The modern world is faced with a multitude of environmental and socio-economic issues, stemming from the way that energy is used and converted. Climate change due to anthropogenic activities (use of fossil fuel resources and its associated CO2 equivalent emissions), has greatly affected humankind and nature in general, by leading to extreme weather phenomena and reducing the quality of life especially of people belonging to vulnerable communities. The unsustainable practices of the energy sector and the increased energy and materials needs of the public, have brought the situation to a point where immediate action is required to mitigate the effects of climate change. Furthermore, as became apparent by studying the impact of the COVID-19 pandemic and the Russo-Ukrainian war, the global energy market is heavily exposed to price and availability shocks that have a significant negative impact on the quality of life of people globally also in the very short term. Overall, the transition of the energy sector to a green and renewable alternative is essential and bioenergy constitutes a crucial piece of the puzzle of such a sustainable future....@en

This work focuses on the numerical modelling and experimental validation of the hydrodynamic behaviour of a novel 50 kW_th indirectly heated bubbling fluidized bed steam reformer. The hydrodynamic behaviour of fluidized beds with immersed vertical tubes and complex fluidized bed geometries in general have not been thoroughly investigated in terms of numerical modelling coupled with experimental validation for pilot scale reactors. Therefore, the present study contributes to the fluidized bed hydrodynamics numerical modelling field, while investigating a novel reactor concept. Simulations were performed employing the Two-Fluid Model approach, using the Kinetic Theory of Granular Flows (KTGF) and the adjusted Syamlal O'Brien drag model. The reactor's hydrodynamic behaviour was simulated successfully, as showcased by a comparison of global hydrodynamic metrics (bed height, pressure drop) between computational and experimental results. Simulations were performed with and without considering an additional nitrogen gas feed on the side of the reactor (feeding system pressurization). Overall, for both cases, for realistic values of the particle restitution coefficient channelling of the gas flow near the reactor walls was observed. Larger bubbles appeared to be forming near the outer wall of the reactor for the no side-flow simulations. The opposite behaviour was encountered for the side-flow simulations due to stream-like behaviour of the side-flow moving up against the reactor's outer wall. The choice to limit the simulations to a 72° symmetry domain was validated, indicating the possibility of further reduction. Finally, it was argued that increasing the reactor's diameter could potentially lead to a reduction of the observed channelling of the fluidization media and improve the mixing achieved in the reactor and thus the conversion efficiency of the IHBFBSR during gasification applications.

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Our work provides a thorough characterization of different biochars produced by a novel 50 kW_th Indirectly Heated Bubbling Fluidized Bed Steam Reformer. This study investigates the effect of temperature and gasification agent on the physico-chemical properties of biochars. We combined macro, micro and nano characterization techniques to provide a clear picture of the biochar characteristics, surface functionality and its “inert” nature toward potential applications. Our results demonstrate that indirect gasification is capable of producing carbon-rich biochars (> 92%) with increased porosity (89–198 cm³.g⁻¹), high heating value (28–31 MJ.kg⁻¹ a.r.) and aromaticity compared to the parent biomass. All biochars have lower O/C (0.02–0.04) and H/C atomic ratios (0.09–0.19), similar to anthracite. For the range of tested gasification conditions, air/steam gasification at an equivalence ratio of 0.20 and steam-to-biomass ratio of 1.2 provides the highest biochar yield (7.3%), while maintaining syngas composition optimal. On the other hand, air gasification produces biochars with relatively high content of inorganic elements. Indirectly heated biochars are compliant with the European Biochar Certificate regarding the carbon content, O/C ratio, H/C ratio. Our biochars may provide an improvement in agricultural yield and CO₂ adsorption, especially those produced under air/steam gasification conditions. Our novel indirect design not only constitutes a promising development in the field of biomass allothermal gasification but also can help improving gasification circularity through the production of high quality biochar.

