Method for enriching heavy metals in waste incineration fly ash based on front-end enhanced condensation and short-range enrichment

Abstract

The invention discloses a method for enriching heavy metals in waste incineration fly ash based on front-end enhanced condensation and short-range enrichment, which comprises the following steps: adding a material containing an alkaline earth metal compound into a flue of an economizer to destroy the high chlorine range of the front-end economizer and reduce the formation of heavy metal chlorides; in combination with regulation and control of outlet smoke of the economizer and smoke flow velocity in a flue of the economizer, the fly ash is subjected to multi-metal enhanced condensation and short-range enrichment in the economizer, so that migration of heavy metal to terminal fly ash is reduced, and the heavy metal can be quickly enriched at the front end; and heavy metals and chlorides thereof are prevented from being migrated to the terminal and enriched in the terminal fly ash, so that the terminal fly ash heavy metal pollution is reduced, the effect of attenuation and even detoxification of the terminal fly ash heavy metals is achieved, and the purpose of treating solid wastes and heavy metal pollution is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of solid waste heavy metal pollution treatment, and more particularly relates to a method for treating heavy metals in waste incineration fly ash based on front-end enhanced condensation and short-range enrichment. BACKGROUND

[0002] Fly ash is a hazardous solid waste rich in heavy metals produced by waste incineration. In the process of waste incineration, heavy metals in waste raw materials have different enrichment behaviors due to their different volatilities. Easily volatile heavy metals (such as Cd and Pb) and moderately volatile heavy metals (such as Zn and Cu) are directly volatilized into gaseous or particulate phases and enter subsequent processes with high-temperature flue gas for treatment. Difficult-to-volatile heavy metals (such as Cr and Ni) are mainly enriched in bottom slag through oxidation and melting. In the waste incineration flue gas, the content of Cl is about 40% or more, belonging to a high-chlorine atmosphere. The high-chlorine atmosphere promotes the volatilization and separation of heavy metals in fly ash, weakens / delays the condensation effect of heavy metals (especially easily volatile heavy metals and moderately volatile heavy metals) from the gas phase to the solid phase, and causes fly ash along the way to be contaminated by heavy metals, thereby increasing the amount and toxicity of terminal fly ash. As a hazardous waste, the terminal fly ash needs to be stabilized and solidified before further disposal due to its high heavy metal content. However, heavy metals in the terminal fly ash are difficult to remove by stabilization and solidification and remain in the fly ash, which still poses a great leaching pollution risk after landfill.

[0003] To remove heavy metals from terminal fly ash, reduce the leaching toxicity of heavy metals, and prevent heavy metal pollution, the existing technology usually takes terminal fly ash as the treatment object, creates a high-chlorine atmosphere by adding chlorides based on the principle that the boiling point of metal chlorides is lower than that of the corresponding metal oxides, and performs high-temperature heat treatment to make the heavy metals in the terminal fly ash volatilize and separate, thereby achieving the purpose of removing heavy metals from fly ash and preventing heavy metal pollution. For example, in patent CN108715519A, added calcium chloride and magnesium chloride are pressed into spherical particles with incineration fly ash, and then calcined to make the heavy metals in the fly ash react with the chlorination agent to generate easily volatile heavy metal chlorides. In patent CN119857716A, terminal fly ash is taken as the treatment object, and magnesium chloride or calcium chloride is added to make the chlorine for decomposing dioxins in the fly ash and the added chlorides react with the easily volatile and semi-volatile heavy metals in the fly ash to form gaseous heavy metal chlorides and remove the heavy metals, while the difficult-to-volatile heavy metals are solidified in the sintered material to reduce leaching and further prevent and control heavy metal pollution.

