Process Characteristics of Synthesis Calcium Carbonate Using

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Process Characteristics of Synthesis Calcium Carbonate using Desulfurization Gypsum in an Integrated Equipment of Reaction and Separation Siqi Zhao, Chunqing Li, Liping Ma, Dongdong Wang, Jie Yang, Yuhui Peng, and Lichun Wang Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 20 Oct 2017 Downloaded from http://pubs.acs.org on October 22, 2017

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Industrial & Engineering Chemistry Research

Process Characteristics of Synthesis Calcium Carbonate using Desulfurization Gypsum in an Integrated Equipment of Reaction and Separation Siqi Zhao, Chunqing Li, Liping Ma*, Dongdong Wang, Jie Yang, Yuhui Peng, Lichun Wang Faculty of Environmental Science and Engineering, Kunming University of Science and Technology, Kunming, Yunnan 650093, China Abstract: Desulfurization gypsum is a byproduct in the processing of limestone-gypsum desulfurization. Preparation of desulfurization gypsum into CaCO3 and (NH4)2SO4 is a means of recycling. This paper presents an integrated equipment of reaction and separation and illustrates the desulfurization gypsum operation efficiency. Different additives and stirring programs were experimented to control the crystal formation and explore the nucleation growth. Besides, the separation mechanism and process characteristics of the integrated equipment have been assigned. What’s more, the flow trajectories and velocity contour were stimulated to study the separation characteristics and the movement and distribution in the equipment was researched by using CFD (Computational Fluid Dynamics) approach. It is found that higher concentration of reactants brings about higher separation efficiency. Moreover the moisture content of solid products is low and solid-liquid separation efficiency decreases when the liquid velocity increases. The best results are obtained: chemical reaction conversion rate and separation efficiency are 83.14% and 81.83%, respectively. Keywords: calcium carbonate; integrated equipment; crystal formation; CFD simulation; separation process

Introduction 1

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Desulfurization gypsum is a sort of industrial byproduct gypsum produced in desulfurization of sulfurous gas. With the rapid development of economy and industry, large quantities of desulfurization gypsum have been generated in recent years, of which the utilization has become an urgent problem at the same time. Recent experiments focusing on the reuse of desulfurization gypsum have been developed, such as the preparation of sulfuric acid, cement [1], bricks boards other building material [2, 3], cement retarder [4], soil amendment [5], calcium carbonate, ammonium sulfate and so on [6, 7]. Because of its high content of calcium and sulfur, desulfurization gypsum can be used as the production of high value-added products: ammonium sulfate and ammonium carbonate. Ammonium sulfate can be used as a sort of fertilizer in agriculture and raw material in industry [8, 9] and calcium carbonate [10-12] can be realized as a kind of sorbent in desulfurization process. These processes are not only the need of environmental protection and resource recovery, but also can bring huge economic and social benefits. The researches of integration system are based on combination of reaction system and separation system. The reaction system [13] and separation system [14] are studied separately as two isolated unit in the traditional chemical process design. The problem is chiefly concerned that the whole process may not perform best in the optimal conditions after integration based on the two systems. Some negative issues [15] might be exposed in the disjoint of reaction and separation process during the chemical process design, such as low product quality, more energy consumption, serious waste, lower profit margins. Therefore, the chemical engineering optimal integration of reaction and separation systems should be design as soon as possible. The purpose of this study lies in the design of a new integrated equipment of reaction and separation, which can achieve full reaction in both solid and liquid phases. What’s more, separating the product synchronously under normal temperature and pressure can shorter reaction and separation time and smaller volume make it easily to realize industrial. The process characteristics during preparation of calcium carbonate in this integrated equipment was investigated. The nucleation growth process of solid-phase calcium carbonate is studied to explore the chemical reaction characteristics of this equipment. The CFD approach is implemented to emulate the movement and the distribution of solid-liquid two-phase flow, and explored the separation characteristics as well as the efficiency of this integrated equipment. 2


