A method for deep removal of heavy metal mercury in flue gas after incineration of high-concentration mercury-containing sludge

Abstract

The application provides a method for deeply removing heavy metal mercury in flue gas after incineration of high-concentration mercury-containing sludge. The method comprises the following steps: spraying sulfur-loaded powdered activated carbon into high-temperature flue gas generated by sludge incineration to make the sulfur-loaded powdered activated carbon contact with the flue gas; wherein the temperature of the high-temperature flue gas is 160-190 DEG C; using the physical adsorption of the sulfur-loaded powdered activated carbon and the chemical reaction of sulfur and mercury to generate mercury sulfide, the gaseous mercury and / or ionic mercury in the flue gas is converted into solid form, and then the sulfur-loaded powdered activated carbon adsorbing mercury is separated from the flue gas through a dust removal device; wherein the sulfur loading amount of the sulfur-loaded powdered activated carbon is 12wt%-18wt%. The application uses the synergistic mechanism of chemical adsorption and physical adsorption to overcome the defect that ordinary activated carbon is easy to desorb at high temperature, significantly improves the mercury removal rate from 10-20% of the prior art to more than 95%, and realizes ultra-low emission.

Description

Technical Field

[0001] This invention relates to the field of flue gas purification technology, specifically to a method for the deep removal of heavy metal mercury from flue gas after incineration of high-concentration mercury-containing sludge. Background Technology

[0002] Mercury, a heavy metal, is liquid at room temperature and is highly volatile, toxic, persistent, and bioaccumulative, posing a significant threat to the ecological environment and human health. Atmospheric mercury has a wide range of sources, with anthropogenic emissions primarily including coal combustion, metal smelting, and waste and sludge incineration. With the rapid urbanization in my country, the volume of urban wastewater treatment has increased dramatically, leading to a corresponding increase in municipal sludge disposal. While sludge incineration offers advantages such as volume reduction, harmlessness, and stabilization, the complex composition of sludge results in the generation of high concentrations of mercury during the incineration process.

[0003] In sludge incineration processes, heavy metals exist in solid, liquid, and gaseous forms within the incinerator. As the flue gas cools, some of the gaseous heavy metals are converted into collectable particles. Currently, the industry-standard heavy metal treatment process involves spraying powdered activated carbon before the dust collector, utilizing the pores of the activated carbon for physical adsorption, and then collecting the particles through a bag filter.

[0004] However, long-term production operation and in-depth research have revealed that the existing activated carbon jet bag filter process has serious limitations in treating sludge incineration flue gas, especially when treating high-concentration mercury-containing sludge, where the following prominent defects exist: High-Temperature Adsorption Failure: The adsorption of mercury by ordinary powdered activated carbon mainly relies on van der Waals forces (physical adsorption). At the typical flue gas emission temperature of sludge incineration (approximately 180°C), physical adsorption is unstable, and the adsorption capacity drops sharply. Actual operation data shows that at 180°C, the removal rate of mercury by ordinary activated carbon is only 10%~20%, far from meeting increasingly stringent environmental emission standards.

[0005] High facility costs: To solve the above problems, existing technologies often use methods such as adding a dedicated mercury adsorption tower or drastically reducing the flue gas temperature (which can lead to dew point corrosion problems), resulting in a significant increase in construction and operation and maintenance costs.

[0006] Lack of targeted materials: Existing technologies lack a specific adsorption material and supporting process that can maintain high chemical stability and efficiently capture gaseous mercury within a specific temperature range of 160~190℃.

[0007] Therefore, developing a method to achieve deep removal of high-concentration mercury (removal rate >95%) under high-temperature (around 180°C) conditions without changing the existing main equipment architecture is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] This invention addresses the lack of a dedicated adsorption material and supporting process in the existing technology that can maintain high chemical stability and efficiently capture gaseous mercury within a specific temperature range of 160~190℃, and provides a method for the deep removal of heavy metal mercury from flue gas after incineration of high-concentration mercury-containing sludge.

