Energetic, economic and environmental assessment of the pyrolysis and combustion of microalgae and their oils

The physico-chemical characteristics of two microalgae species (Scenedesmus sp and Nannochloropsis gaditana) and their extracted oils have been investigated. Microalgae oils had high calorific value, low ash content, high volatile content and low moisture. A comparison of the pyrolysis and combustion performance of microalgae and oils samples was carried out by performing simultaneous TGA (thermogravimetric analysis) and DSC (differential scanning calorimeter) coupled with mass spectrometry (MS). The thermochemical behavior of microalgae samples was a function of their biochemical composition (proteins, carbohydrates and lipids) and inorganic content (ash content). Thermal treatment of microalgae oils released lesser NOx and SOx emissions than those of the parent microalgae. Finally, the economic viability and environmental sustainability of pyrolysis and combustion technologies of microalgae and their oils was evaluated by means of life cycle assessment methodology. Four different scenarios were analyzed and compared in order to provide useful information from the industrial point of view. CO and CO2 were the main gases produced during the pyrolysis and combustion processes. Materials and energy requirements of the processes involved were calculated by process simulation. Microalgae oils were the best option in terms of energetic performance. Selling price of microalgae biomass and plant capacity are critical variables to be considered for establishing the financial feasibility of the thermochemical process.