Flow Patterns of Feed Spray in Different Fluid Catalytic Cracking Feed

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Flow Patterns of Feed Spray in Different FCC Feed Injection Schemes Zihan Yan, Yiping Fan, Xiaotao Bi, Chunxi Lu, and Jing Bian Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 15 May 2017 Downloaded from http://pubs.acs.org on May 22, 2017

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Industrial & Engineering Chemistry Research

Flow Patterns of Feed Spray in Different FCC Feed Injection Schemes Zihan Yana, Yiping Fana, Xiaotao Bib,*, Chunxi Lua,*, Jing Biana a

College of Chemical Engineering, State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, China

b

Department of Chemical and Biological Engineering, University of British Columbia, Vancouver, BC V6T 1Z3, Canada

Abstract Helium tracer method is used to investigate the residence time distribution and flow patterns of feed spray in different FCC feed injection schemes by cold model experiments. Axial Peclet number in the upward and downward oriented feed injection schemes was obtained by fitting the residence time distribution into the one-dimensional axial dispersion model with an open-open boundary condition. Results suggest that the flow pattern of mixed stream is closer to complete mixing in the initial contact region of spray with catalysts when the nozzles are mounted downward. A flow pattern variation index β is proposed to show the flow patterns in the feed injection schemes quantitatively. It is shown that a larger β is obtained when the feed nozzles are faced downward, meaning that the flow pattern of mixed stream in the feeding zone can develop more quickly from a likely complete mixed flow into a likely plug flow.

1. Introduction Fluid catalytic cracking (FCC) is an important primary conversion process in the modern oil refining industry, which provides a variety of high value products such as gasoline, middle distillate and light olefins. In a modern FCC unit, a riser is widely used to accommodate the active molecular sieve cracking catalysts.1 A FCC riser reactor can be divided into four sections according to the different functions, i. e. the pre-lift zone, the feed injection zone, the full reaction zone, and the quenching zone. 2 In the feed injection zone, the feed oil enters the riser reactor through multiple atomizing nozzles, contacts and reacts with the hot regenerated catalyst particles rapidly. The feed injection system is a critical component of the riser reactor because the contact and flow of feed oil and catalyst particles in this zone will directly affect the products of FCC process.3 In a perfect FCC feed injection system, the feed oil should mix with the catalyst particles as fully as

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possible after it is injected into the riser to realize the instantaneous vaporization and fast reaction. Thus a complete mixing is expected in this region. Then the completely vaporized feed and the catalyst particles should move upwards the riser in a plug flow to avoid the over cracking. In other words, the flow pattern of feed-catalyst mixed stream should change into a plug flow from a completely mixed flow as soon as possible in an ideal feed injection system. Besides, the radial profiles of feed concentration and particle concentration should be matched with each other to achieve maximum yield of products.4 However, the contact and flow between feed oil and catalysts in a real feed injection system are different from the ideal one. In a traditional feed injection scheme which is widely used in the industry, the feed oil is injected co-currently into the pre-lift stream to mix and react with the regenerated catalyst particles, with an angle of 30o~40o relative to the riser axis. The complex hydrodynamic behavior in the feed mixing zone of the FCC riser has been investigated both experimentally and numerically. Patel et al.5 found that the pre-cracking in the feed injection zone plays an important role in determining the oil conversion and selectivity. So obtaining an appropriate gas-solid flow pattern in the initial contact region of feed with catalysts is important. Fan et al.2 found that the flow feature is much different from the typical core-annular structure when the feed oil is injected into the riser. The mismatch of catalyst concentration distribution with feed concentration distribution occurs in the traditional feed injection scheme. This is mainly because of the secondary flow of feed jet. Fan et al.17 indicated that the jet secondary flow is mainly caused by the Kutta-Joukowski lifts exerting on feed spray by pre-lift gas and catalyst particles. It extends at first and then emerges into the jet main stream. The direction of secondary flow is towards the riser wall in the traditional upward pointed feed injection scheme. It can cause the seriously back-mixing near the riser wall. E et al.6-7 tested the jet gas concentration distribution in the feed injection zone by cold model experiment. It was found that the operating conditions have a great influence on the concentration distribution of feed jets. Theologos et al.8-10 and Gao et al.1,11 investigated the performance of FCC riser reactors by incorporating lumped kinetic models into 3D computational fluid dynamics. Results showed that the concentration distributions of both catalysts and gas had large gradients in radial, axial and tangential directions. Li et al.12 simulated the effects of nozzle position and angle on the flow of riser feed injection zone by using a comprehensive 3-D heterogeneous reactor model. Results showed that the nozzle angle had significant influence on both the flow field and the cracking reactions in the feed mixing zone. However, most of the previous studies concentrated on the distributions of


