A method and device for determining total nitrogen in exhaust gas of stationary pollution source by gas-phase molecular absorption spectrum-naphthalene ethylenediamine hydrochloride spectrophotometry

Abstract

This invention provides a gas-phase molecular absorption spectrometry-naphthylethylenediamine hydrochloride spectrophotometric method for determining total nitrogen in waste gas from stationary pollution sources. The method comprises the following steps: S1. Reacting the waste gas with an oxidant; S2. Using an absorbent, further reacting the waste gas after S1; S3. Collecting the oxidant after S1, pretreating it to reduce nitrogen-containing compounds to nitric oxide, and detecting the total nitrogen content I; S4. Collecting the absorbent after S2 to obtain the total nitrogen content II; S5. Summing the total nitrogen content I and total nitrogen content II to obtain the total nitrogen content in the current waste gas. This method enables accurate determination of total nitrogen in waste gas from stationary pollution sources.

Description

Technical Field

[0001] This invention relates to the field of instrumental analysis, specifically to a gas-phase molecular absorption spectroscopy-naphthylethylenediamine hydrochloride spectrophotometric method for determining total nitrogen in waste gas from stationary pollution sources. Background Technology

[0002] With the basic completion of ultra-low emission retrofitting in key steel enterprises in major regions, there is an urgent need to address the technical challenges in the ultra-low emission retrofitting and assessment monitoring of steel enterprises. However, the scientific support for oxidation denitrification processes is currently insufficient, actual desulfurization and denitrification systems are complex, and there are very few reports on nitrogen balance studies based on actual waste gas.

[0003] Nitrogen balance refers to the sum of nitrogen input from materials = total nitrogen in flue gas + total nitrogen from dust removal.

[0004] Currently, the ecological and environmental quality standards do not specify the limit for total nitrogen in flue gas from stationary pollution sources. However, there is a lack of corresponding manual analysis methods for total nitrogen in flue gas from stationary pollution sources both domestically and internationally, making it impossible to effectively assess the nitrogen balance problem in the oxidation and denitrification process. Existing manual analysis methods for nitrogen oxides cannot completely determine the total nitrogen in flue gas. Summary of the Invention

[0005] This invention aims to overcome the aforementioned shortcomings by establishing a gas-phase molecular absorption spectrometry method for determining total nitrogen in oxidizing solutions using a two-stage oxidation tube and a three-stage absorption tube absorption system. When the sampling volume is 2.5 L, the detection limit for total nitrogen is 3 mg / m³. 3 This invention effectively supports the ultra-low emission retrofitting of steel enterprises and the evaluation and monitoring of oxidative denitrification processes in sintering mills. Based on the method of this invention, a technical basis and data foundation are established to evaluate the feasibility of oxidative denitrification technology.

[0006] This invention provides a gas-phase molecular absorption spectroscopy-naphthylethylenediamine hydrochloride spectrophotometric determination method for total nitrogen in waste gas from stationary pollution sources, characterized by comprising the following steps:

[0007] S1. Ensure the waste gas reacts fully with the oxidant;

[0008] S2. An absorbent is used to further react the waste gas after the reaction in S1;

[0009] S3. Collect the oxidized liquid after the reaction in S1, pre-treat it, reduce the nitrogen-containing compounds in it to nitric oxide, and detect the total nitrogen content I.

[0010] S4. Collect the absorbent solution after the S2 reaction to obtain the total nitrogen content II;

[0011] S5. The sum of total nitrogen content I and total nitrogen content II is the total nitrogen content in the current exhaust gas.

[0012] Furthermore, the present invention provides a gas-phase molecular absorption spectroscopy-naphthylethylenediamine hydrochloride spectrophotometric determination method for total nitrogen in stationary pollution source exhaust gas, characterized in that:

[0013] The oxidant in S1 is acidic potassium permanganate.

