SUPERSONIC GAS CONDITIONING FIRST COMMERCIAL OFFSHORE EXPERIENCE ABSTRACT

Transcription

1 SUPERSONIC GAS CONDITIONING FIRST COMMERCIAL OFFSHORE EXPERIENCE Job M. Brouwer MSc. Twister BV Rijswijk, the Netherlands Gonneke Bakker MSc Twister BV Rijswijk, the Netherlands Huib-Jan Verschoof MSc Twister BV Rijswijk, the Netherlands Hugh D. Epsom BTech FIMechE Twister BV Rijswijk, the Netherlands ABSTRACT Twister is a revolutionary gas conditioning technology which has been under development for natural gas applications since Condensation and separation at supersonic velocity is the key to some unique benefits. An extremely short residence time prevents hydrate problems, eliminating chemicals and associated regeneration systems. The simplicity and reliability of a static device, with no rotating parts and operating without chemicals, ensures a simple facility with a high availability, suitable for unmanned operation. Full scale test units have been operational since 1998 at five gas plants in the Netherlands, Nigeria and Norway, with varying gas compositions and operating conditions. The first commercial offshore Twister application successfully started-up in December Twister has been selected by Petronas and Shell for the gas dehydration process of B11, a large gas processing platform 120 km offshore Malaysia. The B11 field produces 600 MMSCFD of sour non associated gas feeding the Bintulu LNG plant. The B11 Twister design, including the Twister tubes and Hydrate Separators, and the effects on the overall plant design, will be discussed together with the recent start-up and operating experience of the B11 plant. Its simplicity makes Twister a key enabling technology for subsea gas processing. An update will be provided on Twister s joint industry project for subsea development and pilot testing. 1/16

2 SUPERSONIC GAS CONDITIONING FIRST COMMERCIAL OFFSHORE EXPERIENCE INTRODUCTION Twister is a revolutionary gas conditioning technology which can be used to condense and separate water and heavy hydrocarbons from natural gas. Current applications include: 1. Dehydration 2. Hydrocarbon Dewpointing 3. Natural Gas Liquids extraction 4. Heating Value Reduction. New applications under study include offshore fuel gas treatment for large aero-derivative gas turbines, pre-treatment upstream of CO2 membranes and bulk H2S removal upstream of sweetening plants. The Twister Supersonic Separator has thermodynamics similar to a turbo-expander, combining expansion, cyclonic gas/liquid separation and re-compression in a compact, tubular device. Whereas a turbo-expander transforms pressure to shaft power, Twister achieves a similar temperature drop by transforming pressure to kinetic energy (i.e. supersonic velocity). 1. A Laval nozzle is used to expand the saturated feed gas to supersonic velocity, which results in a low temperature and pressure. A mist of water and hydrocarbon condensation droplets will form. 2. A wing placed in the supersonic flow regime will generate a high vorticity swirl (up to 300,000g), centrifuging the droplets to the wall. 3. The liquids are split from the gas using a cyclone separator. 4. The separated streams are slowed down in separate diffusers, recovering 65-80% of the initial pressure. 5. The liquid stream still contains slip-gas, which will be removed in a compact liquid de-gassing vessel and recombined with the dry gas stream. Expander Cyclone Separator Compressor Saturated Feed Gas Dry Gas 100 bar, 20C (1450psi, 68F) Laval Nozzle 30 bar, -40C (435psi, -40F) Supersonic Wing Mach 1.3 (500 m/s) Cyclone Separator (300,000g) Diffuser Liquids + Slip-Gas Figure 1 Cross-section of a Twister tube 70 bar, 10C (1015psi, 50F) 70 bar, 0C (1015psi, 32F) Condensation and separation at supersonic velocity is the key to some unique benefits. The residence time inside the cold Twister Supersonic Separator is only milliseconds, allowing hydrates no time to form and avoiding the requirement for hydrate inhibition chemicals. The elimination of the 2/16

