A method and system for removing benz[a]pyrene from flue gas

Abstract

The application provides a method and system for removing benzene[a]pyrene in flue gas, the method comprising: using an aqueous solution of dimethyl sulfoxide as a reaction solution; continuously feeding cooled flue gas into the reaction solution under the irradiation of an ultraviolet light source; benzene[a]pyrene in the flue gas is dissolved in the reaction solution and degraded under the action of the irradiation of the ultraviolet light source, and flue gas with benzene[a]pyrene removed is obtained. The aqueous solution of dimethyl sulfoxide is used as a photochemical reaction solution, which can not only completely dissolve benzene[a]pyrene in different phases in the flue gas, but also promote the efficient degradation of benzene[a]pyrene, so that the complete removal of benzene[a]pyrene in the flue gas can be achieved in a short time. After the liquid phase photochemical reaction condition is optimized, the removal rate of benzene[a]pyrene in the flue gas can reach more than 99%. The application has the advantages of simple and reliable operation, low investment, low energy consumption, low operation and maintenance cost, and has a wide popularization and application prospect.

Description

Technical Field

[0001] This invention belongs to the technical field of flue gas treatment, specifically relating to a method for removing benzo[a]pyrene from flue gas, and also to a system for removing benzo[a]pyrene from flue gas. Background Technology

[0002] Benzo[a]pyrene, also known as 3,4-benzo[a]pyrene, is a polycyclic aromatic hydrocarbon compound formed by the fusion of pyrene and benzene. It possesses carcinogenic, mutagenic, and reproductive toxicity, and is classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC). Benzo[a]pyrene is formed during the high-temperature pyrolysis and combustion of organic matter such as coal, petroleum, and firewood. It is widely present in flue gas from coal-fired boilers or stoves, vehicle exhaust, waste incineration, cooking fumes, tobacco smoke, and industrial fumes from smelting, coking, and petrochemical industries, making it a significant environmental hazard threatening human health.

[0003] Currently, most technologies for treating benzo[a]pyrene-containing smoke focus on reducing the amount of benzo[a]pyrene in mainstream cigarette smoke. For example, Chinese patent CN201810261424.1 proposes using chemically modified tobacco stems to prepare filter additives for use in novel ternary composite filter rods, which can reduce the release of benzo[a]pyrene in mainstream cigarette smoke. However, this method is highly specific and not applicable to the removal of benzo[a]pyrene from other types of smoke, such as coal smoke and industrial smoke.

[0004] Chinese patent CN202110590674.1 proposes a method for capturing and removing benzo[a]pyrene from flue gas, utilizing a multi-layered specially designed material trapping bundle to adsorb liquid or solid benzo[a]pyrene from the flue gas. Chinese patent CN201320638838.4 discloses a benzo[a]pyrene flue gas purification device, which sequentially passes the flue gas through filtration, washing, and adsorption devices to achieve the purpose of purifying benzo[a]pyrene. These technologies mainly rely on adsorption to remove benzo[a]pyrene from flue gas; the principle is simple, but the requirements for the properties of the adsorbent and the frequency of replacement are high, and the adsorption efficiency is affected by many factors such as operating conditions, making it difficult to guarantee high efficiency and stability.

[0005] Furthermore, Chinese patent CN200720194408.2 discloses a novel top-fired benzo[a]pyrene digester for coke ovens, which digests harmful substances such as benzo[a]pyrene in flue gas at high temperatures. Such devices can achieve good removal results under suitable air-fuel ratios and residence times, but they require precise operating parameters and design details, and suffer from high energy consumption, high operating and maintenance costs.

[0006] Based on this, a low-cost, rapid and efficient method and system for removing benzo[a]pyrene from flue gas is provided, which is of great significance for promoting green industrial development, maintaining environmental hygiene and safety and human health, and is also a technical problem that urgently needs to be solved. Summary of the Invention

[0007] One of the objectives of this invention is to provide a low-cost, high-efficiency, and stable method for removing benzo[a]pyrene from flue gas.

[0008] The second objective of this invention is to provide a low-cost, high-removal-rate, and stable system for removing benzo[a]pyrene from flue gas.

[0009] One of the technical solutions adopted to achieve the objective of this invention is: to provide a method for removing benzo[a]pyrene from flue gas, comprising the following steps:

[0010] An aqueous solution of dimethyl sulfoxide was used as the reaction solution. Cooled flue gas was continuously passed into the reaction solution under ultraviolet light irradiation. Benzo[a]pyrene in the flue gas dissolved in the reaction solution and degraded under ultraviolet light irradiation to obtain flue gas with benzo[a]pyrene removed.

