• Energy Research

The winery industry produces every year in the world about 270 millions of hectolitres of wine. A consequent amount of grape marc is then generated that has to be somehow treated and processed. For this reason a technique to treat grape marc (bio-drying) was studied and applied at the University of Trento. Grape marc, as is, is not suitable for direct combustion because of its high water content. By bio-drying the lower heating value has been increased up to the limit for a good combustion. This result allows a decentralized management of a grape marc drying differently from the conventional solutions.

The monitoring solid pollutants, moisture and gaseous emissions of wooden biomass utilized in a 30 kW stove have been performed. This paper reports a case study where the control of organic pollutants in biomass was performed by using FT-IR-ATR technology, heavy metals were measured with ED-XRF, radiation was assessed with a pocket Geiger device. Moisture content has been monitored according to the standard EN 14774-2 and exhaust emissions with a MRU Optima 7 analyzer. The analyses showed no concern about organic pollutants, heavy metals or radiation. The moisture content of some biomass specimen was found very high. The gaseous emissions varied with the use of wet biomass or different part of the tree. This work is a part of the BiQueen project funded by Fondazione Caritro.

This work reports the results of an extended kinetic study involving both experimental measurements and modelling elaborations. It is specifically dedicated to investigate the thermal behaviour of biomasses undergoing to torrefaction treatment. Three biomasses, representative of the hardwood family, have been considered: ash-wood, beech-wood and hornbeam. As main purpose, this work evaluates the impact of the TG measurements on the Activation Energy (E a) results achieved by implementing the so-called isoconversional model-free methods on both their differential and integral version. Considering the heterogeneous nature of the biomasses and the thermo-chemical factors conditioning the involved solid-state reactions, several replicates of the TG data sets have been carried out and their impact on the E a reliability has been evaluated. An extended sensitivity analysis of the adopted models allows to identify a Confidential Boundary Range of the TG measurements and, in correspondence, an Activation Energy Boundary Range for the E a results. Considering the “model-free” nature of these methods, a preliminary selection of a kinetic scheme is not required, making particularly attractive this approach to match the purpose of this research. This study provides even a comparison among the models performances and a review of their application limits. Applied to heterogeneous materials, the proposed approach could be considered a general methodology to test the impact of the TG measurements on the Activation Energy results reliability.

Abstract The objective of this experimental study consists in investigating the effects of torrefaction treatment on two different woody biomass chosen from softwood as spruce pine and annual grass lignocellulosic hardwood as reed . This thermal pre-treatment has been conducted in a small batch reactor directly fluxed by a controlled nitrogen flow. Tests have been carried out at different temperatures, ranging from 250 °C to 310 °C, and reaction time from few minutes to 1 h. Properties involved in this investigation are ultimate analysis, thermal quantities among which caloric value (HHV), fibers distribution and equilibrium moisture content. The obtained results confirm that torrefaction is a viable thermal pre-treatment to upgrade biomass and looks promising for a new generation of biomass derived fuel. As main topic, this research focuses on evaluating the role of the Mass Yield (MY) as synthetic parameter of the process. In particular it is made evidence that the properties of the torrefied samples can be led back to the MY without making reference to their thermal-time pathway. As example, considering two samples presenting the same MY of 80%, the former torrefied at 280 °C for 76 min, the second at 310 °C for 17 min, it is verified that the values of the aforementioned properties are very similar for both the samples even if submitted to different thermal pathways. The potentiality of the MY has been enhanced by extending this investigation to additional species of biomass pertaining to two groups, woody biomass and non-woody biomass. Inside the conditions ranges of the proposed experimental tests and for each of the indicated biomass type, an accurate linear correlation is obtained between MY and Energy Yield (EY) with a determination coefficient of ( R 2 ) 0.98 and 0.97 for woody and non-woody biomass respectively. Besides confirming the benefit of the torrefaction in enhancing the quality of the treated biomass, the use of the MY as synthetic parameter can be exploited to improve the torrefaction modeling schemes and to optimize the selection of the process working conditions. The proposed approach can therefore be useful to examine the relevant amount experimental data till now produced on this issue in view of exploiting and orienting their use towards real scale plant design.