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Experiment sections 2.1 Raw materials. The desulfurization gypsum is obtained from Kunming Iron and Steel Group Co., LTD, which is the by-product of sintering flue gas obtained by limestone-gypsum desulfurization process. 2.2 Experiment facilities Calcium carbonate generated in different reaction time (30min, 60min, 120min respectively.) are analyzed by X-ray Diffraction (D/Max 2200 XRD), Particle Size Analyzer(Rise-2006), Scanning Electron Microscope and Energy Dispersive Spectrometer (SSX-550 SEM-EDS). The operating parameters of XRD used a Cu radiation target source, the λ was 0.15406nm, tube voltage is 40KV, pipe flow is 200mA and scanning speed is 10°/min at 2θ within the range of 1070°. The reaction between desulfurization gypsum and ammonium carbonate is performed in the equipment which can realize the organically combination of reaction process and the separation process in one reactor, effectively avoiding the waste of resources. The equipment of reaction and separation is developed and researched by our research group which the schematic diagram is shown in Figure 1. Specific experimental parameters are shown in table 1. Table 1. Experimental parameters Experimental Number 1 2 3 4 5 6 7 8 9

nA/mol

CB/mol·L-1

VB/L

0.01 0.01 0.01 0.05 0.05 0.05 0.1 0.1 0.1

0.1 0.1 0.1 0.55 0.55 0.55 1 1 1

0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 3


v1/ mL·min-1 4 5 6 4 5 6 4 5 6

v2/ mL·min-1 6.6 7.8 8.2 6.6 7.8 8.2 6.6 7.8 8.2


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Annotate: nA = amount of substance of desulfurization gypsum CB = the concentration of ammonium carbonate VB = the volume of ammonium carbonate v1 = inlet velocity of ammonium carbonate solution v2 = exit velocity of the liquid phase reaction product

Figure 1. Integrated equipment of reaction and separation (1-Feeding Port, 2-Reaction Zone, 3-Stirring

Device, 4-Shutter, 5-Separation Zone, 6-Drain Pipes, 7-Discharge Port).

The nucleation growth of the CaCO3 solid phase is studied with instrumental analysis to investigate the characteristics of the chemical reaction process. The separation characteristics of the integrated equipment are explored by using computational fluid dynamic (CFD) approach. The conversion rate can be defined as E(a): X

100%

(Ea)

In which, Xout and Xin are the mass quality of outlet and inlet, respectively. The separation efficiency can be defined as E(b): C

100%

(Eb)

4


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In which, Ctot and Crem are the total and remaining mass quality in separation zone, respectively.

2.3 Experiment method. 2.3.1 Characterization of the integrated equipment The integrated equipment of reaction and separation is used for CaCO3 preparation using desulfurization gypsum. The main steps can be concluded as: a. The (NH4)2CO3 solution and the desulfurized gypsum (CaSO4·2H2O) are thoroughly mixed and fed from the feeding port (section 1) into the reaction zone (section 2). b. Adjust the stirring device (section 3) with a proper stirring rate and stirring time to ensure adequate reaction and further to control the product of CaCO3 crystal and particle size. c. Control the stirring speed (much higher) to insure the product can pass through the shutter (section 4) or across the hole, which is on the bezel to transfer to the separation zone. d. The liquid product (ammonium sulfate) discharged from drain pipe (section 6), which can be used as fertilizer after evaporation and crystallization. The solid product (calcium carbonate) can be directly collected from the discharge port (section 7) and used as sorbent in the process of desulfurization.

2.3.2 Crystal form control of CaCO3 In order to explore the characteristics of nucleation growth and simulate the distribution of the solid-liquid two-phase flow, integrated equipment of reaction and separation and CFD calculation are used. The main reaction through this system can be concluded as: CaSO4·2H2O(s) + (NH4)2CO3(l) = CaCO3(s) + (NH4)2SO4(l) + 2H2O(l)

(R1)

The nucleation growth experiments include three parallel tests according to different additives. Take appropriate amount of ammonium carbonate dissolved in 100ml deionized water,

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adding the desulfurization gypsum. Then, three kinds of crystal control agents are added into it: A. Trisodium citrate dihydrate (the molar ratio of ammonium carbonate to trisodium citrate is 4/1). B. Sulfuric acid (molar ratio of ammonium carbonate to sulfuric acid is 1/1). C. Cetyl ammonium bromide (molar ratio of ammonium carbonate to hexadecylammonium bromide is 4/1). The stirring procedure is controlled as follows, respectively: (I) Stirring at 350 rpm, always; (II) To begin with, stirred at 250 rpm for 40min. Then, stirring at 350 rpm for 40 min. Finally, stirred at 450 rpm for 40 min; (III) The experiment started at 450 rpm for 40 min. After that, stirred at 350 rpm for 40 min, and finally stirred at 250 rpm for 40 min.

