Validation of a detailed dynamic model of palladium ... of a detailed dynamic model of palladium-...

5th Trondheim Conference on CO2 Capture, Transport and Storage, June 16-17.2009

Validation of a detailed dynamic model of palladium- ceramic membranes for hydrogen separation

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Angelo Rossi & Giacomo Lamonaca, STRUTTURA INFORMATICA, Florence (IT), Silvano Tosti & Alessia Santucci, ENEA, Frascati-Rome (IT)

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STRUTTURA INFORMATICA, a Software and Process Engineering Solutions provider, focuses on the study and development of dynamic simulation models of thermal power plants and related technologies addressing both renewable and conventional sources.


ENTE PER LE NUOVE TECNOLOGIE, L’ENERGIA E L’AMBIENTE

ENEA is a public agency operating in the fields of energy, the environment and new technologies to support Country's competitiveness and sustainable development.


Summary- Foreword

- Process description

- Phenomena

- Hypothesis

- Technical platform

- Check of the model

- Experimental results

- Validation

- Conclusions

• Final goal: validation of the model on experimental test of Pd/Ag membranes.

• Tests executed by ENEA in its laboratories in Frascati, ITALY.


FOREWORD

H2 separation from syngas:• cryogenic process• pressure swing adsorption (PSA)• selective permeation process by way of polymeric/metallic membranes.

• The study originates from a research project funded by the Veneto Regional Administration: attention was focused to polymeric and metallic membranes.

• Models developed:• polymeric membrane• extended model of metallic membranes (Pd/Ag alloy).

Module description

This module simulates a membrane separation system to obtain a high purity degree (99,9%) H2 stream from syngas generated in a gassifier.

The module gives us:

• H2 flux through the membrane and porous support

• H2 concentration trend in the Pd bulk

• Un permeate and permeate outlet flow rates pressure, temperature and composition of both sides outlet gas

The gaseous components Pd interacting are limited to the following six: H2 , CO, CO2 , H2 O and O2 as concurrent and H2 S as poison.


GEOMETRICAL SCHEMA


CHEMICAL and PHYSICAL PHENOMENA TAKEN INTO ACCOUNT

UNPERMATE SIDE

• Transports due to mechanical mass motion along membrane longitudinal axis• Axial and radial diffusive transport• Adsorption of the various components into the Pd mono layer• Desorption of the same components as above from mono layer to the laminar one • Heat exchange between gas and membrane and gas and external wall too

INSIDE the Pd

• Atomic hydrogen dissolution into the Pd grid from/to un permeate side mono layer• Atomic hydrogen diffusion into the Pd bulk• Atomic hydrogen dissolution (reversible) from/to porous support side mono layer• Accretion of the various elements atoms into the un permeate side mono layer• H atoms accumulation into the porous support side mono layer


PERMEATE SIDE

• Atomic hydrogen associative desorption from inner mono layer to porous support and molecular hydrogen dissociative adsorption from porous support to this Pd mono layer

• Molecular hydrogen transport through the porous support; the way to move H2 through the support is intermediate between the diffusive motion according to Knudsen law and the Poiseuille transport mechanism

• Mass transport in the permeate gas bulk

Further this model takes into account:

• Momentum balance as regard to gas bulk un permeate and permeate side• Total mass balance and single component balance (where required)• Heat balance as regard to un permeate and permeate gas bulk, Pd bulk and

porous support too where the hydrogen follows the perfect gas law


CHEMICAL and PHYSICAL PHENOMENA TAKEN INTO ACCOUNT

HYPOTHESIS

• At membrane inlet, un permeate side, we find a synthesis gas stream constituted by 14 components that are:H2 O, N2 , O2 , H2 , CO2 , CO, HCl, Ar, H2 S, CH4 , C2 H2 , NH3 , HCN, COS.

Thermal model:

• The gas boundary layers temperature is supposed to be the same as the gas bulk one • The Pd is supposed to be all at the same temperature • The adsorbed gas is supposed to be in thermal equilibrium with the Pd and the

possible superficial reactions between its components are neglected


Chemical model:

• In any axial cell we consider a perfect mixing ( WSR )• The gas stream (un and permeate) is flowing in a turbulent way • The boundary layer is considered ‘glued’ to Pd wall. Its thickness is very little:its

thermal capacity can be neglected • The Pd surface layer has a thickness comparable to the dimension of a mono atomic

layer • Inside the ceramic support, the hydrogen flux driving force is the ΔP between the gas

collected in the pores and the permeate

SECTION OF GEOMETRICAL SCHEMA


Schema of input/output variables and data of the model


THE TECHNICAL PLATFORM: ISAAC DYNAMICSISAAC DYNAMICS is a software package suitable for :

• Dynamic simulators (at PTS/OTS level) of systems for energy production both in a conventional way and from renewable sources

• Dynamic simulators of chemical plants• Simulation of single physical phenomena and single system components.

