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Microturbines
are becoming widespread for distributed power and
combined heat and power applications. They are one
of the most promising technologies for powering
series hybrid electric vehicles. They range from
hand held units producing less than a kilowatt to
commercial sized systems that produce tens or
hundreds of kilowatts.
Part of their success is due to advances in
electronics, which allows unattended operation and
interfacing with the commercial power grid.
Electronic power switching technology eliminates the
need for the generator to be synchronized with the
power grid. This allows the generator to be
integrated with the turbine shaft, and to double as
the starter motor.
Microturbine systems have many advantages over
reciprocating engine generators, such as higher
power density (with respect to footprint and
weight), extremely low emissions and few, or just
one, moving part. Those designed with foil bearings
and air-cooling operate without oil, coolants or
other hazardous materials. Microturbines also have
the advantage of having the majority of their waste
heat contained in their relatively high temperature
exhaust, whereas the waste heat of recriprocating
engines is split between its exhaust and cooling
system.[3] However, reciprocating engine generators
are quicker to respond to changes in output power
requirement and are usually slightly more efficient,
although the efficiency of microturbines is
increasing. Microturbines also lose more efficiency
at low power levels than reciprocating engines.
They accept most commercial fuels, such as gasoline,
natural gas, propane, diesel, and kerosene as well
as renewable fuels such as E85, biodiesel and
biogas.
Microturbine designs usually consist of a single
stage radial compressor, a single stage radial
turbine and a recuperator. Recuperators are
difficult to design and manufacture because they
operate under high pressure and temperature
differentials. Exhaust heat can be used for water
heating, space heating, drying processes or
absorption chillers, which create cold for air
conditioning from heat energy instead of electric
energy.
Typical microturbine efficiencies are 25 to 35%.
When in a combined heat and power cogeneration
system, efficiencies of greater than 80% are
commonly achieved.
MIT started its millimeter size turbine engine
project in the middle of the 1990s when Professor of
Aeronautics and Astronautics Alan H. Epstein
considered the possibility of creating a personal
turbine which will be able to meet all the demands
of a modern person's electrical needs, just like a
large turbine can meet the electricity demands of a
small city. According to Professor Epstein current
commercial Li-ion rechargeable batteries deliver
about 120-150 Wh/kg. MIT's millimeter size turbine
will deliver 500-700 Wh/kg in the near term, rising
to 1200-1500 Wh/kg in the longer term.
Australian inventors are working on
micro-electromechanical systems technology that
could provide a miniature power source to replace
batteries in portable electronic devices. These
micro-electromechanical systems (MEMS) use fuels
such as hydrogen or butane to spin a tiny turbine at
very high speeds of up to 2 million RPM. The turbine
is made using techniques from the microchip industry
and is usually constructed of Silicon. The rotation
of the turbine is then used to power a generator
that supplies electricity.
One advantage of micro-electromechanical systems
technology is that it can also be powered by
hydrogen, just like fuel cells, meaning that the
exhaust would be primarily water. The drawback is
that the fuel source for the microturbine is
flammable, meaning that such portable power devices
may not be allowed on airplanes or other places
where explosives might pose a safety risk. |
