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Computational Fluid Dynamics (CFD) modeling and experimental campaigns have been performed to investigate the performance of a 140 kW biomass fixed-bed boiler. The most widely used modeling approaches in literature, such as those representing the biomass bed as a single or a series of interconnected perfectly stirred reactors, were shown to be unsuited and affected by large uncertainties on the model definition. Indeed, point measurements just above the fuel bed, performed in this work, have shown that, despite the small bed dimension, temperatures are strongly not uniform. In the present work, a simple and efficient method to overcome these limitations is suggested by representing the biomass bed as a porous medium with sources and sinks of chemical species and energy. In this manner the impact of the primary air injection on the resulting field is taken into account. The predictions provide a satisfactory agreement with the available measurements, even though improvements have to be made especially for better describing the kinetics.

Computational Fluid Dynamics (CFD) is a consolidated tool to support industrial projects development and was recently adopted in the framework of consequence assessment and safety analyses. In the present study, a CFD model of pressurized vessels exposed to an accidental fire was developed, with the aim to determine the transient behavior of the stored fluid during the heat-up. An integral model for consequence assessment was adopted in order to set advanced boundary conditions to the CFD model. The results of CFD simulations allowed predicting temperature and velocity of both liquid and vapor phases, as well as the complex recirculation phenomena induced by natural convection. This allowed determining the pressurization rate in the fired tank, thus obtaining key indications for the evaluation of the residual mechanical resistance.

Experimental campaigns were carried out on a 140kW fixed-bed biomass boiler to investigate the effect of primary and secondary air distribution on temperature and combustion products and to validate a numerical model. Specifically, a Computational Fluid Dynamics model for the freeboard, based on a single-phase turbulent reactive flow model, was coupled to an off-line biomass bed model that encompass evaporation, devolatilization and char oxidation of the biomass, using an iterative procedure to take into account the radiative transfer between the biomass bed and the freeboard. The inlet turbulence level affects strongly the turbulent mixing of volatiles and it was proposed to assimilate the flow from the biomass bed as that coming from a perforated plate.

Microalgae have been suggested as one of the most promising feedstock for the production of bioenergy and biofuels, including biodiesel and aviation fuels, because of the high oil content of selected species. In the context of biofuel production from microalgae, anaerobic digestion of microalgal biomass residues after oil extraction has the potential to make the process more sustainable and increase the energy efficiency. The main goal of this study was to assess microalgae residues as substrates for anaerobic digestion and investigate their potential for biomethane production. Biochemical Methane Potential (BMP) tests were carried out on a microalgal species, Nannochloropsis gaditana, selected for its high oil content and fast growth rate. The methane potentials observed for the microalgae residue after lipid extraction were higher than those recorded for the raw microalgae samples. Co-digestion with cellulose did not clearly enhance the anaerobic digestion performances.

Flameless combustion is a novel combustion technology able to ensure high combustion efficacies with low pollutant emissions thanks to the dilution of reactants, usually achieved through recirculation of combustion products. The technology has been successfully applied in several processes and has been found to be able to handle a large variety of fuels, including low grade fuels, industrial by-products and hydrogen. Further development of this innovative combustion technology would benefit of Computational Fluid Dynamics (CFD) tools; however, modelling flameless combustion is much more challenging than conventional flames, because of the strong coupling between turbulent mixing and chemical kinetics. In particular the chemical kinetics plays a fundamental role, even though there no common opinion on the degree a mechanism can be reduced. Some useful works may be found on flameless burners fed with methane, but there is lack of information on different fuels. The present work describes the numerical modelling of an ethylene jet flame issuing in a hot coflow burner, emulating flameless combustion and fully characterised in literature, with the scope of investigating the potential for chemistry reduction in the context of flameless combustion. A Principle Component/Variable Analysis is used to investigate the most important species in the chemical mechanism and subsequently a dimension reduction technique based on the Rate-controlled constrained-equilibrium (RCEE) principle is applied to the detailed mechanism to be coupled to the CFD code, in order to make simulations more affordable. Results indicated that the use of Principle Component/Variable Analysis leads to a good choice of the variables to be retained as results with the reduced scheme were found to be consistent with those obtained with the full mechanism.

