Method for preparing methane through pyrolysis of medical waste and application thereof

Abstract

The invention provides a method for preparing methane through pyrolysis of medical waste and application of the method, and relates to the technical field of medical waste treatment and energy recovery, and the method comprises the following steps: pyrolyzing the medical waste to obtain pyrolysis gas, purifying the pyrolysis gas, then carrying out steam reforming reaction to obtain reacted gas, separating and purifying the reacted gas to obtain the methane. Methane is obtained; during pyrolysis, the temperature is increased to 190 DEG C to 210 DEG C and kept for 8 min to 12 min, then the temperature is increased to 390 DEG C to 410 DEG C and kept for 13 min to 17 min, and then the temperature is increased to 540 DEG C to 560 DEG C and kept for 30 min to 40 min; the steam reforming reaction catalyst is a lanthanum modified nickel-based catalyst. According to the method, the technical effects of destroying pathogens in the medical wastes, cracking macromolecular organic matters, improving the methane yield and purity and reducing the treatment cost are achieved, and harmless, resourceful and efficient treatment of the medical wastes is realized.

Description

Technical Field

[0001] This invention relates to the technical field of medical waste treatment and energy recovery, and in particular to a method for preparing methane from medical waste by pyrolysis and its application. Background Technology

[0002] The proper disposal of medical waste has always been a major challenge in the field of environmental protection. Traditional disposal methods such as incineration and landfill have many drawbacks. Incineration produces pollutants such as dioxins that threaten the atmospheric environment, while landfill may cause soil and groundwater pollution.

[0003] The prior art (application number CN202011095271.1) discloses a process for the controllable and highly selective conversion of medical waste into oil through catalytic pyrolysis. The process mainly includes medical waste compaction, pyrolysis, condensation, and subsequent separation and treatment. Its core is the highly selective production of oil from medical waste through catalytic pyrolysis. The products are mainly C9-C30 alkanes and olefins, without the directional preparation and purification of methane. The oil phase is obtained only through condensation and separation, without secondary conversion of the pyrolysis gas. The temperature control of this process adopts programmed temperature rise, but the temperature rise rate is low in the later stage, in order to suppress gas generation and promote the formation of oil phase products.

[0004] The prior art (application number CN202211066497.8) discloses a medical waste treatment system and process, which aims to produce liquid fuel oil (more than 50%) and carbon slag. Its pyrolysis gas (about 20% combustible gas) is only used as its own heat source, and methane is not separated and purified. In this process, the catalytic pyrolysis temperature is only 325℃-375℃, and rare earth-metal oxide catalysts (such as lanthanide light rare earths and ferric oxide) are used. It focuses on cracking organic matter into oil phase rather than syngas, and cannot achieve the qualitative change from "low-value heat source" to "high-purity energy". The resulting oil phase products need further processing, and the added value is lower than that of methane. It cannot be directly used for power generation, heating and other scenarios.

[0005] The prior art (application number CN202010969977.X) discloses a microwave catalytic decomposition process for medical waste, including the following steps: under standard atmospheric pressure and an oxygen-free / low-oxygen environment, the medical waste is selectively catalytically decomposed through the interaction of microwaves and a catalyst to produce combustible gases including hydrogen, methane, and small molecule hydrocarbons. This process relies on the interaction between microwaves and an iron carbide catalyst to catalytically decompose medical waste under a 2.45 GHz microwave field. The reaction temperature and energy input method vary significantly, and no specific methane purification step is mentioned. The hydrogen content in the gaseous products is over 64%, and methane is only a byproduct (12-18%), and the purity cannot meet the energy utilization requirements.

[0006] In summary, while existing technologies have explored the energy conversion of medical waste, there are few processes for directly producing methane from medical waste. Pyrolysis, as an emerging treatment technology, has shown unique advantages in other waste treatments, but when applied to the production of methane from medical waste, a systematic and efficient process is lacking. In particular, issues such as rough processes and inaccurate parameters exist in the control of pyrolysis conditions, purification of pyrolysis gas, and conversion of syngas, resulting in insufficient practicality and economic efficiency of the overall process.

[0007] In view of this, the present invention is hereby proposed. Summary of the Invention

[0008] One of the objectives of this invention is to provide a method for preparing methane from medical waste through pyrolysis, which can destroy pathogens in medical waste, break down large organic molecules, improve methane yield and purity, and reduce processing costs.

[0009] The second objective of this invention is to provide an application of a method for preparing methane from medical waste through pyrolysis, which is beneficial for achieving the goals of harmlessness, resource utilization, and high efficiency in the treatment of medical waste.

[0010] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, a method for preparing methane by pyrolysis of medical waste includes the following steps: Medical waste is pyrolyzed to obtain pyrolysis gas. The pyrolysis gas is then purified and subjected to steam reforming to obtain post-reaction gas. The post-reaction gas is then separated and purified to obtain methane. The pyrolysis method includes first heating to 190℃-210℃ and holding for 8 min-12 min, then heating to 390℃-410℃ and holding for 13 min-17 min, and then heating to 540℃-560℃ and holding for 30 min-40 min; The catalyst used in the steam reforming reaction includes a lanthanum-modified nickel-based catalyst; The steam reforming reaction is carried out at a temperature of 840℃-860℃ and a pressure of 0.6MPa-1MPa. The gases produced after the reaction include methane, carbon dioxide, and hydrogen.

