Straw briquette fuel and its preparation process and system

Abstract

The present application relates to the technical field of biomass energy, and particularly discloses a straw briquette fuel and a preparation process and system thereof. The preparation process of the straw briquette fuel comprises the following steps: S1, low-temperature carbonization: straw is subjected to low-temperature carbonization treatment to remove volatile substances; S2, crushing: the straw after low-temperature carbonization is crushed to obtain carbonized particles suitable for extrusion molding; S3, moisture adjustment: the carbonized particles are subjected to moisture content adjustment to meet the requirements of extrusion molding; and S4, extrusion molding: the carbonized particles after moisture adjustment are spiral extrusion molded to obtain the briquette fuel. The preparation process of the briquette fuel provided by the present application can not only obtain a straw briquette fuel with higher density, higher calorific value and lower ash content, but also reduce the preparation cost of the straw briquette fuel and improve the economy of the straw briquette fuel.

Description

Technical Field

[0001] This invention relates to the field of biomass energy technology, specifically to a straw-based briquette fuel and its preparation process and system. Background Technology

[0002] The annual production of straw-based biomass is substantial, necessitating reduction, harmless disposal, and high-value utilization. Currently, combustion is the simplest and most effective way to utilize straw-based biomass, suitable for heating, gas supply, and power generation. However, straw-based biomass has relatively low bulk density and energy density, resulting in low efficiency for large-scale direct combustion. Preparing it into briquettes can effectively address this issue. Compared to raw straw, straw briquettes have higher bulk density and energy density, with a calorific value equivalent to low-rank coal.

[0003] Most current straw briquettes are produced using a "crushing-drying-forming" process. This involves first crushing the straw raw material into pellets suitable for subsequent forming, then drying the pellets to a certain degree, and finally extruding them into briquettes. However, the current straw briquette production process is energy-intensive in crushing, drying, and forming, resulting in high production costs and low economic efficiency. Furthermore, the current process only involves removing moisture from the crushed straw without any other pretreatment. While this improves the density and calorific value of the briquettes, the overall quality still has significant room for improvement. The removal of inorganic components such as alkali metals and alkaline earth metals from the straw raw material is also not addressed in the current process. These components can adhere to heat exchangers and other components during combustion, reducing the thermal efficiency of the combustion system.

[0004] Therefore, it is of great significance to develop a new straw briquette fuel preparation process to reduce production costs, improve economic efficiency, and obtain straw briquette fuel with higher density, higher calorific value, and lower ash content. Summary of the Invention

[0005] The purpose of this invention is to provide a process for preparing straw briquettes, which aims to solve the problems of high production costs, low economic benefits, and inability to effectively remove inorganic components such as alkali metals and alkaline earth metals from straw raw materials in existing straw briquette preparation processes.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: This invention provides a process for preparing straw briquettes, which includes the following steps: S1. Low-temperature carbonization: Low-temperature carbonization of straw to remove volatile substances, increase the energy density of straw, and make it easier to break. S2. Crushing: Crushing the straw after low-temperature carbonization to obtain carbonized pellets suitable for extrusion molding. S3. Moisture adjustment: Adjust the moisture content of the carbonized particles to meet the requirements of extrusion molding; S4. Extrusion molding: The carbonized particles with adjusted moisture content are spirally extruded to obtain molded fuel.

[0007] Specifically, this invention addresses the shortcomings of existing straw briquette fuel preparation processes by proposing a new straw briquette fuel preparation process. This process not only yields straw briquette fuel with higher density, higher calorific value, and lower ash content, but also reduces the preparation cost of straw briquette fuel and improves its economic efficiency.

[0008] Furthermore, a preparation process for straw briquettes: the low-temperature carbonization temperature in step S1 is 200-290℃ and the carbonization time is 30-90 minutes; the volatile substances include small molecule oxygen-containing compounds, alkali metals and alkaline earth metals that are prone to slagging and ash accumulation during subsequent briquette combustion, and precursors containing nitrogen, sulfur, and phosphorus that are prone to generating combustion pollutants.

[0009] Furthermore, a process for preparing straw-based briquettes: in step S2, the straw is crushed until the particle size of the resulting carbonized particles does not exceed 20.0 mm.