3 associated chemical regeneration systems avoids harmful BTX emissions to the environment. The simplicity and reliability of a static device, with no rotating parts and operating without chemicals, ensures a simple facility with a high availability, suitable for unmanned operation in harsh and/or offshore environments. A Twister tube designed for 60 MMscfd at 150 bar is only 2 meters long inside a 6 casing. The compact and low weight facilities can be installed on an unmanned, minimum facilities platform, not much larger than a simple wellhead platform. Although a relatively new technology, extensive operating experience has been obtained with commercial scale test units in five different gas plants in the Netherlands since 1998, in Nigeria since 2000 and in Norway since These test units have proved the viability of gas conditioning to typical pipeline specifications as well as the practicality of reliable, safe and unmanned operation. B11 CONCEPT SELECTION Petronas and Sarawak Shell Berhad (SSB) successfully started up the first commercial Twister system on December 30 th The two Twister gas dehydration trains have a combined capacity of 600 MMSCFD. Each train comprises six Twisters and one Hydrate Separator. In 1999 a feasibility study was carried out by the Twister Venture Team, the predecessor of Twister BV, at the request of Shell Sarawak Berhad (SSB) to evaluate the application of Twister technology in the development of the B11 field Offshore Sarawak, Malaysia. Originally SSB s base case development of the field was based on the concept of wet gas evacuation, corrosion in the carbon steel evacuation system being managed through the injection of corrosion inhibitors. During the study, the base case development concept changed in favor of dry gas export using traditional TEG dehydration technology offshore. This decision was driven by the risk of corrosion associated with the high CO2/H2S concentration as well as an opportunity to tie-in to an existing dry export line. The 600 MMSCFD produced and dehydrated on the new B11 platform had to be transferred, combined with dry condensate, through a new 65 km 24 CS pipeline to the already existing E11 riser platform (E11R-B). At E11R-B the gas and condensate was planned to be routed to shore via the existing trunk line network. The gas is feeding the existing Bintulu LNG plant, imposing a contractual system availability of 98%. The feasibility study showed that application of Twister technology compared to a TEG unit, allows the exported gas to be dehydrated with less complex, smaller, lighter, cheaper and emission free facilities. These are mainly resulting from the smaller foot print, reduced utility requirement and reduced or eliminated manning requirements. The high H2S concentration of 75-3,500 ppm was recognized as a major hazard to personnel and a strong incentive for unmanned operation. The cost comparisons showed a cost reduction of 24% for the production platform topsides compared to the base case costs. Lifecycle cost reductions of over 40% were identified for an unmanned platform. The principal disadvantage of Twister was the pressure drop requirement of about 30% which accelerated the need for field depletion compression. This could be mitigated to some extent by retrofitting the newly developed Twister internal design which provides a significantly reduced pressure drop. As part of the feasibility study, tube tests were executed on a plant scale test facility to verify Twister performance for the B11 application. These tube tests showed that the required Twister performance could indeed be achieved. 3/16

