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TRANSCRIPT
Does your
FCC catalyst add up?
Manfred Brown, Johnson Matthey Process Technologies
2
Fluid catalytic cracker (FCC)
catalysts and additives are generally
considered the second greatest
refinery operating expense after
crude oil purchases. This fact is often
quoted, but it is surprising how often
their use is inefficient because of how
they are added to the FCCU thanks
to inadequate addition systems. This
often leads to more catalyst being used
than necessary; erratic control leads to
cat crackers running at non-optimum
activity levels, reduced throughputs
and inferior product yields. Poor control
of additives additions can lead to a
number of expensive consequences
such as loss of compliance in SOX and
NOX emissions or reduced valuable
LPG olefins yields. The cost of poorly
controlled additions is considerable
and erodes refinery operating margins.
This article examines the variety
of addition devices available on
the market today and uses real
world operating data to assess how
accurate and reliable they really are.
Introduction to addition systems
The importance of steady catalyst
activity at the optimum level in an FCC
cannot be understated. It determines
the unit’s activity and product slate,
enhances gasoline, diesel or LPG
olefins yields and, ultimately, whether
the FCC is profitable or not. Steady
activity can only be attained with
continuous, controlled fresh catalyst
additions. If the addition equipment
is unreliable or adds in batches rather
than continuously, there will always be
periods when the FCC is not at its most
profitable.
Early designs of FCCs paid scant
regard to the provision of catalyst
additions. There would be simply a
pipe with aeration points running
from the fresh cat hopper to the FCC
regenerator. Additions were made
on a shift by shift basis, the amount
being controlled by observation of the
regenerator catalyst level. Some units
were controlled semi automatically
where the dosing valves were opened
with timers, but these were prone to
blockages, valve failure or, at best,
variable addition rates. The author
recalls instructions written for such
a system that blocked regularly. The
solution was to ‘rap sharply on the pipe
with a non-sparking implement’. There
were also catalyst feeders, which were
essentially rotary valves. These were
not much better than the pipe design
and also frequently broke down. None
of these early systems gave reliable
additions at the amounts required,
which typically varies from less than
a tonne to tens of tonnes per day.
The shot pot
The first attempts at good catalyst
addition control were based on the
shot pot design. Most FCCs had been
provided with a manual shot pot with
which to add a few kilograms of CO
promoter. These consisted of a funnel
type vessel with a capacity of a few
litres. The funnel was filled with a bag
of promoter and it was then blown into
the regenerator to control afterburn.
Automated versions of these were
built (similar to the layout shown in
Figure 1) and used for fresh catalyst
additions.
The shot pot consisted of a small
pressure vessel, typically with a catalyst
capacity of 50 - 100 kg, mounted on
or suspended from load cells. The
unit was installed underneath the
fresh catalyst hopper. The load cells
measured the weight of the vessel and
its contents. A controller sequenced
the associated valves to depressurise
the vessel, fill from the fresh cat
hopper above, pressurise the vessel
then blow the contents into the FCC
regenerator. In order for the load
cells to weigh the vessel accurately,
all connections to it must be through
flexible joints, typically rubber. Usually
butterfly valves were used for catalyst
control and small gate or ball valves
for air/vent. The inherent weakness
of these systems is the constant and
frequent pressure cycling leading to
failure of the rubber joints and erosion/
sticking/passing of the valves. After the
first year or so of operation, these units
usually require frequent maintenance
and rarely add at reliable rates.
Many variations of this basic design
Does your FCC catalyst add up?
FCC catalysts and additives are generally considered the second greatest refinery
operating expense after crude oil purchases. Manfred Brown, Johnson Matthey, UK,
examines the variety of addition devices available on the market today, using real
world operating data to assess their accuracy and reliability.
Reprinted from Hydrocarbon Engineering, September 2015
have been tried with the addition
of vacuum systems to allow refilling
from tote bins, additional vessels to
hold bulk amounts, multiple source
designs, better valves, etc. Reliability
has improved in recent years but they
still suffer from mechanical failure, an
inevitable consequence of frequent
pressure cycling.
Another issue with these units
is that they rely on summation
of the weights of each shot to
calculate daily additions. Thus any
error in weighing is compounded
by the number of shots in a day.
Additive addition system design
In the late 1980s, Intercat, Inc.
introduced a new design of loader
for the dosing of additives to the FCC.
These used a larger vessel than the
shot pot and dosed directly from it
whilst maintaining constant pressure.
The current design is shown in Figure
2.
The vessel has a volume of 50 ft3
(1.4 m3) and a capacity of 1000 kg of
additive. Additions are in the region of
10 - 500 kg/d. For higher additions,
larger units are available. The whole
unit is supported by three load cells
so the number of flexible hoses is
minimised to two: air supply and
product discharge; high quality 1 in.
SS hoses are used.
