Waste incineration fly ash dechlorination process

Abstract

The invention discloses a waste incineration fly ash dechlorination process which comprises the following steps: S1, mixing fly ash, a dechlorination agent and water, stirring and dissolving to obtain first slurry; s2, adding a flocculating agent into the slurry, and continuously stirring and dissolving to obtain second slurry; s3, the second slurry is subjected to centrifugal treatment, and solid residues and ash washing wastewater are obtained after separation; s4, after clarifying and filtering the ash washing wastewater, returning to the step S1 for recycling; and carrying out photolysis reaction on the solid residues, drying the obtained product, and feeding the dried product into dust removal equipment. The dechlorination agent is added in the fly ash dechlorination link, so that the existence form of chlorine in the fly ash is transferred, the transfer efficiency is high, only one-stage water washing dechlorination is arranged, the water washing procedure is simplified, the mass ratio of water to the fly ash is greatly reduced, and the water resource consumption is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of environmental protection engineering, in particular to a process for dechlorination of fly ash from garbage incineration. Background Art

[0002] Domestic waste fly ash is a powdery substance with a light bulk density and fine particle size collected in the flue gas duct, flue gas purification, separator and dust collector during the waste incineration process. Since fly ash carries high content of chloride, heavy metals and highly toxic dioxins (PCDD / Fs), it is classified as hazardous waste. Therefore, Cl, heavy metals and PCDD / Fs in fly ash are the bottlenecks for the harmlessness and resource utilization of fly ash. Effective dechlorination and desalination, solidification (extraction) of heavy metals and elimination of PCDD / Fs are the key to fly ash treatment and disposal.

[0003] At present, the main methods of fly ash treatment include chemical treatment, high temperature treatment, cement solidification, safe landfill, resource utilization, etc. Among them, high temperature treatment and cement kiln collaborative resource methods can completely treat dioxins and heavy metals in fly ash, and can also be used as resources, so these methods are widely used. However, these technologies all involve high temperature treatment and have strict requirements on chloride ions in fly ash. The chlorine content in fly ash is mostly between 10% and 20%, and can reach up to 30%, which seriously limits the resource utilization of fly ash. Therefore, fly ash dechlorination has become a key step in these technologies.

[0004] At present, common fly ash chlorine removal technologies include water washing dechlorination, acid washing dechlorination and thermal treatment technology. Water washing dechlorination technology is to directly mix water and fly ash, dissolve the chloride salt in the fly ash in water, and then separate the solid and liquid. The wastewater is decalcified and hardened, and then reused after evaporation and crystallization. The solid residue is separated and dried to achieve the purpose of dechlorination. Fly ash acid washing technology is similar to water washing technology, but the difference is that acid is added to the water. In addition to removing water-soluble chlorine, this method can also react with acid to convert non-water-soluble chlorides into water-soluble chlorine and be taken out with the filtrate. Thermal treatment technology is to perform high-temperature heat treatment on fly ash to volatilize heavy metals and chlorine into flue gas for capture, which can achieve the purpose of fly ash dechlorination and heavy metal removal.

[0005] Among the above-mentioned fly ash dechlorination technologies, water washing dechlorination technology is the most widely used. The reason is that acid washing dechlorination is mainly used to remove non-water-soluble chlorides. The other processes are exactly the same as the water washing process, but the non-soluble chlorine content in fly ash is relatively small, about 4% of the total chlorine, so the actual application of acid dechlorination is not very meaningful. High heat treatment technology requires high-temperature treatment of fly ash. The chlorine in the fly ash is easy to form a cycle enrichment in the heat treatment system under high temperature, causing the system to be crusted and blocked, affecting normal operation.

[0006] The main problems with existing fly ash water washing and chlorine removal technology are:

[0007] (1) The existing fly ash washing technology adopts three-stage countercurrent rinsing, with a general water-ash ratio of 3:1, high system water consumption and complex process.

[0008] (2) Existing fly ash washing technology produces wastewater, which is high-salt wastewater. The treatment process mainly adopts MVR (mechanical compression evaporation) technology. This technology not only has high energy consumption itself, but also requires decalcification pretreatment of the wastewater, which results in high reagent consumption and high treatment costs. Summary of the invention

[0009] In view of this, the present invention provides a waste incineration fly ash dechlorination process to solve the problems raised in the above background technology, achieve efficient fly ash dechlorination, and significantly reduce water consumption.

