A biomass sludge composite fuel and its preparation method

Abstract

The purpose of this invention is to provide a biomass sludge composite fuel and its preparation method, belonging to the fields of solid waste resource utilization and biomass energy technology. This composite fuel is made from municipal dried sludge, solid waste from grape cultivation, bentonite, and grape pomace in a mass ratio of 45-70:25-50:1.5-3:3-6. The preparation method involves first coarsely crushing grape branches and other materials, then initially mixing them with the dried sludge. Next, bentonite and grape pomace are added and finely crushed together until microscopically homogeneous. Finally, the mixture is high-pressure molded and dried. This invention uses natural bentonite and grape pomace as binary additives, eliminating the need for chemical binders. These additives synergistically consolidate alkali metals, inhibit slagging, increase calorific value, and enhance formability. Combined with a two-step crushing + co-crushing process, microscopic homogenization of the materials is achieved. The resulting fuel has a moisture content ≤22% and a net calorific value ≥2500 cal / g, making it widely applicable in the field of green energy materials.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization and biomass energy technology, specifically relating to a biomass sludge composite fuel and its preparation method. Background Technology

[0002] Using agricultural biomass and municipal sludge to co-produce solid fuel can solve the problem of waste disposal and produce clean energy, resulting in significant environmental and economic benefits.

[0003] Taking Ningxia as an example, the local grape-growing industry is large-scale, generating a large amount of grape pruning branches (grape branches) every year, along with a large amount of grape skins and pomace, a byproduct of wine processing. While the yield of these biomass resources is considerable, there is a lack of efficient resource utilization methods. Patent CN105368522A discloses a mixture of grapevines, fruit tree branches, and cow dung as fuel, but the process requires the addition of carbonaceous material and several days of fermentation, resulting in a long process cycle and unsuitability for large-scale application. On the other hand, municipal sewage sludge contains a large amount of organic matter, but its calorific value is low and its moisture content is high when burned alone, leading to high energy consumption for disposal.

[0004] Existing technologies have attempted to prepare fuel by mixing biomass and sludge, but these methods generally suffer from the following drawbacks: 1) The physical properties of biomass and sludge differ greatly (fiber structure vs. highly viscous particles), making it difficult to achieve uniform molding through simple mixing, resulting in low mechanical strength and unstable calorific value of the fuel; 2) To address problem 1), some companies rely on chemical binders or additives to improve the molding properties and combustion performance, significantly increasing costs while also causing unstable fuel quality (for example, patent CN103060044A discloses a method for preparing solid fuel by mixing sludge and biomass, which involves drying, crushing, and then mixing separately. However, its drawbacks include the need to add chemical additives such as quicklime, and the process involves step-by-step crushing followed by mixing, making it difficult to achieve homogenization of materials at the microscale, leading to unstable fuel quality). Furthermore, it may introduce secondary pollution; 3) During combustion, the alkali metals (potassium, sodium) contained in the biomass can easily cause slagging and corrosion, affecting the long-term stable operation of the boiler; 4) The preparation process is either too crude and simple, resulting in poor fuel quality, or too complex, leading to high equipment investment and difficulty in large-scale promotion.

[0005] Specifically, further analysis of existing similar technical solutions reveals that the current technological development in this field mainly faces the dilemma of "difficulty in achieving both goals simultaneously": One type of technical solution boasts a simple process flow and low cost and energy consumption, but often sacrifices the overall performance of the fuel. For example, CN109370699A describes directly mixing high-moisture sludge (55-70%) with biomass straw pellets and adding hydroxypropyl methylcellulose (HPMC) as a binder for room-temperature extrusion molding. Although this process eliminates the need for thermal drying, the excessive moisture content of the raw materials significantly reduces the calorific value of the product and increases molding energy consumption. Its energy output capacity is insufficient to efficiently replace fossil fuels, resulting in poor economic efficiency. CN120464441A discloses a method for achieving binder-free physical extrusion molding by optimizing the particle size ratio of biomass and dewatered sludge, with an extremely simple process flow. However, this solution fails to consider that the ash from burning biomass such as straw is rich in alkali metals such as potassium and sodium, which easily leads to slagging and corrosion on the heated surfaces, seriously affecting the long-term stable operation of the combustion equipment.

