Molecular sieve abstract
A process for regenerating spent molecular sieve catalysts from
a fluidized catalytic cracking unit in an oil refinery with high
temperature flue gas from a second group of cyclones with the spent
catalyst in a first riser regenerator to form a mixture of a half-regenerated
catalyst and flue gas, separating the half-regenerated catalyst
from the mixture formed in the previous step in a first group of
cyclones, mixing the half-regenerated catalyst from the first group
of cyclones with a sufficient amount of air for burning off coke
on the spent catalyst in a second riser regenerator to form a mixture
of high-temperature flue gas and a regenerator catalyst, separating
the regenerated catalyst formed from the preceding step from the
mixture in the second group of cyclones and recovering the surplus
heat from the regenerated catalyst from the second group of cyclones
by a regenerated catalyst cooler.
Molecular sieve claims
What is claimed is:
1. A process for regenerating a spent molecular sieve catalyst
comprising the steps of:
(1) mixing a high temperature flue gas that comes from a second
group of cyclones with the spent catalyst in a first riser regenerator
to form a mixture of a half-rengenerated catalyst and a flue gas
at the top of the first riser regenerator;
(2) separating the half-regenerated catalyst from the mixture formed
in step 1 in a first group of cyclones;
(3) mixing the half-regenerated catalyst that comes from the first
group of cyclones with a sufficient amount of air for burning off
all coke on the spent catalyst in a second riser rengerator to form
a mixture of a high temperature flue gas and a regenerated catalyst
at the top of the second riser regenerator;
(4) separating the regenerated catalyst from the mixture formed
in step 3in the second group of cyclones; and
(5) recovering surplus heat from the renegerated catalyst that
comes from the second group of cyclones by a regenerated catalyst
cooler which is located outside of the second riser regenerator.
Molecular sieve description
FIELD OF THE INVENTION
The present invention relates to a process for regenerating a spent
molecular sieve catalysts of the Fluidized Catalytic Cracking Unit
(FCCU) in oil refinery. More particularly, the present invention
relates to a process for regenerating a spent molecular sieve catalysts
using two riser regenerators.
DESCRIPTION OF THE PRIOR ART
Up till now, the molecular sieve catalyst, which has been used
in FCCU, is regenerated in a fluidized bed and a combustion riser.
The combustion riser is not used alone, and must be used in combination
with a fluidized bed. But, the fluidized bed regeneration has the
following problems: long catalyst residence time, serious catalyst
back-mixing, low Carbon Burning Intensity (CBI), complicated inside
structures, difficult to uniformly fluidize and keep a good distribution
of particles, easy damage of the inside equipment, etc.
In recent years, the riser regenerator has received substantial
interest. But, coke combustion in the riser regenerator requires
circulation of a high temperature catalyst and air injection at
various heights of the riser regenerator, and back-mixed problem
has not been solved. It is not able that main operation parameters
such as space-velocity and temperature are both high at the same
time.
BRIEF SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide
a process of regenerating spent molecular sieve catalysts comprising
the steps of:
(1) mixing a high temperature flue gas that comes from a second
group of cyclones with the spent catalyst in a first riser regenerator
to form a mixture of a half-regenerated catalyst and a flue gas
at the top of the first riser regenerator;
(2) separating the half-regenerated catalyst from the mixture in
a first group of cyclones;
(3) mixing the half-regenerated catalyst that comes from the first
group of cyclones with a sufficient amount of air for burning off
all coke on the spent catalyst in a second riser regenerator to
form a mixture of a high temperature flue gas and a regenerated
catalyst at the top of the second riser regenerator;
(4) separating the regenerated catalyst from the mixture in the
second group of cyclones; and
(5) recovering surplus heat from the regenerated catalyst that
comes from the second group of cyclones by a regenerated catalyst
cooler which is located outside of the second riser regenerator.
DESCRIPTION OF THE DRAWINGS
The FIGURE is a schematic representation of a process flow diagram
of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The first group of cyclones and the second group of cyclones are
located outside of the first riser regenerator and the second riser
regenerator, respectively.
The half-regenerated catalyst is formed by burning off the most
of hydrogen and about 50.about.80 wt % carbon on the spent catalyst.
In a preferred embodiment, a slide valve is installed at the entrance
of the last cyclone of the first group of cyclones for adjusting
separation efficiency.
The regenerated catalyst is formed by mixing the high temperature
half-regenerated catalyst with a sufficient amount of air for burning
off all coke on the spent catalyst to burn off the remainder coke
on the half-regenerated catalyst in the second riser regenerator.
