Optimization method of biomass briquette fuel morphology based on stacking characteristics

Abstract

The morphology optimization method of biomass briquette fuel based on stacking characteristics uses a multi-sphere model to construct cylindrical pellet fuel, and uses software with the function of simulating the behavior characteristics or motion process of a loose particle system to simulate the random stacking process of biomass briquette fuel. By changing the physical parameters and morphological parameters, the expression of the stacking void ratio on the morphological parameters is fitted, thereby combining the particle density and the stacking density to give the recommended value range of the morphological parameters. The present invention performs morphological design on biomass briquette fuel, comprehensively considers factors such as the stacking density and stacking void ratio of biomass fuel, and is conducive to the rational and efficient use of biomass briquette fuel, laying a foundation for promoting clean heating in winter in northern regions.

Description

Technical Field

[0001] The invention belongs to the field of biomass energy application and relates to an optimization design method for the morphology of biomass molded fuel. Background Art

[0002] Biomass fuel is a renewable energy source, and its development and utilization is an important way to solve energy and environmental problems. The raw materials of biomass solid fuel are mainly straw and other materials with large volume, low energy density and irregular shape. Therefore, it is necessary to use compression molding technology to process them into solid molded fuels with basically the same shape and size to improve the economy, efficiency and safety of utilization.

[0003] Diameter and aspect ratio are the main morphological parameters of pellet fuel. Their values ​​will directly affect the stacking porosity of the bed, and the porosity is closely related to the stacking density. However, the existing standard system only makes requirements for the stacking density, and does not provide a method for selecting the molding morphological parameters. Even the recommended parameter ranges of different standards are contradictory, resulting in different specifications of products manufactured by different companies, which cannot ensure the efficient use of fuel. Therefore, it is of great significance to identify the relationship between particle morphological parameters, stacking porosity, particle density and stacking density, and to determine the combination range of biomass particle morphological parameters that meet the stacking density under different particle densities, in order to achieve efficient use of biomass fuel. Summary of the invention

[0004] The biomass shaped fuel morphology optimization method based on stacking characteristics provided by the present invention uses a multi-sphere model to construct cylindrical granular fuel, uses software with the function of simulating the behavior characteristics or motion process of a loose particle system to simulate the random stacking process of biomass shaped granular fuel, and fits the expression of stacking void ratio on morphological parameters by changing physical parameters and morphological parameters, thereby giving the recommended value range of morphological parameters in combination with particle density and stacking density. Granular fuel that meets the optimized morphological parameters meets the requirements of the standard on stacking density, which is conducive to the rational and efficient use of biomass shaped fuel.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A biomass pellet fuel morphology optimization method based on stacking characteristics is proposed. A multi-sphere model is used to construct cylindrical pellet fuel. The random stacking process of biomass pellet fuel is simulated using software that has the function of simulating the behavioral characteristics or movement process of a loose particle system. By changing the physical properties and morphological parameters, the expression of the stacking void ratio with respect to the morphological parameters is fitted, and the recommended value range of the morphological parameters is given in combination with the particle density and stacking density.

[0007] Preferably, the design is performed using software that has the function of simulating the behavior characteristics or movement process of a bulk particle system, and the steps include:

[0008] In the first step, a multi-sphere model is used to construct cylindrical fuel particles, that is, several spheres of different sizes are stacked to represent the cylindrical particles;

[0009] The second step is to use software that can simulate the behavior characteristics or movement process of a dispersed particle system to complete the simulation of the random accumulation process of particles;

[0010] The third step is to change the physical and morphological parameters of the particles in the model according to the parameter range of conventional biomass pellet fuel, and fit the expression of the porosity of the accumulation body of particles with different physical parameters with respect to the morphological parameters;

[0011] The fourth step is to calculate the range of morphological parameters of biomass particles from the expression of morphological parameters of stacking void ratio based on the relationship between particle density, porosity of stacking body and stacking density, combined with particle density and the minimum limit of stacking density in existing biomass solid molded fuel standard specifications.

[0012] Preferably, the first step of "using a multi-ball model to construct cylindrical fuel particles" specifically refers to constructing cylindrical particles with a diameter of d and a length of l, first stacking n group A balls with a diameter of d axially to obtain the main part, and then filling the gaps in the radial direction at both ends with group B balls with a smaller diameter, and then filling the outermost gaps in the radial direction at both ends with group C balls with an even smaller diameter, and so on, until the simulated void fraction value meets the calculation accuracy requirements.

