Leo R. Aalund
Managing Editor-Technology
Lost in the controversy over project cost overruns during the late 1980's was the fact that Statoil, Norway's state-owned oil company, was turning its rather ordinary Mongstad plant into one of Europe's most modern refineries.
The expansion and revamp project was completed and put on stream during the last half of 1989. The modernized refinery's output of top quality products has implications for markets not only throughout Scandinavia but also in northwestern Europe and the United States.
Fuel oil made in Norway appeared on the U.S. East Coast during last December's deep freeze. Mongstad gasoline has been imported on the U.S. East Coast and no doubt will play a role in the northeastern states as volatility specifications tighten there this summer.
The refinery, with a capacity now of 6.5 millon tons/year, or 145,000 b/d, (see Table 1 and Fig. 1), owes its strategic importance not only to its new processing configuration but also to its location. It is in a magnificent setting some 25 miles by road and ferry north of Bergen alongside the Fensfjord, one of the many deep fjords slicing into the West Coast of Norway (see cover and Fig. 2). Tankers dock literally on the refinery's doorstep, bringing in crude oil from flush, relatively nearby fields in the North Sea and taking out product. The region has major oil terminals. Not too far from Mongstad is the Sture terminal, the terminus for the first crude oil pipeline to cross the Norwegian trench. It carries crude oil from the Oseberg field. A pipeline link from Sture to Mongstad is, however, not considered feasible.
Underneath the Mongstad site are caverns blasted out of the bedrock. They can hold 8.2 million bbl of crude oil. This is the storage for the Mongstad terminal, which went into operation in March 1988. Crude from the Gullfaks and Statfjord fields in the North Sea, about an 8-hr tanker run away, are brought here and then shipped to Statoil customers around the world in some of the largest tankers afloat. Refiner assays for these two crudes are shown in the accompanying article (p. 37).
Statfjord is the primary crude processed at the Mongstad refinery, which has its own more modest aboveground storage, that can tap the caverns or receive shipments by sea. Gullfaks crude is also processed there in lesser amounts. It is the heaviest and highest sulfur crude produced in the North Sea. Even higher-sulfur crudes, such as Arab Light and Soviet Export Blend, are imported in lesser amounts and processed without exceeding the specifications for the premium coke made there. Up to 10% higher-sulfur crudes can be processed as part of the normal operating slate.
Norway, with its large aluminum industry powered by hydroelectricity, uses anodes made from the Mongstad coke, which the refinery calcines itself. The calcined coke has a typical density of 2.06 kg/cu decimeter, and total sulfur of 1.2 wt %.
The key unit from the expansion is a fluid catalytic cracker, a UOP RCC (Reduced Crude Conversion) unit. It cracks long residue (with a buffer cut from the preflash unit). The coker also cokes long residue. This is only the second such cracker now on stream. The design is a result of the high interest in "resid cracking" which started in the early 1980's in the U.S. and a combined development program by UOP and Ashland Oil. The first unit is at Ashland's Catlettsburg, Ky., refinery.
Except for minor amounts of product transported in tank trucks, practically all the refinery output is shipped by sea. The U.S. is 10 tanker-transit days from Mongstad, northwestern Europe only 3. According to Statoil's refining management, gasoline transportation costs to northwest Germany are $7.00/ton, and $11.00/ton to the U.S. East Coast, or some 3/gal. Partially as a result of the expansion, some 2,000 crude and product ships are expected to call at Mongstad during 1990.
Statoil also owns a 65,000-b/d refinery at Kalundborg, Denmark. It is essentially dedicated to Danish needs, but may eventually be integrated with Mongstad. The largest refinery in Scandinavia is Finland's Neste Oy refinery at Porvoo with a capacity of 197,000 b/cd and access to Russian crude. With combined catalytic cracking and hydrocracking capacity of nearly 43,000 b/cd, it is also a major export refinery.
RATIONALE
There has been a refinery at Mongstad since 1975. In the early 1980's, Statoil planners could see Statoil's crude oil availability growing from less than 20 million tons/year (410,000 b/d) to over 40 million tons/year (820,000 b/d by 1991) and hanging in that region for several years.
The company wanted the capability to obtain higher value for its crude if necessary by upgrading. Recent history in the U.S., where integrated companies with refining and petrochemical operations had healthy earnings even though the price of crude was down, illustrates the soundness of having such capability, the Statoil managers say.
The planners also recognized the trend in the European countries (already well-established in the U.S.) towards the use of high octane, unleaded gasoline, and away from heavy fuel oil.
The revamped operation produces no heavy fuel oil and increases gasoline production fivefold with only a 60% increase in crude charging capacity.
THE PROJECT
The expansion and revamp could be viewed as a threepart project:
- The expansion of the crude capacity with a preflash unit
- Installation of a distributed control system and computer control of the crude tower
- Erection of the new processing units.
The RCC fluid catalytic cracker added during the project is the first FCC at Mongstad. Rated at 41,000 b/d, it is probably the most important unit in the scheme and will be discussed in more detail later.
Crude distillation capacity was raised from 89,400 b/cd to 145,000 b/cd with the preflash unit.