In normal operation, a steady flow
of carrier air flows through the unit
piping, to the FCC, controlled by a
1 in. globe valve. The vessel is kept
pressurised at approximately 4 barg,
depending on the back pressure from
the regenerator. Below the vessel
are two valves: a ball valve and an
Everlasting Valve. The former is kept
open and only closed when abnormal
conditions arise such as unexpected
weight loss. The second valve controls
product flow. This valve is specially
designed for Intercat, Inc. by the
Everlasting Valve Company and is of
a rotating/shearing disk design. It has
many proprietary modifications and
has been found to be very reliable in this
service, typically operating for 10 years
or more without maintenance. The
valve is opened by the controller (IMS)
for a set time, usually approximately
30 seconds and the weight drop
noted. The controller then calculates
how many such shots are required
that day to meet the target addition
rate and thus sets the time to wait
until the next shot. For example, if the
addition rate is to be 240 kg/d and the
last shot was 5 kg, then 48 shots are
required per day so the loader will wait
30 minutes before the next shot. This
calculation is repeated after every shot
so variations in back pressure from the
regenerator or other unit events will
always be accounted for.
The fundamental advantages with
this design are its simplicity and few
pressure cycles. There are only two flex
hoses and the only valve that comes
into frequent contact with catalyst is the
Everlasting Valve. Reinforced seat ball
valves are used for all other valves and
are on/off only (except for the carrier
3
Figure 1. Shot pot design
Figure 2. INTERCATJM
TM AAS
Reprinted from Hydrocarbon Engineering, September 2015
air globe valve). Whereas a shot pot is
expected to pressure cycle 50 or more
times a day, the INTERCATJM
design
only needs refilling every few days.
INTERCATJM
fresh catalyst addition
system design
Following the success of the
INTERCATJM
AAS, systems were
designed for fresh catalyst. These are
of two varieties: a large version of the
AAS and a day hopper design. The
former is simply a large AAS; units with
capacities up to 120 t are in use. These
are refilled directly from bulk trucks in
much the same way as fresh catalyst
hoppers.
The day hopper uses a vessel of 5
or 10 t capacity as an addition system,
automatically refilled from the FCC’s
fresh catalyst hopper. A typical layout
is shown in Figure 3.
The day hopper operates the same
way as the AAS but, when empty,
the IMS controller automatically
refills the day hopper from the fresh
catalyst hopper. These have been very
successful in a number of locations,
again because of their simplicity and
the refill cycles being kept to once a
day or so; although there are units
successfully in operation loading
25 tpd of fresh catalyst, refilling the
day hopper five or six times a day. For
comparison, a 50 kg shot pot would
have to cycle 500 times/d at these rates.
Multi compartment loaders
A recent innovation is the multi
compartment loader. This is a 200
ft3 (5.7 m3) AAS vessel that has
baffles dividing it into (usually) three
compartments, one of 2 t capacity
and two of 1 t capacity. These operate
in the same way as the AAS above but
each compartment has its own outlet,
with valves and refilling line. Thus the
loader can add up to three different
products, be they fresh catalyst or
additives.
As there is only a single vessel, plot
space is far less than three separate
loaders and the controller ensures
no conflicts can occur between the
4
Figure 3. INTERCATJM
AAS with day hopper
Figure 4. INTERCATJM
multi compartment loader (MC3)
Reprinted from Hydrocarbon Engineering, September 2015
5
additions of the three materials.
These units are also being used
as fresh catalyst addition systems
with the large compartment being
auto refilled (as with the CAS above)
and the other two used for additives.
Precision data
Just how accurate are these
addition systems? Most units report a
high level of accuracy on their screens,
but are these numbers real? The
only way to check is by reconciling
the reported addition history from
the addition system with the known
(accurately weighed) deliveries of
catalyst to the refinery. A study was
therefore carried out of a number
of addition systems, covering many
different designs, and this has revealed
some surprising data on the precision
and reliability of these systems.
Shot pot data
Comparing the amounts of material
delivered to the refinery with the sum
of additions to the FCC regenerator,
Table 1 shows the errors of shot pot
loaders at eight different refineries.
The average error of the examples
above is a disappointing 7.8%. There is
also a high degree of variability in these
data, showing that the true accuracy
of these small devices is highly
unpredictable and is fundamentally
limited by the antiquated design.
Single AAS data
The data from three single
INTERCATJM
loaders were looked at
closely to check overall reliability and
precision. Different sized units were
chosen to see if large loaders are less
precise than smaller ones: a 50 ft3 (1
t), a 500 ft3 (10 t) and a 1100 ft3 (25 t).
Example 1: 50 ft3 AAS (1 t capacity)
Details:• Loaded from tote bins.
• Adding ZSM-5 additive at ~150 lb/d (68 kg).
• Data were examined from more than 2.5 years (1013 days) operation.
Figure 5 shows the data from this
unit. The triangles indicate refills from
a tote bin and the diamonds the end
of day weight of additive in the loader.
When one compares the actual
amount of catalyst added over a 2.5
year period with the amount reported
by the addition system, the following
results are achieved:
• Total reported additions to FCC =
104,347 lbs.
• Total refills by tote bin = 104,997
lbs.
• Loader accuracy = 99.4%.
• Loader error = 0.62%.
In other words, the true amount
of catalyst added by this addition
system over a 2.5 year period was
within 0.6% of the reported amount.
This is an impressive result and
testament to the quality and reliability
of this style of addition system.