Results and discussions 3.1 CFD simulation Computational Fluid Dynamics (CFD) is a discrete numerical method to simulate fluid dynamic equations with computer [16], which applied to many areas of chemical reaction engineering [17, 18]. The numerical simulation of fluid flow with CFD has made considerable progress [19-21] in a stirred reactor. Brucato et al [22] simulated three-dimensional distribution of solid particles in the agitation tank. Micale et al [23-25] studied the dispersing of low concentration solid particles in a stirred tank with single and multi-pitch propeller. The results of these studies have proved that the CFD was more successful for the simulations of stirred reactor. In this paper, the driving force of the separation zone was produced by mechanical stirring device, which ensured the feasibility of using CFD to study the separation characteristics of the device.

3.1.1 Governing equations Standard k-ε turbulence model has been successfully applied to simulate flow field of stirred tank with common application and undergo testing [26-28]. Thus, it proved to be feasible to study the characteristics in separation zone by standard k-ε turbulence model. In this model, ε

6


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represented the turbulent dissipation rate is defined by the Eq. (1):

µ  ∂u ′  ε =  t  ρ  ∂xk 

2

(1)

The turbulent viscosity µt can be expressed according Eq. (2):

µ = ρCµ

k2

(2)

ε

The transport equations corresponding the two basic unknown parameters k and ε taking into account the standard k -ε turbulence model can be calculated by the following expressions:

∂(ρk ) ∂kui ∂ + = ∂t ∂xi ∂x j

 µt  µ + σk 

 ∂k    + Gk + Gb − ρε − YM + S k  ∂x j 

(3)

∂(ρε ) ∂εui ∂ + = ∂t ∂xi ∂x j

 µt  µ + σε 

 ∂ε  ε ε2  ( ) ρ + C G + C G − C + Sε  1ε k 3ε b 2ε k k  ∂x j 

(4)

 ∂ui ∂u j  ∂ui  +  ∂x  ∂x ∂ x j i   j

Among then, Gk = µt 

(5)

3.1.2 Mesh generation Mesh generation can be described as: The separation zone is divided into paddle region and paddle outside region. Rotating coordinate system is adopted for paddle area, where the fluid rotated with the blades. Because of its complicated flow distribution, geometry and physical phenomena, tetrahedral mesh generation and refinement process technology were employed. Whereas, for the paddle outside region, the stationary coordinate system and the regular hexahedral mesh generation were used. The test results of mesh quality showed that the negative volume problems had not been detected in these two structures, and the main evaluation criteria of mesh quality: size twist rate and angle distortion rate were both less than 0.6, indicating a good quality of grid division. It must be mentioned that, CFD stimulation in this section only focus on the separation process rather than the physical process of chemical reaction. What’s more, some assumptions have been put forward. Aiming at providing the references to reveal the mechanism of reaction and scale up design of reactor. Fig. 2 is the mesh generation of the interface between the cylinder part and cone part in separation zone.

3.1.3 Boundary Conditions

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(1) Inlet boundary: steady, constant speed along the axial is the conditions of the import speed. The particle volume concentration Cv is assumed equal to the concentration of the solids conveying and evenly distributed at the entrance. (2) Outlet boundary: free outflow boundary. (3) Wall boundary: stationary solid wall is defined as no-slip wall boundary in the device and the standard wall function [29] was used near the wall. (4) Moving Boundary: The stirring paddle is defined as a moving boundary, which moved in the same motion velocity with the fluid region around. However, relative to the inner fluid is stationary.

Figure 2. Mesh generation of part of the separation zone.

3.2 Structural characterization 3.2.1 Analysis of SEM and EDS The result of Scanning Electron Microscope and Energy Dispersive Spectrometer is shown in Figure 3. Significant changes are observed in morphology of solid phase product at the reaction time of 30min, 60min and 120min. The process of nucleation growth of calcium carbonate crystal

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particles is vividly described by SEM images from the superficial morphology perspective. The EDS result reflected from the perspective of element composition illustrated the process that calcium sulfate gradually transformed into calcium carbonate. It means that the sulfur element within solid phase is gradually replaced by carbon element with the reaction proceeds.

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Figure 3. SEM-EDS patterns of solid products (Reaction time of 30min, 60min and 120min, respectively).

