Pyrolysis process with participation of carbon dioxide

Abstract

The invention relates to the technical field of pyrolysis processes, and discloses a carbon dioxide-participated pyrolysis process, which comprises the following steps: mixing carbon dioxide and combustion-supporting gas according to a set proportion to form a pyrolysis atmosphere, regulating and controlling the temperature, atmosphere components, gas flow and residence time, and carrying out a pyrolysis reaction, unreacted carbon dioxide is recycled, is treated by a gas separation and purification device and then is reintroduced into a pyrolysis system for cyclic utilization. Carbon dioxide is introduced to regulate the pyrolysis atmosphere, combustion-supporting gas is supplied in proportion, the pyrolysis reaction efficiency and product activity are improved, meanwhile, unreacted carbon dioxide is recycled through a gas separation and purification device, cyclic utilization is achieved, greenhouse gas emission is reduced, a PLC intelligent control system is adopted to finely adjust the atmosphere components and flow, and the product quality is improved. The method realizes flexible regulation and control of product composition, optimizes energy distribution in the pyrolysis process through a temperature and component monitoring system, effectively improves reaction stability, and reduces energy consumption and carbon emission.

Description

Technical Field

[0001] The present invention relates to the technical field of pyrolysis processes, in particular to a pyrolysis process involving carbon dioxide. Background Art

[0002] Conventional pyrolysis processes typically use air as the pyrolysis atmosphere, with nitrogen accounting for the majority (approximately 78%). As an inert gas, nitrogen does not participate in the pyrolysis reaction and only acts as a carrier gas. However, while the presence of nitrogen helps remove heat from the reaction system, it does not provide effective catalysis for the pyrolysis reaction. Therefore, the use of nitrogen not only increases the gas volume during the pyrolysis process but can also lead to reduced reaction efficiency.

[0003] Furthermore, air contains oxygen. Although oxygen concentrations are typically low during pyrolysis, under high-temperature conditions, oxygen can react with carbon in the raw coal to produce carbon dioxide, gases, and water vapor. While oxygen participation in the reaction can provide a certain degree of combustion, this reaction is not the primary purpose of pyrolysis and often results in the formation of byproducts, affecting the purity and quality of the pyrolysis products.

[0004] Currently, carbon dioxide has not been effectively utilized in traditional pyrolysis processes. Carbon dioxide itself is a gas with high thermochemical reactivity. When reacting with substances in organic raw coal, it can promote the pyrolysis reaction and increase the production of some key products, such as carbon monoxide and hydrogen. In addition, carbon dioxide can also react with carbon materials to produce gaseous products, thereby changing the product distribution during the pyrolysis process. However, in the existing technology, carbon dioxide is often regarded as a direct exhaust gas and has not been effectively utilized in the pyrolysis process, resulting in a waste of resources and a negative impact on the environment.

[0005] In order to improve the efficiency of the pyrolysis reaction and optimize the product composition, existing technologies attempt to control the reaction atmosphere by adding combustion-supporting gases or adjusting the atmosphere composition, but these methods often face problems such as limited adjustment range, high cost and heavy environmental burden. In addition, carbon dioxide, as a major greenhouse gas, directly enters the atmosphere during the emission process, further exacerbating the pressure of climate change. Therefore, how to reduce carbon dioxide emissions during the pyrolysis process and improve reaction efficiency and optimize product distribution by recycling carbon dioxide has become a problem that needs to be solved urgently in the current pyrolysis process. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the present invention provides a pyrolysis process involving carbon dioxide, which solves the technical problems of low energy utilization, uncontrollable product composition and large carbon dioxide emissions in the traditional pyrolysis process.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions: A pyrolysis process involving carbon dioxide comprises the following steps:

[0008] S1. Mixing carbon dioxide and combustion-supporting gas in a set ratio through a mixer to form a pyrolysis atmosphere;

[0009] S2, mixing the pyrolysis atmosphere with raw coal to form a reaction mixture;

[0010] S3, sending the reaction mixture into a pyrolysis device, performing a pyrolysis reaction under heating conditions to generate gaseous, liquid and solid products;

[0011] S4, separating the pyrolysis products to obtain synthesis gas, tar and semi-coke;

[0012] S5, recovering unreacted carbon dioxide during the pyrolysis process and reintroducing it into the mixer for recycling;

[0013] S6. During the pyrolysis process, the temperature, atmosphere composition or reaction gas composition are monitored in real time, and the pyrolysis parameters are adjusted according to the monitoring results.

