Presentación - Batch Processes Introduction - ETH Zurich

8/9/2019 Presentación - Batch Processes Introduction - ETH Zurich

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Introduction to Chemical Batch Processing ICB / ETH Zurich

Introduction to

Chemical Batch Processing


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Outline

Characteristics of Chemical Batch Processes

Analysis and Optimization of Chemical Batch Processes

Examples and Software (Aspen Batch PlusTM)

Case Study (Anti-oxidant production)

Report and Presentation


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Chemical Batch Processes: Definition of Terms

Batch vs Continuous


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What does “Batch” mean?

1. the quantity baked at one time

2. a: the quantity of material prepared or required for one operation

b: the quantity produced at one operation

c: a group of jobs (as programs) that are submitted for processing

(e.g. on a computer) and whose results are obtained at a later time3. a quantity (as of persons or things) considered as a group

4. …


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What is chemical batch processing?

• The discontinuous, “charge wise” production of chemicals

• Several units are designed to be started and stopped frequently

(i.e. in a cycle-mode) for:

Charging (fill with material)

Task performing for a specified period of time

Shutting down and draining (discharging)

Cleaning

• Combinations of batch and continuous mode (using holding

tanks as an interface) are possible.


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Reactor

producttransferred

once each

cycle

Connecting Continuous and Batch Processes: Holding Tanks

Continuous

stream for

batch charge

Batch

Chargetransferred

once each

cycle

Optional

stream forcontinuous

feed

Continuous

stream forreactor

product

Reactor

Feed holding tank

Product holding tank


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Semi-Batch

There are two classes of semi-batch processes:

• Fed-batch processes with some or all chemicals being fed

continuously during the processing (or some time of the

processing). When the processing is finished the products are

removed batchwise.

• In batch-product removal the chemicals are fed to the process

before processing begins, and then the product (or some of the

products) is removed continuously as the processing occurs.


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(Some) History of Chemical Batch Processing

“In the early days of chemical reaction engineering (1950s)

students might well have gained the impression that the ultimate

mission of the chemical engineer was to transform old-fashioned

batch processes into modern continuous ones…”

D.W.T. Rippin, 1983. Computers & Chemical Engineering 7: 137-156


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“…With such a perspective it would be surprising to find that,

today, thirty years later, a significant proportion of the world’schemical production by volume and a much larger proportion by

values is still made in batch plants and it does not seem likely

that this proportion will decline.”


“…With the recent trend of building small flexible plants that

are close to the markets of consumption, there has been

renewed interest in batch processes.” L.T. Biegler, I.E. Grossmann, A.W. Westerberg 1997. Systematic methods of

chemical process design. Prentice Hall, Upper Saddle River.


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Hierarchy of Decisions in Chemical Process Design

1. Batch versus continuous

2. Input-output structure of the flowsheet

3. Recycle structure of the flowsheet

4. General structure of the separation system

a) Vapor recovery systemb) Liquid recovery system

5. Heat-exchanger network

J.M. Douglas, 1988. Conceptual Design of Chemical Processes. McGraw-

Hill, New York.


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1. Production ratea. Sometimes batch if less than 10 * 106 lb/yr

b. Usually batch if less than 1 * 106 lb/yr

2. Market forcesa. Seasonal production or uncertain demand pattern

b. Short product lifetime

c. The process setup/design has to be fast (market

competition)

Batch vs Continuous (Capacity aspects)


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3. Scale-up problemsa. Very long reaction times

b. Handling slurries at low flow rates

c. Rapidly fouling materials

4. Flexibility

a. Operational problems

b. Feedstock variations

Batch vs Continuous (Technical Aspects)

J.M. Douglas, 1988. Conceptual Design of Chemical Processes.

McGraw Hill, New York


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Batch vs Continuous (Conclusively)

• Because of their greater flexibility, batch plants are mostcommon, when a large number of products can/should be

produced in essentially the same processing equipment.

• For seasonal products high storage cost arise when they areproduced over the complete year.

• Batch production is typically used for high-value added

chemicals, e.g. pharmaceuticals, fine chemicals, pesticides,bio-products, foods, polymers etc.


