A double-layer mutual reverse rotor reactor, nano calcium carbonate and a preparation method thereof

Abstract

This invention relates to the field of nano-calcium carbonate preparation technology, specifically to a double-layer reciprocating reactor, nano-calcium carbonate, and a preparation method. The reactor includes a shell and an inner rotor, an outer rotor, and a spray pipe disposed within the shell. The inner and outer rotors are coaxially and rotatably disposed outside the spray pipe, and their rotation directions are opposite. The method involves reacting a Ca(OH)₂ suspension with CO₂ in the reactor to generate nano-calcium carbonate particles in a single reaction, with a single-reaction yield of 20%–30%. Subsequently, the reaction is completed in an aging tank to obtain a carbonized slurry. The carbonized slurry is then post-treated to obtain the finished nano-calcium carbonate product. This nano-calcium carbonate is prepared by this method. This invention can improve the yield of nano-calcium carbonate seed crystals generated from a single reaction of Ca(OH)₂ suspension and CO₂, ensuring a uniform particle size distribution in the nano-calcium carbonate product.

Description

Technical Field

[0001] This invention relates to the field of nano-calcium carbonate preparation technology, specifically to a double-layer reciprocal reactor, nano-calcium carbonate, and preparation method. Background Technology

[0002] Current methods for producing nano-calcium carbonate using centrifugal carbonation primarily involve connecting a centrifugal reactor to a circulating tank. This circulating reaction ensures complete reaction between the Ca(OH)₂ suspension and CO₂, preventing raw material waste. In practice, during the initial centrifugal carbonation process, nano-calcium carbonate seed crystals are generated. In subsequent cycles, these seed crystals enter the uncarbonized Ca(OH)₂ suspension. However, if nano-calcium carbonate seed crystals are present at the initial carbonation stage, crystallization will use these existing seed crystals as nuclei, resulting in larger crystals. The more seed crystals introduced at the initial carbonation stage, the more large crystals are produced, ultimately leading to a wide and uneven particle size distribution in the nano-calcium carbonate product.

[0003] If a single-reaction nucleation method is used to prepare nano-calcium carbonate instead of a cyclic reaction, the problem of uneven particle size distribution in the nano-calcium carbonate product can theoretically be solved. However, the yield of nano-calcium carbonate seed crystals generated from the single reaction of Ca(OH)2 suspension and CO2 is quite high. Even with the most mature industrialized nano-calcium carbonate preparation technology, the yield of nano-calcium carbonate seed crystals generated from a single reaction is only 8%–10%. If the number of nano-calcium carbonate seed crystals generated in a single reaction is too small, too much unreacted reactant will remain, leading to excessive seed crystal growth and ultimately resulting in an excessively large particle size of the nano-calcium carbonate product.

[0004] Therefore, in order to improve the yield of nano-calcium carbonate seed crystals generated by a single reaction of Ca(OH)2 suspension and CO2, and to ensure uniform particle size distribution of the nano-calcium carbonate product, it is necessary to develop a double-layer reciprocating reactor, nano-calcium carbonate, and preparation method. Summary of the Invention

[0005] The purpose of this invention is to provide a double-layer reciprocal reactor, nano-calcium carbonate, and a preparation method thereof. The specific technical solution is as follows:

[0006] In a first aspect, the present invention provides a double-layer reciprocating reactor, comprising a shell and an inner rotor, an outer rotor, and a spray pipe disposed within the shell; an inlet and an outlet are provided at the top of the shell; an outlet and an air inlet are provided at the bottom of the shell; the spray pipe is disposed within the shell, its top end connected to the top of the shell and communicating with the inlet, and its bottom end connected to the bottom of the shell; a plurality of spray holes are provided on the wall of the spray pipe; the inner rotor and the outer rotor are sequentially and coaxially rotatably disposed outside the spray pipe, and their rotation directions are opposite; a plurality of through holes are provided on both the inner rotor and the outer rotor; a first liquid flow gap is provided between the inner rotor and the spray pipe, a second liquid flow gap is provided between the inner rotor and the outer rotor, and a third liquid flow gap is provided between the outer rotor and the shell.

[0007] Optionally, the double-layer reciprocating reactor further includes a first driver for driving the inner rotor to rotate; the first driver is disposed on the shell and its driving end is connected to the shaft of the inner rotor;

[0008] It also includes a second driver for driving the outer rotor to rotate; the second driver is disposed on the housing and its driving end is connected to the shaft of the outer rotor.

[0009] Optionally, the inner rotor includes an inner rotor with a spherical structure; the outer rotor includes an outer rotor with a spherical structure.

