INTRODUCTION TO CHEMICAL PROCESS...

INTRODUCTION TO CHEMICAL PROCESS SIMULATORS

A. Carrero, N. Quirante, J. Javaloyes

October 2016

DWSIM Chemical Process Simulator

A. Carrero , N. Quirante & J. Javaloyes

Introduction to Chemical Process Simulators

2

Contents

Monday, October 3rd 2016

Introduction to Sequential – Modular Steady State ProcessSimulators

Get used to working with DWSIM and COCO

Monday, October 10th 2016

Simulation of Chemical Reactors


Simulation of Distillation Columns


Case studies



3

Flowsheeting

Alexander C. Dimian (2003)

Flowsheeting is a systemic description of material and energy streams in aprocess plant by means of computer simulation with the scope ofdesigning a new plant or improving the performance of an existing plant.Flowsheeting can be used as aid to implement a plantwide controlstrategy, as well as to manage the plant operation.



4

Process Flowsheet

Input streams

OperatingConditions

Unit Parameters

Output streams

Simulation

Process Flowsheet

Input streams

OperatingConditions

Unit Parameters

Output streams

Design

Process Flowsheet

Input streams

OperatingConditions

Unit Parameters

Output streams

Objective Function

Optimization

Process Flowsheet

Input streams

OperatingConditions

UnitParameters

Output streams

ObjectiveFunction

Synthesis



5

Architecture of Process Simulators

Sequential-Modular

Based on the concept of modularity, which extends the chemical engineering concept of the unit operation to a “unit calculation” by the computer code responsible for the calculation of single process unit. The computation of the flowsheet takes place unit by unit following a calculation sequence.

Equation-Oriented (Simultaneous-Nonmodular)

The complete model of the flowsheet is expressed in the form of one large sparse system of nonlinear algebraic equations that is simultaneously solved for all the unknowns.

Simultaneous-Modular

Combination of Sequential-Modular and Equation Oriented approaches



6

Commercial Steady-State Process Simulators

Aspen Plus

Aspen Hysys

ChemCAD

PRO II

UniSim

gProms

VMGSim

Aspen Plus in EO

Aspen Custom Modeler

Sequential – Modular approach Equation – Oriented approach

Free Steady-State Process Simulators

DWSIM

COCO

Sequential – Modular approach

ASCEND

Equation – Oriented approach



7

Sequential – Modular Process Simulators

Executive Program

InputOutput

Graphical User Interface

Numerical routines

Unit module library

Sizing and costing database

Physical property database

Themodynamic methods

Figure reproduced fromIntroduction to Software for Chemical Engineers, M. Martin (2015)



8

Sequential – Modular Process Simulators

+ Easy programming and maintenance.

+ Robustness and reliability. Specific solution methods are developed for each process unit.

+ The unit blocks can be easily added to or removed from the flowsheet.

– SM is well suited to process simulator, but not to design or optimization, since an iterative procedure is required to satisfy the constraints.

– Need for topological analysis and systematic initialization of tear streams.

– Present difficulties with flowsheets involving a large number of recycle streams.

– Rigid direction of computation, normally outputs from inputs.

Advantages

Disadvantages



9

Physical Property Service Facilities

# Supply estimates for a number of different physical properties while thesimulation is running.

# Phase equilibrium represent one of the most important physical properties,as many chemical processes simulations involve distillation, stripping,evaporation or liquid-liquid separation. Solving the mass and energybalances for these operations necessitates predicting the

Vapor – Liquid Equilibrium (VLE)

Liquid – Liquid Equilibrium (LLE)

# Estimation of physical properties can consume up to 90% of thecomputation time of a simulation.

Property packages are used to predict the phase equilibrium behavior of pure components and mixture systems



10

Phase Equilibrium

IsofugacitiesI II Fi i if f f

A closed system that contains more than one phase, at constant Pressure andTemperature, is at equilibrium if:

Where fi is the fugacity of Component i in Phases I, II,… F

V Li if f

Vapor – Liquid Equilibrium

fiV is the fugacity of Component i in the vapor phase

fiL is the fugacity of Component i in the liquid phase



11

Equation-of-State Method

Vapor-phase fugacity

0, ,

1ln

j

P

i

i T P n

V RTdp

RT n P

V V

i i if y P

L L

i i if x PLiquid-phase fugacity

,

,

i i

V Li i

y and x are the mole fraction of Comp i in the vapor and liquid phases respectively

and are the vapor and liquid phase fugacity coefficients respectively

P is the system pressure

where

The fugacity coefficients for each phase are determined with the followingexpression



