Method and system for removing perfluorinated and polyfluoroalkyl substances in sludge

Abstract

The present disclosure relates to methods and systems for removing perfluoroand polyfluoroalkyl species (PFAS) from sludge. The method comprises: drying (101) sludge containing PFAS until the water content is below 15%; pyrolyzing the dried sludge containing the PFAS at the temperature of 700-800 DEG C (103), so that the PFAS in a predetermined proportion or above in the sludge enters pyrolysis gas; performing dust removal on the pyrolysis gas (104) to remove dust particles in the pyrolysis gas; and incinerating (105) the pyrolysis gas at a temperature above the predetermined temperature to obtain an incinerated flue gas, such that PFAS in the pyrolysis gas is decomposed into small molecular inorganic substances.

Description

Technical Field

[0001] This disclosure relates to the field of sludge treatment, and more particularly to methods and systems for removing perfluorinated and polyfluoroalkyl substances (PFAS) from sludge. Background Technology

[0002] Per- and polyfluoroalkyl substances (PFAS) are a new class of persistent, bioaccumulative, and potentially toxic pollutants. They are present in large quantities in municipal and industrial wastewater due to their widespread use in industry and daily life, and ultimately accumulate in the residual sludge of wastewater treatment plants. The carbon-fluorine (CF) bond in the PFAS molecule is one of the strongest chemical bonds in nature, making it highly resistant to conventional physical, chemical, and biological treatment methods.

[0003] Currently, high-temperature incineration is considered an effective method for treating PFAS-containing waste. Theoretically, at sufficiently high temperatures (generally considered to be above 1000℃, with a more conservative view suggesting 1200-1400℃) and sufficiently long residence times, PFAS can be completely decomposed into inorganic small molecules such as carbon dioxide, water, and hydrogen fluoride, thus achieving harmlessness. However, directly applying this theory to sludge with high water content and complex composition faces significant technical and engineering challenges.

[0004] In existing technologies, the mainstream method for treating PFAS-containing sludge still employs the mainstream bubbling fluidized bed incineration process (e.g., patent CN117510029B). The typical process involves: wet sludge undergoing mechanical dewatering (approximately 80% moisture content), then being dried in a dryer, and finally fed into an incinerator for incineration at around 850°C. The flue gas generated from incineration is then purified through waste heat recovery, dust removal, acid removal, and denitrification units before being discharged. A temperature of around 850°C is insufficient to ensure the complete mineralization of all types of PFAS (especially long-chain PFAS). Some PFAS may only undergo cracking, generating short-chain intermediates with unknown toxicity, which are emitted with the flue gas, causing secondary pollution. If the temperature of the mainstream fluidized bed incinerator is forcibly increased to 1400°C to ensure complete PFAS decomposition, it would exceed the melting point of sludge ash (typically between 1100-1200°C). This would cause the ash to melt, adhere to the bed material, disrupt the fluidization state, and prevent the incinerator from operating normally, leading to a shutdown.

[0005] Patent application CN119161079A describes a safe and inorganic process for the pyrolysis of perfluorinated and polyfluoroalkyl substances in sludge based on in-situ solid alkali catalysis. This method involves adding a solid alkali catalyst (such as CaO or KOH) to deeply dried sludge (moisture content <10%) and conducting pyrolysis at 300-1000℃ in an anaerobic or reducing atmosphere. The catalyst promotes the breaking of CF bonds and fixes fluorine into stable metal fluorides (such as CaF2). However, this method is a catalytic pyrolysis, introducing additional chemical agents, increasing operating costs and the complexity of subsequent solid waste treatment; furthermore, it requires extremely high pretreatment of the sludge, necessitating deep dewatering and low-temperature drying, resulting in high energy consumption and a long cycle time. The overall economic viability and universality of the process need further verification.

