Multiscale Calculation on Perforated Sheet Structured Packing To

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Multi-scale calculation on perforated sheet structured packing to predict the liquid distribution based on CFD simulation Botan Liu, Yantong Wen, Chunjiang Liu, Bo Sun, and Xigang Yuan Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b05003 • Publication Date (Web): 24 Jun 2016 Downloaded from http://pubs.acs.org on June 26, 2016

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Industrial & Engineering Chemistry Research

Multi-scale calculation on perforated sheet structured packing to predict the liquid distribution based on CFD simulation

Botan Liua*, Yantong Wenb , Chunjiang Liub, Bo Sunc, Xigang Yuanb a

Tianjin University of Science and Technology College of Chemical Engineering and Materials Science,

Tianjin 300457, China b

State Key Laboratory of Chemical Engineering and School of Chemical Engineering and Technology,

Tianjin University, Tianjin 300072, China c

Shandong Yanhai Construction Resourcess Co., Ltd, Yantai, Shandong 264006, China

Author Information Corresponding Author *[email protected] (Botan Liu)

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ACS Paragon Plus Environment


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Abstract This paper is the subsequent work of our previous study in which the liquid distribution on the imperforate structured packing sheet was predicted. In this study, a novel multi-scale model for describing the liquid distribution on the perforated structured packing sheet is proposed. The large scale model is a mechanistic model, using liquid split coefficients as model parameters derived from a 3D volume of fluid (VOF) simulation within the representative units. The model can theoretically adapt to vary working conditions; and the liquid distribution of all the packing layer/tower can be given. Five types of flow patterns are discussed according to the simulation results. The influence of gas flow and openings on liquid flow are also discussed. This proposed model can supply a deep insight into the mechanism of the liquid distribution inside the packing tower and help understanding the details of inter-phase behavior which are hardly available by experiment.

Keywords: perforated structured packing, multi-scale model, liquid distribution model, stream split fraction coefficients, CFD

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1. Introduction Structured packings is commonly used in distillation, gas absorption and CO2 capture processes due to its high efficiency for gas-liquid separation. Especially, post combustion method to capture CO2 via chemical absorption by means of reactive amine solutions has been identified to be viable and commercial potential, and structured packing is commonly regarded as the necessary internal fillings of the columns. Liquid distribution on packing surface can be assessed in terms of mass-transfer coefficients and operating performance of packed column1,2. Researchers had developed several empirical correlations predicting the holdup and mass transfer area for structured packings, Billet3-5, SRP6,7 and Delft8,9 models for example. Models proposed by Olujic8, Chuang10, and Adisorn11,12 devide the packings into numbers of nodes or units to depict the liquid distribution behavior, which are cited as mechanistic models. However, the model parameters need to be regressed by the experimental data; and once the parameters were determined, they were used for the whole flow domian of the sturcture packing, this obvously neglected the influence of local flow rate of gas and liquid phase on the packing structure liquid flow distribution. The rapid development of computer has promoted the growth of Computational Fluid Dynamics (CFD) technology, which has become a useful tool for the investigation of flow patterns in complex system such as structured packing columns; but it is known that CFD can only be applied to calculate the flow field in a fairly small sections of the packing, which is constrained by the computing power13-19. Sebastia-Saez et al. utilized CFD to simulate the flow of liquid film as well as mass transfer in the elements of structure packing three dimensionally20-23, such simulation 3



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is of micro-scale which may supply useful information to the possible larger scale simulation. Recently, multi-scale approaches combing CFD method and macro-scale calculation have been developed19,24, compromising the computation burden and high accuracy. On the author’s opionion, this kind of models take both the local details and entire performance into account, and may be a good choice for predicting liquid flow distribution. Predicting the liquid flow distribution in the structured packing is the key problem, realizing that the mass transfer efficiency of the column depends on it to a great extent. CFD simulation by VOF model concerning liquid film behavior on the structured packing sheet is helpful to understand it 25-29. There are also some experiments measuring the liquid holdup and the effective wetting area

30-35

. In a word, predicting the liquid distribution is quite important and necessary;

and this issue has attracted large amount of research work. In our previous study, liquid distribution in the packed column has been successfully predicted by multi-scale calculation method24. The packing investigated is the common 350X structured packing without openings on the surface. However, the structure packing used in commercial column has actually openings on it, but until now, less research has been done on the gas-liquid two phase flow on the perforated sheet structured packing by multi-scale method. Therefore, in the present study, the two-phase flow in the structured packing with openings on the surface is simulated in small scale; and then a more sophasicated mechanistic model to depict the particular flow is developed, and the model parameters can also be obtained from the small scale calculation results. On the basis of these, the liquid distribution behavior on perforated structured packings can therefore be easily displayed.