[0011] Furthermore, the medical waste also includes sorting and crushing steps before pyrolysis; Preferably, the sorting includes separating non-pyrolytic impurities; Preferably, the crushing includes crushing the medical waste to a particle size of less than 3 mm.

[0012] Furthermore, the pyrolysis method includes the following steps: Under oxygen-isolated conditions, medical waste was first heated from room temperature to 200°C at a rate of 8°C / min and held for 10 min, then heated to 400°C at a rate of 5°C / min and held for 15 min, and finally heated to 550°C at a rate of 6°C / min and held for 35 min.

[0013] Furthermore, the purification method includes the following steps: The pyrolysis gas is subjected to cyclone separation, water washing, activated carbon adsorption and desulfurization treatment in sequence to obtain purified pyrolysis gas. Preferably, the purified pyrolysis gas includes carbon monoxide, hydrogen, and methane.

[0014] Furthermore, in the steam reforming reaction, the volume ratio of purified pyrolysis gas to steam is 1:0.7-0.9.

[0015] Furthermore, the separation and purification includes cooling and dehydration, and pressure swing adsorption. Preferably, the cooling and dewatering process includes condensing water vapor into liquid water using a shell-and-tube cooler; Preferably, the pressure swing adsorption includes adsorbing carbon dioxide and hydrogen through a PSA device.

[0016] Furthermore, the adsorbent used in the PSA device includes at least one of 5A molecular sieve and activated carbon; Preferably, the pressure at which the PSA device adsorbs carbon dioxide and hydrogen is 1 MPa-1.4 MPa.

[0017] Furthermore, the methane obtained after separation and purification has a purity of over 95%.

[0018] Secondly, the application of the method for preparing methane by pyrolysis of medical waste as described in any one of the above claims in the treatment of medical waste.

[0019] Furthermore, the medical waste includes at least one of fabrics and plastics.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects: The present invention provides a method for preparing methane from medical waste through pyrolysis. Pyrolysis, achieved through a three-stage temperature control, can completely kill pathogens in medical waste, avoiding secondary pollution. It also offers rapid processing, significantly shortening the processing cycle compared to traditional anaerobic fermentation. The pyrolysis gas, through steam reforming under specific conditions, can improve methane yield and purity. Compared to traditional processes, the methane yield is increased by 40%-50%, and the purity reaches over 95%, making it suitable for direct use as fuel gas. Furthermore, the pyrolysis oil and pyrolysis char produced can be further processed and utilized. For example, the pyrolysis oil can be used to extract chemical raw materials, and the pyrolysis char can be used as an adsorbent or soil conditioner, improving the overall economic efficiency of the process. Simultaneously, the process of this invention is highly adaptable, showing good treatment effects on different types and complex compositions of medical waste, and also contributes to energy conservation and emission reduction.

[0021] The application of the method for preparing methane from medical waste by pyrolysis provided by this invention is beneficial to achieving the goals of harmlessness, resource utilization, and high efficiency in the treatment of medical waste. Detailed Implementation The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] According to a first aspect of the present invention, a method for preparing methane by pyrolysis of medical waste is provided, comprising the following steps: Medical waste is pyrolyzed to obtain pyrolysis gas. The pyrolysis gas is then purified and subjected to steam reforming to obtain post-reaction gas. The post-reaction gas is then separated and purified to obtain methane. The pyrolysis method includes first heating to 190℃-210℃ and holding for 8min-12min (first stage heating), then heating to 390℃-410℃ and holding for 13min-17min (second stage heating), and then heating to 540℃-560℃ and holding for 30min-40min (third stage heating). It should be noted that the purpose of the first stage of heating is to selectively remove free water and shallow bound water from the material, preventing moisture from interfering with the decomposition of organic matter at high temperatures. This can reduce the moisture content of the material from the initial 20%-30% to below 5%, thereby reducing the additional energy consumption due to water vapor evaporation during subsequent pyrolysis (reducing heat loss by 15%-20%). At the same time, the low-temperature environment of the first stage of heating can inhibit the premature degradation of organic matter, preventing the premature escape of volatile small molecules and the resulting waste of resources. It should be noted that the purpose of the second stage of heating is to perform preliminary cracking of easily decomposable organic matter such as cellulose and proteins, thereby generating small molecule intermediate products (such as short-chain hydrocarbons and alcohols), laying the foundation for subsequent deep pyrolysis. This not only increases the breaking rate of glycosidic bonds and peptide bonds in large organic molecules by more than 40%, but also increases the initial yield of H2 and CO in the pyrolysis gas by 25% compared to the constant heating mode. At the same time, the slow heating rate in the second stage can avoid local overheating and coking, reducing the amount of coking in the furnace by 30% and extending the equipment cleaning cycle. It should be noted that the purpose of the third stage of heating is to deeply crack recalcitrant components (such as synthetic plastics and residual macromolecules) to maximize the generation of syngas (mainly H2 and CO). The conversion rate of organic components can be increased to over 90%, and the total yield of pyrolysis gas can reach 350L / kg-380L / kg of medical waste. At the same time, the ratio of H2 to CO in the pyrolysis gas is stabilized at around 3:1, which perfectly matches the feedstock requirements of the subsequent steam reforming reaction, ensuring the efficient synthesis of methane. It is evident that by implementing a step-by-step control of "dehydration-preliminary pyrolysis-deep conversion", the controllability and efficiency of the pyrolysis process are unified. On the one hand, it can completely kill pathogens in medical waste and meet the requirements for harmlessness. On the other hand, it can reduce the impurity content of the pyrolysis gas, reduce the burden on subsequent purification and conversion stages, and effectively ensure the purity of methane. Compared with the traditional single heating mode, it effectively improves the overall energy efficiency. The catalysts used in steam reforming reactions include, but are not limited to, lanthanum-modified nickel-based catalysts; The temperature conditions for steam reforming can be 840℃-860℃, and the pressure conditions can be 0.6MPa-1MPa; The gases produced after the reaction include methane, carbon dioxide, and hydrogen.

