Processing of Primary Fischer-Tropsch Products - University of Alberta

! Oxy on I
Air r" I separation ~ Hydrocol gas
.JNatural Gasoline~_] Hydrocarbon ]
Natural Gas "[ separation [ synthesis ]
Natural Synthetic
gasoline gasoline
Water I
separation ] ~ Water
Treating
Product [ .~ Crude alcohol
separation J ~- Diesel oil
Olef'm ]
polymerisation
Figure 4. Integration of natural gas with the Hydrocol HTFT refinery.
~ Gasoline
4.1 Tar integration
The configuration of a tar refinery is dictated by the nature of the coal
pyrolysis products. In general the coal pyrolysis products are aromatic and
contain sulphur, nitrogen and oxygen as hetero-atoms [54]. Since it is especially
rich in phenolic material, phenol, cresols and xylenols (also collectively known
as tar acids) can be extracted economically. In a fuel refining context
hydroprocessing of the tar must be done in such a way that the hetero-atoms are
effectively removed, but that the aromaticity is retained. In the petrol boiling
range aromatics are required for octane and in the diesel boiling range aromatics
are required for density. The products from a tar refinery therefore compliment
that from a FT refinery nicely in terms of redressing octane and density
shortcomings. Integration can take place downstream during fuel blending [9],
but also at refinery level. Hydroprocessing of the more refractory hetero-atom-
rich tar fractions may result in aromatics saturation. This destroys much of the
benefit, but since the naphthenes can improve reforming performance, such
streams can be combined with the FT feed to a reformer.
4.2 Natural gas integration
The condensate from natural gas can be seen as a paraffinic feedstock to
the refinery. When the Hydrocol process was developed, all the condensable
natural gas was used as direct blending stock with the FT derived material (Fig.
4) [6]. Current fuel specifications would make such integration less likely. The
condensate in the diesel boiling range can still be blended directly, but the
condensate in the petrol boiling range requires refining.
The processing scheme used for natural gas integration at the Mossel Bay
refinery was developed with significant influence from the Sasol plants in
Secunda. It targets the production of motor gasoline (Fig. 3) [15]. Therefore, it
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