Feedback control of chemical reactors by modern principles

Plug-Flow Reactors (PFR) belong to frequently used technological plants which exhibit unpleasant behavior. The traditional PID control structure in these cases may fail or demonstrate an unacceptable behavior. The paper brings another approach of control design called robust. It means that the controller is fixed but resistant to the uncertainty of the controlled plant. The studied approach considers a linear system with parametric uncertainty, which covers a family of all feasible plants. A controller with fix parameters is then designed so that for all possible plants, the acceptable stable control behavior is obtained. The structure of the control law is in two degree of freedom (2DOF) which offers better control responses than classical structures. All calculations and simulations of mathematical models and control responses were performed in the Matlab and Simulink environment. Copyright © 2020, AIDIC Servizi S.r.l

Application of method of lines in chemical engineering problems

In this work, two problems in chemical engineering are studied and solved. Estimation of an important parameter of dust explosions, the deflagration index kST , and a study of unsteady state with axial diffusion Plug Flow Reactors are presented. Both problems are approached by characterizing the physical phenomena involved with suitable transport equations. Such equations have been developed with the synergy of both consolidated theoretical models and ad hoc assumptions and semi-empiric approaches, according to the specific problem analyzed. The final equation systems result in a system of non-linear Partial Differential Equations. The numerical solution of such equations has been performed by implementing the Method of Lines, a numerical method based on the discretization of spatial derivative operators, transforming a system of PDEs into a system of ODEs or DAEs. The resulting ODEs/DAEs systems have been implemented and solved inside MAT LABTMenvironment. The Method of Lines is presented for uniform and non-uniform grids, generalized with the use of spatial derivatives discretization stencils of several orders of accuracy. For the estimation of kST , we validated the model with 8 organic dust: Aspirin, Cork, Corn starch, Niacin, Polyethylene, Polystyrene, Sugar and Wheat flour. Results showed an interesting match between experimental and simulated data: predictions for the deflagration index were good, while the evolution of process variables (such as the temperature of the gas phase), still leaves room for improvements. For the PFR study, we propose 1-D models, taking in account the reactor start-up, thermal and material axial diffusion, and the presence of a heating/cooling system. In order to judge the quality of the results, we took as case study a reaction well studied in the literature over the years: the oxidation of Naphthalene. We developed the so-called Runaway Boundaries for the reaction considered. Our results found good matches with the available literature data and analysis. We also noticed a shifting of the Runaway Boundaries when considering a more realistic heating/cooling system

Application of method of lines in chemical engineering problems

In this work, two problems in chemical engineering are studied and solved. Estimation of an important parameter of dust explosions, the deflagration index kST , and a study of unsteady state with axial diffusion Plug Flow Reactors are presented. Both problems are approached by characterizing the physical phenomena involved with suitable transport equations. Such equations have been developed with the synergy of both consolidated theoretical models and ad hoc assumptions and semi-empiric approaches, according to the specific problem analyzed. The final equation systems result in a system of non-linear Partial Differential Equations. The numerical solution of such equations has been performed by implementing the Method of Lines, a numerical method based on the discretization of spatial derivative operators, transforming a system of PDEs into a system of ODEs or DAEs. The resulting ODEs/DAEs systems have been implemented and solved inside MAT LABTMenvironment. The Method of Lines is presented for uniform and non-uniform grids, generalized with the use of spatial derivatives discretization stencils of several orders of accuracy. For the estimation of kST , we validated the model with 8 organic dust: Aspirin, Cork, Corn starch, Niacin, Polyethylene, Polystyrene, Sugar and Wheat flour. Results showed an interesting match between experimental and simulated data: predictions for the deflagration index were good, while the evolution of process variables (such as the temperature of the gas phase), still leaves room for improvements. For the PFR study, we propose 1-D models, taking in account the reactor start-up, thermal and material axial diffusion, and the presence of a heating/cooling system. In order to judge the quality of the results, we took as case study a reaction well studied in the literature over the years: the oxidation of Naphthalene. We developed the so-called Runaway Boundaries for the reaction considered. Our results found good matches with the available literature data and analysis. We also noticed a shifting of the Runaway Boundaries when considering a more realistic heating/cooling system

