00000 Roger D. Kamm

00000 Roger D. Kamm - Spring 2006 Process Dynamics,...

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Spring 2006 Process Dynamics, Operations, and Control 10.450 Lesson 1: Processes and Systems 1.0 context and direction Process control is an application area of chemical engineering - an identifiable specialty for the ChE. It combines chemical process knowledge (how physics, chemistry, and biology work in operating equipment) and an understanding of dynamic systems, a topic important to many fields of engineering. Thus study of process control allows chemical engineers to span their own field, as well as form a useful acquaintance with allied fields. Practitioners of process control find their skills useful in design, operation, and troubleshooting - major categories of chemical engineering practice. Process control, like any coherent topic, is an integrated body of knowledge - it hangs together on a multidimensional framework, and practitioners draw from many parts of the framework in doing their work. Yet in learning, we must receive information in sequence - following a path through multidimensional space. It is like entering a large building with unlighted rooms, holding a dim flashlight and clutching a vague map that omits some of the stairways and passages. How best to learn one’s way around? In these lessons we will attempt to move through a significant portion of the structure - say, half a textbook - in about two weeks. Then we will repeat the journey several times, each time inspecting the rooms more thoroughly. By this means we hope to gain, from the start, a sense of doing an entire process control job, as well as approach each new topic in the context of a familiar path. 1.1 the job we will do, over and over We encounter a process, learn how it behaves, specify how we wish to control it, choose appropriate equipment, and then explore the behavior under control to see if we have improved things. 1.2 introducing a simple process A large tank must be filled with liquid from a supply line. One operator stands at ground level to operate the feed valve. Another stands on the tank, gauging its level with a dipstick. When the tank is near full, the stick operator will instruct the other to start closing the valve. Overfilling can cause spills, but underfilling will cause later process problems. revised 2006 Jan 30 1
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Spring 2006 Process Dynamics, Operations, and Control 10.450 Lesson 1: Processes and Systems To learn how the process works, we write an overall material balance on the tank. i F V dt d ρ = ρ (1.2-1) The tank volume V can be expressed in terms of the liquid level h. The inlet volumetric flow rate F i may vary with time due to supply pressure fluctuations and valve manipulations by the operator. The liquid density depends on the temperature, but will usually not vary significantly with time during the course of filling. Thus (1.2-1) becomes ) t ( F dt dh A i = (1.2-2) We integrate (1.2-2) to find the liquid level as a function of time.
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This note was uploaded on 11/27/2011 for the course CHEMICAL E 20.410j taught by Professor Rogerd.kamm during the Spring '03 term at MIT.

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00000 Roger D. Kamm - Spring 2006 Process Dynamics,...

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