A process and apparatus for anaerobic pyrolysis and steam regeneration of activated carbon

Abstract

This invention discloses a process and apparatus for activated carbon anoxic pyrolysis and steam regeneration, relating to the field of activated carbon regeneration. The process includes: S1 dehydration preparation, reducing the moisture content of the carbon layer to 45% through hydraulic conveying and negative pressure dehydration; S2 drying pyrolysis and stripping, using superheated steam and tail gas circulation to heat the carbon layer to 300-400℃; S3 steam activation, introducing 900℃ tail gas to raise the carbon layer to 800-850℃ for activation reaction; and S4 cooling, using steam and cold water to sequentially cool to below 100℃, completing the activated carbon regeneration. This invention offers excellent energy efficiency and sufficient pore structure recovery, significantly improving the specific surface area, polar group content, and adsorption performance of the regenerated activated carbon, thus extending its service life.

Description

Technical Field

[0001] This invention relates to the technical field of activated carbon regeneration, and in particular to a process and apparatus for activated carbon regeneration via anaerobic pyrolysis and steam regeneration. Background Technology

[0002] Activated carbon, due to its high specific surface area, well-developed pore structure, and excellent adsorption performance, is widely used in industrial waste gas treatment, drinking water purification, and solvent recovery. However, with prolonged adsorption time, the pores in activated carbon become filled or blocked by organic pollutants, leading to a rapid decline in adsorption capacity and necessitating periodic regeneration. Common regeneration methods for activated carbon include physical methods (such as hot air heating and microwave regeneration) and chemical methods (such as alkaline washing, acid washing, and oxidation-reduction). Among these, physical pyrolysis-steam activation is widely used due to its simplicity, lack of chemical residue, and wide applicability.

[0003] The existing pyrolysis steam regeneration process has the following problems: (1) The temperature control in the pyrolysis stage is rough, the heat utilization efficiency is low, the tail gas is not fully utilized, resulting in energy waste; (2) The temperature distribution is uneven and the heat field and airflow path are difficult to coordinate during the steam activation process, which can easily cause the carbon layer structure to be damaged or the activation to be insufficient; (3) Tar-like organic matter is not easy to be completely decomposed during the pyrolysis process, and it is easy to form coking blockage in the subsequent channels; (4) The cooling rate in the cooling stage is unreasonable, which can easily lead to cracking of the carbon skeleton, affecting the structural stability and service life of the regenerated activated carbon.

[0004] Therefore, there is an urgent need for a better regeneration process to improve the regeneration efficiency of activated carbon, extend its lifespan, and reduce operating costs. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a process and apparatus for activated carbon pyrolysis and steam regeneration in the absence of oxygen.

[0006] A process for anaerobic pyrolysis and steam regeneration of activated carbon includes the following steps:

[0007] S1 Dehydration Preparation: Saturated activated carbon is fed into the regeneration tank via hydraulic conveying. The carbon conveying water pump is started to backwash and loosen the carbon layer, and dehydration is carried out under negative pressure to control the overall moisture content of the carbon layer to 45±1%.

[0008] S2 Drying, pyrolysis, steam stripping and tail gas circulation heat transfer: Superheated steam heated to 600±10℃ and pressure of 0.05~0.1 MPaG is introduced into the nth regeneration tank to raise the temperature of the carbon layer, and filtered high-temperature tail gas from the nth regeneration tank is introduced into the n+1th regeneration tank. The high-temperature tail gas is injected into the carbon layer from the bottom and side of the regeneration tank.

[0009] The low-temperature exhaust gas discharged from the (n+1)th regeneration tank is filtered and heat exchanged before being reheated to 900°C and then returned to the nth regeneration tank.

[0010] At the same time, the high-temperature exhaust gas generated from the activation process of the nth regeneration tank is guided to the (n+1)th regeneration tank as the heat source for its pyrolysis stage, so that the temperature of the carbon layer gradually rises from top to bottom to 300~400℃, completing the drying and low-temperature pyrolysis of the activated carbon.

[0011] The high-temperature exhaust gas generated during the activation process of the last regeneration tank is directed to the first regeneration tank as a heat source for its pyrolysis stage.

[0012] S3 Steam Deep Activation: After heating the circulating tail gas to 900℃, a carbon layer is introduced from the side and bottom of the regeneration tank, so that the temperature of the carbon layer in the regeneration tank rises to 800~850℃, and the activation reaction begins.

[0013] S4 Cooling: First, steam is introduced to lower the temperature of the carbon layer to below 300℃, and then cooling water is introduced to further lower it to below 100℃, thus completing the cooling of the regenerated activated carbon, which is then transported out of the tank by hydraulic means.

[0014] This invention provides a highly integrated and synergistic activated carbon pyrolysis and steam regeneration process, significantly improving the quality of regenerated activated carbon and the overall system efficiency. The entire process is designed around maintaining the structure and restoring the porosity of adsorbed saturated carbon, clearly divided into four core processes: dehydration preparation, low-temperature pyrolysis-steam stripping, deep activation, and multi-stage cooling. In stage S1, the carbon bed moisture content is precisely controlled to 45±1% through backflushing of the carbon feed pump and negative pressure suction, ensuring both dehydration efficiency and retaining necessary moisture to support subsequent steam migration and heat transfer. In stage S2, the cross-path of top-down temperature rise and bottom-up stripping effectively promotes the desorption of organic pollutants and tar migration. In step S2, the heat source required for drying and pyrolysis in the n+1 regeneration tanks comes from the high-temperature exhaust gas heating of the nth regeneration tank. During the S2 drying, pyrolysis, steam stripping, and tail gas recirculation heat transfer processes, the high-temperature tail gas from the nth regeneration tank contains over 90% H2O. H2O has an entrainment effect on the organic matter in the activated carbon of the (n+1)th regeneration tank. As a carrier gas, H2O causes incompletely decomposed or incompletely gasified organic matter to be entrained by the steam in droplet form. Some organic matter is stripped off by the steam shear force and migrates with the airflow, resulting in the removal of approximately 20% of the organic matter in the activated carbon through steam entrainment. The organic matter entrained by the steam is heated to 900℃ and decomposed before being recycled to the nth regeneration tank. The remaining small amount of recirculated tail gas is then discharged into the tail gas treatment system.

