Refining Report Dutch refinery nears completion of major renovation

This rear view of the 11,000 b/sd gasifier being built by Shell Nederland Raffinaderij B.V. conveys the magnitude of the upgrade project nearing start-up at the company's refinery in Pernis, The Netherlands. Also added was a 56,000 b/sd hydrocracker.

The project, called PER+, centers around the addition of Shell Gasification Hydrogen Process (SGHP) and hydrocracking units.

The expansion will increase the complexity of Shell's Dutch refinery and enable it to convert low-value streams to useful products such as cleaner-burning transportation fuels, hydrogen, and electricity.

PER+ is a prime example of the kind of innovative planning necessary for European refineries to stay competitive in a tough market. The project reached mechanical completion early this year, and is scheduled to start up in May.

The refinery

The Pernis refinery has been operating since 1936. Most of the refinery had to be rebuilt after World War II. Its current capacity is 374,000 b/d.

The refinery processes about 50 different crude oils in a given year, some imported specifically for lube oil manufacturing, says Herman van Wechem, head of refinery technology.

"We are extremely flexible," said van Wechem. "We do not have a fixed crude diet; it varies frequently."

This flexibility enables the refinery to take advantage of the availability of opportunity crudes.

A flow diagram of the Pernis refinery is shown in Fig. 1 [62121 bytes]. The diagram shows the units that will be retired, as well as the ones being added.

The refinery's major units include:

• Two crude distillation towers

• Four high-vacuum towers (one for lubes production)

• Two fluid catalytic cracking (FCC) units

• Two thermal crackers

• A UOP Platformer

• An HF alkylation unit

• Five hydrodesulfurization (HDS) units

• Three hydrotreaters

• A Hycon unit (Hycon is a Shell process that converts heavy resid to products while removing metals.)

• A base oil and wax complex.

Besides the fuels produced by the refinery, Shell Nederland Chemie B.V. produces 3 million mt/y of chemicals in Pernis. These products include solvents and high-melting-point waxes. Shell began producing chemicals in Pernis in 1949.

The complex employs 3,600 Shell staff and 1,500 contract staff, excluding construction personnel. Two thirds of the refinery's products are exported, including fuel oil bunkered in the Rotterdam area for ocean-going vessels.

Project objectives

Shell designed PER+ to meet several objectives-some externally driven, some internally driven.

External forces affecting Shell's decision include:

• Tightening environmental regulations governing SO₂, NOx, catalyst fines, and oil-in-water (Fig. 2 [72991 bytes])

• Stricter product quality requirements (Tables 1 [37439 bytes] and 2 [31011 bytes])

• Shifting product yield patterns away from motor gasoline, cycle oils, and fuel oil, and toward naphtha and middle distillates (Fig. 3 [88236 bytes])

• Changing crude supply patterns (crudes are becoming heavier and higher in sulfur.)

While these forces were instrumental in the decision to upgrade the Pernis refinery, it should be noted that they affect all refiners operating in Europe.

Driving forces unique to the Pernis refinery include aging units and a maturing infrastructure (Table 3 [16002 bytes]).

In addition to these factors, Shell saw potential to improve profits by:

• Increasing manpower efficiency (for example, the refinery will shut down three control rooms when PER+ starts up)

• Modernizing operations by installing state-of-the-art advanced process control strategies

• Increasing conversion from a cheaper crude package by adding hydrocracking and gasification units.

Process options

To achieve its objectives, Shell had to make two main decisions. It had to choose a cracking process and a hydrogen production process.

For cracking, the choice was between FCC and hydrocracking. For hydrogen production, the options were steam methane reforming (SMR) and gasification.

Dr. van Wechem summarized the characteristics of refineries employing each of the two cracking options.

An FCC refinery:

• Produces olefinic gasoline

• Has the potential for gasoline sulfur problems

• Has the potential for alkylate and oxygenate production

• Produces poor-quality diesel.

A hydrocracking refinery, on the other hand:

• Produces gasoline low in olefins and sulfur

• Has no potential for alkylate and oxygenate production

• Produces high-quality diesel.

Some typical qualities of hydro cracker products are shown in Table 4 [12153 bytes]. Such a unit will produce excellent blending streams to meet the European Union (EU) fuel specifications proposed under the European Auto/Oil Development Programme. Tables 1 and 2 summarize the Auto/Oil Programme's proposed year-2000 specifications for, respectively, gasoline and diesel fuel.

