Method and apparatus for preparing porous carbon

Abstract

The application belongs to the technical field of biomass porous carbon material preparation, and particularly relates to a method for reducing energy consumption of a porous carbon produced by an alkali activation process and a system for realizing the method. The method comprises feeding, preheating, controllable air injection, controllable combustion, atmosphere transformation and activation, and post-treatment. The system integrates a controllable air injection system and a combustion reaction zone. By injecting 15% to 50% of the theoretical complete combustion air, the controllable combustion of volatile combustible gas generated by pyrolysis is realized. The method can directly provide part of the heat required for activation, reduce the external heating requirement, and achieve an energy saving effect of 15% to 30%. In addition, since oxygen is consumed in the combustion process, an anaerobic or reducing environment can be created and maintained in the rear part of the activation section without relying on strict equipment sealing and high-purity inert gas purging, thereby reducing the requirement for equipment airtightness and inert gas consumption.

Description

Technical Field

[0001] This invention belongs to the field of biomass porous carbon material preparation technology, specifically relating to a method for preparing porous carbon and the equipment for implementing the method. Background Technology

[0002] Traditional biomass pyrolysis and alkali activation are among the mainstream technologies for preparing high specific surface area biomass porous carbon. The traditional approach involves: first, pretreating and carbonizing biomass raw materials (such as wood, nutshells, and straw) to obtain initial biochar; then, uniformly mixing the biochar with a solid alkali (usually potassium hydroxide or sodium hydroxide) at a specific mass ratio (impregnation ratio), and activating the mixture under an inert gas (such as nitrogen or argon) within a certain temperature range (usually 600–800°C); finally, acid washing and water washing until neutral, followed by drying, yields high-performance porous carbon material. This process utilizes the alkali reagent to etch the carbon framework at high temperatures, potentially inserting it into the carbon interlayer to create a well-developed pore structure. However, this approach has the following significant drawbacks: 1. High operating costs: The activation process needs to be maintained at high temperature for several hours, relying entirely on an external heat source and requiring continuous inert gas to maintain an anaerobic environment to prevent material oxidation. This results in huge heat energy consumption and high costs associated with the use of high-purity protective gas.

[0003] 2. Energy waste and environmental pollution: The direct emission of large amounts of volatile gases (such as H2, CO, CH4, etc.) generated during pyrolysis not only wastes energy but also pollutes the environment.

[0004] 3. Complex process and high equipment requirements: To ensure an absolutely anaerobic environment, the reaction equipment must have a high degree of airtightness and a reliable temperature control system, which increases the complexity of equipment investment and maintenance.

[0005] 4. The contradiction in activation environment control: Maintaining a stable anaerobic environment is the key to ensuring the success of the activation reaction and product quality, but this is inherently contradictory to using external energy (usually involving combustion, which requires oxygen) for heating.

[0006] Therefore, how to synergistically process pyrolysis products and reduce activation energy consumption is a key issue that the biomass porous carbon preparation industry urgently needs to overcome. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method for preparing porous carbon and an apparatus for implementing the method. By precisely introducing an appropriate amount of air, the volatile combustible gases released during pyrolysis are controlled to burn within the furnace, thereby enabling the utilization of pyrolysis products and reducing activation energy consumption.

[0008] The first aspect of this invention provides a method for preparing porous carbon, comprising: S1 - Feeding: The biomass precursor treated with alkali solution is fed into the kiln and passes through each temperature zone of the kiln in sequence; S2 - Preheating: The temperature of the preheating section is controlled at 200-250℃ to allow the biomass precursor to undergo pyrolysis and release volatile combustible gases; S3 - Air Injection: Inject a preset amount of air into the front of the activation section; S4 - Controlled Combustion: The air injected in step S3 reacts with the volatile combustible gas released in S2 to undergo a combustion reaction; S5 - Activation: The temperature in the latter part of the activation section is controlled at 755-825℃; S6 - Post-treatment: Acid washing, water washing and drying are performed to obtain porous carbon products.

