FCC Troubleshooting - Catalyst Losses

7/23/2019 FCC Troubleshooting - Catalyst Losses

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FCC Trouble Shooting


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Determining the Cause of a Problem

The Fluid Catalytic Cracking (FCC) process has many complex interactions

between catalyst, hardware, feed, and products.

This complexity can make it difficult to determine the cause of a problem.

When a problem arises, the first step must be to define the problem.

This is done by gathering data on current operation and comparing this

information with data from a time of normal operation.

Consider any changes that occurred near the time the problem was first

observed.


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Some Common Major Problems

High Catalyst Losses

Poor Catalyst Circulation

Poor Product Yields


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A: Definition of ProblemHigh Catalyst Loss Rate

Are losses from the reactor, regen., or both?

From one vessel mechanical or operation problem

From both vessels low system pressure or catalyst

problem

Are losses steady or increasing with time?

Steady losses blocked cyclone dipleg

Increasing hole or crack in vessel or line


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A: Definition of ProblemHigh Catalyst Loss Rate, cont.

Is fines fraction (0-40 ) in the eq. cat. decreasing

or increasing? Decreasing poor fines retention;

low fines replacement

Increasing high stream velocity; soft catalyst

Are the gas velocities in the affected vessel within

cyclone design ranges? If no unit pushed beyond operating

envelope


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A: Definition of ProblemHigh Catalyst Loss Rate, cont.

Additional questions:

Has there been a change in the particle size of theescaping catalyst?

When were the high cat. losses first observed?

Did the change occur suddenly or gradually?


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Troubleshooting Check List

OBSERVED DATA POTENTIAL CAUSES INITIAL ACTION

Fines increase inequilibrium catalyst;

high cyclone P

High velocity stream indense phase (>70 m/s)

Soft catalyst

Reduce velocities(replace missing RO,

close bypass valves,

reduce stripping steam) Test catalyst attrition

Loss increases with time Crack in plenum or hole in

cyclones

Reduce vessel

velocity

Fines decrease inequilibrium catalyst

Unit shut-down maybe required


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Troubleshooting Check List, cont.


Losses are steady at thehigher level

Fines decrease in

equilibrium catalyst

Something has broken,not simply cracked; or

flooded/plugged dip leg

Reduce c clone velocit

Additional Data

a APS of losses = 25 a 2nd

sta e c clone roblem

b APS of losses > 30 b 1st

or 2nd

stage cyclone

roblem or hole in lenum


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High Catalyst LossesTroubleshooting Check List, cont.


Losses from both

vessels increase after

the unit operating

pressure was reduced

Losses are normal for the

increased gas volume

(from reduced pressure)

Either increase

operating pressure

or accept higher

losses

Fines in equilibriumcatalyst are decreasing

Losses at the increased

level are steady

Catalyst level in diplegs istoo high, or improper

dipleg seal

Increase operatingpressure until

losses reach an

acceptable level


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B: Definition of ProblemPoor Catalyst Circulation

Is problem in spent, regenerated, or both catalyst

lines? If in one of the lines aeration problem

If in both catalyst problem

Is problem increasing with time?

If yes mechanical problem


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B: Definition of ProblemPoor Catalyst Circulation, cont.

Has the percentage of fines (0-40) in the eq. cat. changed?

If decreasing fines coarse fresh catalyst / poor finesretention

If steady fines poor aeration

Has the pressure profile changed?

If yes make adjustments to aeration to minimize

problem


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Catalyst Circulation



Poor regeneration

Change in yields

Poorer stripping

Coarse catalyst

Loss of fines

No catalyst withdrawals

Lower regen. velocity

Add more or finercatalyst

Unsteady standpipe P Hole in standpipe Alter S/P aeration

High regen. holdup High temps. and stresses Review operatinghistory and standpipedesign

Uneven regen. temps

Uneven flue O2or CO Erosion / Corrosion


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Catalyst Circulation



Unsteady regen. temp. Unsteady reactor temp

Unsteady press diff.

control (PDRC)

Check slide valves

and controllers

Catalyst shifts between

reactor and regen.

Unsteady regen. press.

Slide valve operation - poor instrumentation - sticky slide valves

Adjust aeration in

cat. transfer lines

Poor gas compressor

Unsteady reactor temp. Improper aeration Aeration changes

Catalyst shifts betweenreactor and regen.

Transfer line vibration Fluctuating valve P

Water in aeration medium Water in steam lines Malfunctioning cat. slide

valve actuators

Remove water from aeration system Check SV system


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C: Definition of ProblemPoor Product Yields

Is there a poor weight balance? If yes metering error or exchanger leak

Are yields steadily deteriorating with time? If yesmechanical problem such as feed

nozzle erosion

Are metals on equilibrium catalyst increasing? If yes feed quality or low catalyst

replacement


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Poor Product Yields



High H2 yield High metals in feed Lower feed metals High coke yield Catalyst contamination Segregate feed

Higher riser velocities Poor resid catalyst Increase cat. addition Overloaded gas

compressor

Feed type change Change to metals

tolerant catalyst Low catalyst replacement Inject antimony

Vac. unit op. conditions Increase riser steam


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Poor Product Yields



High coke yield Poor wei ht balance

Leak in exchanger train;Hvy. products in feed

Isolate leaking HXAdjust feed train pressure

balance Partly open S/U valves Close valves, install blinds

Low coke yield Poor wei ht balance Unsteady feed

header pressure

Leak in exchanger train;

Lt. products in feed

Isolate leaking HXAdjust feed train pressure

balance

High coke yield High H in coke

Poor stripping Poor feed vaporization

Increase steam rate Increase rxtr. temp.


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Poor Product Yields



Low catalyst activity High regen. temps. Localized high temps.

