Twister Supersonic Gas Conditioning for Unmanned Platforms and Subsea Gas Processing

Abstract

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

Applications of CFD in Natural Gas Processing and Transportation

“…Common design challenges in all gas processing methods for offshore applications are the compactness and reliability of process equipment. Supersonic nozzles have been introduced as an alternative to treat natural gas for offshore applications and to meet the offshore requirements (Hengwei et al 2005, Alfyorov et al 2005, Okimoto et al, 2002, Karimi & Abedinzadegan Abdi, 2006, Brouwer & Epsom, 2003. In a supersonic separator the gas temperature is lowered based on the principle of gas expansion where no refrigerant is needed.…”

Platform-Free Fields for Stranded Gas Development: Science or Fiction?

“…removal of water vapour, needs a special process involving temperature reduction below dewpoint to condensate water vapour and, then, a gas/liquid separation to remove the water. Brouwer and Epson [19] presented the Twister™ that uses a Laval nozzle to expand gas to supersonic velocity, resulting in a large temperature drop by 60ºC; a strong swirling velocity field produced by twisted wings in the nozzle subsequently removes the mist or hydrocarbon condensate from the gas phase. As the residence time is small due to supersonic velocity, little time is available for hydrate formation at the wall, which otherwise would be a major problem at low temperature.…”

Swirling Effects on the Performance of Supersonic Separators for Natural Gas Separation

“…Supersonic separation is a new technology to condensate and separate water and heavy hydrocarbons from natural gas, working on the two major principles of gas expansion and cyclone separation [2][3][4][5]. The supersonic separator prevents the hydrate problems and eliminates the need for inhibitor and regeneration systems due to the short residence time in the device, providing an environmentally friendly facility.…”

“…Alferov et al [8] introduced a technological process for the supersonic separator and compared the effectiveness of the 3-S separator, the Joule-Thomson valve, and the turbo-expander in extracting C 3 + from natural gas. Liu et al [9] described a supersonic swirling dehydration system for natural gas, and an indoor experiment was carried out to test the unit performance.…”