[0010] To achieve the above object, the present invention provides the following technical solutions:

[0011] The invention discloses a process for dechlorination of fly ash from garbage incineration, comprising the following steps:

[0012] S1, mixing fly ash, dechlorinating agent and water, stirring and dissolving to obtain a first slurry;

[0013] S2, adding a flocculant to the slurry, continuing to stir and dissolve, to obtain a second slurry;

[0014] S3, centrifuging the second slurry to obtain solid residue and ash washing wastewater;

[0015] S4, after the ash washing wastewater is clarified and filtered, it returns to step S1 for repeated use; the solid residue is subjected to a photolysis reaction, and the obtained product is dried and sent to a dust removal device.

[0016] As a further solution of the present invention: the dechlorination agent is silver nitrate or silver carbonate.

[0017] As a further solution of the present invention: in step S1, the addition amount of fly ash and dechlorination agent satisfies the following formula:

[0018] Q1=Q2﹡c / 35.5*169.8*(0.9-1);

[0019] Wherein, Q1 represents the amount of silver nitrate added, in t; Q2 represents the amount of fly ash disposed, in t; c represents the chlorine concentration in fly ash, in w%.

[0020] As a further solution of the present invention: in step S1, the mass ratio of fly ash to water is 1:1-1.2.

[0021] As a further solution of the present invention: in step S1, the stirring speed is 120-150 rpm, and the stirring time is 10 min; in step S2, the stirring speed is 40-50 rpm, and the stirring time is 20 min.

[0022] As a further solution of the present invention: the flocculant is polyferric sulfate, and the added amount is 0.2-0.4‰ of the water mass.

[0023] As a further solution of the present invention: in step S4, the photolysis time is 20-30 min, and the light source frequency is greater than 1.1x10 15 Hz.

[0024] As a further solution of the present invention: in step S4, the moisture content of the obtained product after drying is 3-5%.

[0025] As a further solution of the present invention: in step S4, the temperature after drying is not higher than 150°C.

[0026] As a further solution of the present invention: in step S4, sending to the dust removal equipment specifically includes: the dried product is sent to the electrostatic precipitator and the bag filter in sequence.

[0027] Reaction principle:

[0028] Fly ash, water, dechlorination agent and flocculant are mixed and stirred, and silver nitrate and chloride are reacted in water to form silver chloride precipitation, so that the soluble chloride in the fly ash is transformed into silver chloride precipitation, providing conditions for the subsequent fly ash dechlorination. The initial stirring speed is fast for full reaction to generate silver chloride, and the subsequent stirring speed is slowed down to play a role of flocculation, so as to promote the flocculation of silver chloride and generate particles of a certain particle size (about 5-10um).

[0029] The slurry is centrifuged to achieve solid-liquid separation. The separated liquid is ash washing wastewater, which mainly contains suspended particles, calcium salts, and nitrates. The separated residue is mainly water-washed fly ash and silver chloride particles.

[0030] The ash washing wastewater is sent to the wastewater treatment system to remove suspended particles and then returned for reuse. The number of cycles is set according to the nitrate concentration in the washing wastewater. When the nitrate concentration is close to saturation, a small amount of wastewater is discharged for external treatment.

[0031] The photolysis reaction of washed fly ash mainly uses the principle of silver chloride photolysis, that is, the limit frequency of electronic excitation of silver atoms and the ultraviolet frequency overlap, so when AgCl is irradiated with ultraviolet rays, the following reaction will occur: AgCl-- hv---2Ag+Cl2, so the fly ash residue is sent to the equipment with ultraviolet light source, AgCl in the fly ash residue is decomposed, chlorine enters the gas and is separated from the fly ash, and the fly ash is dechlorinated. The specific photolysis equipment is a belt structure, and the semi-solid residue moves back and forth through the crawler photolysis machine and contacts the ultraviolet light source. The photolysis time is 20-30min, and the decomposed chlorine gas is collected for treatment or utilization, and the silver remains in the solid residue.