[0011] The overall concept of this invention is as follows: This invention provides a method for removing benzo[a]pyrene from flue gas using a liquid-phase photochemical reaction. Extensive research was conducted to screen solvents capable of dissolving benzo[a]pyrene (including benzene, chloroform, methanol, acetonitrile, diethyl ether, acetone, etc.), and an aqueous solution of dimethyl sulfoxide (DMSO) was determined to be used as the reaction solution, combined with ultraviolet (UV) photodegradation. The miscibility of DMSO with water significantly enhances the solubility of benzo[a]pyrene in water, thereby promoting the rapid dissolution of benzo[a]pyrene in flue gas into the aqueous solution. Furthermore, benzo[a]pyrene forms cationic radicals upon UV excitation. The interaction between DMSO and water molecules promotes the photochemical reaction between the benzo[a]pyrene cationic radicals and dissolved oxygen and free water molecules in the reaction solution, thus efficiently degrading benzo[a]pyrene.

[0012] In the above method, an aqueous solution of DMSO is used as the reaction solution, which has high solubility for benzo[a]pyrene in different phases (including gaseous, liquid and solid) in flue gas, thus achieving efficient capture and enrichment of benzo[a]pyrene in different phases in flue gas. Subsequently, a scheme combining "DMSO + water + dissolved oxygen + ultraviolet light degradation" is adopted to achieve effective removal of benzo[a]pyrene.

[0013] Further, the volume percentage of DMSO in the reaction solution is 10% to 80%. Preferably, the volume percentage of DMSO is 33% to 67%. More preferably, when the volume fraction of DMSO is 50%, the interaction between DMSO and water molecules optimizes the levels of dissolved oxygen and free water molecules in the reaction solution, maximizing the photodegradation rate of benzo[a]pyrene, and achieving 100% degradation of benzo[a]pyrene after 40 minutes of illumination.

[0014] Furthermore, the wavelength of the ultraviolet light source is 300–360 nm, and the optical power density is 400–1000 μW / cm². 2 Studies have found that when the wavelength of the ultraviolet light source is less than 300 nm, DMSO will also absorb some of the ultraviolet light. This absorption competes with benzo[a]pyrene for a limited amount of ultraviolet light, reducing the amount of ultraviolet light absorbed by benzo[a]pyrene and the energy available for photodegradation, thus decreasing the photodegradation rate and removal efficiency. However, when the wavelength of the ultraviolet light source is greater than or equal to 300 nm, DMSO absorbs almost no ultraviolet light at this wavelength. Therefore, using an ultraviolet light source with a wavelength of 300–360 nm is more conducive to the efficient photodegradation of benzo[a]pyrene.

[0015] Furthermore, the distance between the ultraviolet light source and the surface of the reaction solution is 8–12 cm, and the irradiation time of the ultraviolet light source is 0.1–120 min.

[0016] Preferably, the ultraviolet light source has a wavelength of 302 nm and an optical power density of 638 μW / cm². 2 The ultraviolet light source is 10 cm away from the reaction solution, and the irradiation time of the ultraviolet light source is 0.1 to 40 min.

[0017] Furthermore, the temperature of the cooled flue gas is 15–35°C. Preferably, the flue gas can be cooled by mixing it with air in a certain proportion.

[0018] Preferably, the concentration of benzo[a]pyrene in the reaction solution is 0.01–10 mg / L. Specifically, the volume of the reaction solution can be adjusted according to the concentration of benzo[a]pyrene in the flue gas to be treated to ensure sufficient dissolution and photodegradation of benzo[a]pyrene.

[0019] Furthermore, the method further includes the following step: the flue gas from which benzo[a]pyrene has been removed is thoroughly dried before being emitted.

[0020] The second objective of this invention is achieved by providing a system for removing benzo[a]pyrene from flue gas using the method described in one of the objectives of this invention. The system includes an induced draft fan, a flue gas cooler, a reactor, a dryer, a circulating pump, and several connecting pipes.

[0021] Furthermore, the reactor contains a reaction solution, and an ultraviolet light source is positioned around the reaction solution. The reaction solution in the reactor is an aqueous solution of DMSO. In the reactor, under ultraviolet light irradiation, cooled flue gas is continuously passed into the reaction solution. Benzo[a]pyrene in the flue gas dissolves in the reaction solution and degrades under the action of ultraviolet light irradiation, resulting in flue gas with benzo[a]pyrene removed.

