Source reduction and resource utilization method for dioxin in fly ash

Abstract

The invention discloses a resource utilization method for source reduction of dioxin in fly ash, and belongs to the technical field of dioxin treatment, in the source reduction of the dioxin in the fly ash, a quadruple dioxin control technology is adopted for dioxin reduction treatment; the quadruple dioxin control technology comprises a low-temperature pyrolysis process, a high-temperature decomposition process, an online control process and an in-furnace inhibition process, dioxin is rapidly decomposed by combining two methods of low-temperature pyrolysis and high-temperature decomposition, two defense lines are set, the content of dioxin in the process is automatically monitored, and a dioxin inhibitor is used for controlling when the content exceeds a control value. Wherein the adopted dioxin inhibitor is a mixed inhibitor of a nitrogen source loaded molecular sieve and calcium hydroxide, so that the formation of dioxin can be inhibited, and the stability of the inhibitor can also be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of dioxin treatment, and specifically relates to a method for reducing the dioxin in fly ash and utilizing it as a resource. Background Art

[0002] In recent years, incineration power generation has become one of the leading processes for urban domestic waste treatment, and has occupied an important position in the harmless treatment of waste. In the process of waste incineration, a large amount of fly ash is produced. Since fly ash contains a large amount of heavy metals, such as Zn, Pb, Cu, Cr, Cd, Ni, etc., as well as organic substances such as dioxins and furans, it is listed as a hazardous waste in the "National List of Hazardous Wastes", and it is clearly pointed out that fly ash needs to be treated and cannot be directly discharged.

[0003] Traditional fly ash treatment methods, such as safe landfill, are to simply treat the fly ash from garbage incineration on site and then send it to a safe landfill for landfill. This method is safe and reliable, but the construction and operation costs are high, which is difficult for garbage incineration plants to bear, and it also cannot achieve the purpose of volume reduction and resource utilization; the solidification / stabilization + landfill fly ash disposal method is to capture, coagulate and inhibit the heavy metals in the fly ash through stabilization agents to form stable substances. After meeting the leaching toxicity standards, it is landfilled in a domestic waste landfill; the treatment process is simple, the cost is low, and it is widely used, but it leads to increased volume and volume, occupies landfill space, and long-term risk hazards have not been assessed.

[0004] Other technical means include biodegradation, chemical removal and low-temperature pyrolysis technology, which are still in the experimental stage. Among them, low-temperature pyrolysis is not effective in removing dioxins, and dioxins still exist in the treated waste gas.

[0005] It can be seen that the current fly ash treatment methods still have problems such as high construction and operation costs, great long-term risks, and high energy consumption, which makes it difficult to achieve the goal of fly ash resource utilization. Summary of the invention

[0006] The purpose of the present invention is to provide a fly ash dioxin source reduction resource utilization method to solve the problems of high cost, low dioxin reduction efficiency and poor effect of existing fly ash treatment methods and inability to recycle them.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] The present invention provides a fly ash dioxin source reduction resource utilization method, wherein the fly ash dioxin source reduction adopts a quadruple dioxin control technology to carry out dioxin reduction treatment; the quadruple dioxin control technology includes a quadruple process of low-temperature pyrolysis, high-temperature decomposition, online control and in-furnace inhibition;

[0009] The controlled pyrolysis temperature of the low-temperature pyrolysis process is 300-550°C;

[0010] The high temperature decomposition process is to conduct secondary combustion of low temperature pyrolysis products through secondary air, and the secondary combustion temperature is 850-1000℃;

[0011] The online control process is to use the fly ash dioxin online control system to automatically monitor the dioxin content in the fly ash and keep the dioxin content below the control value;

[0012] The in-furnace inhibition process uses dioxin inhibitor dosing equipment to automatically start adding dioxin inhibitors when the dioxin content is higher than the control value.

[0013] Preferably, the control value is 50 ng TEQ / kg.

