Method for preparing biomass briquette through co-pyrolysis of biomass and waste plastics

Abstract

The invention belongs to the technical field of biomass energy utilization and solid waste resourceful treatment, and particularly relates to a method for preparing biomass briquette through co-pyrolysis of biomass and waste plastics. The method comprises the following steps: (1) raw material pretreatment: respectively drying biomass and waste plastics until the moisture content is lower than 8%, and respectively grinding; (2) hot press molding: uniformly mixing the pretreated biomass and waste plastics according to a mass ratio of (1-5): 1, and then carrying out hot press molding to form a pressed blank; wherein in the hot press forming process, the pressurization pressure ranges from 4.8 MPa to 5.2 MPa, the hot press temperature ranges from 80 DEG C to 100 DEG C, and the pressure maintaining time ranges from 10 min to 30 min; and (3) pyrolysis: heating the compact obtained in the step (2) to 600-800 DEG C at a heating rate of 5-15 DEG C / min in an inert gas atmosphere, carrying out pyrolysis, continuously introducing inert gas in the pyrolysis process, and cooling to obtain the biomass briquette.

Description

Technical Field

[0001] This invention belongs to the field of biomass energy utilization and solid waste resource treatment technology, specifically relating to a method for preparing biomass briquettes by co-pyrolysis of biomass and waste plastics, and the biomass briquettes prepared by this method. Background Technology

[0002] With the increasing depletion of fossil fuels and the intensification of environmental pollution, the development of renewable and clean energy has become a focus of attention for countries worldwide. Biomass energy, as a abundant and carbon-neutral renewable energy source, is of great significance for alleviating the energy crisis and reducing greenhouse gas emissions. Agricultural and forestry waste (such as straw and sawdust) is an important component of biomass resources, but its inherent disadvantages, such as low bulk density, low energy density, and difficulty in storage and transportation, limit its large-scale industrial application. Converting biomass into biomass briquettes or biochar is an effective way to improve its energy density and utilization value. At the same time, with the acceleration of urbanization, "white pollution" caused by waste plastics (such as polyethylene and polypropylene) has also become a serious environmental problem. Waste plastics are rich in hydrogen and have a high calorific value. If biomass and waste plastics can be co-processed, not only can the resource utilization of waste be achieved, but the high calorific value of plastics can also improve the quality of biomass fuels.

[0003] Currently, research on the co-pyrolysis of biomass and waste plastics mainly focuses on the production of liquid fuels (such as bio-oils and aromatics) or gaseous products. For example, existing technologies (such as CN112300824B and CN102618312B) mostly employ melt blending or catalytic cracking processes, adding catalysts such as molecular sieves to break down macromolecules into high-value-added liquid chemicals or fuels, while treating solid char only as a byproduct or low-value residue. However, for technologies aiming to produce high-quality solid fuels (briquettes), existing processes have significant shortcomings: on the one hand, the products of simple biomass carbonization have a loose structure, low mechanical strength, and are easily broken, making it difficult to meet the drop strength requirements for long-distance transportation and industrial furnaces; on the other hand, traditional physical mixing molding methods, due to poor interfacial compatibility between biomass particles and plastic particles, are prone to delamination or poor bonding during pyrolysis, resulting in low bulk density and poor durability of the final briquettes. In addition, conventional pyrolysis processes often lack precise and coordinated control over forming pressure, holding pressure, and heating rate. This can easily lead to cracks or pores inside the briquettes due to excessively rapid volatile release or uneven distribution of binder, further reducing the physical properties of the product.

[0004] Therefore, how to provide a high-quality biomass briquettes with high bulk density, high drop strength and high calorific value that can overcome the defects of existing biochar materials such as loose structure and low mechanical strength, effectively utilize waste plastics as reinforcing components, and prepare them without relying on expensive catalysts is a technical problem that urgently needs to be solved in the field of biomass solid waste resource utilization. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned shortcomings and provide a method for preparing biomass briquettes by co-pyrolysis of biomass and waste plastics.

[0006] Firstly, a method for preparing biomass briquettes by co-pyrolysis of biomass and waste plastics, employing the following technical solution: A method for preparing biomass briquettes by co-pyrolysis of biomass and waste plastics includes the following steps: Step (1), raw material pretreatment: dry the biomass and waste plastics to a moisture content of less than 8% and grind them separately; Step (2), hot pressing: The pretreated biomass and waste plastics are mixed evenly at a mass ratio of (1~5):1 and then hot pressed into a compact; wherein, during the hot pressing process, the pressure is 4.8 MPa~5.2 MPa, the hot pressing temperature is 80 ℃~100 ℃, and the holding time is 10 min~30 min. Step (3), pyrolysis: The pressed briquettes obtained in step (2) are heated to 600 ℃~800 ℃ in an inert gas atmosphere at a heating rate of 5 ℃ / min~15 ℃ / min. Inert gas is continuously introduced during the pyrolysis process, and the briquettes are cooled to obtain the biomass briquettes.

[0007] Furthermore, in step (1), the proportion of biomass ground to 0.15mm particle size is greater than 90%; the proportion of waste plastic ground to 0.15mm particle size is greater than 95%.

[0008] Furthermore, the biomass is selected from at least one of pine wood, industrial hemp stalks, or corn stalks.

[0009] Furthermore, the waste plastic is selected from at least one of polyvinyl chloride waste plastic or polypropylene waste plastic.