Review regen. operation Use combustion promoter

Hi h Na and V on catal st

Increase cat. addition Minimize metals into FCCU

Excessive steam in re en. Torch oil

Review regen. operation Remove torch oil; install

blind in line


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Poor Product Yields


OBSERVED DATA POTENTIAL CAUSES INITIAL ACTION Poor circulation

Poor regeneration

Coarse catalyst

Loss of fines

Review regen. ops.

Use finer catalyst Poor stripping No catalyst withdrawals Increase cat. addition

Change in riser P Eroded or blocked riser Review riser design

Riser velocity too high Feed injector vel. too low

Change PDRC tocontrol circulation

Check feed injection

High LCO endpoint; low

HCO initial boiling point

Poor LCO/HCO split Adjust pumparound

duties Inefficient HCO stripper Check steam rates Improper tray loading in

Main Column

Review MC operation

and internals


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Conclusions

You Cant Fix a Mechanical Problem by Changing Catalysts (thoughmany try)

BUT

Proper Catalyst Selection May Allow Longer/ Smoother Operation


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Regenerator Cyclone Operation


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Regenerator Cyclone Operation

Catalyst loading to cyclones depends on

operation

- high velocity, 3.5 fps = 1.1 lbs catalyst

per ft3 of flue gas

- low velocity, 2.5 fps = 0.6 lbs/ft3

- entrainment has an exponential curve

Catalyst loading is usually higher than

catalyst circulation.


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FCC Catalyst Entrainment

0.01

0.10

1.00

10.00

1.5 2.0 2.5 3.0 3.5 4.0 4.5

Superficial Velocity @ Bed Outlet, fps

CatalystEntrainment,lb/c


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Cyclone Design Issues

Must be very, very efficient - 99.997 % or

more is a typical target typical loading of reactor cyclones for 30,000

BPD FCC is ~ 18 tons/min, or 26,000

tons/day

99.997 % efficient system means losses of0.8 tons/day from the reactor

Must be able to withstand erosive conditions

in order to meet run length targets

Needs high reliability of support system

Has to handle wide range of operating

conditions


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Typical Cyclone Terminology


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Industry Cyclone Design Targets

DIPLEG FLUX

100-150 lb/ft-secfor Riser and

Regen 1st stage

cyclones

75 lbs/ ft-sec forUpper and Regen

2nd Stage

cyclones

INLET VELOCITIES

Riser 55 - 65 ft/sec

Upper 60 - 75 ft /sec

Regen 1st Stage 60 - 70 ft /sec

2nd Stage 70 - 80 ft/sec

OUTLET VELOCITIES

Riser 45 - 65 ft /sec

Upper 175 ft /sec maximum

Regen 1st Stage 50 - 70 ft /sec

2nd Stage 175 ft/sec max

INLET

OUTLET


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Other Cyclone Parameters

To improve system efficiency

Target first stage cyclone L/D ratio to be at least 3.6,

higher if possible

Target 2nd stage cyclone L/D for 5.0 when possible

Check dipleg pressure balance

Want several feet remaining in the diplegs at all

operating conditions to avoid upsets/carryover

Plan on 1 of hexmesh refractory

AA-22S is industry standard

For trickle valves, plan on partially shrouded designs


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Likely Maintenance Issues For Cyclones

Weld Cracks

Crossover Duct Cracks

Vortex Termination Catalyst/Vapor Entrainment


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Dipleg Erosion

Caused by

vortexbeing

pushed

into top of

dipleg

EXTREMELY

common!


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Localized Erosion

Gouge in refractorythrough to metal

Caused by shape ofinlet horn

this case is minor

Not obvious from

drawings Very obvious from

field inspection

Cause of damage

may not be apparentUNTIL you are in theunit!


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Reactor Cyclone Coking

Approximately 1 of

coke has formed on

the outlet tubeINSIDE the reactor

cyclone

You MUST remove

this if found duringan inspection

VERY likely to fall

off on start up and

plug the dipleg


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Reactor Cyclone Coking Causes

Coke formation is usually due to condensation of heavy

hydrocarbons

Material condenses in the dead area behind the cyclone inlet horn

Can be minimized with:

good feed injection

increased steam in riser

making sure unit is hot when feed is initially injected taking feed out before riser outlet temperature is too low

Fi l C l Th ht


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Final Cyclone Thoughts

Cyclones are listed as one of the top three reasons why FCCUs end

runs early

Many people run higher than design inlet velocities

This is not unacceptable It does carry inherent risk of ending a run early due to mechanical

damage

Erosion to a cyclone is a function of velocity to at least the 3rd

power, if not higher a 10 % increase in velocity corresponds to at least a 33 % increase in

erosion

Units can run for an extended time period with cyclone damage, but

need to be aware of:

fluidization effects due to loss of small particles

potential safety issues

added headache of catalyst management


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TYPICAL FCCU LAYOUT

FLUE GAS

PdRC

TRC

REGENERATOR

REACTOR

STRIPPER

LRC

AIR

STEAM

AIR

STEAM

OIL FEED

RECYCLE

LT. ENDS

PRODUCTS

TPA

MAIN

COLUMN

LCOPRODUCT

HCN

PRODUCT

MPA

BPA

DCO PRODUCT

Steam


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TYPICAL AERATION LAYOUT

STEAM

AIR

AIR

STEAM

STEAM

STEAM

STEAM

FEED

STRIPPER

REGENERATOR

RISER


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TYPICAL 2-STAGE CYCLONE

PlenumPlenum

Gas Outlet TubeGas Outlet Tube

Gas Inlet DuctGas Inlet Duct

BarrelBarrel

ConeCone

DiplegDipleg

Dust HopperDust Hopper

Flapper ValveFlapper Valve

2nd

Stage1st

Stage

Documents

FCC Troubleshooting - Catalyst Losses