A method for preparing high-performance biomass briquette fuel based on steam explosion pretreatment of rice hull and pine addition

Abstract

The present application relates to the technical field of biomass energy, and specifically discloses a preparation method of high-performance biomass briquetting fuel based on steam explosion pretreatment of rice hull and addition of pine wood. The method uses agricultural waste rice hull as the main raw material, realizes efficient removal of hemicellulose and high retention of cellulose and lignin through steam explosion pretreatment, combines particle size optimization, and verifies the natural bonding effect of free sugar on the surface of the residue through water washing, and adds pine wood as a reinforcing agent to significantly improve the comprehensive performance of the briquetting fuel. The present application solves the core problems of low mechanical strength, high water absorption and poor storage stability of existing rice hull fuel, has low process cost and no chemical pollution, is suitable for industrialization, and provides an effective path for realizing high-value utilization of agricultural waste and the carbon neutralization goal.

Description

Technical Field

[0001] This invention relates to the field of biomass energy technology, specifically a method for preparing high-performance biomass briquettes by pretreating rice husks through steam explosion and combining it with pine wood additives. This method significantly improves the mechanical strength, calorific value, and durability of the briquettes by optimizing raw material particle size, verifying the role of free sugars generated during pretreatment, and adding pine wood reinforcing agents. Background Technology

[0002] As the world's largest rice producer, China generates over 40 million tons of rice husks annually. However, most of this is incinerated or landfilled, resulting in resource waste and environmental pollution. Rice husks are rich in cellulose (approximately 35–40%) and lignin (15–20%), making them suitable for energy utilization. Steam explosion pretreatment is a highly efficient, environmentally friendly, and cost-effective technology that degrades hemicellulose through thermomechanical action, producing porous residues. Cellulose provides structural support, while molten lignin acts as a natural binder during hot pressing. This makes rice husk residue an ideal raw material for preparing solid molded fuels, contributing to the high-value conversion of agricultural waste and achieving carbon neutrality goals.

[0003] Although steam-exploded rice husks have the potential for molding, current technologies for directly molding them into fuel still suffer from problems such as low mechanical strength, high water absorption, and poor storage stability. The high ash content and low bulk density of rice husks themselves also result in low calorific value, long combustion time, and poor mechanical properties in the molded fuel. Current research focuses primarily on the effects of moisture content, pressure, and particle density on combustion behavior, but lacks in-depth analysis of raw material particle size system optimization and the binding effect of free sugars on the residue surface. Furthermore, no effective binding and strengthening strategies have been reported, hindering the industrialization of rice husk molded fuel. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing high-performance biomass briquettes. By pretreating rice husks through steam explosion, combined with particle size optimization, water washing verification, and the addition of pine wood, this method solves the problem of low quality in existing rice husk briquettes, while significantly reducing the cost of raw material acquisition and processing, and achieving efficient, low-carbon, and low-cost energy conversion of waste resources.

[0005] This invention systematically studies the influence of raw material particle size distribution on molding quality, identifying 60-100 mesh as the optimal range to reduce energy consumption from excessive grinding while ensuring molding efficiency. Water washing experiments verify the contribution of free sugars on the surface of the residue to the mechanical strength of the particles, elucidating their mechanism of action as a natural binder. Furthermore, 5%-20% pine wood is introduced as a reinforcing agent, effectively improving key performance indicators such as compressive strength, burst strength, and calorific value of the particles without significantly increasing raw material costs. This results in a cost-effective, simple, and widely applicable method for preparing rice husk molded fuel, characterized by the following process steps: 1) Raw material preparation: Screen the rice husks, remove impurities, and air dry them naturally until the moisture content is about 8%-12%.

[0006] 2) Steam explosion pretreatment: The rice husk raw material is subjected to steam explosion, and the pressure, temperature and holding time of the steam explosion are adjusted.

[0007] 3) Water washing pretreatment: Mix the raw material after steam explosion with deionized water, heat and stir, and filter to obtain water-washed steam explosion residue.

[0008] 4) Particle size screening: Both steam explosion residue and water-washed steam explosion residue were dried in an oven at 50 ℃ and screened into >20 mesh (0.56%), 20-60 mesh (6.53%), 60-100 mesh (17.40%), 100-200 mesh (74.53%), and <200 mesh (0.98%).