[0006] Therefore, there is a need for sludge treatment methods and systems that are based on high-temperature incineration theory, are engineering-feasible and economical, in order to remove PFAS from sludge and achieve the harmlessness of PFAS in sludge. Summary of the Invention

[0007] The purpose of this disclosure is to provide a method and system for the safe, efficient, and energy-sustainable disposal of PFAS-containing sludge.

[0008] The technical problems to be solved by this disclosure include:

[0009] - How to create a localized, controllable ultra-high temperature (≥1400℃) environment to ensure efficient mineralization of PFAS in sludge while avoiding ash melting;

[0010] - How to efficiently transfer PFAS from solid sludge to an easily treatable gas phase and complete its decomposition in this ultra-high temperature environment;

[0011] - How to synergistically treat the non-condensable gases containing malodorous substances and VOCs generated during sludge drying to achieve the dual goals of waste treatment and pollution control;

[0012] - How to achieve energy self-balancing throughout the entire disposal process, without the need for external fuel replenishment, thereby reducing operating costs.

[0013] According to a first aspect of this disclosure, a method for removing PFAS from sludge is provided, comprising: drying the PFAS-containing sludge to a moisture content of less than 15%; pyrolyzing the dried PFAS-containing sludge at a temperature of 700-800°C, so that a predetermined proportion or more of the PFAS in the sludge enters the pyrolysis gas; removing dust particles from the pyrolysis gas; and incinerating the pyrolysis gas at a temperature above a predetermined temperature to obtain incineration flue gas, thereby decomposing the PFAS in the pyrolysis gas into small molecule inorganic substances.

[0014] In some embodiments, the predetermined ratio is 99% and the predetermined temperature is 1400°C.

[0015] In some embodiments, the method further includes: obtaining non-condensable gas during the drying process, the non-condensable gas being the uncondensed portion of the gas generated during the drying process after cooling; and, after incineration, subjecting the non-condensable gas to a redox reaction with the incineration flue gas to simultaneously remove NH3 from the non-condensable gas and NO from the incineration flue gas. X .

[0016] In some embodiments, urea is added to the redox reaction to replenish NH3.

[0017] In some embodiments, during the redox reaction, pollutants in the noncondensable gas are oxidized and decomposed, including H2S and VOCs.

[0018] In some embodiments, the method further includes: after the redox reaction, using the heat from the denitrified flue gas after the reaction as heat for pyrolysis to perform a heat recovery of the denitrified flue gas.

[0019] In some embodiments, the pyrolysis heating is achieved through heat transfer via the partition wall.

[0020] In some embodiments, the method further includes: after providing heat for pyrolysis, using the heat from the denitrified flue gas that has undergone primary heat recovery to generate steam for secondary heat recovery of the denitrified flue gas; using the heat from the steam to provide heat for drying to obtain condensate, and using the condensate and the heat from the denitrified flue gas that has undergone primary heat recovery to generate steam again.

[0021] In some embodiments, the steam generation is achieved in a waste heat boiler; the drying heating is achieved through heat transfer via a partition wall; and the condensate is introduced into the waste heat boiler to generate steam again.

[0022] In some embodiments, the method further includes: after generating steam, purifying the denitrified flue gas that has undergone secondary heat recovery, the purification including removing particulate matter, acidic gases, heavy metal vapors and / or residual organic pollutants.

[0023] In some embodiments, the method further includes adding auxiliary fuel to the sludge after drying and before pyrolysis to increase the calorific value of the sludge.

[0024] According to a second aspect of this disclosure, a system for removing PFAS from sludge is provided, comprising: a dryer configured to dry the PFAS-containing sludge to a moisture content of less than 15%; a pyrolysis furnace configured to pyrolyze the dried PFAS-containing sludge at a temperature of 700-800°C, so that a predetermined proportion or more of the PFAS in the sludge enters the pyrolysis gas; a dust collector configured to remove dust particles from the pyrolysis gas; and a high-temperature combustion chamber configured to incinerate the pyrolysis gas at a temperature of 1400°C or higher to obtain combustion flue gas, thereby decomposing the PFAS in the pyrolysis gas into small-molecule inorganic substances.

