Schaeffler bearings selected for wet steam-to-energy generators

Cylindrical roller bearings and angular contact ball bearings are being supplied by Schaeffler to Glasgow-based Heliex Power for use on its 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.

Thermodynamic cycle

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 4500rpm, driving a 3000rpm 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 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 4500rpm down to 3000rpm. 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 200degC. Adds Alexander: "In our Heliex Systems, the function of the bearings is to ensure that the components inside do not clash. In particular, very accurate location is required of the two rotors relative to each other. No oil is present in our machines, although the bearings themselves are oil-lubricated: water vapour is the only lubricant, and so keeping the rotors accurately located is essential. The tolerance between the rotors and the housing is also extremely tight. Movement and back-pressure are critical and so the bearings supplied by Schaeffler are preloaded accordingly. The bearings are also heat stabilised [heat treated] to ensure they can withstand the large temperature ranges that our machines operate in."

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.

Machine development programmes

Mike Addington, Regional Sales Engineer (Scotland) at Schaeffler UK, says: "Schaeffler UK has been working closely with Heliex Power since the company was spun out from City University in 2010. Initially, we were heavily involved in the engineering design work relating to the optimisation of the bearing arrangements for the steam screw expander system. We are now supplying bearings on a regular basis to Heliex for its current range of machines, as well as looking at custom bearings for ongoing machine development programmes at Heliex."

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. Like Heliex, Schaeffler is both entrepreneurial and innovative in its approach and very open to joint development programmes for novel technologies, regardless of how large or small the customer is.

"As Heliex works at the leading edge of engineering technology, we do need support from suppliers like Schaeffler to provide us with custom engineered bearings for very specific applications, which you cannot simply purchase from a bearings catalogue. Having access to Schaeffler's test laboratories and knowledge of materials science is also extremely beneficial. This is where Schaeffler's strengths really come to the fore."