Control and optimization of a three-phase catalytic slurry intensified continuous chemical reactor

International audienceIntensified continuous mini-reactors working in high pressure and temperature conditions are particularly effective at coping with mass transfer limitations during three-phase catalytic reactions. They are highly non-linear, multivariable systems and behave differently from conventional batch, fed-batch or continuous non-intensified reactors. In this paper, the optimization and control of this new process are presented using a two-layer approach consisting of a hierarchical control structure with an optimization layer which calculates the set points for an advanced controller. The latter is based on the concavity of the entropy function and the use of thermodynamic availability as a Lyapunov function. The three-phase catalytic o-cresol hydrogenation performed under high pressure and temperature in a small-scale pilot of the RAPTOR® reactor designed by the French company AETGROUP SAS, is taken as a representative test example to illustrate the strategy. The performance of the control structure is illustrated by simulation

Plantwide Control and Simulation of Sulfur-Iodine Thermochemical Cycle Process for Hydrogen Production

A PWC structure has developed for an industrial scale SITC plant. Based on the performance evaluation, it has been shown that the SITC plant developed via the proposed modified SOC structure can produce satisfactory performance – smooth and reliable operation. The SITC plant is capable of achieving a thermal efficiency of 69%, which is the highest attainable value so far. It is worth noting that the proposed SITC design is viable on the grounds of economic and controllability

Project Exodus

A design for a manned Mars mission, PROJECT EXODUS is presented. PROJECT EXODUS incorporates the design of a hypersonic waverider, cargo ship and NIMF (nuclear rocket using indigenous Martian fuel) shuttle lander to safely carry out a three to five month mission on the surface of Mars. The cargo ship transports return fuel, return engine, surface life support, NIMF shuttle, and the Mars base to low Mars orbit (LMO). The cargo ship is powered by a nuclear electric propulsion (NEP) system which allows the cargo ship to execute a spiral trajectory to Mars. The waverider transports ten astronauts to Mars and back. It is launched from the Space Station with propulsion provided by a chemical engine and a delta velocity of 9 km/sec. The waverider performs an aero-gravity assist maneuver through the atmosphere of Venus to obtain a deflection angle and increase in delta velocity. Once the waverider and cargo ship have docked the astronauts will detach the landing cargo capsules and nuclear electric power plant and remotely pilot them to the surface. They will then descend to the surface aboard the NIMF shuttle. A dome base will be quickly constructed on the surface and the astronauts will conduct an exploratory mission for three to five months. They will return to Earth and dock with the Space Station using the waverider

Integration of microwave heating with continuously operated milli-reactors for fine chemical synthesis

