Twister Supersonic Gas Conditioning Process

Abstract

Twister Supersonic Separator is an innovative and revolutionary gas processing system. The Twister technology was developed by Shell. Twister B.V. was launched as a separate company in April 2000 by Shell Technology Investments Partnership, a 50/50 venture between Shell and the Beacon Group. Twister Supersonic Separator is the resulting synergy from combining aero-dynamics with the traditional gas processing concepts of thermodynamics and fluid dynamics. Twister is based on the following concepts (Figure 1):Gas is expanded in a Laval nozzle to supersonic velocities with resulting lower temperatures.Nucleation of water and hydrocarbon occur, followed by growth of liquid droplets.The gas and liquid droplets enter the wing section, where a very high swirl is created and the liquid droplets are centrifuged onto the walls, creating a liquid film.The gas and liquids are separated in the drainage section.Pressure is recovered in the diffuser section, to about 70– 80% of the initial pressure. This is done without chemicals or rotating equipment, and requiring minimum space and weight, thus saving significant capital and operating costs. Figure 2 shows the phase envelope of a natural gas and the water concentration curve. Twister is compared with the Joule-Thompson Valve and the Turbo- Expander. In this example all three processes have the same outlet pressure (sales pressure), which is typical for most applications. Joule-Thompson is an adiabatic process and the least efficient. Turbo-expander is near 85% isentropic efficiency, so it goes deeper into the phase envelope and uses its re-compressor to reach the outlet pressure. However, Twister has about 90% isentropic efficiency, so it goes the deepest into the phase envelope, then recompresses without rotating equipment to the outlet pressure. Twister is effectively a turboexpander/ separator/re-compressor all in one static piece of equipment. Thus, from a theoretical point of view, Twister has the most favorable thermodynamics. The challenge is to translate this theoretical advantage into the operations of actual gas plants.

An Axisymmetric Flow of a Mixture of Real Gases with a Condensing Component

“…An important problem is that of preliminary drying of gas (removal of steam) in wind tunnels or gas-conveying systems [1,2]. In a more general case, a number of components of a complex natural gas mixture need to be separated successively [3].…”

Trends in Supersonic Separator design development

“…The shock wave is generated by changing the velocity from supersonic to sonic speed. From here, the gas is slowed down in the diffuser that results in recovering about (65-80%) of the initial pressure [7].…”

“…Twister separator which is based on air drying device was originally developed by Stork Product Engineering BV in 1989 [18]. Twister BV company is a joint venture between the Beacon Group and Shell launched in the year 2000 for developing the first generation of supersonic separators, trademarked Twister [19]. This model used a deflecting blade in the supersonic section of the nozzle to generate the swirl required for condensed particles separation and is now referred to as Twister-I as illustrated in Fig.…”

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.…”