[0025] In some embodiments, the system further includes a denitrification reaction chamber configured to cause a redox reaction between the noncondensable gas and the incineration flue gas to simultaneously remove NH3 from the noncondensable gas and NO from the incineration flue gas. X The non-condensable gas is the portion of the gas generated during the drying process that remains uncondensed after cooling.

[0026] In some embodiments, the system further includes a urea supply system configured to add urea to the redox reaction to replenish NH3.

[0027] In some embodiments, the pyrolysis furnace includes a heating jacket, into which the denitrified flue gas after the redox reaction is introduced to use the heat of the denitrified flue gas as heat for pyrolysis, thereby performing a primary heat recovery of the denitrified flue gas.

[0028] In some embodiments, the system further includes: a waste heat boiler, wherein after the pyrolysis heating is provided, the denitrified flue gas with primary heat recovery is introduced into the waste heat boiler to generate steam using the heat of the denitrified flue gas with primary heat recovery for secondary heat recovery of the denitrified flue gas; and a steam condensate circulation system configured to deliver the steam to the dryer to provide drying heating using the heat of the steam, obtain condensate, and deliver the condensate back to the waste heat boiler to generate steam again using the condensate and the heat of the denitrified flue gas with primary heat recovery.

[0029] In some embodiments, the system further includes: a flue gas purification system configured to purify the denitrified flue gas after secondary heat recovery following the generation of steam, the flue gas purification system including a bag filter, a wet desulfurization tower and / or an activated carbon adsorber, the bag filter being configured to remove particulate matter, the wet desulfurization tower being configured to remove acidic gases, and the activated carbon adsorber being configured to remove heavy metal vapors and / or residual organic pollutants.

[0030] In some embodiments, the system further includes an auxiliary fuel supply system configured to add auxiliary fuel to the sludge after drying and before pyrolysis to increase the calorific value of the sludge.

[0031] The core idea of ​​the method and system disclosed herein is "solid phase separation + gas phase high-temperature incineration". Through a pre-treatment anaerobic pyrolysis carbonization step, PFAS is desorbed from the solid sludge and transferred to the combustible gas phase (pyrolysis gas). Then, this pure pyrolysis gas is incinerated at ultra-high temperature in a specially designed high-temperature combustion chamber, thereby avoiding the ash melting problem and achieving complete decomposition of PFAS. Attached Figure Description

[0032] Figure 1 This is a schematic flowchart of a method for removing PFAS from sludge according to an embodiment of the present disclosure;

[0033] Figure 2 A process roadmap is shown to illustrate a system for removing PFAS from sludge according to a preferred embodiment of this disclosure. Detailed Implementation

[0034] Specific embodiments of this disclosure will now be described with reference to the accompanying drawings. It should be understood that the following description is for the purpose of enabling those skilled in the art to quickly understand the contents of this disclosure and is not intended to limit the scope of protection claimed by this disclosure. By reading the following detailed description in conjunction with the accompanying drawings, those skilled in the art will be able to more clearly recognize the features and advantages of this disclosure. Unless otherwise stated, the terminology used herein has its common meaning in the art. The term "comprising" as used herein is open-ended, meaning it does not exclude additional, unlisted members or elements. The term "and / or" as used herein includes any and all combinations of the listed members or elements. Any value of the variables indicated herein (whether or not they are modified with "about") may refer to an exact value or an approximate value, and may include + / -20%, or + / -10%, or + / -5%, or + / -1%, or + / -0% of the value of the indicated variable.

[0035] Figure 1A schematic flowchart of a method 100 for removing PFAS from sludge according to an embodiment of the present disclosure is shown. Method 100 includes the following steps: sludge drying (step 101), optionally adding auxiliary fuel to the sludge (step 102), sludge pyrolysis (step 103), pyrolysis gas dust removal (step 104), pyrolysis gas incineration (step 105), optionally causing a redox reaction between the non-condensable gas generated during drying and the incineration flue gas generated during incineration (step 106), optionally using the heat from the flue gas to heat the pyrolysis (step 107), optionally using the heat from the flue gas to generate steam (step 108), optionally using the heat from the steam to heat the drying process (step 109), and optionally purifying the flue gas (step 110). Figure 2 A system 200 for removing PFAS from sludge according to a preferred embodiment of this disclosure is shown using a process roadmap. The following will be based on... Figure 1 The order of steps, combined Figure 2 Specific embodiments of this disclosure are described below.