Major efforts in the research field of microwave assisted organic synthesis have demonstrated the specific benefits associated with the use of microwave irradiation such as selective and rapid heating of the reaction mixture. In many case studies, these benefits eventually lead to a significant enhancement in the production rates. Therefore, microwave assisted flow synthesis can be an interesting alternative for fine chemical production in conventionally heated batch reactors. However, realization of microwave assisted flow synthesis at kilogram scale requires a proper design of tubular reactors integrated with the microwave heating source, i.e. the cavity. The design of these reactors should primarily be able to overcome the limitations by the penetration depth of the microwaves, i.e. ¿0.013 m. Moreover, operation based on microwave heating should allow accurate temperature control by precise tuning and quantification of the microwave energy distribution. Therefore, being case specific, design efforts are necessary for the microwave setup as well as for the reactor configuration. Heating in monomode microwave equipment is energy efficient and fast in comparison to heating in multimode microwave equipment. State-of-the-art microwave cavities, however, lack in providing important functionalities, such as a predictable electric field pattern, tuning facility, detailed energy distribution and possibilities for modular scale-up. A waveguide type monomode microwave cavity in combination with the short circuit, stub tuners, and isolators can provide the aforementioned functionalities for continuously operated reactors. This type of microwave setup allows an accurate elaboration of energy balances for efficient and uniform heating. Additionally the use of multiple cavities connected to a single microwave generator via a main waveguide permits modular scale-up. The dielectric properties (i.e. dielectric constant and dielectric loss) of a microwave absorbing load (e.g. reaction mixture/solvent) are significantly dependent on temperature. As a consequence, microwave absorption, which involves interaction of the electromagnetic field with the applied load, is a recurring process. Therefore, detailed understanding of the dielectric property change with temperature is a prerequisite for a proper design of the load to be used under stop-flow (batch) and continuous-flow conditions. For stop-flow conditions, the highest heating efficiency (70 %) is observed for a load diameter equal to and larger than half of the wavelength of the microwaves in the liquid medium. For continuous-flow conditions, the heating efficiency increases linearly with the load diameter. However, microwave leakage above the propagation diameter (i.e. half wavelength) limits further increase of the load diameter in continuous operation. The high energy intensity of the focused electromagnetic field in case of waveguide type microwave cavities makes an efficient and controlled continuous operation difficult, especially when a strong microwave absorbing load (e.g. ethanol) is present. In cases, such as the reaction of ethanol and acetic acid to produce ethyl acetate over a strong acid ion-exchange resin, a milli reactor-heat exchanger combination with a co-current flow of a microwave transparent solvent (coolant) can be a solution. Here, rapid volumetric heating to the reaction temperature can be achieved by microwaves before the reaction mixture enters into the catalyst bed. Additionally, the coolant not only limits overheating of the reaction mixture but also permits heat integration, resulting in extended reactor lengths and efficient heating (i.e. 96 %). However, stagnancy in the flow of the microwave absorbing load results in a poor convective heat transport. As a consequence, stagnant layer formation caused either by any insertion (of system components, such as fiber optic sensors) or at the reactor walls, yields higher temperatures and lower microwave energy dissipation regions. One of the promising approaches for scaling microwave assisted flow synthesis is numbering up. The numbering up approach is based on parallelization of tubular structured reactors with a channel diameter in the millimeter range. The performance of such a configuration is evaluated by a multi-tubular milli-reactor/heat exchanger system with a thin Cu film on the inner walls of the reactor tubes. The thin Cu film provides uniform microwave absorption and it improves the production rate by acting as a heated catalytically active surface, as demonstrated in the synthesis of 1,3-diphenyl-2-propynyl-piperidine from benzaldehyde, piperidine, and phenylacetylene. Controlled selective heating of the thin Cu film is achievable by using a counter-current flow of a microwave transparent coolant (toluene). The coolant flow avoids Cu burning and reduces leaching, consequently improving the steady state catalytic performance of the Cu coated reactor tubes. Higher temperatures, i.e. at least 100 K higher than the bulk liquid, are achievable at the locus of the reaction, i.e. the catalyst surface, purely due to selective microwave heating. Another approach to realize higher production rates is utilization of multiple microwave cavities in series. In this approach, the process stream is taken from one cavity to the next where the process efficiency is well optimized over each consecutive cavity. Transient operation through each optimized cavity and utilization of multiple cavities in series increases conversion and consequently results in higher production rate. Additionally, known kinetics allows estimation of the production rate for each additional cavity in the series. This approach of scale-up is possible at minimized grid to applicator losses by connecting multiple cavities to a single microwave generator via a main waveguide. Scale-up approaches based on parallelization of tubular structured reactors as well as on utilization of multiple microwave cavities in series were found to be successful. Application of microwaves as a process intensification tool, especially in the case of organic synthesis, is very attractive for liquid-solid reactions, where the solid is the selectively (microwave) heated catalyst

Modeling, Simulation and multi-objective optimization of industrial, low-density polyethylene reactor

Ph.DDOCTOR OF PHILOSOPH