Novel Chemical Looping Combustion Assisted Residue Fluid Catalytic

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A Novel Chemical Looping Combustion (CLC)-Assisted Residue Fluid Catalytic Cracking (RFCC) Process in order to Reduce CO2 Emission and Gasoline Production Enhancement Neda Nabipour, and Davood Iranshahi Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b00169 • Publication Date (Web): 04 Apr 2017 Downloaded from http://pubs.acs.org on April 7, 2017

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A Novel Chemical Looping Combustion (CLC)-Assisted Residue Fluid Catalytic Cracking (RFCC) Process in order to Reduce CO2 Emission and Gasoline Production Enhancement Neda Nabipour, Davood Iranshahi* Department of Chemical Engineering, Amirkabir University of Technology (Tehran Polytechnic), No. 424, Hafez Avenue, Tehran 15914, Iran

ABSTRACT In this novel study, application of chemical looping combustion (CLC) as the heat source for the endothermic Residue Fluid Catalytic Cracking (RFCC) process has been investigated to stabilize the RFCC riser temperature for increasing efficiency and proficiency of the process. A mathematical conceptual model has been presented to analyze the performance of RFCC process coupled with chemical looping combustion (RFCC-CLC). NiO18-α-Al2O3 particles have been employed as the oxygen carrier agents in CLC system, which have shown unprecedented reactivity and allow for working under high temperatures with complete conversion of CH4 in RFCC-CLC configuration. This structure consisting of three coaxial vertical tubular reactors and the riser reactor is surrounded by the air and fuel reactors, respectively (all three reactors operate in the fluidized regime). The most illustrious advantage of applying CLC technique is the inherent CO2 separation from flue gas. In addition, results indicate that methane conversion tends toward 1 and a 10% by weight increase in gasoline production and a 1.3% by weight reduction in coke formation have been achieved which reveals the supremacy of the RFCC-CLC configuration. Keyword: Chemical looping combustion, Residue fluid catalytic cracking, NiO18-α-Al2O3 particles, CO2 separation, Riser reactor, Air and fuel reactors.

*

Corresponding author. Tel.: +98 21 64543189; Fax: +98 21 66405847. Email address: [email protected].

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1.

INTRODUCTION RFCC (Residue Fluid Catalytic Cracking), which is generally referred to as the core of a

refinery, is one of the most important and efficient refining units as compared to other oil refining units. RFCC is designed to convert high molecular weight hydrocarbons into commercially valuable products especially high octane number gasoline. This unit employs a technology similar to FCC (Fluid Catalytic Cracking) except that it uses heavier feedstock. This unit has been widely accepted because of the higher quality and quantity of the produced gasoline as compared to the gasoline product of thermal cracking 1. RFCC is a comprehensive technology with great potential for increased profitability as well as growth and development. Hence, it is a suitable option for optimization as small advancements in RFCC operations lead to enormous economic advantages. Numerous studies have been carried out to improve the performance of this process. Many researchers such as Blanding (1953) 2 and Voorhies (1945) 3 have studied the kinetics of these reactions. Then significant kinetic models were developed, and later on, strategies for estimation of catalytic cracking parameters were proposed. Due to the complexity of the RFCC feedstock, it cannot be classified into a single group with a certain molecular weight. As a result, the feedstock is classified by grouping several similar chemical compounds into different categories called “lumps”. This theory was expressed by Wei and Kuo (1969) 4. One of the most efficient attempts made to model the catalytic cracking unit is the threelump model developed by Weekman and Nace 5, who studied the conversion percentage of feedstock and selectivity of gasoline. These researchers divided the feedstock and products into three categories namely the feedstock, gasoline, and a compound known as dry gas and coke. This model predicts conversion of feedstock and gasoline productivity in the isothermal state for fixed-bed, moving-bed and fluidized-bed reactors. This three-lump kinetics was used by researchers such as Lee et al. (1989) 6, Markatos and Theologos (1993) 7 to analyze and examine modeling of catalytic cracking units. In catalytic cracking process, precise prediction of coke is important in thermal investigations. Burning of coke provides the heat required for the catalytic cracking reactions. As a result, prediction of coke formation through cracking is necessary for industrial simulation of the catalytic cracking riser reactor as well as regeneration reactor. Nowadays, kinetics has been capable of studying coke formation and catalyst deactivation 8. Lee et al. (1989) proposed a four-lump model, which separated coke from Weekman’s three-lump model to define it as an independent lump. Separating coke from other lumps is substantially


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important for burning of coke in the catalyst regeneration reactor in generating the heat required for endothermic reactions in catalytic cracking riser reactor. This four-lump model has been used by researchers such as Farag et al. (1993) 9, Zheng et al (1994) 10, Ali and Rohani (1997) 11, Blasetti and De Lasa (1997) Rao (2001)

13

12

and Gupta and Subba

in different modeling of catalytic cracking reactors, due to its ability for

expressing the reaction kinetics in simple terms and solving the equations easily. In 1976, a 10-lump model, which introduced a wider range of chemical species with heavier mole fractions, was proposed by Jacob et al.