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concentration or temperature in the feed injection zone. The flow pattern of the gas-solid flow in this mixing and developing region has not been investigated in detail. In order to improve the mixing and reaction of feed oil with catalyst particles in the feed injection zone, some optimization work has been reported. Different types of internals were added into the riser to improve the contact between feed oil and catalyst particles as shown in many patents.13-16 However, it may bring some other problems if the structure of the internal is complex. For example, some internals provide places for coke deposition. A stream of auxiliary steam is introduced from the feed nozzles to control the secondary flow in the research of Fan et al.17 As a result, it improves the mismatch of particle concentration distribution with feed concentration distribution. Also the back-mixing of catalysts near the riser wall is effectively controlled. However, the methods mentioned above are all based on the traditional feed injection scheme, i.e. the feed oil contacts the catalyst particles co-currently. Thus the flow pattern of the gas-solid stream in the initial contact region of oil with catalysts is hard to be close to the complete mixing flow. Lomas et al.18 proposed a set of horizontal feed nozzles to inject the hydrocarbon feed into the particle stream. Li et al.19 investigated the impact of a horizontal gas–solid jet in a high-density riser by CFD simulation. Results showed that the mixing region of feed with particles would be shortened. However, the high-speed horizontal feed may erode the riser wall if the opposite feed jets are not absolutely symmetrical when they are injected into the riser. In addition, Mauleon et al.20 proposed a countercurrent contact feed injection scheme in their patent by installing the feed nozzles at a downward angle relative to the riser axis. Chen et al.21-23 analyzed the direction of secondary flow and the effect of different types of feed injections by 3-D simulation, including upward, horizontal and downward mounted nozzles. Yan et al.24-25 investigated the distributions of particles and feed jets in the downward feed injection scheme in detail by large scale cold model experiments. It was shown that the downward feed injection was desirable to improve the distributions of catalysts and feed, especially in the initial contact region. In addition, the method to know the radial jet penetrations in different cross sections was proposed. However, the accurate axial influence region of feed jet cannot be obtained directly because of the complex gas-solid two-phase flow after multiple feed jets meet with each other in the riser center. Besides, the flow patterns of the gas-solid stream in different types of feed injection schemes have not been studied. In chemical reaction engineering, the residence time distribution (RTD) is widely used to reflect the flow characteristic of materials in a real reactor.26 The physical or non-reactive tracer technique is



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usually employed to obtain the RTD curve in a reactor. Then the variance σ and some model parameters can be extracted and used to describe the flow pattern of the stream. In the gas-solid riser reactor, the residence time distribution and mixing of the gas phase has been investigated by some researchers.27-32 Results show that the gas flow characteristics is closely linked to the solids flow. The back-mixing of gas may occur under some operating conditions, especially near the riser wall. In order to quantify gas back-mixing in the riser reactor, the homogeneous one-dimensional axial dispersion model and the two-region model based on the annular-core concept have been applied by different researchers.33-35 Most of these studies didn’t take the feed injection of the riser into consideration. Namkung et al.36 and Koksal et al.37 investigated the gas mixing in a fluidized bed with horizontal secondary air injection. However, they focused on the local radial gas mixing near the injection inlet, not the flow pattern in the whole injection zone. In this paper, the gaseous tracer method is used to investigate the residence time distribution and the flow behavior of feed injection in both upward and downward feed injection schemes. The one-dimensional axial dispersion model with an open-open boundary condition is used to reflect the flow patterns in different types of feed injection schemes based on the fitted model parameters.

2. Model The impulse trace method is widely used to investigate the characteristics of a flow system by experiments. Usually, a tracer is injected into the system instantaneously and the response is measured. The data are then used to find the parameters of the model which can reflect the investigated system. In a tubular reactor without reactions, the axial dispersion model is widely used to describe the overall flow pattern of fluid in the reactor, as shown in Eq. (1).

dc d 2c =D 2 dt dx

(1)

where, D is the longitudinal dispersion coefficient, which macroscopically determines the mixing process. There are two typical boundary conditions in the real reactor: either the flow is undisturbed as it passes the entrance and exit boundaries (the open b.c.), or it is plug flow outside the vessel up to the boundaries (the closed b.c.). In the feed injection system of a riser reactor, the fluid keeps getting in and out of the region continuously. It can be regarded as an open vessel, in which the flow is undisturbed at the entrance and exit boundaries. Thus the open-open boundary condition is selected. In the riser


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reactor, the one-dimensional axial dispersion model has been used to analyze the overall flow behavior.38 In this study, however, the one-dimensional axial dispersion model with an open-open boundary condition is used to describe the flow pattern of feed spray in the FCC feed zone. If the value of the longitudinal diffusion coefficient D keeps the same in an infinite vessel, then the parameters for the axial dispersion model in different flow cases could be derived by solving Eq. (1). In a homogeneous open-open system as shown in Figure 1, the following equations can be obtained between the input point (Z=0) and the output point (Z=L).39-41

Δσ θ 2 =

θ=

2 8 + 2 Pe Pe

Δt m t

= 1+

(2)

2 Pe

(3)

where, Pe=uL/D, is called the axial Peclet number, which can reflect the degree of back-mixing of the flow. In a linear system,

Δσ θ 2 = σ θL 2 - σ θ 0 2 , Δt m = t mL - t m0 .37

In addition, van der Laan42 investigated the diffusional type of flow in a more general open-open system so as to include the case of varying D, as shown in Figure 2. Assume that an ideal tracer is injected rapidly in the downstream of the entrance of the finite tube (at a distance Z0) and is detected at a distance Zm. The following equations based on the axial dispersion model can be obtained.

∂ ψ ∂ ψ 1 ∂2ψ + ~= 0, ~ ∂ θ ∂ z Pe a ∂ z2

Z ≤ 0;

(a)

∂ ψ ∂ ψ 1 ∂2ψ + ~= δ(θ)δ( Z - Z 0 ), 0 ≤ Z ≤ Z1 ; (b) ~ ∂ θ ∂ z Pe ∂ z2 ∂ ψ ∂ ψ 1 ∂2ψ + ~= 0, Z ≥ Z1 ; (c) ~ ∂ θ ∂ z Pe b ∂ z2 where,

(4)

c t ~ Z , z = . δ(x) is the Dirac ψ, θ , and ~ z are the dimensionless parameter. ψ = , θ = L tm c0

delta function. The general solution is:

θ=

tm t

= 1+

Da - PeZ 0 Db - Pe ( Z1 -Z m ) 1 [2 - (1 )e - (1 )e ] Pe D D

In Figure 2, when Z0=0 and Zm=Z1, Eq. (5) is then simplified to:


(5)


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θ=

tm t

= 1+

1 Da Db ( + ) Pe D D

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(6)

More generally, if the injection at Z0 has a known residence time distribution or the points Z0 and Zm are the two detected points in the system, then Eq. (6) is rewritten as:40

Δt m

θ= Similar to Eq. (3), in a linear system,

t

= 1+

1 Da Db ( + ) Pe D D

(7)

Δt m = t m1 - t m0 .

