Plate-fin heat exchangers - An Ideal Platform for LNGProcess Innovation

Béatrice Fischer Murtaza KhakooPrincipal Research Engineer Senior Process Engineer

Institut Français du Pétrole (IFP) - CEDI BP Exploration

Beatrice Fischer has been a Principal ResearchEngineer in a development division of IFP since1996, working on the development of new gasprocesses and in particular, natural gasliquefaction.She joined IFP in 1977 as a process engineer, in1989 became process group leader (catalyticreformer group).She graduated from Ecole Centrale de Paris in1973, and got a Ph. D. from Université deLyon in 1977.

Joined BP after graduating from UniversityCollege, London in 1977 with a degree inBiochemical Engineering.Initial period spent in R&D and refinery work.Joined E&P in 1982 and worked on many O&Gand LNG projects (e.g. Miller Gas, Vietnam Gas,PNG LNG) and operational support (Das LNGPlant)During 2000, co-ordinated LNG technologydevelopment activities and currently workingon uptake of Liquefin process in emerging BPProjects.

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Abstract

The large expansion of LNG trade foreseen triggers changes in the conception of LNG plants.Major efforts are aimed at increasing efficiency, increasing train capacity and minimising costswhilst improving safety and reducing environment impact.

IFP, in collaboration with BP, has explored new options for achieving these goals using the IFPLIQUEFINTM process. A first study had shown intrinsic benefits using this new process comparedto conventional ones. One of the key elements of this new process is the main exchange linereducing the natural gas temperature from ambient down to cryogenic in one step. This exchangeline is composed of plate-fin heat exchangers, arranged in 4 cold boxes for a capacity about4.5mtpa.

This paper describes in detail the joint efforts of IFP and BP to further develop the design of sucha heat exchange line and explore possibilities for increasing the size or number of cold boxes t oreach capacities of 9mtpa. Selection of the optimal configuration, combining low cost, gooddistribution and minimal stress, has been carried out in collaboration with heat exchanger vendors.This paper will also discuss the assurance efforts and experience from analogues that were key ingaining comfort with the process and equipment innovations.

Introduction

LNG trade has grown rapidly over the last three decades and now accounts for around 25% of allinternational movements in natural gas. Although the major established market of Japan ismature, Korean and European demand is still growing, which when combined with new anddeveloping markets in Asia and the Americas is expected to drive demand growth by as much as10% per annum.

The LNG business has traditionally operated by setting up long-term supply-purchase contractswith producers to satisfy investors’ needs to finance the capital intensive LNG projects. Theemergence of a greater variety of customers and new supply hubs, combined with deregulation insome markets and more flexible supply arrangements, will lead to more competition andincreased pressure to reduce costs. Full chain costs have fallen approximately 30% since the early1990s, and this trend is expected to continue, delivering similar cost reductions again by 2010.

With liquefaction facilities accounting for almost 50% of the costs in a typical value chain, theyare an obvious focus for cost reduction efforts. The unit capital costs for LNG liquefaction plantshave fallen from an average of over US$400/tpa in the early 1990s to around US$200/tpa forrecent, state of the art, greenfield facilities like Trinidad’s Atlantic LNG Train 1. Thedevelopments that enabled these cost reductions were driven by competition between producerswishing to supply LNG into expanding yet competitive gas markets and technology suppliers andcontractors eager to participate in these multi-billion dollar projects. The opportunity presentedby the rapid increase forecast for LNG demand continues to stimulate this process, and hasencouraged others to develop new technologies and bring them to the market.

The Liquefin process developed by IFP, in collaboration with BP, and now marketed by Axens isone such new technology. It is a non-integrated cascade process incorporating two refrigerationcircuits driven by identical drivers to reduce the amount of rotating equipment. Both circuitsutilise multi-component refrigerants, allowing a significant reduction in the size and cost ofcooling equipment in comparison with processes utilising single component refrigerants. Inaddition, the use of brazed aluminium plate-fin heat exchangers in the cold boxes offerssubstantial benefits over spiral-wound heat exchanger designs. This and other features give theLiquefin process a projected unit capital cost 10-15% lower than even the most modernalternative processes.

