Production of biohydrogen from gasification of waste fuels: Pilot plant results and deployment prospects

Waste-to-energy and waste-to-hydrogen with CCS: Methodological assessment of pathways to carbon-negative waste treatment from an LCA perspective

A growing global population and rising living standards are producing ever greater quantities of waste, while at the same time driving ever-larger demand for energy, especially electricity, or new emerging markets, such as hydrogen in more industrialised countries. A key solution to these challenges of waste disposal, rising energy and hydrogen demand is BECCS (Bioenergy with Carbon Capture and Storage); the generation of bioenergy - in the form of electricity (WtE) or hydrogen (WtH2), as well as heat - from the thermochemical processing of waste. The addition of carbon capture and storage (CCS) to WtE or WtH2 has the potential to make waste a zero or even negative emissions energy source, thus contributing to the removal of greenhouse gases from the atmosphere. This work undertakes a pre-screening of different BECCS configurations based on state of the art technologies and then performed an assessment of representative cases in UK for WtE and WtH2, necessary to understand if novel waste thermal treatment processes may become potential alternatives or improvements to current WtE plants when retrofitted with CCS. A systematic and comprehensive examination of different key Life Cycle Assessment methodological aspects reveals the importance of the functional unit and allocation approach in determining the preferred pathway in a specific context.

An LCA answer to the mixed plastics waste dilemma: Energy recovery or chemical recycling?

The study focuses on mixed plastics waste (MPW), whose complex and unpredictable composition (due to high polymer heterogeneity, additives, and contaminants) makes its valorisation a true technical, environmental, economic, and regulatory challenge. Chemical recycling by means of advanced thermochemical treatments (ATT) could be a successful strategy, able to support the transition from a carbon intensive to a carbon negative sector, and alternative to the current treatments of energy recovery or mechanical downcycling. Some of these ATTs provide an efficient recovery of valuable resources, such as fuels and chemicals, but their role is mainly limited by time necessary to complete the process optimization and implement the required infrastructures. A reliable identification of the best alternatives is thus crucial. A specific LCA approach quantifies the environmental performances of a selected set of ATT technologies for resource recovery from MPW. It includes plastics-to-energy, by combustion or gasification; plastics-to-methane and plastics-to-hydrogen, by gasification; and plastics-to-oil, by thermal pyrolysis. The results highlight the crucial role of carbon capture and storage (CCS) units, which partially reduces that of the specific thermochemical treatment. The best performances, particularly for Climate Change category, are those of the MPW-to-hydrogen by gasification, followed by those of MPW-to-energy by combustion or gasification, all equipped with CCS. The sensitivity analysis considers the evolution of the European energy mix, characterised by a larger utilisation of renewable energy sources, and highlights the corresponding increased sustainability of chemical recycling by ATTs. This suggests that the MPW dilemma should be definitively solved in a close future.

Assessment of hydrogen production from municipal solid wastes as competitive route to produce low-carbon H2

An economic and CO₂ emission impact assessment of the production of H₂ from municipal solid waste in the two configurations of retrofitting an existing waste to energy plant with an electrolysis unit (WtE + El) and of hydrogen production via waste gasification (WtH₂) is made with respect to reference cases of H₂ production by steam reforming of methane (SMR) or of water electrolysis (El). The results are analyzed with reference to two scenarios depending on whether the fate of waste disposal emissions for SMR and El is accounted. The costs of H₂ production as a function of waste gate fee and CO₂ taxation as well as the CO₂ emissions for both scenarios and the four cases of H₂ production analyzed are reported. The results show that produce H₂ from a WtE plant hybridized with an electrolyzer could be economic only when the plant is free from depreciation costs and no CO₂ taxation exists. Conversely, WtH₂ solution results preferable when CO₂ taxation will be applied to the non-biogenic fraction of waste. Conditions when WtH₂ may results competitive to SMR are defined, in terms of both cost of production and CO₂ emissions. With respect to El case, WtH₂ results more competitive under the assumption made in terms of combined costs and CO₂ emissions.

Experimental and thermodynamic study of banana peel non-catalytic gasification characteristics

The Gasification performance of banana peel was examined in a fixed bed reactor. Effect of temperature, steam to carbon ratio (S/C), drying treatment on syngas composition, gas yield, CO₂ selectivity and carbon conversion efficiency (CCE) were investigated. The influence of temperature and S/C on hydrogen production was investigated by thermodynamic analysis. The transient characteristics of banana peel steam gasification were investigated by monitoring the evolutionary behavior of syngas production. An increase in S/C can lead to an increase in the selectivity of CO₂, but excess steam (S/C > 21.7) causes a decrease in H₂ yield and CCE. The increase of temperature is beneficial to the increase of CCE, but which leads to a decrease in CO₂ selectivity. When S/C = 27.1, the effect of temperature on H₂ yield can be divided into CCE control region and CO₂ selectivity control region. At temperature < 1023 K, H₂ yield is more sensitive to the changes of CCE. While at temperature > 1023 K, CO₂ selectivity has a more significant effect on H₂ yield. When S/C = 21.7 and temperature is 1023 K, the yield of H₂ produced from the fresh banana peel gasification reaches the maximum value (76.1 ml/g).

Samples of Ba1-xSrxCe0.9Y0.1O3-δ, 0 < x < 0.1, with Improved Chemical Stability in CO2-H2 Gas-Involving Atmospheres as Potential Electrolytes for a Proton Ceramic Fuel Cell

Comparative studies were performed on variations in the ABO₃ perovskite structure, chemical stability in a CO₂-H₂ gas atmosphere, and electrical conductivity measurements in air, hydrogen, and humidity-involving gas atmospheres of monophase orthorhombic Ba_1−xSr_xCe_0.9Y_0.1O_3−δ samples, where 0 < x < 0.1. The substitution of strontium with barium resulting in Ba_1−xSr_xCe_0.9Y_0.1O_3−δ led to an increase in the specific free volume and global instability index when compared to BaCe_0.9Y_0.1O_3−δ. Reductions in the tolerance factor and cell volume were found with increases in the value of x in Ba_1−xSr_xCe_0.9Y_0.1O_3−δ. Based on the thermogravimetric studies performed for Ba_1−xSr_xCe_0.9Y_0.1O_3−δ, where 0 < x < 0.1, it was found that modified samples of this type exhibited superior chemical resistance in a CO₂ gas atmosphere when compared to BaCe_0.9Y_0.1O_3−δ. The application of broadband impedance spectroscopy enabled the determination of the bulk and grain boundary conductivity of Ba_1−xSr_xCe_0.9Y_0.1O_3−δ samples within the temperature range 25–730 °C. It was found that Ba_0.98Sr_0.02Ce_0.9Y_0.1O_3−δ exhibited a slightly higher grain interior and grain boundary conductivity when compared to BaCe_0.9Y_0.1O_3−δ. The Ba_0.95Sr_0.05Ce_0.9Y_0.1O_3−δ sample also exhibited improved electrical conductivity in hydrogen gas atmospheres or atmospheres involving humidity. The greater chemical resistance of Ba_1−xSr_xCe_0.9Y_0.1O_3−δ, where x = 0.02 or 0.05, in a CO₂ gas atmosphere is desirable for application in proton ceramic fuel cells supplied by rich hydrogen processing gases.