[0010] In a second aspect, the present invention provides a method for preparing nano-calcium carbonate using the aforementioned double-layer reciprocal reactor, comprising:

[0011] Step S1, Pretreatment stage; Specifically, the raw material CaO is treated in the pretreatment stage to obtain a Ca(OH)2 suspension;

[0012] Step S2, carbonization stage; specifically, the Ca(OH)2 suspension is introduced from the inlet at the top of the shell through the spray pipe into the first liquid flow gap, the second liquid flow gap, and the third liquid flow gap; compressed and purified CO2 gas is introduced into the shell from the inlet at the bottom of the shell, diffuses in the third liquid flow gap, the second liquid flow gap, and the first liquid flow gap, and under the action of the double centrifugal force field provided by the counter-rotating outer rotor and the inner rotor, the CO2 gas and the Ca(OH)2 suspension complete a single reaction to generate nano-calcium carbonate particles, with a single-cycle yield of 20% to 30%; the rotational speed n1 of the inner rotor and the rotational speed n2 of the outer rotor are both 1000 to 3000 rpm;

[0013] After the single reaction, the nano-calcium carbonate particles generated by the single reaction are carried along with the unreacted Ca(OH)2 suspension into the aging tank through the outlet at the bottom of the shell; CO2 gas is continuously introduced into the aging tank until the unreacted Ca(OH)2 suspension reacts completely with the CO2 gas in the aging tank to obtain carbonized slurry;

[0014] Step S3, post-processing stage; specifically, the unreacted CO2 gas in the aging tank and the shell is fed into a water washing tower through the gas outlet at the top of the shell for tail gas treatment; the carbonized slurry is separated into solid and liquid components to obtain wet material; the wet material is washed and impurities are removed, and then dried to obtain nano-calcium carbonate powder; the nano-calcium carbonate powder is separated by cyclone separation and then packaged to obtain the finished product.

[0015] Optionally, in step S1, the pretreatment step includes grinding raw material CaO to obtain quicklime powder; mixing the quicklime powder with water at a mass ratio of 1:3.5 to 1:4.5, and then subjecting the mixture to a digestion reaction to generate a coarse lime slurry; sieving the coarse lime slurry to remove impurities to obtain a refined lime slurry; adding a dispersant to the refined lime slurry, and after mixing, obtaining a Ca(OH)2 suspension with a concentration of 37 to 59 g / L.

[0016] The dispersant includes at least one of ammonium polyacrylate, polycarboxylic acid, and sodium hexametaphosphate, and is used in an amount of 0.3 to 0.5 wt% of the Ca(OH)2 suspension.

[0017] Optionally, in step S2, the flow rate of the Ca(OH)2 suspension sprayed through the spray holes on the spray pipe is 2-6 m³ / s. 3 / h, preferably 2.8–4.2m 3 / h; the flow rate of the CO2 gas flowing into the casing through the bottom inlet of the casing is 30-85 Nm³. 3 / h, preferably 40-60 Nm 3 / h; the flow rate of the CO2 gas entering the aging tank is 35-45 Nm. 3 / h; the flow rate of the nano-calcium carbonate particles generated in the single reaction mixed with the unreacted Ca(OH)2 suspension entering the aging tank is 3-4 m³ / h. 3 / h.

[0018] Optionally, in step S2, the suspension time of the Ca(OH)2 suspension in the single reaction is t, which is obtained by formula 1);

[0019]

[0020] In Equation 1), H is the maximum radial displacement of the Ca(OH)2 particles inside the inner rotor, which is obtained using Equation 2); v is the settling velocity of the Ca(OH)2 particles, which is obtained using Equation 3.

[0021] Equation 2) is as follows:

[0022]

[0023] In Equation 2), ω1 is the angular velocity of the inner rotor, ω1 = 2πn1; ω2 is the angular velocity of the outer rotor, ω2 = 2πn2; R is the distance from the Ca(OH)2 particle to the center of the spray pipe when it is located in the inner region of the inner rotor; γ is the shear rate of the inner region of the inner rotor.

[0024] Equation 3) is as follows:

[0025]

[0026] In equation 3), r is the radius of the Ca(OH)2 particle; ρ p The density of nano-calcium carbonate particles; ρ f ρ is the density of the Ca(OH)2 suspension; μ is the dynamic viscosity of the Ca(OH)2 suspension.

[0027] Optionally, in step S2, the mass transfer coefficient of the CO2 gas in the single reaction is k. L , its origin

[0028] Equation 4) yields the result;

[0029]

[0030] In Equation 4), a is the gas-liquid specific surface area of ​​CO2 gas and Ca(OH)2 suspension; C is an empirical coefficient, with a value of 1.0; and D is the diffusion coefficient, with a value of 1.0 × 10⁻⁶. -9 m 2 / s; g is the acceleration due to gravity; h is the height of the shell; This represents the centrifugal pressure gradient generated inside the inner rotor under the action of a dual centrifugal force field provided by the counter-rotating outer and inner rotors; centrifugal pressure gradient The value gradually increases along the direction from the inner rotor to the outer rotor, as obtained from equation 5);

[0031]

[0032] Optionally, in step S2, according to classical nucleation theory, the critical nucleation radius for the single reaction to generate nano-calcium carbonate particles is r. * It is obtained from equation 6);

[0033]

[0034] In equation 6), σ represents the interfacial tension of the Ca(OH)₂ suspension; V m C is the molar volume of the solute Ca(OH)₂. r is a constant in the ideal gas law; T is the thermodynamic temperature during the single reaction; S is the supersaturation of CO2 gas, which is obtained from equation 7);

[0035]

[0036] In Equation 7), S0 is the supersaturation of CO2 gas under standard atmospheric pressure; ΔP is the change in centrifugal pressure, which is obtained from Equation 8.

