Biomass pellet fuel as well as preparation method and application thereof

Abstract

The invention relates to the technical field of biomass pellet fuels, and mainly relates to a biomass pellet fuel and a preparation method and application thereof, the biomass pellet fuel comprises the following components by mass: 50%-70% of eucalyptus bark, 10%-25% of sugarcane straw, and 15%-30% of bagasse. The biomass granular fuel is prepared by compounding the eucalyptus bark, the sugarcane stalks and the bagasse as raw materials, and the biomass granular fuel has the advantages of high combustion efficiency, excellent mechanical strength and lower ash content and is more suitable for a process for preparing methanol from biomass. When the biomass granular fuel is applied to a process of biomass gasified methanol, the granular fuel is kept in a complete form in a combustion process due to high mechanical strength, fly ash and fine powder brought out can be reduced, the carbon conversion rate is further improved, and the yield of effective gas is improved.

Description

Technical Field

[0001] This invention relates to the field of biomass pellet fuel technology, and mainly to a biomass pellet fuel, its preparation method, and its uses. Background Technology

[0002] Compared with primary energy sources such as coal, oil, and natural gas, biomass resources have advantages such as being renewable, less polluting, and reducing carbon emissions. Among them, biomass pellet fuel can be processed from agricultural and forestry waste such as straw and sawdust through crushing and mixing processes, and features high combustion efficiency, convenient storage and transportation, and low pollutant emissions.

[0003] To improve resource utilization, biomass pellet fuel is used to synthesize methanol. Currently, biomass pellet fuel is mainly prepared using a single raw material, such as pure sugarcane leaves. Although this method has high combustion efficiency, the loose pellet shape of sugarcane leaves leads to uneven contact with the oxidant during gasification. If used as a feedstock for methanol production, it can cause drastic fluctuations in the composition of the syngas, thus affecting the operation of subsequent sulfur-resistant shift conversion and methanol synthesis processes. Alternatively, pure sugarcane bagasse can also be used as a feedstock for biomass pellet fuel, but due to the low density and low storage and transportation efficiency of sugarcane pellets, it is difficult to produce high-performance biomass pellet fuel. Summary of the Invention

[0004] The purpose of this invention is to provide a biomass pellet fuel, its preparation method and uses, which is prepared by combining eucalyptus bark, sugarcane leaf stalks and sugarcane bagasse to improve the performance of biomass pellet fuel in the biomass gasification to produce methanol.

[0005] To address the above problems, the present invention provides a biomass pellet fuel, which comprises the following components by mass percentage: 50%–70% eucalyptus bark, 10%–25% sugarcane straw, and 15%–30% bagasse.

[0006] In one embodiment, the particle size of the eucalyptus bark, sugarcane stalks, and sugarcane bagasse is 1 mm to 5 mm.

[0007] In one embodiment, the biomass pellet fuel is cylindrical, and the pellet diameter is 6 mm to 10 mm, and the pellet length is 10 mm to 30 mm.

[0008] A second aspect of the present invention provides a method for preparing biomass pellet fuel as described in any of the above embodiments, characterized by comprising the following steps:

[0009] The eucalyptus bark, sugarcane stalks, and sugarcane bagasse are dried and crushed. Weigh out 50%–70% of dried and crushed eucalyptus bark, 10%–25% of sugarcane straw, and 15%–30% of sugarcane bagasse by mass percentage, and put them into a mixer to mix them to obtain a mixture. The mixture is fed into an extrusion granulation device and extruded and granulated at a temperature of 100℃~130℃ and a pressure of 8MPa~12MPa to obtain particulate matter. The particles are cooled and sieved to obtain the biomass pellet fuel.

[0010] In one embodiment, in the step of drying eucalyptus bark, sugarcane stalks and bagasse, the moisture content of the eucalyptus bark, sugarcane stalks and bagasse is reduced to 8% to 15%, and the drying temperature is 80°C to 120°C.

[0011] In one embodiment, after the eucalyptus bark, sugarcane stalks, and sugarcane bagasse are crushed, the particle size of the eucalyptus bark, sugarcane stalks, and sugarcane bagasse is 1 mm to 5 mm.

[0012] In one embodiment, the 50%–70% eucalyptus bark, 10%–25% sugarcane straw, and 15%–30% bagasse are mixed in a mixer for 15–30 minutes, and the mixing speed is 200–300 r / min.

[0013] In one embodiment, the particles are cylindrical, with a particle diameter of 6 mm to 10 mm and a particle length of 10 mm to 30 mm.

[0014] In one embodiment, the particulate matter is placed in a cooling device for cooling for 20 to 40 minutes, the temperature after cooling is ≤35°C, and the moisture content after cooling is 8% to 12%.

[0015] In one embodiment, the defective particles obtained after cooling and sieving the particulate matter are conveyed to the step of crushing eucalyptus bark, sugarcane stalks and bagasse.

[0016] A third aspect of the present invention provides a use of biomass pellet fuel as described in any of the above embodiments, wherein the biomass pellet fuel is used in the production of methanol from biomass.

