Raffaella Ocone

The effect of the flow field recalculation on fibrous filter loading: A numerical simulation

We present a simple model for the loading process of aerosol particles on fibrous filters with the aim to show the influence that the flow recalculation around a single fibre has on the complete loading process, up to the final clogging of the filter. At each loading stage (i.e., at any given degree of particle deposition), the change of shape of the fibre is presented, and information on the flow field around a fibre and the filter efficiency are obtained. The effect of the flow recalculation on the filter efficiency is shown; the single fibre efficiency is proven to be overestimated when the effect of further deposition is neglected. To perform the study, we have developed a CFD code and we have combined it with particle trajectory simulations.

A pseudo‐thermodynamic theory of granular flow rheology

We analyze the existing models of granular flow where the particle’s phase stress tensor is regarded as dominated by translational‐collisional stresses. We extend the commonly used concept of a granular phase pseudo‐temperature to develop a pseudo‐thermodynamic theory of such systems. This is accomplished by introducing the concept of pseudo‐entropy, a quantity which can actually be calculated from the existing theories. The systems considered are shown to exhibit entropic elasticity. The consistency of constitutive equations available in the literature is tested against the pseudo‐thermodynamic theory; the test is mostly successful, except for one term sometimes used in the constitutive equation for the flux of pseudo‐energy, which, according to our theory, should be identically zero.

Techno-economic investigation of a chemical looping combustion based power plant

Among the well-known state-of-the-art technologies for CO2 capture, Chemical Looping Combustion (CLC) stands out for its potential to capture CO2 efficiently from a fuel power plant. CLC involves the combustion of carbonaceous fuel such as coal-derived syngas or natural gas via a redox chemical reaction with a solid oxygen carrier circulating between two fluidised beds. Avoided NOx emissions, high CO2 capture and thermal efficiency are the key concepts that make worth the investigation of this technology. One of the main issues about CLC might concern the impact of the solid metal oxides price and lifetime on the Levelised Cost Of the Electricity (LCOE). A natural gas fired power plant embedding a CLC unit is presented in this work. Detailed fluidised bed models are implemented in Aspen Plus software. Kinetics and hydrodynamics are taken into account to evaluate their effect on the total solid inventory required for full fuel conversion. The models are incorporated into a power plant and a detailed economic evaluation is undertaken by varying two relevant parameters: fuel price and lifetime of the solid particles. The effect of these parameters on the LCOE is investigated and a comparison between CLC and a post-combustion technology employing amines (e.g. monoethanolamine, MEA) is presented. It is shown that the CLC power plant under study leads to a lower LCOE compared to the current MEA post-combustion solution.

Heterogeneous chemical equilibria in multicomponent mixtures

Abstract An analysis of the geometry of the free energy surface for multicomponent mixtures is discussed for conditions where there may be chemical reactions taking place in the mixture, as well as the possibility of phase separation. The latter is shown to take place in a direction orthogonal to the reaction subspace, and can therefore take place only if there are such directions. It is shown that such directions exist unless the brute chemical formulae of all components are multiple of each other. The analysis is generalized to the case of continuous mixtures, where the number of components, of independent reactions, and of possible phases all approach infinity.

ON WAVES OF PARTICULATE PHASE PRESSURE IN GRANULAR MATERIALS

The speed of propagation U of an infinitesimal one‐dimensional disturbance of particulate phase pressure in dry granular flow is analyzed. We regard the propagation of such a discontinuity as the analog of the speed of sound in the classical continuum theory. Indeed, we show that, on the basis of the pseudo‐thermodynamic theory of granular flow which we have recently presented, U is the square root of the inverse iso‐pseudo‐entropic compressibility of the particulate phase. Direct calculation of the value of U is discussed.

Analysis of Process Variables via CFD to Evaluate the Performance of a FCC Riser

Feedstock conversion and yield products are studied through a 3D model simulating the main reactor of the fluid catalytic cracking (FCC) process. Computational fluid dynamic (CFD) is used with Eulerian-Eulerian approach to predict the fluid catalytic cracking behavior. The model considers 12 lumps with catalyst deactivation by coke and poisoning by alkaline nitrides and polycyclic aromatic adsorption to estimate the kinetic behavior which, starting from a given feedstock, produces several cracking products. Different feedstock compositions are considered. The model is compared with sampling data at industrial operation conditions. The simulation model is able to represent accurately the products behavior for the different operating conditions considered. All the conditions considered were solved using a solver ANSYS CFX 14.0. The different operation process variables and hydrodynamic effects of the industrial riser of a fluid catalytic cracking (FCC) are evaluated. Predictions from the model are shown and comparison with experimental conversion and yields products are presented; recommendations are drawn to establish the conditions to obtain higher product yields in the industrial process.

Flow Structures of Geldart a Solids in Circulating Fluidized Beds

The model developed by Ocone et al . 1 to describe particle distribution in a flowing gas-particle mixture was modified to include a counter-diffusive solid concentration term and applied to fluid cracking catalyst in a circulating fluidized bed. Comparison of the local solid flux distribution predicted by the new model with experimental data published previously by Bodelin et al . 2 showed very good agreement.

Extension of dynamics of granular flow methodology to cell biology

In a previous paper (J. Non-Newtonian Fluid Mech. 76 (1998) 5), the analogy between the methodology typical of the dynamics of polymeric liquids and those used in granular flow theory was investigated. It was shown that such a methodology could be successfully extended to granular flow, and then it was speculated on the possibility of extending it to diverse areas. In this paper two important conclusions are reached. Firstly we show that the methodology behind the statistical theories (which starting from the microstructural element eventually leads to the formulation of constitutive equations (AICHE Symposium Series, Vol. 93, 1997, p. 103)) can be extended to an apparently completely different field, namely cell biology. We then show that classical thermodynamics, as applied to epigenetic systems, presents limitations which can be overcome following an axiomatic thermodynamic route (J. Rheol. 37 (1993) 727).

A metabolic thermodynamic theory of cell cycle

Abstract Due to its intrinsic complexity, a complete mathematical description of the cell cycle appears a difficult task. Nevertheless, a preliminary analysis, based on molecular biology, can help in clarifying what are the reliable tools for a quantitative approach. In a previous paper [Physica A 321 (3–4) (2003) 587], the steps to be followed to formulate a metabolic statistical thermodynamics have been established. Here we present a simple mathematical model for the interaction of CyclinB and Cdh1 [The Cell Cycle. An Introduction, Oxford University Press, New York, 1993], with the aim of analysing the properties of the system from a thermodynamic viewpoint. The model is shown to define the Gibbs phase integral of the system and the general Gibbs energy function is obtained. This, together with the analogue of the temperature, defines the working tools indispensable for the formulation of a metabolic statistical thermodynamic-like theory.

Kinetics and Thermodynamics in Multicomponent Mixtures

This article reviews the kinetic and thermodynamic behavior of multicomponent mixtures containing a very large number of components, A flurry of activity can be envisaged in recent literature; however; although the needs for lumping in this area have been clearly identfied, it is not always easy to catch the links and the relationships among different works. We review various techniques and results showing the logical status of the latter and how they can be applied to specijic problems. Overall (or global) quantities of interest are identijied with reference to industrial problems, and chemical reaction engineering of systems, where one is interested only in the overall kinetics, are presented. Mathematical techniques through which results are obtained can ofen be cumbersome, and they rely primarily on jhctional analysis. Such techniques are reviewed in the final section of the article.