intercat_optimizing & troubleshooting the fcc re generator for reduced...

8/7/2019 Intercat_Optimizing & Troubleshooting the FCC Re Generator for Reduced Emissions_RayFletcher_MartinEvans_CatCrackingCom_April2010

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O timizin & Troubleshootin

the FCC Regenerator for

Ray Fletcher & Martin EvansMarch 2010

5/3/20101


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Overview Introduction

Particulate emissions:

Catalyst attrition Cyclone integrity

Analysis & control

Gaseous emissions

Control of NOx emissions

Conclusion

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NPRA Annual Meeting March 2010

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Introduction Substantial experience has been gained during

the last 68+ years related to FCC regenerator

operations

Effective troubleshooting is based upon a solid

set of baseline data taken during normal

operations

Selective use of additives will enable the refiner

to enhance the performance of the regenerator

Refer to reference section of associated paper

for key landmark papers related to regenerator

troubleshooting

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Overview Introduction



Analysis & control

Gaseous emissions


Conclusion

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Attrition in Regenerators Two primary sources of attrition:

Continuous & minor:

Particle attrition at grids

with back eddy

Submerged jet attrition at the grid

Attrition in cyclones

Attrition at load line elbows

Abnormal & substantial:

Improperly designed, eroded, or missing orifices in

steam lines

High turbulence caused by a broken air grid

High catalyst velocities through slide valves

Most units will have a low level of attrition

occurring continuously

Baseline essentialAir

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Attrition in FCC Regenerators Procedure for monitoring catalyst

attrition:

Capture & analyze fines samples regularly

3rdstage separator or 1ststage ESP bin

Plot wt% capture vs. PSD

Normal distribution:

One primary peak at 20-30

One attrition peak at 0-5

One breakage peak at 10-15

Attrition source present:

Primar eak shifted to lower article size

& reduced in magnitude

Attrition peak increases & dominates

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Cyclone Integrity Mechanically related problems:

Broken welds

Holes from erosion or high stress tears in

the cyclone or dipleg

Dipleg valves which do not operate

Dipleg valves which do not close because of

bent or lost closure plates

Operationally related issues Excessive mass flows in cyclones & diplegs

Insufficient dipleg length

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(Conceptual example)


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Dipleg Pressure Balance Knowledge of cyclone dipleg levels is critical

Minimum distance of catalyst level to cyclone

vortex is approximately 600 mm (24 inches)

Increases in charge rate can increase required

dipleg level beyond this minimum

Result: catalyst attrition, erosion in cyclone cones

& hoppers, entrainment

Higher catalyst levels occur in secondary

Plot cyclone dipleg heights vs. catalyst losses to

determine unit specific critical dipleg levelhdl

dl

Primary dipleg: 480 kg/m3 (30 lb/ft3)

Secondary dipleg: 320 kg/m3 (20 lb/ft3)3 3

bed

hbed

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Troubleshooting Cyclones Primary cyclone hole

A secondary peak is observed to the right of

the primary peak

Positioned at >60

The attrition & breakage peaks continue to

be present

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Troubleshooting Cyclones Secondary cyclone hole

A secondary peak is observed to the right of

the primary peak

Positioned at 45-50

The attrition & breakage peaks disappear

Flooded cyclones

Primary peak shifts to the right of a typical

unit

The attrition & breakage peaks continue to

be present

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Overview

Introduction



Analysis & control

Gaseous emissions


Conclusion

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Regenerator Afterburning

Afterburning is any increase in flue gas

temperature after leaving the dense bed

May occur in dilute phase, cyclones, or flue gas

Little catalyst present to absorb heat of combustion

May limit throughput or feedstock flexibility

May result in serious damage to internals leading

to premature shutdown & costly repairs

Two types of afterburn observed:

Kinetic limited afterburn

Due to insufficient regenerator bed residence time

for complete combustionSource: Jack Wilcox, RPS

er urn n uce y poor a r or ca a ysdistribution

Frequently due to inherent design features &/or air

rid mechanical failures

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Kinetic Limited Afterburning

Characteristics:

Well dispersed afterburn across regenerator

cross section

High superficial velocities

Low bed levels

Low bed tempertures

Solutions:

Raise bed level

Increase bed temperatures

Add CO Promoter

Thermodynamically limited units generally

respond well to platinum

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Distribution Induced Afterburning

