DOE OUTLINES GTL RESEARCH STRATEGY

At the American Institute of Chemical Engineers’ Spring National Meeting held in Houston, Texas, in April, V. Venkataraman et al. outlined a Natural Gas-to-Liquids Research and Development Program and Commercialization Strategy for the United States Department of Energy (DOE).

Venkataraman et al. note that converting natural gas to liquids, termed Gas-To-Liquids (GTL) technology, offers the potential of cost effectively producing clean, high-quality diesel and gasoline fuels which are free of the sulfur, nitrogen and aromatic pollutants that contribute to environmental air quality problems. When used to develop the domestic natural gas resources in Alaska, GTL technologies will decrease the nation’s dependence on foreign sources of energy.

The United States has about 200 to 300 trillion cubic feet (tcf) of remote gas, inaccessible to the pipeline system, on Alaska’s North Slope, and offshore Gulf of Mexico. This offers a significant incentive for utilizing GTL technology on the North Slope. In addition, the United States has huge volumes of methane hydrates (100,000 to 300,000 tcf) which represent an enormous natural gas resource. Developments in the last 5 years have both broadened and deepened interest in exploiting methane hydrates as a source of natural gas, but further work is needed to develop production techniques that are safe and economically viable.

DOE recently issued a 5-year Ultra-Clean Fuels Technology Initiative that features a government/industry research and development partnership, aimed at making ultra-clean transportation fuels more widely available. This Initiative will promote the development of technologies to produce ultra-clean transportation fuels for the 21st century.

Due to increased emphasis on the environment and energy security issues, DOE’s research program in the GTL area focuses on processes for making clean fuels from natural gas, the most prominent process being advanced Fischer-Tropsch (F-T) conversion technology. In F-T processing, the majority of the capital investment is for the generation of syngas, with syngas manufacture accounting for about 60 percent of the total cost of making F-T liquids. One focus is on the development of ceramic membrane reactors to replace the conventional synthesis gas generation loop that will result in significant cost savings (25 to 35 percent) by eliminating the cryogenic air separation plant.

As a result of recent breakthroughs in developing ceramic membrane technology, an 8-year program using Ionic Transport Membranes (ITM) was initiated with Air Products and Chemicals. A smaller effort was initiated with the University of Alaska to look at alternative materials and techniques to produce ceramic membrane reactors. The current DOE effort focuses on moving aggressively with Air Products and Chemicals into their Phase II endeavors. The primary focus of Phase II is to demonstrate ITM syngas production technology at a larger scale, appropriate for demonstration size plants. In addition, work will continue with the University of Alaska on oxygen transport ceramic membranes, as well as a study of the use of the Trans Alaska Pipeline System (TAPS) for transporting F-T products.

Another company working on ITMs is Praxair. Praxair has begun development of an advanced technology for producing synthesis gas from natural gas. This process combines the use of a short-reaction time catalyst with Praxair’s gas mixing technology to provide a novel reactor system. This system requires significantly less energy than conventional syngas plants, does not need steam, and has a substantially lower capital requirement. This new technology could be a key contributor to making GTL an economic reality for the exploitation of stranded natural gas reserves. Compactness, elimination of steam, and reduced oxygen requirements make this technology particularly attractive for deployment in remote locations where capital costs are inherently high due to lack of infrastructure and for locations where water quality or availability is a problem.

Continued process and economic analysis of existing and promising new natural gas conversion technologies is a necessary and integral part of the GTL program. Recent studies include the technical and economic potential for offshore GTLs conversion and an economic assessment of Alaska North Slope gas utilization options. Of particular importance in the latter work was the identification of a window of opportunity to extend the life of TAPS. Identification and implementation in the 2009-2016 timeframe of a viable technology to convert natural gas to pipeline quality liquids could extend the life of TAPS by 20 years or more.

Although research and development on GTL technology is continuing, the effort has been sufficiently successful that an initial demonstration-scale plant could be built with only a reasonable technical risk. The main deterrent to implementation of GTL technology is economic; capital costs are high, in the neighborhood of $30,000 per daily barrel of liquid products. Also, economics are highly dependent on the cost of the natural gas feedstock. This means that in the near term, GTL use is likely to be limited to locations where stranded gas is available at a low price. In the United States, the only location with substantial reserves of stranded gas is the North Slope of Alaska. Based on a recent study, there is potential for production of 400,000 barrels per day of liquids.

Methane hydrates represent an enormous natural gas resource. They are solid, ice-like materials containing molecules of methane bound in a lattice of water molecules. These hydrates are stable under conditions of low-temperature and high-pressure and, thus, are found on ocean slopes. Domestically, major deposits are located off the Carolina coast, in the deep-water portions of the Gulf of Mexico slope, and beneath the permafrost in Alaska. The utilization of the methane contained in natural gas hydrates would eliminate concerns regarding the adequacy of energy resources and mitigate global climate change effects by displacing fuels with a higher carbon content.

DOE is developing an Initiative for Methane Hydrate Research and Development Program. While the goals of this program are the determination of the extent of the methane hydrate resource and the commercial production of natural gas from this resource, the basis for achieving these goals is dependent upon the scientific understanding of the nature of methane hydrates, including their formation, dissociation, structure and properties. Through these studies, this program expects to develop technology to the point of providing options for the production of natural gas from methane hydrates in a safe and environmentally acceptable manner.