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This paper gives a brief summary of the process, the key innovations of the liquefactiontechnology and its benefits, and discusses in detail the design and assurance of the key processinnovation, namely the plate-fin heat exchanger based main cryogenic exchanger.

Liquefin Process Description

The Liquefin process operates according to the typical flow scheme presented in Figure 1. Thepre-refrigeration of the gas is achieved by using a mixed refrigerant instead of propane. In thisprocess, the pre-refrigeration cycle is operated at a much lower temperature than when propaneis used and the temperature is decreased down to about –60 °C (-75°F). At this temperature, thecryogenic mixed refrigerant can be completely condensed, so that the quantity of cryogenicrefrigerant is substantially reduced. The molar ratio between the cryogenic mixed refrigerant andLNG can be in some cases lower than one. The overall required power is reduced, as a good part ofthe energy necessary to condense the cryogenic mixed refrigerant is shifted from the cryogeniccycle to the pre-refrigeration cycle. Moreover, this shifting of energy leads to a betterdistribution of the necessary heat exchange area and the same number of cores in parallel can beused all along the line between the ambient and the cryogenic temperatures.

In the Liquefin process, both mixed refrigerants are used in the same way as pure components.The mixed refrigerant is condensed and vaporized at different pressure levels in each section,without any phase separation or fractionation. In this way, the exchange line can be kept verysimple and compact.

A very significant advantage of this new scheme is the opportunity to adjust the power balancebetween the two cycles. It is thus possible to use directly the full power provided by two identicalgas turbines, without any transfer of power from one cycle to the other.

Figure 1 - Liquefin general scheme

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Liquefin Process Innovations

The Liquefin process has much similarity with the well-known propane pre-cooled multi-component refrigeration (C3/MR) process, but with two major differences: namely, it is a dualmixed refrigerant cycle and the exchange line, which consists of a series of cold boxes.

• This dual mixed refrigerant process operates with a very low pre-cooling temperature (typicallyminus 60ºC) obtained by a C2/C3 refrigerant mixture, so that the cryogenic mixed refrigerant iscompletely condensed when entering the cryogenic stage. This configuration has a lot ofadvantages:ÿ a higher efficiency: no energy is lost condensing mixed refrigerant in the cryogenic stageÿ the power can be balanced between the two mixed refrigerant cycles, allowing the use of two

identical turbinesÿ the air-coolers or sea water condensers for the C2/C3 mixed refrigerant are much smaller, as

this mixed refrigerant condenses over a range of temperaturesÿ the cryogenic mixed refrigerant is a simpler C1/C2 mixture with a small quantity of nitrogen

added as required to reach the final temperature. Apart from this composition, the cryogeniccompressors will be very similar to the existing compressors driven by GE Frame 7 gasturbines in the larger LNG plants.

ÿ the use of two mixed refrigerants gives a lot of flexibility: the pre-cooling temperature andthe composition of both mixed refrigerants can be modified so as to follow summer/wintertemperature variations and get optimum efficiency all year round.

The use of a C2/C3 mixture as refrigerant has been proven in existing plants, for instance inthe chilling of the LPG product at Badak LNG Plant [1].

• All the heat exchange between the natural gas and the two mixed refrigerants (and between thetwo mixed refrigerants) is done in a single exchange line, made of plate-fin heat exchangers insidea few cold boxes (see Figure 2)ÿ All major plate-fin heat exchanger vendors can make these cold boxes and IFP/BP have been

working particularly with Chart, Nordon Cryogenie and Kobe in the design development andassurance of the main heat exchanger cold boxes.

ÿ The main heat exchanger design has been based on minimum number of cold boxes eachcompactly laid out to minimise cryogenic pipe runs. Within the cold boxes, the pipingbetween cores is also minimised by creative sizing of cores for the different heat exchangeduties.

