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The aim of this work is to evaluate the performance of a reforming-unit for the treatment of syngas and char produced in an air gasifier. This approach represents an alternative option to produce hydrogen-rich syngas from air gasification. The reformer reactor was operated under a range of temperatures and at different steam flows and for each operating condition the changes and improvements in producer gas composition were measured. The results highlight that in the absence of char and steam no substantial changes are measured in the producer gas composition, while in the absence of char but with a steam flow or in the absence of steam but with a char-bed a maximum hydrogen concentration increase +31 % can be obtained at higher temperatures. On the other hand, the combined effect of char and steam significantly improves the hydrogen concentration of approx. +194 % at 800 °C with the highest steam flow tested. These results provide a guide for future optimization studies into the enhancement of gas quality in air gasification systems., Proceedings of the 30th European Biomass Conference and Exhibition, 9-12 May 2022, Online, pp. 790-793

This work investigated the possibility to exploit woody forest residues and wood, obtained from forest maintenance activities and meteorological extraordinary events, as an additional material for clean energy production. These materials were collected from the Renon highland near the city of Bolzano (South Tyrol, Italy) and they were analyzed in terms of their main physical and chemical characteristics. Subsequently, these materials were tested in an open-top gasifier installed in the Bioenergy and Biofuels labs of the Free University of Bolzano. The tests have shown the potential to use these as feedstocks for clean energy production, although small differences in their respective performances have been observed. The differences mainly depend on the different characteristics of these materials. To evaluate the technical feasibility of using these materials, for additional energy production through an existing CHP plant, the possibilities investigated are twofold: the evaluation of a specific mixture of these residues, capable to guarantee a homogeneous feedstock to the gasifier, and the possibility to consider the wood from extraordinary events as a buffering material in periods of the year when the production of woody forest residues is reduced. The preliminary results obtained from the gasification experiments of these residues were encouraging; however, additional research is required to optimize the process for practical application., Proceedings of the 29th European Biomass Conference and Exhibition, 26-29 April 2021, Online, pp. 458-462

The aim of this work is to develop a gasification model based on the thermodynamic equilibrium approach, able to overcome the issues of the classical equilibrium strategy, that computes the gasification products using the Gibbs energy minimization method at fixed temperature and pressure. The model is applied to describe the gasification process of an open top pilot-scale gasifier placed at the Bioenergy and Biofuel Lab of the Free University of Bolzano. The data used for the tune up of the model have been collected over a period of three years of gasification experiments using several biomasses (wood chips, wood pellet, torrefied pellet and wood pellet mixed with char) at different gasification conditions (from 0.17 up to 0.35 of ER value). In fact, a correction factor has been introduced versus the entire set of experimental data to account for the differences between the theoretical hypothesis implemented in the equilibrium model and the real non-adiabatic system. The model outcomes show a good agreement with the experimental data in terms of parameters of interest for gasification such as producer gas LHV, producer gas yield, char yield and cold gas efficiency. Potential outcomes of this research are, firstly, the characterization of the plant behavior without the need of estimating/measuring the average gasification temperature and secondly, the development of a gasification model suitable for the plant control management and in general able to predict the behavior of fixed-bed gasifier systems., Proceedings of the 29th European Biomass Conference and Exhibition, 26-29 April 2021, Online, pp. 506-510

International audience; The aim of this study is to investigate the possibility of enhancing the gasification process using a pretreated biomass that presents higher heating value, higher C/O ratio and less moisture content than untreated biomass. The aim is to assess the gasification parameters that can be modified in order to achieve the best performance of the gasification system. These research studies have been carried out in collaboration with the Centre RAPSODEE (UMR CNRS 5302, IMT Ecole de mines Albi-Carmaux, France) and the Free University of Bolzano (Italy). The torrefaction of standard pellets is realized using a lab scale rotary kiln unit at RAPSODEE. On the contrary, the gasification tests are carried out at the Free University of Bozen-Bolzano by means of a fixed bed open top gasifier. The tests of pellets torrefaction has been carried out at 250°C and 270°C with two repetitions in order to obtain about 60 kg of pellets for each torrefied condition. The used feedstock is a standard French pellets produced from sawdust of oak and beech following the standard EN 14961-2 (“Wood pellets for non-industrial use”). The pellets are characterized before and after the torrefaction pre-treatment. The gasifier used for the gasification tests is an open top pilot-scale gasifier placed at the Bioenergy and Biofuel Lab of the Free University of Bolzano. The plant is an open top downdraft system, where both gas and feedstock move downward as the reactions proceed. The main difference between un-treated and torrefied pellets is the moisture content. In addition, a slight increase in terms of carbon content and LHV and a slight decrease in terms of volatile matter are observed by moving from standard to torrefied pellets. The torrefied pellets seem to reach lower performances in terms of cold gas efficiency (CGE) and char yield with respect to the standard pellets. However, the trends in terms of ER and CGE suggest that moving toward higher values of ER, higher values of CGE could be reached independently of the material used.