[0009] Preferably, the biomass precursor in step S1 includes one or more of wood, nutshells, or straw.

[0010] Preferably, the alkaline treatment in step S1 refers to immersing the biomass precursor in a potassium hydroxide or sodium hydroxide solution with a mass concentration of 10%-50% for 1-10 hours.

[0011] Preferably, the temperature control range of the preheating section in step S2 is 200-250℃.

[0012] Preferably, the volatile combustible gas in step S2 includes one or more of hydrogen, carbon monoxide, or methane.

[0013] Preferably, the air injection amount in step S3 is 15%-50% of the air required for theoretical complete combustion; more preferably 20%-40%; and even more preferably 25%-35%.

[0014] Preferably, step S3 further includes: using an online monitoring sensor to detect the temperature and residual oxygen concentration at the front of the activation section in real time, and feeding the signal back to the control system; the control system calculates the amount of air to be injected based on this, and injects the corresponding amount of air.

[0015] Preferably, in step S3, the control system precisely measures the amount of air to be injected according to the PID algorithm, thereby synchronously adjusting the fan operation.

[0016] Preferably, based on the real-time deviation e(t) between the measured temperature PVT of the thermocouple at the front of the activation zone and the target process temperature SPT, the output control quantity uk is calculated to achieve closed-loop regulation of the precision metering fan speed. The PID algorithm uses the following formula: Wherein, Kp, Ki, and Kd are the proportional, integral, and derivative coefficients, respectively, obtained through engineering tuning. To further ensure the anaerobic environment in the activation zone, the system introduces the measured value of PVO2 from the oxygen analyzer as a correction factor. When PVO2 exceeds the set threshold SpO2±Δ, an oxygen deviation correction term ΔuO2 will be superimposed on the PID output value uk to achieve coordinated and precise control of temperature and atmosphere.

[0017] Specifically, the combustion reaction in step S4 includes: 2CO + O2 → 2CO2 CH4 + 2O2 → CO2 + 2H2O 2H2 + O2 → 2H2O.

[0018] Specifically, in step S5, the oxygen content in the latter part of the activation section is controlled and stabilized within the range of <0.8%, preferably <0.5%, and more preferably <0.3%.

[0019] The present invention also provides a furnace device for producing porous carbon with reduced energy consumption, for performing the above method. The furnace device is arranged in a long strip along the material conveying direction, and its structure includes, from the outside to the inside, an insulation board layer, an insulation brick layer, a refractory brick layer, and a furnace space located in the center.

[0020] Specifically, the furnace equipment can be divided into multiple zones along the material conveying direction, and the furnace structure of each zone includes the kiln body structure, a controllable air injection system, and an atmosphere control system.

[0021] The kiln body structure includes an outer insulation structure, a middle insulation structure, and an inner refractory structure; the controllable air injection system is symmetrically arranged inside the furnace space, and the controllable air injection system includes: an air source, an air flow meter, an air nozzle, and an air duct; the atmosphere control system includes a thermocouple and an oxygen analyzer.

[0022] The controllable air injection system is symmetrically arranged inside the furnace space, including: Air source: Connected to multiple air flow meters via pipes to provide combustion air.

[0023] Air flow meter: Located on both sides of the furnace, used to detect the air flow rate entering the furnace.

[0024] Air nozzles: They are evenly arranged along the side wall or top of the front part of the kiln activation section or a specific location (such as the concentrated release of volatiles and the primary reaction zone), and are connected to the air flow meter and extend into the furnace to inject air into the combustion zone.

[0025] Gas passage: Located inside the refractory bricks, it allows externally supplied combustion air to enter the combustion reaction zone in the furnace space.

[0026] The atmosphere control system includes: Thermocouple: Located inside the furnace chamber to detect the temperature inside the furnace chamber.

[0027] Oxygen analyzer: Located inside the furnace, used to detect the oxygen content inside the furnace.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows: Energy saving and consumption reduction: The volatile combustible gas released by combustion pyrolysis generates heat energy, which directly provides part of the heat required for activation, reducing the need for external heating, and the energy saving effect can reach 15%-30%.