[0014] By adopting the above technical solution, in order to efficiently remove dioxins in fly ash, control the dioxin level in fly ash to always be below 50ng TEQ / kg and not cause secondary pollution to the environment, the present invention adopts quadruple dioxin control technology to reduce the dioxin content in fly ash from the source, specifically:

[0015] First, the fly ash from garbage incineration is subjected to a low-temperature pyrolysis process, and the pyrolysis temperature is controlled to be slightly higher than the boiling point of dioxins, so that the dioxins in the fly ash are gasified into the flue gas. Then, the fly ash is subjected to a high-temperature decomposition process, and the flue gas containing dioxins is subjected to secondary combustion. Under high-temperature conditions, dioxins are rapidly decomposed, and the decomposition rate reaches 99% or more. At the same time, the dioxin content in the fly ash is automatically monitored according to the online control process. When the content is higher than the control value, the second line of defense is immediately activated, that is, the dioxin inhibitor is sprayed in time by using the in-furnace inhibition process, so that the dioxin generation can be controlled while effectively reducing the dioxins in the fly ash. In addition, the present invention can set the control value of the dioxins in the fly ash to 50ng TEQ / kg, so as to achieve precise control of the dioxin value.

[0016] Preferably, the dioxin inhibitor comprises nitrogen source-loaded molecular sieve and calcium hydroxide in a mass ratio of (6-8):(2-4).

[0017] Preferably, the raw materials for the nitrogen source loaded molecular sieve include urea and molecular sieve in a mass ratio of (0.5-0.7):1.

[0018] Preferably, the molecular sieve is compounded with titanium dioxide; the mass of the compounded titanium dioxide is 20-30% of the mass of the molecular sieve.

[0019] Preferably, the nitrogen source loaded molecular sieve is prepared according to the following method:

[0020] Preparation of molecular sieve composite titanium dioxide: molecular sieve is added to the solvent, and after uniform dispersion, titanium precursor is added, deionized water is added after stirring for 1 to 2 hours, and stirring for 30 to 60 minutes, and finally the molecular sieve composited with titanium dioxide is obtained after washing, drying and calcining;

[0021] Preparation of nitrogen source loaded molecular sieve: The molecular sieve is uniformly dispersed in the urea solution, stirred in a water bath at 60-80° C. for 4-6 hours, and filtered and dried to obtain the nitrogen source loaded molecular sieve.

[0022] Preferably, the solvent includes one or more combinations of ethanol, methanol, isopropanol, n-butanol and n-propanol.

[0023] Preferably, the titanium precursor includes a combination of one or more of tetrabutyl titanate, isopropyl titanate, n-propyl titanate and ethyl titanate.

[0024] Preferably, the urea solution is a urea aqueous solution with a mass fraction of 5 to 10%.

[0025] By adopting the above technical scheme, the dioxin inhibitor used in the present invention is a mixed inhibitor of nitrogen source loaded molecular sieve and calcium hydroxide, wherein the nitrogen source refers to urea, and the lone pair electrons contained in the nitrogen atoms in the urea can form a stable complex with the metal that catalyzes the formation of dioxins, and can not only inhibit the activity of the catalyst but also fix the metal on the molecular sieve, thereby reducing the content of heavy metals in the fly ash, and the ammonia obtained by decomposition can also react with the acidic precursor to reduce the raw materials required for the formation of dioxins; the alkaline property of calcium hydroxide can react with the hydrogen chloride in the raw material to form salt, thereby transferring chlorine to the particle phase, reducing the chlorine element in the gas phase, thereby reducing the formation of dioxins at the source, and the two components are used in combination to inhibit the formation of dioxins from two different perspectives of inhibiting the activity of the catalyst and reducing the raw materials for the formation of dioxins, respectively, and have a more efficient effect than a single inhibitor.

[0026] However, urea is chemically unstable as an inhibitor, and its inhibitory effect at high temperature will be affected. In addition, in the process of high-temperature thermal decomposition, urea can be decomposed to obtain ammonia that is beneficial to inhibiting the formation of dioxins, and it is also easy to generate nitrogen oxides. Nitrogen oxides are still one of the harmful gases that pollute the air, and it is still impossible to effectively achieve the harmless treatment of fly ash. Therefore, the present invention loads urea on a molecular sieve. Through the protection of the molecular sieve and the amplification effect of the molecular sieve on the complexation of urea catalysis metal, the obtained nitrogen source loaded molecular sieve not only has a good dioxin inhibition effect and stability, but also can reduce the probability of urea decomposing into nitrogen oxides in the process, thereby reducing the impact of nitrogen oxides.

