TWI696489B - Exhaust gas treatment method - Google Patents

Abstract

A waste gas treatment method, the waste gas contains nitrogen oxides (NO _X ) and water gas, including the following steps: chlorine dioxide generation step (a): a first supergravity device generates chlorine dioxide gas; oxidation step (b) : Oxidizing the nitrogen dioxide gas in the exhaust gas by the chlorine dioxide gas produced by the first supergravity device to obtain a pretreatment gas containing nitrogen dioxide; and absorption step (c): the pretreatment gas and an alkali The liquids are respectively introduced into a second supergravity device, so that the nitrogen dioxide in the pretreatment gas reacts with the alkaline liquid chemically. The waste gas treatment method can efficiently treat the waste gas through gas-liquid mass transfer, which not only consumes low cost, but also does not easily cause equipment damage and leakage problems.

Description

Exhaust gas treatment method

The invention relates to an exhaust gas treatment method, in particular to an exhaust gas treatment method using a supergravity device.

Nitrogen oxides (NO _X ), carbon oxides (CO _X ), sulfur oxides (SO _X ), suspended particulates (PM), etc. are generally contained in the combustion exhaust gas (i.e., flue gas) emitted through the flue The discharge of pollutants and water vapor into the air will cause many serious adverse effects on the environment and organisms, so it needs to be properly treated to reduce the content of pollutants in flue gas. In addition, because organic solvents are commonly used in industrial processes, exhaust gas containing volatile organic compounds (VOCs) (that is, process exhaust gas) is usually accompanied by emission, resulting in reduced air quality. Among them, for the treatment of waste gas containing nitrogen oxides or waste gas containing volatile organic compounds, one existing method is to use a strong oxidant (such as ozone gas) to oxidize the pollutants, and then remove them by washing with water. For example, nitrogen monoxide (NO), which accounts for the majority of nitrogen oxides in combustion exhaust gas, is oxidized to nitrogen dioxide by performing the chemical reactions shown below.

NO+O ₃ → NO ₂ +O ₂

However, the amount of ozone mole required for oxidation is at least twice that of nitric oxide, and ozone needs to be produced by high-pressure discharge or ultraviolet irradiation. Therefore, the cost of industrial treatment of large amounts of exhaust gas is quite high. In addition, ozone itself is also a pollutant that is irritating to the human body. Equipment and tools made of rubber and other materials are also destructive, which can easily lead to equipment damage (such as broken pipelines) and leakage.

Therefore, the first object of the present invention is to provide an exhaust gas treatment method that can overcome the above-mentioned shortcomings of the prior art.

Therefore, the method for treating exhaust gas containing nitrogen oxides (NO _X ) and water gas in the present invention includes the following steps: chlorine dioxide generation step (a): generating chlorine dioxide (ClO ₂ ) gas with a first supergravity device; oxidation Step (b): oxidize the nitrogen oxide in the exhaust gas with the chlorine dioxide gas generated by the first supergravity device to obtain a pre-treatment gas containing nitrogen dioxide (NO ₂ ); and absorption step (c): The pretreatment gas and an alkaline solution are respectively introduced into a second supergravity device, so that the nitrogen dioxide in the pretreatment gas reacts with the alkaline solution chemically.

Therefore, the second object of the present invention is to provide an exhaust gas treatment method. The exhaust gas treatment method containing volatile organic compounds (VOCs) of the present invention includes the following steps: chlorine dioxide generation step (a): using a first supergravity device Generate chlorine dioxide (ClO ₂ ) gas; oxidation step (b): oxidize the volatile organic compounds in the exhaust gas with the chlorine dioxide gas generated by the first supergravity device to obtain an oxidized organic product (oxidized organic products) ) Pretreatment gas; and absorption step (c): introducing the pretreatment gas and water into a second supergravity device, respectively, so that the oxidized organic product is dissolved in water.

The effect of the present invention is that the waste gas treatment method can efficiently treat nitrogen oxides in flue gas waste gas or volatile organic compounds in process waste gas through gas-liquid mass transfer, which not only consumes low cost, but also is not easy to cause equipment damage (such as The pipeline is damaged) and the problem of leakage occurs.