[0022] Furthermore, the connecting pipes include an intake pipe, a first pipe for connecting the induced draft fan and the flue gas cooler, a second pipe for connecting the flue gas cooler and the reactor, a third pipe for connecting the reactor and the dryer, a fourth pipe for connecting the dryer and the condenser, and an exhaust pipe.

[0023] Furthermore, the operating method of the system for removing benzo[a]pyrene from flue gas includes the following steps:

[0024] S1. Flue gas containing benzo[a]pyrene enters the first pipe through the inlet pipe and the induced draft fan, and then enters the flue gas cooler through the first pipe;

[0025] S2. The flue gas containing benzo[a]pyrene is cooled in a flue gas cooler to obtain cooled flue gas;

[0026] S3. The cooled flue gas enters the reactor through the second pipe to carry out the reaction to remove benzo[a]pyrene, and obtain flue gas with benzo[a]pyrene removed;

[0027] S4. The flue gas after removing benzo[a]pyrene enters the dryer through the third pipe for thorough drying, and the dried flue gas is discharged through the exhaust pipe.

[0028] S5. The condensate produced by the dryer is circulated to the reactor through the fourth pipe and the circulating pump for subsequent reactions.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] (1) The present invention provides a method for removing benzo[a]pyrene from flue gas, which makes full use of the physicochemical properties of DMSO and uses an aqueous solution of DMSO as the photochemical reaction solution. This method can not only completely dissolve benzo[a]pyrene in different phases in flue gas, but also promote the efficient degradation of benzo[a]pyrene, achieving complete removal of benzo[a]pyrene from flue gas in a short time. After optimization of the liquid-phase photochemical reaction conditions, the removal rate of benzo[a]pyrene from flue gas can reach more than 99%.

[0031] (2) The system for removing benzo[a]pyrene from flue gas provided by this invention can achieve low-cost and high-efficiency removal of benzo[a]pyrene from flue gas in a short time. It also has the advantages of simple and reliable operation, low investment, low energy consumption, and low operating and maintenance costs. It is widely applicable to the treatment of benzo[a]pyrene-containing flue gas emitted from various industrial production and domestic processes. The method and system for removing benzo[a]pyrene from flue gas provided by this invention are of great significance for promoting green industrial development, maintaining environmental hygiene and safety, and protecting human health, and have broad prospects for promotion and application. Attached Figure Description

[0032] Figure 1 This is a schematic flowchart of the method for removing benzo[a]pyrene from flue gas in Embodiments 1 and 2 of the present invention;

[0033] Figure 2 The graph shows the changes in (a) benzo[a]pyrene concentration and (b) removal rate of benzo[a]pyrene in flue gas with light exposure time under different DMSO volume fraction conditions in the reaction solution of Example 1 of the present invention.

[0034] Figure 3 This is a schematic diagram of the system for removing benzo[a]pyrene from flue gas provided in Embodiment 3 of the present invention;

[0035] Among them, 1-inlet pipe; 2-exhaust fan; 3-first pipe; 4-flue gas cooler; 5-second pipe; 6-reactor; 7-third pipe; 8-dryer; 9-exhaust pipe; 10-fourth pipe; 11-circulation pump. Detailed Implementation

[0036] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0038] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0039] Example 1

[0040] The operation flowchart of this embodiment is as follows: Figure 1 As shown, the flue gas containing benzo[a]pyrene is discharged after being cooled, reacted, and dried in sequence.

[0041] The coking process was simulated by heating coal to 900℃ in a tubular furnace, producing 0.03m³ of flue gas. 3 The flue gas temperature was 220℃, and the concentration of benzo[a]pyrene was 2.8 μg / m³. 3 The method proposed in this invention is used to remove benzo[a]pyrene from the flue gas.

[0042] Flue gas containing benzo[a]pyrene is passed through a flue gas cooler, which consists of a two-stage cooling structure, both using twice the volume of air for dilution and cooling. After two-stage cooling, the flue gas temperature drops to 33°C. The cooled flue gas is then fed into a reactor and introduced into a reaction solution at a temperature of 25°C, containing 10%-80% DMSO by volume. The reaction solution is irradiated with an ultraviolet light source at a wavelength of 302 nm and a power density of 638 μW / cm². 2 The distance between the flue gas and the reaction solution was 10 cm, and the illumination time was 0-40 min. The total volume ratio of flue gas to reaction solution was 350000:1, and the concentration of benzo[a]pyrene in the reaction solution was approximately 1 mg / L. After the benzo[a]pyrene was degraded by liquid-phase photochemical reaction, the flue gas was discharged from the reactor and then sent to a dryer for drying before being discharged.