[0027] At the same time, the surface of the molecular sieve has a strong affinity for water, and the tiny and uniform pore structure inside is also conducive to the molecular sieve's attraction to water molecules, which can promote the reaction of calcium hydroxide and hydrogen chloride to proceed in the forward direction, thereby improving the inhibition effect.

[0028] Furthermore, titanium dioxide can also be loaded on the molecular sieve. Titanium dioxide can work together with ammonia generated by the decomposition of urea to catalyze the conversion of already formed nitrogen oxides into nitrogen and water. It can reduce the adverse effects of urea decomposition while converting the nitrogen oxides originally existing in the flue gas during the waste incineration fly ash treatment process, thereby achieving harmless treatment of fly ash.

[0029] Preferably, the specific steps of fly ash dioxin source reduction and resource utilization provided by the present invention include:

[0030] S1. Fly ash from waste incineration treated with dioxin reduction technology using quadruple dioxin control technology;

[0031] S2. sorting, crushing and screening the well-fermented domestic waste and other waste to obtain high calorific value waste;

[0032] S3. The fly ash treated with dioxin reduction is mixed evenly with high calorific value garbage and auxiliary materials to prepare garbage-derived fuel;

[0033] S4. The obtained garbage-derived fuel assists the combustion of domestic waste, and its combustion residue is discharged with the slag and enters the slag treatment plant. The tailings are used to prepare fire-free building materials and fix heavy metals for resource utilization.

[0034] Preferably, the particle size of the high calorific value garbage is 1 to 4 cm.

[0035] Preferably, the fly ash subjected to dioxin reduction treatment accounts for 10 to 45 wt % of the waste derived fuel.

[0036] Preferably, the auxiliary material in step S3 includes one or more combinations of sludge, coal slime and coal powder.

[0037] By adopting the above technical scheme, the fly ash from waste incineration is first treated with dioxin reduction through the quadruple dioxin control technology to reduce the presence of dioxins in the fly ash at the source; then the fly ash after dioxin reduction is mixed with high calorific value waste, and the strong alkalinity and viscosity of the fly ash are used to prepare waste-derived fuel, in which the fly ash plays the role of a chlorine-fixing agent, a sulfur-fixing agent and a binder, which can fix chlorine in the slag, thereby significantly reducing the chlorine released into the flue gas; the obtained waste-derived fuel can be further burned with domestic waste after particle size control to improve the combustion efficiency and burnout rate of domestic waste, and can also be used as fuel in other occasions to achieve resource utilization.

[0038] And when waste-derived fuel assists the combustion of domestic waste, the combustion residue is discharged with the slag and enters the slag disposal plant. The tailings can fix heavy metals in the non-burning building materials, thereby achieving the treatment of heavy metals and realizing resource utilization again. The whole process achieves the efficient removal of fly ash dioxins, the fixation of heavy metals and the comprehensive utilization of resources.

[0039] Beneficial effects of the present invention:

[0040] 1. The present invention adopts quadruple dioxin control technology to reduce the dioxins in fly ash, wherein low-temperature pyrolysis and high-temperature decomposition are combined to rapidly decompose dioxins, and two lines of defense are set up to automatically monitor the dioxin content during the process and use dioxin inhibitors to control it when it exceeds the control value. Finally, the dioxin content in the released flue gas is far lower than the national standard.

