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

Dry torrefaction and continuous thermochemical conversion for upgrading agroforestry waste into eco-friendly energy carriers: Current progress and future prospect

Agroforestry Waste (AW) is seen as a carbon neutral resource. However, the poor quality of AW reduced its potential application value. Even more unfortunately, chlorine in AW led to the formation of organic pollutants such as dioxins under higher temperatures. Alkali and alkaline earth metals (AAEMs) in ash may deepen the reaction degree. Co-pretreatment of dry torrefaction and de-ashing followed by thermochemical conversion is a promising technology, which can improve raw material quality, inhibit the release of organic pollutants and transform AW into eco-friendly energy carriers. In order to better understand the process, theoretical basis such as the structural characteristics, thermal properties and separation methods of structural components of AW are described in detail. In addition, dry torrefaction related reactors, process parameters, kinetic analysis models as well as the evaluation methods of torrefaction degree and environmental impact are systematically reviewed. The problem of ash accumulation caused by dry torrefaction can be well solved by de-ashing pretreatment. This paper provides a comprehensive discussion on the role of the two- and three-stage conversion technologies around dry torrefacion, de-ashing pretreatment and thermochemical conversion in products quality enhancement. Finally, the existing technical challenges, including suppression of gaseous pollutant release, harmless treatment and reuse of torrefaction liquid product (TPL) and reduction of torrefaction operating costs, are summarized and evaluated. The future research directions, such as vitrification of the reused TPL (after de-ashing or acid catalysis) and integration of oxidative torrefaction with thermochemical conversion technologies, are proposed.

Life cycle assessment of a biomass based chemical looping combustion

Chemical looping combustion (CLC) is a promising technology that generates energy while inherently separating carbon dioxide from air using oxygen carriers. This allows for an efficient and cost-effective means of carbon capture and storage. Current CLC systems use coal with metal oxides for combustion in the fuel reactor, thus, resulting in some environmental impacts. Recent life cycle assessment (LCA) of CLC studies have indicated the environmental impacts of conventional coal-based CLC, especially on the global warming potential. To mitigate these environmental impacts, this study proposes the use of a biomass-based CLC and evaluates its impacts using LCA. A case study in the Philippines is adopted where rice husks are used as biomass feedstock. A kilowatt-hour of electricity generated from the CLC plant is utilized as the functional unit. A relative comparison of environmental impacts was considered between the coal-based power plant, the coal-based CLC plant, and the biomass-based CLC plant. The single score results have shown that the biomass-based CLC has the least environmental impacts relative to the coal-based power plant and the coal-based CLC plant. However, it is noted that water consumption is the main drawback of utilizing rice husks as CLC biomass feedstock. The majority of the environmental impacts of the coal-based CLC and the coal-based power plant were derived from upstream processes such as coal mining and processing. With the use of rice husks as CLC biomass feedstock, net negative emissions were achieved.

COVID-19 and industrial waste mitigation via thermochemical technologies towards a circular economy: A state-of-the-art review

The increasing awareness of waste circular economy has motivated valorization strategies for minimizing resource consumption and waste production in the private sector. With the rise of various industrial wastes and with the emergence of COVID-19 wastes, a sustainable approach is needed to mitigate the growing concern about wastes. Thermochemical treatment technologies in the form of direct combustion, torrefaction, pyrolysis, and gasification have been identified to have vital roles in the value-creation of various waste streams. Moreover, the alignment of thermochemical processes for waste mitigation concerning the circular economy framework needs to be established. Accordingly, a comprehensive review of the different thermochemical treatment options for industrial and the novel COVID-19 medical wastes streams is conducted in this study. This review focuses on highlighting the instrumental role of thermochemical conversion platforms in achieving a circular economy in the industrial sector. Various strategies in waste mitigation through various thermochemical processes such as management, recovery, reduction, and treatment are discussed. The results show that thermochemical technologies are beneficial in addressing the sustainability concerns on mitigating wastes from the industrial sector and wastes brought by the COVID-19 pandemic. This also includes the current issues faced as well as future perspectives of the thermochemical conversion technologies.