[0006] Another type of technology pursues high performance, but this results in highly complex processes, huge equipment investments, and difficulties in large-scale promotion. For example, CN120904943A uses ultrasonic synergistic technology, combined with a composite additive composed of Ca(OH)2, sodium lignosulfonate, and Fe2(SO4)3, and includes numerous steps such as carbonization ultrasonic pore expansion, gradient drying, and low-temperature curing. Although this technology excels in improving calorific value and reducing pollutant emissions, its high process complexity and strict control precision requirements lead to significant risks and costs in large-scale application. Similarly, CN116064181A designs a composite pellet fuel solution of sludge and plant residue without additional additives, which is formed through two-stage molding and converts combustion ash into high-value ceramsite. However, this technology also faces the problems of high equipment investment, stringent requirements on the financial and technical capabilities of the implementation area, and insufficient regional adaptability.

[0007] In summary, existing biomass sludge fuel preparation processes generally suffer from a "whack-a-mole" problem: simple processes, while low-cost, result in high fuel moisture content, low calorific value, insufficient molding strength, and an inability to suppress alkali metal slagging during combustion, severely hindering their stable and efficient application in actual industrial boilers; efficient processes, on the other hand, involve complex equipment, high energy consumption, and large investments, leading to persistently high costs for large-scale production. Currently, there is a lack of a technical solution that simultaneously achieves high calorific value, low slagging, low cost, and ease of promotion, severely limiting its large-scale application in regional energy projects. Therefore, there is an urgent need to develop an economical, green, efficient, and easily scalable co-production technology. Summary of the Invention

[0008] This invention aims to provide a biomass sludge composite fuel and its preparation method that can systematically optimize raw material compatibility and pretreatment processes without the need for external chemical additives. By introducing natural bentonite and grape pomace as binary natural additives, and combining them with a "two-step crushing + co-crushing" homogenization process, the invention overcomes the shortcomings of existing technologies such as high cost, unstable fuel quality, and easy slagging during combustion, thereby realizing the high-value energy utilization of regional wastes such as grape branches, municipal sludge, and grape pomace.

[0009] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a biomass-sludge composite fuel, which is made from the following raw materials: sludge, biomass, bentonite, and grape pomace. The sludge is municipal dried sludge; the biomass is solid waste from grape cultivation with a moisture content of 10-15%; the grape pomace has a moisture content of 8-12%; and the mass ratio of the sludge, biomass, bentonite, and grape pomace is 45-70:25-50:1.5-3:3-6.

[0010] Preferably, the mass ratio of the bentonite to the grape pomace is 1:2.

[0011] Preferably, the solid waste from grape cultivation includes: branches, stems, and leaves; and the bentonite is calcium-based or sodium-based bentonite.

[0012] More preferably, the composite fuel has a moisture content of ≤22% and a net calorific value of ≥2500 cal / g on an as-received basis; preferably, the solid fuel has a moisture content of ≤18% and a net calorific value of ≥2700 cal / g on an as-received basis.

[0013] In a second aspect, the present invention provides a method for preparing the biomass sludge composite fuel described in the first aspect, comprising the following steps: S1. Raw material pretreatment: Dehydrate the solid waste from grape cultivation to a moisture content of 10-15%; dehydrate the grape pomace to a moisture content of 8-12%; and dry the municipal sludge to obtain dried sludge. S2. Primary crushing and preliminary mixing: The dehydrated solid waste from grape cultivation is coarsely crushed to obtain coarsely crushed biomass; the coarsely crushed biomass is then preliminarily mixed with the dried sludge obtained in step S1 in a certain proportion; S3. Secondary crushing and homogenization: Add bentonite and dehydrated grape pomace to the preliminary mixture obtained in step S2, and crush them together. S4. High-pressure molding: The homogenized mixture obtained in step S3 is compressed and molded to obtain fuel rod green blanks; S5. Drying: Dry the fuel rod green obtained in step S4 to a moisture content of ≤22% to obtain the finished composite fuel.

