System Design

The above figure shows a Process Flow Diagram for a typical Twister® System. Twister is a low temperature separation process, for which performance can be optimised by inlet cooling. This can be achieved by heat integration using the cold gas exiting Twister, supplemented with air or seawater cooling if required. The inlet separator upstream of the Twister tubes is designed to remove produced liquids and prevent carry-over of slugs and solids. In designing a gas conditioning system based on Twister technology, the following issues need to be considered:

• Twister is a fixed actual volumetric flow device. The gas velocity at the throat of the inlet nozzle will always be exactly Mach 1, fixing the flow through the tube. Some turndown flexibility can be achieved by adjusting the operating pressure. However, a typical Twister system will include multiple Twister tubes connected together to provide the required turndown flexibility.
• Twister is a pressure ratio device. For any design pressure, the gas will expand to 30% of feed pressure mid Twister and will recompress to 65 to 80% of the feed pressure on exiting Twister. Higher pressure drops may be required for efficient NGL recovery.

The adjacent figure shows a typical layout developed for an offshore application. Up to six compact Twister tubes, each with a capacity of up to 3 million Sm3/d (105 MMscfd), can be mounted in a vertical position on a vertical liquid degassing vessel. This compact, low weight arrangement provides a revolutionary gas conditioning solution for unmanned minimum facilities platforms and can be a key enabling technology for de-bottlenecking existing space and weight constrained platforms.