[0014] Preferably, the combustion-supporting gas in step S1 is any one of oxygen, air or oxygen-rich mixed gas, and the volume fraction ratio of carbon dioxide to combustion-supporting gas in step S1 is adjustable in the range of 0%-100%, wherein when the volume fraction of the combustion-supporting gas is 100%, it is pure oxygen pyrolysis, when the volume fraction of carbon dioxide is 100%, it is inert atmosphere pyrolysis, and when the volume fraction of carbon dioxide is greater than 0 and less than 100%, it is a carbon dioxide-rich pyrolysis atmosphere.

[0015] Preferably, in step S1, the mixer is provided with a flow regulating device and a gas ratio control valve for adjusting the supply ratio of carbon dioxide and combustion-supporting gas.

[0016] Preferably, in the step S2, the raw coal is pulverized before being mixed with the pyrolysis atmosphere, and the particle size is controlled to be less than 10 mm, and is contacted and mixed with the pyrolysis atmosphere in a co-current, counter-current or cross-current manner.

[0017] Preferably, the pyrolysis device in step S3 is a fixed bed, fluidized bed or rotary kiln structure, the pyrolysis temperature is controlled between 300° C. and 1000° C., and the system pressure is between normal pressure and 0.8 MPa.

[0018] Preferably, after the synthesis gas in the pyrolysis product of step S4 is purified to remove tar and impurities, a portion is introduced into the mixer as reflux gas, and a portion is sent out as a gas product. The synthesis gas in step S4 contains carbon monoxide, hydrogen and methane. The tar in step S4 is separated through the purification section, and the semi-coke in step S4 is discharged through the solid collection system.

[0019] Preferably, the unreacted carbon dioxide in step S5 is treated by a gas separation and purification device and then refluxed to the mixer to participate in the pyrolysis reaction again.

[0020] Preferably, the temperature and atmosphere monitoring in step S6 is achieved through the configured temperature sensor, gas composition analyzer and gas flow meter, and the ratio of carbon dioxide to combustion-supporting gas, heating power or gas residence time is adjusted through the PLC control system.

[0021] The present invention provides a pyrolysis process involving carbon dioxide, which has the following beneficial effects:

[0022] 1. The present invention achieves the technical effect of improving the pyrolysis reaction efficiency and the content of active components in the gas phase products by introducing carbon dioxide as a control atmosphere into the pyrolysis system and combining it with the proportional supply of combustion-supporting gas. Compared with the pyrolysis process in the prior art that relies on a single heat source or inert atmosphere, this solution stimulates secondary cracking and gasification reactions, thereby improving the degree of tar cracking and increasing the yield of carbon monoxide and hydrogen, thereby solving the shortcomings of traditional technologies in terms of low energy efficiency conversion rate and insufficient calorific value of products.

[0023] 2. The present invention realizes the efficient reuse of CO2 by constructing a gas separation and purification device, and returns the unreacted carbon dioxide to the mixer after treatment to participate in the closed-loop control path of re-pyrolysis, thereby achieving the environmental protection effect of reducing direct greenhouse gas emissions. Unlike the existing technology that often directly discharges the reaction exhaust gas or only uses it for simple utilization, this solution fully realizes the resource utilization of carbon dioxide while ensuring the reaction activity, and solves the problems of uncontrollable carbon emissions and poor system circulation capacity in the original process.

[0024] 3. The present invention introduces a gas composition analyzer and flow meter into the pyrolysis system, and cooperates with the PLC intelligent control logic to finely adjust the flow of CO2, supporting gas and synthesis gas, thereby achieving the technical effect of flexibly regulating the product composition according to the target product requirements. Compared with the existing pyrolysis system, which lacks real-time feedback on the reaction process and has a single product structure, this method can change the gas-solid product ratio by adjusting the atmosphere concentration and residence time while maintaining the reaction stability, thereby solving the problem of being unable to customize the product output structure for different application scenarios.

