CN113955787A

CN113955787A - Process for removing dioxin in fly ash

Info

Publication number: CN113955787A
Application number: CN202111013373.9A
Authority: CN
Inventors: 高锦创; 徐丽琴; 罗成
Original assignee: Jiangxi Wannian Zhongnan Environmental Protection Industry Co Operative Research Institute Co ltd; Jiangxi Gaia Environmental Science and Technology Co Ltd
Current assignee: Jiangxi Wannian Zhongnan Environmental Protection Industry Co Operative Research Institute Co ltd; Jiangxi Gaia Environmental Science and Technology Co Ltd
Priority date: 2021-08-31
Filing date: 2021-08-31
Publication date: 2022-01-21
Anticipated expiration: 2041-08-31
Also published as: CN113955787B

Abstract

The process for removing dioxin in fly ash adopted by the invention is based on the carbon dioxide high-pressure leaching of the solid slag after fly ash water washing, then the leached slag is placed in a stainless steel reaction kettle under the condition of high temperature and high pressure after water washing, NaClO is simultaneously put into the stainless steel reaction kettle as an oxidant for reaction, the removal of dioxin by a hydrothermal oxidation method is realized, the removal of dioxin by the hydrothermal oxidation method has the advantages of saving energy consumption compared with the conventional high-temperature burning, the water washing liquid is evaporated and crystallized by an MVR evaporator, potassium salt and mixed salt waste liquid are obtained by separation, the NaClO can be obtained by electrolyzing the mixed salt waste liquid without additionally purchasing the oxidant, on one hand, the reagent is saved, on the other hand, the NaClO has strong oxidizing property, the degradation efficiency of dioxin is higher than that of a common oxidant, the hydrothermal oxidation effect is good, the resource product of fly ash is recycled in the process link of the process, the problem of product treatment such as export and the like does not need to be considered, can also effectively prevent the re-synthesis of dioxin.

Description

Process for removing dioxin in fly ash

Technical Field

The invention belongs to the technical field of harmless treatment of fly ash generated by waste incineration, and particularly relates to a process for removing dioxin in fly ash.

Background

The waste incineration fly ash in China has huge yield, and the waste incineration industry will grow explosively with the increase of the clean transportation volume of the household garbage and the increase of the incineration treatment proportion. By the end of 2020, the total incineration amount of the garbage reaches 59.14 ten thousand tons/day, in the process of garbage incineration, a lot of harmful substances, such as dioxin, acid gases (such as hydrogen chloride and sulfur dioxide), nitrogen oxides, heavy metal dust and the like, can be generated, most of the pollutants can be intercepted by a dust removal system to form fly ash when flue gas purification is carried out, and the fly ash amount generated every year is about 1000 ten thousand tons. The large and medium-sized urban fly ash has large production amount and tense land resources, the disposal mode mainly based on landfill is under greater and greater pressure, and the reclamation, reduction and harmless treatment of the waste incineration fly ash are the final trends. Therefore, how to reasonably utilize the fly ash and realize the reutilization of the waste resources is urgent.

It is clear that the 'domestic waste incineration fly ash' belongs to dangerous waste when the 'national hazardous waste record' is revised in 2008, and the hazardous waste category is HW 18. The main components of the waste incineration fly ash comprise water-soluble salt, calcium components, heavy metals, dioxin and the like, once the fly ash is discharged into the environment, the fly ash can cause serious pollution and damage to water, air and soil, and meanwhile, the heavy metals and the dioxin can cause great harm to the environment and organisms. Dioxin is a highly toxic substance, and the toxicity of the dioxin is 130 times that of the well-known highly toxic substance cyanide and 900 times that of arsenic. Numerous animal experiments have shown that very low concentrations of dioxin can have a lethal effect on animals. Toxicity data and clinical manifestations of dioxins on human bodies have been obtained from occupational exposure and industrial accident victims, and exposure to environments containing PCDD or PCDF can cause skin sores, headaches, hearing loss, depression, insomnia, and possibly chromosomal damage, heart failure, cancer, and the like.

The traditional dioxin removal mode usually adopts high-temperature incineration, and the dioxin can be completely decomposed after staying for 2S in an environment of 850 ℃, but the dioxin is only reduced, the dioxin precursor can be recombined to generate the dioxin at the temperature of 500 ℃ plus materials, the temperature is increased to 1200 ℃, the generated substances do not contain the dioxin precursor, and the probability of subsequent dioxin resynthesis is reduced. However, the traditional high-temperature incineration process has high temperature requirement and large energy consumption.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a process for removing dioxin in fly ash, which mainly solves the technical problems that: the traditional mode for removing dioxin through high-temperature incineration has strict requirements on reaction conditions, and the temperature requirement of the incineration process is high, so that the infrastructure construction cost is high, a continuous high-temperature environment of 850 ℃ is required for removing dioxin, and a continuous high-temperature environment of 1200 ℃ is required for removing dioxin precursors, so that the energy consumption is extremely high, and the method is not beneficial to energy conservation, emission reduction and reduction of the operation cost.