[0009] The technical method of the present invention is as follows: A method for deep removal of heavy metal mercury from flue gas after incineration of high-concentration mercury-containing sludge includes: spraying sulfur-loaded powdered activated carbon into the high-temperature flue gas generated by sludge incineration, so that the sulfur-loaded powdered activated carbon comes into contact with the flue gas; wherein the temperature of the high-temperature flue gas is 160~190℃; utilizing the physical adsorption of sulfur-loaded powdered activated carbon and the mercury sulfide generated by the chemical reaction of sulfur and mercury to convert gaseous mercury and / or ionic mercury in the flue gas into a solid form, and then separating the mercury-adsorbed sulfur-loaded powdered activated carbon from the flue gas through a dust removal device; wherein the sulfur loading of the sulfur-loaded powdered activated carbon is 12wt%~18wt%.

[0010] Optionally, the sulfur-loaded powdered activated carbon uses anthracite as the base carbon, wherein the iodine value of the base carbon is greater than 1000 mg / g and the carbon tetrachloride adsorption value is greater than 60%.

[0011] Optionally, the iodine value of the base carbon is 1000~1100 mg / g, and the adsorption value of carbon tetrachloride is 60%~65%.

[0012] Optionally, the preparation of the sulfur-loaded powdered activated carbon includes: grinding washed coal into coal powder; mixing and extruding the coal powder with coal tar, carbonizing and activating it, and then sieving it into columnar activated carbon; loading elemental sulfur onto the columnar activated carbon using the elemental sulfur impregnation method and grinding it into powder to obtain sulfur-loaded powdered activated carbon.

[0013] Optionally, the particle size of the sulfur-loaded powdered activated carbon is 300-350 mesh.

[0014] Optionally, the temperature of the high-temperature flue gas is controlled at 175~185℃.

[0015] Optionally, the sulfur-loaded powdered activated carbon is conveyed by compressed air and injected into the high-temperature flue gas.

[0016] Optionally, the initial concentration of mercury in the high-temperature flue gas is 0.7~1.0 mg / m³. 3 The sulfur-loaded powdered activated carbon is injected at a rate of 4-5 kg / h per 25,000 Nm³ / h of flue gas.

[0017] The present invention provides a flue gas treatment system, wherein an incinerator, a waste heat boiler, an electrostatic precipitator, a flue gas reactor, a bag filter, and a wet desulfurization tower are arranged sequentially along the flue gas flow direction; the sulfur-loaded powdered activated carbon is injected into the flue gas reactor.

[0018] Optionally, the wet desulfurization tower is located downstream of the bag filter and is used to further remove acidic gases and trace amounts of mercury from the flue gas.

[0019] The beneficial effects of this invention are: I. This invention targets high-temperature operating conditions of 160~190℃. It utilizes the synergistic mechanism of chemical adsorption (the reaction of sulfur and mercury to generate stable HgS) and physical adsorption to overcome the defect of easy desorption of ordinary activated carbon physical adsorption at high temperatures. It significantly improves the mercury removal rate from 10~20% in the prior art to more than 95%, achieving ultra-low emissions.

[0020] Second, the sulfur-loaded activated carbon used in this invention has extremely high reactivity in the range of 160~190℃, which perfectly matches the emission temperature of sludge incineration flue gas, eliminating the need for additional cooling or heating measures.

[0021] Third, this invention can utilize existing activated carbon dosing devices, eliminating the need for expensive fixed-bed adsorption towers. Although the unit price of sulfur-loaded activated carbon is slightly higher, its large adsorption capacity and high removal efficiency result in significantly lower overall operating costs and environmental risks compared to existing technologies.