[0037]

[0038] In Equation 8), K is an empirical coefficient, with a value of 0.55-0.7; Δr is the change in the spatial position of CO2 gas.

[0039] In a third aspect, the present invention provides a nano-calcium carbonate, which is prepared by the method described above for preparing nano-calcium carbonate using a double-layer reciprocal reactor.

[0040] The application of the technical solution of the present invention has at least the following beneficial effects:

[0041] (1) The present invention provides a double-layer reciprocating oscillator reactor, which provides a double centrifugal force field by rotating the outer rotor and the inner rotor in opposite directions, increasing the suspension time of Ca(OH)2 suspension and enhancing the mass transfer efficiency of CO2 gas in Ca(OH)2 suspension, thereby increasing the yield of nano-calcium carbonate particles generated in a single reaction, that is, increasing the number of nano-calcium carbonate seed crystals, so that the unreacted Ca(OH)2 suspension is relatively reduced, and the seed crystals grow appropriately in the aging tank, ensuring that the nano-calcium carbonate product has a uniform particle size distribution.

[0042] (2) The present invention provides a method for preparing nano-calcium carbonate using the aforementioned double-layer reciprocating reactor. In step S1, the raw material CaO is treated into a Ca(OH)2 suspension through a pretreatment step. In step S2, the carbonization step provides a dual centrifugal force field by controlling the reverse rotation of the outer and inner rotors. Furthermore, the rotational speed n1 (i.e., the angular velocity of the inner rotor) and the rotational speed n2 (i.e., the angular velocity of the outer rotor) of both the inner and outer rotors are limited to 1000–3000 rpm. This increases the suspension time of the Ca(OH)2 suspension and enhances the mass transfer efficiency of CO2 gas in the Ca(OH)2 suspension, thereby promoting the flow of CO2 gas within the reactor. The yield of nano-calcium carbonate particles generated by a single reaction of the slurry with Ca(OH)2 suspension is 20%–30%, which is significantly higher than the yield of nano-calcium carbonate seed crystals generated by the existing supergravity carbonation method (8%–10%). This means that this method can increase the number of nano-calcium carbonate seed crystals, thereby reducing the amount of unreacted Ca(OH)2 suspension and allowing the seed crystals to grow appropriately in the aging tank, ensuring a uniform particle size distribution of the nano-calcium carbonate product. In the post-processing stage of step S3, the unreacted CO2 gas is treated as tail gas for secondary use. After the carbonation slurry undergoes solid-liquid separation, washing and impurity removal, drying, and cyclone separation, it is packaged to obtain the finished product.

[0043] (3) The present invention provides a method for preparing nano-calcium carbonate using the aforementioned double-layer reciprocating reactor. By adjusting the values ​​of the angular velocities ω1 of the inner rotor and ω2 of the outer rotor, the critical nucleation radius r for generating nano-calcium carbonate particles in a single reaction can be stably controlled. * This avoids agglomeration and ensures uniform particle size distribution in nano-calcium carbonate products.

[0044] (4) The average particle size of the nano-calcium carbonate prepared by the existing supergravity carbonation method is D50 = 25 nm, and the particle size range is D90-D10≤30 nm; while the average particle size of the nano-calcium carbonate prepared by the present invention is D50 = 20 nm, and the particle size range is D90-D10≤20 nm. This shows that the present invention significantly reduces the generation of large crystal particles by controlling the critical nucleation radius through dual centrifugal force fields, and the nano-calcium carbonate product has a more uniform particle size distribution, which verifies the significant advantage of the double-layer reciprocating ion reactor in controlling particle size uniformity.

[0045] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0046] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0047] Figure 1 This is a schematic diagram of the structure of a double-layer reciprocating reactor in the embodiment (in Figure 1 The image also shows an aging tank and a water washing tower.

[0048] Figure 2 This is a schematic flowchart of the method for preparing nano-calcium carbonate in the embodiments;

[0049] Figure 3 These are particle size distribution diagrams of the various carbonized slurries in the examples and comparative examples;

[0050] Among them, Figure 1 In the diagram, solid arrows indicate the flow path of Ca(OH)2 suspension, i.e., the liquid phase flow path; hollow arrows indicate the flow path of CO2 gas, i.e., the gas phase flow path.