[0014] Preferably, in step S2, the coarsely crushed biomass is an irregular strip 5-10 cm long and 3-5 mm thick.

[0015] Preferably, the particle size of the finely pulverized material in step S3 is 40 mesh.

[0016] Preferably, the bentonite in step S3 is natural bentonite, of the type calcium-based or sodium-based bentonite, with a particle size of 200 mesh and a montmorillonite content of ≥75%.

[0017] Preferably, in step S4, the compression molding processing parameters include: molding pressure of 60~100 MPa, molding temperature of 110-140 ℃, and processing time of 1~3 min.

[0018] Preferably, in step S5, the drying conditions include: a temperature of 40~50℃ and a time of 20~30h.

[0019] Thirdly, the present invention provides the application of the biomass sludge composite fuel described in the first aspect in the preparation of green energy materials.

[0020] The green energy materials include, but are not limited to, the following application scenarios: (1) As an alternative fuel for industrial boilers, hot air furnaces or kilns, it can replace part of the coal or natural gas, and is especially suitable for clean heating systems in small and medium-sized heating enterprises and agricultural product processing parks. (2) As an auxiliary fuel for biomass power plants, it can be co-fired with conventional biomass pellets (such as wood chips and straw) to effectively reduce fuel costs and dispose of municipal sludge. At the same time, the alkali-fixing effect of bentonite can be used to alleviate the slagging problem on the boiler heating surface. (3) After further crushing and screening, it can be made into household or commercial biomass pellet fuel for use in civil heating stoves or fireplaces to meet the needs of clean heating in rural areas; (4) Under specific processes, the fuel rod can be further carbonized or pyrolyzed to prepare biochar-based materials for soil improvement or wastewater adsorption treatment, realizing the cascade utilization of energy and materials.

[0021] Compared with the prior art, the present invention has the following beneficial effects: Firstly, the biomass sludge composite fuel of this invention requires no chemical additives and is green and environmentally friendly: it uses natural bentonite and pretreated grape pomace to form a binary natural additive, which completely replaces chemical binders and avoids secondary pollution during the combustion process.

[0022] Secondly, the components of the invented biomass sludge composite fuel work synergistically, resulting in superior performance: natural bentonite plays a role in dehydration, strengthening, and consolidation of alkali metals (inhibiting slagging); grape pomace plays a role in increasing calorific value, aiding combustion, and acting as a biomass binder. The synergy between the two achieves a "1+1>2" effect.

[0023] Thirdly, the preparation method of the present invention can achieve microscopic homogenization of biomass sludge composite fuel and ensure stable quality: through the unique "preliminary mixing of one powder + co-pulverization of two powders" process, high-fiber biomass, high-viscosity sludge and binary additives are tightly intertwined at the microscale, which significantly improves the physical homogeneity of the mixture and ensures the batch stability of indicators such as fuel calorific value, ash content and moisture content.

[0024] Fourth, this invention is adaptable to regionally unique resources: it provides an economically feasible and environmentally friendly industrial solution for the co-processing of distinctive agricultural wastes such as grape branches and grape pomace with municipal sludge in Ningxia. Attached Figure Description

[0025] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 A photograph of the fuel rod prepared in Example 1 of the present invention (scale 1:1:0.06:0.12).

[0026] Figure 2 Photograph of the fuel rod prepared in Example 2 of the present invention (scale 2:1:0.09:0.18). Detailed Implementation

[0027] In a specific embodiment of the present invention, the solid waste from grape cultivation used contains 80% grape branches, 15% stems, and 5% leaves. It was collected from a grape plantation in Ningxia Hui Autonomous Region and has a moisture content of approximately 10%-15% after drying. The municipal sludge was taken from a municipal wastewater treatment plant in Ningxia. After mechanical pressure filtration and drying, the moisture content was 20-30%, the organic matter content (dry basis) was 40%-60%, mainly consisting of organic debris, bacterial cells, carbohydrates, etc.; the inorganic matter content was 20%-40%, mainly consisting of silt particles, silicon / iron / aluminum / calcium oxides, etc. Natural bentonite is commercially available sodium-based bentonite with a particle size ≤0.075 mm (200 mesh) and a montmorillonite content ≥75%. The main active mineral in natural bentonite, montmorillonite, has excellent cation exchange performance and porous adsorption structure: on the one hand, it can fix free potassium, sodium and other soluble alkali metal ions in sludge and biomass raw materials between the montmorillonite lattice layers through interlayer cation exchange, inhibiting the volatilization and escape of alkali metals during high-temperature combustion; on the other hand, the active silica and alumina produced by the high-temperature decomposition of bentonite can react with alkali metals in a solid phase to generate high-melting-point aluminosilicates, avoiding the melting of low-melting-point alkali metal salts to form sticky slag.