3.2.2 Particle size analysis The products at different reaction time shared a similar particle size distribution as shown in Fig 4, which all in the range of 10-40um. The cumulative distribution curves are gradually tend to be 100%, indicated the uniformity of the particles size gradually getting better as the reaction proceeds. This implied a relatively slow increase in stability of the particles during the nucleation growth process of calcium carbonate crystal. The explanation of different distribution in Fig.4 can be concluded that: With the increase of particle size, the distributions firstly increase and arrive at the maximum when the particle size is near 16um. Then, the distributions begin to decrease with the particle size increase. The product whose size below 20um, reached at the cumulative percentages for 80%, 78%, 72%, corresponding to different reaction time at 30min, 60min and 120min, respectively. These data demonstrated the transformation of the small particles into larger ones, which is consistent with the SEM results.

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Figure 4. Particle size Distribution (At reaction time of (a) 30min, (b) 60min, (c) 120min, respectively).

3.2.3 X-ray diffraction 11



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The solid products at three kinds of reaction time are shown in Figure 5. Adjusting the reaction time to 30min, the diffraction peak of CaCO3 is the weakest, suggesting a least amount of calcium carbonate which presents in the forms of calcite (C), vaterite (V) and aragonite (A). After 60min of reaction, the diffraction peaks of calcium carbonate appeared stronger, indicating the coexistence of calcite (C) and vaterite (V). With the increasing content of calcium carbonate, the stability is improved accordingly. The strongest and widest diffraction peaks are found after 120min of reaction, and merely in a form of calcite phase. Staggered arrangement of Ca2+ and CO32- constituted the calcite whisker, which confirms to be the most thermodynamically stable crystal surface. Formation can be preliminarily summarized as the coexistence of amorphous calcite, vaterite and aragonite gradually transformed into the stable and uniform calcite. According to the thermodynamic minimum energy principle, the growth towards calcite requires the lowest energy for nucleus forming which can induces the most stable crystal. This suggests that the calcium carbonate crystals tend to oriented grow along with a single crystal plane [30].

Figure 5. XRD patterns of the solid phase products at different times.

The chemical reaction characteristics can be summarized: With the proceeding of chemical reaction, calcium carbonate crystals gradually grow into nucleation from the small particle, the uniformity and stability of the particle is enhanced. During the process, calcium sulfate is gradually is transferred by calcium carbonate. Meanwhile, the coexistence of calcite, vaterite and 12


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aragonite are converted to stable single calcite. With the consideration of elements composition and crystal structure, calcium carbonate is the mainly solid phase product that has been tested after 120min of reaction.

3.3 Analysis of crystal formation Different physicochemical properties of different additives, which resulting the differences in additives on CaCO3 whisker growth process of the mechanism and the results are inconsistent. The additives used in this research are organic acid salts (trisodium citrate dihydrate), inorganic acid (sulfuric acid), quaternary ammonium salt surfactant (cetyl ammonium bromide).As shown in fig. 6, the diffraction peaks of calcite (C) are found in the products obtained by adding trisodium citrate dihydrate and cetyl ammonium bromide. The diffraction peaks of other crystals are not found. The XRD patterns of CaCO3 obtained by adding sulfuric acid could see clearly calcite (C), vaterite (V) and aragonite (A) diffraction peaks, that is, when using sulfuric acid as an additive, the resulting of CaCO3 crystals are three crystal form coexisting bodies.

Figure 6. XRD partterns of CaCO3 crystal formation under different additives ((a) cetyl ammonium bromide, (b) sulfuric acid, (c) trisodium citrate dihydrate, respectively).

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Furthermore, experimental process control has a great impact on the nucleation growth of CaCO3 crystals. Stirring procedure can not only promote the full contact and reaction of desulfurized gypsum and ammonium carbonate, but also control the crystal form of the product CaCO3 [31]. When trisodium citrate dihydrate is used as an additive, the effect of the stirring procedure on CaCO3 nucleation growth is less than that of the effect of additives. As shown in Figure 7(a), the main trends are basically the same, but the diffraction peaks of the stirring procedure control conditions (I) and (III) are significantly stronger than those of (II). This phenomenon can be excluded that, with the stirring rate increase, the molecular movement rate is accelerated, the energy consumption increases, to a certain extent, inhibition of calcium carbonate to calcite growth. The effect of trisodium citrate dihydrate on CaCO3 crystal is closely related to the interaction between trisodium citrate dihydrate and Ca2 +. The system has two competing reactions [32]: (1) the reaction between Ca2+ and CO32-. (2) The reaction between Ca2+ and carboxylic acid which in trisodium citrate dihydrate. What’s more, there is a specific interfacial molecular recognition between the negatively charged carboxylate groups and some crystalline surfaces of CaCO3 crystals, which provides a basis for the crystal location of CaCO3 crystals, making orientation growth prone. As shown in Figure 7(b), XRD patterns obtained by the three schemes have many impure peaks. The orders of diffraction intensity in the spectrum are: (III) > (II)> (I). In the corresponding experimental scheme, the optimal experimental scheme is (III). Fast stirring at 450 rpm for 40 min before the start of the experiment enhances the solid-liquid two-phase contact, mixing and mass transfer processes to enhance the diffusion rate and chemical reaction rate. The final 40 min of the

