CN112697532A - Sampling method for nitrogen oxides in ambient air - Google Patents
Sampling method for nitrogen oxides in ambient air Download PDFInfo
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- CN112697532A CN112697532A CN202110020918.2A CN202110020918A CN112697532A CN 112697532 A CN112697532 A CN 112697532A CN 202110020918 A CN202110020918 A CN 202110020918A CN 112697532 A CN112697532 A CN 112697532A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/02—Devices for withdrawing samples
- G01N1/22—Devices for withdrawing samples in the gaseous state
- G01N1/2202—Devices for withdrawing samples in the gaseous state involving separation of sample components during sampling
- G01N1/2214—Devices for withdrawing samples in the gaseous state involving separation of sample components during sampling by sorption
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/02—Devices for withdrawing samples
- G01N1/22—Devices for withdrawing samples in the gaseous state
- G01N1/2202—Devices for withdrawing samples in the gaseous state involving separation of sample components during sampling
- G01N1/2214—Devices for withdrawing samples in the gaseous state involving separation of sample components during sampling by sorption
- G01N2001/2217—Devices for withdrawing samples in the gaseous state involving separation of sample components during sampling by sorption using a liquid
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Abstract
The invention relates to the technical field of environmental monitoring, in particular to a method for sampling nitrogen oxides in ambient air. The method is characterized in that: according to the order of collecting nitrogen dioxide and nitric oxide in turn, the following four sampling pipes are connected in series in turn, nitrogen dioxide is collected by a cradle self-circulation type sampling pipe, absorption liquid is filled in the sampling pipe, a low-branch self-circulation type sampling pipe is used as an oxidation gas washing bottle, the acid potassium permanganate solution is filled in the sampling pipe, and nitric oxide and the absorption liquid are collected by a high-branch self-circulation type sampling pipe and a circulating fluidized bed type sampling pipe. According to the natural circulation working principle, the circulation loop in the absorption bottle is designed, so that the absorption liquid naturally and circularly flows in the circulation loop in the absorption bottle, bubbles naturally and circularly flow along with the absorption liquid until the bubbles grow into larger bubbles and then are broken on the liquid level, and the time of full contact mass transfer reaction between the nitrogen oxides and the absorption liquid is prolonged even if the consumption of the absorption liquid is not increased and finer sieve pores are designed.
Description
Technical Field
The invention relates to the technical field of environmental monitoring, in particular to a method for sampling nitrogen oxides in ambient air.
Background
In gathering nitrogen oxide pollutant sample in the ambient air in-process, no matter short time sampling and long-time continuous sampling all require pollutant and absorption liquid fully to react, and the absorption liquid can not be carried by gas and run off, except causing the gas production pump trouble, still influence the sample in the follow-up absorption liquid and retrieve and the constant volume work, and then influence the representativeness of sampling and data analysis's the degree of accuracy, precision. The Chinese invention patent (with the patent number of CN95218722.1, the patent name of which is an atmospheric sampling absorption tube) discloses a chemical analyzer for monitoring nitrogen oxides and sulfur dioxide in atmospheric environment, which is characterized in that an air-extracting bulb (1) is connected with a ground opening of a reaction tube (2) with the upper part being a pear-shaped and the bottom being a porous glass plate, and a cylindrical colorimetric tube (3) is arranged in an oxidation tube (4) or a connecting tube (5) and is connected with the ground opening of the reaction tube (2). Compared with the atmospheric sampling absorption tube adopted by international standards and domestic standards, the absorption tube has the outstanding advantages of higher absorption rate, better precision, rigorous structure, durability, portability, convenient operation, easy washing and wide adaptability. The invention discloses a common bubble absorbing tube with a short air inlet tube (with the patent number of CN201320455550.3, the patent name of which is a common bubble absorbing tube with a short air inlet tube), which comprises an air inlet, an air outlet, an air inlet tube, an upper absorbing tube and a lower absorbing tube, wherein the length of the air inlet tube extends to the junction of the upper absorbing tube and the lower absorbing tube, the lower end of the air inlet tube is connected with a conduit which is bent towards the side wall of the lower absorbing tube and then extends towards the lower end of the lower absorbing tube, the conduit is arranged at the upper end of the lower absorbing tube, the lower absorbing tube is also internally provided with an L-shaped baffle bent downwards, one end of the L-shaped baffle is fixedly connected to the side wall of the lower absorbing tube, the other end of the L-shaped baffle extends to the lower end of the lower absorbing tube, and. The utility model discloses change the absorption mode that contains gaseous pollutant bubble rising process and for making the bubble descend earlier and absorb the back and go on the absorptive secondary absorption process of bubble rising again, make the bubble descend and increased the absorption chance, make and contain the gaseous pollutant bubble absorbed time increase more than one time to greatly increased absorption efficiency, increase analysis result's accuracy.