[0051] exist Figure 1 In the middle, 1. shell, 2. inner rotor, 3. outer rotor, 4. spray pipe, 5. aging tank, 6. water washing tower;

[0052] exist Figure 3 In the graph, the horizontal axis “Particle size” represents the particle size; the vertical axis “Differential distribution” represents the particle size (differential) distribution. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0054] Example:

[0055] See Figure 1A double-layer reciprocating oscillator reactor includes a shell 1 and an inner rotor 2, an outer rotor 3, and a spray pipe 4 disposed within the shell 1. An inlet and an outlet are provided at the top of the shell 1; an outlet and an air inlet are provided at the bottom of the shell 1. The spray pipe 4 is disposed within the shell 1, with its top end connected to the top of the shell 1 and communicating with the inlet, and its bottom end connected to the bottom of the shell 1. Multiple spray holes are evenly distributed on the wall of the spray pipe 4. The inner rotor 2 and the outer rotor 3 are sequentially and coaxially rotatably disposed outside the spray pipe 4, and their rotation directions are opposite. Multiple through holes are evenly distributed on the inner rotor 2 and the outer rotor 3. A first liquid flow gap is provided between the inner rotor 2 and the spray pipe 4, a second liquid flow gap is provided between the inner rotor 2 and the outer rotor 3, and a third liquid flow gap is provided between the outer rotor 3 and the shell 1.

[0056] The double-layer reciprocating reactor also includes a first driver (not shown in the figure) for driving the inner rotor 2 to rotate; the first driver is disposed on the shell 1 and its driving end is connected to the rotating shaft of the inner rotor 2;

[0057] It also includes a second driver (not shown in the figure) for driving the outer rotor 3 to rotate; the second driver is disposed on the housing 1 and its driving end is connected to the rotating shaft of the outer rotor 3.

[0058] The inner rotor 2 is a spherical inner rotor 2; the outer rotor 3 is a spherical outer rotor 3.

[0059] See Figure 2 A method for preparing nano-calcium carbonate using the aforementioned double-layer reciprocal reactor, comprising:

[0060] Step S1, Pretreatment stage; Specifically, the raw material CaO is treated in the pretreatment stage to obtain a Ca(OH)2 suspension;

[0061] Step S2, carbonization stage; specifically, a centrifugal pump is used to sequentially transport the Ca(OH)2 suspension from the inlet at the top of the shell 1 through the spray pipe 4 into the first liquid flow gap, the second liquid flow gap, and the third liquid flow gap; when the Ca(OH)2 particles in the Ca(OH)2 suspension are in the inner region of the inner rotor 2 (i.e., the first liquid flow gap), the Ca(OH)2 particles are simultaneously affected by the centrifugal force generated by the inner rotor 2 and the outer rotor 3; when the Ca(OH)2 particles are located in the gap region between the inner rotor 2 and the outer rotor 3 (i.e., the second liquid flow gap), the Ca(OH)2 particles are mainly affected by the centrifugal force generated by the outer rotor 3; when the Ca(OH)2 particles are located in the outer region of the outer rotor 3 (i.e., the third liquid flow gap), the Ca(OH)2 particles are... The particles are not affected by the dual centrifugal force field; the raw material CO2 gas produced from the lime kiln is compressed (using a CO2 gas compressor) and purified, then flows into the shell 1 from the air inlet at the bottom of the shell 1, diffuses in the third liquid flow gap, the second liquid flow gap and the first liquid flow gap, and under the action of the dual centrifugal force field provided by the counter-rotating outer rotor 3 and the inner rotor 2, the CO2 gas and the Ca(OH)2 suspension complete a single reaction to generate nano-calcium carbonate particles, with a yield of 20% to 30% (specifically 30%); the rotational speed n1 of the inner rotor 2 is 1000 to 3000 rpm (specifically 2500 rpm); the rotational speed n2 of the outer rotor 3 is 1000 to 3000 rpm (specifically 2500 rpm);

[0062] After the single reaction, a centrifugal pump is used to transport the nano-calcium carbonate particles generated in the single reaction along with the unreacted Ca(OH)2 suspension (i.e., the single reaction slurry) through the outlet at the bottom of the shell 1 into the aging tank 5; CO2 gas is continuously introduced into the aging tank 5 until the unreacted Ca(OH)2 suspension reacts completely with the CO2 gas in the aging tank 5 to obtain carbonized slurry;

[0063] Step S3, post-processing stage; specifically, the unreacted CO2 gas in the aging tank 5 and the shell 1 is fed into the water washing tower 6 through the gas outlet at the top of the shell 1 for tail gas treatment, facilitating secondary utilization; the carbonized slurry is separated into solid and liquid components by a disc centrifuge to obtain wet material; the wet material is conveyed to the washing section by a screw conveyor, and washed and cleaned in a multi-stage countercurrent washing tank to remove impurities (Cl in the wet material). - and Na + After removing impurity ions, the powder is then dried in a flash dryer (drying temperature 150℃, drying time 5min) to obtain nano-calcium carbonate powder. The nano-calcium carbonate powder is then sent to a cyclone separator for separation. After cyclone separation, it is packaged by a fully automatic packaging machine to obtain the finished product.

