A heat transfer calculation method for metallurgical slag waste heat recovery

Abstract

The present invention discloses a heat transfer calculation method for recycling waste heat from metallurgical slag, which belongs to the technical field of energy recovery and biomass conversion. The heat transfer calculation method includes: calculating the momentum of particle movement in a rotary pyrolysis furnace based on a particle flow model; calculating the contact heat transfer amount Q1 between biomass particles and metallurgical slag particles in the rotary pyrolysis furnace based on the heat transfer model and the momentum of particle movement; calculating the contact heat transfer amount Q2 between biomass particles in the rotary pyrolysis furnace and the inner wall of the rotary pyrolysis furnace based on the heat transfer model and the momentum of particle movement; calculating the convection heat transfer amount Q3 between biomass particles and gas in the rotary pyrolysis furnace based on the heat transfer model and the momentum of particle movement; calculating the heat Q4 generated due to chemical reaction or phase change based on the biomass pyrolysis model; and calculating the heat transfer amount Q of the rotary pyrolysis system based on the contact heat transfer amount Q1, the contact heat transfer amount Q2, the convection heat transfer amount Q3, and the heat Q4. transfer .

Description

Technical Field

[0001] The present invention relates to the technical field of energy recovery and biomass conversion, and in particular to a heat transfer calculation method for recycling waste heat from metallurgical slag. Background Art

[0002] The large amount of high-temperature slag produced during non-ferrous metal smelting is a potential energy resource. However, due to its complex phase composition and high-temperature properties, efficient recovery of slag waste heat has been a challenge for the industry. Meanwhile, biomass, as a renewable energy source, has enormous potential for thermochemical conversion. However, traditional biomass pyrolysis and slag waste heat recovery technologies suffer from low heat transfer efficiency and high energy losses, limiting the feasibility of combining the two.

[0003] Rotary reactors, such as rotary pyrolysis furnaces, have gained increasing application in slag waste heat recovery and biomass thermochemical conversion in recent years due to their excellent mixing characteristics and high heat transfer efficiency. However, the mixing and heat exchange between biomass and slag in rotary reactors involves complex multiphase flow, heat transfer, and chemical reactions. A systematic model and calculation method are still lacking to effectively describe and optimize this process. Therefore, an effective heat transfer model calculation method is proposed, which is of great significance for improving the efficiency of slag waste heat recovery and biomass energy utilization. Summary of the Invention

[0004] In order to solve or partially solve the problems existing in the related art, the present invention provides a heat transfer calculation method for metallurgical slag waste heat recovery and utilization, which can accurately describe the heat transfer characteristics and energy exchange process between slag and biomass particles in a rotary reactor as well as the biomass pyrolysis reaction process, thereby providing a theoretical basis and technical support for improving the slag waste heat recovery and biomass thermochemical conversion efficiency.

[0005] This application proposes a heat transfer calculation method for the recovery and utilization of waste heat from metallurgical slag. It establishes a heat transfer model between biomass particles and high-temperature metallurgical slag particles in a rotary pyrolysis furnace, and proposes a heat transfer calculation method that couples the particle flow model, heat transfer model, and pyrolysis model.

[0006] The particle flow model uses the Hertz-Mindlin contact model based on the Hertz contact theory and the Mindlin-Deresiewicz theory. The Hertz-Mindlin contact model is a mathematical model used to describe the behavior of particles when they come into contact with each other and is widely used in simulation software. The heat transfer model proposed in the design covers the contact heat conduction between biomass particles and metallurgical slag particles, the contact heat conduction between biomass particles and furnace walls, the convective heat transfer between biomass particles and gas, and the heat transfer due to chemical reactions and phase changes caused by biomass pyrolysis. The pyrolysis process is a biomass pyrolysis model defined by a multivariate analysis method. The heat transfer calculation method specifically includes the following steps:

[0007] S1. Based on the CFD-DEM numerical method of the particle flow model, a heat transfer model for the waste heat recovery and utilization of high-temperature metallurgical slag particles coupled with the thermochemical conversion reaction of biomass in a rotary pyrolysis furnace was established;

[0008] S2. Calculate the particle motion momentum in the rotary pyrolysis furnace based on the particle flow model;

[0009] S3. Calculate the contact heat transfer Q1 between biomass particles and metallurgical slag particles in the rotary pyrolysis furnace based on the heat transfer model and particle motion momentum;

[0010] S4. Calculate the contact heat transfer amount Q2 between the biomass particles in the rotary pyrolysis furnace and the inner wall of the rotary pyrolysis furnace based on the heat transfer model and the particle motion momentum;

[0011] S5. Calculate the convective heat transfer Q3 between biomass particles and gas in the rotary pyrolysis furnace based on the heat transfer model and particle motion momentum;

[0012] S6. Calculate the heat Q4 generated due to chemical reaction or phase change based on the biomass pyrolysis model;

[0013] Among them, the biomass pyrolysis model is a pyrolysis model in which hemicellulose, cellulose and lignin are decomposed into volatiles and char respectively through a single Arrhenius reaction;

[0014] S7. Calculate the heat transfer Q of the rotary pyrolysis furnace pyrolysis system based on contact heat transfer Q1, contact heat transfer Q2, convection heat transfer Q3 and heat Q4. transfer .

