Recycling method for modifying waste incineration fly ash to control flue gas dioxin

Abstract

The invention relates to the field of environmental engineering and solid waste resource utilization, in particular to a recycling method for controlling flue gas dioxin by modifying waste incineration fly ash, which comprises the following steps: S1, drying the waste incineration fly ash, and screening to obtain a waste incineration fly ash pretreatment basic raw material; s2, uniformly mixing the pretreated fly ash with a functional modifier according to a mass ratio, and feeding the mixture into a high-energy planetary ball mill for mechanochemical synergistic modification to obtain modified fly ash; and S3, the modified fly ash is injected into a garbage incinerator tail gas system, the injection position is arranged at the front section of a bag-type dust collector, and residual dioxin in the tail gas system is absorbed. According to the method, the waste incineration fly ash is subjected to ball-milling load modification treatment and is reused for pollution control of dioxin, so that efficient control of pollutant emission is realized, the production cost is reduced, and meanwhile, the method has the advantages of being green and environmentally friendly.

Description

Technical Field

[0001] This invention relates to the fields of environmental engineering and solid waste resource utilization, and in particular to a method for recycling modified waste incineration fly ash to control dioxins in flue gas. Background Technology

[0002] Municipal solid waste incineration is a key means to achieve the reduction, harmlessness, and resource utilization of solid waste. However, during the cooling of flue gas to 200–400℃, it is highly susceptible to the formation of polychlorinated diphenylene oxides (PCBs) and furans (PCDDs / Fs), which are highly toxic persistent organic pollutants, through the "de novo synthesis" pathway of dioxins. To suppress their emissions, current engineering practices typically employ the injection of activated carbon or calcium oxide into the flue to adsorb dioxins and inhibit their regeneration.

[0003] Chinese patent CN213077965U discloses a dry reaction device for an exhaust gas treatment system, which includes a dry powder injection device and a dry dust filter device. The dry powder injection device and the dry dust filter device are connected sequentially between a spray quench tower and a spray absorption tower. The dry powder injection device includes an activated carbon powder storage tank, a calcium oxide powder storage tank, a Roots high-pressure blower, and a Venturi reactor. The flue gas outlet of the spray quench tower is connected to the flue gas inlet of the Venturi reactor, the flue gas outlet of the Venturi reactor is connected to the flue gas inlet of the dry dust filter device, and the flue gas outlet of the dry dust filter device is connected to the flue gas inlet of the spray absorption tower. The activated carbon powder in the activated carbon powder storage tank and the calcium oxide powder in the calcium oxide powder storage tank are both injected into the Venturi reactor through the Roots high-pressure blower, which can effectively improve the removal rate of harmful substances such as dioxins and acidic gases.

[0004] However, this technical solution faces several bottlenecks: on the one hand, the large quantities and high costs of activated carbon and calcium oxide result in a significant amount of hazardous waste ultimately entering the fly ash; on the other hand, the reagents themselves are difficult to recycle and reuse, leading to resource waste and environmental risks. It is worth noting that waste incineration fly ash is typically rich in activated carbon and calcium oxide residues from the flue gas purification process, and the actual amount added is often excessive, providing a basis for secondary utilization. However, currently, there is no mature process system to reintroduce this type of fly ash into the incineration flue gas for dioxin control, and there is a lack of systematic technical pathways for its recycling and end-of-pipe resource utilization (such as building material use). Therefore, how to achieve modified reuse of waste incineration fly ash has become a key technical challenge in promoting fly ash source reduction and high-value utilization. Summary of the Invention

[0005] The purpose of this invention is to address the industry technical challenges of recycling and end-of-pipe resource utilization of waste incineration fly ash, and to provide a method for controlling dioxin emissions from modified waste incineration fly ash. This method utilizes waste incineration fly ash that has undergone ball mill loading modification treatment to achieve a comprehensive approach that controls dioxin emissions from waste incineration flue gas and realizes the recycling and end-of-pipe resource utilization of modified fly ash.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for recycling modified waste incineration fly ash to control dioxins in flue gas includes the following steps: S1: Dry the fly ash from waste incineration and screen it to obtain the basic raw material for pretreatment of fly ash from waste incineration. S2: After uniformly mixing the pretreated fly ash with the functional modifier at a mass ratio, the mixture is fed into a high-energy planetary ball mill for mechanochemical synergistic modification to obtain modified fly ash. S3: Modified fly ash is injected into the exhaust gas system of the waste incinerator. The injection point is set at the front of the bag filter. The modified fly ash is used to neutralize the acidic gases in the flue gas, adsorb residual dioxin molecules in the flue gas, and inhibit the PCDD / Fs "de novo synthesis" pathway resynthesis reaction, thereby controlling PCDD / Fs emissions.

