Method for preventing and treating particle aggregation in olefin polymerization reactor

Abstract

The invention provides a method for preventing and treating particle aggregation in an olefin polymerization reactor, and belongs to the field of olefin polymerization. According to the olefin polymerization reactor, a gas phase is used as a continuous phase, a solid phase and a liquid phase are used as dispersed phases, and a gas-phase stream is led out from the top for circulation; the method comprises the following steps: acquiring operation conditions of an olefin polymerization reactor in real time in a polymerization process to obtain an agglomeration number predicted value and an agglomeration size predicted value, and judging a particle agglomeration type in the current reactor according to the predicted values and the current operation conditions; when the agglomeration type is reversible agglomeration, particle agglomeration is controlled through feedback adjustment of fluidization gas speed, liquid spraying flow and catalyst feeding flow in sequence, the purpose of preventing and treating particle agglomeration is achieved, and when reversible agglomeration is judged or agglomeration cannot be prevented and treated by changing operation parameters, shutdown treatment is carried out in time. The method provided by the invention can effectively inhibit particle aggregation and growth in the polymerization process, and prevent implosion shutdown.

Description

Technical Field

[0001] The present invention belongs to the field of olefin polymerization, and particularly relates to a method for preventing and controlling particle agglomeration in an olefin polymerization reactor. Background Art

[0002] Polyolefins are a class of thermoplastic resins obtained by homopolymerization or copolymerization of olefin monomers. Due to their rich raw materials, low price, and easy processing and molding characteristics, they are widely used in many fields such as agriculture, packaging, electronics, and automobiles, showing extremely high research value and economic value.

[0003] In order to produce polyolefin products with higher added value or increase the production capacity of the device, the means of introducing a liquid phase into the reactor has been more and more widely used. Typically, such as the multi-temperature zone olefin polymerization process reported in Patent ZL 201510043727.2, the gas-phase polyethylene condensation process disclosed in Patent ZL 200810062156.7, etc. After the liquid phase enters the olefin polymerization fluidized bed reactor, it will form atomized droplets and collide with the active particles, significantly affecting the mass transfer and heat transfer microenvironment of the particles and the interaction force between the particles, and finally changing the structure of the polymerization product. However, when the liquid phase is unevenly dispersed or the injected liquid phase amount is too large, the particles may adhere to form particle agglomeration under the combined action of the solid bridge force and the liquid bridge force when they come into contact and collide. If effective control measures are not taken in time, the agglomeration further evolved into lumps or flakes will have a great impact on the fluidization stability of the reactor and the product quality, and even cause a shutdown accident, resulting in huge economic losses. Therefore, regulating and preventing particle agglomeration is an important technical problem in the field of olefin polymerization reaction engineering.

[0004] Experimental studies by some scholars have found that the structures of the gas-liquid premixer and nozzle determine the size distribution of the atomized liquid and the liquid-solid contact efficiency, thereby affecting the particle agglomeration process. Portoghese et al. [Chemical Engineering Process: Process Intensification, 2007, 46: 924-934] compared the effects of atomization effect, injection angle, and stability on the liquid-solid contact efficiency and found that improving the injection stability is the key to enhancing the liquid-solid contact efficiency and reducing the formation of particle agglomeration. House et al. [Powder Technology, 2008, 186: 89-98] investigated the influence law of different nozzle structures on the liquid-solid contact efficiency and found that improving the liquid injection stability and atomization effect and increasing the interface of the gas-liquid injection area contribute to enhancing the liquid-solid contact and inhibiting the formation of particle agglomeration. Both of the above two researchers emphasized the regulating effect of liquid injection stability on agglomeration. Morales et al. [Canadian Journal of Chemical Engineering, 2016, 94: 886-895] studied the roles of three methods, namely, increasing the atomizing gas flow rate, fluidization gas velocity, and bed temperature in the liquid nozzle, in inhibiting the particle agglomeration process in a fluidized coking pilot plant. They found that the higher the atomizing gas flow rate, the smaller the droplet diameter, which is beneficial to its dispersion among particles and the smaller the agglomeration size formed. Increasing the fluidization gas velocity can accelerate the mixing of the liquid among particles and cause a stronger shear breaking effect on the agglomeration. Although the above studies have discussed the formation and regulation of particle agglomeration in the laboratory and pilot plant, they cannot be applied to industrial reactors with strong dynamics and coupling. Therefore, there is an urgent need to develop a particle agglomeration prevention and control technology for olefin polymerization industrial reactors. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for preventing and controlling particle agglomeration in an olefin polymerization reactor. The method of the present invention calculates the particle agglomeration state parameters and adjusts the operating conditions in real-time feedback to achieve the method of inhibiting the growth of particle agglomeration and preventing explosion polymerization and shutdown.