Other increases were catalytic reforming capacity from 10,100 to 26,600 b/cd; reformer feed hyrotreating from 10,100 to 26,000 b/cd; and hydrotreating of other streams, including light cycle oil from the new catalytic cracker, from 15,600 b/cd to 24,700 b/cd. All this capacity, except for that from the crude unit, came from new units (including a 11,800 b/cd polymerization unit), rather than the expansion or debottlenecking of existing plants. Fig. 3 shows all of the major new units, which were built on a new site separate but contiguous to the existing refinery. The refinery site is on top of a mostly submerged rock mountain. This rock made the huge storage caverns under the site feasible but also made explosives an essential element in the construction of the Mongstad project. Some 300,000 cu m of rock had to be blasted out aboveground to permit foundation work and to create a cooling water pit and trenches for water supply, drains, and electrical and instrument cables.
The terminal storage caverns, which are beneath the site and whose bottoms are 67 m below sea level, required that 2.6 million cu m of rock be blasted out and deposited. This required 1,500 metric tons of explosives.
Twenty two new tanks were added to the refinery during the expansion. They have a total volume of 226,000 cu m or 1.4 million bbl. Products, such as gasoline, are blended in-line between the component tanks and the waiting ships.
The new process area covers 81,000 sq m or 20 acres. For comparison, some 7 million sq m are available with 2.5 million sq m or 617 acres now occupied by the refinery and terminal.
Twenty new buildings were constructed, including a new control building of 4,400 sq m (47,000 sq ft). All the processes and off site operations are controlled from this control building with a distributed control system. Each process has an inside and outside operator. All the processes are linked to an IBM business computer, which continuously monitors the economics of the operation.
In all, 650 persons are involved in running and maintaining the refinery.
FUELS/OCTANE
The 41,000 b/cd RCC fluid catalytic cracker represents a major change in the processing scheme at Mongstad. The unit, according to the process manager, can get over 76 vol % conversion when cracking Statfjord bottoms and yields 56% FCC gasoline, 26 wt % clarified oil, 8 wt % coke.
The design charge is 375 C. + (about 705+ F.) with API gravity of 17-21, UOP K-factor of 11.69-11.85, Concarbon of 4.3-5.0 wt %, and metals of 7-18 ppm.
The decant oil is sent to the coker while the light cycle oil and heavy coker gas oil are hydrotreated to premium diesel. The two-reactor, light cycle oil hydrotreater with quench is rated at 7,800 b/cd. According to the refinery's manager of process and development, the unit, which operates at 80 bar or 1,160 psi pressure and is licensed from Unocal, can with the proper catalyst operate as a mild hydrocracker.
The cracker also produces some 30,000 ton/year of ethylene, which is now going into fuel gas but could eventually be recovered for upgrading. The propylene, butylene output is, however, recovered and charged to an 11,800 b/cd phosphoric acid catalytic polymerization (or condensation) unit. The product has a blending octane of 95.5 RON and 82 MON. Another source of high octane material is an older 3,600 b/cd pentane/hexane isomerization (TIP) unit.
The cracker also produces steam from CO fired in two parallel CO boilers.
A UOP continuous catalytic reformer (CCR) accounts for the new reforming capacity and is the major source of the hydrogen used throughout the refinery. The previously existing capacity is in an Engelhard cyclic reformer. Aromatics, however, won't play the leading role in Europe that they did in the U.S. in the 1970's as more and more unleaded gasoline was mandated.
There is a 5% benzene limit in gasoline sold in Scandinavia and there is a trend to this relatively low amount throughout northwestern Europe.
Nevertheless, with the reformers, the cat cracker, and poly and isom units, management says it will make 98 RON unleaded gasoline that is becoming the gasoline of choice for European motorists,
ENVIRONMENT
The revamp and expansion of the refinery also called for additional facilities to meet more stringent air and water pollution control.
An example of this and of how the planners ingeniously took advantage of the refinery's setting on the cold, deep waters of the fjord is its unusual process cooling water system. A 2.3 km (about 1.6 mile) long man-made tunnel with its inlet 70 m below sealevel to reach the coldest water (4C. or 39F.) in the fjord brings the water to a large pit near the processing area. There the water is pumped at the rate of 7 cu m/sec or 110,000 gpm through plate heat exchangers at the bottom of the pit and takes on heat from the process stream. The water from the process heat exchangers is cooled by this system from about 113 F. to 68 F. The seawater exits 30 m below sealevel to avoid thermal pollution through another tunnel of 30 sq m cross section area at 62 F. Fig. 4 shows these exchangers in the pit.
Refinery management says this closed loop fresh water circulation has four primary advantages:
- No environmental disadvantages
- The boiler feedwater quality fresh water has a low fouling factor of 0.00001.
- Leakages go into the process water because cooling water pressure is always higher.
Seawater is also used to scrub the RCC flue gas after it has gone through the electronic precipitator, to remove catalyst fines, and the CO boiler. Seawater is also used to scrub the tail gas from the sulfur recovery unit.
The principle of the once-through Flakt-Hydro process is that sulfur dioxide is absorbed in the seawater and reacts with oxygen to form sulfate, a natural constituent of seawater. Air is supplied to an aeration basin to complete the reaction before discharge. Other reaction products are CO2, partly dissolved in the water, and water.
Elemental sulfur recovery capacity was increased almost five fold during the expansion, raising capacity from 3,000 to 14,000 ton/year or about 40 ton/day.
Given the Mongstad refinery's location near abundant sources of oil, its cracking and octane capability, and the ample space for expansion, this refinery should play an important role in North American and European product supply for years.
Copyright 1990 Oil & Gas Journal. All Rights Reserved.