[0028] The grape skins and pomace were collected from a winery in Ningxia and dried until the moisture content was about 8%-12%.

[0029] In a specific embodiment of the present invention, the performance testing method for biomass sludge composite fuel is as follows: (1) Moisture content determination: The determination was performed in accordance with the national standard GB / T 28731-2012 "Analytical Methods for Solid Biomass Fuel Industry". The test steps are as follows: First, the prepared fuel rod sample was crushed to 80 mesh. A certain mass of air-dried sample was weighed and placed in a pre-weighed weighing bottle. The weighing bottle was then placed in a drying oven preheated to 105~110℃ and dried until the mass was constant (usually about 2 hours). After removal, it was placed in a desiccator to cool to room temperature and weighed quickly. Finally, a check drying was performed: 30 minutes each time, until the mass reduction after two consecutive drying cycles did not exceed 0.0010 g. After constant weight, the mass of the last drying cycle was taken, and the moisture content was calculated based on the mass loss before and after drying.

[0030] (2) Ash content determination: The determination was carried out in accordance with the national standard GB / T 28731-2012. The test procedure was as follows: Take an air-dried sample and place it in a pre-weighed ash dish. The sample was then heated in a dedicated muffle furnace. First, the furnace temperature was slowly raised to (250±10)℃ over a period of not less than 50 minutes (heating rate 5℃ / min), and held at this temperature for 60 minutes. Then, the temperature was raised to (550±10)℃ over a period of not less than 60 minutes (heating rate 5℃ / min), and then calcined at this temperature for 2 hours. After the ash dish was removed and cooled slightly, it was placed in a desiccator to cool to room temperature. The sample was weighed, and the ash content of the dried basis was calculated based on the mass of the residue.

[0031] (3) Calorific value determination: The determination of calorific value was performed according to the national standard GB / T 30727-2014, "Method for Determination of Calorific Value of Solid Biomass Fuels". The experimental procedure was as follows: A suitable analytical sample was prepared using a dedicated sample preparation machine. Approximately 1 gram of sample was accurately weighed and placed in a dried combustion dish in the oxygen bomb calorimeter. The ignition wire was connected to the electrode. 5 ml of distilled water was injected into the oxygen bomb, and it was then filled with pure oxygen at a pressure of 3.0 MPa. The oxygen bomb was placed in the inner cylinder of the calorimeter, and a measured amount of distilled water was added before starting the experiment. The instrument automatically completed ignition, data acquisition, and calculation, ultimately outputting the higher heating value on an air-dried basis, which was then converted to the lower heating value on an as-received basis using a formula.

[0032] In the description of this invention, it should be noted that unless specific conditions are specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] This embodiment provides a biomass sludge composite fuel and its preparation method. The raw material composition of the biomass sludge composite fuel includes municipal dried sludge (5 kg), grape cultivation solid waste (5 kg), natural bentonite (0.3 kg), and grape pomace (0.6 kg) in a mass ratio of 50:50:3:6, with a total weight of 10.9 kg. The preparation method includes the following steps: Step 1, raw material pretreatment: The solid waste from grape cultivation is dried and dehydrated until the moisture content is 10-15%; the grape skins and pomace are dried and dehydrated until the moisture content is 8-12%; the municipal sludge is dried to obtain dried sludge with a moisture content of 20-30%.