[0041] 2. The dioxin inhibitor used in the present invention is a mixture of a nitrogen source loaded molecular sieve and calcium hydroxide, wherein the nitrogen source is urea. Urea and calcium hydroxide work together to inhibit the formation of dioxins from different angles. Urea loaded on the molecular sieve can improve the inhibitor's dioxin inhibition effect and increase the inhibitor's stability, while also reducing the probability of urea decomposing into nitrogen oxides and reducing the nitrogen oxide content in fly ash. DETAILED DESCRIPTION

[0042] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] Preparation Example

[0044] Preparation Example 1: A nitrogen source loaded molecular sieve is prepared according to the following method:

[0045] Add 10 g of molecular sieve (4A molecular sieve) to 150 mL of ethanol, add tetrabutyl titanate after evenly dispersing, add 40 mL of deionized water after stirring for 1 hour, continue stirring for 40 minutes, and finally wash, dry and calcine to obtain a molecular sieve composited with titanium dioxide, wherein the mass of titanium dioxide composited on the molecular sieve is 25% of the mass of the molecular sieve, the calcination temperature is 400°C, and the calcination time is 3 hours;

[0046] 6 g of urea was dissolved in deionized water to prepare a urea solution with a mass fraction of 5%, 10 g of molecular sieve composited with titanium dioxide was uniformly dispersed in the urea solution, stirred in a water bath at 60° C. for 6 h, and the nitrogen source loaded molecular sieve was obtained after filtration and drying.

[0047] Preparation Example 2, a nitrogen source loaded molecular sieve, is different from Preparation Example 1 only in that the mass of titanium dioxide composited on the molecular sieve is 20% of the mass of the molecular sieve; the amount of urea added is 5g, which is dissolved in deionized water to obtain a urea solution with a mass fraction of 5%.

[0048] Preparation Example 3, a nitrogen source loaded molecular sieve, is different from Preparation Example 1 only in that the mass of titanium dioxide composited on the molecular sieve is 30% of the mass of the molecular sieve; the amount of urea added is 7g, which is dissolved in deionized water to obtain a urea solution with a mass fraction of 5%.

[0049] Preparation Example 4, a nitrogen source loaded molecular sieve, is different from Preparation Example 1 only in that the amount of urea added is 3 g, which is dissolved in deionized water to obtain a urea solution with a mass fraction of 5%.

[0050] Preparation Example 5, a nitrogen source loaded molecular sieve, is different from Preparation Example 1 only in that the amount of urea added is 9 g, which is dissolved in deionized water to obtain a urea solution with a mass fraction of 5%.

[0051] Preparation Example 6, a nitrogen source loaded molecular sieve, is different from Preparation Example 1 only in that the mass of titanium dioxide composited on the molecular sieve is 10% of the mass of the molecular sieve.

[0052] Preparation Example 7, a nitrogen source loaded molecular sieve, is different from Preparation Example 1 only in that the mass of titanium dioxide composited on the molecular sieve is 40% of the mass of the molecular sieve.

[0053] Preparation Example 8, a nitrogen source loaded molecular sieve, prepared according to the following method:

[0054] 6 g of urea was dissolved in deionized water to prepare a urea solution with a mass fraction of 5%, 10 g of molecular sieve (4A molecular sieve) was evenly dispersed in the urea solution, stirred in a water bath at 60° C. for 6 h, and filtered and dried to obtain a nitrogen source loaded molecular sieve.

[0055] Example

[0056] Example 1, a method for reducing the amount of dioxins in fly ash and utilizing them as resources, specifically comprising the following steps:

[0057] S1. The fly ash from garbage incineration is subjected to a quadruple dioxin control technology to obtain fly ash with dioxin reduction treatment; wherein the quadruple dioxin control technology specifically includes: a low-temperature pyrolysis process, wherein the pyrolysis temperature is controlled to be 450°C; a high-temperature decomposition process, wherein the low-temperature pyrolysis product is subjected to secondary air secondary combustion, and the secondary combustion temperature is 900°C; an online control process, wherein the fly ash dioxin online control system is used to automatically monitor the dioxin content in the fly ash, and the dioxin content is kept below the control value of 50ng TEQ / kg; an in-furnace inhibition process, wherein the dioxin inhibitor dosing equipment is used to automatically start the addition of the dioxin inhibitor when the dioxin content is higher than the control value of 50ng TEQ / kg, and the dioxin inhibitor is a mixed inhibitor of the nitrogen source loaded molecular sieve and calcium hydroxide prepared in Preparation Example 1 with a mass ratio of 7:3;

[0058] S2. sorting, crushing and screening the well-fermented domestic waste and other waste to obtain high calorific value waste, wherein the particle size of the high calorific value waste is 1 to 4 cm;

[0059] S3. Evenly mix the fly ash obtained by dioxin reduction treatment with high calorific value garbage and auxiliary material sludge, wherein the fly ash accounts for 30% and the auxiliary material accounts for 5%, to prepare garbage-derived fuel;

[0060] S4. The obtained garbage-derived fuel assists the combustion of domestic waste, and its combustion residue is discharged with the slag and enters the slag treatment plant. The tailings are used to prepare fire-free building materials and fix heavy metals for resource utilization.