[0010] Further, in step (2), the biomass and waste plastics ground in step (1) are mixed at a speed of 200 r / min to 500 r / min for 15 min to 30 min until the materials are evenly mixed.

[0011] Furthermore, in step (3), the heating rate is 8 ℃ / min~12 ℃ / min, and the pyrolysis time is 30 min~60 min.

[0012] Further, in step (3), the flow rate of the inert gas is 100 mL / min to 500 mL / min, and the inert gas is nitrogen or argon.

[0013] Further, in step (3), the cooling step includes the following process: reducing the temperature to below 50°C at a cooling rate of 10°C / min to 20°C / min, and stopping the introduction of inert gas.

[0014] Secondly, a type of biomass briquettes adopts the following technical solution: A biomass briquette prepared by the method described above.

[0015] Furthermore, the bulk density of the biomass briquettes is 0.671 g / cm³. 3 ~0.759 g / cm 3 The drop strength is 93.205%~98.567%, and the calorific value is 31.286 MJ / kg~34.460 MJ / kg.

[0016] The beneficial effects of this invention are: This invention provides a method for preparing biomass briquettes through co-pyrolysis of biomass and waste plastics. Through specific hot-pressing molding and controlled pyrolysis processes, the efficient synergistic conversion of biomass and waste plastics is achieved. This method utilizes the softening rheological properties of waste plastics at 80-100℃, combined with specific pressure and holding time, allowing the softened plastics to act as an in-situ binder, fully penetrating and filling the micropores of the biomass particles, thus constructing a highly dense, physically interlocked structure before pyrolysis. Subsequently, during the pyrolysis stage, a strictly controlled slow heating rate effectively suppresses the violent release of volatiles, preventing microcracks and structural collapse within the briquettes caused by excessive gas pressure, and promoting the tight fusion and bonding of carbonaceous components generated from the pyrolysis of waste plastics with the biomass carbon skeleton. This process not only significantly improves the char yield but also endows the final product with excellent physical and mechanical properties and combustion performance. The biomass briquettes produced have high bulk density and a dense and uniform structure, with a drop strength of up to 98.567%, which can meet the stringent requirements of long-distance transportation and industrial applications. At the same time, the high calorific value of waste plastics is effectively retained and converted into solid products, significantly increasing the calorific value of the briquettes to 3134 MJ / kg, providing a high-quality solid clean fuel. Detailed Implementation

[0017] The following detailed description, in conjunction with embodiments, further illustrates the method for preparing biomass briquettes through co-pyrolysis of biomass and waste plastics according to the present invention. For the sake of simplicity, this document cannot exhaustively list all alternative technical features and embodiments included in the present invention. Therefore, those skilled in the art should understand that any technical feature and embodiment within this embodiment does not limit the scope of protection of the present invention. The scope of protection includes all alternative technical features and embodiments adopted by those skilled in the art without inventive effort. Specifically, any embodiment obtained by replacing any technical feature in the present invention or by combining any two or more technical features provided by the present invention should be within the scope of protection of the present invention. Where specific techniques and conditions are not specified in the embodiments, they are performed according to the techniques and conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0018] This embodiment provides a method for preparing biomass briquettes by co-pyrolysis of biomass and waste plastics, including the following steps: Step (1), raw material preparation and pretreatment.

[0019] The biomass raw materials are mainly derived from agricultural and forestry waste, primarily from agricultural and forestry crops. In a preferred embodiment of this example, the biomass is selected from any one or a combination of pine wood, industrial hemp stalks, or corn stalks. These biomass raw materials are rich in cellulose, hemicellulose, and lignin, forming the basis for constructing a coal skeleton.

[0020] The waste plastic raw materials mainly originate from waste plastics generated in urban life. In a preferred embodiment of this example, the waste plastics are selected from any one or a combination of polyvinyl chloride (PVC) waste plastics and polypropylene (PP) waste plastics. As a hydrogen-rich component, the waste plastics act as a binder and increase the calorific value in subsequent processes.

[0021] To ensure the quality of subsequent molding and pyrolysis, the raw materials must undergo rigorous drying and pulverization. Specifically, biomass and waste plastics are dried separately in drying equipment, controlling the moisture content after drying to be below 8%. This low moisture content prevents micro-cracks from forming inside the green body due to moisture vaporization during hot pressing. After drying, the raw materials are pulverized. Preferably, the proportion of biomass pulverized to 0.15mm particle size is controlled to be greater than 90%, and the proportion of waste plastic pulverized to 0.15mm particle size is controlled to be greater than 95%. This particle size control aims to increase the specific surface area of ​​biomass and plastic particles, improving the uniformity and contact density of their mixing.

[0022] Step (2), mixing and hot pressing.

[0023] The ground biomass and waste plastics are added to a mixing device at a mass ratio of (1~5):1. To ensure the uniform dispersion of the two phases and avoid local structural defects after pyrolysis, a mechanical mixer is preferred for mixing. The specific process parameters are controlled as follows: stirring and mixing at a speed of 200 r / min~500 r / min for 15 min~30 min until a homogeneous mixture is obtained.

