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Due to the rapid growth in digital control•technology because of their • : great advantages,it now possible to consider implementing a digital prog• rammable controller for many industerial processes.In this paper some _ • software aspects of digital controllers for temperature control loop in • crude oil refineries have been discussed and a new method has been developed for rapid tuning of these controllers'parameters through the implementation of digital simulation technique:Different structures of the control loop have been investigated with main emphasis is given to casca• ded and feedforward/feedbackward loops.Cascaded'structures is shown to :reduce the effect of the time delays and yield better dynamic characteristics for the control loop.Preview of the future system disturbance inputs through the feedforward path is shown to be effective to improve the • performance of the overall control system.The results of the present inv• :estigation indicate that the proposed method is capable to detune the parameters of each controlling action either on-line or off-line with substantial improvement in the dynamic -performance -of the control loop.Illus: .trative examples as well as practical applications are also included. INTRODUCTION AND OBJECTIVES In crude oil refineries,the outlet temperature of the crude oil is the macontrol variable in oil heaters and the major disturbance results from the change of fuel gas pressure(fuel oil is used as a primary heating sou-: rce and gas is often used as a secondary heating source)supplied to the •burners.Temperature control is still the objective of many researchers in this field because the temperature as a manipulated variable,has a slow response speed.So an endless studies have been introduced to accelerate that response.At least a PID action is often essential for temperature :control systems to obtain acceptable performance.Cascade control and preview control are also recommended to improve their dynamic behavior. On the other hand,Zigler-Niohols11],Rovira methodNhave developed methods: to detune the controller of a single loop FB system for industerial process which can be presented adequately by second and first order models respectively. * Engineering Office,Cairo Oil Refining CO., Mostorod,Egypt. **,*** Mechanical Engineering Dept. Ain Shams University,Cairo,Egypt. I . ORA --40 FIRST A.M.E. coNreRLN:a 29-31 May 1984, Cairo

IMPROVING THE PERFORMANCE OF TEMPERATURE CONTROL LOOP IN A CRUDE OIL REFINERY THROUGH THE DIGITAL SIMULATION TECHNIQUE