[0015] In some schemes, the geometric model of the rotary pyrolysis furnace is meshed using O-blocking technology combined with hexahedral elements, with local encryption performed at the inlet / outlet bends. Heat transfer calculations within the rotary pyrolysis furnace are performed using computational fluid dynamics (CFD) coupled with the discrete element method (DEM). The design of a user-defined coupling interface takes into account the data format and communication protocol between the CFD and DEM software to ensure accurate data transmission and interpretation. Using the CFD software solver, the initial conditions set include fluid pressure, velocity, and temperature. Using the DEM software solver, the particle parameters set include particle diameter, particle number, shear modulus, Poisson's ratio, friction coefficient, restitution coefficient, thermal conductivity, and specific heat capacity. The CFD software updates the particle properties obtained from the DEM software through user-defined functions (UDFs) and converts them into a data format suitable for the CFD software. Subsequently, the CFD software calculates the fluid phase volume fraction, fluid-particle interaction force and heat flux, and updates the fluid pressure field, velocity field and temperature field. After the CFD software calculates a time step, it passes the calculation results (flow field velocity, pressure distribution, etc.) back to the DEM software through the UDF and coupling interface. The DEM software calculates the contact force between particles based on the Hertz-Mindlin no-slip contact model, and calculates the resistance on the particles and other particle data. The DEM software then updates other data such as the particle position, velocity, angular velocity and temperature. The above calculations are iteratively calculated with each time step as a cycle, thereby realizing the coupling of CFD and DEM; the biomass pyrolysis multivariate analysis model is embedded in the CFD software through the UDF method, thereby realizing the heat transfer calculation that couples the particle flow model, heat transfer model and pyrolysis model; when the preset calculation time is reached, the coupled simulation ends.

[0016] Specifically, in some embodiments, the formula for calculating the momentum of the particles in the rotary pyrolysis furnace in S2 is as follows:

[0017]

[0018] Where m p,i 、 t、 and are the mass, linear velocity, time, contact force, gravity and drag force of particle i respectively;

[0019] The calculation formulas for contact force and gravity are as follows:

[0020]

[0021] Where, subscripts n and t are abbreviations of normal direction and tangential direction, respectively; and are the normal force and tangential force of particle contact, respectively; and are the normal direction and tangent direction from the center of particle i to the center of particle j, respectively; and are the damping components of the normal force and the tangential force respectively; m p is the mass of the particle, is the acceleration due to gravity;

[0022] Normal force of particle contact The calculation formula is as follows:

[0023]

[0024] Where, δ n is the contact deformation distance between particles i and j, E * is the equivalent elastic modulus, that is, the equivalent Young's modulus, R * is the equivalent radius, E i 、v i 、R i and E j 、v j 、R j are the Young's modulus, Poisson's ratio, and sphere radius of particles i and j, respectively; is the normal component of the relative velocity, S n is the normal stiffness, m * is the equivalent mass, β is the damping constant, and e is the coefficient of restitution;

[0025] Tangential force of particle contact The calculation formula is as follows:

[0026]

[0027] Where S t represents the tangential spring constant, and δ t represents the tangential displacement, G * is the equivalent shear modulus; is the tangential component of the relative velocity, τ i is the rolling friction coefficient of the particle motion process, μ r is the rolling friction coefficient, R cpc is the distance from the contact point to the center of mass, is the unit angular velocity vector of the particle at the contact point;

[0028] drag The calculation is based on the Gidaspow drag model, and the calculation formula is as follows:

[0029]

[0030] Where V p represents the particle volume, β g,p is the drag coefficient between the gas phase and the particle, and Represent the gas phase fluidity and particle velocity respectively; among them, β g,p is defined as:

[0031]

[0032] Where, ε p and ε g are the particle volume fraction and gas phase volume fraction, ρ g is the gas phase fluid density, d p,i is the particle diameter; the drag coefficient C D Directly depends on the particle Reynolds number Re p , the calculation formula is as follows,

[0033]

[0034] Where μ g is the dynamic viscosity of the gas.

[0035] Specifically, in some embodiments, the calculation formula for the contact heat transfer Q1 between the biomass particles and the metallurgical slag particles in the rotary pyrolysis furnace in S3 is:

[0036] Q1=h1ΔT1,

[0037] Where h1 represents the heat transfer coefficient between biomass particles and metallurgical slag particles, and ΔT1 represents the temperature difference between biomass particles and metallurgical slag particles. The calculation formula for h1 is:

[0038]

[0039] Where k pi and k pj is the thermal conductivity of biomass particles and metallurgical slag particles, is the normal force after the biomass particles contact the metallurgical slag particles, E * 1 is the equivalent elastic modulus of biomass particles after contact with metallurgical slag particles, R * 1 is the equivalent radius of the biomass particles after contact with the metallurgical slag particles.