4 To reduce the uncertainties and materialize the Twister based plant design, a conceptual design phase started in 2000 resulting in the decision to build a Twister based platform for B11. During the concept design phase a test installation incorporating the B11 Twister plant concept, was built in Leermens (part of the Groningen field in the Netherlands). The operational experience obtained from this plant resulted in some small design adaptations which ultimately enabled a smooth start-up and operation of the B11 plant. B11 PROCESS DESIGN The B11 platform has a design capacity of 600 MMSCFD (17 million Nm3/d). The well stream contains 7-20 mol% CO2 and ppmv H2S. The water dewpoint specification of the combined gas and condensate export stream is 14C at a pressure of 119 bara based on a minimum seabed temperature of 19C. The pipeline normal operating pressure is between 94 and 104 bar. Figure 2 shows a process flow diagram of the B11 gas dehydration system. Gas drying is achieved in two parallel Twister dehydration trains. The produced hydrocarbon condensate (33 bbl/mmscf) is separately dehydrated and recombined with the export gas. Produced water (<6 bbl/mmscf) is reinjected offshore. 104 bar/5c <7C water dewpoint Twister 6X Twister BV scope of supply Well-stream 155 bar/125c 40C 25C LTX 104 bar/15c Air-Cooler GGHX Inlet Sep W 30C W Coalescers for condensate dehydration W <275 ppm free water in condensate 104 bar/30c <14C water dewpoint Export Figure 2 - Process flow diagram for B11 Gas from the wells arrives at the platform with pressures between 160 bar and 145 bar and is cooled from 125C to 40C using air-coolers. Further cooling to 25C is achieved by gas/gas cross-exchange against the cold gas exiting Twister. The liquids from the reservoir and the condensed liquids are separated in the inlet separator. The gas is then routed to one of the two parallel Twister trains. Each Twister train has 6 (including 1 spare) parallel tubes. In the Twister tube the gas is expanded and swirled to condense and concentrate the liquids. Each Twister tube has two outlet streams, a dry primary stream and a mixed secondary stream. The secondary stream from each Twister tube is fed into a 3-phase LTX type Hydrate Separator, equipped with heating coils to melt hydrates. The Hydrate Separator overhead gas recombines with the dry gas leaving the Twister tubes. The combined gas from the Twister trains has a water dewpoint of 7C at a pressure between 97 bar and 107 bar. Fiscal metering of the gas is executed after gas/gas exchange before exporting. 4/16

5 The free water in condensate from the inlet separator and Hydrate Separator is removed in a combination of tilted-plate and porous media coalescers designed to meet 275 ppmv free water in condensate. After fiscal metering, the dry condensate is re-combined with the dehydrated gas export stream. As the Twister tubes are effectively fixed flow rate devices, the flow is set by the number of tubes which are on-line. When making a change to the flow rate, tubes will be brought on- or off-line as required. B11 EQUIPMENT The wet and H2S/CO2 rich gas imposes stringent material requirements. All equipment and piping which can be in contact with wet gas are made from, or clad with, Incoloy 825. This is valid from plant inlet up to the cold outlet of the gas/gas heat exchanger. The Twister tubes are constructed from Inconel 625 and the secondary Hydrate Separators from low temperature carbon steel with internal Inconel 625 cladding. The Twister tubes have a design pressure of 175 barg (1500#) which is equal to the design pressure of the upstream system. The Hydrate Separators and all downstream equipment have a mechanical design pressure of 119 barg (900#), equal to the export pipeline design pressure. Air cooler The air cooler is designed to cool the (mixed) well fluid to an outlet temperature of 41C by ambient air, design temperature of 33C. Accurate temperature control is installed to avoid hydrate blockages in the downstream system. The air cooler is located on a dedicated platform top deck. The cooler type selection was subject to a study to compare direct or indirect seawater cooling with air coolers. Seawater cooling requires less space and could achieve lower gas outlet temperatures. However the fouling risk in case of direct seawater cooling was considered to be unacceptable while the costs of indirect seawater cooling were estimated as higher than for air cooling. Therefore air coolers were selected. Gas-gas heat exchanger The air-cooled gas is further cooled by heat exchange with the cold dehydrated gas. The gas outlet temperature is set as low as possible to improve Twister performance, however entering the hydrate region has to be avoided. The selected design outlet temperature is 25C, which provides a margin of 5C over the expected hydrate formation temperature of 20C. The cold gas enters the heat exchanger at a temperature of about 10C. The hot outlet temperature is controlled by a bypass on the cold side. The heat exchanger is of the shell and tube type and designed as 2 shells in parallel and 2 shells in series. The hot 2-phase fluid flows into the tubes. The design is slightly different from a standard gas/gas heat exchanger due to the hydrate risk. The hot shells have a normal counter current design and the cold shells are co-current to remain above the hydrate formation temperature in any part of the tube. Both shells in series have the same external dimensions and are placed on top of each other. The selection of 2 parallel sets of exchangers is only based on material handling criteria. Production separator The first separator in the plant is the production separator located downstream of the heat exchanger. According to the specifications, no particles or slugs from the wells are expected during normal operation. All produced liquids from the reservoir, and the liquids condensed during cooling, are 5/16

