No description available.

No description available.

No description available.

No description available.

Over the past thirty years, the major factor that has prevented the widespread uptake of advanced gasification technologies for treating municipal solid waste (MSW) and biomass fuels has been the presence of tars and char contaminants in the syngas product, which makes the gas unsuitable for power production using energy efficient gas engines or turbines. Furthermore, the large quantities of ashes and volatile material in waste materials produce a large amount of residues downstream, as well as significant corrosive inorganic vapours and ash deposition issues. Advanced Plasma Power (APP) have developed a 2-stage thermal process where the raw syngas generated in a conventional bubbling fluid bed gasifier (FBG) is further treated in a plasma converter (PC) unit to crack and reform these tar and char species to provide a refined syngas suitable for use in a power island. At the same time, inorganic particulate and ash-type components are converted into a stable vitrified product that can be recycled as ceramic glass or road paving material. The fate of the potential deposit-forming elements arising from waste materials in a two-stage process will clearly influence the conversion efficiency, as well as the nature and extent of any harmful deposits along the thermal plant. Therefore, how the main constituents differentiate into gas phase and solid products can be monitored and controlled in the FBG first, and in the PC after, becomes a very important question. The purpose of this PhD project was to gain a fundamental understanding as to how the key process operating variables may impact the final quality of the syngas exiting the thermal plant, especially with regard to the fate of the ash forming components (i.e. agglomeration, slugging, fouling and vitrification) and the behaviour of the volatile matter (i.e. mixing, segregation and gas phase reaction mechanism) in the two stages. A systematic study was conducted to evaluate the effect of the key operating variables on the quality and quantity of the syngas exiting each unit, with specific attention to the behavior of tar components, and other key contaminants (chlorine, sulphur, heavy metals, etc.). On this side, the FBG reactor seems to play a crucial role on the two stage process efficiency evaluation. Within this context, a large part of the study herein was aimed at developing a fundamental understanding on the fluid dynamic behaviour (fluid-particle and particle-particle interaction) of a bubbling fluidized bed operated at high temperature, up to 800˚C. This included process analysis based on operation of a pilot plant using a municipal waste feedstock (40-100 kg/hr). In addition to fluidization tests, laboratory analyses, such as X-ray diffraction (XRD), X-ray fluorescence (XRF), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS), were carried out to investigate the characterization and speciation of bottom and fly-ashes. The results obtained from these physical tests could be used to explain the phenomena observed for some of the materials tested in demonstration runs at APP, which showed changes in the fluidization behaviour for different ash compositions. In parallel, the potential of thermal plasma for the reforming of fluid bed tars and ash vitrification was investigated. Evaluation of plasma chemistry was performed by comparing experimental data from the pilot plant with thermodynamic and thermal kinetic predictions. Oxygen atoms initially formed from CO2 were identified as the major active species involved in the oxidative decomposition of hydrocarbon intermediates and soot precursors. The same mechanism was used to describe the reforming of organosulphur compounds, produced from gasification of sulphur-rich wastes (e.g. automotive shredded residues, demolition wood, etc.). This provides a clearer understanding of the mechanism as to how potentially hazardous elements evolve and provides guidance in the implementation of two-stage processes utilising solid wastes as alternative fuels.

Advanced decision making in the process industries requires efficient use of information available at the different hierarchical levels. However, given the time and decision space sparsity the consideration of such integrated problems poses a plethora of challenges. It is goal of the present thesis to present some recent algorithmic and modelling developments with special focus on the uncertainty aware integration of control with process operations. To this end, the thesis comprises of two parts that are orchestrated towards the attainment of the aforestated goal. The first part discusses theoretical and algorithmic advances in the field of multiparametric programming. Initially, the case of multi-parametric linear programs under simultaneous variations in the left-handside, right-handside of the constraints and the objective function's coefficients is examined. For the first time theoretical characterisation of the explicit solution is proven while an algorithm for their exact computation is proposed. Later on, the aforementioned algorithm is extended to the mixed-integer case where problems of process synthesis and scheduling under global uncertainty are studied. Next, the concept of multi-setpoint explicit controllers and their potential in the context of enterprise wide optimisation problems is introduced. While a prototype implementation of the aforementioned works is also discussed. The second part is dedicated to the development of a systematic framework for the uncertainty aware integration of process planning, scheduling and control (iPSC) of continuous processes. Initially, a Traveling Salesman Problem based formulation is presented and a decomposition method for the deterministic case is proposed. Next, the multi-setpoint explicit controllers developed in the first part of the thesis, enable the development of a reactive closed-loop framework for the iPSC. Ultimately, proactive and reactive approaches are employed in order to instantiate the uncertainty aware iPSC while Monte-Carlo simulations are conducted to evaluate the robustness of the proposed framework.

