Heat transfer calculation method for metallurgical slag waste heat recycling

Abstract

The invention discloses a heat transfer calculation method for metallurgical slag waste heat recovery and utilization, and belongs to the technical field of energy recovery and biomass conversion. The heat transfer calculation method comprises the following steps: calculating particle motion momentum in the rotary pyrolyzing furnace based on a particle flow model; calculating the contact heat transfer amount Q1 between the biomass particles and the metallurgical slag particles in the rotary pyrolyzing furnace based on the heat transfer model and the particle motion momentum; calculating a contact heat transfer amount Q2 between the biomass particles in the rotary pyrolyzing furnace and the inner wall of the rotary pyrolyzing furnace based on the heat transfer model and the particle motion momentum; calculating the convective heat transfer amount Q3 between the biomass particles and the gas in the rotary pyrolyzing furnace based on the heat transfer model and the particle motion momentum; calculating heat Q4 generated by chemical reaction or phase change based on a biomass pyrolysis model; and calculating the heat transfer quantity Qtransfer of the pyrolysis system of the rotary pyrolysis furnace based on the contact heat transfer quantity Q1, the contact heat transfer quantity Q2, the convective heat transfer quantity Q3 and the heat quantity Q4.

Description

Technical Field

[0001] The 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 the non-ferrous metal smelting process is a potential energy resource, but due to its complex phase composition and high-temperature characteristics, the efficient recovery of slag waste heat has always been a difficult problem faced by the industry. At the same time, biomass, as a renewable energy source, has huge potential for thermochemical conversion. However, traditional biomass pyrolysis and slag waste heat recovery technologies have problems such as low heat transfer efficiency and large energy loss, which limits the feasibility of combining the two.

[0003] Rotary reactors such as rotary pyrolysis furnaces have been gradually applied in the fields of slag waste heat recovery and biomass thermochemical conversion in recent years due to their good mixing characteristics and high heat transfer efficiency. However, the mixing and heat exchange process of biomass and slag in the rotary reactor involves complex multiphase flow, heat transfer and chemical reactions. There is still a lack of systematic models and calculation methods 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 and the biomass pyrolysis reaction process, thereby providing a theoretical basis and technical support for improving slag waste heat recovery and biomass thermochemical conversion efficiency.

[0005] The present application proposes a heat transfer calculation method for recycling waste heat from metallurgical slag, 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 for coupling particle flow model, heat transfer model and pyrolysis model.

[0006] The particle flow model adopts 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 are in contact with each other. It 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 of chemical reactions and phase change processes 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 particle flow model, a heat transfer model for waste heat recovery of high-temperature metallurgical slag particles coupled with biomass thermochemical conversion reaction in a rotary pyrolysis furnace is established;

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

[0009] S3. Calculation of the contact heat transfer Q between biomass particles and metallurgical slag particles in a rotary pyrolysis furnace based on the heat transfer model and particle motion momentum 1 ;

[0010] S4. Calculate the contact heat transfer Q between biomass particles and the inner wall of the rotary pyrolysis furnace based on the heat transfer model and particle motion momentum 2 ;

[0011] S5. Calculation of the convective heat transfer Q between biomass particles and gas in a rotary pyrolysis furnace based on the heat transfer model and particle motion momentum 3 ;

[0012] S6. Calculate the heat Q generated by chemical reaction or phase change based on the biomass pyrolysis model 4 ;

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

[0014] S7, based on contact heat transfer Q 1 , contact heat transfer Q 2 , Convective heat transfer Q 3 and heat Q 4 Calculation of heat transfer Q of rotary pyrolysis furnace pyrolysis system transfer .