Prior art 1 increases the baffling board of "L" type separation blade in the bubble absorption tube, makes gaseous baffling in the absorption tube in order to increase gaseous dwell time at the absorption tube, makes pollutant and absorption liquid can more fully react to satisfy the target of the accuracy, the precision of the representativeness and the data analysis of sampling, but set up the resistance pressure drop that the baffling board can increase the absorption tube, probably make the gas recovery pump unable work. Prior art 2 increases the colour comparison tube as the baffling pipe, and the purpose also makes gaseous baffling in the absorption tube in order to increase gaseous dwell time at the absorption tube, makes pollutant and absorption liquid can more fully react, and in the same way, it can increase the resistance pressure drop of absorption tube to set up the baffling pipe, probably makes the unable work of gas sampling pump.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a method for sampling nitrogen oxides in ambient air, which is characterized by comprising the following steps: firstly, sequentially connecting the following four sampling tubes in series according to the sequence of sequentially collecting nitrogen dioxide and nitric oxide, collecting the nitrogen dioxide by using a cradle self-circulation type sampling tube, and filling absorption liquid in the sampling tube; a low-branch self-circulation sampling pipe is used as an oxidation gas washing bottle, and absorption liquid is filled in the oxidation gas washing bottle; collecting nitric oxide by a high-branch self-circulation type sampling pipe and a circulating fluidized bed type sampling pipe, and filling absorption liquid in the nitric oxide; absorption liquid: weighing 5.0g of sulfanilic acid, dissolving the sulfanilic acid in 200ml of 40-50 ℃ hot water, cooling the solution to room temperature, transferring the solution into a 1000ml volumetric flask, adding 50ml of N- (1-naphthyl) ethylenediamine hydrochloride with the mass concentration of 0.1% and 50ml of glacial acetic acid, diluting the solution with water to scale marks to be used as color development liquid, and mixing the solution with water according to the volume ratio of 4:1 when the solution is used temporarily; acid potassium permanganate solution: weighing 25g of potassium permanganate, dissolving in 500ml of water, adding a mixed solution with the same volume of 1mol/L sulfuric acid, naturally circulating and flowing an absorption liquid, keeping the temperature of 20 +/-4 ℃, and collecting a nitrogen oxide sample under the requirement of short-time and long-time sampling.
And secondly, air is guided in through an air guide pipe and then impacts absorption liquid in the lower bubbles downwards, the air is uniformly distributed in the absorption liquid in the lower bubbles along the concave structure at the bottom of the hanging basket to form countless small bubbles, the absorption liquid in the lower bubbles contacts with the air, the gas-liquid mixture formed by mass transfer and turnover rises to the upper bubbles along the calandria in the hanging basket, the density difference exists between the gas-liquid mixture of the calandria in the hanging basket and the absorption liquid in the spherical partition wall heat exchange descending pipe, the static pressure difference between the absorption liquid and the calandria drives the absorption liquid in the spherical partition wall heat exchange descending pipe to flow into the lower bubbles from the upper bubbles, the absorption liquid naturally and circularly flows in a circulating loop in an absorption bottle, the bubbles naturally and the absorption liquid naturally and flow together until the bubbles grow into larger bubbles, the bubbles are extinguished, the gas-liquid contact time is prolonged, the absorption efficiency is improved, and the absorbed air is.
And thirdly, leading air into the gas inlet pipe and then downwards impacting the absorption liquid at the bottom of the low-branch self-circulation type sampling pipe body to form a plurality of extremely fine bubbles, wherein the bubbles formed by full contact and turnover of the air and the absorption liquid rise along the liquid column of the low-branch self-circulation type sampling pipe body, the grown bubbles are broken near the scale liquid level, the fine bubbles naturally and circularly flow along with the absorption liquid, and because the density difference exists between the gas-liquid mixture of the low-branch self-circulation type sampling pipe body and the absorption liquid in the spherical partition wall heat exchange descending circulation pipe, the static pressure difference between the low-branch self-circulation type sampling pipe body and the absorption liquid drives the absorption liquid in the spherical partition wall heat exchange descending circulation pipe to flow back into the low-branch self-circulation type sampling pipe body, and the bubbles continuously keep contact along with.
And fourthly, leading air into the gas leading-in pipe with the plug, then impacting the absorption liquid at the bottom of the gas absorption main pipe downwards to form a plurality of extremely fine bubbles, enabling the bubbles formed by full contact and turnover of the air and the absorption liquid to rise along a liquid column of the gas absorption main pipe, breaking the grown bubbles near the scale liquid level, enabling the fine bubbles to naturally circulate and flow along with the absorption liquid, driving the absorption liquid in the spherical partition heat exchange descending backflow pipe to flow back into the gas absorption main pipe from the gas absorption branch pipe due to density difference between a gas-liquid mixture of the gas absorption main pipe and the absorption liquid in the spherical partition heat exchange descending backflow pipe, keeping the absorption liquid continuously in contact with the air in natural circulation, prolonging the retention time of nitrogen oxides in the absorption liquid, and leading out the gas after full reaction with the absorption liquid through the gas leading-out pipe with the plug.
And step five, introducing air through a tested gas inlet pipe with a plug, then impacting the absorption liquid at the bottom of the circulating fluidized bed body downwards to form a plurality of fine bubbles, fully contacting the air and the absorption liquid, turning over the formed bubbles, rising along a liquid column of the circulating fluidized bed body, breaking the bubbles near the scale liquid level, enabling the air flow to enter a cyclone cone cylinder body tangentially, collecting liquid drops in the air after cyclone separation along the wall of the cyclone cone cylinder body, flowing into a spherical partition wall for heat exchange, descending back to the circulating fluidized bed body again, and leading out the purified gas through a tested gas outlet pipe with a plug.