In addition, when Da = Db = D, Eq. (7) is the same as Eq. (3). It should be pointed out that the residence time tm obtained from the tracer experiment is not equal to the mean residence time

t in the reaction zone in an open-open system. This is because that a

molecule ceases to accumulate residence time when it temporarily leaves the reaction zone. So it continues to accumulate time between injection and detection, and in fact may be detected many times before finally leaving the system. Thus it can be concluded that t m > t = L / u .26 In this research, the impulse tracer was injected with the feed injection in order to investigate the flow characteristics of the feed gas jet. The tracer gas was detected at different axial positions of the riser and the RTD curves at each measuring point could be obtained. The sketch of the tracer experiment system is shown in Figure 3. In the feed injection zone of the FCC riser, the axial flow of feed jet is not uniform and the dispersion coefficient D of feed spray varies after it is injected into the riser. However, the axial measuring points in the feed injection zone are close to each other. Thus it is assumed that the dispersion coefficient between every two consecutive axial measuring points keeps the same, i.e. D1, D2, D3, ... , Di, …. Correspondingly, the Peclet number are Pe1, Pe 2, Pe 3, ..., Pe i, …, as shown in Figure 3. According to Eq. (7), the relative residence time between two consecutive measuring points is:

θi =

Δt mi ti

= 1+

1 Di-1 Di +1 ( + ) Pei Di Di

(8)

Where, Δtmi is the residence time between the consecutive measuring points calculated by the RTD curves. t i is the mean residence time, t i = Li / u i . According to the characteristic of gas-solid two-phase


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flow, the riser reactor could be assumed as a linear system. Then the time Δtmi could be calculated by: Δtmi=tmi+1-tmi.43 The time tmi+1 and tm are obtained from the RTD curves of each measuring points. In the zone between the consecutive axial measuring points, the Peclet number Pei is:

Pei =

u i Li Di

(9)

Then Eq. (8) is rewritten as :

θi =

Δt mi ti

= 1+

1 ui-1 Li-1 ui +1 Li +1 ( + ) ui Li Pei-1 Pei +1

(10)

Where，Li is the length between the consecutive axial measuring points, m; ui is the real gas velocity in the zone, m/s. In this experiment, a series of equations can be obtained based on Eq. (10):

θ1 = θ2 =

θi =

Δt m1 t1 Δt m2 t2

Δt mi ti

1 u 0 L0 u 2 L2 ( + ) u1 L1 Pe 0 Pe 2 1 u1 L1 u 3 L3 = 1+ ( + ) u 2 L2 Pe1 Pe3 ......

= 1+

= 1+

(11)

1 u i-1 Li-1 u i +1 Li +1 ( + ) u i Li Pei-1 Pei +1

The axial length Li of every zone is known. The tracer will mix with the pre-lift flow and the particles after it is injected into the riser, so the gas velocity ui in Eq. (9) is the real gas velocity in the gas-solid two-phase flow, which is calculated by:

ui =

Ug (1 - ε i )

(12)

In Eq. (12), Ug is the average superficial gas velocity. ε i is the average solids holdup in each zone. The axial distributions of εi in different types of feed injection schemes have been investigated in our previous studies.2,25 Thus the values of ε i in different zones could be obtained. After the feed injection mixes fully with the pre-lift gas and particles, the gas-solid flow in the riser is close to a plug flow. The dispersion characteristic of gas phase in the riser reactor has been investigated with the flow parameters (such as Pe and D) under different operating conditions given.29,43 In the downstream where the feed jets have little influence on the pre-lift flow, the flow parameters can also be obtained by knowing the operating conditions. Therefore, if Li+1 is in the region



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where the feed jet mixes fully with the pre-lift flow and L0 is in the region where the feed injection has little influence on the pre-lift flow, the Peclet numbers Pe0 and Pei+1 are able to be calculated. The distributions of particle concentration and feed jet concentration in different types of feed injection schemes have been investigated, 24-25 which enables us to choose the region of L0 and Li+1. The Peclet numbers Pe1 to Pei could then be obtained by solving Eq. (11).

3. Experiment 3.1 Experimental setup and materials A pilot scale cold model system based on the FCC process was constructed, as shown in Figure 4. It mainly consists of the riser section, the gas-solid separation section and the particle recirculation section. The riser section is 0.186 m in inner diameter and 11 m in height. Four feed nozzles are equipped at a height of 4.5 m above the gas distributor. In order to keep the same geometry and dimension scale with those in commercial devices, the exit cross-sections of the nozzles are rectangular (40 mmx10 mm). Both the upward and downward oriented nozzles are mounted in the experiment, as shown in Figure 5. Recent researches have shown that the concentration distributions of feed jets and particles will be better when the angle of nozzles is 30 o in the downward feed injection scheme.23-25 Therefore, the angles between the nozzles and the riser axis are both set to 30o when the nozzles are mounted upward and downward. The solids used were equilibrium FCC catalyst particles. The physical properties of particles are given in Table 1. In a cold model experiment, it is impossible to inject the real oil into the riser. Thus both the pre-lift gas and the nozzle feed are atmospheric air. The evaporation time of feed oil is very short in an industrial riser reactor (usually less than 0.2 s) 44. It is really hard to simulate this instantaneous vaporization process by a tracer method. Fortunately, we focus on the flow pattern of feed spray after it is injected into the riser in this research. In a real riser reactor, the feed oil evaporate immediately after they contact with the hot catalyst particles in the feed injection zone. Then the main reaction happens between the vaporized oil and the catalysts. Therefore, it is reasonable to use a pure gas injection to instead the liquid oil feed. On the other hand, according to Equations (10) and (11), Pei is calculated by knowing Δtmi (Δtmi =tmi+1-tmi), means that only the difference residence time between measuring points is used in the model. Thus the vaporization process at the beginning will not affect the results a lot. As the evaporation time of feed oil is very short, in this paper, the gas velocity at the exit of nozzles are set to be nearly the same as the velocity of vaporized feed oil in the industrial riser.