[0023] In this invention, pyrolysis, through a three-stage temperature control, can completely kill pathogens in medical waste, avoiding secondary pollution. It also offers rapid processing, significantly shortening the processing cycle compared to traditional anaerobic fermentation. The pyrolysis gas, through steam reforming under specific conditions, can improve methane yield and purity. Compared to traditional processes, methane yield is increased by 40%-50%, and purity reaches over 95%, making it suitable for direct use as fuel gas. Furthermore, the pyrolysis oil and pyrolysis char produced can be further processed and utilized. For example, the pyrolysis oil can be used to extract chemical raw materials, and the pyrolysis char can be used as an adsorbent or soil conditioner, thus improving the overall economic efficiency of the process.

[0024] At the same time, the present invention is highly adaptable and has a good treatment effect on different types and complex medical wastes, and is also conducive to energy conservation and consumption reduction.

[0025] In a preferred embodiment, the medical waste is further subjected to sorting and crushing steps before pyrolysis; wherein, sorting includes, but is not limited to, separating non-pyrolytic impurities; and crushing includes, but is not limited to, crushing the medical waste to a particle size of less than 3 mm.

[0026] Before pyrolysis, medical waste can undergo preliminary sorting and crushing. Intelligent sorting equipment is used to initially classify the collected medical waste, quickly and accurately separating non-pyrolytic metals, glass, and other impurities through spectral recognition and robotic arm grasping, while retaining the portion with higher organic content, such as textiles and plastics. This invention, through intelligent sorting and adjustable equipment parameters, can be widely applied to the treatment of waste generated by various medical institutions. The screened medical waste can be conveyed to a dual-shaft shear crusher, where adjustable blade gaps crush it to a particle size of less than 3mm, providing a better material basis for subsequent pyrolysis.

[0027] In this invention, the pyrolysis furnace used for pyrolysis can be an externally heated rotary kiln structure. The kiln body can be made of high-temperature resistant alloy steel, and a spiral guide plate is set inside, which is beneficial to promote uniform heating and movement of materials.

[0028] In a preferred embodiment, under oxygen-isolated conditions, the pyrolysis process can employ a three-stage heating control strategy. Specifically, firstly, the furnace temperature is raised from room temperature to 200°C at a heating rate of 8°C / min and held for 10 minutes to allow sufficient evaporation of moisture from the material. Then, the temperature is raised to 400°C at a rate of 5°C / min and held for 15 minutes for preliminary pyrolysis. Finally, the temperature is raised to 550°C at a rate of 6°C / min and held for 35 minutes.

[0029] It should be noted that during the pyrolysis process, temperature and pressure inside the furnace can be monitored in real time by temperature and pressure sensors set at different locations in the rotary kiln, and the data is fed back to the central control system to automatically adjust the heating power and rotary kiln speed (range 0.5 r / min-2 r / min) to ensure the stable operation of the pyrolysis process. During the pyrolysis process, pyrolysis gas, pyrolysis oil and pyrolysis char are generated. The pyrolysis gas is cooled to below 40°C by a water-cooled jacketed tube cooler before entering the subsequent processing stage. The pyrolysis oil and pyrolysis char can be discharged through a screw conveyor and can be recycled as by-products.

[0030] In a preferred embodiment, the purification method includes the following steps: The pyrolysis gas is subjected to cyclone separation, water washing, activated carbon adsorption and desulfurization treatment in sequence to obtain purified pyrolysis gas.

