CN103149271A - Method for simultaneously measuring heavy metals with different forms in coal-fired flue gas - Google Patents

Abstract

The invention provides a method for simultaneously measuring heavy metals in different forms in coal-burning flue gas, the steps of which are: using a sample collection system to collect coal-fired flue gas samples. The sampling tube of the nozzle, the filter holder and cyclone separator set in the hot box, and the absorption bottles placed in the ice bath connected sequentially through the catheter, of which the 1st to 3rd absorption bottles contain potassium chloride solution, and the 4th to 3rd absorption bottles are filled with potassium chloride solution. The 5 absorption bottles contain acidic hydrogen peroxide solution, the 6th to 7th absorption bottles contain acidic potassium permanganate solution, and the 8th absorption bottle contains silica gel; after sample collection, the absorption liquid samples in each absorption bottle are sampled separately. recovery, and seal the flue gas samples; then carry out sample digestion on the absorption liquid samples in each absorption bottle; then test the digested samples, and calculate the Concentrations of different forms of heavy metals in flue gas.

Description

A method for simultaneous determination of different forms of heavy metals in coal-fired flue gas

technical field

The invention belongs to the technical field of environmental protection and relates to a method for monitoring pollution sources, more specifically, a method for simultaneously monitoring different heavy metals in different forms in coal-fired flue gas.

Background technique

With the rapid development of my country's economy, heavy metal pollution is becoming more and more serious. According to incomplete statistics, from 2005 to 2009, there were 39 heavy metal pollution incidents across the country, especially since 2009, there were more than 20 serious heavy metal pollution incidents in Fengxiang County of Shaanxi, Wugang City and Liuyang City of Hunan Province. Heavy metal (specific gravity > 5.5g/cm ³ ) pollution has the characteristics of long-term, cumulative, latent and irreversible, which poses a serious threat to human health and has aroused great concern from the academic circles and the government of our country.

Coal is the primary energy source in my country. In 2010, my country's coal consumption reached 3.3 billion tons. The heavy metals in coal are released after combustion, and part of the heavy metals are discharged into the atmosphere through flue gas, making coal burning one of the main sources of atmospheric heavy metal pollution in my country. Atmospheric heavy metals can enter water and soil through dry and wet deposition, damaging the natural environment and ecology; they can also directly enter human blood through the respiratory system, seriously threatening human health. Therefore, it is necessary to strictly control the atmospheric heavy metal pollution caused by coal burning. To control the emission of heavy metals in the atmosphere of coal combustion, it is first necessary to grasp the current situation of heavy metal emissions in the atmosphere of coal combustion in my country. How to accurately monitor the heavy metals in the flue gas of coal combustion will be the key to the control of heavy metal pollution in the atmosphere of my country.

The content of heavy metals in coal combustion flue gas is low (ppb level, even ppt level) and there are particulate and gaseous heavy metals, and gaseous heavy metals include two different forms: water-soluble and water-insoluble. These three different forms of heavy metals in flue gas have different properties, have different impacts on the environment and human health, and can be controlled by different methods. Particulate heavy metals can be removed synergistically through a dust collector, while water-soluble heavy metals can be synergistically removed through a limestone-gypsum wet desulfurization unit. Therefore, it is very meaningful to measure the content of different heavy metals in different forms in flue gas for the control of atmospheric heavy metal pollution. Moreover, the components in coal-fired flue gas are very complex (including water vapor, SO ₂ , NO _x , VOC, etc.), and these components may affect the test accuracy. At present, China's standard methods for the determination of heavy metals in waste gas from stationary sources include cold atomic absorption spectrophotometry (provisional) (HJ543-2009) for the determination of mercury in waste gas from stationary sources, and the determination of arsenic in ambient air and waste gas. Diethyldithiocarbamate Silver Spectrophotometry (Provisional) (HJ540-2009), Determination of Lead in Exhaust Gas from Stationary Pollution Sources Flame Atomic Absorption Spectrophotometry (Provisional) (HJ538-2009), Determination of Cadmium in Atmospheric Stationary Pollution Sources p-Azobenzenediazoaminoazo Benzenesulfonic acid absorption spectrophotometry (HJ/T64.3-2001), determination of cadmium from fixed atmospheric pollution sources Flame atomic absorption spectrophotometry (HJ/T64.1-2001), determination of cadmium from fixed atmospheric pollution sources Graphite furnace atomic absorption spectrometry Photometry (HJ/T64.2-2001). Each standard determination method is for different particulate heavy metals in exhaust gas, only mercury is for gaseous mercury; and different heavy metals require different sample collection and analysis methods. If it is necessary to measure different heavy metals in coal-fired flue gas, these determination methods must be carried out separately, which is not only cumbersome to operate, but also requires a lot of work; moreover, different forms cannot be distinguished. Therefore, it is an urgent problem to be solved in this field to develop a method capable of simultaneously measuring different forms of different heavy metals in coal-fired flue gas.