2. Multi-scale calculation strategy 4


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2.1. Small-scale calculation

(a) Interior unit

(b) Side wall unit

Figure 1 The representative units used in calculation: (a) Interior unit; (b) Side wall unit

Table 1 Geometrical parameters of 250Y perforated packing

Crimp height,

Channel base,

Channel side,

Specific area,

Opening area ratio,

Corrugation angle,

hc (mm)

B (mm)

S (mm)

ap (m2/m3)

εr (%)

θa (°)

11.9

24

17

250

10

45

According to the method mentioned in reference

24

, physical models of two types of

representative units cited as the interior unit and the side wall unit are illustrated in Fig. 1; they are applied to simulate the gas-liquid flow in the interior part and the region close to the side wall in the structured packings, respectively. The packing applied in this paper is Mellapak 250Y corrugated sheet structured packing and the structure parameters are list in Table 1. As Figure 1 (a) displays, four identical interior units of two packing sheet composed the flow domain. For the side wall units shown in Figure 1 (b), the flow domain is composed by a interior unit and two side wall units. Since liquid can flow from packing surface of one side to the other through the openings, regions on the back of the packing as well as the inner parts must be selected as the simulation 5



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domain, where liquid and gas phase contacts count-current. There are two liquid inlets in interior units model, and the inlets cling to the two channels in the top. For the side wall model, only one liquid inlet exists in the top. The width of the liquid inlet is 1 mm, and a range of liquid spray density from 20-100 m3/(m2.h) is applied. The unstructured grid generation technology is applied to deal with the complex geometrical structure. The grid number of the models depict in Figure 1 (a) and (b) are 128,000 and 63,000, respectively. The time-step size of the simulation is 10-5s. This grid size and time step is consistent with the previous work in which the structure packing without openings was simulated.24 Water-air is selected as the simulation system with constant fluid properties (ρ, µ, σ) at 20℃, and the contact angle of water and stainless steel is 59o 36.

2.2. Mathematical model and boundary conditions The VOF (Volume of Fluid) method and commercial CFD code Fluent are chosen to simulate the unsteady gas-liquid two-phase counter flow in the representative unit. The model has been applied in many open literatures to simulate multiphase flow, specially, the model of this work is the same as that of our previous paper 24. Then, for concise this part of comment is omitted.

2.3. Macro-scale calculation The newly established unit network model is the supplement of the model for common structured packings24, and this model can be applied to predict of the liquid distribution on the perforated structured packing. The unit network model is based on the following assumptions: 6


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(1) The liquid distribution in a unit can be divided into four parts, namely, flowing along the channel (f), transverse flow (h), flowing downwards across the node (g), and flowing to the other side of the packing surface through openings (p). The relationship is f+h+g+p=1. (2) The liquid flowing downward across the node is evenly split into two parts, and then flowing along the left-inclining (PL) and right-inclining (PR) channels in the lower unit. The relationship is PL=PR=0.5. (3) Liquid at the column side is partly reflected to the center of the column (r). The liquid distribution law in the interior and side wall unit are illustrated in Figure 2, in which the liquid flowing to the other side of the packing surface is defined in dashed line. In this paper, L and R are defined as the liquid flowing along the left-inclining and right-inclining channels, respectively. G is defined as the liquid flowing vertical downward. For the side wall unit, LWL and LWR represent the liquid flowing close to the left and right column wall. In interior unit model, there are three streams on the two opposite sheets flowing out the original unit (A), namely, liquid flowing along the left-inclining channel (L A (1)), right-inclining channel (R A (2)) and flowing downwards across the node (G A (3)). Here (1), (2), and (3) is the stream number in Figure 2. When L A (1) flows to the openings of unit B, part of the liquid (L A*p (6)) flows through the openings to the other side, and part of the liquid on the back side unit of unit B (ALL_P B’ (4)) also flows to the inner side which converges to the left part of L A (L A*(1-p)). Here B’ stands for the back side of unit B, and the position is relatively higher than B; ALL_P stands for the liquid in unit B flowing to B’ through openings. The converged liquid (L A*(1-p)+ALL_P B’) in unit B is also divided into three parts, part of the liquid flows along the channel ((L A*(1-p)+ALL_P B’)*f (8)), some ((L A*(1-p)+ALL_P B’)*h (10)) flows transversely 7



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to unit C, and the left part ((L A*(1-p)+ALL_P B’)*g (9)) flows downwards to the node. G A (3) in unit A is evenly distributed into two parts, both of which flows right- (G A*PR (15)) and left-inclining (G A* PL (14)) channel of unit D. The distribution of R A (2) is similar to L A (1), and it is not discussed here.