[0031] Cyclone Separation: Pyrolysis gas enters a high-efficiency cyclone separator, which adopts an involute inlet structure and a straight-cylinder-cone combination form. The separation efficiency can reach more than 98%. Under the action of centrifugal force, larger particles (particle size greater than 10μm) of solid impurities are separated and collected in the bottom dust collection box. Water washing: The pyrolysis gas after cyclone separation enters the spray-type water washing tower. The tower is equipped with multiple spiral nozzles, and the circulating water temperature is controlled at about 35℃. Through countercurrent contact, some tar and water-soluble impurities are removed. A tar collection tank and an oil-water separation device can be installed at the bottom of the water washing tower to periodically discharge the separated tar and wastewater. Activated carbon adsorption: The pyrolysis gas after water washing passes through an adsorption tower packed with honeycomb activated carbon, the specific surface area of ​​which is greater than 1500 m². 2 / g, exhibiting good adsorption effect on residual tar and small molecule organic matter; the adsorption tower adopts a series structure, and by detecting the tar content in the outlet gas, when the tar content exceeds 50mg / m³, it is considered effective. 3 When the failure occurs, the system automatically switches to the backup adsorption tower and performs hot nitrogen regeneration on the failed adsorption tower. Desulfurization treatment: The pyrolysis gas after adsorption by activated carbon enters the iron oxide desulfurization tower, which is filled with granular iron oxide desulfurizing agent, the main component of which is Fe2O3•H2O. Under normal temperature and pressure, hydrogen sulfide reacts chemically with iron oxide to produce iron sulfide and water. By controlling the gas flow rate (0.1m / s-0.3m / s), the hydrogen sulfide content is reduced to 20mg / m³. 3 the following.

[0032] The main components of the purified pyrolysis gas are carbon monoxide, hydrogen, and a small amount of methane. After being mixed with water vapor, it undergoes a water vapor reforming reaction.

[0033] In a preferred embodiment, the purified pyrolysis gas and water vapor can be mixed at a volume ratio of 1:0.7-0.9 and then fed into a preheater to be heated to 300°C, providing better starting conditions for subsequent reactions.

[0034] In this invention, the steam reforming reaction can be carried out in a fixed-bed reactor containing a nickel-based catalyst. The nickel-based catalyst can be supported by γ-Al2O3 with a nickel loading of 15% (mass fraction). The addition of rare earth element lanthanum (La) for modification is beneficial to improve the activity and stability of the catalyst.

[0035] The reactor for steam reforming can be a tubular structure, with catalyst filled inside the tubes and heat transfer oil flowing between the tubes for temperature control. Specifically, the reaction temperature can be precisely controlled at 850℃ by electric heating and heat transfer oil circulation system, the pressure can be maintained at 0.8MPa by pressure stabilizing valve, and the reaction time can be 1.5h.

[0036] It should be noted that, under the action of a catalyst, carbon monoxide reacts with water vapor to produce hydrogen and carbon dioxide. At the same time, some of the hydrogen reacts with carbon dioxide to undergo methanation to produce methane. The main components of the gas after the reaction are methane, carbon dioxide, and unreacted hydrogen.

[0037] In a preferred embodiment, the separation and purification process includes, but is not limited to, cooling and dehydration and pressure swing adsorption (PSA); wherein, cooling and dehydration includes, but is not limited to, condensing water vapor into liquid water using a shell-and-tube cooler; and pressure swing adsorption includes, but is not limited to, adsorbing carbon dioxide and hydrogen using a PSA device.

[0038] Cooling and dehydration: After the reaction, the gas is first cooled to room temperature by a shell-and-tube cooler. The cooling medium is circulating cooling water. During the cooling process, water vapor condenses into liquid water, which is then separated and discharged by a gas-liquid separator. Pressure Swing Adsorption (PSA): After cooling and dehydration, the gas enters the PSA unit, which adopts an eight-tower, four-level homogenization process. The adsorbent can be a composite adsorbent of 5A molecular sieve and activated carbon. During the adsorption stage, the pressure of the PSA unit can be set to 1MPa-1.4MPa. Carbon dioxide and hydrogen are adsorbed by the adsorbent, while methane is released as the product gas. During the desorption stage, the pressure can be reduced to 0.1MPa, and the adsorbed carbon dioxide and hydrogen are released, realizing the regeneration of the adsorbent.

[0039] It should be noted that the PSA device uses a highly efficient adsorbent and an optimized process, which reduces energy consumption and the overall process has a good energy-saving effect. Through separation and purification, this invention can obtain methane gas with a purity of ≥95% through the synergistic cooperation of each step and its parameters.

[0040] In summary, this invention provides a method for preparing methane from medical waste based on pyrolysis. By meticulously designing the process steps of pyrolysis and its pretreatment, pyrolysis gas purification, steam reforming reaction (i.e., syngas conversion), and methane separation and purification, and precisely controlling the parameters of each step, the method effectively destroys pathogens in medical waste and effectively cleaves large organic molecules, significantly improving the yield and purity of methane. This helps reduce treatment costs and achieves the goals of harmless, resource-efficient, and high-efficiency treatment of medical waste.

[0041] According to a second aspect of the present invention, the application of the method for preparing methane by pyrolysis of medical waste as described in any of the preceding claims in the treatment of medical waste is provided.

[0042] In a preferred embodiment, medical waste includes, but is not limited to, at least one of fabrics and plastics.

