Use And Application Of Control Systems Via A Digital Computer
Authors: Strycker W.P. 
Published: December 2007

Strycker, W.P., International Business Machines Co., San Francisco, Calif.

This paper will be a review of IBM's experience in the area of Control Systems. Special attention will be given to installed and planned installations of the current 1710 Control System. The paper will cover the concepts of control systems with examples from actual experience. We will attempt to cover the philosophy of closed loop operations and open loop operations. Obvious examples will be oil field production control and refinery control.

Introduction

With the problem of meeting today's marketing conditions of surplus oil and a slower growing market, refiners and oil field operators are carefully evaluating their operating techniques to find new ways to improve efficiency and economy. The result is that more and more attention is being given to the use of electronic computers. The level of activity is up sharply in all areas. Installations that have several months to more than three years of operating experience have shown almost without exception that benefits accruing from computer control exceed the estimates made when the decisions were made to go to computer control. In general payouts have occurred within predicted times or better. IBM has participated in this shift to the use of digital computers for process control. We have projects installed or in the installation phase of refinery processes, pipeline control and oil field automation. The IBM 1710 process control computer system is used in many of these digital control projects. It is used to improve operations in processes such as catalytic cracking, catalytic reforming, distillation, pipeline and oil fields. We will limit our discussions in this paper to three processes that should be able to convey the philosophy of digital computing to the control function. We will discuss the experiences at Standard Oil Co. of California controlling the FCC unit at El Segundo, at American Oil Co.'s Ultraformer in Whiting, Inda., and the Continental Oil Co.'s oil field automation project in Hobbs, N. M.

Discussion

Digital computers with their ability to process the masses of data and measurements necessary to gauge conditions and evaluate changes in a complex system, are ideal controllers of production operations and processes. The control problem for the operator even with highly efficient automatic control systems is the task of integrating the controllers and supervising the process. He is generally confronted with a dynamic operation; 50 or more automatic controllers, each acting independently, and a great number of factors that must be equated and interrelated, not only those related to the chemistry of physics of the process but extrinsic economic ones as well.

From a practical standpoint the operator relies on his own judgment and experience to offset the disturbances such as feed composition changes, impurities and changes in atmospheric conditions. The time lags in detecting the disturbances, the operator's inability to assess analytically the effects of changes in controller set points and conservatism in making changes which may cause violation of limits, preclude maintaining optimal conditions. The meaning of optima depends upon management decision. It may mean maximum profit, maximum yield, minimum cost or highest quality. As shown in Fig. 1 the justification for a digital computer control system depends on its ability to compute the optimum point and maintain the system close to it. The frequency of computation must be at least as great as the frequency of disturbance. As illustrated by Fig. 2, this in turn determines the type of control system required.