6 separated in this separator. The water load will increase over time, until depletion compression is installed. The separator should protect the Twister tube against particles which could impact on the tube internals causing erosion and also against liquid overloading. Therefore the vessel should be able to remove 99% of the liquids and remove solids. The vessel type selected is a 3-phase separator of the SMSM type (Schoepentoeter-Mistmat-Swirldeck-Mistmat), with a diameter of 2.1 m and a height of 8.3 m. The alternative for this type of vessel is a Gasunie separator which will have lower weight and space requirements. This vessel is more adequate to remove smaller particles, however is less suitable for 3-phase separation. Twister tubes Figure 3 shows a cross section of the Twister tube. The B11 platform includes two 60% Twister dehydration trains; each train has six tubes located around an LTX type Hydrate Separator. Normally five of the six tubes per train are in operation; the sixth tube is an installed spare. The Twister tubes are constant volume devices, therefore the capacity of each tube depends on tube inlet pressure, inlet temperature and gas composition. The design throughput fluctuation per tube is MMSCFD per tube. Laval nozzle Wing section Vortex finder Liquid drainage Treated gas diffuser Figure 3 Cross section of B11 Twister tube Although the Twister train could operate with just one tube in use, the plant is designed for a turndown of not less than 30%, so the minimum number of tubes in operation is 3. In the B11 plant vertical Twister tubes are deployed to minimize the space required by the Twister equipment. The feed gas leaving the inlet separator enters the top of the Twister tubes and flows downwards. 6/16

7 Inside the Twister tube the gas expands in the Laval nozzle, causing the gas to accelerate to supersonic velocities. The resulting pressure within Twister could be about 50 bar with a corresponding temperature of -40C. These conditions initiate condensation of water and hydrocarbons. The swirl created by the wing in the supersonic gas forces the liquids to the tube wall. This liquid film is removed with the slip gas (about 33% of the main stream) via a co-axial tube, called a vortex finder. This fluid is the secondary stream. The dry gas leaves the tube as the primary stream. In the tube, downstream of the wing section the gas is decelerated to subsonic resulting in a shock wave. The preferred location of the shock wave is just upstream of the vortex finder. The location of the shockwave can be controlled by manipulation of the vortex finder and by manipulation of the control valve in the downstream primary flow line. The vortex finder position is variable and can be adjusted in the field. This is especially important in case of significant changes in composition and operating conditions. Hydrate Separator The operating conditions of the secondary separator are well within the hydrate formation regime. A compact and highly efficient vessel design has been developed based on conventional LTX technology, using heating coils to melt the hydrates. Both dehydration trains include one such Hydrate Separator in which the secondary streams of six Twister tubes are connected. The vessels are capable to process secondary flow of up to six tubes simultaneously. Top view Twister Gas Twister Heating medium Cond. Hydrate Water Condensate Water Figure 4 3-phase Hydrate Separator The separators are vertical low temperature mono-cyclone separators of the LTX type equipped with various heating coils to melt the hydrates in the vessel. The vessels have a liquid removal efficiency of 99% ensuring that no hydrate blockages in the vessel overhead line will occur. Hot oil is used as the heating medium. The secondary outlet of each Twister tube is directly connected to the secondary separator via a tangential inlet nozzle. The velocity in this nozzle is such that hydrates can not accumulate. The centrifugal forces separate the liquids and hydrates from the gas and drop into the centre part of the 7/16