[0061] Example 2, a method for reducing the source of fly ash dioxins and utilizing them as resources, is different from Example 1 only in that the process parameters of the quadruple dioxin control technology are adjusted, specifically: the low-temperature pyrolysis controls the pyrolysis temperature to 300°C, the dioxin inhibitor is a mixed inhibitor of the nitrogen source-loaded molecular sieve and calcium hydroxide obtained in Preparation Example 1 in a mass ratio of 8:2; the proportion of fly ash in the waste-derived fuel is 10%.

[0062] Example 3, a method for reducing the source of fly ash dioxins and recycling them for resource utilization, is different from Example 1 only in that the process parameters of the quadruple dioxin control technology are adjusted, specifically: the low-temperature pyrolysis controls the pyrolysis temperature to 550°C, the secondary combustion temperature in the high-temperature decomposition is 850°C, the dioxin inhibitor is a mixed inhibitor of the nitrogen source-loaded molecular sieve and calcium hydroxide prepared in Preparation Example 1 in a mass ratio of 6:4; the proportion of fly ash in the waste-derived fuel is 45%.

[0063] Example 4, a method for reducing the source of fly ash dioxins and utilizing them as resources, is different from Example 1 only in that the nitrogen source-loaded molecular sieve prepared in Preparation Example 1 is replaced by an equal amount of the nitrogen source-loaded molecular sieve prepared in Preparation Example 2.

[0064] Example 5, a method for reducing the source of fly ash dioxins and utilizing them as resources, is different from Example 1 only in that the nitrogen source-loaded molecular sieve prepared in Preparation Example 1 is replaced by an equal amount of the nitrogen source-loaded molecular sieve prepared in Preparation Example 3.

[0065] Example 6, a method for reducing the source of fly ash dioxins and utilizing them as resources, is different from Example 1 only in that the nitrogen source-loaded molecular sieve prepared in Preparation Example 1 is replaced by an equal amount of the nitrogen source-loaded molecular sieve prepared in Preparation Example 4.

[0066] Example 7, a method for reducing the source of dioxins in fly ash and utilizing them as resources, is different from Example 1 only in that the nitrogen source-loaded molecular sieve prepared in Preparation Example 1 is replaced by an equal amount of the nitrogen source-loaded molecular sieve prepared in Preparation Example 5.

[0067] Example 8, a method for reducing the source of fly ash dioxins and utilizing them as resources, is different from Example 1 only in that the nitrogen source-loaded molecular sieve prepared in Preparation Example 1 is replaced by an equal amount of the nitrogen source-loaded molecular sieve prepared in Preparation Example 6.

[0068] Example 9, a method for reducing the amount of dioxins in fly ash and utilizing them as resources, is different from Example 1 only in that the nitrogen source-loaded molecular sieve prepared in Preparation Example 1 is replaced with an equal amount of the nitrogen source-loaded molecular sieve prepared in Preparation Example 7.

[0069] Example 10, a method for reducing the source of fly ash dioxins and utilizing them as resources, is different from Example 1 only in that the nitrogen source-loaded molecular sieve prepared in Preparation Example 1 is replaced by an equal amount of the nitrogen source-loaded molecular sieve prepared in Preparation Example 8.

[0070] Example 11, a method for reducing the source of fly ash dioxins and utilizing them as resources, is different from Example 1 only in that the dioxin inhibitor is a mixed inhibitor of the nitrogen source-loaded molecular sieve and calcium hydroxide prepared in Preparation Example 1 in a mass ratio of 5:5.