In order to solve the technical problems, the invention provides a process for removing dioxin in fly ash, which comprises the following steps:

step one, washing fly ash, mixing the fly ash with water to prepare slurry, and then carrying out suction filtration on the prepared slurry by using a suction filter to obtain washing liquid and solid slag;

step two, carbon dioxide high-pressure leaching, namely washing the solid residues with water to prepare slurry, placing the prepared slurry in a high-pressure container, introducing excessive carbon dioxide gas into the slurry, converting calcium contained in the solid residues into calcium bicarbonate by adopting the carbon dioxide high-pressure leaching, dissolving the calcium bicarbonate into water, performing suction filtration on the slurry subjected to the carbon dioxide high-pressure leaching by using a suction filter to obtain leaching residues and filtrate, and decomposing the calcium bicarbonate in the filtrate at normal temperature and normal pressure to generate calcium carbonate;

step three, removing dioxin by adopting a hydrothermal oxidation method, washing the leaching residue with water to prepare slurry, placing the prepared slurry in a reaction kettle with the temperature of 150-250 ℃ and the pressure of 1-5MPa, simultaneously adding an oxidant into the slurry, adding the oxidant into the reactor according to the molar concentration of 0.1-3mol/L, wherein the proportion of the fly ash to the water is 1: 2-6, reacting for 2-6h, and removing dioxin contained in the leaching slag and residual resource slag.

Preferably: the reaction kettle adopted in the third step is a stainless steel reaction kettle, and the adopted oxidant is NaClO.

Preferably: treating the water washing solution, evaporating and crystallizing the water washing solution obtained in the first step through an MVR evaporator, cooling and crystallizing to obtain potassium salt, and obtaining potassium salt and mixed salt waste liquid through centrifugal separation, wherein the potassium salt and the sodium salt are mainly left in the water washing solution, the solubility of sodium chloride is small along with the change of temperature, and is less than that of potassium chloride when the temperature is high, so that the water washing solution is evaporated and crystallized through the MVR evaporator, the potassium salt can be recovered through cooling and crystallization, and the sodium chloride is mainly contained in the remaining mixed waste solution; and electrolyzing the mixed salt waste liquid to obtain NaClO, wherein the NaClO is reused in the link of removing dioxin by the hydrothermal oxidation method.

Preferably: and (3) recycling the resource slag, and recovering valuable metals contained in the resource slag by adopting a mineral separation and leaching mode.

Preferably: in the first step, carbon dioxide gas is introduced into the slurry to adjust the pH value to 6-8, which is beneficial to the precipitation of heavy metal and calcium ions.

Preferably: and calcining the calcium carbonate obtained in the second step to obtain quicklime and carbon dioxide gas, reusing the carbon dioxide gas in a fly ash washing step and a carbon dioxide high-pressure leaching step, and reusing the quicklime in a flue gas purification link of a waste incineration power plant.

Compared with the prior art, the invention has the following advantages:

1. compared with the conventional high-temperature incineration mode, the reaction temperature of the whole system is not more than 250 ℃ and the pressure is not more than 5MPa, so that the energy consumption is relatively low, the reaction conditions are easier to meet, the operation cost is reduced, and the problem of dioxin resynthesis is avoided;

2. NaClO is selected as an oxidant, so that the degradation efficiency of dioxin is high, no additional reagent needs to be purchased, NaClO can be obtained by recycling the fly ash water washing liquid for recycling, the oxidant can be self-sufficient, and the cost can be effectively saved;

3. the process has the advantages of relatively mild operating conditions, simple process steps and easy construction.

Drawings

Fig. 1 is a flow chart of a process for removing dioxin from fly ash.

FIG. 2 is a flow chart of a water washing process of fly ash.

Detailed Description

The present invention provides a process for removing dioxins from fly ash, which is further described below with reference to the preferred embodiments and the accompanying fig. 1-2 of the specification.

