A system and method for preparing syngas from biogas residue by vertical microwave pyrolysis

Abstract

A system and method for preparing syngas from biogas residue by vertical microwave pyrolysis, the system mainly includes: a pretreatment unit and a microwave pyrolysis reaction unit. The pretreatment unit is used for preliminary solid-liquid separation of food waste, and for preheating, drying, and pulverizing the material after preliminary solid-liquid separation to prepare treated material: solid granular powder. The microwave pyrolysis reaction unit includes a vertical fixed-bed microwave reactor, and is used to perform microwave pyrolysis on the treated material under an inert atmosphere, thereby achieving solid-liquid separation of the solid and liquid products obtained from microwave pyrolysis in a vertical direction, and reducing liquid products while increasing gaseous products. This invention, by treating food waste, not only increases the yield of syngas but also increases the proportion of H2 and CO in the pyrolysis gas, thus increasing its calorific value.

Description

Technical Field

[0001] This invention relates to the fields of energy and environmental protection technology and waste treatment, and specifically, particularly to a system and method for preparing syngas from biogas residue by vertical microwave pyrolysis. Background Technology

[0002] With the rapid growth of the global population and the rapid development of the economy, environmental pollution and energy shortages have become serious problems affecting sustainable human development. This urgent issue requires us to accelerate the development of new energy sources while also finding an effective way to utilize waste resources to alleviate environmental pollution.

[0003] Food waste is a type of waste generated by residents in their daily lives, food processing, and catering services. Its production is increasing year by year, especially in cities, where it accounts for over 40% of household waste. Due to its high organic matter and moisture content, food waste is prone to spoilage and rotting, not only emitting foul odors but also producing large amounts of toxins that pollute water and air, harming people's physical and mental health. Therefore, food waste disposal has become a crucial aspect of urban life. Because of its high organic matter and oil content, food waste possesses the dual nature of both waste and resource; therefore, recycling and utilizing it for resource recovery is of profound significance.

[0004] Current treatment routes for food waste recycling mainly include microbial methods, animal feed production, incineration for power generation, and pyrolysis. Microbial methods utilize microorganisms to degrade waste into compost, but they have significant drawbacks: slow processing and large land requirements. Animal feed production converts food waste into high-calorie animal feed, but it poses food safety risks and food homology issues. Incineration for power generation generates secondary pollution such as dioxins during the incineration process, seriously harming the environment and human health. Pyrolysis involves the pyrolysis of food waste under anaerobic conditions, avoiding dioxin formation. Simultaneously, the pyrolysis products (pyrolysis gas and pyrolysis oil) can be used as fuel, offering greater benefits and better environmental protection in terms of resource utilization.

[0005] For example, the following existing technologies:

[0006] Co-pyrolysis of food waste and wood bark to produce hydrogen withminimizing pollutant emissions, Environmental Pollution 270 (2021) 116045,URL:

[0007] https: / / doi.org / 10.1016 / j.envpol.2020.116045

[0008] Effects of operating parameters on products yield and volatilescomposition during fast pyrolysis of food waste in the presence of hydrogen, Fuel Processing Technology 210 (2020) 106558, URL:

[0009] https: / / doi.org / 10.1016 / j.fuproc.2020.106558

[0010] Both of the above existing technologies reveal technical solutions for the traditional pyrolysis of food waste. The problem is that, although pyrolysis is widely used, food waste pyrolysis gas suffers from drawbacks such as low yield and low calorific value, and is generally used for preliminary combustion before emission, resulting in low industrial utilization. Summary of the Invention

[0011] To overcome the shortcomings of low gas yield and calorific value in existing food waste pyrolysis methods, this invention provides a vertical microwave pyrolysis system for preparing syngas from biogas residue, the system comprising:

[0012] Pretreatment unit, microwave pyrolysis reaction unit;

[0013] The pretreatment unit is used to perform preliminary solid-liquid separation on kitchen waste, and to preheat, dry, and pulverize the material after preliminary solid-liquid separation to prepare the processed material: solid granular powder.

[0014] The microwave pyrolysis reaction unit includes a vertical fixed-bed microwave reactor, and the microwave pyrolysis reaction unit is used to perform microwave pyrolysis on the treated material under an inert atmosphere, so that the solid and liquid products obtained by microwave pyrolysis can be separated vertically, and the liquid phase products are reduced while the gaseous products are increased.

[0015] Preferred,

[0016] The microwave pyrolysis reaction unit is used to perform microwave pyrolysis on the treated material under an inert atmosphere, and to achieve solid-liquid separation of the solid and liquid products obtained by microwave pyrolysis in the vertical direction using gravity.

