Updating CRE: Applicationsweb.abo.fi/fak/tkf/tek/Files/cacre2014/MicroKin-PC-5.pdf · 2014. 5....

P. Canu – CRE with µKin CACRE, Åbo Akademi, 2014

Updating CRE: Applications

Prof. Paolo Canu

University of Padova - Italy

Computer-Aided Chemical Reaction Engineering Course

Graduate School in Chemical Engineering (GSCE) Åbo Akademi - POKE Researchers network

May 2014

Contents 3. Kinetics

3.1 Power law 3.2 LHHW

3.3 Detailed 4. Kinetic studies

5. Applications

A.1 Tuning of Sh(z) in a monolith (2.3 + 3.1) A.2 CH4 combustion on Pt in a monolith (2.3 + 3.1) A.3 CO combustion in an annular reactor (2.2 + 3.3) A.4 CH4 partial oxidation on Rh foam (2.2 + 3.3) A.5 CH4 partial oxidation on Pt monolith (2.3 + 3.3) A.6 Herogeneous reaction simulation by CFD (2.3 + 3.1) A.7 H2 oxidation on pure Pt in stagnation flow (2.3 + 3.3)

A1) Tuning of Sh(z) in a monolith CFD+simple kinetics

Correlations for Mass Transfer

in Reacting and Developing Laminar Flow with Arbitrary Kinetics

Fundamental calculation (CFD)

of developing mass- and velocity- boundary layers

A1) Tuning of Sh(z) in a monolith Reaction and diffusion in series Wall mass flux is affected by the rate of consumption

dCN Ddr

= − ⋅

A1) Tuning of Sh(z) in a monolith Simple solutions (effective K):

• Infinitely fast reaction

• First order reaction

• Second order reaction

00,, 0

r C Cr R C= =

= =0 0A A eff A

DN C K CR

′= − ⋅ = − ⋅

r C CNr R Ck

= =0 0

11 1A A eff AN C K C

′′= − ⋅ = − ⋅+

Nr R Ck

0 042A A eff AN C K Ckk

β β β

′′′= ± + ⋅ = − ⋅

A1) Tuning of Sh(z) in a monolith ‘effective/apparent’ K’s

It is a concept that holds only for 1st order kinetics

Arbitrary kinetics requires accounting for both MT and reaction at the same time

It remains a series process (MT → reaction)

but MT is influenced by surface reaction

A1) Tuning of Sh(z) in a monolith local Sh from CFD

From T(r) , Y(r ) profiles, a local, wall Nu and Sh numbers can be calculated

A1) Tuning of Sh(z) in a monolith hm correlations through Sh : HT analogies

• Bräuer and Fetting (’66) (linear correlation)

• i.e. with a first order kinetic Sh lies between constant (=null) wall concentration and constant wall flux (=reaction), with a quadratic function:

(0) ( )(0)(

DaIISh ShS ShDaII Sh

S h −⋅

∞⋅

effK kβ= +

A1) Tuning of Sh(z) in a monolith CFD – First Order Kinetic

• Perfect agreement with asymptotic theoretical value (as expected)

• Experimental correlations for entrance region (very short, semilogx ) not very precise

Variation of Sh number through the reactor channel

Sh FemLabShCShW

Sh(Da)

A1) Tuning of Sh(z) in a monolith CFD – Second Order Kinetic

Actual Sh number • doesn’t match

Bräuer’s correlation! • is no more into the

ShC-ShW region

Variation of Sh number through the reactor channel

Sh FemLabShCShW

Sh(Da)

A1) Tuning of Sh(z) in a monolith Conclusions

CFD gives precise correlations for local Sh and Nu

→ use in pseudo 2D models

it make sense to use more detailed kinetics, whereas CFD cannot manage

A2) CH4 combustion on Pt in a monolith CFD + power law kinetics 1. Investigating the role of transport processes 2. Use of CFD for kinetic studies (as a subroutine)

• Experimental data from literature (10 cm monolith sectioned in 4 segments)