[0007] Preferably, in step S1, the waste incineration fly ash is dried at 105°C for 24 hours and screened with a mesh size of 30-50.

[0008] Preferably, in step S2, the functional modifier introduces alkaline reaction sites into the fly ash, reduces agglomeration during the mechanical ball milling process of the fly ash, increases the specific surface area and pore structure of the modified fly ash, and enhances its physical adsorption capacity and thermal stability.

[0009] Preferably, in step S2, the functional modifier includes calcium oxide (20-30 wt%) and nano-silica (5-10 wt%).

[0010] Preferably, the present invention further includes the following steps: S4: The modified fly ash injected into the flue is collected and separated by a bag filter, then modified in a ball milling system and recycled. S5: Resource-based treatment of fly ash at the end of the recycling cycle.

[0011] Preferably, in step S5, the fly ash at the end of the cycle is first subjected to ambient temperature wet carbonization treatment, so that the soluble chlorine content of the fly ash is less than 1% and the residual toxicity of PCDD / Fs is reduced to less than 50 ng-TEQ / kg.

[0012] Preferably, the ambient temperature wet carbonization conditions are: liquid-to-solid ratio of 5 L / kg, flue gas flow rate of 5-10 L / (min∙kg), and reaction time of 10-20 minutes.

[0013] Preferably, the fly ash treated by ambient temperature and humidity carbonization is mixed with cement clinker and gypsum, and then molded to prepare non-fired bricks. The compressive strength of the non-fired bricks after curing for 28 days exceeds 30 MPa.

[0014] Preferably, the mixing ratio of fly ash, cement clinker, and gypsum is 45%, 50%, and 5%, respectively.

[0015] The beneficial effects of this invention are as follows: (1) This invention involves mixing fly ash from waste incineration with functional modifiers and then performing mechanochemical synergistic modification. The modified fly ash is then reinjected into the waste incinerator tail gas system to control dioxin emissions in the waste incineration tail gas. The concentration in the flue gas can be reduced to below 0.08 ngI-TEQ / Nm³, meeting or even exceeding the emission standards of China and the European Union.

[0016] (2) This invention reduces the reliance on single-use adsorbents such as activated carbon and calcium oxide by reusing fly ash from waste incineration to replace traditional adsorbents, thereby reducing treatment costs. Compared with traditional spray adsorbents, it can reduce the amount of adsorbent material by more than 80% and significantly reduce the total amount of hazardous waste generated.

[0017] (3) The present invention has the characteristics of green and low carbon throughout the entire process. Its entire modification, spraying, recycling, carbonization and brick making process is a low energy consumption process. It can not only seal CO2, but also minimize secondary pollution, which meets the requirements of green, low carbon and environmental protection.

[0018] (4) By stably spraying modified fly ash into the front section of the bag filter, the present invention can achieve seamless connection with the existing flue gas treatment system. It has strong process adaptability, is easy to integrate, and has the potential for engineering promotion and economy.

[0019] (5) This invention utilizes the resource-based treatment of fly ash at the end of the cycle and successfully uses it to prepare non-fired bricks. The compressive strength after 28 days exceeds 30 MPa, which has practical engineering application value.

[0020] In summary, this invention has the advantages of high efficiency in pollution control, low cost, and environmental friendliness. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0022] Example 1 like Figure 1As shown, a method for recycling modified waste incineration fly ash to control dioxins in flue gas includes the following steps: S1: Dry the fly ash from waste incineration and screen it to obtain the basic raw material for pretreatment of fly ash from waste incineration. This step is mainly used for the pretreatment of waste incineration fly ash. The fly ash is dried at 105℃ for 24 hours to remove free moisture and some volatile components. Then it is screened through a 30-50 mesh sieve to remove large and irregular particles, obtaining a basic raw material with uniform particle size suitable for subsequent modification. S2: After uniformly mixing the pretreated fly ash with the functional modifier at a mass ratio, the mixture is fed into a high-energy planetary ball mill for mechanochemical synergistic modification to obtain modified fly ash. In this step, pretreated fly ash is mixed with a functional modifier to prepare modified fly ash.