[0040] Specifically, in some embodiments, the calculation formula for the contact heat transfer Q2 between the biomass particles in the rotary pyrolysis furnace and the inner wall of the rotary pyrolysis furnace in S4 is:

[0041] Q2=h2ΔT2,

[0042] Where h2 represents the heat transfer coefficient between the biomass particles and the rotary pyrolysis furnace wall, and ΔT2 represents the temperature difference between the biomass particles and the rotary pyrolysis furnace wall. The calculation formula for h2 is:

[0043]

[0044] Where k pi is the thermal conductivity of biomass particles, k wall is the thermal conductivity of the rotary pyrolysis furnace wall; is the normal force after the biomass particles contact the rotary pyrolysis furnace wall, E * 2 is the equivalent elastic modulus of the biomass particles after contacting the rotary pyrolysis furnace wall, R * 2 is the equivalent radius of the biomass particles after contact with the rotary pyrolysis furnace wall, which is calculated based on the radius of the biomass particles.

[0045] Specifically, in some embodiments, the calculation formula for the convective heat transfer Q3 between the biomass particles on the upper surface of the rotary pyrolysis furnace and the gas in S4 is:

[0046] Q3=h3ΔT3,

[0047] Where h3 represents the heat transfer coefficient between the biomass particles and the gas in the rotary pyrolysis furnace, and ΔT3 represents the temperature difference between the biomass particles and the gas in the rotary pyrolysis furnace. The calculation formula for h3 is:

[0048] Nu1=2+0.6Re 1 / 2 Pr 1 / 3 ,

[0049] Where k g is the thermal conductivity of gas, Nu1 is the Nusselt number between biomass particles and gas, d1 is the diameter of biomass particles, Re is the Reynolds number, Pr is the Prandtl number, C p is the specific heat capacity of the gas, is the gas flow rate, μ g is the dynamic viscosity of the gas.

[0050] Specifically, in some schemes, the biomass pyrolysis model uses the three main components of biomass, namely hemicellulose, cellulose and lignin, to represent the pyrolysis of biomass. It is assumed that hemicellulose, cellulose and lignin decompose into volatiles and char respectively through a single Arrhenius reaction, as follows:

[0051]

[0052] Wherein, k1, k2 and k3 are the pyrolysis reaction rate constants of hemicellulose, cellulose and lignin, respectively; r1, r2 and r3 represent the yield of biochar generated by pyrolysis of hemicellulose, cellulose and lignin, respectively;

[0053] The calculation formula for heat Q4 generated by chemical reaction or phase change in S6 is:

[0054] Q4=A i,b (-q4)(-ΔH),

[0055] Where A i,b is the reactive surface area of ​​the biomass particle, the negative sign indicates that the concentration of the reactant decreases with time, ΔH is the reaction enthalpy change; q4 is the pyrolysis conversion rate of component i in the biomass, i includes cellulose, hemicellulose and lignin, ρ is the density of the biomass particle, m i , A i and E i are the initial masses of cellulose, hemicellulose, and lignin, the preexponential factor, and activation energy, respectively; R is the ideal gas constant (8.314 J / (mol·K)); and T is the biomass pyrolysis reaction temperature.

[0056] Specifically, in some embodiments, the heat transfer Q of the rotary pyrolysis furnace pyrolysis system in S6 transfer The calculation formula is: Q transfer =Q1+Q2+Q3+Q4.

[0057] Specifically, in some embodiments, the heat transfer algorithm further includes:

[0058] S8. Calculate the mixing index M between particles in the rotary pyrolysis furnace based on the particle flow model. The calculation formula is as follows:

[0059]

[0060] Where C S-B is the contact number between metallurgical slag particles and biomass particles, C S-S is the contact number between metallurgical slag particles, C B-B is the number of contacts between biomass particles.

[0061] The technical solution provided by this application has the following beneficial effects:

[0062] The present invention establishes a heat transfer model for the recovery and utilization of waste heat from high-temperature metallurgical slag particles coupled with the thermochemical conversion reaction of biomass in a rotary pyrolysis furnace, constructs a fluid-solid coupling model of the interaction system between biomass and metallurgical slag particles, and accurately describes the movement and interaction process between the two. At the same time, a multi-component pyrolysis model is established to describe the kinetic behavior of the biomass pyrolysis reaction, comprehensively covering the multi-component reaction paths and characteristics of biomass pyrolysis, and can accurately characterize the pyrolysis behavior of biomass during contact with high-temperature metallurgical slag and its impact on the heat transfer process. By effectively combining these two models, numerical simulation calculations of the biomass-high-temperature metallurgical slag heat transfer process are achieved, and the changing patterns of key parameters such as temperature distribution, heat flow transfer, and pyrolysis conversion rate within the system can be accurately obtained. This helps to deeply understand the complex mechanism of heat transfer between biomass and high-temperature metallurgical slag, and provides strong technical support and theoretical basis for the optimization design of related industrial processes, energy conservation and emission reduction, and comprehensive resource utilization. It has important scientific significance and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 It is a structural diagram of the biomass pyrolysis system of the rotary pyrolysis furnace of the present invention;

