Energy profitability analysis for microalgal biocrude production

• Biocrude production from microalgae was studied to optimize its energy efficiency.
• To recover energy from residual biomass 4 alternatives were energetically compared.
• EROEI (Energy Return on Energy Investment) was calculated as function of oil fraction and residual biomass exploitation.
• Use of wastewater for microalgae growth can improve substantially the EROEI.

This work presents the results of a thorough EROEI (Energy Return on Energy Investment) analysis for biocrude production from microalgae processes. We have investigated different alternatives to maximize the energy recoveries of each process considered, which has been modeled and simulated by Aspen Plus™. The estimates for feeds and recirculation of microalgae and nutrients, working conditions, systemization and equipment requirements were obtained using both literature and own experimental data. The Pinch Technology Analysis was applied to optimize the process operating conditions. It was found that the process which uses the combustion of biomass after biocrude extraction is the most favorable one in energy terms. In particular, 2 cases of this type were addressed and compared to a Base case where all energy requirements (heat and electrical) are provided from external sources: Case 1, electricity is supplied externally whereas the biomass and part of the biocrude produced are burned to meet the requirements of thermal energy, and Case 2, where the energy recovered from both biomass and part of biocrude are used to fulfill all heat and electricity duties. These cases were analyzed also when the nitrogen needed for microalgae growth is obtained from wastewaters. Favorable EROEI figures could be calculated.