12

Equation-of-State Method

Vapor-phase fugacity

0, ,

1ln

j

P

i

i T P n

V RTdp

RT n P

V V

i i if y P

L L

i i if x PLiquid-phase fugacity

,

,

i i

V Li i

y and x are the mole fraction of Comp i in the vapor and liquid phases respectively

and are the vapor and liquid phase fugacity coefficients respectively

P is the system pressure

where

The fugacity coefficients for each phase are determined with the followingexpression

EOS



13

Activity Coefficient Method

0Li i i if x f

Vapor-phase fugacity V V

i i if y P

Liquid-phase fugacity

i i

Vi

i

0i

y and x are the mole fraction of Comp i in the vapor and liquid phases, respectively

is the vapor - phase fugacity coefficient

is the liquid - phase activity coefficient

f is the fugacity of Comp. i at standard state

where

In this case, thermodynamic models are required for i (from a equation of state)

and i (from a liquid-phase activity coefficient model)



14

Activity Coefficient Method

# The vapor phase can be considered ideal 1Vi

# Standard State fugacity

0 0 0exp

sati

cPsat i

i i i ip

vf p dP p

RT

Poynting correction factor0L

i i i if p x

thereforeV

i if y P

therefore

At moderate pressures:



15

Vapor – Liquid Equilibrium Example (Dechema Chemestry Data Series)



16

Decision tree for the selection of the thermodynamic property model

Any polar component?

Any Electrolyte?Any pseudo component?

YesNo

Yes

Under vacuum conditions?

IdealBraun K-10

Yes

Chao-SeaderGrayson-Streed

Braun K-10

No

Peng-Robinson (PR)Soave-Redlich-Kwong (SRK)

Lee-Kesler-Plöcker

No YesElectrolyte NRTL

PitzerBromley-Pitzer

Operat ing pressure low to medium ≤ 10 bar?

Binary iteration coefficients available?

No

YesSchwartzentruber-Renon

PR or RKS with WS mixing rules

PR or RKS with MHV2 mixing rules

PSRK

PR or RKS with MHV2 mixing rulesNo

No

Binary iteration coefficients available?

Yes

Yes No

Liquid-liquid equi librium?

Yes

NRTLUNIQUAC

Liquid-liquid equi librium?

NoUNIFAC

UNIFAC LLE

Yes

WilsonNRTL

UNIQUAC

No

Activity coefficient model Equations of state model

Pressure

Polarity



17

Get used to working with Process Simulators

FIRST STEPS

1. Compounds

2. Property Packages

3. Flash Algorithm

4. System of Units

5. Feed inlet data

6. Units Specifications

7. Activate/recalculate all

8. Review of the results



18

DWSIM

Activate

Abort calculation

Recalculate All

Deactivate

COCO

Validate

Solve

Get used to working with Process Simulators



19


Flash distillation 1An equimolar mixture of benzene and toluene is subjected to flash distillation ata pressure of 1 bar in the separator. Determine the compositions (in molefraction benzene) of the liquid and vapor leaving the separator when the feed is25% vaporized. Estimate the temperature in the separator.

Sensitivity analysis

0% vaporized50% vaporized75% vaporized100% vaporized

A. Carrero , N. Quirante & J. Javaloyes20



Flash distillation 1

100 kmol/hfv = 0.25

T ?

Vapor fraction Temperature (ºC)

0 91.55

0.25 93.17

0.5 94.89

0.75 96.59

1 98.15



21

Get used to working with DWSIM and COCOVapor Liquid Equilibrium

Bubble point

Dew point



22

Get used to working with DWSIM and COCOFlash distillation 2

Calculate the composition of the final stream in the following processflowsheet.

Use UNIQUAC thermodynamic package

Ethanol

41.86 kmol/h

Acetone

38.64 kmol/h

25ºC

95 kPa

65ºC

25ºC

Xacetone

Xethanol

Xacetone

Xethanol

INTRODUCTION TO CHEMICAL PROCESS...

Documents

Transcript of INTRODUCTION TO CHEMICAL PROCESS...