[0064] In step S1, the pretreatment process includes feeding the raw material CaO from the lime kiln into a ball mill to grind it into quicklime powder; mixing the quicklime powder with water at a mass ratio of 1:3.5 to 1:4.5 (specifically 1:4), and then digesting the mixture in a rotary digester to generate coarse lime slurry; finely sieving the coarse lime slurry through a vibrating screen to remove impurities (i.e., fine impurity removal, used to remove undigested CaO particles and sand) to obtain refined lime slurry; adding a dispersant to the refined lime slurry, and then mixing it in a dilution tank to dilute and concentrate it to obtain a Ca(OH)2 suspension with a concentration of 37 to 59 g / L (specifically 45 g / L); according to the needs of continuous production, the Ca(OH)2 suspension can be pumped to a storage tank for storage and to continuously supply material for the carbonation stage in step S2. A feed pump is used for feeding the material.

[0065] The dispersant includes at least one selected from ammonium polyacrylate, polycarboxylic acid, and sodium hexametaphosphate, and its dosage is 0.3-0.5 wt% (specifically 0.4 wt%) of the Ca(OH)2 suspension. Specifically, in this embodiment, the dispersant used is ammonium polyacrylate.

[0066] In step S2, the flow rate of the Ca(OH)2 suspension sprayed through the spray holes on the spray pipe 4 is 2-6 m³ / h. 3 / h (specifically 3.5m) 3 / h); the CO2 gas flows into the housing 1 through the bottom air inlet at a flow rate of 30-85 Nm. 3 / h (specifically 50Nm) 3 / h); the flow rate of the CO2 gas entering the aging tank 5 is 35-45 Nm. 3 / h (specifically 40Nm) 3 / h); the flow rate of the nano-calcium carbonate particles generated in the single reaction mixed with the unreacted Ca(OH)2 suspension entering the aging tank 5 is 3-4 m³ / h. 3 / h (specifically 3.5m) 3 / h).

[0067] In step S2, the suspension time of the Ca(OH)2 suspension in the single reaction is t, which is obtained by formula 1);

[0068]

[0069] In Equation 1), H is the maximum radial displacement of the Ca(OH)2 particles inside the inner rotor 2, which is obtained using Equation 2); v is the settling velocity of the Ca(OH)2 particles, which is obtained using Equation 3.

[0070] Equation 2) is as follows:

[0071]

[0072] In Equation 2), ω1 is the angular velocity of the inner rotor 2, ω1 = 2πn1; ω2 is the angular velocity of the outer rotor 3, ω2 = 2πn2; R is the distance from the Ca(OH)2 particle to the center of the spray pipe 4 when it is located in the inner region of the inner rotor 2; γ is the shear rate in the inner region of the inner rotor 2; since the inner rotor 2 is a spherical structure, its curved surface structure makes the shear rate γ exhibit a gradient distribution along the radial direction of the inner rotor 2;

[0073] Equation 3) is a modified expression of the Stokes settlement velocity formula, as follows:

[0074]

[0075] In equation 3), r is the radius of the Ca(OH)2 particle; ρ p The density of nano-calcium carbonate particles; ρ f ρ is the density of the Ca(OH)2 suspension; μ is the dynamic viscosity of the Ca(OH)2 suspension.

[0076] From equations 1) to 3), we know that if the following conditions are met... The suspension time t can then approach infinity, which is the ideal state. Although the ideal state cannot be achieved in the actual reaction process, the suspension time t can still be significantly increased by adjusting the values ​​of ω1 and ω2, thereby increasing the single reaction time of Ca(OH)2 suspension and CO2 gas, and thus increasing the yield of nano-calcium carbonate particles generated in a single reaction, that is, increasing the number of nano-calcium carbonate seed crystals, so that the unreacted Ca(OH)2 suspension is relatively reduced, and the seed crystals can grow appropriately in the aging tank 5, ensuring that the nano-calcium carbonate product has a uniform particle size distribution.

[0077] In step S2, the mass transfer coefficient of the CO2 gas in the single reaction is k. L It is obtained from equation 4);

[0078]

[0079] In Equation 4), a is the gas-liquid specific surface area of ​​CO2 gas and Ca(OH)2 suspension; C is an empirical coefficient used to revise Equation 4) to better reflect actual production conditions, with a value of 1.0; D is the diffusion coefficient, with a value of 1.0 × 10⁻⁶. -9 m 2 / s; g is the acceleration due to gravity; h is the height of shell 1; This represents the centrifugal pressure gradient generated inside the inner rotor 2 under the action of a dual centrifugal force field provided by the counter-rotating outer rotor 3 and inner rotor 2; centrifugal pressure gradient The value gradually increases along the direction from the inner rotor 2 to the outer rotor 3, as obtained from equation 5);

[0080]

