Apr-2004

Fluidised catalytic cracker hydrotreater revamp

Primary revamp of reactors, exchangers and other FCC pretreater components provided return on investment for a complex refining facility

Raj Patel, Haldor Topsoe
Howard Moore, Harrell Duff and Brian Hamari, Marathon Ashland Petroleum

Article Summary

As part of  the Marathon Ashland Petroleum LLC (MAP) clean fuels programme at the Catlettsburg, Kentucky, refinery, the existing fluid catalytic cracker (FCC) feed hydrotreating unit was revamped to allow increased capacity, processing of tougher feeds, and production of lower sulphur product.  The design rate increased from 40000 to 60000bpsd and the blended feed to the unit will contain 15% deasphalted oil (DAO).  The hydrotreated product sulphur specification is set at 750ppm to produce FCC gasoline that can be blended directly into the gasoline pool and still meet the future low sulphur gasoline specifications. 

The primary revamp included addition of four new reactors, additional exchangers, a new membrane unit for purifying hydrogen, and upgrading of the wash water system.  The unit modifications described here are part of an overall restructuring of the Catlettsburg refinery and will not only enable MAP to meets the requirements of the clean fuels project, but also provide a return on the investment (ROI) with improved FCC operation. 

Gasoline sulphur specifications are tightening throughout the world. In the USA, a company pool average gasoline sulphur specification of 120ppm was begun in January this year.  In January 2005, this is to be reduced to 90ppm and an additional refinery specification of 30ppm will also begin.  In January 2006, a per-gallon limit of 80ppm will be required in the USA generally, with an even more stringent standard in California.

In 2005, the European Union will cut gasoline sulphur to less than 50ppm sulphur and in some locations in the EU will actually start to require zero sulphur gasoline with less than 10ppm sulphur.  By 2009, zero sulphur gasoline will be required throughout the EU.  Gasoline sulphur specifications are also being reduced in the Far East. 

To meet these specifications, refiners with an FCC will have two choices. One option is the post-treat option that requires treating the FCC gasoline.  The second option is the pretreat option, which requires reducing the sulphur in the feed to the FCC.  One problem with post-treatment is the potential loss of octane.  This can be addressed through advanced technology.  The more fundamental problem of post-treatment is that there is little chance for ROI.  The post-treat processes will meet the product sulphur spec but will produce a product that is at best equal to the feed value while incurring capital and operating costs.

The fundamental problem with pretreatment is the high capital cost.  However, due to the improvements in the feed, the yield structure will be more favourable from the FCC and an ROI is possible.  This is especially true if costs can be minimised in a revamp of an existing unit. In general, enhancing FCC feed hydrotreating is economical when the combination of improved FCC yields, heavier feedstocks, and environmental credits are available.

MAP faced the challenges of meeting future gasoline sulphur specifications and turned this adversity to an advantage. MAP chose to revamp their FCC feed pretreater as well as to restructure the refinery operations.

Objectives
The Catlettsburg refinery has operated since 1917, and was the origination of Ashland Oil and Refining Company.  Two additional refineries have been integrated into the facility since that time and petrochemical facilities were added that make it a very complex refinery. This FCC project originally began to increase the severity of an existing catalytic feed hydrotreater and was combined with other projects for refinery streamlining and simplification, as well as gasoline desulphurisation.

The overall refinery objectives were to meet existing and future gasoline sulphur requirements while improving refinery economics.  Specifically, the objectives were:

Improve FCC economics by hydrotreating all of the FCC feed, including all DAO production.

Avoid post-treating cost/investment by reducing FCC gasoline sulphur to a level allowing direct blending to the gasoline pool while meeting 2006 requirements.

Reduce fixed and operating costs, and improve overall refinery reliability, by reducing refinery complexity and multiplicity of equipment.

Avoid major turnaround (TAR)/ revamp costs on existing FCC unit.

Expand distillate hydrotreater, and reduce 2006 ultra low sulphur diesel (ULSD) revamp costs by reducing the quantity and sulphur content of light cycle oil (LCO).

An FCC gasoline sulphur content of 45ppm, when blended with the existing gasoline components, was determined to produce the targeted gasoline pool sulphur. Discussions with technology vendors, internal pilot plant evaluations, and available literature information were used to provide a cat feed (FCC feed) sulphur target of 660ppm.  This level of sulphur would be provided by two units producing 60000bpd of heavy feed at 750ppm sulphur and 35000bpd of lighter feed at 500ppm sulphur, as shown in Figure 1 on previous page. The revamp of the existing cat feed hydrotreater to a high severity heavy cat feed hydrotreater, dubbed high-pressure virgin gasoil (HPVGO) hydrotreating unit, is described in further detail. 

Pre-revamp
Based on an alliance between MAP and Haldor Topsoe, the technology requirements for all of the FCC feed pretreaters in the MAP refining system are provided by Haldor Topsoe.  To date, designs have been completed for four units, in addition to three revamps and one grassroots unit.  Two of the four units have successfully started up, including the Catlettsburg refinery HPVGO hydro-treater. In addition, reactor internals have been provided for other hydrotreating units.