468016 Use of Unconventional Resources in State of the Art Oil Refining Processes
In this study, thermal upgrading of oil sand and heavy bitumen derived from domestic reserves is studied to reveal the processibility of these feedstocks in delayed coker units. In addition to that, these feedstocks are blended with highly aromatic refinery by-products to evaluate the effect of aromaticity on coke and liquid yield as well as coke morphology. Feedstock of the delayed coker unit from a refinery is used as a reference for both upgrading and characterization parts.
Oil sands are subjected to solvent extraction method with toluene to separate sand and hydrocarbon samples. After that, these unconventional feedstocks are evaluated for their elemental composition, SARA content, number and weight average molecular weight, specific gravity, dynamic viscosity and S-value (an indicator for stability of asphaltene molecules and coke morphology). Thermal upgrading reactions are conducted at 500 °C for 90 minutes in a tubing bomb reactor having a 10 mL internal volume. Both neat feedstocks and the ones blended with refinery by-products are used in reactions. Coke and liquid products are characterized by means of scanning electron microscopy (SEM) and gas chromatography (GC-SIMDIS), respectively. Moreover, liquid products are further analyzed for their elemental composition, SARA content, molecular weight, specific gravity and dynamic viscosity.
The characterization results indicated that oil sands and heavy bitumen can be used in delayed coker reactor systems but they should be blended with conventional oils to meet design requirements of the units in terms of sulfur and asphaltene content or specific gravity. Furthermore, thermal upgrading reactions demonstrated that unconventional and reference feedstock give nearly same coke yield (~20% wt.) but their liquid product distributions are quite different from each other. Addition of refinery by-products provides around 10% decrease in coke yield which can be attributed to the prevention of phase separation during thermal upgrading reaction by aromatic compounds which can dissolve maltene fractions and asphaltene precursors. Thereby, polycondensation reactions are retarded and coke yield is decreased. Moreover, the S-value results and microstructures from SEM analysis indicated that addition of highly aromatic refinery by-products affects the coke morphology, which specifies the value of coke and occurrence of hot-spot problems in delayed coker units.
Knowing the fact that liquid products are more valuable as compared to solid coke samples whose annual production capacities may reach up to million tons/year for a single refinery, decreasing coke yield and changing coke morphology with easy-to-implement solutions is a powerful tool to increase the profit of oil refineries in a competitive global market.
See more of this Group/Topical: Fuels and Petrochemicals Division