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In this way, the influence of difference in speed of sound between liquid-gas sprays and pure gas jets can be minimized. 3.2 Measurements In order to obtain the residence time distribution of feed gas jets in the riser, a pulse of helium was injected from the nozzles together with the feed gas. The duration of injection time was less than 0.1 s. The sampling points located at different axial height of the riser. The helium concentration was detected by sampling tubes with an inner diameter of 0.006 m connected to a SR-2050 thermal conductance helium analyzer. The sampling system is sketched in Figure 6. The solid flux was measured in the recirculation section by measuring the time t required for particles to fill the storage tank with a volume V. The solid mass flux in the riser with an inner diameter Dr is calculated by:

Gs = ρbV /(t

π 2 D ) 4 r

(13)

3.3 Measuring points and operating conditions In this paper, the installation height of the nozzles is set to be H=HN. The arrangements of axial measuring positions are based on the influencing region of feed jets in different types of feed injection scheme.2,24 When the feed nozzles are mounted upwards, the axial measuring positions are H-HN=-0.1, 0.185, 0.375, 0.675, 1.075, 1.375 m. When the nozzles are mounted downward, on the other hand, the axial measuring positions are H-HN=-0.375, -0.1, 0.185, 0.375, 0.675, 1.075 m. In order to obtain the full knowledge of the whole cross section, six different radial measuring points are chosen at each height, i. e. r/R= 0, 0.25, 0.5, 0.7, 0.8, & 0.95. In this research, the superficial velocity of the pre-lift gas ranged from 2.4 m/s to 4.1 m/s and the gas velocities at the exit of nozzles ranged from 41.8 m/s to 78.5 m/s. The solid flux in the riser ranged from 64.2 to 98.5 kg/(m2∙s). The main operating conditions cover those typical in an industrial FCC riser.

4. Results and discussions 4.1 Repeatability of the experiment In this experiment, there are six radial measuring points at each cross section. The ci(t) curves of the same radial position were detected simultaneously at different heights. Then the sampling tubes were moved to another radial position together and the ci(t) curves were obtained. To ensure that the



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measured tracer concentrations at all 6 radial positions represent the same operating condition, the repeatability of the experiment is evaluated. At a fixed operating condition, the detected experiments were repeated three times at each measuring points. Figure 7 presents examples of the results. The maximum relative error among different tests is 8.62%. Therefore, the results obtained from different radial points at different repeated runs of the same operating condition can be analyzed to investigate the radial variation of axial gas dispersion. At each cross section, six ci could be obtained at different time. The average value of ci was used to reflect the cross-sectional average concentration for a given operating condition. Then cross-sectional average c(t) curve that represents the average across the whole cross section can be calculated by.

c(t ) =

1 N ∑c (t ) Ai AN i =1 i

(14)

4.2 Distributions of axial Peclet number The distributions of axial Peclet number in different feed injection schemes are obtained from Eq. (11). In order to compare the different cases in the upward and downward feed injection schemes, the momentum ratio K is used in this paper.6,45 It is the ratio between the feed jet momentum Mj and the pre-lift flow momentum Mr, as defined in Eq. (15).

K=

Mj Mr

Nρ jU j 2 Aj

= ( ρ rU r

2

π + GsVp ) Dr 2 4

(15)

Figure 8 presents the distributions of axial Peclet number along the riser in the upward feed injection scheme. It is shown that the Peclet number increases slightly right above the feed injection level. In the region about 0.2~0.7 m above the nozzles, Pe decreases with height. Then the Peclet number keeps increasing until the flow is developed to close to a plug flow. When the nozzles are mounted upward, very little helium tracer can be detected below the nozzles, which means that the main influence region of the feed jets is above the nozzles. In the region below the nozzles, the superficial velocities in the riser are from 2.4 m/s to 4.1 m/s, close to a fast fluidized bed. Therefore, the values of Pe are small for most conditions. For the upward injection case, the direction of feed jets is the same pre-lift flow, the feed spray can promote the axial flow of mixed stream in the feed injection zone. As a result, the Peclet number increases around the injection point. In the traditional feed injection scheme, a secondary flow occurs with its direction towards the riser wall. According to the study of Fan et al.2,24, the secondary flow causes the back-mixing of gas and solids as


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it moves towards the riser wall. The serious back-mixing region occurs about 0.675 m above the nozzles in Fan’s research.2 Therefore, the decrease of Peclet number at the height of 0.2~0.7 m above the nozzles in Figure 8 is mainly caused by the back-mixing induced by the secondary flow. The influence of the secondary flow decreases gradually and the flow pattern of the mixed feed spray and pre-lift flow transforms to close to a plug flow at the height about 1.5 m above the nozzles. The axial Peclet number distribution along the riser for the case of downward mounted nozzles is shown in Figure 9. It is seen that the Peclet number is the lowest right at the downward feed jet injection level. Pe then increases with height above the injection level until the flow is developed to close to a plug flow. In the initial contact region of oil with pre-lift flow, the Peclet number is quite small for the case of downward mounted nozzles, with the value being less than 20 in some cases. This suggests that the flow pattern of the mixed stream of pre-lift flow and feed spray significantly deviates from the plug flow due to the intense mixing in this region. This could be attributed to the countercurrent contact between the feed injection and the pre-lift flow. In the region above the nozzles, the flow pattern of gas-solid mixed stream change back to close to plug flow quickly, indicating that the influencing length of feed spray on the flow is shorter relatively when the nozzles are mounted downward. This result is the same with the conclusion of the previous study.24 Furthermore, the size of the influence region of feed injection can be defined more quantitatively by this method. Based on the experimental results, the Peclet number is correlated with related parameters in the upward and downward feed injection schemes. For the traditional upward case (30o upward):