[0017] As can be seen from the above technical solution, the advantages and positive effects of this invention are as follows: By compounding eucalyptus bark, sugarcane stalks, and bagasse as raw materials to prepare biomass pellet fuel, it has high combustion efficiency, excellent mechanical strength, lower ash content, and is more suitable for the process of biomass to methanol. Specifically, the biomass pellet fuel package contains sugarcane stalks, which have high combustion efficiency, allowing the biomass pellet fuel to release sufficient and stable heat in the incomplete oxidation reaction, providing a continuous high-temperature heat source for the subsequent reduction reaction. On the other hand, the compounding of eucalyptus bark with sugarcane stalks and bagasse can effectively improve the overall formability and give the biomass pellet fuel superior mechanical strength. When applied in the biomass gasification to methanol process, the high mechanical strength allows the pellet fuel to maintain its shape during combustion, preventing local blockage in the combustion zone due to rapid pulverization. This maintains the permeability and flow field uniformity of the material layer in the gasifier, achieving stable flow of biomass fuel during the reaction process. This also reduces fly ash and fine powder carryover, thereby improving carbon conversion rate and the yield of effective gas. On the other hand, it allows for a more uniform spatial distribution of combustion heat and further maintains the thermal balance within the gasifier, providing a stable temperature environment for the continuous gasification reaction. Additionally, the blended biomass pellet fuel has the advantage of low ash content, avoiding the risk of high ash content in biomass pellet fuel combining with water vapor in the gasifier to form a gel-like substance, thus reducing gasification efficiency. Attached Figure Description

[0018] Figure 1 This is a schematic flowchart of the method for preparing biomass pellet fuel in this invention. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. 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. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0020] As used herein, “prepared from” is synonymous with “comprising”. The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0021] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0022] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0023] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (where K is any number representing a multiplier). It is important to understand that, unlike parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0024] The first aspect of the present invention provides biomass pellet fuel, which is formed by compounding eucalyptus bark, sugarcane straw and sugarcane bagasse, giving it the advantages of higher combustion efficiency, higher mechanical strength, lower ash content and better suitability for biomass-to-methanol processes.

[0025] In this embodiment, the biomass pellet fuel comprises the following components by mass percentage: 55%–65% eucalyptus bark, 15%–20% sugarcane straw, and 20%–25% bagasse.

[0026] It should be noted that, since sugarcane leaves and sugarcane stalks are often used interchangeably in agricultural and everyday contexts, sugarcane stalks in this application specifically include sugarcane leaves and sugarcane stalks. Sugarcane leaves refer to the leaf part of the sugarcane plant, which is one of the components of sugarcane stalks; sugarcane stalks refer to all the above-ground parts of the sugarcane plant remaining after the sugar stems (edible or sugar-making parts) are harvested, including the stems and leaves.

[0027] Specifically, eucalyptus bark, as a major raw material with a high proportion in biomass pellet fuel, enables the biomass pellet fuel to possess high mechanical strength and resistance to breakage. This compensates for the shortcomings of pure sugarcane straw, which is easily broken and has a loose shape, and pure sugarcane bagasse, which has low particle density and poor structural stability, resulting in poor mechanical strength of biomass pellet fuel. Biomass pellet fuel prepared from eucalyptus bark has excellent mechanical strength, making it less prone to pulverization during storage, transportation, and feeding to the furnace. It can maintain a regular pellet shape and will not break rapidly in the high-temperature environment of the gasifier, laying the foundation for continuous and uniform feeding and stable reaction in the furnace for the gasification of methanol.

[0028] Sugarcane stalks have the advantage of high calorific value. When added as an auxiliary material, they can compensate for the low calorific value and low combustion efficiency of pure eucalyptus bark pellets, effectively improving the overall calorific value and combustion efficiency of biomass pellet fuel. This sufficient calorific value provides a stable self-supplied heat source for the biomass gasification reaction. When biomass pellet fuel is used in the biomass methanol production process, the ample calorific value provides a stable self-supplied heat source for the biomass gasification reaction, reducing the risk of incomplete gasification affecting gasification efficiency. Furthermore, the high combustion characteristics of sugarcane stalks can also improve the conversion rate of biomass carbon, allowing more carbon elements to be converted into CO and CO2 in the syngas, providing a sufficient carbon source for methanol synthesis.

[0029] The addition of bagasse gives biomass pellet fuel good overall binding and formability. When combined with sugarcane stalks and eucalyptus bark, it can solve the problems of poor formability and easy cracking and flaking during extrusion pelleting that occur when sugarcane stalks are used as raw materials alone, as well as the problems of average formability and high energy consumption during pelleting that occur when eucalyptus bark is used as raw materials alone. It is beneficial to allow the three raw materials to be fully plasticized during the extrusion pelleting process, forming pellet fuel with high density, regular shape, and no cracking.