[0004] However, the terminal fly ash has a large amount of heavy metal enrichment, and the cost of creating a high chlorine atmosphere for high-temperature heat treatment of the terminal fly ash with high heavy metal enrichment is high, and the return is low. However, the present application is contrary to the above, that is, by destroying the high chlorine atmosphere in the front-end flue gas, reducing the formation of volatile heavy metals and medium volatile heavy metal chlorides, and further reducing the migration of heavy metals to the terminal fly ash, promoting the enrichment of heavy metals in the front-end fly ash of the economizer, reducing the content of heavy metals in the terminal captured fly ash, fundamentally preventing heavy metal pollution, achieving the effect of detoxification of the terminal fly ash heavy metals, preventing heavy metal pollution, and making it can be directly landfilled or other ways of disposal without treatment, thereby greatly saving the cost of solid waste treatment and heavy metal pollution prevention. SUMMARY

[0005] In view of the above defects or improvement needs of the prior art, the present application provides a method for short-range enrichment of heavy metals in waste incineration fly ash based on front-end enhanced condensation, which aims to destroy the high chlorine atmosphere in the front-end economizer flue by adding an alkaline earth metal compound material, reduce the migration and enrichment of gaseous heavy metal chlorides with flue gas to the terminal, and at the same time regulate the outlet flue gas temperature of the economizer and the flue gas flow rate in the economizer flue, enhance the condensation and enrichment of heavy metals in the economizer section, significantly reduce the heavy metals in the terminal fly ash, achieve the effect of detoxification of the terminal fly ash heavy metals, and make it can be directly landfilled or other ways of disposal without treatment, thereby solving the technical problems of the prior art that heavy metals migrate and enrich to the terminal, the content of heavy metals enriched in the terminal fly ash is high, the yield is large, and the fly ash needs to be stabilized and solidified before landfill disposal, and the heavy metals remaining in the fly ash still have a high leaching pollution risk after landfill.

[0006] To achieve the above-mentioned purpose, according to one aspect of the present application, a method for short-range enrichment of heavy metals in waste incineration fly ash based on front-end enhanced condensation is provided, which comprises the following steps: (1) Destroy the high chlorine range of the front-end economizer: according to the amount of waste feed, add an alkaline earth metal compound material to the economizer flue, so that the addition rate of the alkaline earth metal compound material is 30-120 kg / h; the main components of the alkaline earth metal compound material include CaO, Ca(OH)2 and / or MgO, Mg(OH)2, and the content of the main components is ≥60%; (2) Enhance the condensation of heavy metals in the front-end economizer: reduce the outlet flue gas temperature of the economizer and the flue gas flow rate in the economizer flue, so that the outlet flue gas temperature of the economizer is reduced to 160-170°C, the condensation of heavy metals is enhanced, and at the same time the flue gas flow rate is regulated to be between 1-3 m / s, so that the fly ash particles carrying the condensed heavy metals are short-range enriched and quickly settled in the front-end of the economizer, and the front-end fly ash enriched with heavy metals is collected.

[0007] Preferably, the method, the average particle size of the material containing alkaline earth metal compound in step (1) is less than or equal to 45 microns.

[0008] Preferably, the method, the main component of the material containing alkaline earth metal compound in step (1) is CaO and Ca(OH)2, and the content of CaO and Ca(OH)2 is 60% to 90%.

[0009] Preferably, the method, the proportion of the material containing alkaline earth metal compound in step (1) with a particle size of less than or equal to 53 microns is greater than or equal to 90%.

[0010] Preferably, the method, the material containing alkaline earth metal compound in step (1) is dry lime powder, and the dry lime powder is added according to the following method: If the garbage feeding amount is 700 to 800 t / d, the dry lime powder feeding rate in the economizer flue is adjusted to 30 to 60 kg / h; If the garbage feeding amount is 800 to 900 t / d, the dry lime powder feeding rate in the economizer flue is adjusted to 60 to 90 kg / h; If the garbage feeding amount is 900 to 1000 t / d, the dry lime powder feeding rate in the economizer flue is adjusted to 90 to 120 kg / h.

[0011] Preferably, the method, the heavy metal includes Pb, Cd, Cu, Zn, Cr and Ni.

[0012] Preferably, the method, the flue gas flow rate in the economizer flue is calculated according to the total of the primary air volume and the secondary air volume of the incinerator divided by the cross-sectional area of the economizer flue in step (2), and the flue gas flow rate in the economizer flue is controlled to be between 1 to 3 m / s by adjusting the primary air volume and the secondary air volume of the incinerator, while ensuring that the temperature of the incinerator is in the range of 850-1000℃.