ÿ All fluids are distributed in single phase between the cold boxes and between the cores insidethe cold boxes. At J-T valves where two phases are generated, there will be one J-T valve percold box with a small distributor drum inside the cold box that separates liquid and vapourbefore distributing them separately between the cores. They are then re-mixed inside thecores with special devices proprietary to each vendor.

ÿ IFP/BP have worked closely with the plate-fin heat exchanger manufacturers to derive a mainheat exchange line with similar architecture of plate-fin heat exchangers inside the coldboxes. Thus, the cold boxes can now be purchased from any of the three vendors withoutimpacting the plant design or the P&I diagrams

ÿ This exchange line is modular: each cold box contains several parallel lines of two cores inseries. The number of cores and cold boxes depends upon the capacity of the unit and the siteconditions (roughly 1-1.5mtpa per cold box or up to 3.25mtpa for the “double pack”arrangement, i.e. 2 rows of parallel sets of two cores in series in one cold box).

ÿ With the modular concept, all limitations in size that exist for spiral-wound exchangers areremoved.

The main exchange line arrangement is at the heart of the liquefaction technology andsignificant effort has been made to ensure optimal and foolproof operation of such anassembly – this is discussed further in later sections.

Cold box

Core (PFHE)

From / To Compressors

about 10 m

top view

about 15 m

Upper core

Lower core

front view40°C

- 60°C

-160°C

about 25 m

Figure 2 – Liquefin typical cold box arrangement

Liquefin Process Benefits

∑ EfficiencyThe first advantage of the process is the high efficiency: comparing like for like, the process will produce about 6-15% more LNG with the same gas turbines than other established liquefaction processes. This efficiency improvement is related both to the use of mixed refrigerant for the pre-cooling and to the use of plate-fin heat exchangers.ÿ The low temperature difference all along the cores between hot and cold side (see Figure 3) brings an improvement of the exergy efficiency and hence the power consumed per tonne of LNG is lower (or for the same gas turbines, the quantity of LNG produced is higher). 4

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Enthalpy Curves - Pre-refrigeration Core

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Figure 3 – Liquefin main exchange line enthalpy curves

ÿ The cryogenic mixed refrigerant enters the cryogenic section in a fully liquid state so that noenergy of this cycle is wasted in condensing the mixed refrigerant. The quantity of cryogenicrefrigerant is much lower than in the C3/MR process (roughly 1 mole of cryogenic mixedrefrigerant for 1 mole of natural gas), thus the overall efficiency is improved.

ÿ The pressure drop is very low on both hot and cold side of the plate-fin heat exchangers andthis brings an additional efficiency advantage for Liquefin.

ÿ As Liquefin is not submitted to the manufacturing limits of main heat exchangers, theefficiency can be as good for very large capacities as it is for smaller ones.

ÿ Liquid turbines, which are now proven and widely used in LNG plants, will bring higherincreases of capacity with Liquefin because the total stream of the cryogenic mixedrefrigerant passes through the turbine.

• EPC scheduleIn a conventional LNG plant project, the critical long-delivery items are the gas-turbines/compressors, main heat exchanger (assumed to be spiral wound) and storage/exportsystem. Pre-ordering of compressors/drivers is usual in LNG projects, so that the critical path isshifted to the main heat exchangers and the LNG storage/export system. The shorter fabricationschedule for plate-fin heat exchanger based cold boxes, as shown in Figure 4, could permit asignificant reduction in the overall LNG project schedule for new plants, provided that anappropriately innovative LNG tank construction contract is employed. As a minimum, it allowsdeferral of the large capital cost of the main heat exchanger and gives more time to firm up theLNG process design. For LNG plant expansions where additional tankage is not required, theschedule benefits can easily be captured.