[0043] Depend on Figure 2 As shown in (a) and (b), as the irradiation time increased from 0 min to 40 min, the concentration of benzo[a]pyrene in the reaction solutions with different DMSO volume fractions all showed a decreasing trend, while the removal rate of benzo[a]pyrene in the treated flue gas showed an increasing trend. Under the same irradiation time, compared with the pure aqueous solution without DMSO (i.e., the reaction solution with 0% DMSO volume fraction), the concentration of benzo[a]pyrene in the reaction solution with added DMSO decreased more rapidly, and the removal rate of benzo[a]pyrene in the treated flue gas was significantly improved. This indicates that under the same ultraviolet irradiation conditions, the removal rate of benzo[a]pyrene in pure water (0% DMSO volume fraction) is extremely low; in contrast, by adding a certain proportion of DMSO, the interaction between DMSO and water molecules can promote the photochemical reaction between benzo[a]pyrene and dissolved oxygen and free water molecules in the reaction solution, thereby significantly improving the removal rate of benzo[a]pyrene.

[0044] Furthermore, by Figure 2It was found that when the volume fraction of DMSO was 50%, the concentration of benzo[a]pyrene in the reaction solution decreased the fastest, and the removal rate of benzo[a]pyrene in the treated flue gas was the highest, reaching 95.4% after 20 min of illumination, 98.9% after 30 min, and 100% after 40 min. These results indicate that when the volume fraction of DMSO is 50%, the interaction between DMSO and water molecules optimizes the levels of dissolved oxygen and free water molecules in the reaction solution, creating the most suitable conditions for the efficient degradation of benzo[a]pyrene.

[0045] Therefore, in the method proposed in this invention, the optimal liquid-phase photochemical reaction conditions are DMSO volume fraction of 50% and illumination time of 40 min under 302 nm ultraviolet light irradiation. Under these conditions, the concentration of benzo[a]pyrene in the treated flue gas is 0.00 μg / m³. 3 The removal rate was 100%.

[0046] Example 2:

[0047] The operation flowchart of this embodiment is as follows: Figure 1 As shown, the flue gas containing benzo[a]pyrene is successively cooled, reacted, and dried before being emitted.

[0048] A diesel vehicle with a displacement of 3.0L emits 1.2m³ of exhaust gas at idle. 3 The exhaust gas temperature was 68℃, and the concentration of benzo[a]pyrene was 0.45 μg / m³. 3 The method proposed in this invention is used to remove benzo[a]pyrene from the exhaust gas.

[0049] The tail gas containing benzo[a]pyrene was sequentially passed through a flue gas cooler, which consisted of a two-stage cooling structure, both using twice the volume of air for dilution and cooling. After the two-stage cooling, the tail gas temperature dropped to 18°C. The cooled tail gas was then fed into a reactor and introduced into a reaction solution at a temperature of 25°C, containing 50% DMSO by volume. The reaction solution was irradiated with an ultraviolet light source at a wavelength of 302 nm and a power density of 638 μW / cm². 2 The distance from the reaction solution was 10 cm, and the illumination time was 40 min. The volume ratio of the total flue gas to the reaction solution was 2,000,000:1, and the concentration of benzo[a]pyrene in the reaction solution was approximately 1 mg / L. After the benzo[a]pyrene was degraded by liquid-phase photochemical reaction, the tail gas was discharged from the reactor and then sent to a dryer for drying before being discharged. The concentration of benzo[a]pyrene in the treated tail gas was 0.00 μg / m³. 3 The removal rate was 100%.

[0050] Example 3:

[0051] Please see Figure 3This embodiment employs a system for removing benzo[a]pyrene from flue gas. The system includes the following structures: an induced draft fan 2, a flue gas cooler 4, a reactor 6, a dryer 8, and a circulating pump 11. It also includes an intake pipe 1, a first pipe 3, a second pipe 5, a third pipe 7, an exhaust pipe 9, and a fourth pipe 10.