[0022] Fourth, this invention, in conjunction with front-end electrostatic dust removal (removing ash and slag to prevent pore blockage) and back-end wet desulfurization (further washing away trace amounts of escaping mercury), forms a complete deep purification system. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the process flow for a deep mercury removal method for incineration flue gas containing high concentrations of mercury sludge, as described in an embodiment of the present invention. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] This invention provides a method for the deep removal of heavy metal mercury from flue gas after incineration of high-concentration mercury-containing sludge, such as... Figure 1 As shown, it includes: S1. Sulfur-loaded powdered activated carbon is sprayed into the high-temperature flue gas generated by sludge incineration, so that the sulfur-loaded powdered activated carbon comes into contact with the flue gas; wherein, the temperature of the high-temperature flue gas is 160~190℃.

[0026] In this embodiment, anthracite is used as the base carbon for the sulfur-loaded powdered activated carbon. The base carbon has an iodine value greater than 1000 mg / g and a carbon tetrachloride adsorption value greater than 60%. Preferably, the iodine value of the base carbon is 1000-1100 mg / g, and the carbon tetrachloride adsorption value is 60%-65%. Here, high-quality anthracite is selected as the base carbon for the sulfur-loaded powdered activated carbon. It is ground into powder (approximately 325 mesh) using a single-element sulfur impregnation method. The optimal sulfur loading range for the powdered activated carbon is 12-18%.

[0027] In this embodiment, the preparation of sulfur-loaded powdered activated carbon includes: grinding washed coal into coal powder; mixing and extruding the coal powder with coal tar, carbonizing, activating, and then sieving into columnar activated carbon; loading elemental sulfur onto the columnar activated carbon using an elemental sulfur impregnation method and grinding it into powder to obtain sulfur-loaded powdered activated carbon. Here, the mass ratio of coal powder to coal tar is approximately 2:1. Elemental sulfur is fully loaded into the pore structure of the activated carbon. Preferably, the particle size of the sulfur-loaded powdered activated carbon is 300-350 mesh.

[0028] Preferably, the temperature of the high-temperature flue gas is controlled at 175~185℃.

[0029] In this embodiment, sulfur-loaded powdered activated carbon is conveyed by compressed air and injected into the high-temperature flue gas.

[0030] S2. Utilizing the physical adsorption of sulfur-loaded powdered activated carbon and the mercury sulfide generated by the chemical reaction of sulfur and mercury, gaseous and / or ionic mercury in the flue gas is converted into a solid form. Subsequently, the mercury-adsorbed sulfur-loaded powdered activated carbon is separated from the flue gas by a dust removal device; wherein the sulfur loading of the sulfur-loaded powdered activated carbon is 12wt%~18wt%. For example, the sulfur loading of the sulfur-loaded powdered activated carbon is 13wt%, 16wt%, or 17wt%.

[0031] In this embodiment, the initial concentration of mercury in the high-temperature flue gas is 0.7~1.0 mg / m³. 3 The injection rate of the sulfur-loaded powdered activated carbon is 4-5 kg / h per 25,000 Nm³ / h of flue gas. The specific rate needs to be adjusted according to the flue gas temperature and other relevant operating conditions. Here, the flue gas injection rate can be 4.3 kg / h or 4.6 kg / h.

[0032] The present invention also provides a flue gas treatment system, wherein an incinerator, a waste heat boiler, an electrostatic precipitator, a flue gas reactor, a bag filter, and a wet desulfurization tower are arranged sequentially along the flue gas flow direction; the sulfur-loaded powdered activated carbon is injected into the flue gas reactor.

[0033] In this embodiment, the wet desulfurization tower is located downstream of the bag filter and is used to further remove acidic gases and trace amounts of mercury from the flue gas.

[0034] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0035] The present invention will be described in detail below through embodiments and experimental examples. However, these are merely examples and do not limit the present invention in any way.