[0036] During step 101, the PFAS-containing sludge is dried to a moisture content of less than 15%. For example, as... Figure 2 As shown, the dewatered sludge is initially stored in a dewatered sludge storage silo. A dewatered sludge pump, with a moisture content of approximately 80%, feeds the sludge into a dryer, where it is dried to a moisture content below 15% (i.e., a dryness of 85% or higher). The dryer described here can be an indirect heating dryer, such as a thin-layer dryer, disc dryer, paddle dryer, or spiral dryer. Preferably, the dryer described here can be an indirect steam dryer, where steam is introduced into a heating jacket located outside the indirect steam dryer to heat the dryer through heat transfer via the indirect jacket. The steam can be generated using the system's own heat (described in detail later). The gases generated during the sludge drying process can be dusted by a dust collector and then cooled by circulating cooling water. The uncondensed portion after cooling is called non-condensable gas, and its main components include air, NH3, H2S, and VOCs. Step 101 can significantly reduce sludge moisture, save energy for subsequent pyrolysis, and generate non-condensable gas containing pollutants such as NH3, H2S, and VOCs.

[0037] In some embodiments, method 100 includes step 102, which involves adding auxiliary fuel to the sludge after step 101 and before step 103, to increase the calorific value of the sludge. For example, such as Figure 2As shown, the dried sludge is fed into a raw material storage silo. Before the dried sludge is fed into the pyrolysis furnace through the raw material storage silo feed screw, auxiliary fuel is added to the dried sludge through an auxiliary fuel supply system. The auxiliary fuel supply system may include, for example, a biomass storage silo and a biomass feed screw. The auxiliary fuel mentioned here may be, for example, biomass, waste-derived fuel (RDF), coal gangue, etc. Step 102 can supplement the system's heat deficit to ensure that the system achieves energy self-sufficiency, that is, to achieve the energy supply required for drying 101 and pyrolysis 103 (which will be described in detail later).

[0038] During step 103, the dried PFAS-containing sludge is pyrolyzed at a temperature of 700-800°C, allowing a predetermined proportion or higher of PFAS in the sludge to enter the pyrolysis gas. For example, as... Figure 2 As shown, the dried sludge is fed into a pyrolysis furnace at 700-800℃ via an inlet airlock discharge valve to pyrolyze the sludge, allowing the majority of PFAS (e.g., ≥99%) to enter the pyrolysis gas. Preferably, the dried sludge is fed into an anaerobic pyrolysis carbonization furnace, where, in an anaerobic environment at 700-800℃, most of the organic matter in the sludge undergoes pyrolysis, converting into pyrolysis gas (mainly composed of hydrocarbons such as H2, CO, and CH4) and solid biochar. For example, as... Figure 2 As shown, solid biochar can enter the biochar storage silo via the outlet airlock discharge valve and the biochar cooling spiral. Preferably, the pyrolysis furnace mentioned here can be an indirect pyrolysis furnace, in which high-temperature gas is introduced into a heating jacket located outside the indirect pyrolysis furnace to heat the pyrolysis furnace through heat transfer between the walls. The high-temperature gas mentioned here can be the high-temperature waste gas generated by the system itself (which will be described in detail later). This temperature range (700-800℃) is much lower than the ash melting point of sludge, that is, the temperature at which the ash produced after sludge combustion begins to soften and melt during the heating process, thus ensuring the stable operation of the pyrolysis furnace; at the same time, this temperature range is sufficient for PFAS to be effectively desorbed or decomposed from the sludge solid phase, allowing most of the PFAS to enter the pyrolysis gas phase, thereby obtaining biochar solid phase products containing no or trace amounts of PFAS (below the pollution control limit), which, together with subsequent resource utilization, ensures that no PFAS-containing solid waste enters the environment.

