Abstract
The intermittent nature of solar energy limits its further deployment to applications where firm supply and constant output is required. While energy storage is a viable option to increase solar share, in itself is not sufficient without an additional dispatchable energy source. Combustion of both fossil-based and renewable fuels can provide the demand ready energy source required and lends itself to hybridisation with tower based Concentrated Solar Thermal, CST, energy. The Hybrid Solar Receiver Combustor, HSRC, is a novel technology that integrates both sources of energy in one device and offers tangible benefits in increased solar share, thermal efficiency and reduced capital and operation costs. This paper reports a brief review of the different findings from experimental and computational research carried out at the Centre for Energy Technology of the University of Adelaide into optimizing the HSRC design, developing the first-of-a-kind laboratory-scale HSRC unit and evaluating its performance under different fuels, operating conditions and modes of operation. It highlights the benefits and need for utilizing MILD combustion in the HSRC to match the heat transfer characteristics and stability required to achieve similar operational range and efficiency from both sources of energy. A 5-kWel xenon-arc solar simulator and the combustion of a wide variety of fuels are used as the energy sources. This paper reports on the effectiveness of MILD combustion under these conditions and in particular it discusses flame stability envelop and its relation to heat extraction, temperature and pollutant emissions. It also reports on thermal efficiency, heat losses and heat flux distribution within the cavity for all fuels and operating conditions. It is found that the HSRC thermal performance is similar under the three operation modes (solar, combustion and combined) and that operating under MILD combustion mode allowed fuel flexibility, homogeneous heat distribution and very low emission of NOx and CO. Also found that H/C ratio plays a minor role in the radiated energy to the heat exchanger within the cavity. Future research and further technology development need is also discussed in this paper.
Highlights
Concerted effort has been spent on carbon abatement from the energy generation sector over the last two decades
Transport is a major contributor to carbon emission, and while electric vehicles are likely to play a role in the light duty transport market, alternative fuels that can utilize existing internal combustion technologies will be needed
This paper provides a review of the different findings from the experimental and computational research into optimizing the Hybrid Solar-Receiver-Combustor (HSRC) design and evaluating its performance under different fuels and operating conditions
Summary
Concerted effort has been spent on carbon abatement from the energy generation sector over the last two decades. They estimated that the HSRC can achieve up to a 19% reduction (depending on the natural gas price) in the levelized cost of electricity relatively to an equivalent cavity receiver with a back-up, stand-alone combustor This estimate could be low as it only considers, as stated by Nathan et al (2017), “the first three of the following five potential benefits that were identified by Nathan et al (2014), as being: (1) reduced heat losses by reducing the total area heat exchange surfaces; (2) avoided start-up and shut-down losses associated with the need to warm-up the combustion system prior to its use; (3) reduced total infrastructure by the need to construct only one device instead of two; (4) increased capacity to manage thermal shock associated with short-term fluctuations in solar resource by using combustion to compensate for any reduction in Concentrating Solar Radiation (CSR); and (5) potential to harvest the solar resource at a lower total flux, owing to the possibility of supplementing the solar resource with combustion”. HSRC design and evaluating its performance under different fuels and operating conditions
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