[0010] Furthermore, a process for preparing straw briquettes: in step S3, the moisture content of the carbonized particles is adjusted to 5.0-12.0%.

[0011] Furthermore, a process for preparing straw-molded fuel: the spiral extrusion molding temperature in step S4 is 100-150℃ and the pressure is 60.0-90.0MPa.

[0012] The present invention also provides a straw briquette fuel, which is prepared by the above-described preparation process.

[0013] The present invention also provides a system for preparing straw briquettes, the system comprising the following structural configuration: A feeding and conveying device is used to feed in and transport straw raw materials; A low-temperature carbonization device is used to receive straw transported by the feeding and conveying device and perform low-temperature carbonization treatment on it. A crushing mechanism is located at the outlet of the low-temperature carbonization device to receive the straw after low-temperature carbonization and crush it to obtain carbonized particles. A moisture regulating device, located downstream of the crushing mechanism, is used to regulate the moisture content of the carbonized particles; And an extrusion molding apparatus, which includes a spiral extruder and a heating jacket disposed outside the spiral extruder, wherein the spiral extruder is used to spirally extrude carbonized particles after moisture adjustment, and the heating jacket is used for temperature regulation during the carbonized particle extrusion molding process.

[0014] Furthermore, a straw briquette fuel preparation system includes a crushing mechanism comprising a crushing roller and a base. The base receives the straw after low-temperature carbonization, and the crushing roller is positioned above the base with an adjustable distance between it and the base for crushing the straw. Specifically, the height of the crushing roller is adjustable, which changes the distance between the roller and the base to accommodate different low-temperature carbonized straw raw materials and allows for control over the size of the crushed straw particles.

[0015] Furthermore, a straw briquetted fuel preparation system is provided: the system is configured to operate intermittently in a modular manner or continuously in an integrated manner; wherein, when the system operates intermittently in a modular manner, the moisture regulating device is configured as an open storage area, and the carbonized particles absorb moisture from the air to obtain the required moisture content; when the system operates continuously in an integrated manner, the moisture regulating device is configured as a closed container, and the carbonized particles are sprayed with water and balanced to obtain the required moisture content.

[0016] Furthermore, a straw briquette fuel preparation system includes a flue gas treatment and recycling system connected to the low-temperature carbonization device. The flue gas treatment and recycling system is used to purify the flue gas generated during the low-temperature carbonization process to obtain combustible components from the flue gas. The combustible components are then recycled back to the low-temperature carbonization device via the flue gas treatment and recycling system. The flue gas treatment and recycling system is also used to supply heat to the heating jacket.

[0017] Specifically, the low-temperature carbonization device is equipped with a flue gas treatment and reuse system, which can purify the flue gas and reuse the combustible components contained in the flue gas for combustion and heating in the low-temperature carbonization device, achieving partial energy self-sufficiency. At the same time, the heat energy contained in the flue gas can also be reused to heat the heating jacket, saving energy consumption. Of course, the heating jacket can also heat itself.