Month 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Core Design

Cold boxesdesign

Manufactureof cores

Manufacture of cold boxes

Cold Box 1ready

Cold Box 2ready

Cold Box 3ready

Cold Box 4ready

Figure 4 - Typical cold box fabrication schedule• Layout

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The use of cold boxes allows a more efficient use of space and reduction in the plot area. Asshown in the 3-D view in Figure 5, the liquefaction unit is limited to refrigeration compressors,aircoolers, the heat exchanger cold boxes and the scrub column - the common facilities such aspre-treatment, fractionation and flash gas sections are not shown. The reduced space necessaryfor the heat exchange line is clear to see - this results in significant reduction of cryogenic pipingwhen compared with pipework in plant layout with large kettle chillers and spiral woundexchanger.

Cold boxesassemblyFrame 7

Figure 5 - 3D view of the liquefaction section

• Large CapacityOne of the major factors in LNG plant cost reductions has been the capacity of the liquefactionunit. In the last 10 years, LNG train size has increased from ~2.5mtpa to 5.2mtpa currently indesign and this has been dominant in reducing LNG plant unit costs to approx. 50% (see Figure6). The capacity is limited mainly:ÿ By the maximum size of gas turbines in mechanical drive (the biggest so far is the GE

Frame 7 - about 80 MW ) ÿ By the maximum size of the spiral wound exchanger used in most large base-load plants

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1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

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Figure 6 - LNG train capacity increase

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The Liquefin process has many features that make it possible to build larger capacity LNG plantsand hence significantly reduce the specific cost:ÿ There is a single compact heat exchange line made up of several plate-fin heat exchangers

(PFHE) in a cold box. The PFHE have large heat exchange area per volume unit (up to 2000m2/m3) and low approach temperatures can be realised with a relatively small exchangervolume. Furthermore, as the cold boxes are modular, there is no size limitation for the heatexchange line. More cores per cold box, or more parallel cold boxes allow unlimited increasein capacity.

ÿ The power in each MR cycle is balanced. Thus the power of two large turbines such as GEFrame 7’s can be fully used without any limitation on operation or efficiency. There is alsothe possibility to use 2 or more parallel lines of gas turbines or electrical motor drivencompressors of equal power, which would give increased capacity and potentially betteravailability. Configurations with 4 GE Frame 6, 4 LM6000, 4 Trent DLE or large electricalmotors (>40MW) have been studied in developing an idealised LNG train that would neverstop producing completely.

Thus, capacities of up to 6mtpa can be reached with two Frame 7 gas turbine drivers and availablegas compressors. With parallel compression lines for each mixed refrigerant and somecompressor development, this limit can be pushed even further.

• CostSeveral factors mentioned in the preceding paragraph lead to potential cost reductions with theLiquefin process:- The ability to increase plant capacity that has a significant bearing on unit cost of LNGproduction;- The single PFHE exchange line that replaces the costly spiral-wound heat exchangers and thelarge kettle chillers;- Compact plot area, which reduces long runs of low temperature pipework- Reduced size of aircooler condensers and- Multi-sourcing of all equipment including the main heat exchange line.

Studies have shown that with Liquefin, the cost of the liquefaction unit itself can be decreased byup to about 15%. Overall, including utilities, pre-treatment, storage, etc, the difference is reducedto something around 7%, but with the increased capacity for the same gas turbines, the cost perton of LNG is lower by up to about 20% when compared with competing process.

• OperabilityA previous study [2] carried out with the help of a major engineering company investigated theoperability and reliability of the Liquefin technology. P&I diagrams and operating procedures(start-up, shut-down, warm-up, turndown) were developed. Potential hazards and operationalupsets were examined to confirm that the Liquefin process could handle these. This analysisconfirmed the advantages of the technology in terms of operability and reliability, due to arelatively simple, modular process that makes it easy to control and manage transients.

Furthermore, the Liquefin process offers unmatched flexibility to adapt process conditions formaximum production in scenario of daily or seasonal temperature variations. This flexibility ismade possible by changing the pre-cooling temperature and/or mixed refrigerant compositions,with appropriate sizing of the equipment.

