A detection system and method for harmful substances in flue gas

Abstract

The application discloses a detection system and a detection method for harmful substances in flue gas. The detection system comprises a flue gas sampling unit, an air purging unit, a sulfur trioxide detection unit, a condensable particulate matter trapping unit, a mercury detection unit, a first automatic sampling instrument, a second automatic sampling instrument and a numerical control device. The flue gas sampling unit, the sulfur trioxide detection unit, the condensable particulate matter trapping unit, the mercury detection unit and the first automatic sampling instrument are sequentially connected. The air purging unit is connected with the flue gas outlet of the flue gas sampling unit. The second automatic sampling instrument is connected with the flue gas outlet of the condensable particulate matter detection unit through a first drying bottle. The numerical control device is electrically connected with the flue gas sampling unit, the air purging unit, the sulfur trioxide detection unit, the condensable particulate matter trapping unit, the mercury detection unit, the first automatic sampling instrument and the second automatic sampling instrument. The detection system is convenient to operate, has strong applicability, has a wide application range and can detect various harmful substances in flue gas.

Description

Technical Field

[0001] The present invention relates to the technical field of flue gas emission control, and in particular to a system for detecting harmful substances in flue gas. The present invention also relates to a method for detecting harmful substances in flue gas. Background Art

[0002] my country has achieved significant results in controlling traditional coal smoke pollution. For example, through the control of pollutants from typical coal-fired power plants, ultra-low emissions of NOx, smoke, and SO2 in coal-fired flue gas have been achieved through flue gas pollution control facilities such as SCR denitrification, electrostatic or bag filters, and wet desulfurization. However, while the above three traditional coal-fired flue gas pollutants have been effectively controlled, severe air pollution in the region remains prominent, restricting sustainable social and economic development and threatening public health. Therefore, in addition to the above three pollutants, pollution caused by condensable particulate matter, heavy metal mercury, SO3, etc. emitted by coal combustion has received increasing attention and become a new research hotspot.

[0003] Particulate matter emitted from coal combustion can be divided into filterable particulate matter (FPM), which is emitted directly in solid form, and condensable particulate matter (CPM). According to the U.S. Environmental Protection Agency (EPA), CPM refers to solid or liquid particulate matter that exists in a gaseous form in the flue and condenses immediately upon emission into the atmosphere. Morphologically, CPM is primarily composed of condensed gaseous matter, with particle sizes generally less than 1 μm, making it a fine particulate matter that exists in the ambient air as an aerosol. CPM is often enriched with pollutants such as heavy metals (such as Se, As, Pb, and Cr) and polycyclic aromatic hydrocarbons (PAHs), many of which are carcinogens and genotoxic mutagens, posing a significant threat.

[0004] According to an analysis of particulate matter emissions from 18 coal-fired flue gases by Louis A. Corio's team in the United States, CPM accounts for an average of 49% of the total particulate matter in flue gas, while FPM accounts for an average of 51%. This means that CPM emissions from coal-fired flue gas are roughly equivalent to FPM, and its contribution to total PM10 and PM2.5 emissions is even greater, making it a significant factor. However, current conventional particulate matter detection methods are only suitable for capturing FPM and do not represent the true level of coal-fired particulate matter emissions. This shows that accurately measuring CPM emissions is crucial for fully estimating particulate matter emissions from coal-fired sources and for truly achieving particulate matter emission reductions.

[0005] The SO3 emitted from coal combustion mainly comes from two sources: on the one hand, about 0.5-1.5% of the sulfur in the coal combustion process will be oxidized into SO3, and on the other hand, during the SCR denitrification process, about 1-2% of the SO2 in the flue gas is converted into SO3 under the action of the catalyst. For the combustion of medium- and high-sulfur coal, the SO3 concentration in the flue gas at the SCR outlet can reach 100-200 mg / m 3 The ammonium bisulfate (ABS) generated by the reaction of SO₃ with ammonia escaped from the SCR process not only affects the catalytic activity of the catalyst itself but also easily adheres to the heat exchange surface of the subsequent air preheater, causing corrosion and blockage of the equipment. Furthermore, SO₃ emitted from the chimney inlet into the atmosphere undergoes complex physical and chemical reactions, resulting in environmental pollution phenomena such as "blue smoke."

[0006] Mercury in coal-fired flue gas is mainly in the form of gaseous zero-valent mercury (Hg 0 ), gaseous divalent ion mercury (Hg 2+ ) and particulate mercury (Hg p ) and other three forms, among which zero-valent mercury (Hg 0 ) accounts for about 30% to 80% of the total mercury content in flue gas. 0 ) is insoluble in water and highly volatile, making it difficult to capture in existing dust removal or desulfurization equipment, and almost all of it is released into the atmosphere; divalent mercury (Hg 2+ ) is easily soluble in water and easily adsorbed by particulate matter in flue gas, so the existing dust removal and desulfurization equipment is 2+ ) has a certain removal efficiency; particulate mercury (Hg p ) is easily captured by dust removal equipment. Therefore, the mercury emitted into the atmosphere from coal-fired flue gas mainly consists of zero-valent mercury (Hg 0 ) and a small amount of divalent mercury (Hg 2+ )composition.

[0007] Currently, most coal-fired flue gas in China is decontaminated using ultra-low emission technologies. Due to the characteristics of the wet desulfurization process, the flue gas emitted after wet desulfurization exhibits high humidity, low temperature, and low pollutant concentrations, placing higher demands on pollutant detection capabilities. Furthermore, most existing coal-fired flue gas pollutant detection methods in my country only detect a single pollutant (there are no relevant standards for CPM detection in particulate matter), and insufficient consideration is given to the mutual interference between detection methods for different pollutants. Therefore, the development of a system and method that can simultaneously detect condensable particulate matter, sulfur trioxide, and heavy metal mercury in coal-fired flue gas is extremely necessary and urgent. Summary of the Invention

[0008] The purpose of the present invention is to solve at least one of the above-mentioned problems, and this purpose is achieved through the following technical solutions.

[0009] The present invention provides a detection system for harmful substances in flue gas, comprising a flue gas sampling unit, an air purge unit, a sulfur trioxide detection unit, a condensable particulate matter capture unit, a mercury detection unit, a first automatic sampler, a second automatic sampler, and a numerical control device;

[0010] The flue gas sampling unit, the sulfur trioxide detection unit, the condensable particulate matter collection unit, the mercury detection unit, and the first automatic sampler are connected in sequence, the air purge unit is connected to the flue gas outlet of the flue gas sampling unit, and the second automatic sampler is connected to the flue gas outlet of the condensable particulate matter detection unit through a first drying bottle;

[0011] The numerical control device is electrically connected to the flue gas sampling unit, the air purge unit, the sulfur trioxide detection unit, the condensable particulate matter capture unit, the mercury detection unit, the first automatic sampler, and the second automatic sampler, respectively.

[0012] Preferably, the flue gas sampling unit includes a flue gas sampling gun, a sampling gun sealing flange, an S-type pitot tube and a heating filter with a built-in quartz filter membrane, the sampling end of the flue gas sampling gun is arranged in the flue, the S-type pitot tube is arranged on the sampling end, the flue gas sampling gun is fixed to the outer wall of the flue through the sampling gun sealing flange, the heating filter is arranged at the flue gas outlet of the flue gas sampling gun, the flue gas outlet of the heating filter is connected to a first three-way valve through a first heating pipe, and the first three-way valve is respectively connected to the sulfur trioxide detection unit and the air purge unit;

[0013] The flue gas sampling gun comprises a quartz glass tube and a stainless steel tube, wherein the quartz glass tube is sleeved inside the stainless steel tube.