[0030] On the other hand, although bagasse pellets have low ash content, they have poor formability and are prone to pulverization. During gasification, the fine powder carries ash, resulting in high actual ash loss. By compounding eucalyptus bark, bagasse, and sugarcane leaves, the high degree of lignification and low content of inorganic mineral impurities in eucalyptus bark result in a much lower ash background than straw and herbaceous biomass. The compounding of these three raw materials not only utilizes their respective low ash advantages but also reduces ash entrainment during gasification through complementary morphological structures. This allows the overall ash content of pellet fuel to be controlled at ≤5%, keeping both the actual measured ash content and the ash impact of the process at a low level, thus reducing the generation of fly ash and slag during gasification. In this way, by compounding eucalyptus bark, sugarcane stalks, and bagasse to prepare biomass pellet fuel, the biomass pellet fuel can simultaneously possess the comprehensive advantages of high mechanical strength, high calorific value, excellent formability, low ash content, and high storage and transportation efficiency. This solves the disadvantages of low mechanical strength and easy pulverization of biomass pellets prepared from pure sugarcane stalks, the disadvantages of low density and easy entrainment of unreacted carbon during gasification of biomass pellets prepared from pure bagasse, and the disadvantages of low calorific value and high ash content of biomass pellets prepared from pure eucalyptus bark.

[0031] Furthermore, biomass pellet fuel is applied in the gasification process for methanol production, directly participating in the gasification reaction. The gasification reaction refers to the gasification of biomass pellet fuel in a gasifier, converting biomass into a mixture of synthesis gases rich in CO, CO2, CH4, water vapor, and sulfides.

[0032] Eucalyptus bark has many long fibers with poor flowability, making it difficult to form and process. Using eucalyptus bark alone to produce biomass pellet fuel results in low yield. However, sugarcane stalks and bagasse have fewer fibers, higher sugar content, and better flowability. Mixing them can improve processing efficiency and increase yield. However, sugarcane leaves are typically collected in large quantities due to different collection methods, and bagasse is high in sugar, making it prone to coking during gasification. The coking material easily adheres to the surface of the pellet fuel and the gasifier walls, disrupting the stable temperature field inside the furnace. Furthermore, the coking material tightly coats the surface of the biomass pellets, preventing carbon in the core of the pellets from participating in the gasification reaction, significantly reducing carbon conversion rate. At the same time, the coking material inhibits pyrolysis and reduction reactions, reducing the generation of CO, H2, and other effective gases for methanol synthesis, while increasing byproducts such as CH4 and heavy hydrocarbons, affecting the yield and efficiency of subsequent methanol synthesis.

[0033] The biomass pellet fuel prepared in this application, through the compounding of eucalyptus bark, sugarcane stalks, and bagasse as raw materials, exhibits high combustion efficiency, excellent mechanical strength, lower ash content, and is more suitable for the biomass-to-methanol process. Specifically, the biomass pellet fuel, containing sugarcane stalks, possesses high combustion efficiency, allowing it to release sufficient and stable heat during the incomplete oxidation reaction, providing a continuous high-temperature heat source for the subsequent reduction reaction. Furthermore, the compounding of eucalyptus bark with sugarcane stalks and bagasse effectively improves the overall formability and gives the biomass pellet fuel superior mechanical strength. When applied in the biomass-to-methanol process, this high mechanical strength ensures the pellet fuel maintains its shape during combustion, preventing localized blockage in the combustion zone due to rapid pulverization. This maintains the permeability and flow field uniformity of the feedstock within the gasifier, ensuring stable flow of the biomass fuel during the reaction. This also reduces fly ash and fine powder carryover, thereby increasing carbon conversion rate and the yield of effective gas. On the other hand, it allows for a more uniform spatial distribution of combustion heat and further maintains the thermal balance within the gasifier, providing a stable temperature environment for the continuous gasification reaction. Additionally, the blended biomass pellet fuel has the advantage of low ash content, avoiding the risk of high ash content in biomass pellet fuel combining with water vapor in the gasifier to form a gel-like substance, thus reducing gasification efficiency.

[0034] Therefore, it can be seen that the compounding and pelleting of biomass pellets by eucalyptus bark, sugarcane straw and sugarcane bagasse can not only improve the processing efficiency of biomass pellets, but also reduce the overall ash content of biomass pellets. In addition, it can also reduce the problem of coking that occurs during the gasification process of biomass pellets.

[0035] Preferably, the biomass pellet fuel comprises, by weight percentage: 55%–65% eucalyptus bark, 15%–20% sugarcane straw, and 20%–25% bagasse.

[0036] By setting the mass percentage of eucalyptus bark to 55%–65%, eucalyptus bark, as a high-proportion core raw material, enables the prepared biomass pellet fuel to possess the core characteristics of high mechanical strength and low ash content. This ensures the morphological integrity of the biomass pellet fuel throughout the entire process of storage, transportation, gasification feeding, and in-furnace reaction, thereby reducing the risk of ash residue forming in the gasifier affecting gasification efficiency. By setting the mass percentage of sugarcane straw to 15%–20%, a sugarcane straw mass percentage greater than 15% can more effectively compensate for the low calorific value of eucalyptus bark, while a sugarcane straw mass percentage less than 20% can avoid the problems of easy pellet cracking and easy pulverization in the furnace caused by the loose fiber characteristics of sugarcane straw, which can damage the overall formability and structural stability of the pellets. Sugarcane straw, as a calorific value supplement, not only increases the calorific value but also avoids the decrease in formability caused by an excessively high proportion. By setting the mass percentage of bagasse to 20%–25%, a mass percentage greater than 20% provides more effective binding properties, thus improving pellet formation. A mass percentage less than 25% avoids the problem of insufficient strength in biomass pellet fuel due to an excessively high proportion. By compounding eucalyptus bark, bagasse, and sugarcane stalks according to the above ratio, the loose eucalyptus bark can be fully plasticized and interlocked with the sugarcane stalks and bagasse, improving overall mechanical strength, breakage resistance, and combustion efficiency, while also reducing ash and moisture content in the fuel.

