High-concentration nitrogen oxide treatment system and treatment method

Abstract

The invention relates to a high-concentration nitrogen oxide treatment system and method.The system comprises an oxidation tower, an absorption tower, a neutralizing tower, a heat exchanger, a first draught fan, a second draught fan and a third draught fan, the bottom of the oxidation tower is connected with a gas inlet pipe, and the top of the oxidation tower is provided with a first gas feeding pipe connected to the bottom of the absorption tower; the heat exchanger and the first fan are arranged on the first air supply pipe, the top of the absorption tower is provided with a second air supply pipe connected to the bottom of the neutralizing tower, the second fan is arranged on the second air supply pipe, the top of the neutralizing tower is provided with an exhaust pipe, and the third fan is arranged on the exhaust pipe. The method comprises the steps of oxidation, cooling, absorption and neutralization. According to the system, nitrogen oxides in waste gas are subjected to large-scale adsorption treatment by using fewer series tower structures, so that the treatment result of a multi-stage series tower structure is achieved, and the cost of the system is saved. According to the treatment method, introduction of other elements can be reduced while nitric oxide is treated, dilute nitric acid is recycled, and energy conservation and emission reduction are achieved.

Description

Technical Field

[0001] The present invention relates to the field of environmental protection technology, and in particular to a high-concentration nitrogen oxide treatment system and method. Background Art

[0002] Nitrogen oxides (NO x ) Common components in tail gas include nitric oxide (NO), dinitrogen monoxide (N2O), nitrogen dioxide (NO2), dinitrogen trioxide (N2O3), dinitrogen tetroxide (N2O4), dinitrogen pentoxide (N2O5), etc. They are common air pollutants. Among them, nitric oxide and nitrogen dioxide are relatively common components. The composition of this exhaust gas is complex and it is also one of the main causes of acid rain. The treatment methods of nitrogen oxides include reduction method, plasma activation method, biochemical method, adsorption method and liquid absorption method. The liquid absorption method is a method of purifying the exhaust gas by absorbing nitrogen oxides in the exhaust gas with water or aqueous solutions of acid, alkali and salt. At present, most of the devices for treating nitrogen oxide tail gas are large-scale multi-stage alkaline spray washing tower devices, which have problems such as large equipment, high operating cost and poor mass transfer effect; and because the reaction and absorption of NaOH on NO2 and NO are limited, the treated exhaust gas still contains nitrogen oxides and sour taste, and the treatment effect cannot be achieved. Reducing agents are used during the redox method, and gases such as ammonia and hydrogen sulfide are inevitably produced during the reaction and decomposition process, causing new pollution.

[0003] Chinese patent CN217829533U discloses a system for reducing nitrogen oxides in tail gas. The system uses an oxidation tower and a seven-stage alkali absorption tower. The pipeline structure is complex and the cost is high. The best state in the embodiment cannot guarantee a high NO x Absorption rate.

[0004] Therefore, it is necessary to develop a new system and process to solve the above problems. Summary of the invention

[0005] The main purpose of the present invention is to provide a high-concentration nitrogen oxide treatment system, which can use fewer series tower structures to perform large-scale adsorption treatment on nitrogen oxides in exhaust gas, and the system cost is low.

[0006] The present invention achieves the above-mentioned purpose through the following technical scheme: a high-concentration nitrogen oxide treatment system, comprising an oxidation tower, an absorption tower, a neutralization tower, a heat exchanger, a first fan, a second fan and a third fan, the bottom of the oxidation tower is connected to an air inlet pipe, the top of the oxidation tower is provided with a first air supply pipe connected to the bottom of the absorption tower, the heat exchanger and the first fan are arranged on the first air supply pipe, the top of the absorption tower is provided with a second air supply pipe connected to the bottom of the neutralization tower, the second fan is arranged on the second air supply pipe, the top of the neutralization tower is provided with an exhaust pipe, and the third fan is arranged on the exhaust pipe.

