Jul-2000

An advanced asphaltene pelletisation process

A description of a new process for pelletising asphaltene from solvent deasphalters to produce solid asphaltene pellets with a higher heating value, and which are claimed to have improved fuel properties over petroleum coke

Murugesan Subramanian and Jon Moretta
Kellogg Brown & Root (Now KBR Technology)
Rick Bloom and Michael Martin, The Devco Companies

Article Summary

Produced crude oil is becoming heavier and heavier over time. Alternative hydrocarbon sources such as oil sand bitumen and shale oil are gaining prominence in Canada and other parts of the world due to government concessions, abundance of reserves and high crude oil prices. Often, valuable products are recovered using bottom of the barrel technologies like solvent deasphalting, delayed coking, residue hydrocracking, visbreaking, and others.

In certain cases, heavy residue is directly blended with high value cutter-stocks to produce specification grade fuel oil. In general, however, refiners are faced with a challenge to utilise the bottom of the barrel from an increasingly heavy feedstock.

Historically, thermal conversion has been widely used to upgrade heavy residues. Visbreaking and coking account for nearly 60 per cent of the existing worldwide upgrading capacity. Increasing environmental pressures and growing market imbalance are making the production of high-sulphur, heavy fuel oil less and less attractive. For this reason, the addition of significant new visbreaking capacity is not expected in the future.

While coking can be used to completely eliminate heavy fuel oil production, there are several inherent drawbacks to this process. The capital and operating costs of a coker are significantly higher than for a visbreaker or solvent deasphalter. In addition, the semi-batch nature of a delayed coker requires a complicated solids management system and is very manpower intensive.

This semi-batch operation also raises concerns of reliability, operability, safety and coke handling. Lastly, the liquid products from a coker are unstable and require substantial hydroprocessing, while the solid coke product is of low value and is difficult to market.

Solvent deasphalting is an attractive alternative to thermal conversion for bottom of the barrel upgrading. The applications and merits of the proprietary ROSE supercritical solvent deasphalting process are discussed later in this article.

Despite the many benefits of solvent deasphalting, the challenge of handling and transporting the asphaltene bottoms product has limited the application of the process. The product is produced as a high viscosity liquid, which solidifies at ambient temperature. In many cases the asphaltene is blended with light cutter-stock for transportation purposes.

Now, a new technology, Aquaform, has been developed by The Devco Companies and Kellogg Brown & Root for pelletising asphaltene from solvent deasphalters. It is a low-cost, high-capacity, continuous process for producing uniform, solid asphaltene pellets. The pellets produced are resistant to dusting and can be easily handled, stored, and transported. The asphaltene pellets have a higher heating value and improved fuel properties versus petroleum coke and thus represent improved fuel value.

By producing asphaltene pellets and freeing higher-value blending cutterstocks, the value of ROSE solvent deasphalting is significantly enhanced.

Solvent deasphalting
The ROSE process is an energy efficient and cost-effective solvent deasphalting technology for the refiner. In total, 31  units have been licensed with an aggregate capacity of over 500000bpd. The process extracts high quality deasphalted oil (DAO) from atmospheric or vacuum residue feedstock.

Depending on the solvent selection, the DAO can be an excellent gasoil feedstock for catalytic cracking, hydrocracking, thermal cracking, or lube oil blending.

The bottom product is low value asphaltene. The asphaltenes are often blended to fuel oil, but can also be used in the production of asphalt blending components, solid fuels, or fuel emulsions. The asphaltene product can also be used as feedstock to conversion processes such as partial oxidation, coking, or visbreaking.

Process description
Figure 1 (on previous page) is a simplified process flow diagram of the ROSE process.The feedstock is mixed with a portion of the solvent and charged to an asphaltene separator where additional solvent is contacted with feed in a countercurrent mode at elevated temperature and pressure.

The heavy asphaltene fraction drops out of the solution and is withdrawn from the bottom. Solvent dissolved in the asphaltenes is separated, recovered, and recycled.

The DAO leaves the top of the asphaltene separator along with most of the solvent. After heat exchange with recovered solvent, this phase is introduced into the ROSE separator where the solvent and oil separate at supercritical conditions. The supercritical separation is very energy efficient as the solvent phase is separated without adding the full energy required for its evaporation.

The solvent, after heat recovery, is circulated back to the asphaltene separator. The DAO leaves from the bottom of the ROSE separator and is recovered by stripping the contained solvent. The DAO yield and quality are determined by the selection of solvent, solvent to oil ratio, and operating conditions in the asphaltene separator.

Advantages
A processing scheme utilising the ROSE solvent deasphalting process offers many advantages to the refiner, such as:
Low cost residue upgrading route (two to four times lower investment than coking).

Maximised recovery of high-quality feed to conversion units, resulting in increased transportation fuel production – recovered DAO has not been thermally cracked.