[0006] To solve the technical problems, the present invention provides a method for preventing and controlling particle agglomeration in an olefin polymerization reactor, and the method includes the following steps:

[0007] S1, taking the unreacted reaction raw material gas as the recycle gas and flowing it out from the top outlet of the olefin polymerization reactor, and after compression, heat exchange, and gas-liquid separation, introducing the separated liquid-phase material and gas-phase material into the olefin polymerization reactor respectively or after partial mixing;

[0008] S2, obtaining the predicted value X of the particle agglomeration quantity according to the operating conditions of the current olefin polymerization reactor agg,caland the predicted agglomeration size D agg,cal ;

[0009] S3. Based on the predicted values obtained in S2 and combined with the operating conditions, determine whether the particle agglomeration in the reactor is reversible or irreversible agglomeration;

[0010] S4. If the particle agglomeration in the reactor is reversible agglomeration, set the upper limit value U of the fluidization gas velocity g,max , the lower limit value Q of the liquid injection flow rate l,min , and the lower limit value Q of the catalyst feed flow rate c,min , and adjust by using one or more of the following adjustment means a - c: a. Increase the fluidization gas velocity; b. Decrease the liquid injection flow rate; c. Decrease the catalyst feed flow rate;

[0011] After each adjustment, repeat steps S2 - S4 until X agg,cal and D agg,cal no longer increase in value;

[0012] If the fluidization gas velocity has been increased to the upper limit value U g,max , the liquid injection flow rate has been decreased to the lower limit value Q l,min , and the catalyst feed flow rate has been decreased to the lower limit value Q c,min but X agg,cal and D agg,cal still continue to increase in value, it indicates that the particle agglomeration trend cannot be reversed. Inject CO into the reactor to kill the activity and then take shutdown measures;

[0013] S5. If S3 determines that the particle agglomeration in the reactor is irreversible agglomeration, inject CO into the reactor to kill the activity and then take shutdown measures.

[0014] As a preferred embodiment of the present invention, the olefin polymerization reactor includes an olefin polymerization reactor such as a fluidized bed, a vertical stirred bed, and a horizontal stirred bed, in which the gas phase is the continuous phase and the solid phase and the liquid phase are the discrete phases.

[0015] As a preferred embodiment of the present invention, the olefin monomer of the olefin polymerization reactor is at least one of ethylene and α - olefin. The α - olefin is selected from propylene, 1 - butene, 1 - pentene, 1 - hexene, 1 - octene, and 1 - decene.

[0016] Preferably, the α - olefin is selected from 1 - butene, 1 - hexene, and 1 - octene.

[0017] As a preferred embodiment of the present invention, the liquid phase material of the olefin polymerization reactor is at least one of a condensing agent and an α - olefin. The condensing agent is selected from n - pentane, isopentane, cyclohexane, n - hexane, and n - heptane. Preferably, the condensing agent is selected from isopentane and n - hexane.

[0018] As a preferred embodiment of the present invention, the liquid-phase material is sprayed into the fluidized bed by one or more nozzles installed on the side wall of the fluidized bed.

[0019] As a preferred embodiment of the present invention, the fluidization gas velocity U g is 1 to 15 times the minimum fluidization gas velocity of the olefin polymerization reactor, and the liquid spraying flow rate Q l is 0.005 to 0.3 times the recycle gas flow rate, and the catalyst feed flow rate Q c is 1.0×10 -5 to 3.0×10 -4 times.

[0020] As a preferred embodiment of the present invention, in the recycle gas, the molar content of the olefin monomer is 1.0% to 70%, and the molar content of the condensing agent is 0.5 to 50.0%.

[0021] As a preferred embodiment of the present invention, the temperature of the olefin polymerization reactor is 40°C to 110°C, and the pressure is 0.5 to 10 MPa.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) During the polymerization process of the present invention, the operating conditions of the olefin polymerization reactor are obtained in real time, and the predicted value of the agglomeration number and the predicted value of the agglomeration size are obtained. According to the predicted values and the current operating conditions, the type of particle agglomeration in the reactor is judged immediately; when the agglomeration type is reversible agglomeration, the fluidization gas velocity, the liquid spraying flow rate, and the catalyst feed flow rate are controlled by feedback regulation to control particle agglomeration. Compared with the traditional method of inferring the particle agglomeration situation in the reactor by sampling through a vibrating screen or off-line characterization of the product, the present invention can suppress and eliminate agglomeration online and quickly, greatly reducing the risk of reactor explosion and unplanned shutdown, and effectively ensuring the safety of the reaction process and the stability and controllability of the product quality.

[0024] (2) The present invention sets reasonable parameter range constraints and regulation strategies for the fluidization gas velocity, the liquid spraying flow rate, the catalyst feed flow rate, etc., effectively avoiding the adverse effects on the production process caused by blind or excessive regulation of parameters. For example, if the fluidization gas velocity increases too fast or the value is too large, it will cause entrainment of fine powder and blockage of the distribution plate, while too low liquid spraying flow rate and catalyst feed flow rate may lead to a decrease in the space-time yield of the reactor and unstable product performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a flow chart of the method for preventing and controlling particle agglomeration in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0027] The method for preventing and controlling particle agglomeration in the olefin polymerization reactor proposed by the present invention mainly includes the judgment steps of S1 - S3 and the operation steps of S4 and S5. Among them, S1 - S3 are briefly described as follows:

[0028] S1, taking the unreacted reaction feed gas as recycle gas and flowing it out from the top outlet of the olefin polymerization reactor. After compression, heat exchange, and gas - liquid separation, the separated liquid phase material and gas phase material are respectively introduced or partially mixed and then introduced into the olefin polymerization reactor;

[0029] S2, obtaining the predicted value X of the particle agglomeration quantity agg,cal and the predicted value D of the agglomeration size agg,cal ;

[0030] S3, according to the predicted values obtained in S2 and in combination with the operating conditions, judging whether the particle agglomeration in the reactor is reversible agglomeration or irreversible agglomeration.

