Hydrogen heat management

While the control structure proposed in Fig. 5.16 satisfies the basic demands of heat management, it is not a scheme we would recommend building. First, we have reservations about the design of the recycle column reboiler and its hot bypass. As shown in Fig. 5.16, the hot gas temperature is over 4253C. When we add the fact that the operating pressure is close to 500 psia and that the stream contains mostly methane and hydrogen, we have to wonder how to design the reboiler and its bypass valve so they will operate safely and reliably. 

Figure 7.1 Heat management in a metal hydride hydrogen storage device.

Direct methanol fuel cell (DMFC) was developed in 1950s-1960s, based on the liquid alkaline or aqueous acid solution as the electrolyte. It converts the methanol directly into electricity, instead of using indirectly produced hydrogen from methanol through the reforming process. Today, DMFC commonly refers to as the one that employs PEM as the electrolyte. Fuel for DMFC is a dilute solution of methanol, usually 3-5 wt% in water. The size of DMFC can be considerably smaller than PEMFC because of the elimination of fuel processor, and complex humidification and heat management systems. The performance of DMFC is relatively low compared to that of PEMFC. 

Different types of membrane reactors for hydrogen production have been proposed in the literature. Most of the previous work has been performed in packed bed membrane reactors (PBMRs) however, there is an increasing interest in novel configurations such as fluidized bed membrane reactors (FBMRs) and membrane micro-reactors (MMRs), especially because better heat management and decreased mass transfer limitations can be obtained in these novel reactor configurations. 

Finally, the reactions for hydrogen production are often quite endothermic (reforming reactions) or exothermic (e.g. CPO). The temperature control is thus quite important because a decrease in temperature on the membrane surface leads to a decrease in hydrogen flux through the membrane while an increase in temperature could result in crack on the membrane surface with a consequent decrease of permselectivity (and thus deteriorating the MR performance). The heat management and temperature control in PBMRs is quite... 

The different fuel processing steps are carried out at different temperatures and range from strongly endothermic to strongly exothermic. Hence proper heat management is indispensable for efficient hydrogen production. 

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