What flow visualisation can What flow visualisation can teach us about reactor designteach us about reactor design

What? Flow visualisation can What? Flow visualisation can teach us about reactor design?teach us about reactor design?

Hugh Stitt [1] & Peter Jackson [2]

[1] [2]

OutlineOutline• In research

– Laboratory experiments, – Model development

• Scale up– Role of flow visualisation– Measurement density

• Flow visualisation in the field– Reactors behaving badly– Knowledge vs. information vs. data– Implementation

Stirred Tank Tomography in 4D Stirred Tank Tomography in 4D at Medium Scaleat Medium Scale

• 3 m3 demonstration scale mixing tank with 8 planes of electrical sensors

R Mann et al., Chem Eng Sci, 52, 2087-2097 (1997)

– Sensor readings reconstructred to give resistivity map

Stirred Tank Tomography in 4DStirred Tank Tomography in 4D• Video frame and tomogram showing tracer

distribution after 3 secs

R Mann et al., Chem Eng Sci, 52, 2087-2097 (1997)

Stirred Tank Tomography in 4DStirred Tank Tomography in 4D• Video frame and tomogram showing tracer

distribution after 3 secs

R Mann et al., Chem Eng Sci, 52, 2087-2097 (1997)

This is great – good picture!! – But gives little quantitative

information on mixing UNLESS

we have a model to compare it with

Getting High Quality Information on Getting High Quality Information on Stirred TanksStirred Tanks

• Needs a Lagrangian experimental approach– Velocimetry – or particle Tracking

Positron Emission Particle Tracking (PEPT)

Computer Automated Radioactive Particle Tracking (CARPT )

Lagrangian Measurements on a Stirred TankLagrangian Measurements on a Stirred Tank

• Loop circulation patterns are severely averaged

• Actual fluid motion is far more random– Direction & velocity

VelocityTrajectory

Fishwick, Winterbottom & Stitt

Lagrangian Measurements on a Stirred TankLagrangian Measurements on a Stirred Tank

Fishwick, Winterbottom & Stitt

• CARPT on 8" dia vessel• PEPT on 4" vessel

Rammohan, Kemoun & Dudukovic

Radioactive Velocimetry on a Radioactive Velocimetry on a Rushton Turbine Agitated Baffled VesselRushton Turbine Agitated Baffled Vessel

• Time-averaged velocity plots

Radioactive Velocimetry on a Radioactive Velocimetry on a Rushton Turbine Agitated Baffled VesselRushton Turbine Agitated Baffled Vessel

• Time-averaged velocity plots

Strength of these spatial velocity data – they can be compared directly to simulations

Great pictures!!Great pictures!! – But they give little quantitative

information on mixing UNLESS

we have a model to compare it with the data

Stirred Tank Experimental vs SimulationStirred Tank Experimental vs SimulationVelocity VectorsVelocity Vectors

• Both give recirculation loop centres at– Upper loop : 0.575, 0.575– Lower loop : 0.225, 0.225

Rammohan, Dudukovic & Ranade: IECRes 42, 2589 (2003)

Stirred Tank Experimental vs SimulationStirred Tank Experimental vs SimulationTurbulent Kinetic EnergyTurbulent Kinetic Energy

Rammohan, Dudukovic, Ranade: IECRes. 42, 2589 (2003)

• Model quality reduced for derived value

• Optical techniques not appropriate– Need penetrative

methods; eg. -rays– Flow visualisation in

highly dispersed multiphase operation

• Understanding of instantaneous effects

• Valuable data for comparison to time averaged models

CREL

Velocimetry in Multiphase Velocimetry in Multiphase Bubble Column OperationBubble Column Operation

