Honed in WWII, gas-to-liquids technology has excelled
Web posted Sunday, July 6, 2008
alaskajournal.com
Gas-to-liquids projects being discussed usually involve the Fischer-Tropsch process that was developed by two German scientists in the 1920s.
Germany fuelled its war machine in World War II with Fischer Tropsch plants making fuel from coal, and after the war the U.S. government built a gas-to-liquids plant in Texas based on the German designs.
When large discoveries of conventional oil were made and crude oil prices dropped the process did not appear to be economic, so efforts in the U.S. dropped off.
South Africa, meanwhile, continued work. With ample coal resources that nation commissioned its government-owned company, Sasol, to develop a domestic fuels industry that would make the nation self-sufficient.
Sasol, now a private company, accomplished that with a large coal and gas-based alternative fuels industry that is now thriving on a commercial basis in South Africa.
Shell became interested in Fischer Tropsch in the 1970s and built a gas-to-liquids plant in Malaysia that is profitable from sales of ultra-clean diesel to the U.S. West Coast market and sales of feedstocks to petrochemical plants in Asia.
Most recently Shell and Sasol have built large GTL plants in Qatar and have projects planned in Nigeria and China.
Chevron is a partner with Sasol in the worldwide marketing of its GTL technology. Other companies, including ExxonMobil, BP and ConocoPhillips have done extensive work on Fischer Tropsch plants. Sasol is interested in developing a coal-to-liquids plant in the U.S. and is considering a location in Alaska as well as in the Lower 48.
The fundamental chemistry involved in Fischer Tropsch is not new. The process involves three stages: the breakdown of a carbon-based material - natural gas, coal or biomass - through a reformer (in the case of gas) or a gasifier (in the case of coal or biomass) into a synthesis gas of hydrogen and carbon monoxide.
The synthesis gas goes to the second stage, a Fischer Tropsch reactor, where the gas is fed through a series of catalysts. These rearrange the hydrocarbon molecules in a way that the gas becomes a solid paraffin wax. The wax is then fed to a third stage, a refinery unit, which manufactures products like diesel or jet fuel from the wax.
The products are clean from an environmental viewpoint, with virtually no sulphur or aromatics. Emissions from burning clean F-T fuels contain low levels of nitrogen oxides. The U.S. Environmental Protection Agency has actually classified drilling fluids made with F-T diesel as non-toxic and biodegradable and cleared it for over-the-side disposal from drilling platforms.
Many companies have been working on their own variations and patented processes for some of these steps, particularly the catalysts that are used. BP is testing a compact small reformer in a test GTL plant in Nikiski, although the process is not expected to be used on the North Slope.
ExxonMobil has done work on its GTL process, which it calls AGC-21.
Despite its promise, industry has been cautious about gas-to-liquids and coal-to-liquids for several reasons. One of the large capital cost in building Fischer-Tropsch plants, which are really large, complex refineries. Sasol and Shell, the industry leaders, have made big advances in bringing costs down, which a Sasol GTL project in Qatar has benefited from, but the recent runup in costs for all energy projects has hit another Qatar GTL project, Pearl, being developed by Shell. Because of high product prices Shell's project will still pencil out, but it has given industry pause when considering new large Fischer-Tropsch plants.
Costs for a North Slope GTL plant will be similarly large, but Richard Peterson, of Alaska Natural Resources-to-Liquids, believe that hefty prices for diesel would make the plant economically viable and more profitable than for a gas pipeline. “These projects aren't for the faint of heart,” Peterson says.
Another problem cited is the low energy efficiency of GTL plants, which can consume a third of the energy value of the feedstock in making the product. In contrast, natural gas pipelines use much less energy to get the gas to market. However, the “energy balance” ratio improves dramatically when waste heat is captured and used for power generation, for example. On the North Slope a GTL plant could generate power for the field, reducing natural gas now burned to make electricity.
A third difficulty is the large amount of carbon dioxide emitted by a GTL plant. In an age of increasing sensitivity to greenhouse gas emissions this has become a matter of concern. However, Fischer-Tropsch plants do have an advantage over other industrial facilities that release emissions in that much of the carbon dioxide is concentrated into a single stream of gas, which means it can be captured and used, or stored. On the North Slope, carbon dioxide captured from a GTL plant could be used in enhanced oil recovery to help produce more oil. Carbon dioxide from a coal-to-liquids plant at Beluga could perform a similar function, making the gas available for enhanced recovery from aging Cook Inlet oil fields. |
