A method for predicting reactor product yields

Abstract

A reactor product yield prediction method, which determines the catalyst surface coke layer thickness based on the mass fraction of coke, and determines the collision restitution coefficient of the catalyst according to the Stokes number containing the inter-particle collision velocity and the critical Stokes number equation, so as to accurately describe the influence law of coke thickness and collision velocity on the collision restitution coefficient of the catalyst, thereby more accurately predicting the product yield; the method can be effectively combined with the determination of the fluid mechanics simulation to obtain more accurate simulation results, and provides an accurate method for the design, optimization and engineering scale-up of the catalytic cracking process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of petroleum processing, in particular to a reactor product yield prediction method. BACKGROUND

[0002] Catalytic cracking is an important processing process in a refinery, and is an effective way to convert heavy oil into light oil and low-carbon olefins. About 70% of the gasoline components and 30% of the diesel components in China's finished oil are from catalytic cracking units, and the amount of propylene produced by catalytic cracking units accounts for about 30% of the total propylene production in China. Catalytic cracking units can also provide carbon two and carbon four olefins as basic chemical raw materials. Under the trend of refining and chemical integration, catalytic cracking units are the key devices for the transformation and upgrading of traditional refineries.

[0003] The riser reactor is the core equipment that determines the overall performance of the catalytic cracking unit. However, due to the high temperature and complex multiphase flow-reaction behavior, it is usually difficult to conduct in-depth research on it through experimental methods. Deterministic fluid mechanics modeling can solve the control equations of fluid mechanics, chemical components and energy through deterministic methods and numerical methods, and deeply reveal the flow-reaction characteristics in the simulation system. With the rapid development of determination ability and model algorithm, deterministic fluid mechanics simulation has gradually become an important means to study fluidized bed reactors, and has strongly promoted the design, optimization and engineering scale-up of such equipment.

[0004] In deterministic fluid mechanics simulation, the collision restitution coefficient of particles is a very important parameter, which is mainly affected by the collision velocity and the material of the particles. This parameter has a significant impact on the predicted flow behavior, such as the volume fraction distribution of particles, and further affects the predicted reaction behavior, such as product yield. For dry and non-chemically reacting hard particles, the collision restitution coefficient of particles is less affected by the collision velocity, so it can be simplified to assume that the collision restitution coefficient remains constant.

[0005] In the catalytic cracking riser reactor, the catalyst particles are wrapped by high-viscosity coke generated by high-temperature catalytic cracking reactions, showing strong adhesion. Its collision restitution coefficient has changed greatly from the initial state without coke, and is significantly affected by the collision velocity between particles. Therefore, in order to obtain accurate simulation results, it is necessary to accurately determine the collision restitution coefficient of the catalyst in the deterministic fluid mechanics simulation of the catalytic cracking riser reactor.

[0006] Applicant has simplified the assumption that the collision restitution coefficient is linearly related to the mass fraction of coke in the determination of the hydrodynamic simulation of the catalytic cracking riser reactor (Particulate Science and Technology, 2020, 38(5), 549-558), but in this method of determining the collision restitution coefficient of the catalyst, the value of the correlation coefficient lacks a theoretical basis, and it also cannot describe the influence of the collision velocity between particles. SUMMARY

[0007] In order to overcome the defects of the prior art described above, the purpose of the present application is to provide a reactor product yield prediction method, which can accurately determine the real-time collision restitution coefficient of the catalyst according to the coke thickness and the collision velocity in the determination of the hydrodynamic simulation, so as to accurately predict the flow-reaction behavior in the reactor, realize the accurate numerical simulation of the reactor, provide accurate basis for the design, optimization and engineering scale-up of the riser reactor, thereby improve the overall performance of the catalytic cracking unit, achieve better economic benefits, and at the same time, the method can also be used to determine the collision restitution coefficient of the catalyst in the catalytic cracking process and the downflow bed and variable diameter fluidized bed reactor.