Gas Sparging in a Stirred TankGas Sparging in a Stirred TankRadioactive Techniques allow interrogation Radioactive Techniques allow interrogation

at high hold up of dispersed phasesat high hold up of dispersed phases• Effect of gas sparging

on liquid velocities– PEPT data

• Gas hold up patterns in a sparged stirred tank– -CT data

No gasGas sparged

Fishwick, Winterbottom & Stitt Rammohan & Dudukovic

Tomography & Velocimetry in Tomography & Velocimetry in Multiphase Flow ReactorsMultiphase Flow Reactors

• Modelling of multiphase reactors is subject to many uncertainties– Multiphase flow regime: bubbly, unstable– Coalescence - redispersion

• Population balance: bubble class models– Momentum transfer– CFD “Closures”

• Require validation of models against detailed experimental data

Tomography on a Bubble ColumnTomography on a Bubble Column• Electrical Resistance

Tomography• Computer Tomography

(-ray)

Williams, Wang et al, Leeds Univ, UK APCI / CREL data

Temporal resolution – but uncertain spatial precision

Time averaged – good spatial resolution

Both have been done on columns 18" diameter

MRI – TBR Trickle-Pulse Flow TransitionMRI – TBR Trickle-Pulse Flow TransitionTrickle regime

1.4 mm/sPulsing regime

L = 13.3 mm/sTransition regime

4.6 mm/s

Gas flow: 112.4 mm/sResolution: 0.7×1.4 mmAcquired at 50 f.p.s.All presented on the same intensity scale

Lim, Sederman, Gladden, Stitt, Chem Eng Sci, in press

Flow transition is a local phenomenon.

Specific information on pulsing, its origin and the bed structures that promote it

Flow Visualisation in the LaboratoryFlow Visualisation in the Laboratory• Range of techniques available for use with

multiphase systems– -ray, X-ray, Electrical, MRI

• Varying cost, spatial and temporal resolution• Important role in building models and

fundamental understanding– Specific information on flow regimes– Model discrimination and validation

• Next questionNext question– How do we exploit these techniques in

scale up and design ?

“The bench scale results were so good that we by-passed the pilot plant”

Design and Scale up Design and Scale up Role of Flow VisualisationRole of Flow Visualisation

• Experimental tomography and velocimetry have a clear role in reactor design and development– Quantitative information for model validation– Qualitative role in understanding flow

behaviour and phase interactions– Quantitative evaluation of changes in mixing /

hydrodynamics behaviour with changes in scale

Low Cost Radial Flow Packed BedLow Cost Radial Flow Packed BedProof of ConceptProof of Concept

• High pressure processes• Ammonia synthesis

– Low P at a premium• Radial flow benefits

– High cost engineering retrofits available

– But a very cost sensitive industry

• Can radial flow be induced by directed packing?

Header Space

FeedFeed distributor

Large dia.inert packing

Smaller dia.catalyst

Exit collector (porous wall)

Exit flow

Low Cost Radial Flow Packed BedLow Cost Radial Flow Packed BedFlow ModellingFlow Modelling

• Radial flow patterns predicted using CFD

• Process gas conditions and flow

– Based on assumptions of global packed bed permeabilities

• But are these predictions correct and realistic ?– Use Electrical Resistance Tomography

Bolton, Hooper, Mann & Stitt:, Chem Eng Sci, 59, 1989-1997 (2004)

Low Cost Radial Flow Packed BedLow Cost Radial Flow Packed BedExperimental Validation with ERTExperimental Validation with ERT

• Electrical Resistance tomography– 4D resolution

• Low spatial resolution• Use 36" diameter vessel

– Packed aspect ratio 1:1– Annular configuration,

• 2 particle diameters• Central collector

– 8 planes of 32 electrodes• Injection of concentrated

brine tracer and monitor conductivity– Reconstruct conductivity maps

Bolton, Hooper, Mann & Stitt, Chem Eng Sci, 54, 1989 (2004)

Radial Flow Packed Bed ERT Flow PatternRadial Flow Packed Bed ERT Flow Pattern

ERT provides demonstration of overall axial / radial flow profile

Bolton, Hooper, Mann & Stitt, Chem Eng Sci, 54, 1989 (2004)