[0013] Preferably, the key to constructing cylindrical particles is to determine the value of n, as well as the diameter and position parameters of the other groups of balls, based on the expected value of the volume percentage of the structure and the accuracy of the void fraction calculation result. The volume percentage, that is, the ratio of the volume of the structure to the actual volume of the cylinder, should be no less than 90%, and the void fraction result deviation should not exceed 5%. Among them, the ratio of the volume of the main part of the structure to the actual cylinder given by n is 1-(ld) 2 / (3d 2 (n-1) 2 ).

[0014] Preferably, the second step of "using software with the function of simulating the behavior characteristics or movement process of a bulk particle system to complete the simulation of the random stacking process of particles" specifically refers to establishing a stacking model including cylindrical biomass particles and a stacking container, and tracking the position and contact information of each particle through a series of calculations of the forces, moments, velocities and accelerations of the particles, thereby obtaining a stacking body.

[0015] Preferably, in the third step, "according to the parameter range of conventional biomass briquetting fuel, changing the physical parameters and morphological parameters of the particles in the model" specifically refers to changing the model parameters within the parameter range of conventional biomass briquetting fuel. Under the condition that the physical parameters remain unchanged, the morphological parameters of the particles are changed to obtain a series of porosity data; the physical parameters are then changed to measure the porosity of the particles with different morphological parameters under the changed physical parameters; and the above operation is repeated.

[0016] Preferably, the morphological parameters mainly include diameter d and aspect ratio AR (ratio of length to diameter), and the physical property parameters mainly include particle density ρ, shear elastic modulus G, recovery coefficient e, rolling friction coefficient μ r and static friction coefficient μ s .

[0017] Preferably, the "fitting out the expression of the porosity of the accumulation of particles with different physical parameters with respect to the morphological parameters" in the third step specifically means: the expression of the porosity with respect to the morphological parameters is in the form of ε=aAR+b, and the expression can be obtained by determining the values ​​of a and b.

[0018] Preferably, a and b are coefficients related to the restitution coefficient and the static friction coefficient. When the restitution coefficient and the static friction coefficient of the biomass molded fuel are determined, the a and b values ​​need to be fitted based on the simulation results of the stacking porosity of particles with an aspect ratio of 2-8.

[0019] Preferably, in the fourth step, "according to the relationship between particle density, porosity of the stack and stacking density, combined with the particle density and the provisions on the minimum limit of stacking density in the existing biomass solid briquette fuel standard, the combination range of morphological parameters of biomass particles is calculated from the expression of stacking porosity on morphological parameters" specifically means: according to the particle density ρ 颗 , the porosity ε of the stack, the stacking density ρ 堆 The relationship among the three 堆 =(1-ε)ρ 颗 , combined with the particle density ρ 颗 The minimum value of the bulk density of biomass pellet fuel in the standard ρ 堆 ', the maximum allowable void fraction ε can be calculated max =1-ρ 堆 ' / ρ 颗 , and then from ε = aAR + b, we can get the maximum value of the aspect ratio [(1-b)ρ 颗 -ρ 堆 '] / [a·ρ 颗 ].

[0020] Due to the adoption of the above technical solution, the present invention has the following beneficial effects:

[0021] The multi-sphere model is used to construct cylindrical pellet fuel and simulate the random stacking process of biomass pellet fuel.

[0022] With the advantages of numerical simulation software, by analyzing the characteristics of particle accumulation with different parameters, we can find the appropriate range of morphological parameters under different physical parameters. Pellet fuels with optimized morphological parameters meet the requirements of the standard on stacking density, which is conducive to the rational and efficient use of biomass molding fuels. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flow chart for the implementation of the biomass pellet fuel morphology optimization method based on stacking characteristics.

[0024] Figure 2 Schematic diagram of the cylindrical particle construction process.

[0025] Figure 3 This is the schematic diagram of DEM technology.

