TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractTwister™ is an innovative gas conditioning technology which has been under development for natural gas applications. 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, operating without chemicals, ensures a simple, environmentally friendly facility, with a high availability, suitable for unmanned operation. Full scale testing has been completed at five gas plants in the Netherlands, Nigeria and Norway, with varying gas compositions and operating conditions. The first commercial offshore Twister application started-up in December 2003 on the Petronas/Sarawak Shell Berhad B11 facility offshore East Malaysia. The key challenges and experience gained during the B11 Twister design, and operating experience to date, have resulted in some significant new developments. This includes the low pressure drop version of the Twister Supersonic Separator which also achieves a significantly improved hydrocarbon and NGL recovery performance. This improved performance has been confirmed during testing and details will be presented to describe the development, testing and initial commercialisation.Twister also has potential to be further developed for other specific future separation applications, such as deep LPG extraction, CO2, H2S and mercury removal, and for sub-sea gas processing.
Twister™ is a revolutionary gas conditioning technology which has been under development for natural gas applications since 1997. 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. Test results have been used to improve and validate sophisticated Computational Fluid Dynamic (CFD) models of the complex combination of aerodynamics, thermodynamics and fluid-dynamics. These CFD models have been paramount in improving Twister performance. Although Twister is a mature technology, Twister BV are developing a second generation Twister design promising a step change performance improvement and reduced pressure drop. Field testing is scheduled for early 2004 with market launch later that year. The first commercial Twister application will start-up in the 4th Quarter of 2003. Twister has been selected for the dehydration process of a large, offshore gas development in Malaysia. The Twister system design will be described. Its simplicity makes Twister a key enabling technology for subsea gas processing. The results of a joint industry feasibility study will be reported. Introduction Twister is a revolutionary gas conditioning technology which can be used to condense and separate water and heavy hydrocarbons from natural gas [1]. Current applications include:DehydrationHydrocarbon dewpointingNatural Gas Liquids extractionHeating value reduction New applications under study include offshore fuel gas treatment for large aero-derivative gas turbines, pre-treatment upstream CO2 membranes and bulk H2S removal upstream sweetening plants. The Twister Supersonic Separator has thermodynamics similar to a turbo-expander, combining expansion, cyclone 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). Error! Reference source not found shows the basic design concept: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.A wing placed in the supersonic flow regime will generate a high vorticity swirl (up to 300,000g), centrifuging the droplets to the wall.The liquids are split from the gas using a cyclone separator.The separated streams are slowed down in separate diffusers, recovering some 65–80% of the initial pressure.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
The efficiency of the gas/liquid separation process can have a significant impact on the economics of planned and potential oil and gas developments, as well as on the profitability of existing production operations.A new type of choke valve that improves the efficiency of downstream gas/liquid separators by enhancing the coalescence of dispersed liquids in a fluid stream has been developed recently by Twister. The initial field test of the technology, known as the SWIRL valve, was performed at a JT-LTS production unit operated by NAM in the Netherlands.The test demonstrated that the replacement of a conventional JT valve with the coalescing choke valve resulted in a significant improvement in the dewpointing performance of the gas-processing facility. This retrofit also allowed the maximum plant operating flow rate to be increased from 650 000 to 735 000 m 3 /d, while still meeting export gas specifications. It was additionally found that by using the coalescing valve, the temperature in the cold separator (SMSM type) could be increased by 4-5°C while still meeting specification, allowing a reduction of approximately 3 bars in the plant feed pressure. Furthermore, it was demonstrated during the field test that the glycol losses normally experienced were significantly reduced.This article presents the initial fieldtest results and an overview of the subsequent development and deployment of the coalescing-valve technology. Technology DescriptionPressure throttling in a conventional choke valve is achieved by dissipation of the kinetic energy present in the gas flow through randomly distributed eddies. The new coalescing valve, which was developed with the aid of proprietary computational fluid-dynamics models, uses the excess free pressure in a fluid stream to establish a coherent vortex motion. The total pressure inside the vortex core is gradually reduced along the axis of the flow path. By reducing the total pressure in a vortex flow, the flow shear rates are lower, compared with conventional chokes, thereby avoiding excessive breakup of liquid drops. However, and more importantly, these micron-size droplets are concentrated around the perimeter of the flow path, thus enhancing the coalescence to larger, more easily separable droplets.To assess the coalescence efficiency of the two different valve designs, analytical calculations and numerical analyses were performed. These data showed that the time to increase droplet sizes from 4 (nonseparable) to 20 micron (separable) is in the order of milliseconds for the coalescing valve, compared with several seconds for normal choke-valve designs. Fig. 1-a) Flow paths of conventional cage valve (left) and the coalescing cage valve; b) Liquid volume fractions for a conventional cage valve (left) and the coalescing cage valve.
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