[0081] According to the shear rate γ of the internal region of the inner rotor 2 provided by Equation 2), due to the dual centrifugal force fields generated by the counter-rotation of the inner rotor 2 and the outer rotor 3, the shear rate inside the inner rotor 2 is significantly increased compared to the single centrifugal force field. According to Kolmogorov's theory, the high shear rate of the spherical inner rotor 2 can easily reach and exceed the critical shear rate, causing the CO2 gas bubbles to break into smaller sizes, increasing the specific surface area, thereby increasing the gas-liquid contact area and improving mass transfer efficiency. Furthermore, according to Henry's Law, the solubility of CO2 gas varies in different pressure zones, and the centrifugal pressure gradient in Equation 5... This provides an additional driving force for mass transfer, enabling CO2 gas to diffuse more rapidly from the bulk gas phase to the bulk liquid phase of the Ca(OH)2 suspension, thereby improving mass transfer efficiency. Furthermore, from equations 2), 5), and 4), it is known that the shear rate γ and the centrifugal pressure gradient... The larger the value, the greater the mass transfer coefficient of the CO2 gas in the single reaction, k. L The larger the value of ω1 and ω2, the stronger the gas-liquid mass transfer capability, which can be controlled by adjusting the values ​​of ω1 and ω2. Improving the gas-liquid mass transfer capability helps to increase the yield of nano-calcium carbonate particles generated in a single reaction, that is, to increase the number of nano-calcium carbonate seed crystals, thereby relatively reducing the amount of unreacted Ca(OH)2 suspension, allowing the seed crystals to grow appropriately in the aging tank 5, and ensuring that the nano-calcium carbonate product has a uniform particle size distribution.

[0082] In step S2, according to classical nucleation theory, the critical nucleation radius for the single reaction to generate nano-calcium carbonate particles is r. * It is obtained from equation 6);

[0083]

[0084] In equation 6), σ represents the interfacial tension of the Ca(OH)₂ suspension; V m C is the molar volume of the solute Ca(OH)₂. r is a constant in the ideal gas law; T is the thermodynamic temperature during the single reaction, T = 298 K, which is controlled by a cooling water jacket system; S is the supersaturation of CO2 gas, which is obtained from equation 7);

[0085]

[0086] In Equation 7), S0 is the supersaturation of CO2 gas under standard atmospheric pressure; ΔP is the change in centrifugal pressure, which is obtained from Equation 8.

[0087]

[0088] In Equation 8), K is an empirical coefficient used to modify Equation 8) to better reflect the actual changes in centrifugal pressure. K takes a value of 0.55-0.7 (specifically 0.6); Δr is the change in the spatial position of CO2 gas.

[0089] From equations 5) to 8), we know that That is, by adjusting the values ​​of ω1 and ω2, the critical nucleation radius r for the formation of nano-calcium carbonate particles in a single reaction can be stably controlled. * This avoids agglomeration and ensures uniform particle size distribution in nano-calcium carbonate products.

[0090] The raw materials, annual consumption, and related data used in the preparation of nano-calcium carbonate products in this embodiment are shown in Table 1.

[0091] Table 1. Raw materials, annual consumption, and related data

[0092]

[0093] The main equipment and key parameters used in the preparation of nano-calcium carbonate products in this embodiment are shown in Table 2.

[0094] Table 2 Main Equipment and Key Parameters

[0095]

[0096]

[0097] In this embodiment, during the preparation of nano-calcium carbonate products, the outer rotor 3 and the inner rotor 2 are controlled to rotate in opposite directions to provide a dual centrifugal force field. Specifically, the rotational speed n1 of the inner rotor 2 is controlled to be 2500 rpm, corresponding to an angular velocity ω1 of 261.8 rad / s; the rotational speed n2 of the outer rotor 3 is also controlled to be 2500 rpm, corresponding to an angular velocity ω2 of 261.8 rad / s. A Malvern Mastersizer 3000 laser particle size analyzer is used to detect the carbonized slurry after complete reaction, obtaining the particle size distribution as shown below. Figure 3 As shown by the solid line in the image.

[0098] Comparative example:

[0099] Unlike Example 1, nano-calcium carbonate was generated using an existing hypergravity carbonation method (see reference: Chen Jianfeng, Chu Guangwen, Zou Haikui. Hypergravity Reaction Engineering [M]. Chemical Industry Press: 202008. 328.). Specifically, a laser particle size analyzer of the model used in the example was used to analyze the carbonized slurry after complete reaction, and the particle size distribution was obtained as shown below. Figure 3 As shown by the dashed line in the image.

[0100] Depend on Figure 3 As can be seen from the embodiments ( Figure 3 The particle size distribution curve of the carbonized slurry obtained (shown by the solid line) has a sharper peak and a smaller span, with an average particle size D50 = 20 nm and a particle size span D90-D10 ≤ 20 nm; while the comparative example (… Figure 3 (As shown by the dashed line) The average particle size of the carbonized slurry obtained using the existing supergravity carbonation method is D50 = 25 nm, and the particle size range is D90-D10 ≤ 30 nm. This indicates that the present invention, by controlling the critical nucleation radius through dual centrifugal force fields in the embodiments, significantly reduces the formation of large crystal particles, resulting in a more uniform particle size distribution of the nano-calcium carbonate product. This verifies the significant advantage of the double-layer reciprocating reactor in controlling particle size uniformity.