And step six, after sampling is finished, the gas extraction pump stops working, in order to prevent the solution from being sucked backwards, the cyclone separator of the circulating fluidized bed type sampling pipe can enable the sucked gas-liquid mixture to be re-returned to the circulating fluidized bed type sampling pipe body after cyclone separation, so that the subsequent sample in the absorption liquid is prevented from being influenced to carry out recovery and constant volume work, and the sampling representativeness and the accuracy and precision of data analysis are further influenced.
The inventor finds that the ecological environment ministry of 'determination of environmental air nitrogen oxides (nitric oxide and nitrogen dioxide) by naphthyl ethylenediamine hydrochloride spectrophotometry' (HJ/479) -2009) indicates that a solution absorption method is adopted for collecting a sample, a porous glass plate absorption tube, an oxidation bottle and a porous glass plate absorption tube are sequentially connected in series, nitrogen dioxide in air is absorbed by absorption liquid in a first porous glass plate absorption tube connected in series, the nitrogen dioxide is dissolved in glacial acetic acid solution to generate nitrous acid, and is subjected to diazotization reaction with sulfanilic acid under an acidic condition to generate diazonium salt, and then subjected to coupling reaction with naphthyl ethylenediamine hydrochloride reagent to generate mauve azo dye; the absorption liquid in the second oxidation bottle connected in series is an acidic potassium permanganate solution, and nitric oxide is oxidized into nitrogen dioxide; the nitrogen dioxide led out from the oxidation bottle is absorbed by absorption liquid in a third absorption tube connected in series, the nitrogen dioxide is dissolved in glacial acetic acid solution to generate nitrous acid, diazotized with sulfanilic acid under acidic condition to generate diazonium salt, and coupled with naphthyl ethylenediamine hydrochloride reagent to generate mauve azo dye. And after sampling is finished, recovering and fixing the volume of the sample in the absorption liquid, and then analyzing the sample.
The inventor finds that in order to improve the sampling efficiency of absorbing nitrogen oxides by the absorption liquid, the air is dispersed into very small bubbles after passing through a sieve plate of the porous glass plate absorption tube, so that the retention time is prolonged, the gas-liquid contact area is increased, the absorption efficiency is improved, and meanwhile, the height of the absorption liquid column is not less than 80 mm. Generally, a way of increasing the using amount of the absorption liquid, namely increasing the height of the absorption liquid column, is not adopted, because the increase of the using amount of the absorption liquid can influence the subsequent recovery and constant volume work of a sample in the absorption liquid, because a detection analysis instrument method has the detection limit constraint on the mercury concentration, when the concentration of a sample solution is lower than the detection limit, the accuracy and precision are influenced, and the quality assurance and the quality control cannot be implemented; the through holes of the sieve plate cannot be designed to be finer, because the resistance pressure drop is improved, the gas extraction pump cannot work in an effective pressure flow efficiency curve, and the particles in the air can block the through holes of the sieve plate. Therefore, the method for increasing the retention time of the nitrogen oxides in the absorption liquid by improving the design of the absorption tube is undoubtedly one of feasible methods, according to the working principle of natural circulation, the circulation loop of the absorption liquid in the absorption bottle is enabled to naturally circulate and flow through the circulation loop, bubbles naturally circulate and flow along with the absorption liquid until the bubbles grow into larger bubbles and then are broken on the liquid surface, and the time for the nitrogen oxides to fully contact with the absorption liquid for mass transfer reaction is increased even if the using amount of the absorption liquid is not increased and finer sieve meshes are designed.
The inventor finds that in order to maintain the stability of diazonium salt and the smooth proceeding of coupling reaction, a constant-temperature heat exchange device is additionally arranged outside a descending tube, the temperature of 20 +/-4 ℃ is kept through the natural circulation flow of absorption liquid, nitrogen oxide samples are collected under the requirement of short-time and long-time sampling, the following four sampling tubes are sequentially connected in series according to the sequence of sequentially collecting nitrogen dioxide and nitric oxide, one hanging basket self-circulation type sampling tube is used for collecting nitrogen dioxide, and the absorption liquid is filled in the sampling tubes; a low-branch self-circulation sampling pipe is used as an oxidation gas washing bottle, and absorption liquid is filled in the oxidation gas washing bottle; a high-branch self-circulation type sampling tube and a circulating fluidized bed type sampling tube are used for collecting nitric oxide, and absorption liquid is filled in the sampling tube. Absorption liquid: weighing 5.0g of sulfanilic acid, dissolving the sulfanilic acid in 200ml of 40-50 ℃ hot water, cooling the solution to room temperature, transferring the solution into a 1000ml volumetric flask, adding 50ml of N- (1-naphthyl) ethylenediamine hydrochloride with the mass concentration of 0.1% and 50ml of glacial acetic acid, diluting the solution with water to scale marks to be used as color development liquid, and mixing the solution with water according to the volume ratio of 4:1 when the solution is used temporarily; acid potassium permanganate solution: 25g of potassium permanganate is weighed and dissolved in 500ml of water, and then an equal volume of mixed solution of 1mol/L sulfuric acid is added.
