presentación - batch processes introduction - eth zurich
TRANSCRIPT
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Introduction to Chemical Batch Processing ICB / ETH Zurich
Introduction to
Chemical Batch Processing
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Introduction to Chemical Batch Processing ICB / ETH Zurich
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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Characteristics of Chemical Batch Processes
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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(Some) History of Chemical Batch Processing
“…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.”
D.W.T. Rippin, 1983. Computers & Chemical Engineering 7: 137-156
“…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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(Some) History of Chemical Batch Processing
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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.”
D.W.T. Rippin, 1983. Computers & Chemical Engineering 7: 137-156
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Introduction to Chemical Batch Processing ICB / ETH Zurich
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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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)
Optimizing a Reactor-Separator Process in Batch Mode
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Feasible region Unfeasible region
Optimizing a Reactor-Separator Process in Batch Mode
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Optimizing a Reactor-Separator Process in Batch Mode
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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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Modes of Processing Subsequent Batches
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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Modes of Processing Subsequent Batches
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