01 Hysys Intro

8/13/2019 01 Hysys Intro

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SeoulN

ationalUniversity

ChemicalProcessControl&Design

Aspen HYSYS :

Steady states and Dynamic Simulator

(Introduction)

TA : Ikhyun Kim

([email protected])

Instructor : En Sup Yoon

Fall Semester, 2013

Seoul National University

Chemical Process Control & Design (2/42)

Nonlinear algebraic equations:

where is the vector of unknown process variables to be

solved for l , are vectors of upper and lower bounds on the

process variables and :

Sequential modular strategy is one approach to solving problem

especially tailored to the network structure of process flowsheets

Typically simultaneous solution of 100s~100,000s of equations

requires an iterative process.

Sequential Modular Strategy

for S-S Process Simulation

( ) 0f

l u

y

y


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Gaussians elimination:

Given a linear system,

Manipulate| to an upper-triangular form

Then, solve backwards from the th row according to:





Example of Gaussians elimination:

And now 1, 3, 1 (problem solved)




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Will it help if can we break the problem into a sequence

of smaller problems?

a. If computation time grows super linearly with problem size then solving a sequence of smaller problems is cheaper than

solving one big problem

b. For example, recall that Gaussian elimination is a cubic

function of the number of equations. If we can break the overall

problem into two subproblems:

2

2

and a lot less effort is expended in achieving a solution

The sequential modular strategy exploits the topology(structure) of

the flowsheet to suggest a partitioning and precedence ordering





Solving recycle problems

a. d

b.




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Solving recycle problems

a. Guess S5

b. Given S1 and S5, solve A for S2

c. Given S2, solve B for S3

d. Given S5`, update guess for S5

e. Repeat from step2 until converged (e.g., S5~S5`=0)

Problems

How to select which stream(s) to tear in order to break the cycle

How to update the guess for the torn stream(s) so that the iterative process

converges rapidly, and when to terminate the iterative process





How to update the guess?

a. Bisection method

- Intermediate value theorem

b. Newtons method (Newton-Raphson method)

- Linearizing the system using Taylors expansion

- Jacobian matrix of partial dervatives

c. Successive over-relaxation

- when the multiplicity of system > 1

d. Secant method / Broyden method(Quasi-Newton method)- Finite difference approximation




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Aspen HYSYS Solvers



Aspen HYSYS

Key design elements

Event driven interface

Modular operations

Subflowsheet architectureMultiple environments

Flowsheet

Simulation basis

Oil characterization

Interactive

Flexible

Insert Figure


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Aspen HYSYS Environments



Via the two main Aspen HYSYS Environments

Aspen HYSYS Environments

Basic Environment Simulation Environment


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Basic Environment

Components

Property Package (Thermodynamic model)

Hypothetical Components

Reactions

Aspen HYSYS Architecture




Aspen HYSYS Library Components

Over 1800 components in main databank

Search by Simulation name, Full name, Synonym or Formula

Use property package or family filters

Aspen Properties Database

Pure component databanks contain over 23000 species

NIST Pure component data and NIST Thermodata Engine

(TDE) for improved data fitting and estimation

Hypothetical Components

Minimum data entry is one property (NBP, MW, density)


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Choosing a Fluid Package

Fluid package sources

HYSYS

Aspen Properties

COMThermo

Property model selection

Property Wizard

Aspen HYSYS documentation

Parameters

Pure component parameters accessed via Component view Interaction parameters are available on the Binary Coeffs. tab



Simulation Environment

Streams, Unit Operations, Analysis tools, etc.



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Aspen HYSYS Color Scheme

Values (Variables):

Blue: User-specified

Red: Default value

Black: Calculated (or fixed) value

Streams:

Light Blue: Not Solved

Dark Blue: Solved

Unit Operations

Red: Connection is missingunable to begin solving

Yellow: Unable to Solve or Solved with Warnings

Black: Solved



What information do we need to enter?

1. Fluid Package information

a. What components do we have (databank, hypos, assays, etc.)b. What thermodynamic method we will use (EOS, activity models,

)

2. Details of your process

a. Unit operations (equations to be solved)

b. Process conditions and equipment specifications (defined

parameters)

Process Simulation


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Basic

Environment

Create a unit set

Select the components

Choose a property package (Thermodynamic model)

Simulation

Environment

Create and Specify the streams

Install and Define the unit operation prior to the column

Install and Define the column

Analysis

DOF & Specification

Analyzing the Result (Case Study, Verification, Optimization, etc.)

Basic Steps for Simulation



The Aspen HYSYS Solver

is responsible for all steady state calculations in the

Aspen HYSYS program

is a nonsequential solver: information can flow forward

and backward through the flowsheet

is interactive and uses a Degrees of Freedom analysis

to trigger solving of unit operations and streams

tracks all numerical values in Aspen HYSYS according

to their source


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Reactor Models

ReactorReactor

[ Balance Based ]

Yield Shift Reactor

Conversion Reactor

[ Balance Based ]

Yield Shift Reactor

Conversion Reactor

[ Equilibrium Based ]

Equilibrium Reactor

Gibbs Reactor

[ Equilibrium Based ]

Equilibrium Reactor

Gibbs Reactor

[ Kinetics Based ]

PFR

CSTR

[ Kinetics Based ]

