Residual biomass has great potential for expansion as alternative bioenergy source

Increasing the amount of alternative renewable energy sources is needed to mitigate environmental challenges such as greenhouse emissions. The efficient use of biomass sources in bioenergy generation is a key issue in this transition. Currently bioenergy is mostly generated from wood-based biomasses, but there are multiple other bio-based residues available.

Clara Mendoza Martinez assessed different residues' potential as an alternative energy source in her doctoral dissertation study. The dissertation written under a joint doctorate agreement between LUT University and the Federal University of Minas Gerais (BRA).

"Biomass has great potential for expansion, as there are existing reserves worldwide. It is also very versatile which can help to meet different energy demands and reduce the accumulation of waste," says Mendoza Martinez.

In her research, Martinez investigated a variety of different biomass-based residue streams from forests, agriculture and industrial processes. These residues represent a large, currently unused source.

"One of the reasons for poor utilization is the considerable diversity found in non-woody biomass sources. The differences in their chemical structure require detailed evaluation of the properties and the corresponding impacts on the chosen conversion processes."

The focus in Martinez's research was to study diverse thermochemical energy conversion processes, such as hydrothermal carbonization, gasification, pyrolysis, and direct combustion. In addition to this physicochemical conversion, briquetting, was examined. The aim was to characterize the studied residues so that their propensity for utilization could be assessed.

As an example, residual biomasses from the coffee production chain for energy purposes was evaluated.

"Even if we have used coffee for centuries, the residues resulting from its production have not been extensively characterized before. Solid coffee residues showed high volatiles, cellulose and hemicelluloses content, which are suitable characteristics to use. The high heating value (HHV) is analogous to biomasses commonly used in energy generation," Mendoza Martinez explains.

The performance of any thermochemical conversion process, depends not only on feedstock characteristics, but also on finding suitable process parameters for used biomass, continues Martinez.

In this study, several globally important woody and non woody waste biomasses were looked at in connection of hydrothermal carbonization (HTC). The examined biomass streams included sludge from pulp mill effluent treatment plant, coffee wood, parchment of coffee cherry and giant bamboo.

The study focused on how to integrate the process, which requires heat to be supplied, with combined heat and power (CHP) plants. Several options were simulated in order to analyze the potential of HTC treatment as an attractive process for a biorefinery using non-woody biomass residues.

Integrating the HTC allowed a simpler process design, and an efficient benefit, provided that extraction steam is available at sufficient pressure levels.

"For coffee residue, several thermochemical conversion technologies were studied through mass and energy balances. Cherry coffee parchment has great potential to generate local heat and electricity using gasification with reported energy conversion rate of 84%," mentions Martinez as an example of her results.

According to Martinez, the results suggest that there is need for a tool to describe the impact of chemical components on thermal decomposition of wood during processing.  "We need to highlight possible further industrial applications for biomass use and conversion into value-added products on a large scale."

Further information:

Clara Mendoza Martinez, Junior researcher, LUT University, Clara.Mendoza.Martinez@lut.fi , +358 504784024

Public examination event:
Clara Lisseth Mendoza Martinez, Master of Science in Technology, will defend her doctoral dissertation in the field of energy technology on 11th May at 3 p.m. in an online event. Her dissertation is titled Assessment of agro-forest and industrial residues potential as an alternative energy source. Professor Raimo Alén, University of Jyväskylä will act as opponent. Professor Esa Vakkilainen of LUT University will act as custos.

Link to follow the event: https://lut.zoom.us/j/69930626886

Library information:
The dissertation has been published in Acta Universitatis Lappeenrantaensis research series number 962 of the university. ISBN 978-952-335-657-3, ISBN 978-952-335-658-0 (PDF), ISSN-L 1456-4491, ISSN 1456-4491. The electronic version can be found from LUTPub-database: http://urn.fi/URN:ISBN:978-952-335-658-0. A printed version of the dissertation may be purchased online from the LUT Shop: https://lutshop.lut.fi/.