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Description
The Combustion and Solar Energy Lab (CSEL) at San Diego State University (SDSU) has been working to increase the efficiency of a solar power plant by using carbon microparticles mixed with air as a solar absorption medium. These carbon microparticles are produced through pyrolysis, where propane is heated in the absence of oxygen in a Carbon Particle Generator (CPG). The efficacy of this power plant relies heavily on carbon particles of a specific size being produced. This research focuses on the conditions needed to produce particle sizes between 500 nm - 1000 nm. A lab-scale CPG has been built at CSEL, and used to test particle generation conditions varying reactor temperature, propane mole fraction, and the inlet gas flow rate. The CPG operated between 1000 ◦C and 1200 ◦C, and a pressure of 6 bar. Testing conditions of the CPG were first modeled on ANSYS CHEMKIN-PRO, a reaction modeling software, and later performed through lab-scale experimentation. Particle sizing was analyzed using a Scanning Electron Microscope (SEM) and a Diesel Particle Scatterometer (DPS). After exiting the CPG, particles were captured on a filter for analysis using the SEM, where a relative particle size distribution was found using FiJi to examine the SEM images. Downstream of this, the particle mixture were further analyzed in real time using the DPS. The DPS utilizes Mie theory from light scattering off of the particles to calculate a relative particle size distribution and index of refraction. These two sampling methods were compared to determine the conditions for optimal particle sizing. Further analysis was done using an extinction tube at the exit of the CPG. As the particle-laden flow passed through the extinction tube, a 532 nm laser would shine through the mixture, and its intensity was measured with a photodiode detector. Laser intensity measurements were used in a modified Beer’s law equation, along with values supplied by the DPS software, to calculate the mass loading of carbon at the CPG exit. Mass loading was ultimately used to determine the carbon conversion efficiency of the CPG.
