No one has yet managed to build a diesel power plant that can make economic use of synthetic fuel. However, researchers at Kansas University believe that they have found a way to eliminate a step in the conversion of natural gas to synthetic diesel fuel, making the fuel cost competitive. Several pilot projects are planned, with one currently under construction.

ARCO and Syntroleum are jointly constructing a pilot scale gas-to-liquid conversion facility at ARCO’s Cherry Point Refinery, near Bellingham, in the state of Washington. The pilot plant will test the production method for these synthetic fuels (synfuels). The synfuels will be blended with refinery streams for final processing. Nominal throughput for the pilot plant will be 70 barrels per day, with start-up due at the end of 1998.

The University of Kansas has carried out an engine test, and found that it could successfully run a diesel engine on the synthetic diesel fuel. Professor Galen Suppes of the University of Kansas said that these preliminary tests indicated that the formulations being used were “probably the best liquid fuel that has ever been recorded for use in a diesel engine”.

John Ford, communications manager of Syntroleum, described synthetic diesel is being a viable niche fuel.

In addition, synthetic diesels are remarkably free of pollutants often found in oil, such as sulphur, nitrogen and heavy metals, which is an increasingly important consideration as environmental concerns increase, and emission levels become tighter.

Conversion of gas to liquid fuel is not exactly new. The Fischer-Tropsch process, on which most current processes are based, dates back to 1923. It was used in Germany during World War II when it was cut off from regular supplies, and more recently, in South Africa during the apartheid era, when an embargo kept it out of world oil markets. The problem with the method was that it was so expensive, it only made economic sense with an oil price greater than $30 per barrel.

This situation is being changed. Syntroleum believes that, in conjunction with Kansas University, it has found a way to modify the conversion process to make it economical with a crude oil price of $15 per barrel.

Most traditional proesses for making synthetic liquid fuel from gas involves three major stages. In the first stage, steam, oxygen and natural gas react to form a mixture of hydrogen and carbon monoxide called ‘syngas’. In the second stage, the syngas is converted to wax. In the final stage, the wax is converted into a liquid fuel.

The Syntroleum process, however, is a two stage process. This uses autothermal reforming with air to produce a nitrogen-diluted syngas, which is then converted to synthetic crude.

This development, if it proves to be viable, will enable natural gas to be transformed into a more easily transportable liquid form. This has major implications, as about half of the world’s natural gas reserves are currently too remote from markets to justify the cost of transport.

Although global stocks of natural gas are enormous, many of the deposits lie far from the sites of demand. Natural gas costs four times as much as oil to transport through pipelines, due to its lower energy density. The so-called stranded gas can be cooled and compressed into a liquid for shipping by tanker. Unfortunately, the conversion facilities required for this are large and complex, and because liquefied natural gas is hard to handle, demand for it is limited.

Currently, the gas released from oil wells in many parts of the world holds so little value that it is either burned on site or reinjected into the ground. The goal of a number of companies, such as Syntroleum, is to try to find ways of economically converting the stranded gas into a usable form. This will tend to make exploration for natural gas in remote areas more attractive, and it will make marginal fields more economically viable. It will also offer the prospect of making landfill gas use more viable.

First use of this synfuel will probably be in the form of a blend.

Testing synthetic diesel fuel


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