Search

CN-122010378-A - Method and system for removing perfluoro and polyfluoroalkyl substances in sludge

CN122010378ACN 122010378 ACN122010378 ACN 122010378ACN-122010378-A

Abstract

The present disclosure relates to methods and systems for removing perfluoro and polyfluoroalkyl materials (PFAS) from sludge. The method comprises the steps of drying sludge containing PFAS (101) until the water content is below 15%, pyrolyzing (103) the dried sludge containing PFAS at the temperature of 700-800 ℃ to enable PFAS with more than a preset proportion in the sludge to enter pyrolysis gas, dedusting (104) the pyrolysis gas to remove dust particles in the pyrolysis gas, and incinerating (105) the pyrolysis gas at the temperature above the preset temperature to obtain incineration flue gas, so that PFAS in the pyrolysis gas is decomposed into micromolecular inorganic matters.

Inventors

  • SHI PING
  • HU MIN

Assignees

  • 苏伊士环境科技(北京)有限公司

Dates

Publication Date
20260512
Application Date
20260401

Claims (18)

  1. 1. A method of removing perfluoro and polyfluoroalkyl materials (PFAS) from sludge comprising: Drying (101) the sludge containing PFAS until the water content is below 15%; Pyrolyzing (103) the dried sludge containing PFAS at a temperature of 700-800 ℃ to enable the PFAS in the sludge to enter pyrolysis gas in a predetermined proportion; Dedusting (104) the pyrolysis gas to remove dust particulates in the pyrolysis gas; incinerating (105) the pyrolysis gas at a temperature above a predetermined temperature to obtain incineration flue gas, such that the PFAS in the pyrolysis gas is decomposed into small molecule inorganic substances.
  2. 2. The method of claim 1, wherein, The predetermined ratio is 99% and the predetermined temperature is 1400 ℃.
  3. 3. The method of claim 1 or 2, further comprising: In the drying (101), non-condensable gas is obtained, wherein the non-condensable gas is a part of gas generated in the drying (101) which is not condensed after being cooled; After the incineration (105), the noncondensable gases are subjected to a redox reaction (106) with the incineration flue gases to simultaneously remove NH 3 in the noncondensable gases and NO X in the incineration flue gases.
  4. 4. The method of claim 3, wherein, In the redox reaction (106), urea is added to replenish NH 3 .
  5. 5. The method of claim 3, wherein, In the redox reaction (106), contaminants in the noncondensable gas are oxidatively decomposed, the contaminants including H 2 S, VOCs.
  6. 6. A method according to claim 3, further comprising: after the redox reaction (106), heat of the reacted denitration flue gas is used for supplying heat (107) for pyrolysis (103) so as to perform primary heat recovery on the denitration flue gas.
  7. 7. The method of claim 6, wherein, The heat supply (107) for pyrolysis is realized by heat transfer of a partition wall.
  8. 8. The method of claim 6, further comprising: Generating steam (108) using the heat of the primary heat recovered denitration flue gas after said heating (107) for pyrolysis to perform secondary heat recovery on the denitration flue gas; and heating (109) the drying (101) by using the heat of the steam, obtaining condensed water, and generating steam (108) again by using the condensed water and the heat of the denitration flue gas subjected to primary heat recovery.
  9. 9. The method of claim 8, wherein, The generation of steam (108) is carried out in a waste heat boiler; The drying heat supply (109) is realized through heat transfer of a partition wall; the condensed water is passed into the waste heat boiler to regenerate steam (108).
  10. 10. The method of claim 8, further comprising: After the steam (108) is generated, the secondary heat recovered denitration flue gas is cleaned (110), and the cleaning (110) comprises removing particulate matters, acid gases, heavy metal vapors and/or residual organic pollutants.
  11. 11. The method of claim 1 or 2, further comprising: An auxiliary fuel (102) is added to the sludge after the drying (101) and before the pyrolysis (103) to increase the calorific value of the sludge.
  12. 12. A system for removing PFAS from sludge, comprising: A dryer configured to dry (101) the PFAS-containing sludge to a water content of 15% or less; A pyrolysis furnace configured to pyrolyze (103) the dried PFAS-containing sludge at a temperature of 700-800 ℃ such that a predetermined proportion or more of the PFAS in the sludge enters a pyrolysis gas; A dust collector configured to dust (104) the pyrolysis gas to remove dust particulates in the pyrolysis gas; A high temperature combustor configured to incinerate (105) the pyrolysis gas at a temperature above 1400 ℃ to obtain incineration flue gas, such that the PFAS in the pyrolysis gas is decomposed into small molecule inorganic substances.
  13. 13. The system of claim 12, further comprising: A denitration reaction chamber configured to cause a redox reaction (106) of non-condensable gas with the incineration flue gas to simultaneously remove NH 3 in the non-condensable gas and NO X in the incineration flue gas, wherein the non-condensable gas is a non-condensable portion of gas generated in the drying (101) after cooling.
  14. 14. The system of claim 13, further comprising: a urea supply system configured to add urea to replenish NH 3 in the redox reaction (106).
  15. 15. The system of claim 13, wherein, The pyrolysis furnace comprises a heating jacket into which the reacted denitration flue gas is introduced after the redox reaction (106) to supply heat (107) to the pyrolysis (103) using the heat of the reacted denitration flue gas to perform primary heat recovery of the denitration flue gas.
  16. 16. The system of claim 15, further comprising: A waste heat boiler, to which the once heat recovered denitration flue gas is introduced after the heating (107) for pyrolysis to generate steam (108) using the heat of the once heat recovered denitration flue gas to perform secondary heat recovery of the denitration flue gas, A steam condensate circulation system configured to deliver the steam to the dryer to provide heat (109) to a dryer (101) using the heat of the steam, obtain condensate, and deliver the condensate back to the waste heat boiler to regenerate steam (108) using the condensate and the heat of the primary heat recovered denitration flue gas.
  17. 17. The system of claim 16, further comprising: A flue gas cleaning system configured to clean (110) the secondary heat recovered denitration flue gas after the steam (108) generation, the flue gas cleaning system comprising a bag-type dust collector configured to remove particulate matter, a wet deacidification tower configured to remove acid gases, and/or an activated carbon adsorber configured to remove heavy metal vapors and/or residual organic contaminants.
  18. 18. The system of claim 12, further comprising: an auxiliary fuel supply system configured to add an auxiliary fuel (102) to the sludge after the drying (101) and before the pyrolysis (103) to increase a heating value of the sludge.