[0039] During step 104, the pyrolysis gas is de-dusted to remove particulate matter. For example, such as... Figure 2 As shown, the PFAS-containing pyrolysis gas exiting the pyrolysis furnace first passes through a dust collector to remove any dust particles it carries, and then the purified pyrolysis gas is introduced into the high-temperature combustion chamber. Step 104 can prevent the pyrolysis gas from melting and slagging during the subsequent high-temperature combustion process 105, for example, in the high-temperature combustion chamber.

[0040] During step 105, the pyrolysis gas is incinerated at a temperature above a predetermined temperature to obtain incineration flue gas, thereby decomposing the PFAS in the pyrolysis gas into small molecule inorganic substances. For example, such as Figure 2 As shown, pyrolysis gas is introduced into a high-temperature combustion chamber, mixed with ambient air introduced by a combustion-supporting fan, and then incinerated by a burner. The high-temperature combustion chamber can be a high-temperature combustion chamber employing regenerative combustion technology or a plasma combustion furnace using a high-temperature plasma jet generated by plasma. The predetermined temperature can be approximately 1000°C, approximately 1200°C, or approximately 1400°C. Preferably, by optimizing the combustion chamber design and adjusting the calorific value of the pyrolysis gas, the combustion temperature is stably maintained at 1400°C or higher. At this high temperature, PFAS in the gas phase are completely and thoroughly decomposed into small-molecule inorganic substances (such as CO2, HF, etc.), achieving ultimate harmlessness of PFAS. Through the above steps of method 100, the technical problem that mainstream incineration processes cannot reach the required temperature due to ash melting can be solved.

[0041] In some embodiments, method 100 includes step 106 after step 105, in which the non-condensable gas generated during drying 101 undergoes a redox reaction with the flue gas generated during incineration 105, so as to simultaneously remove NH3 from the non-condensable gas and NO from the flue gas. X For example, such as Figure 2 As shown, the combustion flue gas discharged from the high-temperature combustion chamber is introduced into the denitrification reaction chamber. Non-condensable gases generated during the drying process are introduced into the denitrification reaction chamber, allowing a redox reaction to occur between the two. The flow rate of the non-condensable gas is, for example, 10-30% of the drying evaporation rate. The redox reaction can be selective non-catalytic reduction (SNCR) or selective catalytic reduction (SCR). NH3 in the non-condensable gas can act as a reducing agent, reacting with NOx in the combustion flue gas to produce N2 and H2O. For SNCR, the reaction temperature is, for example, above 950°C; for SCR, a catalyst layer can be placed in the denitrification reaction chamber to lower the required reaction temperature. In some embodiments, if the NH3 in the non-condensable gas is insufficient, urea can be added to supplement the NH3. For example, as... Figure 2 As shown, urea solution is replenished through a urea supply system, which may include a urea solution storage tank and a urea dosing pump. The urea solution is atomized by compressed air and sprayed into the denitrification reaction chamber. Simultaneously, pollutants in the non-condensable gases are oxidized and decomposed in the high-temperature environment of the denitrification reaction chamber. These pollutants include, for example, H2S and VOCs. Step 106 achieves synergistic treatment of the dried waste gas and denitrification of the incineration flue gas, eliminating the need for a separate drying and deodorization device. Furthermore, step 106 cools the high-temperature incineration flue gas, ensuring that the temperature of the denitrified flue gas is suitable for the material requirements of the heating jacket of the pyrolysis furnace in subsequent steps.

