Fuel
Power
Fluid
Power takes a look at the widening scope of fuel cell technology and
visualises its future in the global market
Fuel cells have a wide range of applications including stationary power
generation (MW), portable power generation (kW) and transportation (kW).
In a fuel cell, since its chemical energy is directly converted to electricity,
it can operate at much higher efficiencies than internal combustion
engines, extracting more electricity from the same amount of fuel. Fuel
cells are capable of converting 40 per cent of the available fuel to
electricity, though the figure can be raised to 80 per cent with heat
recovery. Though the fuel cell itself has no moving parts, offering
a quiet and reliable source of power the systems are environmentally
benign, relatively quiet and generate little or no air pollution. The
only emission from fuel cell is water when hydrogen is fed to it. The
route for total system solutions for the fuel cell industry is by design
only. Controlling the pressure, temperature and flow of fluids in and
out of the fuel cell stack is vital to the overall system of performance.
The far-reaching benefits of hydrogenbased economy are many and are
a continuous challenge along the road towards commercialisation. Competing
industry stakeholders-representing the power generation, portable electronics,
and automotive industries-have created synergistic alliances with each
other to work on problems and several issues are not only common among
them but are also unique and interrelated. Strong interaction with public
policy entities, through deployment initiatives and incentives also
has a positive impact on development. According to the National Fuel
Cell Research Centre, University of California Irvine, fuel cells can
be classified as follows:
Phosphoric Acid Fuel Cell (PAFC)
The electrolyte consists of concentrated phosphoric acid and a
silicon carbide matrix and is used to retain the acid while both electrodes
that also function as catalysts are made from Pt or its alloys when
the operating temperature is maintained between 300- 430OF or 150-220OC
at lower temperatures, phosphoric acid tends to be a poor ionic conductor
and CO poisoning of the Pt electrocatalyst in the anode becomes severe.
The porous electrodes used in PAFCs contain a mixture of the electrocatalyst
supported on carbon black and a polymeric binder to bind the carbon
black particles together forming an integral structure. A porous carbon
paper substrate serves as a structural support for the electrocatalyst
layer and as the current collector. The composite structure consisting
of a carbon black/binder layer on carbon paper substrate forms a three-phase
interface, with the electrolyte on one side and the reactant gases on
the other side of the carbon paper. The conversion efficiency of fuel
bound energy to electricity of a PAFC is typically 40-47 per cent on
a fuel (natural gas) LHV basis.
Molten Carbonate Fuel Cell (MCFC)
The electrolyte typically consists of a combination of alkali (Na
and K) carbonates retained in a ceramic matrix of LiAlO2. The cell operates
at temperature of 1100-1300O F or 600-700O C in order to keep the alkali
carbonates in a highly conductive molten salt form, the carbonate ions
providing ionic conduction. The anode is made from Ni while the cathode
is made from nickel oxide. One of the advantages of the high operating
temperature of the MCFC is that the overall thermal efficiencies is
also high, with a potential of 50 to 60 per cent conversion of fuel
(natural gas) LHV to electricity without recovery and conversion of
the exhaust heat. Also, the exhaust heat from the MCFC is at relatively
high temperatures (1200OF or 650OC)
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