ENERGIES RENOUVELABLES
sol(ID)aires
Coproduction de chaleur et d'électricité
Big Step Forward in Use of 'Wasted' Heat
ENERGIES RENOUVELABLES
SALT LAKE CITY, Nov 27, 2001 (United Press International via COMTEX)
-- Technology that could greatly increase the efficiency of engines and
power plants while at the same time cutting polluting emissions has taken
a significant step forward, according to scientists at MIT and a small
Utah research company.
Researchers announced Tuesday at a scientific meeting
in Boston that they had developed a semiconductor that will capture heat
from machinery that is normally vented into the air and "recycle" it into
electricity.
"Our approach is the first to yield high efficiency
heat energy conversion," said Lew Brown, president of Eneco, Inc., a Salt
Lake City company that specializes in such energy conversion technology.
Tests on early prototypes resulted in the capture
of about 17 percent of the lost heat compared to 10 percent in most current
models, and Eneco told the New York Times it was confident it could improve
that level to near the 50-percent barrier that the laws of physics set
as the maximum amount of heat that can be recovered by a thermoelectric
device.
While still in a primitive state, the so-called
solid-state thermionics technology has the capacity to capture and reuse
larger amounts of heat and also use heat at a lower temperature than currently
possible.
Working in reverse, the technology also could improve
the efficiency of refrigerators, air conditioners and other cooling equipment.
"Potentially, it's an enormous deal," MIT professor
Peter L. Hagelstein told the Times. "This opens a door."
The use of thermionic devices is limited to heat
sources of around 2,000 degrees Fahrenheit, which Eneco said in a release
limits their use to nuclear-powered converters in space probes and a few
specialty military and satellite systems. By bringing the usable heat threshold
down to around 400-800 degrees, a wide range of more earthbound uses opens
up.
Eneco said that the technology is well suited for
use in power plants where significant amounts of heat are lost in the process
of generating electricity. Capturing the heat before it is expelled into
the atmosphere would allow it to be used to augment the coal, gas or other
primary fuel being burned.
"The heat of external combustion of these primary
fuels, when channeled through Eneco devices, can not only produce electricity
but also can simultaneously co-generate useful heat and reduce pollution,"
the company said.
Taking the idea further, Eneco engineers believe
that the size of their devices can be reduced enough to make them fit in
small-scale equipment, including appliances, small-scale power plants and
even planes, ships and automobiles.
"Vehicles of all sizes strive for efficient use
of fuel energy, yet often do little to recover waste exhaust heat," the
company touted. "The heat lost through engine exhausts may be captured
... and converted into electricity to augment or replace a vehicle's electrical
and air conditioning systems."
The idea of compact, efficient power source with
virtually no working parts has attracted the interest of Pentagon officials
who see thermionics as a key to developing silent engines.
Hagelstein called the technology relatively simple;
using three layers of semiconductors, the devices capture radiating heat
on one outside layer and transfer to the other side. Heat gives off large
numbers of electrons that take the form of an electrical current.
Eneco added a number of impurities to the heated
layers in a process called doping that is aimed at increasing the flow
of electrons.
"The region near the hot part is heavily doped,
so it boils off electrons," Hagelstein told the Times. "We get more voltage
and more current."
