CN100410649C - An online atmospheric mercury analyzer - Google Patents

Abstract

The invention relates to an online atmospheric mercury analyzer, which is characterized in that it includes gas circuit components and circuit components; the gas circuit components mainly include a sampling pump connected through a pipeline, a mercury adsorption tube, a mercury removal tube, a detector, Solenoid valve, restrictor pipe and filter; The mercury adsorption pipe is connected between the first and second solenoid valves, the first restrictor pipe is connected between the second and third solenoid valves, and the third and third solenoid valves are connected with each other. The sampling pump and the mercury removal pipe are connected between the fourth electromagnetic valve, and the second current limiting pipe is connected between the fourth and the first electromagnetic valve; the circuit components mainly include: circuit control components and the mercury adsorption tube. The heating device and cooling device outside the tube, the circuit control part is a single-chip microcomputer, and the relay is controlled by the single-chip microcomputer, and the relay controls the heating device, cooling device and four solenoid valves respectively. The invention can not only be used for scientific research in scientific research institutes, but also can be used for air pollution detection by environmental detection institutions, factories and mines, and can also be applied to routine monitoring of government departments.

Description

An online atmospheric mercury analyzer

technical field

The invention relates to an analysis instrument, in particular to an online atmospheric mercury analyzer.

Background technique

Mercury is one of the main pollutants harmful to health in the atmosphere. Since the 1980s, people have done a lot of research on the determination of environmental mercury and achieved some results. The concentration of mercury in the atmosphere is very low, and it is several orders of magnitude lower than the potential interfering substances, so it cannot be directly measured. Therefore, it is required to pre-separate and enrich the sample before the measurement, and the analytical method is required to have high accuracy and reliability. sex.

Among the various existing analytical methods for measuring mercury, the most commonly used and highly sensitive methods are cold atomic absorption spectrometry (CVAAS) and cold atomic fluorescence spectrometry (CVAFS). The corresponding sample collection methods include "chemical method" and " Amalgamation method" two categories. The chemical method is also divided into solution absorption method and solid adsorption method. The solution absorption method uses a solution containing a strong oxidant (such as H ₂ SO ₄ -KMnO ₄ , HI-I ₂ , KI-I ₂ and other absorption systems) to absorb mercury in the atmosphere. , measured after reduction, the general measurement is the concentration of total mercury. The solid adsorption method is to use solid adsorbents (such as mercapto cotton, iodized activated carbon, sulfurized activated carbon, impregnated copper chloride activated carbon, etc.) to adsorb mercury in the atmosphere, and measure it after digestion and reduction.

The amalgamation method is to use precious metals such as gold, silver, or gold-plated, silver-plated carriers (such as gold-plated fine sand, gold-plated glass beads, etc.) to absorb mercury in the air, and the mercury and gold or silver form an amalgam and are collected. Heating and desorption at a certain temperature for measurement. This method has high collection efficiency for atmospheric mercury, is easy to operate, the adsorbent can be reused, and has high sensitivity. It is currently the most widely used method for separating and enriching atmospheric mercury.

In the past, atmospheric mercury was mostly measured for total mercury, and mercury in the atmosphere can be divided into two forms: gaseous mercury (mainly Hg ⁰ , CH ₃ -Hg, C ₂ H ₅ -Hg) and particulate mercury (mainly HgS, dust adsorbed mercury mainly). Different forms of atmospheric mercury have different hazards to the environment and their migration and transformation characteristics in the environment. Therefore, the determination of different forms of atmospheric mercury is of great significance.

Foreign countries have been at the forefront in the research of atmospheric mercury measurement methods, and there are also commercialized instruments that are specially used to measure the concentration of different forms of mercury in the atmosphere. For example, the products of the Canadian Tekran (Tekran) company, using gold amalgamation and cold atomic fluorescence method, have been able to measure the ultra-low concentration of mercury in the ambient atmosphere relatively well online, and have been widely used in many fields. However, although foreign atmospheric mercury online analyzers have been able to measure the ultra-low concentration of mercury in the ambient atmosphere online, due to the need to use cylinders to carry gas, and generally use expensive argon gas, not only the instrument is expensive, but also the instrument is attached. There are many components, so it is not suitable for long-term observation in the field or flexible on-site analysis.

