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INDUSTRIAL SCALE TESTING OF A SPIRAL WOUND HEAT EXCHANGER

TEST A ECHELLE INDUSTRIELLE D’UN ECHANGEUR BOBINE Helmut Reithmeier, Manfred Steinbauer, and Rudolf Stockmann

Linde AG, Germany www.linde-le.com

Arne O. Fredheim, Oddvar Jørstad, and Pentti Paurola Statoil ASA, Norway

www.statoil.com

ABSTRACT

The Statoil-Linde LNG Technology Alliance, established in 1996, reflects the LNG industry’s desire for reduced cost and schedule for the development of base-load LNG plants. In May 1997, the Statoil-Linde LNG Technology Alliance decided to install an industrial scale prototype of a spiral wound heat exchanger (SWHE) for liquefying natural gas in parallel to the existing plate-fin heat exchanger Cold Box of the NG liquefaction plant built by Linde in the PetroSA GTL Refinery (former Mossgas Refinery) in the Republic of South Africa.

The PetroSA facilities comprise an LNG plant with a nameplate capacity of 13.5 tons per hour using a single-flow mixed refrigerant cycle consisting of nitrogen, methane, ethylene and isobutene for the liquefaction of natural gas.

Rigorous LNG process- and heat exchanger models have been developed both by Linde and Statoil during several years, and these formed the backbone of the data acquisition and analysis. A test program was established to demonstrate the mechanical integrity during several tests as well as the correctness of the thermal, hydraulic and geometrical design for different operation scenarios.

Major emphasis was put on the scientific analysis to verify design tools for thermal and hydraulic design of SWHEs based on high quality operational data. The tests and analytical results, from two test periods in 1998 and 2001 and a continuous involvement of the heat exchanger in daily operations at the facility, provides an extremely comprehensive database.

Logging of more than five years of daily operation with frequent start ups and shut downs with quite high temperature gradients has proven mechanical integrity.

RESUME

L’Alliance ”Statoil-Linde Technology”, créée en 1996, illustre la nécessité pour l’industrie GNL de réduire les coûts et les délais de développement des usines de production de GNL. En mai 1997, l’Alliance a décidé d’installer un prototype a échelle industrielle d’échangeur bobiné (SWHE), en parallèle à une boite froide existante (échangeurs à plaques) sur l’usine de liquéfaction de gaz naturel construite par Linde dans la PetroSA GTL Refinery (précédent Mossgas Refinery) en République d’Afrique du Sud.

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Les installations de liquéfaction de gaz de PetroSA consistent en une usine GNL, de capacité égale à 13,5 t/h, par cycle simple flux et multiréfrigérant à base d’azote, méthane, éthylène et isobutène.

Des modèles rigoureux de simulation du procédé et des échanges thermiques ont été développés conjointement par Linde et Statoil et forment un support pour l’acquisition et l’analyse des données recueillies. Un programme de test a été defini en vue de démontrer l’intégrité mécanique du système ainsi que la validité des concepts thermique, hydraulique et géométrique selon divers scenarios opératoires.

Un effort important a été placé dans l’analyse scientifique afin de vérifier les outils de conception thermique et hydraulique de l’échangeur bobiné, sur la base de données opérationnelles de haute qualité.

L’enregistrement de plus de cinq années de données opératoires quotidiennes incluant de nombreux démarrages et arrêts et des gradients de temperature élevés a permis de confirmer l’intégrité mécanique du système.

INTRODUCTION

Statoil had experienced several times during 1985-92 that commercialising of the Snøhvit area reserves was not economically based on conventional project development. This led to a business pull within the company for establishing a more competitive basis for design, engineering and project execution strategy of an LNG chain. In 1993, this need for a new deal in LNG development formed the break-through for establishing an industry alliance.

To Statoil, industrial collaborative developments of new technologies, as a basis for business development, were a common task regarding the offshore developments in the North Sea. Now the same approach should improve the economics of the potential business opportunity of entering into the LNG market, based on the stranded reserves in the Barents Sea and further in international gas ventures.

