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 According
to the Second Law of Thermodynamics, any power plant which burns fuel
to produce heat pays a severe thermodynamic price of 25-30% loss of efficiency
due to the highly irreversible, entropy producing, combustion process.
This tax of nature has been levied on every single power plant from the
earliest days of the industrial revolution to the present. For the last
150 years, however, it has also been known that the tax can be avoided
if the chemical energy of the fuel could be converted directly to electricity
in an electro-chemical device known as a fuel cell. In the past, fuel
cells for power generation have not fulfilled their thermodynamic promise
but advances in materials and fabrication techniques over the last decade
have altered this picture dramatically.
There are several different types of fuel cell, the 'front runner' for
power generation being the solid oxide fuel cell (SOFC). SOFC's can use
natural gas as their fuel and they operate at around 900 C. One possibility
is to replace the combustor of a gas turbine by a SOFC 'stack', the hot
exhaust products then passing through the turbine. Because the fuel cell
stack itself produces electricity, the overall efficiency will be very
high, possibly around 75%. This brand new technology (which could make
a very significant contribution to the UK economy), will not be available
for another decade but the race is on to produce SOFC-GT power systems
which have high efficiency, good reliability and are comercially competitive
with other forms of power generation.
In partnership with Rolls-Royce, we are modelling the thermo-fluid-dynamic
processes which occur in SOFC stacks. This is a very complex problem because
the physical phenomena involved are all inter-related. For example, we
have to include the convection and diffusion of reacting gas mixtures
in the porous electrodes and ceramic support material, the electro-chemical
reactions occurring at the electrode-electrolyte interfaces, and the heat
transfer by convection, conduction and radiation throughout the stack.
The prize, however, is very great. Apart from the very high efficiency
of electricity generation, emissions from SOFC-GT systems will be very
low with near-zero levels of NOX, SOX and particulates. High efficiency
also implies reduced emission of CO2 which is the main 'greenhouse gas'
responsible for global warming. Future developments could even include
fuel pre-processing to reform the primary fuel to H2 and remove the CO2
at source for disposal elsewhere. If this can be achieved, the SOFC-GT
combination really would become the ultra-high efficiency, zero emissions
power plant of the 21st century.
This research is being carried out by Professor John Young and Dr. Alex
White.
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E-mail
Telephone: +44 (0)1223 330263
Fax +44 (0)1223 765311
Other environment related projects:
Airborne pollution
High Efficiency Power generation with Low Emissions
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