[0025] 4. This invention utilizes temperature sensors and a composition monitoring system to track temperature changes and gas composition fluctuations in real time during the pyrolysis process. A PLC control module automatically optimizes heating power and gas supply parameters, enabling intelligent dynamic regulation of the pyrolysis reaction process and reducing carbon emissions at the source. Compared to traditional pyrolysis processes, which suffer from high energy consumption, low carbon efficiency, and the susceptibility to overheating side reactions, this solution effectively addresses the environmental burden of uneven energy distribution and poor temperature control accuracy in pyrolysis systems, and holds great promise for industrial adoption. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the present specification. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0028] Please see the attached Figure 1 The embodiment of the present invention provides a pyrolysis process involving carbon dioxide, comprising the following steps:

[0029] S1. Mixing carbon dioxide and combustion-supporting gas in a set ratio through a mixer to form a pyrolysis atmosphere;

[0030] In this embodiment, step S1 involves mixing carbon dioxide and a combustion-supporting gas in a set ratio to generate the desired pyrolysis atmosphere. This atmosphere plays a decisive role in the entire pyrolysis reaction process, and its composition directly affects the efficiency of pyrolysis and the distribution of products. By adjusting the ratio of carbon dioxide to combustion-supporting gas, the reaction environment can be precisely controlled, thereby optimizing the pyrolysis effect of the coal. Specifically, the mixer is used to provide adjustable gas flow and concentration distribution for subsequent reactions under different atmosphere compositions, ensuring the stable progress of the reaction at each stage.

[0031] Generally, the combustion-supporting gas can be oxygen, air, or an oxygen-enriched mixture. Oxygen, air, and oxygen-enriched gas have different oxygen concentrations, which in turn affect the reaction rate and distribution of pyrolysis products during pyrolysis. For example, a pure oxygen atmosphere significantly increases the reaction rate but may also lead to side reactions; an air atmosphere, with its mixture of oxygen and nitrogen, may be more moderate; and an oxygen-enriched gas provides a moderate oxygen concentration without being excessive, making it suitable for a more stable pyrolysis reaction.

[0032] Alternatively, the ratio of carbon dioxide to combustion-supporting gas can be adjusted within a range of 0% to 100%, with the specific ratio selected depending on the type of coal and the desired product characteristics. When the volume fraction of the combustion-supporting gas is 100%, the atmosphere is pure oxygen, resulting in a more intense reaction and suitable for applications requiring higher pyrolysis efficiency. When the volume fraction of carbon dioxide is 100%, the atmosphere becomes inert, suppressing oxidation reactions during pyrolysis and helping to better maintain the chemical stability of the feedstock. When the volume fraction of carbon dioxide is between 0 and 100%, the atmosphere becomes a carbon dioxide-rich pyrolysis atmosphere, which optimizes the selectivity and reaction rate of pyrolysis products by regulating the reduction reaction pathway of CO2 with coal.

[0033] Specifically, in some embodiments, the mixer precisely adjusts the supply ratio of carbon dioxide and combustion-supporting gas through a flow control device and a gas ratio control valve. The flow control device adjusts the gas flow rate according to preset gas flow requirements, ensuring a stable and consistent gas ratio and flow rate. The gas ratio control valve adjusts the gas ratio based on actual needs, ensuring that each reaction occurs within the set atmosphere.

[0034] In one possible implementation, the mixer, through continuous flow adjustment and real-time control, can adjust the atmosphere ratio in real time based on the dynamic changes in the reaction, further improving the precision of reaction control. This approach is particularly important for large-scale continuous production processes requiring atmosphere stability, as it can avoid unstable pyrolysis processes and uneven product distribution caused by atmosphere fluctuations.

[0035] The innovation of this invention lies in its ability to precisely control the ratio of carbon dioxide to combustion-supporting gas, enabling pyrolysis process control under varying atmospheres. Compared to traditional single-atmosphere control methods, this invention adjusts the atmosphere composition to flexibly adjust the efficiency and product characteristics of the pyrolysis process according to specific needs. This flexible atmosphere control capability enables the invention to achieve superior results when processing different coal types or optimizing specific products (such as syngas and tar).

[0036] S2, mixing the pyrolysis atmosphere with raw coal to form a reaction mixture;

[0037] After the pyrolysis atmosphere is prepared, it must be introduced into a unit process for contact and mixing with the raw coal to ensure sufficient contact and synergistic effect between the atmosphere and the coal. This mixing process is a crucial link in the pyrolysis process chain, directly determining the development of the subsequent pyrolysis reaction path and the starting point of product formation. To improve the uniformity of the reaction mixture and the efficiency of heat and mass transfer, the present invention systematically designs the contact method between the atmosphere and the coal, the control of the raw material state, and constructs a corresponding pre-mixing scheme based on the basic principle of ensuring process stability and continuity.

[0038] In this embodiment, the pyrolysis atmosphere is mixed with the pretreated raw coal before entering the pyrolysis reaction zone to form a reaction mixture.