• CFD: CFX4.2 • Optimization: Levenberg-Marquardt open source fortran routine

Catalytic wall

inlet outlet

Simmetry axis

A2) CH4 combustion on Pt in a monolith 2D Model - density

Catalytic wall

inlet outlet

Simmetry axis

A2) CH4 combustion on Pt in a monolith 2D Model - Axial velocity

A2) CH4 combustion on Pt in a monolith 2D Model - CH4 concentration

Catalytic wall

inlet outlet

Simmetry axis

Catalytic wall

inlet outlet

Simmetry axis

A2) CH4 combustion on Pt in a monolith 2D Model - Temperature

2D Model - literature kinetics

solid = literature kinetics, different A’s dotted = D CH4 / 10

Literature kinetics predicts a sudden ignition MT overestimated

2D Model – kinetics tuned

Higher Tin (leading to clear ignition) is difficult to predict – poor mechanism

2D Model – gas/surface reactions

Homogeneous reactions are negligible

3D Model

Large T gradients along the walls

3D Model – segmentation

Perfect mixing between elements is assumed

3D Model – segmentation

Larger transients in the corners (the most active) Approaches the continuous channel model

3D Model – local CH4 concentration

Corners are active The center supplies CH4 to the walls

3D Model – sensitivity analysis

Sensitivity (final XCH4): D >> A

Evidence of mass transfer control

3D Model – kinetic study

Inhibition by H2O provides a chemical explanation of the data

(unlikely, if MT prevails)

A3) CO combustion in an annular reactor PFR + detailed gas & surface chemistry 1. Goal: validation of literature mechanism 2. Own experimental data

(KTH, syngas from biomass gassification)

A3) CO combustion in an annular reactor CO chemistry 1. The lack of hydrogen simplifies the kinetics 2. Surface mechanism extracted from Deutschmann’s CH4 3. gas phase mechanism from GRI 4. CO inlet composition: 0.5, 1 and 2% in air

A3) CO combustion in an annular reactor The annular reactor • Annular reactor is supposed isothermal (Beretta & al.) • Actually < 10° longitudinal temperature increase on catalyst • The tubular model (CHEMKIN) used for the annular geometry

preserving the same residence time and catalytic area

Quartz, 0.006 m ID

1% Pt- γAl2O3 washcoated

Thermocouple

Mullite, 0.004 m OD

A3) CO combustion in an annular reactor Isothermal simulations • Disagreement with the experiments • Opposite effect of increasing % COin

200 250 300 350 400 450 500 550

Catalyst temperature [°C]

% COin

A3) CO combustion in an annular reactor Sensitivity analysis Reducing rate of adsorption of O2 (!)

Better agreement and correct trend for %Coin!

% COin

200 250 300 350 400 450 500

Catalyst temperature [°C]

A3) CO combustion in an annular reactor Isothermal assumption check

Tcat = in the inner pipe, at xcat

• adiabatic temperature increase: 90 K/1%CO • adiabatic reactor Match the measured ΔT • reactor is NOT isothermal!

A3) CO combustion in an annular reactor Conclusions

• Detailed mechanisms are required for a predictive intrinsic kinetics

• Mass transfer must be included in the reactor model

• Eventually shown that a too simplified (PFR) model can lead to wrong assumptions on kinetic parameters: be aware of this in deducing mechanisms

A4) Kinetics of TOM & POM over Pt in a structured catalyst

• The same in Padua with Pt and KTH with Pt, Rh and Ru • Structured catalyst

Typical experimental setup

cat PT

Experimental Design

• Temperature ramps • Varying C/O GHSV Heating Rate

Equilibrium Analysis – C/O=2

• CH4 exp. concentration vs. equilibrium (■)

0 200 400 600 800 1000

temperatura (°C)

concentrazioneCH4 equilibriotermodinamico

GSHV (H-1)24200,concentrazioneCH4GSHV (h-1)49100,concentrazioneCH4GSHV (h-1)73800,concentrazioneCH4

24200 h-1

49100 h-1

73800 h-1

0 200 400 600 800 1000

temperatura ( °C )

concentrazioneH2 equilibriotermodinamico

GSHV (H-1)24200,concentrazioneH2

GSHV (h-1)49100,concentrazioneH2

• H2 exp. concentration vs. equilibrium (■)

24200 h-1

49100 h-1

73800 h-1

0 200 400 600 800 1000temperatura ( °C )

concentrazioneH2O equilibriotermodinamico

GSHV (H-1)24200,concentrazioneH2O

GSHV (h-1)49100,concentrazioneH2O

GSHV (h-1)73800,concentrazioneH2O

• H2O exp. concentration vs. equilibrium (■)

