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D epartment of Chemical Engineering, Budapest University of Technology and Economics, H-1521 Budapest, Hungary

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### Department of Chemical Engineering, Budapest University of Technology and Economics, H-1521 Budapest, Hungary

Research activities

CAPE-Forum, Veszprem, 2004

DISTILLATION AND ABSORPTION

- Determination of Vapour-Liquid Equilibria and design of Packed Columns.
- Development on distillation and absorption technologies
- Modelling and calculation of thermodynamic properties
- Modelling of batch and continuous countercurrent separation processes
- EXTRACTION AND LEACHING
- Kinetics of Soxhlet-type and Supercritical Solid-Liquid Extraction of Natural Products. Mathematical modelling and optimization of the process.
- Supercritical fluid extraction equipment and R&D capabilities
- REACTIONS
- Mathematical modelling of residence time distribution and chemical reactions
- MIXING OF LIQUIDS

PROCESS DESIGN AND INTEGRATION

- Feasibility of distillation for non/ideal systems
- Hybrid separation systems
- Reactive distillation
- Design of Energy Efficient Distillation Processes
- Energy integrated distillation system design enhanced by heat pumping and dividing wall columns
- Energy recovery systems
- A global approach to the synthesis and preliminary design of
- integrated total flow-sheets
- Process Integration in Refineries for Energy and Environmental Management

CONTROL AND OPERABILITY

- Assessing plant operability during process design
- Transformation of Distillation Control Structures
- Control of units in recycle
- ENVIRONMENTALS
- Waste reduction in the Chemical Industry
- CLEAN TECHNOLOGIES
- Membrane separations
- Cleaning of waste water with physico-chemical tools.
- Solvent recovery
- Synthesis of mass exchange networks with mixed integer nonlinear programming
- Economic and controllability study of energy integrated separation schemes
- Process synthesis of chemical plants

Department of Chemical Engineering, Budapest University of Technology and Economics, H-1521 Budapest, Hungary

Selected topics of our CAPE activities:

Analysis of energy integrated separations

and

Synthesis of mass exchange networks

Mizsey, P., Z. Szitkai, Z. Fonyo

CAPE Forum 2004

Challenges for East-West European Cooperation in

Process Modelling, Control, Synthesis and Optimization

13-14 February 2004, Veszprém, Hungary

Integrated process design

- Challenge in chemical engineering
- Economical and environmental aspects
- Heat integration (HEN) & mass integration (MEN)
- Several synthesis strategies
- The design needs CAPE

Analysis of energy integrated separations

(distillation based)

CAPE Forum 2004

Challenges for East-West European Cooperation in

Process Modelling, Control, Synthesis and Optimization

13-14 February 2004, Veszprém, Hungary

Budapest University of Technology and Economics

Department of Chemical Engineering

Classical distillation schemes for ternary mixture

Base case

for comparison

Direct sequence

Indirect sequence

Heat integration

Forward heat integration

direct sequence (DQF)

Backward heat integration

direct sequence (DQB)

Petlyuk column or dividing wall column (SP)

Forward heat integration (SQF)

backward heat integration (SQB)

Mixture: ethanol

n-propanol

n-butanol

Equimolar feed composition

(0.333, 0.333, 0,333)

Product purity specification: 99 m%

- Selection of controlled variables & manipulated variables,

- degrees of freedom analysis

- steady state indices: Niederlinski index, Morari index,
- condition number, relative gain array

- dynamic evaluation: open-loop & closed-loop

Evaluation of steady state indices

- base case (D) and heat-integrated schemes (DQF and DQB)
- show less interactions,

- (D1-L2-B2) manipulated set proves to be better than (L1-D2-Q2)
- and (L1-D2-B2) for D, DQF and DQB

- serious interactions can be expected for the sloppy schemes
- (SQF & SQB) and for the Petlyuk column (SP)

- Open composition control loops:
- quite similar dynamic behaviour but
- sloppy backward heat integrated (SQB) is the slowest scheme

Evaluation of closed composition control loops:

overshoot, settling time, and their product are evaluated

Closed loop dynamic simulations

- Simple energy integration (heat integration) doesn’t influence
- dynamic behaviour compared to the non-integrated base case

- more complicated systems: higher detuning factor is needed
- due to stronger interactions (they became slower in closed loop)

- The cases, where material and energy flows (energy integration)
- go into the same direction (DQF, SQF), are better than the opposite

- with energy integration about 35% TAC saving can be realised

- simple heat integration shows the best economic and
- controllability features

- sloppy schemes show good economic features but the selection is
- made according to their different controllability features (SQF,SQB)

- example also for the complexity of the process design: economic
- and controllability features are to be simultaneously handled

mix

D3

D1

Group 2

D2

F2

C2

C3

Water

F1

B2

B3

C1

IPAC

ETAC

(MEK)

ETOH

95 w%

W1

H2O

New directions: control of units in recycle

Example:

Synthesis of Mass Exchange Networks

Using Mathematical Programming

CAPE Forum 2004

Challenges for East-West European Cooperation in

Process Modelling, Control, Synthesis and Optimization

13-14 February 2004, Veszprém, Hungary

Budapest University of Technology and Economics

Department of Chemical Engineering

I. Mass Exchange Network Synthesis (MENS)

A Extension of the MINLP model of Papalexandri et al. (1994)

B Comparison of the advanced pinch method of Hallale and Fraser (2000)

and the extended model of Papalexandri et al.