[0036] Example 1: Preparation of sulfur-loaded powdered activated carbon Carbon selection: High-quality anthracite is selected. Key indicators: Iodine value is controlled at 1000-1100 mg / g, and carbon tetrachloride adsorption value is controlled at 60-65%. This is the basis for ensuring sufficient sulfur loading space and remaining physical adsorption pores.

[0037] Preparation process: Washed coal is ground into powder → mixed with coal tar and extruded into shape → carbonization → activation → sieving into columnar activated carbon → impregnation with elemental sulfur (controlling sulfur loading) → grinding to 325 mesh (approximately 300-350 mesh range) powder.

[0038] Finished product specifications: The sulfur loading of the final product is controlled at 12-18% (by weight).

[0039] Application Example 1 Industrial application was carried out at a sludge incineration plant in a certain city.

[0040] Flue gas operating conditions: The processing air volume is approximately 25,000 Nm³. 3 The flue gas temperature remained stable at around 180℃ per hour. The initial mercury concentration in the raw flue gas was 0.95 mg / m³. 3 (It is a high concentration).

[0041] Adsorbent: Sulfur-loaded powdered activated carbon prepared in Example 1 was used, with a sulfur loading of 16% and a particle size of 325 mesh.

[0042] Addition method: Sulfur-loaded powdered activated carbon is injected into the flue gas reactor between the electrostatic precipitator and the bag filter using compressed air.

[0043] Dosage: The spray rate is set to 4.5 kg / h.

[0044] Results: Samples taken from the outlet of the bag filter showed that the mercury concentration in the emitted flue gas decreased to 0.0031 mg / m³. 3 .

[0045] Calculation: Removal rate = (0.95 - 0.0031) / 0.95 × 100% = 99.7%.

[0046] Application Example 2 The operating conditions were adjusted to: flue gas temperature 160℃, and other conditions were the same as in Example 1.

[0047] Results: The mercury concentration in the flue gas was 0.0038 mg / m³. 3 The removal rate was 99.6%, indicating that the chemical reactivity remained good at this temperature.

[0048] Application Example 3 The operating conditions were adjusted to: flue gas temperature 190℃, and other conditions were the same as in Example 1.

[0049] Results: The mercury concentration in the flue gas was 0.0068 mg / m³. 3 The removal rate was 99.3%. Although increased temperature may slightly affect physical adsorption, the chemical reaction rate between sulfur and mercury accelerated, and the overall removal rate remained high.

[0050] Comparative Example 1 Ordinary coal-based powdered activated carbon that is not loaded with sulfur has the same iodine value of 1050 mg / g.

[0051] Flue gas operating conditions: Same as in Application Example 1, temperature 180℃, initial mercury concentration 0.95 mg / m³ 3 .

[0052] Dosage: 4.5 kg / h.

[0053] Results: The mercury concentration at the outlet of the bag filter was 0.78 mg / m³. 3 .

[0054] Calculation: Removal rate = (0.95-0.78) / 0.95×100% = 17.9%.

[0055] Conclusion: At a high temperature of 180℃, ordinary activated carbon almost fails, verifying the defects mentioned in the background technology.

[0056] Comparative Example 2 Ordinary activated carbon with an iodine value of only 600 mg / g was used as the base carbon, with a loading ratio of 16% sulfur.

[0057] Flue gas operating conditions: Same as in Example 1.

[0058] Result: The mercury concentration at the outlet of the bag filter was 0.25 mg / m³. 3 The removal rate was 73.7%.

[0059] Comparative Example 3 Using the same base carbon, with a sulfur loading ratio (12%).

[0060] Flue gas operating conditions: Same as in Example 1.

[0061] Result: The mercury concentration at the outlet of the bag filter was 0.045 mg / m³. 3 The removal rate was 95.2%.

[0062] Conclusion: The pore structure of the base carbon (high iodine value, high carbon tetrachloride adsorption value) is crucial to the final effect. When the pores of low-quality carbon are blocked by sulfur, there is a lack of sufficient channels for mercury molecules to enter and react internally, resulting in a significant reduction in efficiency. The higher the sulfur loading, the better the removal effect.

