LNG technology selectionDr Tariq Shukri, Foster Wheeler, UK, discusses availableLNG technologies and the important criteria for selection.

In this process three mixed refrigerants are used to provide thecooling and liquefaction duty. It has been selected for theSnhvit LNG project (Ekofisk, Norway) which is underdesign/construction. This is a single train 4 million tpy LNGplant. The process is illustrated in Figure 6.

Pre-cooling is carried out in PFHE by the first mixed refrigerant,and the liquefaction and subcooling are carried out in aspiral wound heat exchanger (SWHE) by the other two refrigerants.

The SWHE is a proprietary exchanger made by Linde.It may also be used for the pre-cooling stage. The refrigerantsare made up of components selected from methane, ethane,propane and nitrogen.

The three refrigerant compression systems can have separatedrivers or integrated to have two strings of compression.Frame 6 and Frame 7 gas turbine drivers have been proposedfor large LNG trains (> 4 million tpy). A novel feature of theSnhvit project is that all motor drivers will be used for themain refrigerant compressors, with sizes up to 60 MW.

The SWHE itself is being installed with other liquefactionprocesses, in new and expansion projects or as areplacement for old cryogenic exchangers.

www.lngplants.com/

TPG-4140LNG, fundamentale prinsippBengt Olav Neeraas18/09/2007

Large Capacity LNG Plant Development J.J.B. Pek*, A. van Driel, E.C.J.N. de Jong, R. Klein Nagelvoort

http://www.worldoil.com/Magazine/MAGAZINE_DETAIL.asp?ART_ID=2808&MONTH_YEAR=Feb-2006Global LNG Report Process selection is critical to onshore LNG economics Despite evolving and diversifying, no one liquefaction process is substantially better than others, mandating that project-specific variables and economics be studied. Saeid Mokhatab, University of Wyoming, Laramie, Wyoming, and Michael J. Economides, University of Houston, Houston February 2006

MIXED FLUID CASCADE PROCESS

The Statoil/ Linde LNG Technology Alliance was established to The MFCP is a classic cascade process with one important develop alternative LNG baseload plants for the North Sea. difference - mixed component refrigerant cycles replace single Besides other innovative procedures and concepts, this work resulted component refrigerant cycles, and thereby improve thermodynamic in a new LNG baseload process, the so-called efficiency and operational flexibility. Several characteristics apply Mixed Fluid Cascade Process (MFCP) to the MFC process. 11 First, MFC is new, and, as a whole, without

any industrial references. However, the concept is built up by Within this proprietary process, Fig. 6, purified natural gas is pre-cooled, well-known elements. Additionally, the size and complexity of the liquefied and sub-cooled by three separate mixed refrigerant cycles. separate spiral-wound heat exchangers (SWHE) applied in the MFCP

are considerably less when compared with today's single The pre-cooling cycle's cold is transferred to natural gas via unit used in dual-flow LNG plants. Furthermore, SWHE technology two plate-fin heat exchangers (PFHEs), whereas the cold of the has been tested extensively as an industrial scale prototype, liquefaction and sub-cooling cycle is transferred via two spiral-wound since 1998, for thermal, hydraulic and mechanical duties, in an heat exchangers (SWHEs) by the other two refrigerants. 10 LNG facility in South Africa. Last, but not least, MFC allows larger,

single compressors to handle refrigerant over a larger temperature scale. The SWHE is a proprietary exchanger made by Linde. It may also be used for pre-cooling. Refrigerants are made up 10 Bach, W.A., "Developments in the mixed fluid cascade process of components selected from methane, ethane, propane and nitrogen. (MFCP) for LNG baseload plants," paper presented at the World LNG

Conference, London, England, September 2000.The three refrigerant compression systems can have separate 11 Heiersted, R. S., R. E. Jensen, R. H. Pettersen and S. Lillesund, drivers or be integrated to have two strings of compression. Capacity and Technology for the Snhvit. LNG Plant. Frame 6 and Frame 7 gas turbine drivers have been proposed for LNG 13 Conference, Seoul, 2001large LNG trains (> 4 MTPA).

Hammerfest LNG (Snhvit)TPG 4140 Naturgass Hsten 2007Jostein Pettersen

Mixed Fluid Cascade Process

Fig. 1 shows a sketch of the patented MFCP, consisting of three mixed refrigerant cycles arranged in cascade. The pre-cooling cycle with a mixture of ethane and propane is compressed in compressor C1, liquefied in sea water cooler CW1 and sub-cooled in plate fin heat exchanger E1A. One part is throttled to an intermediate pressure and used as refrigerant in E1A. The other part is further sub-cooled in plate fin heat exchanger E1B, throttled to the suction pressure of C1 and used as refrigerant in E1B.

The liquefaction cycle with a mixture of ethane, propane and methane is compressed in compressor C2, cooled in sea water coolers CW 2A/2B and further cooled in exchangers E1A/1B and E2. It is then throttled and used as refrigerant in spiral wound heat exchanger E2.

The sub-cooling cycle with a mixture of nitrogen, methane and ethane is compressed in compressor C3 and cooled in sea water coolers CW 3A/ 3B as well as exchangers E1A/1B, E2 and E3. It is expanded in liquid expansion turbine X1 and used as refrigerant in sub-cooler E3, which is once again designed as a spiral wound heat exchanger.

The power requirement for the MFCP is provided by three centrifugal refrigerant compressors directly connected to a single Frame 7 gas turbine. The design of the compressor driver string is made by NuovoPignone, having Frame 7 operation experience from baseload LNG plants.