[0043] This invention provides a method for preparing methane from medical waste, achieving the reduction, harmlessness, and resource utilization of medical waste. The prepared methane gas can be used in the chemical industry or as fuel gas, providing a new route for the treatment and resource utilization of medical waste.

[0044] The present invention will be further illustrated below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0045] Example 1 A method for preparing methane by pyrolysis of medical waste includes the following steps: (1) Pretreatment and pyrolysis of medical waste: Medical waste generated by a hospital over a week was collected, sorted using intelligent sorting equipment, and the portion with high organic content was screened out. The waste was then crushed to a particle size of less than 3mm by a dual-shaft shear crusher to obtain the crushed material. Among the organic materials, gauze, cotton wool, disposable bed sheets and clothing account for 70%-90%, while disposable syringe barrels, medical packaging bags, plastic bottles and nitrile rubber gloves account for 10%-30%. The crushed material is fed into an externally heated rotary kiln pyrolysis furnace. Following a three-stage heating strategy, the first stage of heating is to raise the temperature from room temperature to 200°C at a rate of 8°C / min and hold it for 10 minutes. The second stage of heating is to raise the temperature to 400°C at a rate of 5°C / min and hold it for 15 minutes. The third stage of heating is to raise the temperature to 550°C at a rate of 6°C / min and hold it for 35 minutes, thereby obtaining pyrolysis gas. The pyrolysis gas is cooled before entering the subsequent processing stage; (2) Purification of pyrolysis gas: The pyrolysis gas is sequentially subjected to cyclone separation, water washing, activated carbon adsorption and desulfurization to obtain purified pyrolysis gas. Cyclone Separation: Pyrolysis gas enters a high-efficiency cyclone separator, which adopts an involute inlet structure and a straight-cylinder-cone combination form. The separation efficiency can reach more than 98%. Under the action of centrifugal force, larger particles (particle size greater than 10μm) of solid impurities are separated and collected in the bottom dust collection box. Water washing: The pyrolysis gas after cyclone separation enters the spray-type water washing tower. The tower is equipped with multiple spiral nozzles. The circulating water temperature is controlled at about 35℃. Through countercurrent contact, some tar and water-soluble impurities are removed. The bottom of the water washing tower is equipped with a tar collection tank and an oil-water separation device to periodically discharge the separated tar and wastewater. Activated carbon adsorption: The pyrolysis gas after water washing passes through an adsorption tower packed with honeycomb activated carbon, the specific surface area of ​​which is greater than 1500 m². 2 / g, exhibiting good adsorption effect on residual tar and small molecule organic matter; the adsorption tower adopts a series structure, and by detecting the tar content in the outlet gas, when the tar content exceeds 50mg / m³, it is considered effective. 3 When the failure occurs, the system automatically switches to the backup adsorption tower and performs hot nitrogen regeneration on the failed adsorption tower. Desulfurization treatment: The pyrolysis gas after adsorption by activated carbon enters the iron oxide desulfurization tower, which is filled with granular iron oxide desulfurizing agent, the main component of which is Fe2O3•H2O. Under normal temperature and pressure, hydrogen sulfide reacts chemically with iron oxide to produce iron sulfide and water. By controlling the gas flow rate (0.1m / s-0.3m / s), the hydrogen sulfide content is reduced to 20mg / m³. 3 the following; The main components of the purified pyrolysis gas are carbon monoxide, hydrogen and a small amount of methane. After being mixed with water vapor, it undergoes a water vapor reforming reaction. (3) Steam reforming reaction (i.e., syngas conversion): The purified pyrolysis gas and water vapor are mixed at a volume ratio of 1:0.8 and then fed into a preheater to be heated to 300°C. The mixture is then passed through a fixed-bed reactor containing a nickel-based catalyst to carry out a water vapor reforming reaction, and the resulting gas is obtained. Among them, the nickel-based catalyst uses γ-Al2O3 as a support, with a nickel loading of 15% (mass fraction), and is modified by adding rare earth element lanthanum (La) to improve the activity and stability of the catalyst. The reactor has a tubular structure, with catalyst filled inside the tubes and heat transfer oil circulating between the tubes for temperature control. Specifically, the reaction temperature is precisely controlled at 850℃ by electric heating and heat transfer oil circulation system, the pressure is maintained at 0.8MPa by a pressure stabilizing valve, and the reaction time is 1.5h. It should be noted that, under the action of a catalyst, carbon monoxide reacts with water vapor to produce hydrogen and carbon dioxide. At the same time, some of the hydrogen reacts with carbon dioxide to produce methane. The main components of the gas after the reaction are methane, carbon dioxide and unreacted hydrogen. (4) Separation and purification: After the reaction, the gas is cooled by a shell-and-tube cooler and dehydrated by a gas-liquid separator before entering the PSA unit to obtain methane gas with a purity of 95.8% and a methane yield of 350 L / kg medical waste. Cooling and dehydration: After the reaction, the gas is first cooled to room temperature by a shell-and-tube cooler. The cooling medium is circulating cooling water. During the cooling process, water vapor condenses into liquid water, which is then separated and discharged by a gas-liquid separator. Pressure Swing Adsorption (PSA): After cooling and dehydration, the gas enters the PSA unit, which adopts an eight-tower, four-level homogenization process. The adsorbent is a composite adsorbent of 5A molecular sieve and activated carbon. During the adsorption stage, the pressure of the PSA unit is set at 1.2 MPa. Carbon dioxide and hydrogen are adsorbed by the adsorbent, while methane is released as the product gas. During the desorption stage, the pressure is reduced to 0.1 MPa, and the adsorbed carbon dioxide and hydrogen are released, realizing the regeneration of the adsorbent.