[0052] The process for removing benzo[a]pyrene from gas includes the following steps: Flue gas containing benzo[a]pyrene enters the first pipe 3 through the inlet pipe 1 and the induced draft fan 2, and then enters the flue gas cooler 4 through the first pipe 3; the flue gas is cooled in the flue gas cooler 4 to obtain cooled flue gas; the cooled flue gas enters the reactor 6 through the second pipe 5 to carry out the benzo[a]pyrene removal reaction to obtain benzo[a]pyrene-removed flue gas; the benzo[a]pyrene-removed flue gas enters the dryer 8 through the third pipe 7 for thorough drying, and the dried flue gas is discharged through the exhaust pipe 9; the condensate generated by the dryer 8 is circulated back to the reactor 6 through the fourth pipe 10 and the circulation pump 11 for subsequent reactions.

[0053] The smoke volume generated in the bacon smoking workshop of a food processing plant is 600 Nm³. 3 The flue gas temperature was 115℃, and the concentration of benzo[a]pyrene was 13 μg / m³. 3 The emission level exceeded the local emission standard limit of 2.5 μg / m³. 3 The method proposed in this invention is used to remove benzo[a]pyrene from the flue gas.

[0054] Flue gas containing benzo[a]pyrene was fed into a flue gas cooler by an induced draft fan and cooled to 28°C. The cooled flue gas was then fed into a reactor and introduced into a reaction solution at 25°C, containing 50% DMSO by volume. The reaction solution was irradiated with an ultraviolet light source at a wavelength of 302 nm and a power density of 638 μW / cm². 2 The distance from the reaction solution was 10 cm, and the illumination time was 40 min. The volume ratio of the total flue gas to the reaction solution was 77000:1, and the concentration of benzo[a]pyrene in the reaction solution was approximately 1 mg / L. After the benzo[a]pyrene was degraded by liquid-phase photochemical reaction, the tail gas was discharged from the reactor and then sent to a dryer for strict drying before being discharged. The condensate generated in the dryer was recycled back to the reactor. The concentration of benzo[a]pyrene in the treated flue gas was 0.00 μg / m³. 3 The removal rate was 100%.

[0055] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A method for removing benzo[a]pyrene from flue gas, characterized in that, Includes the following steps: An aqueous solution of dimethyl sulfoxide was used as the reaction solution; under ultraviolet light irradiation, cooled flue gas was continuously passed into the reaction solution; Benzo[a]pyrene in the flue gas dissolves in the reaction solution and degrades under ultraviolet light irradiation, resulting in flue gas with benzo[a]pyrene removed.

2. The method according to claim 1, characterized in that, The volume percentage of dimethyl sulfoxide in the reaction solution is 10% to 80%.

3. The method according to claim 1, characterized in that, The ultraviolet light source has a wavelength of 300~360nm and an optical power density of 400~1000μW / cm². 2 .

4. The method according to claim 1, characterized in that, The distance between the ultraviolet light source and the surface of the reaction solution is 8-12 cm, and the irradiation time of the ultraviolet light source is 0.1-120 min.

5. The method according to claim 1, characterized in that, The temperature of the cooled flue gas is 15~35℃.

6. The method according to claim 1, characterized in that, The concentration of benzo[a]pyrene in the reaction solution is 0.01~10 mg / L.

7. The method according to claim 1, characterized in that, The method further includes the following steps: thoroughly drying the flue gas from which benzo[a]pyrene has been removed before emitting it.

8. The method according to claim 1, characterized in that, The method is carried out using a system comprising: an induced draft fan, a flue gas cooler, a reactor, a dryer, a circulating pump, and several connecting pipes.

9. The method according to claim 8, characterized in that, The connecting pipes include an air inlet pipe, a first pipe for connecting the induced draft fan and the flue gas cooler, a second pipe for connecting the flue gas cooler and the reactor, a third pipe for connecting the reactor and the dryer, a fourth pipe for connecting the dryer and the condenser, and an exhaust pipe.

10. The method according to claim 9, characterized in that, The operating method of the system for removing benzo[a]pyrene from flue gas includes the following steps: S1. Flue gas containing benzo[a]pyrene enters the first pipe through the inlet pipe and the induced draft fan, and then enters the flue gas cooler through the first pipe; S2. The flue gas containing benzo[a]pyrene is cooled in a flue gas cooler to obtain cooled flue gas; S3. The cooled flue gas enters the reactor through the second pipe to carry out the reaction to remove benzo[a]pyrene, and obtain flue gas with benzo[a]pyrene removed; S4. The flue gas after removing benzo[a]pyrene enters the dryer through the third pipe for thorough drying, and the dried flue gas is discharged through the exhaust pipe. S5. The condensate produced by the dryer is circulated to the reactor through the fourth pipe and the circulating pump for subsequent reactions.

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