[0007] Specifically, a first spray port and a second spray port are provided at the upper portion of the oxidation tower, a first pH sensor and an ORP potentiometer are provided at the lower portion of the oxidation tower, the first pH sensor obtains the pH value of the liquid in the tower and is used to control the switch of the first spray port, the ORP potentiometer obtains the redox potential value of the liquid in the tower and is used to control the switch of the second spray port, the oxidation tower is provided with a first circulation pipe connecting the top and the bottom, and the first circulation pipe is provided with a first circulation pump that pumps the liquid in the tower from the bottom to the top.

[0008] Specifically, a third spray port is provided at the top of the absorption tower, a second circulation pipe connecting the top and the bottom is provided on the absorption tower, and a second circulation pump for pumping the liquid in the tower from the bottom to the top is provided on the second circulation pipe.

[0009] Specifically, a fourth spray port is provided at the top of the neutralization tower, a second pH sensor is provided at the bottom of the neutralization tower, the second pH sensor obtains the pH value of the liquid in the tower and is used to control the switch of the fourth spray port, and a third circulation pipe connecting the top and the bottom is provided on the neutralization tower, and the third circulation pipe is provided with a third circulation pump for pumping the liquid in the tower from the bottom to the top.

[0010] Another main purpose of the present invention is to provide a method for treating high-concentration nitrogen oxides, which can reduce the introduction of other elements while treating the nitrogen oxides, and recover dilute nitric acid, thereby saving energy and reducing emissions.

[0011] The present invention achieves the above-mentioned purpose through the following technical scheme: A method for treating high-concentration nitrogen oxides, comprising the following steps:

[0012] S1, oxidation: under room temperature, NaOH solution is added into the oxidation tower through the first spray port to control the pH in the tower to be greater than 10.5, and NaClO solution is added into the oxidation tower through the second spray port to control the ORP in the tower to be greater than 300mV. The first fan draws nitrogen oxides into the oxidation tower for oxidation treatment to obtain primary exhaust gas;

[0013] S2, cooling: The second fan draws the primary exhaust gas into the heat exchanger, reducing the temperature of the primary exhaust gas to 10-25℃ before entering the absorption tower;

[0014] S3, absorption: adding reclaimed water into the absorption tower through the third spray port, so that the primary waste gas reacts with the reclaimed water to obtain dilute nitric acid and secondary waste gas;

[0015] S4, neutralization: under room temperature, add NaOH solution into the neutralization tower through the fourth spray port to control the pH in the tower to be greater than 10.5. The third fan draws the secondary exhaust gas into the neutralization tower, and the tail gas is obtained after passing through the NaOH solution, and the tail gas is discharged into the atmosphere.

[0016] Specifically, the concentration of the NaOH solution is 30-50 wt %, and the concentration of the NaClO solution is 10-13 wt %.

[0017] The beneficial effects of the technical solution of the present invention are:

[0018] 1. This system uses fewer series tower structures to carry out large-scale adsorption treatment of nitrogen oxides in exhaust gas, achieving the treatment results of a multi-stage series tower structure, saving system costs.

[0019] 2. This treatment method can reduce the introduction of other elements while treating nitrogen oxides, and recycle dilute nitric acid, saving energy and reducing emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a piping diagram of a high-concentration nitrogen oxide treatment system of an embodiment.

[0021] The numbers in the figure represent:

[0022] 1a-oxidation tower, 1b-absorption tower, 1c-neutralization tower;

[0023] 2-Heat exchanger;

[0024] 3a-first fan, 3b-second fan, 3c-third fan;

[0025] 4a-intake pipe, 4b-first air supply pipe, 4c-second air supply pipe, 4d-exhaust pipe;

[0026] 5a-first spray port, 5b-second spray port, 5c-third spray port, 5d-fourth spray port;

[0027] 6a-first pH sensor, 6b-second pH sensor;

[0028] 7-ORP potentiometer;

[0029] 8a-first circulation pipe, 8b-second circulation pipe, 8c-third circulation pipe;

[0030] 9a - the first circulation pump, 9b - the second circulation pump, 9c - the third circulation pump. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below with reference to specific embodiments.

