A method and system for preparing activated carbon based on negative pressure locking carbon and superheated steam thermal coupling

Abstract

The application discloses a method and system for preparing activated carbon based on negative pressure carbon locking and superheated steam thermal coupling, and relates to the technical field of activated carbon preparation, which comprises: a closed negative pressure bin is arranged at the end of a biomass boiler furnace grate pyrolysis zone or a slag outlet, and the method comprises the following steps: S1, a negative pressure carbon locking stage, including: controlling the temperature of red-hot carbon at 400-500 DEG C; implementing step-by-step slow vacuum pumping: first pumping to-50 Pa, maintaining pressure for 30 seconds; then pumping to-100 Pa, maintaining pressure for 1 minute; finally maintaining a micro-negative pressure state of-100 to-200 Pa; using the internal and external pressure difference to make the residual gas in the carbon body expand, open microcracks, preform micropores, and isolate oxygen to prevent burning loss; S2, a thermal transport stage; and S3, a superheated steam activation stage. The micro-negative pressure environment is constructed at the slag outlet of the boiler to realize "carbon locking and pore forming", and the superheated steam activation is directly carried out by using waste heat, so that the energy loss of cold and hot alternation is eliminated.

Description

Technical Field

[0001] This invention relates to the technical field of biomass resource utilization and activated carbon preparation, and in particular to a method and system for preparing activated carbon based on negative pressure carbon locking and hot coupling of superheated steam. Background Technology

[0002] Activated carbon, with its well-developed pore structure, abundant surface functional groups, and excellent adsorption properties, is widely used in many fields such as water treatment, air pollution control, solvent recovery, food decolorization, energy storage materials, and catalyst carriers. Biomass-based activated carbon, prepared from agricultural and forestry waste, wood residues, and other biomass, offers advantages such as solid waste resource utilization, low carbon emissions, environmental friendliness, and readily available raw materials, making it the mainstream development direction of the activated carbon industry.

[0003] Currently, the industrial production of biomass activated carbon generally adopts a segmented process route. The complete process consists of raw material drying, high-temperature carbonization, natural / forced cooling of the carbon material, low-temperature transfer and storage, reheating for activation, and cooling and sieving of the finished product, i.e., a step-by-step independent operation mode of "carbonization-cooling-reheating-activation". This traditional process has been used in industry for a long time and the equipment is relatively mature. However, it has inherent defects that are difficult to avoid in terms of energy consumption, carbon yield, porosity controllability, and compatibility with continuous production, which seriously restrict the improvement of product production costs and adsorption performance.

[0004] Firstly, the segmented operation of the process results in significant sensible heat loss, leading to persistently high overall production energy consumption. Biomass is carbonized at 500–650℃ to obtain hot biochar. Traditional processes require the high-temperature char to be completely cooled to room temperature before it can be discharged and transported, resulting in the direct loss of a large amount of sensible heat carried by the char itself. Before entering the activation process, the room-temperature char needs to be reheated to an activation temperature above 800℃ using gas or electric heating. These two large temperature cycles result in double heat consumption, and the heat losses from heating and cooling equipment are compounded, leading to high overall production energy consumption and a thermal energy utilization rate of less than 30%, significantly increasing the energy cost and carbon emissions of activated carbon production.

[0005] Secondly, the carbonization stage suffers from severe fixed carbon loss, resulting in a low overall activated carbon yield. Traditional carbonization furnaces have poor sealing performance in the discharge and transfer stages, exposing hot carbon materials to the air environment. At high temperatures, the carbon matrix is ​​highly susceptible to oxidation and combustion reactions with oxygen in the air, causing a large amount of fixed carbon to be burned off. At the same time, the segmented process cannot achieve self-sustaining protection of the carbon material in a completely oxygen-deficient negative pressure closed environment, leading to excessive consumption of effective carbon components in the raw materials. The carbonization yield of conventional biomass raw materials is only maintained at 20% to 30%, resulting in a large amount of raw material loss, low raw material utilization, and poor economic benefits for large-scale production.

