17 research outputs found
Equivalent Reactor Network Model for the Modeling of Fluid Catalytic Cracking Riser Reactor
Modeling
description of riser reactors is a highly interesting
issue in design and development of fluid catalytic cracking (FCC)
processes. However, one of the challenging problems in the modeling
of FCC riser reactors is that sophisticated flow-reaction models with
high accuracy require time-consuming computation, while simple flow-reaction
models with fast computation result in low-accuracy predictions. This
dilemma requires new types of coupled flow-reaction models, which
should own time-efficient computation and acceptable model accuracy.
In this investigation, an Equivalent Reactor Network (ERN) model was
developed for a pilot FCC riser reactor. The construction procedure
of the ERN model contains two main steps: hydrodynamic simulations
under reactive condition and determination of the equivalent reactor
network structure. Numerical results demonstrate that with the ERN
model the predicted averaged error of the product yields at the riser
outlet is 4.69% and the computation time is ā¼5 s. Contrast
to the ERN model, the predicted error with the plug-flow model is
almost three times larger (12.79%), and the computational time of
the CFD model is 0.1 million times longer (6.7 days). The superiority
of the novel ERN model can be ascribed to its reasonably simplifying
transport process and avoiding calculation divergences in most CFD
models, as well as taking the back-mixing behavior in the riser into
consideration where the plug-flow model does not do so. In summary,
the findings indicate the capabilities of the ERN model in modeling
description of FCC riser reactors and the possibilities of the model
being applied to studies on the dynamic simulation, optimization,
and control of FCC units in the future
Numerical Simulation of the Flue Gas and Process Side of Coking Furnaces
A numerical simulation for the flue gas and process sides
of a
coking furnace with floor gas burners was conducted. The computational
fluid dynamics (CFD) approach was employed to simulate flow, combustion,
and heat transfer in the furnace. The process-side conditions were
calculated with a special program. The simulation provides detailed
information about the flue gas velocity, temperature fields, and process
conditions for this type of coking furnace. Good agreement is obtained
between industrial measurement and simulated excess air coefficient,
outlet temperature of flue gas, and outlet pressure on the process
side. Moreover, the simulated results indicate that there are hot
spots on the tubes, located at the height of 1.5ā2.5 m. That
is consistent with the actual phenomenon of industrial coking furnaces.
To investigate the effect of furnace structure on physical field distribution
and process-side conditions, a comparative simulation case with more
wide spacing of burners to walls was conducted. Results indicate that
the comparative case improves the uniformity of heat flux distribution,
obviously, which is beneficial for the run length of coking furnaces
Practical Model for the Induction Period of Heavy Oil during Thermal Reaction
The
induction period is a significant concept for design and operation
of the delayed coking process. To simplify the prediction of the induction
period and make it applicable to operational analysis and real-time
control of the thermal cracking process, a practical model for the
induction period of heavy oil during thermal reaction, which is suitable
for the non-isothermal reaction in the industrial conditions, was
presented. The development of this model was based on the experimental
data of five heavy oils. The model parameters were correlated with
microcarbon residue (MCR) of heavy oil to improve the model universality.
Furthermore, the validity of correlation between MCR and cracking
kinetic parameters was proven. The model-predicted cracking conversion
agrees well with the experimental values. The induction period model
was employed to predict the induction period of two feedstocks reported
in the literature. Results indicated that the induction period model
is available for the thermal reaction of these heavy oils
Adsorption and Separation Mechanism of Thiophene/Benzene in MFI Zeolite: A GCMC Study
Selective removal
of thiophene from aromatic components is one
of the key challenges facing the petrochemical industry. The adsorption
and separation mechanism from the molecular viewpoint can guide and
upgrade the relative adsorption based technology. Therefore, we performed
the grand canonical ensemble Monte Carlo (GCMC) simulation to investigate
the adsorption performance and mechanism of competitive adsorption.