(a) Interior unit model

(b) Side wall unit model

Figure 2 Liquid distribution law of unit network unit: (a) Interior unit model; (b) Side wall unit model

In side wall unit model, two streams can be found flowing out of the original unit A. One stream (LWL A (1)) flows down along the left wall, and the other stream (R A (2)) flows along the right-inclining channel. For LWL A (1), part of stream (LWL A*p) flows to the back side, and the left (LWL A*(1-p)) is also divided into two parts. One part (LWL A*r*(1-p) (7)) is reflected to the column along the right-inclining channel of unit D, the other part (LWL A*(1-r)*(1-p) (6)) flows continuously down along the left side, and converges with the liquid (ALL_P D’(3)) flowing from the back side of the unit D (D’) through openings. The distribution of the stream R A (2) in Figure 2 (b) can be deduced in the same manner as the stream L A (1) in Figure 2 (a), thus it is not explained in this article.

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3. Results and discussions 3.1. Hydrodynamic behavior The water flow behaviors on the perforated structured packings in different spray density and gas dynamic factor (F) are depicted in Figure 3 (a)-(c). Since water flows in the inner packing surface, water flow pattern can not be directly shown in the calculated model picture. Therefore, each figure in Figure 3 (a)-(c) contains two small pictures, which depict the water flow behavior on separate inner packing surface. When the liquid spray density (L) is 10 m3/(m2.h), the dropwise flow behavior dominates. The droplets will be blew scattered to smaller one in opposite direction as the F factor increases to 1 (m/s)(kg/m3)0.5, which leads to entrainment. After the F factor increases to 2 (m/s)(kg/m3)0.5, more droplets appear with a serious entrainment, and water flow behavior on packing surface is dominated by sprayed flow. Under a large F factor 3 (m/s)(kg/m3)0.5, most water droplets are blew off the packing surface without flowing downwards, and the flooding phenomena appears. In Figure 3 (b) and (c), dropwise flow is gradually transformed to film flow pattern at larger spray densities. With the influence of the openings on the water flow behavior, unsteady film flow can be observed at the spray density of 60 m3/(m2·h). In this range of gas and liquid flow rates, liquid film is often broken into droplets, and the flow pattern can be defined as dropwise-film transition flow. When the spray density increases to 80 m3/(m2·h), a stable film flow can be obtained. However, the liquid film is easier to be blew and scattered into small droplets, mixed with the gas phase flowing upwards, which leads to a higher possibility of the occurrence of entrainment.

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F=0 (m/s)(kg/m3)0.5

F=1 (m/s)(kg/m3)0.5

F=2 (m/s)(kg/m3)0.5

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F=3 (m/s)(kg/m3)0.5

(a) L=10 m3/(m2·h)

F=0 (m/s)(kg/m3)0.5

F=1 (m/s)(kg/m3)0.5

F=2 (m/s)(kg/m3)0.5

F=3 (m/s)(kg/m3)0.5

(b) L=60 m3/(m2·h)

F=0 (m/s)(kg/m3)0.5

F=1 (m/s)(kg/m3)0.5

F=2 (m/s)(kg/m3)0.5

F=3 (m/s)(kg/m3)0.5

(c) L=80 m3/(m2·h) Figure 3 The hydrodynamic behavior of water on 250Y structured packing with openings: (a) L=10 m3/(m2·h); (b) L=60 m3/(m2·h); (c) L=80 m3/(m2·h)

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The influence of spray density and gas phase F factor on liquid flow patterns on the structured packings with openings has been summarized in Figure 4. The flooding line in Figure 4 is cited from the data of reference

37

since the liquid flow behavior in four interior units of

structured packing cannot be applied to judge the appearance of flooding phenomena. In the studied range of liquid spray densities, dropwise and droplet-film flow are the main flow patterns. It can be partly attributed to the changed flow direction caused by openings on the packing surface, which easily leads to the breakup of liquid film. Furthermore, it can be found that the smaller the spray density is, the entrainment phenomena is easier to happen, and the liquid flooding is harder to appear. The entrainment and flooding are both inclined to occur at higher F factors. When F=3 (m/s)(kg/m3)0.5, no matter what kind of spray density studied is applied, the entrainment and flooding phenomena can be both observed.