[0071] Example 12, a method for reducing the source of fly ash dioxins and utilizing them as resources, is different from Example 1 only in that the dioxin inhibitor is a mixed inhibitor of the nitrogen source-loaded molecular sieve and calcium hydroxide prepared in Preparation Example 1 in a mass ratio of 9:1.

[0072] Example 13, a method for reducing the source of dioxins in fly ash and utilizing them as resources, is different from Example 1 only in that the dioxin inhibitor is the nitrogen source-loaded molecular sieve prepared in Preparation Example 1.

[0073] Example 14, a method for reducing the source of dioxins in fly ash and utilizing them as resources, is different from Example 1 only in that the dioxin inhibitor is calcium hydroxide.

[0074] Example 15, a method for reducing the source of dioxins in fly ash and utilizing them as resources, is different from Example 1 only in that the dioxin inhibitor is a mixed inhibitor of urea and calcium hydroxide in a mass ratio of 7:3.

[0075] Comparative Example

[0076] Comparative Example 1, a method for reducing the source of fly ash dioxins and utilizing them for resource utilization, is different from Example 1 only in that the process of the quadruple dioxin control technology is adjusted, specifically: a high-temperature decomposition process, in which the waste incineration fly ash is burned at a high temperature, and the combustion temperature is 900°C; an online control process, in which the fly ash dioxin online control system is used to automatically monitor the dioxin content in the fly ash, and the dioxin content is kept below the control value of 50ng TEQ / kg; an in-furnace inhibition process, in which a dioxin inhibitor dosing device is used to automatically start adding a dioxin inhibitor when the dioxin content is higher than the control value of 50ng TEQ / kg, and the dioxin inhibitor is a mixed inhibitor of the nitrogen source loaded molecular sieve and calcium hydroxide prepared in Preparation Example 1 in a mass ratio of 7:3.

[0077] Comparative Example 2, a method for reducing the source of dioxins in fly ash and utilizing them as resources, is different from Example 1 only in that the process of the quadruple dioxin control technology is adjusted, specifically: a low-temperature pyrolysis process, wherein the pyrolysis temperature is controlled to be 450°C; an online control process, wherein the dioxin content in the fly ash is automatically monitored by the fly ash dioxin online control system, and the dioxin content is kept below the control value of 50ng TEQ / kg; an in-furnace inhibition process, wherein the dioxin inhibitor dosing equipment is used to automatically start the addition of the dioxin inhibitor when the dioxin content is higher than the control value of 50ng TEQ / kg, and the dioxin inhibitor is a mixed inhibitor of the nitrogen source-loaded molecular sieve and calcium hydroxide prepared in Preparation Example 1 in a mass ratio of 7:3.

[0078] Comparative Example 3, a method for reducing the source of fly ash dioxins and utilizing them as resources, is different from Example 1 only in that the process of the quadruple dioxin control technology is adjusted, specifically as follows: an online control process, using a fly ash dioxin online control system to automatically monitor the dioxin content in the fly ash to keep the dioxin content below the control value of 50 ng TEQ / kg; an in-furnace inhibition process, using a dioxin inhibitor dosing device to automatically start adding a dioxin inhibitor when the dioxin content is higher than the control value of 50 ng TEQ / kg, the dioxin inhibitor is a mixed inhibitor of the nitrogen source loaded molecular sieve and calcium hydroxide prepared in Preparation Example 1 in a mass ratio of 7:3.

[0079] Performance testing

[0080] The laboratory simulated the combustion conditions on the grate surface, and tested the dioxin content in the fly ash before and after treatment, as well as the nitrogen oxide content in the flue gas released after treatment. The data before treatment was used as a control group, and compared with the dioxin content in the fly ash treated by the fly ash dioxin source reduction and resource utilization method in the embodiment and the comparative example. The test results are shown in Table 1:

[0081] Table 1 Test results

[0082]

[0083]

[0084] According to Table 1, combined with Example 1, Example 2 to Example 5, it can be seen that the content of dioxins in the fly ash after treatment in Example 2 to Example 5 has significantly decreased, and has little change compared with Example 1, and the content of nitrogen oxides has also little change compared with Example 1. This shows that the reduction effect of fly ash dioxins in Example 2 to Example 5 is not significantly different from that in Example 1. The only change in Example 2 to Example 5 compared with Example 1 is that the process parameters and the raw materials and their ratios of the inhibitors are changed within the required range, which shows that the process parameters and raw materials in the process of changing within the required range have little effect on the final fly ash dioxin removal effect.

