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Steaming ahead with energy recovery
Steaming ahead with energy recovery

UK spinout company Heliex Power has found a way to help industry address one of its most enduring waste issues. Will Stirling reports.

Prof Dan Wright explains how wet steam compression works with the clarity of a man who has convinced board directors, MPs and apprentices alike how high-value engineering works and how it can make money. “I learnt early on that anything you make has  to make money,” he said, quoting ex-Ford vice- president Murray Reichenstein, who said that  it was money, not cars, that Ford made. Wright hopes to do that with Heliex Power, his latest company in an engineering career that spans four decades. Indeed, figures suggest there are more than one million customers for this clever energy reclaim technology in China alone.

A born engineer and petrol head, inventor and businessman Wright founded Heliex  in 2009, based on a technology he had investigated while at Howden Compressors, in Glasgow and Johnannesburg, in the mid-1970s with technical support from City University London. His resumé before Heliex reads  like a British engineering almanac. A degree  in aeronautical engineering from Glasgow University was followed by senior engineering and management positions at Ford, Formula One, Fleming Thermodynamics, Ogle Design, Johnston Sweepers, GKN Wheels, consultancy, government advisory and more.

Wright’s current company, Heliex, was spun out from City University in 2010 after City had developed screw expander technology that allowed the recovery of energy from waste  heat and low-pressure steam. Investment  came from BPAEI (BP Alternative Energy International) with a further chunk from Greencoat Capital in 2012.

The core technology is in the rotary screw expanders, which recover medium-grade energy from industrial processes and engine exhausts and convert this to clean electricity and thermal power via a simple thermodynamic cycle.

While high-pressure steam energy recovery is common in gas turbines, Heliex’s technology has a unique selling point, explained Wright: “Normally when power is generated from steam it is superheated – more high temperature than high pressure and therefore dry. You can put dry steam through turbines and have no ill effects. But if you put steam from lower-temperature sources into a turbine, it erodes the blades and causes failure.”

It may look fairly simple but these screw expanders are packed with technology. “The trick is that 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,” said Wright. So the Heliex 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 in a turbine – and other costly components. “We don’t need a gearbox; in fact we have a belt drive that reduces the 4,500rev/min down to 3,000rev/min, and it runs the alternator at synchronous speed – it is a constant-speed machine; this lowers the cost,” he added.

”You can put dry steam through turbines and have no ill effects. But if you put steam from lower-temperature sources into a turbine, it erodes the blades and causes failure. The trick is that the Heliex rotors are positive displacement and, due to the design of the profile, they are able to take in wet steam without suffering any erosion

Dan Wright, Heliex

While industry has known about the wet steam conundrum for many years, no one has come up with a satisfactory solution – until the specific profile of the rotors were developed contained within the expander body, which  can range in size from 160kW to 400KW.

The N profile of the rotors permit the  rotors to touch each other, using steam as  the lubricant, a capability discovered by City University, without any significant wear, again reducing the cost and size of the machine. Other advantages are that their weight and comparative simplicity means they are robust and low maintenance compared with some power reclaim technologies.

The applications include waste heat recovery (WHR) and machines used in parallel with existing pressure-reduction valves (PRV) in a plant. Wright articulates the business  case for the machines, showing the electrical output generated, annual revenue and carbon emissions saved.

 

For the PRV application, additional gas  is burned to power the machine, but there is  still a significant net annual saving from the electricity it produces.

Is the process efficiency reduced? Sometimes a company wants the thermal energy used by the generator replaced for its process. “It might look like we’re just extracting energy from the steam line when this energy is needed for the customer’s process, which is a flaw,” said Wright. “But we find that in 90 per cent of cases with this equipment, the amount of energy we extract and convert to electricity, the resulting energy reduction in the steam has almost no effect on the customer’s process. If the company want the steam energy restored to the levels before we installed, he [or she] has to burn more gas.”

Figures show this conversion rate is very efficient. An HP 145 generator extracts 119kWm (the gross shaft power output), provided to the customer as electricity but removed as thermal input to his or her process. If the customer needs this to be returned, the extra gas required in the boiler to create this energy is 132.9kW. The small difference in this enthalpy is very efficient compared with a thermal power station, Wright said.

The estimated payback period is from two  to five years. “In Italy, not only does [one of  our customers] get paid for electricity and  the thermal energy; they get tradable carbon certificates too, which is why they have fast payback,” he said.

The potential markets are head turning. Heliex claims that every type of industrial process – from chemicals to food and from power generation to chicken manure – produces steam that could have energy regenerated by these expanders. The company has customers in Ireland, Italy and the UK and  a healthy order book. Many of the parts are sourced in Scotland and the UK.

Heliex is enjoying a ‘global niche’, but  it needs to move fast. Spirax Sarco, which collaborated with Heliex for a couple of years, is supposedly developing a competitor machine, and further imitation always follows success. For now, Heliex has some protection: a patent on the screw rotor profiles that allows it to work with the steam as a lubricant, and patents on the thermodynamic, wet steam cycle.

 

This proper engineer is hoping screw technology will provide the late twist that his illustrious career deserves, while building an exporting green British engineering company to be proud of.