Fuel Processing for Fuel Cells - Institut für Technische Chemie und ...

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6 Torsten Kaltschmitt and Olaf Deutschmann
power, unless the entire process chain, from the fuel source to the produced
electricity, is more efficient than the conventional production of
electricity in power plants. Here, the advantages of using fuel cells for
power supply include local independence from the power grid (mobile
and portable applications) and their use as back-up systems in case of a
grid power outage or shortage.
Due to the problems in hydrogen delivery infrastructure and since
efficient hydrogen storage facilities are still under development, an
alternate way of providing hydrogen for the fuel cell is the on-site
production from logistic fuels. Regenerative and liquid fossil fuels
exhibit a much higher volumetric energy density, which makes on-site
production of hydrogen an even more attractive possibility, in particular
for portable and mobile applications. On-site production requires efficient,
compact, and low-cost fuel processors specifically designed for the
application under consideration. A survey of current and potential fuel
cell applications is shown in Table 1, which also shows the large range of
electrical power output needed from the fuel cell stack, ranging from
milliwatts to megawatts.
Though the topic ‘‘fuel processing’’ includes a variety of objectives,
ranging from the development of sulfur-resistant reforming catalysts to
the control of the entire fuel processor/fuel cell system, this chapter focuses
on the physicochemical fundamentals and the engineering aspects of fuel
processors specifically designed for fuel cell applications; books such as the
one by Kolb (2008) and specific literature are frequently referenced for
more details. Figure 1 provides a flowchart of fuel processing from the
original feedstock (natural gas, crude oil, coal, biomass) to the electrochemical
oxidation of the fuel cell’s fuel hydrogen. Here in this chapter, the focus
is on the specific fuel processing in reformers to prepare the fuel for its use
in fuel cells.
The chapter is organized as follows: In Section 2, the requirements on
fuel quality are given from the fuel cell point of view. Section 3 provides a
short overview of all the fuels considered as source for processing for fuel
cell applications. Then, there are three different sections on fuel processing
being (Section 4.1) the cleaning and pre-reforming of the primary fuel
(desulfurization, cracking of long-chain hydrocarbons), (Section 4.2) conversion
of primary hydrocarbon fuels into hydrogen or hydrogen-rich
synthesis gases, and (Section 4.3) the cleaning and composition optimization
of the products such as removal of CO and olefins. In Section 4.2, we
discuss all relevant hydrocarbon conversion processes, which are steam
reforming (SR), partial oxidation (POX), and autothermal reforming
(ATR) from the point of view of the primary fuels being natural gas,
methanol, ethanol, gasoline, and diesel. Section 5 presents current available
technologies and devices on the market and under construction and