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Chemical process engineering dreamed and realized
Computers
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Chemical Engineering Vol. 7, No. 4, pp. 201-202, 1983 Britain.
Printed inGreat
0
w&?-1354/83 $3.00 + .o( 1983 Pergamon Press Ltd
CHEMICAL PROCESS ENGINEERING - DREAMED AND REALIZED -
Sakae Yagi Professor Emertius University of Tokyo
computerization. Though the design procedure of unit operations had been well established, process design was a kind of patchwork combining the design calculations of various kinds of unit operations. We wanted to establish a systematic method of simulating and optimizing, even in recycling processes.
It is a great honour that I was given this opportunity to make the opening address at such an important meeting on process system engineering. In 1963 I introduced a Process Systems Engineering chair at the University of Tokyo and had been in charge of that chair until 1965. After joining Chiyoda Chemical Engineering & Construction Company in 1965. I encouraged the engineers to apply the process systems engineering approach to solve industrial problems. Though I have kept a special interest in and concern for the development of process engineering, I am not qualified enough to give an overview of all the contents of this symposium, nor to give an orientation in a few words. Rather I would like to present my personal experiences and philosophy on process systems engineering.
The first difficulty encountered was due to the nonlinearity of process systems. It prevented us from constructing a systematic network theory for process systems as is present in electrical systems. An additional difficulty was associated with the economical optimization. We considered the application of dynamic programming to a recycling network system. We analyzed the basic concept of Dynamic Programming and.found that it was essentially a hierarchical method consisting of two levels. In general, it can be said that the upper level is concerned with specificationof performance of each component subsystem, and the lower level deals with performing the optimal design of each component subsystem. The sophistication pertinent to DP arises from the combination of these two levels. For a recycling system, these two levels must be separated. The difficult task was to assign feasible inputs and outputs to each component subsystem. We found this task could be solved well by introducing a performance matrix or a linear model of unit operations. It was not a model for a specific unit but an ensemble of units. So it was a hypothetical model. Interface specification could be achieved by simulation of this hypothetical model. Moreover, because of the linearity of the model, the process calculation of recycling systems became very easy. We tried a graphical method for solving mass balancing of recycling processes extensively.
It was more than forty years ago when I first realized the need for a discipline like process engineering. It was when I was at MIT in 1937 and attending the lecture of Professor Warren K. Lewis. His lecture was on the stoichiometry. He made me realize the importance of treating a process as a whole and making a quantitative analysis. I totally agreed with his idea stressing the importance of stoichiometry, though I felt that the method itself could be greatly improved. I felt the need for a network theory for process systems and felt that the theory should be the core of chemical engineering disciplines just like the circuit theory is the core of electrical engineering. Though I realized the necessity of process engineering at that time, I had to wait more than twenty years before I could really start research on process engineering. I thought chemical reaction engineering had to be fully developed before any fruitful results from process engineering could be expected.
This concept made the simulation of recycling processes much easier in the case of optimal design than in the simulation of existing processes because in the former case we could circumvent nonlinearity arising from various constraints imposed on existing processes. This might be a
In 1963, I invited Dr. Nishimura to the assistant professor's chair and we started to work together on process engineering. The first target was to systematize the concept and the procedure of process design so as to meet the trend toward 201
202 typical example of a general principle that may have a simpler solution when it is generalized and solved-mathematically. After we had succeeded in optimization of recycling processes, we at once proceeded to the problem of a process synthesis, which was my ultimate goal in process engineering. In circuit theory or network theory in electrical engineering, synthesis is possible for some simple cases. It was somewhat of a revelation to learn that the scientific method could automatically produce a wanted system. Previously only human ingenuity had been considered to have such ability.
S. YAGI
REFERENCES General (1) YAGI,S. and INSHIMURA, H.(1969). Chemical Process Engineering (Text Book pp.,360 in Japanese) Maruzen Tokyo. YAGI, S. and NISHIMURA, H.(1976). Development of Chemical Process Engineeringby Linear Model Method Chemical Engineering in a Changing World, Proceeding of the Plenary Sessions of the First World Congress on Chemical Engineering, Amsterdam 495-510
Synthesis should be one of the ultimate goals of engineering. We succeeded in two cases: the synthesis of the heat exchanger system and the optimum synthesis of the distillation system. It is commonly agreed that the difficulty in synthesis lies in the fact that the selection of the optimum pattern on structure is possible only after the simulation and optimization of each pattern. We considered a hierarchical approach to this problem also. We divided the problem into two parts. The task of finding the optimum pattern was to be separated from the task of finding the optimum set of parameters. To make this possible, some approximationbecame necessary--approximationin model performance or in objective function. For example, economic index was to be replaced by energy consumption for optimization. Thus the flow pattern obtained may not have been the optimum for the actual problem, but it was a good approximation of it. We would like to call it an ideal system. It reminds us of the concept of ideal gas in physics. It gives a gocd approximation of a real system as well as good insight in to it.
