23-03-2012, 02:08 PM
Magnetohydrodynamics For Advanced Power Generation System
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INTRODUCTION
Magnetohydrodynamic (MHD) power generation has been
studied as a novel commercial power plant due to its
inherent advantage of high-efficiency with high-working
temperatures. Let us review the principle of an MHD power
generation shown in Figure 1. This process is based on
Faraday’s electro-magnetic induction law. In an MHD
generator, electrically conductive fluid is moving across
magnetic field as an armature coil is rotating in magnetic
field in the rotating generator. It is obvious that power
generation is an energy conversion process.
ISSUES OF CURRENT POWER GENERATION SYSTEMS
It is recognized more important to increase efficiency not
only for saving energy resources but also for reducing CO2
emission recently. Electric power generation system is
known as a heat cycle whose efficiency is restricted by the
second law of thermodynamics. Actual efficiency is limited
below the Carnot efficiency which is determined mainly by
the highest cycle temperature because lower heat exhaust
temperature is generally temperature of environment. Figure
2 shows efficiency of various power generation systems.
Plant efficiency of advanced coal fired steam-turbine is
slightly higher than 40% at the temperature of 500C.
Efficiency of advanced BWR in Japan stays below 35% due
to poor steam conditions for safety reasons. We understand
that steam-turbine system can reach up to about 40% and we
have to combine other system working higher temperatures
if higher efficiency is required.
Energy Re-Circulating LNG/MHD System
Figure 5 shows proposed energy re-circulating type MHD
power generation system with LNG heat source which has
been proposed by Prof. Y. Okuno at Tokyo Institute of
Technology.[1] The system does not combined with any
other system and is called closed cycle MHD single system.
We can see that plant efficiency is expected over 60% even
the enthalpy extraction ratio of the MHD generator is only
30%. Thermal input to the MHD generator is 200 and
electric output is 60 in spite of only 100 input thermal
energy to the system because 100 of heat is recovered by
regenerator. Enthalpy extraction ratio of above 30% was
achieved by experiments with shock tube facility.[2] So this
estimation of efficiency is considered to be realistic in near
future.