[0013] Preferably, the method, the heat exchange efficiency is enhanced by increasing the cleaning frequency of the inner wall of the economizer flue and / or adjusting the circulating water supply amount of the economizer in step (2), so that the flue gas temperature at the outlet of the economizer is reduced to 160 to 170℃.

[0014] Overall, compared with the prior art, the above technical solutions conceived by the present application can achieve the following beneficial effects: The method for enriching heavy metals in waste incineration fly ash based on front-end enhanced condensation and short-range enrichment provided by the application can destroy the high-chlorine range of the front-end economizer by adding an alkaline earth metal compound-containing material into the economizer flue, reduce the formation of heavy metal chlorides, and combine the regulation of the outlet flue gas temperature of the economizer and the flue gas flow rate in the economizer flue to cause the multi-metal enhanced condensation and short-range enrichment of the fly ash in the economizer, thereby reducing the migration of heavy metals to the terminal fly ash. Since the method concentrates and enriches heavy metals in the front end of the economizer, the amount of terminal fly ash is reduced, the heavy metal content and leaching toxicity of the terminal fly ash are reduced, and the fly ash landfill disposal problem (landfill site capacity is tight, and the environmental risk of long-term leaching of heavy metals) is alleviated. In addition, the terminal fly ash itself does not have the value of heavy metal recycling, but after the heavy metals are concentrated and enriched in the front end, heavy metal resources can be recycled, which may make the front-end fly ash have the value of resource recycling. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a conventional process flow diagram of fly ash heavy metal enrichment in waste incineration; Figure 2 is a schematic diagram of the method. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical scheme and advantages of the application clearer, the application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the application and do not limit the application. In addition, the technical features involved in each embodiment of the application described below can be combined with each other as long as they do not conflict with each other.

[0017] In the waste incineration flue gas deposition phase, the content of Cl element is about 40% or more, which belongs to a high-chlorine atmosphere. However, under the condition of a high-chlorine atmosphere, volatile and semi-volatile heavy metals form a multi-metal eutectic system in the flue gas, which causes the supercooling problem of heavy metals in fly ash (i.e., the phase transfer of heavy metals from the gas phase to the solid phase is delayed), delays the condensation effect of heavy metals from the gas phase to the solid phase, and causes the volatile and semi-volatile heavy metals to be transported with the flue gas to an area where the flue gas temperature is lower than the melting point of the heavy metals, slowly condenses, settles and deposits in the economizer and the downstream flue, and the fly ash along the way is contaminated by heavy metals, resulting in the problems of large amount of terminal fly ash and high toxicity.

[0018] The present application provides a method for short-range enrichment of heavy metals in fly ash from waste incineration based on front-end enhanced condensation, which can quickly enrich heavy metals at the front end, avoid the migration of heavy metals and their chlorides to the terminal, and significantly reduce the production and heavy metal content in the terminal fly ash, so that the terminal fly ash can be directly landfilled or disposed of in other ways without treatment.

[0019] The present application provides a method for short-range enrichment of heavy metals in fly ash from waste incineration based on front-end enhanced condensation, which can quickly enrich heavy metals at the front end, avoid the migration of heavy metals and their chlorides to the terminal, and significantly reduce the production and heavy metal content in the terminal fly ash, so that the terminal fly ash can be directly landfilled or disposed of in other ways without treatment. (1) Destroying the high-chlorine environment in the front-end economizer: according to the amount of waste feed, add an alkaline earth metal compound-containing material to the economizer flue, so that the addition rate of the alkaline earth metal compound-containing material is 30-120 kg / h; the main components of the alkaline earth metal compound-containing material include CaO, Ca(OH)2 and / or MgO, Mg(OH)2, the content of the main components is ≥60%, and the average particle size of the material is ≤45 μm.

[0020] By introducing alkaline earth metal compounds into the front-end economizer flue, they react with chlorides in the economizer flue, destroying the high-chlorine environment in the economizer flue, overcoming the supercooling effect of heavy metals, and thus enhancing the condensation effect of easily volatile and semi-volatile heavy metals from gas phase to solid phase; on the other hand, it reduces the formation of semi-volatile heavy metal chlorides, avoiding the migration of semi-volatile heavy metals in the form of gaseous metal chlorides to the terminal and enrichment in the terminal fly ash; the average particle size of the added material is ≤45 μm, which increases the proportion of small and medium-sized particles (within 100 μm) carrying heavy metals in the economizer section, promotes the condensation of heavy metals and their settlement in the front-end economizer, and thus enriches heavy metals in the front-end fly ash.