[0024] The above mixture is pressed into shape using a hot press. During the hot pressing process, a specific temperature and pressure field must be applied simultaneously: the pressure is controlled at 4.8 MPa to 5.2 MPa, and the hot pressing temperature is controlled at 80 ℃ to 100 ℃. Within this temperature range, the waste plastic softens or partially melts, exhibiting a certain degree of fluidity; under this pressure, the softened plastic is forced to penetrate into the gaps between the biomass pellets. To ensure the densification of the physical structure, the holding time is controlled at 10 min to 30 min. The holding process allows the polymer chain segments to fully relax and diffuse under pressure, eliminating internal stress during molding, thereby obtaining a high-density molded compact.

[0025] Step (3): Pyrolysis is carried out in the pyrolysis reactor.

[0026] The reaction system is purged with an atmosphere by continuously introducing an inert gas to remove air and prevent oxidation and combustion of the materials. The inert gas is preferably nitrogen or argon, and its flow rate is controlled between 100 mL / min and 500 mL / min.

[0027] During the pyrolysis heating stage, to avoid rapid heating leading to a violent release of volatiles and damaging the integrity of the briquettes, this embodiment employs a slow heating strategy. Specifically, the temperature is increased from room temperature or preheating temperature to a final pyrolysis temperature of 600℃~800℃ at a heating rate of 5℃ / min~15℃ / min (preferably 8℃ / min~12℃ / min). After reaching the final temperature, isothermal pyrolysis is performed, with the pyrolysis time maintained at 30 min~60 min to ensure complete carbonization and thorough integration of the carbon deposits generated from waste plastic pyrolysis with the biochar framework.

[0028] After pyrolysis, the cooling stage begins. To prevent thermal stress cracks from sudden cooling of the high-temperature briquettes, a controlled cooling rate is adopted: under inert gas protection, the reactor temperature is reduced to below 50 ℃ at a cooling rate of 10 ℃ / min to 20 ℃ / min. Then, the inert gas supply is stopped and the product is removed, thus obtaining the biomass briquettes.

[0029] Biomass briquettes prepared using the aforementioned specific process possess excellent physical and mechanical properties and combustion performance. Due to the use of hot-pressing and slow pyrolysis processes, the briquettes have a dense internal structure with no obvious macroscopic cracks.

[0030] Testing revealed that the biomass briquettes met all high-quality requirements: their bulk density was 0.671 g / cm³. 3 ~0.759 g / cm 3 It exhibits excellent density; its drop strength is as high as 93.205%~98.567%, indicating that it has extremely strong anti-breakage ability and is suitable for long-distance transportation; its high calorific value reaches 31.286 MJ / kg~34.460 MJ / kg, which is significantly higher than that of ordinary biomass fuel, and can replace some of the traditional fossil coal.

[0031] Example Example 1 This embodiment 1 provides a method for preparing biomass briquettes by co-pyrolysis of biomass and waste plastics, including the following steps: (1) Raw material pretreatment: Pine wood chips were selected as biomass raw material, and polyvinyl chloride (PVC) waste plastics were selected as plastic raw material. Both were placed in an oven for drying, and the moisture content of the dried pine wood chips and waste plastics was controlled to be 5.0%. After drying, they were ground and screened separately, and the proportion of 0.15mm particles in the pine wood chips and the proportion of 0.15mm particles in the PVC waste plastics were controlled to be 100%.

[0032] (2) Hot pressing: Pretreated pine wood chips and PVC waste plastic were added to a mechanical mixer at a mass ratio of 1:1 and mixed at 300 r / min for 20 min to obtain a homogeneous mixture. The mixture was placed in a hot press mold, and the pressure was set to 5.0 MPa and the hot pressing temperature to 80 ℃. After reaching the pressure and temperature, the pressure was maintained for 20 min to allow the plastic to fully soften and penetrate, thus obtaining a molded preform.

[0033] (3) Pyrolysis: The formed compact is placed in a tubular pyrolysis furnace. Nitrogen gas is first introduced to replace the air at a flow rate of 300 mL / min. Then, under a nitrogen atmosphere, the temperature is increased to 800 °C at a heating rate of 10 °C / min and pyrolyzed at a constant temperature for 30 min.

[0034] (4) Cooling and discharge: After pyrolysis, the temperature is reduced to 50 ℃ at a cooling rate of 15 ℃ / min, nitrogen gas is stopped, and biomass briquettes are obtained.

[0035] Product performance: Testing showed that the yield of the obtained biomass briquettes was 27.36%, and the bulk density was 0.759 g / cm³. 3 Its drop strength is 98.567%, and its high calorific value is 31.286 MJ / kg.

[0036] Example 2 This embodiment 2 provides a method for preparing biomass briquettes by co-pyrolysis of biomass and waste plastics, including the following steps: (1) Raw material pretreatment: Industrial hemp stalks were selected as biomass raw material, and polyethylene (PE) waste plastics were selected as plastic raw material. Both were dried in an oven, and the moisture content of the industrial hemp stalks and waste plastics was controlled to be 6.5% after drying. After drying, they were ground and screened, and the proportion of 0.15mm particles in the industrial hemp stalks was controlled to be 92%, and the proportion of 0.15mm particles in the PE waste plastics was controlled to be 96%.

[0037] (2) Hot pressing: Pretreated industrial hemp stalks and waste PE plastic were added to a mechanical mixer at a mass ratio of 5:1 and mixed at 400 r / min for 15 min to obtain a homogeneous mixture. The mixture was placed in a hot press mold, and the pressure was set to 5.0 MPa and the hot pressing temperature to 90 ℃. After reaching the pressure and temperature, the pressure was maintained for 15 min to allow the plastic to fully soften and penetrate, thus obtaining a molded preform.