[0031] See Figure 1 , after judging the type of the current agglomeration, the present invention further proposes the feedback operation steps of S4 and S5, and these steps are used for preventing and controlling particle agglomeration, and the steps are as follows:

[0032] S4, if the particle agglomeration in the reactor is reversible agglomeration, setting the upper limit value U of the fluidization gas velocity g,max , the lower limit value Q of the liquid spraying flow rate l,min , the lower limit value Q of the catalyst feed flow rate c,min , and adopting one or more of the following adjustment means for adjustment: a. increasing the fluidization gas velocity; b. reducing the liquid spraying flow rate; c: reducing the catalyst feed flow rate;

[0033] After each adjustment, repeat steps S2 - S4 until the values of X agg,cal and D agg,cal no longer increase;

[0034] If the fluidization gas velocity has been increased to the upper limit value U g,max , the liquid spraying flow rate has been reduced to the lower limit value Q l,min , the catalyst feed flow rate has been reduced to the lower limit value Q c,min but the values of X agg,cal and D agg,calIf the numerical value continues to increase, it indicates that the trend of particle agglomeration cannot be reversed. After injecting CO into the reactor to deactivate it, stop the operation.

[0035] S5. If it is determined in S3 that the particle agglomeration in the reactor is irreversible agglomeration, after injecting CO into the reactor to deactivate it, take measures to stop the operation.

[0036] The method of the present invention can be applied to industrial system polymerization reactors with strong dynamics and coupling. The olefin polymerization reactor can be a fluidized bed, a vertical stirred bed, a horizontal stirred bed, etc., which are olefin polymerization reactors with a gas phase as the continuous phase and a solid phase and a liquid phase as the discrete phases.

[0037] Typical but not limited, in the olefin polymerization reactor, the olefin monomer is at least one of ethylene and α-olefin. The α-olefin can be selected from propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, and 1-decene. The liquid phase material of the olefin polymerization reactor is at least one of a condensing agent and an α-olefin; the condensing agent can be selected from n-pentane, isopentane, cyclohexane, n-hexane, and n-heptane.

[0038] In an alternative embodiment of the present invention, the liquid phase material is sprayed into the fluidized bed by one or more nozzles installed on the side wall of the fluidized bed.

[0039] In an alternative embodiment of the present invention, in the recycle gas, the molar content of the olefin monomer is 1.0% - 70%, and the molar content of the condensing agent is 0.5 - 50.0%.

[0040] In an alternative embodiment of the present invention, the temperature of the olefin polymerization reactor is 40°C - 110°C, and the pressure is 0.5 - 10 MPa.

[0041] In the method of the present invention, in step S2, it is necessary to obtain the predicted value X of the agglomeration quantity agg,cal and the predicted value D of the agglomeration size agg,cal . Among them, the operating conditions of the olefin polymerization reactor include: the fluidization gas velocity U g , the liquid spraying flow rate (mass flow rate), the catalyst feed flow rate Q c (mass flow rate), the recycle gas flow rate Q g (mass flow rate), and the real-time temperature T of the reactor.

[0042] In the prior art, some methods or tools have been provided that can predict the predicted value X of the agglomeration quantity agg,cal and the predicted value D of the agglomeration size agg,cal according to the above operating condition parameter values. The present invention does not limit the selection of such methods or tools. Any method or tool that can obtain the predicted value X of the agglomeration quantity during the current reaction period according to the operating condition parameter values agg,caland the predicted value D of the agglomeration size agg,cal All means are applicable to the present invention.

[0043] Preferably, the S2 is specifically: according to the operating conditions of the current olefin polymerization reactor, a particle agglomeration evolution model is used to obtain the predicted value X of the particle agglomeration number agg,cal and the predicted value D of the agglomeration size agg,cal ;

[0044] The operating conditions of the olefin polymerization reactor include: the fluidization gas velocity U g , the liquid spraying flow rate, the catalyst feed flow rate Q c , the recycle gas flow rate Q g , and the real-time temperature T of the reactor;

[0045] The particle agglomeration evolution model includes a particle collision and coalescence model and a particle fragmentation model;

[0046] The particle collision and coalescence model is used to judge whether agglomerates can be formed when different particles come into contact under the current operating conditions; among them, according to the force balance criterion, when the particles come into contact, if the agglomeration force between the particles is greater than the maximum rebound force, the particles coalesce to form agglomerates; and if the agglomeration force between the particles is less than the maximum rebound force, the particles separate; the particle fragmentation model is used to judge whether the agglomerates are stable under the current operating conditions; when the agglomeration force between the particles is less than the fragmentation force, the agglomerates break; and when the agglomeration force between the particles is greater than the fragmentation force, the agglomerates continue to exist; according to the current operating conditions, using the particle agglomeration evolution model, the particle agglomeration evolution situation in the olefin polymerization reactor can be obtained, and then the predicted value X of the particle agglomeration number can be obtained agg,cal and the predicted value D of the agglomeration size agg,cal .