[0032] After the solid residue after photolysis is dried, it enters the electrostatic precipitator and bag filter in turn. The difference in resistivity between fly ash and silver powder is used to efficiently separate the two materials. The resistivity of silver powder is about 1.59x10 -6 Ω.cm, the specific resistivity of fly ash is about 10 7 -10 11 Ω.cm, data comparison of the dust removal efficiency curve of the electrostatic precipitator ( Figure 2 ) It can be seen that:

[0033] The dust removal efficiency of silver powder through electrostatic precipitator is extremely low, less than 2%, while the dust removal efficiency of fly ash through electrostatic precipitator is relatively high, which can basically be stabilized at about 98%, thereby achieving efficient separation of fly ash and silver powder.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. The present invention adds a dechlorinating agent in the fly ash dechlorination link to transfer the existence form of chlorine in the fly ash. The transfer efficiency is high. Only one-stage water washing dechlorination is required, which simplifies the water washing process. In addition, the mass ratio of water to fly ash is greatly reduced, thereby reducing water resource consumption.

[0036] 2. The chlorine in the fly ash of the present invention is transferred in the form of precipitation, and the chlorine is not transferred to the water body, so that the ash washing wastewater can be returned to the water washing process for reuse after a simple treatment process of clarification and filtration, thereby reducing the consumption of water treatment chemicals and energy consumption.

[0037] 3. The present invention removes chlorine from fly ash by transferring chlorine to precipitation and then removing chlorine by photolysis precipitation, and the chlorine removal efficiency is high.

[0038] 4. After the washed fly ash is dried, the present invention utilizes the difference in powder properties to carry out classification processing and collection to obtain high-concentration silver powder dust, thereby effectively reducing the cost of fly ash dechlorination. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a flow chart of the present invention;

[0040] Figure 2 This is the relationship between dust resistivity and electrostatic precipitator efficiency. DETAILED DESCRIPTION

[0041] For ease of understanding of the present invention, the present invention will be described more fully below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0043] The specific information of the raw materials used in the following examples and comparative examples is as follows:

[0044] Chlorine removal agent, silver nitrate, purchased from Tianjin Dongjulong Chemical Technology Development Co., Ltd., grade III;

[0045] All materials are commercially available conventional products.

[0046] It can be understood that the above raw materials and reagents are only examples of some specific embodiments of the present invention, which makes the technical solution of the present invention clearer, and does not mean that the present invention can only adopt the above reagents. The specific scope shall be subject to the scope in the claims.

[0047] Example 1

[0048] The experimental fly ash disposal amount is 1kg, the chlorine concentration in the fly ash is 15%, and the fly ash dechlorination steps are:

[0049] (1) Fly ash and water were fed into the dissolution system in a mass ratio of 1:1, and 0.72 kg of silver nitrate was added simultaneously for stirring at a speed of 150 rpm for 8 min. Subsequently, a flocculant was added and the stirring time was continued for 2 min. Then, the stirring speed was changed to 50 rpm for 20 min to obtain a slurry.

[0050] (2) The slurry is sent to a centrifugal dehydration device, the separated wastewater enters the wastewater treatment stage, and the separated residue enters the photolysis stage.

[0051] Wastewater treatment: After being clarified and filtered to remove suspended solids, the wastewater is returned to the dissolution system in step (1) for reuse. The wastewater treatment sludge enters the water-washed fly ash photolysis equipment, circulates several times, and then the water-washed wastewater is discharged for external treatment.

[0052] Photolysis stage: The washed fly ash residue is sent to a belt photolysis machine for photolysis reaction with a residence time of 30 minutes to obtain solid residue and gas, and the reaction product chlorine gas is collected for resource utilization.

[0053] (3) The gas (chlorine) obtained in step (2) is collected for reuse, and the solid residue is sent to a drying device. The dried powder material is carried by hot air into an electrostatic precipitator. The dust collected by the electrostatic precipitator is chlorine-free fly ash, which is sent to a cement kiln for incineration. The outlet gas of the electrostatic precipitator enters a bag filter, and the dust collected is high-silver dust, which is recycled and reused. The waste gas (waste gas from dried fly ash) is treated and discharged in compliance with the emission standards.