[0009] 5) Granulation raw materials: Add steam explosion residue of different particle sizes and water-washed steam explosion residue to 12% deionized water and equilibrate in a self-sealing bag for 48 hours for later use.

[0010] 6) Granulation: Set the mold temperature, take about 0.5-1 g as the granulation material and fill it into the mold. Keep it heated for 2 min, then compress it at a speed of 10 mm / min. Set the pressure and maintain it for 2 min after reaching the set pressure before ending the compression. The demolding speed is 5 mm / min until the particles are completely extruded.

[0011] 7) Biomass solid fuel pellet performance analysis: mechanical properties and industrial analysis, including (compressive strength, flexural strength, burst strength, durability, calorific value, ash content, volatile matter, fixed carbon content analysis, chemical composition analysis, etc.) 8) Pine wood additives improve fuel performance: Pellet raw materials with optimized pretreatment conditions and optimized particle size are mixed with a certain proportion of oven-dried pine wood as pelleting raw materials.

[0012] The steam explosion pretreatment method is characterized in that the rice husk raw material in step 2) is pressurized at 180-200℃, 1.8 MPa and 1.9 MPa for 10-20 min. The hemicellulose removal rate reaches 85%, and the cellulose destruction rate is less than 10%.

[0013] The raw material washing pretreatment method is characterized in that the raw material in step 3) is mixed with deionized water (w / v = 1:10) and heated and stirred at 60 °C for 2-3 h.

[0014] The raw material particle size optimization method is characterized in that, in steps 4), 6), and 7), 60-100 mesh raw materials are selected based on the performance analysis of the pellet fuel, which have the strongest mechanical properties and the highest calorific value in the shaped fuel.

[0015] The method for preparing biomass solid briquette fuel by steam explosion pretreatment is characterized in that the water content in step 6) is 12%, the pressure is 60 MPa, and the heating temperature is 120 ℃.

[0016] The method for improving fuel performance with pine wood additives is characterized in that the proportion of pine wood added is (5%, 10%, 15% and 20%).

[0017] The high-performance biomass pellet fuel preparation method based on steam explosion pretreatment of rice husks and pine wood provided by this invention has the following significant advantages: 1. This invention uses rice husks, an agricultural waste, as the main raw material. China's annual rice husk production exceeds 40 million tons, making it widely available and inexpensive (approximately 100-200 yuan / ton), significantly reducing the production cost of biomass fuel. Through steam explosion pretreatment, efficient degradation of hemicellulose (removal rate up to 85%) can be achieved without the addition of chemical catalysts, avoiding the use of expensive reagents and further reducing treatment costs.

[0018] 2. Through systematic research on the influence of particle size distribution on the performance of granulated fuel, the optimal range of 60-100 mesh was identified for the first time, achieving the best balance between particle mechanical strength and calorific value. Specifically, the compressive strength reached (5-6 MPa), the flexural strength reached (15-20 MPa), and the calorific value was greater than 17 MJ / kg. Simultaneously, water washing experiments verified the natural binder effect of free sugars on the residue surface, providing a theoretical basis for eliminating the need for external binders. Steam explosion residue can be directly used for pelleting, simplifying the process and saving costs.

[0019] 3. This invention introduces 5%-20% pine wood as a reinforcing agent, significantly improving pellet burst strength (by 3.39-5.38%), flexural strength (by 2.5 times), and compressive strength (by 17.84-77.69%) without significantly increasing raw material costs, with a maximum increase in calorific value of 6.82%. The synergistic effect of pine wood and rice husk residue effectively solves the core problem of poor mechanical properties of rice husk fuel.

[0020] 4. Although the addition of pine wood slightly increases the water absorption of fuel pellets, the water absorption model fitting shows that the storage stability still meets industrial standards (R²>0.95). The entire process is free of chemical pollution, and the energy consumption of steam explosion is lower than that of traditional pyrolysis methods, meeting low-carbon and environmentally friendly requirements.