[0017] Preferred,

[0018] The microwave pyrolysis reaction unit is used to further catalytically pyrolyze the pyrolysis oil obtained from solid-liquid separation in a vertical fixed-bed microwave reactor using a catalyst.

[0019] Preferred,

[0020] The internal structure of the microwave pyrolysis reaction unit facilitates the recovery of the carrier material that absorbs microwaves.

[0021] Preferred,

[0022] The internal structure of the microwave pyrolysis reaction unit further facilitates catalyst recovery.

[0023] Preferably, the system further includes:

[0024] Recycling unit;

[0025] The recovery unit is used to recover the combustible gas products obtained from the microwave pyrolysis reaction unit, as well as the microwave-absorbing heat carrier used in the microwave pyrolysis reaction unit.

[0026] Preferred,

[0027] The recycling unit is also used to recycle the coke obtained from further processing of materials in the microwave pyrolysis reaction unit.

[0028] Preferably, the system further includes:

[0029] Circulating fan;

[0030] The circulating fan is used to circulate the gas generated in the microwave pyrolysis reaction unit by using inert gas to continuously and positively promote the generation of pyrolysis gas.

[0031] Preferred,

[0032] The pretreatment unit includes a centrifuge, a dryer, and a pulverizer;

[0033] Food waste is fed into a centrifugal separator. The lower end of the centrifugal separator is connected to an oil-water recovery tank. The right side of the centrifugal separator is connected to a dryer. The right end of the dryer is connected to a pulverizer. The other end of the pulverizer is connected to the microwave pyrolysis reaction unit.

[0034] The oil-water mixture separated from the kitchen waste is sent to the oil-water recovery tank by a centrifugal separator. The separated kitchen waste is then sent to a dryer and a pulverizer for drying and pulverizing in sequence to obtain the dried and pulverized material. The material is then sent to the microwave pyrolysis reaction unit.

[0035] Preferred,

[0036] The pretreatment unit also includes an air preheater;

[0037] The air preheater provides hot air to preheat the food waste after separation by the centrifuge and before drying by the dryer, so as to remove as much of the volatile substances such as moisture contained therein.

[0038] Preferred,

[0039] The hot air generated by the dryer is passed to the air preheater and recycled as part of the heat source.

[0040] Preferred,

[0041] Air preheaters can be heated by their own heat source or electricity, or they can utilize the waste heat from external devices.

[0042] Preferred,

[0043] The microwave pyrolysis reaction unit also includes a material mixer;

[0044] A material mixer is used to mix the dried and pulverized material from the pretreatment unit with a microwave-absorbing heat carrier.

[0045] Preferred,

[0046] The microwave pyrolysis reaction unit also includes a condenser.

[0047] Preferred,

[0048] The microwave pyrolysis reaction unit also includes a solid sieve.

[0049] Preferred,

[0050] The lower end of the material mixer is connected to the recovery tank I, and the right end of the material mixer is connected to the vertical fixed-bed microwave reactor.

[0051] Preferred,

[0052] The recycling unit includes an oil tank;

[0053] A solid sieve and a condenser, as well as an oil tank in the recovery unit, are connected below the vertical fixed-bed microwave reactor.

[0054] Preferred,

[0055] A circulating fan is installed between the condenser and the vertical fixed-bed microwave reactor.

[0056] Preferred,

[0057] The microwave pyrolysis reaction unit is used to realize the mixing, filling and pyrolysis reaction of material particles.

[0058] Preferred,

[0059] The pyrolysis oil produced by the microwave pyrolysis reaction unit is guided to the oil tank for storage by gravity.

[0060] Preferred,

[0061] The oil and gas produced by the vertical fixed-bed microwave reactor are condensed in the condenser tubes. The resulting liquid oil is sent to the oil tank, while the combustible gas is sent to the syngas collection bag.

[0062] Preferred,

[0063] The coke and microwave-absorbing heat carrier obtained from the processing of materials in the vertical fixed-bed microwave reactor are sent to a solid screen for separation and recycling.

[0064] Preferred,

[0065] The right side of the vertical fixed-bed microwave reactor is connected to the circulating fan.

[0066] Preferred,

[0067] The recycling unit includes recycling tank I, recycling tank II, syngas collection device, oil-water recycling tank, oil-water separator and oil tank.

[0068] Preferred,

[0069] The upper and lower ends of the oil-water recovery tank are connected to a centrifugal separator and an oil-water separator, respectively.