[0008] In order to achieve the above purpose, the technical scheme of the present application is:

[0009] A reactor product yield prediction method, which determines the thickness of the coke layer on the surface of the catalyst based on the mass fraction of the coke layer, and determines the collision restitution coefficient of the catalyst according to the Stokes number and the critical Stokes number equation containing the collision velocity between particles, so as to predict the product yield; specifically comprising the following steps:

[0010] (1) Determining the thickness of the coke layer on the surface of the catalyst

[0011] The thickness δ of the coke layer on the surface of the catalyst is determined by equation (1):

[0012]

[0013] In the formula, Y c is the mass fraction of coke, Y p is the mass fraction of catalyst, ρ c is the density of coke, ρ p is the density of catalyst, x is the mass fraction of the outer surface coke of the catalyst to the total coke, r p is the radius of the catalyst;

[0014] (2) Determining the Stokes number of the catalyst

[0015] The Stokes number St is determined by equation (2):

[0016]

[0017] In the formula, V c denoted as the collision velocity between catalysts, and μ as the viscosity of the coke on the catalyst surface due to the adsorption of high-boiling-point oil and gas.

[0018] Collision velocity V between catalysts in the Euler-Euler method c Determined by equation (3):

[0019]

[0020] In the formula, Θ s The pseudo-temperature of the catalyst is determined using particle kinetics;

[0021] The collision velocity V between catalysts in the Euler-Lagrange method c Determined by equation (4):

[0022]

[0023] In the formula, V p1 and V p2 These are the velocities of the two catalysts that collided;

[0024] (3) Determine the critical Stokes number of the catalyst

[0025] Critical Stokes number St c Determined by equation (5):

[0026]

[0027] In the formula, ε is a dimensionless elastic parameter, determined by equation (6):

[0028]

[0029] In the formula, Y eff The effective Young's modulus is determined by equation (7):

[0030]

[0031] In the formula, ν is Poisson's ratio, Y is Young's modulus, and subscripts 1 and 2 represent the two catalysts that collide.

[0032] (4) Determine the catalyst collision recovery coefficient

[0033] The collision restitution coefficient is determined by equation (8):

[0034]

[0035] In the formula, e is the real-time collision recovery coefficient of the catalyst during the catalytic cracking reaction, and e0 is the initial collision recovery coefficient before the catalyst participates in the reaction;

[0036] (5) Prediction of reactor product yield

[0037] Based on the catalyst collision restitution coefficient obtained by the method of steps (1) to (4), the flow-reaction behavior in the reactor is predicted, and more accurate yield of each product in the reactor is obtained according to the raw material inlet mass flow rate and the outlet mass flow rate of each product.

[0038] The catalytic cracking includes catalytic cracking and catalytic cracking process.

[0039] The reactor includes a riser reactor, a downflow bed reactor or a variable-diameter fluidized bed reactor.

[0040] The density of the coke is ρ c The density of the catalyst is ρ p The mass fraction of the coke on the outer surface of the catalyst in the total coke is x, and the radius of the catalyst is r p The viscosity μ, Poisson's ratio ν, Young's modulus Y and the initial collision restitution coefficient e0 of the catalyst before participating in the reaction of the catalyst surface coke due to the adsorption of high-boiling oil gas are all set values.

[0041] Compared with the existing determination method, the present application has the following advantages:

[0042] (1) The present application does not contain a correlation coefficient lacking theoretical basis, and can accurately describe the influence law of coke thickness and collision velocity on the catalyst collision restitution coefficient.

[0043] (2) The present application can determine the real collision restitution coefficient of the catalyst particles in real time in the determination of the fluid mechanics simulation of the catalytic cracking reactor, thereby accurately predicting the flow-reaction behavior in the reactor and obtaining more accurate yield of each product in the reactor, providing theoretical guidance for the design, optimization and engineering scaling of such equipment, thereby improving the overall performance of the catalytic cracking device and achieving better economic benefits. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 The collision restitution coefficient distribution diagram. DETAILED DESCRIPTION

[0045] The present application will be further described in detail with the application of the present application in the simulation of the catalytic cracking riser reactor as a specific embodiment.

[0046] The simulation object is a small test riser reactor with a height of 2 m and an inner diameter of 0.05 m. The raw material is vacuum gas oil, the catalyst-oil ratio is 10, and the reaction temperature is 520℃. The catalyst diameter is 70μm, the density is 1500kg / m 3The two-fluid model based on the Euler-Euler method is used to determine the fluid dynamics simulation.