[0032] Example:

[0033] like Figure 1 As shown, a high-concentration nitrogen oxide treatment system of the present invention includes an oxidation tower 1a, an absorption tower 1b, a neutralization tower 1c, a heat exchanger 2, a first fan 3a, a second fan 3b and a third fan 3c. The bottom of the oxidation tower 1a is connected to an air inlet pipe 4a, the top of the oxidation tower 1a is provided with a first air supply pipe 4b connected to the bottom of the absorption tower 1b, the heat exchanger 2 and the first fan 3a are arranged on the first air supply pipe 4b, the top of the absorption tower 1b is provided with a second air supply pipe 4c connected to the bottom of the neutralization tower 1c, the second fan 3b is arranged on the second air supply pipe 4c, the top of the neutralization tower 1c is provided with an exhaust pipe 4d, and the third fan 3c is arranged on the exhaust pipe 4d.

[0034] Three fans are used to make the waste gas to be treated pass through the oxidation tower 1a, heat exchanger 2, absorption tower 1b and neutralization tower 1c in sequence. The nitrogen oxides in the waste gas are oxidized into nitrogen dioxide through the oxidation tower 1a. The heat exchanger 2 reduces the temperature of the nitrogen dioxide, which is then absorbed and converted into nitrogen monoxide in the absorption tower 1b. Finally, the neutralization tower 1c absorbs the nitrogen monoxide and nitrogen dioxide into salt.

[0035] like Figure 1 As shown, a first spray port 5a and a second spray port 5b are provided at the upper portion of the oxidation tower 1a, a first pH sensor 6a and an ORP potentiometer 7 are provided at the lower portion of the oxidation tower 1a, the first pH sensor 6a obtains the pH value of the liquid in the tower and is used to control the switch of the first spray port 5a, the ORP potentiometer 7 obtains the redox potential value of the liquid in the tower and is used to control the switch of the second spray port 5b, the oxidation tower 1a is provided with a first circulation pipe 8a connecting the top and the bottom, and the first circulation pipe 8a is provided with a first circulation pump 9a for pumping the liquid in the tower from the bottom to the top.

[0036] The first spray port 5a is used to provide alkaline solution NaOH to remove acidic gases in the exhaust gas and keep the reaction environment of the oxidant in a strong alkaline state. The first pH sensor 6a can detect whether the liquid in the tower maintains a strong alkalinity to prevent NaClO from self-decomposing under acidic conditions. The second spray port 5b is used to provide the oxidant NaClO to reduce nitrogen oxides into NO2 in an alkaline and weak potential environment, thereby making the gas composition entering the absorption tower 1b relatively simple. Because the reaction always occurs after the gas contacts the solution, the concentration of the substance in the solution will gradually become uneven. The first circulation pump 9a makes the liquid in the oxidation tower 1a flow up and down and mix, so that the first pH sensor 6a and the ORP potentiometer 7 are sensitive to changes in the conditions in the tower, so that the reagents can be replenished in time to promote a more complete reaction of nitrogen oxides.

[0037] like Figure 1 As shown, a third spray port 5c is provided at the top of the absorption tower 1b, a second circulation pipe 8b connecting the top and the bottom is provided on the absorption tower 1b, and a second circulation pump 9b for pumping the liquid in the tower from the bottom to the top is provided on the second circulation pipe 8b.

[0038] The nitrogen element treated by the oxidation tower 1a will basically exist in the form of nitrogen dioxide. The absorption tower 1b will allow the nitrogen dioxide to react with water to generate dilute nitric acid and nitric oxide. The second circulation pump 9b mixes the solution in the absorption tower 1b so that the nitrogen dioxide can fully contact with water and improve the absorption efficiency.

[0039] like Figure 1 As shown, a fourth spray port 5d is provided at the top of the neutralization tower 1c, a second pH sensor 6b is provided at the bottom of the neutralization tower 1c, the second pH sensor 6b obtains the pH value of the liquid in the tower and is used to control the switch of the fourth spray port 5d, and a third circulation pipe 8c connecting the top and the bottom is provided on the neutralization tower 1c, and a third circulation pump 9c for pumping the liquid in the tower from the bottom to the top is provided on the third circulation pipe 8c.