[0038] (3) Pyrolysis: The formed compact is placed in a tubular pyrolysis furnace. Argon gas is first introduced to replace the air at a flow rate of 200 mL / min. Then, under an argon atmosphere, the temperature is increased to 600 °C at a heating rate of 8 °C / min and pyrolyzed at a constant temperature for 45 min.

[0039] (4) Cooling and discharge: After pyrolysis, the temperature is reduced to 45 ℃ at a cooling rate of 10 ℃ / min, the argon gas is stopped, and the biomass briquettes are obtained.

[0040] Product performance: Testing showed that the yield of the obtained biomass briquettes was 25.17%, and the bulk density was 0.671 g / cm³. 3 Its drop strength is 93.205%, and its high calorific value is 33.986 MJ / kg.

[0041] Example 3 This embodiment 3 provides a method for preparing biomass briquettes by co-pyrolysis of biomass and waste plastics, including the following steps: (1) Raw material pretreatment: Corn stalks were selected as biomass raw material, and polypropylene (PP) waste plastics were selected as plastic raw material. Both were placed in an oven for drying, and the moisture content of the corn stalks and waste plastics was controlled to be 4.0% after drying. After drying, they were ground and screened, and the proportion of 0.15mm particles in the corn stalks was controlled to be 95%, and the proportion of 0.15mm particles in the PP waste plastics was controlled to be 98%.

[0042] (2) Hot pressing: Pretreated corn stalks and PP waste plastic were added to a mechanical mixer at a mass ratio of 3:1 and mixed at 500 r / min for 15 min to obtain a homogeneous mixture. The mixture was placed in a hot press mold, and the pressure was set to 5.0 MPa and the hot pressing temperature to 100 ℃. After reaching the pressure and temperature, the pressure was maintained for 10 min to allow the plastic to fully soften and penetrate, thus obtaining the molded preform.

[0043] (3) Pyrolysis: The formed compact is placed in a tubular pyrolysis furnace. Nitrogen gas is first introduced to replace the air at a flow rate of 500 mL / min. Then, under a nitrogen atmosphere, the temperature is increased to 700 °C at a heating rate of 12 °C / min and pyrolyzed at a constant temperature for 60 min.

[0044] (4) Cooling and discharge: After pyrolysis, the temperature is reduced to below 50 ℃ at a cooling rate of 20 ℃ / min, nitrogen gas is stopped, and biomass briquettes are obtained.

[0045] Product performance: Testing showed that the yield of the obtained biomass briquettes was 25.48%, and the bulk density was 0.755 g / cm³. 3 Its drop strength is 94.388%, and its high calorific value is 34.460 MJ / kg.

[0046] Example 4 This embodiment 4 provides a method for preparing biomass briquettes by co-pyrolysis of biomass and waste plastics, including the following steps: (1) Raw material pretreatment: Pine wood chips were selected as biomass raw material, and polypropylene (PP) waste plastics were selected as plastic raw material. Both were dried in an oven, and the moisture content of the dried pine wood chips and waste plastics was controlled to be 7.5%. After drying, they were ground and screened, and the proportion of 0.15mm particles in the pine wood chips was controlled to be greater than 90%, and the proportion of 0.15mm particles in the PP waste plastics was greater than 95%.

[0047] (2) Hot pressing: Pretreated pine wood chips and PP waste plastic were added to a mechanical mixer at a mass ratio of 2:1 and mixed at 300 r / min for 25 min to obtain a homogeneous mixture. The mixture was placed in a hot press mold, and the pressure was set to 4.8 MPa and the hot pressing temperature to 95 ℃. After reaching the pressure and temperature, the pressure was maintained for 25 min to allow the plastic to fully soften and penetrate, thus obtaining a molded preform.

[0048] (3) Pyrolysis: The formed compact is placed in a tubular pyrolysis furnace. Nitrogen gas is first introduced to replace the air at a flow rate of 250 mL / min. Then, under a nitrogen atmosphere, the temperature is increased to 650 °C at a heating rate of 5 °C / min and pyrolyzed at a constant temperature for 40 min.

[0049] (4) Cooling and discharge: After pyrolysis, the temperature is reduced to 50 ℃ at a cooling rate of 12 ℃ / min, nitrogen gas is stopped, and biomass briquettes are obtained.

[0050] Product performance: The bulk density of the obtained biomass briquettes is tested to be 0.695 g / cm³. 3 Its drop strength is 95.120%, and its high calorific value is 32.150 MJ / kg.

[0051] Example 5 This embodiment 5 provides a method for preparing biomass briquettes by co-pyrolysis of biomass and waste plastics, including the following steps: (1) Raw material pretreatment: Corn stalks were selected as biomass raw material, and polyvinyl chloride (PVC) waste plastics were selected as plastic raw material. Both were dried in an oven, and the moisture content of the corn stalks and waste plastics was controlled to be 3.0% after drying. After drying, they were ground and screened, and the proportion of 0.15mm particles in the corn stalks was controlled to be greater than 90%, and the proportion of 0.15mm particles in the PVC waste plastics was greater than 95%.