[0064] Figure 2 is a cross-sectional view of a rotary pyrolysis furnace in the present invention;

[0065] Figure 3 is a schematic diagram of direct contact between biomass particles and metallurgical slag particles in the present invention;

[0066] Figure 4 Schematic diagram of direct contact between biomass particles and the wall of the rotary pyrolysis furnace in the present invention;

[0067] Figure 5 It is a flow chart of the heat transfer calculation method in the present invention. DETAILED DESCRIPTION

[0068] The following describes embodiments of the present application in more detail with reference to the accompanying drawings. Although the accompanying drawings illustrate embodiments of the present application, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments described herein. Rather, these embodiments are provided to make the present application more thorough and complete, and to fully convey the scope of the present application to those skilled in the art.

[0069] like Figure 1 As shown, the rotary pyrolysis furnace has two feed ports at its feed end: one for introducing biomass pellets, and the other for introducing metallurgical slag pellets. Both the rotary pyrolysis furnace and the metallurgical slag pellets serve as heat sources, while the biomass pellets serve as the pyrolysis target. The heat transfer model calculation method of this invention is applicable to this type of rotary pyrolysis furnace.

[0070] like Figure 2 Shown is a cross-sectional view of a rotary pyrolysis furnace. Figure 3 Schematic diagram of direct contact between biomass particles and metallurgical slag particles, as shown in Figure 4 The figure shows a schematic diagram of direct contact between biomass particles and the wall of a rotary pyrolysis furnace. The figure clearly illustrates a spatial correspondence formed between the raw material particles as the kiln rotates. In the process of solving the heat transfer rate of the rotary pyrolysis furnace biomass pyrolysis system, all parameters used and formulas established in the present invention are developed around this correspondence.

[0071] The biomass raw material used in this example is discarded cigarette rods from a cigarette processing plant, and the metallurgical slag particles are copper slag crushed at high temperature from a smelter. Given that the geometric model length is ≥ 20 times the particle diameter, the particle flow is negligibly affected by the side walls. To reduce the computational workload, the rotary pyrolysis furnace in this example consists of a horizontal rotating drum with a length of 100 mm and a diameter of 200 mm. The furnace is filled with 19,126 particles with a density of 3150 kg / m 3 , copper slag particles with a diameter of 2 mm and 2750 particles with a density of 220 kg / m 3 , biomass particles with a diameter of 4 mm.

[0072] The relevant physical properties of discarded cigarette rod particles are as follows: Poisson's ratio is 0.25, Young's modulus is 4.2×10 9 Pa, the filling rate of waste tobacco rod particles accounts for 5% of the volume of the rotary pyrolysis furnace. The waste tobacco rod particles are all considered to be normally distributed spherical particles, with a thermal conductivity of 0.17 W / (m·K), a specific heat capacity of 960 J / (kg·K), and an initial temperature of 303 K. The relevant physical properties of the copper slag particles are as follows: Poisson's ratio is 0.30, Young's modulus is 2.1×10 8 Pa, the copper slag particle filling rate accounts for 5% of the rotary pyrolysis furnace volume, the copper slag particles are all considered to be normally distributed spherical particles, the thermal conductivity is 6 W / (m·K), the specific heat capacity is 1100 J / (kg·K), and the initial temperature is 973 K; the relevant physical properties of the rotary pyrolysis furnace are as follows: the rotation speed is 6 rpm, the thermal conductivity is 50 W / (m·K), the Young's modulus is 1×10 8 Pa, Poisson's ratio is 0.30, and the density is 7800 kg / m 3 , the specific heat capacity is 502.48 J / (kg·K), the initial temperature is 973 K; nitrogen is used as the carrier gas, the nitrogen flow rate is 0.07427 m / s, and the gas dynamic viscosity is 1.8×10 -5 Pa, the thermal conductivity of nitrogen is 0.026W / (m·K), and the density is 1.25kg / m 3, the specific heat capacity is 741 J / (kg·K). Before the formal pyrolysis begins, nitrogen is introduced into the rotary pyrolysis furnace at a flow rate of 0.07427 m / s for about 15 minutes to ensure the inert atmosphere of the reaction. The formal heat transfer process is simulated for 300 seconds.

[0073] In addition, it is known that cellulose accounts for 42.6%, hemicellulose accounts for 36.0%, and lignin accounts for 21.4% in discarded tobacco stem particles; for cellulose: the pre-exponential factor A1 is 1.371×10 16 , the activation energy E1 is 189.268 kJ / mol, and the reaction enthalpy change is 172.431 kJ / mol; for hemicellulose: the pre-exponential factor A2 is 5.767×10 15 , the activation energy E2 is 176.357 kJ / mol, and the reaction enthalpy change is 148.896 kJ / mol; for lignin: the pre-exponential factor A3 is 5.259×10 15 , the activation energy E3 is 191.762 kJ / mol, the reaction enthalpy change is 202.352 kJ / mol; the ideal gas constant is 8.314 J / (mol·K).

