Session: 07-01: Experimental Characterization of Particle Flows

Paper Number: 156580

156580 - SOLAR ABSORPTANCE AND THERMAL EMITTANCE OF PARTICLE HEAT CARRIERS IN A SOLAR DRIVEN BIOMASS PROCESS 

Abstract: 

Research on solar‑driven biomass pyrolysis is gaining interest, as CO₂ emissions from the combustion process currently used in state‑of‑the‑art technology can be avoided. The Horizon Europe Project PYSOLO [1] looks at the the integration of a solar‑heated Particle Heat Carrier (PHC) in a biomass pyrolysis process. In this process, the PHC is used as a storage and transport medium for solar thermal energy. The PHC is first heated in a solar receiver, then sent to a pyrolysis reactor, where the thermal energy required for the pyrolysis reaction is released and, after separation from the solid products of this step (mostly biochar and ash), it is sent back to the solar receiver to close the loop.

Materials such as bauxite, magnesium oxide (MgO), olivine, sand or silicon carbide (SiC) could be possible candidates for this process. In the solar receiver step, the PHC is directly irradiated by the concentrated solar energy and information about their optical properties is required. Measuring the optical properties of solid particles has been identified as a challenging task [2], but in recent years a guideline has been developed to obtain this information using spectrophotometers [2, 3]. However, most of the information in the literature relates mainly to fresh materials before being heated with solar energy and, in the case of olivine, little or no data are available at all. In addition, the optical properties of PHC can change depending on the process conditions, for example, whether the PHC enters the solar receiver as 1) fresh material or 2) after passing through the pyrolysis reactor. Also, exposure to the temperature conditions in the solar receiver can affect its optical properties.  

In this study, the solar absorptance of five PHCs at each stage of the process has been obtained using the procedure described by Sutter et al. [2]. The following samples were prepared and measured: i) materials as received, ii) materials heated to 950 °C in air atmosphere to simulate conditions in the solar receiver, and iii) materials mixed with wood chips, which were heated to 800 °C in nitrogen to simulate the pyrolysis stage. After the experiments it was observed that bauxite and SiC materials maintained their dark colour in the three different process steps and changed their optical properties slightly (with differences <3% and <7%, respectively). Significant changes were observed with the MgO, olivine and sand samples. For these three materials, when comparing the samples as received and after being exposed to the pyrolysis conditions, a remarkable increase in their optical properties of 67%, 33% and 78% was observed for MgO, olivine and sand, respectively. When comparing the samples as received and after being heated in air, a much smaller increase was observed: 1%, 7% and 16% for MgO, sand and olivine, respectively. The analysis is complemented with microscopy images (Figure 1), which have shown the colour change of the different samples explaining the results obtained. In addition to the reported solar absorptance values, the thermal emittance at 950 °C of the five materials was estimated following the procedure described in [2, 4].

Figure 1. Microscopy images of olivine samples

Keywords: solar thermal energy, particle heat carrier, solar absorptance, thermal emittance, biomass pyrolysis.

[1] Horizon Europe Project PYSOLO, https://pysolo.eu/  

[2] F. Sutter et al., "Method to evaluate the reflectance, absorptance and emittance of particles for concentrating solar power technology", 2022. SolarPACES. Available online at https://elib.dlr.de/189228/.

[3] Sutter, Florian; Montecchi, Marco; Morales Sabio, Angel; San Vicente, Gema; Fernández-García, Aránzazu; Pernpeintner, Johannes et al. (2023): Round Robin Test of Absorptance and Emittance of Particles for CSP. In SolarPACES Conf Proc 1. DOI: 10.52825/solarpaces.v1i.629.

[4] Caron, Simon; Herding, Leslie; Binyamin, Yaniv; Baidossi, Mubeen; Vinetsky, Yelena; Morales, Angel et al. (2022): Laboratory intercomparison of solar absorptance and thermal emittance measurements at room temperature. In Solar Energy Materials and Solar Cells 238, p. 111579. DOI: 10.1016/j.solmat.2022.111579.

Presenting Author: Juan Pablo Rincon Duarte German Aerospace Center (DLR), Institute of Future Fuels

Presenting Author Biography: Juan Pablo Rincon Duarte is a mechanical engineer from Colombia with a M. Sc. in renewable energy systems. He has beeing working as a researcher since September 2018 at the German Aerospace Center - Institute of Future Fuels. He is a PhD candidate at the RWTH University in Aachen - Chair for Solar Fuel Production - Faculty of Mechanical Engineering. His current research topics are the solarization of industrial processes, design of solar reactors, solar calcination of limestone, particle heat carriers for CST applications and solar hydrogen production.