Distributed Computer Control Systems in Industrial Automation

Dobrivojie Popovic, Vijay P. Bhatkar, VijayP. Bhatkar

• Publisher: Routledge
• Year: 2017
• eBook ISBN: 9781351454698
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

A reference guide for professionals or text for graduate and postgraduate students, this volume emphasizes practical designs and applications of distributed computer control systems. It demonstrates how to improve plant productivity, enhance product quality, and increase the safety, reliability, and

1
Introduction and Overview

The term industrial automation generally refers to the science and technology of process control and includes the control of chemical and petrochemical plants, oil refineries, iron and steel plants, power plants, cement mills, paper pulp and paper mills, pharmaceuticals, food and beverage industries, water and wastewater treatment plants, oil and gas fields, and the like. The industrial revolution witnessed the development of process industries when machines substituted for human physical power. The early production processes were natural scale-up versions of the traditional manual practices. They were usually designed as batch processes. Later, continuous processes were introduced which brought about some economic and technological benefits. Over the years, there has been an increasing trend towards larger and more complex plants to take advantage of the economies of scale and technological developments.

Contrary to what is generally understood, industrial automation is in no way a discovery of the recent past, but is rather as old as the industry itself. From the very beginning, the designer of an industrial production system has attempted to make it run as autonomous as possible, based on the available instrumental tools. Furthermore, there has been a continual development of industrial processes, which required the development of better instrumentation. Conversely, the advancements in control and instrumentation made possible the development of larger and more complex processes, bringing numerous new technological and economic benefits.

The accelerated development trend in the area of industrial automation over the last two decades is a direct consequence of technological innovations and theoretical advances in the area of systems engineering. Automation is presently viewed as a versatile tool for solving crucial problems of process and production control, plant supervision and management, as well as for solving the accompanying financial and organizational problems. Nowadays, full scale automation of typical industrial sectors like electric power generation and distribution, iron and steel, cement, paper, chemical, petrochemical and pharmaceutical plants, oil and gas field exploration, food and beverages processing, water and wastewater treatment, etc. is commonplace.

Likewise, the factory automation in the manufacturing sector has also benefited from automation trends, where high technology equipment and most advanced methods are merged to create what is known as flexible manufacturing, an automation level at which manufacturing cells on the factory floor are integrated. This has provided for a smooth adaptation to the changing manufacturing demands and for optimal use of manufacturing and transport facilities, and assured a high and uniform product quality, and optimizing material and energy flows, etc. This has led to the concept of computer integrated manufacturing (CIM). The CIM concept is aimed at enhancing monitoring and control of production, facilitating planning and design of products, lowering material and energy costs, just-in-time delivery, etc.

Besides in industrial and manufacturing sectors, the modern automation concepts have also found several applications in surface, air, and water transport, as well as in the space missions.

Several factors have contributed to the development of modern automation technology, particularly the following had a decisive impact:

advances in microprocessor, memory, and related VLSI technology developments in intelligent semiconductor sensors and fiber-optic sensors

implementations of programmable controllers

standardization of modular hardware and software for process control

advancements in computer technology

emergence of powerful interactive graphics for human interface standardization of data communication links and networks

adoption of a whole range of methods of modern control and system theory (model building, estimation theory, optimal, adaptive, self-tuning control, etc.) for modeling, simulation, and design of control systems

developments in artificial intelligence and methods of knowledge engineering

In this chapter, we shall first review the general aims of plant automation and the benefits that accrue from it. We shall then see how control and automation evolved from conventional instrumentation to computer-based control, leading to the present day distributed computer control. This will provide an insight into the individual techniques and methods that have already been available for solving plant automation problem, and whose appropriate integration has led, in a natural manner, to the concept of modern distributed computer control systems.

1.1 Aims of Plant Automation

There are three main flows determining an industrial process: material, energy, and information flow. The basic objective of plant automation is to identify the information flow, and to manipulate the material and energy flows of a given process in a desired, optimal way. This, as a rule, is a compromise between some economic and some quality factors and should lead to some benefits. The most common benefits of automation are:

production volume enhancement

production cost reduction

productivity increase

product quality improvement

optimal production flexibility

optimal production scheduling

optimal use of available facilities

inventory control

market competitivity

humanization of work place

environmental pollution control

production reliability

plant safety

The benefits to be realised are also the aims of the automation. In order to achieve them, some means and methods of plant automation should be used that replace actions and the capabilities of plant operators by machines. Nowadays, a combination of conventional and modern automation means, i.e., of process instrumentation and process control computers, as well as methods of systems engineering (model building, parameter estimation, system simulation, adaptive and optimal system control, etc.) are used for optimal solution of complex automation problems in the industry.