[0006] Third, single activation modes present significant challenges in pore size control, leading to bottlenecks in activated carbon adsorption performance. In existing segmented processes, carbonization and activation are isolated processes. The carbonization stage only completes the decomposition of organic matter into carbon, failing to pre-construct a primary microporous framework. Subsequent activation with superheated steam or carbon dioxide can only selectively develop microporous structures, making it difficult to simultaneously achieve the synergistic generation of micropores, mesopores, and macropores. The resulting activated carbon exhibits a uniform pore size distribution, limiting its ability to adsorb multiple pollutants and complex organic waste gases, thus failing to meet the demands of various scenarios and high-load adsorption conditions.

[0007] To address the shortcomings of the segmented process, existing improvement technologies mainly focus on localized improvement solutions such as optimizing the cooling structure of the carbonization furnace discharge and modifying the waste heat recovery pipeline of the activation furnace. For example, adding a water-cooled jacket to the carbonization discharge port, simply sealing the material silo to isolate air, or adding a waste heat exchanger to recover the heat from the activation flue gas. However, the existing improvement schemes can only alleviate local heat loss and slightly reduce the oxidation and burn-off of charcoal. They fail to break the segmented barrier of "carbonization, cooling, and reheating activation" from a process logic perspective. On the one hand, they cannot achieve closed and continuous transfer of high-temperature charcoal without cooling or contact with air. They lack a negative pressure and oxygen-deficient protection channel for hot charcoal throughout the process, making it difficult to complete micropore pre-forming in the hot stage after carbonization and unable to provide a high-quality precursor charcoal skeleton for subsequent activation. On the other hand, they fail to achieve direct coupling and matching between carbonization waste heat and activation heat supply. The high-temperature sensible heat carried by the hot charcoal cannot be directly supplied to the activation reaction. The heat energy of the two processes cannot be used interchangeably, and the heat energy cascade utilization system is missing. At the same time, the existing equipment cannot simultaneously integrate the functions of negative pressure charcoal-locking closed transport, hot in-situ steam pre-activation, and continuous coupling activation. It cannot simultaneously solve the three core technical problems of high energy consumption, low yield, and difficulty in controlling pore structure.

[0008] In summary, the industry urgently needs a new process and supporting system for the preparation of activated carbon that can achieve continuous connection between carbonization and activation in the hot state, full-process closed negative pressure carbon locking, and graded coupling utilization of thermal energy, and can directionally and synergistically control the multi-level pore structure, so as to overcome the multiple defects of the traditional segmented preparation process from the root. Summary of the Invention

[0009] This invention provides a method and system for preparing activated carbon based on negative pressure carbon locking and hot coupling of superheated steam. By creating a micro-negative pressure environment at the boiler slag outlet to achieve "carbon locking and pore formation", and using waste heat to directly activate the activated carbon with superheated steam, the energy loss from alternating hot and cold is eliminated.

[0010] According to one aspect of this disclosure, a method for preparing activated carbon based on negative pressure carbon locking and hot coupling with superheated steam is provided, wherein a sealed negative pressure chamber is set at the end of the pyrolysis zone of the biomass boiler grate or at the slag outlet, and the method includes: S1, negative pressure carbon locking stage, includes: Control the temperature of the red-hot charcoal at 400-500℃; Implement a stepped slow vacuum: first evacuate to -50 Pa and stabilize for 30 seconds; then evacuate to -100 Pa and stabilize for 1 minute; finally maintain a slight negative pressure state of -100 ~ -200 Pa. The internal and external pressure difference is used to expand the residual gas inside the carbon body, opening up microcracks and pre-forming micropores, and isolating oxygen to prevent burn-off. S2, thermal transport stage; S3, superheated steam activation stage.

[0011] In one possible implementation, S2, the thermal transport stage, includes: The red-hot charcoal after being locked is conveyed through a closed screw conveyor at a temperature of 350~400℃. During the transportation process, the flue gas from the tail end of the boiler is introduced for inerting protection to prevent reignition.

[0012] In one possible implementation, S3, the superheated steam activation stage, includes: Hot carbon is introduced into an activation furnace, and superheated steam at a temperature of 420~450℃ is introduced. Control the temperature inside the activation furnace at 850~920℃ and maintain a slight negative pressure of -50 Pa; L. Utilize the waste heat from boiler flue gas to heat steam, thereby achieving cascaded utilization of energy.

