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Chap01 - A Career In Process Control.PPT

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    Chemical and Bio-Process Control

    James B. Riggs

    M. Nazmul Karim

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    Chapter 1

    Introduction

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    A Career in Process Control

    Requires that engineers use all of their

    chemical engineering training (i.e., provides

    an excellent technical profession that can

    last an entire career)

    Can become a technical Top Gun

    Allows engineers to work on projects thatcan result in significant savings for their

    companies (i.e., provides good visibility

    within a company)

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    A Career in Process Control

    Provides professional mobility. There is a

    shortage of experienced process control

    engineers.

    Is a well paid technical profession for

    chemical engineers.

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    Chemical Process Industries (CPI)

    Hydrocarbon fuels

    Chemical products

    Pulp and paper products

    Agrochemicals

    Man-made fibers

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    Bio-Process Industries

    Use micro-organisms to produce useful

    products

    Pharmaceutical industry

    Ethanol from grain industry

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    Importance of Process Control for

    the CPI PC directly affects the safety and reliability

    of a process.

    PC determines the quality of the products

    produced by a process.

    PC can affect how efficient a process is

    operated.

    Bottom Line: PC has a major impact on the

    profitability of a company in the CPI.

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    Safety and Reliability

    The control system must provide safeoperation

    Alarms, safety constraint control, start-up and

    shutdown. A control system must be able to absorb a

    variety of disturbances and keep the process

    in a good operating region:Thunderstorms, feed composition upsets,

    temporary loss of utilities (e.g., steam supply),

    day to night variation in the ambient conditions

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    Benefits of Improved Control

    Time

    Im

    purity

    Concentration

    Limit

    Old Controller

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    Benefits of Improved Control

    Time

    Im

    purity

    Concentration

    Limit

    Time

    Impurity

    Concentration

    Limit

    Old Controller New Controller

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    Better Control Means Products

    with Reduced Variability For many cases, reduced variability

    products are in high demand and have high

    value added (e.g., feedstocks for polymers).

    Product certification procedures (e.g., ISO

    9000) are used to guarantee product quality

    and place a large emphasis on processcontrol.

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    Benefits of Improved Control

    Time

    Im

    purity

    Concentration

    Limit

    Time

    Impurity

    Concentration

    Limit

    Time

    Impurity

    Concentration

    Limit

    Old Controller New Controller

    Improved Performance

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    Maximizing the Profit of a Plant

    Many times involves controlling against

    constraints.

    The closer that you are able to operate to

    these constraints, the more profit you can

    make. For example, maximizing the

    product production rate usually involvingcontrolling the process against one or more

    process constraints.

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    Constraint Control Example

    Consider a reactor temperature control

    example for which at excessively high

    temperatures the reactor will experience a

    temperature runaway and explode.

    But the higher the temperature the greater

    the product yield.

    Therefore, better reactor temperature

    control allows safe operation at a higher

    reactor temperature and thus more profit.

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    Importance of Process Control for the

    Bio-Process Industries

    Improved product quality.

    Faster and less expensive process validation.

    Increased production rates.

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    Driving a Car: An Everyday

    Example of Process Control Control Objective (Setpoint): Maintain car in

    proper lane.

    Controlled variable- Location on the road Manipulated variable- Orientation of the front

    wheels

    Actuator- Drivers arms/steering wheel

    Sensor- Drivers eyes

    Controller- Driver

    Disturbance- Curve in road

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    Logic Flow Diagram for a

    Feedback Control Loop

    Controller Actuator Process

    Sensor

    CVSetpoint

    Disturbance

    +-

    uce

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    Temperature Control for a Heat

    Exchanger: ChE Control Example

    TT

    Condensate

    Steam

    Feed

    TCProduct

    Stream

    Setpoint

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    Heat Exchanger Control

    Controlled variable- Outlet temperature of

    product stream

    Manipulated variable- Steam flow

    Actuator- Control valve on steam line

    Sensor- Thermocouple on product stream

    Disturbance- Changes in the inlet feed

    temperature

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    DO Control in a Bio-Reactor

    Air

    AC

    Variable Speed

    Air Compressor

    AT

    Setpoint

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    DO Control

    Controlled variable- the measured dissolvedO2 concentration

    Manipulated variable- air flow rate to the

    bio-reactor Actuator- variable speed air compressor

    Sensor- ion-specific electrode in contact

    with the broth in the bio-reactor Disturbance- Changes in the metabolism of

    the microorganisms in the bio-reactor

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    Logic Flow Diagram for a

    Feedback Control Loop

    Controller Actuator Process

    Sensor

    CVSetpoint

    Disturbance

    +-

    uce

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    Comparison of Driving a Car and

    Control of a Heat Exchanger Actuator: Drivers arm and steering wheel

    vs. Control valve

    Controller: the driver vs. an electronic

    controller

    Sensor: the drivers eyes vs. thermocouple

    Controlled variable: cars position on the

    road vs. temperature of outlet stream

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    The key feature of all feedbackcontrol

    loops is that the measured value of the

    controlled variable is compared withthe setpoint and this difference is used

    to determine the control action taken.

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    In-Class Exercise

    Consider a person skiing down a mountain.

    Identify the controller, the actuator, the

    process, the sensor and the controlledvariable. Also, indicate the setpoint and

    potential disturbances. Remember that the

    process is affected by the actuator to changethe value of the controlled variable.