Potential industrial partners were contacted and introduced to the Statoil intention to enter into a joint LNG technology development with shared ownership. In 1995, the German company Linde AG became the selected industrial partner.

Statoil and Linde entered into a long-term LNG Technology Alliance in 1996, aiming at more cost effective process technology for base-load LNG plants. The Statoil-Linde LNG Technology Alliance succeeded in both qualifying the Linde fabricated Spiral Wound Heat Exchanger (SWHE) for use in base load LNG plants and in the development of the new and efficient Mixed Fluid Cascade (MFC®) process /1/.

An industrial sized prototype of a SWHE manufactured by Linde was installed in the existing LNG plant in Mossel Bay, South Africa and tested in steady state and dynamic operations. The testing of this heat exchanger represents an important step in the Statoil-Linde qualification and verification of the jointly owned technology. After the initial testing the SWHE was converted into regular operation in the LNG plant.

The Linde SWHE design and manufacturing has, by 2003, been selected for new LNG developments and as replacements in a number of worldwide LNG projects /2/.

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THE STATOIL LINDE TECHNOLOGY ALLIANCE

The Statoil-Linde LNG Technology Alliance aims at improvement of base-load LNG technology, project development procedures and execution strategies, cost reduction and shortening of the construction time, along with the development of economical concepts for LNG projects. The success criteria were set at constructing the first LNG plant with joint technology and obtaining international acknowledgement.

The tasks comprised LNG process design and engineering, procurement by global sourcing, construction leading to the process barge concept and establishing a commercial edge as a technology licensor. At that time Linde had already a long-term commitment in cryogenic design, technology and equipment fabrication.

Further, the Statoil-Linde LNG Technology Alliance is now focusing on developing a technology for the realisation of floating LNG plants. In this context a SWHE qualification program for floaters was started early 2002. As part of this it is planned to complete a test of a 10 % of full scale SWHE operated in motion.

THE PETROSA LNG PROCESS AND HEAT EXCHANGER DESIGN

Between 1990and 1992 Linde performed the engineering, procurement, construction and commissioning of the existing natural gas plant at PetroSA Refinery. The plant comprises natural gas pre-treatment, liquefaction with plate-fin heat exchangers (PFHE) installed in a Cold Box, LNG storage and re-evaporation facilities in order to supply backup feedstock in case of interruption of the offshore gas and condensate production.

Figure 1: Picture of the Cold-Box in the Mossel Bay LNG plant

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The liquefaction process of the LNG plant with a nameplate capacity of 13.5 t/hr is a single flow mixed refrigerant cycle consisting of nitrogen, methane, ethylene and isobutane. A sketch of the process is given in Figure 2.

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Figure 2: Sketch of the liquefaction process with the SWHE in the Mossel Bay LNG plant

The SWHE cooling, liquefying and sub-cooling the purified natural gas consists of three bundles located one above the other in one shell. This NG-Liquefier is installed in a Cold Box together with the separator for removing heavy hydrocarbons (HHC). The natural gas and the high-pressure refrigerant streams are routed in upward flow on the tube side. The purified natural gas stream is pre-cooled in a first step to enable the separation of heavy hydrocarbons and subsequently liquefied and sub-cooled. The compressed refrigerant is partially condensed by cooling water and split into a vapour and liquid phase. The vapour stream is liquefied and sub cooled, whereas the liquid stream is sub-cooled only prior to expansion. The cold refrigerant is distributed equally above each bundle via a proprietary distribution system. The low-pressure refrigerant is evaporated in downward flow on the shell side and finally recycled to the refrigerant compressor.

As a special feature, the design includes the possibility to test forced mal-distribution of the liquid refrigerant fraction on the shell side in order to investigate the impact on the SWHE performance.

The effective heating surface is approximately 4000 m². The design pressure on the tube sides is 48 barg, whereas the design pressure on the shell side is 28 barg to match with existing design requirements. The design temperature is +55/-175 °C. The SWHE is fabricated completely in aluminium with a diameter of 1.5 m and a total height of 28.6 m.