[0039] Before mixing with the pyrolysis atmosphere, the raw coal is mechanically pulverized to control its particle size distribution. Generally, the particle size of the pulverized coal is kept below 10 mm to increase the specific surface area and enhance the reaction interface between the coal and the atmosphere. In the high-temperature pyrolysis environment, smaller coal particles effectively shorten the heat conduction path, reduce the temperature difference between the inside and outside of the particles, and increase the pyrolysis rate while also contributing to a higher degree of gasification.

[0040] Alternatively, particle size control can be achieved through multi-stage screening adjustments via a screening system to optimize the adaptability of different coal types. For lignite-like coals with low thermal stability or a strong coking tendency, appropriately reducing the particle size facilitates the stable release of coking precursors. For coals with low volatility and high fixed carbon, particle size optimization can be used to coordinate and control the gas-solid reaction time.

[0041] Specifically, in some embodiments, the mixing method between the raw coal and the pyrolysis atmosphere can be in the form of co-current, counter-current, or cross-current. In the co-current mixing method, the coal and the atmosphere flow in the same direction, which is conducive to the stability of the system pressure and the improvement of the particle carrying efficiency; in the counter-current mixing method, the atmosphere and the coal flow in opposite directions, which can form a stronger convective heat transfer effect under thermal drive, and is suitable for working conditions with more complex pyrolysis paths and limited product desorption rates; the cross-flow method forms an interlaced mixing interface in a multi-stage reactor or modular device, which can take into account both thermal balance and mass transfer efficiency, and is suitable for systems with mixed coals of different particle sizes or a wide range of reaction intensities.

[0042] In one possible implementation, the mixing system incorporates a flow-guiding structure to guide the atmosphere into a defined velocity field before mixing with the coal, ensuring nearly uniform mixing of the gas and solid phases before entering the reactor. This structure can include nozzles, annular channels, or swirling flow disturbances. The specific design is optimized based on parameters such as the coal's bulk density, gas flow rate, and system design load.

[0043] Furthermore, to prevent coal particle re-mixing or blockage caused by airflow impact during the mixing process, the system features a buffer zone and an adjustable gas-to-solid ratio feed control valve to control the amount and rate of coal-to-atmosphere mixing per unit time. This ratio control mechanism not only enables adaptive operation but also maintains a stable gas-to-solid ratio under varying operating pressures and loads, thereby ensuring consistent pyrolysis efficiency and product quality.

[0044] The mixing method designed in this invention significantly improves the initial contact efficiency between the atmosphere and the coal compared to the simple physical mixing methods used in traditional pyrolysis processes. By controlling the particle size, flow pattern, and ratio, the coal particles achieve a dual coupled response of heat transfer and atmosphere penetration during the initial mixing phase. This shortens the activation phase during the subsequent heating process and accelerates the initiation of the cracking precursor reaction.

[0045] In addition, under certain conditions, the CO2 in the atmosphere can begin to undergo in-situ reduction reaction with some carbonaceous components in the coal at this stage (C+CO2→2CO). The occurrence of this reaction in the mixing zone accumulates synthesis gas components in advance for the subsequent pyrolysis stage, provides pre-loading of heat and gas-phase active substances, and helps to improve the synergy of the overall reaction path.

[0046] In summary, step S2 not only achieves effective mixing of the pyrolysis atmosphere and coal, but also provides a stable, uniform, and fully reactive starting state for the subsequent pyrolysis reaction through flow pattern control, particle size adjustment, gas-solid ratio setting, and mixing device structure optimization. It is one of the key basic links for achieving continuous and efficient operation of the technical solution of the present invention.

[0047] S3, sending the reaction mixture into a pyrolysis device, performing a pyrolysis reaction under heating conditions to generate gaseous, liquid and solid products;

[0048] In this embodiment, step S3 involves feeding the reaction mixture into a pyrolysis unit, where it undergoes a pyrolysis reaction under specific heating conditions. This step is a core component of the entire pyrolysis process. By controlling temperature, pressure, and other conditions, the raw coal is decomposed and converted into gaseous, liquid, and solid products. By appropriately selecting the type of pyrolysis unit and controlling the reaction conditions, the pyrolysis efficiency and the product's utility value can be maximized.

[0049] Specifically, the pyrolysis device can be a fixed bed, fluidized bed or rotary kiln structure. These different types of pyrolysis devices each have unique fluid mechanics and thermodynamics characteristics, and can be optimized according to the specific coal type, reaction requirements and product needs.

[0050] Generally speaking, fixed bed structures are suitable for relatively stable, batch processing processes; fluidized beds are more suitable for large-scale, continuous flow processing and have better temperature uniformity; rotary kilns are suitable for processing situations where the pyrolysis process is more complex and the reactants are easily affected by the external atmosphere.

