Original process
The original Fischer-Tropsch process is described by the following chemical
equation:
The mixture of carbon
monoxide and hydrogen
is called synthesis
gas or syngas. The resulting hydrocarbon products are refined to
produce the desired synthetic
fuel.
The carbon dioxide and carbon monoxide is generated by partial
oxidation of coal
and wood-based
fuels. The utility of the process is primarily in its role in
producing fluid
hydrocarbons
or hydrogen from a solid feedstock, such as coal
or solid
carbon-containing
wastes of various types. Non-oxidative
pyrolysis
of the solid material produces syngas which can be used directly as a
fuel without being taken through Fischer-Tropsch transformations. If liquid
petroleum-like fuel, lubricant, or wax is required, the
Fischer-Tropsch process can be applied. Finally, if hydrogen
production is to be maximized, the water
gas shift
reaction can be performed, generating only carbon dioxide and
hydrogen and leaving no hydrocarbons in the product stream.
Fortunately shifts from liquid to gaseous fuels are relatively easy to
make.
History
Since the invention of the original process by the German
researchers Franz
Fischer and Hans
Tropsch, working at the Kaiser
Wilhelm Institute in the 1920s,
many refinements and adjustments have been made, and the term
"Fischer-Tropsch" now applies to a wide variety of similar
processes (Fischer-Tropsch synthesis or Fischer-Tropsch
chemistry)
The process was invented in petroleum-poor
but coal-rich
Germany
in the 1920s, to produce liquid
fuels. It was used by Germany
and Japan
during World
War II to produce alternative fuels. Germany's yearly synthetic
oil production reached more than 124,000 barrels per day from 25
plants ~ 6.5 million tons in 1944 (http://www.fe.doe.gov/aboutus/history/syntheticfuels_history.html).
After the war, captured German scientists continued to work on
synthetic fuels in the United
States in Operation
Paperclip.
Utilization
Currently, two companies have commercialised their FT technology. Shell
in Bintulu,
Malaysia,
uses natural
gas as a feedstock,
and produces primarily low-sulfur
diesel
fuels. Sasol
in South
Africa uses coal
as a feedstock, and produces a variety of synthetic petroleum
products. The process is today used in South
Africa to produce most of the country's diesel
fuel from coal by the company Sasol.
The process was used in South Africa to meet its energy needs during
its isolation under Apartheid.
This process has received renewed attention in the quest to produce
low sulfur
diesel
fuel in order to minimize the
environmental impact from the use of diesel engines.
A small US-based company, Rentech, is currently focussing on
converting nitrogen-fertiliser plants from using a natural gas
feedstock to using coal
or coke,
and producing liquid hydrocarbons as a by-product.
Also Choren
in Germany and CWT (Changing
World Technologies) have built FT plants or use similar processes.
The FT process is an established technology and already applied on
a large scale, although its popularity is hampered by high capital
costs, high operation and maintenance costs, and the relatively low
price of crude
oil. In particular, the use of natural gas as a feedstock only
becomes practical when using "stranded
gas", i.e. sources of natural gas far from major cities which
are impractical to exploit with conventional gas pipelines and LNG
technology; otherwise, the direct sale of natural gas to consumers
would become much more profitable. There are several companies
developing the process to enable practical exploitation of so-called stranded
gas reserves. It is expected by geologists that supplies of natural
gas will peak 5-15 years after oil does.
There are large coal reserves which may increasingly be used as a
fuel source during oil depletion. Since there are large coal reserves
in the world, this technology could be used as an interim
transportation fuel if conventional oil were to become more expensive.
Combination of biomass
gasification (BG) and Fischer-Tropsch (FT) synthesis is a very
promising route to produce renewable or ‘green’ transportation
fuels.
In Sept. 2005, Pennsylvania
governor Edward
Rendell announced [1]
a venture with Waste Management and Processors Inc. -- using
technology licensed from Shell and Sasol -- to build an FT plant that
will convert so-called waste coal (leftovers from the mining process)
into low-sulfur diesel fuel at a site outside of Mahanoy
City, northwest of Philadelphia.
[2].
The state of Pennsylvania has committed to buy a significant
percentage of the plant's output and, together with the U.S. Dept. of
Energy, has offered over $140 million in tax incentives. Other
coal-producing states are exploring similar plans. Governor Brian
Schweitzer of Montana
has proposed developing a plant that would use the FT process to turn
his state's coal reserves into fuel in order to help alleviate the
United States' dependence on foreign oil. [3]
One issue that has yet to be addressed in the emerging discussion
about large-scale development of synthetic fuels is the enormous
increase in primary energy use and carbon emissions inherent in
conversion of gaseous and solid carbon sources to a usable liquid
form. Recent work by the National Renewable Energy Laboratory
indicates that full fuel cycle greenhouse gas emissions for coal-based
synfuels are nearly twice as high as their petroleum-based equivalent.
Emissions of other pollutants are vastly increased as well, although
many of these emissions can be captured during production. Carbon
sequestration has been suggested as a mitigation strategy for
greenhouse gas emissions. However, while sequestration is already in
limited use, the science and economics around large-scale
sequestration strategies are, as yet, unconvincing. [4]
See also