The content of the present invention will be described in detail below: Preferably, in this step (b), the temperature of the exhaust gas is 180° C. or lower to reduce the degree of decomposition of chlorine dioxide.

In some embodiments of the present invention, in this step (c), the chemical reaction is to convert nitrogen dioxide to nitrite and nitrate.

In some embodiments of the present invention, in this step (c), the chemical reaction is to convert nitrogen dioxide to nitrogen.

Preferably, the lye is an aqueous solution of an alkali, the alkali is selected from sodium hydroxide, potassium hydroxide, calcium hydroxide, calcium carbonate, sodium sulfite, sodium thiosulfate, sodium sulfide, urea, ammonium sulfite or Its combination.

Preferably, the second supergravity device includes a rotating packed bed, and the material of the rotating packed bed is selected from alloy, plastic, rubber or composite materials.

In some specific embodiments of the present invention, the exhaust gas treatment method further includes a recycling step (d): recovering the alkali solution after performing the chemical reaction, recirculating and introducing it into the second supergravity device to be combined with the pretreatment gas Nitrogen dioxide performs this chemical reaction.

Preferably, in the step (a), the chlorine dioxide gas is generated by mixing at least two reactive liquids in the first supergravity device.

Preferably, the pretreatment gas also contains nitric acid.

In some specific embodiments of the present invention, the exhaust gas treatment method further includes a recycling step (d): recovering the dissolved aqueous solution after performing the absorption step (c), recycling and introducing it into the second supergravity device The oxidized organic product in the treatment gas is dissolved in the absorption step (c).

(a): Step of producing chlorine dioxide

(b): oxidation step

(c): absorption step

(d): cycle steps

Other features and functions of the present invention will be clearly presented in the embodiment with reference to the drawings, where: [FIG. 1] is a flowchart of a first embodiment of the exhaust gas treatment method of the present invention; and [FIG. 2] is A flowchart of a second embodiment of the exhaust gas treatment method of the present invention.

The present invention will be further described with respect to the following embodiments, but it should be understood that these embodiments are for illustrative purposes only, and should not be construed as limitations on the implementation of the present invention.

<First embodiment>

In the first embodiment of the exhaust gas treatment method of the present invention, the exhaust gas is a flue gas exhaust gas containing nitrogen oxides (NO _X ) (the content can be 10 to 5000 ppm) and water vapor (the content is 3% or more). Referring to FIG. 1, the specific steps of the first embodiment are as follows:

Chlorine dioxide production step (a): Introduce an aqueous solution of sodium chlorite (NaClO ₂ ) (flow rate of 5 mL/min) and hydrochloric acid (flow rate of 3.6 mL/min) into a first supergravity device while introducing air to In the first super-gravity device, it is sufficiently mixed in the first super-gravity device to react and pass through gas-liquid mass transfer to generate chlorine dioxide (ClO ₂ ) gas. Among them, sodium chlorite and hydrochloric acid undergo a chemical reaction as shown below to generate chlorine dioxide.

5 NaClO ₂ +4 HCl → 4 ClO ₂ +5 NaCl+2 H ₂ O

Oxidation step (b): The chlorine dioxide gas produced by the first supergravity device oxidizes the nitrogen oxides in the flue gas to obtain a pretreatment gas containing nitrogen dioxide (NO ₂ ).

In the first embodiment, the flow rate of the flue gas is about 10 m ³ /min, which contains 27 ppm of nitrogen oxides, and is first cooled to about 90° C. and then mixed with the chlorine dioxide gas. Among them, nitric oxide (NO) in the nitrogen oxide is oxidized into nitrogen dioxide by performing the chemical reaction shown below.

5 NO+2 ClO ₂ +H ₂ O → 5 NO ₂ +2 HCl

If the amount of chlorine dioxide is excessive relative to the nitrogen oxide in the nitrogen oxide, the nitrogen dioxide in the nitrogen oxide can further undergo a chemical reaction as shown below with the chlorine dioxide gas to be oxidized to nitric acid.