The inventor finds that in the sampling process, in order to prevent the particulate matters from blocking the gas circuit, the gas inlet pipe of the first serial hanging basket self-circulation type sampling pipe is thick, so that the particulate matters can be smoothly introduced into the bottom of the hanging basket self-circulation type sampling pipe body and are washed and purified by the absorption liquid, and formed large bubbles are crushed by the hanging basket to improve the gas-liquid contact area. And the fourth cyclone separator of the circulating fluidized bed type sampling pipe connected in series separates the absorption liquid carried by the gas, and the absorption liquid returns to the circulating fluidized bed type sampling pipe body again, so that the absorption liquid is prevented from entering the gas extraction pump to cause faults. After sampling, the gas extraction pump stops working, and in order to prevent the solution from being sucked backwards, the cyclone separator of the circulating fluidized bed type sampling pipe can enable the sucked gas-liquid mixture to be re-returned to the circulating fluidized bed type sampling pipe body through the absorption liquid after cyclone separation, so that the sample in the follow-up absorption liquid is prevented from being influenced to be recycled and subjected to constant volume operation, and the sampling representativeness and the accuracy and the precision of data analysis are further influenced.
The inventor finds that the hanging basket self-circulation type sampling pipe comprises a hanging basket self-circulation type sampling pipe body and a hanging basket air guide assembly with a plug, wherein the hanging basket self-circulation type sampling pipe body is of a dumbbell-shaped structure, an upper bubble and a lower bubble are connected through an intermediate connecting pipe, a hanging basket is placed in the intermediate connecting pipe, spherical partition wall heat exchange descending pipes are designed on two sides of the upper bubble and the lower bubble, and the spherical partition wall heat exchange descending pipes keep the temperature of 20 +/-4 ℃. Utensil stopper hanging basket air guide assembly includes gas induction pipe, gas delivery pipe, utensil dull polish quartz glass stopper, hangs the basket, and the gas induction pipe passes utensil dull polish quartz glass stopper bubble down of cutting straightly, and the welding of gas induction pipe lower extreme has a hanging basket, hanging the basket constitutes for the calandria of a set of parallel, fills in the annular space between gas induction pipe and the intermediate junction pipe, and the bottom is the indent structure. The scale marks on the hanging basket self-circulation type sampling tube body, the absorption liquid is added to enable the liquid level of the hanging basket self-circulation type sampling tube body to be accurate to the scale position, the hanging basket self-circulation type sampling tube body is kept horizontally placed, the absorption liquid cannot submerge the spherical dividing wall heat exchange descending tube due to the fact that the hanging basket self-circulation type sampling tube body cannot be inclined, and the frosted bottle mouth of the hanging basket self-circulation type sampling tube body is fixed with the frosted quartz glass plug through the rubber band to prevent. Air is guided in through the air guide pipe and then impacts absorption liquid in the lower bubbles downwards, the air is uniformly distributed in the absorption liquid in the lower bubbles along the concave structure at the bottom of the hanging basket to form countless small bubbles, the absorption liquid in the lower bubbles contacts with the air, the gas-liquid mixture formed by mass transfer and turnover rises to the upper bubbles along the calandria in the hanging basket, the density difference exists between the gas-liquid mixture of the calandria in the hanging basket and the absorption liquid in the spherical partition wall heat exchange downcomer, the static pressure difference between the absorption liquid and the air drives the absorption liquid in the spherical partition wall heat exchange downcomer to flow into the lower bubbles from the upper bubbles, the absorption liquid naturally circulates and flows in a circulation loop in an absorption bottle, the bubbles naturally circulate and flow together with the absorption liquid until the bubbles grow into larger bubbles and then break on the liquid surface, the gas-liquid contact time is prolonged, the absorption efficiency is improved, and the absorbed air is output through.
The inventor finds that the sampling tube with the low branch self-circulation type comprises a gas outlet tube, a gas inlet tube, a sampling tube body with the low branch self-circulation type, a connecting through-flow tube and a spherical dividing wall heat exchange descending circulating tube, wherein the sampling tube body with the low branch self-circulation type is designed to be thick at the upper part and thin at the lower part, an absorption liquid column can be heightened by the thin and thin lower part of the sampling tube body with the low branch self-circulation type, a measured gas can be fully contacted with the absorption liquid, bubbles which are overturned can be rapidly broken by the expansion of the upper part of the sampling tube body with the low branch self-circulation type, the spherical dividing wall heat exchange descending circulating tube keeps the temperature of 20 +/-4 ℃, the gas outlet tube and the gas inlet tube penetrate through a quartz glass plug, the quartz glass plug is matched with the sampling tube body with the low branch self-circulation type, the upper end of the spherical dividing wall heat exchange descending, the lower end of the spherical dividing wall heat exchange descending circulating pipe is connected with the bottom of the sampling pipe body with a low branch self-circulation type for through flow. The gas inlet pipe is directly inserted into the bottom of the low-branch self-circulation sampling pipe body, a porous screen plate is welded at the bottom end of the gas inlet pipe, and the opening area of the porous screen plate is equivalent to the section area of the gas inlet pipe, so that gas flow is ejected out by uniform ultrafine bubbles after impacting the porous screen plate. The low-branch self-circulation sampling tube body is marked with scales, absorption liquid is added to enable the liquid level of the low-branch self-circulation sampling tube body to be accurate to the scale position, the scale position is 1cm higher than that of the connecting through-flow tube, the low-branch self-circulation sampling tube body is required to be horizontally placed, the absorption liquid cannot submerge the connecting through-flow tube due to the fact that the absorption liquid cannot be inclined, a bottle opening of the low-branch self-circulation sampling tube body is fixed with a quartz glass plug through a rubber band to prevent gas from being flushed away, and gas tightness inspection is required to. Air is guided in through the gas inlet pipe and then downwards impacts absorption liquid at the bottom of the low-branch self-circulation type sampling pipe body to form countless extremely fine bubbles, the bubbles formed by full contact and turnover of the air and the absorption liquid rise along a liquid column of the low-branch self-circulation type sampling pipe body, the grown bubbles are broken and extinguished near a scale liquid level, the fine bubbles naturally circulate and flow along with the absorption liquid, because density difference exists between a gas-liquid mixture of the low-branch self-circulation type sampling pipe body and the absorption liquid in the spherical partition wall heat exchange descending circulation pipe, static pressure difference between the gas-liquid mixture and the absorption liquid drives the absorption liquid in the spherical partition wall heat exchange descending circulation pipe to flow back into the low-branch self-circulation type sampling pipe body, and the bubbles continuously keep contact along with the absorption liquid in the natural circulation flow.
