Papers by Pietro Altimari
AIChE Journal
Networks of N identical catalytic reactors with periodically switched inlet and outlet sections a... more Networks of N identical catalytic reactors with periodically switched inlet and outlet sections are studied for first-order irreversible exothermic reactions. Switching strategies with inlet and outlet sections periodically jumping a fixed number n s of reactors are considered and the mechanisms governing the formation of traveling temperature wave-trains are analyzed as n s and N are varied. To this aim, a geometric approach to the analysis of the network energy balance is developed. Based on this approach, infinite domains of traveling temperature wave-trains are predicted for any n s and N. Analytical approximations are derived for the stability limits and the spatiotemporal patterns of these regimes. Stability boundaries predicted analytically include for any solution the largest part of the stability region computed by numerical simulation. Moreover, good agreement is found between the structure of the spatiotemporal patterns computed numerically and that predicted based on the proposed approach. 909 (a) with n s ¼3 and N ¼ 4, it is impossible for purely thermal fronts to intercept the NTW outlet section between five and six cycles; (b) n s ¼ 1 and N ¼ 4 prevent the possibility to intercept the NTW outlet section during the following three cycles.
Computer Aided Chemical Engineering, 2006
Thermal runaway of chemical reactors has been proved to be strictly related to the experience of ... more Thermal runaway of chemical reactors has been proved to be strictly related to the experience of catastrophic bifurcation operating conditions. In this framework, bifurcation control theory, dealing with the modification of the bifurcation structure of nonlinear systems, is to become a powerful tool to design control systems able to tame thermal runaway hazards. In this work we focus on a novel bifurcation control strategy: the bifurcation tailoring. Bifurcation tailoring aims to globally reshape the bifurcation diagram of a nonlinear system. In order to cope with process constraints, an optimal formulation of the bifurcation tailoring method is proposed and implemented to remove thermal runaway hazards in chemical reactors.
... At temperature values greater than 60 "C, a large growth in the diffusivity of water is,... more ... At temperature values greater than 60 "C, a large growth in the diffusivity of water is, for example, observed due to starch gelatinization (Stapley et al., Please cite this article as: Altimari P., Adiletta G., Albanese D., Crescitelli S. and Di Matteo M., 2011, Experimental analysis and ...
Chemical Engineering Transactions, 2013
ABSTRACT The application of a structured population balance model to the numerical simulation of ... more ABSTRACT The application of a structured population balance model to the numerical simulation of microalgal growth in a continuous photobioreactor is discussed. The analysis is focused on the interplay between microalgal metabolism and photobioreactor operation. The proposed model is structured to describe the evolution of mass distribution among different stages of the cell division cycle. Numerical results provide indications about the impact of the implemented nutrient supply strategy on biomass productivity. These information are of relevance in applications where nutrient deprivation is imposed to enhance the production of prescribed products.
Environmental engineering and management journal
Chemical Engineering Journal, 2015
Hysteresis characteristics of an autothermal methane reforming reactor are analyzed. Bifurcation ... more Hysteresis characteristics of an autothermal methane reforming reactor are analyzed. Bifurcation analysis is performed to determine ignition and extinction boundaries. The mechanisms determining the spatial profiles of oxidation and reforming reaction rates are described. The addition of water to feed can improve reactor controllability.
Computer Aided Chemical Engineering, 2010
Gain scheduling is a method widely applied in industrial practice to control processes where larg... more Gain scheduling is a method widely applied in industrial practice to control processes where large changes of the operating conditions can occur. In its standard implementation, this technique requires to compute a family of steady states covering the operating region of interest and then to design a family of linear feedback controllers ensuring stability and desired output behavior about the selected steady states. In this contribution, a novel approach to design gain-scheduled controllers of nonlinear processes is presented. Parametric continuation and optimization techniques are implemented to compute a parameterized family of steady states covering the output range of interest and, at the same time, fulfilling a prescribed set of control requirements. Then, bifurcation analysis is performed to design a family of linear feedback controllers guaranteeing desired output behavior around the selected steady states and preventing the occurrence of state multiplicity. The method is validated on the problem of controlling a continuous exothermic reactor exhibiting state and input multiplicity.
Computer Aided Chemical Engineering, 2010
A network of catalytic reactors with a periodic switching of the feed and discharge position (als... more A network of catalytic reactors with a periodic switching of the feed and discharge position (also called loop reactor) is studied for reversible exothermic reactions like methanol synthesis. The aim of the study is the comparison of two different switching strategies in overcoming the conversion limits imposed by the thermodynamic equilibrium. The first strategy, that is the only considered in previous works, consists of changing at each switch time the feed/discharge positions, so that the first reactor of the NTW is moved to the last place. The second strategy consists in moving the last reactor in the first place each switch time. We show through numerical simulations that the second forcing strategy is more convenient in terms of yield and methanol conversion, because it is able to create a conversion/temperature path closer to the optimal one.
Computer Aided Chemical Engineering, 2009
A novel method for transition control of nonlinear processes is presented. Gain scheduling is imp... more A novel method for transition control of nonlinear processes is presented. Gain scheduling is implemented to ensure stability and desired output behavior over the operating region of interest while transition between the initial and the final equilibrium is achieved by predictive ...
Electrochimica Acta, 2015
Cobalt nanoparticles were synthesized by pulsed electrodeposition on copper substrate.