Pe = 27.3519 K -0.1005(

H 0.9102 ) HN

(16)

H 4.3837 ) HN

(17)

For the downward case (30o downward):

Pe = 17.2016 K -0.2369(

Figure 10 plots the comparison of the correlation with experimental data. As described above, when the nozzles are mounted upward, the main influence region of the feed jets is above the injection point and the Peclet numbers at the measuring point below the nozzles (H=4.2 m) are obtained from the research of traditional riser without nozzles. Thus the comparison data in Figure 10 does NOT include the points below the nozzles in the 30o upward case. When the nozzles are mounted downward, there



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are two measuring points below the nozzles to test the influence of downward feed jet. Therefore, the measuring points both above the nozzles and below the nozzles are included in Figure 10 in the 30o downward case. 4.3 The length of feed spray influence In order to compare the length of feed jets influence quantitatively, ΔHup is calculated and is plotted versus for both upward and downward feed injection schemes in Figure 11. Here, ΔHup represents the length of feed spray influence above the injection point. The flow is usually regarded as a plug flow when the Peclet number is larger than 40. Thus the height at which Pe=40 is considered by the ending point of feed spray influence, written as Ht=H(Pe=40). In this research, for both the upward and downward feed injection schemes, the injection point is HN=4.5m. Then ΔHup can be obtained by ΔHup = H t – H N. It is seen from Figure 11 that the length of feed spray influence above the injected point is much shorter when the nozzles are mounted downward. It indicates that the gas–solid mixed stream can recover to a pattern of similar to plug flow more quickly with a downward pointed nozzle, as shown by Yan et al.24 In addition, the mixing length ΔH is analyzed to reflect the mixing region in the upward and downward feed injection schemes. The position at which the feed jets can be detected is regarded as the starting point of feed spray influence, written by Hc. Based on the present research, Hc varies with operating conditions, especially the velocity of feed jets. The values of Hc in different types of feed injection schemes and under different operating conditions can be found in the studies of Fan2 and Yan24. We deem that, ΔH= Ht-Hc. For a fixed operating condition, a smaller mixing length ΔH means that the residence time of oil and catalysts in the feed zone is shorter. Figure 12 gives the ΔH-K curves in different types of feed injection schemes. It is seen that the mixing length ΔH in the downward feed injection scheme is shorter than that of the upward case in most conditions. That means the residence time of feed and catalysts in the feed mixing zone is shorter if the feed oil is injected downward. As a result, the over-cracking and coking in the feed mixing zone is likely to be minimized. Also, results show that the mixing length extends as increasing the momentum ratio K in both upward and downward feed injection schemes. Thus a higher momentum of pre-lift flow or a lower momentum of feed injection flow is good for reducing the feed mixing length. Besides, it is seen that


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ΔH increase more significantly with K for the 30o downward case. The momentum ratio K will have a considerable influence on the starting influence point Hc when the nozzles are mounted downward. As a result, both Hc and Ht move further from the injection point with increasing the momentum ratio K. While for the upward injection case, because the main influence region of the feed jets is above the nozzles, only Ht raises as K increases. Therefore, the momentum ratio K will have much more influence on the mixing length when the injection is downward. When the momentum ratio K is larger than 1, the mixing lengths in both the upward and downward feed injection schemes are nearly the same. This is mainly because that the region of feed jets influence under the nozzles expands as the momentum of downward feed injection increases. According to the axial distribution of Pe, the flow pattern of the mixed stream of pre-lift flow and feed spray is closer to complete mixed flow below the nozzles for the 30o downward case. Therefore, the downward injection will promote the mixing and reaction between oil and catalysts. However, if the momentum of feed injection is too high, the contact time between feed oil and catalyst particles may be too long. Thus the momentum ratio K should not be too large in the downward feed injection scheme. Moreover, the results can be used to determine the appropriate operating conditions if the desired residence time of oil and catalysts in the mixing zone is known. 4.4 The flow pattern variation index β In an ideal FCC feed injection system, the flow pattern of the feed-catalyst mixed stream should change back to close to plug flow as soon as possible after intense mixing in the injection zone in order to realize the quick and sufficient reaction. In this research, the distributions of axial Peclet number can reflect the variation of flow pattern in different types of feed injection schemes. In order to compare the results more quantitatively, a flow pattern variation index β is proposed, as shown in Eq. (18).

β=

ΔPe Pe t - Pec = ΔH Ht - Hc

(18)

where, Pet is the Peclet number of the stream when the flow pattern is close to a plug flow. Here we chose Pet=40 as mentioned above. Pec=Pe(H=Hc), is the Peclet number at the starting point of feed spray influence (H=Hc). ΔH is the mixing height of feed spray as defined in Section 4.3. The ratio between ΔPe and ΔH is called the flow pattern variation index β. It indicates the variation of Peclet number in per unit distance, with a dimension of m-1. Pec and Ht can be obtained from the experimental results shown in Figures 8 and 9. The starting height of feed spray influence Hc has been presented in literatures2,24, which are used here to calculate the flow pattern variation index β in different types of