[0052] (2) Hot pressing: Pretreated corn stalks and PVC waste plastic were added to a mechanical mixer at a mass ratio of 4:1 and mixed at 350 r / min for 30 min to obtain a homogeneous mixture. The mixture was placed in a hot press mold, and the pressure was set to 5.2 MPa and the hot pressing temperature to 85 ℃. After reaching the pressure and temperature, the pressure was maintained for 30 min to allow the plastic to fully soften and penetrate, thus obtaining a molded preform.

[0053] (3) Pyrolysis: The formed compact is placed in a tubular pyrolysis furnace. Nitrogen gas is first introduced to replace the air at a flow rate of 400 mL / min. Then, under a nitrogen atmosphere, the temperature is increased to 750 °C at a heating rate of 15 °C / min and pyrolyzed at a constant temperature for 35 min.

[0054] (4) Cooling and discharge: After pyrolysis, the temperature is reduced to below 50 ℃ at a cooling rate of 18 ℃ / min, nitrogen gas is stopped, and biomass briquettes are obtained.

[0055] Product performance: The bulk density of the obtained biomass briquettes is 0.742 g / cm³. 3 Its drop strength is 97.805%, and its high calorific value is 31.980 MJ / kg.

[0056] Example 6 This embodiment 6 provides a method for preparing biomass briquettes by co-pyrolysis of biomass and waste plastics, including the following steps: (1) Raw material pretreatment: A mixture of pine sawdust and corn stalks at a mass ratio of 1:1 was selected as the biomass raw material, and a mixture of polyethylene (PE) and polypropylene (PP) at a mass ratio of 1:1 was selected as the plastic raw material. The raw materials were placed in an oven for drying, and the moisture content after drying was controlled to be 6.0%. After drying, they were ground and sieved, and the proportion of 0.15mm particles in the raw materials was controlled to be greater than 90%.

[0057] (2) Hot pressing: The pretreated mixed biomass and mixed waste plastics were added to a mechanical mixer at a mass ratio of 2.5:1 and mixed at 450 r / min for 18 min to obtain a homogeneous mixture. The mixture was placed in a hot press mold, and the pressure was set to 5.1 MPa and the hot pressing temperature to 90 ℃. After reaching the pressure and temperature, the pressure was maintained for 18 min to allow the plastic to fully soften and permeate, thus obtaining the molded preform.

[0058] (3) Pyrolysis: The formed compact is placed in a tubular pyrolysis furnace. Nitrogen gas is first introduced to replace the air at a flow rate of 300 mL / min. Then, under a nitrogen atmosphere, the temperature is increased to 720 °C at a heating rate of 9 °C / min and pyrolyzed at a constant temperature for 50 min.

[0059] (4) Cooling and discharge: After pyrolysis, the temperature is reduced to 50 ℃ at a cooling rate of 15 ℃ / min, nitrogen gas is stopped, and biomass briquettes are obtained.

[0060] Product performance: The bulk density of the obtained biomass briquettes is tested to be 0.723 g / cm³. 3Its drop strength is 96.450%, and its high calorific value is 33.200 MJ / kg.

[0061] Example 7 This embodiment 7 provides a method for preparing biomass briquettes by co-pyrolysis of biomass and waste plastics, including the following steps: (1) Raw material pretreatment: Industrial hemp stalks were selected as biomass raw material, and polyvinyl chloride (PVC) waste plastics were selected as plastic raw material. Both were dried in an oven, and the moisture content of the industrial hemp stalks and waste plastics was controlled to be 7.0% after drying. After drying, they were ground and screened, and the proportion of 0.15mm particles in the industrial hemp stalks was controlled to be greater than 90%, and the proportion of 0.15mm particles in the PVC waste plastics was controlled to be greater than 95%.

[0062] (2) Hot pressing: Pretreated industrial hemp stalks and PVC waste plastic were added to a mechanical mixer at a mass ratio of 1.5:1 and mixed at 250 r / min for 20 min to obtain a homogeneous mixture. The mixture was placed in a hot press mold, and the pressure was set to 4.9 MPa and the hot pressing temperature to 88 ℃. After reaching the pressure and temperature, the pressure was maintained for 12 min to allow the plastic to fully soften and penetrate, thus obtaining a molded preform.

[0063] (3) Pyrolysis: The formed compact is placed in a tubular pyrolysis furnace. Nitrogen gas is first introduced to replace the air at a flow rate of 350 mL / min. Then, under a nitrogen atmosphere, the temperature is increased to 780 °C at a heating rate of 14 °C / min and pyrolyzed at a constant temperature for 55 min.

[0064] (4) Cooling and discharge: After pyrolysis, the temperature is reduced to 50 ℃ at a cooling rate of 12 ℃ / min, nitrogen gas is stopped, and biomass briquettes are obtained.

[0065] Product performance: The bulk density of the obtained biomass briquettes is tested to be 0.738 g / cm³. 3 Its drop strength is 97.100%, and its high calorific value is 32.850 MJ / kg.

[0066] Example 8 This embodiment 8 provides a method for preparing biomass briquettes by co-pyrolysis of biomass and waste plastics, including the following steps: (1) Raw material pretreatment: Pine wood chips were selected as biomass raw material, and polyethylene (PE) waste plastic was selected as plastic raw material. Both were dried in ovens, and the moisture content of the dried pine wood chips and waste plastic was controlled to be 4.5%. After drying, they were ground and screened, and the proportion of 0.15mm particles in the pine wood chips was controlled to be greater than 90%, and the proportion of 0.15mm particles in the PE waste plastic was controlled to be greater than 95%.