[0014] Furthermore, the present invention provides a gas-phase molecular absorption spectroscopy-naphthylethylenediamine hydrochloride spectrophotometric determination method for total nitrogen in stationary pollution source exhaust gas, characterized in that:

[0015] The absorbent in S2 is prepared from glacial acetic acid, p-aminobenzenesulfonic acid, and naphthylethylenediamine hydrochloride.

[0016] Furthermore, the present invention provides a gas-phase molecular absorption spectroscopy-naphthylethylenediamine hydrochloride spectrophotometric determination method for total nitrogen in stationary pollution source exhaust gas, characterized in that:

[0017] The oxidizing solution in S3 is pretreated as follows:

[0018] S3-0. In an environment of 60-90℃, add oxalic acid to the oxidation solution in portions until it becomes clear. Adjust the pH to neutral and centrifuge to separate the supernatant.

[0019] Specifically, preheat the solution in a constant temperature water bath (80℃±5℃) for 2 minutes. Add oxalic acid to the oxidation solution in small amounts several times while continuously shaking (or stirring with a glass rod). The color of the oxidation solution gradually changes from purple to black until it becomes colorless, clear, and transparent. Add a small amount of 50% NaOH and stir well until a stable white flocculent precipitate appears and the pH is neutral. Transfer the entire oxidation solution to a 50ml centrifuge tube, centrifuge at 4000rpm for 5 minutes, and then analyze the supernatant.

[0020] S3-1. Add alkaline persulfate, such as potassium persulfate or sodium persulfate, to the supernatant sample. The amount used is usually determined by the volume of the absorption solution, generally 10 ml of alkaline persulfate per 50 ml of sample, or in other words, 10 ml of alkaline persulfate solution should be added for every 5-150 μg of total nitrogen (alkaline persulfate solution: weigh 40 g of potassium persulfate and 15 g of sodium hydroxide, dissolve in ammonia-free water, and dilute to 1000 ml).

[0021] S3-2. It is digested and oxidized into nitrate; for digestion, traditional methods such as ultraviolet digestion, high temperature and high pressure digestion, and microwave digestion can be used.

[0022] S3-3 is reduced to nitric oxide by a reducing agent.

[0023] Furthermore, the present invention provides a gas-phase molecular absorption spectroscopy-naphthylethylenediamine hydrochloride spectrophotometric determination method for total nitrogen in stationary pollution source exhaust gas, characterized in that:

[0024] For the absorbent in S4, the total nitrogen content II is calculated based on the fact that the absorbance of the azo dye at a wavelength of 540 nm is proportional to the nitrogen dioxide content.

[0025] Furthermore, the present invention provides a gas-phase molecular absorption spectroscopy-naphthylethylenediamine hydrochloride spectrophotometric determination device for total nitrogen in waste gas from stationary pollution sources, characterized in that:

[0026] It includes an oxidation unit and an absorption unit arranged sequentially along the direction of waste gas flow;

[0027] The oxidation unit includes at least two sets of oxidation devices;

[0028] The absorption unit includes at least two sets of absorption devices.

[0029] Furthermore, the present invention provides a gas-phase molecular absorption spectroscopy-naphthylethylenediamine hydrochloride spectrophotometric determination device for total nitrogen in waste gas from stationary pollution sources, characterized in that:

[0030] Water stop valves are installed between each device. Attached Figure Description

[0031] Figure 1 This embodiment provides a schematic diagram of a gas phase molecular absorption spectroscopy-naphthylethylenediamine hydrochloride spectrophotometric device for measuring total nitrogen in waste gas from stationary pollution sources. Detailed Implementation

[0032] This invention is capable of various modifications and embodiments, and therefore specific embodiments are illustrated and described in the accompanying drawings. However, this is not intended to limit the invention to specific implementations, but should be understood to include all modifications, equivalents, and even substitutions that fall within the spirit and scope of this invention.

[0033] This embodiment provides a gas phase molecular absorption spectroscopy-naphthylethylenediamine hydrochloride spectrophotometric device for measuring total nitrogen in waste gas from stationary pollution sources, which includes an oxidation unit and an absorption unit arranged sequentially along the direction of waste gas flow.

