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CN-121972489-A - Fly ash heavy metal fixing method based on flash joule heating

CN121972489ACN 121972489 ACN121972489 ACN 121972489ACN-121972489-A

Abstract

The invention relates to the technical field of waste treatment, in particular to a fly ash heavy metal fixing method based on flash joule heating. The invention can quickly raise the temperature of fly ash from various sources to high temperature in extremely short time by applying pulse current, realizes high-efficiency stabilization of heavy metal, has the characteristics of high treatment speed, low energy consumption, simple and convenient process, strong universality and the like, and solves the technical problems of long-time high-temperature maintenance, huge energy consumption, high operation cost, complex flow, low universality and the like of the heavy metal in the conventional heat treatment fixed fly ash. The larger the scale of the method is, the lower the treatment energy consumption of each ton of fly ash is, so that the cost is greatly reduced, and the method is beneficial to large-scale application.

Inventors

  • DENG BING
  • LU WENJING
  • LIU YINGCHAO
  • LIU YANJUN
  • YU FENG

Assignees

  • 清华大学

Dates

Publication Date
20260505
Application Date
20260128

Claims (10)

  1. 1. A fly ash heavy metal fixing method based on flash joule heating comprises the following steps: placing fly ash on a conductive heater to form a conductive path; and applying pulse current to the conductive heater to heat the fly ash, so as to obtain fly ash residues.
  2. 2. The method of claim 1, wherein the conductive heater comprises a flat plate heater, and the material of the flat plate heater comprises one or more of carbon paper, graphite felt, carbon fiber, or carbon-carbon composite.
  3. 3. The method of claim 1, wherein the electrical resistance of the conductive path is 0.5 to 5 Ω.
  4. 4. A method according to any one of claims 1 to 3, wherein the pulse meets at least one of the following conditions: the pulse current is 20-120A; the pulse voltage is 70-150V; The pulse duration is 1-20 s.
  5. 5. The method of claim 4, wherein the pulse satisfies any one of the following conditions: when M FA is less than 5g, the pulse current is 20-40A, and the pulse voltage is 70-90V; When 5g < M FA <15g, the pulse current is 100-120A, and the pulse voltage is 130-150V.
  6. 6. A method according to any one of claims 1 to 3, wherein the composition of the fly ash comprises one or more of calcium compounds, chlorides, sulfides, iron compounds, aluminium compounds, heavy metals.
  7. 7. A method according to any one of claims 1 to 3, wherein the heated fly ash meets at least one of the following conditions: The heating temperature is 1000-1500 ℃; The fly ash is heated to 1100-1400 ℃; the heating rate of the heated fly ash is 700-900 ℃ per second.
  8. 8. A method according to any one of claims 1 to 3, wherein the applying of the pulsed current is performed in an environment of an inert gas comprising one or more of nitrogen, argon, helium, neon.
  9. 9. A method according to any one of claims 1 to 3, further comprising fly ash pretreatment, the pretreatment comprising one or more of grinding, sieving, drying.
  10. 10. A method according to any one of claims 1 to 3, wherein the leaching concentration of heavy metals in the fly ash residue is below the domestic waste landfill pollution control standard limit specified in GB 16889-2024.

Description

Fly ash heavy metal fixing method based on flash joule heating Technical Field The invention relates to the technical field of waste treatment, in particular to a fly ash heavy metal fixing method based on flash joule heating. Background The incineration of the urban solid waste (MSW) can realize remarkable reduction and energy recovery, but the generated Fly Ash (FA) only accounts for 3-5% of the total mass of the residues, but the fly ash is enriched with high-concentration chlorides, dioxins and cancerogenic heavy metals, and is clearly listed as dangerous waste by the Chinese dangerous waste directory, so that the method has become a prominent problem of urban environment treatment. At present, harmless treatment of fly ash mainly depends on three technical routes, namely ① separation and extraction, namely, transfer enrichment of heavy metal can only be realized, dioxin cannot be degraded, ② solidification/stabilization, embedding of heavy metal through cement, chelating agent and the like, but Rong Bigao increase and long-term environmental safety is doubtful, ③ heat treatment, namely, the heavy metal can be dissolved in crystal lattices at a high temperature of 900-1400 ℃ and the dioxin can be thoroughly decomposed, and is recognized as the most thorough treatment direction. The traditional sintering method generally needs to be processed in a high-temperature furnace at 900-1200 ℃ for several hours, relies on external radiation-conduction heating, has large thermal inertia, long processing period and high energy consumption, and has the advantages that the vitrification technology needs to be used for quenching the molten fly ash into a glass body under the condition of being higher than 1400 ℃, the harmless effect is optimal, but the equipment refractory and the electricity consumption cost are extremely high, and the external field enhanced heating technology such as microwaves can shorten the heating time to a certain extent, but still needs to keep warm for a long time, has limited whole energy saving range and is difficult to amplify. Therefore, the traditional heat treatment needs long-time high-temperature maintenance, has huge energy consumption and high operation cost, severely restricts the large-scale application of the fly ash, and is difficult to meet the requirements of high-efficiency harmless and recycling of the fly ash. Related technologies are adopted to treat fly ash by flash joule heating, for example, chinese patent CN118417286A discloses a quick detoxification and recycling utilization method of waste incineration fly ash based on joule heat, soluble chloride and calcium components in the fly ash are removed by acid washing reduction, petroleum coke and sodium chloride are matched to improve conductivity, a flash joule heating device is utilized to realize high temperature of more than 3000 ℃ within 1-3 seconds, heavy metals are volatilized, condensation and collection are promoted, chinese patent CN120619034A discloses a quick heavy metal removal method based on flash joule heating technology, the waste incineration fly ash is mixed with conductive heating materials such as carbon black and the like, the resistance is controlled to be less than or equal to 3 omega, the electrical property is regulated and controlled by low-voltage pulse pretreatment, and then flash evaporation treatment of precise voltage (80-380V), time (0.1-1 s) and frequency (1-5 times) is applied, so that the second-level high temperature (1000-3000 ℃) heavy metals are quickly removed. However, the method for removing heavy metals based on flash joule heating has two problems, namely, firstly, the method requires adding conductive additives such as sodium chloride, carbon black and graphite, has high process cost and complex flow, dust of the conductive additives also brings explosion risks, and related technologies can only conduct targeted treatment on fly ash of a single source, so that universality is low, and secondly, the method is based on the principle of volatilization removal of heavy metals, and volatilizes and collects the heavy metals from a fly ash matrix through high temperature. Disclosure of Invention The present invention aims to solve at least one of the technical problems in the related art to some extent. Therefore, the invention provides a fly ash heavy metal fixing method based on flash joule heating, which can quickly raise the temperature of fly ash from various sources to high temperature in a very short time by applying pulse current, realizes high-efficiency stabilization of heavy metal, and has the characteristics of high treatment speed, low energy consumption, simple process, strong universality and the like. The method is different from the prior reported technology in the core characteristics of no need of adding any additional conductive additive and good applicability, and the method is used for solidifying heavy metal, namely, the heavy metal is sealed in a fly ash matr