C New, fairly linear MINLP model for MENS

II. Rigorous MINLP model for the design of

distillation-pervaporation systems

III. Rigorous MINLP model for the

design of wastewater strippers

Approach:

Mixed Integer Nonlinear Programming (MINLP)

optimisation software: GAMS / DICOPT

I. Mass Exchange Network Synthesis

El-Halwagi and Manousiouthakis, AIChE Journal, Vol 35, No.8, pp. 1233-1244

Mass integration for the analogy

of the concept of heat integration.

Absorber, extractor etc. network synthesis

(MSAs)

The synthesis task:

Stream data + equipment data +

equilibrium data + costing

Network structure

lean stream flow rates

min (Total Annual Cost, TAC)

Previous work:

sequential mathematical programming methods

El-Halwagi (1997), Garrison et al. (1995)

Alva-Argaez et al. (1999)

early pinch methods (no supertargeting)

Water pinch: Wang & Smith (1994, 1995), Kuo & Smith (1998)

El-Halwagi & Manousiouthakis (1989a)

El-Halwagi (1997)

advanced pinch method (includes supertargeting)

Hallale & Fraser (1998, 2000)

simultaneous mathematical programming models

Papalexandri et al. (1994)

Papalexandri & Pistikopoulos (1995, 1996)

Comeaux (2000); Wastewater: Benkő, Rév & Fonyó (2000)

I/A Extensions of the MINLP model of Papalexandri et al. (1994)

- Integer stage numbers
- Generation of feasible initial values
- Kremser equation:

Removable discontinuity at A=1

yi*=mijxj*+bij

- Previous mathematical programming models for MENS
- assumed that A is always greater than 1
- Numerical difficulty when using GAMS

- Big-M formulation
- Multi-M formulation
- a Convex-hull like formulation
- Raman & Grossmann (1991)
- Simple logic formulation

are linear but use 3 binary variables

New method

Advantages:

1. faster

2. larger problems can be solved

nonlinear but uses 1 binary variable only

(the models are nonconvex anyway)

Large nonconvex MINLP problems solved by DICOPT++:

There exists a critical upper limit of the number of binary variables

I/B Comparison of the advanced pinch method of

Hallale and Fraser (2000)

and the extended model of Papalexandri et al. (1994)

13 example

problems

have been solved

The two methods perform more or less the same.

Why are the MINLP solutions not always better? The MINLP model is nonconvex.

I/C New, fairly linear MINLP model for MENS

Similar to the HEN superstructure of Yee & Grossmann (1990)

The stagewise superstructure enables almost linear mass balance formulation

minimise

s.t.

big-M constraints for the existenxe of the units

mass balances

driving force constraints

constraints on the number of existing units

concentration constraints

Chen’s approximation for the log mean conc differences

calculation of the mass of the exchangers

Only the lean stream mass balances are bilinear

Example 4.1 (Hallale, 1998)

Extensions: stagewise exchangers, multiple components

The new model is most suitable for solving single component

MENS problems, where packed columns are used exclusively.

In this case, no special initialization is needed.

Two component example

II. Rigorous MINLP model for the design of

distillation-pervaporation systems

- The synthesis task
- is to determine:
- Nth of the column
- feed tray position
- reflux ratio
- membrane structure
- reflux scheme

Rigorous modelling:

Dist. Column: 1 bar, MESH equations, tray by tray, Margules activity coeff.

for the liquid phase, ideal vapour phase, latent heat enthalpy

Membrane unit: transport calculation is based on experimental data

1/3 m2 flat membranes, costing - industrial practice

Adequate costing equations, utility prices

1/3 m2 flat

PVA membranes

in blocks

The blocks (or modules)

can be connected in both

series or parallel

Distillation column superstructure:

Viswanathan & Grossmann (1993)

Membrane superstructure: new

Multiple level optimisation (successive refinement)

enables reducing the number of binary model variables

Modelling of the membranes is based on experimental data

Optimised

Base case

12% savings in the TAC

Other calculations

using the MINLP

model

Ethanol yield - TAC

Membrane surface - TAC

III. Rigorous MINLP model for the design of

wastewater strippers

Wastewater cleaning by stripping

Minor quantities of acetone,

methanol, and ethanol in water

Superstructure

Similar to the distillation column

superstructure of Viswanathan &

Grossmann (1993)

VLE calculation

Wilson binary interactions

Ideal vapour phase

Theoretical stages

1 bar

Latent heat enthalpy

Antoine vapour pressure

- Complex evaluation of distillation based heat integrated separation schemes is presented. Beside the heat integration the new sloppy structures proved to be competitive.
- New, fairly linear, MINLP modell for MENS is developed and succesfully tested for literature examples and industrial case studies.

Thank you for your attention.

Controllability investigations,design

- interactive and challenging part of process design or development.

Control structure synthesis

- control targets are defined,
- the sets of controlled variables and possible manipulated variables are determined (degrees of freedom)
- pairing of the controlled and manipulated variables: steady state control indices, dynamic behaviours in the cases of open and closed control loops of the promising control structures.

Demonstration of interaction between design and control

- comprehensive design of five energy integrated separation schemes
- three-component-alcohol-mixture is separated in five distillation based energy integrated two-column separation systems:
- two heat integrated distillation schemes
- fully thermally coupled distillation column (Petlyuk, Kaibel)
- sloppy separation sequences

Douglas, J. M., Conceptual design of chemical processes, McGraw-Hill Book Company

Marshall & Swift index: 1056.8/280

Project life: 10years

Major sizes are estimated by

HYSYS flowsheet simulator

(Feed: 100 kmol/h)

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