[0054] The chlorine concentration of the tested dechlorination fly ash was 0.7w%, and the chlorine removal efficiency was about (15-0.7) / 15=95.3%. The silver concentration of the collected high-silver dust was about 85w%, and the amount of high-silver dust recovered was 0.48kg.

[0055] Example 2

[0056] In a pilot production line, the fly ash disposal capacity is 1t / h, the chlorine concentration in the fly ash is 10%, and the fly ash dechlorination steps are:

[0057] (1) Fly ash and water are fed into a dissolution tank at a flow rate of 1 t / h, and silver nitrate is added simultaneously at a rate of 0.48 t / h, and stirred continuously at a stirring speed of 150 rpm for 8 min. Subsequently, a flocculant is added and stirred for 2 min, and then the stirring speed is changed to 50 rpm for 20 min to obtain a slurry.

[0058] Step (2) is the same as step (2) of Example 1, except that the optical machine time is 20 minutes.

[0059] Step (3) is the same as step (3) of Example 1.

[0060] The chlorine concentration of the tested dechlorination fly ash was 0.9w%, and the chlorine removal efficiency was about (10-0.9) / 10=91%. The silver concentration of the collected high-silver dust was about 90w%, and the high-silver dust recovery rate was 0.32t / h.

[0061] Although this specification is described according to implementation modes, not every implementation mode includes only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

[0062] Therefore, the above description is only a preferred embodiment of the present application and is not intended to limit the scope of implementation of the present application; that is, all equivalent changes made according to the scope of the claims of the present application are within the protection scope of the claims of the present application.

Claims

1. A process for dechlorination of fly ash from garbage incineration, characterized in that: The following steps are involved: S1, mixing fly ash, dechlorinating agent and water, stirring and dissolving to obtain a first slurry; S2, adding a flocculant to the slurry, continuing to stir and dissolve, to obtain a second slurry; S3, centrifuging the second slurry to separate the solid residue and ash washing wastewater; S4, after being clarified and filtered, the ash washing wastewater is returned to step S1 for repeated use; the solid residue is subjected to a photolysis reaction, and the obtained product is dried and sent to a dust removal device.

2. The process for dechlorination of fly ash from waste incineration according to claim 1, characterized in that: The dechlorination agent is silver nitrate or silver carbonate.

3. The process for dechlorination of fly ash from waste incineration according to claim 1, characterized in that: In step S1, the addition amount of fly ash and dechlorination agent satisfies the following formula: Q1=Q2﹡c / 35.5*169.8*(0.9-1); Wherein, Q1 represents the amount of silver nitrate added, in t; Q2 represents the amount of fly ash disposed, in t; c represents the chlorine concentration in the fly ash, in w%.

4. The process for dechlorination of fly ash from waste incineration according to claim 1, characterized in that: In step S1, the mass ratio of fly ash to water is 1:1-1.

2.

5. The process for dechlorination of fly ash from waste incineration according to claim 1, characterized in that: In step S1, the stirring speed is 120-150 rpm, and the stirring time is 10 min; in step S2, the stirring speed is 40-50 rpm, and the stirring time is 20 min.

6. The process for dechlorination of fly ash from waste incineration according to claim 1, characterized in that: The flocculant is polyferric sulfate, and the added amount is 0.2-0.4‰ of the water mass.

7. The process for dechlorination of fly ash from waste incineration according to claim 1, characterized in that: In step S4, the photolysis time is 20-30 min, and the light source frequency is greater than 1.1x10 15 Hz.

8. The process for dechlorination of fly ash from waste incineration according to claim 1, characterized in that: In step S4, the moisture content of the obtained product after drying is 3-5%.

9. The process for dechlorination of fly ash from waste incineration according to claim 1, characterized in that: In step S4, the temperature after drying is not higher than 150°C.

10. The process for dechlorination of fly ash from waste incineration according to claim 1, characterized in that: In step S4, the step of sending the dried product to the dust removal device is as follows: the dried product is sent to the electrostatic precipitator and the bag filter in sequence.

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