[0047] Typical but not limited, the embodiments of the present invention select a publicly reported particle agglomeration evolution model to realize the prediction of the predicted value X agg,cal and the predicted value D of the agglomeration size agg,cal as follows:

[0048] During the particle collision process, the agglomeration force is the force that promotes the particles to coalesce and form agglomerates, while the fragmentation forces such as the bubble tension, the rebound force generated by particle deformation, the fluid drag force, and the collision force of other particles are the forces that promote the particles to separate. Although for different types or operating states of gas-solid fluidized beds, the particle agglomeration mechanism in the reactor is different, corresponding particle agglomeration evolution models can be established based on the collision and coalescence model and the fragmentation model analysis, so as to realize the mathematical description of the agglomeration mechanism.

[0049] Collision and coalescence model:

[0050] During the dry particle collision process, it is assumed that the collision between particles is an elastic collision, where the rebound force Fr The solid bridge force F between particles sb with a radius of R 1 and R 2 When two spherical particles collide elastically and the deformation is maximum, the collision force F between the particles r is as shown in Equation (1):

[0051]

[0052] In the formula, V rel is the relative collision velocity between particles, and E * is the effective elastic modulus of the particles.

[0053] The solid bridge force F between particles sb is related to the contact time during particle collision and the surface properties of the particles, and can be calculated according to Equation (2)

[0054] F sb = πσ neck y 2 s-b (2)

[0055] In the formula, η s is the surface viscosity of the particles, γ s is the surface tension of the particles, σ neck is the tensile strength of the solid bridge between particles, y s-b is the size of the solid bridge formed during particle contact, t max is the contact time between particles.

[0056] According to the force balance criterion, when the compressive deformation between particles is maximum, that is, when the rebound force is maximum, if the solid bridge force between particles is greater than the maximum rebound force, the particles agglomerate to form aggregates; while if the solid bridge force between particles is less than the maximum rebound force, the particles separate.

[0057] For wet particles, two particles with relative movement speeds of V rel , masses of m 1 , m 2 respectively, and carrying liquid, the initial collision kinetic energy E c0 can be calculated by Equation (3):

[0058]

[0059] Assuming that the particle collision process is an elastic collision and the coefficient of restitution is e p , then the initial kinetic energy E r after the collision and rebound is:

[0060]

[0061] During the particle rebound process, the negative work W done by the liquid bridge force, i.e., the liquid bridge dissipation energy, can be calculated by Equation (5):

[0062]

[0063] When the liquid bridge dissipation energy W is greater than the initial kinetic energy E during particle rebound r , the particles coalesce to form agglomerates; conversely, the particles separate.

[0064] Particle breakage model:

[0065] The upper region of the bubble exerts a tensile force on the surrounding particle agglomerates, and its breakage effect on the agglomerates determines the evolution rate of particles into agglomerates in the reactor.

[0066] The tensile force of the bubble on the agglomerate is mainly related to the diameter of the bubble and the size of the agglomerate, and can be calculated by the following Equation (6):

[0067]

[0068] where D b is the diameter of the bubble, ρ a is the density of the agglomerate, d a is the diameter of the agglomerate, is the dimensionless particle pressure around the bubble, and n k is the coordination number of particle contacts.

[0069] Since only binary collisions are considered in the particle collision and coalescence process, and the simultaneously generated agglomerates are regarded as single particles continuing to participate in the particle collision process, at most one solid bridge is generated in each collision. In the process of bubble breakage of agglomerates, only binary breakage is still considered. When the bubble tensile force F b is greater than the solid bridge force F sb between the particles in the agglomerate, the agglomerate breaks into; while when the bubble tensile force F b is less than the solid bridge force F sb between the particles in the agglomerate, the agglomerate will not break.

[0070] In the dry particle agglomerate breakage model, the bubble tensile force is taken as the dominant force for agglomerate breakage, and an agglomerate breakage model is established. Since in the liquid-holding reactor, the gas formed by liquid evaporation will enter the bubble phase from the emulsion phase, thereby affecting the bubble size and its tensile force. Therefore, the aforementioned agglomerate breakage model needs to be corrected to be applicable to the description of the wet particle agglomerate breakage process.

[0071] After the liquid is atomized by the nozzle, it enters the reactor in the form of droplets. When the liquid flow rate is low, the droplet diameter is small, and it will evaporate completely rapidly after entering the reactor. When the liquid flow rate is high, the droplet diameter is large, and the liquid collides with the particles before complete evaporation and adheres to the particle surface. The difference between the liquid evaporation rate and the liquid spraying flow rate determines the liquid content in the bed. The liquid evaporation rate can be calculated according to the heat balance of the reactor, as shown in Equation (7),

[0072] Q a =Q r -Q g -Q evp -Q loss (7)

[0073] where Q a is the heat accumulation rate of the bed, Q r is the heat release rate of the particles, Q g is the heat transfer rate of the fluidizing gas, Q evp is the heat transfer rate of liquid evaporation, Q loss is the heat dissipation rate of the wall. Equation (7) can be further described by Equation (8) and Equation (9),

[0074]

[0075] where m p is the mass of the graphite-polyethylene wax particles, c p is the specific heat capacity of the particles, T s is the particle temperature in the bed, T bl is the liquid temperature in the bed, q l is the liquid spraying flow rate, q v is the evaporation rate of the liquid, m l is the liquid accumulation in the bed, c l is the specific heat capacity of the liquid, q g is the mass flow rate of the fluidizing gas, c g is the specific heat capacity of the gas, T in is the inlet temperature of the fluidizing gas, T out is the outlet temperature of the gas, ΔH7 r is the heat release rate of the particles, ΔH v is the latent heat of vaporization of the liquid, K w is the convective heat transfer coefficient between the fluidized bed wall and the environment, A w is the contact area between the material and the bed wall, T room is the environmental temperature, T w is the temperature of the fluidized bed wall.

