Continuous fly ash detoxification process

Abstract

The present application relates to the field of fly ash disposal, in particular to a continuous fly ash detoxification method, the system comprises a water washing system, a membrane filtration system, a hydrothermal system, a dehydration system and an auxiliary system, which can realize the removal of soluble chlorine in fly ash, the decomposition of dioxin and the stability of heavy metals. The method is aimed at the current sequential batch operation mode of fly ash water washing, which uses a large proportion of water to ash ratio to wash fly ash, and uses air floatation to separate most of the activated carbon in the fly ash; the membrane filtration system is used to control the solid-liquid ratio of the washed fly ash, and the hydrothermal system is used to realize the detoxification of dioxin and heavy metals in fly ash. The present application can be used for treating fly ash produced by incineration of household garbage, medical waste, hazardous waste and other waste, and can treat fly ash with different pollution levels, and has strong adaptability.

Description

Technical Field

[0001] This invention relates to the field of fly ash disposal, including fly ash washing, detoxification and resource utilization, specifically to a continuous fly ash detoxification method. Background Technology

[0002] Incineration fly ash is mainly generated from flue gas treatment systems following the incineration of municipal solid waste, hazardous waste, and medical waste. Soluble chlorine, dioxins, and heavy metals in fly ash are the main issues that need to be addressed in fly ash disposal and resource utilization.

[0003] Because pollutants in fly ash undergo different detoxification processes, a single treatment technology cannot achieve complete detoxification; a coupled, cascaded process is necessary. Currently, multi-stage countercurrent washing is the mainstream process for removing soluble chlorine, operating in a batch process. Each stage of washing requires a solid-liquid separation unit, resulting in high energy consumption and low overall operational efficiency. Hydrothermal treatment has a certain solidification effect on heavy metals and a certain decomposition effect on dioxins, but its efficiency is low. However, hydrothermal reactions require a feed moisture content of 10-40%. Combining washing with hydrothermal treatment can achieve continuous operation of fly ash washing and detoxification, reducing the number of equipment in the fly ash washing process, simplifying the fly ash detoxification process, and lowering energy consumption and costs. Furthermore, research shows that dioxins in fly ash are mainly concentrated in the activated carbon within the fly ash; hydrothermal treatment may not be sufficient to meet the detoxification requirements for dioxins in fly ash. To address this characteristic, a flotation process can be added to the fly ash washing process to promote the flotation separation of activated carbon, further improving the process's detoxification efficiency for dioxins.

[0004] Based on the above considerations, this invention proposes a continuous fly ash detoxification method, which achieves continuous operation of fly ash detoxification treatment through the coupling effect between processes. Summary of the Invention

[0005] The purpose of this invention is to provide a continuous fly ash detoxification method, which changes the existing sequential batch feeding and discharging mode of fly ash washing.

[0006] This technical solution includes a washing system, a membrane filtration system, a hydrothermal system, a dewatering system, and auxiliary systems. The fly ash washing system employs a high water-to-ash ratio to wash the fly ash, utilizing the solubility of chlorine in the fly ash to achieve rapid dechlorination. During the washing stage, aeration is used to remove fine activated carbon particles from the fly ash, thus initially removing dioxins. The washed fly ash slurry is then filtered using a membrane filtration system to control its solids content. The fly ash slurry with a suitable solids content enters the hydrothermal system, where, under high temperature and pressure, it achieves deep decomposition of dioxins and solidification of heavy metals, further reducing the residual soluble chlorine content in the dechlorinated fly ash.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A continuous fly ash detoxification method includes a water washing system, a membrane filtration system, a hydrothermal system, a dewatering system, and an auxiliary system. The water washing system is connected to the membrane filtration system for dissolving soluble chlorine and separating activated carbon from the fly ash. The membrane filtration system receives the washed fly ash slurry, and its concentrate end (discharge end) is connected to the hydrothermal system to control the solid-liquid ratio of the fly ash slurry. The hydrothermal system is connected to the dewatering system for fly ash dewatering. The auxiliary systems are a tail gas treatment system and a wastewater treatment system, used for treating tail gas generated during the operation of the water washing system and the hydrothermal system, and for treating wastewater generated during the operation of the membrane filtration system and the dewatering system, respectively.

[0009] Further steps include:

[0010] (1) Mix fly ash and water in a water washing system according to the proportion. Ammonia gas is generated during the mixing process. Use the tail gas collection device at the top of the water washing system to collect the gas and discharge it into the tail gas treatment system for treatment.

[0011] (2) The aeration system at the bottom of the pool is used to fully mix the fly ash and water, and the activated carbon in the fly ash is separated by flotation. The activated carbon floats on the liquid surface in the form of foam, and is separated from the liquid phase by a foam scraper. The activated carbon foam produced by the separation is sent out for incineration.

