(265e) Advanced Reactors for Methane Steam Reforming

            Methane steam reforming is
conventionally carried out in a multi-tubular packed bed reactor. To supply the
heat for the endothermic reactions, the reactor tubes are suspended in a
furnace. Pressure drop constraints impose the use of sufficiently large
catalyst particles. Because the main steam reforming reactions are fast,
intra-particle diffusion limitations cannot be avoided and the catalyst is not
used efficiently. The rate of heat transfer between the inner wall of the
reactor tubes and the process gas and material related constraints on the
maximum tube wall temperature are also limiting the throughput.

            The performance of advanced reactors
for methane steam reforming, removing the above mentioned limitations, is
studied in this work. Dual-zone structured catalytic reactors are focused on.
They consist of a central core and an outer casing. The central core is
constructed from perforated cones. The resistance to flow of the core and the
resulting pressure drop and flow distribution over core and casing can be
adjusted by the number of perforations and their size. The outer casing is
designed to improve the heat transfer between the reactor tube inner wall and
the process gas, while maintaining a low pressure drop. It consists of alternating
connected sectors of blades moving the flow towards and away from the wall. The
catalyst is coated on the reactor internals. The use of a thin catalyst layer
allows increasing the catalyst efficiency for the main steam reforming
reactions.

Detailed 3D Computational Fluid Dynamics (CFD)
simulations and under typical commercial operating conditions are presented. A
hybrid CFD model is used. In the casing, close to the wall, the full details of
the geometry are described and the Reynolds Averaged Navier-Stokes
equations are solved. Turbulence is accounted for via the turbulent viscosity,
conductivity and diffusivities. These properties are calculated from the
turbulent kinetic energy and turbulence dissipation rate for which additional
continuity equations are solved. The main steam reforming reactions are
described using detailed reaction kinetics (Xu and Froment, 1989). Because the number of
perforations in the central core is large and their size small, a porous medium
description is adopted for the core. The effective conductivity and
diffusivity in the porous medium are accounted for.

The CFD simulations allow optimizing (i) the reactor geometry and related flow distribution and
heat transfer and (ii) the amount of catalyst and the distribution of the
catalyst in the reactor. The resulting performance of the advanced steam
reformer in terms of methane conversion, pressure drop, catalyst efficiency and
heat transfer is discussed. A comparison with a classical packed bed reactor is
made.

References:

- J.G. Xu,
G.F. Froment, AICHE J., 35 (1), p. 88-96, 1989(a); p. 97-103, 1989.

- J. De
Wilde, G.F. Froment, Fuel, published on-line, 2012 (doi: 10.1016/j.fuel.2011.08.068).