Bearings for rotary screw expander technology

Schaeffler is supplying cylindrical roller bearings and angular contact ball bearings to Glasgow-based company Heliex Power for use on its innovative range of screw expanders and generating sets, which recapture lost energy from ‘wet steam’ to generate electricity in an economically viable way.

Heliex Power’s screw expander technology enables the recovery of energy from waste heat and low-pressure steam found in numerous applications across chemicals, pharmaceuticals, farms, nurseries, glass, steel, distilling, district heating, textiles, food and drink, poultry and waste incineration plants.

Although harnessing energy from steam is nothing new, the key innovation in Heliex Power’s technology is that it can operate with standard industrial 'wet steam' – steam that often contains water droplets that would destroy traditional machines and generators. Due to its patented design, Heliex Systems can generate power, re-energise low pressure steam and drive machinery and air compressors by utilising a factory or building’s existing steam supply.

The Heliex System is a compact, rotary device that converts expansion energy from steam into useable clean electricity via a simple wet steam cycle – the simple thermodynamic cycle of a heat engine that converts heat into mechanical work. The heat is supplied externally to a closed loop, which normally uses water, or in this case steam, as the working fluid. Heliex Systems operate at 4,500rpm, driving a 3,000rpm asynchronous generator via a toothed belt transmission. In the case of the latest machine, the HP Steam Recompressor, they work in reverse. Having built more than 50 machines and achieved in excess of 120,000 operating hours, the Heliex steam screw expander technology is now proven and accepted across the conservative process industries.

Nick Alexander, Engineering Manager at Heliex Power comments: “The rotors are positive displacement and due to the design of the profile, they are able to take in wet steam without suffering any erosion. This means the expander generators can operate in lower-temperature, lower-quality steam regimes than are required for turbines. The design also eliminates timing gears because the screws do not need to reduce to the speed of an alternator as a turbine does. We also don’t require a gearbox – instead we have a belt drive that reduces the 4,500rpm down to 3,000rpm. It is a constant speed machine, which again lowers its cost.”

Bearings play a critical role in the performance of the screw expander machines. The bearings must withstand harsh operating conditions including high temperatures up to 200°C.

To date, Schaeffler has supplied hundreds of cylindrical roller bearings and angular contact ball bearings for use on both test and development machines at Heliex and for the current range of Heliex screw expander machines and generating sets.

On the larger range of screw expander machines, Schaeffler supplies four cylindrical roller bearings, one positioned at each end of the two rotor shafts. In addition, six angular contact ball bearings from Schaeffler are located at the end of each shaft to apply the required preload.

On the smaller Heliex machines, Schaeffler supplies two angular contact ball bearings for the main shafts and two smaller angular contact ball bearings to apply the necessary preload. There are also four cylindrical roller bearings in this machine – two on each shaft.

Dan Wright, CTO and founder of Heliex Power (pictured), recalls: “Where appropriate, Heliex uses bearings from Schaeffler on its screw expanders and generators. In my experience, Schaeffler is a good fit for Heliex Power. It has always provided good technical support when we need it and, unlike many industrial suppliers, is not bound by its product catalogue.”