The research on mercury pollution in the atmosphere started relatively late in my country, and there is no online analysis instrument in China that can be used to monitor and analyze mercury in the atmosphere. At present, the research on atmospheric mercury in China usually adopts the method of manual sampling in the field and subsequent analysis in the laboratory . The collection of gaseous mercury requires a long sampling time, usually from 24 hours to a week, and the collected samples are sealed and then taken to the laboratory for analysis, which takes a long time. This method will bring a lot of errors, including a series of errors such as reagent blank, transportation blank, field blank, laboratory blank, etc., making the measured data difficult to be convincing, especially the measurement in the background area may lead to completely wrong result. And it is impossible to obtain long-term continuous observation data, which causes a lag in the study of atmospheric mercury pollution.

Contents of the invention

In view of the above problems, the main purpose of the present invention is to provide an online atmospheric mercury analyzer, which can be continuously monitored online, is portable, and has high sensitivity.

In order to achieve the above object, the present invention adopts the following technical solutions: an online atmospheric mercury analyzer, characterized in that: it includes gas circuit components and circuit components; the gas circuit components mainly include sampling pumps connected by pipelines, mercury adsorption tube, mercury removal tube, detector, solenoid valve, flow limiting tube and filter; the mercury adsorption tube is connected between the first and second solenoid valves, and the first and second solenoid valves are connected between the second and third solenoid valves A restrictor tube, the sampling pump and the mercury removal tube are connected between the third and fourth electromagnetic valves, and the second restrictor tube is connected between the fourth and first electromagnetic valves; the second and third electromagnetic valves The valves are respectively connected to the detector and the filter, the first solenoid valve is connected to a sampling pipe, and the third port of the fourth solenoid valve is emptied; the circuit components mainly include: circuit control components and The heating device and the cooling device outside the mercury adsorption tube, the circuit control part is a single-chip microcomputer, and the relay is controlled by the single-chip microcomputer, and the relay controls the heating device, the cooling device and four solenoid valves respectively.

The detector is an ultraviolet detector, which includes a light source, a light source lens, an excitation pool, a lens, a photomultiplier tube, and a fluorescent pool. The light radiated by the light source is converged into the excitation pool through the light source lens, so that the mercury vapor The fluorescence generated by the stimulated radiation of the excitation cell is collected by the photomultiplier tube after being converged by the lens.

The incident light path formed by the light source and the light source lens is perpendicular to the receiving light path formed by the photomultiplier tube.

The light source is a low-pressure mercury lamp with a radiation wavelength of 253.7nm.

The heating device is an electric furnace wire wound around the outer periphery of the mercury adsorption tube.

The cooling device is a fan.

The pipelines connecting the components are polytetrafluoroethylene pipes and polytetrafluoroethylene joints.

The pipeline is a polytetrafluoroethylene pipe and a polytetrafluoroethylene joint.

The single-chip microcomputer is connected to a computer through the RS-232 serial interface.

Due to the adoption of the above technical scheme, the present invention has the following advantages: 1. The device of the present invention adopts the most recognized and common pure gold pre-enrichment to separate the gaseous mercury in the atmosphere, and after desorption by heating, the mercury content is analyzed by cold atomic fluorescence spectroscopy , so the detection and analysis sensitivity is high, and it is not disturbed by positive or negative errors, which effectively guarantees the stability and reliability of the analysis results. 2. The gas circuit circulation system of the present invention realizes the two functions of sampling and carrier gas delivery with only one air pump, and directly uses the purified pumped gas as the carrier gas, which not only saves the cost of using argon as the carrier gas, No steel cylinder is needed to carry gas, and the portability of the device of the present invention is greatly improved, which is especially suitable for field observation. 3. The present invention uses a gold-plated fine sand mercury adsorption tube to collect gaseous mercury. Due to the high collection efficiency of the adsorption tube and the low detection limit, the sampling time is greatly shortened compared with the previous ones, and high-time-resolution data can be obtained by sampling in a short time , combined with the cold atomic fluorescence analysis method, realizes the requirement of continuous on-line monitoring in the field, can continuously analyze the ultra-low concentration of gaseous total mercury in the ambient air on-line, and can run continuously all year round, suitable for studying the regional transport law of mercury and using the receptor model Identify sources of mercury contamination. 4. The gas circuit part of the present invention all adopts polytetrafluoroethylene tubes and polytetrafluoroethylene joints, and shortens the delivery pipelines of sample gas and desorption airflow to the greatest extent, ensuring that the loss of samples during sampling and analysis is reduced. to the minimum. 5. In the detector of the present invention, the receiving optical path of the photomultiplier tube is kept vertical to the emitting optical path of the light source, so the interference caused by the light of the ultraviolet light source entering the photomultiplier tube can be avoided, and the accuracy of the detection result is guaranteed. 6. Introducing computer control into the present invention can make the sampling analysis program automatically carry out data transmission and control, and select suitable measurement parameters (such as sampling time, heating time, heating temperature, etc.) according to different environmental conditions, and the operating cost is low. Sampling analysis and data output are automatically performed by computer, easy to operate, friendly user interface, and have broad market prospects. The invention can not only be used for scientific research in scientific research institutes, but also can be used for air pollution detection by environmental detection institutions, factories and mines, and can also be applied to routine monitoring of government departments.

