The Inverted Gas Turbine

Background

“Warming of the climate system is unequivocal.” [1] Fossil fuels have afforded humanity an unprecedented high standard of living at an equally high cost to the environment. As a run-of-the-river hydroelectric power station supervisor I have had the opportunity to experience firsthand the challenges of periodic unavailability of renewable energy. Wind solar and even water are not always available to meet energy demands. The inverted gas turbine cycle, was first implemented by Mordell in the 1950’s at the University of McGill; exhaust gases from a gas turbine were cooled and vented through a stack allowing the turbine to expand to pressures lower than ambient [2]. Mordell’s model economic failure (bulky design) stemmed research interest.

The cycle

The inverted gas turbine has always been used as an add-on to the gas turbine, but a highly endothermic reaction can be used to make the inverted gas turbine into a standalone unit. Starting from atmospheric conditions, air can be expanded through a turbine, cooled by an endothermic reaction, and then exhausted through a compressor. This implementation harnesses heat energy from the atmosphere on a cyclic basis, countering global warming. Conservative gas turbine design calculation can show that this cycle, operating at isentropic efficiencies of 85%, with a pressure ratio of 4 and minimum temperature of 80 Kelvin, can produce 15 kW/kg (output per 1 kg: 83% air and 17% reactant). These calculations assume that calcium hydroxide and ammonium chloride are used as endothermic reactants at a chemical conversion rate of 90%. At a price of US$150 per metric tonne reactant, the cost of reactant per energy produce is US $0.18 per KWh. The chemical products would be calcium chloride (deicing salt), ammonia (common industrial product), ice and air.

Major Challenge

A major engineering challenge to the implementation of the inverted gas turbine by endothermic reaction would be the engineering of an endothermic reaction that can be sustain at sufficiently high conversion rates at low temperatures. In my current field of study, nano-thermites, nanotechnology is used to reduce the ignition temperature of energetic thermite mixtures from 660 Celsius to 25 Celsius (room temperature). This is done by lowering the activation energy through reducing the characteristic diffusion distances via the manipulation of particle size and particle mixing. [3]

Hypothesis and Goals

My hypothesis is that the challenge of implementing the inverted gas turbine can be overcome through employing state-of-the-art nanotechnology; lowering the activation energy of known endothermic reactions through nanotechnology would allow spontaneously initiation of these reactions below room temperature at elevated reaction rates. Unfortunately much work has not been done in the study of endothermic reaction when compared to exothermic reactions, solid state nor otherwise. The goal is to raise research funding for the research of endothermic micro and nano scaled reactions.

References:

[1] Intergovernmental Panel on Climate Change, Switzerland, 2013.
[2] D. Mordell, The Engineer, vol. 203, no. 5272, p. 210, 1957.
[3] M. Petrantoni, Journal of Applied Physics, vol. 108, no. 8, 2010.