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Figure 3: Production of a SWHE at the Linde workshop

The design of the SWHE is characterised by a tube bundle hanging on support bars transmitting the mechanical forces via these support bars to the support arms above. This type of bundle support is a proven Linde design and has been used for more than 160 SWHE designed and built by Linde over the last 25 years with diameters up to 3.9 m and heating surfaces up to 20000 m².

As it is flexible in vertical direction, mechanical stresses between bundle and shell and inside the bundle itself caused by rapid temperature and pressure changes during upset conditions (e.g. refrigerant compressor trip) are absorbed without any harm to the SWHE.

Compared with heat exchanger sizes in presently planned or built base-load LNG-plants all relevant scale-up factors are well within the recognised maximum ratio of 10:1.

TEST OBJECTIVES

The objective of the comprehensive test program comprised extensive data acquisition and analysis of the thermal, hydraulic and mechanical performances. The SWHE is adequately instrumented to demonstrate the quality of the design tools and the engineering and fabrication procedures. Recorded data from transient operation have in addition been used for verification of in-house dynamic simulation tools.

The test program of the SWHE for natural gas liquefaction at normal and abnormal operating conditions included:

• Demonstration of Linde's capability of manufacturing LNG SWHE's • Verification of mechanical design • Verification of the thermal and hydraulic design • Verification of the control philosophy applied • Verification of turn-down capabilities

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• Verification of an impact of shell-side mal-distribution on the performance • Verification of the dynamic simulations models • Gaining operational know-how for all transient situations in a LNG plant

INSTRUMENTATION AND DATA QUALITY

Both the SWHE and the process streams have been extensively instrumented. Most of the instrumentation was new, but some of existing process instrumentation was also used for redundancy purposes. A total of more than 100 transmitters were used in addition to compositional analysis. The high number of instruments ensures an excellent accuracy for both recalculating process parameters and evaluating the performance and efficiency of the SWHE. All measured data were individually judged by using redundant measurements during operation and validated by recalculation using an in-house process simulator. Based on this evaluation a quality-ranking list was established, ensuring that only highest quality data were used as basis for the critical examination of the actual performance of the SWHE.

A total of about ten different flow measurements were used for the overall monitoring of the LNG process and the SWHE. The experienced accuracy of the flow indications varies from 1.5 to 5 % depending on plant load that met the expected values. The pressures of ten different streams were measured with an accuracy of ± 1 %.

The differential pressure was measured across each bundle in the SWHE for all of the different low and high-pressure streams. A total of nine different transmitters were used. The measured total pressure drop on the shell side of the SWHE was confirmed by using the difference in absolute pressure measurements.

A total of 32 temperature elements was installed in the three SWHE bundles. The elements are installed in different positions both in longitudinal and radial. All of them are 4-wire class A PT-100 elements with calibrated transmitter accuracy better than ± 0.15 °C at zero degree. At ambient conditions the overall accuracy of the shell side temperature indicators was found to be within 0.1 °C. A picture of an installed PT-100 element in one of the bundles is given in Figure 4. The overall accuracy of the temperature indications around the SWHE bundles on the different process streams was determined to be better than ± 0.3 °C.

Figure 4: Installation of a PT-100 element in a SWHE bundle

The composition was measured for the natural gas feed stream, the low-pressure refrigerant and the high-pressure gaseous refrigerant. All samples were taken manually by using high-pressure sampling cylinders and analysed in the laboratory. Several composition samples were taken at stable process conditions during the different tests.

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Based on evaluation of the different samples the natural gas composition and the low- pressure (total) refrigerant composition proved to have high accuracy.

THE MOSSEL BAY SWHE TEST PROGRAM

Program Overview

The overall test program for the industrial scale SWHE has been carried out in three different periods where extensive data have been collected:

• 1st test period, October to November 1998 • “Day to Day” production • 2nd test period, May to June 2001

The first period focused mostly on the SWHE performance at steady state operation as well as start-up and trip test. The 2nd test period focused more on the dynamic behaviour of the SWHE as well as the confirmation of the original 100 % load performance. This 2nd test period was carried out after three years of “Day to Day” production with a lot of start-ups and shutdowns according to the feed back-up requirements of the refinery. The different tests from the two periods are classified as:

Steady state operations: • Performance at 100 % load • Maximum load of the SWHE • Turndown capabilities • Maximum load of the individual SWHE bundles

Dynamic operations: • Feed gas trip, refrigerant compressor trip and plant trip • Cool down due to unbalanced supply and demand of refrigeration • Warm up due to unbalanced supply and demand of refrigeration • Step changes of process parameters at different loads

General operations: • Warm and cold start-ups • Shutdowns • Operation with high pressure drop due to solidification of heavy

hydrocarbons • De-riming of fouled NG/LNG tubes • Forced mal-distribution of evaporating refrigerant on the shell side • Operation with a variety of refrigerant compositions

Potential clients have visited the plant during test periods and “Day to Day” production periods.

Steady State Operation

Both start-up and operation of the SWHE proved to be relatively simple. This ease of operation was experienced within the entire operational range of the test period, even below 25 %. The maximum load of about 109 % was limited by the refrigerant compressor capacity. The measured temperature profile for the 100 % load case is presented in Figure 5. This case was selected as reference cases for performance evaluation at 100 % load, as the refrigerant composition and plant process parameters were adjusted as close as possible to the design figures.

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The plant was very stable for each of these operational loads, even though the length of the test periods varied between one to 36 hours. The reason for partially short periods is due to the fact that the plant was in normal production during the tests and therefore influenced by the requirements of the refinery.

One of the main aims of the industrial scale testing of the SWHE at Mossel Bay was the verification of the different methods used for designing spiral wound heat exchangers. Consequently, all the steady state cases of Table 1 were recalculated by using the Linde in-house process design tool Optisim /4/ and the Linde in-house SWHE design tool GENIUS /3/, in order to evaluate plant and heat exchanger efficiency The verification of the thermal and hydraulic design methods was based on the evaluation of:

• Overall performance and maximum capacity • Local heat transfer of each bundle • Measured temperature profile through each bundle • Measured pressure drop through each bundles • Stability and flow regime during turn down • Performance during forced mal-distribution • Dry-out phenomena on the shell side of the first bundle

The recalculations of the test cases with GENIUS show a very good conformity with the measured data. As the results are within the accuracy range of the measured data, there is no need to refine the design methods. To cover the possible uncertainties of design methods a margin on the heat exchanger surface is implemented in the design of SWHEs.

The data from the different tests have also been compared to a Statoil in-house model for calculation of SWHE, called SCoil, which is linked as a user added subroutine to PRO-II. The results from these comparisons are well in line with the comparisons to GENIUS.

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Figure 5: Measured temperature profile of the SWHE at 100 % load

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Dynamic Operation

One of the main objectives for these tests was to observe the dynamic behaviour of the SWHE.

Transient cool-down scenarios were created either by rapid increase of the refrigerant load at constant natural gas flow, with an increase up to + 25 %, or - opposite – rapid reduction of the natural gas flow at constant refrigerant flow, with an decrease of - 55 %. In both cases the SWHE system will start to cool down. The flow rates of the other streams started to drift due to this cool-down. After a given period the changed flow rate was set back to the original set point and then the plant stabilised. The variation in temperature profile of the middle bundle during 55 % reduction of natural gas flow is shown in Figure 6.

The transient warm up scenarios were created in a similar way, but of course just vice versus. An example of such a test is presented in Figure 7 showing a rapid flow reduction of the refrigerant load by nearly 45 %. The duration of the test periods during the warm up scenarios were dependent on the speed of change and limited by the temperature required for HHC removal as well as the maximum LNG product temperature. The different tests showed that the SWHE was able to accept large variations in flow rates and keep the different temperatures within a controllable manner.

Different trip scenarios were performed, both in the first and the second test period. Some of the trips happened during normal operation, e.g. caused by upset conditions of the amine wash unit for CO2 removal or the molecular sieve dryer unit for water removal. In such trip cases the refrigerant compressor was kept in recycle operation. At 100 % capacity a trip of the LNG plant was experienced caused by a high differential pressure across the CO2 absorber. The expansion valves of the refrigerant streams were closed at once and the natural gas supply valve was closed with a delay of 120 seconds. The refrigerant compressor remained in operation and the LNG plant was brought back in normal operation within one hour. Other trips were performed deliberately by tripping the refrigerant compressor. An example of such a test is presented in Figure 8 showing a complete plant trip.

