Process Dynamic Simulation

Systematic plantwide control system design for economically optimal operation of the ethyl benzene process over a large throughput range is studied. As throughput is increased, constraints progressively become active with the highest number of active constraints at maximum throughput. An economic plantwide control system (CS1) is designed for operation at this most constrained operating point using a novel ''top-down'' pairing approach with higher prioritization to the economic objectives over regulatory objectives. This structure is adapted for near optimal low throughput operation with constraints that go inactive taking up additional economic variable control. For comparison, a conventional plantwide control structure (CS2) with the throughput manipulator at a fresh feed and ''bottom-up'' pairing for the control objectives is also synthesized. Four overrides are needed in CS2 to handle the hard equipment capacity constraints at maximum throughput. Rigorous dynamic simulations show that CS1 is dynamically and economically significantly superior to CS2. V V C 2012 American Institute of Chemical Engineers AIChE J, 00: 000–000, 2012

A strategy for adaptive control and energetic optimization of aerobic fermentors was implemented, with both air flow and agitation speed as manipulated variables. This strategy is separable in its components: control, optimization, estimation. We optimized parameter’s estimation (from the usual KLa correlation) using sinusoidal excitation of air flow and agitation speed. We have implemented parameter’s estimation trough recursive least squares algorithm with forgetting factor. We carried separate essays on control, optimization and estimation algorithms. We carried our essays using an original computational simulation environment, with noise and delay generating facilities for data sampling and filtering.

Our results show the convergence and robustness of the estimation algorithm used, improved with use of both forgetting factor and KLa dead-band facilities. Control algorithm used in our work compares favorably with PID using the integrated area criteria for deviation between oxygen molarity and critical molarity (set point). Optimization algorithm clearly reduces energetic consumption, respecting critical molarity. Integration of control, optimization and adaptive algorithms was implemented, but future work is needed for stability. Methods were defined and implemented for stability improvement. We have implemented data acquisition and computer manipulation of air flow and agitation speed for actual fermentors.

One can regard a simulation model as a pilot plant. It can be subjected to a variety of normal and abnormal operating conditions to provide a magnified view of the system response, compared to the more limited picture given by the static evaluations of initial and final states. Furthermore, the dynamic simulation approach can generally tackle problems which are analytically indeterminate. With the aid of dynamic simulation it is therefore possible to identify and rectify engineering problems during the design phase.

The dynamic characteristics of aerospace products play a decisive role in environmental adaptability of products, because aerospace products are subjected to vibration environment during launching process. This paper describes the design of a space truss and the load structure, in order to get the dynamic characteristics, finite element modal analysis and modal test is done on the structural model, through correlation analysis to determine the degree of conformity of the finite element model with the experimental model. It is determined that the finite element mode of truss and load structure is similar to the test mode, the finite element model is acceptable; The dynamic simulation of the structure is carried out by the qualified finite element model, and the dynamic simulation results are verified by the vibration test; The method for obtaining the dynamic characteristics of aerospace products and the way of dynamic simulation for launching process is of great reference value for the design of aerospace products.

Saccharomyces cerevisiae (baker's yeast) can exhibit sustained oscillations during the operation in a continuous bioreactor that adversely affects its stability and productivity. Because of heterogeneous nature of cell populations, the cell population balance equation (PBE) can be used to capture the dynamic behavior of such cultures. In this work, an unstructured-segregated model is used for dynamic simulation and controller synthesis. The mathematical model consists of a partial integro-differential equation describing the dynamics of the cell mass distribution (PBE) and an ordinary integro-differential equation accounting for substrate consumption. In order to solve the mathematical model, three methods, finite difference, orthogonal collocation on finite elements and Galerkin finite element are used to approximate the PBE model by a coupled set of nonlinear ordinary differential equations (ODEs). Then the resulted ODEs are solved by 4 th order Rung-Kutta method. The results indicated that the orthogonal collocation on finite element not only is able to predict the oscillating behavior of the cell culture but also needs much little time for calculations. Therefore this method is preferred in comparison with other methods. In the next step two controllers, a globally linearizing control (GLC) and a conventional proportional-integral (PI) controller are designed for controlling the total cell mass per unit volume, and performances of these controllers are compared through simulation. The results showed that although the PI controller has simpler structure, the GLC has better performance.