The present work aims at investigating the valorization of biomass forestry residues by means of experimental analysis on a small-scale open top gasifier. In order to evaluate the effect of high bark content, experimental test have been performed in an open-top gasifier with increasing shares of bark and woodchips and different levels of secondary air supply, used as adjustable parameter for the optimization of the conversion process. Samples have been characterized using standard methodologies for assessing the moisture and ash content, the elemental composition and the calorific value. Moreover, the bark content in the standard woodchips has been quantified to be 8 % in mass. High content bark samples (30 % and 80 % in mass of total bark) have been then prepared mixing the standard woodchips with barks. Using the prepared mixtures, gasification tests were performed with an open-top gasifier installed at the Free University of Bolzano. This specific pilot-scale gasification plant is a downdraft system, where both gas and feedstock move downward as the reactions proceed. The core of the gasification system is a stainless-steel cylindrical reactor. The air required for gasification is partly drawn from the top, and the remaining from the air nozzle at the char combustion zone. The results of the experimental campaign showed that the generally negative impact of bark addition, demonstrated by a reduction – at a set level of secondary air – of the calorific value of the producer gas and of the cold gas efficiency, can be counterbalanced acting on the secondary air and therefore on the equivalence ratio of the process, a parameter that has been demonstrated to allow an optimization of the process as a whole thanks to a linear correlation with the cold gas efficiency., Proceedings of the 28th European Biomass Conference and Exhibition, 6-9 July 2020, Virtual, pp. 407-410

This work deals with the utilization of lignocellulosic low-cost biomass-residues for the generation of syngas suitable for the upgrade to biofuels, i.e. Fischer-Tropsch (FT), biomethanation. A series of experiment was carried on using three types of biomass: two types of biomass residues, i.e. vineyard pruning and bark, and woodchip. The experiments were carried on in a batch fixed-bed reactor at 700 °C and 800 °C and at different steam flow rate (0.04 g/min and 0.20 g/min). The results show that it is possible to achieve optimal syngas composition for each biofuels upgrade pathway. For Fischer-Tropsch synthesis, a H2/CO ratio of approx. 2 is achieved using the low steam flow rate at 700 °C for pellet and 800 °C for woodchip and bark. For the biomethanation synthesis, the highest hydrogen-to-carbon ratios are achieved with woodchip at 700 °C and low SF, and for pellets at 800 °C and low SF. The results of this work provide further evidence towards the feasibility of renewable biofuels production. (200 words), Proceedings of the 28th European Biomass Conference and Exhibition, 6-9 July 2020, Virtual, pp. 440-444

Fixed-bed biomass gasification is a promising dispatchable option of renewable energy sources to serve flexibility demands in electricity production. To experimentally investigate this potential, this contribution analyses an industrial small-scale fixed-bed biomass gasification system for demand-oriented electricity production by evaluating the effects of an electric power change in terms of transition duration and control accuracy. Therefore, the steady-state operation at different loads and the transient behaviour of the gasification system during stepwise changes of the electric power are evaluated based on measured and derived process parameters. The results from a great number of test runs performed reveal the potential for rapid changes of the electric power (100 kW to 150 kW in less than 1.5 min), a good stationary accuracy for operations at nominal (150 kW ± 3.7 kW) and partial load (100 kW ± 5.1 kW), and hardly any negative effects on the gasification performance (e.g. cold gas efficiency and equivalence ratio remain almost constant during load changes). However, results from partial load reveal an increase in process fluctuations due to the control strategy used. To unleash the systems’ full potential of flexibility, a more advanced control strategy should be applied., Proceedings of the 28th European Biomass Conference and Exhibition, 6-9 July 2020, Virtual, pp. 464-476