In addition a lot of normal start-ups, shutdowns and load changes were performed.

The following conclusion is based on the experience gained from the dynamic tests:

• The dynamic response of the NG-Liquefier to the step changes of the process parameters is moderate and thus less critical for plant operation. Even at relatively large unbalances of demand and supply of refrigeration the necessary corrective measures for returning the plant into the original operational conditions were easily carried out by the operators.

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The graph nomenclature for Figure 6 to 8 is: T-out-HP-vap High pressure gaseous refrigerant stream temperature out of cold end of

the bundle T-out-HP-liq High pressure liquid refrigerant stream temperature out of cold end of the bundle T-out-HP-NG High pressure natural gas stream temperature out of cold end of the bundle T-lev-2 Shell side temperature in the upper part of the bundle T-lev-4 Shell side temperature in the lower part of the bundle DP-NG Pressure drop for natural gas stream DP-HP-vap Pressure drop for gaseous refrigerant stream

“Freeze Out” Of Heavy Hydrocarbons

Solidification of HHC has been experienced in the natural gas path of the upper bundle due to off-design operation of the HHC removal temperature.

The development of the pressure drop during such an operational period is shown in Figure 9. There had been an increasing build up of fouling in the upper bundle resulting in large pressure drops. The indication limit of the differential pressure transmitter is about 250 kPa and during the time period shown the instrument has been out of range for several periods. The figure also shows that the bundle was de-rimed or partly de-rimed during shut down periods.

At the beginning of the second test period, the NG-Liquefier was operated at off-design conditions caused by extensive fouling of the natural gas path of the Upper Bundle (pressure difference of approximately 1800 kPa at about 90 % load) due to “freeze out” of HHC at low temperatures. The middle bundle was used for liquefying the NG, whereas the upper bundle could only serve for sub-cooling the LNG. The temperature at the cold end of the middle bundle was about minus 110 °C and therefore about 50 degrees colder than at normal operation. Consequently, the NG-path of this bundle was largely filled with LNG instead of NG as normal.

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After de-riming the NG-path of the upper bundle, the NG-Liquefier was put back in service and operated slightly above 100 % liquefaction rate. All pressure drops returned to normal as experienced during the initial start-up in 1998. Thus the original thermal and hydraulic design performance of the SWHE was confirmed after three years of “Day to Day” operation. The pressure drop before and after de-riming is given in Figure 10.

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Forced Mal-distribution

To enable forced mal-distribution of the evaporating refrigerant, the liquid distributor tray above the middle bundle is divided into two parts which are individually fed from different liquid refrigerant expansion valves. One half is designed to handle 100 %

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refrigerant flow. The different tests were carried out by opening one valve and closing the other so that the entire refrigerant flow (except the part which flows down from the upper bundle) was routed to one half of the distributor tray. The mal-distribution tests were carried out at a wide spectrum of different liquefaction loads ranging from 50 to 102 % of design capacity.

The results from each mal-distribution test were analysed to evaluate the temperature distribution as well as the performance of both the affected bundle and the entire NG-Liquefier.

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At the beginning of the test (at 85 min.) the overall flow rates were kept constant while the flow to one half of the distributor tray was stopped. As shown in Figure 11 the temperature profile along the heat exchanger bundle was affected by the forced mal-distribution of liquid refrigerant. The temperature close to the top of the bundle dropped by about 2 to 3 °C whereas at the bottom of the bundle the influence was negligible. At a time of 120 min. the valve was opened again and all temperatures returned to the original values.

This temperature drop is an indication of the mal-distribution of the liquid refrigerant. But for this test assembly the liquid is redistributed along the heat exchanger length wetting the heat transfer area and therefore achieving a comparable performance as with normal distribution.