Linear Model (3) YAGI, S. and NISHIMURA, H.(1965). Optimization of Chemical Processes by Linear Model Method. 2nd CHISA Congress. (4) NISHIMURA. H. HIRAIZUMI. Y. and YAGI, S.(i967), (1968): Optimization of Process Network by Linear Model Method Kagaju Kogaku g, 183., Int. Chem. a. S, 186.
It is with great satisfaction that the network theory for chemical processes, which I dreamed of forty years ago, has clearly become established today. It has already surpassed the network theory in electrical engineering in several aspects. It deals with not only linear but nonlinear systems; it covers not only simulation but also optimization of the system; and it serves not only for analysis but also for synthesis.
Application of Linear Model in Industry (At Chiyoda Chemical Engineering h Construction Comuanv) (8) KOMATSU, S.-(lb&) Application of Linearization to Design of a HydrodealkylationPlant Ind. Eng. Chem. 60, (2), 36 (9) KOMATSU, S. and UMEDA, T. (1973) Process Systems Design (In Japanese) Kogyo Chosa Dai, Tokyo.
This success might be due to various factors. Among them, the development of computing facilittieswould come first. However, the importance of approach or method should not be overlooked. I would like to emphasize the importance of the hierarchical approach and successive approximation in the treatment of a complicated system. Good approximationwill always be the basis of good engineering work and it is important to note that such approximation is possible only on the basis of sound knowledge and an understanding of the object process itself.
Synthesis of Distillation System (5) NISHIMURA, H. and HIRAIZUMI, Y.(1969), (1970). Optimal System-Pattern for MulticomponentDistillation Systems Kagaku Kogaku 2, 459. Int. Chem. 3. 11, 188. Synthesis of Heat Exchanger System (6) NISHIMURA, H. and HIRAIZUMI, Y.(1970). Optimal Synthesis of Heat Exchanger System Kagaku Kogaku 36, 1099. (7) NISHIMURA. H.(1980) A Theory for the Optimal Synthesis of Heat-ExchangerSystem J. Opt. Theory and Appl. 30, 423.
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Chemical Engineering Vol. 7, No. 4, pp. 201-202, 1983 Britain.
Printed inGreat
0
w&?-1354/83 $3.00 + .o( 1983 Pergamon Press Ltd
CHEMICAL PROCESS ENGINEERING - DREAMED AND REALIZED -
Sakae Yagi Professor Emertius University of Tokyo
computerization. Though the design procedure of unit operations had been well established, process design was a kind of patchwork combining the design calculations of various kinds of unit operations. We wanted to establish a systematic method of simulating and optimizing, even in recycling processes.
It is a great honour that I was given this opportunity to make the opening address at such an important meeting on process system engineering. In 1963 I introduced a Process Systems Engineering chair at the University of Tokyo and had been in charge of that chair until 1965. After joining Chiyoda Chemical Engineering & Construction Company in 1965. I encouraged the engineers to apply the process systems engineering approach to solve industrial problems. Though I have kept a special interest in and concern for the development of process engineering, I am not qualified enough to give an overview of all the contents of this symposium, nor to give an orientation in a few words. Rather I would like to present my personal experiences and philosophy on process systems engineering.
The first difficulty encountered was due to the nonlinearity of process systems. It prevented us from constructing a systematic network theory for process systems as is present in electrical systems. An additional difficulty was associated with the economical optimization. We considered the application of dynamic programming to a recycling network system. We analyzed the basic concept of Dynamic Programming and.found that it was essentially a hierarchical method consisting of two levels. In general, it can be said that the upper level is concerned with specificationof performance of each component subsystem, and the lower level deals with performing the optimal design of each component subsystem. The sophistication pertinent to DP arises from the combination of these two levels. For a recycling system, these two levels must be separated. The difficult task was to assign feasible inputs and outputs to each component subsystem. We found this task could be solved well by introducing a performance matrix or a linear model of unit operations. It was not a model for a specific unit but an ensemble of units. So it was a hypothetical model. Interface specification could be achieved by simulation of this hypothetical model. Moreover, because of the linearity of the model, the process calculation of recycling systems became very easy. We tried a graphical method for solving mass balancing of recycling processes extensively.