[0051] As an option, the pyrolysis temperature is controlled between 300° C. and 1000° C. This temperature range can ensure that the organic matter in the raw coal undergoes cracking reaction during the pyrolysis process, while avoiding the occurrence of side reactions or the generation of harmful gases due to excessively high temperatures.

[0052] Specifically, at lower temperatures, the volatile matter in the coal is released more fully, while at higher temperatures it helps further cracking of fixed carbon. The composition and properties of the products can change according to the temperature regulation.

[0053] For example, at temperatures below 500°C, coals with higher volatile content will produce more gaseous products under milder pyrolysis conditions, while pyrolysis at higher temperatures may promote the formation of solid products such as coke. Depending on the specific properties of the coal, adjusting the temperature within different ranges can optimize the ratio of gas, liquid, and solid products and their chemical properties.

[0054] In addition, the control range of the system pressure is set from atmospheric pressure to 0.8 MPa. When pyrolysis is carried out at atmospheric pressure, the reaction process is mainly affected by temperature, and the distribution of gaseous products is relatively wide; under conditions slightly higher than atmospheric pressure, especially in the pressure range of 0.2 MPa to 0.8 MPa, excessive expansion of the gas can be limited to a certain extent, thereby increasing the yield of liquid and solid products. An increase in system pressure is usually accompanied by an increase in the pyrolysis reaction rate, but the pressure needs to be reasonably controlled to avoid affecting the stability of the reaction due to excessive gas expansion.

[0055] Specifically, in some embodiments, the combined regulation of temperature and pressure allows the reaction atmosphere to better adapt to the pyrolysis characteristics of different coal types. For example, coal with a high volatile content will have a higher gasification efficiency at a lower temperature, while coal with a low volatile content may require a higher temperature and moderate pressure to achieve a more ideal pyrolysis effect.

[0056] In one possible implementation, the reaction zone of the pyrolysis unit is equipped with a dual temperature and pressure control system. This system monitors the status of the reactants in real time and automatically adjusts heating power and air flow based on parameters such as temperature, pressure, and flow rate to ensure optimal pyrolysis conditions throughout the reaction. The flexibility of this control system enables the pyrolysis reaction to continue stably under varying operating conditions, improving product yield and quality.

[0057] The precise control of temperature, pressure, and equipment selection during the pyrolysis process significantly improves coal pyrolysis efficiency and optimizes the types and ratios of products according to different coal types and production requirements. By rationally selecting pyrolysis equipment and optimizing reaction conditions, incomplete pyrolysis can be effectively reduced, the combustion calorific value of gaseous products and the stability of liquid products can be increased, providing a more advanced technical path for the efficient utilization of coal.

[0058] S4, separating the pyrolysis products to obtain synthesis gas, tar and semi-coke;

[0059] After the pyrolysis reaction is complete, the product formed within the system is a mixture of gas, liquid, and solid phases. To achieve efficient resource utilization and the refined separation requirements of downstream applications, the pyrolysis products require systematic separation and processing. This step plays a connecting role in the overall pyrolysis process, fulfilling both the purification and classification of the products and establishing a circulation path for the reflux of the synthesis gas, which is of great significance for improving the system's thermal efficiency and resource recovery rate.

[0060] In this embodiment, the products obtained after the pyrolysis reaction are sent to the separation module through the product outlet channel, and are purified and collected according to their physical state and composition differences, and finally three target products, synthesis gas, tar and lignite, are obtained.

[0061] Specifically, the pyrolysis products first enter the high-temperature gas-solid separator, where the solid matter lignite is effectively removed under the synergistic action of gravity sedimentation and rotational separation, and is discharged from the system through a solid collection system equipped with cooling and conveying functions.

[0062] Generally speaking, the particle size of lignite is between 3 and 25 mm, and its density is greater than that of pyrolysis gas. After classification treatment, it can be used as industrial fuel or metallurgical reducing agent.

[0063] In some embodiments, the solids collection system is equipped with a multi-stage cooling structure, using circulating water or nitrogen to prevent spontaneous combustion of the semi-coke during discharge. The system can also be equipped with an inert atmosphere protection zone to isolate the pyrolysis carbon residue from the air, further ensuring safety.