[0015] In some schemes, the O-cutting block technology combined with hexahedral units is used to mesh the rotary pyrolysis furnace geometry model, local encryption is performed at the inlet / outlet bends, and computational fluid dynamics (CFD) coupled discrete element method (DEM) is used to calculate the heat transfer in the rotary pyrolysis furnace; the design of the user-defined coupling interface takes into account the data format and communication protocol between the CFD software and the DEM software to ensure that the data can be accurately transmitted and interpreted. Using the CFD software solver, the initial conditions set include the pressure, velocity and temperature of the fluid; 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, specific heat capacity, etc.; the CFD software updates the particle properties obtained from the DEM software through a user-defined function (UDF) and converts them into a data format suitable for the CFD software. Subsequently, the CFD software calculates the volume fraction of the fluid phase, the fluid-particle interaction force and heat flux, and updates the pressure field, velocity field and temperature field of the fluid. After the CFD software calculates a time step, the calculation results (velocity and pressure distribution of the flow field, 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. Subsequently, the DEM software updates other data such as the position, velocity, angular velocity and temperature of the particles. 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 coupling simulation ends.

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

[0017]

[0018] In the formula, 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] In the formula, the subscripts n and t are the abbreviations of the normal direction and the 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] In the formula, 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 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] In the formula, 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 flow rate and particle velocity respectively; among them, β g,p is defined as:

[0031]

[0032] In the formula, ε p and ε g are the particle volume fraction and the 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] In the formula, μ g is the dynamic viscosity of the gas.

[0035] Specifically, in some embodiments, the contact heat transfer Q between the biomass particles and the metallurgical slag particles in the rotary pyrolysis furnace in S3 is 1 The calculation formula is:

[0036] Q 1 =h 1 ΔT 1 ,

[0037] In the formula, h 1 represents the heat transfer coefficient between biomass particles and metallurgical slag particles, ΔT 1 represents the temperature difference between biomass particles and metallurgical slag particles; where h 1 The calculation formula is:

[0038]

[0039] In the formula, 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 the biomass particles after contact with the metallurgical slag particles, R * 1 It is the equivalent radius of the biomass particles after contact with the metallurgical slag particles.

[0040] Specifically, in some embodiments, the contact heat transfer amount Q between the biomass particles in the rotary pyrolysis furnace and the inner wall of the rotary pyrolysis furnace in S4 is 2 The calculation formula is:

[0041] Q 2 =h 2 ΔT 2 ,

[0042] In the formula, h 2 represents the heat transfer coefficient between biomass particles and the rotary pyrolysis furnace wall, ΔT 2 represents the temperature difference between the biomass particles and the rotary pyrolysis furnace wall; where h 2 The calculation formula is:

[0043]

[0044] In the formula, 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 It is the equivalent radius of the biomass particles after they come into contact with the rotary pyrolysis furnace wall, and is calculated based on the radius of the biomass particles.

[0045] Specifically, in some embodiments, the convective heat transfer Q between the biomass particles on the upper surface of the rotary pyrolysis furnace and the gas in S4 is 3 The calculation formula is:

[0046] Q 3 =h 3 ΔT 3 ,

[0047] In the formula, h 3 represents the heat transfer coefficient between biomass particles and gas in the rotary pyrolysis furnace, ΔT 3 represents the temperature difference between biomass particles and gas in the rotary pyrolysis furnace; where h 3 The calculation formula is:

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

[0049] In the formula, k g is the thermal conductivity of the gas, Nu 1is the Nusselt number between biomass particles and gas, d 1 is the diameter of the biomass particle, 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, assuming that hemicellulose, cellulose and lignin are decomposed into volatiles and char respectively through a single Arrhenius reaction, as follows:

[0051]

[0052] Among them, k 1 , k 2 and k 3 are the pyrolysis reaction rate constants of hemicellulose, cellulose and lignin, respectively; r 1 、r 2 and r 3 represent the yields of biochar from pyrolysis of hemicellulose, cellulose, and lignin, respectively;

[0053] S6 calculates the heat Q generated by chemical reactions or phase changes 4 The calculation formula is:

[0054] Q 4 =A i,b (-q 4 )(-ΔH),

[0055] In the formula, A i,b is the reactive surface area of ​​the biomass particle, the negative sign is the decrease in reactant concentration over time, and ΔH is the reaction enthalpy change; q 4 is the pyrolysis conversion rate of component i in biomass, i includes cellulose, hemicellulose and lignin, ρ is the density of biomass particles, m i , A i and E i are the initial masses of cellulose, hemicellulose and lignin, the preexponential factor and the activation energy, 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 =Q 1 +Q 2 +Q 3 +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] In the formula, 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 waste heat recovery and utilization of 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 of the two. At the same time, a multivariate pyrolysis model is established to describe the kinetic behavior of the biomass pyrolysis reaction, comprehensively covering the multi-component reaction path and characteristics of biomass pyrolysis, and can accurately characterize the pyrolysis behavior of biomass in the process of contact with high-temperature metallurgical slag and its influence on the heat transfer process. By effectively combining these two models, the numerical simulation calculation of the biomass-high-temperature metallurgical slag heat transfer process is realized, and the change law of key parameters such as temperature distribution, heat flow transfer and pyrolysis conversion rate in the system can be accurately obtained. It 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, energy conservation and emission reduction, and comprehensive utilization of resources of related industrial processes, which has important scientific significance and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 It is a structural diagram of the rotary pyrolysis furnace biomass pyrolysis system 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 is a schematic diagram of direct contact between biomass particles and the wall surface of a rotary pyrolysis furnace in the present invention;

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

[0068] The embodiments of the present application will be described in more detail below with reference to the accompanying drawings. Although the embodiments of the present application are shown in the accompanying drawings, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, 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 is provided with two feed ports at the feed end, one of which is used to introduce biomass particles into the rotary pyrolysis furnace, and the other feed port is used to introduce metallurgical slag particles into the rotary pyrolysis furnace. The rotary pyrolysis furnace and the metallurgical slag particles are both used as heat sources; the biomass particles are used as pyrolysis objects. The heat transfer model calculation method of the present invention is applicable to such rotary pyrolysis furnaces.

[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, such as 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 corresponding relationship formed in space after the raw material particles rotate with the kiln. In the process of solving the heat transfer of the rotary pyrolysis furnace biomass pyrolysis system of the present invention, all the parameters used and the established formulas are developed around this corresponding relationship.

[0071] The biomass raw materials used in this embodiment are discarded cigarette rods from a cigarette processing plant, and the metallurgical slag particles come from the high-temperature crushed copper slag of a smelter. When the length of the known geometric model is ≥ 20 times the particle diameter, the flow of the particles is less affected by the side wall and can be ignored. In order to reduce the calculation workload, the rotary pyrolysis furnace in this embodiment is made of a horizontal rotating drum with a length of 100 mm and a diameter of 200 mm. The furnace is filled with 19126 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] Among them, the relevant physical properties of the discarded cigarette rod particles are as follows: Poisson's ratio is 0.25, Young's modulus is 4.2×10 9Pa, 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 regarded as normally distributed spherical particles, the thermal conductivity is 0.17W / (m·K), the specific heat capacity is 960J / (kg·K), and the initial temperature is 303K; the relevant physical properties of 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 volume of the rotary pyrolysis furnace, the copper slag particles are all regarded as normally distributed spherical particles, the thermal conductivity is 6W / (m·K), the specific heat capacity is 1100J / (kg·K), and the initial temperature is 973K; the relevant physical properties of the rotary pyrolysis furnace are as follows: the rotation speed is 6rpm, the thermal conductivity is 50W / (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 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: pre-exponential factor A 1 is 1.371×10 16 , activation energy E 1 is 189.268 kJ / mol, and the reaction enthalpy change is 172.431 kJ / mol; for hemicellulose: pre-exponential factor A 2 is 5.767×10 15 , activation energy E 2 is 176.357 kJ / mol, and the reaction enthalpy change is 148.896 kJ / mol; for lignin: pre-exponential factor A 3 is 5.259×10 15 , activation energy E 3 It 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 O-cutting technology combined with hexahedral units is used to mesh the rotary pyrolysis furnace geometry model, local encryption is performed at the inlet / outlet bends, and computational fluid dynamics (CFD) coupled with discrete element method (DEM) is used to calculate the heat transfer in the rotary pyrolysis furnace.