[0074] The geometric model of the rotary pyrolysis furnace was meshed using O-cutting technology combined with hexahedral elements. Local meshing was performed at the inlet / outlet bends. Computational fluid dynamics (CFD) coupled with discrete element method (DEM) was used to calculate the heat transfer in the rotary pyrolysis furnace.

[0075] The user-defined coupling interface design takes into account the data format and communication protocol between the CFD and DEM software to ensure accurate data transfer and interpretation. Using the CFD solver, the initial conditions set include fluid pressure, velocity, and temperature; using the DEM solver, the particle parameters set include particle diameter, particle number, shear modulus, Poisson's ratio, friction coefficient, restitution coefficient, thermal conductivity, specific heat capacity, etc.

[0076] The CFD software updates the particle properties obtained from the DEM software through user-defined functions (UDFs) and converts them into a data format suitable for the CFD software. Subsequently, the CFD software calculates the fluid phase volume fraction, fluid-particle interaction force and heat flux, and updates the fluid pressure field, velocity field and temperature field. When the CFD software completes a time step, the calculation results (flow field velocity, pressure distribution, etc.) are passed back to the DEM software through the UDF and coupling interface. The DEM software calculates the contact force between particles based on the Hertz-Mindlin no-slip contact model, and calculates the resistance on the particles and other particle data. The DEM software then updates other data such as the particle position, velocity, angular velocity and temperature. The above calculations are iteratively calculated with each time step as a cycle, thereby realizing the coupling of CFD and DEM;

[0077] The multivariate analysis model of waste cigarette stem pyrolysis is embedded into the CFD software through the UDF method, thereby realizing the heat transfer calculation that couples the particle flow model, heat transfer model and pyrolysis model; when the preset calculation time is reached, the coupled simulation ends.

[0078] According to the above known data, Figure 5 As shown, the heat transfer calculation method in the embodiment of the present invention is performed according to the following steps S1-S8:

[0079] S1. Based on the CFD-DEM numerical method of the particle flow model, a heat transfer model for the recovery and utilization of waste heat from high-temperature metallurgical slag particles coupled with the thermochemical conversion reaction of biomass in a rotary pyrolysis furnace is established.

[0080] S2. Calculate the particle momentum in the rotary pyrolysis furnace based on the particle flow model. The calculation formula is as follows:

[0081]

[0082] Where m p,i 、 t、 and are the mass, linear velocity, time, contact force, gravity, and drag force of particle i, respectively. The calculation formulas for contact force and gravity are as follows:

[0083]

[0084] Where, subscripts n and t are abbreviations of normal direction and tangential direction, respectively; and are the normal force and tangential force of particle contact, respectively; and are the normal direction and tangent direction from the center of particle i to the center of particle j, respectively; and are the damping components of the normal force and the tangential force respectively; m p is the mass of the particle, is the acceleration due to gravity;

[0085] Normal force of particle contact The calculation formula is as follows:

[0086]

[0087] Where, δ n is the contact deformation distance between particles i and j, E * is the equivalent elastic modulus, that is, the equivalent Young's modulus, R * is the equivalent radius, E i 、vi 、R i and E j 、v j 、R j are the Young's modulus, Poisson's ratio, and sphere radius of particles i and j, respectively; is the normal component of the relative velocity, S n is the normal stiffness, m * is the equivalent mass, β is the damping constant, and e is the coefficient of restitution;

[0088] Tangential force of particle contact The calculation formula is as follows:

[0089]

[0090] Where S t represents the tangential spring constant or tangential stiffness, and δ t represents the tangential displacement, G * is the equivalent shear modulus; is the tangential component of the relative velocity, τ i is the rolling friction coefficient of the particle motion process, μ r is the rolling friction coefficient, R cpc is the distance from the contact point to the center of mass, is the unit angular velocity vector of the particle at the contact point;

[0091] drag The calculation is based on the Gidaspow drag model, and the calculation formula is as follows:

[0092]

[0093] Where V p represents the particle volume, β g,p is the drag coefficient between the gas phase and the particle, and Represent the gas phase fluidity and particle velocity respectively; among them, β g,p is defined as:

[0094]

[0095] Where, ε p and ε g are the particle volume fraction and gas phase volume fraction, ρ g is the gas phase fluid density, d p,i is the particle diameter; the drag coefficient C D Directly depends on the particle Reynolds number Re p , the calculation formula is as follows,

[0096]

[0097] Where μ g is the dynamic viscosity of the gas.

[0098] When the rotary pyrolysis furnace rotates at 6 rpm, after simulating the heat transfer process for 300 seconds, the contact number C between the metallurgical slag particles and the biomass particles in the rotary pyrolysis furnace is finally obtained based on the simulation calculation results. S-B The contact number C between metallurgical slag particles is 4957103340. S-S The contact number C between biomass particles is 25855800376. B-B It is 267183619.