PFR

CSTR



Yield Shift Reactor

Requires a mass balance only, not an atom balance

No reaction stoichiometry required

Is used to simulate reactors in which inlets to the reactor are not

completely known but outlets are known

Conversion Reactor

Performs mass balance calculations based on reaction

stoichiometry(or conversion) and flashes the outlet stream

Used when reactions kinetics are unknown or unimportant

Balanced Based Reactors


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Equilibrium Reactor

Computes combined chemical and phase equilibrium by solving

reaction equilibrium equations

Useful when there are many components, a few known

reactions, and when relatively few components take part in the

reactions

Gibbs Reactor

A Gibbs free energy minimization is done to determine the

product composition at which the Gibbs free energy of the

products is at a minimum

Do not require reactions stoichiometry

Equilibrium Based Reactors



CSTR

Use when reaction kinetics are known and when the reactor

contents have same properties as outlet stream

Can model equilibrium reactions simultaneously with rate-based

reactions

PFR

Handles only rate-based reactions

A cooling stream is allowed

You must provide reactor length and diameter

Kinetics Based Reactors


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Heat of reaction need not be provided for reactions

Heat of reaction are typically calculated as the differencebetween inlet and outlet enthalpies for the reactor

If you have a heat of reaction value that does not match the

value calculated by simulator, you can adjust the heats of

formation of one or more components to make the heat of

reaction match

Heat of reaction can also be calculated or specified at a

reference temperature and pressure in an Conversion

Reactor

Heat of Reaction



Columns in Aspen HYSYS

A column is a specialized sub-flowsheet in Aspen HYSYS

Advantages:

Isolated column solver

Optional use of different fluid packages

Construction of custom templates

Column

subflowsheet

Main simulation environment


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Column Basics

Specifications Pressure Profile required

The number of additional column operating specificationsdepends on the complexity, Degrees of Freedom of the system,usually 0-3

Degrees of Freedom can be tracked on Monitor and Specspage

Active Specs can be entered on Monitor or Specs pages

Estimates can be entered to help with convergence

Results Monitor page contains most results, including convergence

Column Profiles are available on Performance page



Converging a Column

1. All feed streams must be fully solved

2. Never specify product streams directly

3. Activate specs to satisfy Degrees of Freedom analysis

4. Make sure all active specs have a value

5. Balance specifications along the entire tower

6. Click Run to run column solver; reset when necessary


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Pre-built Columns (Templates)

Absorber: contains only a tray section Degrees of Freedom (DOF) =

zero, no additional operating specification can be given

Reboiled absorber: contains a tray section and a reboiler DOF = 1,one additional operating specification has to be given

Refluxed absorber: contains a tray section and a top condenser

With a total/full reflux condenser DOF = 1

With a partial condenser DOF = 2

Distillation column: contains a tray section, condenser and reboiler

With a total/full reflux condenser DOF = 2 With a partial condenser DOF = 3

Side operations add additional Degrees of Freedom



Recycles

What is a Recycle operation?

mathematical / logical unit operation

When to use a Recycle operation?

Required when downstream material stream(s) mix with

upstream material stream(s) and when there is mass I/O across

the flowsheet

R

Assumed Calculated


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Adding Recycle Operations (1)

Procedure 1

1. Solve flowsheet without recycled stream

2. Add Recycle, and only attach the calculated stream

(calculated = estimated)

3. Connect assumed stream to flowsheet

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Adding Recycle Operations (2)

Procedure 2

1. Guess (estimate) assumed stream

2. Solve flowsheet up to calculated stream3. Add and connect recycle operation

3

1


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Sensitivities in Recycle Operation

Sensitivities used in Recycle operation are multipliers tointernal convergence tolerances in Aspen HYSYS

Aspen HYSYS internal tolerances are:Vapor Fraction 0.01

Temperature 0.01

Pressure 0.01

Flow 0.001

Enthalpy 1.00

Composition 0.0001

Actual Tolerance = Sensitivity * Internal tolerance



Sensitivities

Given a molar flow rate of 100 lbmole/hr

Internal tolerance = 0.001

Sensitivity = 10Absolute tolerance = 100 lbmole/hr * 0.001 * 10

Absolute tolerance = 1 lbmole/hr

Recycle is converged if 99 < molar flow < 101


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To minimize the number of tear locations, add recycles

Downstream of gathering points (mixer)

Upstream of distribution points (column, tee, separator)

To minimize the number of recycle variables (T, P, etc.)

Choose a tear location that maximizes number of fixed variables

Add recycle operations at separator inlets

Compressor after cooler outlets

Choose a stable tear location

To minimize effect of fluctuations

Tear Locations



Adding Recycles

Which are the physical recycle streams?

Which are the possible tear streams?

Which is the best choice for the tear stream?

6 and 7

6 and 7; 2 and 4; 3

The best tear stream choice is stream 3; if this stream is used, youonly need to converge one recycle instead of two


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Advanced Modeling

Exercise 1A

Recycle required? If so, how many? Possible location(s)?



Advanced Modeling

Exercise 1A

Recycle required? No closed loop (no I/O in flowsheet)


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Advanced Modeling (2)


Exercise 1B




Recycle required? No downstream material does not mix upstream

Exercise 1B

One stream is on the tube side th

e other on the shell side

There is no mixing of fluids


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Exercise 1C



Exercise 1D

Documents

01 Hysys Intro