Some lucky refiners can rededicate 'monster' units for ultra-low-sulfur fuels

Diesel Fuel News, May 27, 2002 by Jack Peckham

Rather than building grass-roots hydrotreaters or hydrocrackers, some refiners are cleverly recycling existing equipment for new uses - in order to cut costs of meeting upcoming U.S. EPA ultra-low sulfur limits on gasoline and diesel fuel.

A prime example is the $150-million ChevronTexaco clean-fuels project at its 295,000-barrels/day Pascagoula, Miss., refinery (see Diesel Fuel News 5/13/02, p5; 1/7/02, p17).

This project not only will boost throughput capacity by about 10%, it also will allow the early production of at least 25,000 b/d of ultra-low sulfur diesel (ULSD) - three years in advance of EPA ULSD deadlines.

Actual sale of such product assumes that Chevron finds sufficient customers to justify segregated ULSD shipments next year. The project also will allow the production of lower-sulfur (500-ppm) non-road diesel fuel, at least in a current configuration plan.

The project, scheduled to be complete by the second quarter of 2003, will convert a massive, 2,600-psig resid hydrotreater to pretreatment of feeds going to fluid catalytic cracking (FCC) unit.

Refiners normally consider FCC feed pre-treat as the most capital-intensive of all possible options for desulfurizing gasoline (and some diesel streams) to upcoming EPA limits. While such a scheme can boost quality and maximize product yields (unlike typical post-treating schemes), FCC pre-treat capex usually scares most away.

But at Pascagoula, this "monster" resid hydrotreater had already paid for itself, as it's a carryover from the early 1980s. That's because Chevron originally used the unit in order to enable the sale of low-sulfur coke. This was the result of a coker expansion project and a hydrogen plant project in 1983. (The "monster" also treats some vacuum gasoil in addition to resid.)

How times have changed: U.S. fuel-oil and pet-coke markets and margins continue to head south, while the regulatory and market demands for near-zero-sulfur fuels are skyrocketing.

"If we didn't already have that [resid hydrotreater] investment in place, we wouldn't consider FCC feed treating today," as Chevron's Bill DeBruin, clean-fuels project manager, explained to us in an interview.

But why combine the gasoline and ULSD projects together now, when ULSD compliance deadline isn't until 2006?

Reason: By rededicating the resid hydrotreater to FCC feed service for EPA 2004 low-sulfur gasoline compliance, Chevron could then rededicate the existing FCC feed treater to hydrotreat diesel, DeBruin explains. This diesel unit also can treat certain coker naphtha streams as well. It's also a higher-pressure unit than typical diesel hydrotreaters, thus aiding desulfurization capability.

Result: The newly-rededicated diesel hydrotreater will handle about 30,000 b/d of diesel and about 10,000 b/d of naphtha.

This rededication will require some alterations to reactor internals and the fractionator. But it's still a lot cheaper than building a whole new second-stage reactor for ULSD, as some refiners might be forced to do for 2006 compliance. It's also vastly cheaper than attempting grass-roots construction of an FCC feed treatment unit.

It's expected that this new hydrotreating scheme not only will reduce sulfur but also result in other quality improvements (possibly including lower aromatics and higher cetane), one Chevron official told us. Future catalyst selection "will be based on performance characteristics and price," this official added.

As one technology vendor described Pascagoula to us, "it's this synergistic cascading of 'heavier' units into processing 'lighter' feeds that puts Pascagoula in a decent position for clean fuels -- but note that it didn't come cheaply," as $150 million is still a hefty sum, although cheaper than a grass-roots project of equal scale.

Meantime, about 40 resid hydrotreaters are in service at refineries around the world (mostly in Asia), as Criterion Catalyst tech specialist Kevin Carlson showed at the Hart Energy Group clean-fuels refining seminar in Houston earlier this month.

"Conversion of resid hydrotreaters is a unique way to achieve high-quality products with investment being minimized," as Hart Downstrem Energy Services consultant Art Suchanek says. Still, "refinery bottoms have to go somewhere, and that's usually a coker, which is also costly because of environmental considerations in the unit design," he adds.

Several other U.S. refiners are similarly rededicating their own "monsters" for ultra-low sulfur fuels service, as another hydrotreating specialist (who asked not to be quoted by name) at a major refining company's technology division told us at the Hart conference:

"These 'monster' units are resid hydrotreaters whose pressures are more like 2,400 psi or even 1,500 psi in one case, not 2,600 psi.

"For example: Many years ago, Chevron built a resid hydrotreater (called VRDS) at its E1 Segundo, Calif. refinery, that was supposed to make low-sulfur fuel oil for electric power generation. That unit became an FCC pretreater when that fuel-oil deal fell through, and this helped E1 Segundo address the needs for CARP low-sulfur gasoline by doing a great job of getting FCC feed sulfur down.