[0014] Preferably, the air purge unit includes an air compressor, an air filter and an air heater connected in sequence, the air heater is connected to the first three-way valve through a first compressed air pipe, and the air heater is connected to the flue gas inlet of the sulfur trioxide detection unit through a second compressed air pipe, and the second compressed air pipe is provided with a first valve.

[0015] Preferably, the sulfur trioxide detection unit includes a first flue gas condenser, an absorption liquid tank, an absorption liquid pump, an intermediate tank, a flushing water tank, a flushing water pump, a buffer tank, a buffer pump, a developer solution tank, a developer solution pump, a delivery pump and a photometer;

[0016] The first flue gas condenser includes a first serpentine condenser and a second serpentine condenser, one end of the first serpentine condenser is connected to a second heating pipe having a second valve, one end of the second serpentine condenser is connected to a third heating pipe having a third valve, the second heating pipe and the third heating pipe are connected in parallel to one outlet of the first three-way valve, the other end of the first serpentine condenser is provided with a fourth valve, the other end of the second serpentine condenser is provided with a fifth valve, the fourth valve and the fifth valve are respectively connected to the inlet end of a fourth heating pipe having a sixth valve, the flue gas inlet of the condensable particulate matter capture unit is connected to the fourth heating pipe, and the connection position is located at the front end of the sixth valve;

[0017] The absorption liquid tank is connected to the inlet of the first serpentine condenser tube, the inlet of the second serpentine condenser tube and the first valve respectively through the absorption liquid pump. A seventh valve is provided at the connection position between the absorption liquid pump and the first serpentine condenser tube, and an eighth valve is provided at the connection position between the absorption liquid pump and the second serpentine condenser tube.

[0018] The intermediate box is connected to the outlet of the first serpentine condenser tube and the outlet of the second serpentine condenser tube respectively, and a ninth valve is provided at the connection position between the intermediate box and the first serpentine condenser tube, and a tenth valve is provided at the connection position between the intermediate box and the second serpentine condenser tube;

[0019] The photometer includes a light source, a pH electrode, an absorption cell and a detector. The absorption cell is a transparent structure. The light source and the detector are placed on both sides of the absorption cell. The pH electrode is arranged in the absorption cell. The intermediate box is connected to the absorption cell through the delivery pump. The flushing water tank is connected to the absorption cell through the flushing water pump. The buffer solution tank is connected to the absorption cell through the buffer solution pump. The color developer solution tank is connected to the absorption cell through the color developer solution pump.

[0020] Preferably, the condensable particulate matter capture unit comprises a second flue gas condenser, a deionized water tank, a deionized water pump, an impact bottle, a filter with a built-in filter membrane, a second drying bottle, a nitrogen bottle, a n-hexane tank and a n-hexane pump;

[0021] The second flue gas condenser is equipped with a third serpentine condenser, which is connected to the fourth heating pipe through an eleventh valve, and the connection position is located at the front end of the sixth valve. The nitrogen cylinder is connected to the inlet of the third serpentine condenser through a twelfth valve. The n-hexane tank is connected to the inlet of the third serpentine condenser through the n-hexane pump. A thirteenth valve is provided at the connection position between the n-hexane pump and the third serpentine condenser. The deionized water tank is connected to the inlet of the third serpentine condenser through the deionized water pump. A fourteenth valve is provided at the connection position between the deionized water pump and the third serpentine condenser. The outlet of the third serpentine condenser is connected to the impact bottle, the filter and the second drying bottle in sequence. The outlet of the second drying bottle is connected to the first drying bottle through a fifth heating pipe. A fifteenth valve is provided on the fifth heating pipe. The rear end of the sixth valve is connected to the fifth heating pipe. The connection position between the sixth valve and the fifth heating pipe is located at the rear end of the fifteenth valve. The outlet of the first drying bottle is connected to the second automatic sampler through the sixth heating pipe.

[0022] Preferably, the mercury detection unit includes a second three-way valve, a third three-way valve, a total mercury conversion device, a zero-valent mercury conversion device, a third drying bottle and a mercury analyzer. The second three-way valve is connected to the fifth heating pipe, the inlet of the total mercury conversion device is connected to the second three-way valve through the seventh heating pipe, the inlet of the zero-valent mercury conversion device is connected to the second three-way valve through the eighth heating pipe, the outlet of the total mercury conversion device and the outlet of the zero-valent mercury conversion device are respectively connected to the third three-way valve, the third three-way valve is connected to the inlet of the third drying bottle through the ninth heating pipe, the outlet of the third drying bottle is connected to the analyzer through the tenth heating pipe, and the analyzer is connected to the first automatic sampler through the eleventh heating pipe.

[0023] Preferably, the mercury analyzer mainly includes a mercury lamp, a heater, a measuring chamber, and a mercury detector. One end of the measuring chamber is connected to the outlet of the third drying bottle, and the other end of the measuring chamber is connected to the first automatic sampler. The mercury lamp and the mercury detector are respectively arranged on both sides of the measurement, and the heater is arranged close to the measuring chamber.

[0024] The present invention provides a method for detecting harmful substances in flue gas. The method is implemented by the above-mentioned system for detecting harmful substances in flue gas, and is characterized in that it includes the following steps:

[0025] S1: Connect each unit equipment as required, start the numerical control device, set the temperature of the flue gas sampling gun to 200-240℃, set the temperature of the heating filter to 200-240℃, set the temperature of the first heating pipe, the second heating pipe and the third heating pipe to 200-240℃, set the temperature of the fourth heating pipe, the fifth heating pipe, the seventh heating pipe, the eighth heating pipe and the ninth heating pipe to 110-120℃, set the temperature of the sixth heating pipe, the tenth heating pipe and the eleventh heating pipe to 40-50℃, set the temperature of the first flue gas condenser to 60-80℃, set the temperature of the second flue gas condenser to below 30℃, and start sampling when the temperature reaches the control requirements;

[0026] S2: Turn on the first automatic sampler and the second automatic sampler, and control the sampling flow rate through the numerical control device. The first automatic sampler and the second automatic sampler generate negative pressure to make the flue gas to be tested continuously and uniformly enter the flue gas sampling gun with an S-type pitot tube. The heating filter is installed at the rear end of the flue gas sampling gun. The flue gas that has been filtered by the heating filter to remove filterable particulate matter enters the first flue gas condenser through the first heating pipe, the first three-way valve, the second heating pipe or the third heating pipe. At this time, the first three-way valve and the compressed air pipeline of the air purge unit remain closed;

[0027] S3: After the flue gas enters the first flue gas condenser, a first serpentine condenser and a second serpentine condenser are connected in parallel in the first flue gas condenser. The two sets of serpentine condensers work alternately. When one set of serpentine condensers condenses sulfur trioxide in the flue gas into sulfuric acid droplets, the condensed sulfuric acid droplets in the other set of serpentine condensers are mixed with the absorption liquid in the intermediate tank and then sent to the photometer. The photometer reacts with the color developer to detect the sulfur trioxide content in the reaction liquid. After the detection is completed, the serpentine condenser is rinsed with flushing water and switched to the other set of serpentine condensers to continue detecting the next set. The cycle continues.

[0028] S4: The flue gas after condensing sulfur trioxide is passed through the fourth heating pipe to the condensable particulate matter capture unit or the fifth heating pipe to the next component detection unit as required. When the flue gas enters the condensable particulate matter capture unit, it passes through the third serpentine condenser, the impact bottle and the filter in sequence. At this time, the condensable particulate matter in the flue gas is captured by condensation, collision and membrane filtration. After the capture is completed, the filter membrane is removed from the filter and stored in a special container. At the same time, deionized water is first fed into the third serpentine condenser to mix the inorganic components in the condensate with the deionized water in the impact bottle to form an inorganic phase. Then, nitrogen is used to purge the residual liquid in the pipeline and the inorganic phase in the impact bottle. After the purge is completed, n-hexane is fed into the third serpentine condenser to mix the organic components in the condensate with n-hexane in the impact bottle to form an organic phase. The inorganic phase, organic phase and filter membrane are returned to the laboratory for offline analysis of condensable particulate matter.