[0042] In some embodiments, method 100 includes step 107 after step 106, namely, using the heat from the reacted denitrification flue gas to heat pyrolysis 103, so as to perform a primary heat recovery of the denitrification flue gas. For example, as Figure 2 As shown, the denitrified flue gas after the reaction is introduced into the heating jacket of the pyrolysis furnace, where heat is transferred through the partition wall to supply heat for the pyrolysis process. The denitrified flue gas itself does not come into contact with the dried sludge or the auxiliary fuel added therein. The temperature of the denitrified flue gas discharged from the denitrification reaction chamber can be, for example, 800-900℃, and the temperature of the denitrified flue gas after one heat recovery can be, for example, 600-700℃. Step 107 can fully utilize the sensible heat of the high-temperature denitrified flue gas.

[0043] In some embodiments, method 100 includes steps 108 and 109 after step 107, namely, using the heat from the denitrified flue gas that has undergone primary heat recovery to generate steam for secondary heat recovery of the denitrified flue gas, then using the heat from the steam to heat the drying 101 to obtain condensate, and using the condensate and the heat from the denitrified flue gas that has undergone primary heat recovery to generate steam again. For example, as Figure 2 As shown, the denitrification flue gas, after primary heat recovery, exits from the heating jacket of the pyrolysis furnace and enters the waste heat boiler. The waste heat boiler uses the heat from the denitrification flue gas to generate steam, which may include saturated steam or superheated steam. The generated steam is transported to the heating jacket of the indirect steam dryer in the sludge drying step, serving as a drying heat source. After releasing latent heat in the dryer, the steam condenses into water. The condensate is pressurized by a condensate pump and returned to the waste heat boiler, forming a closed steam-condensate circulation system. The temperature of the denitrification flue gas after primary heat recovery can be, for example, 600-700°C, while the temperature of the denitrification flue gas after secondary heat recovery can be, for example, reduced to about 200°C. Steps 108 and 109 can further fully utilize the sensible heat of the high-temperature denitrification flue gas and can greatly improve the utilization efficiency of water and water heat.

[0044] In some embodiments, method 100 includes step 110 after step 109, namely, purifying the denitrified flue gas after secondary heat recovery, the purification including the removal of particulate matter, acidic gases, heavy metal vapors and / or residual organic pollutants. For example, purifying the low-temperature denitrified flue gas after secondary heat recovery by a flue gas purification system, such as... Figure 2 As shown, the low-temperature flue gas from the waste heat boiler passes sequentially through a bag filter (to remove particulate matter) and a wet desulfurization tower (to remove SO2 by spraying alkaline solution). X The flue gas contains acidic gases such as HCl and HF, and is delivered by an induced draft fan to an end activated carbon adsorber (which adsorbs heavy metal vapors such as mercury and cadmium, as well as any remaining trace organic pollutants). Step 110 can achieve ultra-clean emissions of flue gas.

[0045] The above basis Figure 1 The order of steps, combined Figure 2 Specific embodiments of this disclosure are described. The energy self-sufficiency of the system according to a preferred embodiment of this disclosure is analyzed below. The energy input of the entire system is mainly the chemical energy of the organic matter of the sludge itself (and possibly added auxiliary fuels). According to a preferred embodiment of this disclosure, the system can achieve cascaded, targeted, and efficient energy utilization:

[0046] - High-temperature section (1400℃): The temperature is maintained by the heat released from incineration for PFAS decomposition.

[0047] - Medium and high temperature section (950℃-700℃): Heat is transferred through the high temperature flue gas partition for sludge pyrolysis.

[0048] -Medium temperature range (600℃-200℃): Steam is generated by a waste heat boiler for sludge drying.

[0049] - Low temperature range (<200℃): Used for the self-purification of flue gas.

[0050] When the calorific value of the sludge is sufficient and the amount of steam generated by the system can fully meet the drying requirements, energy self-sufficiency can be achieved without the need for external auxiliary fuel. If the calorific value of the sludge is insufficient, it can be adjusted by adding a small amount of auxiliary fuel.