[0023] The functional modifiers include: 20-30 wt% calcium oxide (CaO) is added mainly to introduce basic reaction sites and inhibit the de novo synthesis of PCDD / Fs; 5-10wt% nano silica (SiO2): The addition of nano silica can reduce the agglomeration of fly ash during mechanical ball milling, improve the specific surface area and pore structure of modified fly ash, and enhance physical adsorption capacity and thermal stability.

[0024] In this step, a vertical stirred mill is preferred, specifically the AX-vertical rapid stirred ball mill; the milling time is 2-3 hours, the grinding media is φ10mm zirconia balls, the ball-to-material ratio is 2-5:1, and the rotation speed is 100-200 rpm.

[0025] High-energy planetary ball milling significantly reduces fly ash particle size, enhances specific surface area and surface activity, and develops a more developed microporous structure while improving surface-active functional groups. On the other hand, it can stimulate the reactivity of calcium oxide and activated carbon, thereby improving the adsorption capacity and resynthesis inhibition capacity of dioxins.

[0026] In this embodiment, after adding 20-30 wt% calcium oxide (CaO) and 5-10 wt% nano-silica (SiO2), the specific surface area of ​​the fly ash after ball milling modification is 25 m². 2 / g.

[0027] S3: Modified fly ash is injected into the waste incinerator exhaust gas system, with the injection point located in front of the bag filter to absorb residual dioxins in the exhaust gas system.

[0028] In this step, modified fly ash is stably injected into the waste incinerator tail gas system via a screw feeder or pneumatic conveying system. The injection position is set at the front of the bag filter (i.e., the traditional activated carbon / calcium oxide injection position), which can be seamlessly connected to the existing flue gas treatment system. The flue gas temperature range at this position is 180–250℃, which is the sensitive temperature window for PCDD / Fs secondary synthesis ("de novo synthesis").

[0029] The modified fly ash can achieve a synergistic effect of acid gas neutralization, physical adsorption, and chemical inhibition. (1) Neutralize acidic gases (such as HCl) in flue gas; (2) Adsorb residual dioxin molecules in flue gas; (3) Suppress the resynthesis reaction of PCDD / Fs via the “de novo synthesis” pathway.

[0030] Example 2 like Figure 1 As shown, components that are the same as or corresponding to those in Embodiment 1 are referred to using the same reference numerals as in Embodiment 1. For simplicity, only the differences from Embodiment 1 are described below. The difference between Embodiment 2 and Embodiment 1 is as follows: A method for recycling modified waste incineration fly ash to control dioxins in flue gas further includes the following steps: S4: The modified fly ash injected into the flue is collected and separated by a bag filter, then modified by a ball mill system and recycled.

[0031] Modified fly ash can be recycled in 3–4 cycles. After each cycle, the performance is evaluated based on the specific surface area of ​​the fly ash and its PCDD / Fs adsorption capacity to ensure that its functionality is maintained within a controllable range.

[0032] This invention can reduce the concentration of PCDD / Fs in flue gas to below 0.08 ngI-TEQ / Nm³, meeting or even exceeding the emission standards of China and the European Union.

[0033] Compared with traditional spray adsorbents, this invention can reduce the amount of adsorbent material by more than 80%, significantly reducing the total amount of hazardous waste generated.

[0034] S5: Resource-based treatment of fly ash at the end of the recycling cycle; In this step, after multiple cycles, the surface activity of the modified fly ash decreases, and its ability to adsorb and inhibit dioxins declines. However, its hydration activity is enhanced, giving it the potential for use in building materials.

[0035] At this point, after being treated with ambient temperature and humidity carbonization, the fly ash has a soluble chlorine content of less than 1%, the residual toxicity of PCDD / Fs is reduced to less than 50 ng-TEQ / kg, and the heavy metal leaching concentration meets the requirements for fly ash reuse in the "Technical Specification for Pollution Control of Waste Incineration Fly Ash" (HJ1134-2020).