[0029] S5: Part of the flue gas that has passed through step S4 is discharged from the system after the sampling volume is recorded by the second automatic sampler, and the other part enters the mercury detection unit. After entering the mercury detection unit, the flue gas is divided into two paths: one path is a total mercury conversion device, which is used to convert all divalent mercury in the flue gas into zero-valent mercury; the other path is a zero-valent mercury conversion device, which is used to absorb divalent mercury in the flue gas and retain only zero-valent mercury. The flue gas passing through the conversion device is dried and then enters the mercury analyzer. The mercury analyzer uses atomic absorption spectrometry to detect the concentration of zero-valent mercury in the flue gas. The mercury detection unit realizes the measurement requirements of mercury of different valence states through the control of the second three-way valve and the third three-way valve. The difference between the mercury concentrations in the two paths is the concentration of divalent mercury in the flue gas. The flue gas after mercury detection is discharged from the system through the first automatic sampler.

[0030] Preferably, the zerovalent mercury conversion device comprises a 5-15% KC1 solution washing bottle and a 5-15% first NaOH solution washing bottle connected in series, the KC1 solution washing bottle is connected to the eighth heating pipe, and the first NaOH solution washing bottle is connected to the third three-way valve;

[0031] The total mercury conversion device includes a 5-15% second NaOH solution washing bottle and a 5-15% SnCl2 solution washing bottle connected in series, the second NaOH solution washing bottle is connected to the seventh heating pipe, and the SnCl2 solution washing bottle is connected to the third three-way valve.

[0032] Preferably, the absorption liquid in the sulfur trioxide detection unit is a 5% isopropanol solution, the buffer solution is a dilute NaOH solution, and the developer solution is a dimethyl sulfoxide solution of 1,3-N,N′-bis-[4-(4′-nitrophenylazo)phenyl]isosquaric acid diamide.

[0033] Compared with the prior art, the detection system and method for harmful substances in flue gas provided by the present invention have the following advantages:

[0034] 1. Based on the sampling and detection principles of flue gas condensable particulate matter, sulfur trioxide and mercury, the present invention organically couples the three sampling and detection units. The structure is rationally designed, easy to operate, and can easily achieve simultaneous sampling and detection of the above three components. It can be widely used in monitoring systems for multiple atmospheric pollutants.

[0035] 2. The flue gas pipelines between the detection units of the present invention all use heating pipes, and the heating pipes in different areas control different temperatures, which effectively reduces energy consumption and prevents condensation of flue gas on the flue gas pipelines outside each detection unit, ensuring that all effective components in the flue gas are detected, reducing errors, and through the air purge unit, the system pipelines are regularly back-blown and cleaned to ensure continuous and uninterrupted sampling and detection of the system.

[0036] 3. In the sulfur trioxide detection unit of the present invention, sulfur trioxide in the flue gas is condensed by two sets of parallel serpentine condensers. The two sets of serpentine condensers work alternately to achieve continuous and uninterrupted detection. At the same time, a DMSO solution of an azo dye (BNBPS) is used as a color developer for sulfate ions, and direct spectrophotometry is used to measure SO4 in the condensate. 2- The concentration can be directly measured to determine the SO3 content. Compared with the existing barium salt-indirect spectrophotometry method, it eliminates the tedious separation and precipitation and other interference factors, thus improving the detection accuracy.

[0037] 4. The mercury detection unit of the present invention is equipped with a zero-valent mercury conversion device and a total mercury conversion device connected in parallel, which can be switched at any time as needed. This allows for the simultaneous detection of zero-valent mercury and total mercury in flue gas. The content of divalent mercury is equal to the total mercury minus zero-valent mercury, which means that different valence states of mercury in flue gas can be detected simultaneously online.

[0038] 5. The flue gas of the present invention adopts isokinetic sampling to avoid the detection error of condensable particulate matter in the flue gas caused by non-isokinetic sampling. In addition, a bypass pipeline is set in parallel with the condensable particulate matter capture unit. When the condensable particulate matter is captured and analyzed offline, the flue gas goes directly to the next detection unit through the bypass without affecting subsequent detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. The same reference symbols are used throughout the drawings to represent the same components. In the drawings:

[0040] Figure 1 This is a structural block diagram of the detection system for harmful substances in flue gas provided by the present invention;

[0041] Figure 2 This is a flow chart of the method for detecting harmful substances in flue gas provided by the present invention.

[0042] Reference numerals

[0043] 001 is the first valve, 002 is the second valve, 003 is the third valve, 004 is the fourth valve, 005 is the fifth valve, 006 is the sixth valve, 007 is the seventh valve, 008 is the eighth valve, 009 is the ninth valve, 010 is the tenth valve, 011 is the eleventh valve, 012 is the twelfth valve, 013 is the thirteenth valve, 014 is the fourteenth valve, and 015 is the fifteenth valve;

[0044] 100 is a first heating pipe, 101 is a second heating pipe, 102 is a third heating pipe, 103 is a fourth heating pipe, 104 is a fifth heating pipe, 105 is a sixth heating pipe, 106 is a seventh heating pipe, 107 is an eighth heating pipe, 108 is a ninth heating pipe, and 109 is a tenth heating pipe;

[0045] 1 is a flue gas sampling unit, 11 is a flue gas sampling gun, 12 is an S-type pitot tube, 13 is a sealing flange of the sampling gun, 14 is a heating filter, and 15 is a first three-way valve;

[0046] 2 is an air purge unit, 21 is an air compressor, 22 is an air filter, and 23 is an air heater;

[0047] 3 is a sulfur trioxide detection unit, 301 is a first flue gas condenser, 3011 is a first serpentine condenser, 3012 is a second serpentine condenser, 302 is an absorption liquid pump, 303 is an absorption liquid tank, 304 is an intermediate tank, 305 is a delivery pump, 306 is a buffer pump, 307 is a flushing water pump, 308 is a flushing water tank, 309 is a buffer tank, 310 is a developer solution tank, 311 is a developer solution pump, 312 is a photometer, 3121 is a detector, 3122 is a pH electrode, 3123 is an absorption cell, and 3124 is a light source;

[0048] 4 is a condensable particulate matter capture unit, 41 is a nitrogen bottle, 42 is a second flue gas condenser, 421 is a third serpentine condenser, 43 is a deionized water pump, 44 is a deionized water tank, 45 is a n-hexane tank, 46 is a n-hexane pump, 47 is an impact bottle, 48 is a filter, and 49 is a second drying bottle;

[0049] Reference numeral 5 denotes a mercury detection unit, reference numeral 51 denotes a second three-way valve, reference numeral 52 denotes a zero-valent mercury conversion device, reference numeral 53 denotes a total mercury conversion device, reference numeral 54 denotes a third three-way valve, reference numeral 55 denotes a mercury analyzer, reference numeral 551 denotes a mercury lamp, reference numeral 552 denotes a heater, reference numeral 553 denotes a measurement chamber, reference numeral 554 denotes a mercury detector, and reference numeral 56 denotes a third drying bottle.