[0012] (3) The fly ash slurry after sufficient retention in the washing tank is pumped to the membrane filtration system. By controlling the power of the inlet pump of the membrane, the solid-liquid ratio of the fly ash slurry at the concentrate end (discharge end) is controlled. No less than two sets of membrane filtration systems are set up, and they can be used alternately to achieve continuous operation, with one set on standby and one set on standby. The fly ash slurry generated at the discharge end of the membrane filtration system is temporarily stored in the No. 1 buffer tank.

[0013] (4) Use a pump to extract fly ash slurry from the No. 1 buffer tank. An automatic dosing device is set up after the pump to automatically add heavy metal stabilizer into the pipeline and then into the hydrothermal reactor via a high-pressure plunger pump.

[0014] (5) The hydrothermal reactor is a continuous reactor. The reaction temperature is controlled by electric heating, and the reaction pressure is controlled by the opening of the outlet valve and the high-pressure plunger pump, which can realize the continuous operation of the hydrothermal reaction.

[0015] (6) The fly ash slurry after full hydrothermal treatment is sent to the No. 2 buffer tank from the discharge end of the hydrothermal device. The fly ash slurry is restored to normal pressure in the No. 2 buffer tank and then pumped to the dewatering system.

[0016] (7) The fly ash slurry achieves final dewatering of fly ash in the dewatering system, and the resulting dewatered fly ash is used for resource utilization.

[0017] Furthermore, the washing system includes a washing tank, an aeration device, a foam scraper, and an exhaust gas collection device;

[0018] The washing tank is 5 to 10 meters long and 1 to 2 meters wide. The inlet / outlet is located on the short side of the washing tank. Fly ash, water, collector and foaming agent are fed from one side and discharged from the other side.

[0019] Control the water-cement ratio between 15 and 30:1, and ensure that the feed rate and discharge rate are equal to maintain a basically constant liquid level in the washing tank.

[0020] The dosage ratio of collector and frother is 0-15% of the fly ash feed amount;

[0021] Furthermore, the membrane filtration system may employ ultrafiltration membranes, microfiltration membranes, or other similar forms, with no fewer than two sets used alternately;

[0022] After being treated by the membrane filtration system, the solids content of the fly ash slurry is controlled within the range of 10% to 30%.

[0023] Furthermore, the hydrothermal system includes a feed pump, a No. 1 buffer tank, a hydrothermal reactor, and a No. 2 buffer tank;

[0024] The dosage of heavy metal stabilizer is 0-50% of the total fly ash.

[0025] Heavy metal stabilizers include sodium hydrogen phosphate, sodium sulfide, etc.

[0026] The hydrothermal reaction temperature was controlled at 200–400℃, and the residence time was controlled at 0.5–1 h.

[0027] Furthermore, the dehydration system is a vacuum belt filter.

[0028] The present invention has the following specific beneficial effects:

[0029] This invention combines high water-to-ash ratio washing with membrane technology, effectively reducing suspended solids (SS) in washing wastewater. The entire washing process requires minimal manual intervention, enabling continuous operation of fly ash washing. By considering the solid-liquid ratio of the fly ash slurry after membrane separation, hydrothermal technology is used to treat the slurry, promoting the dissolution and dilution of residual chlorine, the decomposition of residual dioxins, and the mineral phase transformation of heavy metals under hydrothermal conditions. After hydrothermal treatment, the fly ash can be detoxified of dioxins and heavy metals, and the treated fly ash can be used as a concrete admixture and raw material for non-fired blocks. Attached Figure Description

[0030] Figure 1 A process flow diagram for a continuous fly ash detoxification method; Detailed Implementation

[0031] To enable those skilled in the art to better understand the present invention, the invention method will be further described in detail below with reference to the following specific embodiments and accompanying drawings, but this does not limit the invention to the scope of the embodiments.

[0032] Please see Figure 1 A continuous fly ash detoxification method includes a water washing system, a membrane filtration system, a hydrothermal system, a dehydration system, and an auxiliary system.

[0033] The fly ash washing system employs a high water-to-ash ratio to wash the fly ash, removing as much soluble chlorine as possible. Simultaneously, aeration removes small particles of activated carbon from the fly ash. The washed fly ash slurry utilizes a membrane filtration system to regulate the solid-liquid ratio, and a hydrothermal method is employed to decompose dioxins and stabilize heavy metals in the fly ash. This invention simplifies the fly ash disposal process and enables continuous fly ash treatment.

[0034] A case study of a continuous fly ash detoxification method is as follows:

[0035] 1. Add 50g of fly ash and 1000mL and 1500mL of deionized water respectively according to the water-ash ratio. After stirring thoroughly, add 0.25-0.5g of collector and 0.25-0.5g of foaming agent. Use an air pump to introduce air into the solution and aerate for 30 minutes. Remove the scum on the surface of the liquid.