3.0 Sprayed-dropwise transition flow Sprayed flow Dropwise flow Dropwise-film transition flow Film flow

2.5 2.0

F

Floodin g lin

1.5

e

1.0 rai Ent

0.5

e nt nm

line

0.0 0

10

20

30

40 3

50

60

70

80

90

2

L, m /(m .h)

Figure 4 The liquid flow pattern on 250Y structured packing with openings

3.2. Flow direction For two phase flow behavior, the parameters f, h, g, p can be applied to describe the liquid flow direction on structured packing, and the values of them can also depict the effect of gas phase on liquid flow patterns. 11



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The influence of F factor on liquid flow direction is illustrated in Table 2, where “+” represent the unchanged flow direction, and “-” means the appearance of the revered flow direction. In Table 2, five different spray densities and six different F factors were applied, and all these situations were calculated to investigate the effect of F factor. it can be found that the transverse flow is easiest to be influenced by gas phase, and the flow direction is reversed, while the effect on the liquid flowing along the channel is the smallest. This is because the proportion of transverse flow is smallest, and it deviates the original flow direction to a great extent, which make it easiest to be influenced. While since most liquid flows along the packing channel with greater inertia, changing the flow direction is more difficult. Table 2 Liquid flow direction 10 m3/(m2·h)

20 m3/(m2·h)

40 m3/(m2·h)

60 m3/(m2·h)

80 m3/(m2·h)

(m/s)(kg/m3)0.5

f

h

g

f

h

g

f

h

g

f

h

g

f

h

g

0

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

0.5

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

1

+

-

+

+

-

+

+

+

+

+

+

+

+

+

+

1.5

+

-

+

+

-

+

+

+

+

+

+

+

+

+

+

2

+

-

-

+

-

+

+

+

+

+

+

+

+

+

+

3

-

-

-

+

-

-

+

-

+

+

-

+

+

-

+

F

3.3. Stream split fraction coefficients Figure 5 (a)-(d) show the effect of gas phase flow rates on stream split coefficients of perforated structured packing, and the parameters will not work if the reversed flow appears. In Figure 5 (a), due to the retardation of the liquid flowing along the packing channel caused by the 12


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gas phase, the value of f decreases with the increasing of F factors. While the influence of liquid spray density is relatively unstable, which may results from the different flow patterns at different liquid spray densities. However, for dropwise flow behavior with the liquid flow rate at the range of 20 - 40 m3/(m2·h), the value of f decreases with the increase of L. A pronounced effect of liquid spray density on h can be observed in Figure 5 (b). When L=10 m3/(m2·h), approximately 30% of the liquid flows transverse in a sprayed-dropwise transition pattern. However, the value of h decreases to 5% or less after L is larger than 40 m3/(m2·h), and it decreases further with the increase of F factors. The great difference of h in different flow rates indicates the significant effect of flow patterns on the liquid distribution. For the perforated structured packing, sprayed flow behavior performs a better liquid distribution. With the result of f and h, the value of g can be obtained by 1-f-h, which has been shown in Figure 5 (c). Which is different from f and h is that, the value of g increases with L and F factors, and the decreased liquid flowing transverse and along the channel caused by gas phase mixes with the liquid flowing downwards, which leads to the increase of g. The change curve of r and liquid spray density shown in Figure 5 (d) indicates a higher value of r can be obtained at a larger L. a higher ratio of reflected liquid can reduce the wall pressing weir flow, which is helpful to better liquid distribution and higher mass transfer process.