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As the push towards more sustainable ways to produce energy and chemicals intensifies, efforts are needed to refine and optimize the systems that can give an answer to these needs. In the present work, the use of neural networks as modelling tools for lignocellulosic biomass pyrolysis main products yields estimation was evaluated. In order to achieve this, the most relevant compositional and reaction parameters for lignocellulosic biomass pyrolysis were reviewed and their effect over the main products yields was assessed. Based on relevant literature data, a database was set up, containing parameters and experimental results from 32 published studies for a total of 482 samples, including both fast and slow pyrolysis experiments performed on a heterogeneous collection of lignocellulosic biomasses. The parameters that in the database configured as best predictors for the solid, liquid and gaseous products were determined through preliminary tests and were then used to build reduced models, one for each of the main products, which use five parameters instead of the full set for the estimation of yields. The procedures included hyperparameter optimizations steps. The performances of these reduced models were compared to those of the ones obtained using the full set of parameters as inputs by using the root mean squared error (RMSE) as metric. For both the char and gas products, the best results were consistently achieved by the reduced versions of the network (RMSE 5.1 wt% ar and 5.6 wt% ar respectively), while for the liquid product the best result was given by the full network (RMSE 6.9 wt% ar) indicating substantial value in proper selection of the input features. In general, the char models were the best performing ones. Additional models for the liquid and gas product featuring char as additional input to the system were also devised and obtained better performance (RMSE 5.5 wt% ar and 4.9 wt% ar respectively) compared to the original ones. Models based on single studies were also included in order to showcase both the capabilities of the tool and the challenges that arise when trying to build a generalizable model of this kind. Overall, artificial neural networks were shown to be an interesting tool for the construction of setup-unspecific biomass pyrolysis product yield models. The obstacles standing currently in the way of a more accurate modelling of the system were highlighted, along with certain literature discrepancies, which hinder reliable quantitative comparison of experimental conditions and results among separate studies.

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Within this work, a novel 50 kW_th indirectly heated bubbling fluidized bed steam reformer (IHBFBSR) is presented, along with its commissioning experiments. In the IHBFBSR, heat is provided through two radiant tube natural gas burners in the bed and the freeboard area. The aim of this innovative design is sufficient heat provision for biomass steam reforming and cracking reactions and heat loss reduction, thus allowing the possibility of scaling-up to an industrial level. Experiments were performed with two woody biomass feedstocks and two bed material particle sizes under different operating conditions (steam to biomass ratio, lambda, temperature), in order to identify the setup's main characteristics. Product gas composition and quality, as well as the cold gas efficiency of the IHBFBSR were in reasonable agreement to similar systems, however carbon conversion prediction needs further improvement. H₂ production and tar removal are favoured by small bed material particle sizes as well as by char accumulation in the bed area. Furthermore, air injection above the bed led to improved H₂/CO ratios and lower tar yields compared to when air is used as a fluidization agent. Overall, it was shown that the IHBFBSR technology constitutes a promising development in the field of biomass allothermal gasification.

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This work is focused on the process system modelling of an indirectly heated gasifier (10 MW_th) using torrefied wood as feedstock and its integration with methanol and power production using Aspen Plus®. The modelling of the gasification process along with the obtained reaction kinetics were validated with experimental data found in literature. Different processing steps such as gasification, gas cleaning and upgrading, methanol synthesis and energy conversion, were modelled and their performance was optimized through a series of sensitivity studies. The results obtained were then used to investigate the effect of different technologies and the variation of operational parameters on the overall process performance. Three cases were examined: “syngas production” (case 1), “methanol production” (case 2), and “power production” (IGCC) (case 3). Case 1 and case 2 were simulated using sand and dolomite as bed materials respectively, in order to study the incorporation of Absorption Enhanced Reforming (AER) on the syngas and methanol production efficiency. For case 3 the simulation was performed for two different configurations: a conventional Integrated Gasification Combined Cycle (IGCC) and an innovative Inverted Brayton Cycle (IBC) turbine system. Dolomite was used as the bed material for both configurations. For case 1, an increase of 5% in hydrogen yield in the product gas when AER is applied was observed. For case 2, higer values of Cold Gas Efficiency and Net Efficiency (34% and 60% instead of 33% and 55%, respectively) and a slightly lower value of Carbon Conversion (96% instead of 100%) were obtained when AER was employed. Gasification temperature was lowered by 110 °C in this scenario. For case 3, a lower value of Net Efficiency was obtained when IBC was considered (43% instead of 47%), while a value of 60% was obtained for methanol production with AE. Moreover, the results of case 3, showed that the latent heat in the hot syngas is best utilised when IBC is considered. The developed model accurately predicted the composition of the produced gas and the operational conditions of all the identified blocks within the methanol synthesis and power production processes. This way the use of this model as a generic tool to compare the utilization of different technologies on the performance of the overall process was validated.