14

In this model, the adverse effect of nitrogen,

aromatic adsorption and the time influencing catalyst deactivation were taken into account. Other researchers such as Oliveira (1989) (1997)

17

15

, Coxson and Bischoff (1987)

16

and Theologos

made changes to improve the FCC reaction kinetics equations based on this 10-

lump model. A 19-lump kinetic model was also developed by Pitault (1994) 18 to describe the catalytic cracking process. Kinetic models with more lumps are evidently more satisfactory, but with an increase in the number of lumps, the number of kinetic parameters to be determined escalates. Hence, we have to inevitably select a kinetic model with the minimum number of lumps to allow for provision of useful and efficient information on production rates. Endothermic reactions take place in an RFCC process and the heat required for these reactions is supplied through direct combustion of fossil fuels such as natural gas in feedstock pre-heaters. Large volumes of carbon dioxide are produced through combustion of fossil fuels per year, which is one of the most important greenhouse gases with the largest negative effect on the atmosphere and oceans. It warms planet Earth and leads to severe climatic changes. Therefore, due to emission of the CO2 greenhouse gas and limitation of fossil fuel reserves a new combustion technology known as Chemical Looping Combustion (CLC) is used. The concept of CLC was for the first time introduced by Lewis in 1954 19. Chemical Looping Combustion, which has recently captured the attention of many researchers, is a new combustion technique for inherent CO2 separation and known as the green technology. This process takes place in two fluidized bed reactors namely the air reactor (AR) and the fuel reactor (FR). The former reactor handles the oxidation reaction, whereas the latter handles the reduction reaction. In this method circulating metal oxides are used as oxygen carriers (OCs) to transfer O2 from the air reactor to the fuel reactor. The number of reduced metal oxides in the fuel reactor are carried back to the air reactor to allow for metal oxides reformation as a result of exposure to air

20


. This method is capable of

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generating a 100% pure flow of O2 for combustion. Figure 1 depicts a schematic of the CLC process. Figure 1. The oxidation reaction in the air reactor is always exothermic, and the reduction reaction in the fuel reactor can be either endothermic or exothermic while it is normally endothermic. Therefore the entire process is exothermic and the total heat generated in this cycle equals the heat released through normal combustion. CO2 and H2O are the combustion products and are easily separable. Pure CO2 is easily separated through H2O condensation. Separation and storage of CO2 is much easier in this case than in the presence of N2 21. The key parameter in a CLC system is oxygen carriers. Investigations on oxygen-carrying metals suggest that copper, iron, manganese, nickel, calcium and different combinations of minerals can be used as oxygen carriers. The following considerations must be taken into account in selecting OCs 22: -

High rate of oxidation and reduction.

-

High capacity for transfer of oxygen.

-

High affinity for reacting with fuel and rapid regeneration of reduced metal oxides.

-

Lack of affinity for aggregation and agglomeration.

-

Mechanical stability (high resistance to erosion and corrosion).

-

Low cost.

-

Environment-friendly (i.e. with no adverse environmental impact).

Several studies on CLC have examined the feasibility of using different metal oxides as oxygen carrying agents 23. In general, it is not possible to meet all of the specifications of a good oxygen carrier using pure metal oxides. The solution to this problem involves the use of porous supports. NiO particles supported on porous alumina are suitable options as oxygen carriers. Ni-based OCs can be used in CLC systems under high temperature and complete methane conversion can be achieved. Wolf et al.

24

compared performances of nickel- and

iron-based OCs and reported equal yield for both OCs, but stated that it was easier to use CLC systems using nickel-based oxygen carriers. As mentioned, CLC is an exothermic process, the heat produced by which can be used to conduct an endothermic reaction such as catalytic cracking process in a fluidized-bed reactor. The coupling of an endothermic reaction and an exothermic reaction has yielded satisfactory results.


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This idea forms the basis of thermal coupling. Rahimpour et al. 25 used the heat produced in the hydrogenation of nitrobenzene to aniline in methane steam reforming. They also used the CLC-produced heat for natural gas reforming using palladium-mercury membrane and studied hydrogen generation and CO2 capture 26. Iranshahi et al. 27 coupled CLC with naphtha reforming. They used NiO18-α-Al2O3 oxygen carriers to study hydrogen generation and CO2 capture. The present research is aimed to assess the performance of Residue Fluid Catalytic Cracking using CLC as the source of heat. The CLC system is used in this structure to compensate for the decrease in heat caused by cracking reactions in the riser reactor. A mathematical conceptual model is also developed for the RFCC-CLC system, and reactants consumption rate and products production rate are analyzed and compared to corresponding conventional RFCC rates. In fact, in this system, CO2 capture in CLC is coupled with the RFCC process. In addition, production of gasoline increases as a result of coupling with CLC. These results are explained and discussed in details in the following.

2.

PROCESS DESCRIPTION

2.1.