[0050] 6 is a first automatic sampler;

[0051] 7 is a second automatic sampler;

[0052] 8 is a first drying bottle;

[0053] 9 is a numerical control device. DETAILED DESCRIPTION

[0054] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments described herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0055] Please refer to Figure 1 and Figure 2 , Figure 1 This is a structural block diagram of the detection system for harmful substances in flue gas provided by the present invention; Figure 2 This is a flow chart of the method for detecting harmful substances in flue gas provided by the present invention.

[0056] In a specific embodiment, the present invention provides a detection system for harmful substances in flue gas, which is specifically used for simultaneous sampling and detection of condensable particulate matter, sulfur trioxide and mercury in flue gas, including a flue gas sampling unit 1, an air purge unit 2, a sulfur trioxide detection unit 3, a condensable particulate matter capture unit 4, a mercury detection unit 5, a first automatic sampler 6, a second automatic sampler 7 and a numerical control device 9; the flue gas sampling unit 1, the sulfur trioxide detection unit 3, the condensable particulate matter collection unit, the mercury detection unit 5 and the first automatic sampler 6 are connected in sequence, the air purge unit 2 is connected to the flue gas outlet of the flue gas sampling unit 1, and the second automatic sampler 7 is connected to the flue gas outlet of the condensable particulate matter detection unit through a first drying bottle 8; the numerical control device 9 is electrically connected to the flue gas sampling unit 1, the air purge unit 2, the sulfur trioxide detection unit 3, the condensable particulate matter capture unit 4, the mercury detection unit 5, the first automatic sampler 6 and the second automatic sampler 7 respectively. The flue gas sampling gun 11 is fixedly connected to the outer wall of the flue through the sampling gun sealing flange 13. The collection end of the flue gas sampling gun 11 is arranged inside the flue. The flue gas sampling gun 11 is a stainless steel tube with a quartz glass tube embedded in it. The stainless steel tube is equipped with a thermocouple. A heating layer is also arranged on the inner wall of the flue gas sampling gun 11 to maintain the temperature of the flue gas sampling gun 11 at 200-240°C. The thermocouple and the heating layer are connected to the numerical control device 9. When the measured flue gas temperature transmitted by the thermocouple to the numerical control device 9 is low, the numerical control device 9 feeds back a heating signal to the heating layer to ensure that the temperature of the flue gas sampling gun 11 is maintained at 200-240°C, thereby preventing measurement errors caused by condensation of flue gas in the sampling gun.

[0057] Flue gas sampling is achieved through the negative pressure provided by the first automatic sampler 6 and the second automatic sampler 7. The front end of the flue gas sampling gun 11 is also equipped with an S-type pitot tube 12, which is used to measure the difference between the total pressure and static pressure of the flue gas and transmit the pressure signal to the numerical control device 9 in real time. After the numerical control device 9 converts the pressure signal into a flow signal, it is fed back to the second automatic sampler 7. The second automatic sampler 7 adjusts the flue gas sampling flow rate in real time according to the flow signal to ensure that the flue gas flow rate in the flue is consistent with the flue gas sampling flow rate, that is, isokinetic sampling.

[0058] The heating filter 14 is arranged at the rear end of the flue gas sampling gun 11 and is used to filter filterable particulate matter in the flue gas. The heating filter 14 includes a quartz filter membrane (replaceable), a filter membrane support assembly, a heating device and a thermocouple, and maintains the temperature of the heating filter 14 at 200-240°C through temperature signal transmission and feedback between the thermocouple, the numerical control device 9 and the heating device.

[0059] The first three-way valve 15 is arranged at the flue gas outlet of the heating filter 14. One end of the outlet of the first three-way valve 15 is connected to the sulfur trioxide detection unit 3 through the second heating pipe 101 and the third heating pipe 102, and the other end is connected to the air purge unit 2 through a compressed air pipe, wherein the air purge unit 2 includes an air compressor 21, an air filter 22 and an air heater 23. The compressed air provided by the air compressor 21 passes through the air filter 22 to remove impurities such as particles, oil, and moisture in the air, and is then heated to 40-50°C by the air heater 23 before being used for purging the system pipelines to ensure continuous and uninterrupted operation of the system.

[0060] Figure 1 The first heating pipe 100 to the eleventh heating pipe are all double-layer structures with an inner and outer layer. The inner layer is a polytetrafluoroethylene (PTFE) tube, and the outer layer of the polytetrafluoroethylene tube is coated with a heating wire and an insulating outer layer. The required temperature of the flue gas in the heating pipe is maintained by temperature signal transmission and feedback between the numerical control device 9, the heating wire and the insulating outer layer.

[0061] The flue gas collected by the flue gas sampling unit 1 first enters the first flue gas condenser 301 of the sulfur trioxide detection unit 3 through the second heat tracing pipe 101 or the third heat tracing pipe 102. The temperature of the first flue gas condenser 301 is controlled by the numerical control device 9. In this embodiment, the first flue gas condenser 301 is provided with a first serpentine condenser 3011 and a second serpentine condenser 3012 in parallel. The inlets of the two serpentine condensers are connected to the second heat tracing pipe 101 or the third heat tracing pipe 102, the air purge unit 2, and the absorption liquid tank 303 through a tee and corresponding valves, respectively. The outlets of the two serpentine condensers are connected to the intermediate tank 304 and the fourth heat tracing pipe 103 through a tee and corresponding valves.

[0062] For the first serpentine condenser 3011, it is connected to the air purge unit 2 by the first valve 001, connected to the second heating pipe 101 by the second valve 002, connected to the absorption liquid pump 302 by the seventh valve 007, connected to the fourth heating pipe 103 by the fourth valve 004, and connected to the intermediate box 304 by the ninth valve 009; for the second serpentine condenser 3012, it is connected to the air purge unit 2 by the first valve 001, connected to the third heating pipe 102 by the third valve 003, connected to the absorption liquid pump 302 by the eighth valve 008, connected to the fourth heating pipe 103 by the fifth valve 005, and connected to the intermediate box 304 by the tenth valve 010.

[0063] An absorption liquid pump 302 is provided in the absorption liquid tank 303 for pumping the absorption liquid 302 into two serpentine condensers. A delivery pump 305 is provided between the intermediate tank 304 and the photometer 312 for pumping the mixed liquid in the intermediate tank 304 into the absorption tank 3123 in the photometer 312.

[0064] The sulfur trioxide detection unit 3 also includes a flushing water tank 308 and a flushing water pump 307, which are connected to the intermediate box 304 and the absorption cell 3123 in the photometer 312 through pipes, and are used to flush the intermediate box 304 and the absorption cell 3123. Similarly, the buffer tank 309 and the buffer pump 306, and the color developer solution tank 310 and the color developer solution pump 311 are connected to the absorption cell 3123 through corresponding pipes, respectively used to control the pH of the absorption mixture in the absorption cell 3123 and to develop the color of the absorption mixture. A light source 3124 is set on one side of the absorption cell 3123, and the light that passes through the reaction absorption cell 3123 is received by the detector 3121 and converted into SO4 2- The concentration signal is transmitted to the numerical control device 9. A pH electrode 3122 is also installed in the absorption cell 3123. This pH electrode transmits the pH value signal of the solution in the absorption cell 3123 to the numerical control device 9. The numerical control device 9 controls the operation of the buffer pump 306 based on the pH value to ensure that the pH of the absorption solution remains within the test requirements. Drain lines are provided between the intermediate tank 304 and the absorption cell 3123 for drainage.