[0015] In stage S3, the circulating exhaust gas is heated to 900℃ and introduced to rapidly raise the carbon layer temperature to the activation range of 800-850℃, creating a synergistic activation environment of high temperature, oxygen deficiency, and water vapor. This efficiently removes residual carbon and stimulates the reconstruction of the pore structure. Simultaneously, the exhaust gas heat exchange network constructed by the series-connected regeneration tanks allows the high-temperature exhaust gas to be used as a closed-loop heat source for the pyrolysis stage, significantly reducing external energy input. Stage S4 employs a two-way cooling system of steam and water to ensure a stable temperature drop in the structure and reduce the incidence of microcracks.

[0016] Furthermore, in step S2, a polyvinyl alcohol aqueous solution droplet with a mass concentration of 0.05–0.3% is introduced into the superheated steam, wherein the droplet size is controlled to be 5–20 μm.

[0017] Introducing polyvinyl alcohol (PVA) aqueous solution droplets with a mass concentration of 0.05–0.3% during the pyrolysis stage significantly improved the decomposition efficiency of organic pollutants, especially tar, in the carbon layer. PVA is a high-molecular-weight polymer that can be thermally decomposed at 300–400℃. During its decomposition, it releases highly oxidizing •OH free radicals, which can break bonds with the long-chain carbon skeleton in tar molecules, thereby accelerating its decomposition and depolymerization. Simultaneously, controlling the PVA droplet atomization particle size to 5–20 μm facilitates the formation of microscale humid heat transfer zones, establishing a "local hot and humid gas cavity" in the central region of the carbon layer, improving heat penetration and promoting temperature uniformity. The evaporation of the droplets into H2O gas further enhances the steam concentration, solving the problem of uneven steam distribution. Compared with traditional physical steam heating, this free radical excitation mechanism allows tar-like polymers to rapidly break down at lower temperatures, effectively avoiding coking and pore blockage problems in the later activation stage. Especially when PVA droplets and CO2-enriched exhaust gas work together, a free radical-weak oxidation synergistic system is formed, further enhancing the reactivity.

[0018] Furthermore, in the mixed gas introduced in step S2, the volume ratio of steam to reflux tail gas is 0.1 to 0.3.

[0019] Maintaining the volume ratio of steam to exhaust gas in the mixed gas mixture between 0.1 and 0.3 creates a pyrolysis atmosphere dominated by high-temperature exhaust gas, representing a deep optimization strategy for enhancing the thermal energy utilization path and controlling the high-temperature inert field. This low-proportion steam introduction scheme significantly reduces the system's wet heat load, allowing steam to participate primarily in the generation of reactive free radicals rather than as the main heat transfer carrier, thus avoiding problems such as carbon layer temperature drop and tar condensation and leaching caused by excessive water vapor.

[0020] Meanwhile, a high proportion of exhaust gas (over 70%) possesses higher heat capacity and reaction inertness, enabling the creation of a stable and rapidly heating dry-hot atmosphere, thus strengthening the establishment of a vertical pyrolysis gradient from the bottom up in the carbon layer. Components such as CO, CO2, and H2 contained in the exhaust gas participate in some secondary pyrolysis reactions at high temperatures, promoting the decomposition of undesorbed small-molecule organic matter and improving tar migration efficiency.

[0021] In an exhaust-dominated atmosphere, tar is more easily removed by rising airflow, preventing recondensation in the upper carbon layer. Simultaneously, a small amount of introduced steam creates highly reactive reaction sites locally, generating free radicals such as ·OH and ·H, which helps improve the microscopic activity of the reaction zone and promotes tar skeleton decomposition. This proportional design achieves a reaction field control mode of "dry heat-dominated + slightly moist assisted," significantly improving tar removal efficiency and regeneration rate while ensuring temperature field uniformity. It represents a tail-gas-enhanced regeneration technology path that differs from traditional steam-dominated methods.

[0022] Furthermore, in the S4 cooling step, the steam cooling stage adopts a pulsed intermittent injection method, each lasting 1 to 2 minutes, with a total time of 15 to 20 minutes.

[0023] This method employs a pulsed, intermittent steam injection approach during the cooling stage of regenerated activated carbon. Compared to traditional continuous steam injection or direct cooling water spraying, this method offers greater structural responsiveness and microenvironment adaptability. The core of the pulse injection mode lies in establishing a nonlinear temperature decrease path within the carbon layer by intermittently releasing high-temperature wet steam (each cycle lasting 1–2 minutes, with a total cycle time of 15–20 minutes). Since the activated carbon microstructure is highly sensitive to temperature gradients, excessively rapid cooling can easily trigger skeletal thermal shrinkage and microcrack accumulation, ultimately leading to pore structure collapse and deactivation of active sites. Pulsed steam injection creates a humidity-regulating buffer zone on the carbon layer surface and within, transforming the heat transfer rate from a linear abrupt change to a periodic, gradual fluctuation, significantly mitigating the thermal shock effect.

[0024] Furthermore, the dynamic humid heat film formed during intermittent cooling creates brief high-humidity channels between carbon particles. This facilitates the migration and removal of adsorbed moisture and free organic matter, while also suppressing localized over-cooking caused by high-temperature waste heat, thus maintaining the integrity and pore volume stability of the regenerated carbon structure. Simultaneously, this method avoids the increased energy consumption and system load fluctuations associated with continuous steam injection, establishing a relatively ideal balance between steam consumption and cooling efficiency. More importantly, through precise rhythmic control, this method can pre-set suitable interface temperature zones for subsequent cooling water cooling stages, reducing the risk of abrupt changes in thermal gradients and ensuring high consistency and structural protection throughout the entire cooling process.