[0034] In this embodiment, the oxidation unit includes two sets of oxidation devices connected in series. More oxidation devices can be added depending on the specific usage environment and the requirement for higher precision. That is, the absorption of absorbable nitrogen-containing substances and the full oxidation of nitrogen-containing substances can be achieved by using more oxidation bottles.

[0035] In this embodiment, the absorption unit has three sets of absorption devices. Depending on the specific usage environment and the requirement for higher precision, more absorption devices can be added; that is, more absorption bottles can be used to achieve full absorption of the absorbable nitrogen-containing substances.

[0036] Each device is equipped with a water stop valve, and its end has a pump to achieve forward airflow.

[0037] The specific usage methods of the above equipment are as follows:

[0038] In this embodiment, the total nitrogen in the exhaust gas from the stationary pollution source (the sum of nitrogen oxides and other nitrogen-containing compounds in gaseous form, excluding nitrogen gas, and expressed as N) first passes through a two-stage series oxidation bottle after the sampling tube, and a portion of it is oxidized and absorbed by the acidic potassium permanganate solution in the oxidation bottle (e.g., low-valence nitrogen oxides or high-valence nitrogen oxides that are easily soluble in water).

[0039] The oxidizing solution sample was transferred to a 250 ml Erlenmeyer flask. The flask was preheated in a constant temperature water bath (80℃±5℃) for 2 minutes, then removed. Oxalic acid was added to the flask in small, repeated additions until approximately 2.49 g was reached (the amount added may be adjusted according to different samples), while continuously shaking (or stirring with a glass rod). The color of the oxidizing solution gradually changed from purple to black until it became colorless, clear, and transparent. A small amount of 50% NaOH was added and stirred until a stable white flocculent precipitate appeared, and the pH was neutral. The entire oxidizing solution was then transferred to a 50 ml centrifuge tube and centrifuged at 4000 rpm for 5 minutes. The supernatant was then collected for analysis. Add alkaline potassium persulfate (alkaline potassium persulfate solution: weigh 40g potassium persulfate and 15g sodium hydroxide, dissolve in ammonia-free water, and dilute to 1000ml. The solution can be stored in a polyethylene bottle for one week. Add 10ml of alkaline potassium persulfate solution to every 5-150μg of total nitrogen.) to the supernatant sample. After online UV digestion and oxidation to nitrate, the nitrate is then reduced to nitric oxide by titanium trichloride. The nitric oxide is carried into the absorber tube of a gas phase molecular absorption spectrometer using a carrier gas, and the total nitrogen mass absorbed by the acidic potassium permanganate solution in the oxidation bottle is analyzed and calculated at a wavelength of 214.4nm.

[0040] The remaining waste gas is converted into nitrogen dioxide after passing through a two-stage series oxidation process. It is then absorbed and reacted by a subsequent three-stage series absorbent (the absorbent is the same as that used in traditional nitrogen and oxygen determination, which is prepared from glacial acetic acid, p-aminobenzenesulfonic acid, and naphthylethylenediamine hydrochloride) to generate a pink azo dye. The absorbance of the generated azo dye at a wavelength of 540 nm is directly proportional to the nitrogen dioxide content. The total mass of nitrogen absorbed in the absorption bottle is then calculated.

[0041] The total nitrogen concentration (in N) in the exhaust gas from a stationary pollution source is the sum of the total nitrogen mass in the secondary series oxidizing liquid and the tertiary series absorbent liquid, divided by the sampling volume under standard conditions.