• Reconstructed conductivity maps at single horizontal plane for 8 different times

Low Cost Radial Flow Packed BedLow Cost Radial Flow Packed BedQuantitative ValidationQuantitative Validation

• Velocity mapping from ER tomography

• CFD simulation of experiment

Bolton, Hooper, Mann & Stitt, Chem Eng Sci, 54, 1989 (2004)

• Qualitatively reproduces main features– Quantitation is less conclusive

What? Flow visualisation can teach us What? Flow visualisation can teach us about larger scale operation?about larger scale operation?

• Scale up– Use measurement system and measurement

density appropriate to validation of design concept and models

• Does not need same precision as lab scale.• Objective different

– Justification of scale up protocol– Testing of models at increased scale– NOT fundamental understanding and

derivation of models per se

• But what about manufacturing scale ?

• Tracking of fluid movement – within and between oil and gas

reservoir wells • during drilling and production.

• Examination of transfer pipelines to and from processing facilities– for slugging effects, phase flow

rates, solids build-up or blockage, pigging operation monitoring.

It’s only one dimensional and single pass but ……….. it is an invaluable technique

Priority list : 1) Is there a blockage?2) If yes, then where is it? 3) Then characterise the blockage

Tomography & Velocimetry in the Field Tomography & Velocimetry in the Field Large Scale Particle Tracking : An old technologyLarge Scale Particle Tracking : An old technology

Reactors Behaving BadlyReactors Behaving BadlyStirred Tank ReactorsStirred Tank Reactors

Liquid level below top impeller

Impeller damage makes good mixing impossible

• Pelleted catalysts– Shallow bed (4")– Large dia (8´)

• Reactor operating at reduced conversion

• Observation (through spy glass) indicates “dark patches”

Reactor Behaving BadlyReactor Behaving BadlyCatalytic Oxidation ReactorCatalytic Oxidation Reactor

““Field” Particle Tracking Technology?Field” Particle Tracking Technology?• What are the objectives ?

– Detailed diagnosis of flow patterns with high spatial resolution ?

• But how high a spatial resolution is required?

• Customer requirement– Measuring the degree of mixing with

sufficient resolution to establish:• overall quality of mixing and • any severe maloperation • at minimum cost

– Do mixing and flow patterns adversely affect production and profits?

– ——————————————————————————————

• ——————————————————————

Modality for “Field” OperationModality for “Field” Operation

• Key requirements for field and research use are not the same

Research Priorities Field Priorities Resolution Tomography

Technique Spatial Temporal

Transp- ortable

Sees through

Metal -ray Good None Yes Yes e+ emission Good Moderate No Yes X-ray Good Some Moderate Moderate Electrical Moderate Excellent Yes No Optical Good Good Yes No MRI Good Good No No

Modality for “Field” OperationModality for “Field” Operation

• Currently - only -ray systems meet all the requirements for field use

Research Priorities Field Priorities Resolution Tomography

Technique Spatial Temporal

Transp- ortable

Sees through

Metal -ray Good None Yes Yes e+ emission Good Moderate No Yes X-ray Good Some Moderate Moderate Electrical Moderate Excellent Yes No Optical Good Good Yes No MRI Good Good No No

10

100

1000

80 90 100

Information Obtained (%)

Cos

t (A

rbitr

ary)

BUT : Cost vs. Information is exponential

The 80 : 20 RuleThe 80 : 20 Rule• 80% of the information is only 20% of the cost

– And that 80% is normally sufficient to make an educated decision or diagnosis

• Corollary : the remaining 20% of information requires an additional 80% of the total effort

• Cost vs number of data points may be linear

““Field” Tomography Technology?Field” Tomography Technology?• What information are we trying to obtain ?