Contents of the invention

The purpose of the present invention is to provide a method for simultaneous monitoring of heavy metals in different forms (including lead, mercury, chromium, cadmium, manganese, etc.)

To achieve the above object, the present invention adopts the following technical solutions:

A method for simultaneously measuring heavy metals in different forms in coal-fired flue gas, characterized in that the steps are as follows:

(1) Use a sample collection system to collect coal-fired flue gas samples. The sample collection system includes sequentially connected sampling pipes with suction nozzles, particulate heavy metal capture devices, and gaseous heavy metal absorption devices, as well as monitoring systems. Auxiliary devices such as temperature sensors for internal temperature, differential pressure gauges for monitoring and adjusting the air pressure in the system, exhaust pipelines, exhaust pumps and valves, and dry flow meters for monitoring the flow of flue gas in the system;

The particulate heavy metal trapping device includes a filter holder arranged in the hot box and a cyclone separator arranged between the filter holder and the end of the sampling pipe, and a quartz fiber filter paper is placed in the filter holder;

The gaseous heavy metal absorption device includes 8 absorption bottles placed in a cold box connected sequentially through conduits, and the absorption liquid in each absorption bottle from the side close to the particulate heavy metal capture device is: the first to third absorption bottles Inside is potassium chloride solution, which is used to absorb water-soluble heavy metals in flue gas. The fourth to fifth absorption bottles are acidic hydrogen peroxide solution, which is used to collect non-water-soluble heavy metals. The sixth to seventh absorption bottles are acid permanganese. Potassium acid solution is used to collect water-insoluble heavy metals (especially mercury); the eighth absorption bottle is filled with silica gel to absorb moisture in the flue gas;

(2) Perform sample recovery on the absorption liquid samples in each absorption bottle, and seal and store the collected smoke samples;

(3) Digest samples of different absorption liquid samples separately to reduce the influence of SO ₂ , NO _x , and VOC in the flue gas dissolved in the absorption liquid during the analysis process on the analysis results;

(4) Use an inductively coupled plasma-mass spectrometer (ICP-MASS) or an inductively coupled plasma-atomic emission spectrometer (ICP-AES) to detect each sample digested in step (3). Calculate the concentration of heavy metals in different forms in flue gas.

The above-mentioned method, preferably, the composition of each absorption liquid is: the concentration of potassium chloride solution is 1mol/L; the acidic hydrogen peroxide is 4-5% by volume of HNO ₃ and 8-10% by volume of H ₂ O ₂ mixed solution; the acidic potassium permanganate solution is a mixed solution of 3-4% g/L KMnO ₄ and 8-10% volume percent H ₂ SO ₄ .

In the above method, preferably, the temperature in the hot box of the particulate heavy metal capture device is set to 20±5.6°C, and the 8 absorption bottles of the gaseous heavy metal absorption device are placed in an ice bath in the cold box.

