cfd investigation on fire-side of steam cracking furnace · 2017-03-12 · effect of burner...
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Methusalem (M2dcR2) Advisory Board Meeting, Ghent, 24/06/2013
CFD Investigation on Fire-Side of Steam Cracking Furnace
Yu Zhang, Kevin M. Van Geem and Guy B. Marin
http://www.lct.UGent.be E-mail: [email protected]
Laboratory for Chemical Technology
Technologiepark 914, 9052 Ghent, Belgium
European Research Institute of Catalysis
Furnace Geometry
• The furnace is a double radiant box with
common convection section
• Equipped with only long-flame (floor)
burners, which have separated fuel and
air inlet, situated at the bottom of the
furnace
• 44 reactor tubes are suspended in one
row, each has two passes which are
connected by a S-band and U-band
one fourth of a radiant box
Aim To investigate the flow, combustion and
radiation in the fire-side of an industrial
steam cracking furnace and to obtain the
precise heat transfer into tubular reactor
and the NOx emission
Significance • The precise heat flux profile is required
by the cracking reactor simulation
software to better predict the yields,
temperature, and coking rate inside the
tubular reactor, which are essential for
reactor design and optimization
• The radical combustion kinetics which
take NOx formation into account will
give burner designer clues to reduce
NOx emission in the furnace
Fuel Composition
• The fuel gas can be considered
as CH4/H2 mixture
• Excess air inlet flow rate to
ensure the fuel gas is fully
combusted
• Fuel gas flow rate : 2.22 kg/s
• Fuel gas inlet temperature :
288.75 K
• Oxygen excess (vol%) : 2
Models
• Flow model : Re-Normalisation Group
(RNG) k-ε turbulence model
• Species transport model : Finite-
Rate/Eddy-Dissipation model by Magnussen
and Hjertager (1977), the reaction rate is
governed by the minimum of Arrhenius and
eddy-dissipation reaction rates
• Combustion kinetics : two-step reaction
mechanism based on Westbrook and Dryer
(1981)
• Radiation model : discrete ordinates (DO)
radiation model is used to solve the radiative
transfer equation (RTE) for a finite number of
discrete solid angles
• Flue gas absorption model : weighted-sum-
of-gray-gases model (WSGGM)
Magnussen and Hjertager (1977), Symp.
(Int'l.) on Combustion, 16: 719-729
Westbrook and Dryer (1981), Combustion
Science and Technology, 27: 31-43
Conclusions
• The effects of burner geometry on the
simulated flow, combustion and radiation
heat transfer inside steam cracking furnace is
not negligible
• When using detailed combustion kinetics to
predict NOx formation in the furnace ,the
geometry effect must be taken into account
Future Work • Perform furnace simulations in which detailed
combustion kinetics is taken into account to
predict the NOx emission
• Evaluate the applicability of Eddy Dissipation
Concept (EDC) model coupled with detailed
combustion kinetics in non-premixed
combustion
Effect of burner structure on furnace simulation
In most of previous study on fire-side of steam
cracking furnace, the long-flame burners are always
simplified as a plane at the bottom of the furnace
In order to evaluate the geometry effect, two
simulations are preformed with simplified and detailed
burner structure respectively, as shown
Due to the symmetry consideration, only a quarter of
one radiant box is simulated, coupled with cracking
reactor simulation software
simplified burners detailed burners
• The initial velocity of flue gas above the
burners with detailed structures are
significantly higher than that of the simplified
burners, resulting in a stronger recirculation in
the furnace
• Flame shifts towards the furnace wall in the
detailed burner simulation whereas remains
the same place in the simplified one
Flue gas velocity and temperature
Heat transfer into process
• The shifted flame temperature maximum towards the higher elevation and furnace wall leads to shorter
distance between the two heat flux maximum of the tubular reactors
• Non-uniform heat loads between 22 tubular reactors are observed
No. 18
reactor tube No. 1-22
Heat flux of the tubular reactors
No. 9
Heat transfer rate to all tubes
Acknowledgement
This work was carried out using the STEVIN Supercomputer
Infrastructure at Ghent University, funded by Ghent University,
the Flemish Supercomputer Center (VSC), the Hercules
Foundation and the Flemish Government – department EWI