• ModularityThe trend of increasing LNG plant capacities now poses problems in finding a ready market forall the LNG produced: multi-customer demand has to be aggregated before a new project can getoff the ground. This makes LNG projects commercially more complex and they can thereforetake longer to bring to fruition.

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The concept of building an LNG plant that increases production capacity in a “modular” manner,thereby breaking the “scale conundrum”, is therefore attractive in enabling projects to get off theground with fewer customers and a reduced resource pool, whilst maintaining the ability to grow.Such a development concept is now possible with the unique features of the Liquefin Process thatincorporates all the heat exchange for liquefying gas to LNG in one intensified assembly of plate-fin heat exchangers in cold boxes.

It is thus now possible to design a liquefaction unit with a series of “natural gas liquefier units” orNGLU, consisting of such cold boxes supplied with the two levels of refrigerants and clean gas t oproduce LNG. This will permit capacity “upgrade” with additional modules of NGLU’s combinedwith expansion of refrigerant supply and feed gas treatment.

Furthermore each of the NGLU can be delivered to the plant site as a complete pre-assembledunit (PAU) ready for hook-up, commissioning and start-up. This permits significant reduction incost, schedule, safety and 1st years reliability.

Main Heat Exchanger Cold Box Design Assurance

The plate-fin based main heat exchanger cold box is one of the novelties of Liquefin. Althoughthe selected PFHE manufacturers have extensive experience of similar equipment, IFP hasworked to obtain extensive knowledge and assurance of this special equipment.

One of the strengths of IFP is that they have a large number of scientists that work on a widerange of subjects. A team comprising of process engineers, heat transfer specialists, fluiddynamics specialists and mechanical specialists was gathered to study all aspects of the use ofthese exchangers in this specific application, in close co-operation with the PFHE manufacturers.The work of these scientists was twofold: firstly to understand and model the problem, andsecondly to prepare tools that the process engineers could use by themselves for checking thecritical points of the vendors’ designs.

The thermal and hydraulic design of the proposed exchangers was verified first. Severalcommercial tools exist to model the heat exchange in PFHE. These tools have been checked withthe experimentation data within IFP and other research centres and found to be reliable. It hasbeen decided to use the HTFS model, which has a very user-friendly interface and easy links withHysys, so that process engineers can handle it after reasonable training.

• Fluid dynamics studiesFor 4.5mtpa, the number of cores is 24 arranged in 4 cold boxes each with 6 parallel cores as oneoption. For larger capacities (6+mtpa), the number of cores and/or cold boxes would be higher. I tis important to ascertain that the calculated thermal and hydraulic performance will not bedecreased by poor design of the distribution system between the cores.

IFP Fluid Dynamics specialists have developed a model (see Figure 7) to calculate the flow-rate t oeach core of a cold box as a function of the header/manifold arrangement, pipe dimensions andfittings, and taking into account the actual pressure drop across the core. This model has beenlinked through a Visual Basic interface to the HTFS simulator, MULE which allows calculation ofthe thermal performance and associated core pressure drop, starting from the flow-ratesgenerated by the IFP model. Several iterations are necessary to reach convergence.

With this model, it is now possible to verify the design provided by a vendor, and to proposeenhancements if merited. It is also possible to simulate a problem in one of the cores (e.g. partialplugging) and to see the effect on the fluid distribution and on the overall thermal performance.

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24/06/2002FGT= total flowrate kg/h 78408.00 FG=total gas flowrate / number of cores kg/h 13068.00 DPE 76369.8969 PaROE=inlet density kg/m3 30.90ROS=outlet density kg/m3 41.98 N Flow Flow DP Bilans %flow

MUE=inlet viscosity Pas 1.4E-05 1 13106.9032 13107 76370 0.012279 100.30%MUS=outlet viscosity Pas 1.0E-05 2 13082.1348 13082 76370 0.010992 100.11%

3 13064.4849 13064 76369.9 0.002716 99.97%4 13053.3246 13053 76369.8 0.01457 99.89%5 13048.1808 13048 76369.9 0.001796 99.85%

