Auto Turbocharger to Blow Solar-Heated Air for Industrial Drying
A university research team has developed a unique way of using renewable energies to provide direct hot air for industrial drying processes by combining solar thermal collectors with an automotive turbo charger.
“Thanks to the use of the turbocharger; This is a component that is manufactured for charging internal combustion engines such as in cars and trucks, and is the first solar heat for industrial processes that is able to heat air directly solar to 300 ° C to 400 ° C without heat transfer fluids “, explains mechanical engineer Antonio Famiglietti, member of the Research Group for Thermal Engineering, Energy and Atmosphere (ITEA) at the Carlos III University in Madrid.
The university’s engineering group works closely with a local engineering firm; DEMEDE engineering and research focused on solar heat for industrial processes.
Famiglietti is now an R&D engineer at Demede, where he is working on the development of the innovative solar heating technology for commercial use as a Turbocharged Solar Air Heater (T-SAH).
“The T-SAH heats the ambient air right inside the linear concentrating solar panel,” he said. “This reduces complexity, costs and maintenance as well as their environmental impact. Coupling the solar modules with a turbocharger enables the air to be heated directly by reducing the disadvantage of the high pump power consumption that typically occurs when using a linear concentrating collector with air as the heat transfer fluid. “
The team at Applied Thermal Engineering has published three papers on the idea, starting with a feasibility study: Direct solar production of medium temperature hot air for industrial applications in linear concentrating solar panels using an open Brayton cycle. Profitability analysis
“First, we worked on the concept from a theoretical point of view and received a general screening of the technology based on numerical simulations of the possibility of direct air heating within the solar concentration collectors,” he said.
“Direct air heating with parabolic troughs or linear Fresnel is not a common practice in solar thermal energy, mainly because of the high pumping power that the air needs to flow in the vacuum tubes of solar collectors. However, the technology we propose allows us to overcome this main drawback thanks to a special configuration of the Brayton cycle and the use of a turbocharger to avoid the additional consumption of electricity for pumping. This would allow us to avoid the heat transfer medium and the heat exchanger and reduce costs and complexity. “
In 2021, the team released the results of the physical tests of the first T-SAH prototype installed at Carlos III University in Madrid with a 72 square meter Fresnel mirror solar field: Direct solar air heating in a small linear Fresnel collector supported by a turbocharger: experimental characterization
This paper was followed by a numerical assessment of the potential performance of an industrial plant with a 633 square meter solar field that supplies 330 MWh of thermal energy (approx. 2060 hours per year) and provides hot air in the range of 300-400 ° C during the day without external energy consumption for pumping of air based on a typical meteorological year in Madrid.
The next step is to test the new technology on an industrial scale.
“The know-how we have acquired over these years of combined theoretical and experimental research enables us to effectively design and implement a larger-scale demonstration, test the technology in the real world, and put it into the facility of the industrial User, ”said Famiglietti.
How it works
Basically, the linear Fresnel solar field is coupled to a turbocharger that blows hot air directly into the solar receiver tubes for heating before it is fed into the industrial thermal process. No heat transfer fluid or storage is required. The idea is to keep the tech as simple as possible to keep costs down.
“A compressor increases the air density, minimizes speeds and pressure losses over the solar field, in other words the pumping power that is required to blow the air,” explains Famiglietti.
“The turbine, which is installed at the exit of the solar field, can provide the compression power and the pumping power when a sufficient temperature (450-550 ° C) is reached at the entrance so that the system can work without the consumption of external energy for pumping. An auxiliary compressor is only needed for starting transitional and regulating purposes. The turbine outlet air has a temperature of 300-400 ° C and is available for downstream use in air-powered thermal industrial processes. “
Typically, solar panels use a liquid heat transfer fluid to move heat through the solar receiver tubes and then a heat exchanger is needed to transfer the heat to the air. Since the turbocharger instead pushes the air through the pipes, this innovation avoids all installation, maintenance and replacement costs for the heat transfer fluid and heat exchanger.
Originally, the team assumed they would use parabolic trough collectors, which are widely used for generating electricity in CSP plants, but these were hard to find on the scale required and would add complexity. One of the advantages of the linear Fresnel collector is that wind load problems are negligible thanks to a segmented primary reflector with simplified tracking and individual mirrors rotating close to the ground. The flat, deep-set Fresnel solar mirrors enable solar field installations on industrial roofs.
All components are off the shelf. Turbochargers are already being mass-produced for the automotive industry. For the Fresnel modules, they turned to another new Spanish company that now supplies prefabricated Fresnel solar thermal modules in truck-size containers ready for connection; Solatom.
The industrial potential that the team has explored includes companies with high-energy processes that use air as a heat transfer medium. One of the most common methods is drying – for different materials at different temperatures. Biomass, food, sewage sludge, residues, wood and minerals all need to be dried, and some finished products need to be treated with hot air during processing, such as paint curing.
The team is optimistic about the commercial viability of its turbocharged solar air heater for these industrial applications.
“The heat consumption in industry is enormous, so replacing the fossil fuel previously used for production with sustainable energy sources is a challenge of great importance for the energy transition,” said Famiglietti for the team.