In the above method, preferably, each absorption bottle is rinsed and dried with about 0.1 mol/L dilute sulfuric acid and distilled water before adding the absorption liquid.

In the above-mentioned method, preferably, in step (1), the coal-fired flue gas at the sampling point is sampled for 2 to 3 hours by means of isokinetic sampling.

As described above, preferably, the sample recovery described in step (2), the specific operation is:

A. Put the potassium chloride absorption solution in the 1st to 3rd absorption bottles into a 500mL volumetric flask, and add 1~5mL of 10%g/L potassium dichromate and 1~5mL of 5%g/L potassium dichromate dropwise. Potassium permanganate solution, so that the absorption liquid remains light purple, rinse the sampling tube and potassium chloride absorption bottle with a small amount of 0.1mol/L nitric acid, pour the washing liquid into the volumetric flask that collects the potassium chloride absorption liquid and make it to volume, Sealed storage;

B. Put the acidic hydrogen peroxide absorption solution in the 4th to 5th absorption bottles in a 500mL volumetric flask, rinse the acidic hydrogen peroxide absorption bottle with a small amount of 0.1mol/L nitric acid, and pour the washing solution into the container where the acidic hydrogen peroxide absorption solution was collected. In the volumetric flask and constant volume, sealed preservation;

C. Put the acidic potassium permanganate absorption solution in the 6th to 7th absorption bottles in a 500mL volumetric flask, and add 2 to 10mL of 10% g/L potassium dichromate solution dropwise, with a small amount of 0.1mol/L Rinse the acidic potassium permanganate absorption bottle with 1 L of nitric acid, pour the washing solution into the volumetric flask that collects the acidic potassium permanganate absorption solution, make it to volume, and keep it sealed.

As described above, preferably, the sample digestion described in step (3) is performed as follows:

A. For potassium chloride absorption liquid sample: take 10mL of the sample in the volumetric flask containing potassium chloride absorption liquid, add 0.75mL5%g/L potassium persulfate solution, 0.50mL98.3wt% concentrated sulfuric acid, 0.25mL65wt% % concentrated nitric acid and 10mL5%g/L of potassium permanganate solution, after heating at 90°C in a water bath for 2h, dropwise add 10%g/L of hydroxylamine hydrochloride until clarification, and complete the digestion of the water-soluble test solution;

The remaining potassium chloride absorption solution is used as other water-soluble heavy metals to be tested;

B. For the acidic hydrogen peroxide absorbent sample: take 5mL of the sample in the volumetric flask containing the acidic hydrogen peroxide absorbent, add 0.75mL of 5% g/L potassium persulfate solution, 0.25mL of 38wt% concentrated hydrochloric acid and 0.25mL of 65wt% concentrated nitric acid , after cooling in the refrigerator for 15 minutes, add 5% g/L potassium permanganate solution drop by drop, the sample reacts violently at the beginning of dropwise addition, continue to add dropwise until the sample solution remains purple and stable, after heating in a water bath at 90°C for 2 hours , dropwise add 10% g/L of hydroxylamine hydrochloride until clear, and complete the preparation of elemental mercury test solution 1.

The rest of the acidic hydrogen peroxide absorption liquid sample was concentrated to 20mL, and then 30mL of 50% (v/v) nitric acid and 10mL of 3% (v/v) hydrogen peroxide were added (the hydrogen peroxide used was commercially available peroxide with a concentration of 30wt%) Hydrogen, that is, the 3% (v/v) hydrogen peroxide is the solution obtained by diluting a 30wt% hydrogen peroxide solution according to the ratio of 3 volumes of solution: 100 volumes of water) and 50mL of 70°C hot Water, set the volume to 100mL, and complete the preparation of the test solution for heavy metals other than mercury;

C. For acidic potassium permanganate absorption liquid sample: take 10mL of the sample in the volumetric flask containing acidic potassium permanganate absorption liquid, add 0.75mL5%g/L potassium persulfate solution, 0.5mL65wt% concentrated nitric acid and 10mL of 5%g/L potassium permanganate solution was heated in a water bath at 90°C for 2 to 3 hours, and then 10%g/L of hydroxylamine hydrochloride was added dropwise until clarified to complete the preparation of elemental mercury test solution 2.

