Exploitable results
A new route in refinery technology has been investigated. This applies the removal of asphalt from heavy residues by solvent extraction, followed by flash coking of the asphaltenes obtained and hydrotreatment of the products. The project should provide an increased yield of gasoline and fuel oil.
The work programme began with the modification of a bench scale flash coking unit which simulates the LR coking process. Extended flash coking tests were performed with selected solid asphaltenes ranging between 40 and 53 weight in Conradson carbon content. The results revealed a correlation of oil yield with flash coking temperature and heat carrier recycle ratio. The lowest possible coking temperature and recycle ratio were found to be preferable. The LR flash coking obtained was subjected to fractionation into naphtha, gas oil and vacuum gas oil distillate cuts. Inspection of products and subsequent hydrotreatment of coker distillates blended with corresponding SR oil products revealed a great potential for this novel upgrading route for heavy residues.
These results have been confirmed by a conceptual technical and commercial study of this route applied to a million tonnes per year refinery for cold lake bitumen.
Coking (or carbon rejection) and hydrogenation (or addition of hydrogen) are the 2 fundamental principles in converting bitumen, heavy oils and residual oils into valuable products.
The research project pursued a work programme based on laboratory tests to establish a database for the novel combination of processes involving heavy oil deasphalting (SOLVAHL), asphalt flash coking (LR) and hydrotreatment of coker distillates. Research involved:
modification of an existing laboratory scale LR flash coker unit to a continuously operable facility;
selection and extraction of asphalts of different origin to be processed in the modified bench scale LR flash coker;
performance of several LR flash coking tests at different flash coking temperatures and heat carrier ratios;
hydrotreating of the naphtha, gasoil (GO) and vacuum gas oil (VGO) distillate fractions from flash coking which were blended proportionally into the genuine straight run and deasphalted oil (DAO) fractions to evaluate the prospective use of the combined product for catalytic reforming, fuel production, fluid catalytic cracking (FCC) and hydrocracking;
in parallel, direct hydrogenation of the naphtha, GO and VGO distillate fractions from the flash coker was investigated;
analyses of feed and product properties and establishement of a database;
assessment of test results and preparation of a conceptual study for an advanced integrated refinery.
The production of light products from asphalts by flash coking with the LR process is a favourable way to minimize the final residue quantity in a refinery with deep conversion of residues by the ASVAHL indirect way (SOLVAHL deasphalting plus hydrotreating of DAO).
Although a grass route refinery treating only extra heavy crude is technically feasible, the present economic aspects require special consideration.
Instead, extra heavy crudes could be treated in existing refineries, by the stepwise inclusion of the following process route:
addition of a SOLVAHL plant using 4-carbon solvent;
addition of a DAO hydrotreating plant and changing from a 4-carbon to 5-carbon solvent;
addition of a LR coking plant for asphalts.
Thus, maximum conversion would be achieved in the production of normal specification products.
Engineering and construction of a large demonstration unit or small complex is recommended as the next step. Further optimization is feasible with more integration of the process steps.
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