[0018] The straw briquette fuel preparation process provided by this invention has the following significant advantages: ① Significantly improved fuel quality: Traditional straw direct combustion or ordinary briquette fuels easily form slag during combustion. However, this method adopts low-temperature carbonization at 200-290℃, precisely removing alkali metals, alkaline earth metals, and other slag-forming precursors, as well as pollutant precursors containing nitrogen, sulfur, and phosphorus from the straw. This means that the final briquette fuel not only burns more stably but also significantly reduces the frequency of slag removal from combustion equipment, while significantly reducing pollutant emissions and overcoming the problem of combustion slag formation. This eliminates slag formation and dust, achieving efficient and clean combustion. Moreover, the low-temperature carbonization process destroys the cell wall structure of the straw, combined with precise moisture adjustment of 5-12% and 60-90 MPa. The high-pressure spiral extrusion process allows natural binders such as lignin to be fully plasticized and fused, resulting in a molded fuel with extremely strong internal bonding. This makes it less prone to breakage during transportation and drops, and also resistant to a certain degree of moisture absorption and deliquescence, facilitating long-term storage. Secondly, precise control of process parameters: The optimized low-temperature carbonization process parameters ensure effective removal of volatile substances while avoiding over-carbonization that could lead to raw material deactivation and difficulty in molding. Simultaneously, the optimized spiral extrusion molding process achieves the densest molding effect with minimal mechanical wear and energy consumption. Furthermore, by controlling the particle size of the carbonized particles and combining open / closed precise humidity control, uniform stress is ensured during spiral extrusion, effectively preventing bridging or slippage. Smooth material discharge and high molding rate; ③ Innovative system structure: The molding fuel preparation system of this invention is a flexible production design that takes into account both intermittent and continuous operation modes. It can flexibly switch operation modes according to actual production capacity requirements. During small-batch, intermittent production, natural moisture absorption can be used in an open space to regulate moisture with zero energy consumption. During large-scale, continuous, integrated operation, a closed container can be used for precise water spraying balance. This design can meet the needs of small production volumes while also meeting the standards of large production capacity, making it highly adaptable. In addition, the system is also designed with adjustable-gap crushing rollers to gently compress and crush brittle carbonized straw. This not only reduces dust emission during the crushing process but also maintains the complete porous structure of the carbonized particles, leaving better space for subsequent spiral extrusion. ④ Balancing physical space; Environmental protection and energy conservation: The system of this invention constructs a self-circulating zero-emission green closed loop through the design of the flue gas treatment and reuse system. It can purify the waste gas generated by carbonization and extract combustible components (such as CO, CH4, etc.) as fuel for the low-temperature carbonization device itself. At the same time, the waste heat of the high-temperature flue gas is directed to the heating jacket of the extrusion molding device. This design of "using waste to treat waste and reusing waste heat" greatly reduces external energy consumption, resulting in a sharp drop in the operating cost of the entire system. Moreover, since volatile organic compounds and small molecule oxygen-containing compounds have been removed and recycled for combustion in advance during the low-temperature carbonization stage, there will be almost no pungent odor or additional waste gas emissions during the subsequent extrusion molding and final fuel use process, achieving environmental friendliness throughout the entire process.

[0019] The beneficial effects of this invention are: The straw briquette fuel preparation process provided by this invention utilizes low-temperature carbonization, which not only removes moisture from the straw raw material but also removes organic oxygen from the straw in the form of small-molecule oxygenated compounds. This significantly reduces the oxygen content of the straw briquette fuel and increases its calorific value. At the same time, the low-temperature carbonization process also removes alkali metals, alkaline earth metals, and polluting elements such as nitrogen, sulfur, and phosphorus from the straw, greatly reducing slagging and ash accumulation and pollutant emissions during the subsequent combustion process. This avoids the problem of ash adhering to heat exchangers and other components, which would reduce the thermal efficiency of the combustion system.

[0020] Current straw briquette fuel preparation processes begin with the crushing of straw raw materials, requiring specialized crushing equipment, resulting in high power consumption and short mold lifespan. In contrast, the low-temperature carbonization process employed in this invention eliminates the need for any pretreatment of the straw raw materials. Raw straw can be directly fed into the low-temperature carbonization device via a feeding and conveying device. The carbonized straw is brittle and easy to break, resulting in low equipment energy consumption. A simple crushing process using a roller can easily achieve the desired particle size for subsequent spiral extrusion molding. Furthermore, the height of the roller is adjustable, making it suitable for various straw raw materials and highly practical.

[0021] The straw briquette fuel preparation process provided by this invention has low energy consumption. This process eliminates the drying step in the current straw briquette fuel preparation process. Although the low-temperature carbonization process in this invention also consumes energy, thanks to the flue gas treatment and reuse system designed in the straw briquette fuel preparation system of this invention, the combustible components contained in the flue gas generated by the low-temperature carbonization process can be directly reused in the low-temperature carbonization device for combustion and heating. While realizing energy reuse, it can also purify the low-temperature carbonization flue gas, which is more environmentally friendly.