[0099] S3. The calculation formula for the contact heat transfer Q1 between biomass particles and metallurgical slag particles in the rotary pyrolysis furnace based on the heat transfer model and particle motion momentum is:

[0100] Q1=h1ΔT1,

[0101] Where h1 represents the heat transfer coefficient between biomass particles and metallurgical slag particles, and ΔT1 represents the temperature difference between biomass particles and metallurgical slag particles. The calculation formula for h1 is:

[0102]

[0103] Where k pi and k pj is the thermal conductivity of biomass particles and metallurgical slag particles, is the normal force after the biomass particles contact the metallurgical slag particles, E * 1 is the equivalent elastic modulus of biomass particles after contact with metallurgical slag particles, R * 1 is the equivalent radius of the biomass particles after contact with the metallurgical slag particles.

[0104] The final simulation calculation shows that the contact heat transfer amount Q1 between biomass particles and metallurgical slag particles in the rotary pyrolysis furnace is 8987367.10J.

[0105] S4. The calculation formula for the contact heat transfer Q2 between the biomass particles and the inner wall of the rotary pyrolysis furnace based on the heat transfer model and particle motion momentum is:

[0106] Q2=h2ΔT2,

[0107] Where h2 represents the heat transfer coefficient between the biomass particles and the rotary pyrolysis furnace wall, and ΔT2 represents the temperature difference between the biomass particles and the rotary pyrolysis furnace wall. The calculation formula for h2 is:

[0108]

[0109] Where k pi is the thermal conductivity of biomass particles, k wall is the thermal conductivity of the rotary pyrolysis furnace wall; is the normal force after the biomass particles contact the rotary pyrolysis furnace wall, E * 2 is the equivalent elastic modulus of the biomass particles after contacting the rotary pyrolysis furnace wall, R * 2 is the equivalent radius of the biomass particles after contact with the rotary pyrolysis furnace wall, which is calculated based on the radius of the biomass particles.

[0110] The final simulation calculation shows that the contact heat transfer amount Q2 between the biomass particles in the rotary pyrolysis furnace and the inner wall of the kiln is 23263458.09J.

[0111] S5. The calculation formula for the convective heat transfer Q3 between biomass particles and gas in the rotary pyrolysis furnace based on the heat transfer model and particle motion momentum is:

[0112] Q3=h3ΔT3,

[0113] Where h3 represents the heat transfer coefficient between the biomass particles on the upper surface of the rotary pyrolysis furnace and the gas, and ΔT3 represents the temperature difference between the biomass particles and the gas in the rotary pyrolysis furnace. The calculation formula for h3 is:

[0114] Nu1=2+0.6Re 1 / 2 Pr 1 / 3 ,

[0115] Where k g is the thermal conductivity of gas, Nu1 is the Nusselt number between biomass particles and gas, d1 is the diameter of biomass particles, Re is the Reynolds number, Pr is the Prandtl number, C p is the specific heat capacity of the gas, is the gas flow rate, μ g is the dynamic viscosity of the gas.

[0116] The final simulation calculation shows that the convective heat transfer Q3 between the biomass particles on the upper surface of the rotary pyrolysis furnace and the gas is 18210.96J.

[0117] S6. Calculate the heat Q4 generated due to chemical reaction or phase change based on the biomass pyrolysis model.

[0118] Among them, the biomass pyrolysis model is a pyrolysis model in which hemicellulose, cellulose and lignin are decomposed into volatiles and char respectively through a single Arrhenius reaction.

[0119] Specifically, the waste tobacco stem pyrolysis model uses the three main components of waste tobacco stems, namely hemicellulose, cellulose and lignin, to represent the pyrolysis of waste tobacco stems. It is assumed that hemicellulose, cellulose and lignin are decomposed into volatiles and char respectively through a single Arrhenius reaction, as follows:

[0120]

[0121] Wherein, k1, k2 and k3 are the pyrolysis reaction rate constants of hemicellulose, cellulose and lignin, respectively; r1, r2 and r3 represent the yield of biochar generated by pyrolysis of hemicellulose, cellulose and lignin, respectively;

[0122] The calculation formula for heat Q4 generated due to chemical reaction or phase change is:

[0123] Q4=A i,b (-q4)(-ΔH),

[0124] Where A i,b is the reactive surface area of ​​the biomass particle, the negative sign indicates that the concentration of the reactant decreases with time, ΔH is the reaction enthalpy change; q4 is the pyrolysis conversion rate of component i in the biomass, i includes cellulose, hemicellulose and lignin, ρ is the density of the biomass particle, m i , A i and E i are the initial masses of cellulose, hemicellulose, and lignin, the preexponential factor, and activation energy, respectively; R is the ideal gas constant (8.314 J / (mol·K)); and T is the biomass pyrolysis reaction temperature.

