Louisiana State University LSU Digital Commons LSU Historical Dissertations and Theses Graduate School 1981 Simulation and Evaluation of Distillation Control Systems Which Control Pressure With Reboiler Heat. William Bell Stewart Jr Louisiana State University and Agricultural & Mechanical College Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_disstheses Recommended Citation Stewart, William Bell Jr, "Simulation and Evaluation of Distillation Control Systems Which Control Pressure With Reboiler Heat." (1981). LSU Historical Dissertations and Theses. 3619. https://digitalcommons.lsu.edu/gradschool_disstheses/3619 This Dissertation is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Historical Dissertations and Theses by an authorized administrator of LSU Digital Commons. For more information, please contact [email protected]. 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University Microfilms International 300 N, ZEEB ROAD, ANN ARBOR, Ml 48106 18 BEDFORD ROW, LONDON WC1 R 4EJ. ENGLAND 8117649 Stewart, W illiam Bell, Jr. SIMULATION AND EVALUATION OF DISTILLATION CONTROL SYSTEMS WHICH CONTROL PRESSURE WITH REBOILER HEAT The Louisiana State University and Agricultural and Mechanical PH.D. Col1981 University Microfilms International300 N. Zeeb Road, Ann Arbor, MI 48106 "''Simulation and Evaluation of Distillation Control Systems Which Control Pressure With Reboiler Heat\ A Dissertation Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Doctor of Philosophy in The Department of Chemical Engineering by William Bell Stewart. Jr. B.S., Chem. Engr., Louisiana State University, 1975 M.S., Chem. Engr., Louisiana State University, 1977 May 1981 ACKNOWLEDGEMENT The author wishes to express his appreciation to his major professor, Dr. Adrain E. Johnson, Jr. for his advice and encouragement given during the course of this work. His contribution cannot be underestimated. He also wishes to thank the other members of his committee, Dr. Armando B. Corripio, Dr. Frank R. Groves, Jr., Dr. Douglas P. Harrison, and Dr. Thomas G. Ray for their cooperation in serving on the committee. Special thanks go to Dr. Corripio for his helpful suggestions concerning modeling and automatic control. Thanks also go to Dr. Philip A. Bryant, who furnished his excellent steady- state distillation model. He wishes to thank the entire faculty and staff of the Chemical Engineering Department along with Dr. Ray of the Industrial Department for the fine instruction they provided along the way. The financial support of Shell Oil Company and the Chemical Engineering Department was greatly appreciated. Thanks also go the Miss Hazel LaCoste for more than the author can list here. A very special thanks is in order for the author's wife Bess, who not only typed the many drafts of this manuscript, but lent support and love all the way, and his parents for their manifold love, patience, and understanding. TABLE OF CONTENTS Page ACKNOWLEDGEMENT ii LIST OF TABLES iii LIST OF FIGURES V ABSTRACT xi INTRODUCTION xii CHAPTER 1 Literature Review 1 Modeling 1 Control 4 2 Dynamic Distillation Model 7 Introduction 7 Algebraic Variables 9 Derivatives of Integrated Variables 19 Manipulated Variables 31 Arrangement of Computations 31 3 Numerical Integration Procedure 37 4 Automatic Control System 50 Introduction 50 Pressure Control 58 Composition Control of One Product 62 Maintenance of Overall Material Balance 63 Composition Control of the Other Product 64 Page Chapter 5 Results 65 Introduction 65 Development of Model 65 Dynamic Studies 72 Control Studies 103 Summary of Results 152 6 Conclusions 154 NOMENCLATURE 160 REFERENCES 164 APPENDICES A Derivations of Equations in Dynamic Model 167 B Truncation Error Analysis for the JSME Algorithm 174 VITA 178 iv LIST OF