Researchers at Penn State University are investigating several coal-to-liquid processes that differ from traditional direct (Bergius) and indirect (Fischer-Tropsch) liquefaction. The new pathways could introduce coal-derived chemicals or coal into existing oil refinery operations for the production of end products including jet fuel, gasoline, diesel, heating oil and carbon anodes.
The primary focus of the work, which is funded by the Department of Energy, is the development of a coal-based replacement for conventional jet fuel. The coal-to-jet fuel work is in the pilot-plant stage, but along with the jet fuel, the processes produce other hydrocarbon products. For every eight barrels of a Jet A equivalent, the process produces a half barrel of fuel oil, one barrel of diesel and a half barrel of gasoline.
Pilot-scale testing indicates that a prototype fuel meets most of the current specifications for JP-8. Combustion tests in a turboshaft engine show emissions to be generally comparable to those from control experiments with JP-8.
The work focuses on three processes:
Coal tar/refinery solvent blending and hydrotreatment to produce the various product fractions. This is the process demonstrated in the pilot plant.
Co-coking of coal/refinery solvents. This process to produce jet fuel mixes raw, clean coal with decant oil—the liquid found at the bottom after catalytic cracking—and then co-cokes. The liquid from the coker is hydrotreated and fractionated to provide the desired products. This co-coking process aims to produce coke or carbon of much higher quality usable in manufacturing carbon anodes for a variety of uses. Fuel-grade coke, which is a standard fuel in the steel industry, sells for about $20 a ton. The coke used in these anodes is a much higher value than fuel coke.
Coal extraction using refinery solvents. This method uses light cycle oil to extract the liquid components of coal and then the liquid portion, without separation, travels on through the refinery hydrotreater. In initial bench testing, this method produced a 50% yield of liquids. When processed in a multistage reactor, 70% extraction took place. The researchers are continuing this work to reduce the amount of light cycle oil necessary, develop a method to separate liquids and solids, and scale up the process.
Our aim is to integrate the processes and products into existing refinery structures and streams. We need to be sure that these components fit into the refinery stream that they are close enough in composition to be mixed with the components coming from crude oil.—Caroline E. Burgess-Clifford, Penn State Energy Institute
So far, the researchers, including Harold Schobert, professor of fuel sciences; Maria M. Escallon and Utaiporn Suryapraphadilok, graduate students; Gareth D. Mitchell, Omer Gul, Josefa M. Griffith and Parvana Gafarova, research associates, Energy Institute, characterize the gasoline and fuel oil as fitting within the standard crude oil refinery stream. The diesel fuel is different from standard diesel fuel.
Other participants in this project tested the products in real units, including Andre Boehman, professor of fuel science and his group who tested the gasoline and diesel in engines; Bruce Miller, senior research associate and his group who tested the fuel oil in a pilot scale boiler; and Chunshan Song, director of the Energy Institute and professor of fuel science and his group who did related catalyst research.
The produced diesel can be blended with the petroleum diesel without changing the fuel properties significantly. It has not been shown to be bad or have bad effects, it is just different. We are also examining the produced jet fuel to see if it could be used as a diesel fuel, as the jet fuel has undergone extensively more processing than the other products. So far the process has produced really good carbon, but it contains too many residual minerals for anode use. The liquid component does include jet fuel, but the liquid products are very heavy in fuel oil.
The researchers presented their work in a series of papers at the American Chemical Society meeting in Boston. Future work will strive to reduce impurities in the solid carbon product. Researchers will also investigate either fractionating the fuel oil component or improving the liquid yield.
Caroline Burgess-Clifford and Harold H. Schobert, “Development of coal-based jet fuel” (ACS 234, FUEL 84)
Caroline E. Burgess, Omer Gul, Josefa M. Griffith, Parvana Gafarova, Gareth D. Mitchell, Maria M Escallon, Utaiporn Suriapraphadilok, and Harold Schobert, “Integrating coal-to-liquid processes into refinery processes” (ACS 234, FUEL 86)
Maria M Escallon, Benjamin Carlsen, Caroline Burgess-Clifford, and Harold H. Schobert, “Assessment of oils derived from the co-coking: Best conditions toward the improvement of the jet fuel thermal stability” (ACS 234, GEOC 54)