[0022] The straw pellet fuel preparation process provided by this invention can remove organic oxygen elements from the straw carbohydrate components in the form of small molecule oxygenated compounds through a preferred low-temperature carbonization process, without changing the content and characteristics of lignin. Under certain temperature and pressure spiral extrusion conditions, thermoplastic lignin can act as a binder to shape the broken straw pellets without the need for additional binders, thus reducing production costs. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 A process flow diagram of the preparation process of straw briquette fuel provided by the present invention; Figure 2 A simplified structural diagram of the straw briquette fuel preparation system provided by the present invention.

[0025] The markings in the image are as follows: 1-Feeding and conveying device, 2-Low temperature carbonization device, 3-Crushing mechanism, 4-Moisture adjustment device, 5-Extrusion molding device, 6-Flue gas treatment and reuse system. Detailed Implementation

[0026] 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. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0027] Example 1

[0028] This embodiment 1 provides a process for preparing straw briquettes, which includes the following specific steps, and the process flow is as follows: Figure 1 As shown: S1. Low-temperature carbonization: The cotton stalks are carbonized at 200℃ for 90 minutes to remove volatile substances, increase the energy density of the cotton stalks, and make them easier to break. S2. Crushing: The cotton stalks after low-temperature carbonization are crushed to obtain carbonized particles suitable for extrusion molding, that is, cotton stalk particles (carbonized particles) with a particle size ≤20.0mm. S3. Moisture adjustment: The moisture content of the carbonized particles is adjusted to obtain a moisture content of 12% to meet the requirements of extrusion molding; S4. Extrusion molding: The carbonized particles with adjusted moisture content are spirally extruded to obtain molded fuel. The spiral extrusion molding temperature is 150℃ and the pressure is 60.0MPa. The above-mentioned preparation process utilizes a straw briquette fuel preparation system, which is as follows: Figure 2 As shown, it includes the following structural configuration: The feeding and conveying device 1 is used to feed in and transport cotton stalk raw materials. Low-temperature carbonization device 2 is used to receive cotton stalks conveyed by the feeding and conveying device 1 and perform low-temperature carbonization treatment on them. The crushing mechanism 3 is located at the outlet of the low-temperature carbonization device 2. It is used to receive and crush the cotton stalks after low-temperature carbonization to obtain carbonized particles. The crushing mechanism 3 includes a crushing roller and a base. The base is used to receive the straw after low-temperature carbonization. The crushing roller is located above the base and the distance between the crushing roller and the base can be adjusted. It is used to crush the straw after low-temperature carbonization. The distance between the crushing roller and the base can be changed by adjusting the height of the crushing roller, so as to adapt to different low-temperature carbonization straw raw materials and to control the size of the crushed straw particles (i.e., to control the size of the carbonized particles). Moisture regulating device 4, which is located downstream of the crushing mechanism 3, is used to regulate the moisture content of the carbonized particles; The extrusion molding device 5 includes a spiral extruder and a heating jacket disposed outside the spiral extruder. The spiral extruder is used to spirally extrude carbonized particles with adjusted moisture content into shape, and the heating jacket is used for temperature regulation during the carbonized particle extrusion molding process. The system includes a flue gas treatment and reuse system 6, which is connected to the low-temperature carbonization device 2. The flue gas treatment and reuse system 6 is used to purify the flue gas generated during the low-temperature carbonization process to obtain the combustible components in the flue gas. The combustible components are then circulated back to the low-temperature carbonization device 2 through the flue gas treatment and reuse system 6. The flue gas treatment and reuse system 6 is also connected to the heating jacket, which can provide heat to it.

[0029] Specifically, the preparation process of this straw briquette fuel in Example 1 is as follows: cotton stalks are conveyed by a feeding and conveying device 1 to a low-temperature carbonization device 2, where they are carbonized at 200°C for 90 minutes. The carbonized stalks are then discharged from the outlet of the low-temperature carbonization device 2. The carbonized cotton stalks then enter a crushing mechanism 3 and are crushed by a rolling roller to obtain cotton stalk particles (carbonized particles) with a size ≤20.0 mm. These particles then enter a moisture regulating device 4 for moisture control to achieve a moisture content of 12%. Finally, the moisture-controlled carbonized particles are extruded into cotton stalk briquette fuel by an extrusion molding device 5 at 150°C and 60.0 MPa. The density of the obtained cotton stalk briquette fuel is approximately 1.23 g / cm³. 3 It has a calorific value of approximately 24.8 MJ / kg and an ash content of approximately 4.1%.