Energy from biomass is recognised as the renewable energy source with the highest potential towards sustainable development in the near future. Devolatilization is a basic mechanism for all thermochemical processes (pyrolysis, combustion, gasification). A detailed characterization (including reaction kinetics and products distribution) of biomass devolatilization is required to provide fundamental parameters for the feasibility, design, modelling, optimisation and scaling of biomass conversion systems. In the present study the devolatilization behaviour of several biomass fuels of different origins was investigated: biomass from energy crops (miscanthus), agricultural residues (corn cobs, rice husks, vine prunings), and torrefied biomass (from palm kernel shells, with different degrees of torrefaction). Thermogravimetric (TG) analysis was used for the study of devolatilization parameters. An isoconversional model was used for the estimation of the kinetics. Furthermore, thermogravimetric analysis coupled with Fourier Transformed InfraRed spectroscopy of evolved gases (TG-FTIR) was applied to study the compounds evolving in the pyrolysis of the selected biomass fuels. Important information on the devolatilization behaviour, that is the identification and the quantitative determination of major volatile species and the temperature range of release, were obtained.

Detailed information on the biofuels is an essential requirement for the prediction of plant efficiency, carbon in ash, pollutant emissions, surface deposition and corrosion, in thermochemical processes. A fuel- specific comprehensive characterization is required to design, operate and model combustion, oxy-firing and gasification plants. At IFRF it couples fundamental analyses with advanced tests in the Isothermal Plug Flow Reactor (IPFR), which allows high temperature and heating rate, under programmed gaseous environments (N2, O2, CO2, H2O). The aim of this work is to: define the experimental procedures for testing biomass fuels in the IPFR; provide significant results of the recent experimental campaigns on biomass fuels; extrapolate the prerequisites and principles that could be in common with other test facilities (in the frame of the BRISK project) for an advanced characterization. Particular attention is devoted to the qualification of the system and procedures used. Different sources of uncertainty (due to diagnostic limitations, segregation phenomena, fuel heterogeneity) affecting the operating parameters and test outputs (e.g., reaction conversion, obtained with the ash tracer method) are studied. The improvements in the experimental apparatus and procedures, as well as the support of CFD assisted diagnostics (e.g., to estimate the effective thermal history of the particles inside the reactor) have helped in quantifying and reducing the experimental uncertainties. The aim is to provide qualified data for the prediction of operational/design parameters for industrial-scale thermochemical systems. Uniform and reliable data will be finally inserted into the IFRF online Solid Fuel DataBase (SFDB).

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The thermochemical conversion of conventional and alternative biofuels is capable of supplying a wide range of energy vectors and chemicals. Peculiarities of such materials require a comprehensive and detailed characterization to provide the fundamental information and face with the issues of each process step. Innovative technologies, advanced model approaches, optimization procedures, need data which comply with relevant standards. The characterization tools described in this work range from lab-scale tools, used to provide the fuel fingerprint, to pilot scale facilities, which operate under industrial scale conditions. Protocols and procedures have been elaborated for all activities to provide reliable and qualified parameters for practical applications and comprehensive codes. The experimental activities have been supported with a broad set of on-line and off-line measurements and analyses, and coupled with modelling activities to qualify the experiments. Finally, a biofuel database, reporting the data collected in the last years, has been developed.

Coal combustion is investigated in both air and oxy-fuel conditions in a pilot-scale entrained flow reactor able to provide high temperatures, heating rates and residence times. Measurements are carried out with different levels of complexity and are aimed at: assessing the thermal field inside the reactor; evaluating conversions of devolatilization or char combustion tests; identifying phenomena such as volatiles ignition and measuring the ignition delay time. Computational Fluid Dynamics was also used in order to provide a better understanding of the experimental evidences. Among the results, the ignition delay time was found to be larger in oxy-fuel conditions than in air, mainly because of the larger specific heat of the oxy-fuel environment. The proposed investigation may help the qualification of advanced experimental apparatus as entrained flow reactors, with the purpose to make them suitable for heterogeneous kinetics studies in oxy-fuel conditions.