In this work an extended kinetic analysis involving both experimental measurements and modelling procedures to describe the thermal degradation process of biomass is proposed. Three biomasses belonging to the hardwood family are investigated: ash-wood, beech-wood and hornbeam. The experiments are performed with a thermogravimetric balance working at four constant heating rate: 3, 5, 10 and 20 °C/min. This study is specifically dedicated to investigate the thermal behaviour of the selected biomasses when they undergo to torrefaction temperature conditions. The modelling analysis focuses on investigating the capability of consolidated models, usually applied to solids, in determining the activation energy (Ea) of the indicated biomasses within the torrefaction range. The adopted methods belong to the so-called isoconversional “model free” methods and, in this contest, both the differential ones as those of Friedman and Flynn and the integral ones as those of Kissinger-Akahira-Sunose, Doyle and Starink have been applied. The performances reached by adopting the integral methods widely satisfy the accepted accuracy level conventionally set at values lower than 10%. At the same time it is verified even that, when the methods are applied to biomasses belonging to the same family, the resulting Ea vs. α trends are very close for all the biomasses. This condition is exploited to propose a generalized predictive approach for the Ea calculation based on the knowledge of only the conversion fraction α. The presentation of the results includes also the investigation of the limits of the proposed methods in view of indicating their reliable application range when utilized for torrefaction design procedures.

Abstract This study proposes an innovative approach to investigate the thermal degradation kinetic of biomasses when submitted to torrefaction. This process is expected to have a relevant impact in exploiting the potentialities of biomasses in many major end energy uses. The main motivation of this work moves from the observation that the adoption of the “model-free” isoconversional approach is applied, conventionally, limited to the activation energy (E) determination. This work extends the potentialities of these methods and demonstrates their feasibility in setting up a complete kinetic model. Moving from the fundamentals of the isoconversional analysis, this study identifies a specific constrain linking together the Arrhenius pre-exponential factor (A) and the reaction model function f(α). This achievement is exploited to derive a new kinetic parameter (φα) which replaces the two terms A and f(α) that, jointly with E, constitute the conventional kinetic triplet. The introduced parameters E and φα found the new two parameters kinetic equation whose solution is achieved by defining an innovative computational approach based on a finite difference scheme. As main result this study introduces an original exploitation of the “model-free” methods that avoids, contrarily to conventional solutions, any assumption for the f(α) function. Besides, the introduced equation solver scheme can be generalized to any heating program, isothermal or not. Three biomasses, belonging to the same hardwood family, have been specifically investigated. The performances of the model reach, in terms of Absolute Average Deviation, a predictive accuracy level within 1–5%. Considering the encouraging achieved results, the proposed model can be directly applied to support the design procedures specifically pertaining to biomass torrefaction plants.

Abstract This work investigates the opportunity of retrofitting existing small-scale gasifiers shifting from combined heat and power (CHP) to hydrogen and biofuels production, using steam and biomass residues (woodchips, vineyard pruning and bark). The experiments were carried out in a batch reactor at 700 °C and 800 °C and at different steam flow (SF) rates (0.04 g/min and 0.20 g/min). The composition of the producer gas is in the range of 46–70 % H2, 9–29 % CO, 12–27 % CO2, and 2–6 % CH4. A producer gas specific production factor of approx. 10 NLpg/gchar can be achieved when the lower SFs are used, which allows to provide 80 % of the hydrogen concentration required for biomethanation and MeOH synthesis. As for FT synthesis, an optimal H2/CO ratio of approx. 2 can be achieved. The results of this work provide further evidence towards the feasibility of hydrogen and biofuels generation from residual biomass through steam gasification.