Production volume can be increased either by better use of available production capacities, for example by removing plant bottlenecks, or by production acceleration, i.e., by making the production line faster. When applying process control computers, production volume can also be increased by running the plant up to the highest allowable limits of some critical process variables, under continuous monitoring of their actual values as well as their trends.

Production costs can be reduced in different ways: by raw material saving (by better use of given raw materials or by the use of some new, low-price raw materials), by energy saving (by better energy management and by optimal use of internal energy resources), by saving the labour costs (by reducing the process operating staff or by replacing it by less skilled, e.g. inexpensive labor), etc. The last mentioned saving possibility especially holds for computer-based plant automation systems.

Productivity increase is basically a combination of production enhancement and production costs reduction, so that it does not need further comments.

Product quality can be enhanced by better supervision of the process, that enables to keep the run time conditions of the plant within some narrow tolerance limits. On the other hand, the use of mathematical process models essentially contribute to the expedient online re-trimming of relevant plant parameters when raw material properties or ambient conditions have changed. However, the product quality increase depends largely on measurement possibility of the quality itself, which could be rather time-consuming.

When the process control computer is applied in plant automation, the product quality is as a rule enhanced due to the fact that process supervision and optimal process control can better manage exceptional plant situations than the plant operator himself as the computer has a higher, model-based decision support with no “private” or “psychological” problems.

Production flexibility is the major requirement of a production plant working under repeatedly changing conditions. Typical examples are batch-process plants where frequent changeover among different products is generally necessary, especially in chemical or petrochemical industry. The role of computer here is to provide better production scheduling, optimal utilization of available facilities, and better inventory control.

The above mentioned automation aims are in direct response to severe international competition in marketplace driven by increasing quality requirements on the one hand and the rising energy and raw material prices on the other. This is especially the case for traditional industries such as chemical, petrochemical, steel, pulp and paper, etc., where the era of high rise growth is over. Without a successful computer-based plant automation, most industrial sectors can hardly survive in the marketplace.

In addition to economic aspects of production automation, there are other important aspects to be concerned like the increasingly emphasized human and environmental aspects needed. As regards the human aspects, the automation has to essentially contribute to the humanization of workplace, releasing the plant operators or the front-end labor from monotonous, dangerous, heavy burdening and molesting jobs, thus keeping them away from stress, radioactivity, poisons, dust, heat, noise, etc. Automation investments made for this purpose will, of course, not directly pay economically, but certainly contribute to the productivity increase due to improved work conditions. To the same category belong also the environmental aspects, which primarily include the air and water pollution regulations. Here, additional investments are mandatory due to greater social awareness, social obligations, and governmental regulations, noncompliance of which is punishable.

Plant automation should also help to optimally solve the production reliability and plant safety problem by exact control of optimal process conditions or, in batch processes, by exact execution of required successive steps and by vigilant process monitoring and timely prediction of possible hazardous plant situations. When a multicomputer system is used for plant automation a knowledge-based system e.g. an expert system can also be integrated for process diagnostics.

Once the need for automation is recognized, at least two decisions should be made:

what, in the first place, are the aims of automation

how they can be realized under given conditions

Both decisions are unfortunately not entirely unique. The automation aims frequently are difficult to define due to several conflicting requirements arising from complex energy, raw material, and product sale situation in the marketplace. Also, there can be several limitations within the plant itself. Even where the automation aims can be clearly defined, decisions have to be made concerning their implementations whi...

Table of contents

• Cover Page
• Title Page
• Copyright Page
• PREFACE
• 1 INTRODUCTION AND OVERVIEW
• 2 SYSTEM ARCHITECTURE
• 3 SYSTEM ELEMENTS
• 4 DATA COMMUNICATION LINKS
• 5 SOFTWARE
• 6 ALGORITHMS
• 7 RELIABILITY
• 8 APPLICATIONS
• 9 STATE-OF-THE-ART AND FUTURE TRENDS
• BIBLIOGRAPHY
• INDEX