Description of drawings

Fig. 1 is a schematic diagram of the gas circuit structure of the present invention

Fig. 2 is the circuit control schematic diagram of heating desorption device of the present invention

Fig. 3 is the structural representation of ultraviolet detector of the present invention

Detailed ways

The present invention will be described in detail below according to preferred embodiments of the present invention and accompanying drawings.

The invention includes a casing, and an air circuit component and a circuit component are arranged in the casing.

As shown in Figure 1, the gas circuit components mainly include a sampling pump 6, a mercury adsorption tube 2, a mercury removal tube 7, a detector 11, four three-way solenoid valves 1, 3, 5, 8, and two limiting valves. Flow tubes 4, 9 and a filter 12. The mercury adsorption tube 2 is connected between the C end of the first electromagnetic valve 1 and the C end of the second electromagnetic valve 3, and the NO of the first electromagnetic valve 1 is connected with a sampling tube; the NC end of the second electromagnetic valve 3 is connected to the detector 11 The NO end is connected to the first restrictor pipe 4; the other end of the first restrictor pipe 4 is connected to the NO end of the third solenoid valve 5, and the C end and NC end of the third solenoid valve 5 are respectively connected to the sampling pump 6 and the filter 12, the outlet end of the sampling pump 6 is connected to the C end of the fourth solenoid valve 8 through the mercury removal pipe 7, and the NC end of the fourth solenoid valve 8 is connected to the NC end of the first solenoid valve 1 through the second flow limiting pipe 9 , the NO end of the fourth solenoid valve 8 is the exhaust port.

In the above gas circuit embodiment, all the pipelines connecting the gas circuit components are made of polytetrafluoroethylene tubes and polytetrafluoroethylene joints, and the delivery pipelines of the sample gas and the desorption gas flow are shortened to the greatest extent, ensuring that the samples are collected during sampling. And the loss during analysis is minimized. Wherein, the mercury adsorption tube 2 and the mercury removal tube 7 can be manufactured by themselves, and the manufacturing methods thereof are prior art, and will not be repeated here.

As shown in FIG. 2 , the circuit components mainly include circuit control components and a heating and desorption device, and the heating and desorption device includes a heating device 10 and a cooling device 21 arranged outside the mercury adsorption tube 2 . The circuit control part includes a single-chip microcomputer 19, and relays 24, 25, 26 connected with the single-chip microcomputer 19, the relay 24 controls four solenoid valves 1, 3, 5, 8, the relay 25 controls the heating device 10, and the relay 26 controls the cooling device 21. The transformer 20 supplies power to the heating and cooling devices 10 and 21 under the control of the single-chip microcomputer 19 . Transformer 20 outputs AC 24 volts, and since the operating voltages of the fan and the solenoid valve are both DC 24 volts, two rectifier bridges 22 and 23 are used to convert AC to DC. The single-chip microcomputer 19 outputs a high level through the I/O interface, and triggers three solid-state relays 24, 25, 26 successively to realize the whole analysis process.

