A hybrid chemical and biological process for CO2 fixation: an analysis based on process simulation

This thesis is focused on verifying large-scale feasibility of a hybrid chemical and biological process for CO2-fixation, combining carbon dioxide absorption by means of a carbonate-based solvent with microalgal sequestration, where CO2 is fed to the culture in bicarbonates form. A rigorous simulation is carried out using Aspen Plus process simulator to solve material and energy balances, and to check whether this process can be scaled-up at industrial level. The steam methane reforming plant data are taken as the starting point to set up the process simulation. The plant layout includes a first section where the carbon dioxide in the steam methane reforming tail gas is chemically absorbed by using a sodium carbonate aqueous solution. The liquid from the bottom of the column is then fed to the photobioreactor, microalgae are separated from water, which is recycled to the absorption column, after a suitable make up. The model kinetic parameters are obtained from experimental growth data of Arthrospira Platensis species measured in laboratory continuous cultivation systems, and takes into account the effect of temperature and light. Simulation results are used to calculate the volume of the photobioreactor and the irradiated area required, as a function of light intensity. Photosynthetic efficiency and electrical energy consumption are also evaluated. Eventually, a reactor design proposal is suggested, and costs related to energy supply to microalgae culture are presented.