[0025] Furthermore, the cooling water after steam cooling contains 0.1-0.3% disodium EDTA or sodium citrate.

[0026] Introducing 0.1–0.3% disodium EDTA or sodium citrate as a complexing agent at the end of the cooling process of regenerated activated carbon essentially constructs a "thermal-chemical-complexing ternary synergistic purification channel." After the high-temperature activation stage, metal ions (such as Fe, Zn, Ni, Cu, etc.) originating from the original adsorbed pollutants or desorbed structures are inevitably released from the carbon layer. In traditional cooling methods, these ions are prone to redeposition, local coking, or blockage of carbon pores during the cooling process, severely affecting pore permeability and surface adsorption function.

[0027] Disodium EDTA possesses broad-spectrum, stable complexing capabilities, rapidly forming stable complexes with metal ions in weakly alkaline water environments, preventing physical adsorption or deposition of these ions on the carbon structure. Sodium citrate, acting as a mild complexing-buffering complex, both assists the complexation reaction and inhibits carbonate precipitation and scaling in the water-cooling system, thus enhancing the stability of the circulating water system. This complexing cooling pathway not only plays a dual role of "chemical capture + interface cleaning" but also synergistically protects the carbon layer structure from secondary cross-linking and pyrolysis induced by metal ions.

[0028] More importantly, the cooling water complexing agent and the pulsed steam cooling mechanism form a natural link in a thermo-chemical regulation chain. Pulsed steam cooling creates a gradual temperature drop and a moisture film in the carbon layer, significantly reducing thermal shock and stress cracking within the carbon skeleton. The subsequent introduction of cooling water containing the complexing agent at this point not only facilitates the dissipation of residual heat but also allows the highly mobile complexing molecules in the water film to penetrate deep into the pores and capture trace amounts of residual metal. This process not only avoids pore collapse induced by sudden cooling but also prevents secondary adsorption site contamination within the structure.

[0029] Furthermore, during the S3 steam activation process, magnesium chloride and sodium citrate composite particles with a mass ratio of 0.1% to 0.4% are uniformly distributed in the regeneration tank.

[0030] Introducing a composite additive of magnesium chloride and sodium citrate at a mass ratio of 0.1–0.4% during the activation stage overcomes the insufficient ability to regulate the micropore-mesopore structure in traditional physical steam activation processes, achieving hierarchical induced reconstruction of the carbon layer pore structure. Magnesium chloride, as a salt activator, undergoes a chlorination reaction at 800–900℃, promoting slight erosion of the carbon structure, forming medium-sized pores and widening existing channels. This process does not damage the backbone structure, avoiding carbon skeleton embrittlement, and represents a "mildly directional acid etching" structural reconstruction path.

[0031] Meanwhile, sodium citrate can decompose into weakly reducing gases such as CO and CO2 in a high-temperature steam environment, which can neutralize Mg.2+ The induced strong acid reaction trend inhibits carbon particle agglomeration and local carbonization, resulting in a more gentle and balanced pore expansion. The combined use of these two methods establishes a dual mechanism of "acid etching + atmosphere control," which concentrates pore size distribution, preserves the framework sufficiently, and ultimately achieves compatibility between increased specific surface area and structural stability.

[0032] Furthermore, in the S3 steam deep activation step, 0.05-0.2% by mass of urea or melamine powder is added before the mixed gas enters the regeneration tank.

[0033] Introducing urea or melamine powder at a mass ratio of 0.05–0.2% during the steam activation stage essentially establishes a triple regulatory mechanism of "heteroatom induction – micro-defect reconstruction – polar site generation". Urea and melamine can undergo pyrolysis, condensation, and carbon-nitrogen bond breaking reactions in a high-temperature (800–850℃) oxygen-deficient steam atmosphere, releasing nitrogen-containing small molecule gases (NH3, HCN) and active free radicals (such as N•, NH•). These nitrogen source components have strong migration and adsorption capabilities on high-temperature carbon surfaces, initiating the formation of carbon-nitrogen hybrid structures, such as pyrrole-N, graphite-N, or amino-doped surface defects, at the edges and dislocation sites of the carbon skeleton.

[0034] This doping process does not rely on external high-energy reaction conditions, but rather achieves in-situ construction driven by the high temperature of the activation itself. This avoids the complex processes required by traditional nitrogen doping pathways, which require high-purity gas or plasma treatment. Simultaneously, it allows for precise control of the doping concentration and distribution. The introduction of nitrogen increases the polarity and electron cloud density of the carbon surface, which is beneficial for adsorbing polar pollutants (such as volatile organic compounds (VOCs), NH3, SO2, etc.). Furthermore, it induces surface tension and lattice distortion in the microstructure, forming new defect networks and adsorption site communities, increasing specific surface area and pore volume, and enhancing adsorption flux.

[0035] Furthermore, this nitrogen-containing doping strategy can form a synergistic effect with the magnesium chloride-sodium citrate assisted activation system: Mg 2+ Sodium citrate regulates pore size and mesopore structure, while urea / melamine further regulates the functionalized layer and electronic state of the pore wall surface, resulting in a clear and interconnected "structure-function" hierarchy. Compared to the simple structure and surface inertness of carbon materials obtained by traditional physical activation, this method achieves synergistic reconstruction of the material's structural and surface chemical dimensions, making it a highly efficient regeneration solution that combines porous structure regulation capabilities with selective adsorption.