[0063] Conclusion: The pore structure of the base carbon (high iodine value, high carbon tetrachloride adsorption value) is crucial to the final effect. When the pores of low-quality carbon are blocked by sulfur, there is a lack of sufficient channels for mercury molecules to enter and react internally, resulting in a significant reduction in efficiency. The higher the sulfur loading, the better the removal effect.

[0064] The experimental data above clearly demonstrate that the sulfur-loaded powdered activated carbon prepared using a specific sulfur loading (12-18%) and high-quality base carbon, under the unique high-temperature (160-190℃) flue gas environment of sludge incineration, achieves unexpected technical results (removal rate increased from less than 20% to over 95%) through a mechanism dominated by sulfidation chemical reactions. This method can achieve deep purification and compliant emission of high-concentration mercury-containing flue gas without complex equipment modifications.

[0065] Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible subranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0066] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for deep removal of heavy metal mercury from flue gas after incineration of high-concentration mercury-containing sludge, characterized in that, include: Sulfur-loaded powdered activated carbon is sprayed into the high-temperature flue gas generated by sludge incineration, so that the sulfur-loaded powdered activated carbon comes into contact with the flue gas; wherein, the temperature of the high-temperature flue gas is 160~190℃. By utilizing the physical adsorption of sulfur-loaded powdered activated carbon and the mercury sulfide generated by the chemical reaction of sulfur and mercury, gaseous mercury and / or ionic mercury in flue gas are converted into solid form. Subsequently, the mercury-adsorbed sulfur-loaded powdered activated carbon is separated from the flue gas by a dust removal device; wherein, the sulfur loading of the sulfur-loaded powdered activated carbon is 12wt%~18wt%.

2. The depth removal method according to claim 1, characterized in that, The sulfur-loaded powdered activated carbon uses anthracite as the base carbon, wherein the iodine value of the base carbon is greater than 1000 mg / g and the carbon tetrachloride adsorption value is greater than 60%.

3. The depth removal method according to claim 2, characterized in that, The iodine value of the base carbon is 1000~1100 mg / g, and the adsorption value of carbon tetrachloride is 60%~65%.

4. The depth removal method according to claim 1, characterized in that, The preparation of the sulfur-loaded powdered activated carbon includes: Grind washed coal into pulverized coal; Coal powder and coal tar are mixed, extruded, carbonized, activated, and then sieved into columnar activated carbon. Sulfur-loaded powdered activated carbon was obtained by loading elemental sulfur onto columnar activated carbon using the elemental sulfur impregnation method and then grinding it into powder.

5. The depth removal method according to claim 1, characterized in that, The sulfur-loaded powdered activated carbon has a particle size of 300-350 mesh.

6. The depth removal method according to claim 1, characterized in that, The temperature of the high-temperature flue gas is controlled at 175~185℃.

7. The depth removal method according to claim 1, characterized in that, The sulfur-loaded powdered activated carbon is transported by compressed air and injected into the high-temperature flue gas.

8. The depth removal method according to claim 1, characterized in that, The initial concentration of mercury in the high-temperature flue gas was 0.7~1.0 mg / m³. 3 , The sulfur-loaded powdered activated carbon is injected at a rate of 4-5 kg / h per 25,000 Nm³ / h of flue gas.

9. A flue gas treatment system, characterized in that, The flue gas treatment system is provided in sequence along the flue gas flow direction, including an incinerator, a waste heat boiler, an electrostatic precipitator, a flue gas reactor, a bag filter, and a wet desulfurization tower; the sulfur-loaded powdered activated carbon according to any one of claims 1-8 is injected into the flue gas reactor.

10. The flue gas treatment system according to claim 9, characterized in that, The wet desulfurization tower is located downstream of the bag filter and is used to further remove acidic gases and trace amounts of mercury from the flue gas.

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