1.0

0.5 3 0.5

F=0 (m/s)(kg/m ) 3 0.5 F=1 (m/s)(kg/m ) 3 0.5 F=2 (m/s)(kg/m )

0.8

0.4

0.6

f

3 0.5


0.3

h 0.4

0.2

0.2

0.1

0.0

0.0 10

20

30

40

50

60

70

80

10

20

30

40

50 3

60

70

2

L, m /(m .h)

L, m /(m .h)

(a) The change curve of f

(b) The change curve of h

3

2

13


80


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1.0

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1.0 3 0.5


0.8

0.8

0.6

0.6

r

g 0.4

0.4 3 0.5

F=0 (m/s)(kg/m ) 0.2

0.0

0.2

10

20

30

40

50 3

60

70

0.0 30

80

40

50

2

60

70 3

L, m /(m .h)

80

90

100

110

2

L, m /(m .h)

(c) The change curve of g

(d) The change curve of r

Figure 5 The influence of L and F on stream split coefficients of perforated structured packings: (a) The change

curve of f; (b) The change curve of h; (c) The change curve of g; (d) The change curve of r

The effect of L and F factors on p has been shown in Figure 6. When L is smaller than 20 m3/(m2.h), the value of p decreases with the increase of F factors. While if L is larger than 40 m3/(m2.h), the value of p increase first, and then decreases with the increase of F factors. For lower gas phase flow rate, the affected flow direction and decreased liquid velocity leads to more liquid flowing though the packing surface, which results in a larger value of p. After the factor increases to 2 (m/s)(kg/m3)0.5, the larger flow rate of gas phase in the back side of the packing surface act as a effective barrier, and it leads to the decrease of p.

0.5 3

2

L=10 m /(m .h) 3 2 L=20 m /(m .h) 3 2 L=40 m /(m .h) 3 2 L=60 m /(m .h) 3 2 L=80 m /(m .h)

0.4

0.3

p 0.2

0.1

0.0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3 0.5

F, (m/s)(kg/m )

Figure 6 The influence of L and F factors on the model parameter p

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3.4. Liquid distribution in two pieces of packing sheets The flow direction is affected by the openings of the packing surface, which makes part of the liquid flowing along the channel be changed to flow downwards. In order to illustrate the effect of the opening clearly, the liquid distribution behaviors in two pieces of 250Y structured packing with and without openings are depicted in Figure 7. The experimental data of the liquid distribution on the 250Y structured packing without openings are from reference 38, and operating condition of the simulation and experiment are kept the same. Where Qi and Q represent the liquid volume in separate and all the tanks, respectively, and Qi/Q represents the dimensionless liquid volume in each tank. To compare the present model and the multi-scale model of the previous work, the results of the both models are illustrated in the Figure 7. Two different feeding conditions, namely, uniform and single-point feeding, are applied. In Figure 7 (a), it is well distributed in the condition of uniform feeding except a higher liquid distribution ratio at side wall, and almost little difference can be observed for two types of packing structures. While in the condition of single-point feeding, the liquid is fed in the middle of the packing at the top, and more liquid accumulates in the middle for the perforated structured packing. For the general packing, since most liquid flows along the packing channel without being affected by openings, most of the liquid can be found at side wall, which leads to wall pressing wire flow. This result agrees with the conventional theory.

15



0.5

0.4

250Y packing without holes 250Y packing with holes

0.4 0.3

Qi/Q

250Y packing without holes 250Y packing with holes

0.3

Qi/Q

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

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0.2

0.2 0.1

0.1

0.0 -200

-150

-100

-50

0

50

100

150

0.0 -200

200

-150

-100

Transverse position, mm

-50

0

50

100

150

200

Transverse position, mm

(a) Uniform feeding (L=60 m3/(m2·h))

(b) Single-point feeding (L=20 m3/(m2·h))

Figure 7 The influence of packing openings on liquid distribution: (a) Uniform feeding (L=60 m3/(m2·h)); (b) Single-point feeding (L=20 m3/(m2·h))

Figure 8 shows the liquid distribution behavior at various instant with the assumption that the distance of the liquid flowing per unit time (∆t) is 1/2 of the packing height, and liquid is continuously fed into the middle of the packing top. From Figure 8, it can be found that no liquid appears on the two back sides of packing at the initial time (1∆t). After that, bias flow in opposite directions can be observed because there is only one packing channel on the two back packing sides. Since only part of the liquid flows through the openings to the back side surface, and the liquid on the back side will also flows back to the inner side, the fraction of the liquid in the inner side is obviously larger than that on the back side.