Characterized by localized afterburning

Induced b oor air &/or catal st distribution

O2 rich O2 richCO rich

Due to mixing of CO & O2 rich zones above bed Responds less well to CO Promoter

Monitor hotspot temp as Pt concentration increases

Hotspot temperature will drop until O2 is fully

consumed in effected region

Continued additions after temperature fails to drop O2 rich CO rich

NOx emissions will continue to increase

A normally well behaved unit which begins to

afterburn together with a change in losses or

equilibrium PSD indicates air grid damage

Suspected maldistribution may be confirmed

using a portable gas analyzer

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Source: J.W. Wilson, AM-03-44


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Gas Analyzer Verification

Portable gas analyzers are

effective at confirmingCL

Catalyst side-entry

#1

maldistribution

Typical equipment used:

Reaction Mix Sample (RMS)

330

probe

Mott filter element used to

remove catalyst fines from thegas s ream

P1

150190

Catalyst

withdrawalCJI

#2#3

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Overview

Introduction



Analysis & control

Gaseous emissions


Conclusion

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Controlling SOx: Full Combustion

Feedstock effect

About 10% emitted as SOx (range: 5-35%)

Improve SOx additive efficiency: Drive SO2 to SO3 equilibrium towards SO3

Increase excess O u to ~2%

Reduce bed temperature

Increase regenerator pressure

Use Pt based CO promoter

Enhance additive regeneration

Increase cat circulation rate

Factors reducing additive efficiency:

High catalyst losses Large regenerator inventories

Poor stripper efficiencies

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High Fe on equilibrium catalyst

5/3/2010

Total elimination of SOx emissions is achievable


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Controlling SOx: Partial Combustion

SOx additives in partial burn:

Majority of S in reduced form

Sulfur Species Data from European FCC @ 7% CO

COS, CS2,H2S

Oxidation of SSO2SO3 limiting step

Tailored oxidation component required

for maximum additive effectiveness

Measure SO2 is flue gas prior to using

additives in partial burn Approximately 30% of S in oxidized state

Partial burn guidelines:

There is a practical upper limit

Monitor SOxconcentration in flue gasupstream of CO Boiler thru trial

Monitor regenerator CO-to-CO2 ratio as

Deep SOx reductions in partial burn are feasible

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Controlling NOx Emissions

NOx formation:

~10% of N in coke emitted as NOx 200)FluegasNOxvsExcessO2

Excess O2

is the most significant operating

variable affecting NOx emissions

Maldistribution of air & catalyst leads to 50

100

150

NOxEmissions(ppm

high NOx emissions

Additive efficiency is highly unit specific

NOx reducin additives are effective in

0.6 0.8 1.0 1.2 1.4

ExcessOxygen(ppm)

full combustion

There is an effective unit specific maximum

concentration

Exceeding this maximum will have no effector may actually increase NOx

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Designing for Low NOx Emissions

Control of air-to-catalyst mixing critical to

low NOx emissions

Combustor type regenerators with superior air-

to-catalyst mixing control NOx emissions well

Bubbling bed regenerators may be

improved for reduced emissions:

Ensure counter current operation

Distribute spent catalyst uniformly across the Courtesy: KBR

top of the regenerator bed

Inject combustion air uniformly across cross

section of regenerator

ves are e ec ve or ur er reductions as needed

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Troubleshooting NOx Emissions

Detecting maldistribution via comparison of cyclone delta temps

.

combination

Look for obvious pattern differences

Use regression analyses plus time plots identify likely root cause & timing

Perform step tests in unit to confirm suspected process variables

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CO Promotion & NOx Emissions

NOx emissions increase as platinum

content increases

Simultaneous control of afterburn & NOx

emissions is possible via non-Pt promoters

Fully commercialized solution

Utilize best available additive loader

technology for optimum performance

Reliable additive injection is essential

Intercat offers free loader usage for all its

customers

Example of enhanced additive

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reliability


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Overview

Introduction


Catalyst attrition

Cyclone integrity

Analysis & control

Gaseous emissions


Conclusion

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Conclusion

Advanced troubleshooting techniques will

enable the process engineer to effectively

monitor, troubleshoot, & optimize the FCC

regenerator A solid base case taken during normal operations is

fundamental to swift troubleshooting

Intercat has developed a substantial base ofhands on regenerator troubleshooting &

optimization expertise

Refinery support available upon request

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NPRA Annual Meeting March 2010245/3/2010


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www.intercatinc.com

O timizin & Troubleshootin

the FCC Regenerator for

Ray Fletcher & Martin Evans

March 2010

5/3/201025

intercat_optimizing & troubleshooting the fcc re generator for reduced...

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