Hydrocarbon Processing - December 2022 - 56

Refinery-Petrochemical Integration
different reactors are the following:
* Riser plus a dense-phase bed:
Slightly higher propylene and
ethylene yields, but an increasing
coke yield of 4.09 wt%
* Dense-phase bed: Relatively higher
ethylene and propylene yields, but
the highest coke yield of 12.24 wt%
* Fast-fluidized bed: Moderate light
olefin and coke yields
* Specially configured fast-fluidized
bed: Highest propylene yield of
16.63%, a relatively higher ethylene
yield and a moderate coke yield.
The development of
FIG. 2. Temperature profile and activation energy for producing propylene along the axis of the riser.
TABLE 1. Experimental results of DCC of inferior feedstocks in different reactors
Riser +
Reactor
Feedstock
Density (20°C, kg × m-3
CCR
Hydrogen content, wt%
Catalysts
Product distribution
Ethylene, wt%
Propylene, wt%
Coke
3.12
10.93
7.14
3.89
12.67
11.23
go unwanted thermal cracking, producing
byproducts (such as methane and coke)
instead of propylene. When the catalysts
enter the fluidized dense bed, some coke
has accumulated on the surface or in the
pores. Even operating in the dense bed,
these partially deactivated catalysts are
less capable of further cracking intermediates,
such as gasoline to propylene, and
may instead lead to more coke formation.
The temperature at the bottom of the
riser must be controlled to suppress thermal
cracking. The axial temperature drop
along the riser can reach more than 50°C
(122°F). However, the activation energy
to produce propylene rises with the increasing
cracking depth of the feedstock.
Consequently, the temperature profile
within the combined reactor of the DCC
unit is inverse to the desired temperature
profile for propylene production, as
shown in FIG. 2.
56 DECEMBER 2022 | HydrocarbonProcessing.com
)
Riser
dense-phase
bed
Densephase
bed
934.2
5.58
12.15
Customized
catalyst
5.3
14.74
12.24
3.34
12.42
9.5
4.86
16.63
10.24
DCC technology is more suitable for
processing paraffin-based VGO. With
the deterioration of crude oil worldwide,
the availability of suitable feedstocks for
DCC has gradually reduced. When processing
inferior heavy oil, the yields of
coke, light catalytic cycle oil, slurry and
methane increase significantly. Therefore,
new reactors for DCC must be developed
to achieve better ethylene, propylene
and gasoline yields, even with
ultra-inferior feedstocks.
DCC of inferior feedstock in different
types of reactors. To develop a new reactor
suitable for DCC of inferior feedstocks,
the catalytic cracking of an intermediate
base hydrotreated residue was evaluated
in different types of reactors. The experimental
results are shown in TABLE 1. If the
riser's reactor is used as a benchmark, the
product distribution characteristics in the
Fastfluidized
bed
residue-tochemicals
technology. The co-authors'
company has developed a novel residueto-chemicals
(RTC) technologya
to overSpecially
configured
fast-fluidized
bed
come the defect that DCC technology
cannot handle heavier and inferior feedstocks.
The essential difference between
RTC and DCC is that the riser + dense
phase reactor in DCC is replaced by a
high-efficiency fast-fluidized bed reactor,
as shown in FIG. 3. This RTC technology
was successfully commercialized at SINOPEC
Anqing Co.'s refinery in January
2020. Compared with DCC, RTC shows
good adaptability to inferior feedstock
mixed with hydrotreated residue. More
importantly, propylene and ethylene can
be produced with higher selectivity, while
the yields of coke and slurry are reduced.
Technical features of RTC technology.
RTC technology exhibits higher selectivity
for the conversion of heavy oil to
light olefins by applying a fast-fluidized
bed reactor. The technology has the following
technical characteristics:
Higher catalyst concentration in the
RTC reactor. Most FCC reactors use riser
reactors by default, ignoring the effect of
catalyst concentration on product distribution.
However, catalyst concentration
plays the most important role in the production
of light olefins in DCC. Since the
riser reactor operates in the dilute phase
bed, some of the feed molecules that are
not in contact with the catalyst undergo
unwanted thermal cracking to produce
ethylene and methane. In contrast, RTC
technology
uses
a
fast-fluidized bed
with higher catalyst concentrations than
conventional risers. The higher catalyst
concentration in the reactor means that
the feed molecules have a good chance
of contacting the catalyst and that more

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