In the above-mentioned circuit embodiment, the heating device 10 can be an electric heating furnace wire wound on the periphery of the mercury adsorption tube 2, the cooling device 21 can be a fan, the model of the single-chip microcomputer 19 can be 78E5, and the single-chip microcomputer 19 can also be connected via the RS-232 serial interface. It is connected with an external computer (not shown in the figure), and the sampling and analysis program controlled by the computer is used for data transmission and instrument control. The sampling analysis program can select appropriate measurement parameters (such as sampling time, heating time, heating temperature, etc.) according to different environmental conditions in order to obtain ideal data results.

In the above-mentioned embodiments, as shown in FIG. 3 , the detector 11 can be an ultraviolet detector, which includes a light source 13 , a light source lens 14 , an excitation cell 15 , a lens 16 , a photomultiplier tube 17 and a fluorescent cell 18 . The light source 13 adopts a low-pressure mercury lamp, and its radiation wavelength is mainly 253.7nm. The fluorescent pool 18 is processed and shaped by aluminum, and the inner and outer walls are all blackened to eliminate light scattering and reduce interference. The light radiated by the light source 13 converges to the excitation cell 15 through the light source lens 14 , the mercury vapor is stimulated to radiate in the excitation cell 15 , and the fluorescence generated by the mercury atom radiation is collected by the photomultiplier tube 17 through the lens 16 . The photomultiplier tube 17 converts it into an electrical signal, and after amplification and A/D conversion, the single-chip microcomputer 19 performs data processing. The most critical part of the entire optical path of the fluorescent cell is to keep the receiving optical path of the photomultiplier tube 17 perpendicular to the emitting optical path of the light source 13, that is, to prevent the light from the ultraviolet light source 13 from entering the photomultiplier tube 17, so as to avoid interference and ensure the accuracy of the detection results .

During the operation of the present invention, comprise following process (shown in Fig. 1, Fig. 2, Fig. 3):

1. In the sampling process, the sampling pump 6 is first started, and the sampling pump 6 keeps running during the entire sampling and analysis process. At this time, the single-chip microcomputer does not output the I/O signal, and the solenoid valve is in a non-energized state, that is, the sampling gas enters the mercury adsorption tube 2 from the first solenoid valve 1, and the gaseous mercury is adsorbed on the mercury adsorption tube 2 equipped with gold-plated fine sand, so that Mercury and gold form an amalgam and are adsorbed. The sampling gas enters the sampling pump 6 through the second solenoid valve 3, the first flow limiting pipe 4 and the third solenoid valve 5, and then is sent into the mercury removal pipe 7 by the sampling pump 6. Finally, it is exhausted through the NO end of the fourth solenoid valve 8.

2. During the purging process, the pipeline needs to be purged with carrier gas for about 1 minute before the start of the analysis process, so that the entire gas circuit is filled with carrier gas to remove interfering substances in the air. During operation, the single-chip microcomputer 19 outputs a high level to trigger the solid-state relay 24, so that the solenoid valves 1, 3, 5, and 8 are converted into energized states. After the air is filtered by the filter 12, it enters the sampling pump 6 through the third solenoid valve 5, and then It goes through the mercury removal tube 7, the fourth solenoid valve 8, the second flow limiting tube 9, the first solenoid valve 1 and the mercury adsorption tube 2 in sequence, and then reaches the detector 11 and then is emptied.

3. The thermal desorption process keeps the solenoid valves 1, 3, 5, and 8 in the energized state, and the single-chip microcomputer 19 outputs a 5-volt high level, which triggers the solid-state relay 25 to make the electric heating device 10 work, first rapidly heating (keep outputting 5 volt high level) for 15s, so that the temperature rises rapidly to 800°C, and then pulse heating (5 volts and 0 volts alternately output at 1 second intervals) is maintained at 800°C for 45s, and the mercury adsorption tube 2 is heated and desorbed Mercury vapor is brought into the ultraviolet detector 11 through the second electromagnetic valve 3 by a carrier gas with a flow rate of 60ml/min for detection, and the detected gas is discharged from the detector 11.

4. The analysis process is carried out simultaneously with the above-mentioned thermal desorption process. In the detector 11, mercury atoms are excited to an excited state under the radiation of 253.7nm light, and radiate fluorescence at the same wavelength. The fluorescence produced by vertical angle measurement, the light of light source 13 cannot be detected by photomultiplier tube 17, but the fluorescence produced by mercury vapor can be observed and received by photomultiplier tube 17, and its intensity is directly proportional to the amount of mercury.