24200 h-1

49100 h-1

73800 h-1

0 200 400 600 800 1000

temperatura (°C)

concentrazioneCO2 equilibriotermodinamico

GSHV (H-1)24200,concentrazioneCO2

GSHV (h-1)49100,concentrazioneCO2

GSHV (h-1)73800,concentrazioneCO2

• CO2 exp. concentration vs. equilibrium (■)

24200 h-1

49100 h-1

73800 h-1

0 200 400 600 800 1000

temperatura ( °C )

concentrazioneCO equilibriotermodinamico

GSHV (H-1)24200,concentrazioneCO

GSHV (h-1)49100,concentrazioneCO

• CO exp. concentration vs. equilibrium (■)

24200 h-1

49100 h-1

73800 h-1

0 200 400 600 800 1000temperatura (°C)

concentrazioneCH4 equilibriotermodinamico

GSHV (H-1)25100,concentrazioneCH4

GSHV (h-1)49100,concentrazioneCH4

GSHV (h-1)73800,concentrazioneCH4

• CH4 exp. concentration vs. equilibrium (■)

24200 h-1

49100 h-1

73800 h-1

0 200 400 600 800temperatura (°C)

concentrazione H2 equilibriotermodinamico

GSHV (H-1)25100,concentrazioneH2

• H2 exp. concentration vs. equilibrium (■)

24200 h-1

49100 h-1

73800 h-1

0 200 400 600 800 1000temperatura (°C)

concentrazione H2O equilibriotermodinamico

GSHV (H-1)25100,concentrazioneH2OGSHV (h-1)49100,concentrazioneH2OGSHV (h-1)73800,concentrazioneH2O

• H2O exp. concentration vs. equilibrium (■)

24200 h-1

49100 h-1

73800 h-1

0 200 400 600 800 1000temperatura (°C)

concentrazione CO2equilibriotermodinamico

GSHV (H-1)25100,concetrazioneCO2

GSHV (h-1)49100,concetrazioneCO2

GSHV (h-1)73800,concentrazione CO2

• CO2 exp. concentration vs. equilibrium (■)

24200 h-1

49100 h-1

73800 h-1

0 200 400 600 800 1000temperatura (°C)

concentrazioneCO equilibriotermodinamico

GSHV (H-1)25100,concentrazioneCO

• CO exp. concentration vs. equilibrium (■)

24200 h-1

49100 h-1

73800 h-1

Analysis of the global reaction

j j jj

dC RCd

υυτυ

= ⋅ ∆ = ∆= ⋅

Global reaction:

CH4 + aO2 = bH2 + cH2O + dCO + eCO2

A way to look into the data: identify the global reaction occurring into the reactor

0 200 400 600 800-2

T [°C]

Global reaction,C/O=2(- equil, . exp)

vH2vH2OvCOvCO2vCH4vO2

Global reaction stoichiometry - C/O=2

At higher T exp data approach equilibrium Effective reaction: CH4+O2 = 1.25H2+0.75H2O+0.75CO+0.25CO2

Global reaction stoichiometry - C/O=1

Exp stoich. Quite far from equilibrium: Equilibrium reaction: CH4+0.5O2=2H2+CO Effective reaction: CH4+0.77O2= 1.65H2+0.47H2O+1.03CO+0.06CO2

0 200 400 600 800-2

T [°C]

Global reaction,C/O=1(- equil, . exp)

vH2vH2OvCOvCO2vCH4vO2 CO – CO2 reach equil.