[0047] In the simulation process, the real-time collision restitution coefficient of the catalyst is determined by using the determination method provided by the application, and the parameters are set as follows: the density of coke ρ c is 1200 kg / m 3 , the mass fraction of the catalyst outer surface coke x is 0.3, the viscosity μ of the catalyst surface coke due to adsorption of high-boiling oil gas is 0.001 Pa·s, the Poisson ratio ν is 0.17, the Young's modulus Y is 7.26e10 Pa, and the initial collision restitution coefficient e0 of the catalyst before participating in the reaction is 0.95.

[0048] Specifically, the following steps are included:

[0049] (1) determining the thickness of the catalyst surface coke layer

[0050] The thickness δ of the catalyst surface coke layer is determined by equation (1):

[0051]

[0052] In the formula, Y c is the mass fraction of coke, Y p is the mass fraction of catalyst, ρ c is the density of coke, ρ p is the density of catalyst, x is the mass fraction of catalyst outer surface coke in total coke, and r p is the radius of catalyst. When determining the thickness of the surface coke layer in step (1), the mass fraction of coke Y c and the mass fraction of catalyst Y p obtained by the fluid dynamics simulation need to be called.

[0053] (2) determining the catalyst Stokes number

[0054] The Stokes number St is determined by equation (2):

[0055]

[0056] In the formula, V c is the collision velocity between catalysts, and μ is the viscosity of the catalyst surface coke due to adsorption of high-boiling oil gas.

[0057] The collision velocity V c between catalysts in the Euler-Euler method is determined by equation (3):

[0058]

[0059] In the formula, Θs the catalyst pseudo-temperature determined by granular kinetics.

[0060] The step (2) determines the collision velocity V between catalysts in the Euler-Euler method c the catalyst pseudo-temperature determined by granular kinetics obtained by calling the fluid dynamics simulation s .

[0061] (3) determining the critical Stokes number of catalysts

[0062] The critical Stokes number St c is determined by equation (5):

[0063]

[0064] where ε is the dimensionless elastic parameter, determined by equation (6):

[0065]

[0066] where Y eff is the effective Young's modulus, determined by equation (7):

[0067]

[0068] where v is the Poisson's ratio, Y is the Young's modulus, and subscripts 1 and 2 represent two catalysts colliding.

[0069] (4) determining the collision restitution coefficient of catalysts

[0070] The collision restitution coefficient is determined by equation (8):

[0071]

[0072] where e is the real-time collision restitution coefficient of the catalyst in the catalytic cracking reaction process, and e0 is the initial collision restitution coefficient of the catalyst before participating in the reaction.

[0073] (5) prediction of the product yield of the reactor

[0074] Based on the collision restitution coefficient of the catalyst obtained by the method of steps (1) to (4) for the target reactor, the flow-reaction behavior in the reactor is accurately predicted, and according to the inlet mass flow rate of the raw material and the outlet mass flow rate of each product, the yield of each product in the reactor is obtained more accurately.

[0075] Referring to Figure 1 , the mass fraction of coke Y c , the mass fraction of catalyst Y p , and the catalyst pseudo-temperature Θ sThe real-time collision restitution coefficient of the catalyst is determined according to the above equation (1-8), and finally the flow-reaction characteristics in the riser reactor and the product distribution at the outlet are obtained. The real-time collision restitution coefficient distribution of the catalyst in the riser reactor is shown in Table 1. Figure 1 As shown in Table 1, the collision restitution coefficient at the inlet can be kept high due to the low coke mass fraction and high collision velocity, but in the middle and upper part, the collision restitution coefficient is significantly reduced due to the increase of coke mass fraction and the decrease of inter-particle collision velocity. The product distribution at the outlet is shown in Table 1.

[0076] The density of the coke ρ c The density of the catalyst ρ p The mass fraction of the catalyst external surface coke x, the radius of the catalyst r p The viscosity of the catalyst surface coke due to adsorption of high-boiling oil gas μ, the Poisson ratio v, the Young's modulus Y, and the initial collision restitution coefficient of the catalyst before participating in the reaction e0, all of which are set values, are as follows:

[0077] The density of the coke ρ c is 800-1400 kg / m 3 , preferably 1200 kg / m 3 .

[0078] The density of the catalyst ρ p is 1200-2000 kg / m 3 , preferably 1500 kg / m 3 .

[0079] The catalyst is composed of zeolite, inorganic oxide and optional clay.

[0080] The mass fraction of the catalyst external surface coke x is 0.01-0.7, preferably 0.3.