Crystallization is widely employed in the manufacture of pharmaceuticals during the intermediate and final stages of purification and separation. The process defines drug chemical purity and physical properties: crystal morphology, size distribution, habit and degree of perfection. Particulate pharmaceuticals are typically manufactured in conventional batch stirred tank crystallizers that are still inadequate with regard to process controllability and reproducibility of the final crystalline product. Variations in crystal characteristics are responsible for a wide range of pharmaceutical formulation problems, related for instance to bioavailability and the chemical and physical stability of drugs in their final dosage forms. This thesis explores the design of a novel crystallization approach which combines in an integrated unit continuous flow, microreactor technology, and ultrasound engineering. By exploiting the various benefits deriving from each technology, the thesis focuses on the experimental characterization of two different nucleation systems: a droplet-based system and a single-phase system. In the former, channel fouling is avoided using a carrier fluid to segment the crystallizing solution in droplets, thus avoiding the contact with the walls. In the latter channel blockage is prevented using larger channel geometries and employing higher flow rates. The flexibility of the developed setup also allows performing stochastic nucleation studies to estimate the nucleation kinetics under silent and sonicated conditions. The experiments reveal that very high nucleation rates, small crystal sizes, narrow size distributions and high crystal yields can be obtained with both setups when the crystallizing solution is exposed to high pressure field as compared to silent condition. It is concluded that transient cavitation of bubbles and its consequences are a significant mechanism for enhancing nucleation of crystals among several proposed in the literature. A preliminary study towards the development and design of a growth stage is finally performed. Flow pulsation is identified as a potential method to enhance radial mixing and narrow residence time distribution therefore achieving optimal conditions for uniform crystal growth. The results suggest that increasing values of Strouhal number as well as amplitude ratio improve axial dispersion. Helically coiled tubes are identified as potential structures to further improve fluid dynamic dispersion.

Heterogeneously catalysed aerobic oxidation of alcohols has great potential in chemical synthesis, but its wide application is still limited by safety issues with the combination of gaseous oxygen and flammable organics. The aim of this thesis is to develop Teflon AF-2400 membrane reactors for the intrinsically safe use of oxygen in oxidation of alcohols. Initially, oxidation of benzyl alcohol and cinnamyl alcohol on Au-Pd/TiO2 catalyst was studied in a trickle bed microreactor. The catalyst deactivation in cinnamyl alcohol oxidation, rather than benzyl alcohol oxidation, was attributed to Pd leaching and a complex role of oxygen. Then, a Teflon AF-2400 packed tube-in-tube membrane microreactor was investigated for benzyl alcohol oxidation, which allowed continuous oxygen supply during the reaction and presented higher conversion and selectivity as compared to a reactor with oxygen pre-saturated feed. A novel approach using the tube-in-tube membrane contactor was demonstrated for measuring gas solubility in liquids. To simplify the reactor scale-up, a Teflon AF-2400 flat membrane microreactor was developed for benzyl alcohol oxidation, and the mass transfer and reaction in the reactor were experimentally and theoretically investigated with different catalysts. The oxygen transverse mass transfer in the catalyst bed, rather than oxygen permeation through membrane or oxygen internal/external transfer in the catalyst particles, was indicated to be the controlling process. An effectiveness factor analysis akin to internal/external mass transfer and reaction in a catalytic particle was provided to guide the catalyst choice and the membrane reactor design. For direct usage of small catalyst particles in continuous flow reactors, a stirred membrane reactor with a sintered metal filter and an external membrane contactor was experimentally demonstrated and mathematically simulated for benzyl alcohol oxidation. The reactant conversion and the catalyst utilization were indicated to be affected by various operation parameters, which were correlated to guide the reactor design and operation.

Cooling crystallization is extensively used by the pharmaceutical industry to produce and purify Active Pharmaceutical Ingredients. Nucleation, that is the first step of crystallization, is pivotal in determining the final product properties. For these reasons, understanding the nucleation process and the factors that control crystal formation is essential to limit product variations and ultimately to improve the efficacy and the safety of the final drug. This thesis aims to investigate the mechanisms responsible for initiating nucleation in a clear solution and to identify the key process parameters that control nucleation. In particular, we used three experimental systems to explore the influence of micromixing, shear rate and gas bubbles under a wide range of fluid dynamic conditions. The first part of this work focuses on the experimental characterization of two laboratory scale batch systems to explore the effect of micromixing on metastable zone width (MZW) in industrial-like fluid dynamic conditions. The results demonstrated that, although increasing agitation is beneficial in reducing the MZW, the presence of gas bubbles was more effective in inducing nucleation supporting the theory that the gas bubbles offer a surface for heterogeneous nucleation. However, due to the complexity of the systems studied (non-spatially uniform fluid dynamic), it is difficult to untangle the effect of the various process parameters. For this reason, a novel droplet-based crystalliser was used to quantitatively investigate the effect of shear rate in well-controlled fluid dynamic conditions (quiescent-stagnant conditions, low-shear laminar flow and high-shear turbulent flow). The results suggested that a shear field can significantly enhance primary nucleation by increasing the meso-scale cluster collision efficiency. However, further experimentation is necessary in order to verify this hypothesis. Finally, a novel experimental system was proposed to explore the possibility of heterogeneous nucleation on gas bubbles. The experiments revealed that nucleation on gas-liquid interface is favoured.