The inventor finds that the sampling pipe with the high support self-circulation type comprises a gas outlet pipe with a plug, a gas inlet pipe with a plug and a sampling pipe body with the high support self-circulation type, wherein the sampling pipe body with the high support self-circulation type comprises a gas absorption branch pipe, a tying pipe, a gas absorption main pipe and a spherical dividing wall heat exchange descending backflow pipe, the spherical dividing wall heat exchange descending backflow pipe keeps the temperature of 20 +/-4 ℃, the gas outlet pipe with the plug is matched with the gas absorption branch pipe in a grinding mode, the lower portion of the gas absorption branch pipe is communicated with the upper portion of the gas absorption main pipe through the tying pipe, the bottom of the gas absorption branch pipe is designed with the spherical dividing wall heat exchange descending backflow pipe, and the bottom end of the spherical dividing. The gas absorption main pipe, the tying pipe, the gas absorption branch pipe and the spherical dividing wall heat exchange descending reflux pipe form a natural circulation loop, the gas inlet pipe with the plug is directly inserted into the bottom of the gas absorption main pipe, the bottom end of the gas inlet pipe with the plug is welded with a porous sieve plate, the opening area of the porous sieve plate is equivalent to the section area of the gas inlet pipe with the plug, and airflow impacts the porous sieve plate and then is sprayed out in uniform superfine bubbles. The high-branch self-circulation type sampling tube body is marked with scales, absorption liquid is added to enable the liquid level of the high-branch self-circulation type sampling tube body to be accurate to the scale position, the scale position is 1cm higher than that of the tied tube, the high-branch self-circulation type sampling tube body is required to be horizontally placed, the tied tube cannot be submerged by the absorption liquid due to the fact that the absorption liquid cannot be inclined, a bottle opening of the high-branch self-circulation type sampling tube body is fixed with a plug through a rubber band to prevent gas from being flushed away, and gas tightness inspection is required. Air is guided in through the gas guide pipe with the plug and then downwards collides with absorption liquid at the bottom of the gas absorption main pipe to form countless extremely fine bubbles, the bubbles formed by full contact and turnover of the air and the absorption liquid rise along a liquid column of the gas absorption main pipe, the grown bubbles are broken and extinguished near a scale liquid level, the fine bubbles naturally circulate along with the absorption liquid, because density difference exists between a gas-liquid mixture of the gas absorption main pipe and the absorption liquid in the spherical partition wall heat exchange descending backflow pipe, static pressure difference between the gas mixture and the absorption liquid drives the absorption liquid in the spherical partition wall heat exchange descending backflow pipe to flow back into the gas absorption main pipe from the gas absorption branch pipe, the absorption liquid continuously contacts with the air in natural circulation to keep constant temperature and prolong the retention time of nitrogen oxides in the absorption liquid, and the gas after full reaction with the absorption liquid is guided out through the gas guide.
The inventor finds that the circulating fluidized bed type sampling pipe comprises a tested gas outlet pipe with a plug, a tested gas inlet pipe with a plug and a circulating fluidized bed type sampling pipe body, wherein the circulating fluidized bed type sampling pipe body comprises a cyclone cone cylinder body, a circulating fluidized bed body and a spherical partition wall heat exchange descending returner, the spherical partition wall heat exchange descending returner keeps the temperature of 20 +/-4 ℃, the tested gas outlet pipe with the plug and the cyclone cone cylinder body form a cyclone separator, a tangential inlet of the cyclone cone cylinder body is connected with the upper part of the circulating fluidized bed body, the bottom of the cyclone cone cylinder body is provided with the spherical partition wall heat exchange descending returner, and the bottom end of the spherical partition wall heat exchange descending returner is connected with the lower part of the circulating fluidized bed body. The circulating fluidized bed body is designed to be thick at the upper part and thin at the lower part, the absorption liquid column can be heightened due to the thin and thin lower part of the circulating fluidized bed body, the detected gas can be fully contacted with the absorption liquid, the rising bubbles can be rapidly destroyed due to the expansion of the upper part of the circulating fluidized bed body, the detected gas leading-in pipe is plugged into the bottom of the circulating fluidized bed body, a porous plate is welded at the bottom end of the detected gas leading-in pipe, the area of the porous plate is equivalent to the area of the cross section of the detected gas leading-in pipe, and the air flow is ejected out in the form of uniform and fine bubbles after impacting the porous plate. The circulating fluidized bed type sampling tube body is marked with scales, absorption liquid is added to enable the liquid level of the sampling tube body to be accurate to the scale position, the scale position is flush with the top of the spherical dividing wall heat exchange descending returning device, the circulating fluidized bed type sampling tube body is required to be horizontally placed, the absorption liquid cannot submerge the spherical dividing wall heat exchange descending returning device due to the fact that the absorption liquid cannot be inclined, a bottle opening of the circulating fluidized bed type sampling tube body is fixed with a plug through a rubber band to prevent gas from being flushed away, and gas tightness inspection is required to be conducted before the sampling tube body is used. Air is guided in through a gas guide pipe with a plug to be detected and then collides with absorption liquid at the bottom of the circulating fluidized bed body downwards to form a plurality of fine bubbles, the bubbles formed by full contact and turnover of the air and the absorption liquid rise along a liquid column of the circulating fluidized bed body, the bubbles are broken and extinguished near the scale liquid level, airflow tangentially enters a cyclone cone cylinder, liquid drops in the air are collected along the wall of the cyclone cone cylinder after cyclone separation and flow into a spherical partition wall heat exchange and fall back to a returning device and then return to the circulating fluidized bed body again, and the purified gas is guided out through a gas guide pipe with a plug to be detected.