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The present work focuses on the sampling procedure and quantification of the PAH yield from the fast pyrolysis of waste softwood. In particular, fast pyrolysis experiments were conducted using a CDS Pyroprobe 5200 at temperatures between 500 °C and 1000 °C, at a heating rate of 600 °C/s for a sample size of 30 mg. High performance liquid chromatography (HPLC) was used for the determination of the PAH compounds present in the liquid sample fraction, while a micro – GC was employed for the analysis of the main gaseous products (CO, CO₂, CH₄ and H₂). An alternative tar sampling protocol was proposed, which employed the use of a cold trap (50 °C) and an isopropanol filled impinger bottle for the collection of the condensable products. The experiments were compared to heated foil reactor based pyrolysis tests within the same temperature range and heating rate, except for a slightly lower sample size (10 mg). The Pyroprobe and adapted sampling system proved to be more efficient regarding PAH capture and quantification compared to the heated foil reactor. Naphthalene, acenaphthylene and phenanthrene were the main PAH compounds detected. The PAH yields increased with pyrolysis temperature, up to values corresponding to roughly 0.2 wt% of the overall yield at 1000 °C. From the results it was derived that PAH evolution is mainly a product of secondary decomposition of primary tar, since the char yield stabilized for higher temperatures and the yields of CO, H₂ and CH₄ increased. Overall mass balance closure values were around 80 wt% on average. Char and gas yields were determined with high reproducibility, however gravimetric liquid analysis lacked due to the inability to gravimetrically measure the yield condensing in the impinger bottle. Future work is aimed on improving on this particular aspect. Overall, the alternative tar sampling system proposed was successful in the quantification of PAH from biomass fast pyrolysis experiments offering increased flexibility, accuracy and practicality of use.

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The large variations found in literature for the activation energy values of main biomass compounds (cellulose, hemicellulose and lignin) in pyrolysis TGA raise concerns regarding the reliability of both the experimental and the modelling side of the performed works. In this work, an international round robin has been conducted by 7 partners who performed TGA pyrolysis experiments of pure cellulose and beech wood at several heating rates. Deviations of around 20 – 30 kJ/mol were obtained in the activation energies of cellulose, hemicellulose and conversions up to 0.9 with beech wood when considering all experiments. The following method was employed to derive reliable kinetics: to first ensure that pure cellulose pyrolysis experiments from literature can be accurately reproduced, and then to conduct experiments at different heating rates and evaluate them with isoconversional methods to detect experiments that are outliers and to validate the reliability of the derived kinetics and employed reaction models with a fitting routine. The deviations in the activation energy values for the cases that followed this method, after disregarding other cases, were of 10 kJ/mol or lower, except for lignin and very high conversions. This method is therefore proposed in order to improve the consistency of data acquisition and kinetic analysis of TGA for biomass pyrolysis in literature, reducing the reported variability.