[0085] Combining Example 1, Example 6 and Example 7, it can be seen that the dioxin content of the fly ash after treatment in Example 6 and Example 7 is slightly higher than that in Example 1. The reason is that the only change in Example 6 and Example 7 compared with Example 1 is that the amount of urea added is adjusted in the process of nitrogen source loading molecular sieve. The amount of urea added is reduced in Example 6, the content of urea loaded on the molecular sieve decreases, the deactivation effect of the metal in the dioxin formation process decreases, resulting in a decrease in the inhibitory effect on the formation of dioxins, and the dioxin content in the fly ash increases slightly. In Example 7, the amount of urea added is increased. On the one hand, the loading points on the molecular sieve are limited, and the loading of a large amount of urea is not conducive to the attraction of moisture by the molecular sieve, and further, the reaction of calcium hydroxide cannot be promoted to proceed in the forward direction. On the other hand, the large increase in urea will increase the probability of urea decomposing into nitrogen oxides, and the nitrogen oxide content in the released flue gas will also increase slightly.

[0086] Combining Example 1 and Example 8 to Example 10, it can be seen that the dioxin content of the fly ash after treatment in Example 8 to Example 10 is not much different from that in Example 1, but the nitrogen oxide content in the flue gas is significantly increased, especially in Example 8 and Example 10. The reason is that the difference between Example 8 to Example 10 and Example 1 is that the composite amount of titanium dioxide in the nitrogen source loaded molecular sieve is different. In Example 8, the composite amount of titanium dioxide is reduced, which leads to a decrease in the catalytic conversion efficiency of nitrogen oxides, and most of the nitrogen oxides cannot be converted into harmless substances. In Example 10, there is no composite titanium dioxide, and the content of nitrogen oxides in the flue gas is significantly increased.

[0087] Combining Example 1 and Example 11 to Example 14, it can be seen that the dioxin content in the fly ash after treatment in Example 1 to Example 14 is increased compared with that in Example 1, and the nitrogen oxide content in the flue gas released in Example 11 and Example 14 is significantly increased. The reason is that the difference between Example 11 to Example 14 and Example 1 is that the raw material components of the dioxin inhibitor are changed. Specifically, the amount of molecular sieve added in Example 11 is reduced, and the reduction of nitrogen source will lead to a decrease in the effect of nitrogen source on the metal catalytic deactivation effect, and the attraction to moisture is also reduced, thereby reducing the inhibitory effect on dioxin generation. In addition, the reduction in the number of molecular sieves will also lead to a decrease in the conversion efficiency of nitrogen oxides and an increase in the content of nitrogen oxides in the released flue gas. In Example 14, no nitrogen source-loaded molecular sieve is added, and the performance decline is more obvious. In Example 12, the amount of molecular sieve added is increased, and the fixation effect of the dioxin inhibitor on the raw materials that form dioxins is reduced, and the inhibitory effect is also reduced accordingly. In Example 13, only molecular sieves are added, and the inhibitory effect declines more significantly.

[0088] Combining Example 1 and Example 15, it can be seen that the dioxin content in the fly ash after treatment in Example 15 is increased compared with that in Example 1, and the nitrogen oxide content in the released flue gas is also significantly increased. The reason is that the dioxin inhibitor, urea, in Example 15 is not loaded on the molecular sieve, and the urea is unstable during the pyrolysis process and will decompose into a large amount of nitrogen oxides, and the inhibitory effect on the formation of dioxins is reduced.