[0013] A system for preparing activated carbon based on negative pressure carbon locking and hot coupling of superheated steam, the system comprising: a negative pressure carbon locking unit, a hot transport unit, a superheated steam generation unit, and an activation unit; Among them, the negative pressure carbon-locking unit is located at the boiler slag outlet and is equipped with a pressure sensor, an oxygen analyzer and a multi-stage vacuum pump group. The hot transport unit is a screw conveyor with a water-cooled jacket and a flue gas inerting interface; Superheated steam generating unit: A flue-type superheater that uses high-temperature flue gas from the boiler to heat saturated steam. The heat source for the flue-type superheater is high-temperature flue gas from the tail end of the boiler. Activation unit: Rotary activation furnace with built-in steam injection device and temperature interlock system; The screw conveyor is located between the negative pressure carbon-locking unit and the rotary activation furnace.

[0014] Compared with the prior art, the beneficial effects of the present invention are: This invention innovatively employs an integrated preparation process that combines negative pressure carbon locking with superheated steam thermal coupling, completely abandoning the traditional segmented production mode of "carbonization-cooling-reheating-activation". It addresses the industry pain points of high energy consumption, low yield, simple pore structure, and poor production safety of traditional technologies from the perspectives of process mechanism, production system, and equipment control. Compared with traditional processes, it possesses multiple significant technical advantages, the specific technical effects of which are as follows: 1. The cascade utilization of thermal energy results in extremely significant energy-saving and efficiency-enhancing effects. Traditional processes suffer from dual heat losses due to high-temperature cooling and low-temperature reheating of the charcoal, resulting in extremely low thermal energy utilization. This invention achieves seamless integration of carbonization and activation processes. The high-temperature charcoal body after carbonization retains approximately 400°C of inherent sensible heat, eliminating the need for cooling and allowing it to be directly fed into the activation process. This completely eliminates the additional energy consumption from sensible heat loss during cooling and secondary heating. This coupled heating mode maximizes the recovery and utilization of the charcoal body's own waste heat, saving significant heating and cooling energy consumption compared to traditional processes. Actual measurements show that overall production energy consumption is reduced by more than 60% compared to traditional segmented processes, significantly reducing energy costs and carbon emissions for large-scale activated carbon production. The energy-saving economic benefits and green production advantages are outstanding.

[0015] 2. The entire process is sealed to lock in carbon, significantly improving activated carbon yield and raw material utilization. Traditional processes involve open operations during material discharge and transfer, making hot charcoal highly susceptible to oxidation and burn-off due to oxygen exposure, resulting in significant fixed carbon loss and hindering yield improvement. This invention utilizes negative pressure char-locking technology to achieve a completely closed, oxygen-deficient environment throughout the entire process of charcoal discharge, transfer, and furnace loading. This effectively isolates the hot charcoal from air contact, fundamentally eliminating the oxidation and combustion loss of high-temperature fixed carbon and maximizing the retention of effective carbon components in the biomass feedstock. After process optimization, the effective charcoal yield is significantly increased from 20%–30% in traditional processes to approximately 45%, significantly reducing agricultural and forestry biomass feedstock loss and greatly improving the resource utilization rate of solid waste and the overall production line capacity.

[0016] 3. Multi-level pore structure for comprehensive optimization of product adsorption quality. Traditional single activation processes can only develop a single microporous structure, resulting in uneven pore size distribution and a simple pore structure, leading to significant bottlenecks in adsorption performance. This invention combines a stepped negative pressure control mechanism with a superheated steam coupled activation mechanism. The stepped negative pressure environment induces a controllable "micro-burst" effect within the carbon body, directionally constructing a well-connected macroporous and mesoporous framework structure, providing efficient channels for adsorption and mass transfer. Subsequent precise chemical etching with superheated steam further enriches the microporous structure based on the multi-level pore framework, achieving the coordinated and orderly development of micropores, mesopores, and macropores. The resulting biomass activated carbon has a reasonable pore size distribution and well-developed pore structure, with an iodine adsorption value reaching 800~1000 mg / g. Adsorption capacity and mass transfer efficiency are significantly improved, making it suitable for complex adsorption conditions in various scenarios such as water treatment and waste gas treatment. The product demonstrates significant market adaptability and performance advantages.