The above method, wherein the heavy metals include lead, arsenic, cadmium, chromium, cobalt, manganese and mercury.

The above-mentioned method, wherein the coal-fired flue gas includes coal-fired flue gas in the exhaust pipes of coal-fired power plant boilers and industrial boilers.

The above-mentioned method, wherein, the coal-fired flue gas includes flue gas from different positions of the coal-fired power plant, including positions before the denitrification device, before the dust removal device, before the desulfurization device, and after the desulfurization device.

The above-mentioned method, wherein the concentration range of the heavy metal to be detected in the coal combustion flue gas may be between 10 ng/Nm ³ and 100 μg/Nm ³ .

The beneficial effects of the present invention are:

The present invention collects granular heavy metal samples by means of isokinetic sampling, and uses different chemical reagent solutions to absorb gaseous heavy metals in different forms in flue gas, and then analyzes and measures the collected granular heavy metal samples and gaseous heavy metal samples after recovery and digestion The content of different heavy metals in the flue gas, so as to calculate the concentration of different heavy metals in different forms in the flue gas.

The cyclone separation device is added to the particulate heavy metal capture device used in the present invention, which can be adapted to the sampling of high-ash smoke. The present invention also realizes the simultaneous determination of different forms and different heavy metals in the coal-fired flue gas through the effective proportioning of the absorption liquid and the optimization of the analysis instrument, which reduces labor and reagent consumption, and reduces human interference factors in the sample analysis process , improving the analysis accuracy.

The method of the invention can simultaneously and accurately measure the concentrations of heavy metals in different forms and in the flue gas of coal combustion, and has universal applicability. By popularizing the method of the invention, the present situation of heavy metal pollution in my country's coal-fired flue gas can be easily grasped, and reliable data support can be provided for the prevention and control of atmospheric heavy metals in my country.

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Description of drawings

Fig. 1 is a schematic diagram of the steps of the method of the present invention.

Detailed ways

For the purpose of simplicity and clarity, descriptions of known technologies are appropriately omitted below, so as not to affect the description of the technical solution with unnecessary details.

As shown in FIG. 1 , the test procedure of the present invention includes four stages of sample collection, sample recovery, sample digestion, analysis and determination, and calculation. Among them, the sample collection is to collect the coal-fired flue gas samples at the sampling points by means of isokinetic sampling; the sample recovery is used to stabilize the solution on site to absorb the flue gas samples, which is very necessary for volatile heavy metals and is convenient for long-distance transportation and storage; the sample digestion is through The treatment of the sample eliminates the interference of other components in the flue gas absorbed in the sample (such as SO ₂ , NOx, etc.) to facilitate the detection and analysis of the heavy metals to be measured; the analysis and determination is carried out by using an inductively coupled plasma-mass spectrometer (ICP-MASS) Or inductively coupled plasma atomic emission spectrometer (ICP-AES) completes the detection of different heavy metals in different valence states in the flue gas, and then calculates the heavy metals in different forms in the flue gas according to the measured heavy metal content and flue gas volume in each absorption liquid sample concentration.

The core of the sample collection system of the present invention is eight sequentially connected absorption bottles, the 1st to 3rd absorption bottles are respectively equipped with 100mL potassium chloride solution, the 4th to 5th absorption bottles are respectively equipped with 100mL acidic hydrogen peroxide solution, and the 6th to 7th absorption The bottles are respectively filled with 100mL of acidic potassium permanganate solution, and the eighth absorption bottle is filled with 200-300g of silica gel. The coal-fired flue gas passes through these 8 absorption bottles in turn. The water-soluble heavy metals are collected by the 1st to 3rd absorption bottles, the water-insoluble heavy metals are collected by the 4th to 5th absorption bottles and the 6th to 7th absorption bottles, and the 8th absorption bottle Absorb moisture in flue gas.