5. During the cooling process, the solenoid valves 1, 3, 5, and 8 remain energized. After the thermal desorption process is over, stop outputting the 5 volt high level for heating, and output another 5 volt high level to trigger the solid state relay 26, so that the cooling device 21 blows on the electric heating device 10 for about 3 minutes, and cools down to room temperature.

After the above process ends, the single-chip microcomputer 19 stops outputting all I/O signals, and is ready to enter the next sampling and analysis period.

Claims (15)

1. An online atmospheric mercury analyzer, characterized in that: it comprises a housing, gas path components and circuit components; The gas path components mainly include a sampling pump, a mercury adsorption tube, a mercury removal tube, a detector, a solenoid valve, a restrictor tube and a filter connected by a pipeline; The mercury adsorption tube is connected between the first and second solenoid valves, the first restrictor tube is connected between the second and third solenoid valves, and the sampling tube is connected between the third and fourth solenoid valves. The pump and the mercury removal pipe are connected with the second restrictor pipe between the fourth and the first electromagnetic valve; The second and third solenoid valves are respectively connected to the detector and the filter, the first solenoid valve is connected to a sampling pipe, and the third port of the fourth solenoid valve is emptied; The circuit components mainly include: a circuit control component and a heating device and a cooling device arranged on the outside of the mercury adsorption tube. The circuit control component includes a single-chip microcomputer, and a relay controlled by the single-chip microcomputer controls the heating device, Cooling unit and four solenoid valves. 2. A kind of online atmospheric mercury analyzer as claimed in claim 1, is characterized in that: described detector is ultraviolet detector, and it comprises light source, light source lens, excitation pool, lens, photomultiplier tube and fluorescent pool, so The light radiated by the light source converges to the excitation pool through the light source lens, so that the fluorescence generated by the stimulated radiation of mercury vapor in the excitation pool is collected by the photomultiplier tube after being converged by the lens. 3. A kind of online atmospheric mercury analyzer as claimed in claim 2, is characterized in that: the incident light path that described light source and light source lens form is perpendicular to the receiving light path that described photomultiplier tube forms. 4. A kind of online atmospheric mercury analyzer as claimed in claim 2, is characterized in that: described light source adopts the low pressure mercury lamp that radiation wavelength is 253.7nm. 5. A kind of online atmospheric mercury analyzer as claimed in claim 3, is characterized in that: described light source adopts the low pressure mercury lamp that radiation wavelength is 253.7nm. 6. A kind of online atmospheric mercury analyzer as claimed in claim 1 or 2 or 3 or 4 or 5, characterized in that: the heating device is an electric furnace wire wound around the periphery of the mercury adsorption tube. 7. A kind of online atmospheric mercury analyzer as claimed in claim 1 or 2 or 3 or 4 or 5, is characterized in that: described cooling device is a fan. 8. A kind of online atmospheric mercury analyzer as claimed in right 6, is characterized in that: described cooling device is fan. 9. A kind of online atmospheric mercury analyzer as claimed in claim 1 or 2 or 3 or 4 or 5 or 8, characterized in that: the pipelines connecting the gas circuit components are polytetrafluoroethylene tubes and polytetrafluoroethylene connector. 10. A kind of online atmospheric mercury analyzer as claimed in claim 6, is characterized in that: the pipeline that connects each gas circuit component is polytetrafluoroethylene tube and polytetrafluoroethylene joint. 11. A kind of online atmospheric mercury analyzer as claimed in claim 7, is characterized in that: the pipeline that connects each gas circuit component is polytetrafluoroethylene tube and polytetrafluoroethylene joint. 12. A kind of online atmospheric mercury analyzer as claimed in claim 1 or 2 or 3 or 4 or 5 or 8 or 10 or 11, characterized in that: the single-chip microcomputer is connected to a computer through the RS-232 serial interface. 13. A kind of online atmospheric mercury analyzer as claimed in claim 6, is characterized in that: described single-chip microcomputer is connected a computer by RS-232 serial interface. 14. A kind of online atmospheric mercury analyzer as claimed in claim 7, is characterized in that: described single-chip microcomputer is connected a computer by RS-232 serial interface. 15. A kind of online atmospheric mercury analyzer as claimed in claim 9, is characterized in that: described single-chip microcomputer is connected a computer by RS-232 serial interface.

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