Diego Barletta

Characterization of Woody Biomass Flowability

In this paper a simple method for characterizing the flowability of consolidated samples of woody biomass is presented. The apparatus used consists in a cylindrical bin provided with a circular orifice at the centre of its flat bottom. Biomass samples were consolidated in the bin by applying loads on the material bed surface while the bin orifice was closed by a plug. After the consolidation phase the loads were removed and the orifice was opened to assess if an arch or a rathole had formed. Critical values of consolidation loads for the formation of a stable arch were determined for different orifice sizes. These results obtained with two different samples of sawdust were compared in terms of material strength with those of flow functions obtained with a conventional Schulze shear tester.

Flow Properties of Moisturized Powders in a Couette Fluidized Bed Rheometer

This work investigates on the effect of air humidity on the flow properties of powders. The moisture of a powder sample (50 µm glass beads) was conditioned by fluidization with humid air. Air humidity was kept between 0 and 70% at ambient temperature. A Schulze shear cell was used to measure the bulk flow properties of the moisturized samples. A Couette fluidized bed rheometer was used to measure the torque necessary for the rotation of the inner cylinder when the fluidized powder had been moisturized with the same procedure. These experiments show a certain continuity of the results below and above the minimum fluidization velocity, suggesting a similar continuity of the role that interparticle interactions play in the fixed and in the fluidized bed. Experiments below the minimum fluidization velocity were interpreted with a rheological model in which the variable load along the vertical direction in the Couette was calculated with a modified Janssen equation. In this approach the apparent weight of the powder is given by the difference between the gravity and the upward body force determined by the rising gas flow. The agreement between the model and the experiments supports the proposed approach.

Modelling the SO2–limestone reaction under periodically changing oxidizing/reducing conditions: the influence of cycle time on reaction rate

Abstract A simulation model is developed to analyse the dynamic behaviour of the SO 2 –limestone reaction under periodically changing oxidizing/reducing conditions. Reference conditions assumed in the model are those typical of atmospheric fluidized-bed combustors operated with sorbent addition. The reaction network embodies limestone calcination, lime sulphation and sulphate reduction by carbon monoxide, relevant to periodic establishment of mildly reducing atmospheres around the sorbent particle. The model applies to the early conversion of particles and for short periods of time within the sulphation time. The influence of operating conditions on the rate of sulphur uptake by the sorbent is assessed, with particular emphasis on the effect of the cycle time of periodic shift between oxidizing and reducing conditions. Reaction regimes corresponding to the limiting cases of very short and very long cycle times are characterized. Analysis of model results is accomplished in the light of time-scales of circulation and periodic exposure to oxidizing/reducing conditions experienced by sorbent particles in fluidized-bed combustors.

Preliminary Assessment of a Simple Method for Evaluating the Flow Properties of Solid Recovered Fuels

The increasing interest in combustion of solid recovered fuels (SRF), whose physical properties may significantly differ from those of conventional solid fuels, draws attention to the handling of these materials. In this article a simple method for evaluating particulate solids flow properties based on a solid extrusion procedure is assessed. The effects of the main geometrical parameters of the tester and of the testing operating condition are investigated. Results are critically discussed by comparing them with the flow properties evaluated in a Schulze ring shear tester.

Techno-economic analysis of power and hydrogen co-production by an IGCC plant with CO2 capture based on membrane technology

Abstract The techno-economic analysis of an IGCC plant for power and hydrogen production with CO 2 capture by means of Pd-based H 2 membranes was carried out. The case studies were referred to the modifications of the existing 330MWe Integrated Gasification Combined Cycle (IGCC) plant of ELCOGAS based on entrained flow gasification of a dry mixture of coal and pet-coke. The pre-combustion section consisting in a sour water gas shift reactor integrated with Pd-based H2 selective membranes and CO 2 selective membranes was simulated by process simulation techniques. Heat integration of the new process section was also addressed to minimize the energy loss. Power and energy penalty were evaluated as a function of the CO 2 capture percentage and of the electricity and hydrogen output. Economic assessment of the additional capital and production costs was also performed to evaluate the mitigation cost of the carbon capture and storage (CCS) based on membrane technology. Sensitivity analysis was carried out to derive the breakeven price and the threshold performance of hydrogen membranes. The results on the cost of electricity, calculated without accounting for the revenues of the hydrogen sales, provided preliminary data for the economic feasibility of H 2 membranes in the IGCC process.

