fcc regenerator design to minimize catalyst deactivation and … · 2008-10-10 · feed stock type...

FCC Regenerator Design to Minimize Catalyst

Deactivation and Emissions

FCC Regenerator Design to Minimize Catalyst

Deactivation and Emissions

Steve TragesserShaw Energy and Chemicals Group

Shaw Stone & Webster FCCsShaw Stone & Webster FCCs

Resid RFCCs (R2R)Other FCC/DCCs (R1R)

42 RFCC/FCC/DCC Units Licensed

Regenerator Design ObjectivesRegenerator Design Objectives

• Effective regeneration of catalyst• Minimum catalyst deactivation• Efficient use of available air blower capacity • Minimum damage to equipment• Minimum toxic emissions

Typical Regenerator DesignsTypical Regenerator Designs

REGEN

Air

Spent Catalyst

Counter-Current Regeneration

Co-Current Regeneration

REGEN

Air

Spent Catalyst

Typical Co-Current RegeneratorTypical Co-Current Regenerator

Spent catalyst

Air

Regenerator

Reactor

Typical Counter-Current RegeneratorTypical Counter-Current Regenerator

Spent catalyst

Air

Regenerator

Reactor

Interior Particle Temperature RiseInterior Particle Temperature Rise500

450

400

350

300

250

200

1500 2 4 6 108

Tem

pera

ture

Ris

e, °F

Time, Milliseconds

(Co-Current)

(Counter-Current)5% O2

5% C

5% O2

10% C

5% C20% O2

AfterburnAfterburn

Burning of CO Above the Regenerator Bed

1. Can occur in dilute phase, cyclones, plenum chamber and/or flue gas line

2. Temperatures can damage regenerator internals

3. Can be limiting temperature in regenerator

Spent Catalyst DistributionSpent Catalyst Distribution

Spent Catalyst Without DistributorSpent Catalyst Without Distributor

Elimination of Serious Afterburn ProblemsElimination of Serious Afterburn Problems

Principle Causes• Spent Catalyst Distribution• Air Distribution• Shallow Bed

Solutions• Distribute Spent Catalyst Across Bed• Minimum Bed Height (3 – 5 meters)• Air Distribution

– Multiple Rings– Pipe Grids

Axens/Stone & Webster Distributor

Spent Catalyst DistributionSpent Catalyst Distribution

Even catalyst distribution

Side Entry RegeneratorNo Distributor

Poor catalyst distribution

High coke concentration

Bathtub Spent Cat DistributorBathtub Spent Cat Distributor

Bathtub for Counter-current Regeneration and Low NOxBathtub for Counter-current Regeneration and Low NOx

Spent Catalyst DistributorSpent Catalyst Distributor

Bathtub Spent Cat DistributorBathtub Spent Cat Distributor

Bathtub CFD ModelingBathtub CFD Modeling

Combustion Air RingCombustion Air Ring

Cross Section of Ring

Cross Section of Tee

Air Ring Installation Air Ring Installation

Air Ring Nozzle LayoutAir Ring Nozzle Layout

Two Stage Regeneration –The Key to Resid Processing

Two Stage Regeneration –The Key to Resid Processing

Why Two Stages for Resid?• Heat balance control for high

concarbon feeds• Minimizes catalyst deactivation

for severe regeneration required– Lower average catalyst particle

temperature– Less hydrothermal deactivation– Less vanadic acid deactivation

Two Stage Regeneration ConceptTwo Stage Regeneration Concept

1. First stage regenerator design• Countercurrent Regeneration• Heat Removal Via CO

Production (partial burn)2. Second stage regenerator design

• Complete combustion• Minimum moisture

Catalyst Cooler Catalyst Cooler

R2R with Catalyst CoolerR2R with Catalyst Cooler

Catalyst Cooler

SRC Singapore

Regenerator EmissionsRegenerator Emissions

• Particulates

• CO

• SOx

• NOx

Primary Causes of Particulate LossesPrimary Causes of Particulate Losses

• Catalyst Attrition– Fracture– Abrasion

• Cyclone Design• High Superficial Velocities• Damaged Equipment

– Air Distributor– Cyclone System

• Operation– Bed Level– High Velocity Nozzles

Final Particulate Removal OptionsFinal Particulate Removal Options

• 3rd stage cyclonic separation (80 mg/Nm3)• 3rd stage cyclonic separation with 4th stage

underflow filter (50 mg/Nm3)• Wet gas scrubbing (10 to 20 mg/Nm3)• Electrostatic precipitation (10 mg/Nm3)• Physical filtration (less than 10 mg/Nm3)

BP Kwinana Flue Gas FilterBP Kwinana Flue Gas Filter

R1R1

R2R2

140 mg/Nm3140 mg/Nm3

330 mg/Nm3330 mg/Nm3

RegenRegen33rdrd Stage Stage SeparatorSeparator Waste Waste

Heat Heat BoilerBoiler

Orifice Orifice chamberchamber

StackStackReactorReactor Flue Gas Filter by

Pall

2 mg/Nm32 mg/Nm3

BP Kwinana Flue Gas FilterBP Kwinana Flue Gas Filter

TubesheetTubesheetInstallationInstallation

OverviewPictures courtesy of Pall

SOx StrategiesSOx Strategies

• Minimize Coke Yield (Reaction technology)

• Use Desox additive to control small amounts SOx

• Use scrubber to control large amounts SOx

• Avoid Recycle of heavy streams

Wet Gas Scrubbing for SOx Removal

Belco®’s EDV Wet Gas Scrubber

FCC Variable Affecting SOx Emissions and Additive Performance

FCC Variable Affecting SOx Emissions and Additive Performance

Poor stripping will increase SOxStripper Operation

Near-continuous addition improves efficiencyAdditive AdditionIncreasing CO promoter improves efficiencyCO Promoter UsageHigher temp. favors reduction of sulfates to H2SReactor TemperatureIncrease favors SO2 oxidation, hinders SO3 absorptionRegenerator Temp.Increasing excess O2 improves efficiencyRegenerator OperationLarger inventories reduce efficiencyRegenerator InventoryHigher rate improves efficiencyCirculation RateActivity and additives present (SOx & CO)Equilibrium CatalystHigher alumina improves SOx efficiencyFresh Catalyst

Usually heavy coke-sulfur formingRecycle streamsLevel and type of sulfur in feedFeed Stock Type

Effect on Sox Additive PerformanceVariables

NOx ControlNOx Control• Very complex

• Related to feed nitrogen, not combustion air

• High platinum CO promoter & excess oxygen amplifies NOx

• Much of NOx is reduced to N2 or leaves as NH3, HCN, etc. (70 – 95%)

Comparison of NOx Emissions in Commercial FCC Regenerators

Comparison of NOx Emissions in Commercial FCC Regenerators

0

5

10

15

20

30

25

0.0 1.0 2.0 3.0 4.0

Excess Oxygen in Flue Gas

% N in Coke to NOx

Counter-Current (Swirl)Counter-Current (Bathtub)

Optimum Regenerator DesignOptimum Regenerator Design

• Turbulent bed

• Countercurrent regeneration

• Minimum excess oxygen

• Spent catalyst distributed across entire bed

• Minimum gas residence time of 4 seconds

Thank YouThank You

The Shaw Group Inc.