(362g) SMR3D: An Industrial CFD Tool for Large Steam Methane Reformer Design Optimization

Authors: 
Cances, J., AIR LIQUIDE
Camy-Peyret, F., AIR LIQUIDE
Ulber, D., LURGI GmbH


Introduction

The worldwide hydrogen demand has
strongly increased in the past years, mostly for refinery needs in order to
match environmental requirements such as desulfurization. This megatrend is
expected to maintain for a long term period and raise new challenges associated
to the design and operation of large scale hydrogen plants, as of today mostly relying
on steam reforming of natural gas [ 1 ].

As a major actor in the field of hydrogen production, and
hydrogen plant engineering through its subsidiary LURGI, AIR LIQUIDE has
developed advanced in-house simulation tools to understand, predict and
optimize the efficiency, the compactness and the reliability of large scale
steam methane reformers.

The present paper aims at presenting the SMR3D modeling tool
and its application to key aspects of a recent Lurgi reformer
design.

SMR3D presentation

ATHENA, the AIR
LIQUIDE in-house CFD code developed since the 80's, is a robust industrial
tool, which includes several established models dedicated to heat transfers in
industrial furnaces, including oxy-combustion [ 2 ]:

-         
The
averaged three-dimensional flow is solved by use of a RANS approach (Reynolds
Average Navier-Stokes). The Navier-Stokes
equations are computed averaged on time, while turbulent fluctuations are
modeled with using the standard k?e  model
[ 3 ].

-         
The
solver is based on a cell-centered, structured finite volume discretization of Navier-Stokes
equations [ 4 ] and on transport equations of passive
or active scalars (enthalpy, mass fractions, turbulence quantities of RANS
models ?), with a SIMPLE-algorithm segregated solution procedure.

-         
Radiative heat
transfer equations are solved by use of a specific ray tracing method (DTRM:
Discrete Tracing Radiative Method [
5 ]), a method which proved to be adapted to complex geometries. The gas
radiation properties are taken into account with a WSGG model (Weighted Sum of
Grey Gases), with four gray gases tables available for air and oxy- combustion
products of different fuel compositions [ 6 ], with or
without soot.

-         
The
Magnussen model [ 7 ] is commonly used for industrial
furnaces simulations, because it provides several pertinent tuning parameters,
and then enables to use coarse mesh suited to such large geometries, and then
avoid to fully detailing the burner geometry.

The computation of
the flow, heat transfers and chemical endothermic reaction of steam methane
reforming inside the catalytic tubes has been carried out using the code developed
at Gent University described in [ 8 ][ 9 ]. The tube is described as a 1D plug-flow
reactor in the vertical direction and computes the Hougen-Watson
reactions set:

                                              
                                            

The reforming model
takes into account the intrinsic catalytic kinetics and the limitation though
the diffusion into the porous catalysts, using reaction effectiveness factors, ηr. Although these
effectiveness factors could be computed by the gent code, these parameters were
considered as constant in order to speed-up the simulations. Here, the
effectiveness factors were kept constant and their values were established on
the basis of operational data gathered on AIR LIQUIDE operated plants.

The SMR3D solver has
been developed in order to take advantage of large computers. Two levels of
parallelization (MPI + OpenMP) allow running
massively parallel computations involving hundreds of million cells with a
reasonable restitution time. Therefore, simulation of full scale large reformer
with hundreds of tubes and burners is now at hand.

SMR3D has been
validated through confrontation with experimental data gathered on AIR LIQUIDE
operated fireboxes.

Results applications

On one hand, the capacity
of SMR3D to describe the governing physical phenomena inside the firebox,
despite the difficult experimental access, is a clear motivation. For example,
it enables

-         
heat
loss characterization and mapping,

-         
flow
arrangement characterization

-         
hotspots
identification and tube lifetime improved management

-         
tube duty
distribution, etc?

-         
safe
process intensification

In this paper, the
analysis of the SMR3D simulation results is presented on a reformer case,
allowing to get in depth understanding of the coupling
effects between the combustion chamber and the reforming tube, with a level of
details not reported in the literature to our knowledge.

On the other hand,
the continuous improvement of the commercial LURGI reformer is benefitting from
SMR3D simulation capabilities. As an illustration, two of the largest AIR
LIQUIDE operated plants, recently designed by LURGI, were simulated and the
results are compared (~400 tubes each). The HERACLES plant has been commissioned
in 2011, whereas the second project is to be started-up in 2013, and could benefit
of SMR3D inputs to optimize the tube duty distribution and the flue gas flow
arrangement, which yields to significant performance improvements.

Conclusions

SMR3D is the
results of 25 years of continuous efforts for rigorous integration of the most
appropriate models, while keeping the solver highly efficient. It is now
possible to run simulations of full scale large SMR furnace, including
combustion, radiation and the coupling of combustion chamber to individually
calculated reforming tubes.

The understanding
of the key phenomena involved in reformers operation and design has been
greatly improved, yielding to further optimization and benefits in terms of
efficiency, reliability and compactness.

References

[ 1 ]   New York Power Authority, ?Hydrogen fact
sheet: Hydrogen production ? Steam Methane Reforming (SMR)?,
www.getenergysmart.org, 2005

[ 2 ]   Champinot, C.,
Till, M., Haung-Naudin, C., Klug, A., ?Gekoppelte Berechnungen von Glas und
Atmosphäre?, Glas Ingenieur, 1996

[ 3 ]   Jones, W.P., Launder, B.E., ?The prediction
of
laminarization with a two equation model of turbulence?, Heat and mass transfer, 15, pp. 310-314, 1972.

[ 4 ]  
Patankar,
S.V., ?Numerical Heat Transfer and Fluid Flow?, Hemisphere, 1980.

[ 5 ]  
Lockwood,
F.C. and Shah, N.G., ?A new radiation solution method for incorporation in
general combustion prediction procedures?, 18th Symposium (International) on
Combustion
, The combustion Institute,

Pittsburg,
pp. 1405-1414, 1980.

[ 6 ]  
Soufiani, A., Djavdan, E., ?A comparison between weighted sum of grey gases
and statistical narrow band radiation models for combustion applications?,
Combustion and Flame, Vol. 97, 1994

[ 7 ]   Magnussen, B.F., Hjertager, B.H.,
?On Mathematical Modeling of Turbulent Combustion with Special Emphasis on Soot
Formation and Combustion?, 16thSymp.
(Int.) on Combustion
, 1976.

[ 8 ]  
Xu,
J., Froment, G.F., ?Methane Steam Reforming ? I Methanation and Water-Gas Shift: Intrinsic kinetics?; AIChE journal; 1989.

[ 9 ]  
 Xu, J., Froment,
G.F., ?Methane Steam Reforming ? II Diffusional
limitations and reactors simulation?; AIChE journal; 1989.

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