Mechanism recognizing

0 100 200 300 400 500 600 700 800 900-1

T [°C]

Contribution of different reactions,C/O=2(- equil, : exp)

CH4+2O2=CO2+2H2OCH4+H2O=CO+3H2CO+H2O=CO2+H2

0 100 200 300 400 500 600 700 800 900-1

T [°C]

Contribution of different reactions,C/O=1(- equil, : exp)

CH4+2O2=CO2+2H2OCH4+H2O=CO+3H2CO+H2O=CO2+H2

• Sensitive at the hypotheses on the mechanism • WGS equil. is late in comparison with other reactions

scan progressively shorted residence time, to spot the instantaneous stoichiometry

Mechanism recognizing

Data simulation Pseudo 2D model with simplified kinetics Species mass balance

Energy balance

( )v 1...7d a idz

= − ⋅ − =Bc B S

c K c c

( ) 1...7Cata iρ⋅ − = − ⋅ =c B SK c c ν R

( )v cp Bt B S

dT a K T Tdz

ρ⋅ ⋅ = − ⋅ −

( ) ( )t B S Cata K T T ρ⋅ − = − ⋅RR ΔH

Pseudo 2D simplified kinetics • Groppi kinetic mechanism

Transport coefficients Monolith

i ic t

cell cell

Sh D NuK Kd d

λ⋅ ⋅= =

Comparison between 1D MODELs

1D MODELS: PFR vs. Sh,Nu

300 350 400 450 500 550 600 650 700 750 800

T(°C)

GROPPI + Sh,NuEXPGROPPI + PFR

• Bad agreement of the kinetics in the ignition region • PFR over predicts the conversion at high T • Sh, Nu model matches the data at high T

Temperature profiles • Peak in the surface temperature, Tin=750°C • Maximum in gas temperature is shifted downstream • First exothermic, then endothermic surf. reactions

Temperature profiles in the reactor

0 0.002 0.004 0.006 0.008 0.01

) T gas

Exp, out

• Adiabatic reactor

• Channel □ → ○ keeping Scat and τ • Every channel behaves similarly to the others • Calculations made with CHEMKIN PLUG • Deutschmann2001 mechanism

Data simulation PFR model with detailed kinetics

Lower flow rate - conversion

meccanismo DEUTSCHMANN-Pt

0,8 1 1,2 1,4 1,6

T/Tinn

Calcolati con PLUG Sperimentali Sperimentali2

• Channel non-adiab. → rescaled T/Tign • At higher T the regime is mostly diffusive

Higher flow rate - conversion

0,8 1 1,2 1,4 1,6T/Tinn

Calcolati con PLUG Sperimentali Sperimentali2 Sperimentali3

• Transport phenomena are increased, determining a better agreement even at higher T

Conclusion

• Deutschmann2001 mechanism fits quite well our data, suggesting two chemical regimes

0,8 1 1,2 1,4 1,6T/Tinn

Calcolati con PLUG Sperimentali Sperimentali2 Sperimentali3

Total Oxidation

Partial Oxidation - Reforming

Conclusion

• Pseudo 2D models: for kinetics other than first order, Sh number should be calculated numerically

• 1D model: Extend Chemkin PLUG, to account for both detailed kinetics and transport phenomena (pseudo-2D)

A4) CH4 partial oxidation on Rh foam pseudo2D + detailed surface kinetics

• Spatially resolved (x) T and x data

(Horn & Schmidt, MN)

• Validation of literature mechanism (CH4 on Rh)

A4) CH4 partial oxidation on Rh foam Chemistry

Global reactions expected:

Total Oxidation: CH4 + 2O2 = 2H2O + CO2 DH= –803 kJ·mol-1 Partial Oxidation to H2O and syngas: CH4 + O2 = H2 + CO + H2O DH = –278 kJ·mol-1 Partial Oxidation to Syngas: CH4 + 1/2O2 = 2H2 + CO DH = –36 kJ·mol-1

After O2 consumption:

Steam Reforming (SR): CH4 + H2O = 3H2 + CO DH = +206 kJ·mol-1 Water Gas Shift (WGS): H2O + CO = H2 + CO2 DH = –41 kJ·mol-1 Dry Reforming (DR): CH4 + CO2 = 2H2+ 2CO DH = +247 kJ·mol-1

P. Canu – CFD + µΚΙΝ Liège, Sept. 2011

A4) CH4 partial oxidation on Rh foam Chemistry CPO Mech

R. Schwiedernoch, S. Tischer, C. Correa, O. Deutschmann, Chem. Eng. Sci. 58 (2003) 633.

Autothermal Reactor – Rh/Al2O3 Foam Catalyst

FRONT HEAT

SHIELD

BACK HEAT

SHIELD CATALYST

INSULATION

CH4/O2=0.5

Tin = room T

A4) CH4 partial oxidation on Rh foam Catalyst arrangement

A4) CH4 partial oxidation on Rh foam Reactor setup Reactor assembly, axial T, C measurements and computational domain

A4) CH4 partial oxidation on Rh foam Measurements T, C spatially resolved

A4) CH4 partial oxidation on Rh foam Eqs.

