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Title: Computer control of two continuous stirred-tank reactors in series
Author: Egbewatt, Nkongho E.
Awarding Body: Aston University
Current Institution: Aston University
Date of Award: 1984
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This study is focused on reacting systems in a train of reactors and the different digital control strategies that can be developed to eliminate the effect of disturbances entering the system. A Honeywell 316 minicomputer is interfaced via HADIOS to a pilot plant containing two C. S. T. R. s connected in series and a partial simulation of a first order irreversible exothermic chemical reaction taking place in them is carried out. This control system offers only a single communication channel from the user to the output multiplexers and since all the control functions are performed by software of me digital system, the frequency with which the control functions are updated is of utmost importance. The reaction heat is provided by heaters placed in the reactors which are triggered on receipt of appropriate signals from the corrputer. A judicious use of solenoids and multiplexers allows the regulation of two pneumatic process control valves using one air supply line and the scanning of eight thermocouples. Two coils, one in each reactor, provide the conduit for the independently controlled cooling water whose flow rate is used as the manipulative variable for implementing the different control schemes and a surface for heat exchange with reactors. Using differential equations to represent the plant, a total simulation of the system, is achieved in a FORTRAN programme that runs interactively on the HAMS 800 computer and the experimental runs provide data suitable for verification of the theoretical model. Based on the large axial temperature gradient in the cooling coils, the model assumes a chain of cells each of uniform temperature but necessarily different from the rest and twenty five of these are used for the total simulation. All irnplemental control functions are performed by the software of the control computer in the direct digital mode. Unstable systems are stabilised using controllers and the relative stabilities of open and closed loop stable systems are established by constructing Lyapunov's function. The control strategies adopted vary from those based on absolute error of control variables, through absolute values of measured disturbances to others derived from. system equations and plant parameters. The first group consists of feedback controllers centered on the first reactor and a combination of feedback and feedforward controllers in the second reactor. Invariance control of reactor and coil temperatures is attainable on both reactors by using an iterative method that updates the system parameters and calculates flow rates from the system equations. Decoupling control of the model is made possible by first establishing an axial temperature profile in the cooling coil and using piecewise decoupiing to select an appropriate response constant for the system that leaves it within the stated constraints.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Chemical Engineering Automatic control Control theory