[0036] 2. The above-mentioned water-washed fly ash was separated into dechlorinated fly ash and liquid phase by suction filtration. 10g of dechlorinated fly ash was taken and the solid content of the dechlorinated fly ash was adjusted to 10% and 20% respectively with deionized water. 0.5g of sodium phosphate and 0.5g of ferric chloride were added respectively. The hydrothermal reaction was carried out at 200℃ and 250℃ for 1h respectively. The leaching concentrations of soluble chlorine, dioxins and heavy metals in the reaction products were all lower than the limits of the standard in the "Technical Specification for Pollution Control of Fly Ash from Municipal Solid Waste Incineration (Trial)" (HJ 1134-2021).

[0037] 3. Detoxification of soluble chlorine, heavy metals, and dioxins under different conditions:

[0038]

[0039]

[0040] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A continuous fly ash detoxification method, characterized in that, It includes a water washing system, a membrane filtration system, a hydrothermal system, a dehydration system, and an auxiliary system; the water washing system is connected to the membrane filtration system and is used for the dissolution of soluble chlorine and the separation of activated carbon in fly ash; The membrane filtration system is fed with washed fly ash slurry, and the discharge end is connected to the hydrothermal system to control the solid-liquid ratio of the fly ash slurry. The hydrothermal system is connected to the dehydration system for fly ash dehydration; The auxiliary systems are a tail gas treatment system and a wastewater treatment system, which are used to treat the tail gas generated during the operation of the water washing system and the hydrothermal system, and to treat the wastewater generated during the operation of the membrane filtration system and the dewatering system, respectively. Includes the following steps: (1) Mix fly ash and water in a water washing system according to the proportion. Ammonia gas is generated during the mixing process. The gas is collected by the tail gas collection device at the top of the water washing system and discharged into the tail gas treatment system for treatment. (2) The aeration system at the bottom of the pool is used to fully mix the fly ash and water, and the activated carbon in the fly ash is separated by flotation. The activated carbon floats on the liquid surface in the form of foam, and is separated from the liquid phase by a foam scraper. The activated carbon foam produced by the separation is sent out for incineration. (3) The fly ash slurry after sufficient retention in the washing tank is pumped to the membrane filtration system. By controlling the power of the inlet pump of the membrane, the solid-liquid ratio of the fly ash slurry at the concentrate end is controlled. No less than two sets of membrane filtration systems are set up, and they can be used alternately to achieve continuous operation, with one set on standby and one set on standby. The fly ash slurry generated at the outlet end of the membrane filtration system is temporarily stored in the No. 1 buffer tank. (4) Use a pump to extract fly ash slurry from the No. 1 buffer tank. An automatic dosing device is installed after the pump to automatically add heavy metal stabilizer into the pipeline and then into the hydrothermal reactor via a high-pressure plunger pump. (5) The hydrothermal reactor is a continuous reactor. The reaction temperature is controlled by electric heating, and the reaction pressure is controlled by the opening of the outlet valve and the high-pressure plunger pump, which can realize the continuous operation of the hydrothermal reaction. (6) The fly ash slurry after full hydrothermal treatment is sent to the No. 2 buffer tank from the discharge end of the hydrothermal device. The fly ash slurry is restored to normal pressure in the No. 2 buffer tank and then pumped to the dewatering system. (7) The final dewatering of fly ash is achieved in the dewatering system of fly ash slurry, and the dewatered fly ash produced is used for resource utilization.

2. The continuous fly ash detoxification method according to claim 1, characterized in that, The washing system includes a washing tank, an aeration device, a foam scraper, and an exhaust gas collection device; (1) The washing tank is 5-10 meters long and 1-2 meters wide. The inlet / outlet is located on the short side of the washing tank. Fly ash, water, collector and foaming agent are fed from one side and discharged from the other side. (2) Control the water-cement ratio at 15~30:1, and ensure that the feeding rate and the discharge rate are equal to ensure that the liquid level in the washing tank is basically constant. (3) The ratio of collector and foaming agent is 0 to 15% of the fly ash feed amount.

3. The continuous fly ash detoxification method according to claim 1, characterized in that, The membrane filtration system may use ultrafiltration membranes or microfiltration membranes, with no fewer than two sets used alternately. After being treated by the membrane filtration system, the solids content of the fly ash slurry is controlled within the range of 10-30%.

4. The continuous fly ash detoxification method according to claim 1, characterized in that, The hydrothermal system includes a feed pump, a No. 1 buffer tank, a hydrothermal reactor, and a No. 2 buffer tank; (1) The dosage of heavy metal stabilizer is 0-50% of the total fly ash; (2) Heavy metal stabilizers include sodium hydrogen phosphate, sodium phosphate, sodium sulfide, ferric chloride, etc.; (3) The hydrothermal reaction temperature is controlled at 200~400℃ and the residence time is controlled at 0.5~1h.

5. The continuous fly ash detoxification method according to claim 1, characterized in that, The dehydration system is a vacuum belt filter.

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