Conventional Residue Fluid Catalytic Cracking (CRFCC) Process

RFCC is a key process in the petroleum and petrochemical industry which increases the hydrogen to carbon ratio through a continuous process. In other words, this process converts hydrocarbons with high boiling points and molecular weights into more valuable, efficient and lighter materials. This process involves two major reactors: the riser reactor (in which catalytic cracking of hydrocarbons takes place), and the regeneration reactor. These two reactors are interconnected to allow for circulation of the catalyst. In other words, the catalysts consumed in the riser are injected into the regenerator from the top, and regenerated catalysts are afterward injected back into the riser from the bottom of the regenerator. The feedstock, which is in the form of small liquid particles, is injected into the riser reactor from the bottom after it is preheated by the feed preheaters. The feed is afterward evaporated as it collides with the hot reactivated catalysts. During this reaction, the gas (reactants and products) and solid (catalyst) phases are present in the riser. Catalyst particles are carried upward along the riser by the steam and flow into the cyclone where they are separated. Catalysts that are deactivated during the reaction as a result of coke settlement are reactivated in the regenerator by enriched air and are prepared for the next cycle. Since catalytic cracking reactions are extremely endothermic, temperature declines during the reaction and as a result,


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the rate of reactions decreases. Hence, in conventional RFCC, a decrease in temperature and rate of production is generally observed at the end of the riser

8, 28

. Table 1 presents

information on the conventional RFCC operational conditions. Table 1.

2.2.

Residue Fluid Catalytic Cracking Coupled with Chemical Looping Combustion (RFCC-CLC)

Figure 2 demonstrates the diagram of RFCC-CLC configuration consisting of three coaxial vertical tubular reactors. The RFCC-CLC system uses the same feedstock as conventional RFCC. In this structure, the riser reactor is surrounded by the air and fuel reactors (in the order mentioned). All of the three riser, air, and fuel reactors operate in the fluidized state. In RFCC-CLC the heat generated in the air reactor is transferred continuously to the adjacent reactors, i.e. the fuel reactor and RFCC riser reactor. The high gas speed in the CLC system provides the driving force for circulation of Ni-based OCs between the air and fuel reactors. Design characteristics of the air and fuel reactors (including reactor size, solid circulation rate, and OCs inventory) are presented based on experimental results obtained using NiO18-α-Al2O3 OCs in a continuous CLC prototype which are presented in Table 2. Figure 2. Table 2.

3.

REACTION SCHEME AND KINETICS

3.1.

RFCC Section (Four-Lump Model)

To investigate the kinetics of reactions in catalytic cracking process, four-lump model developed by Ali and Rohani

29

is considered. In this model, cracking of gas oil heavy

hydrocarbons is considered as a second-order cracking reaction, whereas other cracking reactions are considered to be first-order reactions. Reaction rate equations for the cracking reactions are written as follows:

rgasoil = −Φ Riser ρcatalyst

 K gasoil → gasoline  2    Fgasoil    + K gasoil →lightgas   +K   Ftotal   gasoil →coke 


(1)

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rgasoline = −Φ Riser ρcatalyst

rlightgas = Φ Riser ρcatalyst

rcoke = Φ Riser ρcatalyst

  Fgasoline   ( K gasoline → lightgas + K gasoline →coke )   −  Ftotal    2    Fgasoil  K    gasoil → gasoline  F   total   

(2)

  Fgasoline    K gasoline →lightgas   +  Ftotal    2    Fgasoil  K    gasoil → lightgas  F   total   

(3)

  Fgasoline    K gasoline →coke   +  Ftotal    2    Fgasoil  K    gasoil →coke  F   total   

(4)

Table 3 presents reaction rate constants, activation energies, standard heats of the reactions, molecular weights of lumps and catalyst deactivation parameters 30. Table 3.

3.2.

Oxidation and Reduction of Oxygen Carriers in CLC

During the CLC process, the OCs reduction and oxidation rate should be considered, because these parameters directly affect the solid inventory of fuel and air reactors. The exothermic oxidation of nickel-based oxygen carriers in the air reactor is expressed as follows.

O2 + 2Ni → 2NiO

(

o −1 ∆H 298 K = −479.4 kJ .mol

)

(5)

Moreover, the endothermic reduction of NiO18-α-Al2O3 oxygen carriers in the fuel reactor is expressed as follows.

CH 4 + 4NiO → 4Ni + CO2 + 2H 2O

(

o −1 ∆H 298 K = 156.5 kJ ⋅ mol

)

(6)

In order to examine the rate of oxidation and reduction of OC particles during the reaction, the shrinking core model is applied. This model considers particles to be small spherical grains with varying and decreasing sizes

31

. The following equations are used to

calculate the rate of oxidation and reduction in both the air and fuel reactors.


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rs =

τ=

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2 dX s 3 = (1 − X s ) 3 dt τ

(7)

ρm rg

(8)

bi kC n

 E  k = k o exp  −   RT 

(9)

Table 4 presents the specifications and kinetic parameters of oxidation and reduction of NiO18-α-Al2O3 oxygen carriers 27. Table 4.

4.

MATHEMATICAL MODELING A differential element of the RFCC-CLC along the system length is depicted in Figure 3

which is used to develop the mass and energy balance equations. The following hypotheses are made for a one-dimensional mathematical modeling of RFCC-CLC system 26-27. -

Release of heat from the walls into the environment is overlooked.

-

There are the gas and solid phases in the reactors and plug flow pattern is employed for both phases.

-

The entire process is assumed to take place under steady state conditions.

-

Specifications of different components of CLC process (such as density and heat capacity) are variant and depend on operational conditions, i.e. system temperature and pressure.

-

Effects of internal and external diffusion and axial dispersion are neglected.

-

The thermal resistance between gas and solid phases is overlooked, and thus the gas and solids are in thermal equilibrium.

-

The system is defined as a one-dimensional system along the reactor length.