[0030] The working principle of this straw briquette fuel preparation system is as follows: the straw raw material is conveyed by the feeding and conveying device 1 to the low-temperature carbonization device 2, where it is carbonized at a low temperature of 200-290℃ for 30-90 minutes. Then, it is discharged from the outlet of the low-temperature carbonization device 2 and crushed by the crushing roller to obtain straw pellets (carbonized pellets) with a size ≤20.0mm. The carbonized pellets then enter the moisture adjustment device 4 to obtain a moisture content of 5-12%. Finally, they are extruded by the extrusion molding device 5 at 100-150℃ and 60.0-90.0MPa to form straw briquette fuel.

[0031] Specifically, the above-mentioned preparation system can not only achieve intermittent modular operation, but also continuous integrated operation: ① When the system is running intermittently in a modular manner, the moisture regulating device 4 is an open storage space, which obtains the required moisture content by absorbing water vapor from the air through straw pellets (carbonized pellets); ② When the system is running continuously in an integrated manner, the moisture regulating device 4 is a closed tank-like container, which obtains the required moisture content by spraying water and balancing.

[0032] Preferably, the aforementioned low-temperature carbonization device 2 is also equipped with a flue gas treatment and reuse system 6, which can purify the flue gas and reuse the combustible components for combustion and heating in the low-temperature carbonization device 2, achieving partial energy self-sufficiency; the height of the crushing roller can be adjusted, thereby changing the distance between the crushing roller and the base to adapt to different low-temperature carbonization straw raw materials, and can realize the size control of the crushed straw particles.

[0033] Example 2

[0034] The difference between Example 2 and Example 1 is that the type of straw, the low-temperature carbonization conditions, the crushing size and moisture content of the carbonized particles, and the extrusion molding conditions are different in Example 2 compared to Example 1, while the other conditions are the same.

[0035] Specifically, the preparation process of this straw briquette fuel in Example 2 is as follows: Corn stalks are conveyed by a feeding and conveying device 1 to a low-temperature carbonization device 2, where they are carbonized at 240°C for 60 minutes. The carbonized stalks are then discharged from the outlet of the low-temperature carbonization device 2. The carbonized corn stalks then enter a crushing mechanism 3 and are crushed by a rolling roller to obtain corn stalk particles (carbonized particles) with a size ≤20.0 mm. These particles then enter a moisture regulating device 4 for moisture control to achieve a moisture content of 8%. Finally, the moisture-controlled carbonized particles are extruded into corn stalk briquette fuel by an extrusion molding device 5 at 140°C and 60.0 MPa. The density of the obtained corn stalk briquette fuel is approximately 1.25 g / cm³. 3 It has a calorific value of approximately 25.6 MJ / kg and an ash content of approximately 3.9%.

[0036] Example 3

[0037] The difference between Example 3 and Example 1 is that the type of straw, the low-temperature carbonization conditions, the crushing size and moisture content of the carbonized particles, and the extrusion molding conditions are different in Example 3 compared to Example 1, while the other conditions are the same.

[0038] Specifically, the preparation process of this straw briquette fuel in Example 3 is as follows: Rice straw is conveyed by the feeding and conveying device 1 to the low-temperature carbonization device 2, where it is carbonized at 220°C for 75 minutes. The carbonized straw is then discharged from the outlet of the low-temperature carbonization device 2. The carbonized rice straw then enters the crushing mechanism 3 and is crushed by the rolling rollers to obtain rice straw particles (carbonized particles) with a size ≤20.0 mm. These particles then enter the moisture regulating device 4 for moisture control to achieve a moisture content of 9%. Finally, the moisture-controlled carbonized particles are extruded into rice straw briquette fuel by the extrusion molding device 5 at 130°C and 75.0 MPa. The density of the obtained rice straw briquette fuel is approximately 1.26 g / cm³. 3 It has a calorific value of approximately 25.1 MJ / kg and an ash content of approximately 4.6%.