NE=number of parallel cores in the cold box (<10)(-) 6.00 6 13052.9432 13053 76370 0.002882 99.88%DCE=cold box inlet pipe diameter m 0.35 0 0 0 0 0 0.00%DLE=core inlet pipe diameter m 0.15 0 0 0 0 0 0.00%LI=Pipe length before the fist T m 3.7 0 0 0 0 0 0.00%LB=Pipe length between T's m 1.8 0 0 0 0 0 0.00%average speed m/s 3.66 total 78408 13068 0.000794average speed m/s 6.65 OBJ 0.04603

DCS=cold box outlet pipe diameter m 0.3 DLS=core outlet pipe diameter m 0.125LE=Pipe length between core and T (inlet) m 0.5LT=Pipe length between core and T (outlet of core)m 0.5average speed m/s 3.67average speed m/s 7.05

Pressure drop in the core Bar 0.745Ku = DP/(flow-rate)2 Pa/(m3/h)^2 5.40E+06

DcsDls

DleDce

Ku

Le

Lt

Li Lb Lb

Figure 7- Part of IFP distribution model interface

For the partial plugging scenario analysed, for example, it can been shown that an incidentaldecrease of mixed refrigerant in one core will reduce the quantity of LNG condensing and increasethe pressure drop in adjacent passages of this core which will hence take less feed gas. As a result,the other cores will get more of the feed gas and more mixed refrigerant, which will ensure anincreased heat exchange so that the average LNG temperature is not significantly changed, i.e.the system is self-correcting (see Figure 8).

MR2 cold side : pressure drop vs flow-rate

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Figure 8 - Effect of abnormal flow-rate in one core

• Mechanical studiesThese exchangers are widely used in a variety of cryogenic applications and the Liquefin coldboxes will not be any bigger or colder than existing ones used for air separation or ethylene.However, the huge cost of LNG plants makes it necessary to avoid any risk and to study carefullythe behaviour of PFHE in this application. The connecting pipework can be studied using existingcodes, but the effect of thermal stresses inside the cores is not something that is well understoodin detail.

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Two effects have been addressed: the effect of axial temperature gradient in the core and theeffect of horizontal temperature variations. Temperature profiles calculated by the processengineers for normal, transient and upset conditions have been used in the computation ofstresses within the core.

The difficulties of the stress calculations come from several factors:ÿ “lacuna” material: the aluminium core has void spaces with relatively thick side-bars and very

thin aluminium finsÿ non-isotropic material: the fins are all oriented in one direction, so that the resulting material

properties are not the same in all directionsÿ rectangular section: there is no axis of symmetry which would simplify the calculation.

The solution was to use homogenisation methods with 3 dimensional finite element analyses.These homogenisation methods will allow passing from the core scale stresses to the fin scale (seeFigure 9) stresses. With these calculation methods, any possible process situation can therefore beanalysed.

s33 analysis

Figure 9 - Analysis of core stresses, first at core scale, then at fin scale in the worst place

Three cases have been investigated on an early process design:ÿ Normal operating conditionsÿ Operational upset: mixed refrigerant compressor trip and ESD malfunction – worst case for

temperature induced stressÿ Thermal shock: a theoretical case where the side bars is 10°C hotter than the fins including

those immediately adjacent

These studies have shown that the resulting stresses in these scenarios are low, confirming thatplate-fin heat exchangers are intrinsically robust in this application.

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• Lessons learned from cold box operation in existing cryogenic plantsInformation on the application and operating experience of plate-fin heat exchangers has beencompiled from many sources. Extracts of lessons learned have been compiled for considerationand appropriate mitigation in the design, engineering and operation of the Liquefin process. Someof the issues to be considered are discussed below:

ÿ Moisture/water: Any water in the exchangers will freeze and is likely to cause inter-passagefailure. It is therefore good practice not to get the PFHE wet and to keep coldbox cores underpressure with nitrogen until they are connected to the plant. Pipework leading to the coldboxhas to be thoroughly dried and, before startup, a procedure for deriming (drying out) the unitshould be implemented.