[0067] (2) Hot pressing: Pretreated pine wood chips and waste PE plastic were added to a mechanical mixer at a mass ratio of 3.5:1 and mixed at 400 r / min for 22 min to obtain a homogeneous mixture. The mixture was placed in a hot press mold, and the pressure was set to 5.0 MPa and the hot pressing temperature to 98 ℃. After reaching the pressure and temperature, the pressure was maintained for 22 min to allow the plastic to fully soften and penetrate, thus obtaining the molded preform.

[0068] (3) Pyrolysis: The formed compact is placed in a tubular pyrolysis furnace. Nitrogen gas is first introduced to replace the air at a flow rate of 100 mL / min. Then, under a nitrogen atmosphere, the temperature is increased to 680 °C at a heating rate of 6 °C / min and pyrolyzed at a constant temperature for 30 min.

[0069] (4) Cooling and discharge: After pyrolysis, the temperature is reduced to 50 ℃ at a cooling rate of 15 ℃ / min, nitrogen gas is stopped, and biomass briquettes are obtained.

[0070] Product performance: The bulk density of the obtained biomass briquettes is tested to be 0.710 g / cm³. 3 Its drop strength is 95.880%, and its high calorific value is 33.540 MJ / kg.

[0071] Comparative Example Comparative Example 1 Comparative Example 1 provides a method for preparing biomass briquettes through co-pyrolysis of biomass and waste plastics. The only difference from Example 1 is that the briquetting temperature is room temperature (25°C). The specific steps are as follows: (1) Raw material pretreatment: Pine wood chips were selected as biomass raw material, and polyvinyl chloride (PVC) waste plastics were selected as plastic raw material. Both were placed in an oven for drying, and the moisture content of the dried pine wood chips and waste plastics was controlled to be 5.0%. After drying, they were ground and screened separately, and the proportion of 0.15mm particles in the pine wood chips and the proportion of 0.15mm particles in the PVC waste plastics were controlled to be 100%.

[0072] (2) Cold pressing: Pretreated pine wood chips and PVC waste plastic were added to a mechanical mixer at a mass ratio of 1:1 and mixed at 300 r / min for 20 min to obtain a homogeneous mixture. The mixture was placed in a press mold, and the pressure was set to 5.0 MPa and the molding temperature was room temperature (25 ℃). After reaching the pressure, the pressure was maintained for 20 min to obtain the molded compact.

[0073] (3) Pyrolysis: The formed compact is placed in a tubular pyrolysis furnace. Nitrogen gas is first introduced to replace the air at a flow rate of 300 mL / min. Then, under a nitrogen atmosphere, the temperature is increased to 800 °C at a heating rate of 10 °C / min and pyrolyzed at a constant temperature for 30 min.

[0074] (4) Cooling and discharge: After pyrolysis, the temperature is reduced to 50 ℃ at a cooling rate of 15 ℃ / min, nitrogen gas is stopped, and biomass briquettes are obtained.

[0075] Product performance: The bulk density of the obtained biomass briquettes is tested to be 0.582 g / cm³. 3 Its drop strength is 76.450%, and its high calorific value is 30.120 MJ / kg.

[0076] Comparative Example 2 Comparative Example 2 provides a method for preparing biomass briquettes through co-pyrolysis of biomass and waste plastics, differing from Example 1 only in that the molding pressure is lower. The specific steps are as follows: (1) Raw material pretreatment: Same as in Example 1.

[0077] (2) Low-pressure thermoforming: Pretreated pine wood chips and PVC waste plastic are mixed evenly at a mass ratio of 1:1. The mixture is placed in a hot press mold, and the pressure is set to 1.0 MPa and the hot pressing temperature is 80 ℃. After reaching the pressure and temperature, the pressure is maintained for 20 min to obtain the molded blank.

[0078] (3) Pyrolysis: Same as in Example 1.

[0079] (4) Cooling and discharge: Same as in Example 1.

[0080] Product performance: The bulk density of the obtained biomass briquettes is 0.495 g / cm³. 3 Its drop strength is 68.210%, and its high calorific value is 29.850 MJ / kg.

[0081] Comparative Example 3 Comparative Example 3 provides a method for preparing biomass briquettes through co-pyrolysis of biomass and waste plastics. The only difference from Example 1 is the faster pyrolysis heating rate. The specific steps are as follows: (1) Raw material pretreatment: Same as in Example 1.

[0082] (2) Hot pressing: Same as in Example 1.

[0083] (3) Rapid pyrolysis: The formed compact is placed in a tubular pyrolysis furnace, and nitrogen is first introduced to replace the air at a flow rate of 300 mL / min. Then, under a nitrogen atmosphere, the temperature is raised to 800 ℃ at a heating rate of 30 ℃ / min and pyrolyzed at a constant temperature for 30 min.

[0084] (4) Cooling and discharge: Same as in Example 1.

[0085] Product performance: The bulk density of the obtained biomass briquettes is 0.610 g / cm³. 3 Its drop strength is 82.330%, and its high calorific value is 30.560 MJ / kg.