[0021] (2) Enhancing the condensation of heavy metals in the front-end economizer: reducing the outlet flue gas temperature of the economizer and the flue gas velocity in the economizer flue, so that the outlet flue gas temperature of the economizer is reduced to 160-170 ℃, the condensation of heavy metals is enhanced, and the flue gas velocity is controlled between 1-3 m / s, so that the fly ash particles carrying condensed heavy metals are quickly and short-range enriched and settled at the front end of the economizer, and the front-end fly ash enriched with heavy metals is collected; the heavy metals include Pb, Cd, Cu, Zn, Cr and Ni. The flue gas velocity in the economizer flue is calculated according to the total amount of primary and secondary air of the incinerator divided by the cross-sectional area of the economizer flue.

[0022] The outlet flue gas temperature of the economizer should not be lower than 160°C, otherwise the downstream pollution control facilities will not operate normally (e.g. the bag filter will be clogged if the outlet flue gas temperature is too low), and the outlet flue gas temperature of the economizer should not be too high, because the heavy metal chlorides cannot be condensed from gas phase to solid phase at a high outlet flue gas temperature. By adjusting the outlet flue gas temperature and the flue gas flow rate of the economizer, the heavy metals in the flue gas can be enriched in the economizer flue, and the migration of the heavy metals to the terminal along the way can be avoided.

[0023] In some embodiments, the high-chlorine range of the front-end economizer is broken down in step (1), and a material containing alkaline earth metal compounds is added to the economizer flue, which mainly contains CaO and Ca(OH)2, and the content of CaO and Ca(OH)2 is 60% to 90%, and the average particle size of the material is ≤45 μm, and the proportion of particles with a particle size of ≤53 μm is greater than or equal to 90%, and most of the particles are much smaller than 45 μm. The purpose of having a proportion of particles with a particle size of ≤53 μm of ≥90% is to avoid having too many large particles. For example, the material containing alkaline earth metal compounds is dry lime powder, which is added according to the following method: If the garbage feed quantity is 700-800 t / d, the dry lime powder addition rate in the economizer flue is adjusted to 30-60 kg / h; If the garbage feed quantity is 800-900 t / d, the dry lime powder addition rate in the economizer flue is adjusted to 60-90 kg / h; If the garbage feed quantity is 900-1000 t / d, the dry lime powder addition rate in the economizer flue is adjusted to 90-120 kg / h.

[0024] In some embodiments, the condensation of heavy metals in the front-end economizer is strengthened in step (2), and the outlet flue gas temperature of the economizer is lowered according to the following method: The outlet flue gas temperature of the economizer is lowered to 160-170°C by increasing the frequency of cleaning the inner wall of the economizer flue and / or adjusting the circulating water supply of the economizer to enhance the heat exchange efficiency.

[0025] The flue gas flow rate is adjusted to 1-3 m / s according to the following method: The flue gas flow rate in the economizer flue is calculated based on the total of the primary air quantity and the secondary air quantity of the incinerator divided by the cross-sectional area of the economizer flue. The flue gas flow rate in the economizer flue is adjusted to be between 1-3 m / s by adjusting the primary air quantity and the secondary air quantity of the incinerator, while ensuring that the temperature of the incinerator is within the range of 850-1000°C.

[0026] The following is an example Taking a domestic waste incineration power plant as an example, the conventional process flow diagram of domestic waste from the incinerator to the terminal fly ash collection is as follows: Figure 1The design capacity of the incinerator is 900 t / d, and the daily waste feeding is about 700-900 t / d. The primary air flow of the incinerator is about 60000-90000 m 3 / h, the secondary air flow is about 10000-35000 m 3 / h, and the end chimney flue gas flow is about 120000-180000 m 3 / h. The dry powder feeding device in the economizer flue has been modified, and the feeding rate is about 30-120 kg / h. The environmental protection material sprayed into the economizer flue is quicklime. The cross-sectional area of the economizer flue is about 8.8 m 2 , the flue gas temperature is about 190-230℃, the flue gas flow rate is about 2.5-4.0 m / s, and the cleaning frequency of the flue wall ash is about 8-24 h / time.