[0037] In some embodiments, the biomass pellet fuel is cylindrical, and the pellet diameter is 6 mm to 10 mm, and the pellet length is 10 mm to 30 mm.

[0038] By extruding biomass pellets into cylindrical shapes, not only are the finished pellets uniform in shape, but their high mechanical strength also prevents pulverization during transportation or gasification, thus avoiding problems that could affect gasification efficiency. Furthermore, the pellet diameter is 6mm–10mm. Setting the pellet diameter to greater than 6mm prevents pellets from being easily carried away by the gasification gas flow, causing incomplete gasification and resulting in feed waste and a decrease in gasification conversion rate. Setting the pellet diameter to less than 10mm reduces the risk of incomplete internal reaction due to overly coarse pellets, where only the surface participates in the gasification reaction, preventing the proper conversion of carbon and hydrogen within the pellets.

[0039] Furthermore, by setting the pellet length to be greater than 10 mm, the problem of biomass pellet fuel being too short and easily breaking into fragments, which would be inconvenient for transportation and storage, can be avoided. This also prevents excessive porosity in the feed layer inside the furnace, which could affect the gas flow velocity in the gasification reactor. Conversely, by setting the pellet length to less than 30 mm, the problem of uneven feed layer distribution and particle entanglement caused by excessively long pellets can be avoided, which would lead to uneven porosity and reduced gasification efficiency. This makes biomass pellet fuel more suitable for gasification reactions, improving storage, transportation, and process operation performance.

[0040] Figure 1 This is a schematic flowchart of the method for preparing biomass pellet fuel in this invention.

[0041] like Figure 1 As shown, another embodiment of this application provides a method for preparing biomass pellet fuel, used to prepare biomass pellet fuel as described in any of the above embodiments, comprising the following steps: S100. Dry and crush eucalyptus bark, sugarcane stalks and sugarcane bagasse.

[0042] Specifically, the three raw materials can be separately fed into a drum dryer or a box dryer for drying, with the drying temperature being 80℃~120℃. This step is used to reduce the moisture content of the raw materials.

[0043] It should be noted that eucalyptus bark, sugarcane stalks, and sugarcane bagasse can be dried separately or simultaneously, and can be crushed separately or simultaneously.

[0044] By controlling the drying temperature to 80℃~120℃, the density of eucalyptus bark can be rapidly reduced, which leads to the formation of more bound water inside. In addition, sugarcane stalks and bagasse have loose fibers, and 80℃~120℃ can efficiently dry sugarcane stalks and bagasse while avoiding fiber carbonization.

[0045] After the above drying process, the moisture content of the raw materials can be controlled at 8% to 15%. This helps to avoid problems such as material sticking and clogging during pelleting and easy moisture absorption and mold growth of finished pellets due to excessive moisture in the subsequent extrusion pelleting process. Moreover, it can avoid problems such as poor material plasticity and easy cracking and breakage during extrusion pelleting due to excessive moisture, which is beneficial to the subsequent extrusion pelleting process of biomass pellet raw materials.

[0046] Preferably, the moisture content of eucalyptus bark, sugarcane stalks, and sugarcane bagasse is controlled at 8% to 15%.

[0047] Furthermore, after crushing the eucalyptus bark, sugarcane stalks, and sugarcane bagasse, the particle size of the eucalyptus bark, sugarcane stalks, and sugarcane bagasse is 1mm to 5mm.

[0048] Specifically, the particle size of eucalyptus bark, sugarcane stalks, and bagasse is 1mm to 5mm. By pulverizing all three raw materials to a particle size of 1mm to 5mm, processing efficiency can be improved by avoiding the negative impact of excessively large particle sizes on production efficiency. Furthermore, this process ensures that the eucalyptus bark, sugarcane stalks, and bagasse can fully contact and uniformly integrate during the subsequent mixing stage, resulting in a uniformly blended fuel pellet. This avoids uneven mixing caused by stratification due to differences in particle size, and allows the biomass pellet fuel to possess the mechanical strength of eucalyptus bark, the calorific value of sugarcane stalks, and the molding properties of bagasse. Simultaneously, pulverizing the raw materials to 1mm to 5mm increases the specific surface area of ​​the three materials. This larger surface area allows for rapid moisture removal during the drying stage, precisely controlling the moisture content within an appropriate range. On the other hand, the uniform fine particle size contributes to a more uniform internal pore structure in the finished biomass pellet fuel after extrusion pelleting. This provides a channel for the contact reaction between the gasifying agent and the pellet interior in the gasifier, improving the carbon conversion rate of the subsequent gasification reaction.

