(565b) CFD Simulation of Heat Transfer in a Microchannel Reactor for Fischer-Tropsch Synthesis Process

CFD Simulation of Heat Transfer in a Microchannel Reactor for
Fischer-Tropsch Synthesis Process

K.
Kshetrimayum, C. Park, I.
Jung, S. Park, J. Na, C. Han

School of Chemical & Biological Engineering,
Seoul National University,

Seoul 151-744, Republic of Korea.

Introduction

Microreactors can have enhanced process intensification due
to its reduced mass and heat transfer distances, when compared to conventional
technology. In this work, heat transfer effect
in a microchannel reactor adapted
for Fischer-Tropsch (FT) synthesis process is being studied. The
process involves substantial heat effect due to high exothermic nature of FT- reacion (heat of reaction = 165
kJ/mol of reactant CO). Computational
Fluid Dyanmic (CFD) modeling and simulation
of heat transfer in a microchannel
can give insights on the thermal behavior
of such a reactor. The knowledge of heat
transfer effect can then be used
to develop a design and obtain tuning parameters for a desired
reactor performance. Understanding the heat effect is essential to achieving an efficient coolant system design
that is considered key to the
performance of microreactor for FT synthesis applications. The main objectives
of the present work have been i) to study
the heat transfer effect in a cross flow microchannel reactor for different
types of coolants (subcooled vapor, liquid water and saturated water) and ii) to
investigate the tuning parameters and best operating conditions that can
maintain the reactor internals to a near isothermal condition for a desired
reactor productivity.

Methodology

Reaction scheme and kinetics as proposed by  Marvast et al.(2005) was considered for the present study. Heat generation profile was independently calculated by simulating the simultaneous reactions in an isothermal
plug flow model using commercial
software-ASPEN. The generated heat
profile is implemented as source condition in the process channels of a
microchanel block comprising of alternate layers of process channel planes and
coolant channel planes [Arzamendi et al., (2010) for detail geometry of
microchannel block considered]. In the microchannel block, heat is
transferred from the  process
channel (where the exothermic reaction is occurring) to the adjacent
coolant channels through channel
walls. For this purpose, a 3D
Computational Fluid Dyanmic (CFD) model of a cross flow microreactor was
developed in commercial CFD software- ANSYS FLUENT.

Results

The heat transfer effect within or interior of the microchannel block was
examined for various scenarios that can be adapted to the actual industrial
operation of compact microchannel reactor for Fisher-Tropsch synthesis purpose.

Table 2: Effect of coolant types

Discussion

CFD simulation
of heat transfer in a microchannel with process channel as heat source(due to
exothermic FT- reaction), gives
insights on the flow and thermal behaviors of a microchannel reactor. Using
the developed CFD model for cross flow microchannel block, effects of different heat generation rates (implying effect of different syn-gas feed rates) were studied. The results help to identify the appropiate
coolant flowrate to be used for a given syn-gas feed rate. Effects of coolant type (subcooled water vapor, liquid water and saturated water) were also
studied. The result indicates that
saturated water as coolant can be the right choice to maintain near isothermal
conditions in the reactor internal. Further, using the CFD model, tuning
parameters and operating
conditions for a desired reactor performance are being investigated.

References

1.   M.A. Marvast, M.
Sohrabi, S Zarrinpashneh, G. Baghmisheh, (2005) J. Chem Engg.,   Vol 28.

2. G. Arzamendi, P.M. Dieguez, M. Montes, J.A. Odriozola, E.F. Sousa-Aguiar, L.M. Gandia, (2010). J. Chem Engg., Vol 160.