[0039] Example 4

[0040] The difference between Example 4 and Example 1 is that the type of straw, the low-temperature carbonization conditions, the crushing size and moisture content of the carbonized particles, and the extrusion molding conditions are different in Example 4 compared to Example 1, while the other conditions are the same.

[0041] Specifically, the preparation process of this straw briquette fuel in Example 4 is as follows: Rapeseed stalks are conveyed by a feeding and conveying device 1 to a low-temperature carbonization device 2, where they are carbonized at 290°C for 30 minutes. The carbonized stalks are then discharged from the outlet of the low-temperature carbonization device 2. After carbonization, the rapeseed stalks enter a crushing mechanism 3 and are crushed by a rolling roller to obtain rapeseed stalk particles (carbonized particles) with a size ≤20.0 mm. These particles then enter a moisture regulating device 4 for moisture control to achieve a moisture content of 7%. Finally, the moisture-controlled carbonized particles are extruded into rapeseed stalk briquette fuel by an extrusion molding device 5 at 100°C and 90.0 MPa. The density of the obtained rapeseed stalk briquette fuel is approximately 1.31 g / cm³. 3 Its calorific value is approximately 27.2 MJ / kg, and its ash content is approximately 3.3%.

[0042] Example 5

[0043] The difference between Example 5 and Example 1 is that the type of straw, the low-temperature carbonization conditions, the crushing size of the carbonized particles, the moisture content, and the extrusion molding conditions are different in Example 5 compared to Example 1, while the other conditions are the same.

[0044] Specifically, the preparation process of the straw briquette fuel in Example 5 is as follows: sorghum stalks are conveyed by the feeding and conveying device 1 to the low-temperature carbonization device 2, where they are carbonized at 280°C for 40 minutes. The carbonized sorghum stalks are then discharged from the outlet of the low-temperature carbonization device 2. After carbonization, the sorghum stalks enter the crushing mechanism 3 and are crushed by the rolling rollers to obtain sorghum stalk particles (carbonized particles) with a size ≤20.0 mm. These particles then enter the moisture adjustment device 4 for moisture control to achieve a moisture content of 5%. Finally, the moisture-adjusted carbonized particles are extruded into sorghum stalk briquette fuel by the extrusion molding device 5 at 120°C and 75.0 MPa. The density of the obtained sorghum stalk briquette fuel is approximately 1.28 g / cm³. 3 It has a calorific value of approximately 26.7 MJ / kg and an ash content of approximately 3.6%.

[0045] Example 6

[0046] The difference between Example 6 and Example 1 is that the type of straw, the low-temperature carbonization conditions, the crushing size of the carbonized particles, the moisture content, and the extrusion molding conditions are different in Example 6 compared to Example 1, while the other conditions are the same.

[0047] Specifically, the preparation process of this straw briquettes in Example 6 is as follows: Wheat straw is conveyed by the feeding and conveying device 1 to the low-temperature carbonization device 2, where it is carbonized at 260°C for 50 minutes. The carbonized straw is then discharged from the outlet of the low-temperature carbonization device 2. The carbonized wheat straw then enters the crushing mechanism 3 and is crushed by the rolling rollers to obtain wheat straw particles (carbonized particles) with a size ≤20.0 mm. These particles then enter the moisture adjustment device 4 for moisture control to achieve a moisture content of 10%. Finally, the moisture-adjusted carbonized particles are spirally extruded into wheat straw briquettes by the extrusion molding device 5 at 110°C and 85.0 MPa. The density of the obtained wheat straw briquettes is approximately 1.30 g / cm³. 3 It has a calorific value of approximately 25.9 MJ / kg and an ash content of approximately 3.7%.

[0048] Comparative Example 1

[0049] Comparative Example 1 is a commercially available briquetted fuel, which is produced using the current "crushing-drying-molding" process and has a density of approximately 1.11 g / cm³. 3 It has a calorific value of approximately 16.7 MJ / kg and an ash content of approximately 7.2%.