[0049] It should be noted that before drying and crushing eucalyptus bark, sugarcane stalks, and bagasse, impurities such as stones, metals, and plastics can be removed from the raw materials. This avoids hard impurities from wearing down core components such as the crusher and extrusion pelletizing equipment during subsequent crushing and pelletizing processes, reducing the probability of equipment failure and extending equipment lifespan. At the same time, it also prevents non-biomass impurities from mixing into the pellet fuel, thus preventing the impurities from burning or gasifying in the gasifier and producing harmful pollutants, or forming additional ash residue due to the impurities' inability to gasify. This improves the purity of the pellet fuel and maintains the cleanliness of the subsequent gasification reaction.

[0050] S200: Weigh 50%–70% of dried and crushed eucalyptus bark, 10%–25% of sugarcane straw, and 15%–30% of sugarcane bagasse by mass percentage, and put them into a mixer to mix and obtain a mixture.

[0051] The mixture consists of 50%–70% eucalyptus bark, 10%–25% sugarcane straw, and 15%–30% sugarcane bagasse. The mixing time is 15–30 minutes, and the mixing speed is 200–300 r / min.

[0052] Specifically, the three dried and pulverized raw materials can be added to a twin-helix mixer or a horizontal mixing device and stirred for 15–30 minutes at a stirring speed of 200–300 r / min. This allows the eucalyptus bark, sugarcane stalks, and bagasse to form strong convection, shearing, and diffusion within the mixing device. This process breaks up the agglomeration of the various raw materials, achieving uniform fusion and avoiding the formation of localized enrichment zones of eucalyptus bark, sugarcane stalks, or bagasse. As a result, after the above mixing steps, a homogeneous mixture is formed, preventing issues such as insufficient mechanical strength and brittleness due to low local eucalyptus bark content, low calorific value due to low local sugarcane stalk content, and poor formability and cracking due to low local bagasse content. On the other hand, when uniformly composed pellet fuel undergoes gasification in the gasifier, the reaction rate, heat release effect, and carbon conversion rate of each part tend to be more consistent, avoiding local temperature fluctuations and uneven syngas composition caused by differences in local composition, thus providing a compositional basis for the stable progress of subsequent gasification reactions.

[0053] S300. The mixture is fed into an extrusion granulation equipment and extruded and granulated at a temperature of 100℃~130℃ and a pressure of 8MPa~12MPa to obtain granules.

[0054] The extruded granules are cylindrical with a diameter of 6 mm to 10 mm and a length of 10 mm to 30 mm. The speed of the extrusion granulation equipment is 150 r / min to 200 r / min.

[0055] Specifically, the extrusion granulation equipment can be a ring die pellet mill. The ring die diameter of the ring die pellet mill is 6 mm to 10 mm. Extrusion granulation is carried out at a temperature of 100℃ to 130℃ and a pressure of 8MPa to 12MPa. This is beneficial for the mixture to undergo thermoplastic softening during the extrusion process, and the binding properties of bagasse are fully utilized. This allows the eucalyptus bark, sugarcane stalks, and bagasse fibers to form a tightly interlocked and intertwined mixture structure, thereby achieving a dense granular structure and solving the problem of easy breakage of single sugarcane stalks or bagasse particles.

[0056] Furthermore, by using a cutter in conjunction with a ring die pellet mill, the length of the pellets can be controlled from 10mm to 30mm, thereby producing cylindrical pellets. By extruding and granulating biomass pellets into cylindrical shapes, not only can the finished pellets have a regular shape, but their high mechanical strength also prevents problems such as pulverization during transportation or gasification, which could affect the efficiency of the gasification reaction.

[0057] Specifically, when the particle diameter or length is too large, the particles may jam or interlock, leading to bridging at the silo outlet or in the conveying pipeline, causing problems such as interruption of feeding and blockage. On the other hand, when the particle diameter or length is too small, the particle fuel will be consumed too quickly during the gasification process without sufficient reaction, affecting the efficiency of the methanol production process.

[0058] In this embodiment, the biomass pellet fuel has a pellet diameter of 6mm to 10mm. By setting the pellet diameter to be greater than 6mm, it avoids the problem of pellets that are too small being easily carried away by the gasification gas flow and leaving the gasifier without fully participating in the gasification reaction, thus causing raw material waste and a decrease in the gasification conversion rate. Setting the pellet diameter to be less than 10mm also reduces the problem of insufficient internal reaction due to excessively large pellets, where only the surface participates in the gasification reaction and the internal carbon and hydrogen elements cannot be converted accordingly. Moreover, by setting the pellet length to be greater than 10mm, it prevents the biomass pellet fuel from becoming too short and easily breaking into fragments, which would be inconvenient for transportation and storage. It also avoids excessive porosity in the feed layer inside the furnace, which would affect the gas flow velocity in the gasification reactor. By setting the particle length to less than 30mm, the problem of uneven distribution of the material layer in the furnace and uneven porosity caused by the particles being too long is avoided, which reduces the gasification efficiency. This makes biomass pellet fuel more suitable for gasification reaction and improves storage, transportation and process operation performance.