[0076] From Equation (10), the liquid evaporation rate q v (t) can be obtained:

[0077]

[0078] Assume that the gas formed by evaporation is an ideal gas, then its volume V evp (t) can be calculated by Equation (11)

[0079]

[0080] where P is the reactor pressure, w i and M i are the mass fraction and molar mass of each component of the liquid, respectively.

[0081] The influence of the gas formed by liquid evaporation on the bubble size is first reflected in the superficial gas velocity U g as shown in Equation (12):

[0082]

[0083] where D t is the diameter of the reactor.

[0084] Furthermore, the bubble diameter D b is calculated according to the empirical correlation proposed by Mori and Wen (1975).

[0085]

[0086] For the liquid spraying process, the agglomeration formed by the action of the liquid bridge force causes the change of the particle size distribution, which further affects the initial fluidization velocity of the bed. According to the research of Lei et al., the initial fluidization velocity U' mf can be described by Equation (14):

[0089]

[0090] where d avg,0 is the initial average particle size, and d' avg is the average particle size during the liquid spraying process.

[0091] Combining Equations (10) to (14) to calculate the bubble size, further using Equation (6) to calculate the bubble tension, and comparing it with the liquid bridge force between particles. When the liquid bridge force between particles is less than the bubble tension, the agglomeration breaks; while when the liquid bridge force between particles is greater than the bubble tension, the agglomeration continues to exist.

[0092] Finally, according to the above dry and wet particle agglomeration models, the predicted value X agg,cal of the agglomeration number and the predicted value D agg,cal of the agglomeration size under the corresponding operating conditions can be obtained.

[0093] In the method of the present invention, it is necessary to determine whether reversible agglomeration or irreversible agglomeration has occurred under the current operating conditions. To this end, an optional method is to set the judgment criteria (thresholds) for reversible agglomeration and irreversible agglomeration. Obviously, under different reactors or different operating conditions, these judgment criteria can vary, and those skilled in the art can select the thresholds according to the actual situation, and the present invention does not limit this.

[0094] In a preferred embodiment of the present invention, the agglomeration number threshold X agg,thr and the agglomeration size threshold D agg,thr corresponding to the reversible agglomeration operation range under each operating condition are obtained through preliminary experiments, and a threshold data set is formed. The two thresholds under the current actual operating conditions are obtained by using the threshold data set, and then it is judged whether the particle agglomeration in the reactor is reversible agglomeration. The specific steps are as follows:

[0095] 3.1) In an experimental or industrial olefin polymerization reactor, the fluidization quality in the reactor is judged in real time by using a pressure pulsation or acoustic emission sensor; when an agglomeration signal is detected or a fluidization loss phenomenon occurs, samples are taken to count the agglomeration number and agglomeration size in the reactor; thus, the agglomeration number threshold X agg,thr and the agglomeration size threshold D agg,thr corresponding to the reversible agglomeration operation range under the current operating conditions are determined;

[0096] 3.2) By repeating the operation in step 3.1) under different fluidization gas velocities and liquid spraying amounts, the agglomeration number threshold X agg,thr and the agglomeration size threshold D agg, thr corresponding to the reversible agglomeration operation range under each operating condition are obtained;

[0097] 3.3) According to the threshold data set corresponding to the reversible agglomeration operation range obtained in step 3.2), combined with the operating conditions of the current actual olefin polymerization reactor, the corresponding agglomeration number threshold X agg,thr and the agglomeration size threshold D agg,thr are obtained from the threshold data set;

[0098] 3.4) If 0 < X agg,cal ≤ X agg,thr and 0 < D agg,cal ≤ D agg,thr , then the particle agglomeration in the reactor is reversible agglomeration;

[0099] If X agg,cal and D agg,cal are not within the above range and X agg,cal > 0, D agg,cal > 0, then the particle agglomeration in the reactor is irreversible agglomeration.