Compared with the prior art, the invention at least has the following advantages: according to the natural circulation working principle, the circulation loop in the absorption bottle is designed, so that the absorption liquid naturally and circularly flows in the circulation loop in the absorption bottle, bubbles naturally and circularly flow along with the absorption liquid until the bubbles grow into larger bubbles and then are broken on the liquid level, and the time of full contact mass transfer reaction between the nitrogen oxides and the absorption liquid is prolonged even if the consumption of the absorption liquid is not increased and finer sieve pores are designed.
Drawings
FIG. 1 is a schematic structural diagram of a front view of the method for sampling nitrogen oxides in ambient air according to the present invention.
FIG. 2 is a schematic structural diagram of a large sample A of the method for sampling nitrogen oxides in ambient air according to the present invention.
FIG. 3 is a schematic structural diagram of a sample B of the method for sampling nitrogen oxides in ambient air according to the present invention.
FIG. 4 is a schematic view of the arrangement structure of the section C-C of the sampling method of nitrogen oxides in ambient air according to the present invention.
FIG. 5 is a schematic diagram of a large sample structure D of the method for sampling nitrogen oxides in ambient air according to the present invention.
FIG. 6 is a schematic diagram of a structure of a sample E of the method for sampling nitrogen oxides in ambient air according to the present invention.
FIG. 7 is a schematic structural diagram of a large sample F of the method for sampling nitrogen oxides in ambient air according to the present invention.
I-cradle self-circulation type sampling tube II-low-branch self-circulation type sampling tube
III-high-branch self-circulation type sampling pipe IV-circulating fluidized bed type sampling pipe V-gas extraction pump
1-hanging basket self-circulation type sampling pipe body 2-air guide component with plug and hanging basket 3-upper air bubble
4-spherical dividing wall heat exchange downcomer 5-middle connecting pipe 6-lower bubble 7-gas guide pipe
8-gas delivery pipe 9-frosted quartz glass plug 10-hanging basket 11-gas delivery pipe
12-gas inlet pipe 13-sampling pipe body with low branch self-circulation 14-connecting draft pipe
15-spherical partition wall heat exchange descending circulation pipe 16-gas outlet pipe with plug
17-gas inlet pipe with plug 18-sampling pipe with high branch self-circulation
19-gas absorption branch pipe 20-series pipe 21-gas absorption main pipe
22-spherical partition wall heat exchange descending reflux pipe 23-tested gas delivery pipe with plug
24-gas inlet pipe 25 with plug for testing-circulating fluidized bed type sampling pipe body
26-cyclone conical cylinder 27-circulating fluidized bed body 28-spherical partition wall heat exchange descending returning device.
Detailed Description
The invention is further described with reference to the following detailed description of embodiments and drawings.
As shown in fig. 1, 2, 3, 4, 5, 6 and 7, the method for sampling nitrogen oxides in ambient air is characterized in that: firstly, sequentially connecting the following four sampling tubes in series according to the sequence of sequentially collecting nitrogen dioxide and nitric oxide, collecting the nitrogen dioxide by a cradle self-circulation type sampling tube I, and filling absorption liquid in the sampling tube I; a low-branch self-circulation sampling pipe II is used as an oxidation gas washing bottle, and the absorption liquid is an acidic potassium permanganate solution; collecting nitric oxide by a high-branch self-circulation type sampling pipe III and a circulation fluidized bed type sampling pipe IV, and filling absorption liquid in the nitric oxide; absorption liquid: weighing 5.0g of sulfanilic acid, dissolving the sulfanilic acid in 200ml of 40-50 ℃ hot water, cooling the solution to room temperature, transferring the solution into a 1000ml volumetric flask, adding 50ml of N- (1-naphthyl) ethylenediamine hydrochloride with the mass concentration of 0.1% and 50ml of glacial acetic acid, diluting the solution with water to scale marks to be used as color development liquid, and mixing the solution with water according to the volume ratio of 4:1 when the solution is used temporarily; acid potassium permanganate solution: weighing 25g of potassium permanganate, dissolving in 500ml of water, adding a mixed solution with the same volume of 1mol/L sulfuric acid, naturally circulating and flowing an absorption liquid, keeping the temperature of 20 +/-4 ℃, and collecting a nitrogen oxide sample under the requirement of short-time and long-time sampling.