– And at what level ?• High levels of information cost money & time• Diagnosis of good, adequate or poor operation

can often be done with little measurement and information– Provided you know what information or data to

measure ……. & how to interpret it• Detailed measurement will only be done in the

field where it is essential– Where it adds value

• Hence - if an operator can get enough information to understand what he critically needs to know by a 1D, 1m measurement– Then he won’t pay for more!!!Then he won’t pay for more!!!

Reactors Behaving BadlyReactors Behaving BadlySteam ReformerSteam Reformer

• Not too good • Not good at all

Reactors Behaving BadlyReactors Behaving BadlySteam ReformerSteam Reformer

• Tube wall temperature surveys can be used routinely to identify zones of misbehaviour– Use Gold Cup Pyrometry

• Zone of hot tubes– Operator needs

to trim burners to avoid premature tube failure

• And the resulting cost penalty

But here we’re lucky. We have observation windows to look through

Dignostics and Tomography at ScaleDignostics and Tomography at ScaleA Case StudyA Case Study

• Pilot plant slurry bubble column reactor, – 18” diameter, heat exchange tube internals,

Base line scan - DensitometryBase line scan - Densitometry

1.0E+03

1.0E+04

1.0E+05

1.0E+06

0 10 20 30 40 50 60

Pin Number

Cou

nts

Two successive sets of scans - Data are nearly identical showing good reproducibility

Field Measurements on a Field Measurements on a Slurry Bubble Column ReactorSlurry Bubble Column Reactor

– 18” diameter, heat exchange tube internals• High number of detectors / scans required to

achieve spatial resolution – Very long time (thus high cost) to collect

statistically significant data set• Internals effect “lines of sight” • Very complex reconstruction• Calibration during operation?

• Questionable value proposition– Consider an alternative approach

Gas Inlet

Slurry outlet

Gas OutletDetector 2

Detector 1

Tracer Study - Application Example 1Tracer Study - Application Example 1Slurry Bubble Column Slurry Bubble Column

• Open Tracer Studies– For axial mixing and

entrainment measurements• Inject gas tracer at gas inlet.

– Responses from detectors 1 & 2 gives mean residence time,

• Axial mixing information– Use third detector at slurry

outlet to measure gas carryover

Tracer Study - Application Example 2Tracer Study - Application Example 2Slurry Bubble ColumnSlurry Bubble Column

• Open tracer studies with ring detectors – Investigate phase distribution

and mixing– Tracers

• Catalyst particles – doped with Mn56

2O3

• “Liquid follower” : – powdered Mn56

2O3

• Open gas tracer : Ar41

Gas Inlet

Slurry outlet

Gas Outlet

– Use of more than one ring allows measurement of rise velocities

Particle Tracer Studies on a SBCRParticle Tracer Studies on a SBCR

• Install several rings of collimated detectors

• Use pulse injection of active particle tracers– “Liquid”– Catalyst

- Pilot plant operated by Air Products- Tracking particles prepared by JM- Data measurement by JM-Tracerco- Data interpretation by CREL,

Particle Tracer Studies on a SBCRParticle Tracer Studies on a SBCR• Catalyst and “liquid follower” particles show

almost identical behaviour

– Assumption of pseudo-homogeneous slurry phase is valid

Particle Tracer Studies on a SBCRParticle Tracer Studies on a SBCR• Pulse injection of multiple particles and ring

detectors used in lieu of single Lagrangian traceor tomography– Simpler to install, calibrate and use

• Ring detector responses compared to model predictions– In general - good comparability– Demonstrates model validity

OR....If we have a model that predicts behaviour then we can assess any deviation from that ideal using simpler (tracing) techniques

• Pelleted catalysts– Shallow bed (4“)– Large dia (8´)

• Reactor operating at reduced conversion

• Observation through (spy glass) indicates “dark patches”

• Modelling– Local extinction of catalyst and stable

“cold channels” with steep thermal gradients • With very high mass flow

Reactor Behaving BadlyReactor Behaving BadlyCatalytic Oxidation ReactorCatalytic Oxidation Reactor