8 concentric bottom compartment. The top section of the vessel is separated from the bottom section by the deflector head. The central part of the bottom compartment contains a mixture of condensate, hydrates and water. The condensate will flow over the weir, while the hydrates drop down and are melted by a submerged heating coil. The water temperature is kept at 25C (about 5C above the hydrate formation temperature). The separation between the top and bottom compartment is such that evaporation of the liquids is minimized. Heating of the vessel walls prevents hydrate accumulation on the walls. The gas temperature in the Hydrate Separator vessel is typically 10C. The pressure in the vessel is in the range of bar, which is about 30% lower than the inlet pressure of the Twister tubes. Condensate dehydration unit The condensate flows from the inlet separator, and from the Hydrate Separators, are dehydrated separately to a free water content of maximum 275 ppmv. Condensate separated from the inlet separator is dehydrated by a combination of tilted plate and porous media coalescers to dry the condensate to the guaranteed free water content. The condensate produced in the inlet separator amounts to about % of the total condensate production. This part of the condensate dehydration system is designed to process about 30% of the water received in the inlet separator. The condensate from both Hydrate Separators contains a small amount of water. The Hydrate Separator condensate is dehydrated in a porous media coalescer. Although the Hydrate Separator vessels are designed to achieve 1000 ppmv water in condensate, the coalescers are designed to remove all the water produced in the Hydrate Separator. Both porous media coalescers are Pall type Phasesep LCS4H1AH. This coalescer type should be able to achieve an even better performance than currently required, provided that vessel operation is smooth and without contaminants. The condensate is boosted to a pressure slightly above the inlet pressure to ensure vapor free condensate metering and sufficient overpressure for spraying into the export line. B11 PROJECT EXECUTION Performance Test The B11 test was carried out by two separate tests, namely the Duration Test and the Performance Test. The objective of the duration test was to meet customer minimum requirement of 400 running hours. The test achieved running hours of 722 hours even with non-twister related shutdowns over the weekends. The internals of the Twister tube were inspected by a third party and visual verification by the customer site team was carried out. The performance test demonstrated that the water dewpoint suppression required for the B11 application could be easily met. The test report concluded that the Twister technology had been demonstrated to be technically satisfactory for application on the B11 development. Prototype Testing A prototype of the B11 Twister system design including two Twister tubes and Hydrate Separator was commissioned at the NAM operated Leermens plant in the Netherlands in early 2002 and performance testing was successfully completed at the end of During the testing the actual mechanical loads and vibrations inside the Twister tube were measured under various process conditions and confirmed to be well within the design envelope. Also the performance of the Hydrate Separator vessel was extensively tested and the tests showed that the Hydrate Separator is able to separate the liquids from the slip gas leaving the Twister tube with an efficiency >99%. Moreover duration tests 8/16

9 showed that the presence of hydrates in the Hydrate Separator is properly managed by applying sufficient heat at the right places as a result of which the Hydrate Separator can be operated reliably and in a stable mode without the need for hydrate inhibition chemicals. The testing also showed that an entire gas dehydration system consisting of multiple Twister tubes, a Hydrate Separator as well as the interconnecting piping, instrumentation and controls can be operated successfully. Figure 5 Twister pilot plant in the Netherlands Design, Manufacturing and supply of Twister and Hydrate Separator Proprietary, calibrated Computational Fluid Dynamics (CFD) models were used to design the Twister tubes for SSB, accurately modeling the supersonic, multi-phase flow behavior and thermodynamics inside the Twister tubes. These exclusive CFD codes were developed and validated inhouse to solve real gas, multiphase flows with condensing and evaporating fluids and are unique. For the support of Twister BV in the design, manufacturing and supply of both the Hydrate Separator and the Twister tube, technical expertise has been sought from a wide range of international specialist contractors: SGSi (gas facilities conceptual design support) Jacobs Engineering (gas facilities conceptual design support) Stork (mechanical design Twister) Menzing (Twister internal manufacturing) Verolme IJsselmonde (Twister Casing detail design and manufacturing) KNM (Hydrate Separator detail design and manufacturing) Installation and Commissioning In order to ensure Twister equipment was properly integrated into the overall construction and to ensure that the Twister surrounding systems were constructed according to approved detailed design documents, Twister BV provided SSB with installation and commissioning support. The objective of the commissioning support was to ascertain that Twister related systems, not being part of the Twister hardware scope of supply, were constructed such that they would enable proper (measurement of) functioning of the Twister technology. The installation and commissioning assistance took place both on shore, at the construction yard, as well as offshore. During the post commissioning phase the first goal was to bring the Twister inside the design envelope and confirm the proper functioning of supporting 9/16

