Efficient CO₂ utilization in the thermochemical conversion of biomass plays an important role in creating a future low-carbon economy. This study attempts to explore the CO₂-assisted chemical looping gasification and co-gasification process of lignocellulosic biomass components (hemicellulose, cellulose, and lignin) with iron oxide oxygen carriers using thermogravimetry and differential thermal analysis. Three different iron oxide oxygen carrier-to-biomass (O/B) ratios were taken into account to deeply understand the thermal degradation characteristics of individual components (O/B ratio: 0) and their blending with iron oxide oxygen carriers (O/B ratio: 0.5 and 1). Meanwhile, the reduction characteristics of three major biomass components were also investigated in terms of X-ray diffraction (XRD), synergistic interaction, and reduction degree. Experimental results suggest that the existence of iron oxide oxygen carriers could accelerate the reaction kinetics under the reactive CO₂ environment, arising from the competitive relationship between the direct reduction reaction by char in biomass and the Boudouard reaction at high temperatures (600–950 °C). Interestingly, the reoxidation behavior of the reduced iron oxide is observed at high temperatures, especially for lignin. Among all the tested biomass materials, their ability to reduce iron oxide oxygen carriers under the CO₂ atmosphere follows the order of biomass mixture (1:1:1 wt%)>lignin>xylan>cellulose. Moreover, the findings indicate that significant synergistic interaction exists during the CO₂-assisted chemical looping co-gasification process.

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Waste-to-energy (WTE) conversion technologies for generating renewable energy and solving the environmental problems have an important role in the development of sustainable circular economy. This paper presents a novel high-efficiency WTE power plant using refuse-derived fuel (RDF) as feedstock by integrating torrefaction (T) pretreatment with plasma gasifier (PG), solid oxide fuel cell (SOFC), and combined heat and power (CHP) system. The combined impacts of torrefaction conditions (i.e. temperature and residence time) and steam-to-fuel (S/F) ratio on the energy and environmental performances of the proposed T-PG-SOFC-CHP power plant without CO₂ capture (System I) is first evaluated. Results show that torrefaction of RDF prior to plasma gasification provides better syngas quality and therefore the system electrical efficiency (SEE) and CHP efficiency (CHPE) of System I can be markedly boosted compared to that of untreated RDF. However, the integration of torrefaction unit shows a negative effect on the energy return on investment (EROI) due to high energy demands for torrefaction and plasma gasification. Overall, the values of CHPE of System I range from 47.25% to 55.39% when the torrefaction temperatures of 200 and 250 °C are adopted. In contrast, the torrefaction of RDF at 300 °C is not a recommended condition for operation in the T-PG-SOFC-CHP power plant because of noticeably negative energy and environmental impacts. Moreover, to prevent the risk of carbon deposition on the SOFC anode, a recirculation ratio (RR) of the anode off-gas of 30% is required. Finally, the introduction of oxy-fuel combustion technology into the T-PG-SOFC-CHP system for CO₂ capture (System II) allows to achieve a zero direct CO₂ emission WTE power plant. However, this results in an energy penalty of about 5.40–6.77% associated with the CO₂ capture and compression process.

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Since municipal solid waste (MSW) is a negatively priced, abundant, and essentially renewable feedstock, energy recovered from MSW is a useful technology to reduce the consumption of fossil fuels, and also reduces the expenses needed to dispose of MSW. Three configurations of MSW-based IGCC power system (Design 1), MSW-based IGCC polygeneration system (Design 2), and CaO-based IGCC polygeneration system (Design 3) are proposed. Design 1 uses a combination of an identified MSW gasifier, an integrated intermittent chemical-loop air separation (IICLAS), and Rankine and Brayton cycles to generate electricity and achieve the high concentration of CO₂ emissions around 93.3%~94.7%. The process for co-production of DME and MeOH in Design 2, which replaces the Rankine cycle in Design 1, could increase the net energy efficiency of Design 1 by 71.6%, but the total CO₂ emissions from Design 2 are merely 7.97% of Design 1. The calcium looping gasification (CaLG) process in Design 3, which replaces the MSW gasifier in Design 2, could increase the production rate of DME of Design 2 by 12.5%. The CO₂ concentration from the calcinator in Design 3 is higher than CO₂ concentration in flue gas from Designs 1 and 2 by 2.0%~3.5%. Through exergy analysis, the overall exergy efficiency of Design 3 is lower than Designs 1 and 2 by 3.2%~10.1% due to the exergy destruction rate and ratio in the gasification zone of Design 3 higher than other designs. The GaLG process could increase the DME yield as well as the outlet CO₂ concentration, but this approach design induces a higher exergy loss.

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Plasma gasification of raw and torrefied woody, non-woody, and algal biomass using three different gasifying agents (air, steam, and CO₂) is conducted through a thermodynamic analysis. The impacts of feedstock and reaction atmosphere on various performance indices such as syngas yield, pollutant emissions, plasma energy to syngas production ratio (PSR), and plasma gasification efficiency (PGE) are studied. Results show that CO₂ plasma gasification gives the lowest PSR, thereby leading to the highest PGE among the three reaction atmospheres. Torrefied biomass displays increased syngas yield and PGE, but is more likely to have a negative environmental impact of N/S pollutants in comparison with raw one, especially for rice straw. However, the exception is for torrefied grape marc and macroalgae which produce lower amounts of S-species under steam and CO₂ atmospheres. Overall, torrefied pine wood has the best performance for producing high quality syngas containing low impurities among the investigated feedstocks.

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A coupled hydro-mechanical model is presented to account for the influence of plants on the mechanical and hydrological behaviour of soil. A modified Cam-clay model is implemented in a finite element code to consider the combined effect of vegetation via root reinforcement and evapotranspiration. The model is calibrated and validated by laboratory tests on soil containing roots. A vegetated soil sample is subjected to cycles of wetting and drying. The pore pressure is measured by tensiometers installed at different depths. Numerous tests on rootreinforced and non-reinforced soil are carried out. The enhancement in soil strength is obtained by comparing the test results. The tests are simulated using the numerical model and the results are compared with the experimental data.@en