[0040] Most of the nitrogen treated by the absorption tower 1b will remain in the absorption tower 1b as nitric acid, and a small part will enter the neutralization tower 1c in the form of nitric oxide and nitrogen dioxide. The sodium hydroxide in the neutralization tower 1c will form sodium nitrate and sodium nitrite with the two, thereby more thoroughly removing the nitrogen in the tail gas. The third circulation pump 9c mixes the solution in the neutralization tower 1c so that the gas can fully contact with the NaOH solution to improve the absorption efficiency.

[0041] The steps for treating high concentrations of nitrogen oxides are as follows:

[0042] S1. Under room temperature, NaOH solution is added into the oxidation tower 1a through the first spray port 5a to control the pH in the tower to be greater than 10.5. At the same time, NaClO solution is added into the oxidation tower 1a through the second spray port 5b to control the ORP in the tower to be greater than 300mV. The first fan 3a draws nitrogen oxides into the oxidation tower 1a for oxidation treatment to obtain primary exhaust gas.

[0043] The main reaction occurring in oxidation tower 1a is: NaClO+NO→NO2+NaCl.

[0044] This reaction can oxidize nitrogen monoxide, which accounts for a large proportion of the exhaust gas, into nitrogen dioxide, which is easier to react with water to obtain nitric acid. Because the processing capacity of the oxidation tower 1a is relatively large, the reaction conditions need to be controlled. Because nitrogen dioxide is an acidic gas, it will consume sodium hydroxide to some extent, so in order to ensure the continuity of the treatment, the solution needs to maintain alkaline conditions. The first pH sensor 6a will monitor the pH of the solution in the oxidation tower 1a in real time. When the sodium hydroxide is lost and the pH drops below 10.5, the first spray port 5a will replenish the alkali solution to return the pH to above 10.5. The potential can affect the oxidation efficiency of sodium hypochlorite, so it also needs to be maintained above 300mV. If the ORP (oxidation-reduction potential) is lower than this value, the second spray port 5b needs to be supplemented with sodium hypochlorite solution. This can improve the stability of the reaction in the oxidation tower 1a.

[0045] S2, the second fan 3b draws the primary exhaust gas into the heat exchanger 2, so that the temperature of the primary exhaust gas is reduced to 10-25°C before entering the absorption tower 1b.

[0046] Because the reaction between nitrogen dioxide and water is a partially reversible reaction, too high a temperature will cause the newly generated dilute nitric acid to decompose into NO2 again, resulting in a decrease in absorption efficiency. Therefore, it is necessary to use a heat exchanger 2 to reduce the temperature of nitrogen dioxide so that the temperature of the absorption tower 1b can be stably kept in a safe state.

[0047] S3. Adding reclaimed water into the absorption tower 1b through the third spray port 5c causes the primary waste gas to react with the reclaimed water to obtain dilute nitric acid and secondary waste gas.

[0048] The main reaction occurring in absorption tower 1b is: 3NO2+H2O→2HNO3+NO.

[0049] The solution in the absorption tower 1b is in contact with nitrogen dioxide in a continuous cycle. The nitrogen in the nitrogen dioxide undergoes a disproportionation reaction, 2 / 3 of which will be transferred to nitric acid and then remain in the absorption tower 1b, and the other 1 / 3 of the nitrogen will be reduced to nitric oxide and further adsorbed in the neutralization tower 1c. When the nitric acid accumulates to a certain amount in the adsorption tower 1b, it can be discharged and recycled as dilute nitric acid, which is simple to handle.

[0050] S4. At room temperature, NaOH solution is added into the neutralization tower 1c through the fourth spray port 5d to control the pH in the tower to be greater than 10.5. The third fan 3c draws the secondary exhaust gas into the neutralization tower 1c, and the tail gas is obtained after passing through the NaOH solution, and the tail gas is discharged into the atmosphere.

[0051] The main reaction occurring in the neutralization tower 1c is: NO+NO2+2NaOH→2NaNO2+H2O.

[0052] There is a slight excess of nitrogen dioxide, but it will also participate in the reaction. The product sodium nitrite dissolves in water and can be simply collected and processed. Theoretically, there will be no nitrogen oxide residue in this step, and the nitrogen content in the tail gas will be less than 100ppm, which can directly meet the national tail gas emission standards.