[0064] After separating the solid products, the gas-liquid mixture flows through a condenser for temperature control, maintaining a temperature range of 25°C to 60°C, to achieve a preliminary separation of the gaseous products from the tar. Tar, the liquid organic product of the pyrolysis reaction, primarily contains polycyclic aromatic hydrocarbons, phenols, ketones, and esters, requiring further purification and extraction.

[0065] As an option, the tar purification process includes filtration, centrifugation, and water washing. The specific process can be adjusted according to the type of coal used and the pyrolysis conditions. The purified tar can be used as a chemical feedstock or a fuel oil base component. The light components contained in the tar can be extracted by vacuum distillation for subsequent fine chemical synthesis.

[0066] The gas phase, or syngas, undergoes initial purification in a dust collector and condenser before entering a gas purification unit to further remove residual tar, particulate matter, and acidic impurities (such as H2S and NH3). Gas purification can be performed using spray absorption, dry adsorption, or membrane separation to meet the purity requirements of different applications.

[0067] In one possible implementation, the purified synthesis gas can be monitored online by a gas composition analysis device, where the main components include carbon monoxide (CO), hydrogen (H2) and methane (CH4). The gas mixture has a certain calorific value and has the potential for reuse.

[0068] As part of a closed-loop process, a portion of the syngas is piped back to the mixer, where it is remixed with the feed coal and used as a supplemental gas source for the pyrolysis atmosphere. This recirculation design helps conserve external energy input and create a self-sufficient pyrolysis cycle. The remaining syngas is exported as product gas for downstream applications such as industrial gas, combined heat and power generation, and hydrogen production.

[0069] Furthermore, to maximize separation efficiency, the system can be equipped with an online control module to dynamically adjust the tar condensation temperature, purification unit switching frequency, and reflux ratio based on changes in gas flow and composition. This control strategy enhances the system's ability to adapt to complex operating conditions and improves the operational stability and economic efficiency of the pyrolysis system.

[0070] In summary, step S4 achieves efficient extraction and classified utilization of gas, liquid, and solid three-phase pyrolysis products through multi-stage phase separation and target product diversion, constituting a key resource recovery and utilization unit in the coal-based pyrolysis system of the present invention. This not only ensures the closed-loop operation of the system, but also provides high-quality raw material support for downstream processes. The diversified configuration and reflux design of this separation system enhance the overall coordinated control capabilities of the system and are an important technical foundation for the present invention to achieve a high thermal efficiency and low energy consumption operation mode.

[0071] S5, recovering unreacted carbon dioxide during the pyrolysis process and reintroducing it into the mixer for recycling;

[0072] During the pyrolysis reaction, external gas is usually introduced into the system as a control medium to increase the proportion of active components in the gaseous products and adjust the reaction atmosphere. Carbon dioxide, a commonly used modifying gas in pyrolysis processes, can not only be used to control the thermal balance of the reaction system, but can also undergo a secondary gasification reaction with some organic components to increase the production ratio of carbon monoxide and hydrogen. Because not all carbon dioxide can participate in the pyrolysis reaction under actual working conditions, some unreacted CO2 will flow out with the gaseous products. In order to reduce resource waste and achieve a closed-loop system, this part of the gas needs to be effectively recovered and reused.

[0073] In this embodiment, the gaseous portion of the pyrolysis products undergoes condensation and purification before entering a dedicated gas separation device. This device, based on physical adsorption, pressure swing adsorption (PSA), or membrane separation technology, can separate unreacted carbon dioxide from the mixed gas and extract high-purity CO2 without compromising the quality of other gaseous products.

[0074] Generally, CO2 separation is preferably achieved using a multi-stage membrane separation structure or PSA process. The former offers advantages such as low energy consumption and continuous and stable operation, while the latter facilitates achieving a dynamic balance between separation efficiency and purity. The gas separation unit is equipped with an online gas analysis system to monitor the CO2 content in the outlet gas, facilitating the stability control of the recovery process.

[0075] Specifically, the separated CO2 enters a purification unit equipped with dehydration, impurity removal, and cooling modules to ensure that the reflux gas does not carry moisture or harmful impurities that could affect the mixer and subsequent pyrolysis processes. Common impurities include small amounts of sulfides, phenols, and high-boiling-point organic gases. These impurities can be treated in the purification process using cooling absorption, alkaline solution washing, or solid adsorbents.

[0076] In one possible implementation, the purified carbon dioxide is temporarily stored in a gas buffer tank, and its reflux rate is adjusted by a mass flow controller so that it forms a mixed gas with the raw gas newly entering the mixer (including the reflux portion of the synthesis gas), thereby adjusting the reducing property and heat load distribution of the pyrolysis reaction atmosphere.