[0017] 4. Multiple interlocking protections completely eliminate the risk of combustion and explosion during hot production, ensuring extremely high safety. During the hot preparation of activated carbon, the mixture of high-temperature carbon powder and combustible steam is prone to causing combustion and explosion hazards, and traditional processes lack a systematic safety control mechanism. This invention is equipped with a DCS automated interlocking control system, which constructs a triple real-time monitoring and interlocking protection mechanism for pressure, oxygen content, and temperature. It can collect furnace operating parameters in real time throughout the process. Once the parameters deviate from the safety threshold, the system automatically triggers protective actions such as interlocking regulation, pressure relief, oxygen isolation, and cooling, accurately avoiding the risk of combustion and explosion caused by high-temperature carbon powder oxidation and combustible gas accumulation. It completely solves the safety hazards in the hot carbon material transfer and activation process, realizes continuous, stable, and safe industrial operation of the entire production line, and significantly reduces the probability of production safety accidents and operation and maintenance risks. Attached Figure Description

[0018] Figure 1 The diagram shows a flowchart of a method for preparing activated carbon based on negative pressure carbon locking and hot coupling of superheated steam according to an embodiment of the present disclosure.

[0019] Figure 2 This diagram illustrates a system block diagram for preparing activated carbon based on the hot coupling of negative pressure carbon locking and superheated steam according to an embodiment of the present disclosure. Detailed Implementation

[0020] Various exemplary embodiments, features, and aspects of this disclosure will now be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings denote elements that have the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise.

[0021] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0022] Furthermore, to better illustrate this disclosure, numerous specific details are set forth in the following detailed description. Those skilled in the art will understand that this disclosure can be practiced without certain specific details. In some instances, methods, means, components, and circuits well known to those skilled in the art have not been described in detail in order to highlight the main points of this disclosure.

[0023] A method for preparing activated carbon based on negative pressure carbon locking and hot coupling with superheated steam involves setting up a sealed negative pressure chamber at the end of the pyrolysis zone or slag outlet of a biomass boiler grate. The method includes: S1, negative pressure carbon locking stage, includes: Control the temperature of the red-hot charcoal at 400-500℃; Implement a stepped slow vacuum: first evacuate to -50 Pa and stabilize for 30 seconds; then evacuate to -100 Pa and stabilize for 1 minute; finally maintain a slight negative pressure state of -100 ~ -200 Pa. The internal and external pressure difference is used to expand the residual gas inside the carbon body, opening up microcracks and pre-forming micropores, and isolating oxygen to prevent burn-off. S2, thermal transport stage; S3, superheated steam activation stage.

[0024] In one possible implementation, S2, the thermal transport stage, includes: The red-hot charcoal after being locked is conveyed through a closed screw conveyor at a temperature of 350~400℃. During the transportation process, the flue gas from the tail end of the boiler is introduced for inerting protection to prevent reignition.

[0025] In one possible implementation, S3, the superheated steam activation stage, includes: Hot carbon is introduced into an activation furnace, and superheated steam at a temperature of 420~450℃ is introduced. Control the temperature inside the activation furnace at 850~920℃ and maintain a slight negative pressure of -50 Pa; By utilizing the waste heat from boiler flue gas to heat steam, energy can be utilized in a cascade manner.

[0026] A system for preparing activated carbon based on negative pressure carbon locking and hot coupling of superheated steam, the system comprising: a negative pressure carbon locking unit, a hot transport unit, a superheated steam generation unit, and an activation unit; Among them, the negative pressure carbon-locking unit is located at the boiler slag outlet and is equipped with a pressure sensor, an oxygen analyzer and a multi-stage vacuum pump group. The hot transport unit is a screw conveyor with a water-cooled jacket and a flue gas inerting interface; Superheated steam generating unit: A flue-type superheater that uses high-temperature flue gas from the boiler to heat saturated steam. The heat source for the flue-type superheater is high-temperature flue gas from the tail end of the boiler. Activation unit: Rotary activation furnace with built-in steam injection device and temperature interlock system; The screw conveyor is located between the negative pressure carbon-locking unit and the rotary activation furnace.