[0051] The method and system for removing PFAS from sludge according to this disclosure have the following significant advantages:

[0052] (1) Complete removal of PFAS without secondary pollution: In this disclosure, PFAS is desorbed from the sludge and then incinerated at 1400°C in an independent high-temperature combustion chamber to completely break the CF bonds and achieve complete decomposition of PFAS; even if there are trace amounts of PFAS (below the pollution control limit), they will only remain in the biochar, and with subsequent resource utilization, it is ensured that no PFAS-containing solid waste enters the environment. At the same time, the dried non-condensable gas is treated by high-temperature oxidation to avoid the escape of pollutants and ensure that there is no secondary pollution in the entire treatment process.

[0053] (2) Avoiding conflicts in high-temperature operation: Through the separate design of "solid phase pyrolysis carbonization + gas phase high-temperature combustion", the pyrolysis furnace operates under mild conditions of 700-800℃, avoiding sludge ash melting; the high-temperature combustion chamber focuses on pyrolysis gas combustion and can stably maintain a high temperature of 1400℃, which solves the contradiction between high-temperature operation and ash melting in traditional incinerators.

[0054] (3) High energy utilization efficiency and low operating cost: The system achieves steam recycling through pyrolysis gas combustion and flue gas heat recovery, and combined with auxiliary fuel replenishment as needed to achieve energy self-sufficiency and significantly reduce external energy consumption; non-condensable gas and flue gas denitrification are treated in synergistic manner, eliminating the need for a separate deodorization device and reducing equipment investment and operating costs.

[0055] (4) High degree of sludge resource utilization: The biochar produced after treatment contains no or trace amounts of PFAS (below the pollution control limit), and the heavy metal leaching meets the standards. It can be used as a soil conditioner, clean fuel, etc. to achieve resource utilization; it can also be used in building material production, truly achieving the goals of sludge reduction, harmlessness and resource utilization.

[0056] (5) Strong process adaptability and easy engineering: The method and system disclosed herein can be adapted to sludge with different PFAS pollution concentrations and different moisture contents. The auxiliary fuel addition ratio can be flexibly adjusted to meet the needs of different working conditions. The equipment used in the system is an optimized combination of mature industrial equipment. The process route is clear and easy to promote and apply on a large scale.

[0057] The foregoing has described some features, steps, apparatuses, and / or functions of some embodiments of this disclosure in conjunction with the accompanying drawings. However, it should be understood that those skilled in the art can make various changes and equivalent substitutions without departing from the scope defined by the claims. Furthermore, where appropriate, the various features, steps, apparatuses, and / or functions described in different embodiments can be combined with each other, and these combinations are also intended to fall within the scope of protection claimed in this disclosure.

Claims

1. A method for removing perfluorinated and polyfluoroalkyl substances (PFAS) from sludge, comprising: The PFAS-containing sludge is dried (101) to a moisture content of less than 15%; At a temperature of 700-800℃, the dried PFAS-containing sludge is pyrolyzed (103) so that a predetermined proportion or more of the PFAS in the sludge enters the pyrolysis gas. The pyrolysis gas is subjected to dust removal (104) to remove dust particles from the pyrolysis gas; At a temperature above a predetermined temperature, the pyrolysis gas (105) is incinerated to obtain incineration flue gas, thereby decomposing the PFAS in the pyrolysis gas into small molecule inorganic substances.

2. The method according to claim 1, wherein, The predetermined ratio is 99%, and the predetermined temperature is 1400℃.

3. The method according to claim 1 or 2, further comprising: In the drying (101), non-condensable gas is obtained, which is the uncondensed portion of the gas generated in the drying (101) after cooling; After the incineration (105), the noncondensable gas is subjected to a redox reaction (106) with the incineration flue gas to simultaneously remove NH3 from the noncondensable gas and NO from the incineration flue gas. X .

4. The method according to claim 3, wherein, In the redox reaction (106), urea is added to replenish NH3.

5. The method according to claim 3, wherein, In the redox reaction (106), pollutants in the noncondensable gas are oxidized and decomposed, including H2S and VOCs.