ÿ Mercury: Hg contamination is a consideration in any facility using aluminium PFHE. Feed gasmercury content needs to be checked and, if amounts detected are significant, Hg guard bedsshould be installed.

ÿ Mol sieve dust/particle removal: If molecular sieve particles or fines enter the heat exchanger,they may wedge within the fins of the plate-fin exchanger. Good filters specified to removeparticles to 1 micron should be provided. It is also advisable to install facilities to back-puffthe exchangers to remove any dust that may build up. This is accomplished by installing arupture disc (set at 3-5bar) on the outlet flange and back flowing nitrogen into the exchangers.

Similarly, it is also good practice to consider at an early stage other solid contamination suchas scale, “compressor material”, and make appropriate provision.

ÿ Other Contaminants: On the refrigerant side, it is important to keep seal and lube oil out ofthe system so that it does not accumulate in low points or congeal on the plates. In thisrespect, the use of gas seals would be preferred. Where use of seal oil is unavoidable, provisionof connections to hook-up solvent wash facilities, either vapour degreasing or a pumpedsolvent circuit, would be advisable.

ÿ Cooldown/warm up rate: PFHEs are tolerant of upsets, fast cooldown and overpressure butstreams have to be kept balanced. A check of the startup procedure is necessary to confirmthat it is possible to lower the temperature at the rate recommended by the vendor.Installation of skin thermocouples to measure the progress of core heating and cooling rates isalso required.

ÿ Mechanical design/piping: Every effort needs to be made to avoid undue stress on thealuminium cores, whether mechanical or thermal, during handling, pipework fit-up andoperation. Attention needs to be given to the two-phase flow patterns around the pipeworkarrangement in terms of hydraulic design, sizing and appropriate slopes.

ÿ Leak Detection/Repair: The cold box with its perlite insulation should be purged with nitrogenand the exhaust fitted with gas detectors to detect when leaks occur. A procedure to repairleaks or to change out cores should be provided by the vendor.

ÿ Performance monitoring: Adequate temperature measurement points must be provided acrossthe cold box passes to enable long-term trends in exchange efficiency to be monitored.

Careful application of lessons such as the above learned from operating plants will be key t oensure successful application of plate-fin heat exchangers in a Liquefin technology basedliquefaction unit.

Conclusion

Our work has confirmed the feasibility of building an LNG plant based on the Liquefin process andthe plate-fin based main heat exchanger. A number of leading contractors have carried outengineering studies at various project stages from preliminary to front-end design. They have

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confirmed the viability and advantages stated in this paper and their willingness to engineer aplant based on the Liquefin technology.

BP have participated in the development and evaluation of the Liquefin process and are welladvanced in assurance of the design of the main heat exchanger cold boxes – the key innovationin Liquefin. BP has included Liquefin in the ‘select’ phase of its emerging LNG projects, where itis competing with evolving technology from established suppliers.

IFP, the technology owners, are currently licensing the technology through Axens (an IFPwholly owned subsidiary) and a large team is already set up to support licensing and technologyenhancement. Axens is currently working on a number of baseload projects at various stage ofdevelopment from preliminary studies to front-end engineering. We hope that at least one ofthese will progress to execution phase in the near future.

In conclusion, we believe that plate-fin heat exchanger based cold boxes have now developedsufficiently for use in base-load LNG production. Their application in the Liquefin process couldbecome a new standard for the LNG business and will offer distinct competitive advantages overother current technologies.

References

[1] Budi Santoso, Fatchurrachman Driving Revenue by Eliminating LPG flaring Session 113 - AIChemE spring National Meeting, New Orleans, Louisiana, March 10-14,2002

[2] Khakoo M., Fischer B., Raillard J.C. The Next Generation of LNG plants LNG13, Seoul, Korea, May 14-18, 2001