The model construction is based on a collection of modules representing a single plant component.The modules are assembled in libraries according to the working fluid. The libraries are:

• Water• Gas

• Molten salts• Oils (Terminoil – VP1)

It is also possible, during a run, to modify some physical, geometrical and even topological parameters, allowing in this way awareness studies about dimensioning and scaling up of plants or part of them.

This package makes easy to build a task ( plant model ): the operator has only to collect from the libraries the appropriate icons corresponding to the components in the same succession as in the plant and then to connect them through the exchangeable variables; in this last operation he is aided by the software suggesting what should be joint.


Check of the modelThe check tests allow us to verify that:• the theoretical model reactions are in a good agreement with the physical system ones we are expecting• the equation system can be easily and quickly solved• the accuracy of the achieved resultsThese tests have been executed in the following logic point of view:


Hydraulics Tests

Variable Initial steady state

Ending steady state

Pressure (bar)

2 4


Thermal Tests

T PdW Unp.

P Unp.T Unp.


Chemical Tests


Validation

The model validation is based on experimental data coming from the research activity performed by ENEA in its Frascati laboratories and aimed at hydrogen separation through metallic membranes: to be more precise, they have been tuned up to evaluate the Pd-Ag membrane behaviour during a work cycle of long duration. Anyway, these results may be an excellent opportunity to validate this model.

The tests are referred to two different experimental campaigns executed using two metallic membranes of the same material, but of different thickness, i.e. 50 and 61 microns.


Experimental apparatus


Experimental results

---------------------------------------------------------------------------------------Physical/geometrical data

------------------------------------------------------------------------------------------------Membrane Alloy Pd - Ag 23%wtPorous support NoneMembrane length 148 mmWall thickness 61 micronMembrane diameter 10 mmExternal duct diameter 42 mm-------------------------------------------------------------------------------------------------

Operative data-------------------------------------------------------------------------------------------------Lumen pressure (unpermeate) ”Press.In” 100 - 300 kPaShell pressure (permeate) ”Press.shell” 100 kPaTemperature ”T.membr.” 150 - 400 °CNitrogen inlet flow rate ”Shell flow” 1000 sccm-------------------------------------------------------------------------------------------------

61 MICRON MEMBRANE

Test GF 1.2.1 13/10/2004



61 MICRON MEMBRANE

GF 1.2.1 18/10/2004

GF 1.2.1 15/11/2004


----------------------------------------------------------------------------------------------------Physical/geometrical data

------------------------------------------------------------------------------------------------------------Membrane Alloy Pd - Ag 23%wt

Porous support NoneMembrane length 150 mmWall thickness 50 micronMembrane diameter 10 mmExternal duct diameter 42 mm--------------------------------------------------------------------------------------------------------------

Operative data----------------------------------------------------------------------------------------------------

Lumen pressure (unpermeate) ”Press.In” 100 - 160 kPaShell pressure (permeate) ”Press.shell” 100 kPaTemperature ”T.membr.” 450 - 450 °CNitrogen inlet flow rate ”Shell flow” 1000 sccm---------------------------------------------------------------------------------------------------------

50 MICRON MEMBRANE


Test del 3/04/2008



Test del 4/04/2008

50 MICRON MEMBRANETest del 11/04/2008.

Test del 11/04/2008.


Model data


•The experimental apparatus has been simulated with the following main data:•External radius of un permeate duct = 0.025 meters•Internal radius of un permeate duct = 0.015 meters•Metallic membrane thickness = 61.E-6 meters and 50.E-6 meters•Porous support thickness = 5.E-3 meters•Membrane length = 0.148 meters•Alloy composition = Ag 23%•Pd thermal conductivity = 72 W/M/°C•Pd density = 12000 Kg/M**3•Pd specific heat = 244 J/Kg/°C•Porous support thermal conductivity = 0.2 W/M/°C•Porous support density = 3000 Kg/M**3•Porous support specific heat = 1000 J/Kg/°C•Porosity = 0.3•Pore radius = 0.00001 m•Tortuosity = 1.

