The purpose of this unit is to reduce the sulphur and nitrogen contents of the feed and to improve the combustion characteristics of the transportation fuels which will ultimately be derived from the synthetic crude. In addition to sulphur and nitrogen removal, hydrotreating reduces the amount aromatic hydrocarbons which can give jet kerosene a poor smoke point and diesel fuel a poor cetane number.
The individual naphtha/jet streams are combined, pre-heated and mixed with a hydrogen-rich recycle gas stream under pressure. The combined feed, plus recycle gas, is heated to reaction temperature and injected into a multiple-catalyst bed reactor where, in the presence of the catalyst, the hydrogenation reactions occur.
The hot vapours from the reactor are condensed and separated into gas and liquid phases. Before it is recycled, the hydrogen-rich gas contacts an aqueous amine solution which absorbs the hydrogen sulphide.
The ammonia formed in the hydrogenation reaction is dissolved in the process water which is removed as sour water. Since some chemical conversion of the jet kerosene into lighter components occurs in the reactors, these lighter components, along with dissolved hydrogen sulphide, are removed in a jet fuel stripper.
The stripped jet kerosene product is routed to storage for blending into the synthetic crude.
Diagram used with permission (© SAIT Polytechnic, MacPhail School of Energy, 2009)