We’re always on the hunt for the latest and greatest technology that we can apply at our clients site to improve their site performance. We’ve been following Screw Expander technology for a while, and have recently started investigating a specific opportunity at a particular site so have a bit of detail to present.
To set the scene a bit, steam is the main source of process heat worldwide. Boilers burn fuel to generate steam at high pressures. Higher pressure boilers have more capacity for steam than a lower pressure one, and it’s fairly common to produce steam at higher pressure than required for the process. Boiler pressure is usually reduced through a Pressure Reducing Valve (PRV) to its processing pressure, superheating the steam in the process.
While a PRV reduces the pressure, other technologies could reduce the pressure and produce energy. Sure, you remove some of the energy… but often the superheat isn’t required and may reduce the heat transfer effectiveness within heat exchangers. A steam turbine is one of the most well known, efficient and mature technologies for steam energy generation. But they’re expensive to buy and maintain and require dry steam. On the other hand, screw expanders are cheaper, easier to maintain and can expand saturated or wet steam (or for that matter, hot water or other fluids).
Screw expanders are versatile and fairly bulletproof – think a refrigeration screw compressor in reverse. They can operate on waste heat that can generate wet steam. As high pressure steam enters the screw expander, it moves the rotor that is coupled with a generator to produce power.
Aside from industrial applications (like the PRV example, or just using some waste heat), screw expanders could be used in a geothemal applications. They’re easily expandable and cost in the region of $1,100/kW to install, operating at greater than 60% efficiency. They’re not for everybody, but it’s another option to consider if you’ve got some under-utilised waste heat on site.