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In response to the escalating global challenge of mounting plastic waste and the imperative to adopt more sustainable practices for resource utilization, our study focuses on the utilization of plastic solid waste (PSW) through a two-stage thermal pyrolysis process. This aims to demonstrate its potential as a high-performance alternative to existing two-stage catalytic pyrolysis methods. The experimentation involved processing real scrap PSW material in a lab-scale batch set-up, emphasizing optimizing residence time in the cracking reactor to maximize gas yield and its lower heating value (LHV). The study underscores the advantages of the employed two-stage thermal pyrolysis apparatus through a comparative analysis with established set-up dedicated to maximizing gas yield. Once the operative conditions were explored, resulting pyrolysis products underwent detailed characterization to assess their suitability as a sustainable fuel source. The study also presents a practical application of the produced gaseous fuel, envisioning its combustion in an internal combustion engine (ICE), known for its flexibility regarding fuel properties. This application is demonstrated through a simulation conducted in Unisim Design©. The successful processing of real PSW material in the two-stage lab-scale experimental set-up showcased optimal gas yield achievements (>65 % w/w) with an LHV (∼41 MJ/kg), comparable to that of natural gas. This emphasizes the potential of these sustainable alternatives to replace fossil fuels, especially in the context of ICE applications. The integration of the pyrolysis plant with an ICE demonstrated promising prospects for generating electricity in the transportation sector and facilitating thermal power for heat integration in pyrolysis reactors., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

The present study investigated the effect of torrefaction on the devolatilization characteristics of three lignocellulosic biomass feedstocks with different degrees of torrefaction together with their parent fuel, palm kernel shell, a residue of palm oil production. Thermogravimetric (TG) analysis was employed for the study of the devolatilization process. A kinetic model based on three parallel reactions corresponding to biomass chemical components was applied to TG data and used for the evaluation of reaction kinetics. The results obtained indicated that the torrefaction process led to a significant reduction of the hemicellulose content of the investigated biofuels. The characterization of volatile products evolved during biofuel devolatilization was performed by TG analysis coupled with Fourier transform infrared spectroscopy. The emission characteristics and the yields of the main volatile products were assessed. Specific linear correlations between volatile yields and the torrefaction degree could be observed., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

The use of biopolyesters, as polymeric matrices, and natural fillers derived from wastes or by-products of food production to achieve biocomposites is nowadays a reality. The present paper aims to valorize mussel shells, 95% made of calcium carbonate (CaCO 3 ), converting them into high-value added products. The objective of this work was to verify if CaCO 3 , obtained from Mediterranean Sea mussel shells, can be used as filler for a compostable matrix made of Polylactic acid (PLA) and Poly(butylene adipate- co -terephthalate) (PBAT). Thermal, mechanical, morphological and physical properties of these biocomposites were evaluated, and the micromechanical mechanism controlling stiffness and strength was investigated by analytical predictive models. The performances of these biocomposites were comparable with those of biocomposites produced with standard calcium carbonate. Thus, the present study has proved that the utilization of a waste, such as mussel shell, can become a resource for biocomposites production, and can be an effective option for further industrial scale-up.

Gasification of Short Rotation Forestry (SRF) poplar wood chips and anaerobic digestion of the microalga Chlorella vulgaris have been analyzed as alternative supply chains for the production of biomethane. Life Cycle Assessment (LCA) was performed from the biomass cultivation to the upgrading stages. Process simulation of gasification and upgrading was carried out, environmental impacts of the entire supply chains have been estimated and discussed. The highest CO 2 removal has been reached by absorption on monoethanolamine. Electricity requirements heavily affect the SRF chain, while productions of carbon dioxide and fertilizers are the main sources of impact of the microalgae cultivation. The recycle of non-absorbed fertilizers, as well as integration of microalgae digestion in wastewater plants, are recommended. Capture and re-injection of the CO 2 lost during the upgrading stages would result, simultaneously, in an 8.53% reduction of the atmospheric emission, and in a minor demand to promote algal growth., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