-

The ideal gas law applies to the gas phase.

-

Reactor bed porosity along the axial and radial directions is assumed to be invariant.

-

Cracking reactions take place on the surface of catalyst particles.

-

Gas-solid reactions in the reactors are considered to be homogenous.

Figure 3. The governing mass and energy balance equations, as well as boundary conditions of RFCC and the air and fuel reactors, are presented in Table 5. Table 6 lists the equations


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required for calculation of physical properties and mass and energy transfer coefficients. The derivation of governing equations is provided in the Supporting Information. Table 5. Table 6.

5.

NUMERICAL SOLUTION The present model involves a set of ordinary differential equations (ODEs) consisting of

including the mass and energy balance equations and a set of nonlinear algebraic equations, resulted from kinetic model, and auxiliary and hydrodynamic relations. The finite difference method is applied to solve this set of ODE equations. The length of each reactor is divided into 100 segments, and the nonlinear algebraic equations are solved for each segment using the Gauss–Newton method, which is employed for all nodes along the reactor length and the results of each node are used as the input condition for the subsequent node 27.

6.

MODEL VALIDATION The present model is validated by comparing results of RFCC simulation and a set of

industrial data of a fluidized-bed reactor under steady state conditions. A summary of the results is presented in Table 7. As seen, results predicted using this model are properly in line with the related industrial data. In addition, results of simulating the developed RFCC-CLC model in corresponding conditions are presented in this table (the industrial data are not available for RFCC-CLC configuration). These results reflect the higher mass fraction of gasoline in the RFCC-CLC as compared to the CRFCC model, which are discussed further in the following sections. Table 7.

7.

RESULTS AND DISCUSSION

7.1.

RFCC Section

7.1.1. Gas Oil Figure 4 illustrates the comparison between the mass fractions of gas oil in the CRFCC and RFCC-CLC processes. In the figure, the dimensionless length of the system is written as follows.


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η=

z L

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(24)

Where L denotes the riser length. Figure 4. As seen, the consumption rate of gas oil in the RFCC-CLC coupled system is considerably higher than the CRFCC system. During the RFCC-CLC process, the rate of cracking of heavy hydrocarbons in the feed escalates due to the effective heat transfer from the air reactor, which drives the reactors toward increased gas oil consumption. 7.1.2. Gasoline, Coke, Light Gas Figure 5 shows the mass fractions of various products obtained from cracking sections of both CRFCC and RFCC-CLC configurations. Gasoline is the most valuable product of the catalytic cracking process, and attempts have always been made to increase its production. Based on this diagram, the production rate of gasoline increased in the coupled state (RFCCCLC) as compared to the CRFCC state. Therefore, Figure 5 depicts superiority of RFCCCLC over CRFCC. In addition, a drastic decrease is observed in coke production in the coupled state, which provides better operational conditions for activity of catalysts. The decrease in coke production reduces the air required for catalyst regeneration and reduces operational and capital costs of selecting the air blower type and the regeneration process. Other products of the catalytic cracking process are light gases, including C3 and C4. These gases partly result from the cracking of gas oil heavy hydrocarbons and partly from a secondary cracking process, which involves cracking of gasoline hydrocarbons. As seen in Figure 5, light gas production decreased. Figure 5. 7.1.3. Conversion of Residue Fluid Catalytic Cracking Process Figure 6 depicts the advancement of the reaction at the axial coordinates of the reactor in the CRFCC and RFCC-CLC systems. As expected, in the coupled mode due to improvement of the reactor operational conditions, the conversion is higher. Figure 6. 7.1.4. Pressure Effect in RFCC Riser Figure 7 depicts pressure along the riser length in the CRFCC and RFCC-CLC configurations. In fact, the pressure difference along the riser length suits the static head of


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the catalyst in the riser. As seen in figure, pressure in the riser output is higher in the coupling mode and has increased by 0.008 bar as compared to the uncoupled mode which reveals the preference of RFCC-CLC configuration to the CRFCC configuration. In other words, the RFCC-CLC managed to reduce pressure decline. Figure 7.

7.2.

CLC SECTION

As seen in Figure 2, the Chemical Looping Combustion (CLC) process, which is simulated in this novel configuration, differs from its conventional types used traditionally in previous articles (Figure 1) 23, 32. In the current structure, the air reactor is surrounded by the fuel reactor. In other words, the fuel reactor acts as a coating for the air reactor. The reaction in the air reactor is extremely exothermic and supplies the heat required by the entire system. Figure 8-a depicts the variations of oxygen and nitrogen mole percents along the air reactor length. As seen, oxygen is completely consumed inside the air reactor, but it does not reach zero on the diagram due to injection of excess oxygen. Variations of CO2, H2O and CH4 mole percentages along the fuel reactor length are shown in Figure 8-b. Results suggest that methane is completely consumed along the reactor length, and as shown in Figure 9 the methane conversion tends toward 1 due to the high reactivity of NiO-based oxygen carriers. The produced CO2 can be captured after H2O condensation without any further energy required for separation. Evidently, the CO2 generated in this method is completely pure. Figure 8. Figure 9.

7.3.

