This work presents an Euler-Euler hydrodynamic and heat transfer numerical analysis of the multiphase flow involving desert sand and a continuous gas phase in a compact-size fluidised bed. The latter is part of a novel conceptual solar power design intended for domestic use. Desert sand is a highly available and unused resource with suitable thermal properties to be employed as thermal energy storage medium. It also allows for high working temperatures owing to its high resistance to agglomeration. Computational Fluid Dynamics simulations are used here to assess the heat transfer between desert sand and several proposed working fluids (including air, argon, nitrogen and carbon dioxide) to justify the design in terms of equipment dimensions and suitability of the materials used. The results show that the device can provide up to 1,031 kW when using carbon dioxide as the heat transfer fluid.
A Novel Circulating Fluidised Bed Solar Receiver Design for Thermal Energy Conversion and Storage
(2019)
he middle east and northern Africa (MENA) regions rely heavily on fossil fuels as an energy source. The region consumes high amounts of energy for their air cooling and water desalination needs. For the GCC region this amounts to 60-70% of their energy consumption and has one of the highest carbon dioxide emissions per capita in the world.
The GCC countries are in an area of high direct normal irradiance from the sun and thus, investigating the use of solar power as an alternative energy source is valid. Concentrated Solar Power (CSP) technology is a promising energy capture technology that uses optical devices to concentrate the power of the sun on to a surface and in turn generates power by means of a thermal-to-electric conversion. CSP technology integrates Thermal Energy Storage (TES) materials to store heat and thus enable power production in the absence of sunlight, at night or in poor weather conditions. While CSP technology is a promising alternative energy source its high levelized cost of energy (LCOE) is a drawback to its widespread implementation. A major factor to the high LCOE is the use of molten salts as the TES material carrying with it, high capital costs and high operating and maintenance cost. This is due to molten salts being corrosive and having a low working temperature limiting its thermal-to-electric efficiency.
This contribution introduces a novel conceptual design of a circulating fluidised bed as the solar receiver for a CSP plant. The use of raw desert sand as an alternative TES material was investigated. An optimum heat transfer fluid (HTF) was selected from Carbon dioxide, Nitrogen, Argon and Air.
This work will also argue that these changes to current CSP plants will significantly reduce the LCOE. The results of this study show that the proposed design can allow up to six times higher mass flowrates of the heat transfer fluid to circulate the sand than current designs. Moreover, 1000 oC uniform outlet temperature was also achieved.
For this purpose, Carbon dioxide was found to be the optimum HTF, achieving the highest heat transfer rates. Thus, the new configuration of a fluidised bed receiver proves desert sand to be an effective alternative TES material leading to high thermal energy outputs per m2 and a substantial reduction in the LCOE for CSP technology.