Figure 5. Example 1: 50 ft3 refills and additions
Reprinted from Hydrocarbon Engineering, September 2015
Refinery A 3.6%
Refinery B 24.9%
Refinery C 5.3%
Refinery D 0.7%
Refinery E 7.9% 5.6%
4.9%
Refinery F 18.0% 12.9%
7.0%
Refinery G 3.9% 3.1%
1.6%
Refinery H 6.5% 6.6%
6.4%
10.0%
Single
shot pots Error
Multi source
shot pots
Overall
error
Individual
product error
Table 1. Shot pot errors
Example 2: 500 ft3 AAS (10 t capacity)
Details:
• Loaded from bulk trucks.
• Adding SOX reduction additive at
~1500 lb/d (680 kg).
• Data were examined from more
than 1.5 years (604 days)
operation.
• Refill data are from the supplier
shipment amounts and are
therefore guaranteed to be
accurate.
When one compares the actual
amount of catalyst added over a
1.5 year period with the amount
reported by the addition system,
the following results are achieved:
• Total reported additions to FCC =
683,085 lbs.
• Total catalyst deliveries from bulk
trucks = 681,500 lbs.
• Loader accuracy = 100.2%.
• Loader error = -0.23%.
In other words, the true amount
of catalyst added by this addition
system over a 1.5 year period was
within 0.2% of the reported amount.
Once again this is a remarkable result,
reinforcing the fundamental accuracy
of this design of addition system.
Example 3: 1100 ft3 AAS (25 t capacity)
Details:
• Loaded by trucks.
• Adding SOX additive at ~1000
lb/d.
• Data were examined from more
than 1.5 years (588 days)
operation.
• Once again, refill data are from
the supplier shipment amounts
and are therefore guaranteed to
be accurate.
• Comparing totals, one can
conclude the following:
• Total reported additions to FCC =
486,505 lbs.
• Total catalyst deliveries from bulk
trucks = 493,105 lbs.
• Loader accuracy = 98.7%.
• Loader error = 1.3%.
In other words, the true amount of
catalyst added by this addition system
over a 1.5 year period was within 1.3%
of the reported amount. Once again
this is an impressive level of accuracy.
Multi compartment data
Multi compartment loader units
can show similar low errors to
conventional AAS. Data from two
MC3 loaders that are using the large
6
Reprinted from Hydrocarbon Engineering, September 2015
Figure 7. Equilibrium catalyst MAT
Figure 6. Fresh catalyst addition deviations on 8 tpd
Information contained in this publication or as may be otherwise supplied by Johnson Matthey is believed to be accurate and correct at the time of publication and
is given in good faith. JOHNSON MATTHEY GIVES NO WARRANTIES, EXPRESS OR IMPLIED, REGARDING MERCHANTABILITY OR FITNESS OF ANY PRODUCT
FOR A PARTICULAR PURPOSE. Each User must determine independently for itself whether or not the Products will suitably meet its requirements. Johnson
Matthey accepts no liability for loss or damage resulting from reliance on this information other than damage resulting from the death or personal injury caused by
Johnson Matthey’s negligence or by a defective product. Freedom under Patent, Copyright and Designs cannot be assumed.
7
compartment for fresh catalyst have
recently been reviewed. Both show
excellent accuracy for fresh catalyst,
0.4% and 0.3% errors respectively,
and very good accuracy for additives,
1.4% and 0.8% respectively.
Fresh catalyst loader
CAS shows the same accuracy and
precision as AAS. A very good example
was previously published for a BP unit.1
This was a 70 m3 system, designed
to add up to 12 tpd with occasional
additions at 30 tpd. Target daily
additions at 8 tpd gave the deviations
shown in Figure 6. These show addition
accuracy within 0.2%. This resulted in
far better control of unit equilibrium
catalyst activity (MAT) as shown in
Figure 7. This superior control of MAT
permitted inferior feeds to be run and/
or higher MATs to be targeted. This
project paid for itself in less than a year.
Conclusion
Control of fresh catalyst and additive
additions to an FCC unit is critical
for unit throughput, yields, product
slate, environmental compliance and,
ultimately, profitability.
Simple pipe valve and shot pot
systems are inaccurate, unreliable, require
high maintenance and will reduce the
cracking margins on the operating FCC.
When running, the error of shot pots
is almost 8% when reconciled against
catalyst deliveries to the refinery. Would
this degree of inaccuracy be acceptable
for other major refinery expenditures
such as raw oil or energy?
Larger INTERCATJM
additive and
fresh catalyst addition systems have
been shown to consistently operate at
less than 2% error, usually well below
1%. This is true of small, large and multi
compartment systems. This results in
higher in unit catalyst activity, lowers
maintenance requirements, improves
yields, allows higher throughput and
the processing of cheaper feeds.
References
BROWN, M., and CAMERON, A.,
"A Fresh Approach", March 2006,
Hydrocarbon Engineering.
Reprinted from Hydrocarbon Engineering, September 2015
For further information on Johnson Matthey, please contact your local sales representative of visit our website.
INTERCAT is a trademark of the Johnson Matthey group of companies.