[0065] After sulfur trioxide detection by the sulfur trioxide detection unit 3, the flue gas enters the condensable particulate matter capture unit 4 along the fourth heat tracing pipe 103. Since condensable particulate matter in the flue gas is captured and analyzed offline in this embodiment, a bypass, a three-way valve, the eleventh valve 011, the sixth valve 006, and the fifteenth valve 015 are arranged in parallel with the condensable particulate matter capture unit 4. After each condensable particulate matter capture is completed, the flue gas enters the next detection unit through the bypass, thereby not affecting the continuous and uninterrupted operation of the system. The temperature of the second flue gas condenser 42 in the condensable particulate matter capture unit 4 is controlled by the numerical control device 9. A third serpentine condenser 421 is provided in the second flue gas condenser 42. The eleventh valve 011, the twelfth valve 012, the thirteenth valve 013, and the fourteenth valve 014 control the connection between the inlet of the third serpentine condenser 421 and the fourth heat tracing pipe 103, the nitrogen cylinder 41, and the deionized water tank 44. The outlet of the third serpentine condenser 421 is sequentially provided with an impact bottle 47, a filter 48, and a second drying bottle 49. The filter 48 includes a quartz filter membrane (replaceable), a filter membrane support assembly, and a temperature sensor. The temperature sensor is connected to the numerical control device 9 to detect and control the flue gas temperature at the filter 48 to be no greater than 30°C. A deionized water pump 43 is provided between the deionized water tank 44 and the third serpentine condenser 421 to pump the deionized water 43 from the deionized water tank 44 into the third serpentine condenser 421. A n-hexane pump 46 is provided between the n-hexane tank 45 and the third serpentine condenser 421 to pump the n-hexane 46 from the n-hexane tank 45 into the third serpentine condenser 421.

[0066] Flue gas passing through condensable particulate matter capture unit 4, along with fifth heat tracer 104, partially passes through third drying bottle 56 and second automatic sampler 7, and is discharged from the system. The remaining portion enters mercury detection unit 5. The first and second automatic samplers 7 are equipped with flow, temperature, and pressure detection instruments, and these parameters are transmitted to numerical control device 9 for sample volume analysis.

[0067] Flue gas entering the mercury detection unit 5 is split into two paths, controlled by the second and third three-way valves 51 and 54, which control the flow of flue gas into either the total mercury conversion device 53 or the zero-valent mercury conversion device 52. The outlet of the third three-way valve 54 is connected to the third drying flask 56, the mercury analyzer 55, and the first automatic sampler 6 in sequence via the ninth heat tracer pipe 108. A mercury lamp 551 is positioned on one side of the measurement chamber 553 of the mercury analyzer 55. Light emitted by the lamp 551 is absorbed by mercury atoms in the measurement chamber 553 and then illuminates the mercury detector 554. The mercury detector 554 converts the light signal into a mercury concentration signal, which is then transmitted to the numerical control unit 9. Furthermore, a heater 552 is provided in the mercury analyzer 55 to maintain a stable temperature within the optical unit and prevent baseline drift caused by temperature.

[0068] In this embodiment, the numerical control device 9 detects, displays, records, feeds back and controls the temperature, pressure, flow, pH, concentration and other signals of each of the above units. 2- The sulfur trioxide concentration in the flue gas is calculated based on the concentration signal and the sampling volume signal from the second automatic sampler 7. The total mercury concentration and zero-valent mercury concentration in the flue gas are displayed based on the mercury concentration signal detected by the mercury analyzer 55 (506) and the connection signal from the second three-way valve 51 and the third three-way valve 54, and the divalent mercury concentration is calculated. In addition, the numerical control device 9 records the sampling volume of the second automatic sampler 7 during the capture of flue gas condensable particulate matter, and calculates the concentration of flue gas condensable particulate matter together with the weight of condensable particulate matter analyzed offline.

[0069] Please continue to refer to Figure 1 and Figure 2 The present invention provides a method for detecting harmful substances in flue gas. The method is implemented by the above-mentioned system for detecting harmful substances in flue gas, and is characterized in that it includes the following steps:

[0070] S1: Connect each unit equipment as required, start the numerical control device 9, set the temperature of the flue gas sampling gun 11 to 200-240°C, set the temperature of the heating filter 14 to 200-240°C, set the temperature of the first heating pipe 100, the second heating pipe 101 and the third heating pipe 102 to 200-240°C, set the temperature of the fourth heating pipe 103, the fifth heating pipe 104, the seventh heating pipe 106, the eighth heating pipe 107 and the ninth heating pipe 108 to 110-120°C, set the temperature of the sixth heating pipe 105, the tenth heating pipe 109 and the eleventh heating pipe to 40-50°C, set the temperature of the first flue gas condenser 301 to 60-80°C, set the temperature of the second flue gas condenser 42 to below 30°C, and start sampling when the temperature reaches the control requirements;

[0071] S2: The first three-way valve 15 is adjusted to connect the flue gas sampling unit 1 with the second heating pipe 101 or the third heating pipe 102, the first automatic sampler 6 and the second automatic sampler 7 are turned on, and the sampling flow rate is controlled by the numerical control device 9. The first automatic sampler 6 and the second automatic sampler 7 generate negative pressure so that the flue gas to be measured continuously and uniformly enters the flue gas sampling gun 11 with the S-type pitot tube 12. The heating filter 14 is installed at the rear end of the flue gas sampling gun 11. The flue gas that has been filtered by the heating filter 14 to remove filterable particulate matter enters the first flue gas condenser 301 through the first heating pipe 100, the first three-way valve 15, the second heating pipe 101 or the third heating pipe 102. At this time, the first three-way valve 15 and the compressed air pipeline of the air purge unit 2 remain closed;

[0072] S3: After the flue gas enters the first flue gas condenser 301, a first serpentine condenser tube 3011 and a second serpentine condenser tube 3012 are connected in parallel in the first flue gas condenser 301. The two sets of serpentine condensers work alternately. When one set of serpentine condensers condenses sulfur trioxide in the flue gas into sulfuric acid droplets, the condensed sulfuric acid droplets in the other set of serpentine condensers are mixed with the absorption liquid in the intermediate tank 304 and then sent to the photometer 312. In the photometer 312, a color reaction is carried out with a color developer to detect the sulfur trioxide content in the reaction liquid. After the detection is completed, the serpentine condenser tubes are rinsed with flushing water and switched to the next set of serpentine condensers to continue testing the next set. The operation cycle continues. Specifically, the third valve 003, the first valve 001, the seventh valve 007, the eighth valve 008, and the tenth valve 010 remain closed. The second valve 002 is opened to allow the flue gas to pass through the first serpentine condenser tube 3011. The sulfur trioxide in the flue gas is condensed into sulfuric acid droplets. The flue gas condensation time is controlled to be 5 to 10 minutes according to the flow rate. After sampling is complete in the first serpentine condenser 3011, valve 2 (valve 002) is closed and valve 3 (valve 003) is opened, switching to the second serpentine condenser 3012 to continue condensing sulfur trioxide in the flue gas. Valve 7 (valve 007) and valve 9 (valve 009) are now opened, and the 5% isopropyl alcohol solution from the absorption liquid tank 303 is pumped into the first serpentine condenser 3011 via the absorption liquid pump 302. The amount of 5% isopropyl alcohol solution pumped in is controlled to 30-50 mL, and the pumping time is controlled to be 30-60 seconds. The mixture of 5% isopropyl alcohol and sulfuric acid droplets is then delivered to the intermediate tank 304 via valve 9 (valve 009). After the absorption liquid pump 302 is completed, it is closed. Simultaneously, valve 1 (valve 001) is opened, and compressed air from the air purge unit 2 is used to blow the remaining liquid in the first serpentine condenser 3011 into the intermediate tank 304. The purge time is controlled to be 30-60 seconds. After the purge is completed, close the first valve 001, the second valve 002, and the ninth valve 009, and start the delivery pump 305 to deliver a small amount of the mixed liquid in the intermediate tank 304 to the absorption cell 3123 in the photometer 312. After closing the delivery pump 305, start the color developer solution pump 311 to pump a certain amount of color developer in the color developer solution tank 310 into the absorption cell 3123, and then start the buffer pump 306 to pump the dilute NaOH solution in the buffer tank 309 into the absorption cell 3123, and adjust the pH value of the mixed liquid in the absorption cell 3123 to 4.5-7.5. After adjusting the pH, turn off the buffer pump 306 and the color developer solution pump 311. At this time, the light source 3124 emits light with a wavelength of 630-650nm. After being absorbed by the absorption cell 3123, the transmitted light is received by the detector 3121 and SO4 2- The concentration signal is fed back to the numerical control device 9. SO4 is obtained 2- After the concentration signal is received, the mixed liquid in the intermediate tank 304 and the absorption tank 3123 is discharged, and the flushing water pump 307 is turned on at the same time. The deionized water pump 43 of the flushing water tank 308 is pumped into the intermediate tank 304 and the absorption tank 3123. After flushing the relevant containers and discharging the waste liquid, the flushing water pump 307 is turned off. At this time, the first set of measurements is completed.

