• Energy Research
• 2016-2025close

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.

The present study analyzes an innovative method for the disposal and effective exploitation of sewage sludges, based on the integration of oxy-steam co-gasification in downdraft gasifier with wood chips and novel methanization plant for the final production of added value bio-methane. The analysis of the co-gasification process with oxygen-steam, as well as the following one of methanization, was performed numerically by creating a model of the overall plant within the Aspen Plus commercial code. The gasification model was validated with the experimental results obtained with a full-scale air gasifier fed with sewage sludge and wood chips. During the experimental activity, no reactor blockage nor ash discharge problems were recorded until the sewage sludge percentage (by mass) did not overcome roughly 30%. The numerical results show that the oxy-steam co-gasification process has a high energy conversion efficiency that reaches roughly 80% and the overall methane yield of the process is about 20% (by mass) of the feedstock utilized. The water consumption, which is higher than 1.0 kg/kg methane, and the electricity demand, around 0.70 kWh/kg methane, result critical issues for methane production. Therefore, the present research represents a further insight into the possibility to co-gasify biomass with sewage sludge, giving new information on this alternative route for waste exploitation both experimentally and numerically with the production of bio-methane.

Modeling lithium-ion batteries is crucial for electrochemical energy storage to characterize their behavior and predict their State-Of-Charge and State-Of-Health. Equivalent Circuit Models can identify voltage and temperature profiles under a given input current with little computational cost. However, they cannot explain relevant microscopic phenomena that determine the battery's capability to deliver power and be efficiently charged. Conversely, Physics-Based Models can consider advanced physics and account for microscopic information at an increased cost, precluding their utilization in Battery Management Systems. This paper proposes to validate and integrate the two cited modelling approaches applied to a commercial lithium iron phosphate battery. The latter are validated with discharge-charge experimental tests, and microstructural data directly measured through the experimental disassembly of the battery. In this way, equivalent battery models become ideally linked to physics-based ones to fit all the internal electrochemical processes for a complete understanding of the evolution of battery states over time.

Abstract Biomass combustion performance is greatly affected by the particle size distribution, which influences heat and mass transport phenomena. The present work investigates the effect of woodchip size distribution on combustion in a 140 kW underfeed stoker boiler. Three different fuel sizes were prepared, and their combustion performance was measured by monitoring temperatures inside and above the fire pit and the gas composition above the fuel bed. The gas composition was then correlated to the particle mean diameter. Although minor effects could be detected in the temperature and composition of the flue gases, a more uniform spatial distribution of volatiles was observed when employing bigger woodchips. The present results can improve the understanding of the impact of fuel size on the performance of woodchip-fired boilers and can be valuably used for numerical model validation.

Abstract The world energy demand growth is more and more supplied by renewable energy sources. In this scenario, biomass has a key role in both heat and power generation. Particularly, biomass combustion can be used in small size micro and distributed generation systems, or in smart grids together with wind and solar energy where a programmable energy source is necessary to keep the electric grid stable. In this paper, a small size 140 kWth biomass fixed bed boiler of the University of Pisa, located at the Biomass to Energy Inter-University Research Centre (CRIBE), was studied experimentally to characterize the biomass combustion process. Emissions of NOx, O2, CO2 and CO, together with the temperature data, were measured in the flue gases. Moreover, the spatial distribution of volatile products from the fixed bed surface, such as H2, CO, CO2, CH4, C2H6, C2H4, C2H2, together with temperature data, was studied in the early combustion stage. The parametric variation of the feed air flow and its effect on the emissions and performances was also investigated. The results indicate that the primary air mainly affects the volatiles distribution on the biomass combustion surface. Therefore, the CO emission was minimized at values of 0.03%vol with an air excess equal to 2 and a 0.06 secondary to primary air mass flow ratio.

Abstract In this paper an extensive experimental campaign about the co-gasification of virgin wood biomass with organic and waste matrices in a full-scale downdraft air gasifier is presented. In particular, wastes from cherry processing, plastic wastes, sewage sludges and hazelnut shells were co-gasified with biomass adopting different mixtures. The syngas composition was continuously measured in order to assess the gasifier behaviour and performances using these mixtures. Results obtained mixing biomass with other feedstocks up to 60% (by mass) showed that the downdraft gasifier adopted, characterized by a patented internal air distribution system, was able to maintain a good gasification performance in terms of syngas lower heating value (LHV) (>5.18 MJ/Nm3), syngas flow rate (>400 Nm3/h) and cold gas efficiency (>71.9 %). A pseudo-kinetic model of the gasifier using Aspen Plus® code was developed as well. The model, calibrated with the experimental data, proved to fit the syngas composition and physical properties with satisfying accuracy. The numerical model confirmed its usefulness in predicting the performance of the gasifier as the operating parameters vary and clearly highlighted that secondary air flow and preheating of the gasifying air are effective ways for the enhancement of the cold gasification efficiency, which can reach values around 80%.

Abstract Biomass gasification is a thermochemical process in which the biomass is converted into a mixture of gases, called syngas, commonly utilised in thermal machines to produce electricity and heat. In the present research activity, the conventional air-gasification in downdraft gasifier is replaced by oxy-CO2 gasification technology. This strategy allows to obtain a nitrogen-free syngas, mainly composed by CO, H2, CO2 and CH4, which can be used into the synthesis of various bio-fuels like methanol or synthetic natural gas (SNG). Carbon dioxide is utilized as gasifying agent together with oxygen to mitigate the reactivity of the latter, which can lead to excessive reaction temperatures. In particular, the present work shows the preliminary results of an experimental campaign carried on utilizing a small scale downdraft gasifier (max thermal power of roughly 100 kW) fed with wood pellet and using a mixture of oxygen and CO2 as gasification agent. The experimental results have been utilized to calibrate a pseudo-kinetic model of the oxy-CO2 gasification process, implemented in Aspen Plus environment. To analyse the possibility to transform the produced syngas into methane, an additional numerical model of a methanation plant was then utilised. As a whole, the numerical analysis confirms its usefulness in predicting the performance of the gasifier, which can reach a cold gas efficiency of around 70%, while the methanation plant can achieve a production of roughly 20 kg of methane per 100 kg of gasified wood.