Control and automation in chemical engineering : problems (original) (raw)

Laboratory Exercise No. 1 Basic Concepts of Process Dynamics and Control 1

Objective: The activity aims to understand the basic concepts of process dynamics and control. 2. Intended Learning Outcomes (ILOs): The students shall be able to: 1. Determine the input and output in the different chemical processes. 2. Provide instrumentation requirements for a chemical process. 3. Identify the different process variables in a chemical process. 4. Specifiy the controlled variables (CVs), manipulated variables (MVs) and disturbance variables (DVs) from the different chemical processes. 3. Discussion: Most chemical processing plants were run essentially manually prior to the 1940s. Only the most elementary types of controllers were used. Many operators were needed to keep watch on the many variables in the plant. Large tanks were employed to act as buffers or surge capacities between various units in the plant. These tanks, although sometimes quite expensive, served the function of filtering out some of the dynamic disturbances by isolating one part of the process from upsets occurring in another part. With increasing labor and equipment costs and with the development of more severe, higher-capacity, higher-performance equipment and processes in the 1940s and early 195Os, it became uneconomical and often impossible to run plants without automatic control devices. At this stage feedback controllers were added to the plants with little real consideration of or appreciation for the dynamics of the process itself. Rule-of-thumb guides and experience were the only design techniques. In the 1960s chemical engineers began to apply dynamic analysis and control theory to chemical engineering processes. Most of the techniques were adapted from the work in the aerospace and electrical engineering fields. In addition to designing better control systems, processes and plants were developed or modified so that they were easier to control. The concept of examining the many parts of a complex plant together as a single unit, with all the interactions included, and devising ways to control the entire plant is called systems engineering. The current popular " buzz " words artificial intelligence and expert systems are being applied to these types of studies. The rapid rise in energy prices in the 1970s provided additional needs for effective control systems. The design and redesign of many plants to reduce energy consumption resulted in more complex, integrated plants that were much more interacting. So the challenges to the process control engineer have continued to grow over the years. This makes the study of dynamics and control even more vital in the chemical engineering curriculum than it was 30 years ago.

Chemical process control education and practice

IEEE Control Systems Magazine, 2001

C hemical process control textbooks and courses differ significantly from their electrical or mechanical-oriented brethren. It is our experience that colleagues in electrical engineering (EE) and mechanical engineering (ME) assume that we teach the same theory in our courses and merely have different application examples. The primary goals of this article are to i) emphasize the distinctly challenging characteristics of chemical processes, ii) present a typical process control curriculum, and iii) discuss how chemical process control courses can be revised to better meet the needs of a typical B.S.-level chemical engineer.

Successful industrial application of advanced control theory to a chemical process

This paper reports the experiences and results of a project aimed at designing an automatic control scheme for titanium dioxide rotary kilns. The process was studied by way of computer simulations, both steadystate and dynamic, from which a low order model was derived by matching the input-output frequency responses. Use of LQG theory then led to the conclusion that the kiln can be considered as a single-input, singleoutput process. Plant trials and simulation studies finally led to the adoption of a control scheme incorporating a self-tuning regulator in a feedback loop around a kiln controlled by a discrete regulator designed on minimum-variance principles. This scheme has been in use for three years and resulted in great improvement in control performance. Long term industrial results are presented. Practical considerations concerning implementation and acceptance by plant personnel are given.

Process control: modeling, design, and simulation

2003

There are a variety of courses in a standard chemical engineering curriculum, ranging from the introductory material and energy balances course, and culminating with the capstone process design course. The focus of virtually all of these courses is on steady-state behavior; the rare exceptions include the analysis of batch reactors and batch distillation in the reaction engineering and equilibrium stage operations courses, respectively. A concern of a practicing process engineer, on the otherhand, is how to best operate a process plant where everything seems to be changing. The process dynamics and control course is where students must gain an appreciation for the dynamic nature of chemical processes, and develop strategies to operate these processes.