[0036] Step 2, First Powdering: The dried solid waste from grape cultivation is fed into a hammer crusher for coarse crushing to obtain irregular strips of coarsely crushed biomass, 5-10cm long and 3-5mm thick. This coarsely crushed biomass is then added to a twin-shaft mixer with the prescribed amount of dried sludge and mixed at 100rpm for 5 minutes to achieve initial uniformity.

[0037] Step 3, Secondary pulverization: The above preliminary mixture, along with the prescribed amounts of natural bentonite and pretreated grape pomace, is fed into an ultrafine pulverizer (such as a disc pulverizer) for co-pulverization. The pulverized mixture should pass through a 40-mesh standard sieve (0.425 mm aperture). This step ensures that the fibers, sludge, bentonite, and pomace are thoroughly interwoven and homogenized at the microscopic level.

[0038] Step 4, molding: The homogenized mixture is fed into a ring die molding machine and pressed into a cylindrical fuel rod with a diameter of 10 mm under molding pressure of 80 MPa and molding temperature of 130 ℃ for 2 minutes.

[0039] Step 5, Drying: Place the fuel rod briquettes in a ventilated area and use the waste heat from the production line (40-50℃) to dry them at a low temperature for 24 hours until constant weight is achieved.

[0040] The prepared fuel rod greens were tested for moisture, ash content and calorific value. The test results are shown in Tables 1-3.

[0041] Example 2

[0042] This embodiment provides a biomass sludge composite fuel and its preparation method. The raw material composition of the biomass sludge composite fuel includes municipal dried sludge (6.666 kg), solid waste from grape cultivation (3.334 kg), natural bentonite (0.3 kg), and grape pomace (0.6 kg) in a mass ratio of 50:25:2.25:4.5, with a total weight of 10.9 kg. The preparation method is the same as in Example 1.

[0043] The prepared fuel rod greens were tested for moisture, ash content and calorific value. The test results are shown in Tables 1-3.

[0044] Table 1. Moisture test results for Examples 1 and 2

[0045] Note: The moisture content is calculated based on the final constant weight result of the last measurement.

[0046] Table 2 Ash content test results for Examples 1 and 2

[0047] Table 3. Calorific value test results of Examples 1 and 2

[0048] Note: The samples in Examples 1 and 2 were measured twice in parallel.

[0049] Comparative Example 1

[0050] Without adding natural bentonite and grape pomace, the remaining ingredients are formulated in the same proportions as in Example 2: 7.266 kg of municipal dried sludge and 3.634 kg of solid waste from grape cultivation, in a ratio of 50:25, for a total of 10.9 kg. The preparation method is the same as in Example 2, except for the sun-drying process to remove grape skins and pomace, and the addition of natural bentonite and grape skins and pomace.

[0051] The prepared fuel rod greens were tested for moisture, ash content and calorific value. The test results are shown in Tables 4-6.

[0052] Table 4. Moisture test results of Comparative Example 1

[0053] Table 5 Ash content test results of Comparative Example 1

[0054] Table 6. Calorific value test results of Comparative Example 1

[0055] Note: The sample of Comparative Example 1 was measured twice in parallel.

[0056] Comparative Example 2

[0057] Without adding grape pomace, the remaining ingredients are formulated in the same proportions as in Example 2: 7.055 kg of municipal dried sludge, 3.528 kg of solid waste from grape cultivation, and 0.317 kg of bentonite, in a ratio of 50:25:2.25, for a total of 10.9 kg. The preparation method is the same as in Example 2, except for the sun-drying process to remove grape skins and the addition of grape skins.

[0058] The prepared fuel rod greens were tested for moisture, ash content and calorific value. The test results are shown in Tables 7-9.

[0059] Table 7. Moisture test results of Comparative Example 2 Comparative Example 2 102.3357 1.0020 103.1149 103.1135 103.1130 103.1128 22.45% Table 8 Ash content test results of Comparative Example 2

[0060] Table 9. Calorific value test results of Comparative Example 2

[0061] Note: The sample of Comparative Example 2 was measured twice in parallel.