TABLES TABLES PAGE 2-1 Sequencing of Computations in 36 Functional Evaluation Model 3-1 Comparison of Simple Euler# Improved 48 Euler, and JSME Algorithm Integrating Sine (x) with Constant Step Size 3-2 Comparison of Improved Euler and JSME 49 Algorithms Integrating Sine (x) with Variable Step Size 5-1 Physical Data Used in Dynamic Studies 73 v LIST OF FIGURES Typical Column Tray 11 Flooded Condenser 17 Conventional Column Control of 32 Distillate Product Quality Typical Material Balance Control of 55 Distillate Product Quality Modified Material Balance Control of 57 Distillate Product Quality Open-Loop Pressure Response to a Step 79 Increase in Steam Valve Position Open-Loop Pressure Response to a Step 83 Decrease in Steam Valve Position Open-Loop Pressure Response to a Step 85 Increase in Cooling Water Temperature Open-Loop Pressure Response to a Step 87 Increase in Feed Temperature Open-Loop Pressure Response to a Step 90 Change in Feed Composition Open-Loop Top Tray Temperature Response 91 to a Step Change in Feed Composition Open-Loop Condensing Temperature 92 Response to a Step Change in Feed Composition vi FIGURE PAGE 5-8 Open-Loop Pressure Response to a Step 94 Increase in Feed Rate 5-9 Open-Loop Top Tray Temperature Response 95 to a Step Increase in Feed Rate 5-10 Open-Loop Condensing Temperature Response 96 to a Step Increase in Feed Rate 5-11 Open-Loop Pressure Response to a Step 99 Increase in Distillate Product Rate 5-12 Open-Loop Top Tray Temperature Response 100 to a Step Increase in Distillate Product Rate 5-13 Open-Loop Condensing Temperature Response 101 to a Step Increase in Distillate Product Rate 5-14 Closed-Loop Pressure Response to a Step 105 Change in Cooling Water Temperature With Excessive Pressure Control Gain 5-15 Open-Loop Temperature Response to a Step 106 Change in Cooling Water Temperature With Excessive Pressure Controller Gain 5-16 Response of Pressure to a Step Change in 109 Pressure Set Point 5-17 Response of Manipulated Steam Flow to a 110 Step Change in Pressure Set Point vii FIGURE PAGE 5-18 Closed-Loop Pressure Response to a Step 113 Increase in Feed Rate With Pressure Control Only 5-19 Response of Manipulated steam Flow to a 114 Step Increase in Feed Rate with Pressure Control Only 5-20 Open-Loop Temperature Response to a Step 115 Increase in Feed Rate with Pressure Control Only 5-21 Temperature Response During Open-Loop 117 Tuning With Excessive Pressure Controller Gain 5-22 Closed-Loop Pressure Response During Open 118 Loop Tuning With Excessive Pressure Controller Gain 5-23 Response of Manipulated Steam Flow During 119 Open-Loop Tuning With Excessive Pressure Controller Gain 5-24 Temperature Response During Closed-Loop 123 Tuning With Excessive Pressure Controller Gain 5-25 Response of Manipulated Distillate 124 Product Rate During Open-Loop Tuning With Excessive Pressure Controller Gain viii FIGURE PAGE 5-26 Closed-Loop Pressure Response During 125 Closed-Loop Tuning With Excessive Pressure Controller Gain 5-27 Response of Manipulated Steam Flow 126 During Closed-Loop Tuning With Excessive Pressure Controller Gain 5-28 Temperature Response During Open-Loop 129 Tuning With Moderate Pressure Controller Gain 5-29 Closed-Loop Pressure Response During 130 Open-Loop Tuning With Moderate Pressure Controller Gain 5-30 Temperature Response During Closed-Loop 132 Tuning With Temperature Controller Gain of 0.010 5-31 Response of Manipulated Distillate 133 Product Rate During Open-Loop Tuning With Temperature Controller Gain of 0.010 5-32 Closed-Loop Pressure Response During 134 Closed-Loop Tuning With Temperature Controller Gain of 0.010 5-33 Response of Manipulated Steam Flow 135 During Closed-Loop Tuning With Temperature Controller Gain of 0.010 ix FIGURE PAGE 5-34 Temperature