[0101] Compared to the comparative example, in this embodiment, during the carbonization step S2, a dual centrifugal force field is provided by controlling the outer rotor 3 and the inner rotor 2 to rotate in opposite directions. Furthermore, the rotational speed n1 of the inner rotor 2 (i.e., the angular velocity of the inner rotor 2) and the rotational speed n2 of the outer rotor 3 (i.e., the angular velocity of the outer rotor 3) are both limited to 1000–3000 rpm (specifically 2500 rpm). This increases the suspension time of the Ca(OH)₂ suspension and enhances the mass transfer efficiency of CO₂ gas in the Ca(OH)₂ suspension, promoting the suspension of CO₂ gas and Ca(OH)₂ within the reactor. The yield of nano-calcium carbonate particles generated in a single reaction is 30%, significantly higher than the 8%–10% yield of nano-calcium carbonate seed crystals generated in a single reaction using the existing hypergravity carbonation method. This means that this method can increase the number of nano-calcium carbonate seed crystals, thereby relatively reducing the amount of unreacted Ca(OH)₂ suspension, allowing the seed crystals to grow appropriately in the aging tank 5, ensuring a uniform particle size distribution in the nano-calcium carbonate product. In this embodiment, by adjusting the angular velocities ω₁ of the inner rotor 2 and ω₂ of the outer rotor 3, the critical nucleation radius r for generating nano-calcium carbonate particles in a single reaction can be stably controlled. * This avoids agglomeration and ensures uniform particle size distribution in nano-calcium carbonate products.

[0102] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A double layer reciprocal-rotor reactor characterized in that, The shell (1) and the inner rotor (2), the outer rotor (3) and the spray pipe (4) arranged in the shell (1) are included; the liquid inlet and the exhaust port are arranged at the top of the shell (1); the liquid outlet and the air inlet are arranged at the bottom of the shell (1); the spray pipe (4) is arranged in the shell (1), the top end of the spray pipe (4) is connected with the top of the shell (1) and communicates with the liquid inlet, and the bottom end of the spray pipe (4) is connected with the bottom of the shell (1); a plurality of spray holes are arranged on the pipe wall of the spray pipe (4); the inner rotor (2) and the outer rotor (3) are coaxially and rotatably arranged outside the spray pipe (4) in sequence, and the rotating directions of the inner rotor (2) and the outer rotor (3) are opposite; a plurality of through holes are arranged on the inner rotor (2) and the outer rotor (3); the first liquid flow gap is arranged between the inner rotor (2) and the spray pipe (4), the second liquid flow gap is arranged between the inner rotor (2) and the outer rotor (3), and the third liquid flow gap is arranged between the outer rotor (3) and the shell (1); The inner rotor (2) includes a spherical inner rotor (2); the outer rotor (3) includes a spherical outer rotor (3).

2. The dual-layer, reciprocal-rotor reactor of claim 1, wherein, The first driver for driving the inner rotor (2) to rotate is further included; the first driver is arranged on the shell (1), and the driving end of the first driver is connected with the rotating shaft of the inner rotor (2); The second driver for driving the outer rotor (3) to rotate is further included; the second driver is arranged on the shell (1), and the driving end of the second driver is connected with the rotating shaft of the outer rotor (3).

3. A method for producing nano-sized calcium carbonate using the double-layered reciprocal-rotor reactor according to claim 2, characterized in that, It includes: Step S1, a pretreatment link; specifically, CaO is treated to obtain Ca(OH)2 suspension; Step S2, carbonization step; specifically, the Ca(OH)2 suspension flows from the liquid inlet at the top of the shell (1) into the first liquid flow gap, the second liquid flow gap and the third liquid flow gap in sequence through the spray pipe (4); the compressed and purified CO2 gas flows into the shell (1) from the gas inlet at the bottom of the shell (1), diffuses in the third liquid flow gap, the second liquid flow gap and the first liquid flow gap, and under the action of the double centrifugal force field provided by the counter-rotation of the outer rotor (3) and the inner rotor (2), the CO2 gas and the Ca(OH)2 suspension complete a single reaction to generate nano calcium carbonate particles, with a single yield of 20%~30%; the rotation speed of the inner rotor (2) n 1 and the rotation speed of the outer rotor (3) n 2 are both 1000~3000rpm; After the single reaction, the nano calcium carbonate particles generated by the single reaction and the unreacted Ca(OH)2 suspension flow into the aging tank (5) through the liquid outlet at the bottom of the shell (1); the CO2 gas is continuously introduced into the aging tank (5) until the unreacted Ca(OH)2 suspension and the CO2 gas in the aging tank (5) are completely reacted, and carbonized slurry is obtained; Step S3, a post-treatment link; specifically, the unreacted CO2 gas in the aging tank (5) and the shell (1) flows into the water washing tower (6) from the gas outlet at the top of the shell (1) for tail gas treatment; after the carbonized slurry is separated, wet material is obtained; After the wet material is washed and impurities are removed, the nano calcium carbonate powder is obtained after drying treatment; the nano calcium carbonate powder is separated by cyclone separation, and then packaged to obtain a finished product.

