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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


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


AAS with day hopper


multi compartment loader (MC3)


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


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


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:


683,085 lbs.

• Total catalyst deliveries from bulk

trucks = 681,500 lbs.


• 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.


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:


486,505 lbs.

• Total catalyst deliveries from bulk

trucks = 493,105 lbs.


• 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


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.


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.

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