Figure 5. Methanol and oxygen mole fraction contour plots in the
thermally coupled reactor for conducting simultaneous endothermic and
exothermic reactions.
The chemical enthalpy and sensible enthalpy contour plots are
illustrated in Figure 6 in the thermally coupled reactor for conducting
simultaneous endothermic and exothermic reactions. A thin layer of a
slurry containing the ceramic precursor is applied on the surface by
means of spraying, painting, or dipping. After applying for the coat,
the slurry is dried and calcined at a temperature usually in the region
of 350-1000 °C. Finally, the ceramic layer is impregnated with the
catalytic active material. Alternatively, the catalytic active material
is applied for simultaneously with the ceramic precursor. Unfortunately,
a number of disadvantages of the catalyzed hardware reactors compared to
fixed bed reactors exists. The catalyst layer cannot be replaced if it
loses its activity either by ageing or by poisoning. The catalytic layer
can only be applied to certain materials. The reactor tubes have to be
made of this type of material which may be more expensive than a
conventional tube material. The steam reforming reactions occurs under
pressurized conditions and the tube thickness is large, hence the cost
of materials influences the price significantly. Furthermore, production
of long catalyzed hardware reactor tubes can be difficult. The reactor
tube can have a length of 50 mm or more. It will be difficult to obtain
an even thickness of the reforming catalyst layer throughout such a
length, and means to obtain an even layer, which can be used for small
scale application such as centrifuging the tube, is more difficult to
apply for this size of tubes. Additionally, appropriate heat treatment
of a tube of this size can be difficult. These drawbacks can be overcome
by producing the catalyzed hardware separately from the reactor. A metal
support is cut into an appropriate size. The sheet is wash-coated. After
the wash-coating, the sheet is formed into the appropriate shape.
Alternatively, the sheet is formed into the final shape prior to the
wash-coating. The metallic support is formed substantially to have the
same shape as the reactor wall and is arranged in a direct heat
conduction relationship with the reactor wall. It will be possible to
change the catalytic layer if it no longer has sufficient catalytic
activity. The expensive steel used to obtain adhesion of the catalyst to
the metal surface will only comprise a small fraction of the total metal
consumption. The catalyzed hardware can be produced in smaller sections,
which will be easier to manufacture and handle. Pressure drop in the
catalyzed reformer tube is much lower than in the conventional case for
the same tube diameter. This enables the use of reactor tubes with a
smaller diameter and still maintaining an acceptable pressure drop.
Smaller tube diameter results in an increased tube lifetime, tolerates
higher temperatures and reduces the tube material consumption.