[0100] Further considering the cost of operation, in a preferred embodiment of the present invention, the step S4 is implemented according to the following process:

[0101] S4. If the particle agglomeration in the reactor is reversible agglomeration, gradually increase the fluidization gas velocity, and set the upper limit value of the fluidization gas velocity as U g,max ; After each increase in the fluidization gas velocity, repeat S2 - S4 until X agg,cal and D agg,cal values no longer increase;

[0102] If the fluidization gas velocity has been increased to the upper limit value U g,max but X agg,cal and D agg,cal values still continue to increase, gradually decrease the liquid injection flow rate, and set the lower limit value of the liquid injection flow rate as Q l,min ; After each decrease in the liquid injection flow rate, repeat S2 - S4 until X agg,cal and D agg,cal values no longer increase;

[0103] If the fluidization gas velocity has been increased to the upper limit value U g,max and the liquid injection flow rate has been decreased to the lower limit value Q l,min but X agg,cal and D agg,cal values still continue to increase, gradually decrease the catalyst feed flow rate, and set the lower limit value of the catalyst feed flow rate as Q c,min ; After each decrease in the catalyst feed flow rate, repeat S2 - S4 until X agg,cal and D agg,cal values no longer increase;

[0104] If the fluidization gas velocity has been increased to the upper limit value U g,max and the liquid injection flow rate has been decreased to the lower limit value Q l,min and the catalyst feed flow rate has been decreased to the lower limit value Q c,min but X agg,cal and D agg,cal values still continue to increase, it indicates that the particle agglomeration trend cannot be reversed, inject CO into the reactor to kill it and then take shutdown measures;

[0105] According to the preferred method of the present invention, the fluidization gas velocity U g is 1 - 15 times the minimum fluidization gas velocity of the olefin polymerization reactor, the liquid injection flow rate Q l is 0.005 - 0.3 times the recycle gas flow rate, and the catalyst feed flow rate Q c is 1.0×10 -5 -3.0×10 -4 . The upper limit value of the above fluidization gas velocity U g range can be directly used as the upper limit value U of the fluidization gas velocity g,max ; Correspondingly, the liquid injection flow rate Ql Lower limit value of the range, catalyst feed flow rate Q c The lower limit value of the range can be directly used as the lower limit value of the liquid injection flow rate Q l,min , lower limit value of catalyst feed flow rate Q c,min .

[0106] The method of the present invention will be elaborated in detail below in conjunction with embodiments.

[0107] Embodiment 1

[0108] The operating conditions of the ethylene polymerization fluidized bed reactor are fluidization gas velocity U g = 0.5 m / s, liquid injection flow rate Q l = 18 t / h, catalyst feed flow rate Q c = 11.0 kg / h, recycle gas flow rate Q g = 420 t / h, the reactor temperature T = 86 °C is collected, and the verified particle agglomeration evolution model is input to predict the agglomeration number X agg，cal = 5%, agglomeration size D agg，cal = 10 mm. According to the threshold data set obtained from the preliminary experiment and the current operating conditions, X agg,thr = 2%, D agg,thr = 3 mm, then it is judged that the situation of X agg，cal = 5% and D agg，cal = 10 mm corresponds to the occurrence of irreversible particle agglomeration. Therefore, CO is injected into the reactor to deactivate the catalyst, and the reactor is gradually operated to stop.

[0109] Embodiment 2

[0110] The operating conditions of the ethylene polymerization fluidized bed reactor are fluidization gas velocity U g = 0.5 m / s, liquid injection flow rate Q l = 12 t / h, catalyst feed flow rate Q c = 10.0 kg / h, recycle gas flow rate Q g = 420 t / h, the reactor temperature T = 86 °C is collected, and the verified particle agglomeration evolution model is input to predict the agglomeration number X agg，cal = 4%, agglomeration size D agg，cal = 7 mm. According to the threshold data set obtained from the preliminary experiment and the current operating conditions, X agg,thr = 6%, D agg,thr = 12 mm, then it is judged that the situation of X agg，cal = 4% and D agg，cal = 8 mm corresponds to the occurrence of reversible particle agglomeration. Therefore, the fluidization gas velocity U g is increased to 0.6 m / s, the reactor temperature is collected, and the verified particle agglomeration evolution model is input again to predict the particle agglomeration number X agg，cal= 4%, agglomeration size D agg，cal = 10 mm, indicating that the degree of particle agglomeration is still increasing. Further reduce the liquid spraying flow rate to 10 t / h, collect the reactor temperature, and input it into the particle agglomeration evolution model to predict X agg，cal = 1%, agglomeration size D agg，cal = 4 mm, indicating that the particle agglomeration tends to decrease. Therefore, maintain this operating condition until non-agglomerated fluidization is achieved.

[0111] Example 3

[0112] The operating conditions of the ethylene polymerization fluidized bed reactor are fluidization gas velocity U g = 0.5 m / s, liquid spraying flow rate Q l = 16 t / h, catalyst feed flow rate Q c = 10.0 kg / h, recycle gas flow rate Q g = 420 t / h, collect the reactor temperature T = 86 °C, input the verified particle agglomeration evolution model, and predict the agglomeration number X agg，cal = 5%, agglomeration size D agg，cal = 9 mm. According to the threshold data set obtained from the preliminary experiment and the current operating conditions, X agg,thr = 6%, D agg,thr Then judge X agg，cal = 5% and D agg，cal = 9 mm corresponds to the occurrence of reversible particle agglomeration. Therefore, increase the fluidization gas velocity U g to 0.6 m / s, collect the reactor temperature, and input the verified particle agglomeration evolution model again to predict the particle agglomeration number X agg，cal = 5.5%, agglomeration size D agg，cal = 10 mm, indicating that the degree of particle agglomeration is still increasing. Further reduce the liquid spraying flow rate to 14 t / h, collect the reactor temperature, and input it into the particle agglomeration evolution model to predict X agg，cal = 6%, agglomeration size D agg，cal = 10 mm, indicating that the degree of particle agglomeration is still increasing. Further reduce the catalyst feed flow rate to 8.0 kg / h, collect the reactor temperature, and input it into the particle agglomeration evolution model to predict X agg，cal = 4%, agglomeration size D agg，cal = 8 mm, indicating that the particle agglomeration tends to decrease. Therefore, maintain this operating condition until non-agglomerated fluidization is achieved.