[0029] Simplified equipment and control: By consuming oxygen through controlled combustion, an anaerobic or reducing environment can be created and maintained in the later part of the activation section without relying on strict equipment sealing and high-purity inert gas purging, thus reducing the requirements for equipment airtightness and inert gas consumption.

[0030] Stable product quality: The control system uses a PID algorithm to control the temperature of the core area of ​​the activation section within ±10℃ and the oxygen concentration below 0.8%, ensuring the stable progress of the activation reaction and good product stability and consistency.

[0031] Environmentally friendly: The volatile combustible gases released during thermal decomposition are directly utilized, reducing energy waste and pollution caused by external emissions and realizing the secondary utilization of resources. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a front view of the furnace chamber of a pusher kiln.

[0034] Figure 2 This is a side sectional view of the furnace chamber of a pusher kiln.

[0035] Figure 3 This is a main sectional view of the furnace chamber of a pusher kiln. Detailed Implementation

[0036] To make the technical problem to be solved, the technical solution, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0037] The main objective of this invention is to address the critical issue of high energy consumption and the contradiction between high furnace environmental control in the alkaline activation process for preparing porous carbon. This invention innovatively introduces a precise amount of air to completely burn the volatile combustible gases generated from the pyrolysis of biomass precursors under controlled conditions. This not only achieves energy conservation and consumption reduction but also precisely consumes oxygen within the furnace, more effectively creating and maintaining the anaerobic environment necessary for the activation reaction, thus fundamentally simplifying the complexity of environmental control.

[0038] To achieve the above objectives, this invention integrates a key "controllable air injection system" and a "combustion reaction zone" into the traditional pusher kiln system. The main new structures include: an air flow meter, air ducts, air nozzles, and supporting online temperature and atmosphere monitoring sensors (such as thermocouples and oxygen analyzers). These components, together with the kiln body (including the preheating section, activation section, and cooling section), constitute a closed-loop control system. These new structures ensure that the injected air immediately mixes with the volatile combustible gases (such as H2, CO, CH4, etc.) generated by the pyrolysis of biomass precursors and diffused into the area, and undergoes a controlled combustion reaction at a high temperature. This combustion process releases a large amount of reaction heat, directly and efficiently increasing the temperature of the local reaction zone and adjacent furnace space. This additional heat energy effectively compensates for the external heat energy input required for the activation process through thermal radiation, convection, and conduction, thereby significantly reducing the overall energy consumption of the system. In addition, the control system (not shown) dynamically adjusts the output of the air nozzles based on the real-time temperature and oxygen concentration signals fed back by sensors set at key process points, thereby achieving precise and continuous control of the air injection volume, and ultimately achieving the dual purpose of maintaining the target process temperature and creating a stable anaerobic activation atmosphere.

[0039] The first aspect of this invention provides a method for preparing porous carbon, comprising: S1-Feed: The biomass precursor treated with alkali solution is carried by the pusher plate into the kiln and passes through each temperature zone of the kiln in sequence; S2 - Preheating: The temperature of the preheating section is controlled at 200-250℃ to allow the biomass precursor to undergo pyrolysis and release volatile combustible gases; S3 - Controllable Air Injection: When the biomass precursor after S2 treatment is carried by the pusher plate into the front of the activation section, the online monitoring sensor detects the temperature and residual oxygen concentration in the area in real time and feeds the signal back to the control system. The control system then instructs the precise metering fan to operate and inject a quantitative amount of air into the front of the activation section through the air duct and air injection nozzle. S4 - Controlled Combustion: The air injected in S3 reacts with the volatile combustible gas released in S2 to replenish the heat required for the activation stage; S5 - Atmosphere Transformation and Activation: The combustion reaction in S4 not only consumes the oxygen injected in S3, but also continuously consumes the oxygen-consuming components in the pyrolysis gas, thereby rapidly transforming and stabilizing the atmosphere in the furnace, especially in the later part of the activation section, into an anaerobic or reducing environment with extremely low (even close to zero) oxygen content, controlling the temperature in the later part of the activation section at 755-825℃, and activating the biomass precursor.