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Inner side (1∆t)

Inner side (3∆t)

Inner side (5∆t)

Back side1 (1∆t)

Back side2 (1∆t)

Back side1 (3∆t)

Back side2 (3∆t)

Back side1 (5∆t)

Back side2 (5∆t)

17



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Inner side (8∆t)

Back side1 (8∆t)

Inner side (12∆t)

Back side1 (12∆t)

Back side2 (12∆t)

Inner side (15∆t)

Back side1 (15∆t)

Back side2 (15∆t)

Inner side (18∆t)

Back side1 (18∆t)

Back side2 (8∆t)

Back side2 (18∆t)

Figure 8 The liquid distribution on the perforated structured packing at various constant

In case of sidewall, the liquid distribution under different spray density in the condition of single-point feeding is depicted in Figure 9. As mentioned above, the coefficient r increases with the increasing of L on Mellapak 250Y perforated structured packing. Therefore, when L=100 18


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m3/(m2·h), more liquid is reflected to the middle of the structured packing, and a better distribution can be obtained compared with that in the condition of 60 m3/(m2·h). Moreover, for different packing structures, the coefficient r performs a different changing trend with L. Such as the decreased trend of r with the increasing of L on Mellapak 350X corrugated sheet structured packing24. Thus, this can be considered as one reason of different liquid distribution for different packing structures.

Inner side

Back side1

Back side2

(a) L=60 m3/(m2·h)

Inner side

Back side1

Back side2

(b) L=100 m3/(m2·h) Figure 9 The influence of liquid flow rate on wall pressing weir flow: (a) L=60 m3/(m2·h); (b) L=100 m3/(m2·h)

4. Conclusions The developed multi-scale model is a complement for the model proposed in reference 19


24

,


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which provides an effective and feasible way to predict the liquid distribution in the perforated structured packing. The effect of counter-current gas phase flow is also considered in the model. The conclusions are as follows, 1. The liquid flow distribution on the structured packing with openings is more complex than that without openings for the liquid can pass through the opening to the back sides, thus the new parameter p has to be introduced to consider all the possible flow splits. The domain of the simulation is extended to gain the information of the flow on the back of the sheets. However, this does not weaken the rightness of the large scale model, but only make it more complicated. 2. Five types of flow patterns, namely, sprayed flow, spray-dropwise transition flow, dropwise flow, dropwise-film transition flow, and film flow can be observed on the packing surface under different gas and liquid phase flow rates. And the topological graph is given in the paper on the basis of simulation result. 3. Five stream split coefficients f, h, g, r, and p are defined to describe the liquid flow behavior in the perforated structured packing, and the transverse flow is more inclined to be affect to change flow direction. The value of f, h, g, and p are significantly influenced by liquid flow patterns, while for the coefficient r, increases with the increasing of L for all the flow patterns. 4. The liquid flow direction may be changed by the openings on the packing surface, and part of the liquid flowing along the packing channel is varied to flow downwards, which results in more liquid accumulating in the middle of the packing and better liquid distribution. There are some literatures about measurement of liquid distribution in structure packing sheets35, but these work dealt with the structure packing without openings. The liquid 20


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distribution in the perforated structured packing sheets is hardly obtained experimentally at present due to the limitation of experimental technique. Nevertheless, the simulation method is the same as the previous work in reference 24 in which the simulation results were compared to the experiment and validated. As such, the method can be regarded correct and it should be noted that the results of this study seem reasonable and sensible. If it were not because the multi-scale method has successfully predicted the hydrodynamic behaviors of the structured packing sheet in a column of industrial interest, this convincing flow behavior can hardly be obtained. This on the other hand demonstrates that simulation has become a powerful tool to understand this world. The multi-scale method is potent and prospective to predict the performance of the whole column; and as long as the constraints of computation capacity goes on, the multi-scale may be the correct path to deal with the complex problem in the various chemical industrial processes.

Acknowledgements This work was financially supported by and the National Key Technology Support Program of China (No. 2015BAC04B00).

Symbols used D

Hydrodynamic diameter, m

FLG

Source term of drag force, N/m3 21



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FVOL

Source term of surface tension, N/m3

F

Gas phase kinetic energy factor, (m/s)(kg/m3)0.5

fi

Drag force coefficient

f

Proportion of liquid flow along the channel

G

Liquid mixing in the node, L/h

g

Proportion of liquid mixing in the node

h

Proportion of liquid flows transverse

hc

Crimp height, mm

k

Turbulent kinetic energy, m2/s2

L

Liquid spray density, m3/(m2·h)

