The principal product being examined for the Coal to Liquids plant under development by Monash Energy, using the Fischer Tropsch process, is an ultra clean, high quality synthetic diesel commonly known as Fischer Tropch FT diesel or GTL fuel (for Gas to Liquids fuel)
This product can be used as a blending component to assist in the preparation of conventional diesel which meets the most stringent global emissions standards. Alternatively it can be used as a direct diesel in niche locations (eg. within cities) to maximise the environmental benefits of such a superior fuel.
The exceptional quality of the GTL product occurs because of the processing steps used in its manufacturing. The coal is processed to produce a sulphur and contaminant-free stream of pure hydrogen and carbon monoxide, knows as synthetic gas or “syngas”. The syngas is then reacted over a catalyst to form long chain paraffinic hydrocarbons, which are then processed in the presence of more hydrogen to produce the required products. This process avoids the production of the undesirable polycyclic aromatic compounds found in diesel made from naturally occurring crude oil.
Advantages of GTL Fuel
These include:
| • | GTL contains virtually no sulphur or aromatics. In a properly tuned engine this leads to lower particle exhaust emissions |
| • | The absence of sulphur means that oxidation catalysts and particulate traps will operate at maximum efficiency |
| • | The existing diesel infrastructure can be used, unchanged, for GTL |
| • | GTL can be used in existing diesel engines |
| • | Diesel is one of the safest of the automotive fuels |
| • | A GTL plant does not produce any of the less desirable co-products from a refinery, such as heavy fuel oil or coke |
| • | Provided a GTL plant uses an oxygen feed, it produces a pure CO2 stream that provides an option for the capture and storage of CO2 |
While diesel is the principal product being examined, a wide range of products can be produced from syngase, as discussed further in the section on “Future plants”.
Of particular interest is that over three quarters of the process used to produce FT liquids is identical to that used to produce hydrogen. Thus the plant can be readily modified to produce large amounts of hydrogen to help make the bridge to the hydrogen economy. The technological constraints on using hydrogen as an energy carrier lie with the distribution system and the end-use aspects, not the capacity to produce it from coal.
The diagram below shows the closeness of the syngas and hydrogen options, in both cases co-producing electricity with the fuel.