Secondly, the air is introduced through the air inlet pipe 7 and then impacts the absorption liquid in the lower air bubbles downwards, the air is uniformly distributed in the absorption liquid in the lower air bubbles 6 along the concave structure at the bottom of the hanging basket 10 to form countless small air bubbles, the absorption liquid in the lower air bubbles 6 contacts with the air, the air-liquid mixture formed by mass transfer and overturning rises to the upper air bubbles 3 along the calandria in the hanging basket 10, because the density difference exists between the gas-liquid mixture of the calandria in the hanging basket 10 and the absorption liquid in the spherical dividing wall heat exchange downcomer 4, the absorption liquid in the spherical dividing wall heat exchange downcomer 4 is driven by the static pressure difference of the two to flow into the lower bubbles 6 from the upper bubbles 3, the absorption liquid naturally circulates and flows in a circulation loop in an absorption bottle, the bubbles naturally circulate and flow along with the absorption liquid until the bubbles grow into larger bubbles and then are broken on the liquid surface, the gas-liquid contact time is prolonged, the absorption efficiency is improved, and the absorbed air is output through the gas guide pipe 8.
And step three, air is introduced through the gas introduction pipe 12 and then downwards impacts the absorption liquid at the bottom of the low-branch self-circulation type sampling pipe body 13 to form a plurality of extremely fine bubbles, the bubbles formed by full contact and turnover of the air and the absorption liquid rise along the liquid column of the low-branch self-circulation type sampling pipe body 13, the grown bubbles are broken near the scale liquid level, the fine bubbles naturally and circularly flow along with the absorption liquid, density difference exists between the gas-liquid mixture of the low-branch self-circulation type sampling pipe body 13 and the absorption liquid in the spherical partition wall heat exchange descending circulation pipe 15, the absorption liquid in the spherical partition wall heat exchange descending circulation pipe 15 is driven by static pressure difference of the low-branch self-circulation type sampling pipe body and the bubbles continuously keep contact along with the absorption liquid in the natural circulation flow, and therefore the oxidation degree of the nitric oxide is improved.
And fourthly, leading air into the gas leading-in pipe 17 with a plug, then impacting the absorption liquid at the bottom of the gas absorption main pipe 21 downwards to form a plurality of extremely fine bubbles, leading the air and the absorption liquid to fully contact and turn over to form bubbles, rising along the liquid column of the gas absorption main pipe 21, breaking the grown bubbles near the scale liquid level, leading the fine bubbles to naturally circulate and flow along with the absorption liquid, driving the absorption liquid in the spherical partition wall heat exchange descending return pipe 22 to flow back into the gas absorption main pipe 21 from the gas absorption branch pipe 19 due to the density difference between the gas-liquid mixture of the gas absorption main pipe 21 and the absorption liquid in the spherical partition wall heat exchange descending return pipe 22, keeping the absorption liquid continuously in contact with the air in natural circulation to keep constant temperature and prolonging the retention time of nitrogen oxides in the absorption liquid, and leading out the gas after fully reacting with the absorption liquid through the gas leading-out pipe 16 with a.
And step five, after being guided by the gas guide-in pipe 24 with a plug, air downwards impacts absorption liquid at the bottom of the circulating fluidized bed body 27 to form a plurality of fine bubbles, the bubbles formed by full contact and turnover of the air and the absorption liquid rise along the liquid column of the circulating fluidized bed body 27, the bubbles are broken near the scale liquid level, airflow tangentially enters the cyclone conical cylinder 26, liquid drops in the air are collected along the wall of the cyclone conical cylinder 26 after cyclone separation and flow into the spherical partition wall heat exchange descending return device 28 and then return to the circulating fluidized bed body 27 again, and the purified gas is guided out by the gas guide-out pipe 23 with a plug.
And step six, after sampling is finished, the gas extraction pump V stops working, in order to prevent the solution from being sucked backwards, the cyclone separator of the circulating fluidized bed type sampling pipe IV can enable the sucked gas-liquid mixture to be re-returned to the circulating fluidized bed type sampling pipe body 25 after cyclone separation, so that the subsequent sample in the absorption liquid is prevented from being influenced to be recycled and subjected to constant volume operation, and the sampling representativeness and the accuracy and precision of data analysis are further influenced.
