Takeichiro Takamatsu

Theory and practice of optimal control in continuous fermentation process

In this paper a mathematical model of aminoacid fermentation using bacteria is built based on the kinetic study of experimental data of the pilot plant. This model makes it possible to formulate mathematically two optimal control problems in the actual process: (1) the problem of optimal start-up to a desired steady state, involving the optimization of the steady state, and (2) the problem of dynamical operation aiming at the maximum production of the amino-acid within a specified operation period. Both problems are solved by the maximum principle and Greens theorem. The numerical results suggest one of the most practical patterns of operation.

Comparison of simple population models in a baker's yeast fed-batch culture

Abstract In this paper, three models describing the population balance of microorganisms based on the assumption of symmetric cell division are discussed in terms of whether it is possible or not to use them to explain the dynamic behavior of the RBC. The ideal optimal control laws of the overall specific growth rate which maximizes the fermentative activity in the making of bread are obtained based on three models, It is a very interesting feature that the optimal pattern of μ becomes a bang-bang-type one based on both the Age and Mass models. Fed-batch culture according to the ideal optimal control coincides with a synchronously dividing culture. From the experimental study, the age model is shown to be most suitable for explaining the data. The optimal control policy is, for the most part, achieved experimentally by manipulating the glucose feed rate in the fed-batch culture and is shown to be valid.

Profile control of the specific growth rate in fed-batch experiments

SummaryThe aim of this paper is to apply a computer control scheme to a laboratory scale fermentor so that the specific growth rate in a bakers yeast fed-batch culture, which cannot be measured directly, will follow as accurately as possible the desired profile specified in advance. Using an extended Kalman filter and programmed controller/feedback compensator (PF) system proposed previously, profile control of the specific growth rate (μ) was achieved experimentally in a bakers yeast fed-batch culture. Also, bang-bang type profile control of μ minimized the proportion of budding cells, which have a strong correlation with the fermentative activity in bread-making.

Optimal scheduling and minimum storage tank capacities in a process system with parallel batch units

Abstract It is first presumed that a chemical process system is operated continuously as a whole, but some part of the system is composed of a parallel batch section and intermediate storage tanks. The problem of determining the scheduling of the parallel batch operations and the tank capacities is discussed here. For the case where a batch section is composed of parallel identical units, optimal scheduling is obtained analytically. Then the case in which each batch section has different operation times is dealt with. For this case, it is shown that the search domain necessary can be reduced to an extremely small size.

ADAPTIVE INTERNAL MODEL CONTROL AND ITS APPLICATION TO A BATCH POLYMERIZATION REACTOR

Abstract In this paper, the internal model control (IMC) and the adaptive parameter identification technique by the model refernece adaptive system (MRAS) are newly combined, and the combined one is called the adaptive IMC (AIMC). The proposed AIMC inherits the advantageous points from IMC, e.g., easiness to evaluate the robustness of the modelling error and to design a filter of an AIMC taking into account of its robustness. Moreover, parameters of the internal model are adjusted by MRAS in the proposed scheme. Then, the system can be controlled perfectly if the order of the system is appropriately assumed and if the system is a minimum phase one. One more advantageous point which is most significant one in practical application of the AIMC is; if the model is taken as 1st order system, the AIMC can be reduced to an auto-tuning proportional-plus-integral (PI) feedback controller. The proposed AIMC is applied to the control of a batch polymerization reactor. Temperature of the reactor is controlled so as to follow the desired temperature profile by the AIMC. The system equation of the batch reactor is time-dependent, and parameter adaptation will be required for getting a sophisticated controller. For this problem, the proposed AIMC can be utilized successfully and is shown to be superior compared with a traditional PI controller by the computer simulation.

Optimization of the activated sludge process—optimum volume ratio of aeration and sedimentation vessels

Abstract As the first step in optimizing the total activated sludge system, the optimum volume ratio of the aeration and sedimentation tanks has been considered. Two objective functions, the total volume and total capital cost, have been minimized. Both objective functions have given rise to approximately the same results. The optimum volume ratio of the aeration to sedimentation tanks and sludge recirculation ratio are in the range of 0.8∼1.2 and 0.3∼0.6, respectively depending on the degree of mixing in the aeration tank. They do not vary greatly from the design conditions adopted in current plants.

The nature and role of process systems engineering

Abstract In this article the author is going to attempt to establish Process Systems Engineering as an important core field in Chemical Engineering. Therefore, the definition of Process Systems Engineering, its necessity in the field of Chemical Engineering, its philosophical backbone and an opinion on the general structure of Process Systems Engineering are given first. later, the important roles which Process Systems Engineering have played in the past and will have to play in the future are mentioned with concrete examples of research done in the authors laboratory. The need for continuous research and development in this field is stressed in conclusion.

Model identification of wet-air oxidation process thermal decomposition

Abstract The thermal decomposition reaction by the wet-air oxidation of artificially grown activated sludge has been followed. A mathematical model of the thermal decomposition process is identified by the variables COD and weight of solid matter, soluble non-evaporative matter and soluble evaporative matter in the sludge. The parameters of this mathematical model are estimated from experimental data by using the steepest descent method.

Application of mixed-integer linear programming in multiterm expansion planning under multiobjectives

Abstract A procedure to expand plant capacities over a time horizon is presented under multiobjectives. A stepwise interactive approach has been proposed to formulate a problem that is small but complete enough to provide a best-compromise solution for decision-making. The approach relies on the relaxation of flexible constraints and the sensitivity analysis of linear programming. It yields the significant feature of identifying the expansion increments associated with specific objectives or with structural infeasibility. The resulting multiobjective mixed-integer linear programming problem was solved advantageously by an interactive goal programming algorithm. An illustrative example is provided to clarify the procedure and show its computational effectiveness.

Effects of flow conditions on the efficiency of a sedimentation vessel

Abstract Removal efficiency in a sedimentation vessel is greatly subject to the motion of fluids. Ordinary rectangular sedimentation vessels are large in scale and are affected by various environmental conditions. Hence, the features of flow in such vessels are too involved to be strictly analysed based on hydrodynamic equations of fluid-motion. Consequently, no theoretical approaches to predict the removal efficiency in a practical sedimentation vessel are yet available, in spite of much previous work on this problem. In general, the properties of flow are characterized by two types of motion of fluids i.e. the one is that of local mean velocity and the other is homogeneous turbulence. In this paper, these types of motion are represented separately by simple flow models, named “diffusion model” and “circulation model”, respectively. These simple models can give a reasonable interpretation of the complicated motion of fluids in a sedimentation vessel, and the removal efficiency is also derived in a simple form. Moreover, the calculated values obtained by these models are found to be in good agreement with the experimental data.