10 systems as soon as possible. Once this was established, the actual fine tuning of the Twister hardware took place. Figure 6 - B11 production platform (right), wellhead platform and drilling rig Training In view of the novelty of this equipment, trained SSB operators capable of operating the Twister system with minimum vendor support was seen as crucial to the overall success of the B11 project. Therefore intensive training of SSB operators was provided by Twister BV, both at the Leermens test site in the Netherlands as well as offshore on the B11 platform. Maintenance and Operations support The first three years of operation, Twister BV will provide SSB with manpower and materials to support and maintain the process guarantee, guaranteeing 98% availability and performance to gas specification. The support will consist of data collection, on-line remote monitoring and analysis of Twister performance using a state of the art, web-based infrastructure, accessing local process data in real time, as well as inspection of the Twister hardware in order to continuously improve the performance of the entire gas treatment facilities and enable optimal operation. 10/16

11 B11 TWISTER PERFORMANCE Plant conditions The B11 plant started-up on 30 December 2003 and has been running up to now (beginning of March 2004) with just minor incidental shutdowns for concurrent construction and commissioning activities. Plant conditions during this initial period of operation can be summarized as follows: The plant design capacity is 600 MMSCFD, this throughput is currently not yet achievable as not all wells are available. Also the downstream LNG processing plant puts some limits on B11 production. The maximum throughput up to now has been 420 MMSCFD with 7 Twister tubes in operation. The minimum stable plant throughput up to now has been 120 MMSCFD with 2 tubes in operation. The amount of H 2 S and CO 2 contaminants is in the low range of the design, respectively 20 to 75 ppmv H 2 S and 7 to 9 mol% CO 2. The amount of heavy components in the feed is less than design, however with a longer heavy tail. Current condensate production is about 15 bbl/mmscf. Water production is at the design limits of 6 bbl/mmscf. The plant inlet pressures vary between 130 and 160 bar, depending on export conditions. Twister tubes Twister tube performance closely matches the design: the optimum gas slip stream quantity is about 33% of the main stream, tube operation is not affected by smooth variation of the inlet pressure and the tubes quickly recover from fast pressure dips and peaks. for a Twister inlet temperature of 25C, the mixed gas (secondary plus primary) temperature is about 10C. The pressure drop over the Twister system is only slightly (2 bar) higher than specified. It is expected that this pressure drop will be reduced as part of the Twister optimization activities. Hydrate Separator performance The gas/liquid separation of the secondary LTX type Hydrate Separator is well within the design limits as no hydrate build-up in the separator overhead system has been detected and no negative impact on the water dew point of the dry gas has been observed. Liquid drainage, liquid/liquid separation efficiency and prevention of hydrate carry-over into the condensate system rely on continuous heat supply. The heat duty required for smooth separator operation is about 300 kw per train (300MMSCFD), which is well below the (conservative) original design. It is likely that further optimization could reduce this figure. Product quality Karl Fisher type dew point spot checks indicate a water content of the product gas of 150 ppmv (115 mg/sm3), which ensures a water dew point of 2 to 5C (depending on which equation of state used), well below the specification of 7C. The on-line (continuous) Hygrophil dew point meter indicates that this value is not exceeded, even during incidental process upsets. Incidental dew point verification with Shaw and Panametric probes showed the same results. Although the condensate dehydration is not part of the Twister system, its performance affects the performance of the overall plant. Spot check measurements indicate a water in condensate fraction within the design range (275 ppmv). However, as condensate properties are different from design, this subject needs further investigation. 11/16

