value of the mercury concentration in the gas to be measured to obtain the concentration of mercury in the gas to be measured includes: using atomic absorption spectrometry to measure and obtain the absorption spectrum intensity I ₁ of the gas to be measured; The correction factor k is calculated from the incident light intensity I ₀ and the absorption spectrum intensity I ₁ of the gas to be measured, and the calculation formula is as follows:

; Use the correction factor to correct the estimated value of the mercury concentration in the gas to be measured to obtain the mercury concentration value c _Hg in the gas to be measured, and the calculation formula is as follows:

. 2. The method according to claim 1, wherein the step of calibrating the mercury concentration measurement parameter comprises: Inject zero gas into the dual-spectrum flue gas mercury analysis device, and measure the light intensity of the zero gas absorption spectrum as the incident light intensity; A first mercury-containing gas and a second mercury-containing gas are injected into the dual-spectrum flue gas mercury analysis device, and corresponding fluorescence spectrum intensities are obtained by measuring, wherein the mercury concentrations in the first and second mercury-containing gases different. 3. The method according to claim 1, characterized in that, based on the calibration-based mercury concentration measurement parameters, using the dual-spectrum flue gas mercury analysis device and atomic fluorescence method to measure the estimated value of mercury concentration in the gas to be measured. Steps include: injecting the gas to be measured in the dual-spectrum flue gas mercury analysis device; Using the atomic fluorescence method to measure the fluorescence spectrum intensity of the gas to be measured; Based on the calibrated mercury concentration measurement parameters and the fluorescence spectral intensity of the gas to be measured, an interpolation method is used to obtain an estimated value of the mercury concentration in the gas to be measured. 4. The method of claim 1, wherein the light source is a low pressure mercury lamp. 5. The method of claim 1, wherein the light source generates ultraviolet rays of 253.7 nm. 6. The method of claim 1, wherein the photodetector is a photomultiplier tube. 7 . The method according to claim 1 , wherein the dual-spectrum flue gas mercury analysis device further comprises a display module, and the display module is connected to the control module for displaying data sent by the control module. 8 . .

Images