January 2021

Special Focus: Sustainability

Ras Tanura: The creation of a clean-fuels complex

The primary objective of the Ras Tanura Refinery Clean Fuels Project is to enable the Ras Tanura refinery—the largest refinery in Saudi Arabia—to produce transportation fuels that will be compliant with future specifications.

The primary objective of the Ras Tanura Refinery Clean Fuels Project is to enable the Ras Tanura refinery—the largest refinery in Saudi Arabia—to produce transportation fuels that will be compliant with future specifications. The project targets the ability to produce gasoline and diesel products to Euro 5 specifications, as well as to maximize refinery gasoline production, especially through the utilization of Khuff gas condensate naphtha. The scope of the project is to install new process units that provide flexibility for maximizing fuels production in the near term, while being able to transition to petrochemical production in the future.

The Ras Tanura refinery is a major gasoline producer in the Middle East. It can produce up to 170,000 bpd of gasoline, primarily using reformate from its three reforming units. It operates one continuous catalyst regeneration (CCR) reforming unit and two fixed-bed semi-regenerative reformers. Due to the use of the fixed-bed reformers, the reformate pool tends to have high levels of benzene. Mitigation measures to reduce these levels (e.g., cut point adjustments) are insufficient to adhere to upcoming clean fuels specifications. This is especially problematic when trying to maximize gasoline production.

The refinery’s naphtha supply also exceeds the current reformer capacity. Under the previous specifications, the relatively low sulfur content of the Khuff naphtha allowed for direct inclusion into the gasoline pool. This naphtha inclusion provided for a means to dilute the benzene and aromatics of the reformate pool. The lower sulfur levels mandated by the new specifications no longer allow this practice to continue. In the future, even these lower sulfur naphtha streams must also be desulfurized to be included in the gasoline pool.

At the early stages of project development, it was decided to replace the two fixed-bed reforming units with a new, larger CCR reforming unit. The new CCR reformer was to be designed primarily to process Khuff condensate naphtha. Additionally, the project was to maximize the octane (through isomerization) of the large, light-naphtha stream that was also available.

The selected approach was to install a world-scale naphtha reforming complex consisting of a naphtha hydrotreating unit, a CCR reforming unit and an isomerization plant. The near-term objective was for the reformer to produce a low-benzene reformate stream. With the availability of other relatively high-octane streams, including the new isomerate, it would be possible to operate the reformer at a relatively low severity for total aromatics control in the gasoline pool. The reforming unit was to also have the ability to maximize aromatics—particularly mixed xylenes—in the future.

Clean fuels complex

Saudi Aramco is building a world-scale clean fuels complex at the Ras Tanura refinery. The process units’ capacities are to be some of the largest in the world. For example, the complex will include a 140,000-bpd naphtha hydrotreating unit, a 90,000-bpd CCR reforming unit^a (FIG. 1) and a 65,000-bpd C₅–C₆ isomerization unit. The CCR reforming unit will initially be configured for refinery gasoline production but could also be reconfigured for aromatics production for use in petrochemical production. A simplified blockflow diagram of the CCR reforming unit is shown in FIG. 2.

FIG. 1. View of the CCR reforming unit under construction at the Ras Tanura refinery.

FIG. 2. A simplified blockflow diagram of the CCR reforming unit.

The Ras Tanura refinery’s CCR reforming unit will be one of the world’s largest reformers that operates at an ultra-low pressure. The installation of such a high-capacity unit was a technical challenge. However, the unit offers the following benefits:

• A side-by-side reactor arrangement for ease of construction and maintenance, a low structure for better access and safety, and flexibility in reactor design to optimize unit performance at a minimum cost
• A continuous catalyst circulation system that exhibits the industry’s lowest catalyst attrition rate for high on-stream performance—and features a non-pulsing lift system for a smooth operation
• The latest regenerator design, featuring two distinct burning zones and a protective “dry-burn loop” for significantly reduced catalyst aging, with minimum loss of chlorides. The optimized oxychlorination section results in a further reduction in chloride consumption.

The C₅–C₆ isomerization process^b employed a chlorinated alumina process, characterized by using active and selective chlorinated-alumina catalyst. It has demonstrated a high activity, which enhances equilibrated reactions involved in the isomerization process.

As depicted in FIG. 3, the reactor system consists of two reactors in a series, with special valve arrangements—allowing each reactor to be operated in the lead or tail position. Hydrogen utilization is optimized in this once-through scheme, requiring neither a recycle compressor nor a separator drum.

FIG. 3. Simplified once-through isomerizationb blockflow diagram.

A robust, reliable and simple-to-operate management system of catalyst contaminants was implemented, as well. This includes the removal of water through specific dryers, along with the purification of hydrogen makeup to remove carbon monoxide (CO) and carbon dioxide (CO₂). This arrangement has proven efficient, with the simple catalyst protection helping to maintain long run performances and achieve extended catalyst life.

Project achievements

The primary goal of the Ras Tanura Clean Fuels project is to make the Ras Tanura refinery a premier producer of Euro 5 gasoline in Saudi Arabia, as well as in the Middle East. With this new complex, the capacity for refinery gasoline production could reach 240,000 bpd—enabling the refinery to maximize the value of its naphtha streams. HP

NOTES

        ^a Axens’ Octanizing™ CCR reforming technology using Axens’ CR 600 catalyst series
           ^b Axens’ C₅–C₆ isomerization technology using Axens’ ATIS-2L catalyst

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