[0059] S400: Cool the particles and screen them to obtain biomass pellet fuel.

[0060] Specifically, the particulate matter is placed in a cooling device for cooling for 20 to 40 minutes, so that the particulate matter is cooled to room temperature, the temperature of the particulate matter after cooling is ≤35℃, and the moisture content after cooling is 8% to 12%.

[0061] In the S300 extrusion granulation process, high temperatures are generated, causing some residual moisture in the raw material to vaporize into water vapor. Under high pressure, this water vapor cannot escape quickly and instead fills the gaps between the raw material fibers. When the pellets are extruded from the die, the temperature drops rapidly, and the water vapor condenses back into liquid water, which is then reabsorbed into the fiber gaps. Particles with high moisture content, when used in the biomass-to-methanol process, result in excessive water vapor during gasification, affecting the gasification reaction efficiency and reducing the yield of the gasification products. In this embodiment, the pellets obtained from the S300 extrusion granulation are fed into an air-cooled cooling device to cool them to room temperature. This effectively removes internal moisture from the pellets and avoids the formation of internal stress due to rapid cooling, which can cause structural cracking and reduced mechanical strength. Furthermore, reducing the moisture content of the finished biomass pellet fuel reduces the impact of water vapor on the thermal balance of the gasification reaction, minimizing interference and improving the reaction efficiency.

[0062] Since the particle size may change due to temperature variations, the particles are cooled to reduce their moisture content before being screened again. Specifically, a double-layer screening device can be used, with screen apertures of 5mm and 11mm, to remove fragments smaller than 5mm and particles larger than 11mm.

[0063] Furthermore, the unqualified particles obtained after cooling and screening the particles are conveyed to the step of crushing eucalyptus bark, sugarcane stalks and bagasse, and then re-enter the subsequent mixing, granulation, cooling and screening processes for reuse, thereby improving the utilization rate of raw materials.

[0064] Another aspect of the present invention provides a use of biomass pellet fuel in the production of methanol from biomass.

[0065] Specifically, compared to current single-fuel fuels such as pure eucalyptus bark pellets (low calorific value, high ash content), pure sugarcane straw pellets (poor formability, insufficient combustion stability), and pure bagasse pellets (low density, low storage and transportation efficiency), the biomass pellet fuel of this application possesses excellent mechanical strength, high calorific value, low ash content, and low moisture content. The good mechanical strength of the biomass pellet fuel prevents pulverization during storage, transportation, and pre-furnace feeding, maintaining a regular pellet shape. Furthermore, it does not rapidly break down in the high-temperature environment of the gasifier, laying the foundation for continuous and uniform feeding and stable in-furnace reaction in methanol gasification. The good calorific value and high combustion efficiency of the biomass pellet fuel provide a stable self-supplied heat source for the biomass gasification reaction. When applied to the biomass methanol production process, the sufficient combustion calorific value provides a stable self-supplied heat source for the biomass gasification reaction, reducing the risk of incomplete gasification affecting gasification efficiency and providing a sufficient carbon source for methanol synthesis. In addition, biomass pellet fuel has the advantage of low ash content, which reduces the generation of fly ash and slag during gasification. This avoids the risk that the ash and slag formed by the high ash content of biomass pellet fuel will combine with water vapor in the gasifier to form a gel-like substance, thereby reducing gasification efficiency.

[0066] The inventors of this application have achieved the preparation of biomass pellet fuel by strictly designing the content of each component and the parameters in each step. The preparation method of biomass pellet fuel is described below through various embodiments.

[0067] Example 1 The method for preparing biomass pellet fuel in this embodiment includes the following steps: S110. Dry eucalyptus bark, sugarcane stalks and sugarcane bagasse at a drying temperature of 80℃ until the moisture content is 15%, and then crush them to a particle size of 1-5mm. S120. Weigh out 55% of dried and crushed eucalyptus bark, 15% of sugarcane straw and 30% of sugarcane bagasse by mass percentage, put them into a mixer and mix for 30 minutes at a stirring speed of 200 r / min to obtain a mixture. S130. The mixture is fed into an extrusion granulation device and extruded and granulated at a temperature of 100°C and a pressure of 8MPa to obtain particulate matter. S140. Cool the particulate matter to room temperature for 40 minutes and then sieve it to obtain the biomass pellet fuel.

[0068] Example 2 The method for preparing biomass pellet fuel in this embodiment includes the following steps: S110. Dry eucalyptus bark, sugarcane stalks and sugarcane bagasse at a drying temperature of 80℃ until the moisture content is 15%, and then crush them to a particle size of 1-5mm. S120. Weigh out 65% of dried and crushed eucalyptus bark, 20% of sugarcane straw and 15% of sugarcane bagasse by mass percentage, put them into a mixer and mix for 30 minutes at a stirring speed of 200 r / min to obtain a mixture. S130. The mixture is fed into an extrusion granulation device and extruded and granulated at a temperature of 100°C and a pressure of 8MPa to obtain particulate matter. S140. Cool the particulate matter to room temperature for 40 minutes and then sieve it to obtain the biomass pellet fuel.