Density distribution and radial distribution functions (RDF) analysis
give a more detailed description of the adsorption sites. For pure
component adsorption, donut-shaped adsorption sites were obtained
for both benzene and thiophene from the straight channel point. From
the viewpoint of the zigzag channel, the sorbates follow the straight
line shape distribution at low loading and the S shape distribution
at high loading. As for the binary component adsorption, more benzene
adsorbs in the zeolite than thiophene at low pressure; however, thiophene
competes successfully at high pressure. This can be explained by the
key factor: at low pressure, the size effect plays an important role.
While the pressure increases, the interaction energy dominates the
process. Analyzing RDFs of the binary adsorption, we observed that
when benzene competes with thiophene, the preferential adsorption
sites do not change; however, the emergence possibility of benzene
gets smaller
Multifunctional Two-Stage Riser Catalytic Cracking of Heavy Oil
The continuous deterioration of feedstocks, the increasing
demand
of diesel, and the increasingly strict environmental regulations on
gasoline call for the development of fluid catalytic cracking (FCC)
technology. To increase the feed conversion and the diesel yield as
well as produce low-olefin gasoline, the multifunctional two-stage
riser (MFT) FCC process was proposed. Experiments were carried out
in a pilot-scale riser FCC apparatus. Results show that a higher reaction
temperature is appropriate for heavy cycle oil (HCO) conversion, and
the semispent catalyst can also be used to upgrade light FCC gasoline
(LCG). The synergistic process of cracking HCO and upgrading LCG in
the second-stage riser can significantly enhance the conversion of
HCO while reducing the olefin content of gasoline at less expense
of gasoline yield. Furthermore, the novel structure riser reactor
can increase the conversion of olefins in gasoline. Because of the
significant increase of HCO conversion, the fresh feedstock can be
cracked under mild conditions for producing more diesel without negative
effects on the feed conversion. Compared with the TSR FCC process,
in the MFT FCC process, the increased feed conversion, diesel and
light oil yields can be achieved, at the same time, the olefin content
of gasoline decreased by approximately 17 wt %
Residue Catalytic Cracking Process for Maximum Ethylene and Propylene Production
Effects
of operating conditions on residue fluid catalytic cracking
(RFCC) were studied in a pilot-scale FCC unit. Experimental results
indicated that both high reaction severity and long residence time
promoted the production of ethylene and propylene. A novel RFCC process
for maximum ethylene and propylene (MEP) production was further proposed,
which was characterized by high operating severity, application of
olefin-selective catalyst, and stratified reprocessing of light gasoline
and butenes. Simulation experiments of the MEP process demonstrated
that both light cycle gasoline and recycled butenes were effectively
converted; meanwhile, the semispent catalyst still retained sufficient
activity to further crack residue feedstock. When treating Daqing
AR, the MEP process yielded up to 8.85 wt % ethylene and 25.97 wt
% propylene. In contrast, due to elevated catalyst activity in a second-stage
riser, the two-stage riser MEP process produced more propylene and
LPG at the expense of light oil. Also, ethylene yield was still up
to a comparative level
In Situ Upgrading of Light Fluid Catalytic Cracking Naphtha for Minimum Loss
The key to reducing the olefin content
in fluid catalytic cracking (FCC) gasoline is to upgrade the olefin-rich
light FCC naphtha (LCN). To minimize the naphtha loss, several parameters
were investigated in a pilot-scale riser FCC apparatus. The results
indicate that, besides the reaction temperature, the catalyst-to-oil
ratio, and the catalyst type, the boiling range and the olefin content
of LCNs also have significant influence on the upgrading effect. Moreover,
a relatively short residence time is beneficial for efficiently upgrading
LCNs. In addition, the influence of the reactor structure should be
brought to our attention. When a novel structurally changed reactor
with a multinozzle feed system was used, significantly increased olefin