[0125] The calculated q4 of cellulose, hemicellulose and lignin are 9397.49W, 15333.78W and 5756.60W respectively. There are 2750 discarded tobacco rod particles. Assuming that the number of particles is calculated according to the proportion of cellulose, hemicellulose and lignin, the number of cellulose, hemicellulose and lignin particles is 1171, 990 and 589 respectively. According to the surface area calculation formula of spherical particles, the surface area of ​​a single particle can be calculated to be 5.027×10 -5 m 2 , it can be further calculated that the reactive surface areas of cellulose, hemicellulose and lignin particles are approximately 0.05887 m 2 , 0.04977m 2 , 0.02961m 2However, during the pyrolysis reaction, the biomass particles will undergo dehydration and decomposition of macromolecular compounds, which usually causes the particle size to become smaller as the reaction occurs. According to repeated experimental experience, the surface area of ​​the biochar formed after pyrolysis is about 0.6-0.8 times that of the original biomass particles. That is, assuming that the reactive surface areas of cellulose, hemicellulose and lignin particles are about 0.047096 m 2 , 0.039816m 2 , 0.023688m 2 ; Further calculations show that the heat generated by chemical reactions or phase changes of cellulose, hemicellulose and lignin particles is 7.632×10 7 J, 9.091×10 7 J, 2.759×10 7 J; the total heat Q generated by chemical reaction or phase change i,c is 1.948×10 8 J.

[0126] S7. Calculate the heat transfer Q of the rotary pyrolysis furnace pyrolysis system based on contact heat transfer Q1, contact heat transfer Q2, convection heat transfer Q3 and heat Q4. transfer , the calculation formula is: Q transfer =Q1+Q2+Q3+Q4.

[0127] Finally, the heat transfer Q of the rotary pyrolysis furnace pyrolysis system is calculated. transfer is 2.271×10 8 J.

[0128] In addition, in the embodiment of the present invention, the mixing index can be calculated to evaluate the mixing degree between different particles in the rotary pyrolysis furnace. Specifically, the embodiment of the present invention can also include step S8.

[0129] S8. Calculate the mixing index M between particles in the rotary pyrolysis furnace based on the particle flow model. The calculation formula is as follows:

[0130]

[0131] Where C S-B is the contact number between metallurgical slag particles and biomass particles, C S-S is the contact number between metallurgical slag particles, C B-B is the number of contacts between biomass particles.

[0132] In the above-mentioned waste cigarette stem pyrolysis model, the calculated mixing index M is 0.1595; the mixing index is a direct and reliable indicator for measuring the degree of mixing of different particles within a particle system, reflecting the degree to which the mixing deviates from complete mixing. According to literature reports, it is almost impossible to achieve complete mixing between different particles. It is generally believed that when the M value is between 0.2-0.5, the degree of mixing is high, and the larger the M value, the higher the degree of mixing of the particles. Therefore, in this process system, in order to improve the degree of mixing between biomass particles and copper slag particles, the speed of the rotary pyrolysis furnace can be increased to achieve this goal.

[0133] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A heat transfer calculation method for metallurgical slag waste heat recovery, characterized in that: include: S1. Based on the CFD-DEM numerical method of the particle flow model, a heat transfer model for the waste heat recovery and utilization of high-temperature metallurgical slag particles coupled with the thermochemical conversion reaction of biomass in a rotary pyrolysis furnace was established; The heat transfer model covers the contact heat conduction between biomass particles and metallurgical slag particles in the rotary pyrolysis furnace, the contact heat conduction between biomass particles and the furnace wall, the convective heat transfer between biomass particles and gas, and the heat transfer during the chemical reaction and phase change process caused by biomass pyrolysis. The particle flow model is the Hertz-Mindlin contact model based on the Hertz contact theory and the Mindlin-Deresiewicz theory. S2. Calculate the particle motion momentum in the rotary pyrolysis furnace based on the particle flow model; S3. Calculate the contact heat transfer Q1 between biomass particles and metallurgical slag particles in the rotary pyrolysis furnace based on the heat transfer model and particle motion momentum; S4. Calculate the contact heat transfer amount Q2 between the biomass particles in the rotary pyrolysis furnace and the inner wall of the rotary pyrolysis furnace based on the heat transfer model and the particle motion momentum; S5. Calculate the convective heat transfer Q3 between biomass particles and gas in the rotary pyrolysis furnace based on the heat transfer model and particle motion momentum; S6. Calculate the heat Q4 generated due to chemical reaction or phase change based on the biomass pyrolysis model; Among them, the biomass pyrolysis model is a pyrolysis model in which hemicellulose, cellulose and lignin are decomposed into volatiles and char respectively through a single Arrhenius reaction; S7. Calculate the heat transfer Q of the rotary pyrolysis furnace pyrolysis system based on contact heat transfer Q1, contact heat transfer Q2, convection heat transfer Q3 and heat Q4. transfer .