Fig. 4 [85484 bytes] shows typical yield flexibilities for FCC and hydrocracking. Clearly, a hydrocracker will enable the Pernis refinery to maximize production of either gasoline or diesel fuel, depending on market conditions.

For the hydrogen-production options, Shell chose gasification over steam methane reforming for several reasons. SMR does not reduce fuel oil production, as gasification does. SMR does, however, diminish crude flexibility, in terms of both sulfur and gravity, says van Wechem. For this reason, a more expensive crude diet is required with SMR, as is costly natural gas feed.

Careful analysis of these factors led Shell to install a hydrocracker and an SGHP unit.

The 8,000 mt/sd (56,000 b/sd) hydrocracker was designed by Shell and will use Shell catalyst. It is a once-through, single-reactor design that will achieve high conversion rates, says van Wechem.

Shell will incorporate two catalysts in the single hydrocracking reactor. Denitrogenation catalyst is used in the top portion of the reactor, while the bottom beds contain a proprietary cracking catalyst.

The SGHP unit will convert 1,650 mt/sd (11,000 b/sd) of visbreaker bottoms to hydrogen. The three-train gasifier will incorporate: two-stage CO shift; methanation; and Lurgi A.G.'s Rectisol process for H₂S and CO₂ removal.

Under normal operating conditions, two trains will produce adequate hydrogen to feed the new hydrocracker. The third SGHP train is a spare and will supply feedstock to generate electricity.

To feed the gasifier, Air Products B.V. has built a dedicated air-separation plant 8 km west of the refinery. About 1,600 tons/day oxygen will be piped from the unit to Pernis.

The SGHP process

A flow diagram of the Shell Gasification Hydrogen Process is shown in Fig. 5 [62121 bytes].

Visbreaker residue, oxygen, and steam are fed to gasification reactors equipped with specially designed burners. Here, noncatalytic partial oxidation of the hydrocarbons takes place via an endothermic reaction at 1,500° C. (2,732° F.):

C_xH_y + x/2 O₂ ' xCO + y/2 H₂

The CO and H₂ products contain contaminants such as H₂S, COS, HCN, nickel, iron, carbonyls, ash, and soot. The syngas flows from the reactor into a waste-heat exchanger, where primary heat recovery takes place.

The stream is cooled to about 340° C. (644° F.) by exchange with boiler feedwater. High-pressure (100 bar), saturated steam is produced. Part of the steam generated in the waste-heat exchanger is used to preheat the gasifier feeds.

Saturated steam from the waste-heat exchanger is superheated in the fired waste-heat exchanger of the gas turbines, says Piet Zuideveld, department manager of gasification and hydrogen manufacturing for Shell International Oil Products B.V., Amsterdam.

"Part of the HP steam will be used as moderator in the gasifiers; the remainder will be sent to steam turbines for generation of electricity and LP steam," said Zuideveld.1

Soot ash removal

The cooled syngas stream enters one of three soot ash removal sections, which use a two-stage water wash to remove soot (free carbon) and ash. The water wash comprises a quench pipe, a soot separator, and a packed tower, or soot scrubber.

"In the quench pipe, about 95% of the soot is removed by a direct water spray," says Zuideveld. "In the scrubber, the gas is washed in counter-current flow in two packed beds," he added.

"After leaving the scrubber at a temperature of about 40° C., the gas has a residual soot content of less than 1 mg/cu m, and is suitable for feeding to the desulfurization unit," said Zuideveld.

The soot slurry is flashed to atmospheric pressure in a slurry tank. The slurry flows to the Soot Ash Removal Unit (SARU), where it is filtered, leaving a filter cake that consists of about 80 wt % water, and a clear water filtrate. The water is reused in the SGHP scrubbing section.

The filter cake from the SARU contains carbon, nickel, and vanadium. The carbon is burned from the cake, and the remaining ash is sold as vanadium and nickel oxide ore.

A flow diagram of the SARU process is shown in Fig. 6 [65952 bytes].

Syngas treatment

After leaving the SGHP scrubbers, H₂S is removed from the raw syngas in a Rectisol unit. Acid gas from the Rectisol unit is sent to the refinery's Claus unit.