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Batch vs Continuous (Conclusively)

“There are indeed some products, for which it is not possible orat least would be unreasonably demanding in time and

resources, to develop reliable continuous processes. However,

many more products which could be manufactured

continuously are in fact made in batch plants on economicgrounds.”



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Outline


Analysis and Optimization of Chemical Batch Processes

Examples and Software (Aspen Batch PlusTM)

Case Study (Anti-oxidant production)

Report and Presentation


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Analysis and Optimization of Chemical Batch

Processes

Design and Operation of Batch Process Units

Design of Reactor-Separator Processes

Dedicated, Multiproduct, Multipurpose Batch Plants


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The batch reactor

Reactor

product

transferred

once eachcycle

Batch

Charge

transferred

once eachcycle

Reactor

Reaction:.

1 2

exothn A n B →←

1 2

1 2

1 2

1 2

1 2

n n A A B

E E

n no o RT RT A B

dC

r k C k C dt

k e C k e C − −

= − = −

= −

0 0

, ( )[ / ]

A BC C mol l

[ ]V l

(A formulation of) Optimal Control Problem:

Determine the profile of operating temperature T(t)

that reaches a certain conversion (or yield) in the

minimum batch time (τ min).

0 0

0 0

( ) ( )

( .)

A A A A A

A A

n n t C C t X

n C

density const

− −= =

=


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(A general formulation of the) Optimal Control Problem: Determine the profile of (all or some) operating parameters

(e.g. temperature, feed rate, removal rate, reflux ratio,…) to

achieve a certain performance (e.g. minimum batch time for a

given conversion, minimum batch size etc.)

Optimal Control Problem


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Coding in Matlab


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Results for the Isothermal case

450 K

470 K

490 K

510 K

530 K

t

C A

( t )


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Deriving the Optimum Profile

1 2

1 2

2

1

1 2

2 1

2 2

1 1

0

ln

E E

n no o RT RT

A B

opt n o

B

n o

A

r k e C k e C E E dr

T C k E dT

RC k E

− −

= −

−= ⇒ =

The minimum batch time is achieved by applying a

temperature profile that maximizes the reaction rate at eachpoint in time:


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0 500 1000 1500 2000 2500 3000 3500 4000 4500 50000.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

time t

s o l u t

i o n C a

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000450

500

550

600

650

700

750

800

850

900

time

T e m p e

r a t u r e [ K ]

Deriving the Optimum Profile


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Batch Distillation

A mixture of methanol, water and

propylene glycol has to be separated

using a batch distillation operation atnormal pressure.


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Batch Distillation

Operation:

Methanol Recovery:1) Bring the column to total reflux operation, with the

distillate valve closed.

2) Using a constant reflux ratio distill with a constant

rate to the methanol receiver. Continue until themole fraction of water exceeds a specification.

3) Bring the column to total reflux.

4) Using a higher constant reflux ratio distill with alower rate to the methanol receiver. Continue until

the same water specification is reached.


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Batch Distillation

Operation:

Propylene Glycol Recovery:1) Bring the column to total reflux operation, with the

distillate valve closed.

2) Using a constant reflux ratio distill with a constant

rate to the water receiver. Continue until the molefraction of propylene glycol exceeds the given

specification.

3) Pump the contents of the still pot into the

propylene glycol receiver.


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Optimizing a Reactor-Separator Process1 in Batch Mode

1Barrera et al., 1989. Chem. Eng. Comm., 82, 45-66.

The process consists of two units (with given capacities Vr, Vc)

with unlimited intermediate storage between them:


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The column is assumed to

operate in a way that it producesperfect splits (A, then B, then C).

The operation time to recover

product B is simply given by:

where Fd

(mol/hr) is the constant

distillate rate.

Optimizing a Reactor-Separator Process in Batch Mode


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The objective is to minimize the total cost of the campaign to

produce a required amount of product Btot

(mol) in a given

horizon time Thor (hr).

The following operational and cost factors are given:

tci: cleaning time between batches for i-equipment (i=r, c) (hr)

P j: cost (or credit) of j-material ( j=A, rA, C) ($/mol)

rk : equipment rental rates (k =r, s, c) ($/hr)

Ccli: equipment cleaning cost ($/batch)

Pu: distillation utility cost ($/mol)



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Feasible region Unfeasible region



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What is needed to create a batch process ?