OPERATIONAL EXPERIENCE AND MECHANICAL INTEGRITY

After the successful first test period in 1998, PetroSA decided to operate the LNG Plant with the SWHE Cold Box instead of the PFHE Cold Box due to the robust behaviour and ease of operation experienced, especially at low plant loads. Due to the fact that this LNG plant supplies back up feed stock to the refinery, the operation has been periodically at a variety of different process parameters such as flow rate, pressures, refrigerant composition etc. Also the start-up conditions ranges from quite cold

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conditions (immediate re-start after a plant trip, “Cold Start-up”) to ambient temperature conditions (“Warm Start-up”) when back-up service was not required for a longer period.

An overview of the number of start-ups of the LNG plant is given in Table 3. Some data are missing for some of the periods, but nevertheless the complete number of warm start-ups exceeds 40 and the number of cold start-ups exceeds 70 over a period of 5 years. This by far exceeds the number of operational cycles for a SWHE in a base-load LNG plant.

Table 1: Operational overview for start-up of the LNG plant

Warm Cold (Approximately) Test period I 1 6 1999 12 18 2000 6 28 2001 -> April 2 11 Test period II 2 3 June 2001 – April 2002 ? ? April 2002 -> 12+ ? Sum documented 35 66 Most likely number of start-ups 40 - 50 70 - 80

In addition to the number and type of start-ups relevant process parameters have been

collected such as • Cool down rate of the SWHE Cold Box • Temperature differences between bundles and shell for evaluating the resulting

mechanical stresses • Production rate • Suction and discharge pressures of the refrigerant compressor • Settle-out pressure after trip or shutdown • Accumulation of liquid in the bottom of the SWHE after trip or shutdown

Operational data of the test periods as well as from the “Day to Day” operation clearly demonstrate that some of the start-ups have been rough. In less than three hours the SWHE Cold Box was cooled down from ambient temperature to almost minus 160 °C at the cold end of the Upper Bundle exceeding - of course – the recommended cool-down temperature gradients. As a consequence, the SWHE has been exposed to extremely rapid temperature changes during several of the start-ups. An example of an extremely fast start-up is given in Figure 12.

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Despite numerous start-ups and shutdowns as well as some rough start-ups leakages or tube rupture within the NG-Liquefier have not been detected after five year of operation. This proves mechanical integrity of the SWHE.

VERIFICATION OF MODELS FOR DYNAMIC SIMULATION OF SWHE

A dynamic SWHE simulation model, named DCoil, has been developed by Statoil /4,5/. The model performance has been compared to some of the experimental data from the second test period.

The main goal of the comparison between measured data and model predictions is to verify that the modelling is capable of describing the dynamic behaviour of the SWHE with sufficient accuracy. The measured data consist of uniformly sampled time series of the different process data at each 30 sec. Due to the manual sampling of the composition, the different streams are considered to have constant composition throughout the simulations. Each of the three bundles is treated separately in the simulations.

An example of the model verification is given in Figure 13. The results show that the predicted temperatures are generally in good accordance with the measured. The shell side outlet temperature of the lower bundle is the only exception. The deviation is assumed to result from using constant composition in the simulations, and general uncertainties in the measured flow parameters.

DCoil has also been benchmarked to commercial dynamic simulators. DCoil gives a more accurate description of the dynamic behaviour of a SWHE compared to models in conventional simulation tools, especially for the temperature profiles. DCoil is successfully implemented in a commercial dynamic process simulator.

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QUALIFICATION OF SWHE IN FLOATING ENVIRONMENT

The Statoil-Linde LNG Technology Alliance is now focussing on developing a technology for the realisation of floating LNG plants. As part of this a test program for verification of the performance of a SWHE in a marine operation environment has been started. The main focus of the verification program is:

• Investigation of effect from stationary tilt and continuous movements on SWHE

performance • Determination of fluid flow mal-distribution and impact on heat transfer

To achieve the objective a test program has been established where:

• Characterisation of the real movements of different floater concepts in varying wind, wave and current conditions

• Experimental investigation of fluid flow in a small scale SWHE model at different bundle inclinations by use of a hydrocarbon model fluid

• Experimental investigation of hydrodynamic- and heat transfer-behaviour in a multiple layer lab-scale SWHE at different incline and moving conditions by use of a hydrocarbon fluid

• CFD modelling of shell side fluid flow distribution

An industrial scale SWHE, with 10 % base-load LNG plant capacity is planned to be installed in a commercially operated LNG plant and tested at realistic tilt and roll conditions during 2006. A complete test program including recalculation of the heat and mass balance and of the performance of the SWHE will be established.

