1st Edition

Distillation Control, Optimization, and Tuning Fundamentals and Strategies

By Lanny Robbins Copyright 2011
    144 Pages 25 B/W Illustrations
    by CRC Press

    144 Pages 25 B/W Illustrations
    by CRC Press

    Emphasis on improved quality and performance of distilled products and the demand for reduced operating costs place a heavy burden on both the personnel responsible for profitability and the manufacturing department charged with operating the processing equipment. There have been dramatic improvements in the computer software and hardware used to simulate and model the distillation process and potential response to experimentation, but mastering the art of distillation process and control still requires solid understanding of a large body of information.

    With a focus on achieving product purity at low cost, Distillation Control, Optimization, and Tuning: Fundamentals and Strategies highlights core concepts. These include process variables for continuous binary distillation columns and the four basic control strategies, the distillate and bottoms product quality performance objectives, and the tuning of process control loops. Without dwelling on complex mathematical descriptions, the book presents the fundamentals of process control of a distillation column as a separation and purification unit operation. It covers the concepts and functional criteria that are critical to successful implementation of process control, as well as measurement and improvement of product quality performance. It describes how process control loops for distillation columns can be tuned for stable operation, with a balance between minimum variability from setpoint changes and excellent response to load disturbances.

    Designed for students, engineers, technicians, and plant operators alike, this book emphasizes the prevailing need to strike a balance between the details of hypotheses and good engineering judgment. The author outlines learning objectives at the beginning of each chapter and includes chapter-end summaries, exercises, and references to help readers acquire essential knowledge and understanding. The result is a resource that will inform future decisions for the design, operation, and troubleshooting of distillation process control systems.

    Unit 1: Introduction and Overview
    Course Coverage
    Audience and Prerequisites
    Study Materials
    Organization and Sequence
    Course Objectives
    Course Length

    Unit 2: Distillation Control Variables
    Distillation Column Inlet Streams
    Distillation System Outlet Streams
    Controlled Variables

    Unit 3: Separation Power
    Relative Volatility in One Theoretical Stage
    Separation Power with Multiple Stages
    Separation Power and Energy Consumption

    Unit 4: Distillate/Feed Material Balance Split
    Material Balances
    Temperature Gradient per Theoretical Stage
    Temperature Change from D/F Shift

    Unit 5: Distillation Control Strategies
    Column Pressure Control
    Temperature Control with Distillate Flow Rate
    Temperature Control with Reflux Flow Rate
    Temperature Control with Boilup(Steam Rate)
    Temperature Control with Bottoms Flow Rate
    Side Draw Flow Rate
    Distillate Vapor Flow Rate

    Unit 6: Constraints
    Mechanical and Hydraulic Constraints
    Heat Transfer Constraints
    Stripping Mass Transfer Constraint
    Rectification (Absorption) Mass Transfer Constraint

    Unit 7: Optimizing Product Quality Performance
    Quality Performance Measurement
    Frequency of Failure
    Optimize MRT Between Distillate and Bottoms Quality
    Avoid Excessive Use of Steam
    Reduce Variability
    Optimize with Expert System Advisor

    Unit 8: PID Feedback Control Loop
    The Feedback Control Loop
    Parallel and Series Algorithms

    Unit 9: Closed Loop Tuning of Controllers
    Trial and Error Tuning of Control Loops
    Ultimate Gain Tuning of Control Loops
    Troubleshooting an Oscillating Control Loop
    Quarter Decay Ratio tuning of Control Loops
    Pattern Recognition Tuning of Self Regulating Control Loops
    Effect of Proportional Gain
    Effect of Integral (Reset) Action
    Pattern Recognition Tuning of Integrating Control Loops

    Unit 10: Open Loop Testing of Process Response
    Self Regulating Process Response
    Ziegler-Nichols (Z-N) Open Loop Tuning Rules
    Two Point Characterization of FOPDT Process Response
    Quarter Decay Ratio (QDR) Tuning Rules
    Internal Model Control (IMC) Tuning Rules
    Integrating Process Response



    Dr. Lanny Robbins is the president of Larco Technologies. He retired as a Research Fellow after 37 years at The Dow Chemical Company in Midland, Michigan. He received the Marston Medal, the top honor awarded by the Engineering Department at Iowa State University. His expertise is in fundamental chemical engineering research and pilot plant process development, especially for separation and purification processes.