[0040] S6 - Post-processing: After the biomass precursor is activated by steps S1-S5, it is subjected to acid washing, water washing and drying to obtain porous carbon products.

[0041] in, The biomass precursors mentioned in step S1 include one or more of wood, nutshells, or straw.

[0042] The soaking alkaline solution mentioned in step S1 refers to immersing the biomass precursor in a potassium hydroxide or sodium hydroxide solution with a mass concentration of 10%-50% for 1-10 hours.

[0043] In step S2, the temperature control range of the preheating section is 200-250℃.

[0044] The volatile combustible gas mentioned in step S2 includes one or more of hydrogen, carbon monoxide, or methane. In conventional processes, these gases are typically extracted and incinerated, with no energy utilized. In this invention, these pyrolysis gases are introduced into the subsequent activation stage along with the biomass precursor.

[0045] The air injection amount in step S3 is much lower than the stoichiometric ratio required for complete combustion of pyrolysis gases, with the aim of achieving a controllable incomplete combustion environment. Specifically, the air injection amount in step S3 is 15%-50% of the air required for theoretical complete combustion; preferably 20%-40%; more preferably 25%-35%.

[0046] In step S3, the control system precisely measures the amount of air to be injected according to the PID algorithm, thereby synchronously adjusting the fan operation.

[0047] The PID algorithm uses the following formula: The combustion reaction described in step S4 includes: 2CO + O2 → 2CO2 CH4 + 2O2 → CO2 + 2H2O 2H₂ + O₂ → 2H₂O In step S5, the oxygen content in the latter part of the activation section is controlled and stabilized within the range of <0.8%, preferably <0.5%, and more preferably <0.3%.

[0048] Explanation of the principle of the method of the present invention The injected air mixes instantly with the pyrolysis volatile combustible gases permeating the furnace, and a combustion reaction occurs. This process follows the core principles below: Energy internal circulation and energy-saving principle: The combustion reaction rapidly releases a large amount of heat (ΔH<0). This heat is directly absorbed by the kiln activation section as a supplementary heat source to maintain the high-temperature activation environment (usually 700-900℃), thereby significantly reducing the energy input of external heating systems (such as electric heating elements or gas burners) and achieving significant energy saving and consumption reduction. The chemical energy of the pyrolysis gas is utilized on-site and efficiently.

[0049] The principle of atmosphere self-balancing and simplified control: The limited amount of oxygen injected is rapidly consumed while initiating combustion. The combustion reaction not only consumes the injected oxygen but also continuously consumes oxygen-consuming components in the pyrolysis gas. As a result, downstream of the combustion zone, the furnace atmosphere rapidly transforms into and is stably maintained in an anaerobic or reducing environment with extremely low (even close to zero) oxygen content. This environment is essential for alkali-activated reactions (such as the reaction of KOH, NaOH, and carbon materials) and effectively prevents the raw materials from being oxidized and burned off at high temperatures.

[0050] This invention also provides a furnace device, which is arranged above a support and in a long strip along the material conveying direction. Its structure, from the outside to the inside, includes an insulation board layer, an insulation brick layer, a refractory brick layer, and a furnace space formed therein.

[0051] Specifically, the furnace equipment can be divided into multiple zones along the material conveying direction, and the furnace structure of each zone includes the kiln body structure, a controllable air injection system, and an atmosphere control system.

[0052] The kiln body structure includes: External insulation structure: An insulation board is installed on the outside of the kiln body to reduce heat loss.

[0053] Intermediate insulation structure: Insulating bricks are installed on the inner side of the insulation board to form an insulation structure and reduce heat conduction to the outside.

[0054] Inner refractory structure: Refractory bricks are set inside the insulating bricks. The refractory bricks enclose and form a furnace space that extends along the material conveying direction. It can withstand the high-temperature combustion environment and is used to accommodate the pusher plate and the sintered material.