[0027] Example: Application of a 20t / h biomass boiler 1. Parameter settings: Target pressure of negative pressure chamber: -150 Pa.

[0028] Superheated steam flow rate: 1 t / h.

[0029] Activation time: 1.5 h.

[0030] 2. Operating Procedures: After the biomass (bamboo chips / wood chips) is pyrolyzed on the grate, it enters the bottom sealed negative pressure chamber.

[0031] The PLC control system starts the vacuum pump and executes it according to the step curve of -50 Pa → -100 Pa → -150 Pa.

[0032] When the oxygen analyzer detects O2 < 2% and temperature > 350℃, the hydraulic gate opens, and the red-hot charcoal falls into the screw conveyor.

[0033] The superheater uses the high-temperature flue gas in front of the boiler economizer to heat the steam to 420°C and then injects it into the rotary activation furnace.

[0034] The activated exhaust gases (CO, H2) are recovered and sent to the boiler combustion chamber to aid combustion.

[0035] 3. Product testing: The resulting activated carbon had a moisture content of < 5%, an ash content of < 5%, an iodine value of 950 mg / g, and a methylene blue value of 180 mg / g.

[0036] This invention provides a method for preparing activated carbon with low energy consumption, high yield, and high quality. It achieves "carbon locking and pore formation" by creating a micro-negative pressure environment at the boiler slag outlet and directly activating it with superheated steam using waste heat, thus eliminating energy loss from alternating hot and cold temperatures.

[0037] The various embodiments of this disclosure have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for preparing activated carbon based on negative pressure carbon locking and hot coupling with superheated steam, characterized in that, A sealed negative pressure chamber is installed at the end of the pyrolysis zone or slag outlet of the biomass boiler grate. Methods include: S1, negative pressure carbon locking stage, includes: Control the temperature of the red-hot charcoal at 400-500℃; Implement a stepped slow vacuum: first evacuate to -50 Pa and stabilize for 30 seconds; then evacuate to -100 Pa and stabilize for 1 minute; finally maintain a slight negative pressure state of -100 ~ -200 Pa. The internal and external pressure difference is used to expand the residual gas inside the carbon body, opening up microcracks and pre-forming micropores, and isolating oxygen to prevent burn-off. S2, thermal transport stage; S3, superheated steam activation stage.

2. The method for preparing activated carbon based on negative pressure carbon locking and hot coupling with superheated steam according to claim 1, characterized in that, S2, the thermal transport stage, includes: The red-hot charcoal after being locked is conveyed through a closed screw conveyor at a temperature of 350~400℃. During the transportation process, the flue gas from the tail end of the boiler is introduced for inerting protection to prevent reignition.

3. The method for preparing activated carbon based on negative pressure carbon locking and hot coupling with superheated steam according to claim 2, characterized in that... S3, the superheated steam activation stage, includes: Hot carbon is introduced into an activation furnace, and superheated steam at a temperature of 420~450℃ is introduced. Control the temperature inside the activation furnace at 850~920℃ and maintain a slight negative pressure of -50 Pa; By utilizing the waste heat from boiler flue gas to heat steam, energy can be utilized in a cascade manner.

4. A system for preparing activated carbon based on negative pressure carbon locking and hot coupling with superheated steam, characterized in that, The system includes: a negative pressure carbon locking unit, a hot transport unit, a superheated steam generation unit, and an activation unit; Among them, the negative pressure carbon-locking unit is located at the boiler slag outlet and is equipped with a pressure sensor, an oxygen analyzer and a multi-stage vacuum pump group. The hot transport unit is a screw conveyor with a water-cooled jacket and a flue gas inerting interface; Superheated steam generating unit: A flue-type superheater that uses high-temperature flue gas from the boiler to heat saturated steam. The heat source for the flue-type superheater is high-temperature flue gas from the tail end of the boiler. Activation unit: Rotary activation furnace with built-in steam injection device and temperature interlock system; The screw conveyor is located between the negative pressure carbon-locking unit and the rotary activation furnace.

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