Pretreated residual biomasses in fluidized beds for chemical looping Gasification: Experimental devolatilizations and characterization of ashes behavior

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.

Gasification characteristics and synergistic effects of typical organic solid wastes under CO2/steam atmospheres

Gasification technology is an effective way to achieve efficient, safe, and resourceful disposal of organic solid wastes (OSWs). Due to the complex sources and variable components of the OSWs, the co-disposal is highly essential. Various typical OSWs, including food waste (cooked rice, CR), agricultural waste (rice husk, RH; sugarcane bagasse, SB), and industrial waste (furfural residue, FR), were selected for this study. The gasification characteristics and synergistic performance were examined in terms of thermal weight loss characteristics under the CO2 atmosphere and gaseous product characteristics under the steam atmosphere. The synergistic indices of performance parameters were introduced to quantify the synergistic effects. The gasification activity of FR was remarkably higher than that of other OSWs. In the co-gasification with CR under the CO2 atmosphere, FR played an excellent positive synergistic effect, but the agricultural wastes played a slight or no synergistic effect. In the steam co-gasification, RH, SB, and FR all promoted the generation of syngas, in which FR showed still significant synergistic effects, with the synergistic indices of H2 yield, syngas yield, CCE, and CGE being 4-12 times higher than those of other blended wastes. The excellent performance of FR in (co-)gasification was mainly attributed to the acidic properties of FR, which was confirmed by comparing the (co-)gasification performance of FR with and without water-washing pretreatment. The work provides guidance for the co-disposal of OSWs in industrial applications.

(Co-)gasification characteristics and synergistic effect of hydrothermal carbonized solid/liquid products derived from fresh kitchen waste

Kitchen waste has high moisture and rich organics, which can be transformed into hydrochar by hydrothermal carbonization (HTC) and then used for gasification efficiently. But process water (liquid product from HTC, containing organic compounds) has not been well utilized in the way of thermochemistry. In this study, a scheme of co-gasification of solid and liquid products of kitchen waste HTC process was proposed, and the separate gasification and co-gasification were studied. The results showed that after HTC process, the obtained hydrochar size became smaller and uniform, and the high heating value increased from 19.90 MJ/kg to 28.03 MJ/kg. The carbon skeleton of hydrochar was mainly composed of aromatic and alkyl C, which was easily converted into coke during gasification. Process water mainly contained pyrazine organics, and its C and N content were 18.94 g/L and 3.25 g/L, respectively. The co-gasification syngas yield of solid and liquid products was significantly higher than the calculated total yield of separate gasification. There was obvious synergistic effect in the coke co-gasification stage, and the H2 production was 1.24 times of the calculated value. Synergistic effect was mainly caused by the introduction of process water, which contained 785.82 mg/L of K and would catalyze the coke co-gasification. HTC coupled with co-gasification is an efficient disposal for kitchen waste with high moisture.

Valorization of biomass through gasification for green hydrogen generation: A comprehensive review

Green and sustainable hydrogen from biomass gasification processes is one of the promising ways to alternate fossil fuels-based hydrogen production. First off, an overview of green hydrogen generation from biomass gasification processes is presented and the corresponding possible gasification reactions and the effect of respective experimental criteria are explained in detail. In addition, a comprehensive explanation of the catalytic effect on tar reduction and hydrogen generation via catalytic gasification is presented regarding the functional mechanisms of various types of catalysts. Furthermore, the commercialization aspects, the associated technical challenges and barriers, and the prospects of a biomass gasification process for green hydrogen generation are discussed. Finally, this comprehensive review provides the related advancements, challenges, and great insight of biomass gasification for the green hydrogen generation to realize a sustainable hydrogen society via biomass valorization.

Syngas biomethanation: Current state and future perspectives

In regions highly dependent on fossil fuels imports, biomethane represents a promising biofuel for the transition to a bio-based circular economy. While biomethane is typically produced via anaerobic digestion and upgrading, biomethanation of the synthesis gas (syngas) derived from the gasification of recalcitrant solid waste has emerged as a promising alternative. This work presents a comprehensive and in-depth analysis of the state-of-the-art and most recent advances in the field, compiling the potential of this technology along with the bottlenecks requiring further research. The key design and operational parameters governing syngas production and biomethanation (e.g. organic feedstock, gasifier design, microbiology, bioreactor configuration, etc.) are critically analysed.