5 NO ₂ +ClO ₂ +3 H ₂ O → 5 HNO ₃ +HCl

Absorption step (c): The pre-treatment gas and the aqueous solution containing sodium hydroxide and sodium sulfide (as lye) are introduced into a second super-gravity device to transmit the dioxide in the pre-treatment gas through gas-liquid mass transfer Nitrogen and remaining nitric oxide undergo chemical reactions as shown below to reduce the concentration of nitric oxide and nitrogen dioxide in the exhaust gas to 0 ppm. In the first embodiment, the second supergravity device includes a rotating packed bed, and the material of the rotating packed bed is stainless steel.

NO ₂ +NO+2 NaOH → 2 NaNO ₂ +H ₂ O

2 NO ₂ +2 NaOH → NaNO ₂ +NaNO ₃ +H ₂ O

2 NO ₂ +Na ₂ S → Na ₂ SO ₄ +N ₂

In another embodiment of the present invention (not shown in the figure), an aqueous solution of sodium sulfide is used as an alkaline solution, and the nitrogen dioxide in the pretreatment gas and the aqueous solution of sodium sulfide are carried out as follows by gas-liquid mass transfer. The chemical reaction shown.

2 NO ₂ +Na ₂ S → N ₂ +Na ₂ SO ₄

In another embodiment of the present invention (not shown), the sodium sulfite aqueous solution is used as the alkaline solution, and the nitrogen dioxide in the pretreatment gas and the sodium sulfite aqueous solution are carried out as follows by gas-liquid mass transfer. chemical reaction.

2 NO ₂ +4 Na ₂ SO ₃ → N ₂ +4 Na ₂ SO ₄

Circulation step (d): recovering the alkaline solution after the chemical reaction in the absorption step (c), recycling into the second supergravity device to perform the absorption step (c) with the nitrogen dioxide in the pretreatment gas chemical reaction.

<Second Embodiment>

In the second embodiment of the exhaust gas treatment method of the present invention, the exhaust gas is a process exhaust gas containing volatile organic compounds (VOCs) (content can be 1 ppb to 100,000 ppm). Referring to FIG. 2, the specific steps of the second embodiment are as follows:

Chlorine dioxide production step (a): Introduce an aqueous solution of sodium chlorite (NaClO ₂ ) (flow rate of 100 mL/min) and an aqueous solution of sodium persulfate (Na ₂ S ₂ O ₈ ) (flow rate of 100 mL/min) into a first In a super-gravity device, air is introduced into the first super-gravity device at the same time, so that it is fully mixed in the first super-gravity device for reaction and mass transfer through gas-liquid to generate chlorine dioxide (ClO ₂ ) gas. Among them, sodium chlorite and sodium persulfate undergo chemical reactions as shown below to generate chlorine dioxide.

2 NaClO ₂ +Na ₂ S ₂ O ₈ → 2 ClO ₂ +2 Na ₂ SO ₄

Oxidation step (b): The chlorine dioxide gas produced by the first supergravity device is used to oxidize the volatile organic compounds in the process exhaust gas to obtain a product containing oxidized organic products The pretreatment gas of oxidized organic products, and the removal rate of volatile organic compounds in the exhaust gas reaches more than 85%.

In the second embodiment, the flow rate of the process exhaust gas is about 400 m ³ /min, which contains 16 ppm of dimethyl sulfide (DMS), and its temperature is room temperature; the organic product after oxidation is soluble Dimethyl sulfoxide (DMSO) in water.

In another embodiment of the present invention, the process exhaust gas contains triethylamine (TEA), which is oxidized by chlorine dioxide by performing the chemical reaction shown below.

_{(C 2 H 5) 3 N} + 2 ClO 2 + H 2 O → (C 2 H 5) 2 NH 2 + ClO 2 - + HClO 2 + CH 3 CHO

Absorption step (c): The pre-treatment gas and water are introduced into a second supergravity device to dissolve the oxidized organic products in the pre-treatment gas in water through gas-liquid mass transfer. Chlorine oxide gas can also be dissolved in water. In the second embodiment, the second supergravity device includes a rotating packed bed, and the material of the rotating packed bed is stainless steel.