[0036] Furthermore, the processing conditions for ambient temperature wet carbonization are: liquid-to-solid ratio of 5 L / kg, flue gas flow rate of 5-10 L / (min∙kg), and reaction time of 10-20 minutes.

[0037] Example 3 like Figure 1 As shown, components that are the same as or corresponding to those in Embodiment 1 are referred to using the same reference numerals as in Embodiment 1. For simplicity, only the differences from Embodiment 1 are described below. The difference between Embodiment 3 and Embodiment 1 is as follows: In the process of resource-based treatment of fly ash at the end of the recycling cycle; Furthermore, the dechlorinated fly ash is mixed with cement clinker and gypsum, and then molded to prepare non-fired bricks. After curing for 28 days, the compressive strength exceeds 30 MPa, realizing a closed loop of resource utilization from pollution control to functional building materials.

[0038] The mixing ratio of fly ash, cement clinker, and gypsum is: 45% fly ash, 50% cement clinker, and 5% gypsum.

[0039] Comparative Example 1 A method for recycling modified waste incineration fly ash to control dioxins in flue gas includes the following steps: S1: Dry the fly ash from waste incineration and screen it to obtain the basic raw material for pretreatment of fly ash from waste incineration. This step is mainly used for the pretreatment of waste incineration fly ash. The fly ash is dried at 105℃ for 24 hours to remove free moisture and some volatile components. Then it is screened through a 30-50 mesh sieve to remove large and irregular particles, obtaining a basic raw material with uniform particle size suitable for subsequent modification. S2: After uniformly mixing the pretreated fly ash with the functional modifier at a mass ratio, the mixture is fed into a high-energy planetary ball mill for mechanochemical synergistic modification to obtain modified fly ash. The functional modifiers include: 20-30 wt% calcium oxide (CaO) is added mainly to introduce basic reaction sites and inhibit the de novo synthesis of PCDD / Fs; In this step, a vertical stirred mill is preferred, specifically the AX-vertical rapid stirred ball mill; the milling time is 2-3 hours, the grinding media is φ10mm zirconia balls, the ball-to-material ratio is 2-5:1, and the rotation speed is 100-200 rpm.

[0040] In this embodiment, the specific surface area of ​​the fly ash after ball milling is 1 m². 2 / g, because calcium oxide absorbs water severely during ball milling, fly ash agglomerates, which significantly reduces its specific surface area and thus affects the adsorption performance of modified fly ash during reuse.

[0041] Comparative Example 2 A method for recycling modified waste incineration fly ash to control dioxins in flue gas includes the following steps: S1: Dry the fly ash from waste incineration and screen it to obtain the basic raw material for pretreatment of fly ash from waste incineration. This step is mainly used for the pretreatment of waste incineration fly ash. The fly ash is dried at 105℃ for 24 hours to remove free moisture and some volatile components. Then it is screened through a 30-50 mesh sieve to remove large and irregular particles, obtaining a basic raw material with uniform particle size suitable for subsequent modification. S2: After uniformly mixing the pretreated fly ash with the functional modifier at a mass ratio, the mixture is fed into a high-energy planetary ball mill for mechanochemical synergistic modification to obtain modified fly ash. The functional modifiers include: 5-10wt% nano silica (SiO2): The addition of nano silica can reduce the agglomeration of fly ash during mechanical ball milling, improve the specific surface area and pore structure of modified fly ash, and enhance physical adsorption capacity and thermal stability.

[0042] In this step, a vertical stirred mill is preferred, specifically the AX-vertical rapid stirred ball mill; the milling time is 2-3 hours, the grinding media is φ10mm zirconia balls, the ball-to-material ratio is 2-5:1, and the rotation speed is 100-200 rpm.

[0043] In this embodiment, the specific surface area of ​​the fly ash after ball milling is 30 m². 2 / g, by adding nano-silica, the non-water-absorbing function of silica greatly reduces the phenomenon of fly ash agglomeration and disperses fly ash particles, thereby increasing the specific surface area of ​​fly ash after ball milling.