[0113] Comparative Example 1

[0114] The operating conditions of the ethylene polymerization fluidized bed reactor are fluidization gas velocity U g = 0.5 m / s, liquid spraying flow rate Q l = 22 t / h, catalyst feed flow rate Q c= 10.0 kg / h, recycle gas flow rate Q g = 420 t / h, the temperature of the reactor T = 86 °C is collected. Without adopting the method for preventing particle agglomeration described in the present invention, only by inferring the particle agglomeration and caking conditions in the reactor based on the change of the loose density of the fluidized bed and the caking conditions in the discharge vibrating screen, it is impossible to regulate the operating conditions in real time and accurately to inhibit the growth of particle agglomeration, resulting in adverse consequences such as explosion polymerization and shutdown.

[0115] Comparative Example 2

[0116] The operating conditions of the ethylene polymerization fluidized bed reactor are the fluidization gas velocity U g = 0.5 m / s, liquid spraying flow rate Q l = 12 t / h, catalyst feed flow rate Q c = 10.0 kg / h, recycle gas flow rate Q g = 420 t / h, the temperature of the reactor T = 86 °C is collected. Without adopting the method for preventing particle agglomeration described in the present invention, only by inferring the particle agglomeration and caking conditions in the reactor based on the change of the loose density of the fluidized bed and the caking conditions in the discharge vibrating screen, it is selected to reduce the particle agglomeration by increasing the fluidization gas velocity U g to 0.9 m / s. However, due to the excessive fluidization gas velocity, a large amount of fine powder is entrained out of the reactor by the recycle gas, blocking the heat exchanger and the compressor, seriously affecting the stable operation of the device.

[0117] Comparative Example 3

[0118] The operating conditions of the ethylene polymerization fluidized bed reactor are the fluidization gas velocity U g = 0.5 m / s, liquid spraying flow rate Q l = 12 t / h, catalyst feed flow rate Q c = 10.0 kg / h, recycle gas flow rate Q g = 420 t / h, the temperature of the reactor T = 86 °C is collected. Without adopting the method for preventing particle agglomeration described in the present invention, only by inferring the particle agglomeration and caking conditions in the reactor based on the change of the loose density of the fluidized bed and the caking conditions in the discharge vibrating screen, it is selected to reduce the liquid spraying flow rate to 5 t / h. After the reaction is completed, it is found that due to the too low liquid spraying flow rate, both the production load of the reactor and the product performance index are lower than the design values, seriously affecting the stable operation of the device and product development.

[0119] The above embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation to the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

1. A method for preventing and controlling particle agglomeration in an olefin polymerization reactor, characterized in that: The method comprises the following steps: S1, unreacted reaction raw gas is discharged from the top outlet of the olefin polymerization reactor as circulating gas, and after compression, heat exchange, and gas-liquid separation, the separated liquid phase material and gas phase material are introduced separately or partially mixed and then introduced into the olefin polymerization reactor; S2, according to the current operating conditions of the olefin polymerization reactor, obtain the predicted value X of the particle agglomeration amount agg,cal and predicted value of aggregate size D agg,cal ; S3, judging whether the particle agglomeration in the reactor is reversible agglomeration or irreversible agglomeration according to the predicted value obtained in S2 and the operating conditions; S4, if the particles in the reactor are reversible agglomeration, set the upper limit of the fluidization gas velocity U g,max , spray flow lower limit Q l,min , Catalyst feed flow rate lower limit Q c,min , and one or more of the following adjustment means ac are used for adjustment: a. increasing the fluidizing gas velocity; b. reducing the spray flow rate; c. reducing the catalyst feed flow rate; After each adjustment, repeat steps S2-S4 until X agg,cal and D agg,cal The value no longer increases; If the fluidizing gas velocity has been increased to the upper limit value U g,max , the spray flow rate has been reduced to the lower limit value Q l,min , the catalyst feed flow rate has been reduced to the lower limit value Q c,min But X agg,cal and D agg,cal If the value continues to increase, it means that the particle agglomeration trend is irreversible, and CO is injected into the reactor to kill the particles and then shut down the reactor. S5, if S3 determines that the particle agglomeration in the reactor is irreversible agglomeration, CO is injected into the reactor to kill the particle agglomeration and then the reactor is shut down.