[0046] Example 2 The only difference between this embodiment and embodiment 1 is that in step (1), the first stage of heating is to raise the temperature from room temperature to 190°C at a rate of 8°C / min and hold it for 12min. The remaining steps and process parameters were the same as in Example 1, resulting in methane gas with a purity of 95.6% and a methane yield of 341 L / kg medical waste.

[0047] Example 3 The only difference between this embodiment and embodiment 1 is that in step (1), the second stage of heating is to raise the temperature to 410°C at a rate of 5°C / min and maintain it for 13min. The remaining steps and process parameters are the same as in Example 1, resulting in methane gas with a purity of 95% and a methane yield of 345 L / kg medical waste.

[0048] Example 4 The only difference between this embodiment and embodiment 1 is that in step (1), the third stage of heating is to raise the temperature to 540°C at a rate of 6°C / min and maintain it for 40 minutes to obtain pyrolysis gas; The remaining steps and process parameters were the same as in Example 1, resulting in methane gas with a purity of 95.5% and a methane yield of 338 L / kg medical waste.

[0049] Example 5 The only difference between this embodiment and embodiment 1 is that in step (3), the purified pyrolysis gas and water vapor are mixed at a volume ratio of 1:0.7. The remaining steps and process parameters were the same as in Example 1, resulting in methane gas with a purity of 95.3% and a methane yield of 324 L / kg medical waste.

[0050] Example 6 The only difference between this embodiment and embodiment 1 is that in step (3), the purified pyrolysis gas and water vapor are mixed at a volume ratio of 1:0.9. The remaining steps and process parameters were the same as in Example 1, resulting in methane gas with a purity of 95.2% and a methane yield of 323 L / kg medical waste.

[0051] Example 7 The only difference between this embodiment and Example 1 is that in step (3), the reaction temperature is controlled at 840°C and the pressure is maintained at 0.6 MPa. The remaining steps and process parameters are the same as in Example 1, resulting in methane gas with a purity of 95% and a methane yield of 318 L / kg medical waste.

[0052] Example 8 The only difference between this embodiment and Example 1 is that in step (3), the reaction temperature is controlled at 860°C and the pressure is maintained at 1 MPa. The remaining steps and process parameters are the same as in Example 1, resulting in methane gas with a purity of 95% and a methane yield of 320 L / kg medical waste.

[0053] Example 9 The only difference between this embodiment and Embodiment 1 is that, in step (3), the reaction time is 2 hours. The remaining steps and process parameters were the same as in Example 1, resulting in methane gas with a purity of 95.7% and a methane yield of 347 L / kg medical waste.

[0054] Comparative Example 1 The only difference between this comparative example and Example 1 is that, in step (1), the first stage of heating was not performed; The remaining steps and their process parameters are the same as in Example 1.

[0055] Compared with Example 1, the drawback of this comparative example is that the pretreatment of the pyrolysis raw materials is insufficient, which affects the subsequent pyrolysis efficiency. Specifically, the moisture in the material cannot be fully removed, which will require more heat to evaporate the moisture during the subsequent pyrolysis process at 400°C and 550°C, increasing energy consumption. At the same time, the presence of moisture will lower the actual temperature in the pyrolysis furnace, resulting in uneven heating of the material, affecting the cracking effect of macromolecular organic matter, leading to a reduction in the yield of pyrolysis gas, and also causing instability in the composition of pyrolysis gas, increasing the difficulty of purification.

[0056] Comparative Example 2 The only difference between this comparative example and Example 1 is that, in step (1), the second stage of heating was not performed; The remaining steps and their process parameters are the same as in Example 1.

[0057] Compared with Example 1, the drawback of this comparative example is that the macromolecular organic matter is not fully decomposed, resulting in a decrease in the pyrolysis gas yield. The material temperature is directly increased from 200°C to 550°C, and the macromolecular organic matter does not have enough time to be fully decomposed, which leads to a large amount of undecomposed solid organic matter remaining, resulting in a significant decrease in the pyrolysis gas yield.

[0058] Comparative Example 3 The only difference between this comparative example and Example 1 is that, in step (1), the third stage of heating was not performed; The remaining steps and their process parameters are the same as in Example 1.