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feed injection schemes. A larger ΔPe means that the flow pattern of the stream changes into a likely plug flow from a likely completed mixing flow. As mentioned above, a smaller ΔH results in a shorter residence time of oil and catalysts in the feed influencing zone. Therefore, if the value of β is larger, the flow pattern can change into a likely plug flow from a likely complete mixing flow more quickly. In the feed injection zone, a larger β is desirable for the reaction between feed oil and catalyst particles. Figure 13 presents the flow pattern variation index β under different operating conditions in the upward and downward feed injection schemes. It is seen that the value of β is clearly larger when the nozzles are mounted downward. For the case of downward nozzles, the feed injection contacts with the pre-lift flow countercurrently. At the beginning, the flow pattern of the mixed stream is closer to a complete mixing flow. Smaller Pectlet numbers are obtained in this region as shown in Figure 9. Thus the variation of Pe in the feed injection zone is larger. As analyzed above, the mixing length ΔH in the downward feed injection scheme is shorter than that of the upward case in most conditions. Therefore, a larger flow pattern variation index is obtained in case of downward pointed nozzles. According to the meaning of β, the advantage of the downward pointed nozzles is confirmed quantitatively. The effects of feed injection velocity and pre-lift gas velocity are also investigated and the results are shown in Figures 14 and 15. It is seen from Figure 14 that β increases with increasing the velocity of feed jets in both upward and downward feed injection schemes. In the research of Fan et al.17 and Yan et al.24, it is found that the effect of jet secondary flow becomes weaker with decreasing the feed jet velocity. Then the backing-mixing caused by the jet secondary flow decreases. In addition, under the conditions of lower jet gas velocity, the feed main flow and secondary flow can mix with the pre-lift flow quickly. Thus larger ΔPe and smaller ΔH can be obtained, result with a larger β. When the nozzles are mounted downward, the Peclet number is smaller and the flow pattern is closer to complete mixing in the initial contact region of oil with catalysts under the condition of higher feed jet velocity. Meanwhile, the length of feed spray influence above the nozzles extends with increasing the feed jet velocity. As a result, the flow pattern variation index β decreases at a higher feed jet velocity. Therefore, the feed jet velocity should not be too large in both upward and downward feed injection schemes in order to obtain a better reaction condition between feed oil and catalyst particles.


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In Figure 15, it is shown that β keeps nearly the same in the upward feed injection scheme when the pre-lift flow velocity varies. In the downward feed injection scheme, β increases with increasing the pre-lift flow velocity. The mixing between feed spray and pre-lift flow is more intense when the pre-lift flow velocity is higher. As a result, smaller Peclet number is obtained in the initial contact region of oil with catalysts. Besides, the influence region of feed injection above the nozzles narrows by increasing the pre-lift flow velocity. Thus a larger flow pattern variation index is obtained by increasing the pre-lift flow velocity. Therefore, a higher pre-lift flow velocity is good for the mixing and reaction between oil and catalysts in the downward feed injection scheme.

5. Conclusions The gaseous tracer technique is used in this research to investigate the residence time distributions and the flow patterns of feed spray in different types of feed injection schemes. The distributions of axial Peclet number in the upward and downward feed injection schemes are obtained by using the one-dimensional axial dispersion model with an open-open boundary condition. Correlations for estimating the distribution of axial Peclet number in the feed injection zone are presented based on the experimental results. Moreover, the length of feed spray influence and the mixing region of feed oil with catalyst particles are analyzed. In order to compare the flow pattern of mixed stream in different types of feed injection schemes more quantitatively, a flow pattern variation index β is proposed. When the feed is injected downward, the flow pattern of mixed stream is closer to complete mixing in the initial contact region of oil with catalysts. Then the gas-solid mixed stream changes into a likely plug flow over a short distance. Compared with the traditional upward feed injection scheme, the length of feed spray influence above the nozzles is shortened by mounting the feed nozzles downward. The mixing length of feed with catalysts is also shorter in the downward feed injection scheme as shown in the results of axial Peclet number distribution. As a result, the over cracking and coking in the feed mixing zone is likely to be minimized. Furthermore, the flow pattern variation index β is larger when the nozzles are mounted downward. It indicates that the flow pattern of mixed stream in the feed influence zone can change into a likely plug flow from a likely complete mixing flow more quickly, which is good for the mixing and reaction between feed oil and catalyst particles. Besides, the influences of pre-lift gas velocity and feed jet velocity on β are analyzed. It is shown that a larger pre-lift gas velocity or a moderate feed jet velocity will promote the mixing of feed with catalysts in the downward feed injection zone. In this research, the recommended flow rates are Ur=4.1 m/s and



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Uj=64.2 m/s when the nozzles are mounted downward.

Author information Corresponding authors E-mail: [email protected] (C. Lu), [email protected] (X. Bi)

Acknowledgements The authors gratefully acknowledge the supports from the National Key Basic Research Development Project (973 Program) of China (No. 2012CB215004) and the Chinese Scholarship Council.

Nomenclature A

area, m2

c

tracer concentration

D

longitudinal dispersion coefficient, m2/s

Dr

inner diameter of riser, m

Gs

solid flux, kg/(m2·s)

H

axial height, m

Hc

the starting influence point of feed spray, m

HN

installation height of the nozzles, m

Ht

ending influence point of feed spray, m

ΔH

mixing height, m

ΔHup

influence height of feed spray above the injection point, m

K

momentum ratio

L

length of finite tube, m

Mj

momentum of feed jets, kg∙m/s

Mr

momentum of prelift flow, kg∙m/s

N

number of measured points

Pe

Peclet number

Q

volume flow rate, m3/s

R

radius of riser, m

r

distance to the riser center, m


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t

time, s

tmi

residence time obtained from the tracer experiment, s

ti

mean residence time, s

Ug

superficial gas velocity, m/s

Uj

feed jet velocity, m/s

Ur

prelift flow velocity, m/s

ui

real gas velocity in the gas-solid two phase flow, m/s

u

average gas velocity, m/s

V

volume of particles accumulated in the storage tank, m3

Z

axial location, m

~z

non-dimensional length

Greek letters β

flow pattern variation index, 1/m

Δ

change value

εi

average solids holdup

θ

non-dimensional time (t/tm)

θ

non-dimensional time (tm/ t )

