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.