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PORTLAND, Oregon, US, August 16, 2006 (Refocus
Weekly)
A study funded by the U.S. Department of Energy
shows a potential application for using high-temperature solar
process heat in the production of aluminum.
There are three processes which are “particularly suitable for
the use of high-temperature solar energy as process heat,” concludes
J. Murray in the 48-page report, ‘ ’ produced for DOE’s National
Renewable Energy Laboratory (NREL) and researched at Portland State
University. The work is not a feasibility study of a new solar-based
process, but a preliminary technical examination of the “enormous
number of processes” developed over the past 120 years for the
manufacture of aluminum.
The use of solar process heat might solve technical or process
problems previously encountered, and could be a critical component
in the economic or technical success of the process, and Murray
“looked for processes that might adapt easily to the use of
high-temperature solar energy,” with particular emphasis for a
process that did not require tight temperature control for success
and did not require high-temperature heat storage.
The aluminum industry is highly concentrated and vertically
integrated, with six firms in the U.S., Canada, France and
Switzerland controlling most of the world production. The industry
is “one of the most energy-intensive industrial sectors” in the
world, with most energy required for the smelting stage, and used as
electricity for the electrolysis of alumina.
Production of aluminum accounts for 4% of total electricity for OECD
countries, but is 16% in Norway and 44% in Iceland. Smelting
facilities are located near “relatively cheap and abundant sources
of electric power,” the report explains, with 50% of U.S. capacity
located in the Pacific Northwest and Tennessee Valley where it has
access to federal hydroelectric power.
“Hydropower is the most important source of cheap electricity for
the aluminum industry” and, in 1981, half of the power consumed by
the aluminum industry in the western world came from hydro sites,
with coal-generated electricity contributing 28%, nuclear 6% and oil
/ gas generating 14% combined. Non-OECD countries relied more
heavily on hydro.
It is “thermodynamically wasteful to use electrical energy” in the
process, Murray explains, but “several difficulties are encountered
in the attempt to design a single thermal process to make aluminum
along the lines of a thermal blast-furnace process used for other
metals.” Temperatures need to be in the 2,000oC range and “there is
no way to decrease this amount of energy; the only option the
process designer has is to attempt to find a series of steps that
might apportion the energy economically among the available sources:
thermal, chemical or electrical.”
“Metals produced by thermal processes have the lowest market price,”
and the past market for aluminum has expanded by replacing other
metals when the cost of aluminum decreased due to technological
improvements to the process,” the report notes. The international
competitiveness of the aluminum industry is determined by its costs
of production, and “electrolytic processes are inherently more
expensive than thermal,” it continues.
“Solar energy is a unique source of process heat” because
“highly-concentrated sunlight is capable of supplying process heat
for chemical reactions at very high temperatures,” and the use of
high-temperature solar would also “drastically reduce CO2 emissions
from the aluminum industry,” he concludes. Two of the most common
problems in aluminum production “could also be solved through the
use of solar process heat.”
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