[0075] The design of the coupling interface compiled by the user takes into account the data format and communication protocol between the CFD software and the DEM software to ensure that the data can be accurately transmitted and interpreted. Using the CFD software solver, the initial conditions set include fluid pressure, velocity and temperature, etc.; 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, specific heat capacity, etc.;

[0076] The CFD software updates the particle properties obtained from the DEM software through a user-defined function (UDF) 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 calculates 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 UDF, 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 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 momentum of particle movement in the rotary pyrolysis furnace based on the particle flow model. The calculation formula is as follows:

[0081]

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

[0083]

[0084] In the formula, the subscripts n and t are the abbreviations of the normal direction and the 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] In the formula, 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 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] In the formula, 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, μr 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 flow rate and particle velocity respectively; among them, β g,p is defined as:

[0094]

[0095] In the formula, ε p and ε g are the particle volume fraction and the 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] In the formula, μ g is the dynamic viscosity of the gas.

[0098] When the rotation speed of the rotary pyrolysis furnace is 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 according to the simulation calculation results. S-B is 4957103340, the contact number C between metallurgical slag particles and metallurgical slag particles S-S The contact number C between biomass particles is 25855800376. B-B It is 267183619.

[0099] S3. Calculation of the contact heat transfer Q between biomass particles and metallurgical slag particles in a rotary pyrolysis furnace based on the heat transfer model and particle motion momentum 1 The calculation formula is:

[0100] Q 1 =h 1 ΔT 1 ,

[0101] In the formula, h 1 represents the heat transfer coefficient between biomass particles and metallurgical slag particles, ΔT 1 represents the temperature difference between biomass particles and metallurgical slag particles; where h 1 The calculation formula is:

[0102]

[0103] In the formula, 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 the biomass particles after contact with the metallurgical slag particles, R * 1 It is the equivalent radius of the biomass particles after contact with the metallurgical slag particles.

[0104] The final simulation calculation obtained the contact heat transfer Q between the biomass particles and the metallurgical slag particles in the rotary pyrolysis furnace. 1 It is 8987367.10J.

[0105] S4. Calculate the contact heat transfer Q between biomass particles and the inner wall of the rotary pyrolysis furnace based on the heat transfer model and particle motion momentum 2 The calculation formula is:

[0106] Q 2 =h 2 ΔT 2 ,

[0107] In the formula, h 2 represents the heat transfer coefficient between biomass particles and the rotary pyrolysis furnace wall, ΔT 2 represents the temperature difference between the biomass particles and the rotary pyrolysis furnace wall; where h 2 The calculation formula is:

[0108]

[0109] In the formula, 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 * 2It is the equivalent radius of the biomass particles after they come into contact with the rotary pyrolysis furnace wall, and is calculated based on the radius of the biomass particles.

[0110] The final simulation calculation obtained the contact heat transfer Q between the biomass particles and the inner wall of the rotary pyrolysis furnace 2 It is 23263458.09J.

[0111] S5. Calculation of the convective heat transfer Q between biomass particles and gas in a rotary pyrolysis furnace based on the heat transfer model and particle motion momentum 3 The calculation formula is:

[0112] Q 3 =h 3 ΔT 3 ,

[0113] In the formula, h 3 represents the heat transfer coefficient between the biomass particles on the upper surface of the rotary pyrolysis furnace and the gas, ΔT 3 represents the temperature difference between biomass particles and gas in the rotary pyrolysis furnace; where h 3 The calculation formula is:

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

[0115] In the formula, k g is the thermal conductivity of the gas, Nu 1 is the Nusselt number between biomass particles and gas, d 1 is the diameter of the biomass particle, 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 obtained the convective heat transfer Q between the biomass particles on the upper surface of the rotary pyrolysis furnace and the gas 3 It is 18210.96J.

[0117] S6. Calculate the heat Q generated by chemical reaction or phase change based on the biomass pyrolysis model 4 .