Description

Method and system for removing perfluoro and polyfluoroalkyl substances in sludge Technical Field The present disclosure relates to the field of sludge treatment, and in particular to a method and system for removing perfluoro and polyfluoroalkyl materials (PFAS) from sludge. Background Perfluoro and polyfluoroalkyl materials (PFAS) are a new class of contaminants with durability, bioaccumulation and potential toxicity, which are largely present in municipal and industrial sewage due to their wide use in industry and life, and are ultimately enriched in the excess sludge of sewage treatment plants. The carbon-fluorine (C-F) bond in PFAS molecules is one of the strongest chemical bonds in nature, making them extremely resistant to conventional physical, chemical and biological treatment methods. High temperature incineration is currently considered an effective means of disposing PFAS-containing waste. In theory, PFAS can be thoroughly decomposed into inorganic small molecules such as carbon dioxide, water and hydrogen fluoride at sufficiently high temperatures (typically considered to be above 1000 ℃ and more conservative considered to be up to 1200-1400 ℃) and sufficiently long residence times to render them harmless. However, when this theory is directly applied to sludge with high water content and complex components, huge technical and engineering challenges are faced. In the prior art, the mainstream method of treating PFAS-containing sludge still employs the mainstream bubbling fluidized bed incineration process (for example, patent CN 117510029B). The typical process is that wet sludge is mechanically dewatered (with water content of about 80%), sent to a dryer for drying, and then sent to an incinerator for incineration at about 850 ℃. And the flue gas generated by incineration is discharged after passing through a purifying unit such as waste heat recovery, dust removal, deacidification, denitration and the like. Temperatures around 850 ℃ are not sufficient to ensure that all kinds (especially long-chain) of PFAS are fully mineralized, and part of PFAS may only crack, generating short-chain intermediates with unknown toxicity, and discharging with flue gas, causing secondary pollution. If the temperature of the mainstream fluidized bed incinerator is forced to rise to 1400 ℃ to ensure complete PFAS decomposition, the melting point of the sludge ash (typically 1100-1200 ℃) will be exceeded. This can cause ash to melt, adhere to the bed material, destroy the fluidization state, and cause the incinerator to fail to operate normally, resulting in an accident of furnace shutdown. Patent application CN119161079a describes a process for the pyrolytic safe conversion and inorganization of perfluoro and polyfluoroalkyl materials in sludge based on solid base in situ catalysis. According to the method, a solid base catalyst (such as CaO, KOH and the like) is added into sludge with deep drying (the water content is less than 10%), pyrolysis is carried out in an oxygen-free or reducing atmosphere at 300-1000 ℃, and the catalyst is used for promoting C-F bond rupture and fixing fluorine element into stable metal fluoride (such as CaF 2). However, the method belongs to catalytic pyrolysis, introduces additional chemical agents, increases the operation cost and the complexity of subsequent solid waste treatment, has extremely high requirements on pretreatment of sludge, requires deep dehydration and low-temperature drying, and has high energy consumption and long period, and the economy and universality of the whole process are to be verified. Therefore, a sludge treatment method and system based on a high-temperature incineration theory, which are simultaneously feasible and economical in engineering, are needed to remove PFAS in sludge and realize the harmless treatment of PFAS in sludge. Disclosure of Invention It is an object of the present disclosure to provide a method and system that enables safe, efficient and energy-self-sustaining disposal of PFAS-containing sludge. The technical problem to be solved by the present disclosure includes: How to create a local and controllable ultra-high temperature (more than or equal to 1400 ℃) environment on the premise of avoiding ash fusion, so as to ensure the efficient mineralization of PFAS in the sludge; how to transfer PFAS from solid phase sludge to a gas phase that is easy to handle with high efficiency and complete the decomposition in this ultra-high temperature environment; How to cooperatively treat non-condensable gases containing malodor, VOCs and other pollutants generated in the sludge drying process, so as to realize the dual purposes of waste treatment and pollution control; How to achieve energy self-balancing of the whole treatment process, without external refueling, reducing operating costs. According to a first aspect of the present disclosure, there is provided a method for removing PFAS in sludge, comprising drying the PFAS-containing sludge to