As shown in fig. 1, the process for removing dioxin from fly ash adopted by the present invention is based on a process for recovering quick lime by carbon dioxide high-pressure leaching solid slag after fly ash water washing, then the leached slag is washed with water and placed in a stainless steel reaction kettle under a high-temperature and high-pressure condition, and at the same time, NaClO is added as an oxidant to carry out a reaction, so as to remove dioxin by a hydrothermal oxidation method, the removal of dioxin by the hydrothermal oxidation method is more energy-saving compared with the conventional high-temperature incineration, NaClO oxidation is selected because water washing liquid is recycled to obtain NaClO, the water washing liquid is evaporated and crystallized by an MVR evaporator, potassium salt is crystallized by cooling, potassium salt and mixed salt waste liquid are obtained by centrifugal separation, the NaClO can be obtained by electrolyzing the mixed salt waste liquid, no additional reagent is required to be purchased, on one hand, the reagent is saved, on the other hand, the NaClO has strong oxidizing property, and the efficiency of degrading dioxin is higher than that of a common oxidant, the hydrothermal oxidation effect is good, the resource product of the fly ash is reused in the process link of the fly ash, and the problem of product treatment such as export sales and the like does not need to be considered; the rest is resource slag, the main component of the resource slag is valuable metal, and the valuable metal can be recovered by adopting conventional ore dressing and leaching modes.

As described above, the present invention can remove dioxin in fly ash under relatively mild reaction conditions, can effectively prevent the dioxin from being resynthesized, does not require additional purchase of an oxidizing agent, has brief process steps, and has the advantages of low operation energy consumption and low cost.

Example 1, as shown in fig. 1, it comprises the following steps:

step two, carbon dioxide high-pressure leaching, namely washing the solid residues with water to prepare slurry, placing the prepared slurry in a high-pressure container, introducing excessive carbon dioxide gas into the slurry, converting calcium contained in the solid residues into calcium bicarbonate by adopting the carbon dioxide high-pressure leaching, dissolving the calcium bicarbonate into water, performing suction filtration on the slurry subjected to the carbon dioxide high-pressure leaching by using a suction filter to obtain leaching residues and filtrate, and decomposing the calcium bicarbonate in the filtrate at normal temperature and normal pressure to generate calcium carbonate; in addition, the calcium carbonate can be calcined to obtain quicklime and carbon dioxide gas, the quicklime is reused in a flue gas purification link of a waste incineration power plant, and the carbon dioxide gas is reused in a carbon dioxide high-pressure leaching step, so that reduction, harmlessness and recycling of fly ash are realized, products are reused in the treatment process, and links of further additional treatment are saved;

Step four, treating the water washing solution, evaporating and crystallizing the water washing solution obtained in the step one through an MVR evaporator, cooling and crystallizing potassium salt, obtaining potassium salt and mixed salt waste liquid through centrifugal separation, wherein the potassium salt and the sodium salt are mainly left in the water washing solution, and the water washing solution is evaporated and crystallized through the MVR evaporator because the solubility of the sodium chloride is small along with the temperature change and is lower than that of the potassium chloride when the temperature is high, the potassium salt can be recovered through cooling and crystallization, and the sodium chloride is mainly contained in the remaining mixed waste solution; and electrolyzing the mixed salt waste liquid to obtain NaClO, wherein the NaClO is reused in the link of removing dioxin by the hydrothermal oxidation method.

And fifthly, recycling the resource slag, and recovering valuable metals contained in the resource slag by adopting a mineral separation and leaching mode.

Example 2, as shown in fig. 1 and 2, it comprises the following steps:

step one, washing fly ash, adopting a multi-stage reverse pulping fly ash washing mode,

1) mixing fly ash and water according to the proportion of 1: 3-5, and simultaneously introducing carbon dioxide gas into the slurry to adjust the pH value to 6-8, so as to be beneficial to precipitation of heavy metal and calcium ions;

2) carrying out suction filtration on the slurry prepared in the step 1) by using a suction filter to obtain water washing liquid and primary solid slag;

3) mixing the primary solid slag obtained in the step 2) with water according to the ratio of 1: 3-5 of solid-to-liquid ratio to prepare slurry;

4) carrying out suction filtration on the slurry prepared in the step 3) by using a suction filter to obtain water washing liquid and secondary solid slag;

5) mixing the secondary solid slag obtained in the step 4) with water according to the ratio of 1: 3-5 of solid-to-liquid ratio to prepare slurry;

6) carrying out suction filtration on the slurry prepared in the step 5) by using a suction filter to obtain water washing liquid and three times of solid residues;

7) mixing the third solid slag obtained in the step 6) with water according to the ratio of 1: 5-8, mixing and diluting to prepare slurry;

8) carrying out suction filtration on the slurry prepared in the step 7) by using a suction filtration machine to obtain diluted washing liquor and solid slag, concentrating the diluted washing liquor by using a DTRO membrane to obtain concentrated water and fresh water, recycling the concentrated water in the step 1) for mixing with fly ash to prepare the slurry, further improving the pulping concentration by recycling the reverse concentrated water, maximally improving the salt content in the water washing solution, further recovering soluble salt resources in the concentrated water, and recycling the fresh water in the step 7) for mixing with the solid slag to dilute to prepare the slurry, so that water resources can be recycled; the desalination rate after washing with water for three times and once increasing the solid-to-liquid ratio can reach about 95 percent;

