Chemical and Biomolecular Engineering

Official blog of the Lehigh University Chemical Engineers

Controls vs. Process Design

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I like how the concepts and methods that we learn in process control class this semester is going to be directly applied to our process design project next semester. This reason that controller are not used this semester in the Ethylene Oxide Production project is that we’re currently only modelling the steady state aspect of the EO plant. Using the Aspen+ software, the steady state behavior of the EO plant will be modeled, and then next semester, using Aspen+ Dynamics, the dynamic portion of the project will be modeled and it will require implementation of system controllers to regulate the plant.

Currently in my controls class, some of the homework problem asks us to find places in our plant where certain types of controllers can be applied. For example, in the most recent homework, the problems asks us to indicate one place in our design project where Override Control can be used. After carefully assessing my project and using guidance from the internet, I decided that one way a Override Control can be used is to protect the equipment from damaging. The way override controllers work is that it reads two input signals and give one output action, all based on which input is more important at a certain scenario. For instance, it can be used to protect a compressor from damagingCapture.

In this figure, TRC checks the operating temperature against the set-point temperature, and PRC checks pressure against the the set-point pressure against gas is being compressed. The input to the controller would be the measured temperature and measured pressure. It is previously set that if measured  temperature or the measured pressured reaches certain maximum, the valve will close to prevent damages to the compressor. So the controller takes into account whichever input signal is more important (reaches maximum first), and takes the action based upon that.

It’s good to think about what we’re currently running in controls and relate to design next semester. It keeps things more interesting.

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Author: Jerry Jin

Hello, My name is Jerry Jin. I'm a senior at Lehigh University pursuing a degree in Chemical Engineering. I'm from Allentown, PA, but I was born in Shanghai, China. I moved here when I was fourteen years old. I'm currently the secretary for Southeast Asia at Lehigh Club, and treasurer for SASE. I'm also on the Lehigh Ultimate Frisbee Team and I enjoy being spontaneous.

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