ρb

bulk density, kg/m3

σ θ2

variance of tracer curve

ψ

non-dimensional tracer concentration

References (1) Gao, J.; Xu, C.; Lin, S., Yang, G.; Guo, Y. Simulations of gas-liquid-solid 3-phase flow and reaction in FCC riser reactors. AIChE J. 2001, 47, 677–692. (2) Fan, Y.; Ye, S.; Chao, Z.; Lu, C.; Sun, G.; Shi, M. Gas–solid two-phase flow in FCC riser. AIChE J. 2002, 48, 1869–1887. (3) Chen, Y. M. Recent advances in FCC technology. Powder Technol. 2006, 163, 2–8. (4) Helmsing, M. P.; Makkee, M.; Moulijn, J. A. Short contact time experiments in a novel benchscale FCC riser reactor. Chem. Eng. Sci. 1996, 51, 3039–3044. (5) Patel, R.; Wang, D.; Zhu, C.; Ho, T. C. Effect of Injection Zone Cracking on Fluid Catalytic



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

Cracking. AIChE J. 2013, 59, 1226-1235. (6) E, C.; Fan, Y.; Zhang, K.; Zhang, H. Concentration profile of jet gas in the feed injection zone of a FCC riser. Prog. Nat. Sci. 2008, 18, 1285-1291. (7) E, C.; Fan, Y.; Lu, C.; Xu, C. The profiles of solid hold-up in the feed injection section of the riser. 3rd Asian Particle Technology Symposium. Beijing, 2007. (8) Theologos, K. N.; Markatos, N. C. Advanced modeling of fluid catalytic cracking riser-type reactors. AIChE J. 1993, 39, 1007–1014. (9) Theologos, K. N.; Nikou, I.; Lygeros, A. I.; Markatos, N. C. Simulation and design of fluid catalytic cracking riser-type reactors. AIChE J. 1997, 43, 486–498. (10) Theologos, K. N.; Lygeros, A. I.; Markatos, N. C. Feedstock atomization effects on FCC riser reactors selectivity. Chem. Eng. Sci. 1999, 54, 5617-5625. (11) Gao, J.; Xu, C.; Lin, S.; Yang, G.; Guo, Y. Advanced model for turbulent gas–solid flow and reaction in FCC riser reactors. AIChE J. 1999, 45, 1095-1113. (12) Li, J.; Fan, Y. P.; Lu, C. X.; Luo, Z. H. Numerical simulation of influence of feed injection on hydrodynamic behavior and catalytic cracking reactions in a FCC riser under reactive conditions. Ind. Eng. Chem. Res. 2013, 52, 11084−11098. (13) Maroy, P.; Loutaty, R.; Patureaux, T. Process and apparatus for contacting a hydrocarbon feedstock with the hot solid particles in tubular reactor with a rising fluidized bed. U.S. Patent 5348644, 1994. (14) Dries, H. W. A. Reactor riser for fluidized-bed catalytic cracking plant. U.S. Patent 6596242B1, 2003. (15) Zheng, M.; Hou, S.; Zhong, X.; Li, S. Determining the particle velocity distribution in FCC riser with different structures. Pet. Process. Petrochem. 2000, 31, 45–51. (in Chinese) (16) Fan, Y.; Cai, F.; Shi, M.; Xu, C. The gas-solid two-phase flow and the improvement in the feedstock injection-mixing zone of FCC riser. Acta. Petrolei. Sinica.(Petroleum processing section) 2004, 20, 13-19. (in Chinese) (17) Fan, Y.; E, C.; Shi, M.; Xu, C.; Gao, J.; Lu, C. Diffusion of feed spray in fluid catalytic cracker riser. AIChE J. 2010, 56, 858-868. (18) Lomas, D. A.; Haun, E. C. FCC riser with transverse feed injection. U.S. Patent 5139748, 1992. (19) Li, T.; Guenther, C. A CFD study of gas-solid jet in a CFB riser flow. AIChE J. 2012, 58,


Page 18 of 38

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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


756-769. (20) Mauleon, J. L.; Sigaud, J. B. Process for the catalytic cracking of hydrocarbons in a fluidized bed and their applications. U.S. Patent 4883583, 1989. (21) Chen, S.; Wang, W.; Yan, Z.; Fan, Y.; Lu, C. Numerical simulation on flow and mixing of gas-solid two-phase in FCC riser feedstock injection zone by using EMMS drag model. 2014 Technical Congress on Resources, Environment and Engineering. Hong Kong, 2014, 301–308. (22) Chen, S.; Fan, Y.; Yan, Z.; Wang, W.; Lu, C. CFD simulation of gas–solid two-phase flow and mixing in a FCC riser with feedstock injection. Powder Technol. 2016, 287, 29–42. (23) Chen, S.; Fan, Y.; Yan, Z.; Wang, W.; Liu, X.; Lu, C. CFD optimization of feedstock injection angle in a FCC riser. Chem. Eng. Sci. 2016, 153, 58-74. (24) Yan, Z.; Fan, Y.; Wang, Z.; Chen, S.; Lu, C. Dispersion of feed spray in a new type of FCC feed injection scheme. AIChE J. 2016, 62, 46-61. (25) Yan, Z.; Chen, S.; Wang, Z.; Li, C.; Fan, Y.; Lu, C. Distributions of solids holdup and particle velocity in the FCC riser with downward pointed feed injection scheme. Powder Technol. 2016, 304, 63-72. (26) Nauman, E. B. Residence Time Theory. Ind. Eng. Chem. Res. 2008, 47, 3752-3766. (27) Li, J.; Weinstein, H. An experimental comparison of gas backmixing in fluidized beds across the regime spectrum. Chem. Eng. Sci. 1989, 44, 1697–1705. (28) Patience, G. S.; Chaouki, J. Gas phase hydrodynamics in the riser of a circulating fluidized bed. Chem. Eng. Sci. 1993, 48, 3195–3205. (29) Chan, C. W.; Seville, J. P. K.; Parker, D. J.; Baeyens, J. Particle velocities and their residence time distribution in the riser of a CFB. Powder Technol. 2010, 203, 187-197. (30) Namkung, W.; Kim, S. D. Gas backmixing in the dense region of a circulating fluidized bed. Korean J. Chem. Eng. 1999, 16, 456-461. (31) Sterneus, J.; Johnsson, F.; Leckner, B. Gas mixing in circulating fluidised-bed risers. Chem. Eng. Sci. 2000, 55, 129–148. (32) Hua, L.; Wang, J.; Li, J. CFD simulation of solids residence time distribution in a CFB riser. Chem. Eng. Sci. 2014, 117, 264-282. (33) Amos, G.; Rhodes, M. J.; Mineo, H. Gas mixing in gas-solids risers. Chem. Eng. Sci. 1993, 48, 943-949.