L

Liquid flowing down along the left-inclining channel, L/h

LL

Laplace number

PL, PR

Half of the liquid mixing in the node

p

Proportion of liquid flowing through the packing surface

R

Liquid flowing down along the right-inclining channel, L/h

r

Reflected part of the liquid flowing down along the side wall

α

Volume fraction

αe

The effective interfacial area per unit volume, m2/m3

θ

Solid-liquid contact angle, °

θa

Corrugation angle, °

σ

Surface tension, N/m

δ

Thickness of the liquid film, m 22


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κ

Free surface curvature, 1/m

ε

Turbulent dissipation rate, m2/s3

εr

Opening area ratio

References (1) Zhang, P.; Liu, C.; Tang, Z.; Yu, G. Experimental determination of axial mixing in two-phase flow through structured packings at elevated pressure: Axial mixing in gas phase. J. Chem. Ind. Eng. 2001, 52,381. (2) Qiu, J.; Chen, G.; Ji, J. Liquid distribution in corrugated sheet structured packed column. J. Chem. Ind. Eng. 2003, 54,646. (3) Billet, R.; Schultes, M. Modelling of pressure drop in packed columns. Chem.Eng.Technol. 1991, 14,89. (4) Billet, R.; Schultes, M. Predicting mass transfer in packed columns. Chem.Eng.Technol. 1993, 16, 1. (5) Billet, R.; Schultes, M. Prediction of mass transfer columns with dumped and arranged packings, updated summary of the calculation method of billet and schultes. Trans. Icheme. 1999, 77,498. 23



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

(6) Rocha, J.A.; Bravo, J.L.; Fair, J.R. Distillation columns containing structured packings a comprehensive model for their performance. 2. mass transfer mode. Ind. Eng. Chem. Res. 1996, 35,1660. (7) Rocha, J.A.; Bravo, J.L.; Fair, J.R. Distillation columns containing structured packings a comprehensive model for their performance 1.hydraulic models. Ind. Eng. Chem. Res. 1993, 32, 641. (8) Olujic, Z. Development of a complete simulation model for predicting the hydraulic and separation performance of distillation columns equipped with structured packings. Chem. Biochem. Eng. Q. 1997, 11, 31. (9) Olujic, Z.; Kamerbeek, A.B.; de Graauw, J. A corrugation geometry based model for efficiency of structured distillation packing. Chem. Eng. Prog. 1999, 38,683. (10) Wen, X.; Shu, Y.; Nandakumar, K.; Chuang, K.T. Predicting liquid flow profile in randomly packed beds from computer simulation. AIChE J. 2001, 47,1770. (11) Adisorn, C.; Amit, T.; Paitoon, V. Mathematical modelling of mass-transfer and hydrodynamics in CO2 absorbers packed with structured packings. Chem. Eng. Sci. 2003, 58,4037. (12) Aroonwilas, A.; Tonitawachwuthikul, P. Mechanistic model for prediction of structured packing mass transfer performance in CO2 absorption with chemical reactions. Chem. Eng. Sci. 2000, 55, 3651. (13) Fernandesa, J.; Lisboa , P.F.; Simoes, P.C.; Mota, J.P.B.; Saatdjian, E. Application of CFD in the study of supercritical fluid extraction with structured packing: Wet pressure drop calculations. J. Supercrit. Fluids. 2009, 50,61. 24


Page 24 of 27

Page 25 of 27

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


(14) Nikou, M.R.K.; Ehsani, M. R. Turbulence models application on CFD simulatin of Hydrodynamics, heat and mass transfer in a structured packing. Int. Commun. Heat Mass Transf. 2008, 35,1211. (15) Gao, G.; Zhang, L.; Li, X.; Sui, H. CFD Simulation of Film Flow and Gas/Liquid Countercurrent Flow on Structured Packing. Trans. Tianjin Univ. 2011, 17, 194. (16) Chen, J.; Liu, C.; Yuan, X.; Yu, G. CFD Simulation of Flow and Mass Transfer in Structured Packing Distillation Columns. Chin. J. Chem. Eng. 2009, 17,381. (17) Haroun, Y.; Raynal, L.; Legendre, D. Mass transfer and liquid hold-up determination in structured packing by CFD. Chem. Eng. Sci. 2012, 75,342. (18) Raynal, L.; Royon-Lebeaud, A. A multi-scale approach for CFD calculations of gas-liquid flow within large size column equipped with structured packing. Chem. Eng. Sci. 2007, 62,7196. (19) Wu, J.; Jiang, B.; Chen, J.; Yang, Y. Multi-scale study of particle flow in silos. Adv. Powder Technol. 2009, 20,62. (20) Sebastia-Saeza, D.; Gu, S.; Ranganathana, P.; Papadikis, K. Micro-scale CFD study about the influence of operative parameters on physical mass transfer within structured packing elements. Int. J. Greenh. Gas Control, 2014, 28, 180. (21) Sebastia-Saez, D.; Gu, S.; Ranganathan, P. Volume of Fluid Modeling of the Reactive Mass Transfer of CO2 Into Aqueous Amine Solutions in Structured Packed Elements at Micro-scale. Energy Procedia, 2014, 63,1229 . (22) Sebastia-Saeza, D.; Gu, S.; Ranganathana, P.; Papadikisb, K. Micro-scale CFD modeling of reactive mass transfer in falling liquid films within structured packing materials. Int. J. Greenh. Gas Control, 2015, 33, 40. 25