[0073] After the next set of measurements is completed for the sampling of the second serpentine condenser 3012, the third valve 003 is closed, the second valve 002 is opened, and the sampling is switched to the first serpentine condenser 3011. The measurement method of the sulfuric acid droplets in the second serpentine condenser 3012 is the same as that of the first serpentine condenser 3011, except that the corresponding valves are changed from the seventh valve 007 and the ninth valve 009 to the eighth valve 008 and the tenth valve 010.

[0074] S4: After the sulfur trioxide is condensed, the flue gas passes through the fourth heat tracing pipe 103 and enters the condensable particulate matter capture unit 4 or the fifth heat tracing pipe 104 and enters the next component detection unit according to requirements. When the flue gas enters the condensable particulate matter capture unit 4, it passes through the third serpentine condenser 421, the impact bottle 47 and the filter 48 in sequence. At this time, the condensable particulate matter in the flue gas is captured by condensation, collision and membrane filtration. After the capture is completed, the filter membrane is removed from the filter 48 and stored in a dedicated container. First, deionized water is fed into the third serpentine condenser 421 to mix the inorganic components in the condensate with the deionized water in the impact bottle 47 to form an inorganic phase. Then, nitrogen is used to purge the residual liquid in the pipeline and the inorganic phase in the impact bottle 47. After the purge is completed, n-hexane is fed into the third serpentine condenser 421 to mix the organic components in the condensate with the n-hexane in the impact bottle 47 to form an organic phase. The inorganic phase, organic phase and filter membrane are returned to the laboratory for offline analysis of condensable particulate matter.

[0075] Specifically, when flue gas needs to pass into the condensable particulate matter capture unit 4, valves 11 (valve 011) and 15 (valve 015) are opened, while valves 12 (valve 012), 14 (valve 014), 6 (valve 006), and 13 (valve 013) are closed. The flue gas then passes through the third serpentine condenser tube 421, impactor bottle 47, and filter 48 in the second flue gas condenser 42. Condensable particulate matter in the flue gas is captured through condensation, collision, and membrane filtration. After capturing the condensable particulate matter, the flue gas passes through the second drying bottle 49 to remove moisture from the flue gas before being passed along the fifth heat tracing pipe 104 to the next detection unit. Each condensable particulate matter capture period lasts no less than 60 minutes. After the capture period is complete, valves 11 (valve 011) and 15 (valve 015) are closed, and valve 6 (valve 006) is opened. The flue gas from the sulfur trioxide detection unit 3 then bypasses the filter 48 and directly enters the next detection unit. The quartz filter membrane is then removed from the filter 48 and stored in a dedicated container. A new quartz filter membrane is then installed in the filter 48. Then, valve 14 014 is opened, and deionized water pump 43 (404) is simultaneously turned on to pump deionized water from deionized water tank 44 into third serpentine condenser 421. The amount of deionized water pumped in is controlled at 50-100 mL, and the pumping time is controlled at 30-60 seconds. The deionized water and the inorganic components in the condensable particulate matter condensate are then sent through the pipeline into impact bottle 47 to form an inorganic phase. After the deionized water pump 43 is finished, valve 14 014 is closed, and valve 12 012 is simultaneously opened. Nitrogen from nitrogen bottle 41 is used to purge the inorganic phase in third serpentine condenser 421 and impact bottle 47. The purge time is controlled at 5-10 minutes to blow out SO2 that may be dissolved in the inorganic phase, thereby reducing the impact of SO2 on the condensable particulate matter test results. After the purge is complete, valve 12 (valve 012) is closed and valve 13 (valve 013) is opened. Simultaneously, n-hexane pump 46 is started, pumping n-hexane from tank 45 into third serpentine condenser 421. The n-hexane volume is controlled at 50–100 mL, and the pumping time is controlled at 30–60 seconds. The n-hexane and organic components in the condensable particulate matter condensate are then fed through a pipe into impingement bottle 47 to form an organic phase. This capture process is now complete, and impingement bottle 47 is replaced with a new one for the next condensable particulate matter capture cycle. The inorganic and organic phases in impingement bottle 47, along with the quartz filter membrane, are brought back to the laboratory for offline analysis of condensable particulate matter. Laboratory analysis of condensable particulate matter samples is performed according to EPA Method 202, the standard of the U.S. Environmental Protection Agency (EPA).

[0076] S5: After step S4, a portion of the flue gas passes through the second automatic sampler 7 to record the sampling volume and is then discharged from the system. The sampling volume information of the second automatic sampler 7 is transmitted to the numerical control device 9. The other portion enters the mercury detection unit 5. After entering the mercury detection unit 5, the flue gas is divided into two paths: one path is the total mercury conversion device 53, which is used to convert all divalent mercury in the flue gas into zero-valent mercury; the other path is the zero-valent mercury conversion device 52, which is used to absorb divalent mercury in the flue gas and retain only zero-valent mercury. The flue gas passing through the conversion device is dried and then enters the mercury analyzer 55. The mercury analyzer 55 uses atomic absorption spectrometry to detect the concentration of zero-valent mercury in the flue gas. The mercury detection unit 5 achieves the measurement requirements of mercury of different valence states by controlling the second three-way valve 51 and the third three-way valve 54. The difference between the mercury concentrations in the two paths is the concentration of divalent mercury in the flue gas. The flue gas after mercury detection is discharged from the system through the first automatic sampler 6. Specifically, when the second three-way valve 51 and the third three-way valve 54 are simultaneously switched to the total mercury conversion device 53 channel, the flue gas passes through the first 10% NaOH solution wash bottle and the second 10% SnCl2 solution wash bottle, converting all divalent mercury in the flue gas to zero-valent mercury. The flue gas is then dried by the second drying bottle 49 before entering the mercury analyzer 55. At this point, the mercury lamp 551 emits light with a wavelength of 253 nm. After being absorbed by mercury atoms in the flue gas in the measurement chamber 553, the transmitted light is received by the mercury detector 554, which transmits the mercury concentration signal to the numerical control device 9. The total mercury concentration in the flue gas is measured. When the second three-way valve 51 and the third three-way valve 54 are simultaneously switched to the zero-valent mercury conversion device 52 channel, the flue gas passes through the first 10% KCl solution wash bottle and the second 10% NaOH solution wash bottle, and the mercury analyzer 55 measures the zero-valent mercury concentration in the flue gas. The difference between the mercury concentrations in the two flue gas channels is the divalent mercury concentration in the flue gas. The flue gas after mercury detection passes through the first automatic sampler 6 to record the sampling volume and then is discharged from the system.