[0026] Figure 4 Schematic diagram of the simulation of random particle stacking process. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0028] The present invention provides a method for optimizing the morphology of biomass briquette fuel based on stacking characteristics, and the process is as follows: Figure 1 As shown in the figure: first, cylindrical particles are constructed using a multi-sphere model; then, a random stacking process model of biomass pellet fuel is constructed using software that has the function of simulating the movement process of a loose particle system; then, the expression of the void ratio of the stacking body with respect to the morphological parameters of particles with different physical parameters is fitted; finally, based on the relationship between particle density, void ratio of the stacking body and stacking density, combined with the standard specifications for biomass solid molded fuel, the range of morphological parameters of biomass particles is calculated from the expression of stacking void ratio with respect to morphological parameters.

[0029] The above-mentioned biomass briquette fuel morphology optimization method based on stacking characteristics includes the following steps:

[0030] The first step is to use a multi-ball model to construct cylindrical fuel particles: to construct cylindrical particles with a diameter of d and a length of l, first use n group A balls with a diameter of d to stack along the axial direction to obtain the main part, then use group B balls with a smaller diameter to fill the gaps in the radial direction at both ends, and then use group C balls with a smaller diameter to fill the outermost gaps in the radial direction at both ends, and so on. The key to constructing cylindrical particles is to determine the value of n, as well as the diameter and position parameters of other groups of balls. The more element balls used in the construction, the denser the arrangement, and the smaller the diameter of the smallest ball, the closer the volume of the obtained structure is to the volume of the actual cylinder and the closer the void ratio calculation result is to the value of the stacking void ratio of the cylindrical particles, but the amount of calculation is also greater. In order to make the generated particles close to the real cylinder and not waste computing resources, the number of element balls selected should be as small as possible while meeting the calculation accuracy requirements. The volume percentage, that is, the ratio of the volume of the structure to the actual volume of the cylinder, should not be less than 90%, and the void ratio result deviation should not exceed 5%.

[0031] In a specific embodiment, the steps of constructing a cylindrical particle with a diameter of d and a length of l are: first, 6(ld) / d+1 balls of group A with a diameter of d are stacked axially to obtain the main body, and the distance between the centers of two adjacent balls is l / 6, and then the gaps are filled with balls of group B with a diameter of d / 2 at every 22.5° radially at both ends, and finally, the outermost gaps are filled with balls of group C with a diameter of d / 5 at every 11.25° radially at both ends. In the embodiment of the present invention, taking the construction of a cylindrical particle with a diameter of 3mm and a length of 9mm as an example, the specific steps are shown in Figure 2 There are 13 balls in group A with a diameter of 3 mm, 32 balls in group B with a diameter of 1.5 mm, and 64 balls in group C with a diameter of 0.6 mm. The total number of element balls used is 109, and the volume share is 97.5%. The porosity error obtained by simulation calculation is less than 2%.

[0032] The second step is to use software that can simulate the behavior characteristics or motion process of loose particle systems to complete the simulation of the random stacking process of particles: establish a stacking model including biomass particles and stacking containers in the software to complete the simulation of the random stacking process of particles: import the single cylindrical particle model built in the first step, and define the physical parameters of the particles according to the particle density, shear elastic modulus, static friction coefficient, rolling friction coefficient, recovery coefficient and other parameters obtained from experimental tests, set the physical parameters and size of the container, contact parameters, set the particle factory, calculation time, save interval, contact search radius range, and GPU number. Figure 3 The series of calculations of the forces, moments, velocities, and accelerations of the particles shown in the figure tracks the position and contact information of each particle, thereby obtaining Figure 4 The stacking process is shown, as well as stacking information such as void fraction.

[0033] In the embodiment of the present invention, the software EDEM developed based on the discrete element method is used as an example: the diameter of the imported cylindrical particles is 6 mm and the length is 24 mm; the particle physical property parameters are set to a density of 1100 kg / m 3 , shear elastic modulus 2×10 7 Pa, static friction coefficient between particles 0.5, rolling friction coefficient 0.06, restitution coefficient 0.6; cylindrical container diameter 200mm height 850mm, physical parameters set to density 7850kg / m 3 , shear elastic modulus 8×10 10 Pa, static friction coefficient between particles and container is 0.3, rolling friction coefficient is 0.03, and recovery coefficient is 0.5; there are 2506 accumulated particles with a total mass of 1.87kg, which are evenly generated within 0.8s, with random generation positions and angles, and the initial falling speed is 0; the calculation time is 2s, the saving interval is 0.01s, and the contact search radius range is 4R. The final pile height is 109.5mm. In order to ensure that the porosity result is not affected by the uneven looseness of the top layer of particles and to make the statistical area contain as many particles as possible, the height of the statistical porosity area is taken as 0.95 times the pile height, and the calculated porosity value is 0.4908, which deviates from the average value of 0.4880 of multiple experiments by 0.57%.