Hot (active) catalyst)

Dark patches

Catalytic Oxidation ReactorCatalytic Oxidation Reactor• CFD modelling of gas

distribution system and head space indicated no problem

• If modelling is correct (catalyst extinction and cold flow channels) …..– Would expect massive

mal-distribution of gas flow• Significantly higher flow

though cold zones

Hot (active) catalyst)

Dark patches

Evaluation of Flow (mal)Distribution Evaluation of Flow (mal)Distribution Through a Packed Bed ReactorThrough a Packed Bed Reactor

• Flow distribution study using – Open 85Kr tracer – Ring of detectors just above catalyst bed

Detectors were not colliimated

Reactor Flow Distribution using TracerReactor Flow Distribution using Tracer• Typical test trace

Inletdetector

response

Ring detector responses – showing significant differences

Reactor Flow Distribution Using TracerReactor Flow Distribution Using Tracer• Flow distribution by Segment

High response at locations of persistent dark patches- Consistent with model

Unexpected area of low flow

• Repeat runs, and detectors at bottom of catalyst bed all gave similar results

Flow Visualisation in the fieldFlow Visualisation in the field• High measurement density not appropriate

– Financial considerations• Information rich data, with few

measurements feasible based on– Selecting appropriate measurements

• Not necessarily the same as in the lab– Open tracers, chordal scans, ………

– A priori knowledge of what results represent poor / bad behaviour

– Availability of models to interpret data and relate to lab-based understanding

• Validation of model scalability

But sometimes we need a “map”But sometimes we need a “map” Development of Tomography for Field UseDevelopment of Tomography for Field Use• A portable -ray tomographic toolkit

• For process diagnostic application on steel vessels– Robust & portable. Accurate, repeatable & quick to

analyse, Non-intrusive and non-invasive, Easy to install & remove. Economic

• Experimental & Methods– Steel vessel, thin walled, 40 cm diameter

• Source : 137Cs : 662 keV – Use of Phantoms

• Steel bar, tube and plate, Hollow polystyrene block– Ab initio reconstructions

• From calculated line densities

Darwood et al., WCIPT3, Sept 2003

Densitometry : Results for Dual PhantomsDensitometry : Results for Dual Phantoms

Experimental 20 x 8 grid

Theoretical 40 x 4 grid

• Ghost images on both experimental and theoretical reconstructions– Grid scanning not able to discriminate multiple

features at low numbers of scans

Steel Pipe

Steel Plate

Fan-beam Tomograms of PhantomsFan-beam Tomograms of Phantoms

Drilled polystyrene block32 nodes x 6 scans

Pipe & plate dual phantom32 nodes x 6 scans

• Tomograms show good representation– Note absence of ghost images on

tomogram of dual phantom

-ray Computed Tomography Scanning -ray Computed Tomography Scanning Imaging of Process Vessels & ReactorsImaging of Process Vessels & Reactors

“Fan beam” arrangement

of sensors

Use multiple source positions

• 6.2 m dia. packed column– 32 source locations– 6 scans per position

Tomography of Commercial UnitsTomography of Commercial Units

• Tomography can be done on commercial units with reduced number of scans– Scale limited by -ray attenuation

• Particle tracking also feasible but issues on tracer retrieval

6.2 m dia fractionation column 1m dia FCC Riser

What? Flow Visualisation Can Teach us What? Flow Visualisation Can Teach us about Reactor Design and Operation ?about Reactor Design and Operation ?

• Research– Building fundamental understanding

• Model building, discrimination and validation• Requires high density of measurements

• Scale up and Design– Objective to test the model at the larger scale

• Lower measurement density probably adequate• Manufacturing scale

– Objective is diagnostic• Good operation or not: is it a financial burden?• Even lower (single point?)

measurement may suffice

What? What? Flow visualisation Flow visualisation cancan teach us about reactor teach us about reactor design and operationdesign and operation