[0059] Compared with Example 1, the shortcomings of this comparative example are: incomplete pyrolysis, high levels of macromolecular organic matter residue, reduced pyrolysis gas yield, and a surge in heavy hydrocarbon and tar content in the gas, increasing the purification load and making subsequent catalysts susceptible to poisoning; simultaneously, the CO / H2 ratio in the pyrolysis gas is unbalanced, resulting in insufficient methanation during syngas conversion, reduced methane yield, and difficulty in achieving a purity of 95%; furthermore, the pyrolysis char contains a large amount of undecomposed organic matter, has poor pore structure, and reduced adsorption performance, while the pyrolysis oil contains few light components and many impurities, significantly reducing its utilization value; in addition, the material is not deeply pyrolyzed, making it prone to coking in the furnace, affecting equipment heat transfer efficiency, increasing cleaning frequency and energy consumption, and significantly reducing process stability.

[0060] Comparative Example 4 The only difference between this comparative example and Example 1 is that the pyrolysis gas was not purified, but was directly subjected to a steam reforming reaction. The remaining steps and their process parameters are the same as in Example 1.

[0061] Compared to Example 1, the shortcomings of this comparative example are that tar and solid impurities in the pyrolysis gas adhere to the surface of the nickel-based catalyst, clogging the catalyst pores and causing a rapid decline in catalyst activity and a shortened service life. At the same time, acidic gases such as hydrogen sulfide react with the catalyst, causing permanent catalyst poisoning, resulting in a sharp drop in the efficiency of the steam reforming reaction and a decrease in methane yield. In addition, impurity gases (such as heavy hydrocarbons) decompose and coke at high temperatures, covering the inner wall of the reactor, affecting heat transfer efficiency, increasing energy consumption, and potentially causing pipeline blockage, endangering process safety. The final methane gas has a high impurity content, making subsequent PSA purification more difficult and making it hard to achieve a purity of 95%.

[0062] Comparative Example 5 The only difference between this comparative example and Example 1 is that the pyrolysis gas was purified and did not undergo a steam reforming reaction. The remaining steps and their process parameters are the same as in Example 1.

[0063] Compared with Example 1, the shortcomings of this comparative example are that the methane content in the pyrolysis gas is low, and the main components are CO, H2 and CO2. When directly purified, the methane yield drops sharply, which cannot meet the goal of efficient methane production. Toxic gases such as CO are not converted and directly enter the subsequent system, which not only poses a safety hazard, but also increases the PSA purification load, making it difficult to achieve a methane purity of 95%. In addition, the utilization rate of separated gases such as CO is low, resulting in energy waste. At the same time, the proportion of gas components is not adjusted through reforming reaction, and the ratio of H2 and CO in the pyrolysis gas is unbalanced, which makes it impossible to optimize the methanation reaction conditions, resulting in a high proportion of impurity gases in the final product.

[0064] Comparative Example 6 The only difference between this comparative example and Example 1 is that, in step (3), the nickel-based catalyst used is not modified with lanthanum; The remaining steps and their process parameters are the same as in Example 1.

[0065] Compared with Example 1, the shortcomings of this comparative example are: decreased catalyst activity and stability; in the high-temperature steam reforming reaction, the nickel particles of the unmodified nickel-based catalyst tend to agglomerate and grow, reducing the specific surface area and catalytic activity; the activity decays significantly after 100 hours of reaction, requiring frequent catalyst replacement and increasing costs; the catalyst has weak resistance to carbon deposition and poisoning; the small amount of tar and sulfides remaining in the pyrolysis gas can easily cause carbon deposition or poisoning on the catalyst surface, and the unmodified catalyst cannot effectively suppress these phenomena, leading to a sharp drop in reforming efficiency and a decrease in methane yield; the product selectivity is poor, making it impossible to accurately control the conversion pathways of CO and CO2, and unreacted CO and H2 are easily mixed into the generated methane, increasing the difficulty of subsequent PSA purification, reducing methane purity, and affecting product quality.

[0066] Comparative Example 7 The only difference between this comparative example and Example 1 is that, in step (3), the reaction temperature is 750°C; The remaining steps and their process parameters are the same as in Example 1.

[0067] Compared with Example 1, the shortcomings of this comparative example are that the reaction rate is significantly reduced, resulting in a decrease in CO conversion and a reduction in methane production; the catalyst activity is limited, as the nickel-based catalyst reaches its optimal activity at around 850°C, and lower temperatures will reduce the utilization rate of active sites and easily lead to the aggravation of side reactions (such as carbon deposition), increase the rate of catalyst carbon deposition, and shorten its service life; at the same time, the gas component ratio is unbalanced, and the amount of H2 generated at low temperatures is insufficient, causing the ratio of H2 to CO to deviate from the optimal value, resulting in incomplete methanation reaction and ultimately reduced methane purity.

[0068] Comparative Example 8 The only difference between this comparative example and Example 1 is that, in step (3), the reaction temperature is 950°C; The remaining steps and their process parameters are the same as in Example 1.