Dynamic process simulation differs from purely steady-state simulation in that the former requires the mechanical construction of process items be taken into account; the amount of mechanical detail being dependant upon the particular application. The reason for this is that dynamic mass, energy and momentum balances have to be continuously updated. These calculations are fundamental to dynamic process simulation and they require knowledge of volumes, metal mass, etc., to predict the proper dynamic behaviour of a particular plant. ...

Passive strategies for environmental sustainability and energy reduction in construction industry are becoming increasingly important in both the scientific community and the industrial world. Particularly, cool roofs showed acknowledged contribution in cooling energy saving and reducing urban overheating phenomenon, such as urban heat island. Additionally, high albedo strategy has shown also promising benefits from a global scale perspective, by counteracting global warming measured by means of CO2eq emissions' offset. In this view, the present research work combines experimental, numerical, and analysitical analysis approaches with the purpose of estimating the environmental and energy impact of the application of cool clay tiles over the roof of a residential area with single family buildings located in central Italy, where a continuous monitoring setup has been operating since 2010. The multiscale and multipurpose investigation demonstrated a global year-round CO2 emission compensation by more than 700 tons, of which the 15% is produced by the passive cooling contribution at building scale and the remaining part is produced by the climate mitigation technique. The work therefore showed that local energy saving strategies must be combined with larger scale models for performing an exhaustive environmental analysis.

Partial differential equations (PDEs) have been developed and used in science and engineering for more than 200 years, yet they remain a very active area of research because of both their role in mathematics and their application to virtually all areas of science and ...

Post-combustion CO2 capture methods are the most studied and anticipated to be commercialized in large scale in power plants. One of the major advantages of these technologies over others is that they can be more easily retrofitted with existing power plants. However, transient response of these processes can be slow compared to the power plant. Therefore, it is important to study transient performance of such systems coupled with power plants for determination of operability and control strategy. Dynamic process simulation can be a useful tool for the analysis. A number of articles in the literature discuss dynamic simulation of post-combustion capture processes, however, most have focused on the capture process itself and have not considered the complete power plant. In most of the analyses, flue gas has been considered as the only parameter from power plant that effects the capture processes and considered as a boundary condition for analyzing effects of different transients, such as part load operation.
Use of chemical absorption post-combustion processes reduces the overall efficiency of the power plant due to heat requirement in the reboiler of the regenerator, work requirement in pumps and in the CO2 compression train. However, several methods have been proposed in the literature for mitigation of such reduction and most of them require intense heat integration between power plant and post-combustion plants. This increases the complexity of the plant and thereby may affect operability and control strategy. Dynamic process simulation can be used to investigate how such integration affect the operation of power plant and the overall efficiency mitigation achievable. In addition, suitable modifications in equipment sizing and in cycle configuration can be predicted for achieving maximum overall efficiency of such plants.
It has been found that some commercial process simulators are good for simulating post-combustion processes due to availability of suitable model and property libraries while others are better for simulating thermal power plants. This means, a good option for simulating the integrated power and capture plant, could be to connect different process simulators. In this work, three different process simulators have been used to model the complete plant. Aspen HYSYS has been used for the post-combustion amine-based system and the open physical modeling language Modelica, using the Dymola environment, has been used for the steam cycle. GT PRO has been used to model the gas turbine. The Dymola model can be exported as a Functional Mock-up Unit (FMU) and can be accessed via a Functional Mock-up Interface (FMI) add-in in Microsoft EXCEL or via Matlab Simulink, which can serve as the platform for integrating the process models. This methodology has been implemented using a typical natural gas based combined cycle together with post-combustion capture process with an amine (MEA) based CO2 absorber and stripper. It has
been assumed that the heat duty at the reboiler of regenerator is supplied by steam extracted from the combined cycle. The focus of the transient analysis has been on plant load changes as in the part-load operation. Results of the simulation of the integrated model have been discussed.

This paper discusses the selection of a process simulator for dynamic modelling of post-combustion CO2 capture processes and validation of simulation results using pilot plant data available in literature. Based on a comparative study among three available simulators, Aspen HYSYS® has been selected mostly for the property package for amines. Dynamic simulations of stand-alone models of absorber, stripper and the complete plant have been performed and temperature profiles of absorber and stripper for all have been generated and compared. As the column models are equilibrium-based, the results have also been compared with simulation results of rate-based models obtained from literature.