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CONCLUSIONS

The tests in Mossel Bay, South Africa represent an important step in the qualification of Linde Spiral Wound Heat Exchanger (SWHE) for base-load LNG plants. This NG-Liquefier was installed in parallel to an existing Plate-Fin Heat Exchanger (PFHE) Cold Box of a Linde build LNG plant for Moss Gas Refinery.

Results from both the two test periods and the experience from the “Day-to-Day” operation confirm that the Linde SWHE met all key success criteria preset by the Statoil-Linde Technology Alliance. Through a wide range of industrial scale testing, a thorough understanding of the behaviour of SWHEs for natural gas liquefaction was gained regarding both normal and upset operating conditions. Due to the ease of operation and robustness of the SWHE, PetroSA decided to use the SWHE Cold Box instead of the existing PFHE Cold Box after the successful first test period.

As the NG-liquefier in the Mossel Bay LNG plant has been in operation since the first start-up in November 1998 an excellent mechanical integrity has been demonstrated at extreme operation conditions characterised by:

• Numerous scheduled start-ups and shutdowns exceeding vastly the number of operating cycles of a SWHE in a commercial operated base-load LNG plant

• Additional trips caused by upset conditions of the pre-treatment section of the plant

The Linde SWHE has already been selected for new LNG developments and as replacements in a number of worldwide LNG projects:

• North West Shelf, Australia – Two (2) SWHEs for the Train 4 of C3MR

• Snøhvit LNG, Norway – Two (2) SWHEs and two (2) PFHE-assemblies arranged in a very large Cold Box for the Mixed Fluid Cascade (MFC®) process

• Brunei – Four (4) SWHE replacements in existing trains of C3MR

• Sakhalin, Russia – Eight (8) SWHEs for two new trains of DMR

The tests related to mal-distribution facilitated the establishment of an adequate test program for qualifying SWHEs in floating environment in order to reduce technical risks to such a level enabling to launch a world-scale LNG FLPO project.

The joint Statoil-Linde Technology, consisting of design and manufacturing of SWHE and licensing of MFC® process technology is a good basis for commercialising the first floating LNG plant.

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Figure 14: Transport of base load SWHE’s from the Linde workshop to site

ACKNOWLEDGMENTS

The authors would like to thank PetroSA (former Mossgas) in Mossel Bay, South Africa, for their permission to install a new cold box in the existing LNG plant. They also would like to thank the plant supervisors and the plant operators for their excellent support during the different test periods.

REFERENCES CITED

1. W. Förg, W. Bach, R. Stockmann, Linde AG and R.S. Heiersted, P. Paurola, A.O. Fredheim, Statoil: A New LNG Baseload Process and Manufacturing of the Main Heat Exchangers. LNG 12 Conference, Perth, May 1998

2. R.S. Heiersted, Statoil ASA: Snovit LNG Project - Concept Selection for

Hammerfest LNG Plant. Gastech 2002, Qatar, October 2002 3. M. Steinbauer, T. Hecht, Linde AG: Optimised Calculation of Helical-Coiled

Heat Exchangers in LNG Plants. Eurogas 96, Trondheim, June 1996 4. Dr. G. Engl, Dr. H. Schmidt, Linde AG: The optimization of natural gas

liquefaction processes. Progress in Industrial Mathematics at ECMI 96 5. S. Vist, M. Hammer, H. Nordhus, I. L. Sperle, G. Owren and O. Jørstad,

“Dynamic modelling of spiral wound LNG heat exchangers – model description”, AIChE spring meeting, New Orleans, 2003

6. M. Hammer, S. Vist, H. Nordhus, I. L. Sperle, G. Owren and O. Jørstad,

“Dynamic modelling of spiral wound LNG heat exchangers – comparison to experimental results”, AIChE spring meeting, New Orleans, 2003