created at universidad de guanajuato & École polytechnique de montréal

Tier 2 Modulo 15 NAMP

Process Control and Process Integration 1

Created atUniversidad de Guanajuato & École Polytechnique de

Montréal

Module 15: Process Control and Module 15: Process Control and Process IntegrationProcess Integration – Tier 2 – Tier 2

Program for North American Mobility in Higher Education (NAMP)

Introducing Process Integration for Environmental Control in

Engineering Curricula (PIECE)



This module is divided in three essentials complements, it will demonstrate the relationship between the use of PI tools in order to design a process and the control strategies.



Tier one:•Basic Concepts About Process Control

Tier Two:•Use of PI tools and especially dynamic simulation to address control strategies

Tier Three:•Analysis of a real process.

Structure



Index:

Tier one:

•Comparison between Steady Sate and Dynamic State.

•Important Definitions about dynamic state.

• Dynamic Models.



Index:

Tier two:

• Relationship between Process Design and Process Control

• Dynamic Effect on recycle Structures.



Tier 2



Objective:

Understand the interaction between process design and process control.

Understand the effect of recycle structures on dynamic behavior.

Tier 2



Process Control in a Integrated Perspective



Identification and creation of potential opportunities to satisfy societal needs and to generate profit.

Any process starts with



Manufacturing process



Natural Resources

Basic Chemical products

Basic Chemicals industrial Products

Basic Chemical products

Industrial Products

Consumer Products



Process Creation

The next step is



?

Process design starts with the synthesis of a process to convert raw material into desired products

Feed Streams

Product Streams



Process FlowsheetIs a diagrammatic representation of the process

steps using icons to represent process units and arrows to represent connections among them

Feed Streams

Product Streams



It is common the presence of recycles (process integration) because its advantages to recover energy. However is important to know how they affect the dynamic properties.

Simulation Steady State



Is a mathematical model of the process that attempts to predict how the process would behave if it were constructed or modified

Simulation

Steady Sate Simulation the operating conditions are changed to others ones in order to evaluate new

operating sceneries

Operating Condition New Operating Condition

FeedProduct



Having the process flowsheet the next step is to evaluate the process control configuration.

♣ Effect of the recycle in process dynamic

Effect of the heat integration in process dynamic.

How to control the process.

Dynamic State Simulation allows to test different control strategies and to know the influence of changes in the process design on the dynamic behavior.



The role of Control Process in Process Design



Effect of recycle



Recycle StructuresThese structures are used often in process plants

to return material for reprocessing and to recover energy from effluent streams trough heat exchanger.



Heat Recycle

Fresh feed is heating using the stream leaving the reactor

This stream goes trough a heat exchanger in order to recover heat



Block diagram for this system

+

GH2(s)

GR(s)GH1(s)T0(s) T1(s) TR(s)Tf(s)

T2(s)

)()()(

10

1 sGsTsT

H )()()(

22 sGsTsT

HR

)()()( 21 sTsTsT f

)()()( sGsTsT

Rf

R



Now using block diagram algebra to determine el behavior of the integrated system transfer function is:

)()()( 3 sTsGsT RR )()()()()( 012sTsGsTsGsGT HRHRR

)()(1)()(

)()(

2

1

0 sGsGsGsG

sTsT

HR

HRR

Block Diagram

Characteristic Equation

Poles of overall system are different to the poles of the individual units. The stability of this system cannot be guaranteed even if each individual system is stable.



1 103)(

s

sGR4.011 HH KG 3.0

22 HH KG

Now defining

With Recycle

110012

)()(

0

ssTsTR

Without Recycle

1102.1

)()(

0

ssTsTR

Gain

Time Constant



Performing a Dynamic Simulation to know the dynamic behavior

Time constant and gain have been increased in the reactor with recycle



500

100

500



Increase in T0

Affects Tf

Affects TR

The output is reinforced through the recycle exchanger

There is a positive feedback

Why ?



• The time constant and the steady state gain of the overall system with recycle can be changed substantially from their values without recycle.

• Recycle can alter the stability and possibility for a periodic behavior of the overall system, because it affects the poles of the overall system.

• This effect should be considered when the process control is developed because the time constant is related with the speed of response of the process.

According the previous slides



QUIZ



1.- The effect of a positive feedback is not desirable because :

a) Its actions tends to increase the error from desired.

b) Its action tends to reduce the error from desired.



2.- If time constant increases its value , it implies :

a) A slow system´s response when changes on manipulated variables are made to produce changes on controllable variable.

b) A faster system´s response when changes on manipulated variables are made to produce changes on controllable variable.



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Now you have finished Tier 2

created at universidad de guanajuato & École polytechnique de montréal

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