The foundation of the Thermafficient® heat engine is NASA’s Supercritical Carbon Dioxide “CO2″ Champagne Heat pump patent, which was originally designed for the cooling of spacecraft.  rexorce has extended the core technology, particularly in the area of power generating. 

rexorce’s development effort has yielded an innovative version of the Rankine cycle coupled with the opportunity to use a binary working fluid comprising a liquid absorbent and supercritical carbon dioxide. This cycle is the foundation of the rexorce WHR product offering.  A 250 kW (net) skid-based system is currently in design for deployment at demonstration sites.   rexorce has built and is optimizing an electrical generating laboratory scale system (appx. 15kW) at its Akron, Ohio facilities.

The Thermafficient® heat engine is made up of five primary components, (i) heat exchangers, (ii) working fluids, (iii) pumps, (iv) an expansion device and (v) a generator, allowing it to uniquely produce power from a wide range of thermal sources.  Each component offers current technology advantages as well as the opportunity to dramatically improve the component design yielding even greater performance in next generation systems.  rexorce has partnered with world class research institutions and industry leaders to advance the overall performance of each of these components.

Why CO2?

Supercritical CO2, alone or in combination with other working fluids, serves as the key working fluid in the system as it passes through and drives an expansion device transforming the thermal energy into mechanical/electrical energy.  Carbon dioxide is a superior heat transfer fluid when used alone and presents numerous advantages over conventional working fluids such as steam and organic fluids; namely, CO2 is relatively inert (allowing direct thermal contact with the waste heat source), non-toxic (an important advantage in distributed energy applications), and energy dense (allowing a very small physical footprint and smaller components while producing substantial amounts of power). 

When compared to single component working fluids, the rexorce binary working fluids can achieve superior performance characteristics.  One unique attribute of a binary, CO2 based working fluid, is that one of the working fluids can absorb CO2, thus enabling the combined fluid to be pumped in a liquid state to high pressure with less energy input than required to compress CO2.   In addition, supercritical CO2 is extremely “energy dense” as it is capable of retaining significant amounts of energy in a relatively small volume; consequently, binary working fluids generate significant pressures from very small volumes of working fluids.  Other working fluid combinations achieve additional and different advantages - providing a wide range of options in designing a waste heat recovery system.

Our Lab Scale Successes Lead to our Commercial Future

To date, rexorce has completed 3 different prototype systems.  The first system, completed in 2007, was an absorption heat pump using carbon dioxide and a preferred secondary fluid.  rexorce built what NASA conceived: an absorption cycle in which carbon dioxide was absorbed into a secondary fluid to improve energy efficiency at the pump.   The second lab scale system, completed in early 2009, involved a pure carbon dioxide system driving a power generation cycle.   There, rexorce obtained proof that a transcritical cycle heat engine could be built for commercial application and established the technology development pathway for its first commercial units.  Currently, rexorce is operating its newest 15kWe lab scale prototype as a scaled version of its larger pilot scale unit (see below) and completed early runs with its proprietary equipment set.  Through this testing and working with its partners, rexorce continues to optiminze the control and design of its larger unit.  Together with many hours of operation, the construction of these prototype systems have validated the thermodynamic approach to power generation using carbon dioxide as a working fluid and provided rexorce with a sound foundation to pursue its commercial scale products.

Current Progress

rexorce’s 250kWe demonstration unit is currently on schedule to be completed in December, 2009.  A highly qualified team of development partners and suppliers has been assembled, a equipment portfolio sourced from well regarded industrial equipment brands has been procured and final assembly is ongoing with a tier one power generation packager.  Following assembly, demonstration partners have committed to host a multi-stage demonstration.  This will provide rexorce with the opportunity to test its system in a controlled setting as well as validate that its thermal engine will connect to the electrical grid seamlessly; thereafter, rexorce will move the demonstration system to its intended commercial environment, an industrial plant for subsequent endurance and related demonstration testing.

What’s Next?

Beyond its focused effort to deliver a product line of thermal engines that will shift the paradigm for waste heat recovery opportunities at larger sizes, rexorce has also developed other technologies for which it actively seeks development partners and/or market driven projects.  Among these, rexorce is most active in regard to its absorption cycle research and development, its thermal management solution for jet aircraft turbines, and its thermal hydraulic transmission prototyping (for automotive and wind applications).