Circulating step (d): recovering the dissolved aqueous solution in the absorption step (c), recycling into the second supergravity device to perform the absorption in the absorption step (c) with the oxidized organic product in the pretreatment gas .

In summary, the exhaust gas treatment method of the present invention oxidizes nitrogen oxides in the flue gas or volatile organic compounds in the exhaust gas of the flue gas by the chlorine dioxide gas generated by the first supergravity device, and uses alkaline liquid or water in the The second hypergravity device performs chemical reaction or dissolution to achieve effective absorption, and can efficiently process nitrogen oxides in flue gas exhaust or volatile organic compounds in process exhaust gas through gas-liquid mass transfer, which not only consumes low cost, but also Although chlorine dioxide is a strong oxidant, it is better for many materials The material compatibility is less likely to cause the deterioration of the material of the equipment (such as damage to the pipeline) and leakage problems, so it can indeed achieve the purpose of the invention.

However, the above are only examples of the present invention, and should not be used to limit the scope of implementation of the present invention, any simple equivalent changes and modifications made according to the scope of the patent application of the present invention and the content of the patent specification still belong to This invention covers the patent.

(a): Step of producing chlorine dioxide

(b): oxidation step

(c): absorption step

(d): cycle steps

Claims (10)

An exhaust gas treatment method, the exhaust gas contains nitrogen oxides and water gas, the exhaust gas treatment method includes the following steps: (a) chlorine dioxide generation step: generating chlorine dioxide gas with a first supergravity device; (b) oxidation step : Oxidizing the nitrogen dioxide in the exhaust gas by the chlorine dioxide gas produced by the first supergravity device to obtain a pretreatment gas containing nitrogen dioxide, the temperature of the exhaust gas is below 180°C; and (c) absorption step : Introduce the pre-treatment gas and an alkaline solution into a second supergravity device, so that the nitrogen dioxide in the pre-treatment gas reacts with the alkaline solution chemically. The exhaust gas treatment method according to claim 1, wherein in the step (c), the chemical reaction is to convert nitrogen dioxide to nitrite and nitrate. The exhaust gas treatment method according to claim 1, wherein in the step (c), the chemical reaction is to convert nitrogen dioxide to nitrogen gas. The exhaust gas treatment method according to claim 1, wherein the alkaline solution is an aqueous solution of an alkali, the alkali is selected from sodium hydroxide, potassium hydroxide, calcium hydroxide, calcium carbonate, sodium sulfite, sodium thiosulfate, Sodium sulfide, urea, ammonium sulfite, or a combination thereof. The exhaust gas treatment method according to claim 1, wherein the second supergravity device includes a rotating packed bed, and the material of the rotating packed bed is selected from alloys, plastics, rubber, or composite materials thereof. The exhaust gas treatment method according to claim 1, further comprising a recycling step (d): recovering the alkali solution after the chemical reaction, recycling and introducing it into the second supergravity device to dissolve the nitrogen dioxide in the pretreatment gas Perform this chemical reaction. The exhaust gas treatment method according to claim 1, wherein in the step (a), the chlorine dioxide gas is generated by mixing at least two reactive liquids in the first supergravity device. The exhaust gas treatment method according to claim 1, wherein the pretreatment gas further contains nitric acid. An exhaust gas treatment method, the exhaust gas contains volatile organic compounds, the exhaust gas treatment method includes the following steps: (a) chlorine dioxide generation step: a first super-gravity device to generate chlorine dioxide gas; (b) oxidation step: make the The chlorine dioxide gas produced by the first supergravity device oxidizes the volatile organic compounds in the exhaust gas to obtain a pre-treatment gas containing the oxidized organic product, the temperature of the exhaust gas is below 180°C; and (c) absorption step: The pretreatment gas and water are respectively introduced into a second supergravity device, so that the oxidized organic products in the pretreatment gas are dissolved in water. The exhaust gas treatment method according to claim 9, further comprising a recycling step (d): recovering the dissolved aqueous solution after performing the absorption step (c), recycling and introducing it into the second supergravity device to be combined with the pre-treatment gas The organic product after oxidation is dissolved in the absorption step (c).

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