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Furfural is a very promising product of lignocellulosic biomass-based biorefineries and has the potential to become a useful resource for further conversion and utilization. Aquatic plants show an enormous potential as feedstock since they do not compete for land use, and they require minimal water consumption in a biorefinery concept due to their very high water content. This work is focused on experimental studies of furfural production from water hyacinth (Eichhornia crassipes) by means of aqueous, acid-catalyzed dehydration. The temperature range of the process, and the acid and seawater presence were chosen based on the previous relevant studies. The aim of the study was to determine whether water hyacinth is suitable for furfural production. The experiments were performed between 160°C and 200°C with a water hyacinth concentration of 2 wt%. The results suggest that the effects of acid catalyst presence on biomass dehydration are similar to the case of pure pentose dehydration. Furthermore, the addition of seawater did not have a positive catalytic effect in terms of the furfural yield. The maximum yield was 53.2 mol% based on the C5 sugar content in the original biomass. The furfural yield of 7.9 wt% of water hyacinth input was comparable to the yield of feedstocks such as corn cob, bagasse, and oat's residue and higher than the cases of rice straw or hulls. Thanks to the comparatively high pentose potential, water hyacinth shows promising results as a candidate feedstock for furfural production. A certain variability of pentosan should be taken into account, as the chemical composition of the plant depends on the source and harvesting seasons.

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The present study explored a thermochemical treatment method as an alternative approach to process animal feedlot (poultry litter). Fast pyrolysis of poultry litter experiments was conducted using a Pyroprobe 5200 reactor in the temperature range of 400-600 °C. The influence of reactor temperature on the yield of pyrolytic gases, condensate (bio-oil) and biochar yield was reported along with the mass balance. The biochar yield decreased consistently with an increase in temperature (from ~62 wt.% at 400 °C to ~ 40 wt.% at 600 °C), whereas the maximum bio-oil yield 23.2 wt.% was reported at 600 °C. The evolved pyrolytic gases were dominated by CO and CO2 and have shown an increasing trend with the temperature. Evolved gases were measured by a micro-gas Chromatograph. The yield of the liquid fraction (bio-oil) and biochar were quantified for the mass balance analysis. The yield of liquid and biochar are in agreement with previous work.

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This work focused on system modelling regarding the investigation of biomass gasification and its integration with methanol synthesis and power production. Indirect gasification technology was chosen and modelledusing Aspen Plus®. The gasification process along with the reaction kinetics were validated with experimental data from the literature. Different processing steps towards the conversion of biomass to methanol were identified and modelled. The identified process blocks were: Gasifier, Gas Cleaning Unit, Methanol Synthesis and the Energy Conversion Network were optimised by performing a series of sensitivity studies. The optimised model was then used to study the effect of choosing different technologies and parameters within the blocks on the overall process behaviour. Two different case studies were examined, each distinct from each other by a difference in technology of one of the blocks. The two cases concerned the impact of incorporation of Absorption Enhanced Reforming (AER) on the methanol synthesis process, simulated by using dolomite as the bed material. Sankey plots for each of these cases were drawn to visualize the energy losses in such complicated systems. The developed model accurately predicted the composition of the major product gas and operational conditions of all the identified blocks within the methanol synthesis process. The effect of incorporating AER on the overall methanol synthesis process was simulated. The developed model proved its use as a generic tool to compare the effect of different choices in technology on the performance of the overall process.@en

In this study torrefied feedstocks, consisting of mixed wood and wood residues torrefied at 300 °C and ash wood torrefied at 250 and 265 °C, were pyrolyzed in a pyroprobe at five pyrolysis temperatures (600–1000 °C) and a fast heating rate (600 °C·s−1) to investigate the effect of torrefaction on the formation of volatiles and their evolution in a 100 kW circulating fluidized bed gasifier. Results showed that torrefaction converted mostly the hemicellulose content of feedstocks. Furthermore, torrefaction resulted in decreasing the bio-oil and gas yields, increasing the char and phenol yields and not affecting the polyaromatic hydrocarbons yield. Phenol and naphthalene showed the largest yield at 600–700 °C and 800–1000 °C, respectively. At such high temperatures, the rest polyaromatic hydrocarbons showed yields similar to phenol's. At 900 °C torrefaction affected mainly the phenolic species, with 4-propyl-phenol being the dominant species of its group for mixed wood and wood residues feedstock. In the gasifier, H2 and CO2 yields increased, CH4 yield remained constant, and CO yield depended on tar conversion and oxidation and steam reactions. The phenol and naphthalene yields further decreased and increased, respectively, whereas, polyaromatic hydrocarbons did not change in the gasifier.@en