Thermal Effect

Figure 10 depicts variations of temperature along the riser length in the RFCC and RFCCCLC processes. Since the fluid catalytic cracking reaction is extremely endothermic, temperature declines significantly along the riser length. Using a heat source in the RFCCCLC system (i.e. the air reactor) leads to a mild temperature decrease, which results in a mild increase in the cracking reaction rates. At the beginning of the riser reactor, heat consumption is higher than the heat received from the air reactor. Hence, the effect of temperature decrease is dominant in this zone. Afterward, the amount of heat received from the air reactor becomes higher than the heat consumption and an increase in temperature is observed. Figure 10.


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Figure 11 shows variations of temperature along the fuel reactor. As seen, the effect of heat consumption is dominant at the beginning of the fuel reactor. So, the temperature slightly decreases, whereas the effect of heat transfer from the air reactor is dominant at the end of the reactor. Figure 11. Figure 12 illustrates variations of temperature in the air reactor. Since the heat transferred to the fuel reactor and the RFCC riser, is lower than the heat generated in the air reactor, the air reactor temperature rises continuously. The temperature differences between air reactorfuel reactor and air reactor-riser are the heat transfer driving force, which escalates along the reactor length. As a result, in spite of the decrease in heat generation in the air reactor heat transfer to the adjacent reactors increases. Figure 12.

8.

Conclusion

In this study, an efficient innovation is developed for application of CLC to stabilization of RFCC riser temperature for increasing productivity and performance of the process and eventually increasing gasoline production. The NiO18-α-Al2O3 particles are used as carriers of oxygen in the RFCC-CLC system. CLC consists of two interconnected fluidized-bed reactors; air and fuel reactors that operating co-currently. The flow regime in the air and fuel reactors is a fast fluidized regime. Cracking of gas oil takes place in a fluidized bed reactor in the presence of zeolite catalysts. The main product of the catalytic cracking process is gasoline that an increase in production rate of gasoline reveals superiority of the new RFCCCLC configuration (production of gasoline in this system showed a 10% by weight growth as compared to the CRFCC system). Using CLC, the coke production shows a 1.3% by weight reduction that clearly leads to a remarkable decrease in the capital and operational costs of the catalyst regeneration process. Another outcome of this innovation was complete consumption of methane in the fuel reactor due to the use of nickel-based oxygen carriers.

Supporting Information Available: The derivation of governing equations (mass and energy balances) for both Residue Fluid Catalytic Cracking (RFCC) and Chemical looping combustion (CLC) sections. This information is available free of charge via the Internet at http://pubs.acs.org/.


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Nomenclatures AC= Cross-Section Area, (m2) bi= Stoichiometric Coefficient C= Concentration, (mol/m3) Cjo= Inlet Concentration of Component j, (mol/m3) Cp = Specific Heat Capacity at Constant Pressure, (J/mol.K) CT = Total Concentration, (mol/m3) Cv = Specific Heat Capacity at Constant Volume, (J/mol.K) De = Effective Diffusivity, (m2/s) E= Activation Energy, (kJ/mol) Fj= Mass Flow Rate of Component j, (kg/s) keff = Effective Thermal Conductivity, (W/m.K) L= Reactor Length, (m) P= Total Pressure, (Pa) Pper= Heat Transfer Surface Between Reactors, (m) R= Gas Constant, (J/mol.K) RAR = Reaction Rate in the Air Reactor, (mol/m3.s) RFR = Reaction Rate in the Fuel Reactor, (mol/m3.s) rg = Grain Radius, (m) ri = Rate of Reaction for Reaction i, (kg/m3.s) rs = Oxidation and Reduction Rate of Oxygen Carriers, (s-1) TAR = Temperature of the Air Reactor, (K) TFR = Temperature of the Fuel Reactor, (K) TR = Temperature of Catalytic Cracking Riser, (K) uz = Feed Velocity, (m/s) U = Overall Heat-Transfer Coefficient Between Two Sides of the Reactor, (W/m2.K) Uj = Internal Energy of Component j, (J/mol) z = Axial Coordinate, (m)

Abbreviations Al2O3= Alumina


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AR= Air Reactor CLC= Chemical Looping Combustion FBP= Final Boiling Point, ˚C FR= Fuel Reactor IBP= Initial Boiling point, ˚C Ni= Nickel NiO= Nickel Oxide OC= Oxygen Carrier RFCC= Residue Fluid Catalytic Cracking RFCC-CLC= Residue Fluid Catalytic Cracking coupled with Chemical Looping Combustion

Greek letters ε= Void fraction of catalyst bed µ= Viscosity of gas, (kg/m.s) η= Dimensionless length ρ= Density of gas, (kg/m3) ρb= Reactor bulk density, (kg/m3) τ= Time required for complete conversion, (s) ∆H= Heat of reaction, (kJ/kg) Ф= Catalyst activity

Superscripts & Subscripts AR= Air Reactor FR= Fuel Reactor g= Gas phase i= Reaction Identification j= Component Identification OC= Oxygen Carrier OX= Oxidation Reaction R=Riser RE=Reduction Reaction s= steam ss= steady state