[0070] Preferred,

[0071] The oil-water separator is connected to the oil tank at the bottom, and a vertical fixed-bed microwave reactor is connected to the top of the oil tank.

[0072] Preferred,

[0073] The right end of the oil tank is connected to a condenser pipe to recover the pyrolysis oil.

[0074] Preferred,

[0075] A syngas collection device is also connected below the condenser tube, which is used to collect the combustible gas products generated by pyrolysis.

[0076] Preferred,

[0077] Recycling tank I is metal recycling tank I, and recycling tank II is metal recycling tank II.

[0078] Preferred,

[0079] Recovery tanks I and II are connected to a solid separator, respectively, and are used to recover the heat carrier that absorbs microwaves and the pyrolysis product coke.

[0080] Preferred,

[0081] The recycling tank I is also connected to a material mixer to mix the recovered microwave-absorbing heat carrier with the material for reuse.

[0082] Preferred,

[0083] Above the material mixer, silicon carbide is mixed in before the microwave pyrolysis reaction unit starts working, and silicon carbide is replenished to the microwave pyrolysis reaction unit whenever it needs to be replenished during operation.

[0084] Preferred,

[0085] The interior of the vertical fixed-bed microwave reactor is a cylindrical shape in the vertical direction.

[0086] Furthermore, this invention also discloses a method for preparing syngas from biogas residue by vertical microwave pyrolysis, the method comprising the following steps:

[0087] Pre-treatment steps: preliminary solid-liquid separation of kitchen waste, and preheating, drying and pulverizing the material after preliminary solid-liquid separation to prepare the processed material: solid granules and powder;

[0088] Microwave pyrolysis reaction steps: Under an inert atmosphere, the treated material is subjected to microwave pyrolysis, and the solid-liquid products obtained by microwave pyrolysis are vertically separated. The pyrolysis oil obtained by solid-liquid separation is further catalytically pyrolyzed by a catalyst to reduce liquid products and increase gaseous products.

[0089] Preferably, the method further includes the following steps:

[0090] Recovery step: The combustible gas products and coke obtained from the microwave pyrolysis reaction step are recovered, as well as the microwave-absorbing heat carrier used in the microwave pyrolysis reaction step.

[0091] In summary, by processing kitchen waste, this invention can not only increase the yield of syngas (such as combustible gases H2 and CO), but also increase the proportion of H2 and CO in the pyrolysis gas to improve its calorific value. Attached Figure Description

[0092] Figure 1 This is a schematic diagram of the overall structure of a system for preparing syngas from biogas residue using vertical microwave pyrolysis in one embodiment of the present invention;

[0093] Figure 2 This is a schematic diagram of the unit structure of the system in one embodiment of the present invention when the air preheater is not included;

[0094] Figure 3 This is a schematic diagram of the structure of each unit in one embodiment of the system of the present invention, when the system includes an air preheater;

[0095] Figure 4A , Figure 4B These are schematic diagrams of gaseous products and corresponding data sources in one embodiment of the present invention.

[0096] Figure 5A , Figure 5B These are schematic diagrams of gaseous products and corresponding data sources in a comparative example of this invention.

[0097] Figure 6 This is a schematic diagram comparing gas yield and main gas components of a specific embodiment of the present invention with prior art techniques 1 and 2.

[0098] Figure 7 This is a schematic diagram of the connection between the vertical fixed-bed microwave reactor and the microwave source in one embodiment of the present invention. Detailed Implementation

[0099] To facilitate understanding of the present invention by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0100] In one embodiment, the present invention discloses a system for preparing syngas from biogas residue by vertical microwave pyrolysis, the system mainly comprising a pretreatment unit and a microwave pyrolysis reaction unit. Preferably, see [link to preferred embodiment]. Figure 1 The system also includes a recycling unit.

[0101] See Figure 2 The pretreatment unit includes (1) a bag-breaking machine, (2) a centrifuge, (3) a dryer, and (4) a pulverizer. This pretreatment unit is used to perform preliminary solid-liquid separation, drying, and pulverizing of kitchen waste into solid granular powder.

[0102] For an even better option, see [link to previous section]. Figure 3 The pretreatment unit also includes (5) an air preheater. (1) The bag breaking machine is connected to (2) the centrifuge. The lower end of (2) the centrifuge is connected to (14) the oil-water recovery tank. The right side of (2) the centrifuge is connected to (3) the dryer. The lower part of (3) the dryer is connected to (5) the air preheater. The right end of (3) the dryer is connected to (4) the pulverizer. The other end of (4) the pulverizer is connected to (6) the material mixer. The oil-water mixture separated by (2) the centrifuge is sent to (14) the oil-water recovery tank. The hot air generated by (3) the dryer is sent to (5) the air preheater as a partial heat source for recycling.