[0053] The concentration of the NaOH solution used in this embodiment is 30-50 wt %, and the concentration of the NaClO solution is 10-13 wt %. The reagents are easy to obtain and the concentration control is simple.

[0054] This system uses a relatively small number of series-connected tower structures to perform large-scale adsorption treatment on nitrogen oxides in the exhaust gas, achieving the treatment results of a multi-stage series-connected tower structure, saving system costs. The treatment method can reduce the introduction of other elements while treating nitrogen oxides, and recycle dilute nitric acid, saving energy and reducing emissions.

[0055] The above are only some embodiments of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the creative concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A high concentration nitrogen oxide treatment system, characterized in that: The invention comprises an oxidation tower, an absorption tower, a neutralization tower, a heat exchanger, a first fan, a second fan and a third fan. The bottom of the oxidation tower is connected to an air inlet pipe. The top of the oxidation tower is provided with a first air supply pipe connected to the bottom of the absorption tower. The heat exchanger and the first fan are arranged on the first air supply pipe. The top of the absorption tower is provided with a second air supply pipe connected to the bottom of the neutralization tower. The second fan is arranged on the second air supply pipe. The top of the neutralization tower is provided with an exhaust pipe, and the third fan is arranged on the exhaust pipe.

2. The high concentration nitrogen oxide treatment system according to claim 1, characterized in that: The upper part of the oxidation tower is provided with a first spray port and a second spray port, the lower part of the oxidation tower is provided with a first pH sensor and an ORP potentiometer, the first pH sensor obtains the pH value of the liquid in the tower and is used to control the switch of the first spray port, the ORP potentiometer obtains the redox potential value of the liquid in the tower and is used to control the switch of the second spray port, the oxidation tower is provided with a first circulation pipe connecting the top and the bottom, and the first circulation pipe is provided with a first circulation pump for pumping the liquid in the tower from the bottom to the top.

3. The high concentration nitrogen oxide treatment system according to claim 1, characterized in that: The top of the absorption tower is provided with a third spray port, the absorption tower is provided with a second circulation pipe connecting the top and the bottom, and the second circulation pipe is provided with a second circulation pump for pumping the liquid in the tower from the bottom to the top.

4. The high concentration nitrogen oxide treatment system according to claim 1, characterized in that: A fourth spray port is provided at the top of the neutralization tower, and a second pH sensor is provided at the bottom of the neutralization tower. The second pH sensor obtains the pH value of the liquid in the tower and is used to control the switch of the fourth spray port. A third circulation pipe connecting the top and the bottom is provided on the neutralization tower, and a third circulation pump is provided on the third circulation pipe to pump the liquid in the tower from the bottom to the top.

5. A method for treating high concentration nitrogen oxides using the system according to any one of claims 1 to 4, characterized in that the steps include: S1. Under room temperature, NaOH solution is added into the oxidation tower through the first spray port to control the pH in the tower to be greater than 10.

5. At the same time, NaClO solution is added into the oxidation tower through the second spray port to control the ORP in the tower to be greater than 300mV. The first fan draws nitrogen oxides into the oxidation tower for oxidation treatment to obtain primary exhaust gas. S2, the second fan draws the primary exhaust gas into the heat exchanger, reducing the temperature of the primary exhaust gas to 10-25℃ before entering the absorption tower; S3, adding reclaimed water into the absorption tower through the third spray port, so that the primary waste gas reacts with the reclaimed water to obtain dilute nitric acid and secondary waste gas; S4. Under room temperature, NaOH solution is added into the neutralization tower through the fourth spray port to control the pH in the tower to be greater than 10.

5. The third fan draws the secondary exhaust gas into the neutralization tower, and the tail gas is obtained after passing through the NaOH solution, and the tail gas is discharged into the atmosphere.

6. The method for treating high concentration nitrogen oxides according to claim 5, characterized in that: The concentration of the NaOH solution is 30-50 wt %, and the concentration of the NaClO solution is 10-13 wt %.

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