[0036] Furthermore, in step S3, the activation duration is controlled to be 30-60 minutes, and the temperature gradients of the upper, middle and lower parts of the carbon layer are set to 780-800℃, 800-820℃ and 820-850℃ respectively.

[0037] This invention incorporates a three-tiered temperature distribution within the activated carbon layer during the steam activation stage: 820–850°C, 800–820°C, and 780–800°C from bottom to top. This temperature arrangement is not uniform but rather purposefully applied to different parts of the carbon layer. The lower layer, with the highest temperature, thoroughly removes residual carbonaceous matter and deposits from the activated carbon, while simultaneously forming larger pores to allow subsequent gases and contaminants to pass through quickly. The middle region, with its moderate temperature, is the "main battleground" for the redevelopment of the carbon structure and the formation of medium-sized pores, thus enhancing the overall adsorption capacity of the material. The upper region, with its lower temperature, prevents the microporous structure on the carbon surface from being burned away, thereby preserving small, useful adsorption pores.

[0038] This bottom-up temperature-layered structure assigns three distinct tasks—"removing residues," "developing mesopores," and "protecting micropores"—to different carbon layers, allowing each layer to perform its optimal function. It solves the problems of structural instability and discontinuous pores caused by uneven temperature or coarse control in traditional activation processes, making the entire activated carbon regeneration process more orderly, the reaction more balanced, and ultimately resulting in a more stable and efficient material.

[0039] Furthermore, this temperature-stratified structure works well with the additives used in the preceding steps. For example, PVA droplets added during the pyrolysis stage release free radicals upon heating, breaking down complex organic compounds like tar and distributing them throughout the carbon layer. Once this tar enters the S3 stage, it can be completely decomposed in the high-temperature zone at the bottom of the carbon layer, aiding in the development of pore structures in the middle region, and preventing micropore blockage in the upper region, thus achieving a continuous effect of "premature decomposition - stratified decomposition - structural reconstruction".

[0040] For example, the previously added magnesium chloride and sodium citrate each play their proper role in these three temperature zones: magnesium chloride slightly corrodes the carbon structure in the high-temperature zone, helping to open up the pores; while sodium citrate releases a slight reducing gas in the medium-temperature zone, preventing the structure from agglomerating or collapsing due to sintering. The reaction regions and functions of the two substances perfectly match the temperature control zones, synergistically enhancing the layering and stability of the carbon structure.

[0041] Meanwhile, urea or melamine powder added before activation releases different types of nitrogen free radicals at different temperature zones. These nitrogen sources can be incorporated into the carbon surface, forming nitrogen functional sites with specific adsorption capabilities. For example, pyrrole nitrogen is easily formed in the mid-temperature zone, which helps adsorb polar organic matter; while graphitic nitrogen is easily generated in the high-temperature zone, improving the material's conductivity and heat resistance. The distribution of different nitrogen sites also occurs naturally with temperature zones, enabling simultaneous structural regulation and functional enhancement.

[0042] An activated carbon pyrolysis and steam regeneration device, comprising:

[0043] At least four regeneration tanks, numbered sequentially from tank 1 to tank 4, are configured to work in series in rotation. Each regeneration tank has a carbon layer cavity, a carbon conveying water pump interface, multi-layer steam / circulating exhaust gas injection branch pipes at the bottom and sides, a bottom exhaust gas outlet, and temperature and pressure sensors.

[0044] The steam system includes an electromagnetic heater, a steam generator, and a steam condenser. The electromagnetic heater is used to heat the steam to 600±10℃ and 900±10℃ and then introduce it into each regeneration tank.

[0045] The exhaust gas recirculation system includes a high-temperature exhaust gas duct, a heat exchanger, a particulate filter, and a circulating fan. It is used to guide the high-temperature exhaust gas generated by the nth regeneration tank to the top of the (n+1)th regeneration tank, and to heat the low-temperature exhaust gas from the (n+1)th regeneration tank before circulating it to the nth regeneration tank.

[0046] The activation section mixed gas heating system includes two-stage electromagnetic heaters and a mixed gas pipeline, which is used to mix the exhaust gas with steam and heat it to 900°C before introducing it into the bottom of the regeneration tank to be activated.

[0047] The control system is used to automatically switch the working status of the four tanks based on sensor signals, realize the rotation of each stage of dehydration, pyrolysis, activation and cooling, and adjust the temperature, pressure and mixed gas ratio in each regeneration tank.

[0048] The device consists of four regeneration tanks that can be operated in rotation, combined with a tail gas heat exchange and steam reuse system, forming a continuous closed-loop pyrolysis-activation cycle. The multi-layer steam injection branch pipes and the upper and lower ventilation paths work together to form a synergistic regeneration environment that matches the upper and lower temperature difference and the stripping path, which helps to improve regeneration efficiency and system thermal energy utilization.

[0049] Furthermore, each regeneration tank is equipped with 2 to 4 layers of horizontally arranged porous screens, with radially distributed micropores on the screens for uniformly distributing the injected steam.

[0050] The porous sieve tubes ensure that the injected steam is evenly distributed in the carbon layer, improving the permeability and reaction consistency of the pyrolysis and stripping processes. The transverse sieve tube arrangement, combined with the bottom-in, top-out fluid path, enhances the thermal field stability of the carbon layer and the reaction depth in the middle of the particle layer, ensuring the overall regeneration uniformity of the reaction layer.