This work proposes a simple and accurate tool for predicting the main parameters of biomass gasification (syngas composition, heating value, flow rate), suitable for process study and system analysis. A multizonal model based on non-stoichiometric equilibrium models and a repartition factor, simulating the bypass of pyrolysis products through the oxidant zone, was developed. The results of tests with different feedstocks (corn cobs, wood pellets, rice husks and vine pruning) in a demonstrative downdraft gasifier (350kW) were used for validation. The average discrepancy between model and experimental results was up to 8 times less than the one with the simple equilibrium model. The repartition factor was successfully related to the operating conditions and characteristics of the biomass to simulate different conditions of the gasifier (variation in potentiality, densification and mixing of feedstock) and analyze the model sensitivity., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Tests with vine pruning and rice husks were carried out in a demonstrative downdraft gasifier (350 kW), to prove the reactor operability, quantify the plant efficiency, and thus extend the range of potential energy feedstocks. Pressure drops, syngas flow rate and composition were monitored to study the material and energy balances, and performance indexes. Interesting results were obtained for vine pruning (syngas heating value 5.7 MJ/m(3), equivalent ratio 0.26, cold gas efficiency 65%, power efficiency 21%), while poorer values were obtained for rice husks (syngas heating value 2.5-3.8 MJ/m(3), equivalent ratio 0.4, cold gas efficiency 31-42%, power efficiency 10-13%). The work contains also a comparison with previous results (wood pellets, corn cobs, Miscanthus) for defining an operating diagram, based on material density and particle size and shape, and the critical zones (reactor obstruction, bridging, no bed buildup, combustion regime)., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Biomass gasification couples the high power efficiency with the possibility of valuably using the byproducts heat and biochar. The use of agricultural wastes instead of woody feedstock extends the seasonal availability of biomasses. The downdraft type is the most used reactor but has narrow ranges of feedstock specifications (above all on moisture and particle size distribution), so tests on a demonstrative scale are conducted to prove the versatility of the gasifier. Measurements on pressure drops, syngas flow rate and composition are studied to assess the feasibility of such operations with corn cobs. Material and energy balances, and performance indexes are compared for the four tests carried out under different biomass loads (66-85 kg/h). A good operability of the plant and interesting results are obtained (gas specific production of 2 m3/kg, gas heating value 5.6-5.8 MJ/m3, cold gas efficiency in the range 66-68%, potential net power efficiency 21.1-21.6%)., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

A new simplified approach based on equilibrium modeling is proposed in this work to describe the correlations among syngas species experimentally observed in a pilot scale downdraft biomass gasifier operated with different feedstocks (biomass pellets and vine prunings). The modeling approach is based on experimental evidence on the presence of devolatilization products in the syngas and fluctuations of syngas composition during stationary operation, accounted for by introducing two empirical parameters, a by-pass index and a permeability index. The simplified model correctly reproduces the correlations among the main syngas species (including methane and ethylene) resulting from experimental data of pilot tests with different feedstocks and under a wide range of operating conditions., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

A pilot scale throated downdraft gasifier was operated with vine prunings as feedstock to assess the effect of biomass loading rate on process performance. A distributed 1D model of mass and heat transfer and reactions was applied to aid the interpretation of experimental evidence. The model takes into account peculiar gasifier design features (air inlets and throat) and it reproduces satisfactorily the temperature profiles and the mass fluxes of gaseous species at different biomass loading rates. The integration of pilot-scale experiments and numerical simulations provides sound indications for the gasifier operation. In particular, simulations performed at different loading rates and feedstock humidity show that steady state operation and stable performance of the gasifier rely on the thermal balance between the enthalpy of cold biomass moving downward and the counter-current radiative heat fluxes moving upward from the oxidation zone. This balance can be destabilized by high loading rate and moisture contents., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

This work presents a pilot-scale investigation aimed at assessing the feasibility and reliability of biomass pellet gasification. Wood sawdust and sunflower seeds pellets were tested in a 200 kW downdraft gasifier operating with air as gasifying agent. The gasification of pelletized biomass led to rather high and unstable pressure drops, reducing the gasifier productivity and stability. Furthermore the generation of fine residues compromised the operation of wet ash removal systems. On the other hand, good syngas compositions (H(2) 17.2%, N(2) 46.0%, CH(4) 2.5%, CO 21.2%, CO(2) 12.6%, and C(2)H(4) 0.4%), specific gas production (2.2-2.4 N m(3) kg(-1)) and cold gas efficiency (67.7-70.0%) were achieved. For these reasons pelletized biomass should be considered only as complementary fuel in co-gasification with other feedstock., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Different thermochemical configurations (gasification, combustion, electrolysis and syngas separation) are studied for producing hydrogen from biomass fuels. The aim is to provide data for the production unit and the following optimization of the "hydrogen chain" (from energy source selection to hydrogen utilization) in the frame of the Italian project "Filiera Idrogeno". The project focuses on a regional scale (Tuscany, Italy), renewable energies and automotive hydrogen. Decentred and small production plants are required to solve the logistic problems of biomass supply and meet the limited hydrogen infrastructures. Different options (gasification with air, oxygen or steam/oxygen mixtures, combustion, electrolysis) and conditions (varying the ratios of biomass and gas input) are studied by developing process models with uniform hypothesis to compare the results. Results obtained in this work concern the operating parameters, process efficiencies, material and energetic needs and are fundamental to optimize the entire hydrogen chain., (Copyright 2010 Elsevier Ltd. All rights reserved.)