In a preferred embodiment, the mixture in the first and second
riser regenerator flows in plug flow form.
By comparing with the prior art, the process according to this
invention possesses the following effects:
(1) The coke on the spent catalyst can be fully burnt off. The
regenerated catalyst can be restored to the highest activity.
(2) All catalyst inventories in the regenerators can be reduced
to a very low level. The CBI is about 10 times of the fluidized
bed.
(3) The carbon burning time is very short and usually about 10
second per a circulation. The summation of carbon burning time is
about 1.21 hours every day. The activity of the regenerated catalyst
is remained well.
(4) The poisoning of the catalyst caused by the heavy metal such
as nickel can be restrain by the high temperature and more than
10 volume percent oxygen flue gas in the second riser regenerator
and the fluidization air in the regenerated catalyst cooler.
(5) The investment is the most economical, the production cost
is very low, the operation range is wide and the maintenance of
the equipment is easy.
(6) The plug flow may extenuate the back-mixing degree of the catalyst.
(7) The CO oxidation promoter is eliminated because this process
has not the harm of after-burning.
(8) The slide valve can be fit up on the entrance of the last cyclone
of the first group of cyclones to reduce the loss of the catalyst.
Now referring to the FIGURE, a spent molecular sieve catalyst flows
down the spent catalyst pipe 10 to the first riser regenerator 1.
The spent catalyst at the bottom of the first riser regenerator
mixes with a high temperature flue gas 6 which comes from the second
group of cyclones 5 to bum off most hydrogen and about 50.about.80
wt % carbon and to form a mixture of a half-regenerated catalyst
and a flue gas. The mixture is introduced into the first group of
cyclones 4 located outside of the first riser regenerator 1. The
half-regenerated catalyst is separated from the mixture in the first
group of cyclones 4. The half-regenerated catalyst may flow down
a pipe to a buffer tank (not shown), then to the second riser regenerator
2 or directly flow down a pipe 17 to the second riser regenerator
2. A sufficient amount of air 16 for burning off all coke on the
spent catalyst is introduced into the bottom of the second riser
regenerator 2 through air heater 18. The half-regenerated catalyst
mixes with air 16 in the second riser regenerator 2 to burn off
the remainder coke on the half-regenerated catalyst and to form
a mixture of a high temperature flue gas and a regenerated catalyst.
The mixture is introduced into the second group of cyclones 5 located
outside of the second riser regenerator 2. The regenerated catalyst
is separated from the mixture in the second group of cyclones 5.
Then, the regenerated catalyst flows down a pipe to cooler 3 to
recover surplus heat from it. Finally, the regenerated catalyst
flows down the regenerated catalyst pipe to a riser reactor 7. The
high temperature flue gas 6 which is from the second group of cyclones
5 contains more than 10 volume percent oxygen and some fine catalyst
particles and is introduced into the bottom of the first riser regenerator
1 to carry, heat and ignite the coke on the spent catalyst.
In the FIGURE, reference numeral 8 refers to fluidization air,
reference numeral 11 refers to flue gas, reference numeral 13 refers
to water steam, reference numeral 14 refers to deoxidizing water,
reference numeral 15 refers to a circulation pipe of the catalyst
for start-up, and reference numeral 19 refers to a air pipe.
EXAMPLE
Suppose a regeneration system of FCCU has a capacity of 200000
tons per year of fresh feed, and coke yield is 8 wt %, the calculation
results are as follows:
First riser Second riser regenerator Regenerator Top temperature/.degree.
C. 690 730 Pressure/MPa 0.195 0.200 Diameter/m 1.12 0.987 Length/m
30.0 40.0 Space velocity/m/s 6.0 8.0 Carbon burning time/sec. 5.0
5.0 Catalyst inventory/ton 0.547 0.547 CBI/kg/(h.t) 1827.0 1827.0
The CBI of the fluidized bed regenerator is the range of from 100
to 250 kg/(h.t). The CBI of the fluidized bed with the combustion
riser is the range of from 400 to 600 kg/(h.t).
The average CBI of the riser regenerator of this invention is about
1827 kg/(h.t).
This invention makes three important breakthroughs in center task
of the regeneration process of the catalyst.
1. The coke on regenerated catalyst can be burned to zero.
2. Its CBI is about 10 times that of the fluidized bed.
3. The environment of bum coke is good enough for retaining high
activity and selectivity of the catalyst that is important for raising
the product rate of light oil and reducing the production cost of
the FCCU. |