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

(23) Sebastia-Saeza, D.; Gu, S.; Ranganathana, P.; Papadikisb, K. 3D modeling of hydrodynamics and physical mass transfer characteristics of liquid film flows in structured packing elements. Int. J. Greenh. Gas Control, 2013, 19, 492. (24) Sun, B.; He, L.; Gu, F.; Liu, B.; Liu C. A new multi-scale model based on CFD and macroscopic calculation for corrugated structured packing column. AIChE J. 2013, 59, 3319. (25) Chen, J.; Liu, C.; Li, Y.; Huang, Y.; Yuan, X.; Yu, G. Experimental Investigation of Single-phase Flow in Structured Packing by LDV. Chin. J. Chem. Eng. 2007, 15, 821. (26) Valluri, P.; Matar, O.K.; Hewitt, G.F.; Mendes, M.A. Thin film flow over structured packings at moderate Reynolds numbers. Chem. Eng. Sci. 2005, 60,1965. (27) Haroun, Y.; Raynal, L.; Alix, P. Prediction of effective area and liquid hold-up in structured packings by CFD. Chem. Eng. Res. Des. 2014,92, 2247. (28) Zhang, X.; Yao, L.; Qiu, L.; Zhang, X. Three-dimensional Computational Fluid Dynamics Modeling of Two-phase Flow in a Structured Packing Column. Chin. J. Chem. Eng. 2013, 21, 959. (29) Xu, Y.; Zhao, M.; Paschke, S.; Wozny, G. Detailed Investigations of the Countercurrent Multiphase (Gas−Liquid and Gas−Liquid−Liquid) Flow Behavior by Three-Dimensional Computational Fluid Dynamics Simulations. Ind. Eng. Chem. Res. 2014, 53, 7797. (30) Viva, A.; Aferka, S.; Toye, D.; Marchot, P.; Crine, M.; Brunazzi, E. Determination of liquid hold-up and flow distribution inside modular catalytic structured packings. Chem. Eng. Res. Des. 2011, 89, 1414. (31) Marchot, P. ;Toye, D.; Pelsser, A.M.; Crine, M.; L'Homme, G.; Olujic, Z. Liquid distribution images on structured packing by X-ray computed tomography. AIChE J. 2001, 47, 1471. 26


Page 26 of 27

Page 27 of 27

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


(32) Green, C.W.; Farone, J.; Briley, J.K.; Eldridge, R.B.; Ketcham, R.; Nightingle, B. Novel application of X-ray computed tomography: Determination of gas/liquid contact area and liquid holdup in structured packing. Ind. Eng. Chem. Res. 2007, 46, 5734. (33) Calvo, S. Phase distribution measurements in metallic foam packing using X-ray radiography and micro-tomography. Chem. Eng. Process. 2009, 48, 1030. (34) Viva, A.; Aferka, S.; Brunzz, E.; Marchot, P.; Crine, M.; Toye, D. Processing of X-ray tomographic images: A procedure adapted for the analysis of phase distribution in Mellapak Plus 752.Y and Katapak-SP packings. Flow Means. Instrum. 2011, 22, 279. (35) Zhang, H.; Yuan, X.; KALBASSI M.A. Laser induced fluorescence technique for measuring liquid distribution in structured packing. CIESC Journal, 2014, 65, 3331. (36) Elioni, M.A.; Fair, J.R. Liquid flow over textured surfaces. 1. Contact angles. Ind. Eng. Chem. Res. 1999, 39, 284. (37) Gao, Y. The Hydrodynamic Performance of Pipple Trays. Petrol Eum Processing and Prtrochemicals, 2005, 36, 15. (38) Gu, F.; Liu, C.; Yuan, X.; Yu, G. CFD Simulation of liquid film flow on inclined plates. Chem. Eng. Technol. 2004, 27, 1099.

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