Figure 1. Hydrogen mole fraction and temperature contour plots in the
thermally coupled reactor for conducting simultaneous endothermic and
exothermic reactions.
The steam and carbon dioxide mole fraction contour plots are illustrated
in Figure 2 in the thermally coupled reactor for conducting simultaneous
endothermic and exothermic reactions. When a combustion furnace for
burning methanol to be heated is used as an industrial furnace, ceramic
tubular reactors are preferably used both in a high-temperature
reforming section and in a low-temperature reforming section. When an
industrial furnace is a combustion furnace, gases in the industrial
furnace and an exhaust gas from the industrial furnace may contain
various corrosive components. These components are generally rendered
harmless after being discharged from the furnace and are emitted. On the
other hand, heat is preferably recovered in the furnace or immediately
after discharging from the furnace so as to recover and use the energy
of waste heat more efficiently. A tubular reactor, if arranged in an
atmosphere containing corrosive components, must include a
corrosion-resistant material [47, 48]. Metals may not be used due to
corrosion even at temperatures lower than their allowable temperature
limits under some conditions upon use [49, 50]. Some ceramics,
however, can be used even under such severe conditions. Consequently,
steam reforming can be carried out, and the waste heat of the furnace
can be effectively used under conditions where metal tubular reactors
are not usable even at temperatures lower than 300 °C. This can be
achieved by using a ceramic tubular reactor made from a ceramic material
in accordance with a contained corrosive component. When a kiln is used
as an industrial furnace, a low-temperature reforming section preferably
includes a metal tubular reactor in view of economic efficiency, but it
may include a ceramic tubular reactor. Even if a kiln is used as an
industrial furnace, the low-temperature reforming section preferably
includes a ceramic tubular reactor when an atmosphere in the
low-temperature reforming section may cause corrosion. The sizes and
numbers of metal tubular reactors and ceramic tubular reactors can be
set as appropriate according to the size of the kiln, the amount of the
combustion gas, the temperature of the combustion gas, and locations of
the tubular reactors. Such tubular reactors may have a simple
cylindrical form but may also have, for example, protrusions or blades
on their outer surface. The resulting tubular reactors have increased
heat-receiving areas and thereby receive increased heat per unit length
of the reforming tubes. In addition, a shape having the length necessary
for a predetermined reaction quantity may be employed. Accordingly, the
waste heat can efficiently be recovered in a location at temperatures of
600 °C or higher and lower than 1000 °C, although the reactivity of a
steam reforming reaction is low in such a low-temperature region,
because a reforming catalyst effectively acts. The waste heat can also
efficiently be recovered even in the absence of a reforming catalyst in
a location at temperatures of 1000 °C or higher and 1800 °C or lower
because the reactivity of a steam reforming reaction is high in such a
high-temperature region. In addition, the advantages obtained by using
the steam reforming apparatus can be obtained. The steam reforming
apparatus in the kiln is configured as to be heated by part of the
combustion heat to cause a steam reforming reaction as in the steam
reforming apparatus. The part of the combustion heat herein includes a
directly received heat and a radiant-heat-derived heat. Specifically,
the combustion gas comes in direct contact with a metal tubular reactor
and a ceramic tubular reactor to give heat to the metal tubular reactor
and the ceramic tubular reactor.