Environmental Engineering Reference
In-Depth Information
Process water
HT coolant
LT coolant
Electric
motor
H
2
Humidified air
Humidifier
heater
PEFC
stack
Humidified
hydrogen
Condenser
Demister
Radiator
Exhaust
Air
Condensate
Water tank
Pump
Compressor/motor/expander
Figure 28.2
Schematic diagram of a hydrogen-fueled, polymer electrolyte fuel cell system for automotive applications. reprinted with
permission from ref. [21]. © Elsevier.
The fuel cell stack in Figure 28.2 is an assembly of elementary cells (anode, polymer membrane, cathode) interconnected by
bipolar plates in a planar technology configuration. The thermal and water management system consists of two coolant circuits
and a process water circuit. The high-temperature circuit delivers the coolant (mixture of ethylene glycol and water) to the stack
and rejects the stack waste heat in an air-cooled radiator. The high-temperature coolant also preheats the cathode and anode
streams and provides the latent heat of humidification. The low-temperature circuit delivers the coolant to the shell-and-tube
condenser and also cools the electric motor. The condenser of the vehicle's air-conditioning system can be cooled by means of
the low-temperature coolant as well. The process water circuit uses deionized water to humidify the anode and cathode streams.
A general overview of the current research on fuel cells for vehicular applications is given by Veziroglu and macario [22].
it includes technical aspects of fuel cell vehicle development, environmental impact, economic analysis, and comparison of
different hydrogen vehicle technologies. The technical aspects are connected with such subjects as degradation and durability
of the proton exchange membrane [23], potential hydrogen production methods [24, 25], and onboard hydrogen storage [26].
The subject of degradation and durability has attracted attention over the last years [27]. Various factors affect the fuel cell
performance, inducing irreversible changes in the kinetic and transport properties of the cell. The main factors are fuel and
oxidant impurities [28], temperature and relative humidity conditions [29], cyclic current-loading conditions [30], as well as
problems of start-up and shutdown [31], and fuel and air starvation [32]. A comprehensive review of the current progress in the
study of fuel cell degradation was performed by Borup et al. [33].
The problem of hydrogen production, storage, distribution, and dispensing is critical in the development of hydrogen fuel cell
vehicles. hydrogen can be produced on-site at the filling station or in larger production plants, from where it is distributed to the
filling stations in pipelines or by trucks. in the latter case, hydrogen can be carried in either compressed or liquid form [34].
The main methods of hydrogen industrial production now are steam methane reforming (close to 50% of the global demand for
hydrogen), oil or naphtha reforming from refinery or chemical industrial off-gases (about 30%), coal and biomass gasification
(about 18%), water electrolysis (3.9%), and others (0.1%) [35]. hydrogen onboard storage technologies are an important factor in
the overall performance of hydrogen fuel vehicles [36]. Storage options include metal hydrides [37], carbon nanostructures [38],
compressed gas [39], and liquid organic carriers [40].
The potential change in emissions and energy use by the replacement of fossil-fuel on-road vehicles with hydrogen fuel
cell vehicles was examined by Paster et al. [41]. As estimations show, the net quantity of most types of emissions associated
with air pollution would decrease considerably, including nitrogen oxides, volatile organic compounds, particulate matter,
ammonia, and carbon monoxide. On the other hand, as noted by huo et al. [42], pollutant emissions from vehicles must be
separated into total and urban emissions to differentiate the locations of emissions, because the main emissions are related