The aim of this study is to assess the load modulation capability of a pilot plant open top downdraft gasifier using standard wood pellet. The input gasifying agent, which is air, can be split into primary air (from the top) and into secondary air, where the remaining required air is fed directly into the reduction zone of the reactor through a nozzle. The novelty of this research reside in the investigation of the effect of the supplied secondary air flow rate at different loads, with the aim to improve the load modulation capabilities by means of controlling the air distribution and achieving the higher possible conversion efficiency with varying amounts of producer gas power production. The gasifier was tested at different loads. The equivalence ratio (ER) is related to the mass flow rate of secondary air, thus by increasing the secondary air the equivalence ratio increases as well. The results confirm that it is possible to have high gas conversion at different loads using the mass flow rate of secondary air as a control parameter for the management of the equivalence ratio into the reactor., Proceedings of the 27th European Biomass Conference and Exhibition, 27-30 May 2019, Lisbon, Portugal, pp. 802-806

Assessing the operational behaviour of biomass gasification systems is a crucial basis for further improvements in terms of operational behaviour and robustness in order to increase the technologies’ operational and economic viability. However, in most fixed-bed biomass gasification systems not all parameters required for the assessment can be measured directly. Typically, unknown parameters are determined by using as many balance equations as parameters have to be determined neglecting the additional information provided by other available but not chosen balance equations. Thus, these approaches do not incorporate all measurement data available resulting in a lack of reliability in their results. A detailed analysis of these approaches emphasises that even small deviations in the measurement data can lead to significant deviations in the calculated parameters, demonstrating that individual choices of equations can be highly sensitive regarding measurement uncertainties. Therefore, an adjusted weighted least squares approach is developed utilizing an overdetermined system of equations incorporating all balance equations simultaneously. Thus, all measurement data available is taken into account, minimizing the influences of measurement uncertainties on the determined parameters. A comprehensive analysis shows that this approach is less sensitive to measurement uncertainties, allowing for a more reliable and accurate assessment of fixed-bed biomass gasifiers., Proceedings of the 27th European Biomass Conference and Exhibition, 27-30 May 2019, Lisbon, Portugal, pp. 849-860

Gas-fired and coal based power generation plants result in the emission of CO2, a major greenhouse gas responsible for climate change. On an average, the flue from such power plants contain approximately 12– 17 vol.% CO2, 75 – 77 vol.% N2 and ~ 4.4 vol.% O2 with fractions of CO, NOx, H2 and SO2 in ppm range. While the capture and storage of this CO2 stream have been addressed actively in the literature, or even implemented rather unsustainably, its application in the fuel making process is imperceptibly addressed. This work examines the thermochemical biomass conversion with air and CO2 as gasification media to explore the possibilities and limitations of CO2 capture and its application in the fuel making process by the employment of the Boudouard reaction in the high temperature char zone to yield carbon monoxide. While this study revolves around the direct use of CO2 from the flue of diesel engines. The experimental investigations are based on the configuration of a downdraft reactor utilizing dried biomass pellets as feedstock. The mass flow rates of air and CO2 are measured and controlled using calibrated mass flow controllers and the biomass consumption rate is measured by placing the reactor over a digital weighing balance. A complete carbon balance is implemented in order to analyse the rate of formation of char under various conditions. This work demonstrates a mode of effective utilization of CO2 from the flue of exhaust gases in the power generation process that can even be integrated with a bio-refinery plant., Proceedings of the 26th European Biomass Conference and Exhibition, 14-17 May 2018, Copenhagen, Denmark, pp. 732-736

In these last years, in the context of thermochemical conversion processes, the mild thermal process known also as “torrefaction” has emerged as particularly strategic in view of enhancing the entire biomass chain exploitation value. In particular the kinetic studies of this process has become important in supporting the design procedure expected to widespread the industrial applications linked to torrefaction. The aim of this study consists in proposing a kinetic model for torrefaction of lignocellulosic materials based on a combination of the three independent reactions set up to describe the thermal degradation of each of the constituent fibres: hemicelluloses, cellulose and lignin. This approach is based on the hypothesis proposed by Shafizadeh and McGinnis that assumed that the three fibres, during thermal degradation, present the behaviour they have when they are treated separately. By utilizing the thermogravimetric data (TGA) of the single fibers, in this work it is demonstrated that it is possible to set up a kinetic model for the thermal degradation of different biomasses that presents an enhanced predictive character. Within the torrefaction temperature conditions, usually in the range of 475K – 590K, the maximum deviation errors is nearby 4% while AAD to 1%., Proceedings of the 23rd European Biomass Conference and Exhibition, 1-4 June 2015, Vienna, Austria, pp. 1152-1158