[0077] In some embodiments, the CO2 recovery ratio is controlled within a range of 10% to 35% of the total gas production. The specific ratio is adjusted based on the coal type, reaction temperature, and product requirements. Research has shown that appropriate CO2 recirculation can promote tar cracking, increase CO and H2 production, and inhibit excessive coke accumulation.

[0078] As an option, part of the CO2 can also react with the solid carbon residue produced during the pyrolysis reaction to undergo Boudouard reaction. The reaction proceeds spontaneously in the high-temperature zone (>700°C), providing an additional source of CO for the system, which is beneficial to improving the calorific value of the synthesis gas and enhancing the carbon cycle capacity within the system.

[0079] The CO2 recirculation system is designed to operate independently, forming a coordinated control mechanism with the syngas recirculation system. This configuration not only ensures a stable gas supply but also automatically adjusts the recirculation ratio when system load fluctuates, maintaining process stability and reaction balance during the pyrolysis process.

[0080] In summary, step S5, by recovering and purifying the unreacted CO₂ during the pyrolysis process, not only achieves efficient utilization of the feed gas and reduces the gas emission load, but also effectively establishes a carbon cycle pathway within the system centered on CO₂. This technical solution contributes to the goal of a green and energy-efficient pyrolysis process and is a key component of the present invention in terms of efficient resource recovery and system self-circulation control. It has clear engineering feasibility and industrial promotion value.

[0081] S6. During the pyrolysis process, the temperature, atmosphere composition or reaction gas composition are monitored in real time, and the pyrolysis parameters are adjusted according to the monitoring results.

[0082] During the continuous operation of the pyrolysis system, the stability of the pyrolysis reaction and the quality of the products are easily disturbed by multiple factors such as raw material fluctuations, environmental changes, and changes in system load. In order to achieve precise control of the reaction process and ensure that key parameters such as atmosphere composition and reaction temperature are always in the optimal state, a real-time monitoring and automatic adjustment mechanism must be introduced during the reaction process. This mechanism, as the dynamic control center of the entire process, is directly related to the reaction efficiency, product composition, and the thermal energy utilization level of the system. Together with the aforementioned steps such as gas reflux and product separation, it forms an information-feedback-execution closed-loop structure.

[0083] In this embodiment, step S6 implements real-time monitoring of temperature, atmosphere composition, and gas composition by deploying multiple sensor components at key locations within the pyrolysis apparatus. Specifically, multiple thermocouples or infrared temperature sensors are installed within the pyrolysis reactor and at its outlet to capture the instantaneous temperature distribution within the reaction zone and its boundary regions.

[0084] Typically, the pyrolysis temperature setting range is 300°C to 1000°C, and can be adjusted within this range based on the target product requirements. The system's temperature control module adjusts the heating power of the electric heater or gas furnace in real time based on sensor feedback, achieving rapid response and precise compensation.

[0085] As an option, temperature data can also be linked with changes in gas composition to identify whether there is abnormal heat release or reaction stagnation in the reaction, allowing for early risk intervention.

[0086] Atmosphere composition monitoring utilizes a spectral gas analyzer, capable of continuously measuring the concentration ratios of key components in the syngas, including CO, H₂, CH₄, and CO₂, with a response time of less than 2 seconds and an adjustable sampling frequency. This analyzer, located between the reactor outlet pipe and the separation module, ensures that the data accurately reflects the composition of the gaseous products after the reaction in real time.

[0087] In some embodiments, the gas flow monitoring system utilizes differential pressure or thermal mass flow meters located at each gas inlet branch, including the return CO2 path, the fresh combustion-supporting gas path, and the syngas return line. By analyzing the mass balance between total gas input and output, the reaction residence time can be inferred, assisting the system in determining reaction completion.

[0088] Specifically, the pyrolysis parameter adjustment module is composed of a PLC programmable controller. After receiving signals from the temperature sensor, component analyzer, and flow meter, it calculates and outputs through built-in PID control logic or adaptive model. The controller can automatically adjust the following operating conditions:

[0089] The mixing ratio of carbon dioxide and combustion-supporting gas;

[0090] The heating current of the electric heating unit or the degree of opening of the combustion control valve;

[0091] The opening of the gas inlet throttle valve is used to adjust the residence time.

[0092] In one possible implementation, the PLC system connects to a database, recording real-time data and creating historical trend charts for subsequent operating condition optimization and anomaly tracking analysis. The system features remote monitoring and manual intervention interfaces, allowing operators to adjust control logic weights or set different control strategy scenarios through the human-machine interface (HMI).

