• Energy Research

This study aims to investigate the kinetic compensation effects (KCE) and gain insights into the mechanisms, during gasification of Loy Yang brown coal char with steam, in an in-situ fluidized bed gasification operation for two-particle size ranges (106–150 and 180–212 µm). The instantaneous rate of char gasification and CO, CO₂, and H₂ formation was measured by continuous monitoring of product gas composition through a quadrupole mass spectrometer. Gasification of the smaller particle size range (106–150 µm) in kinetics-controlled regime shows less importance of char-catalyzed element on the WGS reaction, as revealed by the apparent activation energy and apparent frequency factor for CO and CO₂ formation. However, the study of kinetic parameters of char consumption on gasification using coal char with larger particle sizes (180–212 µm) indicated the limitations of intraparticle diffusion. That potentially affects the CO₂ formation by catalyzed WGS through re-adsorption of CO on catalytic char surface at a higher conversion level (> 0.3) as revealed by the difference in the extent of KCE for CO and CO₂ formation. The difference in the extent of KCE for char consumption and H₂ formation for bigger particles indicates the intraparticle diffusion limitations also appear to affect the route of H₂ formation, i.e., significantly produced through adsorption on catalytical active site with less involving the carbon active sites on char surface.

Study aims to experimentally investigate the physical significance of continuously evolved kinetic parameters i.e.lnAapp and Eapp including the importance of parameters, i.e., m and c, in the kinetic compensation effect (KCE) lnAapp = mEapp + c during steam gasification of char. To gain further insights into the char gasification mechanism in the steam atmosphere, an understanding of KCE is desirable. Two low-rank coals, viz., Loy Yang brown coal and Collie sub-bituminous coal samples of particle sizes 106150 µm and 180212 µm, are selected for fluidized bed gasification. The high-sensitive, quadrupole mass spectrometer (QMS) is used to measure the product gas composition for determining the instantaneous rate of char-H₂O reactions. Results suggest that the difference in Eapp with the change in coal sample at fixed conversion level, signifies the relative condensation of residual char, whereas the respective differences in lnAapp reflects the difference in the relative proportion of active sites consumed during char gasification under the reaction controlled by the chemical reactivity of char. However, the continuous variation in Eapp with conversion in the event of char gasification of any coal sample, displays the change in the rate of surface reaction following surface desorption with conversion and the variation of lnAapp potentially presents the change in the rate of adsorption of gasifying agents with conversion. In the subsequent KCE, the slope ‘m’ shows the reactiveness of char by displaying the impact of change in the rate of surface reaction with the desorption on the rate of surface adsorption during char gasification. The degree of deviation in char reactivity due to the evolution of KCE from a foreseeable condition of having non-KCE is indicated by intercept ‘c’.

This work demonstrates the feasibility of using biochars derived from a variety of waste feedstocks, such as food organics and garden organics (FOGOs), garden organics (GOs), and biosolids (BSs), provided by Barwon Water (BW) and South East Water (SEW), as active electrode material for supercapacitor application. Four different biochars were produced by the co-pyrolysis of pre-treated mixed waste feedstocks, which were fabricated into a two-electrode symmetric supercapacitor set-up to evaluate their energy storage potential. Two different approaches, (i) carbon nanoparticle coating/modification and (ii) thermochemical activation, were employed to improve the electrochemical properties of the biochars. Potassium hydroxide-activated biochar derived from BW’s triple waste feedstock mixture (comprising 70% GOs, 20% FOGOs, and 10% BSs) demonstrated the highest specific capacitance (30.33 F/g at 0.1 A/g), energy density (4.21 Wh/kg), and power density (2.15 kW/kg) among the tested samples. Such waste-derived biochar offers several benefits for energy storage, including cost-efficiency and sustainable alternatives to traditional electrode materials. The biochar’s electrochemical performance can be further improved by improving the feedstock quality by different pre-treatments.

Per- and polyfluoroalkyl substances (PFAS) are a group of fluorinated synthetic chemicals that are highly recalcitrant, toxic, and bio-accumulative and have been detected in biosolids worldwide, posing potential risks to humans and the environment. Recent studies suggest that the organic C-F bond in PFAS can be destructed and potentially mineralised into inorganic fluorides during thermal treatment. This study focuses on thermodynamic equilibrium investigations and the fate of fluorine compounds post-PFAS destruction during biosolid thermal treatment. The results indicate that gas-phase fluorine compounds are mainly hydrogen fluoride (HF) and alkali fluorides, whereas solid-phase fluorine compounds include alkaline earth fluorides and their spinels. High moisture and oxygen content in the volatiles increased the concentration of HF in the gas phase. However, adding minerals reduced the emission of HF in the gas phase significantly and enhanced the capture of fluorine as CaF2 spinel in the solid phase. This study also investigates the effect of feedstock composition on the fate of fluorine. High ash content and low volatile matter in the feedstock reduced HF gas emissions and increased fluorine capture in the solid product. The findings of this work are useful in designing thermal systems with optimised operating conditions for minimising the release of fluorinated species during the thermal treatment of PFAS-containing biosolids.

AbstractBiogas contains significant quantities of undesirable and toxic compounds, such as hydrogen sulfide (H2S), posing severe concerns when used in energy production-related applications. Therefore, biogas needs to be upgraded by removing H2S to increase their bioenergy application attractiveness and lower negative environmental impacts. Commercially available biogas upgradation processes can be expensive for small and medium-scale biogas production plants, such as wastewater treatment facilities via anaerobic digestion process. In addition, an all-inclusive review detailing a comparison of biochar and hydrochar for H2S removal is currently unavailable. Therefore, the current study aimed to critically and systematically review the application of biochar/hydrochar for H2S removal from biogas. To achieve this, the first part of the review critically discussed the production technologies and properties of biochar vs. hydrochar. In addition, exisiting technologies for H2S removal and adsorption mechanisms, namely physical adsorption, reactive adsorption, and chemisorption, responsible for H2S removal with char materials were discussed. Also, the factors, including feedstock type, activation strategies, reaction temperature, moisture content, and other process parameters that could influence the adsorption behaviour are critically summarised. Finally, synergy and trade-offs between char and biogas production sectors and the techno-economic feasibility of using char for the adsorption of H2S are presented. Biochar’s excellent structural properties coupled with alkaline pH and high metal content, facilitate physisorption and chemisorption as pathways for H2S removal. In the case of hydrochar, H2S removal occurs mainly via chemisorption, which can be attributed to well-preserved surface functional groups. Challenges of using biochar/hydrochar as commercial adsorbents for H2S removal from biogas stream were highlighted and perspectives for future research were provided. Graphical abstract

This study aimed to experimentally investigate the kinetic compensation effects (KCEs) during Loy Yang brown coal char gasification in an O2 environment at atmospheric pressure in a fluidized-bed g...