[0069] Example 3 The method for preparing biomass pellet fuel in this embodiment includes the following steps: S310. Dry eucalyptus bark, sugarcane stalks and sugarcane bagasse at a drying temperature of 80℃ until the moisture content is 15%, and then crush them to a particle size of 1-5mm. S320. Weigh 50% of dried and crushed eucalyptus bark, 25% of sugarcane straw and 25% of sugarcane bagasse by mass percentage, put them into a mixer and mix for 30 minutes at a stirring speed of 200 r / min to obtain a mixture. S330. The mixture is fed into an extrusion granulation device and extruded and granulated at a temperature of 100°C and a pressure of 8MPa to obtain particulate matter. S340. Cool the particulate matter to room temperature for 40 minutes and then sieve it to obtain the biomass pellet fuel.

[0070] Example 4 The method for preparing biomass pellet fuel in this embodiment includes the following steps: S410. Dry eucalyptus bark, sugarcane stalks and sugarcane bagasse at a drying temperature of 100℃ until the moisture content is 11%, and then crush them to a particle size of 1-5mm. S420. Weigh out 60% of dried and crushed eucalyptus bark, 18% of sugarcane straw and 22% of sugarcane bagasse by mass percentage, put them into a mixer and mix for 20 minutes at a stirring speed of 250 r / min to obtain a mixture. S430. The mixture is fed into an extrusion granulation device and extruded and granulated at a temperature of 115°C and a pressure of 10MPa to obtain particulate matter. S440. Cool the particulate matter to room temperature for 30 minutes and then sieve it to obtain the biomass pellet fuel.

[0071] Example 5 The method for preparing biomass pellet fuel in this embodiment includes the following steps: S510. Dry eucalyptus bark, sugarcane stalks and sugarcane bagasse at a drying temperature of 120℃ until the moisture content is 8%, and then crush them to a particle size of 1-5mm. S520. Weigh 70% of the dried and crushed eucalyptus bark, 10% of sugarcane straw and 20% of sugarcane bagasse by mass percentage, put them into a mixer and mix for 15 min at a stirring speed of 300 r / min to obtain a mixture. S530. The mixture is fed into an extrusion granulation device and extruded and granulated at a temperature of 130°C and a pressure of 12MPa to obtain particulate matter. S540. Cool the particulate matter to room temperature for 20 minutes and then sieve it to obtain the biomass pellet fuel.

[0072] Comparative Example 1 The difference between Comparative Example 1 and Example 4 is that the raw material used is a single type of eucalyptus bark.

[0073] Comparative Example 2 The difference between Comparative Example 2 and Example 4 is that the raw materials used are sugarcane straw and sugarcane bagasse in a mass ratio of 1:1.

[0074] Comparative Example 3 The difference between Comparative Example 3 and Example 4 is that the raw materials consist of 60% eucalyptus bark and 40% sugarcane straw.

[0075] Comparative Example 4 The difference between Comparative Example 4 and Example 4 is that the raw materials consist of 60% eucalyptus bark and 40% sugarcane bagasse.

[0076] The performance of the biomass pellet fuels prepared in Examples 1-5 and Comparative Examples 1-4 was evaluated using the following methods: (1) Method for testing heat generation: According to GB / T30727-2014 "Method for Determination of Calorific Value of Solid Biomass Fuel", the prepared biomass pellet sample is ground to the specified particle size, a quantitative sample is weighed and placed in an oxygen bomb and charged with high-pressure oxygen. The combustion temperature rise is measured using an oxygen bomb calorimeter. After correction for heat capacity and heat of formation of nitric acid, the calorific value of the sample is calculated, and then the constant volume higher calorific value and constant volume lower calorific value are calculated.

[0077] (2) Methods for testing ash content: According to GB / T28731-2012 "Analytical Methods for Solid Biomass Fuel Industry", 1±0.1g of air-dried sample with a particle size ≤0.2mm was placed in an ash dish, placed in a muffle furnace, and slowly heated to 550±10℃ according to the program and ignited at a constant temperature until constant weight. The ash content was determined as the percentage of the mass of the residue to the dry basis mass of the sample.

[0078] (3) Methods for testing combustion efficiency: According to GB / T35811-2018 "Test Method for Combustion Performance of Biomass Fuels", a simulated combustion test bench was built to measure the flue gas composition (such as CO and CO2 concentration), heat loss and burnout rate when biomass pellets are burned in the boiler. Combustion efficiency was calculated by combining the ratio of input heat to effective heat utilization.

[0079] (4) Methods for testing mechanical strength: According to GB / T28735-2012 "Determination of Mechanical Durability of Solid Biofuel Pellets" (equivalent to ISO17831), a certain amount of biomass pellet sample is weighed and placed into a rotary drum tester. After rotating at a specified speed (50 r / min) for a specified time (10 min), the pellets larger than the specified particle size are collected by sieving with a standard sieve. The mechanical durability (mechanical strength) is characterized by the percentage of its mass to the initial mass of the sample.

[0080] The data obtained according to the above testing method are shown in Table 1.