This study investigates both the hydrophobicity behaviour of two types of biomasses and the evolution of their fibres content when thermally treated at different torrefaction degrees. The two woody biomasses have been chosen from softwood as spruce (picea abies) and annual grass lignocellulosic hardwood as reeds. Selected samples of the indicated biomasses were torrefied at different reaction time and temperature values, ranging from 250°C to 310°C, on a small batch reactor utilizing a direct flux of nitrogen as thermal carrier. Before treatment all samples were dried in a convection oven at 103 C° for 24 h. The Mass Yield Ratio (MYR) is the parameter utilized to define the torrefaction degree and, for this investigation, torrefied samples present a MYR of 90%, 80% and 70% for spruce and 80%, 70% and 60% for reeds. The hydrophobicity was determined in terms of EMC (Equilibrium Moisture Content) at a constant temperature of 25°C and Relative Humidity (RH) ranging from 24% to 75%. The fibres content, lignin, cellulose and hemicellulose, was determined for both raw and torrefied samples according to the so called Van Soest method. Regarding the hydrophobic behaviour, for both the biomasses, it can be observed that up to a MYR at 80%, the moisture absorption reduces progressively from raw to torrefied samples. Regarding the fibres content analysis, it is confirmed that as torrefaction becomes stronger in terms of MYR, a near-complete breakdown of hemicellulose is observed., Proceedings of the 23rd European Biomass Conference and Exhibition, 1-4 June 2015, Vienna, Austria, pp. 1159-1164

Among the renewable energy sources, woody biomass offers advantages over other traditional fossil fuels, because it is abundant and widely available, and it is still largely used in mountains and agricultural communities. However, direct combustion for simple heating is a very low efficient process and, if the process is not well controlled, high carbon dioxide and particulate emissions are realised in atmosphere. The pollutant emissions are strongly influenced by the moisture content and the type of wood stove adopted. In the present work the gaseous and NMVOC(Non Methane Volatile Organic Compounds) emissions produced by a two staged ­high efficiency­ air gasifying wood stove have been analyzed. In the stove tested the sub processes of the combustion process (pyrolysis and combustion) take place in two separate zones within the combustion chamber to improve the control of the combustion. The combustion technology adopted confirms that gasification technology significantly limits the emission of unburned compounds even if a fuel of heterogeneous size and composition, such as wood logs, is used. The levels of the carbon monoxide and NOx emissions are comparable to the pellet burners’ ones., Proceedings of the 19th European Biomass Conference and Exhibition, 6-10 June 2011, Berlin, Germany, pp. 880-886

Small-scale gasification of woody biomass is a technology that has had a rapid development in the last years, mainly driven by favorable subsidization regimes. Biomass gasification process produces a minor fraction of solid carbonaceous by-product, known as char. Even though char presents chemical and physical characteristics that make it a potentially interesting and valuable product in the view of pushing gasification from a co-generative process to a poly-generative platform, economically viable solutions are not available yet and the disposal of char still represents a non-negligible cost in the plant management. For this reason, most of the recent developments in the small-scale gasification technology available in the market aim at reducing as much as possible the amount of material to be disposed, integrating into the plant an additional oxidizing section, i.e. afterburner, in order to have an outlet material stream mainly composed by ashes. The aim of the present work is to investigate an alternative solution for reducing the amount of generated char and at the same time increasing the efficiency of the whole conversion process. The proposed solution, investigated in a small-scale open-top gasifier installed at the Free University of Bolzano, is to recirculate the char inside the gasifier in order to increase the residence time and the conversion yields., Proceedings of the 27th European Biomass Conference and Exhibition, 27-30 May 2019, Lisbon, Portugal, pp. 527-532

The purpose of this work is to model a CHP system made up of an open-top downdraft gasifier and a 4kW single-cylinder diesel engine in operation at the Bioenergy & Biofuels Lab of the Free University of Bozen-Bolzano (Italy). In particular, the present study aims to couple a multi-stage and multi-phase thermodynamic model of the gasifier with a 0-D thermodynamic model describing dual fuel combustion inside the engine.Preliminary results have been obtained in terms of gas composition and engine power output. Future developments include enhancements of the predictive capacity of the modelling strategy, technical improvements in terms of gasifier automation and engine fueling diversification and finally the realization of a systematic experimental campaign in order to describe the behavior of the energy system in several conditions., Proceedings of the 25th European Biomass Conference and Exhibition, 12-15 June 2017, Stockholm, Sweden, pp. 788-793