Modeling and simulation of photobioreactors for biological hydrogen production

Androga, Dominic Deo
In applications of photofermentative hydrogen production, maintaining optimal temperature, feed composition, pH range and light intensity is the most critical objective for growth and proper functioning of the photosynthetic bacteria. Response Surface Methodology was applied to optimize temperature and light intensity for indoor hydrogen production using Rhodobacter capsulatus. Surface and contour plots of the regressions models developed revealed a maximum hydrogen production rate of 0.566 mol H2/m3/h at 27.5°C and 287 W/m2 and a maximum hydrogen yield of 0.326 mol H2/mol substrate at 26.8°C and 285 W/m2. For outdoor photofermentative hydrogen production many parameters are beyond manipulation, hence effective control of temperature in photobioreactors is a challenge. In this thesis, an internal cooling system was designed and built, and its performance in outdoor tubular photobioreactors was tested during summer months in Ankara, Turkey. Four tubular reactors with and without Rhodobacter capsulatus were operated in parallel. Counter-current and co-current cooling modes were implemented to stabilize the reactor temperature. The temperatures were found to be strongly influenced by the solar irradiance and the ambient air temperature during daytime; however, the surface temperature was found to be approximately constant along the reactor length. Counter-current cooling was found to be more effective compared to co-current cooling in controlling temperatures inside the reactor. High biomass growth rate (0.10 per hour) and hydrogen production rate (1.3 mol H2/m3/h) was achieved in the outdoor operations. The flow distribution in tubular reactors operated at steady state conditions was analyzed using computational fluid dynamics. A one-dimensional dynamic thermal model to describe the variations of temperature in tubular reactors operated outdoors with or without internal cooling was developed and verified with experimental data. The transient model included the effects of convection and radiative heat exchange on the reactor temperature throughout the day. The model established is useful in estimating the cost-effectiveness of producing hydrogen in large scale outdoors.
Citation Formats
D. D. Androga, “Modeling and simulation of photobioreactors for biological hydrogen production,” Ph.D. - Doctoral Program, Middle East Technical University, 2014.