2. The method according to claim 1, characterized in that The S2 is specifically: according to the current operating conditions of the olefin polymerization reactor, using the particle agglomeration evolution model, obtain the particle agglomeration quantity prediction value X agg,cal and predicted value of aggregate size D agg,cal ; The operating conditions of the olefin polymerization reactor include: fluidizing gas velocity U g , liquid injection flow, catalyst feed flow Q c , circulating gas flow Q g , reactor real-time temperature T; The particle agglomeration evolution model includes a particle collision and aggregation model and a particle breakage model; The particle collision and aggregation model is used to determine whether different particles can form agglomerates when they come into contact under the current operating conditions; according to the force balance criterion, when particles come into contact, if the agglomeration force between particles is greater than the maximum rebound force, the particles aggregate to form agglomerates; and if the agglomeration force between particles is less than the maximum rebound force, the particles separate; the particle crushing model is used to determine whether the agglomerates are stable under the current operating conditions; when the agglomeration force between particles is less than the crushing force, the agglomerates are crushed; and when the agglomeration force between particles is greater than the crushing force, the agglomerates continue to exist; According to the current operating conditions, the particle agglomeration evolution model is used to obtain the particle agglomeration evolution in the olefin polymerization reactor and obtain the particle agglomeration number prediction value X agg,cal and predicted value of aggregate size D agg,cal .

3. The method according to claim 1, characterized in that The S3 is specifically: 3.1) In an experimental or industrial olefin polymerization reactor, a sensor is used to determine the fluidization quality in the reactor in real time; when an agglomeration signal is detected or a loss of fluidization occurs, the number of agglomerates and the size of agglomerates in the reactor are sampled and counted; thereby determining the agglomeration number threshold X corresponding to the reversible agglomeration operating range under the current operating conditions agg,thr and the aggregation size threshold D agg,thr ; 3.2) By repeating the operation of step 3.1) under different fluidizing gas velocities and liquid spraying amounts, the agglomeration number threshold value X corresponding to the reversible agglomeration operating range under each operating condition is obtained. agg,thr and the aggregation size threshold D agg,thr ; 3.3) According to the threshold data set corresponding to the reversible agglomeration operation range obtained in step 3.2), combined with the current actual operating conditions of the olefin polymerization reactor, the corresponding agglomeration number threshold value X is obtained from the threshold data set. agg,thr and the aggregation size threshold D agg,thr ; 3.4) If 0 <X agg,cal ≤X agg,thr and 0 <D agg,cal ≤D agg,thr , then the particle agglomeration in the reactor is reversible agglomeration; If X agg,cal and D agg,cal Not within the above range and X agg,cal >0,D agg,cal >0, the particle agglomeration in the reactor is irreversible agglomeration.

4. The method according to claim 1, characterized in that The adjustment in S4 is preferably: first gradually increase the fluidizing gas velocity, and repeat S2-S4 after each increase in the fluidizing gas velocity until X agg,cal and D agg,cal The value no longer increases; If the fluidizing gas velocity has been increased to the upper limit value U g,max But X agg,cal and D agg,cal If the value continues to increase, the spray flow rate is gradually reduced, and S2-S4 is repeated each time the spray flow rate is reduced until X agg,cal and D agg,cal The value no longer increases; If the fluidizing gas velocity has been increased to the upper limit value U g,max , the spray flow rate has been reduced to the lower limit value Q l,min But X agg,cal and D agg,cal If the value continues to increase, the catalyst feed flow rate is gradually reduced, and S2-S4 is repeated each time the catalyst feed flow rate is reduced until X agg,cal and D agg,cal The value no longer increases; If the fluidizing gas velocity has been increased to the upper limit value U g,max , the spray flow rate has been reduced to the lower limit value Q l,min , the catalyst feed flow rate has been reduced to the lower limit value Q c,min But X agg,cal and D agg,cal If the value continues to increase, it means that the trend of particle agglomeration is irreversible, and CO2 should be injected into the reactor to kill the particles and then shut down the reactor.

5. The method according to claim 1 or 4, characterized in that: In S4, The fluidizing gas velocity is gradually increased at a rate of 1%-100%, and the upper limit of the fluidizing gas velocity is U g,max 15 times the minimum fluidizing gas velocity of the olefin polymerization reactor; The spray flow rate is gradually reduced at a rate of 1%-100%, and the lower limit of the spray flow rate is Q l,min 0.005 times of circulating air flow; The catalyst feed flow rate is gradually reduced at a rate of 1%-100%, and the catalyst feed flow rate lower limit Q c,min The circulating air flow is 1.0×10 -5 times.

6. The method according to claim 1, characterized in that In the olefin polymerization reactor, the gas phase is a continuous phase, the solid phase and the liquid phase are discrete phases; and the olefin monomer is at least one of ethylene and α-olefin.

7. The method according to claim 1, characterized in that The liquid phase material of the olefin polymerization reactor is at least one of a condensing agent and an alpha-olefin; the liquid phase material is sprayed into the fluidized bed through one or more nozzles installed on the side wall of the fluidized bed.

8. The method according to claim 1, characterized in that Fluidizing gas velocity U g The minimum fluidizing gas velocity of the olefin polymerization reactor is 1 to 15 times, and the liquid injection flow rate Q l It is 0.005 to 0.3 times of the circulating gas flow rate, and the catalyst feed flow rate Q c The circulating air flow is 1.0×10 -5 ~3.0×10 -4 times.

9. The method according to claim 1, characterized in that: In the circulating gas, the molar content of olefin monomer is 1.0% to 70%, and the molar content of condensing agent is 0.5 to 50.0%.

10. The method according to claim 1, characterized in that The temperature of the olefin polymerization reactor is 40° C. to 110° C., and the pressure is 0.5 to 10 MPa.

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