[0027] Example 1: Method for strengthening condensation at the front end and short-range enrichment of heavy metals in waste incineration fly ash The real-time operating conditions of the municipal solid waste incineration power plant A are as follows: The waste feeding amount is about 722 t / d, the primary air flow and the secondary air flow of the incinerator are 75891 m 3 / h and 13475 m 3 / h, respectively, and the end chimney flue gas flow is about 127206 m 3 / h.

[0028] The flue gas temperature in the economizer flue is 196℃, the flue gas flow rate is about 2.8 m / s (calculated by dividing the total of the primary air flow and the secondary air flow (89366 m 3 / h) by the cross-sectional area of the economizer flue (8.8 m 2 )), and the cleaning frequency of the flue wall ash is about 8 h / time (daily working frequency of the incineration plant).

[0029] According to the method, the process flow diagram of municipal solid waste from the incinerator to the terminal fly ash collection is as Figure 2 shown, and for the municipal solid waste incineration power plant A, the specific treatment according to the method is as follows: (1) Destroy the high chlorine range of the front-end economizer: The waste feeding amount of the municipal solid waste incineration power plant A is 700-800 t / d, and the dry powder feeding rate of quicklime in the economizer flue is adjusted to about 30-60 kg / h.

[0030] (2) Strengthen the condensation of heavy metals in the front-end economizer: adjust the cleaning frequency of the inner wall of the economizer flue to 4h / time, moderately adjust the circulating water supply of the economizer to improve the heat exchange efficiency, and finally adjust the flue gas temperature at the outlet of the economizer to be in the range of 160-170℃; the flue gas temperature at the outlet of the economizer should not be lower than 160℃, otherwise it will cause the abnormal operation of the pollution control facilities downstream of the economizer (such as the bag filter will be caked if the flue gas temperature is too low); At the same time, adjust the primary air volume of the incinerator to be in the range of 30000-60000m 3 / h, adjust the secondary air volume to be in the range of 3000-10000m 3 / h, and the end chimney flue gas flow is about 50000-100000m 3 / h (generally, the end chimney flue gas flow is about 1-1.5 times of the total of the primary air volume and the secondary air volume), so that the flue gas flow rate in the economizer flue is reduced to be in the range of about 1.0-2.2m / s (calculated by the total of the primary air volume and the secondary air volume (33000-90000m 3 / h) divided by the cross-sectional area of the economizer flue (8.8m 2 ).

[0031] The primary air volume and the secondary air volume of the incinerator can also be adjusted according to the operation experience, while the temperature of the incinerator should be ensured to be in the range of 850-1000℃.

[0032] Example 2 The real-time operation conditions of the household waste incineration power plant B are as follows: The waste feeding amount is about 889t / d, the primary air volume and the secondary air volume of the incinerator are 89805m 3 / h and 30836m 3 / h respectively, and the end chimney flue gas flow is 167206m 3 / h. The flue gas temperature in the economizer flue is 217℃, the flue gas flow rate is about 3.8m / s, and the cleaning frequency of the inner wall of the flue is about 8h / time.

[0033] For the household waste incineration power plant B, the specific treatment according to the method is as follows: (1) The waste feeding amount of the household waste incineration power plant B is 800-900t / d, and the feeding rate of dry lime powder in the economizer flue is adjusted to be 60-90kg / h; the waste feeding amount is increased, and the material addition amount is increased accordingly.

[0034] (2) Strengthen the condensation of heavy metals in the front-end economizer: adjust the cleaning frequency of the inner wall of the economizer flue to be about 2h / time (the material addition amount is increased, and the cleaning frequency is increased accordingly), adjust the circulating water supply of the economizer to improve the heat exchange efficiency, and finally adjust the flue gas temperature at the outlet of the economizer to be in the range of about 160-170℃.

[0035] At the same time, the primary air volume of the incinerator is adjusted to 50000-70000m 3 / h, and the secondary air volume is adjusted to 3000-20000m 3 / h, and the terminal chimney flue gas flow is about 80000-135000m 3 / h, so that the flue gas flow rate in the economizer flue is reduced to about 1.5-2.8m / s.