[0093] In some embodiments, predictive models based on reaction mechanisms (such as pyrolysis kinetic models) are incorporated to proactively intervene in reactions by comparing real-time data with predicted data. If the system detects a component concentration fluctuation exceeding a threshold or an abnormal temperature increase, the control module automatically reduces the gas input flow rate and increases the cooling capacity of the pyrolysis zone to prevent side reactions or equipment overheating.

[0094] The monitoring and control system also communicates data with the gas purification system. For example, if CO2 concentration in the syngas remains high, indicating incomplete pyrolysis or excessive CO2 recirculation, the system will automatically reduce the CO2 recirculation ratio and prompt the operator to check the reaction activity.

[0095] In summary, step S6 achieves real-time monitoring and dynamic adjustment of key variables in the pyrolysis process by establishing a closed-loop feedback control system encompassing temperature, atmosphere, and gas composition. This system, with its multidimensional monitoring capabilities, rapid response mechanism, and coordinated control logic, is the core technology of the present invention in achieving a highly efficient and stable pyrolysis process. It plays an irreplaceable role in ensuring product quality, safe system operation, and optimized energy utilization.

[0096] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A pyrolysis process involving carbon dioxide, characterized in that: The following steps are involved: S1. Mixing carbon dioxide and combustion-supporting gas in a set ratio through a mixer to form a pyrolysis atmosphere; S2, mixing the pyrolysis atmosphere with raw coal to form a reaction mixture; S3, sending the reaction mixture into a pyrolysis device, performing a pyrolysis reaction under heating conditions to generate gaseous, liquid and solid products; S4, separating the pyrolysis products to obtain synthesis gas, tar and semi-coke; S5, recovering unreacted carbon dioxide during the pyrolysis process and reintroducing it into the mixer for recycling; S6. During the pyrolysis process, the temperature, atmosphere composition or reaction gas composition are monitored in real time, and the pyrolysis parameters are adjusted according to the monitoring results.

2. A pyrolysis process involving carbon dioxide according to claim 1, characterized in that: The combustion-supporting gas in step S1 is any one of oxygen, air or an oxygen-rich mixed gas. The volume fraction ratio of carbon dioxide to the combustion-supporting gas in step S1 is adjustable within the range of 0%-100%, wherein when the volume fraction of the combustion-supporting gas is 100%, it is pure oxygen pyrolysis, when the volume fraction of carbon dioxide is 100%, it is inert atmosphere pyrolysis, and when the volume fraction of carbon dioxide is greater than 0 and less than 100%, it is a carbon dioxide-rich pyrolysis atmosphere.

3. The pyrolysis process involving carbon dioxide according to claim 1, characterized in that: In step S1, the mixer is provided with a flow regulating device and a gas ratio control valve for adjusting the supply ratio of carbon dioxide and combustion-supporting gas.

4. The pyrolysis process involving carbon dioxide according to claim 1, characterized in that: In the step S2, the raw coal is pulverized before being mixed with the pyrolysis atmosphere, and the particle size is controlled to be less than 10 mm. The raw coal is contacted and mixed with the pyrolysis atmosphere in a downstream, countercurrent or cross-current manner.

5. The pyrolysis process involving carbon dioxide according to claim 1, characterized in that: In the step S3, the pyrolysis device is a fixed bed, fluidized bed or rotary kiln structure, the pyrolysis temperature is controlled between 300°C and 1000°C, and the system pressure is between normal pressure and 0.8 MPa.

6. The pyrolysis process involving carbon dioxide according to claim 1, characterized in that: After the synthesis gas in the pyrolysis product of step S4 is purified to remove tar and impurities, a portion is introduced into the mixer as reflux gas, and a portion is sent out as a gas product. The synthesis gas in step S4 contains carbon monoxide, hydrogen and methane. The tar in step S4 is separated through the purification section, and the semi-coke in step S4 is discharged through the solid collection system.

7. The pyrolysis process involving carbon dioxide according to claim 1, characterized in that: The unreacted carbon dioxide in step S5 is processed by a gas separation and purification device and then refluxed to the mixer to participate in the pyrolysis reaction again.

8. The pyrolysis process involving carbon dioxide according to claim 1, characterized in that: The temperature and atmosphere monitoring in step S6 is achieved through the configured temperature sensor, gas composition analyzer and gas flow meter, and the ratio of carbon dioxide to combustion-supporting gas, heating power or gas residence time is adjusted through the PLC control system.

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