Tuesday, July 26, 2011

Colloquium at UniMelb

In case it will be of interest to any Melbourne-based readers of this blog, I’ll mention that I have accepted an invitation to give a colloquium at the Department of Mathematics and Statistics at the University of Melbourne.  This will be on Tuesday, 9 August 2011, and the title and abstract are as follows:

Applications for a New Thermodynamic Cycle

Take hot dry air, then sequentially expand it, spray cool it and re-compress it to the inlet pressure whilst allowing further evaporative cooling.  That thermodynamic cycle defines a heat engine with advantages for certain applications.  The thermodynamic cycle will be analysed and two applications will be described.

For a continuous-flow version, the result is a 20% boost in gas turbine output with no extra fuel consumption or emissions.  For a piston-in-cylinder version, there is the prospect of unconventional but cheap solar power, including the possibility of thermal storage so as to give 24/7 despatchability.


I’ll also take this opportunity to describe where things stand with my research program.  Earlier this year, I started simulations of thermal storage in a bed of packed rock, with the intention of presenting the work at the 2011 Conference of the Australian Solar Energy Society.  The application, of course, was for power generation using my evaporation engine, with heat collected under a transparent insulated canopy (see here for details).  That work has proceeded slowly and I now cannot finish it in time for the submission deadline, so that research topic is deferred until next year.

Instead, I now plan that my AuSES presentation will be on “ECET Boost to Solar-Hybrid Gas Turbines”.  This work builds on my main research focus for the year, namely to investigate various applications for the Expansion-Cycle Evaporation Turbine (ECET).  The solar-hybrid gas turbine application has been extensively studied in Europe, see e.g. the SOLGATE project (PDF, 3.546 MB), and I’ll look at how the power output can be boosted using various bottoming cycles.  These include the conventional Rankine steam cycle, the ECET, and the Air Heat Recovery Turbine Unit.  My analysis is finished and I’m currently writing the paper.

Meanwhile, I continue on my principal current mission – to pursue commercialisation prospects for the ECET.

Friday, July 15, 2011

ECET paper accepted

I imagine every scientist receives a thrill when they hear that their latest paper has been accepted for publication.  That’s certainly the case for me, even at my mature age of 62 years.

The Editor of the Journal of Engineering for Gas Turbines and Power wrote today saying that my manuscript “The Expansion-Cycle Evaporation Turbine” has been approved for publication.  I’m delighted about this, for I think the ECET concept is important.

The abstract for the paper is as follows:

“This paper investigates a continuous-flow heat engine based on evaporative cooling of hot air at reduced pressure.  In this device, hot air is expanded in an expansion turbine, spray-cooled to saturation and re-compressed to ambient pressure in several stages with evaporative cooling between each stage.  More work is available in expansion than is required during re-compression, so the device is a heat engine.  The device provides a relatively cheap way to boost the power output of open-cycle gas turbines.

The principal assumptions for the theoretical model developed herein are that air and water vapour are regarded as ideal gases with constant specific heat capacities.  In the absence of losses associated with expansion and compression, the engine produces more power as the inlet temperature and the pressure ratio increase.  The effects of irreversibilities are subsequently included in the expansion and compression stages, with realistic values used for the adiabatic efficiencies of turbine and fans.  Purification and injection of water are also considered in the overall energy budget. 

As a typical result for the new engine, if the inlet air is the exhaust of a 56 MW open-cycle gas turbine, the adiabatic efficiencies of turbine and fan are 0.9, the pressure ratio is 6.5 and there is four-stage re-compression, then the power output is 20.5% that of the gas turbine.  The power output is sensitive to the adiabatic efficiencies of turbine and fans.”  

A reviewer, who described the concept as “innovative”, suggested that I should modify the paper to include a coarse economic evaluation of the ECET.  I accepted that suggestion, and I’ll mention the details here:

I assumed the ECET boosted the output of the upstream Open-Cycle Gas Turbine (OCGT) by 20%.  (The OCGT was the 56 MW unit used in my case study; its efficiency was 34%.)  I assumed the specific capital cost of the ECET is the same as for the upstream OCGT, namely $750/kW.  Other assumptions were: taxation implications neglected, cost of capital 8%, payback period 25 years, annual non-fuel O&M costs are 1% of the capital cost, and price of natural gas $6/GJ.  The table below gives results for two different capacity factors.

Levelized Electricity Cost ($/MWhr) and CO2 emissions (kg/MWhr) for an OCGT with and without ECET boost.  The capacity factor (CF) is the proportion of time the generator is active.

OCGT unboosted
CF = 0.1
CF = 0.2
LEC
152
CO2
582
LEC
108
CO2
582

OCGT with ECET boost
CF = 0.1
CF = 0.2
LEC
142
CO2
485
LEC
97
CO2
485

These results imply that, at peak times in the electricity grid, the ECET will reduce the Levelised Electricity Cost by 6-10% and marginal CO2 emissions by 17%.  That’s why I think this is an important paper.

Acknowledgement:  Thanks again to Anthony Kitchener for suggesting this work and for advice provided along the way.