Wherein, the concentration of the potassium chloride solution is 1mol/L; the acid hydrogen peroxide is 4-5% (v/v) HNO ₃ and 8-10% (v/v) H ₂ O ₂ Mixed solution; the acidic potassium permanganate solution is a mixed solution of 3-4% g/L KMnO ₄ and 8-10% (v/v) H ₂ SO ₄ .

The key step of the method of the present invention is sample digestion. Different methods are used to digest samples for different absorption liquid samples and heavy metal elements to be detected, so as to reduce SO ₂ and NO _x dissolved in the flue gas in the absorption liquid during the analysis process. And the influence of VOC etc. on the analysis results.

Another key improvement of the present invention is that a cyclone separator is added between the hot box filter holder and the sampling gun of the sample collection device, which solves the problem of high ash sampling.

Example 1

At present, most coal-fired power plants in my country have installed flue gas purification devices such as desulfurization and dust removal or denitrification. The composition of flue gas in different locations is different, which may affect the concentration of heavy metals in flue gas. Therefore, choose different locations of typical power plants in my country to burn coal Experimental study of flue gas.

1. Sample collection

A. Preparation before sampling

Weigh several 200 to 300 g portions of silica gel to the nearest 0.5 g in an airtight container. Record the total weight of the silica gel plus the container on each container; alternatively, weigh the silica gel directly in the 8 Absorber Vial immediately prior to assembling the sample collection system components.

Dry the filter holder at a temperature of 20 ± 5.6°C (68 ± 10°F) and ambient pressure for 24 to 36 h, weigh at least every 6 h until constant weight, and record the result to the nearest 0.1 μg.

Clean all glassware in the sampling system and cover all glassware openings where contamination occurs until sampling begins.

Measure 100mL of each prepared absorption solution, and fill them into the 1st to 7th absorption bottles according to the above-mentioned corresponding relationship; transfer about 200 to 300g of silica gel from the above-mentioned airtight container to the 8th absorption bottle. Weigh and record the weight of each absorption bottle, which is used to calculate the water content of the sampled flue gas. Put the weighed quartz fiber filter paper into the filter holder with disposable gloves. Connect the entire sample collection system and check for leaks.

B. Sampling

Clean the suction nozzle before sampling, confirm that the filter holder and suction nozzle in the hot box reach the specified temperature of 20±5.6°C (68±10°F), start the suction pump, open and adjust the valve until a constant sampling rate is obtained , to maintain the differential pressure value at the time of isokinetic sampling, at all sampling points and during the sampling period.

When transferring the sample collection system between different sampling points, close the valve and stop the aspirator pump. During the sampling process, regularly check the sampling temperature of the suction nozzle and the outlet of the filter holder and the zero position of the differential pressure gauge, and adjust it if necessary. Add more ice if necessary to keep the temperature at the outlet of the cold box/silicone bottle <20°C (68°F).

During the sampling process, if the purple color of the acidic permanganate solution is completely bleached, it indicates that the reduction reaction of KMnO ₄ by other components in the flue gas except elemental lead and other heavy metals has occurred. Therefore, if two acidic potassium permanganate absorbers lose their purple color, sampling must be redone. If the gas stream is known to contain significant amounts of reducing components (i.e., >2500 ppm SO ₂ ), or has had a breakthrough during a previous sampling run, then the acid hydrogen peroxide in the fourth absorber bottle The quantity should be doubled, or an absorption bottle containing acidic hydrogen peroxide should be added, or both should be used at the same time to increase the oxidation capacity of reducing gas components before the acidic potassium permanganate absorption bottle.

During the entire sampling process, use the same component, unless it is necessary to sample at two or more sampling points at the same time, or equipment failure requires replacement of components.