[0062] Comparative Example 3

[0063] Without adding natural bentonite, the remaining ingredients are formulated in the same proportions as in Example 2: 6.855 kg of municipal dried sludge, 3.428 kg of solid waste from grape cultivation, and 0.617 kg of grape pomace, in a ratio of 50:25:4.5, for a total of 10.9 kg. The preparation method is identical to Example 2 except for the addition of natural bentonite.

[0064] The prepared fuel rod greens were tested for moisture, ash content and calorific value. The test results are shown in Tables 10-12.

[0065] Table 10 Moisture test results of Comparative Example 3

[0066] Table 11 Ash content test results of Comparative Example 3

[0067] Table 12 Calorific value test results of Comparative Example 3

[0068] Note: The sample of Comparative Example 3 was measured twice in parallel.

[0069] In summary, the results show that Example 2, compared to Example 1 and all comparative examples, has the highest calorific value, lowest moisture content, and moderate economical ash content. Furthermore, although Example 1's calorific value is not significantly different from Comparative Example 1, its moisture content is significantly lower. In actual industrial boilers, this results in easier ignition, more stable combustion, and no slagging in the furnace, making its overall engineering value far superior to Comparative Example 1. These results confirm that the binary natural additive system of "bentonite + grape pomace" is superior to adding either one alone; the combination of the two can achieve a composite fuel with lower moisture content and higher calorific value.

[0070] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents. The embodiments described above merely illustrate several implementations of the invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the invention, and these all fall within the protection scope of the invention. Therefore, the protection scope of this invention should be determined by the appended claims.

Claims

1. A biomass sludge composite fuel, characterized in that, The biomass-sludge composite fuel is made from the following raw materials: sludge, biomass, bentonite, and grape pomace. The sludge is municipal dried sludge; the biomass is solid waste from grape cultivation with a moisture content of 10-15%; the grape pomace has a moisture content of 8-12%; and the mass ratio of the sludge, biomass, bentonite, and grape pomace is 45-70:25-50:1.5-3:3-6.

2. The biomass sludge composite fuel according to claim 1, characterized in that, The mass ratio of the bentonite to the grape pomace is 1:

2.

3. The biomass sludge composite fuel according to claim 1, characterized in that, The solid waste from grape cultivation includes: branches, stems, and leaves; the bentonite is calcium-based or sodium-based bentonite.

4. The biomass sludge composite fuel according to any one of claims 1 to 3, characterized in that, The composite fuel has a moisture content of ≤22% and a net calorific value of ≥2500 cal / g.

5. The method for preparing biomass sludge composite fuel according to claim 1, characterized in that, Includes the following steps: S1. Raw material pretreatment: Dehydrate the solid waste from grape cultivation to a moisture content of 10-15%; dehydrate the grape pomace to a moisture content of 8-12%; and dry the municipal sludge to obtain dried sludge. S2. Primary crushing and preliminary mixing: The dehydrated solid waste from grape cultivation is coarsely crushed to obtain coarsely crushed biomass; The coarsely crushed biomass is initially mixed with the dried sludge obtained in step S1 in a certain proportion; S3. Secondary crushing and homogenization: Add bentonite and dehydrated grape pomace to the preliminary mixture obtained in step S2, and crush them together. S4. High-pressure molding: The homogenized mixture obtained in step S3 is compressed and molded to obtain fuel rod green blanks; S5. Drying: Dry the fuel rod green obtained in step S4 to a moisture content of ≤22% to obtain the finished composite fuel.

6. The method according to claim 5, characterized in that, In step S2, the coarsely crushed biomass is an irregular strip of material that is 5-10 cm long and 3-5 mm thick.

7. The method according to claim 5, characterized in that, The particle size of the finely pulverized material in step S3 is 40 mesh.

8. The method according to claim 5, characterized in that, The bentonite mentioned in step S3 is natural bentonite, of the type of calcium-based or sodium-based bentonite, with a particle size of 200 mesh and a montmorillonite content of ≥75%.

9. The method according to claim 5, characterized in that, In step S4, the compression molding processing parameters include: molding pressure of 60~100 MPa, molding temperature of 110-140 ℃, and processing time of 1~3 min.

10. The application of the biomass sludge composite fuel according to claim 1 in the preparation of green energy materials.

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