12 Ongoing optimization Commissioning and fine-tuning of the total Twister system is nearing completion. However, the following optimization activities are still ongoing: The robustness of the system downstream the Twister tubes and secondary vessels is currently being optimized to cope with operational upsets. Hydrates may occur once operating outside the design envelope and once present take time to remove. Tube settings are fine tuned to achieve stable operation at minimum pressure drop. The Hydrate Separator heat supply could be optimized such that hydrates are prevented for all conditions and throughputs, but with minimum heating duty. B11 EVALUATION B11 Challenges During the execution of the B11 project various challenges have been faced, of which two will be highlighted here. Firstly, the application of a new technology requires an open mind from all parties involved, especially as it involves one or more new design concepts. During project execution, Twister BV, SSB and the contractors involved were exposed to a number of unique problems requiring novel solutions. Close cooperation between SSB, Twister BV and the other contractors as an integrated team proved to be a key success factor. Secondly, since the scope of supply for Twister BV excluded many equipment items which are critical to the overall Twister system performance, interface management was crucial and extremely challenging for both SSB and Twister BV. Functional descriptions and technical requirements had to be defined for all critical systems prior to construction by SSB s contractors. From a performance guarantee and project efficiency perspective, the Twister BV scope of supply should in future, preferably, be an integrated Twister module including gas-gas heat exchanger, inlet separator as well as all interconnecting piping, valving, instruments and controls. Technology upgrade Although Twister is a mature technology, an extensive research and development program is in place to further improve the Twister performance envelope. An exciting development is the second generation Twister technology (patents pending). The working principles are similar to that of the current Twister, so the same benefits apply. The main difference is that the swirl is generated at the inlet of the tube whilst in the current Twister the swirl is generated in the high speed section in the middle of the tube. Principle improvements include enhanced separation efficiency due to the higher speed, concentric vorticity, elimination of re-evaporation, as well as the reduction of pressure losses. The pressure drop over the Twister can be reduced to 20-25%. Analysis with validated CFD models has been completed confirming a step change performance improvement. Field testing is scheduled towards the end of 2004 with market launch thereafter. The Twister tubes installed at B11 can be upgraded with this second generation Twister technology. The new technology is expected to lower the required pressure drop from 30% to 20-25%, reducing and postponing the requirement for depletion compression. 12/16

13 Optimization areas Not all potential benefits of the adoption of the Twister process were fully implemented on the B11 platform as it is the first commercial plant equipped with Twister Supersonic Separation. The inherent space and weight savings resulting from the Twister process are not fully visible on the B11 plant as other (external or third party) design requirements required a significant amount of additional equipment, reducing the impact of Twister on the platform design. The main items affecting weight and space thus costs - which might not be needed in other plant designs are: The complete manning facilities required for future depletion compression were installed on B11. If this was not required, a saving of living quarters, including the related utility facilities and workshops, could have been achieved. Application of an LTX type Hydrate Separator as a secondary separator is only required if hydrate formation is expected. If required, the Hydrate Separator could also be designed as a 2-phase separator, thus simplifying the vessel design, control and heating facilities and minimizing weight and footprint. See figure 7 for a schematic as well as a Computational Fluid Dynamic (CFD) analyses used to optimize the Hydrate Separator mono-cyclone design. Unique CFD codes have been developed and validated in-house to solve real gas, multiphase flows with condensing and evaporating fluids. Top view Twister Gas Pressure let-down valve (alternative) Heating medium Water & Condensate Figure 7-2-phase Hydrate Separator including CFD analysis of the mono-cyclone top section Note that the Hydrate Separator could also be used to manage hydrates downstream of the pressure let-down valves as indicated in figure 7. Air coolers are applied on B11 for the gas cooling. These air coolers require a significant amount of space and have to be located on the top deck. If fouling risks can be mitigated, the use of seawater cooling (direct or indirect) could be advantageous. The ongoing development of an innovative self cleaning seawater cooler presents a promising approach to managing scaling and bio-fouling in direct seawater cooling applications. The principal is based on a fluidized bed of solid particles, continuously cleaning the heat exchange area. See figure 8 for a schematic. 13/16

