Fuels & Chemicals

Development of Upgrading Technology for the Residual Oil

Residual oil

Residual oil is the heaviest fraction that remains after crude oil, for example from the Middle East, is distilled to separate out lighter fractions such as naphtha, gasoline, kerosene, and diesel. Typically, the residual oil is diluted and used as a fuel for power generators or ships and is used to make paving asphalt. But it often contains large amounts of impurities such as metals and sulfur, so it is necessary to remove the impurities into environmentally friendly products.

Removing impurities from residual oil

There are two types of residual oil: atmospheric residue (AR), which is obtained from an atmospheric distillation unit; and vacuum residue (VR), which comes from a vacuum distillation unit. To get the very most out of the limited resource that is petroleum, and to ensure a stable supply of inexpensive fuels, it is critical that both types of residual oil should be used smartly. Because VR contains larger amounts of metals and sulfur, it must be pretreated to remove these impurities. ENEOS is the only firm in Japan to have a solvent deasphalting (SDA) unit (Fig. 1) for this purpose. After pretreatment, the deasphalted oil (DAO) is mixed with atmospheric residue and run through a residue desulfurization (RDS) unit to remove the impurities (Fig. 2).

Fig.1 Solvent deasphalting unit.
Fig.2 Bottom flow in petroleum refining process.

Simulation technology for stable operation of the RDS unit

Fig.3 Prediction example of differential pressure in a reactor column.

Treating AR and DAO, with their very different characteristics, in an RDS unit requires not only high performance desulfurization catalysts but also high precision prediction techniques. We leveraged our years of experience operating an RDS to develop new predictive simulators.
One such example is a simulator for predicting catalyst life. The reactions for residual oil are highly complex due to the huge numbers of molecules involved, and reaction prediction requires a high performance simulator. An RDS unit is filled with layers of different catalysts that remove sulfur, metals, and other impurities. The catalyst life simulator factors in the reactions for each catalyst and predicts catalyst reactions and deactivation. We even built a new function into the simulator that can predict catalyst activity and life when AR and DAO (which differ in reactivity) are both processed at the same time.
Another example is a differential pressure prediction simulator, which is used to predict pressure differentials inside a reactor column. Typically, if the differential pressure between at the inlet and at the outlet becomes too large, the unit must be shut down to prevent damage to the equipment. When oils quite different in nature (e.g. AR and DAO) are mixed, the difference in solubility between the two can lead to large amounts of precipitation, which tends to push up the differential pressure within the reactor column. Using our differential pressure prediction simulator has given us a much better understanding of these phenomena (Fig. 3).

Japan imports nearly all of its crude oil. Moving forward, we'll need ways to make fuller use of low quality crudes that are currently untreatable. This will mean a growing role for RDS units, which are able to remove the large amounts of impurities found in heavier fractions. Simulation technology will help us keep our daily stable operation and contribute to energy security in Japan.

Esso and Mobil are trademarks of Exxon Mobil Corporation, used under license.