[0050] Table 1. Parameters and quality of briquettes in Examples 1-6 and Comparative Example 1

[0051] It can be seen that the straw raw materials of the present invention can be carbonized well at low temperatures, resulting in straw briquettes with high calorific value and low ash content. Moreover, under the set molding temperature and molding pressure, the crushed straw particles in each embodiment can be well shaped. It can be seen that the density and calorific value of the straw briquettes prepared by the process of the present invention are significantly higher than those of commercially available briquettes, while the ash content is lower.

[0052] The above-described preferred embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of the invention. Any obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A process for preparing straw briquettes, characterized in that, The process includes the following steps: S1. Low-temperature carbonization: Low-temperature carbonization of straw to remove volatile substances; S2. Crushing: Crushing the straw after low-temperature carbonization to obtain carbonized pellets suitable for extrusion molding. S3. Moisture adjustment: Adjust the moisture content of the carbonized particles to meet the requirements of extrusion molding; S4. Extrusion molding: The carbonized particles with adjusted moisture content are spirally extruded to obtain molded fuel.

2. The preparation process of straw briquetted fuel according to claim 1, characterized in that, The low-temperature carbonization temperature in step S1 is 200-290℃ and the carbonization time is 30-90 minutes; the volatile substances include small molecule oxygen-containing compounds, alkali metals and alkaline earth metals that are prone to slagging and ash accumulation during subsequent fuel combustion, and precursors containing nitrogen, sulfur and phosphorus that are prone to generating combustion pollutants.

3. The preparation process of straw briquetted fuel according to claim 1, characterized in that, In step S2, the particle size of the resulting carbonized particles is not more than 20.0 mm.

4. The preparation process of straw briquetted fuel according to claim 1, characterized in that, In step S3, the moisture content of the carbonized particles is adjusted to be 5.0-12.0%.

5. The preparation process of straw briquetted fuel according to claim 1, characterized in that, The temperature of the spiral extrusion molding in step S4 is 100-150℃ and the pressure is 60.0-90.0MPa.

6. A type of straw-based briquetted fuel, characterized in that, It is prepared using the preparation process described in any one of claims 1 to 5.

7. The straw briquette fuel preparation system according to claim 6, characterized in that, The preparation system includes the following structural configuration: The feeding and conveying device (1) is used to feed in and transport straw raw materials; Low-temperature carbonization device (2), which is used to receive the straw conveyed by the feeding and conveying device (1) and perform low-temperature carbonization treatment on it; The crushing mechanism (3) is located at the outlet of the low-temperature carbonization device (2) and is used to receive the straw after low-temperature carbonization and crush it to obtain carbonized particles. A moisture regulating device (4) is located downstream of the crushing mechanism (3) and is used to regulate the moisture content of the carbonized particles. And an extrusion molding device (5), which includes a spiral extruder and a heating jacket disposed outside the spiral extruder. The spiral extruder is used to spirally extrude carbonized particles after moisture adjustment, and the heating jacket is used for temperature regulation during the carbonized particle extrusion molding process.

8. The straw briquette fuel preparation system according to claim 7, characterized in that, The crushing mechanism (3) includes a crushing roller and a base. The base is used to receive the straw after low-temperature carbonization treatment. The crushing roller is set above the base and the distance between the roller and the base can be adjusted. It is used to crush the straw after low-temperature carbonization treatment.

9. The straw briquette fuel preparation system according to claim 7, characterized in that, The system is configured to operate either intermittently in a modular fashion or continuously in an integrated manner. When the system operates intermittently in a modular manner, the moisture regulating device (4) is set as an open storage location, and the carbonized particles absorb moisture from the air to obtain the required moisture content; when the system operates continuously in an integrated manner, the moisture regulating device (4) is set as a closed container, and the carbonized particles are sprayed with water and balanced to obtain the required moisture content.

10. The straw briquette fuel preparation system according to claim 7, characterized in that, The system also includes a flue gas treatment and reuse system (6), which is connected to the low-temperature carbonization device (2). The flue gas treatment and reuse system (6) is used to purify the flue gas generated during the low-temperature carbonization process to obtain the combustible components in the flue gas. The combustible components are then circulated back to the low-temperature carbonization device (2) through the flue gas treatment and reuse system (6). The flue gas treatment and reuse system (6) is also used to provide heat for the heating jacket.

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