In this article, we present a case published by Turck (2008) where we provided Simms Machinery International with Fluorosint® 500 for the rotor shrouds of their gas expander. Their high-tech compressor/expander for liquefied natural gas spins at over 60,000 rpm while cranking out nearly 950 hp (0,7 MW), thanks partly to abradable advanced polymer solutions, PTFE, on the rotor shrouds that lets fast-moving blade tips lightly touch the shroud without destroying either the rotor or shrouds.
This XXM turbo compressor/expander, an enhanced version of an older model, has better rotors that efficiently handle higher speeds and larger flow volumes. It is built by Simms Machinery International, Santa Maria, Calif. and sits in a UGI Energy Services plant near Reading, Pa. It works in a refrigeration cycle that condenses high-pressure gas from an interstate pipeline into LNG for storage at low pressures. A stream of gas, dried and precooled to 20°F (-6.6°C), goes into the expander-end of the machine at 840 psia (58 bar). It exits at 80 psia (5.5 bar) and –158°F (-105°C). The cold gas from the expander flows through a heat exchanger where it condenses and subcools a second gas stream that then flows through three stages of flash separation to reach the equilibrium temperature of –256°F (-160°C) in the LNG storage tank.
On the warm side of the exchanger, the expander discharge returns to the compressor-end of the expander/compressor where it is boosted to 160 psia (11 bar) and delivered into a pipeline that feeds a gas-distribution network. Energy extracted from the gas by the expander would otherwise be wasted in a pressure-regulating station where pressure would normally be reduced across a regulator or control valve.
The expander uses relatively tight rotor-blade-to-shroud clearances to boost efficiency. This increases the risk of rotor-to-shroud rubs that could cause catastrophic failures. To reduce this risk, Simms sought an abradable material for the shrouds that would let fastmoving blade tips make light contact without harm.
Mitsubishi Chemical Advanced Materials provided Simms Engineers with its innovative Fluorosint® 500-enhanced PTFE.
To better accommodate Simms’ requirements, we fabricated a set of prototype inserts for Simms to install and finish.
The incremental horsepower, made possible partly by the Fluorosint®, increased liquefaction at the original plant from 2.5 to 4.6 mmscfd (2790 – 5133 Nm³/hr@0°C) without adding fuel or power. Fluorosint® 500 on the rotor shrouds of the expander and compressor also reduced risks of mechanical failure.