News Article

Novel Turboexpander Technology

May 27, 2022

Jeff Earl explains how a high-efficiency turboexpander-generator uses advanced magnetic technologies to enable waste-pressure energy recovery

Natural gas networks around the world use Joule-Thomson (J-T) valves to reduce line pressure upstream of city gas distribution. These mechanical valves are effective, but they generate significant amounts of waste-pressure energy, which can be captured and converted to electric power in a turboexpander-generator (TEG).

To that end, Sapphire Technologies (Sapphire), a spinoff from US-based Calnetix Technologies, has developed and deployed an integrated high-speed TEG system operating on advanced magnetic technologies. The system efficiently converts waste-pressure energy into electricity, which can be used locally
or sold back to the grid.

Advanced Magnetic Technologies

Sapphire’s FreeSpin In-line Turboexpander (FIT) system includes advanced active magnetic bearings (AMBs), a high-speed permanent magnet (PM) generator and a high-frequency variable-speed drive (VSD). As shown in Fig. 1, high-pressure gas flows into the FIT and expands through a radial turbine wheel. The gas’ kinetic energy drives the wheel to rotate, which spins a directly coupled PM generator. Current produced by the generator is transferred to the VSD, where frequency and voltage are regulated to match the local grid. After expanding through the wheel and passing through the FIT housing, the gas exits the FIT at a pressure and temperature required by distribution regulations.