[0055] The controllable air injection system is symmetrically arranged inside the furnace space, including: Air source: Connected to multiple air flow meters via pipes to provide combustion air.

[0056] Air flow meter: Located on both sides of the furnace, used to detect the air flow rate entering the furnace.

[0057] Air nozzles: They are evenly arranged along the side wall or top of the front part of the kiln activation section or a specific location (such as the concentrated release of volatiles and the primary reaction zone), and are connected to the air flow meter and extend into the furnace to inject air into the combustion zone.

[0058] Gas passage: Located inside the refractory bricks, it allows externally supplied combustion air to enter the combustion reaction zone in the furnace space.

[0059] The atmosphere control system includes: Thermocouple: Located inside the furnace chamber to detect the temperature inside the furnace chamber.

[0060] Oxygen analyzer: Located inside the furnace, used to detect the oxygen content inside the furnace.

[0061] The following description is based on specific embodiments: Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available, and techniques not described in detail were performed according to standard methods well known to those skilled in the art.

[0062] The furnace equipment used in the embodiments and comparative examples of this invention is divided into 8 zones along the material conveying direction, of which zones 1-2 are preheating zones, zones 3-6 are activation zones, and zones 7-8 are cooling zones. The process parameters and effect evaluation of the scheme are shown in Tables 1-2 below.

[0063] Table 1 Process parameters and effects Table 2 Specific temperatures of each zone during the activation process The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing porous carbon, comprising: S1 - Feeding: The biomass precursor treated with alkali solution is fed into the kiln and passes through each temperature zone of the kiln in sequence; S2 - Preheating: The temperature of the preheating section is controlled at 200-250℃ to allow the biomass precursor to undergo pyrolysis and release volatile combustible gases; S3 - Air Injection: Inject a preset amount of air into the front of the activation section; S4 - Controlled Combustion: The air injected in step S3 reacts with the volatile combustible gas released in S2 to undergo a combustion reaction; S5-Activation: Control the temperature in the latter part of the activation section at 755-825℃; S6 - Post-treatment: Acid washing, water washing and drying are performed to obtain porous carbon products.

2. The method as described in claim 1, characterized in that, The biomass precursors mentioned in step S1 include one or more of wood, nutshells, and straw.

3. The method as described in claim 1, characterized in that, The alkaline treatment mentioned in step S1 refers to immersing the biomass precursor in a potassium hydroxide or sodium hydroxide solution with a mass concentration of 10%-50% for 1-10 hours.

4. The method as described in claim 1, characterized in that, The volatile combustible gas mentioned in step S2 includes one or more of hydrogen, carbon monoxide, or methane.

5. The method according to any one of claims 1-4, characterized in that, The preset amount mentioned in step S3 is 15%-50% of the air required for theoretical complete combustion.

6. The method as described in claim 5, characterized in that, The preset amount is 25%-35% of the air required for theoretical complete combustion.

7. The method according to any one of claims 1-6, characterized in that, Step S3 further includes: using an online monitoring sensor to detect the temperature and residual oxygen concentration at the front of the activation section in real time, and feeding the signal back to the control system; the control system calculates the amount of air to be injected based on this, and injects the corresponding amount of air.

8. A furnace apparatus for producing porous carbon, for performing the method as described in any one of claims 1-7, the furnace apparatus being arranged in a long strip along the material conveying direction, the furnace apparatus comprising, from the outside to the inside, an insulation board layer, an insulation brick layer, a refractory brick layer, and a furnace space located at the center.

9. The structure as described in claim 8, characterized in that, The furnace equipment is divided into multiple zones along the material conveying direction. The furnace structure of each zone includes the kiln body structure, a controllable air injection system, and an atmosphere control system.

10. The structure as described in claim 9, characterized in that, The kiln body structure includes an outer insulation structure, a middle insulation structure, and an inner refractory structure; the controllable air injection system is symmetrically arranged inside the furnace space, and the controllable air injection system includes: an air source, an air flow meter, an air nozzle, and an air duct; the atmosphere control system includes a thermocouple and an oxygen analyzer.

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