[0044] However, modified fly ash after ball milling without the addition of calcium oxide could not inhibit the de novo synthesis of PCDD / Fs, and the concentration of PCDD / Fs in the flue gas was greater than 0.08 ngI-TEQ / Nm³.

[0045] Comparative Example 3 A method for recycling modified waste incineration fly ash to control dioxins in flue gas includes the following steps: S1: Dry the fly ash from waste incineration and screen it to obtain the basic raw material for pretreatment of fly ash from waste incineration. This step is mainly used for the pretreatment of waste incineration fly ash. The fly ash is dried at 105℃ for 24 hours to remove free moisture and some volatile components. Then it is screened through a 30-50 mesh sieve to remove large and irregular particles, obtaining a basic raw material with uniform particle size suitable for subsequent modification. S2: The pretreated fly ash is fed into a high-energy planetary ball mill for mechanochemical synergistic modification to obtain modified fly ash; In this step, a vertical stirred mill is preferred, specifically the AX-vertical rapid stirred ball mill; the milling time is 2-3 hours, the grinding media is φ10mm zirconia balls, the ball-to-material ratio is 2-5:1, and the rotation speed is 100-200 rpm.

[0046]

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for recycling modified waste incineration fly ash to control dioxins in flue gas, characterized in that, Includes the following steps: S1: Dry the fly ash from waste incineration and screen it to obtain the basic raw material for pretreatment of fly ash from waste incineration. S2: After uniformly mixing the pretreated fly ash with the functional modifier at a mass ratio, the mixture is fed into a high-energy planetary ball mill for mechanochemical synergistic modification to obtain modified fly ash. S3: Modified fly ash is injected into the exhaust gas system of the waste incinerator. The injection point is set at the front of the bag filter. The modified fly ash is used to neutralize the acidic gases in the flue gas, adsorb residual dioxin molecules in the flue gas, and inhibit the PCDD / Fs "de novo synthesis" pathway resynthesis reaction, thereby controlling PCDD / Fs emissions.

2. The method for recycling modified waste incineration fly ash to control dioxins in flue gas according to claim 1, characterized in that, In step S1, the fly ash from the waste incineration is dried at 105°C for 24 hours and screened to a mesh size of 30-50.

3. The method for recycling modified waste incineration fly ash to control dioxins in flue gas according to claim 1, characterized in that, In step S2, the functional modifier introduces alkaline reaction sites into the fly ash, reduces agglomeration during the mechanical ball milling process, increases the specific surface area and pore structure of the modified fly ash, and enhances its physical adsorption capacity and thermal stability.

4. The method for recycling modified waste incineration fly ash to control dioxins in flue gas according to claim 3, characterized in that, In step S2, the functional modifier includes calcium oxide (20-30 wt%) and nano-silica (5-10 wt%).

5. The method for recycling modified waste incineration fly ash to control dioxins in flue gas according to claim 1, characterized in that, It also includes the following steps: S4: The modified fly ash injected into the flue is collected and separated by a bag filter, then modified in a ball milling system and recycled. S5: Resource-based treatment of fly ash at the end of the recycling cycle.

6. The method for recycling modified waste incineration fly ash to control dioxins in flue gas according to claim 5, characterized in that, In step S5, the fly ash at the end of the cycle is first subjected to ambient temperature wet carbonization treatment, so that the soluble chlorine content of the fly ash is less than 1% and the residual toxicity of PCDD / Fs is reduced to less than 50 ng-TEQ / kg.

7. The method for recycling modified waste incineration fly ash to control dioxins in flue gas according to claim 6, characterized in that, The ambient temperature wet carbonization conditions are: liquid-to-solid ratio of 5 L / kg, flue gas flow rate of 5-10 L / (min∙kg), and reaction time of 10-20 minutes.

8. The method for recycling modified waste incineration fly ash to control dioxins in flue gas according to claim 6, characterized in that, Fly ash treated by regular warm and humid carbonization is mixed with cement clinker and gypsum, and then molded to prepare non-fired bricks. The compressive strength of the non-fired bricks exceeds 30 MPa after 28 days of curing.

9. A method for recycling modified waste incineration fly ash to control dioxins in flue gas, as described in claim 8, characterized in that, The fly ash, cement clinker, and gypsum are mixed in a ratio of 45%, 50%, and 5%, respectively.

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