Bioenergy co-products derived from microalgae biomass via thermochemical conversion – Life cycle energy balances and CO2 emissions

•An experimental study of thermochemical conversion of microalgae was carried out.•Energy balance and efficiency of co-products char, bio-oil and gas was determined.•Energy balance equations were established for process life cycle efficiencies.•Comparisons were made with other energy indicators from...

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Bibliographic Details
Published in:Bioresource technology 2013-09, Vol.143, p.298-307
Main Authors: Khoo, H.H., Koh, C.Y., Shaik, M.S., Sharratt, P.N.
Format: Article
Language:English
Subjects:
Biofuel production
Biological and medical sciences
Biomass
Biotechnology
Carbon dioxide
Carbon Dioxide - metabolism
Computing time
Derivatives
Drying
Energy
Energy efficiency
Fundamental and applied biological sciences. Psychology
Gasification
Industrial applications and implications. Economical aspects
Life cycle energy input–output
Life cycle engineering
Microalgae - metabolism
Microalgae-to-bioenergy
Pyrolysis
Renewable energy
Thermochemical process
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Summary:•An experimental study of thermochemical conversion of microalgae was carried out.•Energy balance and efficiency of co-products char, bio-oil and gas was determined.•Energy balance equations were established for process life cycle efficiencies.•Comparisons were made with other energy indicators from literature.•Life cycle CO2 results displayed more CO2 emissions released than absorbed. An investigation of the potential to efficiently convert lipid-depleted residual microalgae biomass using thermochemical (gasification at 850°C, pyrolysis at 550°C, and torrefaction at 300°C) processes to produce bioenergy derivatives was made. Energy indicators are established to account for the amount of energy inputs that have to be supplied to the system in order to gain 1MJ of bio-energy output. The paper seeks to address the difference between net energy input–output balances based on a life cycle approach, from “cradle-to-bioenergy co-products”, vs. thermochemical processes alone. The experimental results showed the lowest results of Net Energy Balances (NEB) to be 0.57MJ/MJ bio-oil via pyrolysis, and highest, 6.48MJ/MJ for gas derived via torrefaction. With the complete life cycle process chain factored in, the energy balances of NEBLCA increased to 1.67MJ/MJ (bio-oil) and 7.01MJ/MJ (gas). Energy efficiencies and the life cycle CO2 emissions were also calculated.
ISSN:0960-8524
1873-2976
DOI:10.1016/j.biortech.2013.06.004