Process Design of a Multi-Product Lignocellulosic Biorefinery

Abstract Several alternative process pathways including biochemical and thermochemical conversions are available for the second generation biorefineries. In this view conceptual design of a superstructure and optimization methods for process synthesis are widely used in order to find the optimal process flowsheet (Stefanakis et al., 2014). In the present work the flowsheet resulting from the economic optimization of a multiproduct lignocellulosic biorefinery superstructure was simulated by a process simulator (Aspen Plus). As a result, rigorous methods were used to calculate the stream thermodynamic properties and to model the process units. Economic analysis was applied to assess the economic feasibility of the process. Sensitivity analysis on the size of the plant, the product prices and the biomass price was carried out as well.

Design of a wheat straw supply chain network in Lower Saxony, Germany through optimization

Abstract In this work, a biomass supply chain model for the region of Lower Saxony in northern Germany has been developed. Because of Germany’s high demand for biofuels, the production and distribution of levulinic acid and bioethanol is studied by using the Advanced Interactive Multidimensional Modeling (AIMMS) software. The economic benefits that this supply chain provides show to what extent Lower Saxony can become fossil fuel independent. These results are used to answer the following question: has biomass the potential to successfully take up the torch from fossil fuels?”

A Model on the Stability of a Pipe in an Aerated Silo

Abstract The limiting aeration condition necessary to produce the collapse of established pipes (ratholes) is evaluated in a powder bed stored in a flat-bottomed aerated silo. The main parameters tested are the powder properties and the width of the aeration pad at the silo bottom. The measured quantities are the aeration rate and the corresponding size of the pipe. The gas pressure gradient close to the pipe is estimated from the numerical solution of the air flow field in the bulk solids assuming the Darcy flow regime. The powder permeability necessary for this calculation is estimated by fluidization experiments. The hoop stress evaluated according to Johanson (2004) is in good agreement with the unconfined yield strength of the powder, provided that the contribution of aeration to powder consolidation during the pipe formation is properly accounted for.

Experiments and simulation of torque in Anton Paar powder cell

ABSTRACT Torque measurements were performed with the powder cell mounted on an Anton Parr rheometer using glass beads of two different sizes and different impeller geometries. A discrete element method simulator was used to perform simulations of the experiments to compare calculated torque values with those of the experimental torque values. Experimental torques obtained with flat two-blade impeller helped to find the correct sliding friction coefficient between beads. Experimental torques obtained with the circular impeller allowed to obtain the sliding friction coefficient between the impeller and beads. To estimate the wall friction coefficient, it was necessary to activate particle shear on the wall in configurations in which the gap between the impeller and wall is comparable with the bead size. It was verified that at the low shear rates used in this paper, the particle restitution coefficient is not significant and, therefore, higher impeller rotational velocities should be used to calibrate this parameter. Also, the differences between the torque values and time series of different impeller shapes were attributed to the different shearing surfaces and to the formation of instantaneous high magnitude force chains.

Modeling of an air quality monitoring network with high space-time resolution

Abstract With regard to pollution produced in urban areas, low-cost sensors offer the possibility to collect temporal and spatial data and they have a great potential to change the way to monitor the exposure of the population to the atmospheric pollution. However, one of the challenges associated with data coming from this kind of sensors is to try to make them more significant by combing sensors in network. In this work a dispersion model is used to test the distribution of dust (10 μm) measured by individual points of the network. The monitoring area considered is within a seaside town in southern Italy. The monitoring network is made of three sensors placed in points sensitive for the anthropic activity. We have applied an interpolation model to determine the areas of greatest pollution concentration within the monitored area. The model simulated the pollution movements at the level of the individual monitoring points taking into account the weather conditions.