[0103] The microwave pyrolysis reaction unit includes (6) a material mixer, (7) a vertical fixed-bed microwave reactor, (8) a condenser, (9) a circulating fan, and (10) a solid sieve. The lower end of the (6) material mixer is connected to the (11) metal recovery tank I, and the right end is connected to the (7) vertical fixed-bed microwave reactor. The (7) vertical fixed-bed microwave reactor is connected to the (10) solid sieve, (16) an oil tank, and (8) a condenser. The (9) circulating fan is located between the (8) condenser and the (7) vertical fixed-bed microwave reactor. The pyrolysis oil generated by microwave pyrolysis is guided to the (16) oil tank for storage by gravity. The liquid oil generated by the oil and gas generated by microwave pyrolysis is condensed in the (8) condenser and then sent to the (16) oil tank for storage. At the same time, the combustible gas generated is sent to the (13) syngas collection bag for storage. The solid products generated after the microwave pyrolysis reaction and the heat carrier that absorbs microwaves are sent to the (10) solid sieve for separation and recycling.

[0104] The recovery unit includes (11) a metal recovery tank I, (12) a metal recovery tank II, (13) a syngas collection bag, (14) an oil-water recovery tank, (15) an oil-water separator, and (16) an oil tank. The upper and lower ends of the (14) oil-water recovery tank are connected to (2) a centrifuge and (15) an oil-water separator, respectively. The lower part of the (15) oil-water separator is connected to the (16) oil tank. The upper part of the (16) oil tank is connected to (7) a vertical fixed-bed microwave reactor, and the right end is connected to (8) a condenser tube, used to recover pyrolysis oil. The (8) condenser tube is also connected to (13) a syngas collection bag below, used to collect combustible gas products generated during pyrolysis. (11) Metal recovery tank I and (12) Metal recovery tank II are respectively connected to the (10) solid separator. After pyrolysis, the solid products are sent to the (10) solid separator for vibrating sieving to separate the microwave-absorbing heat carrier and coke, which are stored in (11) Metal recovery tank I and (12) Metal recovery tank II respectively. (11) Metal recovery tank I is also connected to the (6) material mixer to send the recovered microwave-absorbing heat carrier to the (6) material mixer to mix with the reaction materials for reuse.

[0105] It is understandable that the recovered microwave-absorbing heat carrier and activated carbon can be reused. A circulating fan is not mandatory; it is sufficient as long as the inert gas introduced into the microwave pyrolysis reaction unit can consistently drive away the combustible gases produced during pyrolysis.

[0106] Preferably, the material entering the material mixer should have a smaller particle size to facilitate the efficient microwave pyrolysis reaction. In addition, the particle size of the material should be clearly distinguishable from that of the microwave-absorbing heat carrier (such as silicon carbide) to facilitate the separation of the microwave-absorbing heat carrier by vibrating sieving in a solid separator.

[0107] The present invention will be further explained below by comparing it with the prior art techniques 1 and 2.

[0108] the term:

[0109] "Moisture content" is the ratio of the mass of water in food waste to the total mass of food waste.

[0110] Prior art 1 is used as the first comparative scheme, conventional pyrolysis

[0111] Food waste sourced from a waste treatment plant in Seoul was used as raw material. First, the food waste was dehydrated using a screw press to achieve solid-liquid separation, then dried at 60°C for one day to reduce its moisture content. The dried food waste was then pulverized into 0.6-1mm particles and loaded into a continuous flow pyrolysis reactor. This pyrolysis reactor consisted of a quartz tube reactor, a tubular furnace, a mass flow controller, a temperature controller, and a cold trap. The pyrolysis process was carried out under oxygen-free conditions under N2 protection, with the mass flow controller controlling the N2 flow rate at 100ml / min. The combustible gas generated after the pyrolysis reaction was carried by a carrier gas to the cold trap for condensation and collection, while the solid and liquid products were collected separately.

[0112] The pyrolysis temperature is 300-700℃, ensuring complete pyrolysis.

[0113] Based on the prior art 1, two different comparative examples were carried out. Using materials from the same source, at pyrolysis temperatures of 600℃ and 700℃, with other conditions remaining unchanged, two sets of data were obtained respectively, as detailed in Table 1 below.

[0114] Existing technology 2 serves as a second comparative scheme, conventional pyrolysis.