After sampling, close the valve, draw out the suction nozzle and turn off the suction pump. Wait for the suction nozzle to cool down, wipe off the particles near the suction nozzle, and cover the suction nozzle to avoid contamination or sample loss, and let the filter holder cool down at the same time. Before moving the sampling bottle to a clean place, detach the suction nozzle from the connection and cover both ends, so as not to lose any condensation that may occur. Close the first and last absorbent bottle. Disconnect all connection points. The sampling tube, cyclone, and sample absorber bottle are ready for sample recovery.

3. Sample recovery

A. Put the potassium chloride absorption solution in a 500mL volumetric flask, and add dropwise 1-5mL of 10%g/L potassium dichromate and 1-5mL of 5%g/L potassium permanganate solution to absorb The liquid remains light purple. In order to ensure the accuracy of the analysis, rinse the sampling tube and the potassium chloride absorption bottle with a small amount of 0.1mol/L nitric acid, pour the washing solution into the volumetric flask that collects the potassium chloride absorption solution, dilute to volume, and seal it for storage.

B. Put the acidic hydrogen peroxide absorption solution in a 500mL volumetric flask. In order to ensure the analysis accuracy, rinse the acidic hydrogen peroxide absorption bottle with a small amount of 0.1mol/L nitric acid, pour the washing solution into the volumetric flask for collecting the acidic hydrogen peroxide absorption solution, make it to volume, and keep it sealed.

C. Put the acidic potassium permanganate absorption solution in a 500mL volumetric flask, and add 2-10mL of 10% g/L potassium dichromate solution dropwise. In order to ensure the analysis accuracy, rinse the acidic potassium permanganate absorption bottle with a small amount of 0.1mol/L nitric acid, pour the washing solution into the volumetric flask that collects the acidic potassium permanganate absorption solution, dilute to volume, and seal it for storage.

4. Sample digestion

A. For potassium chloride absorption liquid sample: take 10mL of the sample in the volumetric flask containing potassium chloride absorption liquid, add 0.75mL5%g/L potassium persulfate solution, 0.50mL98.3wt% concentrated sulfuric acid, 0.25mL65wt% % concentrated nitric acid and 10mL5%g/L of potassium permanganate solution, after heating at 90°C in a water bath for 2h, dropwise add 10%g/L of hydroxylamine hydrochloride until clarification, and complete the digestion of the water-soluble test solution;

The remaining potassium chloride absorption solution is used as other water-soluble heavy metals to be tested.

B. For the acidic hydrogen peroxide absorbent sample: take 5mL of the sample in the volumetric flask containing the acidic hydrogen peroxide absorbent, add 0.75mL of 5% g/L potassium persulfate solution, 0.25mL of 38wt% concentrated hydrochloric acid and 0.25mL of 65wt% concentrated nitric acid , after cooling in the refrigerator for 15 minutes, add 5% g/L potassium permanganate solution drop by drop, the sample reacts violently at the beginning of dropwise addition, continue to add dropwise until the sample solution remains purple and stable, after heating in a water bath at 90°C for 2 hours , drop 10% g/L of hydroxylamine hydrochloride until clarification, and complete the preparation of elemental mercury test solution 1;

The rest of the acidic hydrogen peroxide absorption liquid sample was concentrated to 20mL, and then 30mL of 50% (v/v) nitric acid and 10mL of 3% (v/v) hydrogen peroxide were added (the hydrogen peroxide used was commercially available 30wt% hydrogen peroxide, ie The 3% (v/v) hydrogen peroxide is the solution obtained by diluting the 30wt% hydrogen peroxide solution according to the ratio of 3 volumes of solution: 100 volumes of water) and 50mL of 70°C hot water. to 100mL to complete the preparation of the mercury-removing heavy metal test solution.