[0021] 5. This invention features a simple process, low equipment requirements, and is easy to scale up and promote. The calorific value of the briquetted fuel reaches up to 18.48 MJ / kg, approaching that of lignite, and can replace fossil fuels for industrial boilers or rural energy supply, promoting the energy utilization of agricultural waste. Attached Figure Description

[0022] Figure 1 This is a process flow diagram of the embodiment combination. Detailed Implementation

[0023] The invention is further illustrated below with reference to the following embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0024] Example 1 Rice husk residue after steam explosion pretreatment (1.8 MPa, 200 ℃, pressure holding for 15 min), dried and without particle size separation, with moisture content adjusted to 12%. It was then pressed into pellets at 120 ℃ and 60 MPa in a universal testing machine, with each batch weighing 1 ± 0.3 g. The resulting pellets had a compressive strength of 5.09 MPa, a flexural strength of 15.31 MPa, a bursting strength of 91.52%, and a calorific value of 16.14 MJ / kg. The raw material after steam explosion contained 90% cellulose and lignin. Compared to rice husk raw material, the pellet fuel produced from the steam-exploded raw material showed significant performance improvements.

[0025] Example 2 Rice husk residue after steam explosion pretreatment (1.8 MPa, 200 ℃, pressure holding for 15 min) was dried and sieved to 60-100 mesh, with the moisture content adjusted to 12%. 10 g of the raw material was pressed into shape in a universal testing machine at 120 ℃ and 60 MPa. The resulting particles had a compressive strength of 5.38 MPa, a flexural strength of 16.29 MPa, a bursting strength of 94%, and a calorific value of 17.30 MJ / kg. This particle size range achieved the best balance between mechanical strength and calorific value, and was also the most economical in terms of crushing energy consumption and pretreatment efficiency.

[0026] Example 3 Rice husk residue after steam explosion pretreatment (1.9 MPa, 190 ℃, pressure holding for 20 min) was dried and sieved to 60-100 mesh, and the moisture content was adjusted to 12%. 10 g of the raw material was pressed into pellets in a universal testing machine at 120 ℃ and 60 MPa. The resulting pellets had a compressive strength of 4.61 MPa, a flexural strength of 10.41 MPa, a bursting strength of 92%, and a calorific value of 16.38 MJ / kg, slightly weaker than the steam-exploded raw material at 1.8 MPa. After absorbing water for 48 h, the equilibrium moisture content was 3.43%.

[0027] Example 4 Rice husk residue after steam explosion (1.8 MPa, 200 ℃, pressure held for 15 min, 60-100 mesh) was stirred with deionized water (w / v=1:10) at 60 ℃ for 2 h, and then filtered to obtain water-washed residue. Under the same conditions, compression molding resulted in a decrease in particle compressive strength to 4.47 MPa (approximately 17% lower than the unwashed group), and a similar decrease in flexural strength of approximately 18%. This confirms that free sugars do indeed contribute significantly to mechanical strength.

[0028] Example 5 95% of the steam-exploded rice husk residue (1.8 MPa, 200 ℃, pressure held for 15 min, 60-100 mesh) was mixed with 5% pine wood raw material and compressed into pellets at 120 ℃ and 60 MPa. The compressive strength of the pellets reached 5.87 MPa, the flexural strength reached 17.33 MPa, the calorific value increased to 17.89 MJ / kg, and the bursting strength was 5.31% higher than that of the group without pine wood. After 48 h of water absorption, the equilibrium moisture content was 3.51%, similar to that of the group without pine wood. Sealed storage experiments showed that the pellets showed no obvious mold growth within 30 days, and the storage stability still met industrial standards.

[0029] Example 6 80% of the steam-exploded rice husk residue (1.8 MPa, 200 ℃, pressure held for 15 min, 60-100 mesh) was mixed with 20% pine wood and compressed into pellets at 120 ℃ and 60 MPa. The compressive strength of the pellets reached 9.56 MPa, the flexural strength reached 41.04 MPa, the calorific value increased to 18.48 MJ / kg, and the bursting strength increased to 99.94%. However, after 48 hours of water absorption, the equilibrium moisture content was 4.06%, which was 12% higher than that of the raw material without added pine wood. Sealed storage experiments showed that the pellets showed no obvious mold growth within 30 days, and the storage stability still met industrial standards.

[0030] Comparative Example 1 Using steam-exploded rice husk residue (1.9 MPa, 190 ℃, pressure held for 20 min, 100-200 mesh), compressed and molded using a universal testing machine at 120 ℃ and 60 MPa, the compressive strength of the particles was only 2.42 MPa and the flexural strength was only 7.56 MPa. The mechanical properties were lower than those of unexploded rice husk raw materials, and the particles were prone to pulverization during the molding process.