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References 1. Fernandes, J. L.; Verstraete, J. J.; Pinheiro, C. I.; Oliveira, N. M.; Ribeiro, F. R., Dynamic modelling of an industrial R2R FCC unit. Chemical engineering science 2007, 62 (4), 1184-1198. 2. Blanding, F. H., Reaction rates in catalytic cracking of petroleum. Industrial & Engineering Chemistry 1953, 45 (6), 1186-1197. 3. Voorhies Jr, A., Carbon formation in catalytic cracking. Industrial & Engineering Chemistry 1945, 37 (4), 318-322. 4. Wei, J.; Kuo, J. C., Lumping analysis in monomolecular reaction systems. Analysis of the exactly lumpable system. Industrial & Engineering chemistry fundamentals 1969, 8 (1), 114-123. 5. Weekman, V. W.; Nace, D. M., Kinetics of catalytic cracking selectivity in fixed, moving, and fluid bed reactors. AIChE Journal 1970, 16 (3), 397-404. 6. Lee, L. S.; Chen, Y. W.; Huang, T. N.; Pan, W. Y., Four‐lump kinetic model for fluid catalytic cracking process. The Canadian Journal of Chemical Engineering 1989, 67 (4), 615-619. 7. Theologos, K.; Markatos, N., Advanced modeling of fluid catalytic cracking riser‐type reactors. AIChE Journal 1993, 39 (6), 1007-1017. 8. Xu, O.-g.; Su, H.-y.; Mu, S.-j.; Chu, J., 7-lump kinetic model for residual oil catalytic cracking. Journal of Zhejiang University SCIENCE A 2006, 7 (11), 1932-1941. 9. Farag, H.; Ng, S.; de Lasa, H., Kinetic modeling of catalytic cracking of gas oils using in situ traps (FCCT) to prevent metal contaminant effects. Industrial & engineering chemistry research 1993, 32 (6), 10711080. 10. Zheng, Y.-Y., Dynamic modeling and simulation of a catalytic cracking unit. Computers & chemical engineering 1994, 18 (1), 39-44. 11. Ali, H.; Rohani, S.; Corriou, J., Modelling and control of a riser type fluid catalytic cracking (FCC) unit. Chemical Engineering Research and Design 1997, 75 (4), 401-412. 12. Blasetti, A.; De Lasa, H., FCC riser unit operated in the heat-transfer mode: Kinetic modeling. Industrial & engineering chemistry research 1997, 36 (8), 3223-3229. 13. Gupta, A.; Rao, D. S., Model for the performance of a fluid catalytic cracking (FCC) riser reactor: effect of feed atomization. Chemical Engineering Science 2001, 56 (15), 4489-4503. 14. Jacob, S. M.; Gross, B.; Voltz, S. E.; Weekman, V. W., A lumping and reaction scheme for catalytic cracking. AIChE Journal 1976, 22 (4), 701-713. 15. Oliveira, L. L.; Biscaia, E., Catalytic cracking kinetic models. Parameter estimation and model evaluation. Industrial & engineering chemistry research 1989, 28 (3), 264-271. 16. Coxson, P. G.; Bischoff, K. B., Lumping strategy. 1. Introductory techniques and applications of cluster analysis. Industrial & engineering chemistry research 1987, 26 (6), 1239-1248. 17. Theologos, K.; Nikou, I.; Lygeros, A.; Markatos, N., Simulation and design of fluid catalytic-cracking riser-type reactors. AIChE Journal-American Institute of Chemical Engineers 1997, 43 (2), 486-494. 18. Pitault, I.; Nevicato, D.; Forissier, M.; Bernard, J.-R., Kinetic model based on a molecular description for catalytic cracking of vacuum gas oil. Chemical engineering science 1994, 49 (24), 4249-4262. 19. Richter, H. J.; Knoche, K. F. In Reversibility of combustion processes, ACS Symposium series, Oxford University Press: 1983; pp 71-85. 20. (a) Fan, L.-S.; Zeng, L.; Wang, W.; Luo, S., Chemical looping processes for CO 2 capture and carbonaceous fuel conversion–prospect and opportunity. Energy & Environmental Science 2012, 5 (6), 72547280; (b) Mattisson, T.; Lyngfelt, A., Capture of CO2 using chemical-looping combustion. ScandinavianNordic Section of Combustion Institute 2001, 163-168. 21. Zaman, M.; Lee, J. H., Carbon capture from stationary power generation sources: a review of the current status of the technologies. Korean Journal of Chemical Engineering 2013, 30 (8), 1497-1526. 22. (a) Adanez, J.; Abad, A.; Garcia-Labiano, F.; Gayan, P.; Luis, F., Progress in chemical-looping combustion and reforming technologies. Progress in Energy and Combustion Science 2012, 38 (2), 215-282; (b) Cho, P.; Mattisson, T.; Lyngfelt, A., Comparison of iron-, nickel-, copper-and manganese-based oxygen carriers for chemical-looping combustion. Fuel 2004, 83 (9), 1215-1225. 23. Kang, K.-S.; Kim, C.-H.; Bae, K.-K.; Cho, W.-C.; Kim, S.-H.; Park, C.-S., Oxygen-carrier selection and thermal analysis of the chemical-looping process for hydrogen production. International journal of hydrogen energy 2010, 35 (22), 12246-12254. 24. Wolf, J.; Anheden, M.; Yan, J., Comparison of nickel-and iron-based oxygen carriers in chemical looping combustion for CO 2 capture in power generation. Fuel 2005, 84 (7), 993-1006.