International Journal of Bifurcation and Chaos, 2010
Bifurcation tailoring is a method developed to design control laws modifying the bifurcation diag... more Bifurcation tailoring is a method developed to design control laws modifying the bifurcation diagram of a nonlinear dynamical system to a desired one. In its original formulation, this method does not account for the possible presence of constraints on state and/or manipulated inputs. In this paper, a novel formulation of the bifurcation tailoring method overcoming this limitation is presented. In accordance with the proposed approach, a feedforward control law generating an optimal bifurcation diagram is computed by constrained minimization of an objective functional. Then, a feedback control system enforcing stability of the computed equilibrium branch is designed. In this context, bifurcation analysis is exploited to select feedback controller parameters ensuring desired output behavior and, at the same time, preventing the occurrence of multistability. The method is numerically validated on the problem of tailoring the bifurcation diagram of an exothermic chemical reactor.
Industrial & Engineering Chemistry Research, 2008
The nonlinear behavior of plug-flow reactor−separation−recycle systems, where the endothermic fir... more The nonlinear behavior of plug-flow reactor−separation−recycle systems, where the endothermic first-order reaction A → R + Q and the exothermic second-order reaction B + Q → P simultaneously take place, is investigated. As the physical properties of the species involved vary, ...
Computers & Chemical Engineering, 2009
A systematic investigation of plug-flow reactor (PFR)-separation-recycle systems where first-orde... more A systematic investigation of plug-flow reactor (PFR)-separation-recycle systems where first-order exothermic and endothermic reactions are simultaneously performed is presented. The nonlinear behaviour is analyzed for two flowsheet alternatives and four plantwide control structures. It is shown that the system can exhibit a complex nonlinear behaviour. For the parameter values used, regions of unfeasibility, two or three multiple steady states and branches of isolated solutions were found. The undesired nonlinear phenomena can be avoided by fixing the reactor-inlet flow rates of each reactant or, when this is impossible due to the flowsheet structure, by providing sufficient cooling capacity.
Computers & Chemical Engineering, 2009
The problem of integrated design and control of plantwide systems coupling endothermic and exothe... more The problem of integrated design and control of plantwide systems coupling endothermic and exothermic reactions is addressed. Processes simultaneously carrying on the endothermic first-order reaction A → R + Q and the exothermic second-order reaction B + Q → P are considered. As the physical properties of the species involved vary, possible flowsheets are identified and feasible control strategies are suggested. Multiple steady states are detected at fixed values of the plantwide-control variables. Singularity theory is exploited to divide the space of reactor-design parameters into regions characterized by qualitatively different solution diagrams. The implications of the observed behaviour on plant controllability are thoroughly discussed.
Chemical Product and Process Modeling, 2000
The paper illustrates the operational difficulties arising from simultaneously performing exother... more The paper illustrates the operational difficulties arising from simultaneously performing exothermic and endothermic reactions, and demonstrates that the plant can be built and safely operated by integrating the design and plantwide control issues. The behaviour of reactorseparationrecycle systems carrying the coupled reactions A →P + Q (endo) and B + Q → R (exo) is investigated. Irrespective of the control structure, state multiplicity cannot be removed if the intermediate component Q is recycled. Therefore, the chemical reactor should be designed such the recycle of Q can be avoided without economic penalty. The theoretical findings are applied to the design and control of a plant coupling ethylbenzene dehydrogenation and nitrobenzene hydrogenation for simultaneous production of styrene and aniline. After plant design, a rigorous dynamic model is developed using AspenDynamics. A plantwide control structure is implemented and shown to be able to achieve large production rate changes and to effectively reject various disturbances. .
Chemical Engineering Journal, 2014
Copper biosorption by wild type and two engineered (Rim101, Och1) Saccharomyces cerevisiae biom... more Copper biosorption by wild type and two engineered (Rim101, Och1) Saccharomyces cerevisiae biomasses was analyzed. Potentiometric titrations revealed that carboxylic, amino and, to less extent, phosphoric groups are responsible for the biosorption of copper.
Chemical Engineering Journal, 2011
Networks of catalytic reactors with periodically switched inlet and outlet sections offer a compe... more Networks of catalytic reactors with periodically switched inlet and outlet sections offer a competitive technological solution to the operation of reversible exothermic reactions. Traditionally, this operation mode is implemented by periodically shifting inlet and outlet sections so as to jump a single reactor unit in the flow direction. Here, a network of four catalytic reactors carrying on the methanol synthesis process is considered and the effect of varying the number (n s ) of reactor units jumped by inlet and outlet sections on network stability and performance is investigated. Increasing n s , a greater variety of periodic regimes giving rise to trains of temperature waves characterized by spatial periodicity are detected as the switching velocity varies. These regimes well reproduce the inter-stage cooling effect of multistage fixed bed reactors and, hence, guarantee in general large conversion values. Moreover, an intriguing coexistence between T-periodic and multi-periodic temperature wave trains is revealed, T being the period needed for the system to recover its initial configuration. A T-periodic symmetric wave train characterized by k waves always coexists with a number of k − 1 stable symmetric kT-periodic regimes, except when symmetry breaking is encountered. The k − 1 coexisting regimes correspond to wave trains with a number of waves ranging between 1 and k − 1. Bifurcational analysis is performed to characterize the stability range of periodic regimes and to systematically analyze multiplicities and bifurcations as the switching velocity is varied and at different n s .
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Papers by Pietro Altimari