• A market, a demand pattern, and product requirements

• A recipe (or: process step procedure), i.e. a list of physico-

chemical operations (tasks) and their duration

• Available equipment units


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The Batch Process Recipe – an Example

List of tasks to be completed:

• Mix raw materials A and B. Heat to 80 oC and react during

2 hours to form product C

• Add raw material D and react during 1 hour at 80 oC to

obtain product E• Mix with solvent F for 1.5 hours at ambient conditions; cool

and age for 3.5 hours; E will crystallize

• Centrifuge for 2 hours to separate solid product E

• Dry in a tray for 1 hour at 60 oC.


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Available Equipment Units – an Example

3 reactors, 1 centrifuge, 1 dryer


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Challenges of Chemical Batch Processing

The general flexibility of batch processes offers a wide range of

possibilities. To take full advantage of this flexibility advancedplanning and modeling tools are required for:

• Dynamic nature of operations/processes

• Dynamic nature of plant operation (demand patterns, newproducts, scheduling changes)

• Good manufacturing practice (GMP rules)

Not taking full advantage might have severe economicimplications !


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Design Tasks for Batch Processes

• Which units in the flowsheet should be batch and which

continuous?

• Which processing steps should be carried out in which

equipment with or without other steps?

• When is it advantageous to use parallel batch units to speed

up production?

• How much intermediate storage is required, and where

should it be located?


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The Batch Process Layout – one Example


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Types of Chemical Batch Plants

• Single-product / dedicated plants: only one product

• Multiproduct / flowshop plants: every product follows

(approximately) the same sequence through all the process

steps

• Multipurpose / jobshop plants: each product follows its own

distinct processing sequence by using the available equipment

in a product specific layout; either only one production runs

in the plant at a given time or many run concurrently


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Single Product / Dedicated Batch Plant

Similarities with continuous processes:

• Only one product is produced

• Highly automated• Several continuous operations


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Multiproduct / Flowshop Batch Plant

In this type of plant every product follows the same sequence of

operations and uses the same equipment units for (almost) all theprocess steps.


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Multipurpose / Jobshop Batch Plant

Here each product follows its own distinct processing sequenceby using the available equipment in a product-specific layout.


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Modes of Processing Subsequent Batches

• Non-overlapping mode

A subsequent batch is only started when the previous one is

completed.

• Overlapping modeSeveral batches are processed simultaneously; this reduces

the idle (or dead) time of an equipment significantly.


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Gantt chart representation of example process layout


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Definition of “Times”

Occupancy time (OT j) of an equipment is the time that a stage takingplace in this equipment needs to be completed (ti). If more than one

stages take place in an equipment then OT j=∑ ti.

Cycle time, CT= t f - ts final time– initial time of a cycle

Batch time, BT the time required to produce 1 batch

Makespan, MT the time required to produce N batches(or Campaign time)


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Gannt chart representation of example process layout

CT=11 h

BT=11 h

CT=5 h

BT=11 h


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Occupancy times – one Example

OT1=2 h OT2=1 h OT3=5 h OT4=2 h OT5=1 h


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Campaign Types in Flowshop / Jobshop Batch Plants

CT=? hBT=? h

MT=? h

CT=? h

BT=? h

MT=? h


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Transfer and Storage Policies for Batch Plants

Zero-wait (ZW)

At any stage the material is transferred immediately to thenext stage.

Unlimited Intermediate Storage (UIS)

The batch can be stored without any capacity limit in vessels.

No Intermediate Storage (NIS)

It is possible to hold the material inside the production vessel.


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Transfer and Storage Policies for Batch Plants


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Bottlenecks in Batch Processes


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Special Characteristics of Batch Processes


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Special Characteristics of Batch Processes


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Storage / Inventory

• Storage capacities have to be planned and managed well.

• Cost factor.

• Planning required, i.e. matching raw material availability and

customer requests.

• Supply chain management is important.


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Structure of a Multipurpose Batch Plant


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Structure of a Multipurpose Batch Plant


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Typical Equipment Units in Batch Plants


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Literature

Documents

Presentación - Batch Processes Introduction - ETH Zurich