C. For acidic potassium permanganate absorption liquid sample: take 10mL of the sample in the volumetric flask containing acidic potassium permanganate absorption liquid, add 0.75mL5%g/L potassium persulfate solution, 0.5mL65wt% concentrated nitric acid and 10mL of 5%g/L potassium permanganate solution was heated in a water bath at 90°C for 2h, and then 10%g/L of hydroxylamine hydrochloride was added dropwise until clarified to complete the preparation of elemental mercury test solution 2.

5. Analysis and determination

The inductively coupled plasma atomic emission spectrometer (ICP-AES) was used to detect the above-mentioned liquids to be tested to complete the detection of heavy metals in different valence states in the flue gas. To lower the instrument detection limit of mercury, a main engine coupled with a hydride generator (HG-ICP-AES) was used.

6. Calculate the concentration of different heavy metals in different forms in the flue gas

The heavy metal content and flue gas volume in each absorption liquid sample were measured according to the above method, and the concentrations of heavy metals in different forms in the flue gas were calculated.

7. Practical application of the inventive method

By adopting the method of the present invention, the boilers of Inner Mongolia Tuoketuo Power Plant, Hubei Jingzhou Power Plant and Guizhou Anshun Power Plant are tested and monitored respectively.

The basic principles, main features and advantages of the present invention have been shown and described above through the drawings and embodiments. Those skilled in the industry should understand that the present invention is not limited only by the above embodiments, and the protection scope of the present invention is defined by the claims. Any equivalent replacement foreseeable by those skilled in the art falls within the protection scope of the present invention.

Claims (7)