[0115] Using kitchen waste from the Qingdao campus canteen of China University of Petroleum as raw material, the waste mainly consists of leftover food (rice, meat, and vegetables) and a small amount of melon rinds. First, the kitchen waste is dehydrated. Then, the solid residue, after removing oil and water, is sun-dried for half a month. After removing impurities such as sand and metal, it is dried at 105℃ for 24 hours to significantly reduce the moisture content. Next, the kitchen waste is pulverized and thoroughly mixed, with the material pulverized into particles of approximately 0.25 mm. The powder particles are loaded into a tubular pyrolysis reactor, which consists of a stainless steel tube reactor, an electric resistance furnace, a flow meter, a temperature controller, and a collection system. The pyrolysis process is carried out under an atmosphere of H2 and N2, with H2 controlled at 0-15% and a carrier gas flow rate of 100-250 ml / min. A rapid pyrolysis method is used. The combustible gas generated during pyrolysis is collected in a gas bag after passing through a condenser, and the solid and liquid products are collected separately.

[0116] The pyrolysis temperature is 700-900℃ and the pyrolysis time is 2 minutes.

[0117] Based on existing technology 2, two different comparative examples were carried out. Using materials from the same source, at pyrolysis temperatures of 700℃ and 750℃, with other conditions remaining unchanged, two sets of data were obtained respectively, as detailed in Table 1 below.

[0118] The technology for preparing syngas from biogas residue using vertical microwave pyrolysis according to this invention: Microwave pyrolysis

[0119] The secondary food waste used comes from Ningbo Kaicheng Food Waste Treatment Co., Ltd., and mainly originates from urban residents' kitchen waste, including vegetables, meat, fish, and staple foods. After impurity removal and mixing, the food waste undergoes fermentation and fermentation-oxidation processes to obtain secondary food waste: biogas residue and oxidized black sludge. The secondary food waste can then undergo the pretreatment steps described above, or be sent to a pretreatment unit.

[0120] Synthetic gas is prepared using the system or method for preparing syngas from vertical microwave pyrolysis of biogas residue disclosed in the preceding embodiments of this invention.

[0121] For example, the fermented secondary kitchen waste-biogas residue is first centrifuged and dehydrated to achieve solid-liquid separation. Then, it is dried at 80℃ for 24 hours to reduce the moisture content of the kitchen waste. The solid is then pulverized into particles with a diameter of 0.5-1 mm. The material particles and silicon carbide particles are uniformly mixed at a mass ratio of (3-5):20. For example, the silicon carbide particles are preferably 3-5 mm in diameter. Activated carbon particles are spread in the lower layer of the vertical fixed-bed microwave reactor, with a mass ratio of activated carbon to biogas residue material particles of 1:1. The upper layer of the vertical fixed-bed microwave reactor contains material particles and silicon carbide particles. The mixture of material particles and silicon carbide particles is transferred to the upper layer of the vertical fixed-bed microwave reactor for microwave pyrolysis, which is carried out under a protective atmosphere. For example, N2 is introduced into the vertical fixed-bed microwave reactor before the reaction to obtain an inert atmosphere. During the pyrolysis reaction, N2 is continuously introduced at a flow rate of 50 ml / min to drive away the generated gas and positively promote the generation of pyrolysis gas. The microwave power for pyrolysis is 615W, and the frequency is 2460Hz. The combustible gas generated by pyrolysis is recovered after condensation, and the generated pyrolysis oil is recovered through solid-liquid separation by gravity. The solid residue and silicon carbide after pyrolysis are separated and recovered by vibrating sieve due to their different particle sizes. The collected silicon carbide can be mixed with the reactants again for reuse.

[0122] Preferably, the microwave pyrolysis temperature and time are: microwave pyrolysis reaction temperature 400-750℃, pyrolysis time 40min.

[0123] Based on the vertical microwave pyrolysis of biogas residue to prepare syngas according to the present invention, in one embodiment, a set of data was obtained at a pyrolysis temperature of 600℃ and a pyrolysis time of 40 min, as detailed in Table 1 below. Furthermore, the gas product spectrum corresponding to this embodiment is as follows: Figure 4A As shown, the corresponding data source is as follows: Figure 4B As shown.