14 Figure 8 - Self Cleaning Heat Exchanger Condensate is re-injected in the export pipeline and needs to be dehydrated. Condensate processing requires a significant amount of equipment which is avoided if the condensate is reinjected into the reservoir. This could be an option for a very lean field where just small amounts of condensate are produced. Optimization of the platform layout with the current knowledge of the B11 design could reduce the area for the current available process equipment by about 25%. If an integrated (drilling and production) platform design is adapted, significant savings could be achieved. TWISTER SUBSEA GAS PROCESSING UPDATE Simplicity and reliability are critical success factors in subsea applications. Twister scores high on both counts and is therefore widely recognised as the missing link for subsea gas processing and a key enabling technology for the development of currently uneconomical gas reserves. Twister BV, FMC Kongsberg Subsea and Shell Technology Norway have completed a joint study, sponsored by Demo2000 and Norske Shell, to investigate the feasibility of Subsea Gas Conditioning based on Twister technology [1, 2]. Several prospective gas field developments were studied confirming significant potential CAPEX savings of Twister Subsea Gas Processing compared to conventional development options. Although no show stoppers were identified, several components included in such a subsea processing plant need to be further developed and qualified prior to installation and operation on the seabed. 14/16

15 Figure 9 Subsea Gas Conditioning template including a Twister module. Twister BV, FMC and various other partners have secured an EU subsidy for a four year development program which will result in the design, construction, installation and testing of the first pilot Twister subsea gas processing installation by 2007/8. Operators are invited to contact Twister BV to discuss participation and possible pilot plant locations. CONCLUSION The first commercial Twister application successfully started operation in December 2003 on the Petronas/Sarawak Shell Berhad B11 platform offshore East Malaysia. The B11 application clearly demonstrates that Twister can be a highly competitive development option and that the commercialization of this technology constitutes an important milestone in obtaining industry acceptance. Second generation Twister technology promises a step change performance improvement with a significant reduction in pressure drop and may be retrofitted to the B11 platform. An EU subsidy has been secured for a four year development program which will result in the design, construction, installation and testing of the first pilot Twister subsea gas processing installation by 2007/8. Operator participation is being sought. ACKNOWLEDGEMENT The achievements presented in this paper would not have been possible without valuable input and support from many parties, most notably NAM, SPDC, SSB, Menzing Industriele Toelevering, Verolme Special Equipment, KNM Steel, Jacobs Engineering, Stork Product Engineering, Sime SembCorp Engineering and MMC Oil & Gas Engineering. 15/16

16 REFERENCES CITED Fred T. Okimoto, Marco Betting and David M. Page, Twister Supersonic Gas Conditioning, GPA paper, 2001 Twister BV and FMC Kongsberg Subsea AS, Demonstration of Twister for subsea application, REP , November, 2002 Fred T. Okimoto, Job M. Brouwer, Twister Supersonic Gas Conditioning Studies, applications and results, GPA paper, 2003 ABBREVIATIONS TEG = Tri-Ethylene Glycol MEG = Mono-Ethylene Glycol CRA = Corrosion Resistant Alloy CS = Carbon Steel LTS = Low Temperature Separator LTX = LTS with heating coils GGHEX = Gas/Gas Heat Exchanger CAPEX = Capital Expenditure OPEX = Operating Expenditure ppm = Parts per million CFD = Computational Fluid Dynamics 16/16