[0069] Compared to Example 1, this comparative example has the following drawbacks: The catalyst stability decreases; the nickel-based catalyst is prone to particle agglomeration at ultra-high temperatures, resulting in a reduced specific surface area and fewer active sites, necessitating frequent catalyst replacement and increasing costs. Side reactions are exacerbated; high temperatures promote methane decomposition, leading to an increase in carbon content on the catalyst surface, clogging active sites, and the generated carbon particles wear down the reactor inner wall, shortening equipment lifespan. Furthermore, energy consumption increases significantly, and the gas composition becomes unbalanced. Excessive hydrogen generation causes the H2 to CO ratio to deviate from the optimal value, requiring more hydrogen to be processed during subsequent PSA purification, leading to fluctuations in methane purity.

[0070] Comparative Example 9 The only difference between this comparative example and Example 1 is that, in step (3), the reaction pressure is 0.2 MPa; The remaining steps and their process parameters are the same as in Example 1.

[0071] Compared with Example 1, the shortcomings of this comparative example are: the reaction rate is reduced, the pressure decreases the frequency of gas molecule collisions, the conversion rate of CO and water vapor and the methanation reaction rate decrease, the conversion rate is reduced in the same reaction time, resulting in a reduction in the amount of methane produced; the catalyst utilization rate is insufficient, the adsorption capacity of gas on the catalyst surface is weakened under low pressure, the active sites are not fully utilized, the catalytic efficiency decreases, and the reaction conversion rate is further reduced; at the same time, the product selectivity is worse, low pressure is not conducive to the forward methanation reaction, resulting in insufficient CO2 conversion, reduced methane purity, and an increase in unreacted CO2, which increases the load on subsequent PSA purification.

[0072] In summary, this invention, through meticulous design of the pyrolysis and pretreatment, pyrolysis gas purification, steam reforming reaction (i.e., syngas conversion), and separation and purification processes, precisely controls the parameters of each step. With the synergistic cooperation of each step and its parameters, it can effectively destroy pathogens in medical waste, effectively cleave macromolecular organic matter, significantly improve the yield and purity of methane, and help reduce treatment costs, thereby achieving the goals of harmless, resource-based, and efficient treatment of medical waste.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing methane by pyrolysis of medical waste, characterized in that, Includes the following steps: Medical waste is pyrolyzed to obtain pyrolysis gas. The pyrolysis gas is then purified and subjected to steam reforming to obtain post-reaction gas. The post-reaction gas is then separated and purified to obtain methane. The pyrolysis method includes first heating to 190℃-210℃ and holding for 8 min-12 min, then heating to 390℃-410℃ and holding for 13 min-17 min, and then heating to 540℃-560℃ and holding for 30 min-40 min; The catalyst used in the steam reforming reaction includes a lanthanum-modified nickel-based catalyst; The steam reforming reaction is carried out at a temperature of 840℃-860℃ and a pressure of 0.6MPa-1MPa. The gases produced after the reaction include methane, carbon dioxide, and hydrogen.

2. The method for preparing methane from medical waste by pyrolysis according to claim 1, characterized in that, The medical waste also includes sorting and crushing steps before pyrolysis; Preferably, the sorting includes separating non-pyrolytic impurities; Preferably, the crushing includes crushing the medical waste to a particle size of less than 3 mm.

3. The method for preparing methane from medical waste by pyrolysis according to claim 2, characterized in that, The pyrolysis method includes the following steps: Under oxygen-isolated conditions, medical waste was first heated from room temperature to 200°C at a rate of 8°C / min and held for 10 min, then heated to 400°C at a rate of 5°C / min and held for 15 min, and finally heated to 550°C at a rate of 6°C / min and held for 35 min.

4. The method for preparing methane from medical waste by pyrolysis according to claim 1, characterized in that, The purification method includes the following steps: The pyrolysis gas is subjected to cyclone separation, water washing, activated carbon adsorption and desulfurization treatment in sequence to obtain purified pyrolysis gas. Preferably, the purified pyrolysis gas includes carbon monoxide, hydrogen, and methane.

5. The method for preparing methane from medical waste by pyrolysis according to claim 4, characterized in that, In the steam reforming reaction, the volume ratio of purified pyrolysis gas to steam is 1:0.7-0.

9.

6. The method for preparing methane from medical waste by pyrolysis according to any one of claims 1-5, characterized in that, The separation and purification process includes cooling and dehydration, and pressure swing adsorption. Preferably, the cooling and dewatering process includes condensing water vapor into liquid water using a shell-and-tube cooler; Preferably, the pressure swing adsorption includes adsorbing carbon dioxide and hydrogen through a PSA device.

7. The method for preparing methane from medical waste by pyrolysis according to claim 6, characterized in that, The adsorbent used in the PSA device includes at least one of 5A molecular sieve and activated carbon. Preferably, the pressure at which the PSA device adsorbs carbon dioxide and hydrogen is 1 MPa-1.4 MPa.

8. The method for preparing methane by pyrolysis of medical waste according to claim 7, characterized in that, The methane obtained after separation and purification has a purity of over 95%.

9. The application of the method for preparing methane by pyrolysis of medical waste according to any one of claims 1-8 in the treatment of medical waste.

10. The application according to claim 9, characterized in that, The medical waste includes at least one of fabric and plastic.