[0089] Combining Example 1 and Comparative Examples 1 to 3, it can be seen that the content of dioxins in the fly ash after treatment in Comparative Examples 1 to 3 is significantly increased compared with that in Example 1, and the increase is more obvious in Comparative Example 3. The reason is that the difference between Comparative Examples 1 to 3 and Example 1 is that in the quadruple dioxin control technology, Comparative Example 1 did not undergo a low-temperature pyrolysis process, resulting in some dioxins solidified in the fly ash, which is difficult to remove only by high-temperature decomposition; Comparative Example 2 did not undergo a high-temperature decomposition process, and the dioxins gasified into the flue gas could not be removed, resulting in an increase in the amount of dioxin residues; and Comparative Example 3 did not undergo either low-temperature pyrolysis or high-temperature decomposition, and was only controlled by inhibitors, so the removal efficiency of dioxins was limited, and the content of dioxins remaining in the fly ash was significantly increased.

[0090] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0091] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for reducing the amount of dioxins in fly ash and utilizing them as resources, characterized in that: The fly ash dioxin source reduction adopts a quadruple dioxin control technology to reduce dioxins; the quadruple dioxin control technology includes a quadruple process of low-temperature pyrolysis, high-temperature decomposition, online control and in-furnace inhibition; The controlled pyrolysis temperature of the low-temperature pyrolysis process is 300-550°C; The high temperature decomposition process is to subject the low temperature pyrolysis products to secondary combustion through secondary air, and the secondary combustion temperature is 850-1000°C; The online control process is to use the fly ash dioxin online control system to automatically monitor the dioxin content in the fly ash and keep the dioxin content below the control value; The in-furnace inhibition process is to use a dioxin inhibitor dosing device to automatically start dosing the dioxin inhibitor when the dioxin content is higher than a control value.

2. The fly ash dioxin source reduction and resource utilization method according to claim 1, characterized in that: The control value was 50 ng TEQ / kg.

3. The fly ash dioxin source reduction and resource utilization method according to claim 1, characterized in that: The dioxin inhibitor comprises nitrogen source loaded molecular sieve and calcium hydroxide in a mass ratio of (6-8):(2-4).

4. The fly ash dioxin source reduction and resource utilization method according to claim 3 is characterized in that: The raw materials of the nitrogen source loaded molecular sieve include urea and molecular sieve in a mass ratio of (0.5-0.7):

1.

5. The fly ash dioxin source reduction and resource utilization method according to claim 4, characterized in that: The molecular sieve is compounded with titanium dioxide; the mass of the compounded titanium dioxide is 20-30% of the mass of the molecular sieve.

6. The fly ash dioxin source reduction and resource utilization method according to claim 4, characterized in that: The nitrogen source loaded molecular sieve is prepared according to the following method: Preparation of molecular sieve composite titanium dioxide: molecular sieve is added to the solvent, and after uniform dispersion, titanium precursor is added, deionized water is added after stirring for 1 to 2 hours, and stirring for 30 to 60 minutes, and finally the molecular sieve composited with titanium dioxide is obtained after washing, drying and calcining; Preparation of nitrogen source loaded molecular sieve: The molecular sieve is uniformly dispersed in the urea solution, stirred in a water bath at 60-80° C. for 4-6 hours, and filtered and dried to obtain the nitrogen source loaded molecular sieve.

7. The fly ash dioxin source reduction and resource utilization method according to claim 1, characterized in that: The specific steps of reducing and recycling resources include: S1. Fly ash from waste incineration treated with dioxin reduction technology using quadruple dioxin control technology; S2. sorting, crushing and screening the well-fermented domestic waste and other waste to obtain high calorific value waste; S3. The fly ash treated with dioxin reduction is mixed evenly with high calorific value garbage and auxiliary materials to prepare garbage-derived fuel; S4. The obtained garbage-derived fuel assists the combustion of domestic waste, and its combustion residue is discharged with the slag and enters the slag treatment plant. The tailings are used to prepare fire-free building materials and fix heavy metals for resource utilization.

8. The fly ash dioxin source reduction and resource utilization method according to claim 7, characterized in that: The particle size of the high calorific value garbage is 1 to 4 cm.

9. The fly ash dioxin source reduction and resource utilization method according to claim 7, characterized in that: The fly ash treated for dioxin reduction accounts for 10-45 wt % in the waste-derived fuel.

10. The fly ash dioxin source reduction and resource utilization method according to claim 7, characterized in that: The auxiliary materials in step S3 include one or more combinations of sludge, coal slime and coal powder.

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