[0051] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in the following aspects:

[0052] This invention utilizes a regeneration tank designed for rotating operation, forming a system structure for heat recycling. Combined with multiple process steps including carbon layer dehydration, tail gas heating, segmented temperature-controlled steam activation, and step-by-step cooling, it effectively achieves efficient regeneration of adsorbed saturated activated carbon. For the first time, polyvinyl alcohol aqueous solution droplets are introduced into the pyrolysis stage, using free radicals to assist in the decomposition of tar, thereby enhancing the migration and depolymerization capabilities of organic pollutants. During high-temperature activation, magnesium chloride-sodium citrate particles and urea / melamine powder are introduced to achieve simultaneous reconstruction of pore size distribution and nitrogen-doped functional sites. Combined with pulsed steam cooling and complexing agent water cooling technology, it effectively avoids structural degradation caused by thermal shock and heavy metal contamination. Overall, this invention not only significantly improves the specific surface area, mesopore volume, and moisture adsorption capacity of the regenerated activated carbon, but also outperforms existing technologies in key performance aspects such as tar and residual carbon removal efficiency, the degree of nitrogen functional group introduction, and the maintenance of structural integrity. Attached Figure Description

[0053] Figure 1 This is a flowchart of the activated carbon pyrolysis and steam regeneration process in Example 1.

[0054] Attached reference numerals: 1-1, 1-2, 1-3, 1-4: regeneration tank; 2-1, 2-2, 2-3, 2-4: primary electromagnetic heater; 3-1, 3-2, 3-3, 3-4: secondary electromagnetic heater; 4-1, 4-2, 4-3, 4-4: return fan; 5-1, 5-2, 5-3, 5-4: precooler; 6-1, 6-2, 6-3, 6-4: steam source; 7. vacuum pump. Detailed Implementation

[0055] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0056] Example 1

[0057] Reference Figure 1 This embodiment discloses a process and apparatus for activated carbon anoxic pyrolysis and steam regeneration. The activated carbon anoxic pyrolysis and steam regeneration apparatus includes: four regeneration tanks, numbered sequentially as tank 1 to tank 4, configured to operate in series in rotation. Each regeneration tank has a carbon layer cavity, a carbon conveying water pump connection, multi-layer steam injection branch pipes at the bottom and sides, a top tail gas inlet, a bottom mixed gas inlet, and temperature and pressure sensors. Each regeneration tank has four layers of horizontally arranged porous screens with radially distributed micropores for uniformly distributing the injected steam.

[0058] The steam system includes an electromagnetic heater, a steam generator, and a steam condenser. The electromagnetic heater is used to heat the steam to 600±10℃ and 900±10℃ and then introduce it into each regeneration tank.

[0059] The exhaust gas recirculation system includes a high-temperature exhaust gas duct, a heat exchanger, a particulate filter, and a circulating fan. It is used to guide the high-temperature exhaust gas generated by the nth regeneration tank to the top of the (n+1)th regeneration tank, and to heat the low-temperature exhaust gas from the (n+1)th regeneration tank before circulating it to the nth regeneration tank.

[0060] The activation section mixed gas heating system includes two-stage electromagnetic heaters and a mixed gas pipeline, which is used to mix the exhaust gas with steam and heat it to 900°C before introducing it into the bottom of the regeneration tank to be activated.

[0061] The control system is used to automatically switch the working status of the four tanks based on sensor signals, realize the rotation of each stage of dehydration, pyrolysis, activation and cooling, and adjust the temperature, pressure and mixed gas ratio in each regeneration tank.

[0062] The activated carbon pyrolysis and steam regeneration process includes the following steps:

[0063] S1 Dehydration Preparation:

[0064] Saturated granular activated carbon (2 mm in diameter) is hydraulically conveyed into regeneration tank number 1. A bottom-up backflushing pump is activated to break up the dense carbon layer structure formed during transport. Subsequently, a dehydration process is initiated using a negative pressure suction device connected to the top of the tank, operating under a -0.02 MPa vacuum for 30 minutes to stabilize the carbon layer moisture content at 45±1%.

[0065] S2 Drying, pyrolysis, and steam stripping:

[0066] Superheated steam at a pressure of 0.1 MPa and a temperature of 600±10℃ is introduced into the first regeneration tank to raise the temperature of the carbon layer. Filtered high-temperature exhaust gas from the first regeneration tank is introduced into the second regeneration tank, which is injected into the carbon layer from the bottom and side of the regeneration tank. The low-temperature exhaust gas discharged from the second regeneration tank is filtered and heat-exchanged, then reheated to 900℃ and returned to the first regeneration tank. The volume ratio of steam to returned exhaust gas is 0.2.

[0067] At the same time, the high-temperature exhaust gas generated from the activation process of the first regeneration tank is guided to the second regeneration tank as the heat source for its pyrolysis stage, so that the temperature of the carbon layer gradually rises from top to bottom to 300~400℃, completing the drying and low-temperature pyrolysis of activated carbon;

[0068] The above process is repeated until the fourth regeneration tank. The high-temperature exhaust gas generated during the activation process in the fourth regeneration tank is guided to the first regeneration tank as a heat source for its pyrolysis stage. Under the combined effect of top-down heating of the exhaust gas and bottom-up purging of the mixed gas, the temperature of the carbon layer gradually increases, from approximately 280°C at the top to 400°C at the bottom. The high-temperature exhaust gas mainly contains CO, CH4, and tar-like products; some of the exhaust gas is recycled back after heat exchange.

[0069] S3 Steam Activation:

[0070] After heating the circulating exhaust gas to 900℃, a carbon layer is introduced from the side and bottom of the regeneration tank, raising the temperature of the carbon layer in the regeneration tank to 800~850℃, and starting the activation reaction.

[0071] This stage establishes a three-segment temperature gradient structure within the carbon layer:

[0072] The upper part of the carbon layer is controlled at 780℃, where mild gasification is the main process, effectively preserving the microporous structure and preventing high-temperature collapse.

[0073] The temperature in the central region is 800℃, which is the main activation window for mesopore formation and framework structure reorganization;

[0074] The lower region is maintained at 820℃, which enhances the depolymerization ability of the carbon skeleton by utilizing high temperature, which is beneficial for opening up large pores and improving pore connectivity.