[0118] Among them, the biomass pyrolysis model is a pyrolysis model in which three types of biomass, 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] Among them, k 1 , k 2 and k 3 are the pyrolysis reaction rate constants of hemicellulose, cellulose and lignin, respectively; r 1 、r 2 and r 3 represent the yields of biochar from pyrolysis of hemicellulose, cellulose, and lignin, respectively;

[0122] Heat Q is generated due to chemical reaction or phase change 4 The calculation formula is:

[0123] Q 4 =A i,b (-q 4 )(-ΔH),

[0124] In the formula, A i,b is the reactive surface area of ​​the biomass particle, the negative sign is the decrease in reactant concentration over time, and ΔH is the reaction enthalpy change; q 4 is the pyrolysis conversion rate of component i in biomass, i includes cellulose, hemicellulose and lignin, ρ is the density of biomass particles, m i , A i and E i are the initial masses of cellulose, hemicellulose and lignin, the preexponential factor and the activation energy, R is the ideal gas constant (8.314 J / (mol·K)), and T is the biomass pyrolysis reaction temperature.

[0125] Calculated q of cellulose, hemicellulose and lignin 4 are 9397.49W, 15333.78W and 5756.60W respectively. It is known that there are 2750 waste 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 calculated to be 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 2 However, during the pyrolysis reaction, the biomass particles will undergo dehydration and decomposition reactions of macromolecular compounds, which usually cause the particle size to become smaller. 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 approximately 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, based on contact heat transfer Q 1 , contact heat transfer Q 2 , Convective heat transfer Q 3 and heat Q 4 Calculation of heat transfer Q of rotary pyrolysis furnace pyrolysis system transfer , the calculation formula is: Q transfer =Q 1 +Q 2 +Q 3 +Q 4 .

[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] In the formula, 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, CB-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 to measure the degree of mixing of different particles in the 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. The larger the M value, the higher the degree of mixing of the particles. Therefore, under this process system, in order to increase the degree of mixing between biomass particles and copper slag particles, the speed of the rotary pyrolysis furnace can be increased to achieve the goal.

[0133] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. 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 particle flow model, a heat transfer model for waste heat recovery of high-temperature metallurgical slag particles coupled with biomass thermochemical conversion reaction in a rotary pyrolysis furnace is established; Among them, 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 of chemical reactions and phase changes 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 momentum of particle movement 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 three types of biomass, 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: In the formula, 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: In the formula, the subscripts n and t are the abbreviations of the normal direction and the 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; Normal force of particle contact The calculation formula is as follows: In the formula, 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 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; Tangential force of particle contact The calculation formula is as follows: In the formula, 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, 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; 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 flow rate and particle velocity respectively; among them, β g,p is defined as follows: In the formula, ε p and ε g are the particle volume fraction and the 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: In the formula, μ g 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: Q1=h1ΔT1 Where h1 represents the heat transfer coefficient between biomass particles and metallurgical slag particles, ΔT1 represents the temperature difference between biomass particles and metallurgical slag particles; the calculation formula of h1 is: In the formula, 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 the biomass particles after contact with the metallurgical slag particles, R * 1 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: Q2=h2ΔT2 Wherein, 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 of h2 is: In the formula, 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 contacting 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: Q3=h3ΔT3, Wherein, h3 represents the heat transfer coefficient between biomass particles and gas in the rotary pyrolysis furnace, and ΔT3 represents the temperature difference between biomass particles and gas on the upper surface of the rotary pyrolysis furnace; the calculation formula of h3 is as follows: Nu1=2+0.6Re 1 / 2 P.S. 1 / 3 , In the formula, 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.

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: Q4=A i,b (-q4)(-ΔH), In the formula, A i,b is the reactive surface area of ​​the biomass particle, the negative sign is the decrease in the concentration of the reactant over 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 the activation energy, R is the ideal gas constant (8.314 J / (mol·K)), 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 Q of the pyrolysis system of the rotary pyrolysis furnace in S7 transfer The calculation formula is: transfer =Q1+Q2+Q3+Q4.

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: In the formula, 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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