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experiment is the growth of nucleation period of CaCO3 whisker, which could effectively promote the formation of intact crystal form. The three groups show the dominant peak at 29°, which proves that the three products all contain large amounts of calcite-type of CaCO3. In the case of cetyl ammonium bromide as an additive, the rate of agitation is beneficial to the calcite growth during the experiment, the obvious diffraction peaks are calcite diffraction peaks (see Figure 7(c)). Cetyl ammonium bromide is a typical surfactant, and has good coordination with cationic, nonionic and amphoteric surfactants. When the surfactant concentration in the system is relatively high, the cetyl ammonium bromide micelles will adhere to the macromolecular chain structure formed by the micellar rupture due to the electrostatic effect, which will form the composite micelles of the chain structure [33]. The basic particles of CaCO3 crystal will gradually nucleate and grow under the action of composite micelles. Since the hydrophobic of the cetyl ammonium bromide composite micelles faces outward, the surface of the base particles exhibits hydrophobicity and the control of the calcium carbonate crystals is greatly enhanced due to the hydrophobic synergistic effect of the final formation of the spherical aggregates structure [34].

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Figure 7. XRD patterns of CaCO3 crystals formation under different stirring rate ((a) trisodium citrate 16


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dehydrate, (b) sulfate acid, (c) cetyl ammonium bromide, respectively).

3.4 Analysis of separation process 3.4.1 Analysis of conversion rate and separation efficiency The reaction between desulfurization gypsum and ammonium carbonate solution belongs to unreacted shrinking core model and the control step appertains to solid membrane diffusion control. Increasing the concentration of reactants can make the diffusion reduce, which results in the reaction conversion decrease. Meanwhile the reaction conversion forms a declining trend with the increasing of the import and export of velocity of liquid phase (Fig 8). Higher concentration of reactants brings about higher separation efficiency of solid-liquid products. Moreover the moisture content of solid products is low and solid-liquid separation efficiency decreases when the import and export liquid velocity increases (Fig 8). Considering the reaction conversion and the solidliquid separation efficiency, the best results were obtained: the chemical reaction conversion rate is 83.14% and the solid-liquid phase separation efficiency is 81.83%. The purpose of this process is to explore the process of the CaCO3 nucleation growth and the chemical reaction characteristics of the integrated equipment. In other words, the abstract chemical reaction equation is embodied as the nucleation growth process of calcium carbonate, which is then abstracted into chemical reaction properties.

Figure 8. Chemical reaction conversion rate and solid-liquid separation efficiency of experiment groups. 17



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3.4.2 Analysis of flow trajectories and velocity contour It is clearly that Z = 0.03m is the most representative interface between the cylindrical portion and the conical portion of the separation zone (equipment designed), it is essential to select this interface in order to explore the separation characteristics of solid-liquid two-phase flow. Fig. 9 illustrates the particle flow trajectories. As shown in Figure 9, the solid particles are gradually flowing outward via the rotation of the impeller. Because the shear stress is greater than gravity, the particles sank along the cone. The stress distribution of liquid phase was in contrast with the solid phase and the liquid can easily flow out of the pipe which realized the separation of solid phase and liquid phase. As shown above, Fig.9 shows a better separation efficiency which coincides with the calculation of relative high separation efficiency of the solid/liquid phase. The liquid flow insulation region is formed just below the stirrer due to the existence of inverted vertebral flow type [35]. The shear stress of fluid flow is relatively small in this region which resulting in a comparatively low volume fraction of the solid phase. The bottom surface of the stirred tank is at right angles to the wall surface and was the steering point of the loop in the entire tank. The phenomenon of fluidity obstructed and relatively low solid volume fraction [36] is easy to cause. The movement and distribution in liquid phase and solid phase are affected by the drag force, which is influenced by many factors, such as: Reynolds number, turbulent motion, fluid compressibility, concentration of the particles, the shape of the particles, the presence of the wall, the temperature difference between fluid and particles and so on.