[0075] This stage lasts for 50 minutes, during which the water-gas reaction (C + H2O → CO + H2) occurs inside the activated carbon, removing residual carbon from the pores, opening the mesopores and macropores, and forming a multi-level porous structure with distinct layers.

[0076] S4 Cooling:

[0077] After activation, the high-temperature gas source is first turned off, and the cooling phase begins. Steam is injected intermittently (1.5 minutes each time, with a 0.5-minute interval) for 10 cycles to reduce the carbon layer temperature from 820°C to about 280°C. Then, softened water (20°C) is injected from the top to further reduce the carbon layer temperature to below 100°C within 5 minutes.

[0078] The difference between Example 2 and Example 1 is that a 0.1% polyvinyl alcohol aqueous solution mist was introduced, with the particle size controlled at 20 μm.

[0079] The S2 drying, pyrolysis, and steam stripping steps are changed to the following steps:

[0080] Superheated steam at a pressure of 0.1 MPa and a temperature of 600±10℃ is introduced into the first regeneration tank to raise the temperature of the carbon layer. Filtered high-temperature exhaust gas from the first regeneration tank is introduced into the second regeneration tank, which is injected into the carbon layer from the bottom and side of the regeneration tank. The low-temperature exhaust gas discharged from the second regeneration tank is filtered and heat-exchanged, then reheated to 900℃ and returned to the first regeneration tank along with polyvinyl alcohol aqueous solution droplets. The volume ratio of steam to returned exhaust gas is 0.2.

[0081] At the same time, the high-temperature exhaust gas generated from the activation process of the first regeneration tank is guided to the second regeneration tank as the heat source for its pyrolysis stage, so that the temperature of the carbon layer gradually rises from top to bottom to 300~400℃, completing the drying and low-temperature pyrolysis of activated carbon;

[0082] The above process is repeated until the fourth regeneration tank. The high-temperature exhaust gas generated during the activation process in the fourth regeneration tank is guided to the first regeneration tank as a heat source for its pyrolysis stage. Under the combined effect of top-down heating of the exhaust gas and bottom-up purging of the mixed gas, the temperature of the carbon layer gradually increases, from approximately 280°C at the top to 400°C at the bottom. The high-temperature exhaust gas mainly contains CO, CH4, and tar-like products; some of the exhaust gas is recycled back after heat exchange.

[0083] The difference between Example 3 and Example 2 is that in step S3, 0.2% by mass of magnesium chloride and sodium citrate composite particles are uniformly incorporated into the carbon layer, wherein the mass ratio of magnesium chloride to sodium citrate is 1:1.5.

[0084] The difference between Example 4 and Example 3 is that in step S3, 0.1% by mass of urea powder is added to the mixed gas before it enters the regeneration tank.

[0085] The difference between Example 5 and Example 4 is that in step S4, a 0.2% sodium ethylenediaminetetraacetate aqueous solution is used instead of cooling water during the cooling process.

[0086] The difference between Example 6 and Example 5 is that in step S3, the carbon layer temperature is isothermally controlled at 800°C.

[0087] The difference between Examples 7 and 8 and Example 4 lies in the different parameter settings shown in Table 1 below.

[0088] Table 1

[0089] Example PVA droplet content Steam to exhaust gas volume ratio Activation temperature gradient Content of magnesium chloride and sodium citrate composite particles Urea or melamine powder content Cooling water additives Example 7 0.05% 0.1 790 / 810 / 830 0.1% 0.05% melamine 0.1% Example 8 0.3% 0.3 800 / 820 / 850 0.4% 0.2% urea 0.3%

[0090] Comparative Example 1

[0091] This comparative example discloses an activated carbon regeneration process, including the following steps:

[0092] S1 Dehydration Preparation:

[0093] Saturated granular activated carbon (2 mm in diameter) was hydraulically conveyed into regeneration tanks numbered 1, 2, 3, and 4. A bottom-up backflushing circulation was initiated using a carbon conveying pump to break up the dense carbon layer structure formed during transport. Subsequently, a dehydration process was started using a negative pressure suction device connected to the top of the tanks, operating under a vacuum of -0.02 MPa for 30 minutes to stabilize the carbon layer moisture content at 45±1%.

[0094] S2 Drying, pyrolysis, and steam stripping:

[0095] Superheated steam at a pressure of 0.1 MPa and a temperature of 600±10℃ is introduced into the first regeneration tank to raise the temperature of the carbon layer. Filtered high-temperature exhaust gas from the first regeneration tank is introduced into the second regeneration tank, which is injected into the carbon layer from the bottom and side of the regeneration tank. The low-temperature exhaust gas discharged from the second regeneration tank is filtered and heat-exchanged, then reheated to 900℃ and returned to the first regeneration tank. The volume ratio of steam to returned exhaust gas is 0.2.

[0096] At the same time, the high-temperature exhaust gas generated from the activation process of the first regeneration tank is guided to the second regeneration tank as the heat source for its pyrolysis stage, so that the temperature of the carbon layer gradually rises from top to bottom to 300~400℃, completing the drying and low-temperature pyrolysis of activated carbon;

[0097] The above process is repeated until the fourth regeneration tank. The high-temperature exhaust gas generated during the activation process in the fourth regeneration tank is guided to the first regeneration tank as a heat source for its pyrolysis stage. Under the combined effect of top-down heating of the exhaust gas and bottom-up purging of the mixed gas, the temperature of the carbon layer gradually increases, from approximately 280°C at the top to 400°C at the bottom. The high-temperature exhaust gas mainly contains CO, CH4, and tar-like products; some of the exhaust gas is recycled back after heat exchange.

[0098] S3 Steam Activation:

[0099] After heating the recirculating exhaust gas to 900°C, a carbon layer is introduced from the side and bottom of the regeneration tank, raising the temperature of the carbon layer inside the regeneration tank to 850°C and initiating the activation reaction.