Validation test logic scheme


61 Microns Membrane


Thickness 61 micronAlloy composition 75% Pd 23%AgLength 150 mm

50 Microns Membrane


Thickness 50 micronAlloy composition 75% Pd 23%AgLength 160 mm

TEST

Unp. Pressure(Pa)

Per. Pressure (Pa)

Pd Tempe rature (K)

Unp. H2 In Flow rate (sccm)

Per. Sweep gas In flow rate (sccm)

Experimental Test Calculation results

Permeate H2 flux

(moles/m2

/s)

Permeability (moli/m/s

pa0.5)

Permeate H2 flux (moles/m2

/s)

Permeabi lit (moli/m/ s/pa0.5)

1 137984 103762 673 300.1 498.79 3.091* 10-2

8.11576* 10-9

3.1050* 10-2

8.172* 10-9

2 123400 103280 723 300.18 498.95 2.895* 10-2

8.28340* 10-9

3.0630* 10-2

8.474*10-9

Error Consideration


As we can see model and experimental data are in a satisfactory agreement considering also the possible errors of instrumentation system monitoring the experimental apparatus. This system consists on:

Each of them may cause an error of about two percent, so that as total they may give rise to an about twelve percent error.

• Two flow rate controllers (MFC)• One flow rate meter unpermeate side (MFM)• Three manometers (PI), two unpermeate side and one permeate• Two thermocouples (TI) respectively placed on the membrane and on the Pyrex of the external duct

CONCLUSIONS


Validation

The validation of the model has been performed using Verification and Validation method (V&V).This kind of approach allows to evaluate the numerical simulation accuracy identifying and quantifying the main error sources. Synthetically they are:

• Theoretical model errors ( approximation/idealisation)• Programming errors• Space and time discrete step integration errors• Iteration errors

Trying to be closed to this method and making sensitivity analysis of the main parameters such as pre exponential diffusion coefficient and H2 activation energy, we have achieved a satisfactory fitting between experimental and computational results, so that we can consider resolved this first campaign of validation activity that could be followed by another one.

CONCLUSIONS


Innovative features of the model

The features that characterize this model are:

• The complexity of the phenomena simulated:• axial and radial diffusion• axial mass transport• adsorption and desorption dynamically treated• accretion of element concentration into the mono layers• diffusion through the Pd bulk layers• energy, momentum and mass balances

• The manipulation of certain parameters that define the dynamics of the processes considered, so that it is possible to make sensitivity studies shown below

• The possibility to couple this model to other ones, as CO-Shift, to study the activity improvement of the involved reactions to enhance the development of chemicals reformers and industrial devices

CONCLUSIONS


Sensitivity analysis

Trend of H2 stream through the membrane as a function of D0 i.e. pre exponential factor of the diffusion coefficient

CONCLUSIONS



H2 Stream vs sticking coefficient at zero coverage S0

H2 Stream vs desorption activation energy

CONCLUSIONS



Difference between H2 stream experimental data and calculated ones as function of (Punp

0.5 – Pper0.5) using as parameter D0, i.e. pre exponential factor of the diffusion

coefficient

CONCLUSIONS



CO Inhibition Effects

In a 300 /250 ° C temperature range, the CO inhibition at first decreases and then disappears according to the literature

Pure Hydrogen

Ptot = 1.24 Bar

CONCLUSIONS


Pending developments of this module

The foreseen activities incident to this model are:

• Permeate side sweep gas introduction

• Axial multi cells modelling

• Membrane behaviour taking into account alloy composition effects as function of metal temperature

• Further validation campaign

CONCLUSIONS


Model applications

This model, developed on ISAAC Dynamics platform, could be a used to analyse the hydrogen permeation through a metallic Pd membrane wrapped on a porous support.By means of such a study, it could be achieved:

• An improvement of the main parameters controlling the permeation process• The hydrogen concentration trend through the membrane and its support• The influence of each step (adsorption/diffusion/desorption) on the whole process and during different operative conditions• Accuracy in the design of a membrane maximizing the H2 flux

Furthermore: Simulation of a fully symmetric membrane bundle, coupled with other modules representing reformers or industrial devices, performing: sensitivity studies, components synergy, chemical reaction activity and chemical/industrial device design.

As a part of a simulator task, a simplified module has been developed, based on the total permeability of a metallic membrane. This parameter, driving the whole functionality of the membrane, can be calculated by means of the extended model.

Modelling:

• Process Engineering;

• Model Implementation for Thermal Energy Plants;

• Development of Dynamic Simulators;

• Feasibility Studies.

IT solutions:

• Web modelling: Software solutions for remote accessing and running of simulation models;

• Publishing of results via web;

• Knowledge Management and Document Management Systems.

Who we are…


Internal view of offices in Florence

More Info…

Contact:

[email protected]

Phone +39 055 4379027

Phone +39 050 40763

www.strutturainformatica.it


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Validation of a detailed dynamic model of palladium ... of a detailed dynamic model of palladium-...

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