It was more than forty years ago when I first realized the need for a discipline like process engineering. It was when I was at MIT in 1937 and attending the lecture of Professor Warren K. Lewis. His lecture was on the stoichiometry. He made me realize the importance of treating a process as a whole and making a quantitative analysis. I totally agreed with his idea stressing the importance of stoichiometry, though I felt that the method itself could be greatly improved. I felt the need for a network theory for process systems and felt that the theory should be the core of chemical engineering disciplines just like the circuit theory is the core of electrical engineering. Though I realized the necessity of process engineering at that time, I had to wait more than twenty years before I could really start research on process engineering. I thought chemical reaction engineering had to be fully developed before any fruitful results from process engineering could be expected.
This concept made the simulation of recycling processes much easier in the case of optimal design than in the simulation of existing processes because in the former case we could circumvent nonlinearity arising from various constraints imposed on existing processes. This might be a
In 1963, I invited Dr. Nishimura to the assistant professor's chair and we started to work together on process engineering. The first target was to systematize the concept and the procedure of process design so as to meet the trend toward 201
202 typical example of a general principle that may have a simpler solution when it is generalized and solved-mathematically. After we had succeeded in optimization of recycling processes, we at once proceeded to the problem of a process synthesis, which was my ultimate goal in process engineering. In circuit theory or network theory in electrical engineering, synthesis is possible for some simple cases. It was somewhat of a revelation to learn that the scientific method could automatically produce a wanted system. Previously only human ingenuity had been considered to have such ability.
S. YAGI
REFERENCES General (1) YAGI,S. and INSHIMURA, H.(1969). Chemical Process Engineering (Text Book pp.,360 in Japanese) Maruzen Tokyo. YAGI, S. and NISHIMURA, H.(1976). Development of Chemical Process Engineeringby Linear Model Method Chemical Engineering in a Changing World, Proceeding of the Plenary Sessions of the First World Congress on Chemical Engineering, Amsterdam 495-510
Synthesis should be one of the ultimate goals of engineering. We succeeded in two cases: the synthesis of the heat exchanger system and the optimum synthesis of the distillation system. It is commonly agreed that the difficulty in synthesis lies in the fact that the selection of the optimum pattern on structure is possible only after the simulation and optimization of each pattern. We considered a hierarchical approach to this problem also. We divided the problem into two parts. The task of finding the optimum pattern was to be separated from the task of finding the optimum set of parameters. To make this possible, some approximationbecame necessary--approximationin model performance or in objective function. For example, economic index was to be replaced by energy consumption for optimization. Thus the flow pattern obtained may not have been the optimum for the actual problem, but it was a good approximation of it. We would like to call it an ideal system. It reminds us of the concept of ideal gas in physics. It gives a gocd approximation of a real system as well as good insight in to it.
Linear Model (3) YAGI, S. and NISHIMURA, H.(1965). Optimization of Chemical Processes by Linear Model Method. 2nd CHISA Congress. (4) NISHIMURA. H. HIRAIZUMI. Y. and YAGI, S.(i967), (1968): Optimization of Process Network by Linear Model Method Kagaju Kogaku g, 183., Int. Chem. a. S, 186.
It is with great satisfaction that the network theory for chemical processes, which I dreamed of forty years ago, has clearly become established today. It has already surpassed the network theory in electrical engineering in several aspects. It deals with not only linear but nonlinear systems; it covers not only simulation but also optimization of the system; and it serves not only for analysis but also for synthesis.
Application of Linear Model in Industry (At Chiyoda Chemical Engineering h Construction Comuanv) (8) KOMATSU, S.-(lb&) Application of Linearization to Design of a HydrodealkylationPlant Ind. Eng. Chem. 60, (2), 36 (9) KOMATSU, S. and UMEDA, T. (1973) Process Systems Design (In Japanese) Kogyo Chosa Dai, Tokyo.
This success might be due to various factors. Among them, the development of computing facilittieswould come first. However, the importance of approach or method should not be overlooked. I would like to emphasize the importance of the hierarchical approach and successive approximation in the treatment of a complicated system. Good approximationwill always be the basis of good engineering work and it is important to note that such approximation is possible only on the basis of sound knowledge and an understanding of the object process itself.
Synthesis of Distillation System (5) NISHIMURA, H. and HIRAIZUMI, Y.(1969), (1970). Optimal System-Pattern for MulticomponentDistillation Systems Kagaku Kogaku 2, 459. Int. Chem. 3. 11, 188. Synthesis of Heat Exchanger System (6) NISHIMURA, H. and HIRAIZUMI, Y.(1970). Optimal Synthesis of Heat Exchanger System Kagaku Kogaku 36, 1099. (7) NISHIMURA. H.(1980) A Theory for the Optimal Synthesis of Heat-ExchangerSystem J. Opt. Theory and Appl. 30, 423.