[0034] The third step is to change the physical and morphological parameters of the particles in the model according to the parameter range of conventional biomass pellet fuel, and fit the particles with different physical parameters. The expression of the porosity of the accumulation body with respect to the morphological parameters is as follows: input particle density ρ, shear elastic modulus G, recovery coefficient e, rolling friction coefficient μ r and static friction coefficient μ s By changing the particle diameter d and aspect ratio AR (ratio of length to diameter) with the same physical parameters, the values ​​of a and b in the void fraction expression ε=aAR+b are fitted.

[0035] In the embodiment of the present invention, the particle diameters involved in the test include 6mm, 8mm, and 10mm, the aspect ratio range is 2-8, and the particle density range is 900kg / m 3 -1700kg / m 3 , shear elastic modulus range 2×10 6 Pa-2×10 10Pa, the range of restitution coefficient is 0.3-0.8, the range of rolling friction coefficient is 0.02-0.10, the range of static friction coefficient is 0.2-0.8, and the simulated value of void ratio is between 0.42-0.63. The results show that the void ratio of the accumulation body under various conditions increases with the increase of accumulation rate (the volume of particles passing through a unit area per unit time), and shows a trend of first increasing and then stabilizing near a certain value, that is, the void ratio has a maximum value, and when the accumulation rate exceeds the critical rate value, the void ratio is equal to the maximum void ratio, and the dumping rate in actual production is generally greater than the critical value. The results show that the void ratio is independent of the diameter, particle density, shear elastic modulus, and rolling friction coefficient, and is related to the aspect ratio, restitution coefficient, and static friction coefficient. When the restitution coefficient is between 0.4-0.7 and the static friction coefficient is between 0.3-0.6, the expression of the void ratio can be approximately written as ε=0.0338AR+0.3593, and the prediction error does not exceed 5%.

[0036] The fourth step is to calculate the range of morphological parameters of biomass particles from the expression of morphological parameters of stacking porosity according to the relationship between particle density, porosity of stacking body and stacking density, combined with the standard specification of biomass solid briquette fuel: 颗 , the porosity ε of the stack, the stacking density ρ 堆 The relationship among the three 堆 =(1-ε)ρ 颗 , combined with the particle density ρ 颗 The minimum value of the bulk density of biomass pellet fuel in the standard ρ 堆 ', calculate the maximum allowable void ratio ε max =1-ρ 堆 ' / ρ 颗 , and then from the expression of stacking void ratio on morphological parameters ε = aAR + b, the maximum value of aspect ratio is [(1-b)ρ 颗 -ρ 堆 '] / [a·ρ 颗 ].

[0037] In the embodiment of the present invention, the recovery coefficient of conventional biomass pellet fuel is between 0.4-0.7, the static friction coefficient is between 0.3-0.6, and the 堆 '=500kg / m 3 When 颗 =1000kg / m 3 The corresponding maximum aspect ratio is 4, ρ 颗 =1100kg / m 3 The corresponding maximum aspect ratio is 5, ρ 颗 =1200kg / m 3 The corresponding maximum aspect ratio is 6.