[0081] The viscosity of the catalyst surface coke due to adsorption of high-boiling oil gas μ is 0.0001-0.01 Pa·s, preferably 0.001 Pa·s.

[0082] The Poisson ratio v is 0.1-0.3, preferably 0.17.

[0083] The Young's modulus Y is 1e9-1e11 Pa, preferably 7.26e10 Pa.

[0084] The initial collision restitution coefficient of the catalyst before participating in the reaction e0 is 0.8-1, preferably 0.95.

[0085] Comparative Example

[0086] The comparative example is directed to the same simulation system, and the basic settings are kept consistent, but the existing method is used to simplify the assumption that the collision restitution coefficient is linearly related to the coke mass fraction, and the correlation coefficient is 30. The product distribution at the outlet of the riser reactor obtained is shown in Table 1.

[0087] From the comparison of the product distribution at the outlet in Table 1, it can be seen that compared with the comparative example, the determination method of the catalyst collision restitution coefficient provided by the present application can more accurately predict the product yield of the riser reactor in the determination of the hydrodynamic simulation, and the relative error of the yield of the main products diesel, gasoline and liquefied gas is reduced by about 10-20%, which can provide more reliable simulation results for the prediction of product yield under other operating conditions, and guide the optimization and control of the riser reactor.

[0088] Table 1 Product yield of the example and the comparative example

[0089]

[0090] The above is a further detailed description of the present application in combination with specific preferred embodiments, and the specific implementation of the present application cannot be limited to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, a number of simple deductions or substitutions can be made without departing from the concept of the present application, and all of them should be regarded as falling within the protection scope of the present application.

Claims

1. A method of predicting reactor product yields, characterized by, Specifically comprising the following steps: (1) determining the thickness of the coke layer on the catalyst surface The thickness of the coke layer on the catalyst surface δ is determined by equation (1): wherein Y c is the mass fraction of coke, Y p is the mass fraction of catalyst, p c is the density of coke, p p is the density of catalyst, x is the mass fraction of coke on the outer surface of the catalyst, r p is the radius of the catalyst; (2) determining the catalyst Stokes number The Stokes number St is determined by equation (2): In the formula, V c denoted as the collision velocity between catalysts, and μ as the viscosity of the coke on the catalyst surface due to the adsorption of high-boiling-point oil and gas. Collision velocity V between catalysts in the Euler-Euler method c Is determined from equation (3): where Θ s is the catalyst pseudo-temperature determined using granular kinetics; Collision velocity V between catalysts in the Euler-Lagrange approach c From equation (4) it is determined that: where V p1 and V p2 are the velocities of the two catalysts that collide, respectively; (3) determining the critical Stokes number of the catalyst Critical Stokes number St c Is determined from equation (5): In the formula, ε is a dimensionless elastic parameter, which is determined by equation (6): where Y eff is the effective Young's modulus, determined from equation (7): In the formula, ν is the Poisson's ratio, Y is the Young's modulus, and the subscripts 1 and 2 represent the two catalysts that collide; (4) determining the collision restitution coefficient of the catalyst The collision restitution coefficient is determined by equation (8): In the formula, e is the real-time collision restitution coefficient of the catalyst in the catalytic cracking reaction process, and e0 is the initial collision restitution coefficient of the catalyst before it participates in the reaction; (5) predicting the product yield of the reactor For the target reactor, based on the collision restitution coefficient of the catalyst obtained by the method of steps (1) to (4), the flow-reaction behavior in the reactor is predicted, and then according to the inlet mass flow rate of the raw material and the outlet mass flow rate of each product, the yield of each product in the reactor is obtained more accurately.

2. The method of predicting reactor product yields according to claim 1, wherein, The catalytic cracking includes catalytic cracking and catalytic cracking process.

3. The method of predicting reactor product yields of claim 1, wherein, The reactor includes a riser reactor, a downflow bed reactor or a variable-diameter fluidized bed reactor.

4. The method of predicting reactor product yields of claim 1, wherein, The density p of the coke c The density p of the catalyst p The mass fraction x of the coke on the outer surface of the catalyst in the total coke, the radius r of the catalyst p The viscosity μ, the Poisson's ratio v, the Young's modulus Y and the initial collision restitution coefficient e0 of the catalyst surface coke due to the adsorption of high-boiling oil gas are all set values.

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