2. The heat transfer calculation method according to claim 1, characterized in that: The calculation formula for the particle motion momentum in the rotary pyrolysis furnace in S2 is as follows: ， Where m p,i 、 ,t, 、 and are the mass, linear velocity, time, contact force, gravity and drag force of particle i respectively; The calculation formulas for contact force and gravity are as follows: ， ， Where, subscripts n and t are abbreviations of normal direction and tangential direction, respectively; and are the normal force and tangential force of particle contact, respectively; and are the normal direction and tangent direction from the center of particle i to the center of particle j, respectively; and are the damping components of the normal and tangential forces, respectively; is the mass of the particle, is the acceleration due to gravity; Normal force of particle contact The calculation formula is as follows: ， ， ， ， ， ， ， Where, δ n is the contact deformation distance between particles i and j, E ∗ is the equivalent elastic modulus, that is, the equivalent Young's modulus, R ∗ is the equivalent radius, E i 、v i 、R i and E j 、v j 、R j are the Young's modulus, Poisson's ratio, and sphere radius of particles i and j, respectively; is the normal component of the relative velocity, S n is the normal stiffness, m * is the equivalent mass, is the damping constant, e is the restitution coefficient; Tangential force of particle contact The calculation formula is as follows: ， ， ， ， Where S t represents the tangential spring constant, δ t represents the tangential displacement, G * is the equivalent shear modulus; is the tangential component of the relative velocity, is the rolling friction coefficient of the particle motion process, 𝜇 𝑟 is the coefficient of rolling friction, 𝑅 cpc is the distance from the contact point to the center of mass, is the unit angular velocity vector of the particle at the contact point; drag The calculation is based on the Gidaspow drag model, and the calculation formula is as follows: ， Where V p represents the particle volume, β g,p is the drag coefficient between the gas phase and the particle, and Represent the gas phase fluidity and particle velocity respectively; among them, β g,p is defined as follows: ， Where, ε p and ε g are the particle volume fraction and gas phase volume fraction, ρ g is the gas phase fluid density, d p,i is the particle diameter; the drag coefficient C D Directly depends on the particle Reynolds number Re p , the calculation formula is as follows: ， ， Where, is the dynamic viscosity of the gas.

3. The heat transfer calculation method according to claim 1 or 2, characterized in that: The calculation formula for the contact heat transfer Q1 in S3 is: ， Where h1 represents the heat transfer coefficient between biomass particles and metallurgical slag particles, and ΔT1 represents the temperature difference between biomass particles and metallurgical slag particles. The calculation formula for h1 is: ， Where, and is the thermal conductivity of biomass particles and metallurgical slag particles, is the normal force after the biomass particles come into contact with the metallurgical slag particles, is the equivalent elastic modulus of the biomass particles after contact with metallurgical slag particles, It is the equivalent radius of the biomass particles after contact with the metallurgical slag particles.

4. The heat transfer calculation method according to claim 1 or 2, characterized in that: The calculation formula for the contact heat transfer Q2 in S4 is: ， Where h2 represents the heat transfer coefficient between the biomass particles and the rotary pyrolysis furnace wall, and ΔT2 represents the temperature difference between the biomass particles and the rotary pyrolysis furnace wall. The calculation formula for h2 is: ， Where, is the thermal conductivity of biomass particles, is the thermal conductivity of the rotary pyrolysis furnace wall; is the normal force after the biomass particles come into contact with the rotary pyrolysis furnace wall, is the equivalent elastic modulus of the biomass particles after contact with the rotary pyrolysis furnace wall, It is the equivalent radius of the biomass particles after contact with the rotary pyrolysis furnace wall.

5. The heat transfer calculation method according to claim 1 or 2, characterized in that: The calculation formula for the convective heat transfer Q3 in S5 is: ， Where h3 represents the heat transfer coefficient between the biomass particles and the gas in the rotary pyrolysis furnace, and ΔT3 represents the temperature difference between the biomass particles on the upper surface of the rotary pyrolysis furnace and the gas. The calculation formula for h3 is as follows: ， ， ， ， Where, is the thermal conductivity of the gas, is the Nusselt number between biomass particles and gas, is the diameter of the biomass particle, is the Reynolds number, is the Prandtl number, is the specific heat capacity of the gas, is the gas flow rate, is the dynamic viscosity of the gas.

6. The heat transfer calculation method according to claim 1 or 2, characterized in that: The calculation formula for heat Q4 in S6 is as follows: ， ， Where, is the reactive surface area of ​​the biomass particles, and the negative sign indicates that the concentration of reactants decreases with time. is the reaction enthalpy change; is the pyrolysis conversion rate of component i in biomass, i including cellulose, hemicellulose and lignin, is the density of the biomass particles, , and are the initial masses of cellulose, hemicellulose and lignin, the pre-exponential factor and the activation energy, R is an ideal gas, and T is the biomass pyrolysis reaction temperature.

7. The heat transfer calculation method according to claim 1 or 2, characterized in that: Heat transfer of the pyrolysis system of the S7 rotary pyrolysis furnace The calculation formula is: .

8. The heat transfer calculation method according to claim 1 or 2, characterized in that: Also includes: S8. Calculate the mixing index M between particles in the rotary pyrolysis furnace based on the particle flow model. The calculation formula is as follows: ， Where C S-B is the contact number between metallurgical slag particles and biomass particles, C S-S is the contact number between metallurgical slag particles, C B-B is the number of contacts between biomass particles.

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