[0038] The above description of the embodiments is to facilitate the understanding and use of the present invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for optimizing the morphology of biomass briquette fuel based on stacking characteristics, characterized in that: The cylindrical pellet fuel was constructed using a multi-sphere model, and the random stacking process of biomass pellet fuel was simulated using software that simulates the behavior characteristics or motion process of a loose particle system. By changing the physical properties and morphological parameters, the expression of the stacking void ratio with respect to the morphological parameters was fitted, and the recommended value range of the morphological parameters was given in combination with the particle density and stacking density. Design using software that can simulate the behavior characteristics or motion process of bulk particle systems, including: In the first step, a multi-sphere model is used to construct cylindrical fuel particles, that is, several spheres of different sizes are stacked to represent the cylindrical particles; The second step is to use software that can simulate the behavior characteristics or movement process of a dispersed particle system to complete the simulation of the random accumulation process of particles; The third step is to change the physical parameters and morphological parameters of the particles in the model according to the parameter range of conventional biomass briquette fuel, wherein the physical parameters include particle density ρ, shear elastic modulus G, recovery coefficient e, rolling friction coefficient μ r and static friction coefficient μ s , the morphological parameters mainly include diameter d and aspect ratio AR; refer to the parameter range of conventional biomass briquette fuel, change the model parameters within this range; under the condition that the physical property parameters remain unchanged, change the morphological parameters of the particles to obtain a series of porosity data, then change the physical property parameters, and measure the porosity of the accumulation of particles with different morphological parameters under the changed physical property parameters; repeat the above operation; fit the particles with different physical property parameters, and the expression of the porosity of the accumulation body with respect to the morphological parameters is ε=aAR+b, and the expression can be obtained by determining the values ​​of a and b; The fourth step is to calculate the range of morphological parameters of biomass particles from the expression of morphological parameters of stacking void ratio according to the relationship between particle density, porosity of stacking body and stacking density, combined with particle density and the minimum limit of stacking density in the existing biomass solid briquette fuel standard specification; according to particle density ρ 颗 , the porosity ε of the stack, the packing density ρ 堆 The relationship among the three 堆 =(1-ε)ρ 颗 , combined with the particle density ρ 颗 The minimum value of the bulk density of biomass pellet fuel in the standard ρ 堆 ', the maximum allowable void fraction ε can be calculated max =1-ρ 堆 ' / ρ 颗 , and then from ε = aAR + b, we can get the maximum value of the aspect ratio [(1-b)ρ 颗 -ρ 堆 '] / [a·ρ 颗 ]; that is, if the coefficient of restitution and static friction of the particles are known, the range of aspect ratios of particles with different particle densities can be obtained according to the minimum limit of the stacking density, which can be used as the design size of biomass pellet fuel.

2. The method for optimizing the morphology of biomass briquette fuel based on stacking characteristics according to claim 1 is characterized in that: The first step of "using a multi-ball model to construct cylindrical fuel particles" means that when constructing a cylindrical particle with a diameter of d and a length of l, first use n group A balls with a diameter of d to stack along the axial direction to obtain the main part, and then use group B balls with a smaller diameter to fill the gaps in the radial direction at both ends, and then use group C balls with an even smaller diameter to fill the outermost gaps in the radial direction at both ends, and so on, until the simulated void fraction value meets the calculation accuracy requirements.

3. The method for optimizing the morphology of biomass briquette fuel based on stacking characteristics according to claim 2 is characterized in that: The ratio of the volume of the main part structure given by n to the actual cylinder volume is 1-(ld) 2 / (3d 2 (n-1) 2 ).

4. The method for optimizing the morphology of biomass briquette fuel based on stacking characteristics according to claim 2 is characterized in that: The key to constructing cylindrical particles is to determine the value of n, as well as the diameter and position parameters of other groups of spheres, based on the expected value of the volume percentage of the structure and the accuracy of the void fraction calculation results; the volume percentage is the ratio of the volume of the structure to the actual volume of the cylinder.

5. The method for optimizing the morphology of biomass briquette fuel based on stacking characteristics according to claim 4 is characterized in that: The value of the volume percentage should not be less than 90%, and the void ratio result deviation should not exceed 5%.

6. The method for optimizing the morphology of biomass briquette fuel based on stacking characteristics according to claim 1 is characterized in that: The second step of "using software that can simulate the behavior characteristics or movement process of scattered particle systems to complete the simulation of the random particle stacking process" refers to establishing a stacking model including cylindrical biomass particles and stacking containers, and tracking the position and contact information of each particle through a series of calculations of the forces, moments, velocities and accelerations of the particles, thereby obtaining a stacking body.

7. The method for optimizing the morphology of biomass briquette fuel based on stacking characteristics according to claim 1 is characterized in that: a and b are coefficients related to the coefficient of restitution and the coefficient of static friction. When the coefficient of restitution and the coefficient of static friction of the biomass molded fuel are determined, the values ​​of a and b need to be fitted based on the simulation results of the stacking porosity of particles with an aspect ratio of 2-8.

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