[0124] Furthermore, a targeted comparative example was designed, still using the conditions of the present invention's vertical microwave pyrolysis of biogas residue to prepare syngas, also at a pyrolysis temperature of 600℃, but without activated carbon particles laid in the lower layer of the vertical fixed-bed microwave reactor:

[0125] First, the secondary kitchen waste—oxidized black sludge—that has undergone fermentation and oxidation treatment is dehydrated and dried to achieve solid-liquid separation. The liquid is recycled, and the solid is pulverized into particles with a diameter of 0.5-1 mm. The material particles and silicon carbide particles are then uniformly mixed at a mass ratio of (3-5):20. The silicon carbide particle size is the same as in the previous embodiment. The mixture of material particles and silicon carbide particles is transferred to a vertical fixed-bed microwave reactor for microwave pyrolysis. Pyrolysis is carried out under a protective atmosphere. Before the reaction, N2 is introduced into the vertical fixed-bed microwave reactor to obtain an inert atmosphere. During the pyrolysis reaction, N2 is continuously introduced at a flow rate of 50 ml / min to drive away the generated gas and positively promote the generation of pyrolysis gas. The microwave power for pyrolysis is 615 W, and the frequency is 2460 Hz. The combustible gas generated by pyrolysis is recovered after condensation. The generated pyrolysis oil is recovered by solid-liquid separation by its own gravity. The solid residue and silicon carbide after pyrolysis are separated and recovered by vibrating sieve due to their different particle sizes. The collected silicon carbide can be mixed with the reactants again for reuse.

[0126] In the comparative example designed above, the microwave pyrolysis reaction temperature was 600℃ and the pyrolysis time was 40 min, and a set of data was obtained, as detailed in Table 1 below. Furthermore, the gaseous product spectrum corresponding to this embodiment is as follows: Figure 5A As shown, the corresponding data source is as follows: Figure 5B As shown.

[0127] for Figure 4B and Figure 5B The data shown is explained as follows:

[0128] Retention time: Every substance has a specific retention time.

[0129] Peak area: The volume fraction of a substance is directly proportional to the peak area.

[0130] Retention time:

[0131] CH4: 1.301 (FID1)

[0132] C2H4: 2.258 (FID1)

[0133] C2H6: 2.747 (FID1)

[0134] C3H8: 6.667 (FID1)

[0135] C4H6: 10.422 (FID1)

[0136] C4H8: 10.585 (FID1)

[0137] C4H 10 10.801 (FID1)

[0138] CO: 6.921 (TCD2)

[0139] CO2: 3.166 (TCD2)

[0140] N2: 3.969 (TCD2)

[0141] right Figure 4B , Figure 5B The calculations from two data sources illustrate that:

[0142] For substances with the same retention time, compare their corresponding peak areas, except for N2 (where N2 is the carrier gas, where...). Figure 5B The corresponding examples are significantly more than Figure 4A (Corresponding example is high); for other components, Figure 4B The data is significantly higher than Figure 5B The data is much larger, indicating Figure 4B In the corresponding example, the concentration of gaseous products is higher. Through standard gas correction calculations, the content of the main products can be obtained; hydrogen is calculated by estimating the total gas concentration to be 100% based on theoretical calculations. The total mass of gaseous products can be calculated using the flow rate of carrier gas N2 (with a fixed total volume), thereby calculating the pyrolysis gas yield. Therefore, based on the above embodiments and comparative examples of the design of this invention, the following table 1 is obtained using this calculation method:

[0143] Table 1

[0144]

[0145] Table 1 shows two existing technologies for comparison:

[0146] (1) Two comparative examples of technology 1, using the traditional pyrolysis method, have the following parameters and gas yields as shown in Table 1;

[0147] (2) The two comparative examples of technology 2 adopt the traditional pyrolysis method. The parameter index and gas yield are shown in Table 1 below;

[0148] The embodiments and comparative examples of this invention employ microwave pyrolysis, and the parameter indicators and gas yields are shown in Table 1 below. It should be noted that the carrier gas used in this invention can be an inert gas, such as nitrogen or argon. For ease of comparison with existing technologies 1 and 2, nitrogen is used in the embodiments and specially designed comparative examples of this invention.

[0149] From the table above, it can be seen that the highest gas yields of existing technologies 1 and 2 are 17.5% and 45.3%, respectively, with corresponding sums of H2 and CO of 43.9% and 41.5%. However, in the present invention's vertical microwave pyrolysis of biogas residue to produce syngas, when activated carbon particles are used as a catalyst in the lower layer of the vertical fixed-bed microwave reactor, the gas yield reaches as high as 52.6%, and the sum of the main gas components H2 and CO reaches 89.2%. Figure 6 As shown.

[0150] See Figure 6 It can be observed that the gas yield and CO and H2 composition of the present invention are significantly improved compared with the two existing technologies. The inventors analyze that the reasons include at least the following:

[0151] (1) Compared with traditional heating, microwave heating has the characteristics of instantaneous heating and selective heating. Therefore, the pyrolysis heating rate is fast and the predetermined temperature is reached in a short time, avoiding unnecessary side reactions in the pyrolysis process. At the same time, the instantaneous high temperature promotes the rapid gasification of the generated pyrolysis oil, and the carbon-hydrogen bonds of organic matter are further broken to generate small molecules of H2 and CO.