[0100] S4 Cooling:

[0101] Instead of using steam cooling, cold water was directly injected for 5 minutes, causing the carbon layer to drop sharply from 850°C to below 100°C.

[0102] Comparative Example 2

[0103] This comparative example discloses an activated carbon regeneration process, including the following steps:

[0104] S1 Dehydration Preparation:

[0105] Saturated granular activated carbon (2 mm in diameter) was hydraulically conveyed into regeneration tanks numbered 1, 2, 3, and 4. A bottom-up backflushing circulation was initiated using a carbon conveying pump to break up the dense carbon layer structure formed during transport. Subsequently, a dehydration process was started using a negative pressure suction device connected to the top of the tanks, operating under a vacuum of -0.02 MPa for 30 minutes to stabilize the carbon layer moisture content at 45±1%.

[0106] S2 Drying, pyrolysis, and steam stripping:

[0107] Superheated steam at a pressure of 0.1 MPa and a temperature of 600±10℃ is introduced into the first regeneration tank to raise the temperature of the carbon layer. Filtered high-temperature exhaust gas from the first regeneration tank is introduced into the second regeneration tank, which is injected into the carbon layer from the bottom and side of the regeneration tank. The low-temperature exhaust gas discharged from the second regeneration tank is filtered and heat-exchanged, then reheated to 900℃ and returned to the first regeneration tank. The volume ratio of steam to returned exhaust gas is 0.5.

[0108] At the same time, the high-temperature exhaust gas generated from the activation process of the first regeneration tank is guided to the second regeneration tank as the heat source for its pyrolysis stage, so that the temperature of the carbon layer gradually rises from top to bottom to 300~400℃, completing the drying and low-temperature pyrolysis of activated carbon;

[0109] The above process is repeated until the fourth regeneration tank. The high-temperature exhaust gas generated during the activation process in the fourth regeneration tank is guided to the first regeneration tank as a heat source for its pyrolysis stage. Under the combined effect of top-down heating of the exhaust gas and bottom-up purging of the mixed gas, the temperature of the carbon layer gradually increases, from approximately 280°C at the top to 400°C at the bottom. The high-temperature exhaust gas mainly contains CO, CH4, and tar-like products; some of the exhaust gas is recycled back after heat exchange.

[0110] S3 Steam Activation:

[0111] After heating the recirculating exhaust gas to 900°C, a carbon layer is introduced from the side and bottom of the regeneration tank, raising the temperature of the carbon layer inside the regeneration tank to 850°C and initiating the activation reaction.

[0112] S4 Cooling:

[0113] Instead of using steam cooling, cold water was directly injected for 5 minutes, causing the carbon layer to drop sharply from 850°C to below 100°C.

[0114] Detection methods

[0115] I. Determination of specific surface area and pore structure

[0116] Method Name: Nitrogen Adsorption-Desorption Isotherm Test

[0117] Refer to GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method";

[0118] step:

[0119] The sample was pretreated under vacuum at 300 °C for 4 hours to remove surface adsorbed water.

[0120] The tests were conducted using an automated specific surface area and pore size analyzer.

[0121] The specific surface area was calculated using the BET model, and the micropore volume and mesopore volume were calculated using the DFT model (pore size range is divided into: micropores <2 nm, mesopores 2~50 nm).

[0122] II. Tar Residue Content (wt%)

[0123] Method Name: Solvent Extraction-Gravimetric Method

[0124] step:

[0125] Accurately weigh 1.0000 g of sample and reflux extract using dichloromethane or benzene as solvent for 4 hours.

[0126] The extract was concentrated to constant weight by rotary evaporation, and the residual tar mass was determined.

[0127] Tar residue content = mass of extract / mass of original sample × 100%.

[0128] III. Residual carbon content (wt%)

[0129] Method Name: Thermogravimetric Analysis (TGA)

[0130] parameter:

[0131] The heating rate was 10 °C / min, the atmosphere was air, and the final temperature was 900 °C.

[0132] The percentage of remaining mass is the residual carbon content.

[0133] IV. Nitrogen content (wt%)

[0134] Method Name: Elemental Analyzer Method (CHNS)

[0135] illustrate:

[0136] The measured mass fraction of nitrogen can be used to evaluate the doping effect of urea / melamine.

[0137] V. Moisture adsorption capacity (mg / g)

[0138] Method Name: Static Moisture Absorption Test

[0139] step:

[0140] First, dry the sample at 105 °C to constant weight;

[0141] The dried sample was placed in a desiccator containing a saturated NaCl solution at 25 ℃ and 75% relative humidity;

[0142] Weigh the sample after 48 hours of equilibration and calculate the water absorption mass per unit mass of the sample.

[0143] VI. pH value measurement (surface acidity / alkalinity index)

[0144] Method Name: Aqueous Immersion Method (according to HG / T 4363-2012)

[0145] step:

[0146] Take 1.000 g of sample and place it in 100 mL of deionized water, then shake for 2 hours;

[0147] Use a pH meter to measure the pH value of the supernatant;

[0148] It can reflect changes in the acidity or alkalinity of oxygen / nitrogen groups on the carbon surface.

[0149] The results of all the above tests are shown in Tables 2 and 3 below.

