Abstract
The demand for better hygiene has increased the need for developing more effective sanitation systems and facilities for the safe disposal of human urine and faeces. Non-Sewered Sanitary systems are considered to be one of the promising alternative solutions to the existing flush toilet system. An example of these systems is the Nano Membrane Toilet (NMT) system being developed at Cranfield University, which targets the safe disposal of human waste while generating power and recovering water. The NMT will generate energy from the conversion of human waste with the use of a micro-combustor; the heat produced will power a Stirling engine connected to a linear alternator to generate electricity. This study presents a numerical investigation of the thermodynamic analysis and operational characteristics of a quasi steady state model of the gamma type Stirling engine integrated into a combustor in the back end of the NMT system. The effects of the working gas, at different temperatures, on the Stirling engine performance are also presented. The results show that with the heater temperature of 390 °C from the heat supply via conduction at 820 W from the flue gas, the Stirling engine generates a daily power output of 27 Wh/h at a frequency of 23.85 Hz.
Highlights
Heat recovery and waste utilisation are rapidly advancing fields of research, due to the high priority currently given to energy generation and environmental sustainability
An evaluation was carried out by Kuosa et al [17] on the numerical evaluation of an alpha Stirling engine using the fouling factor to determine the effect of heat exchangers on Stirling engines for combined heat and power (CHP) application; the analysis considered the brake efficiency, output power and heat recovery to optimise the cleaning interval of the heat transfer surfaces when the cost model is combined with the performance model
The quasi steady state model developed in this study was validated with the experimental results from the gamma type Stirling engine reported by Gheith et al [25]
Summary
Heat recovery and waste utilisation are rapidly advancing fields of research, due to the high priority currently given to energy generation and environmental sustainability. Non-sewered technologies, often without or with limited necessity for flush water, are being investigated Some of these novel toilet systems are described as functioning as thermochemical conversion units, where faeces are thermally treated to produce useful by-products [3]. The Nano Membrane Toilet (NMT) is being developed to treat human waste into clean water and heat without the external supply of water, energy, and sewer This unit requires the development of new technologies for power generation, and the use of human faecal material as an energy source is one example. The combined benefits of the novel systems embedded in this unit (i.e. membrane technology for urine filtration, and micro-combustor for continuous conversion of human faeces) can improve access to clean water and sanitation around the world, as well as enhance alternative and environmentally-friendly power generation for communities lacking basic amenities [5]. Heat recovery from combustion-based systems is important, and electrical energy is vital for the functioning of the self-sustaining/offgrid NMT system reliant on pumps and ignition systems
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