[0081] Table 1 Performance of Biomass Pellet Combustion

[0082] As shown in Table 1, the biomass pellet fuels prepared in Examples 1-5 have better calorific value and mechanical strength than those in Comparative Examples 1-4. It should be noted that the ash content of the biomass pellet fuels prepared in Examples 1-5 is lower than that of Comparative Examples 1 to 3. Although Comparative Example 4 has the lowest ash content, its calorific value, combustion efficiency, and mechanical strength are inferior.

[0083] The biomass pellet fuels prepared in Examples 1 and 3-5 all exhibited higher combustion efficiencies than those in Comparative Examples 1 and 3-4. While Comparative Example 2 had a higher combustion efficiency than Comparative Example 2, its high ash content made it unsuitable for biomass gasification to produce methanol, and its overall performance, including ash content, calorific value, and mechanical strength, was poor.

[0084] Compared to Comparative Examples 1 to 4, Example 4 exhibits superior calorific value, combustion efficiency, ash content, and mechanical strength compared to the biomass pellet fuels prepared in the comparative examples. This demonstrates that eucalyptus bark, sugarcane straw, and bagasse can complement each other in terms of performance, offering advantages such as high calorific value, high mechanical strength, low ash content, high combustion efficiency, and strong stability compared to using only a single raw material or only two of them. Furthermore, regarding mechanical strength characteristics, Comparative Examples 1 and 4 both possess a mechanical strength of 90%, indicating relatively high mechanical strength among the comparative examples. However, due to the lack of sugarcane straw, their overall performance is poor. Comparative Examples 2 and 3 show lower mechanical strength because the sugarcane straw fibers and bagasse fibers are loose, resulting in poor formability and an inability to form a dense pellet structure. It is evident that eucalyptus bark can provide core mechanical strength support for pellet fuel. The binding properties of bagasse allow the fibers of eucalyptus bark and sugarcane stalks to be tightly interlocked and entangled, forming a dense pellet structure. This solves the problems of poor formability of eucalyptus bark alone and easy breakage of sugarcane stalks and bagasse alone, thereby improving mechanical strength.

[0085] It is understood that those skilled in the art can make equivalent substitutions or changes to the technical solution and inventive concept of the present invention, and all such changes or substitutions should fall within the protection scope of the present invention.

Claims

1. A biomass pellet fuel, characterized in that, By weight percentage, it comprises the following components: 50%–70% eucalyptus bark, 10%–25% sugarcane stalks, and 15%–30% sugarcane bagasse.

2. The biomass pellet fuel according to claim 1, characterized in that, The particle size of the eucalyptus bark, sugarcane stalks, and sugarcane bagasse is 1 mm to 5 mm. The biomass pellet fuel is cylindrical, with a pellet diameter of 6 mm to 10 mm and a pellet length of 10 mm to 30 mm.

3. A method for preparing biomass pellet fuel, used to prepare biomass pellet fuel as described in any one of claims 1 to 2, characterized in that, Includes the following steps: The eucalyptus bark, sugarcane stalks, and sugarcane bagasse are dried and crushed. Weigh out 50%–70% of dried and crushed eucalyptus bark, 10%–25% of sugarcane straw, and 15%–30% of sugarcane bagasse by mass percentage, and put them into a mixer to mix them to obtain a mixture. The mixture is fed into an extrusion granulation device and extruded and granulated at a temperature of 100℃~130℃ and a pressure of 8MPa~12MPa to obtain particulate matter. The particles are cooled and sieved to obtain the biomass pellet fuel.

4. The method for preparing biomass pellet fuel according to claim 3, characterized in that, In the step of drying eucalyptus bark, sugarcane stalks and bagasse, the moisture content of the eucalyptus bark, sugarcane stalks and bagasse is reduced to 8% to 15%, and the drying temperature is 80℃ to 120℃.

5. The method for preparing biomass pellet fuel according to claim 3, characterized in that, After the eucalyptus bark, sugarcane stalks, and sugarcane bagasse are crushed, the particle size of the eucalyptus bark, sugarcane stalks, and sugarcane bagasse is 1 mm to 5 mm.

6. The method for preparing biomass pellet fuel according to claim 3, characterized in that, The 50%–70% eucalyptus bark, 10%–25% sugarcane straw, and 15%–30% sugarcane bagasse are added to the mixer and mixed for 15–30 minutes at a speed of 200–300 r / min.

7. The method for preparing biomass pellet fuel according to claim 3, characterized in that, The particles are cylindrical, with a particle diameter of 6 mm to 10 mm and a particle length of 10 mm to 30 mm.

8. The method for preparing biomass pellet fuel according to claim 3, characterized in that, The particulate matter is placed in a cooling device for cooling for 20 to 40 minutes, the temperature after cooling is ≤35°C, and the moisture content after cooling is 8% to 12%.

9. The method for preparing biomass pellet fuel according to claim 3, characterized in that, The unqualified particles obtained after cooling and sieving the particulate matter are conveyed to the step of crushing eucalyptus bark, sugarcane stalks and bagasse.

10. A use of biomass pellet fuel as described in claim 1 or 2, characterized in that, The biomass pellet fuel is used in the production of methanol from biomass.

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