conversion and decreased naphtha loss can be achieved. The calculation
of hydrogen balance indicates that, because of the decrease of dry
gas and coke yields, more hydrogen in the feed can be distributed
into the desired products
Mechanistic Insights into the Pore Confinement Effect on Bimolecular and Monomolecular Cracking Mechanisms of <i>N</i>āOctane over HY and HZSMā5 Zeolites: A DFT Study
Bimolecular and monomolecular
cracking mechanisms of alkanes simultaneously
occur and have a competitive relationship, which strongly influences
the product distribution. In this work, the density functional theory
(DFT) calculation is first carried out to elucidate two cracking mechanisms
in HZSM-5 and HY zeolites. It is found that the overall apparent reaction
barrier for the monomolecular cracking reaction at 750 K in the HZSM-5
zeolite is 5.30 kcal/mol, much lower than that (23.12 kcal/mol) for
bimolecular cracking reaction, indicating that the monomolecular mechanism
is predominant in the HZSM-5 zeolite. In contrast, the bimolecular
mechanism is predominant in the HY zeolite because of a lower apparent
reaction barrier energy barrier (6.95 kcal/mol) for bimolecular cracking
reaction than that (24.34 kcal/mol) for the monomolecular cracking
reaction. Moreover, the intrinsic reason for the different mechanisms
is further elucidated. The confinement effect can effectively decrease
the energy barrier when the size of transition states is comparable
to the pore size of zeolite. The insights in this work will be of
great significance to the understanding of confinement on catalytic
cracking mechanism and to the design of highly efficient cracking
catalysts
Fluid Catalytic Cracking Study of Coker Gas Oil: Effects of Processing Parameters on Sulfur and Nitrogen Distributions
To
investigate the effects of operating conditions and the catalyst
activity on the transfer regularity of sulfur and nitrogen during
the cracking process of coker gas oil (CGO), the CGO was catalytically
cracked in a pilot-scale riser fluid catalytic cracking (FCC) apparatus
at different test environments. Then the cracked liquid products were
analyzed for sulfur and nitrogen distributions with boiling point,
from which the sulfur and nitrogen concentrations of gasoline, light
cycle oil (LCO), and heavy cycle oil (HCO) fractions were determined.
The sulfur and nitrogen compounds in each product cut, and their possible
reaction pathways were reviewed and discussed. The results show that
sulfur-containing species are easier to crack but more difficult to
be removed from the liquid product, while nitrogen compounds are easier
to form coke, then be removed from the liquid product. The sulfur
distribution of CGO is different from that of conventional feedstocks.
Different processing parameters can significantly affect the sulfur
and nitrogen distribution yields and concentrations in liquid products.
Increasing the reaction temperature and the catalyst-to-oil ratio
as well as shortening the residence time cannot only increase the
light oil yield but also improve the product quality and reduce the
SO<sub><i>x</i></sub> and NO<sub><i>x</i></sub> emissions in the regenerator
Isomerization of <i>n</i>āButane over SO<sub>4</sub><sup>2ā</sup>/Al<sub>2</sub>O<sub>3</sub>āZrO<sub>2</sub> in a Circulated Fluidized Bed Reactor: Prospects for Commercial Application
The
stability of alumina-promoted sulfated zirconia (SZA) was investigated
to achieve the isomerization of <i>n</i>-butane in a circulating
fluidized bed (CFB) unit. The pilot-scale evaluation in a CFB unit
showed high stability of the SZA catalyst and that the catalytic activity
was dominated by the residence time of <i>n</i>-butane rather
than its linear velocity. Increases in the reaction and regeneration
temperature both led to an increase in the conversion of <i>n</i>-butane and a decrease in the selectivity to isobutane, caused by
increasing side reactions. Although the regeneration was conducted
in air, a trace of SO<sub>2</sub> evolved during the regeneration,
which could be minimized at the appropriate gas stripping temperature,
low regeneration temperature, and high space time of the feed. Compared
with conventional fixed-bed technologies, the CFB process shows lower
selectivity to isobutane due to the inevitable axial back-mixing and
severe ādimerization-crackingā reaction