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Figure 9. Particle flow trajectories (m/s) at Z = 0.03m.

Through its own rotating, the blade transfers mechanical energy to solid-liquid two-phase flow, forcing the solid-liquid two-phase flow nearby the region to produce highly turbulent motion and promoting the solid-liquid phase from the separation region to circulate along certain pathways. The contour of velocity magnitude at the corresponding plane (Z = 0.03m) is shown in Figure 10. The black line indicates a decrease of speed which from moving area to static area. Thus, it makes the separation efficiency decrease in solid-liquid phase, especially in the interface of the solid and liquid phases. Overall, velocity of the moving area is significantly greater than that of the static area, which not only corresponded to the reality, but also consisted with the zoning concept of the meshing geometry model. The velocity distribution of moving area indicated an increasing trend of speed from the center to the outward. The phenomenon above can be ascribed to the rotation of the impeller that compelled the solid-liquid phase to produce shear stress and the shear stress increased with the radius enlarged.

Figure 10. Velocity contour (m/s) at Z = 0.03m.

The stress distribution (see figure 11) along the X-axis direction is analyzed. With the rotation of stirring blades, the pressure of moving area is obviously smaller than the static area. This result can be explained in a fluid system by Bernoulli's principle: the faster flow rate and the smaller pressure. In this system, the speed of moving area is much greater than the static area, so that the pressure of the moving area is significantly smaller than the static area. According to the

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theory, the movement of a spherical particle in a flow field which under the pressure gradient▽p, the pressure gradient can be defined as:

4 Fp = − πrs3∇p 3

(5)

The pressure gradient gets larger when the pressure gradient increases or particles far away from the center position, which contributes to the separation of the solid-liquid phase.

Figure 11. Pressure profile along the x-axis direction at Z = 0.03m.

Conclusion (1) Conversion rate and separation efficiency. With application of the integrated equipment, adequate reactions and the separation of the solid-liquid phase product (calcium carbonate and ammonium sulfate) can be realized by only one equipment. Meanwhile the conversion rate of desulfurization gypsum reached at 70%-80% and the separation efficiency of solid-liquid phase product reached more than 85%. (2) Chemical characteristics. The chemical characteristics in this integrated equipment can be concluded that: the sulfur in solid phase was replaced by carbon gradually in the process of synthesizing; calcium carbonate crystal gradually grew nuclear from the small particles and amorphous calcium carbonate including calcite, vaterite and aragonite, gradually transformed into stable single calcite. (3) Separation characteristics. The separation characteristics in this integrated equipment

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were obtained by CFD technology. (a) Solid phase. The particles move outwardly with the rotation, since the shear stress is greater than the gravity to ensure the particles sank along with the cone. (b) Liquid phase. The gravity was smaller than the shear stress which leads the liquid phase discharged along the pipe. Thus, it realized the separation of the solid and liquid phases during the reaction.

Author information Corresponding Author *: E-mail: [email protected]. Tel: 86- 871-65920508. Fax: 86-871-65920508.

Notes

The authors declare no competing financial interest. Acknowledgments

Financial support for this project was provided by National Natural Science Foundation of China (No.21666016), which is greatly acknowledged.

Nomenclature nA = amount of substance of desulfurization gypsum [mol] CB = the concentration of ammonium carbonate [mol·l-1] VB = the volume of ammonium carbonate [l] v1 = inlet velocity of ammonium carbonate solution [ml·min-1] v2 = exit velocity of the liquid phase reaction product [ml·min-1] µ= fluid viscosity [Pa·s] ρ = fluid density [kg·m-3] Gb = the turbulent kinetic energy k produce items caused by buoyancy, for an incompressible fluid, Gb = 0, YM = Pulsation expansion contribution in the process of the compressed fluid turbulence, for an incompressible fluid, YM = 0,

C1ε 、 C2ε 、 C3ε = Empirical constants, value are 1.44, 1.92 and 0.09, respectively.

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σ k 、 σ ε = Prandtl number corresponding to the turbulent kinetic energy k and dissipation rate ε, respectively.

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Table of Contents graphic

An integrated equipment of reaction and separation has been put forward and the separation characteristics of its separation zone have been deeply explored. What’s more, particle flow trajectories (Z = 0.03m) and velocity contour are stimulated at the same time.

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Process Characteristics of Synthesis Calcium Carbonate Using

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