For almost all of 2011, I have been working on a secret project, culminating in today’s launch of the Expansion-Cycle Evaporation Turbine (ECET).
Let me explain …
I invented the evaporation engine in May 2004 as a device to generate power from hot air collected passively under a transparent insulated canopy. I quickly realised there were two straightforward ways the thermodynamic cycle (evaporative cooling of hot air at reduced pressure) could be manifested:
· piston-in-cylinder, and
· continuous-flow using turbines and compressors.
I also had a related concept for a Bernoulli heat engine, which excited me enormously, but which seemed to require condensation at reduced pressure. That was cause for much anguish: why should some of the engines work on evaporative cooling at reduced pressure, and yet the Bernoulli engine by condensation at reduced pressure? It took me an embarrassingly long time to work out why – my mathematical model for the Bernoulli device had an error with the pressure calculation during evaporation, which was found by a sharp-eyed reviewer of a manuscript I’d submitted for publication. Once I’d corrected the error, all three heat engines relied on evaporative cooling at reduced pressure.
After that, the Bernoulli device remained my favourite for a while longer, but since its output was limited by the pressure drop accessible via the Bernoulli effect and since losses in acceleration, evaporative cooling and deceleration were likely to be severe, I eventually stopped working on it. The continuous-flow version with expansion turbine and subsequent compressor(s) was attractive because of its mechanical simplicity, but I was concerned about losses in expansion and re-compression. I knew the device could be mounted behind an open-cycle gas turbine to provide a power boost, but I thought the boost wouldn’t be all that substantial and that it was therefore wisest to focus on a piston-in-cylinder version in which losses could be better controlled.
That led me on a four-year journey in which I designed and built a piston-in-cylinder evaporation engine, tested it, and considered what its output would be when the hot air was provided by solar heat collection under a transparent insulated canopy. Details of that passive solar work are given at www.sunoba.com.au. Meanwhile, the concept of using an evaporation engine to generate power from the exhaust of internal combustion engines remained attractive, especially for combined heat and power in buildings, but just never got to the top of my priority list.
That all changed at the start of this year when a fellow inventor, Anthony Kitchener, finally persuaded me make a thorough analysis of the use of the continuous-flow evaporation engine to boost the power of open-cycle gas turbines. Figure 1 shows the ECET layout (click to see original jpg diagram).
Figure 1: Flow-sheet for a four-stage expansion-cycle evaporation turbine.
My analysis surprised me. Losses on expansion and re-compression are present of course, but will not be too severe provided the adiabatic efficiencies of the turbines and compressors are high enough. At www.sunoba.com.au (follow the link to Expansion-Cycle Evaporation Turbine), I provide a case study that shows the ECET can boost the output of a commercially available OCGT by more than 20%. Now that is useful, and exciting too since the specific capital cost of the ECET, in $/MW for example, should be no greater than the specific capital cost of the upstream OCGT.
So, the ECET can boost the OCGT power by more than 20%, not use any extra fuel, and won’t cost any more per MW to build than the OCGT itself. That should lead to commercial prospects for the OCGT+ECET combination as peaking plants in the electricity grid, which is a huge market worldwide.
Well, that’s what I’ve been working on for four months. The concept was launched today with a revision of the website www.sunoba.com.au.
With respect to the passive solar application, I plan to attend the 2011 Solar World Congress in Kassel, Germany, where, provided my submitted abstract is accepted, I’ll present results of my canopy-engine simulations for a sloping canopy. I also plan to attend the 2011 Conference of the Australian Solar Energy Society at which I hope to report on thermal storage calculations for the passive solar application. That is work that needs to be done. I’d better get started.
Acknowledgement: Many thanks to Anthony Kitchener for encouragement, useful information and good ideas.