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    Types of Feedback Controllers

    On-Off Control- e.g., room thermostat

    Manual Control- Used by operators and based on

    more or less open loop responses

    PID control- Most commonly used controller.Control action based on error from setpoint

    (Chaps 6-8).

    Advanced PID- Enhancements of PID: ratio,cascade, feedforward (Chaps 9-11).

    Model-based Control- Uses model of the process

    directly for control (Chap 13).

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    Duties of a Control Engineer

    Tuning controllers for performance and

    reliability (Chap 7)

    Selecting the proper PID mode and/oradvanced PID options (Chap 6, 10-12)

    Control loop troubleshooting (Chap 2 & 8)

    Multi-unit controller design (Chap 14)

    Documentation of process control changes

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    Characteristics of Effective

    Process Control Engineers

    Use their knowledge of the process to guide

    their process control applications. They areprocess control engineers.

    Have a fundamentally sound picture of

    process dynamics and feedback control. Work effectively with the operators.

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    Operator Acceptance

    A good relationship with the operators is a

    NECESSARY condition for the success of a

    control engineer.

    Build a relationship with the operators

    based on mutual respect.

    Operators are a valuable source of plant

    experience.

    A successful control project should make

    the operators job easier, not harder.

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    Process Control and

    Optimization

    Control and optimization are terms that are

    many times erroneously interchanged.

    Control has to do with adjusting flow rates

    to maintain the controlled variables of the

    process at specified setpoints.

    Optimization chooses the values for keysetpoints such that the process operates at

    the best economic conditions.

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    Optimization and Control of a CSTR

    TC

    Feed

    Product

    TTSteam

    FC

    RSP

    OptimizerRSP

    FT

    FV

    CA0

    CA,C

    B, C

    C

    ABC

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    Optimization Example

    balances.

    molefromcalculatedareandLikewise,

    ]/exp[

    1

    forSolving

    ]/exp[

    :AonbalanceMole

    11

    0

    110

    CB

    r

    AA

    A

    rAAA

    CC

    Q

    VRTEk

    CC

    C

    VCRTEkCQCQ

    CBA

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    Economic Objective Function

    AFACCBBAA VCQVCQVCQVCQ 0

    VB

    > VC, V

    A, orV

    AF

    At low T, little formation of B

    At high T, too much of B reacts to form C

    Therefore, the exits an optimum reactor

    temperature, T*

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    Optimization Algorithm

    1. Select initial guess for reactor

    temperature

    2. Evaluate CA, CB, and CC

    3. Evaluate

    4. Choose new reactor temperature and

    return to 2 until T* identified.

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    Graphical Solution of Optimum

    Reactor Temperature, T*

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    Process Optimization

    Typical optimization objective function,

    : = Product values-Feed costs-Utility costs

    The steady-state solution of process models

    is usually used to determine processoperating conditions which yields flow rates

    of products, feed, and utilities.

    Unit costs of feed and sale price of products

    are combined with flows to yield

    Optimization variables are adjusted until

    is maximized (optimization solution).

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    Generalized Optimization

    Procedure

    Numerical

    Optimization

    Algorithm

    Process

    Model

    Economic

    Parameters

    Economic

    Function

    Evaluation

    Optimization

    Variables

    Economic

    Function

    Value

    Model

    Results

    Initial Estimate

    of Optimization

    Variables

    Optimum

    Operating

    Conditions

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    Optimization and Control of a CSTR

    TC

    Feed

    Product

    TTSteam

    FC

    RSP

    OptimizerRSP

    FT

    FV

    CA0

    CA,C

    B, C

    C

    ABC

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    In-Class Exercise

    Identify an example for which you use

    optimization in your everyday life. List the

    degrees of freedom (the things that you arefree to choose) and clearly define the

    process and how you determine the

    objective function.

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    Overview of Course Material

    Control loop hardware (Chap 2)

    Dynamic modeling (Chap 3)

    Transfer functions and idealized dynamic

    behavior (Chap 4-6)

    PID controls (Chap 7-10)

    Advanced PID controls (Chap 12-14)

    Control of MIMO processes (Chap 15-18)

    F d t l U d t di d

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    Fundamental Understanding and

    Industrially Relevant Skills

    Fundamental Understanding-

    Laplace tranforms and transfer functions (Ch 4-5)

    Idealized dynamic behavior (Ch 6)

    Frequency response analysis (Ch 11)

    Industrially Relevant Skills-

    Control hardware and troubleshooting (Ch 2&10)

    Controller Implementation and tuning (Ch 7-9)Advanced PID techniques (Ch 12-14)

    MIMO control (Ch 15-18)

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    Process Control Terminology

    Important to be able to communicate with

    operators, peers, and boss.

    New terminology appears in bold in the text

    New terminology is summarized at the end

    of each chapter.

    Review the terminology regularly in orderto keep up with it.

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    Overall Course Objectives

    Develop the skills necessary to function asan industrial process control engineer.

    Skills

    Tuning loops Control loop design

    Control loop troubleshooting

    Command of the terminology

    Fundamental understanding Process dynamics

    Feedback control

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    Overview

    All feedback control loops have acontroller, an actuator, a process, and a

    sensor where the controller chooses control

    action based upon the error from setpoint. Control has to do with adjusting flow rates

    to maintain controlled variables at their

    setpoints while for optimization thesetpoints for certain controllers are adjusted

    to optimize the economic performance of

    the plant.


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