[0031] Comparative Example 2 Only 8-mesh rice husks were used as raw material and pressed into pellets at 120 ℃ and 60 MPa in a universal testing machine. The resulting pellet fuel had a compressive strength of 3.53 MPa, a flexural strength of 19.50 MPa, a bursting strength of 86%, a calorific value of 13.23 MJ / kg, and a pellet density of 910 kg / m³. 3 It does not meet the standards for industrial pellet fuel.

Claims

1. The purpose of this invention is to provide a method for preparing high-performance rice husk biomass pellet fuel. By pretreating rice husks through steam explosion, combined with particle size optimization, water washing verification, and the addition of pine wood, this method solves the problem of low quality in existing rice husk pellet fuels, while significantly reducing raw material acquisition and processing costs, achieving efficient, low-carbon, and low-cost energy conversion of waste resources. This invention systematically studies the influence of raw material particle size distribution on pellet quality, identifying 60-100 mesh as the optimal range, ensuring pelleting efficiency while reducing energy consumption from excessive grinding. Water washing experiments verify the contribution of free sugars on the residue surface to the mechanical strength of the pellets, elucidating their mechanism of action as a natural binder. Furthermore, 5%-20% pine wood is introduced as a reinforcing agent, effectively improving key performance indicators such as compressive strength, burst strength, and calorific value of the pellets without significantly increasing raw material costs. This forms a cost-controllable, simple, and widely applicable method for preparing rice husk pellet fuel. Its characteristics are... The process includes the following steps: 1) Raw material preparation: Screen the rice husks, remove impurities, and air dry them naturally until the moisture content is about 8%-12%. 2) Steam explosion pretreatment: The rice husk raw material is subjected to steam explosion, and the pressure, temperature and holding time of the steam explosion are adjusted. 3) Water washing pretreatment: Mix the raw material after steam explosion with deionized water, heat and stir, and filter to obtain water-washed steam explosion residue. 4) Particle size screening: The steam explosion residue and the water-washed steam explosion residue were dried to absolute dryness in an oven at 50 ℃ and then screened into >20 mesh (0.56%), 20-60 mesh (6.53%), 60-100 mesh (17.40%), 100-200 mesh (74.53%), and <200 mesh (0.98%). 5) Granulation raw materials: Add steam explosion residue of different particle sizes and water-washed steam explosion residue to 12% deionized water and equilibrate in a self-sealing bag for 48 hours for later use. 6) Granulation: Set the mold temperature, take about 0.5-1 g as the granulation material and fill it into the mold. Keep it heated for 2 min, then compress it at a speed of 10 mm / min. Set the pressure and maintain it for 2 min after reaching the set pressure before stopping the compression. The demolding speed is 5 mm / min until the particles are completely extruded. 7) Biomass solid fuel pellet performance analysis: mechanical properties and industrial analysis, including (compressive strength, flexural strength, burst strength, durability, calorific value, ash content, volatile matter, fixed carbon content analysis, chemical composition analysis, etc.) 8) Pine wood additives improve fuel performance: Pellet raw materials with optimized pretreatment conditions and optimized particle size are mixed with a certain proportion of oven-dried pine wood as pelleting raw materials.

2. The method as described in claim 1, characterized in that... The rice husk raw material in step 2) is subjected to pressure treatment at 180-200℃, 1.8MPa, and 1.9MPa for 10-20 minutes. The hemicellulose removal rate reaches 85%, and the cellulose destruction rate is less than 10%.

3. The method as described in claim 1, characterized in that... The raw materials in step 3) are mixed with deionized water (w / v = 1:10) and heated and stirred at 60 °C for 2-3 h.

4. The method as described in claim 1, characterized in that... In steps 4), 6), and 7), 60-100 mesh raw materials are selected based on the performance analysis of pellet fuel, as these have the strongest mechanical properties and the highest calorific value in their shaped fuel.

5. The method as described in claim 1, characterized in that... The moisture content in step 6) is 12%, the pressure is 60 MPa, and the heating temperature is 120 ℃.

6. The method as described in claim 1, characterized in that... The proportion of pine wood added is (5%-20%).

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