[0086] Comparative Example 4 Comparative Example 4 provides a method for preparing biomass briquettes through co-pyrolysis of biomass and waste plastics. The only difference from Example 1 is that the raw materials are not fully dried. The specific steps are as follows: (1) Raw material pretreatment (high moisture content): Pine wood chips and PVC waste plastic were selected and were not subjected to deep drying treatment. The moisture content was measured to be about 15%. They were ground and screened separately to meet the particle size requirements.

[0087] (2) Hot pressing: Mix the high moisture content raw materials at a mass ratio of 1:1. Set the pressure to 5.0 MPa and the hot pressing temperature to 80 ℃ in the hot press, and hold the pressure for 20 min. (Note: A small amount of steam was observed to overflow during the operation, and cracks appeared on the surface of the pressed blank.) (3) Pyrolysis: Same as in Example 1.

[0088] (4) Cooling and discharge: Same as in Example 1.

[0089] Product performance: The bulk density of the obtained biomass briquettes is tested to be 0.520 g / cm³. 3 Its drop strength is 65.150%, and its high calorific value is 28.900 MJ / kg.

[0090] Comparative Example 5 Comparative Example 5 provides a method for preparing biomass briquettes through co-pyrolysis of biomass and waste plastics. The only difference from Example 1 is that the pressure is immediately released after hot pressing, without a pressure-holding process. The specific steps are as follows: (1) Raw material pretreatment: Same as in Example 1.

[0091] (2) Pressureless molding: Pretreated pine wood chips and PVC waste plastic are mixed evenly at a mass ratio of 1:1. The mixture is placed in a hot press mold, and the pressure is set to 5.0 MPa and the hot pressing temperature is 80 ℃. When the pressure and temperature reach the set values, the pressure is immediately released and the mold is demolded to obtain the molded blank.

[0092] (3) Pyrolysis: Same as in Example 1.

[0093] (4) Cooling and discharge: Same as in Example 1.

[0094] Product performance: The bulk density of the obtained biomass briquettes is tested to be 0.645 g / cm³. 3 Its drop strength is 85.600%, and its high calorific value is 30.800 MJ / kg.

[0095] Comparative Example 6 Comparative Example 6 provides a method for preparing biomass briquettes through co-pyrolysis of biomass and waste plastics. The only difference from Example 1 is that the raw material particles are coarser. The specific steps are as follows: (1) Raw material pretreatment (coarse particles): Select pine wood chips and PVC waste plastic, and dry them to a moisture content of 5.0%. Do not perform fine grinding, but directly crush them into coarse particles with a particle size of about 2~5 mm.

[0096] (2) Hot pressing: The coarse granular raw materials were mixed at a mass ratio of 1:1. The hot pressing conditions were the same as in Example 1 (pressure 5.0 MPa, temperature 80 ℃, holding pressure for 20 min). (Note: After molding, the surface of the compact was observed to be rough, and there were visible gaps between the particles.) (3) Pyrolysis: Same as in Example 1.

[0097] (4) Cooling and discharge: Same as in Example 1.

[0098] Product performance: The bulk density of the obtained biomass briquettes is tested to be 0.550 g / cm³. 3 Its drop strength is 72.500%, and its high calorific value is 30.900 MJ / kg.

[0099] Comparative Example 7 Comparative Example 7 provides a method for preparing biomass briquettes through co-pyrolysis of biomass and waste plastics. The only difference from Example 1 is that only biomass is used as the raw material. The specific steps are as follows: (1) Raw material pretreatment: Only pine wood chips are selected, dried to a moisture content of 5.0%, and ground to a particle size of 0.15mm with a particle size ratio of 100%. No waste plastics are added.

[0100] (2) Hot pressing: Pine wood chips are placed in the hot press mold. Since there is no plastic softening, the hot pressing temperature must be increased to 150℃ (relying on lignin softening) for molding, the pressure is 5.0 MPa, and the pressure is held for 20 min.

[0101] (3) Pyrolysis: Same as in Example 1.

[0102] (4) Cooling and discharge: Same as in Example 1.

[0103] Product performance: The bulk density of the obtained biochar was tested to be 0.480 g / cm³. 3 Its drop strength is 55.600%, and its high calorific value is 24.500 MJ / kg.

[0104] Comparative Example 8 Comparative Example 8 provides a method for preparing biomass briquettes through co-pyrolysis of biomass and waste plastics. The difference from Example 1 is that pyrolysis is performed first, followed by briquetting. The specific steps are as follows: (1) Raw material pretreatment: Same as in Example 1.

[0105] (2) Pyrolysis first: The uniformly mixed pine wood chips and PVC powder are placed directly into the pyrolysis furnace in a loose pile state, and pyrolyzed for 30 min at 800 ℃ under nitrogen protection at a rate of 10 ℃ / min.

[0106] (3) Post-molding: Take out the pyrolyzed biochar / plastic char mixed powder (at this time, the plastic has basically decomposed and carbonized, and lost its binding properties). In order to mold, add 5% starch binder and 10% water, mix evenly, cold press at 5.0 MPa, and dry again.

[0107] Product performance: The bulk density of the obtained briquettes is 0.510 g / cm³. 3 Its drop strength is 80.200%, and its high calorific value is 28.100 MJ / kg.