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

(34) Kruse, M.; Schoenfelder, H.; Werther, J. A two-dimensional model for gas mixing in the upper dilute zone of a circulating fluidized bed. Can. J. Chem. Eng. 1995, 73, 620–634. (35) Bi, X. T. Gas and solid mixing in high-density CFB risers. Int. J. Chem. React. Eng. 2004, 2, A12. (36) Namkung, W.; Kim, S. D. Radial gas mixing in a circulating fluidized bed. Powder Technol. 2000, 113, 23–29. (37) Koksal, M.; Hamdullahpur, F. Gas mixing in circulating fluidized beds with secondary air injection. Chem. Eng. Res. Des. 2004, 82, 979–992. (38) Mahmoudi, S.; Seville, J. P. K.; Baeyens, J. The residence time distribution and mixing of the gas phase in the riser of a circulating fluidized bed. Powder Technol. 2010, 203, 322-330. (39) Levenspiel, O.; Smith, W. K. Notes on the diffusion-type model for the longitudinal mixing of fluids in flow. Chem. Eng. Sci. 1957, 6, 227-233. (40) Bischoff, K. B.; Levenspiel, O. Fluid dispersion-generalization and comparison of mathematical models-I Generalization of models. Chem. Eng. Sci. 1962, 17, 245-255. (41) Gibilaro, L. G. On the residence time distribution for systems with open boundaries. Chem. Eng. Sci. 1978, 33, 487-491. (42) van der Laan, E. T. Notes on the diffusion-type model for the longitudinal mixing of fluids in flow. Chem. Eng. Sci. 1958, 7, 187-191. (43) Dry, R. J.; White, C. C. Gas residence-time characteristics in a high-velocity circulating fluidised bed of FCC catalyst. Powder Technol. 1989, 58, 17-23. (44) Diu, D.; Han, J. Evaluation on commercial application of LPC type nozzle for FCC feed. Petroleum Refinery Engineering. 1992, 2, 49-52. (in Chinese) (45) Yan, Z.; Wang, Z.; Chen, S.; Fan, Y.; Lu, C. Matching between oil and catalyst in new scheme of FCC feed injection. CIESC J. 2016, 67, 3304-3312. (in Chinese)

List of Figures Figure 1 Sketch of a homogeneous open-open system Figure 2 Sketch of an inhomogeneous open-open system Figure 3 Sketch of the tracer experiment system Figure 4 Experimental setup Figure 5 Nozzle orientations used in this investigation


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Figure 6 The helium tracer sampling system Figure 7 RTD curves of repeated experiments Figure 8 Axial Peclet number distribution along the riser for upward oriented nozzles Figure 9 Axial Peclet number distribution along the riser for downward mounted nozzles Figure 10 Comparison between correlations and experimental data Figure 11 The length of feed spray influence in different feed injection schemes Figure 12 The mixing length in different types of feed injection schemes Figure 13 Flow pattern variation index β under different operating conditions Figure 14 Variation of β at different feed jet velocity Figure 15 Variation of β at different pre-lift flow velocity

List of Tables Table 1 Properties of tested FCC catalysts



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For Table of Contents Only 47x26mm (600 x 600 DPI)


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Figure 1 Sketch of a homogeneous open-open system 39x16mm (300 x 300 DPI)



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Figure 2 Sketch of an inhomogeneous open-open system 39x16mm (300 x 300 DPI)


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Figure 3 Sketch of the tracer experiment system 80x106mm (300 x 300 DPI)



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Figure 4 Experimental setup 64x64mm (300 x 300 DPI)


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Figure 5 Nozzle orientations used in this investigation 70x61mm (300 x 300 DPI)



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Figure 6 The helium tracer sampling system 64x64mm (300 x 300 DPI)


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Figure 7 RTD curves of repeated experiments 99x142mm (300 x 300 DPI)



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Figure 8 Axial Peclet number distribution along the riser for upward oriented nozzles 49x35mm (300 x 300 DPI)


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Figure 9 Axial Peclet number distribution along the riser for downward mounted nozzles 49x35mm (300 x 300 DPI)



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Figure 10 Comparison between correlations and experimental data 49x26mm (300 x 300 DPI)


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Figure 11 The length of feed spray influence in different feed injection schemes 49x35mm (300 x 300 DPI)



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Figure 12 The mixing length in different types of feed injection schemes 49x35mm (300 x 300 DPI)


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Figure 13 Flow pattern variation index β under different operating conditions 49x35mm (300 x 300 DPI)



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Figure 14 Variation of β at different feed jet velocity 49x35mm (300 x 300 DPI)


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Figure 15 Variation of β at different pre-lift flow velocity 49x35mm (300 x 300 DPI)



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Table 1 Properties of tested FCC catalysts 24x12mm (300 x 300 DPI)


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Flow Patterns of Feed Spray in Different Fluid Catalytic Cracking Feed

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