The role that fluidized bed reactors and other unit operations play for a wide range of industries is well recognized. Although fluidized bed systems offer several advantages such as high heat transfer rate, rapid solids mixing, large surface contact, high heat and mass transfer rates between gas and particles, a complete understanding of the phenomena occurring in these reactors is still a challenge, with reference to the role of the process conditions, such as pressure, temperature and humidity. Generally, the temperature affects both the properties of the material and the fluid, such as density and fluidizing gas viscosity. These changes can influence significantly the design and efficiency of the reactor. For these reasons, the effect of the temperature on fluidization became the center of a significant academic effort aimed at providing a theoretical framework to underpin the major physical phenomena involved and, in particular, to develop correlations for the scale-up of fluidized bed reactors. Several works have demonstrated that process conditions can influence the role of the interparticle forces (IPFs) in the fluidization behaviour of powders. Given the complexity of the phenomena involved, a direct quantification of the particle-particle interactions in fluidized beds and of their changes at process conditions is very difficult. Within this framework, powder rheology represents an appealing tool to evaluate indirectly the effects of the interparticles forces on fluidization. The main objective of the present work is to provide a basis for understanding the factor responsible for changes in fluidization behaviour of industrial particles under realistic process conditions. In order to address the problem of assessing the fluidization behavior of powders at high temperature, a multidisciplinary approach linking micro and macro properties of the particulate system is adopted in this project. On the one hand, the investigation of the fluidization behavior at process conditions is carried out by means of standard fluidization tests; on the other hand, the characterization of the flow properties of the same powders is performed by means of powder rheology tests. To this end, the 5 experimental campaign was performed using a 140x1000 mm heated gas fluidized bed and a modified Schulze annular shear cell. Both experimental apparatuses allowed a safe operation of the system up to 600 °C. Five cuts of the same mother particles covering Group B, A and C of Geldart’s classification were investigated over a range of temperatures from ambient to 500 °C. Furthermore, two reacted samples of the same mother particles but, containing different levels of impurities were tested. Shear test experiments show changes of the flow properties at high temperatures. The powder cohesion is the parameter which appears to be mostly affected by temperature while the angle of internal friction shows a weaker dependence on temperature and consolidation level. A model combining the continuum approach and the particle–particle interaction description was used to correlate the powder tensile strength with the interparticle forces. In the presence of only van der Waals forces, the model with the assumption of plastic deformation at contact points and a reasonable value of the mean curvature radius is able to predict the correct order of magnitude of the tensile strength. Furthermore, the significant increase of the cohesion of the reacted material with increasing temperature can be only justified by considering an active role of capillary bridges between the particle asperities. These findings, together with the nature of the impurities characterized by means of EDX analysis applied to SEM imaging, strongly suggest that the observed changes for the reacted material are due to the occurrence of capillary bridges between particles, even if thermal analyses are not able to detect any significant phase changes. This work assessed also the validity of some classical concepts and equations commonly used for describing the fluidization behaviour at low and high temperature. The minimum fluidization conditions were well predicted by the Ergun equation when accounting for the experimental values of the bed voidage. The bed collapse test was used to quantify changes in the aeratability of the powders between low and high temperature and to identify the minimum bubbling conditions. For systems dominated by IPFs the analysis of the voidage of the dense phase and the overall bed expansion as a function of the flow rate allowed reconstructing the sequence of phenomena through which a stable flow of bubbles across the solid mass were achieved. 6 The role of hydrodynamic forces and of interparticle forces on the fluidization behaviour of the particulate systems studied was investigated by looking at the applicability of the Foscolo and Gibilaro stability criterion [Chem Eng Sci. 1984, 39 (12): 1667-1675]. In particular the analysis followed the approach indicated by Valverde et al. [Europhys Lett. 2007, 54: 329-334.], which makes use of the initial settling velocity of cohesive particles and of the Bond number derived from rheometry results. The results of the analysis show the capability of predicting the final structure of the bed with temperature when considering an aggregative fluidization behaviour caused by interparticle adhesive forces. These results also suggest the potential use of the powder rheometry carried out at high temperature as a sensitive method to detect phase changes in particulate systems that are limited to the particle surface that can significantly affect the working conditions of fluidized bed reactors. More in general, the results indicate that shear testing results at ambient and high temperatures allow to correctly estimate the intensity of interparticle forces in particulate systems.