Energy balance of torrefied microalgal biomass with production upscale approached by life cycle assessment

Diana Rose T Rivera; Aristotle T Ubando; Wei-Hsin Chen; Alvin B Culaba

doi:10.1016/j.jenvman.2021.112992

Energy balance of torrefied microalgal biomass with production upscale approached by life cycle assessment

J Environ Manage. 2021 Sep 15:294:112992. doi: 10.1016/j.jenvman.2021.112992. Epub 2021 Jun 8.

Authors

Diana Rose T Rivera¹, Aristotle T Ubando², Wei-Hsin Chen³, Alvin B Culaba⁴

Affiliations

¹ Mechanical Engineering Department, Far Eastern University Institute of Technology, Manila, Philippines; Mechanical Engineering Department, De La Salle University, 2401 Taft Avenue, 0922, Manila, Philippines; Department of Aeronautics and Astronautics, National Cheng Kung University, Tainan, 701, Taiwan.
² Mechanical Engineering Department, De La Salle University, 2401 Taft Avenue, 0922, Manila, Philippines; Center for Engineering and Sustainable Development Research, De La Salle University, Manila, 0922, Philippines; Thermomechanical Laboratory, De La Salle University, Laguna Campus, LTI Spine Road, Laguna Blvd, Biñan, Laguna, 4024, Philippines.
³ Department of Aeronautics and Astronautics, National Cheng Kung University, Tainan, 701, Taiwan; Research Center for Smart Sustainable Circular Economy, Tunghai University, Taichung, 407, Taiwan; Department of Mechanical Engineering, National Chin-Yi University of Technology, Taichung, 411, Taiwan. Electronic address: weihsinchen@gmail.com.
⁴ Mechanical Engineering Department, De La Salle University, 2401 Taft Avenue, 0922, Manila, Philippines; Center for Engineering and Sustainable Development Research, De La Salle University, Manila, 0922, Philippines.

PMID: 34116302
DOI: 10.1016/j.jenvman.2021.112992

Abstract

Torrefaction is a thermochemical process used to convert the biomass into solid fuel. In this study, torrefaction increased the raw microalgal biomass' energy content from 20.22 MJ⋅kg^-1 to 27.93 MJ⋅kg^-1. To determine if more energy is produced than energy consumption from torrefaction, this study identified the energy balance of torrefied microalgal biomass production based on a life cycle approach. The energy analysis showed that, among all processes, torrefaction had the least amount of energy demand. The experimental setup, defined as scenario A, revealed that the principal source of energy demand, about 85%, was consumed on the microalgal growth using a photobioreactor system. A sensitivity analysis was also performed to determine the varying energy demand for torrefied microalgal biomass production. The different types of cultivation methods and various production scales were considered in scenarios B to D. Scenario D, which represented the commercial production-scale, the energy demand drastically decreased by 59.46% as compared to the experimental setup (scenario A). The open-pond cultivation system resulted in the least energy requirement, regardless of the production scale (scenarios B and C) among all the given scenarios. Unlike scenarios A and D, scenarios B and C identified the drying process to consume a high amount of energy. All the scenarios have shown an energy demand deficit. Therefore, efforts to decrease the energy demand on the upstream processes are needed to make the torrefied microalgal biomass a viable alternative energy source.

Keywords: Energy balance; Energy consumption; Life cycle assessment; Microalgae; Torrefaction.

MeSH terms

Animals
Biofuels
Biomass
Life Cycle Stages
Microalgae*

Substances

Biofuels