Coal to Liquids - An Explanation
Could the future of fuel production lie in the technology of the past? Coal-to-liquid researchers think so, and are making great strides toward bringing this technology to the mainstream. Coal-to-Liquid technology (also known as "Fischer-Tropsch" technology) offers a range of important products that are produced by liquefying coal. These methods and technologies produce synthetic fuels and waxes that are environmentally friendly and extremely useful to various industries.
During the 1920's, German scientists working at the Kaiser Wilhelm Institute discovered a way to liquefy coal for the production of synthetic fuels. The process became known as "Fischer-Tropsch Synthesis" after its creators, chemists Franz Fischer and Hans Tropsch. During World War II, Fischer-Tropsch fuels were used to power planes and tanks for the German army.
In recent decades, Fischer-Tropsch technology has reemerged with a new found fervor. With heavy foreign oil dependence proving costly and dangerous for many countries, governments and private industries are looking for alternatives to petroleum based fuels. Scientists, researchers and lawmakers are working together to bring Coal-to-Liquid programs into the mainstream economy.
The first step in converting coal to liquid fuels is gasification. Gasification is a process that converts carbon materials into carbon monoxide and hydrogen. Many materials are gasified for this purpose, including petroleum, petroleum coke, biomass and of course, coal.
Coal is fed into a vessel called a gasifier. Within the gasifier, controlled amounts of heat, pressure and oxygen are added to break up the molecular structure of the coal. The gasifier only allows a portion of the coal to burn, resulting in the partial oxidation of the coal. This reaction produces carbon monoxide and hydrogen rich synthesis gas.
Synthesis gas, or syngas, is then fed into an F-T reactor where it is condensed over a catalyst. A "catalyst" is a substance that accelerates a chemical reaction without being consumed. Catalysts used in the F-T process are typically iron or cobalt, but vary based on the desired product. The exposure to the catalyst converts the syngas into liquid and wax products that can be refined into synthetic fuels. The conversion of the syngas is known as "Fischer-Tropsch Synthesis." The term "Coal-to-Liquids" has become synonymous with Fischer-Tropsch products and technologies.
Coal-to-liquid products are versatile. CTL fuels can be used to run a variety of vehicles including cars, trucks, tanks and jets. In addition, F-T waxes may be stored indefinitely. Depending on the catalyst and conditions in the F-T reactor, coal-to-liquid products vary in density, composition and prospective use. Excess steam from the gasification process can be used to produce electricity.
The environmental challenges of Coal-to-Liquid fuel production and use are currently being examined by scientists and researchers. Carbon dioxide, a leading cause of global warming, is released when coal is liquefied and again when the CTL fuel is burned. In order for CTL products to enter the mainstream as a viable source of transportation fuel, scientists and researchers must find a way to limit carbon dioxide emissions. There are several methods of carbon dioxide capture and sequestration that are under development. These processes and technologies would capture and condense carbon dioxide during coal gasification. The carbon dioxide could then be stored safely and permanently in underground structures such as saline aquifers. Saline aquifers are large, geological structures that occur naturally and have high pressures suitable for CO2 storage. Also, captured carbon can be sold commercially to oil companies and other fuel producing industries. Enhanced Oil Recovery, for example, is a technique that uses captured carbon dioxide to increase oil field yield by injecting it into depleted oil wells.
With coal-to-liquids technology, emissions are removed before the fuel is burned. Because coal gasification uses oxygen rather than air to produce syngas, the resulting gas stream is smaller and more condensed. The small gas stream can be stripped of emissions easily and efficiently. By removing these emissions during the gasification process, the resulting fuel products are considered "clean-burning." CTL diesel, for example, is sulfur free.
Building a coal-to-liquids plant can cost billions of dollars, and many lawmakers and industry officials find the financial risk too great for a relatively "unproven" technology. However, many researchers and industry analysts argue that the benefits of producing fuel from America's natural resources outweigh the costs. America's coal reserves may offer a solution to the country's dependence on foreign oil. In using American coal to produce synthetic fuels, the country is no longer dependent on unstable regimes and is also protected from devastating supply chain collapses caused by global natural disasters.
At the University of Kentucky's Center for Applied Energy Research, scientists research and test CTL methods in state-of-the art laboratories. Thanks to the efforts of CAER scientists, the world of CTL research has been enriched in many ways. The lab focuses on testing as a means to gather data, and serve several industries and agencies in their scientific pursuits.
Coal-to-Liquids technology represents a family of innovations that are changing the world of fuel production. With increased investment in these technologies, further research and development can be done in order to widen the scope of applications for CTL fuels and products. With its roots in the early part of the 20th century, CTL technology continues to reach into the future.
Article written by Brittany Bailey, CAER Publications
Questions? Contact Dr. Burt Davis, CAER Associate Director and Clean Fuels Scientist - Email