4. The method of claim 3, wherein the double-layered reciprocal-rotor reactor for preparing nano-sized calcium carbonate is characterized by, In the step S1, the pretreatment link includes grinding raw material CaO to obtain lime powder; the lime powder and water are mixed in a mass ratio of 1:3.5~1:4.5, and then a coarse lime milk slurry is generated by digestion reaction; the coarse lime milk slurry is screened to remove impurities to obtain fine lime milk slurry; a dispersing agent is added to the fine lime milk slurry, and after mixing, a Ca(OH)2 suspension with a concentration of 37~59g / L is obtained; The dispersant includes at least one of ammonium polyacrylate, polycarboxylic acid and sodium hexametaphosphate, and the amount is 0.3-0.5 wt% of the Ca(OH)2 suspension.

5. The method of claim 3, wherein the double-layered reciprocal-rotor reactor for preparing nano-sized calcium carbonate is characterized by, In the step S2, the flow rate of the Ca(OH)2 suspension sprayed through the spraying holes of the spraying pipe (4) is 2-6 m 3 / h; the flow rate of the CO2 gas flowing into the shell (1) through the bottom gas inlet of the shell (1) is 30-85 Nm 3 / h; the flow rate of the CO2 gas flowing into the aging tank (5) is 35-45 Nm 3 / h; the flow rate of the nano calcium carbonate particles generated in a single reaction mixed with the unreacted Ca(OH)2 suspension flowing into the aging tank (5) is 3-4 m 3 / h.

6. The method of claim 3, wherein the double-layered reciprocal-rotor reactor for preparing nano-sized calcium carbonate is characterized by, In said step S2, the suspension time of the Ca(OH)2suspension in the single reaction is t obtained from formula 1). Formula 1); In formula 1), H is the radial maximum displacement of the Ca(OH)2particles inside the inner rotor (2), which is obtained using formula 2); v is the settling velocity of the Ca(OH)2particles, which is obtained using formula 3); The formula 2) is as follows: Formula 2); In formula 2), ω 1 is the angular velocity of the inner rotor (2), ω 1 = 2π n 1; ω 2 is the angular velocity of the outer rotor (3), ω 2 = 2π n 2; R is the distance of the Ca(OH)2particles located in the inner region of the inner rotor (2) to the center of the spray pipe (4); γ is the shear rate of the inner region of the inner rotor (2). The formula 3) is as follows: Formula 3); In formula 3), R is the radius of the Ca(OH)2particles; ρ p p is the density of the nano calcium carbonate particles; ρ f p is the density of the Ca(OH)2suspension; µ p is the dynamic viscosity of the Ca(OH)2suspension.

7. The method of claim 6, wherein the double-layered reciprocal-rotor reactor for preparing nano-sized calcium carbonate is characterized by, In said step S2, the mass transfer coefficient of said CO2 gas in said single reaction is k L which is obtained from formula 4) Formula 4); in formula 4), is the gas-liquid specific surface area of CO2 gas and Ca(OH)2 suspension; C is an empirical coefficient, C and takes the value of 1.0; D is the diffusion coefficient, D and takes the value of 1.0 x 10 -9 m 2 / s; g is the acceleration of gravity; is the height of the housing (1); represents the centrifugal pressure gradient generated inside the inner rotor (2) under the action of the double centrifugal force field provided by the counter-rotation of the outer rotor (3) and the inner rotor (2); the centrifugal pressure gradient gradually increases in the direction of the inner rotor (2) to the outer rotor (3), which is obtained from formula 5); Formula 5).

8. The method of claim 7, wherein the double-layered reciprocal-rotor reactor for preparing nano-sized calcium carbonate is characterized by, In the step S2, according to the classical nucleation theory, the critical nucleation radius of the single reaction to generate the nano calcium carbonate particles is which is obtained from formula 6). Formula 6); in formula 6), σ the interfacial tension of the Ca(OH)2 suspension; V m the molar volume of the solute Ca(OH)2; C r the constant in the ideal gas state equation; T the thermodynamic temperature at the single reaction; S the supersaturation of the CO2 gas, which is obtained from formula 7) Formula 7); In formula 7), S 0 is the degree of super-saturation of CO2 gas at standard atmospheric pressure; is the centrifugal pressure change amount, which is obtained from formula 8); Formula 8); In formula 8), K is an empirical coefficient, K and takes a value of 0.55-0.7; is the amount of change in the spatial position of the CO2 gas.

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