[0077] Compared with the prior art, the detection system and method for harmful substances in flue gas provided by the present invention have the following advantages:

[0078] 1. Based on the sampling and detection principles of flue gas condensable particulate matter, sulfur trioxide and mercury, the present invention organically couples the three sampling and detection units. The structure is rationally designed, easy to operate, and can easily achieve simultaneous sampling and detection of the above three components. It can be widely used in monitoring systems for multiple atmospheric pollutants.

[0079] 2. The flue gas pipelines between the detection units of the present invention all use heating pipes, and the heating pipes in different areas control different temperatures, which effectively reduces energy consumption and prevents condensation of flue gas on the flue gas pipelines outside each detection unit, ensuring that all effective components in the flue gas are detected, reducing errors, and through the air purge unit, the system pipelines are regularly back-blown and cleaned to ensure continuous and uninterrupted sampling and detection of the system.

[0080] 3. In the sulfur trioxide detection unit of the present invention, sulfur trioxide in the flue gas is condensed by two sets of parallel serpentine condensers. The two sets of serpentine condensers work alternately to achieve continuous and uninterrupted detection. At the same time, a DMSO solution of an azo dye (BNBPS) is used as a color developer for sulfate ions, and direct spectrophotometry is used to measure SO4 in the condensate. 2- The concentration can be directly measured to determine the SO3 content. Compared with the existing barium salt-indirect spectrophotometry method, it eliminates the tedious separation and precipitation and other interference factors, thus improving the detection accuracy.

[0081] 4. The mercury detection unit of the present invention is equipped with a zero-valent mercury conversion device and a total mercury conversion device connected in parallel, which can be switched at any time as needed. This allows for the simultaneous detection of zero-valent mercury and total mercury in flue gas. The content of divalent mercury is equal to the total mercury minus zero-valent mercury, which means that different valence states of mercury in flue gas can be detected simultaneously online.

[0082] 5. The flue gas of the present invention adopts isokinetic sampling to avoid the detection error of condensable particulate matter in the flue gas caused by non-isokinetic sampling. In addition, a bypass pipeline is set in parallel with the condensable particulate matter capture unit. When the condensable particulate matter is captured and analyzed offline, the flue gas goes directly to the next detection unit through the bypass without affecting subsequent detection.

[0083] It should be understood that although the terms first, second, third, etc. may be used herein to describe multiple elements, components, regions, layers, and / or sections, these elements, components, regions, layers, and / or sections should not be limited by these terms. These terms may only be used to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Unless the context clearly indicates otherwise, terms such as "first," "second," and other numerical terms do not imply a sequence or order when used herein.

[0084] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A detection system for harmful substances in flue gas, characterized in that: It includes a flue gas sampling unit, an air purge unit, a sulfur trioxide detection unit, a condensable particulate matter capture unit, a mercury detection unit, a first automatic sampler, a second automatic sampler and a numerical control device; The flue gas sampling unit, the sulfur trioxide detection unit, the condensable particulate matter collection unit, the mercury detection unit, and the first automatic sampler are connected in sequence, the air purge unit is connected to the flue gas outlet of the flue gas sampling unit, and the second automatic sampler is connected to the flue gas outlet of the condensable particulate matter detection unit through a first drying bottle; The numerical control device is electrically connected to the flue gas sampling unit, the air purge unit, the sulfur trioxide detection unit, the condensable particulate matter capture unit, the mercury detection unit, the first automatic sampler, and the second automatic sampler respectively; The sulfur trioxide detection unit includes a first flue gas condenser, an absorption liquid tank, an absorption liquid pump, an intermediate tank, a flushing water tank, a flushing water pump, a buffer tank, a buffer pump, a color developer solution tank, a color developer solution pump, a delivery pump and a photometer; and the sulfur trioxide detection unit condenses sulfur trioxide in the flue gas through two sets of parallel serpentine condensers, and the two sets of serpentine condensers work alternately to achieve continuous and uninterrupted detection. At the same time, a DMSO solution of azo dye BNBPS is used as a color developer for sulfate ions, and direct spectrophotometry is used to measure SO4 in the condensate. 2- concentration, directly measuring the SO3 content; the mercury detection unit includes a second three-way valve, a third three-way valve, a total mercury conversion device, a zero-valent mercury conversion device, a third drying bottle and a mercury analyzer, the second three-way valve is connected to the fifth heating pipe, the inlet of the total mercury conversion device is connected to the second three-way valve through the seventh heating pipe, the inlet of the zero-valent mercury conversion device is connected to the second three-way valve through the eighth heating pipe, the outlet of the total mercury conversion device and the outlet of the zero-valent mercury conversion device are respectively connected to the third three-way valve, the third three-way valve is connected to the inlet of the third drying bottle through the ninth heating pipe, and the The outlet of the third drying bottle is connected to the analyzer through the tenth heating pipe, and the analyzer is connected to the first automatic sampler through the eleventh heating pipe; the flue gas after the sulfur trioxide detection by the sulfur trioxide detection unit enters the condensable particulate matter capture unit, and a part of the flue gas passing through the condensable particulate matter capture unit passes through the third drying bottle and the second automatic sampler in sequence and is discharged from the system, and the other part enters the mercury detection unit, and a bypass pipeline is set in parallel with the condensable particulate matter capture unit. When the condensable particulate matter is captured and offline analysis is performed, the flue gas goes directly to the next detection unit through the bypass.

2. The detection system for harmful substances in flue gas according to claim 1, characterized in that: The flue gas sampling unit includes a flue gas sampling gun, a sampling gun sealing flange, an S-type pitot tube and a heating filter with a built-in quartz filter membrane. The sampling end of the flue gas sampling gun is arranged in the flue, and the S-type pitot tube is arranged on the sampling end. The flue gas sampling gun is fixed to the outer wall of the flue through the sampling gun sealing flange. The heating filter is arranged at the flue gas outlet of the flue gas sampling gun. The flue gas outlet of the heating filter is connected to a first three-way valve through a first heating pipe. The first three-way valve is connected to the sulfur trioxide detection unit and the air purge unit respectively. The flue gas sampling gun comprises a quartz glass tube and a stainless steel tube, wherein the quartz glass tube is sleeved inside the stainless steel tube.

3. The detection system for harmful substances in flue gas according to claim 2, characterized in that: The air purge unit includes an air compressor, an air filter and an air heater connected in sequence. The air heater is connected to the first three-way valve through a first compressed air pipe. The air heater is connected to the flue gas inlet of the sulfur trioxide detection unit through a second compressed air pipe. The second compressed air pipe is provided with a first valve.

4. The detection system for harmful substances in flue gas according to claim 3, characterized in that: The first flue gas condenser includes a first serpentine condenser and a second serpentine condenser, one end of the first serpentine condenser is connected to a second heating pipe having a second valve, one end of the second serpentine condenser is connected to a third heating pipe having a third valve, the second heating pipe and the third heating pipe are connected in parallel to one outlet of the first three-way valve, the other end of the first serpentine condenser is provided with a fourth valve, the other end of the second serpentine condenser is provided with a fifth valve, the fourth valve and the fifth valve are respectively connected to the inlet end of a fourth heating pipe having a sixth valve, the flue gas inlet of the condensable particulate matter capture unit is connected to the fourth heating pipe, and the connection position is located at the front end of the sixth valve; The absorption liquid tank is connected to the inlet of the first serpentine condenser tube, the inlet of the second serpentine condenser tube and the first valve respectively through the absorption liquid pump. A seventh valve is provided at the connection position between the absorption liquid pump and the first serpentine condenser tube, and an eighth valve is provided at the connection position between the absorption liquid pump and the second serpentine condenser tube. The intermediate box is connected to the outlet of the first serpentine condenser tube and the outlet of the second serpentine condenser tube respectively, and a ninth valve is provided at the connection position between the intermediate box and the first serpentine condenser tube, and a tenth valve is provided at the connection position between the intermediate box and the second serpentine condenser tube; The photometer includes a light source, a pH electrode, an absorption cell and a detector. The absorption cell is a transparent structure. The light source and the detector are placed on both sides of the absorption cell. The pH electrode is arranged in the absorption cell. The intermediate box is connected to the absorption cell through the delivery pump. The flushing water tank is connected to the absorption cell through the flushing water pump. The buffer solution tank is connected to the absorption cell through the buffer solution pump. The color developer solution tank is connected to the absorption cell through the color developer solution pump.