[0150] Table 2

[0151] Group <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Micropore volume (cm 3 / g)]]> <![CDATA[Mesopore volume (cm 3 / g)]]> Tar residue (wt%) Example 1 920 0.48 0.28 2.5 Example 2 980 0.51 0.32 1.8 Example 3 1040 0.54 0.36 1.2 Example 4 1095 0.57 0.4 0.9 Example 5 1125 0.58 0.42 0.8 Example 6 980 0.5 0.35 1.4 Example 7 1005 0.53 0.37 1 Example 8 1150 0.6 0.45 0.6 Comparative Example 1 780 0.41 0.22 4.3 Comparative Example 2 720 0.39 0.18 5

[0152] Table 3

[0153] Group Residual carbon content (wt%) Nitrogen content (wt%) Moisture adsorption capacity (mg / g) pH value Example 1 5.2 0.3 125 7.1 Example 2 4 0.3 130 7.2 Example 3 3 0.4 140 7.3 Example 4 2.5 0.9 145 7.3 Example 5 2.3 0.9 150 7.4 Example 6 3.8 0.3 130 7.2 Example 7 2.9 1.2 138 7.4 Example 8 2 1.5 160 7.5 Comparative Example 1 7 0.2 95 6.8 Comparative Example 2 7.5 0.2 90 6.7

[0154] The specific surface area of ​​Examples 1-8 was significantly higher than that of the comparative examples, reaching a maximum of 1150 m² / g (Example 8), which was nearly 60% higher than that of Comparative Example 2. The volumes of micropores and mesopores were also significantly increased, indicating that the present invention significantly optimized the pore distribution and hierarchical structure.

[0155] The tar residue in Examples 3 to 8 was controlled below 1.2%, significantly lower than that in Comparative Example 1 (4.3%) and Comparative Example 2 (5.0%), verifying the synergistic advantages of PVA droplets and the tail gas-steam stripping coupling pathway in tar migration and cracking. The carbon residue content also decreased significantly with the enhancement of temperature gradient, steam activation, and synergistic induction by composite particles, demonstrating the improved deep activation efficiency driven by water-gas reaction.

[0156] In Examples 4, 7, and 8, the addition of urea or melamine significantly increased the nitrogen content in the carbon samples to 0.9%–1.5%, far exceeding that of the comparative example (only 0.2%). Combined with the activation temperature-controlled partitioning, these nitrogen sources are transformed into surface active nitrogen sites (such as pyrrole nitrogen and graphitic nitrogen), endowing the activated carbon with stronger polar adsorption capacity and selectivity.

[0157] The water adsorption capacity of each embodiment was superior to that of the comparative example, reaching a maximum of 160 mg / g (Example 8), indicating a synergistic improvement in the number of surface polar groups and pore structure. Simultaneously, the pH value remained stable between 7.1 and 7.5, without any obvious alkalization or acidification trend, reflecting a stable chemical environment on the surface of the regenerated activated carbon, suitable for subsequent applications.

[0158] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A process for anaerobic pyrolysis and steam regeneration of activated carbon, characterized in that, Includes the following steps: S1 Dehydration Preparation: Saturated activated carbon is fed into the regeneration tank via hydraulic conveying. The carbon conveying water pump is started to backwash and loosen the carbon layer, and dehydration is carried out under negative pressure to control the overall moisture content of the carbon layer to 45±1%. S2 Drying, pyrolysis, steam stripping and tail gas circulation heat transfer: Superheated steam heated to 600±10℃ and pressure of 0.05~0.1 MPaG is introduced into the nth regeneration tank to raise the temperature of the carbon layer, and filtered high-temperature tail gas from the nth regeneration tank is introduced into the n+1th regeneration tank. The high-temperature tail gas is injected into the carbon layer from the bottom and side of the regeneration tank. The low-temperature exhaust gas discharged from the (n+1)th regeneration tank is filtered and heat exchanged before being reheated to 900°C and then returned to the nth regeneration tank. At the same time, the high-temperature exhaust gas generated from the activation process of the nth regeneration tank is guided to the (n+1)th regeneration tank as the heat source for its pyrolysis stage, so that the temperature of the carbon layer gradually rises from top to bottom to 300~400℃, completing the drying and low-temperature pyrolysis of the activated carbon. The high-temperature exhaust gas generated during the activation process of the last regeneration tank is directed to the first regeneration tank as a heat source for its pyrolysis stage. Furthermore, in step S2, a polyvinyl alcohol aqueous solution mist with a mass concentration of 0.05–0.3% is introduced into the superheated steam; S3 Steam Deep Activation: After heating the circulating tail gas to 900℃, a carbon layer is introduced from the side and bottom of the regeneration tank, so that the temperature of the carbon layer in the regeneration tank rises to 800~850℃, and the activation reaction begins. In step S3, the activation duration is controlled to be 30-60 minutes, and the temperature gradients of the upper, middle and lower parts of the carbon layer are set to 780-800℃, 800-820℃ and 820-850℃ respectively. Furthermore, in the S3 steam deep activation step, 0.05-0.2% by mass of urea or melamine powder is added before the mixed gas enters the regeneration tank; During the S3 steam activation process, magnesium chloride and sodium citrate composite particles with a mass ratio of 0.1-0.4% are uniformly distributed in the regeneration tank. S4 Cooling: First, steam is introduced to lower the temperature of the carbon layer to below 300℃, and then cooling water is introduced to further lower it to below 100℃, thus completing the cooling of the regenerated activated carbon, which is then transported out of the tank by hydraulic means.

2. The activated carbon pyrolysis and steam regeneration process according to claim 1, characterized in that: The droplet size of the polyvinyl alcohol aqueous solution is controlled to be 5–20 μm.

3. The activated carbon pyrolysis and steam regeneration process according to claim 2, characterized in that: In step S2, the volume ratio of steam to reflux tail gas in the mixed gas is 0.1 to 0.

3.

4. The activated carbon pyrolysis and steam regeneration process according to claim 1, characterized in that: In the S4 cooling step, the steam cooling stage adopts a pulsed intermittent injection method, each lasting 1 to 2 minutes, with a total time of 15 to 20 minutes.

5. The activated carbon pyrolysis and steam regeneration process according to claim 4, characterized in that: The cooling water after steam cooling contains 0.1-0.3% disodium EDTA or sodium citrate.

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