The treated syngas is then reacted with steam in a CO shift unit, where the following exothermic reaction takes place:

H₂ + CO + H₂O <--> 2H₂ + CO₂

The CO₂ in the syngas is removed in another Rectisol unit, and the remaining hydrogen stream is sent to the methanation unit, which converts the last traces of carbon monoxide to methane by the following exothermic reaction:

CO + 3H₂ ' CH4 + H₂O

Power, hydrogen production

Two thirds of the syngas product will be converted to hydrogen. The gasifier will produce 255 tons/day hydrogen to be used in the new hydro cracker.

The remaining third of the syngas production will be converted to 115 mw of electricity in a combined cycle plant comprising two gas turbines.

"A large share of the electricity generated will be exported to the public grid," said Zuideveld.

Fig. 7 [73225 bytes] shows the integration of utilities with hydrogen manufacture via gasification.

Environmental issues

PER+ is part of a refinery environmental plan that has been agreed upon by Shell, the Dutch government, and environmental groups. This "Plan van Aanpak," or environmental master plan, covers refinery activities through 2010.

Table 5 [63286 bytes] summarizes the projected environmental impacts of the PER+ project, in terms of both transportation fuel properties and refinery emissions. The table shows an interesting aspect of the PER+ project, and one that is likely to make it successful: While refinery throughput will remain the same after project start-up, crude and product yield patterns will change dramatically, as will refinery emissions.

According to Zuideveld, "The refinery mass balance shows that, despite a 30% increase in the high-sulfur crude intake of the refinery, SO₂ emissions will be reduced by 30%, and NOx emissions will decline by 40%."

Fig. 8 [36895 bytes] shows changes in the Pernis refinery's sulfur distribution from 1980 to 2000. The figure includes sulfur in products leaving the refinery, sulfur emissions in flue gas, and elemental sulfur production.

In 1980, only 17% of the refinery's sulfur output took the form of elemental sulfur. In 2000, partially as a result of PER+, elemental sulfur will account for 74% of sulfur output.

Shell also has tracked total SO₂ emissions from Pernis. The refinery has reduced SO₂ output from 120,000 mt/y in 1970 to 32,500 mt/y in 1995. PER+ should reduce SO₂ emissions further, to about 24,000 mt/y.

Clearly, Shell's progress in reducing sulfur emissions is impressive.

After start-up of PER+, the Plan van Aanpak calls for Shell to revamp its No. 2 FCC unit. This upgrade will entail installing catalytic de-NOx capabilities and adding more air cooling to replace water cooling. In addition, once the new hydrocracker is operating smoothly, Shell will demolish its No. 1 FCC unit.

Neighbors

The Pernis refinery is surrounded by an urban area with a population of about 400,000. Keeping these people informed of the refinery's activities is an important factor when operating in such a heavily populated area, says van Wechem.

The Pernis refinery has instituted an outreach program for this purpose. In September 1996, Shell gave its first presentation to the neighborhood communities. During this meeting, Shell explained the environmental benefits of the project.

In addition, the company notifies the citizens in advance when activities that may cause a nuisance are executed. Shell, however, makes all efforts to minimize such nuisances by applying silencers during steam-blowing of piping.

"If they are informed about all activities and effects, they are less frightened," said van Wechem.

Construction

Fig. 9 [102070 bytes] shows the PER+ construction schedule. The project reached mechanical completion early this year. Start-up is scheduled for May.

To convey an idea of the scope of the project, van Wechem says it entailed:

• A 3 billion NLG ($2+ billion) budget

• About 10 million man-hours

• 1,000 pieces of equipment

• 700 km of pipe

• 11,300 piles

• 8,500 tie-ins.

The combination of constant distillation capacity, improved environmental performance, and innovative gasification technology makes PER+ uniquely suited to Europe's challenging operating environment. Because of these factors, Shell can consider its upgrade a model for refiners around the world.

References

1. Koenders, L.O.M., Posthuma, S.A., and Zuideveld, P.L., "The Shell Gasification Process for Conversion of Heavy Residues to Hydrogen and Power," Gasification Technologies Conference, Oct. 2-4, 1996, San Francisco.

2. Foster Wheeler Hydrogen-The Refinery Green Light, Institute of Petroleum, Apr. 25, 1996, London.

Copyright 1997 Oil & Gas Journal. All Rights Reserved.