[0108] Performance testing Performance testing methods and standards The biomass briquettes prepared in Examples 1-8 and Comparative Examples 1-8 were subjected to product performance tests according to the following performance parameter determination methods and standards: Drop strength: The test is conducted in accordance with standard MT / T 925—2004 "Test Method for Drop Strength of Industrial Briquettes". The briquettes are dropped from a specified height, and the percentage of the total weight of fragments with a particle size greater than 13mm (or a specified size) is calculated.

[0109] High calorific value: The calorific value of coal was determined using an oxygen bomb calorimeter (constant temperature calorimeter method) in accordance with the standard GB / T 213—2008 "Determination of calorific value of coal".

[0110] Bulk density: The volume-to-mass ratio of coal briquettes is determined using geometric measurement or water displacement method.

[0111] Particle size analysis: The proportion of raw material particle size was determined using the standard sieve method.

[0112] The performance test results of the biomass briquettes prepared in Examples 1-8 and Comparative Examples 1-8 are shown in Table 1 below.

[0113] Table 1. Performance test results of biomass briquettes obtained in Examples 1-8 and Comparative Examples 1-8

[0114] As shown in Table 1, Examples 1-8 all achieved excellent performance indicators, with bulk densities ranging from 0.671 to 0.759 g / cm³. 3 Between these parameters, the drop strength was consistently above 93% (reaching a maximum of 98.567%), and the high calorific value exceeded 31 MJ / kg. This indicates that the present invention successfully prepared high-quality biomass briquettes by controlling low moisture content raw materials, micronized particle size, specific hot-pressing molding parameters (temperature / pressure / holding pressure), and a slow pyrolysis process.

[0115] Comparative Example 1 shows that relying solely on pressure without temperature (cold pressing) prevents the waste plastic from softening and flowing, hindering its effective binding and resulting in a significant drop strength of 76.45%. Comparative Example 2 shows that insufficient molding pressure (1.0 MPa) fails to achieve the necessary dense packing of the material, leading to a loose product structure and extremely low performance indicators. Comparative Examples 3 and 4 confirm the importance of "slow heating" and "low moisture content." Rapid heating and high moisture content in the raw materials both result in excessive internal pressure during pyrolysis, causing micro-cracks or even macro-cracks, severely damaging the strength of the briquettes. Comparative Example 5 shows that the lack of a "pressure holding" step leads to insufficient plastic penetration and unresolved internal stress, resulting in a significant decrease in strength compared to Example 1. Comparative Examples 6, 7, and 8, respectively, demonstrate the non-obviousness of the technical solution of this invention from three dimensions: raw material particle size, component synergy, and process sequence. In particular, the results of Comparative Example 7 (pure biomass) and Comparative Example 8 (pyrolysis followed by molding) clearly reveal that in-situ hot-pressing bonding and co-pyrolysis modification of waste plastics are indispensable key factors for obtaining high-strength, high-calorific-value briquettes.

[0116] For those skilled in the art, other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, but obvious variations or modifications derived therefrom are still within the scope of protection of the claims of this invention.

Claims

1. A method for preparing biomass briquette by co-pyrolysis of biomass and waste plastic, characterized in that, The method comprises the following steps: Step (1), raw material pretreatment: drying the biomass and waste plastics to a moisture content of less than 8% respectively, and grinding them respectively; Step (2), hot-pressing molding: mixing the pretreated biomass and waste plastics uniformly at a mass ratio of (1-5):1, and then hot-pressing molding into a compact; wherein, during the hot-pressing molding process, the pressurizing pressure is 4.8 MPa-5.2 MPa, the hot-pressing temperature is 80-100℃, and the pressure maintaining time is 10-30 min; Step (3), pyrolysis: pyrolyzing the compact obtained in step (2) under an inert gas atmosphere at a temperature rising rate of 5-15 ℃ / min to 600-800 ℃, continuously introducing inert gas during the pyrolysis process, and cooling to obtain the biomass briquette.

2. The method of claim 1, wherein, In step (1), the biomass is ground to a particle size of 0.15 mm, and the proportion of the particle size is greater than 90%; the waste plastics are ground to a particle size of 0.15 mm, and the proportion of the particle size is greater than 95%.

3. The method of claim 1, wherein, The biomass is selected from at least one of pine wood, industrial hemp stem or corn stalk.

4. The method of claim 1, wherein, The waste plastics are selected from at least one of polyvinyl chloride waste plastics or polypropylene waste plastics.

5. The method of claim 1, wherein, In step (2), the ground biomass and waste plastics in step (1) are mixed at a rotating speed of 200-500 r / min for 15-30 min until the materials are uniformly mixed.

6. The method of claim 1, wherein, In step (3), the temperature rising rate is 8-12 ℃ / min, and the pyrolysis time is 30-60 min.

7. The method of claim 1, wherein, In step (3), the flow rate of the inert gas is 100-500 mL / min, and the inert gas is nitrogen or argon.

8. The method of claim 1, wherein, In step (3), the cooling step comprises the following process: reducing the temperature to below 50℃ at a temperature decreasing rate of 10-20 ℃ / min, and stopping the introduction of inert gas.

9. A biomass briquette prepared by the method according to any one of claims 1-8.

10. The biomass briquette according to claim 9, characterized in that, The bulk density of the biomass briquette is 0.671 g / cm 3 0.759 g / cm 3 The falling strength is 93.205%~98.567%, and the heat value is 31.286 MJ / kg~34.460 MJ / kg.

Images