6. The method according to claim 3, further comprising: After the redox reaction (106), the heat from the denitrified flue gas after the reaction is used to heat the pyrolysis (103) (107) to recover heat from the denitrified flue gas.

7. The method according to claim 6, wherein, The heat supply for pyrolysis (107) is achieved through heat transfer through the partition wall.

8. The method according to claim 6, further comprising: After the pyrolysis heating (107), steam (108) is generated using the heat from the denitrification flue gas that has undergone primary heat recovery, in order to perform secondary heat recovery on the denitrification flue gas. The heat of the steam is used to heat the drying (101) (109), condensate is obtained, and the heat of the condensate and the denitrified flue gas after one heat recovery is used to generate steam again (108).

9. The method according to claim 8, wherein, The steam generation (108) is achieved in a waste heat boiler; The drying heating (109) is achieved through heat transfer through the partition wall; The condensate is fed into the waste heat boiler to generate steam again (108).

10. The method of claim 8, further comprising: After the steam (108) is generated, the denitrified flue gas is purified (110) by secondary heat recovery, the purification (110) including the removal of particulate matter, acidic gases, heavy metal vapors and / or residual organic pollutants.

11. The method according to claim 1 or 2, further comprising: After the drying (101) and before the pyrolysis (103), auxiliary fuel (102) is added to the sludge to increase the calorific value of the sludge.

12. A system for removing PFAS from sludge, comprising: A dryer configured to dry the PFAS-containing sludge (101) to a moisture content of less than 15%; A pyrolysis furnace is configured to pyrolyze the dried PFAS-containing sludge at a temperature of 700-800°C (103), so that a predetermined proportion or more of the PFAS in the sludge enters the pyrolysis gas. A dust collector configured to remove dust (104) from the pyrolysis gas to remove particulate matter from the pyrolysis gas; A high-temperature combustion chamber is configured to incinerate (105) the pyrolysis gas at a temperature above 1400°C to obtain combustion flue gas, thereby decomposing the PFAS in the pyrolysis gas into small molecule inorganic substances.

13. The system according to claim 12, further comprising: The denitrification reaction chamber is configured to allow non-condensable gases to undergo a redox reaction (106) with the incineration flue gas, thereby simultaneously removing NH3 from the non-condensable gases and NO from the incineration flue gas. X The non-condensable gas is the portion of the gas generated in the drying (101) that has not condensed after cooling.

14. The system of claim 13, further comprising: A urea supply system is configured to add urea to the redox reaction (106) to replenish NH3.

15. The system according to claim 13, wherein, The pyrolysis furnace includes a heating jacket. After the redox reaction (106), the denitrified flue gas after the reaction is introduced into the heating jacket so as to use the heat of the denitrified flue gas after the reaction to heat the pyrolysis (103) (107) and to perform a heat recovery of the denitrified flue gas.

16. The system of claim 15, further comprising: After the pyrolysis heating (107), the denitrified flue gas, which has undergone primary heat recovery, is introduced into the waste heat boiler to generate steam (108) using the heat from the denitrified flue gas, thus performing secondary heat recovery on the denitrified flue gas. A steam condensate circulation system is configured to deliver the steam to the dryer to use the heat of the steam to heat the drying (101) (109), obtain condensate, and deliver the condensate back to the waste heat boiler to use the heat of the condensate and the denitrified flue gas after primary heat recovery to generate steam again (108).

17. The system of claim 16, further comprising: A flue gas purification system configured to purify (110) denitrified flue gas after secondary heat recovery following the generation of steam (108), the flue gas purification system comprising a bag filter, a wet desulfurization tower and / or an activated carbon adsorber, the bag filter being configured to remove particulate matter, the wet desulfurization tower being configured to remove acidic gases, and the activated carbon adsorber being configured to remove heavy metal vapors and / or residual organic pollutants.

18. The system of claim 12, further comprising: An auxiliary fuel supply system is configured to add auxiliary fuel (102) to the sludge after the drying (101) and before the pyrolysis (103) to increase the calorific value of the sludge.

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