[0042] Specific experiments are as follows:

[0043] Total nitrogen (TNO) in the exhaust gas from a company's denitrification project was monitored for three consecutive days. The manual analysis method for TNO followed the declared method. The sampling and analysis conditions were as follows: a five-stage absorption tube system was connected in series during sampling, and samples were collected using a constant flow sampling method (sampling flow rate of 0.5 L / min, single sampling time of 5 min). The first and second stages used acidic potassium permanganate oxidation solution (concentration and preparation referenced HJ479), and were determined using gas phase molecular absorption spectrometry (referenced HJ / T199). The third, fourth, and fifth stages used naphthylethylenediamine hydrochloride absorption solution (concentration and preparation referenced HJ43), and were determined using naphthylethylenediamine hydrochloride spectrophotometry (referenced HJ43). The total nitrogen content was obtained by summing the nitrogen content in the five absorption tubes. To reduce the impact of fluctuations in production conditions, in accordance with the "Technical Specification for Monitoring Stationary Source Exhaust Gas" (HJ / T397-2007), three samples were collected at equal time intervals within one hour each day, and the average value was taken.

[0044] Data analysis results show that, using the method described in this embodiment to monitor the actual flue gas outlet, the nitrogen oxide concentration (converted from total nitrogen) measured by gas-phase molecular absorption spectrometry in the dual-phase (oxidizing liquid) system was 2.09 mg / m³. 3 The concentration of nitrogen oxides in the triplet (absorption solution) was determined to be 13.43 mg / m³ using spectrophotometry. 3 This indicates that there is a certain amount of nitrogen-containing substances in the 2-phase (oxidation solution), which was previously overlooked due to a lack of analytical methods.

[0045] While the foregoing has focused on embodiments, these are merely illustrative and do not limit the invention. Those skilled in the art will understand that various modifications and applications not illustrated above can be made without departing from the essential characteristics of these embodiments. For example, the constituent elements specifically shown in the embodiments can be implemented through modifications. Furthermore, various differences related to such modifications and applications should be interpreted as being included within the scope of the invention as defined in the appended claims.

Claims

1. A gas-phase molecular absorption spectroscopy-naphthylethylenediamine hydrochloride spectrophotometric method for determining total nitrogen in waste gas from stationary pollution sources, characterized in that, It includes the following steps: S1. The waste gas is first reacted fully with an oxidant, wherein the oxidant is an acidic potassium permanganate solution; S2. An absorbent is used to further react the waste gas after the reaction in S1. The absorbent is prepared from glacial acetic acid, p-aminobenzenesulfonic acid and naphthylethylenediamine hydrochloride. S3. Collect the oxidized liquid after reaction S1, and after pretreatment, reduce the nitrogen-containing compounds in it to nitric oxide. The total nitrogen content (I) is determined by gas phase molecular absorption spectrometry. The oxidized liquid undergoes the following pretreatment: S3-0. In an environment of 60-90℃, add oxalic acid to the oxidation solution in portions until it becomes clear. Adjust the pH to neutral and centrifuge to separate the supernatant. S3-1. Add alkaline persulfate to the supernatant sample; S3-2 is oxidized to nitrates by ultraviolet light digestion; S3-3. Reduced to nitric oxide by a reducing agent; S4. Collect the absorbent solution after reaction S2 and determine the total nitrogen content II by the naphthylethylenediamine hydrochloride spectrophotometric method. S5. The sum of total nitrogen content I and total nitrogen content II is the total nitrogen content in the current exhaust gas.

2. The method for gas-phase molecular absorption spectroscopy-naphthylethylenediamine hydrochloride spectrophotometric determination of total nitrogen in stationary source exhaust gas as described in claim 1, characterized in that: For the absorbent in S4, the total nitrogen content II is calculated based on the fact that the absorbance of the azo dye at a wavelength of 540 nm is proportional to the nitrogen dioxide content.

3. The method for gas-phase molecular absorption spectroscopy-naphthylethylenediamine hydrochloride spectrophotometric determination of total nitrogen in stationary source exhaust gas as described in claim 1, characterized in that: An oxidation unit and an absorption unit are sequentially arranged along the direction of the waste gas flow. The oxidation unit includes at least two sets of oxidation devices; The absorption unit includes at least two sets of absorption devices.

4. The method for gas-phase molecular absorption spectroscopy-naphthylethylenediamine hydrochloride spectrophotometric determination of total nitrogen in stationary source exhaust gas as described in claim 3, characterized in that: Water stop valves are installed between each device.

Images