Energy & Fuels

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25. Aboosadi, Z. A.; Rahimpour, M.; Jahanmiri, A., A novel integrated thermally coupled configuration for methane-steam reforming and hydrogenation of nitrobenzene to aniline. international journal of hydrogen energy 2011, 36 (4), 2960-2968. 26. Abbasi, M.; Farniaei, M.; Rahimpour, M. R.; Shariati, A., Enhancement of hydrogen production and carbon dioxide capturing in a novel methane steam reformer coupled with chemical looping combustion and assisted by hydrogen perm-selective membranes. Energy & Fuels 2013, 27 (9), 5359-5372. 27. Rimaz, S.; Iranshahi, D., A Novel Chemical Looping Combustion (CLC)-Assisted Catalytic Naphtha Reforming Process for Simultaneous Carbon Dioxide Capture and Hydrogen Production Enhancement. Energy & Fuels 2015, 29 (3), 2022-2033. 28. Ancheyta, J., Modeling and simulation of catalytic reactors for petroleum refining. John Wiley & Sons: 2011. 29. Ali, H.; Rohani, S., Dynamic modeling and simulation of a riser‐type fluid catalytic cracking unit. Chemical engineering & technology 1997, 20 (2), 118-130. 30. Ahari, J. S.; Farshi, A.; Forsat, K., A mathematical modeling of the riser reactor in industrial FCC unit. Petroleum and Coal 2008, 50 (2), 15-24. 31. Levenspiel, O., Chemical engineering reaction. Wiley-Eastern Limited, New York 1972. 32. Mattisson, T.; Johansson, M.; Lyngfelt, A., The use of NiO as an oxygen carrier in chemical-looping combustion. Fuel 2006, 85 (5), 736-747.


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Table Captions:

Table 1. Specifications of reactors, feedstock, catalyst and operating conditions of Conventional Residue Fluid Catalytic Cracking (CRFCC). Table 2. Design characteristics and operating condition of AR and FR in RFCC-CLC system. Table 3. Rate constants, activation energies, heat of reactions, molecular weights and catalyst deactivation parameters for residue fluid catalytic cracking. Table 4. Specifications and kinetic parameters of oxidation and reduction of NiO18-α-Al2O3 oxygen carriers in CLC system. Table 5. Mass and energy balances for RFCC-CLC system. Table 6. Auxiliary relations. Table 7. Comparison between model prediction and industrial plant data.


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Table 1. Operating Conditions Feed flow rate (kg/s)

25.7

Inlet pressure (Pa)

290

Feed temperature (K)

494

Catalyst temperature (K)

1033

Steam temperature (K)

773

Riser Reactor Specifications Riser diameter (m)

0.8

Riser height (m)

33 Feedstock Specifications

Feed quality (API)

21.7

Total sulfur (wppm)

8700

Total nitrogen (wppm)

1600

Refractive index (at 67 °C)

1.4924

Aniline point

79.4

Carbon residue

0.6

Carbon-to-hydrogen ratio

84.7-12.4

Viscosity (cSt @ 100 °C)

7.32 ASTM (˚C)

IBP

211.9

10 wt %

320.3

20 wt %

354.9

30 wt %

382.4

40 wt %

408

50 wt %

428.9

60 wt %

449.7

70 wt %

473.7

80 wt %

501.6

90 wt %

536.6

FBP

623.7 Typical properties of catalyst

Size range (µm)

10-200

Mean size (µm)

50-80

3

Density (kg/m )


1500-1800

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Energy & Fuels

Heat capacity (J/kg K)

1087

Table 2. Air Reactor Inlet temperature (K)

880

Inlet pressure (bar)

20

Inside diameter (m)

2.65

Void fraction

0.52-0.8

Solid inventory (kg)

42900

Excess air

20%

NiO circulation rate (mol/s)

600

Feed velocity (m/s)

8

Particle size (µm)

40 Fuel Reactor

Inlet temperature (K)

840

Inlet pressure (bar)

10

Inside diameter (m)

3.75

Void fraction

0.52-0.8

Solid inventory (kg)

42900

Excess air

20%

NiO circulation rate (mol/s)

600

Feed velocity (m/s)

7

Particle size (µm)

40


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Table 3. Reaction

ko

E (kJ/mol)

∆H (kJ/kg)

gasoil → gasoline

1475.5

57.36

195

gasoil → lightgas

127.59

52.75

670

gasoil → coke

1.98

31.82

754

gasoline → lightgas

256.81

65.73

530

gasoline → coke

0.000629

66.57

690

Arrhenius equation is applied to determine the reaction rates and catalyst deactivation rate. MW (kg/mol) Gas oil 0.333

Gasoline

Light gas

Coke

0.1067

0.040

0.144

Catalyst Deactivation Parameters ko

E (kJ/mol)

83800

117.72

Arrhenius equation is applied to determine the reaction rates and catalyst deactivation rate.