5. The detection system for harmful substances in flue gas according to claim 4, characterized in that: The condensable particulate matter capture unit includes a second flue gas condenser, a deionized water tank, a deionized water pump, an impact bottle, a filter with a built-in filter membrane, a second drying bottle, a nitrogen bottle, a n-hexane tank and a n-hexane pump; The second flue gas condenser is equipped with a third serpentine condenser, which is connected to the fourth heating pipe through an eleventh valve, and the connection position is located at the front end of the sixth valve. The nitrogen cylinder is connected to the inlet of the third serpentine condenser through a twelfth valve. The n-hexane tank is connected to the inlet of the third serpentine condenser through the n-hexane pump. A thirteenth valve is provided at the connection position between the n-hexane pump and the third serpentine condenser. The deionized water tank is connected to the inlet of the third serpentine condenser through the deionized water pump. A fourteenth valve is provided at the connection position between the deionized water pump and the third serpentine condenser. The outlet of the third serpentine condenser is connected to the impact bottle, the filter and the second drying bottle in sequence. The outlet of the second drying bottle is connected to the first drying bottle through a fifth heating pipe. A fifteenth valve is provided on the fifth heating pipe. The rear end of the sixth valve is connected to the fifth heating pipe. The connection position between the sixth valve and the fifth heating pipe is located at the rear end of the fifteenth valve. The outlet of the first drying bottle is connected to the second automatic sampler through the sixth heating pipe.

6. The system for detecting harmful substances in flue gas according to claim 1, characterized in that: The mercury analyzer includes a mercury lamp, a heater, a measuring chamber and a mercury detector. One end of the measuring chamber is connected to the outlet of the third drying bottle, and the other end of the measuring chamber is connected to the first automatic sampler. The mercury lamp and the mercury detector are respectively arranged on both sides of the measuring chamber, and the heater is arranged close to the measuring chamber.

7. A method for detecting harmful substances in flue gas, the method being implemented by the system for detecting harmful substances in flue gas according to any one of claims 1 to 6, characterized in that: The steps include: S1: Connect each unit equipment as required, start the numerical control device, set the temperature of the flue gas sampling gun to 200-240°C, set the temperature of the heating filter to 200-240°C, set the temperature of the first heating pipe, the second heating pipe and the third heating pipe to 200-240°C, set the temperature of the fourth heating pipe, the fifth heating pipe, the seventh heating pipe, the eighth heating pipe and the ninth heating pipe to 110-120°C, set the temperature of the sixth heating pipe, the tenth heating pipe and the eleventh heating pipe to 40-50°C, set the temperature of the first flue gas condenser to 60-80°C, set the temperature of the second flue gas condenser to below 30°C, and start sampling when the temperature reaches the control requirements; S2: Turn on the first automatic sampler and the second automatic sampler, and control the sampling flow rate through the numerical control device. The first automatic sampler and the second automatic sampler generate negative pressure to make the flue gas to be tested continuously and uniformly enter the flue gas sampling gun with an S-type pitot tube. The heating filter is installed at the rear end of the flue gas sampling gun. The flue gas that has been filtered by the heating filter to remove filterable particulate matter enters the first flue gas condenser through the first heating pipe, the first three-way valve, the second heating pipe or the third heating pipe. At this time, the first three-way valve and the compressed air pipeline of the air purge unit remain closed; S3: After the flue gas enters the first flue gas condenser, a first serpentine condenser and a second serpentine condenser are connected in parallel in the first flue gas condenser. The two sets of serpentine condensers work alternately. When one set of serpentine condensers condenses sulfur trioxide in the flue gas into sulfuric acid droplets, the condensed sulfuric acid droplets in the other set of serpentine condensers are mixed with the absorption liquid in the intermediate tank and then sent to the photometer. The photometer reacts with the color developer to detect the sulfur trioxide content in the reaction liquid. After the detection is completed, the serpentine condenser is rinsed with flushing water and switched to the other set of serpentine condensers to continue detecting the next set. The cycle continues. S4: The flue gas after condensing sulfur trioxide is passed through the fourth heating pipe to the condensable particulate matter capture unit or the fifth heating pipe to the next component detection unit as required. When the flue gas enters the condensable particulate matter capture unit, it passes through the third serpentine condenser, the impact bottle and the filter in sequence. At this time, the condensable particulate matter in the flue gas is captured by condensation, collision and membrane filtration. After the capture is completed, the filter membrane is removed from the filter and stored in a special container. At the same time, deionized water is first fed into the third serpentine condenser to mix the inorganic components in the condensate with the deionized water in the impact bottle to form an inorganic phase. Then, nitrogen is used to purge the residual liquid in the pipeline and the inorganic phase in the impact bottle. After the purge is completed, n-hexane is fed into the third serpentine condenser to mix the organic components in the condensate with n-hexane in the impact bottle to form an organic phase. The inorganic phase, organic phase and filter membrane are returned to the laboratory for offline analysis of condensable particulate matter. S5: Part of the flue gas that has passed through step S4 is discharged from the system after the sampling volume is recorded by the second automatic sampler, and the other part enters the mercury detection unit. After entering the mercury detection unit, the flue gas is divided into two paths: one path is a total mercury conversion device, which is used to convert all divalent mercury in the flue gas into zero-valent mercury; the other path is a zero-valent mercury conversion device, which is used to absorb divalent mercury in the flue gas and retain only zero-valent mercury. The flue gas passing through the conversion device is dried and then enters the mercury analyzer. The mercury analyzer uses atomic absorption spectrometry to detect the concentration of zero-valent mercury in the flue gas. The mercury detection unit realizes the measurement requirements of mercury of different valence states through the control of the second three-way valve and the third three-way valve. The difference between the mercury concentrations in the two paths is the concentration of divalent mercury in the flue gas. The flue gas after mercury detection is discharged from the system through the first automatic sampler.

8. The method for detecting harmful substances in flue gas according to claim 7, characterized in that: The zerovalent mercury conversion device includes a 5-15% KC1 solution washing bottle and a 5-15% first NaOH solution washing bottle connected in series, the KC1 solution washing bottle is connected to the eighth heating pipe, and the first NaOH solution washing bottle is connected to the third three-way valve; The total mercury conversion device includes a 5-15% second NaOH solution washing bottle and a 5-15% SnCl2 solution washing bottle connected in series, the second NaOH solution washing bottle is connected to the seventh heating pipe, and the SnCl2 solution washing bottle is connected to the third three-way valve.

9. The method for detecting harmful substances in flue gas according to claim 7, characterized in that: The absorption liquid in the sulfur trioxide detection unit is a 5% isopropanol solution, the buffer solution is a dilute NaOH solution, and the color developer solution is a dimethyl sulfoxide solution of 1,3-N,N'-bis-[4-(4'-nitrobenzeneazo)phenyl]isosquaric acid diamide.

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