[0036] The terminal fly ash after the existing method (real-time operation condition) and the terminal fly ash after the method of embodiment 1 and embodiment 2 are collected respectively, and the total amount of heavy metals in each terminal fly ash and the leaching toxicity of the terminal fly ash after chelation are detected, and the results are shown in the following table.

[0037] Table 1 Total amount of heavy metals and leaching toxicity of terminal fly ash by different treatment methods As can be seen from the results in Table 1, compared with the existing traditional treatment method, the terminal fly ash after stabilization and solidification treatment may not necessarily meet the landfill standard by 100%. The method enriches heavy metals in the front-end fly ash, directly reduces the total amount of heavy metals in the terminal fly ash, so that the content of heavy metals in the collected terminal fly ash is low, especially the content of heavy metals Pb and Cd in the terminal fly ash is significantly reduced, the leaching toxicity of heavy metals in the fly ash is lower than the heavy metal leaching limit value, so that the terminal fly ash can be directly landfilled or disposed by other means without treatment, thereby reducing heavy metal pollution.

[0038] Those skilled in the art will readily understand that the above description is only a preferred embodiment of the present application, and is not intended to limit the present application, and any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for enriching heavy metals in waste incineration fly ash based on front-end enhanced condensation and short-range enrichment, characterized in that, Includes the following steps: (1) Disrupting the high-chlorine range of the front-end economizer: Add materials containing alkaline earth metal compounds into the economizer flue according to the amount of garbage fed, so that the addition rate of the alkaline earth metal compound materials is 30~120kg / h; the main components of the alkaline earth metal compound materials include CaO, Ca(OH)2 and / or MgO, Mg(OH)2, and the content of the main components is ≥60%; (2) Enhance the condensation of heavy metals in the front-end economizer: reduce the outlet flue gas temperature of the economizer and the flue gas velocity in the economizer flue, so that the outlet flue gas temperature of the economizer is reduced to the range of 160~170℃, enhance the condensation of heavy metals, and at the same time control the flue gas velocity between 1~3m / s, so that the fly ash particles carrying the condensed heavy metals are enriched in the front end of the economizer in a short distance, settle quickly, and the front fly ash enriched with heavy metals is collected.

2. The method as described in claim 1, characterized in that, The material containing alkaline earth metal compounds in step (1) has an average particle size ≤45μm.

3. The method as described in claim 2, characterized in that, The material containing alkaline earth metal compounds mentioned in step (1) mainly consists of CaO and Ca(OH)2, with the contents of CaO and Ca(OH)2 being 60%~90%.

4. The method as described in claim 3, characterized in that, The proportion of alkaline earth metal compound-containing materials in step (1) with a particle size ≤53μm is greater than or equal to 90%.

5. The method as described in claim 4, characterized in that, The material containing alkaline earth metal compounds in step (1) is quicklime powder, which is added according to the following method: If the garbage feed rate is 700~800t / d, adjust the quicklime dry powder feeding rate in the economizer flue to 30~60kg / h; If the garbage feed rate is 800-900 t / d, adjust the quicklime dry powder feeding rate in the economizer flue to 60-90 kg / h; If the waste feed rate is 900~1000t / d, adjust the quicklime dry powder feeding rate in the economizer flue to 90~120kg / h.

6. The method according to any one of claims 1 to 5, characterized in that, The front-end fly ash is enriched with heavy metals including Pb, Cd, Cu, Zn, Cr, and Ni.

7. The method as described in claim 6, characterized in that, Step (2) Calculate the flue gas velocity in the economizer flue by dividing the sum of the primary and secondary air volumes of the incinerator by the cross-sectional area of ​​the economizer flue. Adjust the primary and secondary air volumes of the incinerator to keep the flue gas velocity in the economizer flue between 1 and 3 m / s, while ensuring that the incinerator temperature is within the range of 850-1000℃.

8. The method as described in claim 7, characterized in that, Step (2) By increasing the frequency of cleaning the ash buildup on the inner wall of the economizer flue and / or adjusting the circulating water supply of the economizer, the heat exchange efficiency is enhanced, and the outlet flue gas temperature of the economizer is reduced to 160~170℃.

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