[0152] (2) The activated carbon layer at the bottom of the vertical fixed-bed microwave reactor acts as a catalyst. After the reaction, the pyrolysis oil is drawn by gravity and flows through the activated carbon layer. Activated carbon has efficient adsorption and catalytic capabilities. Under microwave pyrolysis conditions, the activated carbon further catalyzes the pyrolysis oil, reducing liquid phase products and increasing gaseous products, thereby achieving efficient conversion of kitchen waste into syngas. Among them, the liquid phase products include: guaiacol, catechol, eugenol, vanillin, furfural, isoeugenol, pyranone, acetic acid, formic acid and other carboxylic acids.

[0153] In one embodiment, Figure 7 This diagram illustrates the connection between a vertical fixed-bed microwave reactor and a microwave source. It is understood that this invention is not limited to a specific vertical fixed-bed microwave reactor; any reactor with an internal structure that facilitates solid-liquid separation of the solid-liquid products obtained from microwave pyrolysis, reducing liquid phase products and increasing gaseous products, is acceptable. Preferably, the internal structure of the vertical fixed-bed microwave reactor also facilitates the recovery of the microwave-absorbing carrier material. Optionally, the internal structure of the vertical fixed-bed microwave reactor further facilitates the recovery of the catalyst.

[0154] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0155] (1) This invention realizes a system and method for preparing syngas from biogas residue by vertical microwave pyrolysis, and also provides a food waste treatment system and microwave pyrolysis process, including dehydration, drying, crushing, material mixing, microwave pyrolysis, and product recovery of secondary food waste. Compared with traditional pyrolysis, this method has lower energy consumption and simpler operation. The process provided in the examples greatly improves the resource utilization rate of food waste.

[0156] (2) This invention uses silicon carbide as a microwave absorption carrier, which is inexpensive, has a high reusability rate, and can effectively improve the heating rate of kitchen waste. The pyrolysis oil produced is further pyrolyzed into combustible gas through the activated carbon layer, thereby effectively improving the yield of syngas. The upper and lower layer structure of the vertical fixed bed microwave reactor allows the solid and liquid products obtained from the upper layer of microwave pyrolysis to be separated by gravity. The silicon carbide carrier particles and solid residues have different particle sizes and can be separated by simple vibration sieving. The separated silicon carbide can be reused as a microwave pyrolysis carrier, reducing operation and material costs. Furthermore, the activated carbon in the lower layer further catalyzes the pyrolysis oil, reducing liquid products and increasing gaseous products, thereby achieving efficient conversion of kitchen waste into syngas. This invention realizes microwave pyrolysis using biogas residue as raw material, significantly increasing gaseous products and significantly improving the proportion of H2 and CO, resulting in a higher calorific value.

[0157] (3) The production of syngas from kitchen waste via microwave pyrolysis has good market prospects and environmental benefits. The syngas produced can be used as a chemical raw material, the pyrolysis oil can be used as fuel, and the solid waste can be treated as inorganic fertilizer. The production process produces little waste and no toxic substances, reducing secondary pollution to the environment, making it both economical and environmentally friendly.

[0158] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A vertical microwave pyrolysis apparatus for preparing syngas from biogas residue, characterized in that, The device includes: Pretreatment unit, microwave pyrolysis reaction unit; The pretreatment unit is used to perform preliminary solid-liquid separation on kitchen waste, and to preheat, dry, and pulverize the material after preliminary solid-liquid separation to prepare the processed material: solid granular powder. The microwave pyrolysis reaction unit includes a vertical fixed-bed microwave reactor, and the microwave pyrolysis reaction unit is used to perform microwave pyrolysis on the treated material under an inert atmosphere, so that the solid and liquid products obtained by microwave pyrolysis can be separated vertically, and the liquid phase products are reduced while the gaseous products are increased. in, When activated carbon particles are used as a catalyst in the lower layer of a vertical fixed-bed microwave reactor, the gas yield reaches as high as 52.6%, and the sum of H2 and CO components reaches 89.2%. The upper layer of the vertical fixed-bed microwave reactor contains material particles and silicon carbide particles. The mixture of material particles and silicon carbide particles is transferred to the upper layer of the vertical fixed-bed microwave reactor for microwave pyrolysis. Pyrolysis is carried out under a protective atmosphere. Before the reaction, N2 is introduced into the vertical fixed-bed microwave reactor to obtain an inert atmosphere. During the pyrolysis reaction, N2 is continuously introduced at a flow rate of 50 ml / min to drive away the generated gas and positively promote the generation of pyrolysis gas. The microwave power for pyrolysis is 615 W. The combustible gas generated by pyrolysis is recovered after condensation. The generated pyrolysis oil is recovered through solid-liquid separation by gravity. The solid residue and silicon carbide after pyrolysis are separated and recovered by vibrating sieve due to their different particle sizes. The collected silicon carbide is mixed with the reactants again for reuse. The activated carbon layer at the bottom of the vertical fixed-bed microwave reactor serves as a catalyst. After the reaction, the pyrolysis oil is drawn by gravity and flows through the activated carbon layer. Activated carbon has high adsorption and catalytic capacity. Under microwave pyrolysis conditions, the activated carbon further catalyzes the pyrolysis oil, reducing liquid products and increasing gaseous products. The bottom layer of the vertical fixed-bed microwave reactor is covered with activated carbon particles, and the mass ratio of activated carbon to biogas residue particles is 1:

1. The microwave pyrolysis reaction temperature is 400-750℃, and the pyrolysis time is 40 min. The microwave pyrolysis reaction unit also includes a material mixer; A material mixer is used to mix the dried and pulverized material from the pretreatment unit with a microwave-absorbing heat carrier. The smaller the particle size of the material entering the material mixer, the better, so as to facilitate the efficient microwave pyrolysis reaction. In addition, the particle size of the material and the particle size of the microwave-absorbing heat carrier silicon carbide should be clearly distinguished so as to facilitate the separation of the microwave-absorbing heat carrier by vibrating sieving in the solid separator. Above the material mixer, silicon carbide is mixed in before the microwave pyrolysis reaction unit starts working, and silicon carbide is replenished to the microwave pyrolysis reaction unit whenever it needs to be replenished during operation.

2. The apparatus according to claim 1, wherein, The device further includes: Recycling unit; The recovery unit is used to recover the combustible gas products obtained from the microwave pyrolysis reaction unit, as well as the microwave-absorbing heat carrier used in the microwave pyrolysis reaction unit.

3. The apparatus according to claim 1, wherein, The device further includes: Circulating fan; The circulating fan is used to circulate the gas generated in the microwave pyrolysis reaction unit by using inert gas to continuously and positively promote the generation of pyrolysis gas.

4. The apparatus according to claim 1, wherein, The pretreatment unit includes a centrifuge, a dryer, and a pulverizer; Food waste is fed into a centrifugal separator. The lower end of the centrifugal separator is connected to an oil-water recovery tank. The right side of the centrifugal separator is connected to a dryer. The right end of the dryer is connected to a pulverizer. The other end of the pulverizer is connected to the microwave pyrolysis reaction unit. The oil-water mixture separated from the kitchen waste is sent to the oil-water recovery tank by a centrifugal separator. The separated kitchen waste is then sent to a dryer and a pulverizer for drying and pulverizing in sequence to obtain the dried and pulverized material. The material is then sent to the microwave pyrolysis reaction unit.

5. The apparatus according to claim 4, wherein, The pretreatment unit also includes an air preheater; The air preheater provides hot air to preheat the food waste separated by the centrifuge and before drying by the dryer, so as to remove as much moisture and volatile substances as possible.

6. The apparatus according to claim 5, wherein, The hot air generated by the dryer is passed to the air preheater and recycled as part of the heat source.

7. The apparatus according to claim 5, wherein, Air preheaters can have their own heat source or power supply, or they can utilize the waste heat from external devices.

8. The apparatus according to claim 1, wherein, The microwave pyrolysis reaction unit also includes a condenser.

9. A method for preparing syngas from biogas residue by vertical microwave pyrolysis, characterized in that, The method is based on the apparatus for preparing syngas from vertical microwave pyrolysis biogas residue as described in any one of claims 1 to 8, and the method includes the following steps: Pre-treatment steps: preliminary solid-liquid separation of kitchen waste, and preheating, drying and pulverizing the material after preliminary solid-liquid separation to prepare the treated material: solid granular powder; Microwave pyrolysis reaction steps: Under an inert atmosphere, the treated material is subjected to microwave pyrolysis, and the solid-liquid products obtained by microwave pyrolysis are vertically separated. The pyrolysis oil obtained by solid-liquid separation is further catalytically pyrolyzed by a catalyst to reduce liquid products and increase gaseous products.

Images