Variations and modifications to the above-described embodiments may occur to those skilled in the art, which fall within the scope and spirit of the above description. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and variations of the present invention should fall within the scope of the claims of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
Claims (7)
1. The sampling method of the nitrogen oxides in the ambient air is characterized by comprising the following steps: step one, absorbing liquid: weighing 5.0g of sulfanilic acid, dissolving the sulfanilic acid in 200ml of 40-50 ℃ hot water, cooling the solution to room temperature, transferring the solution into a 1000ml volumetric flask, adding 50ml of N- (1-naphthyl) ethylenediamine hydrochloride with the mass concentration of 0.1% and 50ml of glacial acetic acid, diluting the solution with water to scale marks to be used as color development liquid, and mixing the solution with water according to the volume ratio of 4:1 when the solution is used temporarily; acid potassium permanganate solution: weighing 25g of potassium permanganate, dissolving in 500ml of water, adding a 1mol/L sulfuric acid isovolumetric mixed solution, naturally circulating and flowing an absorption liquid, keeping the temperature at 20 +/-4 ℃, and collecting a nitrogen oxide sample under the requirement of short-time and long-time sampling; step two, air is guided in through an air guide pipe and then impacts absorption liquid in the lower air bubbles downwards, air is uniformly distributed in the absorption liquid in the lower air bubbles along the concave structure at the bottom of the hanging basket in a dispersing mode to form countless small air bubbles, and the absorbed air is output through an air guide pipe; step three, after being guided by the gas inlet pipe, air downwards impacts the absorption liquid at the bottom of the low-branch self-circulation type sampling pipe body to form a plurality of extremely fine bubbles, and the bubbles continuously keep contact with the absorption liquid in a natural circulation flow, so that the oxidation degree of nitric oxide is improved; leading air into the gas leading-in pipe with the plug, then impacting the absorption liquid at the bottom of the gas absorption main pipe downwards to form a plurality of extremely fine bubbles, keeping the absorption liquid in constant temperature in continuous contact with the air in natural circulation and prolonging the retention time of nitrogen oxide in the absorption liquid, and leading out the gas after fully reacting with the absorption liquid through the gas leading-out pipe with the plug; step five, leading air into the circulating fluidized bed through a gas leading-in pipe with a plug, then impacting the absorption liquid at the bottom of the circulating fluidized bed downwards to form a plurality of fine bubbles, and leading out the purified gas through a gas leading-out pipe with a plug; and step six, after sampling is finished, the gas extraction pump stops working, in order to prevent the solution from being sucked backwards, the cyclone separator of the circulating fluidized bed type sampling pipe can enable the sucked gas-liquid mixture to be re-returned to the circulating fluidized bed type sampling pipe body after cyclone separation, so that the subsequent sample in the absorption liquid is prevented from being influenced to carry out recovery and constant volume work, and the sampling representativeness and the accuracy and precision of data analysis are further influenced.
2. The method of sampling ambient air nitrogen oxides as recited in claim 1, wherein: according to the order of collecting nitrogen dioxide and nitric oxide in turn, the following four sampling pipes are connected in series in turn, nitrogen dioxide is collected by a cradle self-circulation type sampling pipe, absorption liquid is filled in the sampling pipe, a low-branch self-circulation type sampling pipe is used as an oxidation gas washing bottle, the acid potassium permanganate solution is filled in the sampling pipe, and nitric oxide and the absorption liquid are collected by a high-branch self-circulation type sampling pipe and a circulating fluidized bed type sampling pipe.
3. The method of sampling ambient air nitrogen oxides as recited in claim 1, wherein: the absorption liquid in the lower bubble contacts with air, mass transfer and turnover are carried out to form a gas-liquid mixture, the gas-liquid mixture rises to the upper bubble along the calandria in the hanging basket, and the density difference exists between the gas-liquid mixture in the calandria in the hanging basket and the absorption liquid in the spherical partition wall heat exchange descending pipe, so that the absorption liquid in the spherical partition wall heat exchange descending pipe is driven by the static pressure difference to flow into the lower bubble from the upper bubble.
4. The method of sampling ambient air nitrogen oxides as recited in claim 1, wherein: the absorption liquid flows in a natural circulation way in the circulation loop in the absorption bottle, the bubbles naturally and circularly flow along with the absorption liquid until the bubbles grow into larger bubbles and then are broken on the liquid level, and the gas-liquid contact time is prolonged, so that the absorption efficiency is improved.
5. The method of sampling ambient air nitrogen oxides as recited in claim 1, wherein: air and absorption liquid fully contact and turn over to form bubbles to rise along the liquid column of the sampling tube body with the low branch self-circulation mode, the grown bubbles are broken and extinguished near the scale liquid level, fine bubbles naturally and circularly flow along with the absorption liquid, and due to the fact that density difference exists between a gas-liquid mixture with the sampling tube body with the low branch self-circulation mode and the absorption liquid in the spherical partition wall heat exchange descending circulation tube, static pressure difference between the gas-liquid mixture and the absorption liquid drives the absorption liquid in the spherical partition wall heat exchange descending circulation tube to flow back into the sampling tube body with the low branch self-circulation.
6. The method of sampling ambient air nitrogen oxides as recited in claim 1, wherein: air and absorption liquid fully contact and are overturned to form bubbles which rise along a liquid column of the gas absorption main pipe, the grown bubbles are broken near the liquid level of the scale, fine bubbles naturally and circularly flow along with the absorption liquid, and the static pressure difference between the gas-liquid mixture of the gas absorption main pipe and the absorption liquid in the spherical partition wall heat exchange descending backflow pipe drives the absorption liquid in the spherical partition wall heat exchange descending backflow pipe to flow back into the gas absorption main pipe from the gas absorption branch pipe.
7. The method of sampling ambient air nitrogen oxides as recited in claim 1, wherein: air and absorption liquid are fully contacted and stirred to form bubbles which rise along a liquid column of the circulating fluidized bed body, the bubbles are broken near the liquid level of the scale, air flow tangentially enters the cyclone cone cylinder, liquid drops in the air are subjected to cyclone separation and then are converged along the wall of the cyclone cone cylinder to flow into the spherical partition wall for heat exchange and then fall back to the circulating fluidized bed body again.
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