Compared to other LNG baseload processes the MFCP offers as a main advantage that both spiral wound heat exchangers for natural gas liquefaction and sub-cooling are of similar size. This split of the liquefaction and subcooling cycle capacity into two results in smaller suction volumes for the recycle compressors C2 and C3 and also smaller diameters of the heat exchangers E2 and E3. Therefore, these spiral wound heat exchangers are well within the limits of Lindes manufacturing capabilities and are not the limiting factor for the size of the liquefaction train.

Developments in the Mixed Fluid Cascade Process (MFCP)for LNG Baseload Plants*

* Paper given at the World LNG Conference in London in September 2000Wilfried A. Bach, Manchen

*

LNG process selection, no easy taskPierre-Yves Martin, Jrome Pigourier, Axens, franceBatrice Fischer, IFP, FranceHydrocarbon engineering May 2004

For a long time, the LNG industry has demanded innovations The minimized fuel gas consumption consequently No separator is needed. As that is a relativelyto reduce the costs and construction times of liquefaction results in low emissions to the environment. large item of equipment, the cost can be kept low.plants. Because of that, Linde AG and Statoil founded Increased economy of a LNG baseload plant makes it Less circulating hydrocarbon is needed. That hasthe Linde-Statoil LNG Technology Alliance in June, possible to increase the capacity for an individual process good effects with respect to the volume and safety1996. The objectives of the alliance were improvement train up to 8 to 10 MTPA LNG production. Two major of flammable hydrocarbons. It is particularly importantof LNG baseload technology, improvement of project pieces of LNG plant equipment limit capacities to about for compact installations such as that on the Snhvitdevelopment procedures and strategies, cost reduction, 5 MTPA in the single and double mixed fluid processes: LNG process barge or on floating LNG productionand shortening of the construction time, along with The centrifugal cycle compressors, which have plants.development of economical LNG concepts. After several fabrication limits at about 90 MW shaft power The mixed circulation can be adapted directlyyears of comprehensive activities in selection, investigation, requirement, along with the gas intake volumes for the three mixtures, and does not depend onand optimization, the results of the joint technology The main cryogenic heat exchanger (coil-wound two-phase equilibrium in a separator.development peaked with a new LNG process, the MFC heat exchanger) The loop portion in the liquefier-heat exchangerprocess (Mixed Fluid Cascade Process) and in numerous The trend toward large LNG production capacities need not be overheated out of its subcooling. Thatjoint accompanying patents. can be observed at the Snhvit LNG project. The first is linked with lower heat exchanger dimensions

approach was a capacity of 3.4 MTPA in one train, and lower costs.Development of the Mixed Fluid which was finally increased, to the current 4.3 MTPA. The MFC Process has other benefits:Cascade (MFC) Process Given those benchmarks, Linde-Statoil Technology The three cycle compositions enable optimized match

Alliance subjected the potential process options to the three sections of the cooling curve compared toThe development of LNG production processes for baseload to detailed examination, taking into consideration the only one or two cycle mixtures. That offers excellentoperation are targeted at the following main criteria: thermophysical properties of the natural gas and the efficiency or low energy requirement. Minimizing cycle compressor shaft power requirement possible coolant-cycles. The split of the refrigerant duty to three cycles and Reducing investment cost by increasing single train From that basis, Linde-Statoil Technology Alliance compressors instead of one or two allows LNG productionLNG production capacity, or, in other words providing developed the MFC LNG baseload process (Figure 2). capacities of up to 8 MTPA in one train, where the otherthe benefits of higher train capacity. (See also page 4). processes have to install costly 2 x 50 % train configurationsThis minimum shaft power criterion drives the arguments This process consists of three mixed refrigerant cycles. for the compressors and heat exchangers. investment cost and environmental friendliness together The precooling cycle consisting of a mixture of C2H6with other criteria, in a positive direction, although and C3H8 is compressed in compressor C1, liquefied in Eginhard Berger, Wolfgang Frg, this may frequently be considered as contradictory: sea water cooler CW1 and subcooled in cryogenic heat Roy Scott Heiersted, Pentti Paurola With minimum shaft power the costs for the cycle exchanger E1A. The MFC (Mixed Fluid Cascade) Process for the compressors, the drivers (mostly gas turbines) and the The first European LNG baseload plant operating first European Baseload LNG Production Plantcooling system are minimized. That represent a major with the newly developed Linde-Statoil MFC process The Snhvit Projectportion of the plant investment cost together with is currently being built on Melkya Island off the Norwegian Linde Technology I 1/2003 11minimized instrumentation, electrical, piping, structural coast near Hammerfest, to recover the Snhvit Reports on Science and Technologysteel, construction work, etc. hydrocarbon deposit in the Barents Sea. Space and weight of the plant are minimized, The MFC process is distinguished by several noteworthywhich is of great importance for land-based and, in advantages:particular, 9 for offshore installations. The simultaneous reduction of fuel gasconsumption reduces the operating cost

NATURAL GAS LIQUEFACTION PROCESSES COMPARISONCOMPARAISON ENTRE PROCEDES DE LIQUEFACTIONDE GAZ NATURELPierre-Yves MartinJrme PigourierAxens (France)www.axens.frBatrice FischerIFP (France)Poster PO-39PO-3 9.1

This process is a three cycle process, like the cascade process, but with mixed refrigerant on all cycles (see figure 5). Compared to the cascade, the efficiency is better, as mixed refrigerants allow to have a closer approach. However, the power is not the same on all three cycles, unlike the new cascade. Plate-fin exchangers are used on the first cycle, and spiralwound exchangers on the two colder cycles.

REFERENCES CITED3. H. Bauer - A Novel Concept for Large LNG Baseload Plants - AICHE Spring National Meeting, 2001

Hammerfest LNG (Snohvit)TPG 4140 Naturgass - Hosten 2007Jostein PettersenStatoil