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Energy & Fuels

Table 4. Specifications NiO content

20 wt% 2

BET surface area (m /g)

7

Porosity

43% 3

Density (g/cm )

2.5 Kinetic Parameters

(

)

(

n

k o mol 1− n m 3n − 2s −1

Reduction with CH4

0.2

0.2

5

Oxidation with O2

0.7

0.84

22


E kJ ⋅ mol −1

)

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Table 5. RFCC

D ej

m ∂C j  ∂C j 1 ∂  1 ∂ AC R u z C j + ρb Φ ∑ν ij ri = ε  AC R − A C R ∂z  ∂ z  AC R ∂ z ∂t i =1

(

)

(10)

Φ = exp ( −k deactivationt c ) Arrhenius equation is applied to determine catalyst deactivation rate. j= 1, 2, 3, ..., n i= 1, 2, 3, …, m

∂T R  ∂T R PperR 1 ∂   m  + U (T A R −T R ) +  K eff AC R  − Φρb  ∑ ∆H i ri  − u z C p ∂z  ∂z AC R ∂z  AC R  i =1  ∂C T ∂T R ε RT R = ε C T CV ∂t ∂t

(11)

Air Reactor

Dej

∂ 2C j ∂z 2

−uz

∂C j ∂z

+ (1 − ε b )υ j R AR = ε

∂C j

(12)

∂t

(u ρC ) + (u ρC )  ∂T A R + (1 − ε )υ R ∆H − PperR U (T −T ) − PperAR U (T −T ) + p OC p g b j AR OX AR R AR FR   ∂z AC AR AC AR 1 AC AR

∂ ∂z

(13)

n n ∂C j ∂T AR  ∂T AR  ′ = + K A C C ε ε b ∑U j  eff C AR  b∑ j Vj ∂z  ∂t ∂t  j =1 j =1

Fuel Reactor

Dej

∂ 2C j ∂z 2

−uz

∂C j ∂z

+ (1 − ε b )υ j R FR = ε

∂C j ∂t

(u ρC ) + (u ρC )  ∂T FR + (1 − ε )υ R ∆H − PperA R U (T −T ) + 1 ∂  K ′ A ∂T FR  p OC p g b j FR RE FR AR  eff C FR    ∂z AC FR AC FR ∂z  ∂z  n

= ε b ∑ C j CV j j =1

(14)

(15)

n ∂C j ∂T FR + ε b ∑U j ∂t ∂t j =1

Boundary and initial conditions

z = 0:

C j = C j0

(16)


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Energy & Fuels

T =T 0 z =L:

∂C j ∂z

=0

(17)

∂T =0 ∂z

t = 0:

C j = C ssj

(18)

T = T ss T s = T sss Φ=1


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Table 6. Component Heat Capacity

C p = a + bT + cT 2 + dT −2

(19)

2

    c3 c5     T T  +c4   c1 + c 2   sinh  c 3    sinh  c 5         T  T 

2

(20)

Component Viscosity

µ=

c1T c 2 c c 1 + 2 + 42 T T

(21)

Heat-Transfer Coefficient Between the Gas Phase and the Reactor Wall

 c µ  2 3  0.458  µ  p   =  ε B  ρud p C p ρµ  K     h

  

0.407

(22)

Overall Heat-Transfer Coefficient

D  A i ln  o  1 1  D i  + Ai  1  = +   U hi 2π LK w A 0  h0 


(23)

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Energy & Fuels

Table 7. Inlet Conditions Industrial plant

CRFCC

RFCC_CLC

Temperature (K)

868

868

868

Pressure (bar)

2.9

2.9

2.9

Industrial plant

CRFCC

RFCC_CLC

801

814

859

Pressure (bar)

2.530

2.838

2.846

Gasoline (wt%)

52.5

58

68

Light gas (wt%)

19.4

21

17.5

Coke (wt%)

4.1

3.5

2.2

Outlet Results

Temperature (K)


Energy & Fuels

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Figure Captions:

Figure 1. Scheme of conventional Chemical Looping Combustion (CLC) process. Figure 2. Schematic diagram for Residue Fluid Catalytic Cracking Coupled with Chemical Looping Combustion (RFCC-CLC) (a) Top view, (b) Front view. Figure 3. Depiction of the differential element with length dz along the length of RFCC-CLC system. Figure 4. Variation of gas oil mass fraction along the dimensionless length of RFCC and RFCC-CLC systems. Figure 5. Variation of (a) gasoline, (b) coke and (c) light gas mass fractions along the dimensionless length of RFCC and RFCC-CLC systems. Figure 6. Conversion of cracking reactions along the dimensionless length of RFCC and RFCC-CLC systems. Figure 7. Pressure of riser along the dimensionless length of RFCC and RFCC-CLC systems. Figure 8. Variation of mole percent of various components along the length of reactors in the RFCC-CLC (a) in the air reactor and (b) in the fuel reactor. Figure 9. Methane conversion along the length of fuel reactor. Figure 10. Thermal profile of riser in RFCC and RFCC-CLC configurations. Figure 11. Temperature variation profile along the fuel reactor. Figure 12. Temperature variation profile along the air reactor.


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Figure 1.


Energy & Fuels

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Figure 2. (a)


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Figure 2. (b)


Energy & Fuels

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Figure 3.


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Figure 4.


Energy & Fuels

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Figure 5. (a)


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Figure 5. (b)


Energy & Fuels

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Figure 5. (c)


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Figure 6.


Energy & Fuels

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Figure 7.


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Figure 8. (a)


Energy & Fuels

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Figure 8. (b)


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Figure 9.


Energy & Fuels

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Figure 10.


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Figure 11.


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Figure 12.


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Novel Chemical Looping Combustion Assisted Residue Fluid Catalytic

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