step two, carbon dioxide high-pressure leaching, namely washing the solid residues with water to prepare slurry, placing the prepared slurry in a high-pressure container, introducing excessive carbon dioxide gas into the slurry, converting calcium contained in the solid residues into calcium bicarbonate by adopting the carbon dioxide high-pressure leaching, dissolving the calcium bicarbonate into water, performing suction filtration on the slurry subjected to the carbon dioxide high-pressure leaching by using a suction filter to obtain leaching residues and filtrate, and decomposing the calcium bicarbonate in the filtrate at normal temperature and normal pressure to generate calcium carbonate; in addition, the calcium carbonate can be calcined to obtain quicklime and carbon dioxide gas, the quicklime is reused in a flue gas purification link of a waste incineration power plant, and the carbon dioxide gas is reused in a fly ash water washing step and a carbon dioxide high-pressure leaching step, so that reduction, harmless and recycling treatment of fly ash and product reuse in the treatment process are realized, and the link of further additional treatment is saved;

Step four, mixing the water washing liquid obtained in the step 2), the step 4) and the step 6), then treating, evaporating and crystallizing the water washing liquid obtained in the step one through an MVR evaporator, cooling and crystallizing to obtain potassium salt, and obtaining potassium salt and mixed salt waste liquid through centrifugal separation, wherein the rest of the water washing liquid mainly contains potassium salt and sodium salt, and the water washing liquid is evaporated and crystallized through the MVR evaporator because the solubility of sodium chloride is small along with the temperature change and is less than that of potassium chloride when the temperature is high, the potassium salt can be recovered through cooling and crystallizing, and the rest of the mixed waste liquid mainly contains sodium chloride; and electrolyzing the mixed salt waste liquid to obtain NaClO, wherein the NaClO is reused in the link of removing dioxin by the hydrothermal oxidation method.

Comparative example 1: patent publication No. CN111467726A proposes a dechlorination and detoxification treatment process of dioxin in waste incineration fly ash, and the invention provides a dechlorination and detoxification treatment process of dioxin in waste incineration fly ash, wherein the fly ash after waste incineration is washed and filtered, and then is fully mixed with inorganic sulfur-containing compounds and then is granulated; and placing the granulated mixture into a closed reaction container, and carrying out heating reaction in a nitrogen atmosphere, wherein the toxicity equivalent concentration of dioxin in the obtained granules after the reaction is greatly reduced.

Compared with the method for removing dioxin by heating in CN111467726A, the method saves energy consumption and has milder reaction conditions.

Designing an experiment: an experiment is designed to research the influence of three factors, namely temperature, NaClO concentration and reaction time, on the dioxin degradation efficiency in a hydrothermal method.

Three-factor four-level study experiments were set up herein: three factors and four levels were scheduled in the experiment.

Statistical differences: table 1 shows statistical examples 1-2 and comparative examples.

	Reduction rate of toxicity equivalent of dioxin%
		Example 1	88.31
Example 2	95.72
		Comparative example 1	92.91

As can be seen from table 1, compared with the conventional way of burning and removing dioxin at high temperature, the process for removing dioxin from fly ash provided by the invention has the advantages of milder reaction conditions, easier satisfaction of the conditions required by the reaction, lower cost, less energy consumption, and no worry about the problem of resynthesis of dioxin after decomposition.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all simple modifications, changes and equivalent process changes made to the above embodiment according to the technical spirit of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A process for removing dioxin in fly ash is characterized by comprising the following steps:

2. The process for removing dioxins in fly ash according to claim 1, wherein: the reaction kettle adopted in the third step is a stainless steel reaction kettle, and the adopted oxidant is NaClO.

3. The process for removing dioxins in fly ash according to claim 2, wherein: treating the water washing solution, evaporating and crystallizing the water washing solution obtained in the first step through an MVR evaporator, cooling and crystallizing to obtain potassium salt, and performing centrifugal separation to obtain potassium salt and mixed salt waste liquid; and electrolyzing the mixed salt waste liquid to obtain NaClO, wherein the NaClO is reused in the link of removing dioxin by the hydrothermal oxidation method.

4. The process for removing dioxins in fly ash according to claim 3, wherein: and (3) recycling the resource slag, and recovering valuable metals contained in the resource slag by adopting a mineral separation and leaching mode.

5. The process for removing dioxins in fly ash according to claim 4, wherein: in the first step, carbon dioxide gas is introduced into the slurry to adjust the pH value to 6-8, which is beneficial to the precipitation of heavy metal and calcium ions.

6. The process for removing dioxins in fly ash according to claim 5, wherein: and calcining the calcium carbonate obtained in the second step to obtain quicklime and carbon dioxide gas, reusing the carbon dioxide gas in a fly ash washing step and a carbon dioxide high-pressure leaching step, and reusing the quicklime in a flue gas purification link of a waste incineration power plant.