1. a method for simultaneously measuring the heavy metals of different forms in coal-fired flue gas, is characterized in that, it comprises the steps: (1) Use a sample collection system to collect coal-fired flue gas samples. The sample collection system includes sequentially connected sampling pipes with suction nozzles, particulate heavy metal capture devices, and gaseous heavy metal absorption devices, as well as monitoring systems. Temperature sensors for internal temperature, differential pressure gauges for monitoring and adjusting the air pressure in the system, exhaust pipelines, exhaust pumps and valves, and dry flowmeters for monitoring the flow of flue gas in the system; The particulate heavy metal trapping device includes a filter holder arranged in the hot box and a cyclone separator arranged between the filter holder and the end of the sampling pipe, and a quartz fiber filter paper is placed in the filter holder; The gaseous heavy metal absorption device includes 8 absorption bottles placed in a cold box connected sequentially through conduits. The absorption liquid in each absorption bottle is: potassium chloride solution in the 1st to 3rd absorption bottles, and potassium chloride solution in the 4th to 5th absorption bottles. The first absorption bottle is acidic hydrogen peroxide solution, the sixth to seventh absorption bottle is acidic potassium permanganate solution; the eighth absorption bottle is filled with silica gel; (2) Perform sample recovery on the absorption liquid samples in each absorption bottle, and seal and store the collected smoke samples; (3) Carry out sample digestion for different absorption liquid samples; (4) Use an inductively coupled plasma-mass spectrometer or an inductively coupled plasma atomic emission spectrometer to detect each sample digested in step (3), and calculate the difference in the flue gas according to the measured heavy metal content in each absorption liquid sample. Speciation of heavy metal concentrations. 2. method as claimed in claim 1, is characterized in that, the composition of described each absorbing liquid is: the concentration of potassium chloride solution is 1mol/L; Acidic hydrogen peroxide is _HNO3 and volume percentage of 4～5% by volume percentage A mixed solution of 8-10% H ₂ O ₂ ; the acidic potassium permanganate solution is a mixed solution of 3-4% g/L KMnO ₄ and 8-10% volume percent H ₂ SO ₄ . 3. method as claimed in claim 1, is characterized in that, the temperature in the hot box of described granular heavy metal capture device is set to 20 ± 5.6 ℃, and 8 absorption bottles of described gaseous heavy metal absorption device are in cold box Place in an ice bath. 4. The method according to claim 1, characterized in that, in step (1), each absorption bottle is rinsed and dried with 0.1 mol/L sulfuric acid and distilled water before adding the absorption liquid. 5. The method according to claim 1, characterized in that in step (1), the coal-fired flue gas at the sampling point is sampled for 2-3 hours by means of isokinetic sampling. 6. The method according to any one of claims 1 to 5, characterized in that the sample recovery described in step (2) is performed as follows: A. Put the potassium chloride absorption solution in the 1st to 3rd absorption bottles into a 500mL volumetric flask, and add 1~5mL of 10%g/L potassium dichromate and 1~5mL of 5%g/L potassium dichromate dropwise. Potassium permanganate solution, so that the absorption liquid remains light purple, rinse the sampling tube and potassium chloride absorption bottle with 0.1mol/L nitric acid, pour the washing liquid into the volumetric flask that collects the potassium chloride absorption liquid, dilute to volume, and seal save; B. Put the acidic hydrogen peroxide absorption liquid in the 4th to 5th absorption bottles in a 500mL volumetric flask, rinse the acidic hydrogen peroxide absorption bottle with 0.1mol/L nitric acid, pour the washing liquid into the volume of the acidic hydrogen peroxide absorption liquid In the bottle and constant volume, sealed preservation; C. Put the acidic potassium permanganate absorption solution in the 6th to 7th absorption bottles in a 500mL volumetric flask, and add 2 to 10mL of 10% g/L potassium dichromate solution dropwise, with 0.1mol/L Rinse the acidic potassium permanganate absorption bottle with nitric acid, pour the lotion into the volumetric flask that collects the acidic potassium permanganate absorption solution, dilute to volume, and seal it for storage. 7. The method according to claim 6, characterized in that, the specific operation of the sample digestion in step (3) is: A. Take 10mL of the sample in the volumetric flask containing potassium chloride absorption solution, add 0.75mL of 5%g/L potassium persulfate solution, 0.50mL of 98.3wt% concentrated sulfuric acid, 0.25mL of 65wt% concentrated nitric acid and 10mL of 5%g /L of potassium permanganate solution, after heating at 90° C. in a water bath for 2h, drip the hydroxylamine hydrochloride of 10%g/L until clarification, and complete the preparation of the water-soluble heavy metal test solution; The remaining potassium chloride absorption liquid samples are used as other water-soluble heavy metals to be tested; B. Take 5mL of the sample in the volumetric flask filled with acidic hydrogen peroxide absorption solution, add 0.75mL of 5% g/L potassium persulfate solution, 0.25mL of 38wt% concentrated hydrochloric acid and 0.25mL of 65wt% concentrated nitric acid, and place it in the refrigerator for 15min , add 5% g/L potassium permanganate solution drop by drop, the sample reacts violently at the beginning of dropping, continue to drop until the sample solution remains purple and stable, after heating in a water bath at 90°C for 2 hours, add 10% g/L dropwise L of hydroxylamine hydrochloride until clarification, complete the preparation of elemental mercury test solution 1; Concentrate the other samples to 20mL, then add 30mL of 50% by volume nitric acid, 10mL of hydrogen peroxide solution and 50mL of 70°C hot water, and set the volume to 100mL to complete the preparation of the test solution for heavy metals other than mercury; wherein, the Hydrogen peroxide solution is the hydrogen peroxide solution obtained after diluting commercially available 30wt% hydrogen peroxide solution according to 3 volumes of solution: 100 volumes of water; C. Take 10mL of the sample in the volumetric flask filled with acid potassium permanganate absorption solution, add 0.75mL of 5%g/L potassium persulfate solution, 0.5mL of 65wt% concentrated nitric acid and 10mL of 5%g/L of potassium permanganate solution, after heating in a water bath at 90°C for 2 to 3 hours, add 10% g/L of hydroxylamine hydrochloride dropwise until clarification, and complete the preparation of the elemental mercury test solution 2.

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