A4) CH4 partial oxidation on Rh foam Bulk simulations Axially resolved results Vs. measurements

A4) CH4 partial oxidation on Rh foam Simulations - Pure PFR model Axially resolved results Vs. measurements

Exit compositions very close to the experimental → end-of-the-tube data can be misleading

(poorly informative) 70

A4) CH4 partial oxidation on Rh foam Simulations - surface

Axially resolved results at the surface

A4) CH4 partial oxidation on Rh foam Simulations - Coverages Axially resolved results Coverages

A4) CH4 partial oxidation on Rh foam Analysis of mass-transport limitations

Difference between bulk and superficial mole fractions (∆X), transport coefficient (KC) and production rate ( ˙s) for each species, all scaled with respect to the values of CH4

Marked limitations for both

• species of low diffusivity • species with high net production rates. caution in using the Chilton–Colburn analogy for fast reacting species

A5) Herogeneous reaction simulation by CFD Hands-on illustration of CFD calculation through Multiphysics:

1. Arbitrary geometry

2. Generic chemistry

3. velocity distribution (simple and variable geometry)

4. homogeneous reaction

5. (simplified) surface reaction

Applications feasible with ordinary hardware and limited time

A6) CH4 partial oxidation on Pt monolith CFP+µkin

Direct illustration of coupling mKIN to CFD through Multiphysics:

1. Cantera provides , given C at the surface

2. MP→ Matlab → Cantera

Applications quite manageable

A6) CH4 partial oxidation on Pt monolith CFP+µkin CH4 combustion on Pt Honeycomb with inlet

CH4 (1%) O2 (1%)

T=500°C

A6) CH4 partial oxidation on Pt monolith CFP+µkin CFD (Comsol MP) uses:

• Navier-Stokes eq. for Momentum • Stefan-Maxwell eq. for Species • Convection and Conduction for T gas • Conduction for T solid • Idel Gas Law for density

Detailed surface mechanism* (as BCs, through Cantera, via Matlab interface)

30 steps including: 7 molecular species 11 adsorbed species adsorption/desorption/ surface reaction

(see rsurf.m)

* R. Quiceno, J. Perez-Ramyrez, J. Warnatz, O. Deutschmann. Appl. Catal. A: General (2006)

Methane catalytic partial oxidation Detailed chemistry

R. Quiceno, J. Perez-Ramyrez, J. Warnatz, O. Deutschmann , Appl. Catal. A: General (2006)

z= –10 mm

z=10 mm

TG CH4 , O2 H2O , CO2 H2 , CO

max TS

Catalyst (1cm)

computational domain (3 cm)

2D model Carrier Ar, vIN = 0.25 m/s TIN = 500°C

Solid T

Very localized heating 81

-10 -5 0 5 100

z [mm]

Upstream flow

Experimental

CATALYST

Impressive axial diffusion (He =carrier) Agreement with experimental exit composition

At TIN=500°C, syngas negligible

-0.01 -0.008 -0.006 -0.004 -0.002 0 0.002 0.004 0.006 0.008 0.01770

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01

Surface T

mean gas T

Upstream heat diffusion (He)

Surface coverages

Besides the first 0.1 mm, the surface is almost free Pt(S) sites CO(S) is the main coverage after O2 is consumed

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.0110

PT(S)H(S)H2O(S)OH(S)CO(S)C(S)O(S)

ABOVE 1%

A6) CH4 partial oxidation on Pt monolith CFP+µkin - Conclusions

1. Coupling CFD and detailed chemistry is feasible 2. Surprising effects of interactions

between M/HT and chemistry are spotted

3. Still limited on homogeneous chemistry

A7) H2 oxidation on pure Pt in stagnation flow CFP+µkin

Just demonstration by Multiphysics

Updating CRE: Applicationsweb.abo.fi/fak/tkf/tek/Files/cacre2014/MicroKin-PC-5.pdf · 2014. 5....

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